JP6155982B2 - Power control apparatus and image forming apparatus - Google Patents

Description

  The present invention relates to a technique for controlling power output from a power generation device, and more particularly to output control of a power generation device mounted on an image forming apparatus.

  A power generation device refers to all devices that generate electrical energy from other energy such as motion, heat, light, and chemistry. The power generation device includes a turbine generator, a thermoelectric conversion element, a solar cell, and a fuel cell. Turbine generators use electromagnetic induction to convert turbine rotational energy into electrical energy. Turbine generators are classified into thermal power, nuclear power, wind power, hydraulic power, etc., depending on the driving force that rotates the turbine. The thermoelectric conversion element generates carrier movement, that is, current due to a temperature difference between different heat sources. Solar cells generate current by moving valence electrons to the conduction band by photoexcitation. A fuel cell combines hydrogen and oxygen by a chemical reaction, and supplies energy of electrons released at that time as an electromotive force.

  In recent years, the use of power generation devices that create electrical energy from alternative energy has been expanding. Alternative energy is a generic term for energy that replaces fossil fuels and nuclear power, and includes natural energy such as biomass, solar power, wind power, hydropower, and geothermal energy. Alternative energy also includes waste heat and residual heat from plants such as power plants, garbage incinerators, steelworks, etc., heat engines such as automobiles, air conditioners and refrigerators, and heating equipment such as boilers and water heaters. Introducing a power generation device that uses alternative energy into a plant such as a power plant helps to alleviate the problems of thermal power and nuclear power generation. On the other hand, reducing the size of these power generation devices and incorporating them as auxiliary power sources into systems such as automobiles, heating equipment, and electrical equipment helps to save energy in the systems. For example, the image forming apparatuses disclosed in Patent Documents 1 and 2 collect waste heat and residual heat from the fixing unit as electric power by a thermoelectric conversion element. The electric power is reused to drive the exhaust fan or keep the fixing unit warm. In addition, the rice cooker disclosed in Patent Document 7 converts waste heat from the induction heating device into the electric power, and the refrigerator disclosed in Patent Document 8 converts waste heat from the compressor into electric power by a thermoelectric conversion element. Use.

  In order for a power generating device that uses alternative energy to maintain its power generation efficiency high, its output should be changed according to changes in environmental conditions. In fact, in these power generators, a peak (maximum power point) appears in the voltage-power characteristics. If the output voltage is equal to the value at the maximum power point, the maximum power is delivered. However, the maximum power point is greatly displaced as the environmental conditions change. For example, the maximum power point depends on the temperature in a thermoelectric conversion element / fuel cell, depends on the amount of sunlight in a solar cell, depends on the wind speed in a wind power generator, and depends on the amount of water in a hydroelectric generator. Therefore, to maintain high power generation efficiency in these power generation devices, it is only necessary to readjust the output each time a change in temperature, amount of sunlight, wind speed, or water volume is detected, and to send a larger amount of power. .

  For power generators whose output characteristics greatly depend on environmental conditions, maximum power point tracking (MPPT) control is known as output control effective for maintaining high power generation efficiency (see, for example, Patent Documents 3-6). . In MPPT control, first, the displacement of the maximum power point is determined by repeatedly measuring the output of the power generation device at a constant period, and then the output is changed so as to follow the fluctuation. For example, in the MPPT control disclosed in Patent Documents 3 and 5, first, every time one of the output voltage and current of the power generator is changed, the other measurement is repeated to obtain a plurality of samples. Next, the peak of the voltage-power characteristic curve, that is, the maximum power point is obtained from these samples, and the output voltage of the power generator is adjusted to the value at the maximum power point. On the other hand, the MPPT control disclosed in Patent Documents 4 and 6 first measures the open circuit voltage of the power generator. Next, based on the relationship between the open circuit voltage and the maximum power point indicated by the voltage-power characteristic curve of the power generator, the maximum power point is calculated from the measured open voltage, and the output voltage of the power generator is calculated as the maximum power. Adjust to the value at the point. As a result of the above operation being repeated at a constant cycle, the change in the output of the power generator follows the displacement of the maximum power point. That is, the power generation efficiency is maintained high.

JP 2013-025280 A JP 2011-164424 A JP 2010-278036 A JP 2010-186338 A JP 2008-300745 A Japanese Patent No. 4715340 JP-A-10-271704 JP 2001-074348 A

  To further improve the efficiency of power generation using alternative energy, further improvement of MPPT control is necessary. In fact, the power generation efficiency of the power generation device itself that uses alternative energy is generally low. Therefore, it is necessary to improve the MPPT control so that a larger portion of the electric power generated by the power generation apparatus is supplied to the load.

  As an improvement point of MPPT control, first, it is conceivable to make the change in the output of the power generator more accurately follow the displacement of the maximum power point. For this purpose, the detection accuracy of the maximum power point must be further increased, and therefore the measurement cycle for the output of the power generator should be shortened.

  Next, it is conceivable to reduce the ratio of the time during which the power supply is substantially interrupted with respect to the time when the power is continuously supplied from the power generator to the load. In fact, every time the output of the power generator is measured, the MPPT control greatly deviates the output from the maximum power point or stops the power supply from the power generator to the load. Therefore, in order to reduce the above ratio, the measurement cycle for the output of the power generator should be extended.

  In order to make both of the above two improvements effective, the measurement cycle with respect to the output of the power generation device may be changed according to changes in environmental conditions. In fact, when the environmental conditions vary greatly, it is effective to accurately follow the change in the output of the power generation device to the displacement of the maximum power point, so the measurement cycle should be shortened. On the contrary, when the fluctuation of the environmental condition is small, it is effective to continue the power supply from the power generation device to the load, and therefore the measurement cycle should be extended.

  If the environmental conditions change regularly, the measurement cycle may be changed periodically. For example, the MPPT control disclosed in Patent Document 5 stores in advance the time, time zone, or season when the solar cell is covered with a shadow such as a building. At these times, etc., the amount of sunshine for the solar cell varies greatly, so that the maximum power point is greatly displaced. Therefore, at those times, the measurement cycle is shortened compared to other times. Thereby, the power generation efficiency of the solar cell is maintained high.

  However, it is not known how to change the measurement cycle when the environmental conditions vary irregularly. For example, in the image forming apparatuses disclosed in Patent Documents 1 and 2, a thermoelectric conversion element is installed in the vicinity of the fixing unit as a power generation apparatus. The power generation efficiency of the thermoelectric conversion element depends on the temperature of the installation location. The temperature is determined by the amount of heat from the fixing unit, and the amount of heat differs between printing and standby. That is, the temperature at the location where the thermoelectric conversion element is installed fluctuates irregularly depending on the operating state of the image forming apparatus. Under such circumstances, how to change the measurement cycle to further improve the power generation efficiency of the thermoelectric conversion element is not obvious to those skilled in the art, and is a major issue.

  An object of the present invention is to solve the above-described problem, and in particular, even when environmental conditions fluctuate irregularly, it is possible to appropriately change the timing for measuring the output of the power generation device according to the fluctuation. An object of the present invention is to provide a power control apparatus that can perform the above.

A power control apparatus according to one aspect of the present invention is a power generation apparatus that generates heat by waste heat from a system, which is incorporated in a system that generates heat in accordance with an operation mode that can be set for the operation and that generates heat with waste heat from the system Is a device for controlling the power output from the power source to the load, and includes a switching unit, an adjustment unit, a measurement unit, an instruction unit, and a switching control unit. The switching unit alternately repeats connection and disconnection between the power generation device and the load. The adjustment unit adjusts the output of the power generation device to a target value when the switching unit connects the power generation device to the load. The measurement unit measures the output of the power generation device when the switching unit disconnects the power generation device from the load. The instructing unit calculates the maximum power point of the power generator from the value measured by the measuring unit, determines a target value based on the maximum power point, and instructs the adjusting unit. When the system switches the operation mode , the switching control unit assumes the system environmental temperature fluctuation pattern in the operation mode after switching from the combination of operation modes before and after switching, and determines the speed of the environmental temperature fluctuation from the inclination of the pattern. The switching unit is made to change a cycle for cutting between the power generation device and the load according to a change with time of the speed .

  The switching control unit may monitor the operation mode of the system, and when the system switches the operation mode, the cutting cycle may be shortened from the previous value. The switching control unit may also acquire a schedule related to the change of the operation mode from the system, specify a time point at which the system switches the operation mode from the schedule, and shorten the cutting cycle from the previous value at that time. .

The switching control unit stores a numerical table or a mathematical expression indicating an assumed environmental temperature fluctuation pattern of the system for each operation mode of the system, and a cutting cycle using the numerical table or the mathematical expression corresponding to the actual operation mode. May be determined. The switching control unit may extend the cutting cycle as the period during which the fluctuation speed of the environmental temperature of the system indicated by the assumed pattern is low. In addition, the switching control unit causes the switching unit to maintain the connection between the power generation device and the load during the period when the fluctuation speed is below the threshold, while generating power from the value measured by the measurement unit before that period. The output of the apparatus may be predicted, and the predicted value may be provided to the instruction unit instead of the measurement unit.

In the period when the operation mode after switching indicates the standby state of the system, the switching control unit extends the disconnection cycle from the previous value, or causes the switching unit to maintain the connection between the power generation device and the load, The output of the power generation device may be predicted from the value measured by the measurement unit before the system enters the standby state, and the predicted value may be provided to the instruction unit instead of the measurement unit.

The switching control unit may perform any one of the following three operations in a period in which the operation mode after switching indicates a system stop state: (1) Extending the cutting cycle from the immediately preceding value; (2) While the switching unit maintains the connection between the power generation device and the load, the output of the power generation device is predicted from the value measured by the measurement unit before the system enters the stop state, and the predicted value is measured. (3) The switching unit maintains the connection between the power generation device and the load, and the adjustment unit causes the output of the power generation device to be sent to the load as it is.

  When the change in the value measured by the measurement unit exceeds the threshold, the switching control unit may shorten the cutting cycle from the previous value.

  When the system is an image forming apparatus and the power generation apparatus includes a thermoelectric conversion element that converts waste heat from the fixing unit of the image forming apparatus into electric power, the above power control apparatus may be used.

  An image forming apparatus according to one aspect of the present invention includes a feeding unit, an image forming unit, a fixing unit, an operation control unit, a power generation unit, a power control unit, and an output unit. The feeding unit feeds a plurality of sheets one by one. The image forming unit forms a toner image on the sheet fed by the feeding unit based on the image data. The fixing unit thermally fixes the toner image. The operation control unit instructs an operation mode to the fixing unit and provides image data to the image forming unit. The power generation unit includes a thermoelectric conversion element and generates power using waste heat from the fixing unit. A thermoelectric conversion element is an element that converts heat into electric power, and its output characteristics change with temperature fluctuations. The power control unit controls the power output from the power generation unit. The output unit stores or outputs the electric power.

The power control unit includes a switching unit, an adjustment unit, a measurement unit, an instruction unit, and a switching control unit. The switching unit alternately repeats connection and disconnection between the power generation unit and the output unit. The adjustment unit adjusts the output of the power generation unit to a target value when the switching unit connects the power generation unit to the output unit. The measurement unit measures the output of the power generation unit when the switching unit disconnects the power generation unit from the output unit. The instruction unit calculates the maximum power point of the power generation unit from the value measured by the measurement unit, determines a target value based on the maximum power point, and instructs the adjustment unit. When the operation control unit switches the operation mode of the fixing unit, the switching control unit assumes a temperature fluctuation pattern of the power generation unit in the operation mode after switching from the combination of the operation modes before and after switching , and the temperature from the inclination of the pattern. The speed of fluctuation is obtained, and the switching unit is caused to change the cycle for cutting between the power generation unit and the output unit in accordance with the temporal change of the speed .

The switching control unit may monitor the operation mode of the fixing unit, and when the operation control unit switches the operation mode of the fixing unit , the cutting cycle may be shortened from the immediately preceding value. The operation control unit creates a schedule for changing the operation mode of the fixing unit, and the switching control unit identifies a time point at which the operation control unit switches the operation mode of the fixing unit from the schedule, and disconnects at that time. The period may be shortened from the previous value.

For each type of operation mode of the fixing unit, the switching control unit stores a numerical table or a mathematical expression indicating a temperature variation pattern of the assumed power generation unit, and uses a numerical table or a mathematical expression corresponding to the actual operational mode, You may determine the period to cut | disconnect. The switching control unit may extend the cutting cycle as the period during which the temperature variation rate of the power generation unit indicated by the assumed pattern is low. In addition, the switching control unit allows the switching unit to maintain the connection between the power generation unit and the output unit during the period when the speed of the temperature fluctuation is lower than the threshold value, and is measured by the measurement unit before that period. The output of the power generation unit may be predicted from the value, and the predicted value may be provided to the instruction unit instead of the measurement unit.

The switching control unit extends the disconnection cycle from the previous value during the period in which the operation mode of the fixing unit is the standby mode, or causes the switching unit to maintain the connection between the power generation unit and the output unit while fixing. The output of the power generation unit may be predicted from the value measured by the measurement unit before the operation mode of the unit shifts to the standby mode, and the predicted value may be provided to the instruction unit instead of the measurement unit.

The switching control unit may perform any of the following three operations during the period in which the operation mode of the fixing unit is the sleep mode: (1) Extending the cutting cycle from the previous value; (2) The switching unit maintains the connection between the power generation unit and the output unit, while predicting the output of the power generation unit from the value measured by the measurement unit before the operation mode of the fixing unit shifts to the sleep mode. (3) The switching unit maintains the connection between the power generation unit and the output unit, and the adjustment unit outputs the output of the power generation unit as it is. Send to output.

  When the change in the value measured by the measurement unit exceeds the threshold, the switching control unit may shorten the cutting cycle from the previous value.

  In the power control apparatus according to the above aspect of the present invention, the switching control unit assumes a variation pattern of environmental conditions according to the operation mode of the system in which the power generation apparatus is incorporated. Therefore, even if the operation mode switching itself is irregular, a pattern of fluctuations in environmental conditions between the switching and the next switching is assumed. The switching control unit further causes the switching unit to change a cycle for cutting between the power generation device and the load according to the pattern. As a result, the power control apparatus can appropriately change the timing for measuring the output of the power generation apparatus in accordance with changes in environmental conditions. Thereby, this electric power control apparatus can improve the utilization efficiency of the electric power which a power generator produces, irrespective of the fluctuation | variation of environmental conditions.

  The image forming apparatus according to the above aspect of the present invention causes the power control unit to assume a temperature variation pattern of the power generation unit according to the operation mode instructed by the operation control unit to the fixing unit. Therefore, even if the operation mode switching itself is irregular, a pattern of temperature fluctuation of the power generation unit between the switching and the next switching is assumed. The power control unit further causes the switching unit to change a cycle for cutting between the power generation unit and the output unit according to the pattern. As a result, the image forming apparatus can appropriately change the timing for measuring the output of the power generation unit in accordance with the temperature fluctuation of the power generation unit. Thereby, this image forming apparatus can improve the utilization efficiency of the electric power that it generates regardless of the temperature fluctuation of the power generation unit.

1 is a schematic front view illustrating a structure of an image forming apparatus according to an embodiment of the present invention. (A) is a perspective view which shows typically the external appearance of the electric power generation part shown by FIG. 1, and its vicinity. (B) is a top view and a side view of the thermoelectric conversion element shown in (a). It is typical sectional drawing of a pair of semiconductor element vicinity which the thermoelectric conversion element shown by (b) of FIG. 2 contains. (A), (b) is a graph which respectively shows the electric current-voltage characteristic and electric power-voltage characteristic of the thermoelectric conversion element shown by (b) of FIG. FIG. 2 is a functional block diagram of the image forming apparatus shown in FIG. 1. FIG. 2 is a state transition diagram of the image forming apparatus illustrated in FIG. 1. (A), (b), and (c) are respectively the operation control units shown in FIG. 5 that “transition from the sleep mode to the operation mode”, “transition from the sleep mode to the standby mode”, 6 is a graph showing a change over time in the surface temperature of the fixing unit, which is assumed when each of “transition from an operation mode to a sleep mode” is instructed. 6 is a timing chart illustrating an example of a correspondence relationship between transition of an operation mode of the image forming apparatus, assumed temperature fluctuation of the power generation unit, and a period during which the power generation unit is disconnected from the constant current circuit. It is a flowchart of MPPT control by an electric power control part. FIG. 10 is a flowchart of step S905 shown in FIG. 9, that is, a process in which the power control unit adjusts the output of the power generation unit. (A) is a perspective view of the rice cooker which utilizes a thermoelectric conversion element for waste heat power generation. (B) is a perspective view of the refrigerator which uses a thermoelectric conversion element for waste heat power generation.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings.

  [Outline of structure of image forming apparatus]

  FIG. 1 is a schematic front view showing the structure of an image forming apparatus according to an embodiment of the present invention. In FIG. 1, elements inside the image forming apparatus 100 are depicted as if they were seen through the front surface of the housing.

  Referring to FIG. 1, an image forming apparatus 100 is, for example, a color laser printer, and includes a feeding unit 10, an image forming unit 20, a fixing unit 30, a power generation unit 40, an operation unit 50, an operation control unit 60, and power control. A unit 70 and an output unit 80 are provided. The feeding unit 10 feeds a plurality of sheets SHT one by one to the image forming unit 20. The image forming unit 20 generates toner images of four colors, yellow (Y), magenta (M), cyan (C), and black (K), on the sheet SH2 sent from the feeding unit 10 as image data. Form based on. The fixing unit 30 thermally fixes the toner image. The power generation unit 40 generates power using the waste heat from the fixing unit 30. The operation unit 50 includes a push button or a touch panel, receives a job instruction requested by the user through those operations by the user, and transmits information related to the instruction to the operation control unit 60. The operation unit 50 is also connected to a network through an external interface, receives a job request and image data from other electronic devices on the network, and passes them to the operation control unit 60. The operation control unit 60, the power control unit 70, and the output unit 80 are electronic circuits mounted on a single substrate. The operation control unit 60 controls other elements in the image forming apparatus 100 based on information from the operation unit 50. In particular, the operation control unit 60 instructs the fixing unit 30 on the operation mode and provides the image forming unit 20 with image data. The power control unit 70 controls the power output from the power generation unit 40. The output unit 80 stores or outputs the electric power. This output power is used, for example, as standby power or auxiliary power during a power failure by the operation unit 50, the operation control unit 60, or the power control unit 70.

  [Feeding department]

  Referring to FIG. 1, the feeding unit 10 includes a storage tray 11, a feed roller 12, a transport roller 13, and a timing roller 14. The storage tray 11 is built in the lower part of the image forming apparatus 100 and can store a plurality of sheets SHT. The material of the sheet SHT is, for example, paper. The feeding roller 12 feeds the uppermost sheet SH1 among the sheets SHT toward the conveying roller 13. The sheet SH1 is further conveyed to the timing roller 14 by the conveying roller 13. The timing roller 14 is generally stopped at the start of the conveyance, and starts to rotate in response to a drive signal from the operation control unit 60. Accordingly, the sheet SH2 sent from the transport roller 13 is sent out from the timing roller 14 to the image forming unit 20 at the timing indicated by the drive signal.

  [Image creation part]

  Referring to FIG. 1, the image forming unit 20 includes four image forming units 21Y, 21M, 21C, 21K, four primary transfer rollers 22Y, 22M, 22C, 22K, an intermediate transfer belt 23, and a secondary transfer. A roller 24 is provided. The image forming units 21Y,..., 21K are arranged at predetermined intervals along the horizontal direction. The primary transfer rollers 22Y,..., 22K are arranged so as to face one of the image forming units 21Y,. The intermediate transfer belt 23 is stretched around two rollers 23L and 23R, and rotates with the rotation thereof. The portion of the intermediate transfer belt 23 that is stretched in the horizontal direction passes between the image forming units 21Y,..., 21K and the primary transfer rollers 22Y,. When the intermediate transfer belt 23 rotates, each part on the surface contacts the primary transfer rollers 22Y,. The secondary transfer roller 24 is installed in parallel with one of two rollers 23R around which the intermediate transfer belt 23 is stretched, and the intermediate transfer belt 23 is sandwiched between the rollers 23R. The sheet SH2 fed from the timing roller 14 is inserted into a contact portion between the intermediate transfer belt 23 and the secondary transfer roller 24, that is, a nip.

  Each of the four image forming units 21Y,..., 21K has the same configuration, and each includes a photosensitive drum 25, a charger 26, an exposure unit 27, a developing unit 28, a cleaner 29, and an eraser lamp (see FIG. 1). Is not shown.) The outer periphery of the photosensitive drum 25 is surrounded by a charger 26 and the like. The charger 26 uniformly charges the opposed portion of the outer peripheral surface of the photosensitive drum 25. The exposure unit 27 includes a light emitting element and a lens. The light emitting element is, for example, a laser diode. The exposure unit 27 uses these to expose the charged portion on the outer peripheral surface of the photosensitive drum 25. At that time, the area where the light actually hit is neutralized. The shape of the region is determined according to the drive signal from the operation control unit 60. Thus, the area remains on the outer peripheral surface as an electrostatic latent image. The developing device 28 develops the toner of the color assigned to the image forming units 21Y,..., 21K on the electrostatic latent image. The cleaner 29 removes the remaining toner from the portion of the outer peripheral surface of the photosensitive drum 25 immediately after contacting the intermediate transfer belt 23. The eraser lamp discharges the light by uniformly irradiating light to the opposed portion of the outer peripheral surface of the photosensitive drum 25.

  Since the primary transfer voltage is applied to the primary transfer rollers 22Y,..., 22K, an electric field is generated between the primary transfer rollers 22Y,. The toner image is transferred from the photosensitive drum 25 to the surface of the intermediate transfer belt 23 by the electric field. The four image forming units 21Y,..., 21K shift the timing of the respective image forming operations in accordance with the rotation of the intermediate transfer belt 23. As a result, the toner images of the colors assigned to the respective image forming units 21Y,..., 21K are sequentially transferred to the same position on the surface of the intermediate transfer belt 23 and overlapped. In this way, a color toner image is formed on the surface of the intermediate transfer belt 23.

  Since a secondary transfer voltage is applied to the secondary transfer roller 24, an electric field is generated between the secondary transfer roller 24 and the intermediate transfer belt 23. Due to the electric field, the color toner image on the intermediate transfer belt 23 is transferred to the surface of the sheet SH2 passing through the nip between the intermediate transfer belt 23 and the secondary transfer roller 24. Thereafter, the secondary transfer roller 24 sends the sheet SH2 to the fixing unit 30.

  [Fixing part]

  The fixing unit 30 includes a fixing roller 31, a pressure roller 32, and a temperature sensor 34. The fixing roller 31 and the pressure roller 32 are arranged in parallel with each other and are in contact with each other. The sheet SH2 fed from the image forming unit 20 is inserted into a contact portion between them, that is, a fixing nip. The fixing roller 31 incorporates a halogen lamp as a heater, and applies heat released therefrom to the portion of the sheet SH2 inserted into the fixing nip. On the other hand, the pressure roller 32 applies pressure to the portion of the sheet SH2 and presses it against the fixing roller 31. When the portion of the sheet SH2 where the toner image is formed by the image forming unit 20 is inserted into the fixing nip, the toner image is formed by the heat from the fixing roller 31 and the pressure from the pressure roller 32. It settles on the surface of SH2. The temperature sensor 34 is installed in the vicinity of the central portion of the fixing roller 31, measures the temperature of the fixing roller 31, and notifies the operation control unit 60 of the temperature. The measured value of the temperature is used by the operation control unit 60 to control the amount of heat generated by the halogen lamp, that is, to control the temperature.

  The fixing unit 30 causes the sheet SH2 after being subjected to the heating / pressurizing process to enter between a pair of guide plates 35 arranged in parallel. Since the space partitioned by the guide plates 35 is connected from the upper part of the fixing unit 30 to the discharge port 36, the sheet SH2 moves toward the discharge port 36 along the space. A pair of discharge rollers 37 is installed at the discharge port 36, and the sheet SH3 reaching the discharge port 36 is drawn into a nip between them, and the sheet SH3 is discharged to an external discharge tray 38.

  [Power generation section]

  Referring to FIG. 1, the power generation unit 40 is installed outside the portion of the housing of the image forming apparatus 100 where the inner side faces the fixing unit 30. This part is suitable for the installation location of the power generation unit 40 in that it satisfies the following three conditions: (A) The location is maintained at a temperature sufficiently higher than room temperature by waste heat from the fixing unit 30; (B) Even if the power generation unit 40 absorbs heat at that location, the temperature of the fixing nip of the fixing unit 30 does not change; (C) the temperature change at that location shows high followability to the temperature change of the fixing unit 30. (That is, heat is easily transmitted from the fixing unit 30 and easily escapes to other places). If it is a place where the condition (A) is satisfied, the output power of the power generation unit 40 is high. If the place satisfies the condition (B), the power generation unit 40 can be used while maintaining high printing quality. If the location satisfies the condition (C), the temperature variation pattern can be easily assumed from the temperature variation pattern of the fixing unit 30, which is advantageous for MPPT control with respect to the output of the power generation unit 40. The reason will be described later.

  FIG. 2A is a perspective view schematically showing the external appearance of the power generation unit 40 shown in FIG. 1 and the vicinity thereof. Referring to FIG. 2A, on the lower side of the discharge port 36, the upper surface of the discharge tray 38 in which the surface of the casing of the image forming apparatus 100 is vertically cut and smoothly curved downward from the horizontal direction. Intersects the edge of The power generation unit 40 is installed in the vicinity of the intersection with the upper surface of the paper discharge tray 38 on the surface of the housing. In the power generation unit 40, a plurality of thermoelectric conversion elements 41 are arranged in a matrix. All of these thermoelectric conversion elements 41 are connected in series by wiring in the power generation unit 40.

  FIG. 2B is a top view and a side view of the thermoelectric conversion element 41 shown in FIG. Referring to FIG. 2B, the thermoelectric conversion element 41 includes two substrates 42 and 43, a plurality of P-type semiconductor elements 44P, and the same number of N-type semiconductor elements 44N. The substrates 42 and 43 are both rectangular insulators, for example, ceramics, both have the same width WD, and the length L1 of one substrate 42 is shorter than the length L2 of the other substrate 43. As an example, the width WD is 14 mm, and the lengths L1 and L2 are 14 mm and 18 mm, respectively. The P-type semiconductor element 44P and the N-type semiconductor element 44N are obtained by adding trace amounts of antimony (Sb) and selenium (Se) to a bismuth (Bi) -tellurium (Te) based semiconductor, for example. The semiconductor elements 44P and 44N are arranged in a matrix between the two substrates 42 and 43. In particular, the P-type semiconductor element 44P and the N-type semiconductor element 44N are adjacent to each other. The height HT of the thermoelectric conversion element 41, that is, the distance from the upper surface of one of the two substrates to the bottom surface of the other 43 in a state where the semiconductor elements 44P and 44N are sandwiched therebetween is, for example, 2.2 mm. Although not shown in FIG. 2, the two substrates 42 and 43 include conductive layers on the surfaces facing each other. These conductive layers connect the upper end of the P-type semiconductor element 44P to the upper end of the adjacent N-type semiconductor element 44N, and connect the lower end to the lower end of another adjacent N-type semiconductor element 44N. Thereby, all the P-type semiconductor elements 44P and the N-type semiconductor elements 44N are alternately connected in series.

  FIG. 3 is a schematic cross-sectional view in the vicinity of a pair of semiconductor elements 44P and 44N included in the thermoelectric conversion element 41 shown in FIG. Hereinafter, the principle of power generation by the thermoelectric conversion element 41 will be described with reference to FIG.

  One of the two substrates 42 contacts the surface of the casing of the image forming apparatus 100 to absorb the waste heat from the fixing unit 30, and the other 43 is exposed to the external space and releases the waste heat to the space. . At this time, since a temperature difference ΔT is generated between the substrates 42 and 43, a thermal gradient is generated in each semiconductor element 44P and 44N in the direction from the high temperature substrate 42 to the low temperature substrate 43 (FIG. (See arrow HGR shown in 3). This thermal gradient concentrates the carriers (holes HLE and electron ELC) of the semiconductor elements 44P and 44N on the low temperature side rather than on the high temperature side. As a result, a potential difference is generated between both ends of each of the semiconductor elements 44P and 44N. This is the so-called Seebeck effect. Since all the semiconductor elements 44P and 44N are connected in series by the conductive layers 45, 46 and 47 of the substrates 42 and 43, the sum of the potential difference in all the semiconductor elements 44P and 44N occurs at both ends of the series connection. Appears as power EMF. Thus, the thermoelectric conversion element 41 converts waste heat from the fixing unit 30 into DC power.

  4A and 4B are graphs showing current-voltage characteristics and power-voltage characteristics of the thermoelectric conversion element 41 shown in FIG. 2B, respectively. Referring to FIG. 4A, the thermoelectric conversion element 41 reduces the output current substantially linearly (that is, within an allowable range) as the output voltage increases. Therefore, as shown in FIG. 4B, the power-voltage characteristic is substantially represented by an upwardly convex parabola. A pair of the voltage value VPK and the current value when the vertex PK of the parabola or the maximum value of the power represented by the vertex PK is output is referred to as a “maximum power point”.

  Referring to FIG. 4B, the power-voltage characteristic of the thermoelectric conversion element 41 varies depending on the temperature difference ΔT between the two substrates 42 and 43. In particular, the maximum power point PK is displaced along the alternate long and short dash line CV shown in FIG. Table 1 shows an example of the relationship between the temperature difference ΔT and the maximum power point PK.

  Here, the open voltage is a voltage value when the output end of the thermoelectric conversion element 41 is disconnected from the load and opened, and the characteristic curves shown in FIGS. 4A and 4B are other than the origin. It is equal to the voltage value VOP when intersecting the coordinate axes of “current = 0 [mA]” and “power = 0 [mW]”. As can be seen from Table 1, the voltage value VPK at the maximum power point is substantially equal to 1/2 the open circuit voltage VOP: VPK = VOP / 2.

  In the installation location of the power generation unit 40 shown in FIGS. 1 and 2, the temperature difference ΔT between the substrates 42 and 43 of the thermoelectric conversion element 41 is that of the portion of the housing whose inner side faces the fixing unit 30. Corresponds to the difference between temperature and room temperature. The temperature change in that portion of the casing shows high followability with respect to the temperature change of the fixing unit 30. On the other hand, the change in the room temperature is negligible compared to the temperature change in that portion. Therefore, it may be considered that “the maximum power point PK of the thermoelectric conversion element 41 changes with the temperature of the portion of the casing in which the power generation unit 40 is installed”.

  [Operation control unit]

  The operation control unit 60 includes a CPU, a RAM, and a ROM. The CPU controls other functional units in the image forming apparatus 100 according to the firmware. The RAM provides a work area for executing firmware to the CPU. The ROM includes a non-writable memory and a rewritable memory such as an EEPROM. The former stores firmware, and the latter provides a storage area for environment variables and the like for the CPU.

  FIG. 5 is a functional block diagram of the image forming apparatus 100 shown in FIG. Referring to FIG. 5, the operation control unit 60 first causes the operation unit 50 to accept a job request JBR or image data IMG from a user or a network according to the firmware. Next, the operation control unit 60 operates the other function units of the image forming apparatus 100 such as the feeding unit 10, the image forming unit 20, the fixing unit 30, the power control unit 70, the output unit 80, and the like based on the request JBR. To control. Specifically, the operation control unit 60 instructs each function unit to select an operation mode to be selected at the present time. For example, the operation control unit 60 represents the type of operation mode to be instructed by one of environment variables, and prompts each function unit to refer to the environment variable. Thereby, the operation control unit 60 causes each function unit to start processing according to the instructed operation mode.

  FIG. 6 is a state transition diagram of the image forming apparatus 100 shown in FIG. Referring to FIG. 6, the operation mode of the image forming apparatus 100 is roughly divided into three types: an operation mode RNG, a standby mode WTG, and a sleep mode SLP. Execute printing. In this mode, the feeding unit 10 continuously feeds the required number of sheets, the image forming unit 20 repeats the formation of the toner image and the transfer to the sheet, and the fixing unit 30 heats and heats the sheet. Continue with pressure. The standby mode WTG prepares and maintains a state where a sheet can be printed. In this mode, the feeding unit 10 and the image forming unit 20 are stopped, and the fixing unit 30 preheats the fixing roller 31 and keeps it at an appropriate temperature. Sleep mode SLP minimizes power consumption. In this mode, the fixing unit 30 is stopped in addition to the feeding unit 10 and the image forming unit 20, and in particular, power supply to the heater 31A is shut off.

  The operation control unit 60 updates the value of the environment variable indicating the current operation mode according to the event that has occurred in the image forming apparatus 100. Thereby, each operation mode RNG, WTG, SLP shifts to another mode. For example, the operation mode RNG shifts to the standby mode WTG in response to the stop event STP, and shifts to the sleep mode SLP in response to the power-off event PFF. The stop event STP includes completion of printing, pressing of a stop button, and reception of a stop command from the network. The power off event PFF includes pressing of the power off button. The operation mode RNG is also continued when a new print request JBR occurs. The standby mode WTG shifts to the operation mode RNG in response to the print request JBR, and shifts to the sleep mode SLP in response to the expiration of the standby period WTP or the power-off event PFF. The sleep mode SLP shifts to the operation mode RNG according to the print request JBR, and shifts to the standby mode WTG according to the return event WKP. The return event WKP includes pressing of an arbitrary push button, touching the touch panel, and receiving a return command from the network.

  The operation control unit 60 further provides necessary information for each operation mode to each functional unit. For example, the operation mode RNG is instructed as follows: For the feeding unit 10, the operation control unit 60 rotates the type and number of sheets to be fed continuously and the timing roller 14. The timing for starting the operation is determined and transmitted by the drive signal DS1 (see FIG. 5). For the image forming unit 20, the operation control unit 60, based on the image data IMG, information on the toner images to be formed on the photosensitive drums 25 of the respective image forming units 22Y,. Is determined and transmitted by the drive signal DS2. For the fixing unit 30, the operation control unit 60 first requests the measured value of the temperature sensor 34, and determines the temperature control amount for the fixing roller 31, that is, the amount of heat generated by the heater 31A based on the measured value. Communicate with signal DS3.

  [Power control unit]

  Referring back to FIG. 5, the power control unit 70 includes a switching unit 71, a constant current circuit 72, a measurement unit 73, an instruction unit 74, and a switching control unit 75. Using these function units 71-75, the power control unit 70 performs MPPT control on the output of the power generation unit 40.

  The switching unit 71 connects the power generation unit 40 to the constant current circuit 72 and the measurement unit 73 alternately. That is, the switching unit 71 repeats the following two operations (A) and (B): (A) The power generation unit 40 is disconnected from the constant current circuit 72 and connected to the measurement unit 73, and the state is maintained for a predetermined time. . The time is set to a predetermined value, for example, 0.5 seconds in advance based on the time required for measurement by the measurement unit 73. (B) The power generation unit 40 is disconnected from the measurement unit 73 and connected to the constant current circuit 72, and the state is maintained for a predetermined time. The switching unit 71 determines the time based on an instruction from the switching control unit 75. The instruction defines, for example, a cycle for disconnecting the power generation unit 40 from the constant current circuit 72.

  The constant current circuit 72 connects the switching unit 71 to the output unit 80, and supplies the current output from the power generation unit 40 to the output unit 80 while being connected to the power generation unit 40 by the switching unit 71. At that time, the constant current circuit 72 adjusts the amount of the current to maintain the target value instructed from the instructing unit 74. That is, the constant current circuit 72 functions as an adjustment unit for the output of the power generation unit 40.

  The measurement unit 73 measures the open circuit voltage of the power generation unit 40 when connected to the power generation unit 40 by the switching unit 71. As is clear from FIG. 4B, ½ of this open circuit voltage VOP corresponds to the output voltage VPK at the maximum power point of the power generation unit 40: VPK = VOP / 2.

  The instruction unit 74 calculates the maximum power point of the power generation unit 40 from the voltage value measured by the measurement unit 73. For example, the instructing unit 74 stores a numerical table or a mathematical expression representing the current-voltage characteristics shown in FIG. 4A, and sets the current value corresponding to 1/2 of the measured voltage value. Calculate from the number table or mathematical formula. The instructing unit 74 further determines the current value at the maximum power point as a target value and instructs the constant current circuit 72.

  The switching control unit 75 determines a cycle for disconnecting the power generation unit 40 from the constant current circuit 72 and instructs the switching unit 71. This period is substantially equal to the period in which the measurement unit 73 measures the open circuit voltage of the power generation unit 40. In particular, the switching control unit 75 assumes a temperature variation pattern of the power generation unit 40 in accordance with the operation mode instructed from the operation control unit 60, and plans the change of the cycle according to the pattern. Specifically, the switching control unit 75 first obtains the value of the environment variable representing the type of the current operation mode from the operation control unit 60 in accordance with an instruction from the operation control unit 60, and from that value, the operation mode Identify Next, the switching control unit 75 retrieves a numerical table or a mathematical expression representing a pattern assumed in the operation mode, for example, from a storage device built therein. The storage device stores in advance a numerical table representing an assumed pattern for each type of operation mode. Subsequently, the switching control unit 75 calculates the slope at each point of the pattern from the retrieved numerical table or the like, that is, the speed at each time point of the temperature fluctuation of the power generation unit 40, and based on the calculated value, To determine the value that the above cycle should take. The switching control unit 75 further determines the value to be taken for the cycle according to the change over time in the inclination of the pattern, the duration of the operation mode, or the change rate of the measurement value of the measurement unit 73, that is, the open circuit voltage of the power generation unit 40. Corresponds to the rate of change. In this way, the change of the period is planned. Further, the switching control unit 75 monitors the duration of the operation mode or the change rate of the measurement value of the measurement unit 73, and changes the cycle so that the above cycle corresponds to the plan as planned.

  [Output section]

  Referring to FIG. 5, the output unit 80 includes a constant voltage circuit 81, a storage battery 82, a switch 83, and an output port 84. Using these functional units 81-84, the output unit 80 stores the electric power output from the power generation unit 40 or outputs it to other functional units such as the operation unit 50, the operation control unit 60, and the power control unit 70. To do.

  The constant voltage circuit 81 is connected between the constant current circuit 72 and the storage battery 82 and supplies the current output from the constant current circuit 72 to the storage battery 82. At that time, the constant voltage circuit 72 adjusts the level of the voltage applied to the storage battery 82 and maintains the target value instructed from the operation control unit 60.

  The storage battery 82 is, for example, a lithium ion battery, and is connected between the constant voltage circuit 81 and the ground conductor. The operation control unit 60 changes the target value to be instructed to the constant voltage circuit 81 according to the charging method of the storage battery 82. The charging method is determined by the type of storage battery 82. For example, when the storage battery 82 is a lithium ion battery, the operation control unit 60 performs charging by a constant current constant voltage method (CCCV method).

  The switch 83 connects the connection point between the constant voltage circuit 81 and the storage battery 82 to the output port 84 or disconnects the connection point from the output port 84 in accordance with an instruction from the operation control unit 60. For example, the operation control unit 60 causes the switch 83 to connect the constant voltage circuit 81 and the storage battery 82 to the output port 84 in the sleep mode or during a power failure. As a result, the power generated by the power generation unit 40 and the power stored in the storage battery 82 are sent to the operation unit 50, the operation control unit 60, or the power control unit 70 through the output port 84, and used as standby power or auxiliary power. Used.

  [MPPT control by power control unit]

  The thermoelectric conversion element 41 has low power generation efficiency compared to, for example, a solar cell. Therefore, it is important to increase the utilization efficiency of the power generated by the power generation unit 40 as much as possible. For the purpose of improving the utilization efficiency, the power control unit 70 uses the following three facts (1) to (3) for MPPT control on the power generation unit 40: (1) The maximum power point of the thermoelectric conversion element 41 is 1 and 2 depends on the temperature of the installation location of the power generation unit 40 shown in (a); (2) The temperature change at that location is highly followable to the temperature change of the fixing unit 30; (3) The temperature fluctuation of the fixing unit 30 shows a characteristic pattern according to the operation mode. Details of the temperature fluctuation of the fixing unit according to the operation mode will be described later.

  By utilizing these facts (1) to (3), the MPPT control according to the embodiment of the present invention is particularly characteristic in the following two points. First, the power control unit 70 assumes a temperature variation pattern of the power generation unit 40 according to the operation mode instructed by the operation control unit 60 to the fixing unit 30. Specifically, based on the facts (2) and (3), the pattern is determined under the assumption that “the pattern has the same characteristics as the temperature fluctuation pattern of the fixing unit 30”. Second, the power control unit 70 sets a cycle for causing the switching unit 71 to disconnect the power generation unit 40 from the constant current circuit 72 according to an assumed pattern, that is, a cycle for causing the measurement unit 73 to measure the open circuit voltage of the power generation unit 40. change. Specifically, from the fact (1), since the inclination of the assumed pattern, that is, the speed of temperature fluctuation of the power generation unit 40 corresponds to the speed of displacement of the maximum power point, the power control unit 70 determines the inclination of the pattern. The period is shortened in a period where the temperature is large, that is, in a period where the temperature fluctuation of the power generation unit 40 is fast. On the other hand, the period is extended in a period in which the inclination is small, that is, in a period in which the temperature fluctuation is slow. Details of the change of the period according to the operation mode will be described later.

  Due to these two characteristics, the power control unit 70 appropriately changes the timing of measuring the open-circuit voltage of the power generation unit 40 according to the temperature fluctuation of the power generation unit 40, thereby further improving the utilization efficiency of the power generated by the power generation unit 40. Can be improved. Actually, the measuring unit 73 frequently measures the output of the power generation unit 40 during a period in which rapid temperature fluctuations of the power generation unit 40 are assumed, so the instruction unit 74 updates the target value frequently. As a result, the constant current circuit 72 can accurately follow the change in the output current of the power generation unit 40 with the displacement of the maximum power point. On the contrary, during the period in which the gradual temperature fluctuation of the power generation unit 40 is assumed, the switching unit 71 maintains the connection between the power generation unit 40 and the constant current circuit 72 for a long time. The amount of power supplied to the output unit 80 can be increased.

    -Fluctuation in temperature of the fixing unit according to the operation mode-

  The fixing unit 30 changes the temperature control condition for the fixing roller 31 in accordance with the operation mode instructed from the operation control unit 60. Specifically, in the operation mode RNG, regardless of continuous sheet printing, the heat generation amount of the heater 31A is adjusted to a sufficiently large value so that the temperature of the fixing roller 31 is maintained at an appropriate value, for example, 180 ° C. The In the standby mode WTG, the fixing roller 31 is preheated and kept warm so that printing of a sheet is immediately executed as required. Further, when the standby mode WTG continues for a predetermined time, for example, 40 minutes, the temperature target value is lowered from the appropriate value in the operation mode RNG: for example, changed from 180 ° C. to 160 ° C. As a result, the amount of heat generated by the heater 31A can be suppressed, so that power consumption in the standby mode WTG is reduced. In the sleep mode SLP, since the power supply to the heater 31A is cut off, the temperature control for the fixing roller 31 is stopped.

  When the fixing unit 30 changes the temperature control condition for the fixing roller 31 according to the operation mode, the adjustment method of the heat generation amount of the heater 31A changes for each operation mode. As a result, the temperature fluctuation of the fixing unit 30 shows a characteristic pattern according to the operation mode.

  7A, 7 </ b> B, and 7 </ b> C, the operation control unit 60 performs “transition from sleep mode to operation mode”, “transition from sleep mode to standby mode”, and “operation mode”, respectively. 6 is a graph showing a change with time in the surface temperature of the fixing unit 30 that is assumed when each of the commands “transition from to sleep mode” is instructed. As these graphs show, the change over time shows a characteristic pattern according to the operation mode before and after the transition.

  Referring to FIG. 7A, after the transition from the sleep mode to the operation mode, the change in the surface temperature of the fixing unit 30 is assumed as follows. Since the heat generation of the heater 31A is stopped in the sleep mode, the surface temperature is substantially equal to room temperature. In the first period PR1 immediately after the transition, the temperature of the fixing roller 31 rapidly increases from around room temperature due to the heat generated by the heater 31A, and thus the surface temperature also increases rapidly. Thereafter, when the temperature of the fixing roller 31 reaches an appropriate value, for example, 180 ° C., the first period P01 shifts to the second period P02. In the second period PR2, since the heat generation amount of the heater 31A is adjusted so that the temperature of the fixing roller 31 is maintained at an appropriate value, the surface temperature is also maintained substantially constant.

  Referring to FIG. 7B, after the transition from the sleep mode to the standby mode, the surface temperature of the fixing unit 30 changes as follows. In the first period PW1 immediately after the transition, the fixing roller 31 is preheated and its temperature rises rapidly from around room temperature, so the surface temperature also rises sharply. Thereafter, when the temperature of the fixing roller 31 reaches an appropriate value, for example, 180 ° C., the first period PW1 shifts to the second period PW2. In the second period PW2, since the amount of heat generated by the heater 31A is adjusted so that the temperature of the fixing roller 31 is maintained at an appropriate value, the surface temperature is also maintained substantially constant. Since the heat generation amount of the heater 31A is suppressed when the standby mode continues for a predetermined time, for example, 40 minutes, the second period PW2 shifts to the third period PW3. In the third period PW3, since the temperature of the fixing roller 31 decreases, the surface temperature also decreases. Thereafter, when the temperature of the fixing roller 31 falls to the next target value, for example, 160 ° C., the third period PW3 shifts to the fourth period PW4. In the fourth period PW4, the heat generation amount of the heater 31A is adjusted so that the temperature of the fixing roller 31 is maintained at the target value, so that the surface temperature is also maintained substantially constant.

  Referring to FIG. 7C, after the transition from the operation mode to the sleep mode, the surface temperature of the fixing unit 30 changes as follows. Since the heating value of the heater 31A is maintained at a large value in the operation mode, the surface temperature is considerably higher than the room temperature, as shown in FIG. In the first period PS1 immediately after the transition, the temperature of the fixing roller 31 rapidly decreases due to the stop of the heater 31A, and thus the surface temperature also rapidly decreases. Thereafter, the temperature of the fixing roller 31 is less likely to drop as it approaches its surrounding temperature. The first period PS1 shifts to the second period PS2 when the temperature decrease rate of the fixing roller 31 falls below a predetermined threshold. In the second period PS2, since the temperature decrease of the fixing roller 31 is gentle, the surface temperature also gradually decreases.

  According to FIG. 6, in addition to the above-mentioned combinations of operation modes that can be shifted, “transition from standby mode to operation mode”, “transition from operation mode to standby mode”, and “from standby mode” Transition to sleep mode ”. For these combinations as well, the temporal change in the surface temperature of the fixing unit 30 is assumed as follows.

  The temporal change of the surface temperature assumed for the transition from the standby mode to the operation mode is the same as that shown in FIG. In fact, immediately after the transition, the heat transfer from the fixing roller 31 to the sheet starts, but the heat generation amount of the heater 31A is changed so that the temperature of the fixing nip is maintained at an appropriate value regardless of the movement. The As a result, the temperature of the fixing roller 31 fluctuates greatly, and the surface temperature of the fixing unit 30 also fluctuates greatly. Thereafter, if the printing operation is continuously continued, the amount of heat generated by the heater 31A is kept constant, so that any fluctuation in the temperature of the fixing roller 31 and the surface temperature of the fixing unit 30 is stabilized.

  The temporal change of the surface temperature assumed for the transition from the operation mode to the standby mode is the same as that shown in FIG. 7B. In fact, immediately after the transition, there is no heat transfer from the fixing roller 31 to the sheet, so the heat generation amount of the heater 31A is adjusted again so that the temperature of the fixing nip is maintained at an appropriate value in consideration of that amount. The As a result, the temperature of the fixing roller 31 fluctuates relatively greatly, and the surface temperature of the fixing unit 30 also fluctuates greatly. Thereafter, the temperature of the fixing roller 31 is maintained at an appropriate value until the continuation time of the standby mode reaches a predetermined value, and after that point, the temperature is maintained at a value lower than the appropriate value. Therefore, the change in the surface temperature of the fixing unit 30 is the same as that in the second period PW2, the third period PW3, and the fourth period PW4 shown in FIG.

  The temporal change of the surface temperature assumed for the transition from the standby mode to the sleep mode is the same as that shown in (c) of FIG. Actually, in the standby mode, the temperature of the fixing roller 31 is as high as that in the operation mode, so the surface temperature of the fixing unit 30 is considerably higher than the room temperature. Therefore, immediately after the transition, the temperature of the fixing roller 31 rapidly decreases due to the stop of the heater 31A, so that the surface temperature also decreases rapidly. Thereafter, since the rate of temperature decrease of the fixing roller 31 is decreased, the surface temperature is gradually decreased.

  As described above, the temperature fluctuation of the fixing unit 30 shows a characteristic pattern according to the operation mode. However, these patterns are common in the following two points. First, the temperature fluctuation is severe immediately after switching the operation mode. Second, the temperature stabilizes after a certain amount of time has elapsed since the operation mode was switched. The length of the period in which the temperature fluctuation is intense and the length of time required for temperature stabilization differ depending on the operation mode.

    -Change of period according to operation mode-

  As described above, the temperature fluctuation of the fixing unit 30 shows a characteristic pattern according to the operation mode. It is inferred from the above facts (2) and (3) that the same characteristic pattern also shows the temperature fluctuation of the power generation unit 40. Accordingly, the numerical table or mathematical expression stored in advance in the switching control unit 75 is set so as to represent the temperature variation pattern of the fixing unit 30 shown in FIG.

  In response to an instruction from the operation control unit 60, the switching control unit 75 first searches a number table corresponding to the current operation mode from the stored ones, and uses the searched ones for the pattern. Calculate the slope. Next, the switching control unit 75 determines a cycle for disconnecting the power generation unit 40 from the constant current circuit 72 according to the magnitude of the inclination. For example, the speed of displacement of the maximum power point that satisfies the condition that “the maximum power point is displaced by the upper limit of the measurement error of the measurement unit 73 while the measurement unit 73 repeats the measurement twice at a specific period” is obtained. The magnitude of the pattern inclination corresponding to the speed is set as the threshold value. When the calculated magnitude of the slope is equal to or smaller than the threshold value, the maximum power point is displaced only at a speed equal to or lower than the speed satisfying the above condition. That is, while the measurement unit 73 repeats the measurement twice at a specific cycle, the displacement amount of the maximum power point does not exceed the allowable upper limit of the measurement error of the measurement unit 73, so that even if the maximum power point is considered to be constant. Good. Therefore, the cycle for disconnecting the power generation unit 40 from the constant current circuit 72 is determined to be equal to or greater than a specific cycle. On the other hand, when the calculated magnitude of the slope exceeds the threshold, the displacement of the maximum power point is faster than the speed that satisfies the above condition. That is, while the measurement unit 73 repeats the measurement twice at a specific cycle, the maximum power point is displaced beyond the allowable upper limit of the measurement error of the measurement unit 73, and thus the displacement cannot be ignored. Therefore, the cycle for disconnecting the power generation unit 40 from the constant current circuit 72 is shorter than the specific cycle.

  The switching control unit 75 plans to change the cycle for disconnecting the power generation unit 40 from the constant current circuit 72 in accordance with the temporal change in the assumed inclination of the pattern. In the plan, the value to be taken in the cycle is associated with the duration of the operation mode or the change rate of the measurement value of the measurement unit 73, that is, the change rate of the open circuit voltage of the power generation unit 40. Further, the switching control unit 75 changes the above period according to the duration of the operation mode or the change rate of the measurement value of the measurement unit 73 according to the plan.

  FIG. 8 is a timing chart showing an example of the correspondence between the transition of the operation mode of the image forming apparatus 100, the assumed temperature fluctuation of the power generation unit 40, and the period during which the power generation unit 40 is disconnected from the constant current circuit 72. It is. Referring to FIG. 8, the image forming apparatus 100 switches the operation mode according to events that occur at times T1, T2, T3, and T4. In response to the switching, the operation control unit 60 instructs the operation mode after switching to the fixing unit 30, the switching control unit 75, and the like. The fixing unit 30 changes the temperature control condition for the fixing roller 31 according to the instructed operation mode. The switching control unit 75 assumes a temperature fluctuation pattern of the power generation unit 40 according to the instructed operation mode, and plans a change in the cycle for disconnecting the power generation unit 40 from the constant current circuit 72 according to the pattern. The period changes according to the plan at times T1, T2, T21, T3, T31, T32, T33, T4, and T41.

  The transition of the operation mode shown in FIG. 8 is as follows. The sleep mode is maintained until the first time T1. At the first time T1, a return event occurs, and the sleep mode shifts to the standby mode accordingly. At the second time T2, printing is requested, and the standby mode shifts to the operation mode accordingly. At the third time T3, all the requested printing is completed, and the operation mode shifts to the standby mode accordingly. Thereafter, no new job is requested until a predetermined standby time elapses, so that the standby mode shifts to the sleep mode at the fourth time T4 after the standby time from the third time.

  The switching control unit 75 assumes a temperature fluctuation pattern of the power generation unit 40 at each of the times T1, T2, T3, and T4 at which the operation mode is switched, and the power generation unit 40 is connected from the constant current circuit 72 according to the pattern. Plan to change the cutting cycle. Further, according to the plan, the switching control unit 75 changes the period according to the duration of the operation mode from each time T1,..., T4 or the change rate of the measurement value of the measurement unit 73. As a result, the cycle changes as follows.

  Until the first time T1, the temperature of the power generation unit 40 is stably maintained in the vicinity of room temperature, and thus the above period is maintained at an allowable upper limit value, for example, 60 seconds.

  At the first time T1, a pattern of four periods PW1-PW4 shown in FIG. 7B is assumed. That is, after the first time T1, the temperature of the power generation unit 40 rapidly increases from around room temperature in the first period PW1, stabilizes in the second period PW2, decreases rapidly in the third period PW3, and decreases in the fourth period PW4. Stabilize again. According to this pattern, the change of the cycle after the first time T1 is planned as follows. Since the operation mode is switched at the first time T1, the cycle is shortened to an allowable lower limit value, for example, 2 seconds. In the first period PW1 and the third period PW3, the inclination of the pattern exceeds the threshold value, so that the cycle is shortened to the allowable lower limit value. In the second period PW2 and the fourth period PW4, the inclination of the pattern falls below the threshold value, so that the cycle is extended from the allowable lower limit value. According to this plan, the period is actually maintained at the allowable lower limit after the first time T1. However, since the second time T2 is earlier than the second period PW2 assumed at the first time T1, the above plan is discarded at the second time T2.

  At the second time T2, patterns of two periods PR1 and PR2 shown in FIG. 7A are assumed. That is, after the second time T2, the temperature of the power generation unit 40 varies rapidly in the first period PR1, and stabilizes in the second period PR2. According to this pattern, the change of the cycle after the second time T2 is planned as follows. Since the operation mode is switched at the second time T2, the cycle is maintained at the allowable lower limit value. In most of the first period PR1, the inclination of the pattern exceeds the threshold value, so that the period is maintained at the allowable lower limit value in the first period PR1. In the second period PR2, since the inclination of the pattern falls below the threshold value, the cycle is extended from the allowable lower limit value, and is set to 30 to 60 seconds, for example. Since the cycle is changed according to this plan, the cycle actually changes as described above in the period from the second time T2 to the third time T3.

  At the third time T3, patterns of four periods PW1 to PW4 shown in FIG. 7B are assumed. That is, after the third time T3, the temperature of the power generation unit 40 varies rapidly in the first period PW1, stabilizes in the second period PW2, falls rapidly in the third period PW3, and stabilizes again in the fourth period PW4. To do. According to this pattern, the change of the period after the third time T3 is planned as follows. Since the operation mode is switched at the third time T3, the cycle is shortened to the allowable lower limit value. In most of the first period PW1, since the inclination of the pattern exceeds the threshold value, the period is maintained at the allowable lower limit value in the first period PW1. In the second period PW2, since the inclination of the pattern falls below the threshold value, the cycle is extended from the allowable lower limit value, and is set to 30 to 60 seconds, for example. In the third period PW3, since the inclination of the pattern exceeds the threshold value, the cycle is shortened to the allowable lower limit value. In the fourth period PW4, since the inclination of the pattern falls below the threshold value, the cycle is extended from the allowable lower limit value, and is set to 30 to 60 seconds, for example. Since the cycle is changed according to this plan, the cycle actually changes as described above in the period from the third time T3 to the fourth time T4.

  At the fourth time T4, a pattern of two periods PS1 and PS2 shown in FIG. 7C is assumed. That is, after the fourth time T4, the temperature of the power generation unit 40 rapidly decreases during the first period PS1 and stabilizes during the second period PS2. According to this pattern, the change of the cycle after the fourth time T4 is planned as follows. Since the operation mode is switched at the fourth time T4, the cycle is shortened to the allowable lower limit value. In the first period PS1, since the inclination of the pattern exceeds the threshold value, the cycle is maintained at the allowable lower limit value. In the second period PS2, since the inclination of the pattern falls below the threshold value, the cycle is extended from the allowable lower limit value, and is set to 30 to 60 seconds, for example. Since the cycle is changed according to this plan, the cycle actually changes as described above after the fourth time T4.

  In the above plan, the switching control unit 75 associates the value to be taken of the period with the duration of the operation mode or the change rate of the measurement value of the measurement unit 73, that is, the change rate of the open circuit voltage of the power generation unit 40. Accordingly, the switching control unit 75 determines the time at which the cycle should be changed during the period in which one operation mode continues, that is, the end time T21 of the first period PR1 after the second time T2, and the three times after the third time T3. The end times T31, T32, T33 of the periods PW1, PW2, PW3 and the end time T41 of the first period PS1 after the fourth time T4 are detected as follows. The switching control unit 75 estimates the end times T21, T31, T32, T33, and T41 of the periods PR1, PW1, PW2, PW3, and PS1 from the assumed pattern, and the duration of each operation mode, that is, the second time. From the elapsed time from T2, the third time T3, and the fourth time T4, estimated end times T21, T31,..., T41 are detected. In addition, the switching control unit 75 estimates the threshold for the change rate of the open circuit voltage of the power generation unit 40 from the threshold for the inclination of the pattern used to identify each period PR1, PR2, PW1, ..., PW4, PS1, PS2. The end times T21, T31,..., T41 are detected from the result of comparing the change rate of the measurement value of the measurement unit 73 and the threshold value.

  As described above, the switching control unit 75 assumes a pattern of temperature fluctuation of the power generation unit 40 according to the operation mode, and the cycle of disconnecting the power generation unit 40 from the constant current circuit 72 according to the magnitude of the inclination of the pattern. To change. As a result, during a period in which fast temperature fluctuations are assumed, such as when the operation mode is switched, the power generation unit 40 is frequently connected to the measurement unit 73, and moderate temperature fluctuations such as long-term continuation of the standby mode are assumed. In the period, the power generation unit 40 is connected to the constant current circuit 72 for a long time.

    -Flow chart of MPPT control-

  FIG. 9 is a flowchart of MPPT control by the power control unit 70. This control is started when the main power supply of the image forming apparatus 100 is turned on.

  In step S901, the switching control unit 75 assumes a temperature fluctuation pattern of the power generation unit 40 in the current operation mode. Specifically, the switching control unit 75 searches a stored numerical table or mathematical expression representing an assumed pattern according to the operation mode. Thereafter, the process proceeds to step S902.

  In step S <b> 902, the switching control unit 75 plans to change the cycle for disconnecting the power generation unit 40 from the constant current circuit 72 in accordance with the temporal change in the assumed pattern inclination. Specifically, the switching control unit 75 first calculates the gradient of the temperature variation pattern using the numerical table searched in step S901, and determines the above-described cycle according to the magnitude of the gradient. Next, the switching control unit 75 associates the value to be taken of the period with the duration of the operation mode or the change rate of the measurement value of the measurement unit 73 according to the change of the inclination with time. Thereafter, the process proceeds to step S903.

  In step S903, the switching control unit 75 detects the duration of the operation mode or the change rate of the measurement value of the measurement unit 73, and determines whether or not to change the above cycle according to the plan in step S902 from the detected value. to decide. As a result, if the above cycle should be changed, the process proceeds to step S904, and if not, the process proceeds to step S905.

  In step S904, the duration of the operation mode detected in step S903 or the change rate of the measurement value of the measurement unit 73 is associated with the change point of the period in the plan in step S902. Therefore, the switching control unit 75 causes the switching unit 71 to change the above period as planned. Thereafter, the process proceeds to step S905.

  In step S905, the power control unit 70 adjusts the output of the power generation unit 40 by MPPT control. The flow will be described later. Thereafter, the process proceeds to step S906.

  In step S906, the switching control unit 75 checks whether or not the operation control unit 60 has instructed to change the operation mode. Specifically, the switching control unit 75 acquires the value of the environment variable indicating the type of the current operation mode from the operation control unit 60, identifies the operation mode from the value, and the operation mode is the previous operation mode. It is determined whether or not the operation mode has been changed. If changed, the process proceeds to step S907. If not changed, the process is repeated from step S903.

  In step S907, the switching control unit 75 is instructed by the operation control unit 60 to change the operation mode. The switching control unit 75 further confirms whether or not the instructed operation mode means turning off the main power. If not, the process proceeds to step S908. If so, the process ends.

  In step S908, the switching control unit 75 shortens the period to the allowable lower limit value according to the change of the operation mode. Thereafter, the process is repeated from step S901.

  FIG. 10 is a flowchart of step S905 shown in FIG. 9, that is, the process in which the power control unit 70 adjusts the output of the power generation unit 40.

  In step S951, the switching unit 71 determines whether the power generation unit 40 should be connected to the measurement unit 73 at the present time according to the cycle instructed by the switching control unit 75. If so, the process proceeds to step S952. If the power generation unit 40 should not be connected to the measurement unit 73, the process proceeds to step S954.

  In step S952, the switching unit 71 disconnects the power generation unit 40 from the constant current circuit 72 and connects it to the measurement unit 73, and maintains this state for a predetermined time, for example, 0.5 seconds. Accordingly, the measurement unit 73 measures the open circuit voltage of the power generation unit 40. Thereafter, the process proceeds to step S953.

  In step S953, the instruction unit 74 calculates the maximum power point of the power generation unit 40 from the voltage value measured by the measurement unit 73. Specifically, the instructing unit 74 calculates a current value corresponding to ½ times the measured voltage value from the numerical table or mathematical expression representing the current-voltage characteristic shown in FIG. To do. Thereafter, the process proceeds to step S954.

  In step S954, the switching unit 71 disconnects the power generation unit 40 from the measurement unit 73 and connects it to the constant current circuit 72. In this state, the instruction unit 74 determines the current value at the maximum power point as a target value and instructs the constant current circuit 72. Thereafter, the process proceeds to step S955.

  In step S955, the constant current circuit 72 adjusts the amount of current supplied from the power generation unit 40 to the output unit 80 and maintains the target value instructed from the instruction unit 74. Thereafter, the process proceeds to step S906.

  [Advantages of the embodiment]

  The image forming apparatus 100 according to the embodiment of the present invention causes the power control unit 70 to assume a temperature variation pattern of the power generation unit 40 according to the operation mode instructed by the operation control unit 60 to the fixing unit 30. Accordingly, even if the operation mode is switched irregularly, for example, at times T1, T2, T3, and T4 shown in FIG. 8, the temperature of the power generation unit 40 during these times T1,. Variation patterns are assumed. Further, the power control unit 70 causes the switching unit 71 to change the cycle for cutting between the power generation unit 40 and the output unit 80 according to the pattern. As a result, the image forming apparatus 100 can appropriately change the timing for measuring the output of the power generation unit 40 according to the temperature fluctuation of the power generation unit 40, thereby further improving the utilization efficiency of the power generated by the power generation unit 40. it can.

  The switching control unit 75 shortens the above cycle to the allowable lower limit value when the operation control unit 60 switches the operation mode. At that time, a sudden temperature fluctuation of the power generation unit 40 is assumed, so by shortening the cycle, the power control unit 70 follows the change of the output of the power generation unit 40 quickly and accurately, following the displacement of the maximum power point. Can be made.

  [Modification]

  (A) The image forming apparatus 100 is a color laser printer. In addition, the image forming apparatus may be any apparatus that thermally fixes a toner image on a sheet, such as a monochrome laser printer, a facsimile machine, a copier, or a multifunction peripheral (MFP).

  (B) The material of the sheet handled by the feeding unit 10 is paper. In addition, the material may be resin like an OHP film. The feeding unit 10 may also include a plurality of storage trays, and may store sheets of different sizes such as A3, A4, A5, and B4. The feeding unit 10 may further include a mechanism for double-sided printing.

  (C) In the fixing unit 30, the heater 31A built in the fixing roller 31 is a halogen lamp. In addition, the heater 31A may be an induction heating device. The fixing unit 30 may also include a combination of a fixing belt that contacts the sheet and a device for heating the belt instead of the fixing roller 31.

  (D) As shown in FIGS. 1 and 2, (D) the power generation unit 40 includes the above conditions (A) to (C) in the vicinity of the fixing unit 30 in the housing of the image forming apparatus 100. It is installed in the part that meets all of the above. In addition, the power generation unit is in the vicinity of the elements of the image forming apparatus 100 that emits a large amount of heat, such as a power supply device, a motor for driving various rollers and belts, and a CPU built in the operation control unit 60. -You may install in the place which satisfy | fills the conditions similar to (C).

  (E) The power generation unit 40 uses a thermoelectric conversion element 41 shown in FIG. The structure of the thermoelectric conversion element 41 is merely an example, and the size and shape of the substrates 42 and 43 and the number, shape, size, arrangement, and type of the semiconductor elements 44P and 44N can be changed. In the power generation unit 40, as shown in FIG. 5, all of the plurality of thermoelectric conversion elements 41 are connected in series. In addition, the number of the thermoelectric conversion elements 41 may be only one, and the series connection of the thermoelectric conversion elements 41 may be divided into a plurality and connected in parallel. The power generation unit 40 may use a small Stirling generator instead of the thermoelectric conversion element 41.

  (F) The operation control unit 60, the power control unit 70, and the output unit 80 are mounted on a single substrate. In addition, any of those functional units 60-80 may be separated on different substrates. Further, these functional units 60-80 may be integrated on one chip.

  (G) The operation control unit 60 causes the operation unit 50 to receive the image data IMG from the network. In addition, the image forming apparatus 100 may include a scanner or a camera, and the operation control unit 60 may acquire image data from them. The image forming apparatus 100 may further include a video input terminal such as a USB port, a memory card / slot, and the like, and the operation control unit 60 may acquire image data from an external electronic device therethrough.

  (H) The operation control unit 60 switches the operation mode of the image forming apparatus 100 among three types of operation mode RNG, standby mode WTG, and sleep mode SLP shown in FIG. In addition, the image forming apparatus 100 may include a copy function or a scanner function, and the operation control unit 60 may switch the operation mode between those additional functions and the above three types.

  (I) The operation control unit 60 switches the operation mode in response to a job request received from the user or the network by the operation unit 50 in real time. In addition, the operation control unit 60 may cause the user to set a schedule for changing the operation mode, and switch the operation mode according to the schedule using a built-in timer. The schedule defines, for example, an operation mode to be set for each time zone of the day or for each day of the week. Specifically, for example, the standby mode is defined in the time zone of 8:30 to 12:00 on weekdays and 13:00:00 to 19:00, and the sleep mode is set on the other days on weekdays and all day on Saturdays and Sundays. Is defined. In this case, the operation control unit 60 switches the operation mode from the sleep mode to the standby mode at 8:30 and 13:00 on weekdays, and vice versa at 12:00 and 19:00 on weekdays.

  (J) In the power control unit 70, the constant current circuit 72 functions as an adjustment unit for the output of the power generation unit 40. In addition, instead of or in addition to the constant current circuit 72, a constant voltage circuit may function as the adjustment unit.

  (K) The power control unit 70 calculates the output voltage VPK at the maximum power point from the open circuit voltage VOP of the power generation unit 40. The power control unit 70 can also calculate the maximum power point from the output current amount obtained when the output voltage of the power generation unit 40 is maintained at a specific level and the characteristic curve shown in FIG. Good. The power control unit 70 further obtains a plurality of samples by repeatedly measuring the other one of the output voltage and the output current of the power generation unit 40 to obtain a plurality of samples, and the peak of the voltage-power characteristic curve from those samples, That is, the maximum power point may be searched.

  (L) In the power control unit 70, the switching unit 71 alternately connects the power generation unit 40 to the constant current circuit 72 and the measurement unit 73 at a cycle instructed by the switching control unit 75. In addition, the switching control unit 75 may send a signal to the switching unit 71 at a cycle determined by itself, and switch the connection destination of the power generation unit 40 each time the switching unit 71 receives the signal.

  (M) The numerical table or mathematical expression stored in the switching control unit 75 represents the temperature fluctuation pattern of the fixing unit 30 shown in FIG. In addition, the temperature fluctuation of the installation location of the power generation unit 40 is actually measured in advance for each operation mode, and the pattern of temperature fluctuation that is typical in each operation mode is determined from the measurement result, and in the form of a numerical table, etc. It may be stored in the switching control unit 75.

  (N) The switching control unit 75 uses the stored numerical table or the like to calculate the gradient of the temperature variation pattern represented by the numerical table, and the power generation unit 40 is connected to the constant current circuit 72 according to the magnitude of the gradient. Determine the period to cut from. In addition, for each operation mode, the correspondence between the duration or the change rate of the open circuit voltage of the power generation unit 40 and the cycle to be set is based on the temperature variation pattern of the power generation unit 40 in each operation mode in advance. It may be determined and stored in the switching control unit 75 in the form of a numerical table or the like.

  (O) The switching control unit 70 identifies three types of operation modes: an operation mode RNG, a standby mode WTG, and a sleep mode SLP shown in FIG. In addition, the switching control unit 70 may identify the operation mode of the copy function or the scanner function. The switching control unit 75 may further subdivide the operation mode into different operation modes depending on the size and material of the sheet, the number of printed pages, and single-sided / double-sided printing. If these parameters are different, the amount of heat transferred from the fixing nip to the sheet changes, so that the temperature variation pattern of the fixing unit 30 differs. The power control unit 70 can further improve the reliability of the MPPT control by causing the switching control unit 70 to treat operation modes having different parameters as different operation modes.

  (P) When the operation control unit 60 causes the user to set a schedule for changing the operation mode, the switching control unit 75 specifies the time at which the operation control unit 60 switches the operation mode from the schedule, and sets the cycle at that time. For example, the value may be shortened from the previous value to an allowable lower limit value.

  (Q) As shown in FIG. 8, the switching control unit 75 extends the cycle as the period in which the assumed temperature fluctuation of the power generation unit 40 is gentle, that is, the period in which the inclination of the pattern is small. In addition, the switching control unit 75 causes the switching unit 71 to maintain the connection between the power generation unit 40 and the output unit 80 during the period when the speed of the temperature fluctuation is lower than the threshold value, while the power generation unit 40 by the measurement unit 73 Instead of the measured value of the open circuit voltage, the predicted value may be provided to the instructing unit 74. The predicted value is calculated by extrapolation from, for example, a value measured by the measurement unit 73 before the temperature fluctuation speed of the power generation unit 40 falls below the threshold value. The above threshold value for the speed of temperature fluctuation of the power generation unit 40 is such that the predicted pattern of the temperature fluctuation can be regarded as linear, and the predicted value of the open circuit voltage of the power generation unit 40 is calculated with sufficient accuracy from the pattern. Is set. Examples of the period during which the speed of temperature fluctuation of the power generation unit 40 is lower than the threshold value include the second period PW2 and the fourth period PW4 in the standby mode shown in FIG. 7B, and FIG. There is a second period PS2 of the sleep mode shown.

  In this way, when the open circuit voltage of the power generation unit 40 is accurately obtained by calculation instead of measurement, the power control unit 70 maintains the connection between the power generation unit 40 and the output unit 80, while the power generation unit 40 The change in output can be made to follow the displacement of the maximum power point. Thereby, the utilization efficiency of the electric power generated by the power generation unit 40 can be further improved.

  In the sleep mode, the switching control unit 75 causes the switching unit 71 to maintain the connection between the power generation unit 40 and the output unit 80, and the adjustment unit, that is, the constant current circuit 72 outputs the output of the power generation unit 40 as it is. The data may be sent to the output unit 80. This is because, since the fixing unit 30 is stopped in the sleep mode, the temperature of the power generation unit 40 is substantially maintained at room temperature, and the maximum power point can be regarded as constant.

  (R) The switching control unit 75 plans the value that the cycle should take according to the duration of the operation mode or the change rate of the value measured by the measurement unit 73, that is, the change rate of the open circuit voltage of the power generation unit 40, Change the cycle according to the plan. Further, when the change rate of the value measured by the measurement unit 73 exceeds the threshold value, the switching control unit 75 may shorten the cycle from the previous value to, for example, an allowable lower limit value. As a result, even if the temperature of the power generation unit 40 fluctuates suddenly, the measurement unit 73 repeats the measurement quickly, so the power control unit 70 quickly and accurately changes the output of the power generation unit 40 to the maximum power It is possible to follow the displacement of the point.

  (S) The output unit 80 supplies the power output from the power generation unit 40 to the operation unit 50, the operation control unit 60, or the power control unit 70 as standby power or auxiliary power during a power failure. In addition, the output unit 80 may use the electric power for preheating / warming the fixing roller 31 or driving the exhaust fan in the standby mode. When the output power from the power generation unit 40 is sufficiently high, the output unit 80 may be omitted, and the output from the constant current circuit 72 may be supplied directly to the load.

  (T) The storage battery 82 may be a nickel-cadmium storage battery or a nickel-hydrogen storage battery in addition to the lithium ion battery. In that case, the output unit 80 charges those storage batteries by a constant current method.

  (U) The thermoelectric conversion element 41 is used for waste heat power generation in the image forming apparatus 100. In addition, thermoelectric conversion elements are also used for waste heat power generation in systems such as electrical equipment other than image forming apparatuses, automobiles, and heating equipment. In general, these systems have a plurality of operation modes, and the amount of waste heat varies in different patterns for each operation mode. Therefore, the temperature at the place where the thermoelectric conversion element is installed also varies in different patterns for each operation mode. Therefore, in those systems, using a power control device similar to the power control unit 70 described above for output control of the thermoelectric conversion element is effective in further improving the utilization efficiency of the power generated by the thermoelectric conversion element. It is.

  (A) of FIG. 11 is a perspective view of the rice cooker which utilizes a thermoelectric conversion element for waste heat power generation. Referring to (a) of FIG. 11, the rice cooker 200 includes an inner pot storage unit 201, a power generation device 202, an operation panel 203, and a control device 204. The storage unit 201 includes an induction heating device for heating the inner pot stored therein. The power generation device 202 is installed below the storage unit 201, and converts waste heat from the bottom surface of the storage unit 201 into electric power using a built-in thermoelectric conversion element. The operation panel 203 is incorporated in the upper surface of the casing of the rice cooker 200, interprets the setting information from the user's operation and transmits it to the control device 204, and displays the setting information on the screen. The setting information includes the type of rice to be cooked, such as non-washed rice, white rice, brown rice, and the reservation time for cooking. The control device 204 is installed on the back side of the operation panel 203 and controls the induction heating device of the storage unit 201 according to setting information from the operation panel 203. The control device 204 includes a power control device and a power storage device. The power control device performs MPPT control on the power output from the power generation device 202. The power storage device stores the electric power and supplies it to the operation panel 203 and the control device 204.

  The operation mode of the rice cooker 200 is roughly divided into a rice cooking mode and a heat retention mode, and the rice cooking mode is further subdivided into different operation modes depending on the type of rice to be cooked. In these operation modes, the change with time of the set temperature of the inner pot is different. Therefore, the temperature variation on the bottom surface of the storage unit 201 is also assumed to have a different pattern depending on the operation mode. The power control device assumes a temperature fluctuation pattern of the power generation device 202 according to the operation mode, and changes the cycle for disconnecting the power generation device 202 from the power storage device, that is, the cycle for measuring the open circuit voltage of the power generation device 202 according to the pattern. To do. Specifically, the period is shortened in a period where the inclination of the assumed pattern is large, and is extended in a small period. In particular, since the temperature of the bottom surface of the storage unit 201 is assumed to change rapidly between the start of rice cooking and the time when the rice cooking mode shifts to the heat retention mode due to the rice cooking, the power control device has the above cycle. Is shortened from the previous value. As a result, the power control apparatus frequently measures the output during a period in which rapid temperature fluctuation of the power generation apparatus 202 is assumed, and causes the change in the output of the power generation apparatus 202 to accurately follow the displacement of the maximum power point. On the other hand, during a period in which a gradual temperature fluctuation of the power generation device 202 is assumed, the power control device maintains the connection between the power generation device 202 and the power storage device for a long time, and increases the amount of charge per fixed time. Thus, the power control device can appropriately change the timing of measuring the output according to the temperature fluctuation of the power generation device 202, and can further improve the utilization efficiency of the power generated by the power generation device 202.

  FIG. 11B is a perspective view of a refrigerator that uses a thermoelectric conversion element for waste heat power generation. Referring to FIG. 11B, the refrigerator 300 includes a compressor 301, a power generation device 302, an operation panel 303, a control device 304, and a blower 305. The compressor 301 compresses the refrigerant and increases its pressure. The power generation device 302 is installed in the vicinity of the compressor 301 and converts waste heat from the surface of the compressor 301 into electric power using a built-in thermoelectric conversion element. The operation panel 303 is incorporated in the front surface of the door of the refrigerator 300, interprets the setting information from the user's operation and transmits it to the control device 304, and displays the setting information on the screen. The setting information includes the setting temperature of a room such as a refrigeration room and a freezing room, and the setting of cooling conditions such as quick freezing. The control device 304 is installed on the back side of the operation panel 303 and controls the compressor 301 according to setting information from the operation panel 303. The control device 304 has a built-in power control device. The power control device performs MPPT control on the power output from the power generation device 302. The electric power is supplied to loads such as the blower 305 and the interior lamp. The blower 305 sends the air cooled by the refrigerant to the refrigerator compartment and the freezer compartment.

  The operation mode of the refrigerator 300 differs depending on the set temperature of each room and the cooling conditions. In these operation modes, since the operating state of the compressor 301 is different, the temporal change in the amount of heat released from the surface is different. Therefore, the temperature variation of the power generation apparatus 302 is also assumed to have a different pattern depending on the operation mode. The power control device assumes the pattern according to the operation mode, and changes the cycle of disconnecting the power generation device 302 from the load, that is, the cycle of measuring the open-circuit voltage of the power generation device 302, according to the pattern. Specifically, the period is shortened in a period where the inclination of the assumed pattern is large, and is extended in a small period. In particular, since it is assumed that the surface temperature of the compressor 301 will fluctuate rapidly between the time when the set temperature is changed and the time when the quick freezing starts and ends, the power controller shortens the above cycle from the previous value. To do. As a result, the power control apparatus frequently measures the output during a period in which rapid temperature fluctuation of the power generation apparatus 302 is assumed, and causes the change in the output of the power generation apparatus 302 to accurately follow the displacement of the maximum power point. Conversely, during a period in which a gradual temperature fluctuation of the power generation device 302 is assumed, the power control device maintains the connection between the power generation device 302 and the load for a long time, and increases the amount of charge per fixed time. In this way, the power control device can appropriately change the timing for measuring the output according to the temperature fluctuation of the power generation device 302, and can further improve the utilization efficiency of the power generated by the power generation device 302.

  Waste heat power generation using thermoelectric conversion elements is also used in systems such as air conditioners, automobiles, and motorcycles. The power control apparatus according to the invention can also be used in these systems. Actually, the operation mode of the air conditioner varies depending on the cooling and heating, the set temperature and the air volume, the difference between the set temperature and the actual room temperature, the number of people in the room, and the like. Automobiles and motorcycles have different operation modes depending on speed, engine speed, gears, when traveling on ordinary roads and when traveling on highways, the presence or absence of traffic, road surface conditions, and the like. In these operation modes, generally, the temporal change in the amount of waste heat is different, and therefore, the temperature variation of the thermoelectric conversion element is assumed to be a different pattern depending on the operation mode. The power control apparatus assumes the pattern according to the operation mode, and changes the cycle for measuring the open voltage of the thermoelectric conversion element according to the pattern. Thereby, the power control apparatus can further improve the utilization efficiency of the electric power created by the thermoelectric conversion element by appropriately changing the timing of measuring the output according to the temperature fluctuation of the thermoelectric conversion element.

  (V) The power generation apparatus targeted by the power control apparatus according to the invention may be a solar cell, a fuel cell, a wind power generator, or the like in addition to the thermoelectric conversion element. There is a maximum power point in the output characteristics of these power generators, and they are greatly displaced as the environmental conditions change. When these power generators are incorporated and used in another system, it is generally assumed that the environmental conditions vary in different patterns depending on the operation mode of the system. The power control apparatus assumes the pattern according to the operation mode, and changes the cycle for measuring the output of the power generation apparatus necessary for MPPT control according to the pattern. As a result, the power control device can appropriately change the timing of measuring its output in accordance with changes in environmental conditions, and can further improve the utilization efficiency of the power generated by the power generation device.

  The present invention relates to MPPT control with respect to the output of a power generator, and as described above, assumes a pattern of variation in environmental conditions according to the operation mode of the system in which the power generator is incorporated, and measures the output of the power generator according to the pattern. Change the cycle. Thus, the present invention is clearly industrially applicable.

PR1 First period of operation mode
PR2 Second period of operation mode
First period of PW1 standby mode
Second period of PW2 standby mode
Third period of PW3 standby mode
4th period of PW4 standby mode
First period of PS1 sleep mode
PS2 Sleep mode second period
T1 1st time
T2 Second time
T3 3rd time
T4 4th time
End time of the first period PR1 of T21 operation mode
End time of the first period PW1 in T31 standby mode
End time of second period PW2 in T32 standby mode
End time of the third period PW3 in T33 standby mode
End time of the first period PS1 in T41 sleep mode

Claims (19)

In order to control the power output to the load from the power generation device that generates heat with waste heat from the system, which is incorporated in a system that generates heat in accordance with the operation mode that can be set for itself and that generates heat. Equipment,
A switching unit that alternately repeats connection and disconnection between the power generation device and the load,
An adjustment unit that adjusts the output of the power generation device to a target value when the switching unit connects the power generation device to the load;
A measuring unit that measures an output of the power generation device when the switching unit disconnects the power generation device from the load;
An instruction unit that calculates the maximum power point of the power generation device from the value measured by the measurement unit, determines the target value based on the maximum power point, and instructs the adjustment unit; and
When the system switches the operation mode, assuming the pattern of the environmental temperature fluctuation of the system in the operation mode after the switching from the combination of the operation modes before and after the switching , obtain the speed of the environmental temperature fluctuation from the inclination of the pattern , A switching control unit for causing the switching unit to change a cycle for cutting between the power generation device and the load according to a change with time in speed ;
A power control device. The switching control unit monitors the operation mode of the system, and at the time when the system switches the operation mode, the cycle for cutting is shortened from the previous value.
The power control apparatus according to claim 1, wherein: The switching control unit obtains a schedule for changing the operation mode from the system, identifies a time point at which the system switches the operation mode from the schedule, and shortens the cutting cycle from the previous value at the time point. ,
The power control apparatus according to claim 1, wherein: The switching control unit stores a numerical table or a mathematical expression indicating an assumed environmental temperature variation pattern of the system for each operation mode of the system, and uses the numerical table or mathematical expression corresponding to the actual operation mode. Determining the cutting period;
The power control apparatus according to claim 1, wherein: The switching control unit extends the cutting cycle as the period when the fluctuation rate of the environmental temperature of the system indicated by the pattern is low,
The power control apparatus according to claim 1, wherein: The switching control unit causes the switching unit to maintain a connection between the power generation device and the load in a period in which the fluctuation speed of the environmental temperature of the system indicated by the pattern is lower than a threshold value. Predicting the output of the power generation device from the value previously measured by the measurement unit, and providing the predicted value to the instruction unit instead of the measurement unit;
The power control apparatus according to claim 1, wherein: In the period when the operation mode after the switching indicates the standby state of the system,
Extending the cutting period from the previous value, or
The switching unit maintains the connection between the power generation device and the load, while predicting the output of the power generation device from the value measured by the measurement unit before the system shifts to a standby state. Providing the indicated value to the instruction unit instead of the measurement unit;
The power control apparatus according to claim 1, wherein: In the period during which the operation mode after the switching indicates the stop state of the system,
Extend the cutting period from the previous value,
While making the switching unit maintain the connection between the power generation device and the load, predict the output of the power generation device from the value measured by the measurement unit before the system shifts to a stop state, Providing the indicated value to the instruction unit instead of the measurement unit, or
The switching unit maintains the connection between the power generation device and the load, and the adjustment unit causes the output of the power generation device to be sent to the load as it is.
The power control apparatus according to claim 1, wherein: When the change in the value measured by the measurement unit exceeds a threshold value, the switching control unit shortens the cutting cycle from the previous value.
The power control apparatus according to claim 1, wherein: The system is an image forming apparatus;
The power generation device includes a thermoelectric conversion element that converts waste heat from the fixing unit of the image forming apparatus into electric power.
The power control apparatus according to any one of claims 1 to 9. A feeding unit for feeding a plurality of sheets one by one;
An image forming unit that forms a toner image on a sheet fed by the feeding unit based on image data;
A fixing unit for thermally fixing the toner image;
An operation control unit for instructing an operation mode to the fixing unit and providing the image data to the image forming unit;
An element that converts heat into electric power, including a thermoelectric conversion element whose output characteristics change with temperature fluctuations, and that generates electricity using waste heat from the fixing unit,
A power control unit for controlling power output from the power generation unit, and
An output unit for storing or outputting the electric power;
With
The power control unit is
A switching unit that alternately repeats connection and disconnection between the power generation unit and the output unit,
An adjustment unit that adjusts the output of the power generation unit to a target value when the switching unit connects the power generation unit to the output unit;
A measuring unit that measures the output of the power generation unit when the switching unit disconnects the power generation unit from the output unit;
An instruction unit that calculates the maximum power point of the power generation unit from the value measured by the measurement unit, determines the target value based on the maximum power point, and instructs the adjustment unit; and
When the operation control unit switches the operation mode of the fixing unit, the temperature variation pattern of the power generation unit in the operation mode after switching is assumed from the combination of the operation modes before and after the switching , and the temperature variation is determined from the inclination of the pattern . A switching control unit that obtains a speed and causes the switching unit to change a cycle of cutting between the power generation unit and the output unit according to a change with time in the speed ;
An image forming apparatus. The switching control unit monitors the operation mode of the fixing unit, and when the operation control unit switches the operation mode of the fixing unit , the cutting cycle is shortened from the immediately preceding value.
The image forming apparatus according to claim 11, wherein: The operation control unit creates a schedule relating to a change in the operation mode of the fixing unit ,
The switching control unit identifies a time point at which the operation control unit switches the operation mode of the fixing unit from the schedule, and shortens the cutting cycle from the previous value at the time point.
The image forming apparatus according to claim 11, wherein: The switching control unit stores a numerical table or a mathematical expression indicating an assumed temperature fluctuation pattern of the power generation unit for each type of operation mode of the fixing unit, and the numerical table or mathematical expression corresponding to the actual operational mode. To determine the cutting period,
The image forming apparatus according to claim 11, wherein: The switching control unit extends the cutting cycle as the period of the temperature fluctuation rate of the power generation unit indicated by the pattern is low.
The image forming apparatus according to claim 11, wherein: The switching control unit causes the switching unit to maintain a connection between the power generation unit and the output unit during a period in which the speed of temperature fluctuation of the power generation unit indicated by the pattern is below a threshold, while the period Predicting the output of the power generation unit from the value measured by the measurement unit before and providing the predicted value to the instruction unit instead of the measurement unit,
The image forming apparatus according to claim 11, wherein: In the period when the operation mode of the fixing unit is a standby mode,
Extending the cutting period from the previous value, or
While the switching unit maintains the connection between the power generation unit and the output unit, the output of the power generation unit is calculated from the value measured by the measurement unit before the operation mode of the fixing unit shifts to the standby mode. Predicting and providing the predicted value to the indicating unit on behalf of the measuring unit;
The image forming apparatus according to claim 11, wherein: In the period in which the operation mode of the fixing unit is a sleep mode, the switching control unit
Extend the cutting period from the previous value,
While the switching unit maintains the connection between the power generation unit and the output unit, the output of the power generation unit from the value measured by the measurement unit before the operation mode of the fixing unit shifts to the sleep mode And providing the predicted value to the instruction unit on behalf of the measurement unit, or
The switching unit maintains the connection between the power generation unit and the output unit, and the adjustment unit causes the output of the power generation unit to be sent to the output unit as it is.
The image forming apparatus according to claim 11, wherein: When the change in the value measured by the measurement unit exceeds a threshold value, the switching control unit shortens the cutting cycle from the previous value.
The image forming apparatus according to claim 11, wherein:

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