JP7639508B2 - Image forming device - Google Patents

Description

The present invention relates to image forming devices equipped with a fixing device, such as copiers, printers, facsimiles, and combination machines thereof, and in particular to a method for efficiently supplying power to the fixing device.

In order to fix a toner image to paper in an image forming apparatus, a fixing device equipped with a fixing member in which a fixing roller or fixing belt (a heated rotating body) and a pressure roller (a pressure rotating body) are in pressure contact is widely used. In this fixing device, a recording material such as paper is passed through the fixing nip formed by the heating roller and pressure roller, and heat and pressure are applied to the toner image to melt and fix it to the recording material.

In response to the recent demand for power saving, it is important for fixing devices such as those described above to be able to warm up in a short time. In addition, the fixing device needs to heat the fixing member using a heating section, and then use the fixing member to heat the recording material, so the proportion of power consumption by the fixing device in the entire image forming device becomes large.

On the other hand, image forming devices must be designed to operate within the rated power (rated current, rated voltage) as an electrical condition. For example, in the case of a 100V AC commercial power source, the regulated current value in Japan is set at 15A, and a current exceeding 15A cannot be used. For this reason, a limit is set on the total current that can be input from the commercial power source to the image forming device.

Therefore, in order to improve warm-up performance, fixing performance, and image formation efficiency (productivity), it is necessary to allocate as much power as possible to the fixing device, without the total current of the image forming device exceeding the limit value.

For example, Patent Document 1 discloses an image forming apparatus that includes a second current detection unit that detects the value of a current supplied to an excitation coil of an induction heating type fixing device, a fixing current calculation unit that feeds back the current value detected by the second current detection unit and calculates the current value to be supplied to the excitation coil with the rated current value of the commercial power source as a target value, an allowable current calculation unit that calculates the current value to be supplied to the excitation coil by subtracting the rated current value of the commercial power source from the total drive current value of the entire apparatus from the current value detected by the second current detection unit, an IH control unit that calculates a frequency corresponding to the current values calculated by the fixing current calculation unit and the allowable current calculation unit, and a switching unit that switches whether to have the fixing current calculation unit or the allowable current calculation unit calculate the current value to be supplied to the excitation coil depending on the total drive current value.

Patent document 2 discloses an image forming apparatus that includes an instruction power calculation unit that calculates an instruction power to the fixing unit to set the temperature of the fixing unit to a predetermined temperature; an allowable current calculation unit that calculates an allowable current for the fixing unit, which is a value obtained by subtracting the load current from the limit value, and setting the total current input to the image forming apparatus from the commercial power source as the sum of the fixing current and the load current, in order to control the total current to be equal to or less than the limit value; an allowable power calculation unit that calculates the allowable power, which is a value obtained by multiplying the allowable current and the fixing voltage; and a target power determination unit that determines the instruction power as a target power if the instruction power is equal to or less than the allowable power, and determines the allowable power as a target power if the instruction power is greater than the allowable power.

JP 2012-173364 A JP 2015-191134 A

Even when the fixing current is controlled by detecting the total current input to the image forming device, the fixing current distributed to the fixing device, and the secondary current distributed to devices other than the fixing device, as in Patent Documents 1 and 2, the time-series load operation of the image forming device is not always the same, so the control of the fixing current has an aspect of predictive control.

Therefore, when the total current input to the image forming device is close to the limit value and there is no room for improvement, if an attempt is made to allocate as much fixing current as possible to the fixing device, there is a risk that the total current will exceed the limit value in the short term depending on the status of load operations other than the fixing device.

In view of the above problems, the present invention aims to provide an image forming device that can supply maximum power to a fixing device while reliably preventing the total current input to the image forming device from exceeding a limit value.

In order to achieve the above object, the first configuration of the present invention is an image forming apparatus including an image forming section, a fixing device, a power supply section, and a control section. The image forming section forms a toner image on a recording medium. The fixing device includes a heated rotating body, a pressure rotating body that is pressed against the heated rotating body at a predetermined fixing nip pressure to form a fixing nip section, a heating section that heats the heated rotating body, and a temperature detection section that detects the temperature of the heated rotating body, and performs a fixing process in which a toner image is fixed to the recording medium by heating and pressurizing the recording medium passing through the fixing nip section. The power supply section is connected to a commercial power source and supplies power to the entire image forming apparatus including the fixing device. The control section determines the fixing current Ifuser flowing through the heating section to be the current instruction value Iht(n) when the current instruction value Iht(n) determined based on the detection result of the temperature detection section is equal to or less than the fixing upper limit current Q(n), and determines the fixing current Ifuser to be the fixing upper limit current Q(n) when the current instruction value Iht(n) is greater than the fixing upper limit current Q(n). When the total device current Im(n) exceeds a total current threshold Ithresh that is lower than the rated current Imax of the image forming device by a predetermined value α during image formation, the control unit sets the upper fixing current Q(n) by total current threshold control so that the total device current Im(n) does not exceed the rated current Imax, and corrects the upper fixing current Q(n) in multiple stages based on the power margin of the image forming device.

According to the first configuration of the present invention, the correction amount in the total current threshold control when the total device current Im(n) exceeds the total current threshold Ithresh is set in multiple stages according to the power margin. This results in a power control system that keeps the current that can be distributed to the fixing device as large as possible while preventing the total device current Im(n) from exceeding the rated current Imax.

FIG. 1 is a schematic cross-sectional view showing an internal structure of an image forming apparatus according to an embodiment of the present invention. 1 is a side cross-sectional view of a fixing device 13 mounted in an image forming apparatus 100. A block diagram showing an example of a control path of the image forming apparatus 100. FIG. 1 is a block diagram showing an example of a power control system for an image forming apparatus according to a first embodiment of the present invention. 1 is a flowchart showing a first control example of current control executed in the image forming apparatus 100 according to the first embodiment; FIG. 13 is a diagram showing the fixing current Ifuser and the secondary side current Ieng(n) under conditions 1 to 5 in which the total device current Im(n) is different in the first control example. 1 is a flowchart showing a second example of current control executed in the image forming apparatus 100 according to the first embodiment; 11 is a flowchart showing a third example of the current control executed in the image forming apparatus 100 according to the first embodiment. FIG. 13 is a diagram showing the fixing current Ifuser and the secondary side current Ieng(n) under conditions 1 to 5 in which the total device current Im(n) is different in the third control example. FIG. 11 is a block diagram showing an example of a power control system for an image forming apparatus according to a second embodiment of the present invention. 11 is a flowchart showing a fourth control example of the current control executed in the image forming apparatus 100 according to the second embodiment. FIG. 12 is a diagram showing the fixing upper limit current Q(n) and the secondary side current Ieng(n) under conditions 1 to 4 in which the device total current Im(n) is different in the control example of FIG. 11 .

Below, an embodiment of the present invention will be described with reference to the drawings. FIG. 1 is a schematic cross-sectional view showing the internal structure of an image forming apparatus 100 according to one embodiment of the present invention. Inside the main body of the image forming apparatus 100 (here a color printer), four image forming units Pa, Pb, Pc, and Pd are arranged in order from the upstream side in the transport direction (the right side in FIG. 1). These image forming units Pa to Pd are provided corresponding to images of four different colors (cyan, magenta, yellow, and black), and each sequentially forms images of cyan, magenta, yellow, and black through the processes of charging, exposure, development, and transfer.

These image forming units Pa to Pd are provided with photoconductor drums (image carriers) 1a, 1b, 1c, and 1d that carry visible images (toner images) of each color. In addition, an intermediate transfer belt 8 that rotates in a clockwise direction in FIG. 1 is provided adjacent to each image forming unit Pa to Pd. The toner images formed on these photoconductor drums 1a to 1d are sequentially transferred and superimposed on the intermediate transfer belt 8 that moves while abutting against each of the photoconductor drums 1a to 1d. The toner images transferred to the intermediate transfer belt 8 are then transferred to a sheet S, an example of a recording medium, by a secondary transfer roller 9. The sheet S to which the toner image has been transferred is then ejected from the main body of the image forming apparatus 100 after the toner image is fixed by the fixing device 13. The image forming process for each of the photoconductor drums 1a to 1d is performed while the photoconductor drums 1a to 1d are rotated in a counterclockwise direction in FIG. 1 by the main motor 40 (see FIG. 3).

The paper S onto which the toner image is secondarily transferred is stored in a paper cassette 16 located at the bottom of the main body of the image forming apparatus 100, and is transported to the nip between the secondary transfer roller 9 and the drive roller 11 of the intermediate transfer belt 8 via a paper feed roller 12a and a pair of registration rollers 12b. The intermediate transfer belt 8 is made of a sheet made of a dielectric resin, and is generally a seamless belt. In addition, a blade-shaped belt cleaner 19 is located downstream of the secondary transfer roller 9 to remove toner and other substances remaining on the surface of the intermediate transfer belt 8.

Next, the image forming units Pa to Pd will be described. Around and below the rotatably arranged photoconductor drums 1a to 1d, there are provided charging devices 2a, 2b, 2c, and 2d that charge the photoconductor drums 1a to 1d, an exposure device 5 that exposes image information onto each of the photoconductor drums 1a to 1d, developing devices 3a, 3b, 3c, and 3d that form toner images on the photoconductor drums 1a to 1d, and cleaning devices 7a, 7b, 7c, and 7d that remove developer (toner) remaining on the photoconductor drums 1a to 1d.

When image data is input from a host device such as a personal computer, first, the surfaces of the photoconductor drums 1a to 1d are uniformly charged by the charging devices 2a to 2d. Next, the exposure device 5 irradiates light according to the image data, and electrostatic latent images corresponding to the image data are formed on the photoconductor drums 1a to 1d. The developing devices 3a to 3d are filled with a predetermined amount of two-component developer containing toner of each color, cyan, magenta, yellow, and black. When the ratio of toner in the two-component developer filled in each developing device 3a to 3d falls below a specified value due to the formation of a toner image described below, toner is replenished from the toner containers 4a to 4d to each developing device 3a to 3d. The toner in the developer is supplied onto the photoconductor drums 1a to 1d by the developing devices 3a to 3d and electrostatically adheres to them. As a result, a toner image corresponding to the electrostatic latent image formed by exposure from the exposure device 5 is formed.

Then, primary transfer rollers 6a-6d apply an electric field with a predetermined transfer voltage between the primary transfer rollers 6a-6d and the photoconductor drums 1a-1d, and the cyan, magenta, yellow and black toner images on the photoconductor drums 1a-1d are primarily transferred onto the intermediate transfer belt 8. These four color images are formed with a predetermined positional relationship for forming a predetermined full-color image. After that, toner and the like remaining on the surfaces of the photoconductor drums 1a-1d after the primary transfer are removed by cleaning devices 7a-7d in preparation for the subsequent formation of a new electrostatic latent image.

The intermediate transfer belt 8 is stretched over a driven roller 10 on the upstream side and a driving roller 11 on the downstream side. When the intermediate transfer belt 8 starts to rotate clockwise with the rotation of the driving roller 11 by a belt drive motor (not shown), the paper S is transported from the registration roller pair 12b to the nip portion (secondary transfer nip portion) between the driving roller 11 and the secondary transfer roller 9 provided adjacent to it at a predetermined timing, and the full-color image on the intermediate transfer belt 8 is secondarily transferred onto the paper S. The paper S to which the toner image has been secondarily transferred is transported to the fixing device 13.

The paper S transported to the fixing device 13 is heated and pressurized by the fixing belt 21 and pressure roller 22 (see FIG. 2) to fix the toner image onto the surface of the paper S, forming a predetermined full-color image. The paper S on which the full-color image has been formed is then redirected by the branching section 14, which branches into multiple directions, and is discharged directly (or after being sent to the double-sided transport path 18 and having images formed on both sides) onto the discharge tray 17 by the discharge roller pair 15.

Figure 2 is a side cross-sectional view of the fixing device 13 mounted on the image forming apparatus 100. The upper side of Figure 2 is the downstream side of the paper insertion direction (transport direction) relative to the fixing device 13, and the lower side is the upstream side of the paper insertion direction relative to the fixing device 13. As shown in Figure 2, the fixing device 13 includes a fixing belt 21 (heated rotating body), a pressure roller 22 (pressurizing rotating body), a heating section 23, a nip forming member 24, a belt guide 25, and a frame member 26.

The fixing belt 21 is supported on the housing (not shown) of the fixing device 13 so as to be rotatable around a horizontal axis. The fixing belt 21 is endless and is configured in a cylindrical shape with an outer diameter of, for example, 20 mm to 50 mm, and has approximately the same axial length (width direction length of the paper S) as the pressure roller 22. The fixing belt 21 rotates in the clockwise direction in FIG. 2 along the insertion direction of the paper S, which is the recording medium.

The fixing belt 21 has a laminated structure in which an elastic layer and a release layer are laminated on the outer periphery of a heat generating layer, which is a base layer. The heat generating layer is made of, for example, a 30-50 μm thick metal film such as nickel, or a 50-100 μm thick polyimide film containing metal powder such as copper, silver, or aluminum. The elastic layer is made of, for example, a 100-500 μm thick silicone rubber. The release layer is made of, for example, a 30-50 μm thick fluorine-based resin such as PFA (tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer).

The pressure roller 22 is supported on the housing of the fixing device 13 so as to be rotatable around a horizontal axis. The pressure roller 22 is cylindrical and has approximately the same axial length (widthwise length of the paper S) as the fixing belt 21. A predetermined pressure is applied to the pressure roller 22 toward the fixing belt 21 by a pressure mechanism 30 (see FIG. 3). The outer peripheral surface of the pressure roller 22 is pressed against the outer peripheral surface of the fixing belt 21 by pressing the nip forming member 24 through the fixing belt 21, thereby forming a fixing nip portion N.

The pressure roller 22 is connected to the fixing drive motor 45 (see FIG. 3) and rotates in a counterclockwise direction in FIG. 2. The pressure roller 22 contacts the outer peripheral surface of the fixing belt 21 and applies a rotational drive force to the fixing belt 21 in the clockwise direction.

The pressure roller 22 has a laminated structure in which an elastic layer 22b is laminated on the outer periphery of a core metal 22a, and a release layer (not shown) is laminated on the surface of the elastic layer 22b. The core metal 22a is made of a metal such as aluminum with a diameter of about 20 mm. The elastic layer 22b is made of silicone rubber with a thickness of about 8 mm. The release layer is made of a fluororesin such as PFA with a thickness of about 10 μm to 50 μm.

The heating unit 23 is an induction heating (IH) type heater that generates heat in the heat generating layer of the fixing belt 21 by induction heating, and is disposed facing the outer circumferential surface of the fixing belt 21 across a specified gap in an area opposite the side of the fixing belt 21 where the pressure roller 22 is disposed. The heating unit 23 extends slightly longer than the fixing belt 21 along the axial direction of the fixing belt 21 (the width direction of the paper S, the direction perpendicular to the paper surface of FIG. 2). The temperature of the fixing belt 21 is detected by a thermistor 47 (see FIG. 3).

The heating unit 23 heats the fixing belt 21. It includes an exciting coil 23a, a holding member, a core, etc. (not shown). The exciting coil 23a and the core are held in a predetermined position by the holding member. The exciting coil 23a is made of a Litz wire made of multiple conductive wires bundled together, and is wound so as to extend along the axial direction of the fixing belt 21. The exciting coil 23a is configured in an arc shape along the outer circumferential surface of the fixing belt 21 in the circumferential direction of the fixing belt 21.

The nip forming member 24 is disposed on the inside of the fixing belt 21, facing the pressure roller 22 across the fixing belt 21. The nip forming member 24 contacts the inner peripheral surface of the fixing belt 21, and forms a fixing nip portion N between the fixing belt 21 and the pressure roller 22.

The nip forming member 24 has a generally rectangular parallelepiped shape that extends along the axial direction of the fixing belt 21 with approximately the same length as the fixing belt 21. The nip forming member 24 has a base material made of a metal such as aluminum or a heat-resistant resin such as a liquid crystal polymer.

The belt guide 25 is disposed on the inside of the fixing belt 21, facing the heating unit 23 across the fixing belt 21. The belt guide 25 contacts the inner peripheral surface of the fixing belt 21 except for the fixing nip portion N, and supports the fixing belt 21 from the inside. The belt guide 25 is made of a metal plate that extends along the axial direction of the fixing belt 21, and has approximately the same length as the fixing belt 21. The belt guide 25 is made of an elastic magnetic metal, such as SUS430, having a thickness of 0.1 mm to 0.5 mm.

The frame member 26 is supported by the housing of the fixing device 13 and holds the nip forming member 24 and the belt guide 25. The frame member 26 is disposed at approximately the radial center of the fixing belt 21, between the belt guide 25 and the nip forming member 24. The frame member 26 extends slightly longer than the fixing belt 21 along the axial direction of the fixing belt 21.

A fixing entrance guide 27 is disposed upstream of the fixing nip N in the paper insertion direction (lower side in FIG. 2). The fixing entrance guide 27 guides the paper S that has passed through the secondary transfer nip (see FIG. 1) to the fixing nip N.

A separation claw 29 is disposed downstream of the fixing nip N in the paper insertion direction (upper side in FIG. 2). The separation claw 29 separates the paper S after fixing processing from the surface of the fixing belt 21. The separation claw 29 is disposed at a predetermined angle so that its tip faces upstream (counter direction) with respect to the rotation direction of the fixing belt 21 and is close to the outer circumferential surface of the fixing belt 21.

Figure 3 is a block diagram showing an example of a control path of the image forming device 100. Note that since various controls are performed on each part of the device when using the image forming device 100, the following description will focus on the parts of the control path that are necessary for implementing the present invention. Also, descriptions of parts that have already been described will be omitted.

The low-voltage power supply 52 is connected to the power supply unit 51, and distributes the power supplied from the power supply unit 51 to each part of the device in response to an output signal from the control unit 90. Specifically, a part of the AC voltage supplied from the power supply unit 51 is distributed directly to the fixing power control board 53 (see FIG. 4). In addition, a predetermined DC voltage is generated from the remaining AC voltage and distributed to the secondary load 60 (see FIG. 4). The power control system of the image forming apparatus 100, which includes the power supply unit 51 and the low-voltage power supply 52, will be described later.

The image input unit 70 is a receiving unit that receives image data sent from a personal computer or the like to the image forming device 100. The image signal input from the image input unit 70 is converted into a digital signal and then sent to the temporary storage unit 94.

The operation unit 80 is provided with an LCD display unit 81 and LEDs 82 that indicate various states, and is configured to indicate the state of the image forming device 100, the image formation status, and the number of copies to be printed. In addition, the type and size of paper S can be input by specifying the paper cassette 16 or manual paper feed tray (not shown) from which paper S is fed from the operation unit 80. Various settings for the image forming device 100 are made from the printer driver of the computer.

The control unit 90 includes at least a CPU (Central Processing Unit) 91 as a central processing unit, a ROM (Read Only Memory) 92 as a read-only memory unit, a RAM (Random Access Memory) 93 as a readable and writable memory unit, a temporary memory unit 94 that temporarily stores image data, etc., a counter 95, and multiple (here, two) I/Fs (interfaces) 96 that transmit control signals to each device in the image forming device 100 and receive input signals from the operation unit 70.

ROM 92 stores control programs for image forming apparatus 100, numerical values necessary for control, and other data that will not change while image forming apparatus 100 is in use. RAM 93 stores necessary data that is generated during the control of image forming apparatus 100, data that is temporarily required for the control of image forming apparatus 100, and the like.

The temporary storage unit 94 temporarily stores the image signal input from the image input unit 60 and converted into a digital signal. The counter 95 accumulates and counts the number of printed pages.

Figure 4 is a block diagram showing an example of a power control system of the image forming apparatus 100 according to the first embodiment of the present invention. The power control system of the image forming apparatus 100 according to the first embodiment includes a power supply unit 51, a low-voltage power supply 52, a fixing power control board 53, a CT board 57, and a control unit 90.

The power supply unit 51 is connected to a commercial power source AC via an inlet (not shown) and supplies AC voltage from the commercial power source AC to the low-voltage power source 52. A power control circuit 50 is connected to the low-voltage power source 52. The low-voltage power source 52 distributes a portion of the AC voltage supplied from the power supply unit 51 directly to the fixing power control board 53. In addition, it generates a predetermined DC voltage from the remaining AC voltage and distributes it to the secondary load 60.

The fixing power control board 53 includes a current detection circuit that detects the AC current input to the fixing power control board 53 from the low-voltage power supply 52, and controls the current (fixing current) flowing through the fixing device 13 (particularly the heating unit 23) based on the fixing power determined by the control unit 90. Specifically, when the heating unit 23 is an induction heating (IH) type as shown in FIG. 2, the control unit 90 monitors the current detected by the CT board 57 and compares it with the current command value (Iht(n)) based on the temperature control by the thermistor 47 to determine the fixing power. The fixing power control board 53 changes the driving frequency of the AC current input to the excitation coil 23a so as to stably maintain the fixing power determined by the control unit 90. As the actual fixing current (Ifuser), the smaller of the upper limit fixing current Q(n) and the current command value Iht(n) commanded by the temperature control is selected. If a CPU or the like is mounted on the fixing power control board 53, it is also possible to obtain only the power instruction value (Iht(n)) from the control unit 90 and monitor the fixing voltage and fixing current within the fixing power control board 53 to control the power.

The control unit 90 directly controls the current (secondary current) input to the secondary load 60 used to execute the printing operation in the image forming device 100. Note that the secondary load 60 here refers to a load other than the fixing device 13 (a load different from the fixing device 13), and refers to, for example, a motor, solenoid, etc. used to drive the image forming units Pa to Pd, the paper transport mechanism 61 from the paper cassette 16 to the discharge roller pair 15 (see FIG. 1), etc.

The CT (Current Transformer) board 57 detects the current (total device current Im(n)) supplied from the commercial power source AC via the power supply unit 51 to the low-voltage power source 52. In other words, the CT board 57 functions as a total current detection unit that detects the total device current Im(n) used to drive the image forming device 100. Note that other current detection mechanisms can be used instead of the CT board 57.

Next, we will explain the current control executed in the image forming apparatus 100 according to the first embodiment of the present invention. First, we will explain an example in which an induction heating (IH) heater with a rated voltage of 100 V and a rated current of 15 A is used as the heating section 23 of the fixing device 13. In this configuration, the upper fixing current limit Q(n) is determined by two-stage control: PID control (hereinafter referred to as total current PID control) and threshold control based on the threshold value of the device total current (total current threshold).

When using an induction heating (IH) heater, power control is based on PID control (hereafter referred to as power PID control), but when starting up the image forming device 100, power table control is performed based on a power table of frequency-power characteristics, and then power PID control is performed. Specifically, PID control of the IH drive frequency is performed so that the specified IH power level is reached. On the other hand, if the total current threshold is exceeded by a large amount and the upper fixing current value Q(n) becomes smaller than the specified current value Iht(n), it is necessary to quickly reduce the fixing current to the Q(n) level.

In this case, if the IH power is varied using power PID control, the time response is slow, so by temporarily switching from power PID control to power table control, the fixing current and total device current Im(n) can be quickly reduced. However, power table control has lower control accuracy for the commanded IH power level compared to power PID control, and there is a tendency for the difference between the final fixing current (Ifuser) and the current command value Iht(n) to be large.

Therefore, if power table control occurs frequently, the range of change in fixing current and power per unit time increases, making the current control itself unstable and increasing the amount of fluctuation in the total device current Im(n), which can result in cases where the target of (total current < rated current) cannot be achieved.

Therefore, in the first control example of this embodiment, when an induction heating (IH) heater is used, the power control is a two-stage control consisting of total current PID control and total current threshold control, thereby reducing the frequency of total current threshold control and reducing the number of times that IH power control switches to power table control, thereby preventing the power control from becoming unstable.

The specific procedure for current control when an induction heating (IH) heater is used as the heating unit 23 will be described below. FIG. 5 is a flowchart showing a first control example of current control executed in the image forming apparatus 100 of the first embodiment. FIG. 6 is a diagram showing the fixing current and secondary current in conditions 1 to 5 in which the total device current Im(n) is different in the first control example.

As a premise for the current control described below, the detection of the total device current Im(n) by the CT board 57 is performed by detecting the current at a cycle of 2 to 2.5 msec and averaging the detected current value every 40 msec. In addition, the variable instruction cycle of the upper fixing current limit Q(n) by the control unit 90 is set to 80 msec, and the cycle of the power control (power PID control, power table control) of the heating unit 23 is set to 40 msec.

The maximum value Qmax of the upper fixing current is set to a range that does not exceed the rated current Imax even when the secondary load 60 is operating at maximum capacity with no optional devices attached to the image forming apparatus 100. In the current control described below, the upper fixing current Q(n) is corrected to be smaller according to the excess current amount of the total device current Im(n) so that Im(n) < Imax is ensured, with Qmax being the maximum current that can be supplied to the fixing device 13.

As shown in FIG. 5, first, the CT board 57 detects the total device current Im(n) (step S1). Next, the control unit 90 determines whether Im(n) is equal to or less than the total current threshold Ithresh (step S2). Ithresh is a current value that is lower than the rated current Imax by a predetermined value α1 (total current threshold margin, α1<γ).

If Im(n)≦Ithresh (Yes in step S2), the control unit 90 calculates Q(n) so that Im(n) becomes the target value Ipid of the total current in the total current PID control (step S3). Ipid is a current value lower than the rated current Imax by a predetermined value γ (total current target value margin), and Ithresh>Ipid.

Conditions 1 to 3 in Figure 6 show the fixing current Ifuser (hatched area) and secondary current Ieng(n) (white area) when Im(n) ≦ Ithresh. The actual fixing current Ifuser is selected to be the smaller of the current command value Iht(n) or the upper fixing current limit Q(n). Condition 1 shows the case where Iht(n) is selected as Ifuser (Iht(n) < Q(n) = Qmax), and condition 2 shows the case where Q(n) is selected as Ifuser (Q(n) = Qmax).

Even when Im(n) exceeds Ipid as in the left graph of condition 3, PID calculation of Q(n) is performed with Ipid as the target value so that Im(n) approaches Ipid through total current PID control within the range of Im(n)≦Ithresh. In the right graph, Im(n) has fallen to Ipid. However, although the PID calculation targets Ipid, the calculation result does not necessarily become Ipid. In this way, when Im(n) is equal to or less than Ithresh, the frequency with which Im(n) exceeds Ithresh can be significantly reduced by performing PID control with Ipid as the target value and determining Q(n).

If Im(n)>Ithresh (No in step S2), the total current PID control is switched to total current threshold control. Specifically, the excess current value (Im(n)-Ithresh) from the total current threshold is calculated (step S4).

Then, a provisional upper limit value Q'(n) is calculated by subtracting the excess current value (Im(n)-Ithresh) from the immediately preceding upper limit fixing current Q(n-1) using the following formula (1) (step S5).
Q'(n)=Q(n-1)-(Im(n)-Ithresh)...(1)
In equation (1), the provisional upper limit value Q'(n) is calculated by correcting the immediately preceding Q(n-1) using the excess current value Im(n)-Ithresh as the basic correction amount.

Next, the control unit 90 determines Q(n) based on the calculated Q'(n) and the power margin. In this specification, "power margin" is defined as a state where Q(n) = Qmax (Im(n) ≦ Ithresh) is maintained as having a power margin, a state where Q(n) is fluctuating around Q(n) < Qmax (Im(n) > Ithresh) as not having a power margin (small shortage), and a state where Q(n) is fluctuating around Q(n) << Qmax (Im(n) >> Ithresh) as not having a power margin (large shortage).

The specific power margin is determined using the excess current value (Im(n) - Ithresh) (steps S2 and S6). If (Im(n) - Ithresh) ≤ 0 (Yes in step S2), it is determined that there is a power margin. If 0 < (Im(n) - Ithresh) ≤ δ (Yes in step S6), it is determined that there is no power margin (small shortage). In this case, Q(n) is set to Q'(n) calculated in step S7 (step S7).

If (Im(n) - Ithresh) > δ (No in step S6), it is determined that there is no power margin (a large shortage), and the value obtained by subtracting the correction value β1 from Q'(n) is set to Q(n) (step S8). The correction value β1 is set to 0.2 to 0.5 [A]. Furthermore, the threshold value δ of Im(n) - Ithresh when determining the power margin is set to approximately 0.3 to 0.6 [A].

Condition 4 in Figure 6 shows the fixing current Ifuser and secondary current Ieng(n) when Im(n) > Ithresh and (Im(n) - Ithresh) ≦ δ. As in the left graph of condition 4, if Im(n) exceeds Ithresh but the excess amount is δ or less, Q(n) = Q'(n) and Im(n) is reduced to Ithresh as shown in the right graph.

Condition 5 in Figure 6 shows the fixing current Ifuser and secondary current Ieng(n) when Im(n) > Ithresh and (Im(n) - Ithresh) > δ. If Im(n) exceeds Ithresh as in the left graph of condition 5 and the excess amount is greater than δ, then Q(n) = Q'(n) - β1, and Im(n) is reduced to a value lower than Ithresh as in the right graph.

Then, it is determined whether the set Q(n) exceeds Qmax (step S9), and if Q(n) > Qmax (Yes in step S9), Q(n) = Qmax (step S10).

As described above, according to the first control example of this embodiment, the correction amount in the total current threshold control when the device total current Im(n) exceeds the total current threshold Ithresh is set in multiple stages according to the power margin. This results in a power control system that keeps the current that can be allocated to the fixing device 13 as large as possible while preventing the device total current Im(n) from exceeding the rated current Imax.

Focusing on the magnitude of the excess current value (Im(n) - Ithresh), when Im(n) - Ithresh is large, Q(n) is calculated by subtracting the correction value β1 from Q'(n). This allows a larger correction amount for the upper fixing current Q(n) when the total device current Im(n) exceeds the total current threshold Ithresh, and the difference with the rated current Imax becomes larger. Therefore, even if the operations of the secondary loads 60 overlap, the risk of the total device current Im(n) exceeding the rated current Imax can be reduced.

In the above control example, when there is no power margin (when (Im(n) - Ithresh) > δ), the value Q(n) is calculated by subtracting the correction value β1 from Q'(n), but Q(n) may also be calculated by subtracting the value obtained by multiplying the basic correction amount Im(n) - Ithresh by the correction coefficient β2 from Q(n-1). The correction coefficient β2 should be 1.5 to 3.

Figure 7 is a flowchart showing a second control example of the current control executed in the image forming apparatus 100 of the first embodiment. In the second control example shown in Figure 7, when the total device current Im(n) exceeds the total current threshold Ithresh (No in step S2), the excess current value (Im(n) - Ithresh) is calculated (step S4), the excess current value (Im(n) - Ithresh) is subtracted from the immediately preceding upper limit fixing current Q(n-1) to calculate a tentative upper limit value Q'(n) (step S5), and then the power margin is determined with attention paid to the sequence timing (operating state) of the image forming apparatus 100, and multiple correction amount settings for the upper limit fixing current Q(n) are provided according to the power margin.

Specifically, after warm-up (WU) in which the fixing temperature is increased to the standby temperature, it is determined whether a predetermined time has elapsed (step S6). If the predetermined time has elapsed (Yes in step S6), it is determined that there is no power margin (small power shortage), and Q'(n) calculated in step S5 is set to Q(n) (step S7).

On the other hand, if the specified time has not elapsed (No in step S6), it is determined that there is no power margin (large power shortage), and the value obtained by subtracting the correction value β1 from Q'(n) is set as Q(n) (step S8). The correction value β1 is set to 0.2 to 0.5 [A].

The detection period of the total device current Im(n) by the CT board 57, the variable instruction period of the upper fixing current limit Q(n) by the control unit 90, and the period of power control (power PID control, power table control) of the heating unit 23 are the same as in the first control example.

As described above, according to the second control example of this embodiment, if a predetermined time has not elapsed after warm-up, Q(n) is set to the value obtained by subtracting the correction value β1 from Q'(n). As a result, during the period immediately after warm-up when the fixing belt 21 and pressure roller 22 are not sufficiently heated and the amount of heat absorbed by the members until the entire fixing device 13 accumulates heat is large, that is, during the period when there is no power margin (large shortage), the correction amount of the upper limit fixing current Q(n) can be made large, and the difference from the rated current Imax becomes large. Therefore, even if the operations of the secondary load 60 overlap, the risk of the total device current Im(n) exceeding the rated current Imax can be reduced.

In the second control example, instead of using the value obtained by subtracting the correction value β1 from Q'(n) as Q(n), the value obtained by multiplying the basic correction amount Im(n)-Ithresh by the correction coefficient β2 and subtracting it from Q(n-1) may be used as Q'(n). The correction coefficient β2 is set to 1.5 to 3.

Figure 8 is a flowchart showing a third control example of current control executed in the image forming apparatus 100 of the first embodiment. Figure 9 is a diagram showing the fixing current and secondary side current under conditions 1 to 5 in which the device total current Im(n) is different in the third control example. In the third control example shown in Figures 8 and 9, an example is described in which a halogen heater is used as the heating section 23 of the fixing device 13. In this configuration, the fixing upper limit current Q(n) is determined by total current threshold control (one-stage control) based on the device total current threshold (total current threshold).

For example, in the case of a halogen heater with a rated voltage of 100V and a rated power of 1000W, when a full-wave AC waveform of 100V is input, it consumes 1000W of power and generates the corresponding amount of heat. When controlling the power of a halogen heater, the fixing power control board 53 detects the zero-cross timing of the AC waveform, rather than a full-wave AC waveform, and controls the current duty by inputting a half-wave waveform (or phase control waveform) with a specified cycle and duty, thereby driving the heater at the desired power. Therefore, there is basically no feedback in the power control of a halogen heater. In this way, with power control without a feedback system, when a power command is received, it is possible to operate at a power equivalent to the command power immediately without the delay of the feedback system.

In this type of power control, the upper fixing current Q(n) is calculated using the total current threshold control with the above-mentioned formula (1). In formula (1), the responsiveness of the heater power affects the total current Im(n), but as described above, with a halogen heater, power control is possible without control delays, so the power control itself can stably output the command power. A factor that can cause fluctuations in the power control of a halogen heater is the change in the upper fixing current Q(n) due to total current control, but with a halogen heater, there is no need to consider issues related to the use of total current PID control and total current threshold control, as in the first and second control examples assuming power control of an induction heating (IH) heater, and there is no risk of the threshold control becoming unstable.

As shown in FIG. 8, first, the total device current Im(n) is detected by the CT board 57 (step S1). Next, the control unit 90 calculates the excess current value Im(n)-Ithresh (step S2). Then, the calculated Im(n)-Ithresh is subtracted from the previous fixing upper limit current Q(n-1) to calculate the tentative upper limit value Q'(n) (step S3).

Next, the control unit 90 determines Q(n) based on the calculated Q'(n) and the power margin. To determine the specific power margin, the control unit 90 uses the excess current value Im(n)-Ithresh calculated in step S2 to determine whether (Im(n)-Ithresh)≦δ (step S4).

Conditions 1 to 3 in Figure 9 show the fixing current Ifuser (hatched area) and secondary current Ieng(n) (white area) when Im(n) ≦ Ithresh. The actual fixing current Ifuser is selected to be the smaller of the current command value Iht(n) or the upper fixing current limit Q(n). Condition 1 shows the case where Iht(n) is selected as Ifuser (Iht(n) < Qmax), and conditions 2 and 3 show the case where Q(n) (= Qmax) is selected as Ifuser.

If (Im(n) - Ithresh) ≦ δ (Yes in step S4), it is determined that there is a power surplus or no power surplus (small shortage), and Q(n) is set to Q'(n) calculated in step S3 (step S5).

Condition 4 in Figure 9 shows the fixing current Ifuser and secondary current Ieng(n) when Im(n) - Ithresh) ≦ δ. As shown in the left graph of condition 4, Im(n) exceeds Ithresh, but if the excess amount is δ or less, Q(n) = Q'(n) and Im(n) is reduced to Ithresh as shown in the right graph.

On the other hand, if (Im(n) - Ithresh) > δ (No in step S4), it is determined that there is no power margin (a large shortage), and the value obtained by subtracting the correction value β1 from Q'(n) is set to Q(n) (step S6). The correction value β1 is set to 0.2 to 0.5 [A]. Furthermore, the threshold value δ of Im(n) - Ithresh when determining the power margin is set to approximately 0.3 to 0.6 [A].

Condition 5 in Figure 9 shows the fixing current Ifuser and secondary current Ieng(n) when (Im(n) - Ithresh) > δ. If Im(n) exceeds Ithresh as in the left graph of condition 5, and the excess amount is greater than δ, then Q(n) = Q'(n) - β1, and Im(n) is reduced to a value lower than Ithresh as in the right graph.

Then, it is determined whether the set Q(n) exceeds Qmax (step S7), and if Q(n) > Qmax (Yes in step S7), Q(n) = Qmax (step S8).

As described above, according to the third control example of this embodiment, the correction amount in the total current threshold control when the device total current Im(n) exceeds the total current threshold Ithresh is set in multiple stages according to the power margin. This results in a power control system that keeps the current that can be allocated to the fixing device 13 as large as possible while preventing the device total current Im(n) from exceeding the rated current Imax.

Also, similar to the first control example, attention is focused on the magnitude of the excess current value (Im(n) - Ithresh), and when Im(n) - Ithresh is large, the value Q(n) is set to Q'(n) minus the correction value β1. This allows a larger correction amount for the upper fixing current Q(n) when the total device current Im(n) exceeds the total current threshold Ithresh, and the difference with the rated current Imax becomes larger. Therefore, even if the operations of the secondary loads 60 overlap, the risk of the total device current Im(n) exceeding the rated current Imax can be reduced.

In the above control example, when there is no power margin (large shortage) (when δ<(Im(n)-Ithresh)), Q(n) is calculated by subtracting the correction value β1 from Q'(n). However, Q(n) may also be calculated by subtracting the value obtained by multiplying the excess current value (Im(n)-Ithresh) by the correction coefficient β2 from Q(n-1). The correction coefficient β2 should be 1.5 to 3.

Furthermore, similar to the second control example, the power margin can be determined by focusing on the sequence timing (operating state) of the image forming device 100, and multiple correction amount settings for the fixing upper limit current Q(n) can be set according to the power margin.

Figure 10 is a block diagram showing an example of a power control system of an image forming apparatus 100 according to a second embodiment of the present invention. The power control system of the image forming apparatus 100 according to the second embodiment includes a first power supply unit 51a and a second power supply unit 51b. The first power supply unit 51a is connected to the commercial power supply AC via an inlet (not shown) and supplies AC voltage from the commercial power supply AC to the fixing power control board 53. The second power supply unit 51b is connected to the commercial power supply AC via an inlet (not shown) different from the first power supply unit 51a and converts the AC voltage from the commercial power supply AC into DC voltage by a low-voltage power supply 52, and then supplies it to the secondary load 60.

The CT board 57 detects the current supplied from the commercial power source AC to the low-voltage power source 52 via the second power supply unit 51b. That is, the CT board 57 functions as a secondary current detection unit that detects the input current (secondary current Ieng(n)) of the power supply system for the secondary load 60. Note that other current detection mechanisms can be used instead of the CT board 57.

In this embodiment, the power supply system is divided into two systems: a power supply system connected to the heating unit 23 of the fixing device 13 via the fixing power control board 53 from the first power supply unit 51a, and a power supply system connected to the secondary load 60 via the low-voltage power supply 52 from the second power supply unit 51b. For example, as shown in FIG. 10, the power cord may be configured with two cords, one of which is connected to the first power supply unit 51a and used exclusively as a power supply for the heating unit 23 of the fixing device 13, and the other is connected to the second power supply unit 51b and used as a power supply for the secondary load 60 (two-outlet configuration), or the power supplied from one power cord may be branched to the first power supply unit 51a and the second power supply unit 51b (one-outlet configuration).

In this embodiment, the total device current Im(n) and the upper limit fixing current Q(n) are calculated by the following equations (2) and (3).
Im(n)=Q(n-1)+Ieng(n)...(2)
Q(n)=Ithresh-Ieng(n)...(3)

The advantage of detecting the secondary side current Ieng(n) as in this embodiment is that since the values of the fixing current and power are not included in the calculation, in the process of determining the final fixing current (Ifuser) from the upper limit fixing current Q(n) and the current command value Iht(n) based on temperature control, Q(n) and Ifuser are independent parameters. Therefore, even if the total current control is performed only by the total current threshold control, the fixing current Ifuser and the total device current Im(n) do not become unstable, and the control configuration can be simplified.

However, because the total device current Im(n) is calculated, it is prone to errors in the total device current, in contrast to the first embodiment in which the total device current Im(n) is detected by the CT board 57. For this reason, the total current threshold margin α2 used when setting the total current threshold Ithresh must be set larger than the total current threshold margin α1 in the first embodiment.

Figure 11 is a flowchart showing an example of current control executed in the image forming apparatus 100 of the second embodiment. Figure 12 is a diagram showing the fixing current and secondary current under conditions 1 to 5 in which the total device current Im(n) is different in the control example of Figure 11. In the control example shown in Figures 11 and 12, a two-outlet configuration with a rated voltage of 100V and a rated current of 20A is used, with one 15A outlet dedicated to the heating section 23 of the fixing device 13 and the other 15A outlet allocated to the secondary load 60. Then, the total device current control is performed with a rated current of 20A for the two outlets in total. In this configuration, the fixing upper limit current Q(n) is determined by threshold control (one-stage control) based on the threshold value of the total device current (total current threshold).

As shown in FIG. 11, first, the secondary current Ieng(n) is detected by the CT board 57 (step S1). The control unit 90 adds the previously set upper limit fixing current Q(n-1) to the detected secondary current Ieng(n) to calculate the total device current Im(n) (step S2).

Next, the control unit 90 calculates the excess current value Im(n)-Ithresh using Im(n) calculated in step S2 (step S3). Ithresh is a current value lower than the rated current Imax by a predetermined value α2 (total current threshold margin, α2>α1). In addition, the control unit 90 calculates the provisional upper limit value Q'(n) by subtracting Ieng(n) from Ithresh using the above-mentioned equation (3) (step S4).

Here, the relationship between formula (3) and formula (1) for calculating the provisional upper limit value Q'(n) in the first embodiment will be described. In formula (1), the provisional upper limit value Q'(n) is set by subtracting the excess current value Im(n)-Ithresh, which is the difference between the total device current Im(n) and Ithresh, from the previously set upper limit fixing current Q(n-1). Substituting formula (2), which is a parameter when detecting the secondary side current Ieng(n), into formula (1) and transforming it, we obtain
Q'(n)=Q(n-1)-(Im(n)-Ithresh)
=(Im(n)-Ieng(n))-(Im(n)-Ithresh)=Ithresh-Ieng(n)
Thus, equation (3) for calculating Q'(n) in the second embodiment in which the secondary side current is detected is derived. That is, the essential control of comparing the device total current Im(n) with the total current threshold Ithresh to set the upper fixing current limit Q(n) is the same as in the first embodiment in which the device total current is detected.

Next, the control unit 90 determines Q(n) based on the calculated Q'(n) and the power margin. To determine the specific power margin, the control unit 90 uses the excess current value Im(n)-Ithresh to determine whether (Im(n)-Ithresh)≦δ (step S5).

Conditions 1 and 2 in FIG. 12 show the upper fixing current Q(n) and secondary current Ieng(n) when Im(n) ≦ Ithresh. Condition 1 shows the case where Im(n) < Ithresh, and condition 2 shows the case where Im(n) = Ithresh. In this control example, the actual fixing current Ifuser is allowed up to the upper fixing current Q(n), so Im(n) is the sum of the secondary current Ieng(n) and the upper fixing current Q(n). Therefore, for example, the total device current Im(n) that actually flows under condition 1 is as shown in the graph on the right, which combines Ifuser (hatched area) and the secondary current (white area).

If (Im(n) - Ithresh) ≦ δ (Yes in step S5), it is determined that there is a power surplus or no power surplus (small shortage), and Q(n) is set to Q'(n) calculated in step S4 (step S6). Condition 4 in FIG. 12 shows the upper fixing current Q(n) and secondary side current Ieng(n) when (Im(n) - Ithresh) ≦ δ. As in the left graph of condition 4, Im(n) exceeds Ithresh, but if the excess is δ or less, Q(n) = Q'(n) and Im(n) is reduced to Ithresh as in the right graph.

On the other hand, if δ<(Im(n)-Ithresh) (No in step S5), it is determined that there is no power margin (a large shortage), and the value obtained by subtracting the correction value β1 from Q'(n) is set to Q(n) (step S7). The correction value β1 is set to 0.2 to 0.5 [A]. Furthermore, the threshold value δ of Im(n)-Ithresh when determining the power margin is set to approximately 0.3 to 0.6 [A].

Condition 4 in Figure 12 shows the fixing current Q(n) and secondary current Ieng(n) when (Im(n) - Ithresh) > δ. If Im(n) exceeds Ithresh and the excess amount is greater than δ, as in the left graph of condition 5, Q(n) = Q'(n) - β1, and Im(n) is reduced to a value lower than Ithresh, as in the right graph.

Then, it is determined whether the set Q(n) exceeds Qmax (step S8), and if Q(n) > Qmax (Yes in step S8), Q(n) = Qmax (step S9).

As described above, according to the current control example of this embodiment, the correction amount in the total current threshold control when the device total current Im(n) exceeds the total current threshold Ithresh is set in multiple stages according to the power margin. This results in a power control system that keeps the current that can be allocated to the fixing device 13 as large as possible while preventing the device total current Im(n) from exceeding the rated current Imax.

Focusing on the magnitude of the excess current value (Im(n) - Ithresh), when Im(n) - Ithresh is large, Q(n) is calculated by subtracting the correction value β1 from Q'(n). This allows a larger correction amount for the upper fixing current Q(n) when the total device current Im(n) exceeds the total current threshold Ithresh, and the difference with the rated current Imax becomes larger. Therefore, even if the operations of the secondary loads 60 overlap, the risk of the total device current Im(n) exceeding the rated current Imax can be reduced.

In the above control example, when there is no power margin (large shortage) (when δ<(Im(n)-Ithresh)), Q(n) is calculated by subtracting the correction value β1 from Q'(n). However, Q(n) may also be calculated by subtracting the value obtained by multiplying the excess current value (Im(n)-Ithresh) by the correction coefficient β2 from Q(n-1). The correction coefficient β2 should be 1.5 to 3.

In addition, in a configuration like this control example where the secondary current Ieng is detected by the CT board 57 and the total device current Im(n) is calculated from the upper limit fixing current Q(n-1) and Ieng(n) using equation (2), the responsiveness of the fixing power control does not affect the measurement value of the CT board 57. Furthermore, the fixing power control does not affect Q(n) calculated using equation (3). Therefore, the correction of Q(n) using the above calculation does not cause the fixing power control or total current control to become unstable. Therefore, whether the heating unit 23 is an induction heating (IH) heater or a halogen heater, it can be handled with just the same total current threshold control.

In this embodiment, as in the second control example of the first embodiment, the power margin can be determined by focusing on the sequence timing (operating state) of the image forming device 100, and multiple correction amount settings for the fixing upper limit current Q(n) can be set according to the power margin.

The present invention is not limited to the above-described embodiments, and various modifications are possible without departing from the spirit of the present invention. For example, in the above-described embodiments, when the heating unit 23 is a halogen heater, power control is performed by controlling the current duty of the AC voltage, but power control may be performed by incorporating a current detection circuit and a voltage detection circuit in the fixing power control board 53 and monitoring the current and voltage.

In addition, in each of the above embodiments, a sliding belt type fixing device 13 in which an endless fixing belt 21 slides against a nip forming member 24 as a heated rotating body is exemplified, but it is of course possible to apply the present invention in exactly the same way to a fixing device using a uniaxial belt type in which the fixing belt 21 is wrapped around a fixing roller, a biaxial belt type in which the fixing belt 21 is stretched between a fixing roller and a heating roller, or a fixing device equipped with a heated rotating body other than the fixing belt 21.

In addition, the image forming device 100 is not limited to a tandem type color printer as shown in FIG. 1, but can be applied to various image forming devices equipped with a fixing device, such as monochrome copiers, digital multifunction machines, facsimiles, and laser printers.

The present invention can be used in an image forming apparatus equipped with a fixing device that applies heat and pressure to a toner image by inserting the recording medium into a fixing nip formed by a heated rotating body and a pressure member to melt and fix the toner image onto the recording medium. By using the present invention, it is possible to provide an image forming apparatus that can supply maximum power to the fixing device while reliably preventing the total current input to the image forming apparatus from exceeding a limit value.

Pa to Pd: image forming section; 13: fixing device; 21: fixing belt (heated rotating body);
22 Pressure roller (pressure rotating body)
23 Heating unit 30 Pressurizing mechanism 47 Thermistor (temperature detection unit)
50 Power control circuit 51 Power supply unit 52 Low voltage power supply 51a First power supply unit 51b Second power supply unit 53 Fixing power control board 55 Secondary power control board 57 CT board 60 Secondary load 90 Control unit 100 Image forming apparatus N Fixing nip unit S Paper (recording medium)

Claims (8)

an image forming unit that forms a toner image on a recording medium;
A heated rotating body;
a pressure rotating body that is pressed against the heated rotating body at a predetermined fixing nip pressure to form a fixing nip portion;
A heating unit that heats the heated rotating body;
A temperature detection unit that detects the temperature of the heated rotating body;
a fixing device that performs a fixing process of fixing the toner image onto the recording medium by applying heat and pressure to the recording medium passing through the fixing nip portion;
a power supply unit connected to a commercial power source and supplying power to the entire image forming apparatus including the fixing device;
a control unit that, when a current command value Iht(n) determined based on a detection result of the temperature detection unit is equal to or smaller than an upper limit fixing current Q(n), determines a fixing current Ifuser flowing through the heating unit to be the current command value Iht(n), and, when the current command value Iht(n) is greater than the upper limit fixing current Q(n), determines the fixing current Ifuser to be the upper limit fixing current Q(n);
In an image forming apparatus comprising:
The control unit is
when the total device current Im(n) exceeds a total current threshold Ithresh that is lower than a rated current Imax of the image forming device by a predetermined value α during image formation, the fixing upper limit current Q(n) is set by total current threshold control so that the total device current Im(n) does not exceed the rated current Imax, and the fixing upper limit current Q(n) is corrected in multiple stages based on a power margin of the image forming device;
when the device total current Im(n) exceeds the total current threshold Ithresh, the control unit determines the power margin based on an excess current value Im(n)-Ithresh which is a difference between the device total current Im(n) and the total current threshold Ithresh, and calculates a tentative upper limit value Q'(n) by subtracting the excess current value Im(n)-Ithresh from the previous fixing upper limit current Q(n-1),
an image forming apparatus, characterized in that, when the excess current value Im(n)-Ithresh is equal to or smaller than a predetermined value δ, the fixing upper limit current Q(n) is set to the tentative upper limit value Q'(n), and, when the excess current value Im(n)-Ithresh exceeds a predetermined value δ, the fixing upper limit current Q(n) is set to a value smaller than the tentative upper limit value Q'(n) . an image forming unit that forms a toner image on a recording medium;
A heated rotating body;
a pressure rotating body that is pressed against the heated rotating body at a predetermined fixing nip pressure to form a fixing nip portion;
A heating unit that heats the heated rotating body;
A temperature detection unit that detects the temperature of the heated rotating body;
a fixing device that performs a fixing process of fixing the toner image onto the recording medium by applying heat and pressure to the recording medium passing through the fixing nip portion;
a power supply unit connected to a commercial power source and supplying power to the entire image forming apparatus including the fixing device;
a control unit that, when a current command value Iht(n) determined based on a detection result of the temperature detection unit is equal to or smaller than an upper limit fixing current Q(n), determines a fixing current Ifuser flowing through the heating unit to be the current command value Iht(n), and, when the current command value Iht(n) is greater than the upper limit fixing current Q(n), determines the fixing current Ifuser to be the upper limit fixing current Q(n);
In an image forming apparatus comprising:
The control unit is
when the total device current Im(n) exceeds a total current threshold Ithresh that is lower than a rated current Imax of the image forming device by a predetermined value α during image formation, the fixing upper limit current Q(n) is set by total current threshold control so that the total device current Im(n) does not exceed the rated current Imax, and the fixing upper limit current Q(n) is corrected in multiple stages based on a power margin of the image forming device;
when the device total current Im(n) exceeds the total current threshold Ithresh, the control unit calculates a provisional upper limit value Q'(n) by subtracting an excess current value Im(n)-Ithresh, which is a difference between the device total current Im(n) and the total current threshold Ithresh, from the previous fixing upper limit current Q(n-1);
an image forming apparatus, characterized in that, when a predetermined time has elapsed after a warm-up for raising the temperature of a heated rotating body to a standby temperature, the fixing upper limit current Q(n) is set to the provisional upper limit value Q'(n), and, when the predetermined time has not elapsed after the warm-up, the fixing upper limit current Q(n) is set to a value smaller than the provisional upper limit value Q'(n) . 3. The image forming apparatus according to claim 1, further comprising a total current detection unit that detects the device total current Im(n) supplied from the power supply unit, and the control unit performs the total current threshold control to set the upper limit fixing current Q(n) by comparing the device total current Im( n ) detected by the total current detection unit with the total current threshold Ithresh. 4. The image forming apparatus according to claim 3, wherein the control unit performs two-stage control to set the upper limit fixing current Q(n) by total current PID control when the total device current Im(n) is equal to or less than the total current threshold Ithresh, and to set the upper limit fixing current Q(n) by total current threshold control when the total device current Im(n) exceeds the total current threshold Ithresh . 5. The image forming apparatus according to claim 4 , wherein the heating section is an induction heater that generates heat by induction heating a heat generating layer of the heated rotating body. The power supply unit includes:
a first power supply unit connected to the commercial power source and supplying power to the fixing device;
a second power supply unit connected to the commercial power source and supplying power to a secondary load other than the fixing device;
It is composed of
a secondary current detection unit that detects a secondary current Ieng(n) supplied from the second power supply unit,
6. The image forming apparatus according to claim 1, wherein the control unit performs the total current threshold control to calculate the total device current Im(n) by adding a previously set upper limit fixing current Q(n-1) to the secondary side current Ieng(n) detected by the secondary side current detection unit, and to set the upper limit fixing current Q(n) by comparing the calculated total device current Im(n) with the total current threshold Ithresh . The image forming apparatus according to any one of claims 1 to 6, characterized in that when the excess current value Im(n) - Ithresh exceeds a predetermined value δ, or when a predetermined time has not elapsed after a warm-up for raising the temperature of the heated rotating body to a standby temperature, the control unit sets a value obtained by subtracting a correction amount β1 from the provisional upper limit value Q'(n) to the upper limit fixing current Q(n) . 7. The image forming apparatus according to claim 1, wherein the control unit sets the fixing upper limit current Q(n) to the provisional upper limit value Q'(n) calculated by multiplying the excess current value Im(n)-Ithresh by a correction coefficient β2 and subtracting the value obtained by multiplying the excess current value Im(n)-Ithresh by a correction coefficient β2 from the previous fixing upper limit current Q(n-1), when the excess current value Im(n)-Ithresh exceeds a predetermined value δ or when a predetermined time has not elapsed after a warm-up for raising the temperature of the heated rotating body to a standby temperature.

Images