JP2018130861A - Image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an image forming device that can remedy a problem caused by charged potentials of a photosensitive drum by dealing with variation or fluctuation in photosensitive characteristics of the photosensitive drum in the device and controlling the charged potentials of each photosensitive drum more properly with a simple and easily downsizable structure.SOLUTION: The image forming device has: a first light source for applying light to a photosensitive drum 100, including a plurality of first light emitting elements 302 arranged in an array shape in a main scanning direction; a second light source including a plurality of second light emitting elements 304 similarly arranged; first driving means 303(a) for driving the first light source; and second driving means 303(b) for driving a second light source. The first driving means and the second driving means expose a region as an imaging part to which a developer of the photosensitive drum 100 is made to adhere, by light emission of the first light source and the second light source, and expose a region as a non-imaging part to which the developer is not made to adhere, by light emission of the second light source without light emission of the first light source, where the number of second light emitting elements arrayed in the main scanning direction is smaller than the number of the first light emitting elements arrayed similarly.SELECTED DRAWING: Figure 1

Description

  The present invention relates to an image forming apparatus used for an electrophotographic recording system such as a laser printer, a copying machine, and a facsimile.

  Conventionally, an image forming apparatus such as a copying machine or a laser printer using an electrophotographic recording method is known. In this electrophotographic recording type image forming apparatus, for example, the following electrophotographic process is executed. First, the surface of the photosensitive drum is uniformly charged to, for example, −600 V by a charging device. Thereafter, laser light is emitted by a laser exposure device to form an electrostatic latent image on the photosensitive drum. Then, a toner image is attached to the electrostatic latent image by the developing device, and the toner image is transferred to the transfer target by the transfer device.

  Further, the toner remaining on the photosensitive drum is removed by a drum cleaning device, and the photosensitive drum is prepared for the next image formation by removing the residual potential by light irradiation by a pre-exposure lamp (see, for example, Patent Document 1).

In such an image forming apparatus, a solid exposure head that forms an arbitrary latent image on a photoreceptor has been proposed. The solid exposure head collects light emitted from a light emitting element such as a light emitting diode (hereinafter referred to as “LED”) arranged in an array to selectively expose a photoconductor, and light emitted from the light emitting element. It is configured by combining optical systems. Further, as the light emitting element, an organic Electro Luminescence (hereinafter referred to as “organic EL”) element can also be used. Such a solid exposure head forms an arbitrary latent image on the photosensitive member by controlling lighting of the light emitting element according to image data. Solid-state exposure heads that use organic EL elements as light emitting sources do not need to arrange chips with high precision like LED elements, and can be formed monolithically on a low-temperature polysilicon substrate. There is.

  The solid exposure head is composed of an organic EL substrate in which a plurality of solid exposure heads are arranged, and lenses such as a gradient index rod lens array and a microlens array (see Patent Document 2).

JP 2001-281944 A JP 2010-234684 A JP 2013-007989 A

  In the electrophotographic image forming apparatus as described above, in order to form an electrostatic latent image on the surface of the photosensitive drum, it is important to control the charged potential on the surface of the photosensitive drum in advance. In particular, in the case of a color printer, it is necessary to deal with variations in photosensitive characteristics caused by individual differences among the photosensitive drums and usage status differences. Various control methods such as the pre-exposure lamp described above have been proposed for the control of the charging potential, but a simpler configuration is desired from the viewpoint of cost and miniaturization of the apparatus body.

From such a viewpoint, the invention described in Patent Document 3 has been proposed. Here, a semiconductor laser is used as the exposure device, and in accordance with the input of print data, the semiconductor laser is emitted with a light amount of the first light emission level for printing in the image portion and with a light amount of the second light emission level for minute light emission in the non-image portion. The charged potential of the photosensitive drum is controlled by emitting light. However, there is a problem that light emission in a very small region becomes unstable due to the characteristics of the semiconductor laser as a light emitting element, and there is a limit to downsizing as proposed in Patent Document 2.

  In view of this, the present invention copes with variations or fluctuations in the photosensitive characteristics (EV curve characteristics) of the photoconductors, and appropriately controls the charging potentials of the photoconductors with a simple and easy-to-compact configuration. The purpose is to improve the problems caused by the problem.

In order to solve the above problems, the present invention is an image forming apparatus that forms a latent image by exposing a charged photosensitive member, and developing the latent image with a developer.
A light source for irradiating the photosensitive member with light, and a first light source including a plurality of first light emitting elements arranged in an array in the main scanning direction;
A light source for irradiating the photosensitive member with light, and a second light source including a plurality of second light emitting elements arranged in an array in the main scanning direction;
First driving means for driving the first light source;
Second driving means for driving the second light source;
Have
The first driving means and the second driving means expose an area of an image portion to which the developer of the photosensitive member is attached by light emission of the first light source and light emission of the second light source, and An area that is a non-image area to which the developer is not attached is exposed by light emission of the second light source without causing the first light source to emit light,
The number of the second light emitting elements arranged in the main scanning direction is smaller than the number of the first light emitting elements arranged.

  According to the present invention, the charging potential of each photoconductor can be appropriately controlled by a simple and stable configuration that can cope with variations or fluctuations in the photosensitivity of the photoconductor, and can be made smaller. It can improve the problems caused.

Image forming apparatus sectional view (a), photosensitive drum sectional view (b) and photosensitive characteristic diagram (c) FIG. 2 (a) is a set of solid exposure heads, and FIG. 2 (b) is an exploded view thereof. Configuration diagram of organic EL substrate 301 The figure which shows an example of the electric current-luminance characteristic of the organic electroluminescent light emitting element of a TFT drive circuit Circuit diagram of TFT circuit 303 (a), (b) Diagram showing processing path of image input data Explanatory diagram of relationship between photosensitive drum film thickness, charging potential, development potential and exposure potential Flow chart showing exposure parameter setting processing, etc. A table in which the photosensitive drum usage status and each EL light emitting element parameter are associated with each other

  DESCRIPTION OF EMBODIMENTS Hereinafter, embodiments for carrying out the present invention will be exemplarily described in detail with reference to the drawings. However, the dimensions, materials, shapes, and relative arrangements of the components described in this embodiment should be appropriately changed according to the configuration of the apparatus to which the invention is applied and various conditions. That is, it is not intended to limit the scope of the present invention to the following embodiments. Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

[Electrophotographic image forming apparatus]
The image forming apparatus of this embodiment will be described with reference to FIG. FIG. 1A is a schematic cross-sectional view of the image forming apparatus 10 of the present embodiment. The image forming apparatus 10 of this embodiment is a full-color laser printer that employs an inline method and an intermediate transfer method.
The image forming apparatus 10 can form a full-color image on recording paper 1000 (for example, recording paper, plastic sheet, cloth, etc.) according to the image information. The image information is input to the image forming apparatus 10 from an image reading apparatus (not shown) connected to the image forming apparatus 10 or a host device such as a personal computer connected to the image forming apparatus 10 so as to be communicable. The image forming apparatus 10 includes, as a plurality of image forming units, first, second, and third images for forming yellow (Y), magenta (M), cyan (C), and black (K) images, respectively. And fourth image forming units SY, SM, SC, and SK. In the present embodiment, the first to fourth image forming units SY, SM, SC, and SK are arranged in a line in the horizontal direction. In the present embodiment, the configurations and operations of the first to fourth image forming units are substantially the same except that the colors of images to be formed are different. Therefore, in the following, unless there is a particular distinction, the subscripts Y, M, C, and K given to the reference numerals to indicate that they are elements provided for any color are omitted, and generally explain.

  In the present embodiment, the image forming apparatus 10 includes four drum-type electrophotographic photosensitive members, that is, photosensitive drums 100 arranged in parallel in the horizontal direction as a plurality of image carriers. The photosensitive drum 100 is rotationally driven in a direction indicated by an arrow (clockwise direction) by a driving unit (a driving source) (not shown).

First, around the photosensitive drum 100, there is a charging roller 400 as a charging unit that uniformly charges the surface of the photosensitive drum 100 to a negative polarity.
Next, a solid exposure head 300 is disposed as exposure means (exposure device) that irradiates light based on image data to form an electrostatic latent image on the photosensitive drum 100.
Further, a developing unit 200 is disposed around the photosensitive drum 100 as a developing unit that develops an electrostatic image as a toner image. In the present embodiment, the developing unit 200 uses a non-magnetic one-component developer, that is, toner, as the developer. In this embodiment, the developing unit (developing unit) 200 performs development by bringing a developing roller 210 as a developer carrying member into contact with the photosensitive drum 100. That is, in this embodiment, the developing roller 210 in the developing unit 200 is connected to the developing roller 210 and the ground by applying a voltage having the same polarity as the charging polarity of the photosensitive drum 100 (negative polarity in this embodiment). An electric field is generated between the photosensitive drum 100 and the photosensitive drum 100. As a result, the electrostatic image is developed by attaching the negatively charged toner to a portion (image portion, exposure portion) where the charge is attenuated by exposure on the photosensitive drum 100, and a toner image is formed as a developer image. To do.

  Further, an intermediate transfer belt 500 as an intermediate transfer member for transferring the toner image on the photosensitive drum 100 to the recording paper 1000 is disposed opposite to the four photosensitive drums 100. Here, the intermediate transfer belt 500 formed of an endless belt as an intermediate transfer member abuts on all the photosensitive drums 100 and circulates (rotates) in the direction indicated by the arrow (counterclockwise). The intermediate transfer belt 500 is stretched around a plurality of support members, a primary transfer roller 501, a secondary transfer counter roller 505, a driven roller 503, and a drive roller 504. On the inner peripheral surface side of the intermediate transfer belt 500, four primary transfer rollers 501 as primary transfer means are arranged in parallel so as to face the respective photosensitive drums 100. The primary transfer roller 501 presses the intermediate transfer belt 500 toward the photosensitive drum 100 to form a primary transfer portion where the intermediate transfer belt 500 and the photosensitive drum 100 abut. A bias having a polarity opposite to the charging polarity of the toner is applied to the primary transfer roller 501 from a primary transfer bias power source (high voltage power source) as a primary transfer bias applying unit (not shown). As a result, the toner image on the photosensitive drum 100 is transferred (primary transfer) onto the intermediate transfer belt 500.

  A secondary transfer roller 502 as a secondary transfer unit is disposed at a position facing the secondary transfer counter roller 505 on the outer peripheral surface side of the intermediate transfer belt 500. The secondary transfer roller 502 is pressed against the secondary transfer counter roller 505 via the intermediate transfer belt 500 to form a secondary transfer portion where the intermediate transfer belt 500 and the secondary transfer roller 502 come into contact with each other. A bias having a polarity opposite to the normal charging polarity of the toner is applied to the secondary transfer roller 502 from a secondary transfer bias power source (high voltage power source) as a secondary transfer bias applying unit (not shown). As a result, the toner image on the intermediate transfer belt 500 is transferred (secondary transfer) to the recording paper 1000 fed from the paper feeding unit.

Further, a cleaning device 900 is disposed as a cleaning unit that removes toner (transfer residual toner) remaining on the surface of the photosensitive drum 100 after transfer.
In this way, charging, exposure, development, transfer, and cleaning are performed in the order of rotation of the photosensitive drum 100.

Finally, the recording paper 1000 having the toner image transferred thereon is conveyed to a fixing device 800 as a fixing unit. The toner image is fixed on the recording paper 1000 by applying heat and pressure to the recording paper 1000 in the fixing device 800.
The secondary transfer residual toner remaining on the intermediate transfer belt 500 after the secondary transfer process is cleaned by the intermediate transfer belt cleaning device 506.

Note that the image forming apparatus 10 can also form a single-color or multi-color image using only a desired single or some (not all) image forming units.
The configuration of the image forming apparatus described so far is merely an example for explaining the embodiment of the present invention, and is not limited to the gist of the present invention.

  FIG. 1B shows an example of a cross section of the photosensitive drum 100K (the same applies to 100C, 100M, and 100Y). In the photosensitive drum 100K, a charge generation layer 23K and a charge transport layer 24K are stacked on a conductive support base 22K. The conductive support base 22K is, for example, an aluminum cylinder having an outer diameter of 30 mm and a thickness of 1 mm. The charge generation layer 23K is, for example, a phthalocyanine pigment having a thickness of 0.2 μm. The charge transport layer 24K has, for example, a thickness of 20 μm, uses polycarbonate as a binder resin, and contains an amine compound as a charge transport material. Of course, FIG. 1B is an example of the photosensitive drum 100K, and dimensions and materials are not limited to those described here.

FIG. 1C is an example of an EV curve showing the photosensitive characteristics of the photosensitive drum 1, and the horizontal axis represents the exposure amount E (
μJ / cm ² ), and the vertical axis represents the photosensitive drum 1 potential (photosensitive drum potential) V (V). Vcdc is a charging voltage, and this graph is obtained when −1100 V is applied as the charging voltage Vcdc. FIG. 1C shows the potential attenuation when the photosensitive drum 1 having the surface charged to V is exposed so that the exposure amount is E (μJ / cm ² ) on the surface of the photosensitive drum. Show.

In the figure, an EV curve at an initial stage when the photosensitive drum is started to be used and an EV curve when the photosensitive drum is continuously used are respectively shown. In Fig. 1 (c), the dashed curve is
For example, the EV curve is such that the rotational speed r of the photosensitive drum is 75000 ≦ r <112500. The sensitivity characteristic of the photosensitive drum shown in FIG. 1C is an example, and application of a photosensitive drum having various EV curves is assumed in this embodiment.

A solid exposure head 300 in the image forming apparatus 10 according to the present invention shown in FIG.
FIG. 2A shows an assembly diagram of the solid exposure head 300, and FIG. 2B shows an exploded view of the solid exposure head 300. As shown in FIG. 2B, the solid exposure head 300 includes an organic EL substrate 301, an organic EL exposure head frame 320, and a lens array optical system 310. The organic EL substrate 301 and the lens array optical system 310 are aligned at an appropriate position determined by the focal position of the lens array optical system 310, and are positioned and fixed to the organic EL exposure head frame 320. The lens array optical system according to the present embodiment used a SELFOC (registered trademark) lens array SLA20D (trade name: manufactured by Nippon Sheet Glass Co., Ltd.), which is a rod lens array. This is configured by arranging a plurality of rod lenses arranged in the main arrangement direction (Y direction) as the first direction. Thus, an erecting equal-magnification imaging system is configured in a cross section perpendicular to the main array direction and a cross section parallel to the main array direction.

Next, the configuration of the organic EL substrate 301 in the solid exposure head 300 will be described.
FIG. 3 shows a configuration diagram of the organic EL substrate 301. In FIG. 3, the organic EL substrate 301 is monolithically formed with an image organic EL light emitting element 302 and a TFT driving circuit 303 (a), and a potential adjusting organic EL light emitting element 304 and a TFT driving circuit 303 (b). A low-temperature polysilicon substrate 305. Here, the organic EL light-emitting element for image 302 is a plurality of first light-emitting elements, and the organic EL light-emitting element for potential adjustment 304 is a plurality of second light-emitting elements. The image organic EL light emitting element 302 is a first light source, and the TFT drive circuit 303 (a) is a first drive means. The potential adjustment organic EL light emitting element 304 is a second light source, and the TFT drive circuit 303 (b) This is a second drive circuit. The potential adjusting organic EL light emitting element 304 emits light mainly with a small light emission amount along the main arrangement direction (Y direction) to adjust the potential of the photosensitive drum 100 described later, so as to adjust the potential of the TFT driving circuit 303 (b). Driven by. The image organic EL light emitting element 302 is driven by the TFT drive circuit 303 (a) so as to emit light with a light amount of a normal print level and form a latent image corresponding to the image signal on the photosensitive drum 100. The potential adjusting organic EL light emitting element 304 emits light mainly with a small light emission amount along the main arrangement direction (Y direction) to adjust the potential of the photosensitive drum 100 described later, so as to adjust the potential of the TFT driving circuit 303 (b). Driven by. In other words, the organic EL light-emitting element for image 302 and the organic EL light-emitting element for potential adjustment 304 form different latent image patterns on the same portion of the photoconductor (photosensitive drum 100).

  Before reaching the exposure position by the solid exposure head 300, the potential of the photosensitive drum 100 is charged by the charging roller 400 to be the charging potential Vd. The region of the photosensitive drum 100 subjected to the superposed exposure by the light emission of the image organic EL light emitting element 302 and the light emission of the potential adjusting organic EL light emitting element 304 becomes an image portion of the potential Vl for attaching the toner. This image portion is a region that becomes an image portion to which the developer of the photosensitive member is attached. On the other hand, a region exposed only by light emission of the organic EL light emitting element 304 for potential adjustment without causing the organic EL light emitting element 302 for image on the photosensitive drum 100 to emit light becomes a non-image part having a potential Vd_bg for preventing toner from adhering. . This non-image portion is a region that becomes a non-image portion to which the developer of the photosensitive member is not attached. That is, under the control of the TFT drive circuit 303 (a) and the TFT drive circuit 303 (b), normal exposure (normal light emission) is performed by the light emission of the image organic EL light emitting element 302 and the light emission of the potential adjusting organic EL light emitting element 304. . Then, a fine exposure (a slight light emission) is performed by the light emission of the potential adjusting organic EL light emitting element 304 under the control of the TFT drive circuit 303 (a) and the TFT drive circuit 303 (b). In this embodiment, a solid exposure head using an organic EL light emitting element is described. However, the present invention is not limited to this, and an inorganic EL light emitting element may be used.

FIG. 4 shows current-luminance characteristics of the organic EL light emitting elements 302 and 304 driven using the TFT drive circuits 303 (a) and 303 (b). In addition to maintaining good linearity with respect to the current value, other laser light sources become unstable due to mode transition between the LED mode and the laser mode in the minute light amount region, while also in the minute light amount region Stable light emission (both light intensity and light emission intensity distribution) can be obtained.

  The image organic EL light emitting element 302 is a bottom emission type, and is sealed from the front side of FIG. 3 by a glass sealing member (not shown). As shown in FIG. 3, the organic EL light emitting elements 302 for images are arranged in a staggered manner on the low-temperature polysilicon substrate 305. By controlling the light emission timing of the image organic EL light emitting elements 302, spots formed on the photosensitive drum 100 by the light emitted from the image organic EL issuing elements 201 arranged in a staggered manner are aligned on a straight line. ing. At this time, the spot shape after passing through the lens array optical system 310 on the photosensitive drum 100 is designed to slightly overlap.

  The potential adjusting organic EL light-emitting element 304 is a bottom emission type like the image organic EL light-emitting element 302, and light is emitted from the same direction. The image organic EL light-emitting elements 302 are arranged in accordance with the resolution of the image, whereas the potential adjusting organic EL light-emitting elements 304 are arranged in the main arrangement direction in a smaller number. Since the width of the light emitting surface in the main array direction of the organic EL light emitting element for potential adjustment 304 is larger than that of the organic EL light emitting element for image 302, the light emitting area is correspondingly large. The organic EL light emitting elements 304 for potential adjustment are arranged in a line as shown in FIG. 3, and the spot shape after the light emitted from the adjacent light emitting elements passes through the lens array optical system 310 on the photosensitive drum 100 is slightly. Designed to overlap.

Although the number of potential adjusting organic EL light emitting elements 304, the light intensity distribution in the main array direction (Y direction) of one light emitting element is ± 3% in consideration of uneven light emission in the plane of the organic EL substrate 301. The area is determined to fit. Thus, by adjusting the current value driven by the TFT drive circuit 303 (b) for driving the individual light emitting elements, the main array direction (Y direction) when all the potential adjusting organic EL light emitting elements 304 emit light. ) Of the light amount unevenness within ± 3%.
In this embodiment, the size of one light emitting element of the image organic EL light emitting element 302 is 0.
0438 mm × 0.042 mm, the element pitch was 0.0423 mm (600 dpi), and 5438 (230 mm) were arranged. Further, the size of one light emitting element of the organic EL light emitting element 304 for potential adjustment was set to 60 mm × 0.042 mm, and it was realized by arranging four pieces (240 mm) in the same manner. Thereby, the space | interval between the organic EL light emitting element 302 for images and the organic EL light emitting element 304 for electric potential adjustment can be set to about 0.1 mm. An exposure image for image and potential adjustment can be formed in a good state on the photosensitive drum 100 with the same lens array optical system 310. Regarding the main arrangement direction, the number of potential adjustment organic EL light emitting elements 304 arranged is smaller than the number of image organic EL light emitting elements 302 arranged. Of course, the element size, the number of elements, and the interval are not limited to the above.

  FIG. 5 shows a circuit diagram of the TFT drive circuits 303 (a) and (b) shown in FIG. In this embodiment, five TFT elements 900 are connected as shown in FIG. 5 as a constant current circuit for driving the organic EL element 302, so that the organic EL element according to the amplitude value sent by the data signal line is connected. The value of the current flowing through 302 is controlled. The organic EL element 302 emits light with a luminance corresponding to the current value supplied from the TFT drive circuit 303. With such a configuration, a current corresponding to an image signal sent from the data signal line flows through the organic EL element 302, and light can be emitted with a luminance corresponding to the image signal as image information (amplitude modulation).

  The organic EL substrate 301 is connected to the substrate on the main body side by a cable through a mounting portion (not shown) on the substrate. By controlling the current value in the TFT drive circuits 303 (a) and (b) according to the image input data input from the substrate on the main body via the cable, the image organic EL can be selectively selected with a desired luminance. The light emitting element 302 and the potential adjusting organic EL light emitting element 304 are caused to emit light.

In order to explain data input to the organic EL light-emitting element 302 for image and the organic EL light-emitting element 304 for potential adjustment, the processing path of the image input data is shown in FIG.
The video controller 350 includes a CPU and a memory, and holds image input data input from an external device such as a host computer. The engine controller 351 sends a control signal for moving the image forming apparatus 10. In addition to this, the engine controller 351 supplies the organic EL exposure head controller 352 with image data (VIDEO) in the video controller 350 and a control signal (CTRL) based on information on the characteristics of the photosensitive drum 100. The organic EL exposure head controller 352 converts data relating to image input into luminance data corresponding to the organic EL exposure head for each color while referring to the light amount correction data in the correction memory 353. Thereafter, processing for correcting the staggered arrangement to a straight line is performed, and a signal (VIDEO2) based on the image data is transmitted to the TFT organic EL light emitting element 302 (a) for driving the organic EL light emitting element for potential adjustment 302 for the image. . Then, a signal (CTRL2) based on the photosensitive drum information 354 is transmitted to the TFT drive circuit 303 (b) that drives the organic EL light emitting element 304 for potential adjustment. The correction memory 353 and the organic EL head controller 352 are mounted as driver boards 359 (a) to (d), and are arranged for each color together with the organic EL exposure head 300 in FIG. 1 (a).

  The operation and effect of the image forming apparatus using the solid exposure head 300 serving as the exposure apparatus of FIG. 1 described so far will be described. Specifically, based on the configuration of FIG. 1A, a method and an effect of driving the potential adjusting organic EL light emitting element 304 by each exposure apparatus (light irradiation means) will be described with reference to FIG. Further, a description will be given of causing each exposure apparatus 100 to emit light by adding the organic EL light-emitting element 302 for image and the organic EL light-emitting element 304 for potential adjustment to the portion where the toner image is visualized. In the following description, the configuration and operation of the exposure apparatus 300K in the first image forming station will be mainly described. However, it is assumed that the same configuration and operation are performed for the exposure apparatuses 300C, 300M, and 300Y in the second to fourth image forming stations.

  First, the problem relating to the difference in the film thickness of the photosensitive drum will be described with reference to FIG. As the use of the photosensitive drum 100 progresses, the surface of the photosensitive drum deteriorates due to the discharge of the charging roller 400, and the surface of the photosensitive drum is scraped by rubbing against the cleaning device 900, and the film thickness is reduced. At this time, if photosensitive drums 100 having different usage situations (for example, cumulative rotation speed) are mixed, the film thicknesses of the photosensitive drums 100 vary. When a constant charging voltage Vcdc is applied to the photosensitive drum 100 in this state, generally, the potential difference generated in the air gap between the charging roller 400 and the photosensitive drum 100 is different, and the charging potential Vd on the surface of the photosensitive drum varies. Specifically, the photosensitive drum 100 with a small number of image formations is thick, and the absolute value of the charging potential Vd on the surface of the photosensitive drum is small. On the other hand, the photosensitive drum 100 having a large cumulative number of rotations is thin, and the absolute value of the charging potential Vd on the surface of the photosensitive drum is large.

  For example, in the thick photosensitive drum 100, the development potential Vdc and the charging potential Vd are set so that the back contrast Vback (= Vd−Vdc), which is the contrast between the development potential Vdc and the charging potential Vd, is in a desired state. In this case, there are the following problems as shown in FIG. That is, in the image forming station having the thin photosensitive drum 100, the absolute value of the charging potential Vd increases (VdUp), and the back contrast Vback increases. When the back contrast Vback increases, toner that cannot be charged to the normal polarity (in the case of reversal development as in this embodiment, toner that is not negatively charged but charged to 0 to positive) is transferred from the developing roller 210 to the photosensitive drum 100. The image is transferred to the non-image area and fog occurs.

Further, in an image forming station where the film thickness of the photosensitive drum 100 is small, the charging potential Vd increases, and therefore, in a configuration where the exposure intensity is constant, the exposure potential Vl (VL) also increases (VlUp). Therefore, the development contrast Vcont (= Vdc−Vl), which is the difference value between the development potential Vdc and the exposure potential Vl (VL), becomes small, and the toner can be sufficiently transferred electrostatically from the development roller 210 to the photosensitive drum 100. This is not possible, and the density of the solid black image is likely to occur.

  On the other hand, as shown in FIG. 7B, the development potential Vdc and the charging voltage Vcdc are fixed, and the exposure intensity is changed from E1 to E2 (> E1). At this time, the development contrast Vcont, which is the difference value between the development potential Vdc and the exposure potential Vl (VL), can be controlled to be substantially constant by individual control of each exposure intensity. Therefore, the concentration can be kept constant. However, the back contrast Vback, which is the contrast between the development potential Vdc and the charging potential Vd, spreads, and the problem of fogging remains as described above.

In this embodiment, this problem is solved by performing the following correction process using the flowchart shown in FIG. A process for controlling the light quantity E0 of the exposure apparatuses 300K, 300Y, 300C, and 300M based on information about the characteristics of the photosensitive drums 100K, 100Y, 100C, and 100M in the background portion (non-image portion) where toner is not attached will be described. . Here, as information relating to the characteristics of the photosensitive member, for example, a description will be given of a process of correcting the information by changing it in relation to the life of the photosensitive drum 100. That is, the target voltage Vref21 of the light emission level for minute light emission is set to the photosensitive drums 100K, 100Y, 100C,
Change in relation to the remaining life of 100M. Here, control is performed based on information relating to the characteristics of the photosensitive member as information different from the image information. The information related to the characteristics of the photoconductor includes information related to the remaining life of the photoconductor (photosensitive drum).

  First, in step (hereinafter referred to as “S”) 101, the engine controller 351 detects the photosensitive drum as information relating to the remaining life of the photosensitive drum 100 from a storage member (memory tag) (not shown) provided in each image forming station. Information on 100 accumulated revolutions is read. Here, the storage unit that stores information relating to the remaining life of each photosensitive drum 100 is not limited to the storage member of each image forming station. For example, the information read from the storage member of each image forming station may be temporarily stored in another storage unit, and the information stored in the other storage unit may be subsequently read and updated. In this case, when the power of the apparatus main body is turned off or when the print job is finished, the information of another storage unit is reflected on the storage member of each image forming station. Here, as information relating to the characteristics of the photosensitive drum 100, information relating to how the photosensitive drum 100 having high relevance is rotated or used is used. In addition, as a modification of the information on the characteristics of the photosensitive drum 100, other information correlated with the film thickness of the charge transport layer 24 of the photosensitive drum 100, for example, the intermediate transfer belt rotation speed, the charging roller rotation speed, and the paper size are taken into account. Information on the number of prints can be used. Even if these pieces of information are used, the same effect can be obtained. Further, as acquisition means for acquiring information relating to the characteristics of the photosensitive member, means for directly detecting the film thickness of the photosensitive drum 100 is provided corresponding to each photosensitive drum 100, and the detection result is related to the remaining life of each photosensitive drum 100. The information was also good. Further, a motor driving time of a motor that drives the photosensitive drum 100 may be used.

In S102, the engine controller 351 refers to the table shown in FIG. 9 in which the correspondence relationship between the integrated rotation speed of the photosensitive drum 100 (the photosensitive drum usage status) and the parameters related to the normal exposure is defined. Since the information acquired in S101 may differ for each photosensitive drum, the table in FIG. 9 is referred to for each photosensitive drum. The engine controller 351 sets the exposure parameters of the image organic EL light-emitting element 302 and the potential adjustment organic EL light-emitting element 304 based on the information on the accumulated rotational speed acquired in S101. At this time, the exposure parameters of the image organic EL light emitting element 302 and the potential adjusting organic EL light emitting element 304 are set so as to be the exposure potential Vl (VL) of each photosensitive drum 100 in a state where two lights are superimposed. ing. By the process of S102, the engine controller 351 sets the exposure potential Vl (VL) of each photosensitive drum 100 to the target potential or a potential within an allowable range regardless of the sensitivity characteristic (EV curve characteristic) of each photosensitive drum 100. A light emission value for obtaining the value is acquired. As a result, the variation in the post-exposure potential Vl (VL) after the normal exposure in each of the plurality of photosensitive drums 100 can be reduced at least. The target exposure potential of each photosensitive drum 1 is basically the same / substantially the same, but may be set individually according to the characteristics of each photosensitive drum 100 in some cases.

  In step S103, the engine controller 351 refers to the table in FIG. 9 for each photosensitive drum as the light amount of the potential adjusting organic EL light emitting element 304 based on the accumulated number of revolutions. Through the process of S103, the engine controller 351 allows the charged potential Vd of each photosensitive drum 100 to be the target potential (value of the corrected charged potential Vd_bg) or to be allowed regardless of the sensitivity characteristic (EV curve characteristic) of the photosensitive drum. The setting for setting the potential of the range can be acquired. Since the organic EL light emitting element 304 for potential adjustment is disposed within a range of ± 3% luminance unevenness over the entire main scanning direction of the photosensitive drum 100, the background portion (non-image portion) in each of the plurality of photosensitive drums 1. The variation in the charged potential after correction can be reduced at least. The target exposure potential of each photosensitive drum is basically the same / substantially the same, but may be set individually according to the characteristics of each photosensitive drum 100 in some cases.

  As described above, by the processes in S102 and S103, it is possible to appropriately set the exposure amount of the fine exposure (micro light emission) and the normal exposure (normal light emission) in relation to the remaining life of each photosensitive drum. . In S102 and 103, the engine controller 351 has been described with reference to the table of FIG. 9, but the present invention is not necessarily limited thereto. For example, the CPU in the engine controller 351 may be configured to calculate a calculation formula. In this way, the CPU may perform calculation, and a desired set value may be obtained from a parameter related to the remaining life of the photosensitive drum 100 (for example, the integrated rotation speed of the photosensitive drum). Alternatively, all the values calculated by the above calculation formula may be stored in advance in a table, and the table may be referred to by the engine controller 351 each time. In addition, a plurality of EV curves corresponding to each use state of the photosensitive drum 100 as shown in FIG. 1C may be stored and held in a memory tag (not shown). In this case, the engine controller 351 specifies an EV curve according to the acquired information relating to the usage state of the photosensitive drum 100, and further, a necessary exposure amount (μJ) from the specified EV curve and a desired photosensitive drum potential. / Cm2). Then, the engine controller 351 calculates the necessary light amount for the image organic EL light-emitting element 302 and the potential adjusting organic EL light-emitting element 304 from the exposure amount (μJ / cm 2) obtained each time, and the result is calculated as S102, Set as a parameter corresponding to S103.

  Returning to the description of FIG. 8, in step S <b> 104, each member executes the series of image forming operations and controls described according to FIG. 1A under the control instruction of the engine controller 351. In S105, the engine controller 351 measures the number of rotations of the photosensitive drum 100 rotated in a series of image formation. This measurement process is performed in order to update the usage status of the photosensitive drum 100. Moreover, this S105 is actually performed in parallel with the process of S104.

  In S106, the engine controller 351 determines whether or not the image formation is completed. If it is determined that the image formation is completed in S106, the process proceeds to S107. In S107, the engine controller 351 adds the measurement result of each photosensitive drum 100 measured in S105 to the corresponding integrated rotational speed, and in S108, the updated integrated rotational speed is stored in the nonvolatile storage of each image forming station. Stored in a memory tag (not shown). Information regarding the remaining life of the photosensitive drum 100 is updated by the process of S108.

Here, as an example, the case where the density of the latent image recorded by the image organic EL light emitting element 302 has a gradation of 100% is shown. However, in order to improve the expressiveness of the color image to be obtained, even if gradation is given to the latent image (arbitrary gradation information with a density of 100% or less is superimposed), all other gradations are stable. High exposure distribution. At that time, only the image portion exposure amount in FIG. 9 is a coefficient corresponding to the gradation (for example, coefficient = 0.5 in the case of 50% gradation).
), And the amount of light in the non-image area is not changed.

  The effect of the flowchart of FIG. 8 is demonstrated using FIG.7 (c). In this embodiment, when the thickness of the charge transport layer 24 of the photosensitive drum 100 is the largest (the photosensitive drum 100 in the initial state), the thickness is 20 μm, and the charging potential Vd after passing through the charging roller 400 is about −600V. (See FIG. 1C). On the other hand, when the cumulative number of rotations of the photosensitive drum 100 is increased and the thickness of the charge transport layer 24 is reduced, the charging potential Vd becomes about −700 V and the −100 V charging potential Vd varies. When photosensitive drums having different usage conditions coexist or when photosensitive drums having different characteristics are mixed, a difference in EV characteristics occurs between the photosensitive drums.

  When the charge transport layer 24 becomes thinner, the charging potential Vd increases (see FIGS. 7A and 7B). Therefore, when the exposure amount for image portion exposure is constant, the post-exposure potential Vl (VL) increases ( FIG. 7 (a)). Therefore, the exposure amount at the time of full light emission is increased from E1 to E2 in accordance with the cumulative number of rotations of the photosensitive drum 100 that is inversely proportional to the film thickness of the charge transport layer 24, and after exposure as shown by the solid line portion in FIG. The potential Vl (VL) is kept substantially constant. Therefore, the development contrast Vcont (= Vdc−Vl), which is the difference value between the development potential Vdc and the exposure potential Vl (VL), can be maintained at a constant value regardless of the film thickness of the charge transport layer 24 of the photosensitive drum 100, and the image density is low. Is suppressed.

In addition, when the value of the total number of rotations of the photosensitive drum 100 is increased, the light amount during non-image area exposure (determined by the light amount of the organic EL light emitting element 304 for potential adjustment) is increased from Ebg1 to Ebg2. This is as described in the table of FIG. Even when the voltage is applied to the charging roller 400 at a constant value, the increase in the charging potential Vd caused by the change in the thickness of the charge transport layer 24 of the photosensitive drum 100 (A → B in FIG. 7C) is corrected. It becomes possible. As a result, the corrected charging potential Vd_bg of the non-image portion becomes substantially constant regardless of the film thickness of the charge transport layer 24, as indicated by the thick solid line portion in FIG. Even when the development potential Vdc is a constant value, the back contrast Vback, which is the potential difference between the development potential Vdc and the corrected charging potential Vd_bg, is kept constant. This is different from the case where only E1 <E2 as shown in FIG. Accordingly, it is possible to suppress the fog generated when the toner that has not been normally charged (in the case of reversal development, the toner charged with 0 to positive polarity instead of negative polarity) is transferred to the non-image portion.

According to the present embodiment, not only the charging potential (background portion potential) is kept constant to suppress the deterioration of the reversal fog, but also a sufficient leveling effect is secured by increasing the exposure amount E0 for microexposure. Yes. In addition to such effects, the background portion potential can be formed without causing a decrease in the uniformity of the charging potential due to charging roller contamination or the like. Therefore, it can be said that effective countermeasures can be taken against the increase in background portion potential and the decrease in uniformity as the degree of use progresses. Further, since the background portion potential is kept constant at each image forming station, there is an advantage that deterioration of fog can be suppressed even when a voltage is supplied to each developing roller 210 from the same power source.
The potential adjustment organic EL light-emitting element 304 does not need to be controlled with fine resolution in the main array direction as compared with the image organic EL light-emitting element 302. For this reason, with respect to the main arrangement direction, the number of potential adjustment organic EL light-emitting elements 304 arranged is smaller than the number of image organic EL light-emitting elements 302 arranged. For this reason, the apparatus can be reduced in size and cost. Further, complication of the TFT driving circuit 303 (b) can be avoided.

DESCRIPTION OF SYMBOLS 10 ... Image forming apparatus, 100 ... Photosensitive drum, 200 ... Developing unit, 300 ... Solid exposure head, 301 ... Organic EL substrate, 302 ... Organic EL light emitting element for images, 303 (a) (b) ... TFT circuit, 304 ... Organic EL light emitting element for potential adjustment, 305... Low temperature polysilicon substrate, 310. Lens array optical system, 352. Organic EL exposure head controller, 354.

Claims (8)

An image forming apparatus that exposes a charged photoreceptor to form a latent image and develops the latent image with a developer to form a developer image,
A light source for irradiating the photosensitive member with light, and a first light source including a plurality of first light emitting elements arranged in an array in the main scanning direction;
A light source for irradiating the photosensitive member with light, and a second light source including a plurality of second light emitting elements arranged in an array in the main scanning direction;
First driving means for driving the first light source;
Second driving means for driving the second light source;
Have
The first driving means and the second driving means expose an area of an image portion to which the developer of the photosensitive member is attached by light emission of the first light source and light emission of the second light source, and An area that is a non-image area to which the developer is not attached is exposed by light emission of the second light source without causing the first light source to emit light,
The number of the second light emitting elements arranged in the main scanning direction is smaller than the number of the first light emitting elements arranged.   The image forming apparatus according to claim 1, wherein the first light emitting element and the second light emitting element are EL light emitting elements.   The image forming apparatus according to claim 1, wherein the plurality of first light emitting elements and the plurality of second light emitting elements are formed on the same substrate.   4. The image according to claim 1, wherein the light emitted from the first light source and the second light source is imaged on the photoconductor via the same optical system. 5. Forming equipment.   The image forming apparatus according to claim 1, wherein the first driving unit is controlled based on image information corresponding to a developer image to be formed.   6. The image forming apparatus according to claim 5, wherein the second driving unit is controlled based on information different from the image information.   The image forming apparatus according to claim 6, wherein the information different from the image information is information relating to characteristics of the photosensitive member.   The image forming apparatus according to claim 7, further comprising an acquisition unit configured to acquire information relating to characteristics of the photoconductor.