JP4089412B2 - Electrophotographic equipment - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an electrophotographic apparatus equipped with an exposure head in which a light emitting element is used as a light source.
[0002]
[Prior art]
Conventionally, a configuration in which a laser beam emitted from a laser light source is scanned using a rotating polygon mirror (polygon mirror) to form a latent image on a photosensitive member, or an exposure head in which a plurality of light emitting elements are linearly arranged is used. An electrophotographic apparatus having a configuration for forming a latent image on a photoreceptor is known.
[0003]
Among these, an electrophotographic apparatus equipped with an exposure head is advantageous for miniaturization because the optical system can be configured simply, and is not subject to restrictions on the rotational speed of the rotary polygon mirror. This is also advantageous in terms of conversion.
[0004]
As a conventional exposure head, an LED head in which a large number of minute LED elements are linearly arranged has been put into practical use. The LED element can generally obtain high luminance, but is basically manufactured using a semiconductor process, and therefore, when attempting to increase the length, the yield rapidly deteriorates. For this reason, the degree of integration of the light emitting elements is, for example, about 512 pixels at most per chip in the case of 1200 dpi (dot / inch). As described above, since one chip is short, when realizing a long exposure head, it is necessary to accurately arrange a large number of chips in a line. In addition, since the LED head forms a PN junction for each LED element by a semiconductor process, it is known that the luminance variation is large (up to about ± 25% in one chip). In general, the current value for driving the LED is controlled based on the light amount correction data acquired in advance by causing each LED element or a plurality of LED elements to emit light in a predetermined sequence, A method of controlling is known.
[0005]
On the other hand, as another example of the exposure head, an exposure head using an organic EL (electroluminescence) element in which a plurality of light emitting elements are arranged in a straight line is known.
[0006]
Since the organic EL element generates a small amount of heat, it is possible to eliminate cooling fins and the like, and the exposure head itself can be downsized to a thickness of about 3 mm or less, for example.
[0007]
Some element structures of organic EL elements are disclosed in Japanese Patent Application Laid-Open Nos. 10-1664 and 2001-63136.
[0008]
In Japanese Patent Laid-Open No. 10-48925, a change in the amount of light of an optical unit composed of an LED array or the like is determined based on the temperature of the optical unit, and the charged potential of the photosensitive member is kept constant based on the determination result. In addition, an electrophotographic apparatus for controlling the developing bias voltage is disclosed. More specifically, this is a technique for changing the developing bias potential closer to the photosensitive member charging potential while keeping the charging potential of the photosensitive member constant when the amount of light emitted from the optical means decreases. .
[0009]
[Patent Document 1]
Japanese Patent Laid-Open No. 10-1664
[Patent Document 2]
JP 2001-63136 A
[Patent Document 3]
Japanese Patent Laid-Open No. 10-48925
[0010]
[Problems to be solved by the invention]
Here, in order to keep the electrophotographic image forming conditions constant, it is necessary to expose the photoconductor with a constant light amount. However, the organic EL element has a large light amount deterioration as compared with the LED element (both are the same). The light intensity half-life under the driving conditions is that the LED element is 10,000 hours while the organic EL element is approximately 500 hours), and the necessary light quantity cannot be obtained gradually.
[0011]
If the drive current is increased, the amount of light emitted from the organic EL element can be kept constant. However, when the drive current increases, the deterioration of the organic EL element progresses at an accelerated rate, so there is a limit to the increase in drive current.
[0012]
By the way, in the two-component development technique in which the developer includes toner and carrier, the gap between the charging potential of the photosensitive member and the developing bias potential is set to be relatively small so that the carrier does not adhere to the photosensitive member (so-called carrier jump). (Absolute value is about 100V). As described above, when the technology described in Japanese Patent Laid-Open No. 10-48925, in which the developing bias potential is brought close to the charging potential of the photosensitive member in a small setting range between the charging potential and the developing bias potential, the surface of the photosensitive member is exposed. There is a case where so-called scumming occurs where toner adheres to a non-existing region.
[0013]
SUMMARY An advantage of some aspects of the invention is that it provides an electrophotographic apparatus capable of maintaining constant image forming conditions without accelerating deterioration of a light emitting element.
[0014]
[Means for Solving the Problems]
  In order to solve this problem, an electrophotographic apparatus of the present invention provides an exposure including a light source in which a plurality of light emitting elements are arranged in the main scanning direction.headAnd the exposureheadA photosensitive member on which an electrostatic latent image is formed by the exposure light, and developing means for supplying toner to the electrostatic latent image to form a toner image on the photosensitive member;A pixel count / maximum extraction unit that counts and accumulates the number of lighting times of each light emitting element of the exposure head and extracts the maximum value of the lighting number, and a count smaller than the maximum value of the number of lighting times extracted by the pixel count / maximum extraction unit A head control unit that makes the number of lighting of each light emitting element uniform by selecting and turning on the light emitting element of the value, and in a non-printing state, after the selective driving of the light emitting element by the head control unit,SaidPart of exposure headBased on the detection means for detecting the light emission amount of the light emitting element and the detection result of the detection means, along with the decrease in the light emission amount of the light emitting elementBased on the ratio of the initial light intensity to the reduced light intensityThe exposureheadAnd a control means for extending the exposure time.
[0015]
This makes it possible to compensate for the amount of light that has decreased during the one-line formation period due to an increase in exposure time, so that the image forming conditions can be kept constant without accelerating the deterioration of the light emitting elements.
[0016]
DETAILED DESCRIPTION OF THE INVENTION
  The invention according to claim 1 of the present invention is an exposure comprising a light source in which a plurality of light emitting elements are arranged in the main scanning direction.headAnd the exposureheadA photosensitive member on which an electrostatic latent image is formed by the exposure light, and developing means for supplying toner to the electrostatic latent image to form a toner image on the photosensitive member;A pixel count / maximum extraction unit that counts and accumulates the number of lighting times of each light emitting element of the exposure head and extracts the maximum value of the lighting number, and a count smaller than the maximum value of the number of lighting times extracted by the pixel count / maximum extraction unit A head control unit that makes the number of lighting of each light emitting element uniform by selecting and turning on the light emitting element of the value, and in a non-printing state, after the selective driving of the light emitting element by the head control unit,SaidPart of exposure headBased on the detection means for detecting the light emission amount of the light emitting element and the detection result of the detection means, along with the decrease in the light emission amount of the light emitting elementBased on the ratio of the initial light intensity to the reduced light intensityThe exposureheadAnd an electrophotographic apparatus having a control means for extending the exposure timeis there.
[0028]
Hereinafter, embodiments of the present invention will be described with reference to FIGS. In these drawings, the same members are denoted by the same reference numerals, and redundant description is omitted.
[0029]
FIG. 1 is a schematic view showing a configuration of an electrophotographic apparatus according to an embodiment of the present invention, FIG. 2 is an explanatory view showing a developing station in the electrophotographic apparatus of FIG. 1, and FIG. 3 is an exposure in the electrophotographic apparatus of FIG. FIG. 4 is a block diagram showing the configuration of the controller in the electrophotographic apparatus of FIG. 1, FIG. 5 is a block diagram showing the configuration of the engine control unit in the electrophotographic apparatus of FIG. 1, and FIG. 7 is a circuit diagram showing a detailed configuration of the exposure head and the head control unit, FIG. 7 is an explanatory diagram showing the relationship between the line formation period and the exposure period in the electrophotographic apparatus, and FIG. 8 is a driver provided corresponding to each driver chip. FIG. 9 is a block diagram showing a detailed configuration of the current setting unit, and FIG. 9 is a graph showing a change in relative luminance with respect to the input time in the organic EL element.
[0030]
In FIG. 1, an electrophotographic apparatus 40 has four color developing stations, a yellow developing station 41Y, a magenta developing station 41M, a cyan developing station 41C, and a black developing station 41K, arranged in a stepwise manner in the vertical direction. A paper feed tray 43 that accommodates the recording paper 42 is disposed above, and a conveyance path for the recording paper 42 supplied from the paper feed tray 43 is provided at a location corresponding to each developing station (41Y to 41K). The recording paper conveyance path 44 is arranged in the vertical direction from the top to the bottom.
[0031]
The developing stations (41Y to 41K) form toner images of yellow, magenta, cyan, and black in order from the upstream side of the recording paper conveyance path 44, and include a photoconductor (47Y to 47K) and a developing sleeve (not shown). 1), a charger (not shown), and the like.
[0032]
Now, the developing station 41 will be described in detail with reference to FIG. The developing stations 41Y to 41K are different in the color of the filled developer, but the configuration is the same regardless of the development color.
[0033]
In FIG. 2, the developing station 41 is filled with a developer 45 which is a mixture of carrier and toner. 46a and 46b are stirring paddles for stirring the developer 45, and the toner in the developer 45 is charged to a predetermined potential by friction by the rotation of the stirring paddles 46a and 46b, and also circulates in the developing station 41. The toner and the carrier are sufficiently stirred and mixed. A photoconductor 47 is rotated in a direction D3 by a driving source (not shown). A charger 48 charges the surface of the photoreceptor 47 to a predetermined potential. Reference numeral 49 is a developing sleeve (developing means), and 50 is a thinning blade. The developing sleeve 49 has a mag roll 51 in which a plurality of magnetic poles are formed. The layer thickness of the developer 45 supplied to the surface of the developing sleeve 49 is regulated by the thinning blade 50, and the developing sleeve 49 is rotated in the direction D4 by a driving source (not shown). As a result, the developer 45 is supplied to the surface of the developing sleeve 49, and the developer that has not been transferred to the photoreceptor 47 is collected in the developing station 41.
[0034]
52 is an exposure head (exposure means). The exposure head in the present embodiment is configured to arrange two element rows by arranging organic EL elements (light emitting elements) in a staggered manner, and by using either or both of these element rows, An electrostatic latent image of maximum A4 size is formed on the photoreceptor. Only the toner of the developer 45 supplied to the surface of the developing sleeve 49 adheres to the electrostatic latent image portion, and the electrostatic latent image is visualized.
[0035]
A support member 53 supports the exposure head 52. Reference numeral 54 denotes a light amount sensor (detection means) constituted by a photosensor or the like, which is disposed at an angle at which light irradiated from the exposure head 52 and reflected by the surface of the photoreceptor 47 is directly incident. A scattering plate (not shown) is disposed on the light incident surface of the light amount sensor 54, and the amount of received light does not change greatly even if the incident position of the light slightly changes due to, for example, eccentricity of the photoconductor 47. It is like that. The light quantity sensor 54 has a characteristic that the output current changes linearly with respect to the received light quantity. By referring to the output of the light quantity sensor 54, a light emitting element (organic EL element) arranged in a predetermined range of the exposure head 52 is used. ) Can be detected.
[0036]
A transfer roller 55 is provided at a position facing the recording sheet conveyance path 44 with respect to the photoreceptor 47, and is rotated in the direction D5 by a driving source (not shown). A predetermined transfer bias is applied to the transfer roller 55, and the toner image formed on the photoreceptor 47 is transferred to the recording paper conveyed through the recording paper conveyance path 44.
[0037]
Hereinafter, returning to FIG. 1, the description will be continued.
[0038]
A toner bottle 56 stores toners of yellow, magenta, cyan, and black. A toner transport pipe (not shown) is provided from the toner bottle 56 to each of the development stations (41Y to 41K), and supplies toner to the development stations (41Y to 41K).
[0039]
Reference numeral 57 denotes a paper feed roller, which rotates in a direction D1 by controlling an electromagnetic clutch (not shown), and sends the recording paper 42 loaded in the paper feed tray 43 to the recording paper transport path 44.
[0040]
A registration paper 58 and a pinch roller 59 pair are provided in the recording paper conveyance path 44 located between the paper feed roller 57 and the transfer portion of the most upstream yellow developing station 41Y as nip conveyance means on the inlet side. The registration roller 58 and the pinch roller 59 pair temporarily stop the recording paper 42 conveyed by the paper supply roller 57 and convey it in the direction of the yellow developing station 41Y at a predetermined timing. This temporary stop restricts the leading edge of the recording paper 42 in parallel with the axial direction of the registration roller 58 and the pinch roller 59 pair, thereby preventing the recording paper 42 from skewing.
[0041]
Reference numeral 60 denotes a recording paper passage sensor. The recording paper passage sensor 60 is constituted by a reflective sensor (photo reflector), and detects the leading edge and the trailing edge of the recording paper based on the presence or absence of reflected light.
[0042]
When the rotation of the registration roller 58 is started (the power transmission is controlled by an electromagnetic clutch (not shown) and the rotation is turned ON / OFF), the recording paper 42 is conveyed along the recording paper conveyance path 44 toward the yellow developing station 41Y. However, with the rotation start timing of the registration roller 58 as a starting point, the electrostatic latent image writing timing by the exposure head (see reference numeral 52 in FIG. 2) mounted in each developing station (41Y to 41K) is independently controlled. The
[0043]
A fixing unit 62 is provided as a nip conveying means on the outlet side in the recording paper conveyance path 44 located further downstream of the most downstream black developing station 41K. The fixing device 62 includes a heating roller 63 and a pressure roller 64. The heating roller 63 is a multi-layered roller composed of a heating belt, a rubber roller, and a core material (both not shown) in order from the surface. Among them, the heat generating belt is a belt having a three-layer structure, and is composed of a release layer, a silicon rubber layer, and a base material layer (both not shown) from the side closer to the surface. The release layer is made of a fluororesin having a thickness of about 20 to 30 μm and imparts release properties to the heating roller 63. The silicone rubber layer is made of about 170 μm silicone rubber and gives the pressure roller moderate elasticity. The base material layer is made of a magnetic material that is an alloy of iron, nickel, chromium, or the like.
[0044]
Reference numeral 65 denotes a back core including an exciting coil. Inside the back core 65, an excitation coil in which a predetermined number of copper wires (not shown) whose surfaces are insulated is bundled in the direction of the rotation axis of the heating roller 63, and heated at both ends of the heating roller 63. It is formed to circulate along the circumferential direction of the roller 63. When an alternating current of about 30 kHz is applied to the exciting coil from an exciting circuit (not shown) that is a semi-resonant inverter, a magnetic flux is generated in a magnetic path constituted by the back core 65 and the base layer of the heating roller 63. Due to this magnetic flux, an eddy current is formed in the base material layer of the heat generating belt of the heating roller 63, and the base material layer generates heat. The heat generated in the base material layer is transmitted to the release layer through the silicon rubber layer, and the surface of the heating roller 63 generates heat.
[0045]
Reference numeral 66 denotes a thermistor (Thermal Sensitive Resistor) provided as a temperature detecting means of the heating roller 63. A thermistor is a ceramic semiconductor that is obtained by sintering at a high temperature using a metal oxide as the main raw material. By applying the fact that the load resistance changes according to the temperature, the temperature of the contacted object can be measured. . The output of the thermistor 66 is input to a control device (not shown), and the control device controls the power output to the exciting coil in the back core 65 based on the output of the thermistor 66, and the surface temperature of the heating roller 63 becomes about 170 ° C. Control as follows.
[0046]
When the recording paper 42 on which the toner image is formed is passed through the nip formed by the temperature-controlled heating roller 63 and pressure roller 64, the toner image on the recording paper 42 is added to the heating roller 63. A fixed image can be obtained by being heated / pressurized by the pressure roller 64.
[0047]
Reference numeral 67 denotes a recording paper trailing edge detection sensor for monitoring the discharge state of the recording paper 42. Reference numeral 71 denotes a toner image detection sensor. The toner image detection sensor 71 is a reflective sensor unit that uses a plurality of light emitting elements (both visible light) having different emission spectra and a single light receiving element, and changes the image color between the background of the recording paper 42 and the image forming portion. Accordingly, the image density is detected by utilizing the fact that the absorption spectrum is different. In addition, since the toner image detection sensor 71 can detect not only the image density but also the image forming position, in the electrophotographic apparatus according to the present embodiment, two toner image detection sensors 71 are provided in the width direction of the apparatus, and on the recording paper 42. The image formation timing is controlled based on the detection position of the image position deviation amount detection pattern formed in the above.
[0048]
Reference numeral 72 denotes a recording paper transport drum. The recording paper transport drum 72 is a metal roller whose surface is covered with rubber having a thickness of about 200 μm, and the recording paper 42 after fixing is transported in the direction D2 along the recording paper transport drum. At this time, the recording sheet 42 is cooled by the recording sheet conveying drum 72 and is bent and conveyed in the direction opposite to the image forming surface. As a result, curling that occurs when a high-density image is formed on the entire surface of the recording paper can be greatly reduced. Thereafter, the recording paper 42 is conveyed in the direction D6 by the kicking roller 74 and discharged to the paper discharge tray 78.
[0049]
Reference numeral 73 denotes a face-down paper discharge unit. The face-down paper discharge unit 73 is configured to be rotatable about the support member 75. When the face-down paper discharge unit 73 is opened, the recording paper 42 is discharged in the direction D7. In the closed state, the face-down paper discharge unit 73 is formed with ribs 76 along the transport path on the back surface so as to guide the transport of the recording paper 42 together with the recording paper transport drum 72.
[0050]
Reference numeral 77 denotes a driving source, which employs a stepping motor in this embodiment. By a drive source 77, a peripheral portion of each developing station (41Y-41K) including a paper feed roller 57, a registration roller 58, a pinch roller 59, a photoconductor (47Y-47K) and a transfer roller (55Y-55K), a fixing device 62 The recording paper transport drum 72 and the kicking roller 74 are driven.
[0051]
A controller 80 receives image data from a computer (not shown) via an external network and generates printable image data.
[0052]
Reference numeral 81 denotes an engine control unit. The engine control unit 81 controls the hardware and mechanism of the electrophotographic apparatus 40, forms a color image on the recording paper 42 based on the image data transferred from the controller 80, and performs overall control of the electrophotographic apparatus. .
[0053]
Reference numeral 82 denotes a power supply unit. The power supply unit 82 supplies power of a predetermined voltage to the drive source 77, the controller 80, and the engine control unit 81, and supplies power to the heating roller 63 of the fixing device 62. In addition, a so-called high voltage power source such as charging of the surface of the photosensitive member 47, a developing bias applied to the developing sleeve (reference numeral 49 in FIG. 2), a transfer bias applied to the transfer roller 55, and the like is included in this power source unit.
[0054]
The power supply unit 82 includes a power supply monitoring unit 83 so that at least the power supply voltage supplied to the engine control unit 81 can be monitored. This monitor signal is detected by the engine control board 81 and detects a decrease in power supply voltage when the power switch is turned off or a power failure occurs.
[0055]
Next, the configuration of the exposure head will be described with reference to FIG.
[0056]
As shown in FIG. 3, the exposure head 52 has a head support member 53 that supports the exposure head. The exposure head 52 is an organic electroluminescence element (organic EL element) which is a light emitting element 86 as a light source mounted on a base material 84 and hermetically sealed with a sealing material 85 provided on a head support member 53. And a driver 87 which is provided on the substrate 84 and supplies a voltage corresponding to the image data to the organic EL element 86 to emit light. Further, on the substrate 84, the light from the organic EL element 8 is reflected to convert the optical path by 90 °, the fiber 88 that collects and transmits the light from the prism 88, and the fiber array 89. A cylindrical lens 90 that narrows the light in the sub-scanning direction is mounted.
[0057]
As described above, the organic EL elements 86 form two element rows that are staggered with respect to each other. These element rows can emit light for each row, a high resolution mode that drives both element rows simultaneously, that is, a high resolution mode, and a low resolution mode that drives only one element row, that is, a low resolution mode. Is realized. Note that the organic EL element 86 may form one element row.
[0058]
Next, the configuration and operation of the controller in the electrophotographic apparatus of this embodiment will be described with reference to FIG.
[0059]
In FIG. 4, reference numeral 100 denotes a computer. The computer 100 transfers image data and print job information to the controller 80 via the network 101. Reference numeral 102 denotes a network interface. The controller 80 receives image data and print job information transferred from the computer 100 via the network interface 102, and conversely transmits so-called status information such as an error state of the electrophotographic apparatus to the computer 100.
[0060]
Reference numeral 103 denotes a CPU (control means) that controls the operation of the controller 80 based on a program stored in the ROM 104.
[0061]
Reference numeral 105 denotes a RAM which is used as a work area of the CPU 103 and temporarily stores image data received by the network interface 102, print job information, printable image data developed in units of pages, and the like. The
[0062]
Reference numeral 106 denotes an image processing unit. The image processing unit 106 performs image processing (conversion processing from printer language to raster data, color correction) based on image data transferred from the computer 100 and print job information (both are temporarily stored in the RAM 105). , Edge correction, screen generation, etc.) to generate image data for printing, and store it again in the RAM 105.
[0063]
Reference numeral 107 denotes a printer interface, and image data in units of pages stored in the RAM 105 is transferred to the engine control unit 81 via the printer interface 107.
[0064]
Next, the configuration and operation of the engine control unit will be described with reference to FIG.
[0065]
In FIG. 5, reference numeral 110 denotes a controller interface. The controller interface 110 receives image data for each page and print mode information transferred from the controller 80.
[0066]
A CPU (control means) 111 controls the operation of the printer engine based on a program stored in the ROM 112. A RAM 113 is used as a work area when the CPU 111 operates. Reference numeral 114 denotes a so-called rewritable nonvolatile memory such as an EEPROM. The non-volatile memory 114 stores life information such as the rotation time of the photoconductor 47 of the electrophotographic apparatus and the operation time of the fixing device 62, and the accumulated lighting value of the light emitting element described in detail later. Reference numeral 115 denotes a serial interface. Information from the sensor group such as the recording paper passing sensor 60 and the recording paper trailing edge detection sensor 67, and the power supply monitoring unit 83 (before the CPU 111 operation is detected by detecting a decrease in the power supply voltage, each light emitting element of the exposure head). The output of the accumulated number of lighting times is stored in the nonvolatile memory 114. The output of the serial conversion unit (not shown) is converted into a serial signal having a predetermined cycle and received by the serial interface 115. The serial signal received by the serial interface 115 is converted into a parallel signal and then read by the CPU 111. On the other hand, the drive source 77 for driving the paper feed roller 57, the photoconductors (47Y to 47K), the heating roller 63 of the fixing device, the recording paper transport drum 72, and the like, and the driving of the paper feed roller 57 and the registration roller 58 are driven. A control signal to an actuator such as an electromagnetic clutch (not shown) for controlling force transmission, a control signal for setting a potential of a high voltage power source such as a developing bias / transfer bias / charging potential, and the like are serial signals 115 as parallel signals. Sent to. The serial interface 115 converts this parallel signal into a serial signal and outputs it to the actuator group. In this embodiment, sensor input and actuator control signal output that do not need to be detected at high speed are all performed via the serial interface 115.
[0067]
On the other hand, the input from the toner image detection sensor 71 (the image displacement detection pattern requires a detection resolution of about 10 μm) that requires high-speed sampling is directly connected to the input terminal of the CPU 111. Further, the analog level signal of the light quantity sensor 54 is connected to an analog input port of the CPU 111, and the CPU 111 can detect the output level of the light quantity sensor 54 at an arbitrary time.
[0068]
120Y, 120M, 120C, and 120K are head controllers that control the driving of the exposure head (see reference numeral 52 in FIG. 2) corresponding to each print color. The head controllers (120Y to 120K) include functions for performing exposure timing control of the exposure head 52 and driving voltage control of the organic EL elements 86 mounted on the exposure heads (52Y to 52K). 121Y, 121M, 121C, and 121K are buffer memories having a capacity of several lines. The image data transferred via the controller interface 110 is temporarily stored in buffer memories (121Y to 121K) provided independently for each print color. The image data stored in the buffer memories (121Y to 121K) is transferred to an exposure head (52Y to 52K) corresponding to each print color by a DMA circuit (not shown). Note that the buffer memories (121Y to 121K) are constituted by a dual port RAM, and can be read and written by the CPU 111 via a path (not shown).
[0069]
Reference numerals 122Y, 122M, 122C, and 122K denote drivers, which are organic EL elements based on control signals output from the head control units (120Y to 120K) and image data transferred from the buffer memories (121Y to 121K). The light emitting elements (123Y to 123K) are driven.
[0070]
Next, the driving of the exposure head 52 will be described in detail with reference to FIG.
[0071]
In FIG. 6, reference numeral 150 denotes 39 driver chips arranged linearly in the line direction. Reference numeral 151 denotes a 256-bit shift register provided in the unit of the driver chip 150, 152 denotes a 256-bit latch arranged corresponding to the shift register 151, and 153 denotes an output signal of the latch 152 and strobe signals (STB) 1 to 13. A gate that operates in response to the operation, 154 is a driver transistor that is turned on / off based on an output signal of the gate 153, and 123 is an organic EL element that emits light based on a current driven by the driver transistor 154.
[0072]
The image data (DATA) output from the buffer memory 121 is transferred in bit units in the shift register 151 in synchronization with the clock signal (CLK), and is output to the adjacent shift register 151 when the transfer of 256 bits is completed. The When the image data (DATA) is sent to all the shift registers 151, the load signal (LOAD) is input to the latch 152, and the image data (DATA) in the shift register 151 is collectively held in the latches.
[0073]
When the image data is latched, the strobe signals (STB) 1 to 13 are sequentially output, and the image data (DATA) and the strobe signals (STB) 1 to 13 already held in the latch are ANDed at the gate 153. When the strobe signals (STB) 1 to 13 are set to a predetermined logic (for example, High state), the driver transistor is turned on in accordance with the latched image data, and a driving current is supplied to the organic EL element 123, so that the organic EL The element lights up.
[0074]
Reference numeral 131 denotes a pixel count / maximum value extraction unit. The pixel count / maximum value extraction unit 131 receives image data for one line from the buffer memory 121 based on the clock signal (CLK) output from the head drive timing generation unit 130 and the line synchronization signal (LSYNC) indicating the head of one line. When the image data is ON (that is, the lighting state), the accumulated value stored in the dual port memory 132 (hereinafter simply referred to as the memory 132) (the accumulated value is also naturally emitted). The number of elements is prepared).
[0075]
Further, the pixel count / maximum value extraction unit 131 is equipped with a function of updating the maximum value of the cumulative number of all the light emitting elements every time the ON state of each light emitting element is accumulated. As a result, the CPU 111 can extract, for example, the cumulative number of times of light emission pixel units for each print page and the maximum value among these cumulative values.
[0076]
Next, the head drive voltage setting unit 133 will be described. In the head drive voltage setting unit 133, 156 is a DA converter and 157 is a head power supply. By setting a value from the CPU 111 to the DA converter 156, a power supply voltage supplied to the entire driver transistor 154 is determined. Reference numeral 158 denotes a driver current setting unit, which is provided independently for each driver chip 150. The driver current setting unit 158 receives a line synchronization signal (LSYNC) and a clock signal (CLK), and can set a current value supplied to each driver chip 150 in synchronization with the transfer of image data. ing.
[0077]
Here, the control of the exposure time by the CPU 111 will be described.
[0078]
When the CPU 111 monitors the output of the light amount sensor 54 connected to the analog port and detects that the light amount of the exposure head 52 has decreased, the CPU 111 extends the period during which the strobe signals (STB) 1 to 13 described above are output. To do. As a result, the period during which the driver transistor is turned on becomes longer, and the lighting time of the organic EL element 123, that is, the exposure time becomes longer. Further, since the amount of light reduced in one line formation cycle can be compensated by such an extension of the exposure time, it becomes possible to keep the image forming condition constant without accelerating the deterioration of the organic EL element. .
[0079]
At this time, in FIG. 7, it is necessary to prevent the exposure end time of the Nth line from reaching the next line formation start time, that is, the exposure start time of the (N + 1) th line. Since the latent image size of the photoreceptor is generally larger than the pixel size of the light emitting element in order to ensure the density at the time of solid printing, when the exposure end time of the Nth line reaches the exposure start time of the (N + 1) th line, it is not originally exposed. Pixels are also exposed. In order to prevent this, the maximum exposure period is extended within a range of a predetermined maximum exposure time within a line formation cycle defined according to the printing speed (that is, the peripheral speed of the photoreceptor). .
[0080]
Now, when the exposure period is determined based on the deterioration of the light quantity, specifically, when the exposure period is extended by N% when the light quantity is reduced by N% with respect to the initial light quantity, for the above reason, the exposure period exceeds the maximum exposure period. Cannot be extended.
[0081]
Here, if the printing speed is slowed down, the line formation cycle becomes long and the maximum exposure time becomes long. Conversely, if the printing speed is made fast, the line formation cycle becomes short and the maximum exposure time becomes short. Thus, the maximum exposure time is a time that varies depending on the printing speed. Therefore, if the exposure time at a given printing speed exceeds the maximum exposure time, the exposure time can be further extended by slowing the printing speed and extending the line formation cycle, and increasing the maximum exposure time. Can do. After the printing speed is reduced, the exposure period is extended based on the light amount detection result using the amount of time until the newly secured maximum exposure time.
[0082]
The peripheral speed Vo2 rotating in the direction D3 of the photoconductor 47 due to the decrease in the printing speed is defined as L1 for the initial light quantity of the organic EL element 86, L2 for the reduced light quantity, and Vo1 for the initial light quantity.
Vo2 = (L2 / L1) × Vo1
Control to be
[0083]
At this time, if the CPU 111 controls the peripheral speed of the photoconductor 47 to a low speed in this way, the peripheral speed of the developing sleeve 49 is also controlled to a low speed. That is, in the present embodiment, the circumferential speed Vs2 of the developing sleeve 49 is Vs1, where the circumferential speed of the developing sleeve 49 at the initial light amount is Vs1.
Vs2 = (L2 / L1) × Vs1
That is, control is performed so that the ratio of the peripheral speeds of the photosensitive member 47 and the developing sleeve 49 is constant.
[0084]
In general, the peripheral speed (rotational speed) of the developing sleeve 49 is set to be approximately 1.1 to 1.5, which is higher than the peripheral speed (rotational speed) of the photoconductor 47. This is because a predetermined development density is ensured by providing a difference between the peripheral speeds of the two. Therefore, the peripheral speed ratio between the photosensitive member 47 and the developing sleeve 49 is always kept constant even when the printing speed is lowered. The reason for making the speed ratio constant is to keep the amount of toner supplied per unit area of the photoconductor 47 constant and to suppress density fluctuation due to speed change.
[0085]
In the case described above, if the light amount of the exposure head 52 is reduced, the exposure time is immediately extended by the CPU 111. However, if the light amount is reduced, the light emission amount of the organic EL element 86 is first increased. The setting of the head drive voltage setting unit 133 described above is changed so as to be constant, the drive current is increased to keep the image forming condition constant, and then the drive current of the organic EL element 86 is preset. When the upper limit value is reached (for example, the upper limit value in a range where the deterioration rate of the element is moderate), the exposure time may be extended.
[0086]
Here, reducing the printing speed means that the initial specifications of the product are in a state of being damaged. Therefore, reducing the printing speed is only a provisional measure. Therefore, when the photosensitive member 47 becomes a predetermined peripheral speed or less, a message warning that the organic EL element as the light source has reached the end of its life is output to the display device (notification unit) arranged on the operation panel or the like. It is preferable to prompt the user to replace the exposure head by turning on or turning on a warning light. Further, the CPU 111 may prohibit the printing operation as long as the photosensitive member 47 becomes a predetermined peripheral speed or less as a result of the control.
[0087]
As described above, the light amount sensor 54 disposed in the vicinity of the light source detects light irradiated from the organic EL element 86 of the exposure head 52 and reflected by the surface of the photosensitive member 47 ( (See FIG. 2). In this way, by utilizing the reflected light from the photoreceptor 47, the number of pixels of the exposure head 52 can be the minimum number of dots necessary for printing. In addition, since it is not necessary to arrange a sensor on the photosensitive member 47 side, the apparatus size can be reduced.
[0088]
Next, a means for correcting the light amount variation in the driver current setting unit 158 provided corresponding to each driver chip 150, that is, a means for equalizing the light amount deterioration between the organic EL elements 86 is shown in FIG. Will be described together.
[0089]
In FIG. 8, 160 is a correction data setting unit, and 161 is a correction data memory. The data stored in the correction data memory 161 is obtained in advance by measuring the amount of light for each exposure head, and is stored in the ROM 112 (see FIG. 5). The correction data is transferred from the CPU 111 via the serial interface 115 already described when the power is turned on.
[0090]
The correction data setting unit 160 extracts 4-bit correction data from the correction data memory 161 based on the clock signal (CLK) and the line synchronization signal (LSYNC) output from the head drive timing setting unit 130 and outputs them to the DA converter 162. . The DA converter 162 includes four switching elements 163 and a resistor 164 connected in series to each switching element 163, and the four switching elements are turned ON / OFF according to the output of the correction data setting unit 160. . Each resistor 164 is formed so that current values of i_1, i_1 × 2, i_1 × 4, and i_1 × 8 flow when equal voltages are applied to both ends thereof. Current flows from i_0 to i_0 + i_1 × 15. That is, here, the current value supplied to the driver transistor 154 can be controlled in 16 stages.
[0091]
In the present embodiment, 256 driver transistors 154 are mounted on each driver chip 150. However, when forming an image, the image data side is masked so that the 256 driver transistors 154 are substantially provided. Thus, it is divided into four groups, and 64 are selected according to a specific timing and subjected to ON / OFF control. For example, image data other than 0-63rd in the first group is not printed, image data other than 64-127th in the second group, other than 128-191 in the third group, and other than 192-255th in the fourth group. Is masked as non-printing data. By forcing a specific portion on the image data side to be non-printing data with a mask, the driver chip 150 is substantially time-divided and driven.
[0092]
In accordance with the timing of this time division, the correction data setting unit 160 changes the 4-bit correction data output to the DA converter 162, and as a result, corrects the variation in light quantity in units of 64 pixels. As a result, the light quantity deterioration between the organic EL elements 86 is made uniform, and the print quality of the toner image exposed and developed by the organic EL elements 86 can be made uniform.
[0093]
The amount of light of the organic EL element 86 strongly depends on the thickness of the light emitting layer, but the light emitting layer is formed by vacuum deposition and has a very uniform thickness. For this reason, the light amount distribution of the exposure head using the organic EL element 86 does not have a spike-like peak and has a relatively flat characteristic (the light amounts of adjacent light emitting elements are substantially equal, that is, the adjacent correlation is very high). Therefore, even when a configuration in which 64 pixels are driven with the same current is adopted, sufficient variation in light quantity can be corrected.
[0094]
As described above, the number of times the organic EL element of the exposure head is turned on is counted and accumulated by the pixel count / maximum value extraction unit 131, and at the same time, the maximum value of the count value of each organic EL element is also held. By selecting an organic EL element having a count value smaller than the maximum value according to these values and driving (of course, driving in a non-printing state), the deterioration state of all elements can be made uniform.
[0095]
After correcting the variation in the amount of light, since the deterioration is made uniform in this way, the emitted light amount of all the elements is uniformly and similarly deteriorated. Therefore, the light amount sensor 54 emits light from some elements of the exposure head. By detecting it, it becomes possible to detect the light amount deterioration of the entire exposure head.
[0096]
Here, in the above, the CPU 111 detects the light emission amount of the organic EL element 86 by the light amount sensor 54. However, the CPU 111 is provided with a predicting unit (not shown) for predicting the light emission amount of the organic EL element 86. The peripheral speed of the photoconductor 47 may be controlled to a low speed in accordance with the prediction of the decrease in the amount of light emitted from the organic EL element 86 by the prediction means.
[0097]
That is, in the graph of FIG. 9 showing the change in relative luminance with respect to the charging time in the organic EL element 86, the luminance of the organic EL element 86 (here, green light) is the initial ratio of 80% in 100 hours and the same in 55 hours. % Is down.
[0098]
Therefore, if the relationship between the lighting time of the organic EL element 86 and the luminance change is tabulated and stored in the nonvolatile memory in the apparatus, or the light amount deterioration rate is stored in the nonvolatile memory, This is because it is possible to uniquely determine the amount of emitted light for an arbitrary cumulative lighting time, that is, to predict the degree of deterioration of the organic EL element 86 that is a light source.
[0099]
If a predicting unit that predicts the amount of light emitted from the organic EL element 86 is used, the light amount sensor 54 such as a photosensor for measuring the amount of light becomes unnecessary, and the cost can be reduced. Note that the amount of light emitted from the organic EL element 86 may be predicted by counting the number of times of lighting instead of the lighting time.
[0100]
In the above description, the case where the present invention is applied to a color electrophotographic apparatus has been described. However, the present invention can also be applied to a monochrome electrophotographic apparatus such as black. Further, when applied to a color electrophotographic apparatus, the development colors are not limited to four colors of yellow, magenta, cyan and black.
[0101]
In the present embodiment, the exposure head using the organic EL element is mainly referred to. However, the present invention is easy if the exposure head uses an element (for example, a fluorescent tube) whose light amount deteriorates with the cumulative lighting time. Needless to say, it can be applied.
[0102]
【The invention's effect】
As described above, according to the present invention, it is possible to compensate for the amount of light that has decreased in one line formation cycle due to an increase in exposure time, so that the image forming conditions are kept constant without accelerating the deterioration of the organic EL element. It is possible to obtain an effective effect that it is possible to maintain the same.
[Brief description of the drawings]
FIG. 1 is a schematic diagram showing a configuration of an electrophotographic apparatus according to an embodiment of the present invention.
2 is an explanatory view showing a developing station in the electrophotographic apparatus of FIG. 1. FIG.
3 is an explanatory diagram showing the internal structure of an exposure head in the electrophotographic apparatus of FIG. 1. FIG.
4 is a block diagram showing a configuration of a controller in the electrophotographic apparatus of FIG.
5 is a block diagram showing a configuration of an engine control unit in the electrophotographic apparatus of FIG.
FIG. 6 is a circuit diagram showing a detailed configuration of an exposure head and a head controller.
FIG. 7 is an explanatory diagram showing a relationship between a line formation period and an exposure period in an electrophotographic apparatus.
FIG. 8 is a block diagram showing a detailed configuration of a driver current setting unit provided corresponding to each driver chip;
FIG. 9 is a graph showing a change in relative luminance with respect to charging time in an organic EL element.
[Explanation of symbols]
47Y, 47M, 47C, 47K photoconductor
49 Developing sleeve (developing means)
52 Exposure head (exposure means)
54 Light quantity sensor (detection means)
86 Light emitting device (organic EL device)
111 CPU (control means)
123Y, 123M, 123C, 123K Light emitting element (organic EL element)

Claims (1)

An exposure head including a light source in which a plurality of light emitting elements are arranged in the main scanning direction;
A photoreceptor on which an electrostatic latent image is formed by exposure light of the exposure head ;
Developing means for supplying toner to the electrostatic latent image to form a toner image on the photoreceptor;
A pixel count / maximum extraction unit that counts and accumulates the number of lighting times of each light emitting element of the exposure head, and extracts a maximum value of the number of lighting times;
A head control unit that makes the number of lighting of each light emitting element uniform by selecting and lighting a light emitting element having a smaller count value than the maximum value of the number of lighting extracted by the pixel counting / maximum extraction unit;
In a non-printing state, after the light-emitting element is selected and driven by the head control unit, a detecting unit that detects the light emission amount of a part of the light-emitting elements of the exposure head ;
Control means for extending the exposure time by the exposure head based on the ratio of the initial light quantity and the reduced light quantity as the light emission quantity of the light emitting element decreases based on the detection result of the detection means. Electrophotographic device.

Images