JP2004191459A - Electrophotographic apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To maintain image forming conditions without increasing deterioration speed of an organic EL element, in an electrophotographic apparatus using the organic EL element as the exposure head. <P>SOLUTION: The electrophotographic apparatus includes: an exposure head 52 having a light source in which the organic EL elements are arranged in a main scanning direction; a photoreceptor 47 on which an electrostatic latent image is formed with exposure light from the exposure head 52; a development sleeve 49 which forms a toner image on the photoreceptor 47 by supplying toner to the electrostatic latent image; a light amount sensor 54 which detects an amount of light emitted from the organic EL element; and a CPU 111 which, based upon the result of the detection by the light amount sensor 54, prolongs the time for which exposure is performed by the exposure head 52, as the amount of light emitted from the organic EL element decreases. <P>COPYRIGHT: (C)2004,JPO&NCIPI

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to an electrophotographic apparatus equipped with an exposure head using a light emitting element as a light source.
[0002]
[Prior art]
Conventionally, 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. 2. Description of the Related Art There is known an electrophotographic apparatus having a configuration in which a latent image is formed on a photoreceptor by heating.
[0003]
Among them, the electrophotographic apparatus equipped with an exposure head is advantageous in miniaturization because the optical system can be configured simply, and it is not restricted by the rotation speed of the rotating polygon mirror, so high speed can be achieved if the light intensity of the light emitting element is sufficient. It is also advantageous in terms of conversion.
[0004]
As a conventional exposure head, an LED head in which a number of minute LED elements are linearly arranged has been put to practical use. In general, high brightness can be obtained from an LED element. However, since the LED element is basically manufactured using a semiconductor process, the yield is rapidly deteriorated when an attempt is made to increase the length. Therefore, the integration degree of the light emitting element is, for example, at most 512 pixels per chip in the case of 1200 dpi (dot / inch). In order to realize a long exposure head because one chip is short as described above, it is necessary to accurately arrange a large number of chips in a line. Further, it is known that the LED head forms a PN junction for each LED element by a semiconductor process, so that the luminance variation is large (up to about ± 25% in one chip). In general, each LED element or a plurality of LED elements emit light in a predetermined sequence to control the current value for driving the LEDs based on the light amount correction data, or to adjust the light emission time. Control methods are known.
[0005]
On the other hand, as another example of an exposure head, an exposure head using an organic EL (electroluminescence) element in which a plurality of light emitting elements are linearly arranged is known.
[0006]
Since the organic EL element generates a small amount of heat, cooling radiating fins and the like can be eliminated, and the size of the exposure head itself can be reduced to, for example, about 3 mm or less.
[0007]
In addition, about the element structure of an organic EL element, there exist some which are disclosed by Unexamined-Japanese-Patent No. 10-1664, 2001-63136, etc. FIG.
[0008]
Japanese Patent Application Laid-Open No. 10-48925 discloses that 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 charging potential of the photoconductor is kept constant based on the determination result. Then, an electrophotographic apparatus for controlling a developing bias voltage has been disclosed. More specifically, when the amount of light emitted from the optical unit decreases, the charging potential of the photoconductor is kept constant, and then the developing bias potential is changed in a direction closer to the photoconductor charging potential. .
[0009]
[Patent Document 1]
JP-A-10-1664 [Patent Document 2]
JP 2001-63136 A [Patent Document 3]
JP-A-10-48925
[Problems to be solved by the invention]
Here, in order to keep the image forming conditions of the electrophotography constant, it is necessary to expose the photoreceptor with a constant amount of light. Under the driving condition, the half life of the light amount is about 500 hours for the LED element for 10,000 hours and the organic EL element is about 500 hours, so that the required light amount cannot be obtained gradually.
[0011]
If the drive current is increased, the light emission amount of the organic EL element can be kept constant. However, if the drive current increases, the organic EL element deteriorates at an accelerated rate, so that there is a limit to the increase in the drive current.
[0012]
By the way, in the two-component developing technique in which the developer contains a toner and a carrier, the gap between the charging potential of the photoconductor and the developing bias potential is set relatively small in order to prevent the carrier from adhering to the photoconductor (so-called carrier jump). (About 100 V in absolute value). With the setting width of the charging potential and the developing bias potential being small as described above, if the technique described in JP-A-10-48925, in which the developing bias potential is brought close to the charging potential of the photoconductor, the surface of the photoconductor is exposed. There is a case where toner adheres to a non-existing area, that is, a so-called background stain occurs.
[0013]
Accordingly, it is an object of the present invention to provide an electrophotographic apparatus capable of keeping image forming conditions constant without accelerating deterioration of a light emitting element.
[0014]
[Means for Solving the Problems]
In order to solve this problem, an electrophotographic apparatus according to the present invention is configured such that an electrostatic latent image is formed by an exposure unit having a light source in which a plurality of light emitting elements are arranged in a main scanning direction, and exposure light from the exposure unit. A photoreceptor, developing means for supplying a toner to the electrostatic latent image to form a toner image on the photoreceptor, detecting means for detecting a light emission amount of the light emitting element, and detecting the light emitting element based on a detection result of the detecting means. And a control means for extending the exposure time by the exposure means with a decrease in the amount of emitted light.
[0015]
This makes it possible to compensate for the amount of light that has decreased during one line forming cycle due to an increase in the exposure time, so that the image forming conditions can be kept constant without accelerating the deterioration of the light emitting element.
[0016]
BEST MODE FOR CARRYING OUT THE INVENTION
The invention according to claim 1 of the present invention provides an exposure unit including a light source in which a plurality of light emitting elements are arranged in a main scanning direction, a photoconductor on which an electrostatic latent image is formed by exposure light of the exposure unit, Developing means for supplying toner to the electrostatic latent image to form a toner image on the photoreceptor; detecting means for detecting the amount of light emitted from the light emitting element; and reducing the amount of light emitted from the light emitting element based on the detection result of the detecting means. And a control means for extending the exposure time by the exposure means in accordance with the above. Since the exposure time is increased and the amount of light reduced during one line forming cycle can be compensated, deterioration of the light emitting element Has the effect that the image forming conditions can be kept constant without accelerating the image formation.
[0017]
The invention according to claim 2 of the present invention provides an exposure unit including a light source in which a plurality of light emitting elements are arranged in a main scanning direction, a photoconductor on which an electrostatic latent image is formed by exposure light of the exposure unit, Developing means for supplying toner to the electrostatic latent image to form a toner image on the photoreceptor; predicting means for predicting the light emission amount of the light emitting element; An electrophotographic apparatus having a control means for extending an exposure time by means for increasing the exposure time and compensating for a reduced amount of light in one line forming cycle, thereby accelerating the deterioration of the light emitting element. Therefore, it is possible to keep the image forming conditions constant. Further, since the detection means for measuring the amount of light is not required, there is an effect that the cost can be reduced.
[0018]
According to a third aspect of the present invention, in the second aspect of the present invention, the prediction means calculates the light emission amount of the light emitting element by accumulating the lighting time of each light emitting element or by counting the number of times of lighting. This is an electrophotographic apparatus for estimating, and has an effect that cost reduction can be achieved because detection means for measuring the amount of light becomes unnecessary.
[0019]
According to a fourth aspect of the present invention, in the invention according to any one of the first to third aspects, the control means increases a driving current of the light emitting element so that a light emitting amount of the light emitting element becomes constant. An electrophotographic apparatus that, when the driving current reaches a preset upper limit, extends the exposure time by the exposure unit in accordance with the decrease or prediction of the amount of light emission of the light emitting element, and accelerates the deterioration of the light emitting element. This has the effect that the image forming conditions can be kept constant without causing the image forming conditions to be maintained.
[0020]
According to a fifth aspect of the present invention, in the invention according to any one of the first to fourth aspects, the control means controls a range of a maximum exposure time within a line forming cycle defined according to a printing speed. This is an electrophotographic apparatus that extends the exposure time within the device, and has an effect that the image forming conditions can be kept constant without accelerating the deterioration of the light emitting element.
[0021]
According to a sixth aspect of the present invention, in the invention according to any one of the first to fifth aspects, the control means performs printing when the exposure time at a predetermined printing speed exceeds the maximum exposure time. This is an electrophotographic apparatus in which the exposure time is further extended by reducing the speed, and has the effect that the image forming conditions can be kept constant without accelerating the deterioration of the light emitting element.
[0022]
According to a seventh aspect of the present invention, in the invention according to any one of the first to sixth aspects, it is notified that the light source has reached the end of its life if the photosensitive member has fallen below a predetermined peripheral speed. This is an electrophotographic apparatus having an informing means that performs an operation of prompting a user to replace an exposure head.
[0023]
According to an eighth aspect of the present invention, in the invention according to any one of the first to seventh aspects, the control means prohibits a printing operation when the photosensitive member has fallen below a predetermined peripheral speed. This is an electrophotographic apparatus, and has an effect that it is possible to prompt a user to replace an exposure head.
[0024]
According to a ninth aspect of the present invention, there is provided the electrophotographic apparatus according to any one of the first to fourth aspects, wherein the detecting means is a photosensor installed near the light source. This has the effect that it is possible to directly detect the light from the light source and to improve the detection accuracy of the degree of light quantity deterioration.
[0025]
According to a tenth aspect of the present invention, in the ninth aspect, the photo sensor is an electrophotographic apparatus that receives the reflected light of the light emitting element irradiated on the photoconductor, and the reflected light from the photoconductor. The effect is that the minimum number of pixels required for printing is sufficient for the number of pixels of the light source. Further, since there is no need to dispose a sensor on the photoconductor side, the size of the apparatus can be reduced.
[0026]
According to an eleventh aspect of the present invention, there is provided the electrophotographic apparatus according to any one of the first to tenth aspects, further comprising means for making uniform the light quantity deterioration among the plurality of light emitting elements. Since the light emitting elements are uniformly deteriorated, the printing quality of the toner image exposed and developed by such light emitting elements is made uniform, and the light amount of some organic EL elements is detected. This has the effect that the degree of light quantity deterioration of the whole can be estimated.
[0027]
According to a twelfth aspect of the present invention, there is provided the electrophotographic apparatus according to any one of the first to eleventh aspects, wherein an organic EL element is used as a light emitting element. The size of the exposure head can be reduced, and as a result, the size of the electrophotographic apparatus can be reduced.
[0028]
Hereinafter, an embodiment of the present invention will be described with reference to FIGS. 1 to 9. In these drawings, the same members are denoted by the same reference numerals, and redundant description is omitted.
[0029]
FIG. 1 is a schematic diagram 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 exposure in the electrophotographic apparatus of FIG. FIG. 4 is a block diagram showing a configuration of a controller in the electrophotographic apparatus of FIG. 1, FIG. 5 is a block diagram showing a configuration of an engine control unit in the electrophotographic apparatus of FIG. 1, and FIG. FIG. 7 is a circuit diagram showing a detailed configuration of an exposure head and a head control unit. FIG. 7 is an explanatory diagram showing a relationship between a line forming cycle and an exposure period in an electrophotographic apparatus. FIG. 8 is a driver provided corresponding to each driver chip. FIG. 9 is a block diagram illustrating a detailed configuration of the current setting unit. FIG. 9 is a graph illustrating a change in relative luminance with respect to a turn-on time in the organic EL element.
[0030]
In FIG. 1, an electrophotographic apparatus 40 has a developing station for four colors of a yellow developing station 41Y, a magenta developing station 41M, a cyan developing station 41C, and a black developing station 41K, which are vertically arranged in a stepwise manner in the apparatus. A paper feed tray 43 for accommodating the recording paper 42 is provided above, and a portion corresponding to each of the developing stations (41Y to 41K) serves as a conveyance path for the recording paper 42 supplied from the paper feed tray 43. The recording paper transport path 44 is arranged vertically from the upper side to the lower side.
[0031]
The developing stations (41Y to 41K) form yellow, magenta, cyan, and black toner images in order from the upstream side of the recording paper transport path 44, and include a photoconductor (47Y to 47K) and a developing sleeve (not shown). ), A charger (not shown), etc., which realize a series of electrophotographic development processes.
[0032]
Now, the developing station 41 will be described in detail with reference to FIG. The developing stations 41Y to 41K differ in the color of the filled developer, but since the configuration is the same regardless of the developing color, the description will be given without simplification of the color for simplicity.
[0033]
In FIG. 2, the inside of the developing station 41 is filled with a developer 45 which is a mixture of a carrier and a toner. Reference numerals 46a and 46b denote stirring paddles for stirring the developer 45. The rotation of the stirring paddles 46a and 46b causes the toner in the developer 45 to be charged to a predetermined potential by friction and circulates inside the developing station 41. The toner and the carrier are sufficiently stirred and mixed. Reference numeral 47 denotes a photosensitive member which is rotated in a direction D3 by a driving source (not shown). A charger 48 charges the surface of the photoconductor 47 to a predetermined potential. 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 a 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 not transferred to the photoconductor 47 is collected in the developing station 41.
[0034]
52 is an exposure head (exposure means). The exposure head according to the present embodiment is one in which organic EL elements (light-emitting elements) are arranged in a staggered pattern with respect to each other to form two element rows, and by using one or both of these element rows, An electrostatic latent image having a maximum size of A4 is formed on the photosensitive member. Only the toner of the developer 45 supplied to the surface of the developing sleeve 49 adheres to this electrostatic latent image portion, and the electrostatic latent image is visualized.
[0035]
53 is a supporting member for supporting the exposure head 52. Numeral 54 denotes a light quantity sensor (detection means) constituted by a photo sensor or the like, which is arranged at an angle at which light emitted from the exposure head 52 and reflected on the surface of the photoconductor 47 is directly incident. A scattering plate (not shown) is provided on the surface of the light amount sensor 54 on which the light is incident. Even if the incident position of the light slightly changes due to, for example, the eccentricity of the photoconductor 47, the received light amount does not largely change. It has become. 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 provided. ) Can be detected.
[0036]
A transfer roller 55 is provided at a position opposing the recording paper transport path 44 with respect to the photoconductor 47, and is rotated in a direction D5 by a driving source (not shown). A predetermined transfer bias is applied to the transfer roller 55, and transfers the toner image formed on the photoreceptor 47 to the recording paper conveyed through the recording paper conveyance path 44.
[0037]
Hereinafter, the description will be continued by returning to FIG.
[0038]
Reference numeral 56 denotes a toner bottle which stores yellow, magenta, cyan, and black toners. From the toner bottle 56, a pipe for conveying toner (not shown) is provided at each of the developing stations (41Y to 41K) to supply toner to the developing stations (41Y to 41K).
[0039]
Reference numeral 57 denotes a paper feed roller, which rotates in the direction D1 by controlling an electromagnetic clutch (not shown), and sends out the recording paper 42 loaded in the paper supply tray 43 to the recording paper transport path 44.
[0040]
A pair of registration rollers 58 and a pair of pinch rollers 59 are provided as a nip conveyance unit on the entrance side of the recording paper conveyance path 44 located between the paper supply roller 57 and the transfer site of the uppermost stream yellow developing station 41Y. The pair of the registration roller 58 and the pinch roller 59 temporarily stops the recording paper 42 conveyed by the paper feed roller 57 and conveys the recording paper 42 in the direction of the yellow developing station 41Y at a predetermined timing. The temporary stop restricts the leading end of the recording paper 42 to be parallel to the axial direction of the pair of registration rollers 58 and pinch rollers 59, 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 reflection type 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 (power transmission is controlled by an electromagnetic clutch (not shown) to turn ON / OFF), the recording paper 42 is transported along the recording paper transport path 44 in the direction of the yellow developing station 41Y. However, starting from the rotation start timing of the registration roller 58, the writing timing of the electrostatic latent image by the exposure head (see reference numeral 52 in FIG. 2) mounted on each of the developing stations (41Y to 41K) is independently controlled. You.
[0043]
A fixing device 62 is provided as a nip conveying means on the exit side in the recording paper conveying path 44 located further downstream of the blackest developing station 41K at the most downstream side. 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. The heat generating belt is a belt having a three-layer structure, and includes a release layer, a silicone rubber layer, and a base material layer (both not shown) from the side closer to the surface. The release layer is made of a fluorine resin 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 pressing roller an appropriate elasticity. The base layer is made of a magnetic material that is an alloy of iron, nickel, chromium, or the like.
[0044]
65 is a back core in which the exciting coil is included. Inside the back core 65, an exciting coil formed by bundling a predetermined number of copper wires (not shown) whose surface is insulated is extended in the rotation axis direction of the heating roller 63, and heated at both ends of the heating roller 63. The roller 63 is formed so as to rotate 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) which is a semi-resonant inverter, a magnetic flux is generated in a magnetic path formed by the back core 65 and the base layer of the heating roller 63. An eddy current is formed in the base layer of the heating belt of the heating roller 63 by this magnetic flux, and the base layer generates heat. The heat generated in the base material layer is transmitted to the release layer via the silicone 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 unit for the heating roller 63. A thermistor is a ceramic semiconductor obtained by sintering at a high temperature using a metal oxide as a main raw material. It can measure the temperature of a contacted object by applying that the load resistance changes according to the temperature. . The output of the thermistor 66 is input to a control device (not shown), and the control device controls the power output to the excitation coil inside the back core 65 based on the output of the thermistor 66, and the surface temperature of the heating roller 63 becomes approximately 170 ° C. Control.
[0046]
When the recording paper 42 on which the toner image is formed passes through a nip formed by the heating roller 63 and the pressure roller 64 whose temperature is controlled, the toner image on the recording paper 42 is heated by the heating roller 63. The image is heated / pressed by the pressure roller 64 and a fixed image can be obtained.
[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 detecting sensor 71 is a reflection type sensor unit using a plurality of light emitting elements (both visible light) having different emission spectra and a single light receiving element. The image density is detected by utilizing the fact that the absorption spectrum differs depending on the image density. Further, since the toner image detecting 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 detecting sensors 71 are provided in the width direction of the apparatus, The image forming timing is controlled on the basis of the detection position of the image position shift amount detection pattern formed in (1).
[0048]
72 is 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 along the recording paper transport drum in the direction D2. At this time, the recording paper 42 is cooled by the recording paper transport drum 72 and transported while being bent in a direction opposite to the image forming surface. As a result, it is possible to greatly reduce the curl generated when a high-density image is formed on the entire surface of the recording paper. Thereafter, the recording paper 42 is conveyed in the direction D <b> 6 by the kick-out roller 74 and is discharged to the discharge tray 78.
[0049]
Reference numeral 73 denotes a face-down paper discharge unit. The face-down discharge unit 73 is configured to be rotatable around the support member 75, and when the face-down discharge unit 73 is opened, the recording paper 42 is discharged in the direction D7. When the face-down sheet discharge section 73 is closed, a rib 76 is formed on the back surface along the conveyance path so as to guide the conveyance of the recording sheet 42 together with the recording sheet conveyance drum 72.
[0050]
A driving source 77 employs a stepping motor in the present embodiment. The driving source 77 causes a peripheral portion of each of the developing stations (41Y to 41K) including the paper feed roller 57, the registration roller 58, the pinch roller 59, the photoconductors (47Y to 47K) and the transfer rollers (55Y to 55K), and the fixing device 62. The recording paper transport drum 72 and the kick-out roller 74 are driven.
[0051]
Reference numeral 80 denotes a controller, which receives image data from a computer or the like (not shown) via an external network and generates printable image data.
[0052]
81 is 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]
82 is 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 also supplies power to the heating roller 63 of the fixing device 62. A so-called high-voltage power supply such as charging of the surface of the photoconductor 47, a developing bias applied to the developing sleeve (49 in FIG. 2, and a transfer bias applied to the transfer roller 55) is included in the power supply unit.
[0054]
Further, the power supply unit 82 includes a power supply monitoring unit 83 so that at least a 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 that the power supply switch is turned off or a drop in the power supply voltage at the time of a power failure or the like.
[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 electroluminescent element (organic EL element), which is a light emitting element 86 as a light source, which is mounted on a base material 84 and hermetically sealed by a sealing material 85 provided on the head supporting member 53. And a driver 87 provided on the base material 84 to supply a voltage corresponding to the image data to the organic EL element 86 to emit light. Further, on the base material 84, a prism 88 that reflects the irradiation light from the organic EL element 8 and changes the optical path by 90 °, a fiber array 89 that collects and transmits the light from the prism 88, and a fiber array 89 from the fiber array 89 A cylindrical lens 90 for focusing light in the sub-scanning direction is mounted.
[0057]
As described above, the organic EL elements 86 form two element rows that are mutually staggered. These element rows can emit light for each row, and a high-resolution mode that drives both element rows at the same time, 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 be configured as one element row.
[0058]
Next, the configuration and operation of the controller in the electrophotographic apparatus of the present 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. 102 is a network interface. The controller 80 receives image data and print job information transferred from the computer 100 via the network interface 102, and transmits status information such as an error state of the electrophotographic apparatus to the computer 100.
[0060]
A CPU (control means) 103 controls the operation of the controller 80 based on a program stored in the ROM 104.
[0061]
A RAM 105 is used as a work area of the CPU 103, and temporarily stores image data and print job information received by the network interface 102, printable image data expanded in page units, and the like. You.
[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, page-by-page) based on the image data transferred from the computer 100 and print job information (both temporarily stored in the RAM 105). , Edge correction, screen generation, etc.) to generate image data to be printed, and store the image data in the RAM 105 again.
[0063]
Reference numeral 107 denotes a printer interface. Image data in page units 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 in page units and print mode information transferred from the controller 80.
[0066]
Reference numeral 111 denotes a CPU (control means) which 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, for example, 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 cumulative lighting value of the light emitting element described in detail later. 115 is a serial interface. Information from a group of sensors such as the recording paper passing sensor 60 and the recording paper trailing edge detection sensor 67, the power supply monitoring unit 83 (detects a decrease in the power supply voltage, and stops the operation of the CPU 111 before stopping the operation of the CPU 111). The accumulated value of the number of times of lighting is stored in the non-volatile memory 114.) is converted into a serial signal of a predetermined cycle by a serial converter (not shown) and received by the serial interface 115. The serial signal received by the serial interface 115 is read by the CPU 111 after being converted into a parallel signal. On the other hand, the start / stop of a 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 drive for the paper feed roller 57 and the registration roller 58 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 supply such as a developing bias / transfer bias / charging potential, and the like are converted as parallel signals into the serial interface 115. Sent to The serial interface 115 converts this parallel signal into a serial signal and outputs it to the actuator group. In the present embodiment, all sensor inputs and actuator control signal outputs that do not need to be detected at high speed are performed via the serial interface 115.
[0067]
On the other hand, an input from the toner image detection sensor 71 (an image displacement detection pattern needs a detection resolution of about 10 μm) that requires high-speed sampling is directly connected to an input terminal of the CPU 111. Further, the analog level signal of the light amount sensor 54 is connected to an analog input port of the CPU 111, so that the CPU 111 can detect the output level of the light amount sensor 54 at any time.
[0068]
Reference numerals 120Y, 120M, 120C, and 120K denote head control units that control the driving of the exposure heads (see reference numeral 52 in FIG. 2) corresponding to each printing color. The head control unit (120Y to 120K) has a function of controlling the exposure timing of the exposure head 52 and the drive voltage of the organic EL element 86 mounted on the exposure head (52Y to 52K). Reference numerals 121Y, 121M, 121C, and 121K denote 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 printing color. The image data stored in the buffer memories (121Y to 121K) is transferred to exposure heads (52Y to 52K) corresponding to each printing color by a DMA circuit (not shown). The buffer memories (121Y to 121K) are constituted by dual port RAMs, and can be read and written by the CPU 111 via a path (not shown).
[0069]
Drivers 122Y, 122M, 122C, and 122K 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. 151 is a 256-bit shift register provided for each driver chip 150; 152 is a 256-bit latch arranged corresponding to the shift register 151; 153 is an output signal of the latch 152 and strobe signals (STB) 1 to 13; A gate 154 that receives and operates is a driver transistor that turns 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 inside 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. You. 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 held in the latches.
[0073]
When the image data is latched, strobe signals (STB) 1 to 13 are sequentially output, and the image data (DATA) already held in the latch and the strobe signals (STB) 1 to 13 are AND-operated by the gate 153. When the strobe signals (STB) 1 to 13 become 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 element 123 is turned on. The element lights up.
[0074]
Reference numeral 131 denotes a pixel counting / maximum value extracting unit. The pixel count / maximum value extractor 131 extracts one line of image data from the buffer memory 121 based on the clock signal (CLK) output from the head drive timing generator 130 and the line synchronization signal (LSYNC) indicating the start of one line. The lighting state of each light emitting element unit is detected, and if 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) (of course, the accumulated value also emits light). Are prepared for the number of elements).
[0075]
Further, the pixel counting / maximum value extracting unit 131 has a function of updating the maximum value of the cumulative number of all light emitting elements each time the ON state of each light emitting element is accumulated. Thus, the CPU 111 can extract the cumulative number of times of light emission for each light-emitting pixel and the maximum value of these cumulative values for each print page.
[0076]
Next, the head drive voltage setting unit 133 will be described. In the head drive voltage setting unit 133, reference numeral 156 denotes a DA converter, and 157 denotes a head power supply. The power supply voltage supplied to the entire driver transistor 154 is determined by setting a value from the CPU 111 to the DA converter 156. A driver current setting unit 158 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 transfer of image data. ing.
[0077]
Here, control of the exposure time by the CPU 111 will be described.
[0078]
The CPU 111 monitors the output of the light amount sensor 54 connected to the analog port, and when detecting that the light amount of the exposure head 52 has decreased, the CPU 111 extends the period during which the above-described strobe signals (STB) 1 to 13 are output. I do. Accordingly, the period during which the driver transistor is in the ON state becomes longer, and the lighting time of the organic EL element 123, that is, the exposure time becomes longer. Since the amount of light reduced during one line forming cycle can be compensated for by extending the exposure time, it is possible to keep the image forming conditions 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 photoconductor is generally larger than the pixel size of the light emitting element in order to secure 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, the exposure is not performed originally. 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 forming cycle defined according to the printing speed (that is, the peripheral speed of the photoconductor). .
[0080]
When the exposure period is determined based on the light amount deterioration, specifically, when the exposure period is extended by N% when the light amount is reduced by N% with respect to the initial light amount, the exposure period exceeds the maximum exposure period for the above reason. Cannot be extended.
[0081]
Here, if the printing speed is reduced, the line forming cycle becomes longer, so that the maximum exposure time becomes longer. Conversely, if the printing speed is increased, the line forming cycle becomes shorter, and the maximum exposure time becomes shorter. As described above, 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 printing speed should be slowed to extend the line formation cycle, and the maximum exposure time should be extended to further extend the exposure time. Can be. After the printing speed is reduced, the exposure period is extended by using the newly secured maximum exposure time based on the light amount detection result.
[0082]
The peripheral speed Vo2 rotating in the direction D3 of the photoconductor 47 due to the decrease in the printing speed is represented by L1 as the initial light amount of the organic EL element 86, L2 as the decreased light amount, and Vo1 as the peripheral speed at the initial light amount.
Vo2 = (L2 / L1) × Vo1
Is controlled so that
[0083]
At this time, if the CPU 111 controls the peripheral speed of the photoconductor 47 to a low speed, the CPU 111 also controls the peripheral speed of the developing sleeve 49 to a low speed. That is, in the present embodiment, if the peripheral speed of the developing sleeve 49 at the time of the initial light amount is Vs1, the peripheral speed Vs2 of the developing sleeve 49 is as follows.
Vs2 = (L2 / L1) × Vs1
, Ie, the ratio of the peripheral speeds of the photoconductor 47 and the developing sleeve 49 is controlled to be constant.
[0084]
Generally, the peripheral speed (rotational speed) of the developing sleeve 49 is higher than the peripheral speed (rotational speed) of the photoconductor 47 and is set to about 1.1 to 1.5. This is because a predetermined developing density is ensured by providing a difference between the two peripheral velocities. 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 reduced. The reason for keeping the speed ratio constant is to keep the amount of toner supplied per unit area of the photoreceptor 47 constant and suppress the density fluctuation due to the speed change.
[0085]
In the above-described case, if the light amount of the exposure head 52 decreases, the exposure time is immediately extended by the CPU 111. However, if the light amount decreases, the light emission amount of the organic EL element 86 first decreases. The setting of the above-described head drive voltage setting unit 133 is changed so as to be constant, the drive current is increased to keep the image forming conditions constant, and then the drive current of the organic EL element 86 is set in advance. If the upper limit value is reached (for example, the upper limit value in a range in which the deterioration rate of the element is gentle), the exposure time may be extended.
[0086]
Here, lowering the printing speed means that the initial specifications of the product have been impaired. Therefore, lowering the printing speed is only a provisional measure. Therefore, when the photoconductor 47 becomes lower than a predetermined peripheral speed, a message warning that the life of the organic EL element as the light source has reached the end of its life is output to a display device (notifying unit) arranged on the operation panel or the like. It is preferable to urge 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 if the photoconductor 47 becomes lower than a predetermined peripheral speed as a result of the control.
[0087]
The light amount sensor 54 disposed near the light source detects the light emitted from the organic EL element 86 of the exposure head 52 and reflected on the surface of the photoconductor 47 as described above ( (See FIG. 2). In this way, by utilizing the reflected light from the photoconductor 47, the number of pixels of the exposure head 52 can be reduced to the minimum number of dots required for printing. Further, since there is no need to dispose a sensor on the photoconductor 47 side, the size of the apparatus can be reduced.
[0088]
Next, the means for correcting the light amount variation in the driver current setting section 158 provided corresponding to each driver chip 150, that is, the means for equalizing the light amount deterioration between the organic EL elements 86, is shown in FIG. Will be described together.
[0089]
8, reference numeral 160 denotes a correction data setting unit, and 161 denotes a correction data memory. The data stored in the correction data memory 161 is obtained by measuring the amount of light for each exposure head in advance, and is stored in the ROM 112 (see FIG. 5). The correction data is transferred from the CPU 111 via the already described serial interface 115 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 the data to the DA converter 162. . The DA converter 162 includes four switching elements 163 and a resistor 164 connected in series with each switching element 163. The four switching elements are turned on / off according to the output of the correction data setting unit 160. . Each resistor 164 is formed such that currents of i_1, i_1 × 2, i_1 × 4, i_1 × 8 flow when an equal voltage is applied to both ends thereof. Means that a current of i_0 + i_1 × 15 flows from i_0. That is, here, the current value supplied to the driver transistor 154 can be controlled in 16 steps.
[0091]
In this embodiment, 256 driver transistors 154 are mounted on each driver chip 150. However, at the time of image formation, masking is performed on the image data side so that 256 driver transistors 154 are substantially formed. It is divided into four groups, and 64 groups are selected and ON / OFF controlled according to a specific timing. For example, in the first group, image data other than the 0th to 63rd image data is not printed, in the second group, the image data other than the 64th to 127th, in the third group, the image data other than the 128th to 191st, and in the fourth group, the image data other than the 192th to 255th image data Is masked as non-print data. The driver chip 150 is substantially driven in a time-sharing manner by forcibly setting a specific portion on the image data side to non-print data by using a mask.
[0092]
The correction data setting unit 160 changes the 4-bit correction data output to the DA converter 162 according to the timing of the time division, and corrects the variation in the light amount in units of 64 pixels as a result. As a result, the deterioration of the light amount between the organic EL elements 86 is made uniform, and the printing quality of the toner image exposed and developed by the organic EL elements 86 can be made uniform.
[0093]
Although the light quantity of the organic EL element 86 depends strongly on the thickness of the light emitting layer, the light emitting layer is formed by vacuum evaporation and has a very uniform thickness. Therefore, the light quantity distribution of the exposure head using the organic EL element 86 does not have a spike-like peak and has relatively flat characteristics (the light quantity of the adjacent light emitting elements is almost equal, that is, the adjacent correlation is very high). Therefore, even if a configuration in which 64 pixels are driven by the same current is employed, it is possible to sufficiently correct the variation in light amount.
[0094]
As described above, the number of times the organic EL elements of the exposure head are turned on is counted and accumulated by the pixel counting / maximum value extracting unit 131, and at the same time, the maximum count value of each organic EL element is also held. By selecting and driving (of course driving in a non-printing state) an organic EL element having a count value smaller than the maximum value according to these values, the deterioration state of all elements can be made uniform.
[0095]
After the variation correction of the light quantity is performed, by making the deterioration uniform in this way, the light emission quantity of all the elements is uniformly and similarly deteriorated. By detecting, it is possible to detect the light quantity deterioration of the entire exposure head.
[0096]
Here, in the above description, the CPU 111 detects the light emission amount of the organic EL element 86 by the light amount sensor 54. However, a prediction unit (not shown) for estimating the light emission amount of the organic EL element 86 is provided. The peripheral speed of the photoconductor 47 may be controlled to be low in accordance with the prediction of the decrease in the amount of light emitted from the organic EL element 86 by the prediction unit.
[0097]
That is, in the graph of FIG. 9 showing a change in relative luminance with respect to the application time in the organic EL element 86, the luminance of the organic EL element 86 (green light in this case) is 80% of the initial ratio in 100 hours and 55% in 500 hours. Is down to%.
[0098]
Therefore, if the relationship between the lighting time of the organic EL element 86 and the change in luminance is tabulated and stored in the non-volatile memory in the apparatus, or the light amount deterioration rate is stored in the non-volatile memory, This is because it is possible to uniquely determine the light emission amount for an arbitrary cumulative lighting time, that is, to predict the degree of deterioration of the organic EL element 86 as the light source.
[0099]
If the predicting means for predicting the light emission amount of the organic EL element 86 is used, the light amount sensor 54 such as a light sensor for measuring the light amount becomes unnecessary, and the cost can be reduced. Note that the light emission amount of the organic EL element 86 may be predicted by counting the number of times of lighting instead of the lighting time and not by the number of times.
[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 monochromatic electrophotographic apparatus such as black. Further, when applied to a color electrophotographic apparatus, the developed colors are not limited to four colors of yellow, magenta, cyan and black.
[0101]
In this embodiment, an exposure head using an organic EL element has been mainly described. However, the present invention can be easily applied to an exposure head using an element (for example, a fluorescent tube) whose light quantity deteriorates with the accumulation of lighting time. Needless to say, it can be applied to
[0102]
【The invention's effect】
As described above, according to the present invention, it is possible to compensate for the decreased light amount in one line forming cycle due to an increase in the exposure time, so that the image forming conditions can be kept constant without accelerating the deterioration of the organic EL element. Is effective.
[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. FIG. 2 is an explanatory view showing a developing station in the electrophotographic apparatus of FIG. 1. FIG. FIG. 4 is a block diagram illustrating a configuration of a controller in the electrophotographic apparatus of FIG. 1; FIG. 5 is a block diagram illustrating a configuration of an engine control unit in the electrophotographic apparatus of FIG. 1; FIG. 7 is a circuit diagram showing a detailed configuration of an exposure head and a head control unit. FIG. 7 is an explanatory diagram showing a relationship between a line forming cycle and an exposure period in an electrophotographic apparatus. FIG. 8 is provided corresponding to each driver chip. FIG. 9 is a block diagram showing a detailed configuration of a driver current setting unit. FIG. 9 is a graph showing a change in relative luminance with respect to a turn-on time in an organic EL element.
47Y, 47M, 47C, 47K Photoconductor 49 Developing sleeve (developing means)
52 Exposure head (exposure means)
54 light intensity sensor (detection means)
86 Light-emitting device (organic EL device)
111 CPU (control means)
123Y, 123M, 123C, 123K Light emitting device (organic EL device)

Claims (12)

Exposure means having a light source in which a plurality of light emitting elements are arranged in the main scanning direction,
A photosensitive member on which an electrostatic latent image is formed by exposure light of the exposure unit,
Developing means for supplying toner to the electrostatic latent image to form a toner image on the photoconductor,
Detecting means for detecting the amount of light emitted from the light emitting element;
An electrophotographic apparatus, comprising: a control unit that extends an exposure time of the exposure unit based on a detection result of the detection unit as a light emission amount of the light emitting element decreases. Exposure means having a light source in which a plurality of light emitting elements are arranged in the main scanning direction,
A photosensitive member on which an electrostatic latent image is formed by exposure light of the exposure unit,
Developing means for supplying toner to the electrostatic latent image to form a toner image on the photoconductor,
Prediction means for predicting the light emission amount of the light emitting element,
An electrophotographic apparatus comprising: a control unit that extends the exposure time of the exposure unit in accordance with the prediction of a decrease in the amount of light emitted from the light emitting element by the prediction unit. 3. The electrophotographic apparatus according to claim 2, wherein the prediction unit predicts a light emission amount of the light emitting element by accumulating a lighting time of each of the light emitting elements or by counting a lighting number. The control means increases the driving current of the light emitting element so that the light emitting quantity of the light emitting element becomes constant, and decreases the light emitting quantity of the light emitting element when the driving current reaches a preset upper limit. The electrophotographic apparatus according to any one of claims 1 to 3, wherein an exposure time of the exposure unit is extended in accordance with a predicted decrease. 5. The electrophotographic apparatus according to claim 1, wherein the control unit extends the exposure time within a range of a maximum exposure time within a line forming cycle defined according to a printing speed. 6. apparatus. The control means according to any one of claims 1 to 5, wherein, when the exposure time at a predetermined printing speed exceeds the maximum exposure time, the printing speed is reduced to further extend the exposure time. The electrophotographic apparatus according to the above. 7. The electrophotographic apparatus according to claim 6, further comprising: a notifying unit for notifying that the light source has reached the end of its life when the photosensitive member has fallen below a predetermined peripheral speed. 8. An electrophotographic apparatus according to claim 6, wherein said control means prohibits a printing operation when said photosensitive member has fallen below a predetermined peripheral speed. The electrophotographic apparatus according to any one of claims 1 to 4, wherein the detecting means is a photo sensor installed near the light source. The electrophotographic apparatus according to claim 9, wherein the photosensor receives reflected light of the light emitting element irradiated on the photoconductor. The electrophotographic apparatus according to any one of claims 1 to 10, further comprising a unit configured to make light amount deterioration among the plurality of light emitting elements uniform. The electrophotographic apparatus according to claim 1, wherein the light emitting device is an organic EL device.

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