JPH11235842A - Image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an image forming device capable of preventing the dislocation or lowering of images with ease even in the event where dislocation takes place in an exposure means. SOLUTION: Only a part of light-emitting blocks among a plurality of light- emitting blocks are controlled in a lighting manner relative to exposure means 12a including a plurality of light emitting blocks provided in rows in the main scanning direction and performing exposure with respect to an image forming body. The exposure means 12a is controlled by altering blocks in turn. During dynamic light control is carried out, the light emitting blocks to be light controlled are altered successively in terms of the order of blocks stored in the third block to be controlled in a lighting manner. Furthermore, from another point of view, the order of the light emitting blocks to be controlled in a lighting manner can be done with respect to its set alteration.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image forming apparatus for forming an image on an image forming body by relatively moving an image forming body and an exposing means in a sub-scanning direction.
The present invention relates to an apparatus having a plurality of light-emitting blocks as exposure means and dynamically controlling the plurality of light-emitting blocks.

[0002]

2. Description of the Related Art Heretofore, by moving an exposing means in which a plurality of light emitting blocks are arranged in a main scanning direction and an image forming body relatively in a sub scanning direction orthogonal to the main scanning direction,
Some form an image. As one of them, there is an image forming apparatus using an electrophotographic process. This image forming apparatus uses a photoconductive drum having a photoconductive photoconductive layer as an image forming body, and after uniformly charging the rotating photoconductive drum, a plurality of photoconductive drums extend in the main scanning direction. An image (latent image) for one page is formed on a photosensitive drum by performing image exposure based on an image signal by an exposing unit in which a plurality of light-emitting blocks (hereinafter, referred to as LEDs) are arranged. . Then, the latent image on the photosensitive drum is visualized with toner by a developing unit, and is developed into a toner image. Thereafter, the toner image is transferred onto a separately conveyed transfer paper and fixed by a fixing unit, whereby an image is formed on the transfer paper.

As one method of controlling such an exposure unit, only a part of the plurality of light-emitting blocks is controlled to be lit, and the light-emitting blocks to be lit are sequentially controlled. Change, so-called,
There is a dynamic lighting control method. In the dynamic lighting control method, the number of circuits is reduced and the cost can be reduced as compared with a so-called static lighting control method in which lighting control of all the plurality of light-emitting blocks is performed at once.

Conventionally, in this dynamic lighting control method, a shift register or the like has been used to change the light emitting blocks that are controlled to be lit. Each is shifted to an adjacent light-emitting block.

[0005]

By the way, even if a plurality of light-emitting blocks are intended to be properly arranged in the main scanning direction, they may be bent or may be attached at an inclined angle when the exposure means itself is attached. Exposure means may be displaced from the arrangement. Therefore, as in the conventional dynamic lighting control method using a shift register, when the light emitting blocks to be controlled to be lighted are shifted one by one to adjacent light emitting blocks, the light emitting blocks are moved to the exposure position by the displacement of the exposure means. Deviation occurs, and the intended exposure cannot be performed. That is, the image on the image forming body is displaced, and the image quality is reduced. In particular, in an image forming apparatus that forms a color image by using a plurality of exposure units, color misregistration occurs, resulting in extreme deterioration in image quality.

In order to prevent such image shift and deterioration of image quality, it is necessary to mount exposure means and to arrange a plurality of light-emitting blocks accurately. This leads to higher costs.

SUMMARY OF THE INVENTION It is an object of the present invention to provide an image forming apparatus which can easily prevent an image from being displaced or degraded even if a displacement occurs in the exposure means.

[0008]

The above object can be attained by the following constitution.

(1) Exposure means having a plurality of light-emitting blocks arranged in the main scanning direction for exposing an image forming body, and controlling such that only some of the plurality of light-emitting blocks can be turned on. And a control unit that controls the exposure unit by sequentially changing the light-emitting blocks that are controlled to be illuminated, and the image forming body and the exposure unit include the main scanning direction. In an image forming apparatus that forms an image on the image forming body by relatively moving in the orthogonal sub-scanning direction, the image forming apparatus includes a storage unit that stores an order of light-emitting blocks that are controlled to be lighted, The control unit controls the exposure unit by sequentially changing the light-emitting blocks to be turned on and off based on the order stored in the storage unit. apparatus.

(2) The order stored in the recording means can be changed in setting (1).
An image forming apparatus according to claim 1.

(3) A plurality of light-emitting blocks arranged in the main scanning direction, and an exposure means for exposing the image forming body, and only a part of the plurality of light-emitting blocks are controlled to be lighted. And a control unit that controls the exposure unit by sequentially changing the light-emitting blocks that are controlled to be illuminated, and the image forming body and the exposure unit include the main scanning direction. In an image forming apparatus that forms an image on the image forming body by relatively moving in the orthogonal sub-scanning direction, the order of the light-emitting blocks that are controlled to be lit by the control unit can be changed. An image forming apparatus comprising:

[0012]

DESCRIPTION OF THE PREFERRED EMBODIMENTS First, an image forming process and respective mechanisms according to an embodiment of the present invention are shown in FIG. 1 which is a cross-sectional view of a color image forming apparatus showing an embodiment of the image forming apparatus according to the present invention. , The exposure unit 12 will be described with reference to FIG.

A photosensitive drum 10, which is an image forming body, has a transparent conductive layer and a transparent conductive layer formed on the outer periphery of a cylindrical transparent substrate formed of a transparent member such as glass or transparent acrylic resin.
A photoconductor layer such as a Si layer or an organic photosensitive layer (OPC) is formed. The photosensitive drum 10 is rotated clockwise as indicated by an arrow in FIG. 1 with the transparent conductive layer grounded by power from a drive source (not shown).

As a material of the transparent substrate of the photoreceptor drum 10, an acrylic resin, particularly a polymer obtained by polymerizing a methacrylic acid methyl ester monomer, is preferably used because of its excellent transparency, strength, precision, surface properties and the like. In addition, various translucent resins such as acrylic, fluorine, polyester, polycarbonate, and polyethylene terephthalate used for general optical members and the like can be used. In addition,
The light transmittance of the transparent substrate does not need to be 100%, but may be such that a certain amount of light is absorbed when the exposure beam is transmitted. If it is, it may be colored, as long as it can provide an appropriate contrast. The transparent conductive layer is made of indium-tin-oxide (ITO), tin oxide, lead oxide, indium oxide, copper iodide, or a thin metal film of Au, Ag, Ni, Al, or the like that maintains light transmission. As a film forming method, a vacuum evaporation method, an active reaction evaporation method, various sputtering methods, various CVD methods, a dip coating method, a spray coating method, and the like are used. As the photoconductor layer, an amorphous silicon (a-Si) alloy photosensitive layer, an amorphous selenium alloy photosensitive layer, or various organic photosensitive layers (OPC) can be used.

Scorotron charger 11, exposure unit 1
2. The developing device 13 is used for an image forming process of each color of yellow (Y), magenta (M), cyan (C) and black (K). With respect to the rotation direction of the photosensitive drum 10 shown in FIG.
Y, M, C, and K are arranged in this order.

The scorotron charger 11, which is a charging means for each color, has a corona discharge electrode (no symbol), a U-shaped side plate (no symbol) as a shield member, and a control attached to the side plate. The charging member is formed by a grid (no symbol), and is attached to the photosensitive drum 10 in a direction orthogonal to the moving direction of the photosensitive drum 10 (a direction perpendicular to the paper surface in FIG. 1) so as to face and be close to the photosensitive drum 10. The scorotron charger 11 has a charging function (corresponding to the present embodiment) by a corona discharge electrode for performing corona discharge of the same polarity as the toner and a control grid maintained at a predetermined potential with respect to the organic photoconductor layer of the photoconductor drum 10. , A uniform potential is applied to the photosensitive drum 10.

Exposure unit 12 as exposure means for each color
Are arranged inside the photoconductor drum 10 such that the exposure position on the photoconductor drum 10 is on the downstream side in the rotation direction of the photoconductor drum 10 with respect to the scorotron charger 11 for each color. Each of the exposure units 12 for each color is shown in FIG.
As shown in FIG. 1, a light-emitting element which emits a plurality of image exposure lights arranged in an array parallel to the axis of the photosensitive drum 10 (in the main scanning direction, and perpendicular to the paper surface in FIG. 1). An LED array 12a composed of diodes (hereinafter, referred to as LEDs) 121, a light converging light transmitter (hereinafter, Selfoc lens (trade name)) 12b, and L
It has a holder 12c to which the ED array 12a and the SELFOC lens 12b are attached. The exposure unit 12 for each color is attached to a columnar holding member 20 and housed inside the base of the photosensitive drum 10.
In this embodiment, the LED 121 is used as the light emitting element. In addition to the LED 121, FL (phosphor emission), E
A linear element in which a plurality of light-emitting elements such as L (electroluminescence) and PL (plasma discharge) are arranged in an array may be used.

The exposure unit 12 appropriately performs image processing based on image data of each color sent from a separate computer (not shown) and stored in an image memory (not shown) to form an image signal. Thereafter, image exposure is performed on the uniformly charged photoconductor drum 10 to form a latent image (image) on the photoconductor drum 10. The light-emitting wavelength of the light-emitting element used in this embodiment is generally 6 which has high transmittance for Y, M, and C toners.
The wavelength in the range of 80 to 900 nm is good, but the wavelength may be shorter than this, since the color toner does not have sufficient transparency because the image is exposed from the back surface. The lighting control of the LED array 12a of the exposure unit 12 will be described later in detail.

The developing devices 13 as developing means for each color have a thickness of, for example, 0.5 mm to 1 mm and an outer diameter of 15 to 2 mm, respectively.
5 mm cylindrical developing sleeve 131 which is a developer carrier made of non-magnetic stainless steel or aluminum material
And a developing casing (unsigned), with yellow (Y), magenta (M), cyan (C),
Two components of one color of black (K) (one component may be used)
Of developer. The developing sleeve 131 contains a fixed magnet (not shown) in which N and S magnetic poles are alternately arranged, and is stirred and mixed by a stirring screw (no sign), and is supplied from a stirring unit by a supply roller (no sign). The transported and supplied two-component developer is supplied to the developing unit. At this time, the layer thickness of the two-component developer on the peripheral surface of the developing sleeve 131 is made of a metal material having a circular cross section of a magnetic material having a diameter of 3 to 10 mm and is uniformly pressed against the peripheral surface of the developing sleeve 131 with a predetermined load. It is regulated by a thin layer forming rod (not shown) as a thin layer forming member. The two-component developer that has passed through the developing section has one end of the long side of the belt shape
A scraper made of a plate-like elastic member such as SUS, urethane rubber, etc., provided by pressing in parallel with
The toner is removed from above the developing sleeve 131, is conveyed to the stirring unit by the supply roller, and is stirred and mixed by the stirring screw so as to have a predetermined toner concentration.

In the developing section, the developing sleeve 131 is kept out of contact with the photosensitive drum 10 by a contact roller (not shown) with a gap of a predetermined value, for example, 100 μm to 1000 μm. By rotating the developing sleeve 131 in the forward direction with respect to the rotation direction, a DC voltage of the same polarity as the toner (minus polarity in the present embodiment) or a superimposed voltage of DC and AC is applied to the developing sleeve 131 as a developing bias. Non-contact reversal development is performed on the exposed portion of the photosensitive drum 10. The precision of the developing interval at this time is preferably about 20 μm or less in order to prevent image unevenness.

As described above, the developing unit 13 converts the electrostatic latent image on the photosensitive drum 10 formed by charging by the scorotron charger 11 and image exposure by the exposure unit 12 to
In a non-contact state, the toner image is formed by reversal development with toner having the same polarity as the charged polarity of the photoconductor drum 10 (in the present embodiment, the photoconductor drum is negatively charged and the toner has a negative polarity).

Therefore, in the image forming apparatus of the present embodiment, a driving source (not shown) is started by starting image formation.
Is driven to rotate the photosensitive drum 10 in the clockwise direction indicated by the arrow in FIG. 1, and at the same time, the application of the potential to the photosensitive drum 10 is started by the charging action of the scorotron charger 11 (Y). After a potential is applied to the photosensitive drum 10, the exposure unit 12 (Y) starts exposure with an electric signal corresponding to the image signal of the first color, that is, yellow (Y), and the surface of the photosensitive drum 10 is rotated by rotating the drum. The electrostatic latent image corresponding to the yellow (Y) image of the original image is formed on the photosensitive layer. This latent image is reversely developed by the developing unit 13 (Y) in a non-contact state, and a yellow (Y) toner image is formed on the photosensitive drum 10.

Next, the photoreceptor drum 10 places a scorotron charger 11 on the yellow (Y) toner image.
A potential is applied by the charging action of (M), exposure is performed by an electric signal corresponding to the second color of the exposure unit 12 (M), that is, an image signal of magenta (M), and the developing unit 13 (M) , A magenta (M) toner image is superimposed on the yellow (Y) toner image.

By the same process, the scorotron charger 11 (C), the exposure unit 12 (C) and the developing device 13
By (C), a toner image of a third color, that is, a cyan (C) toner corresponding to a cyan (C) image signal, is further provided by a scorotron charger 11 (K), an exposure unit 12 (K), and a developing device. 13 (K) for the fourth color,
That is, the black (K) corresponding to the black (K) image signal
Are sequentially superimposed and a color toner image is formed on the peripheral surface within one rotation of the photosensitive drum 10. As described above, the image forming process in the image forming apparatus according to the present embodiment is a process of forming a color toner image by superimposing a toner image on the photosensitive drum 10, but is not limited thereto. The image forming apparatus may be an image forming apparatus that superimposes a toner image thereon, or may be an image forming apparatus that forms a monochrome image.

As described above, in this embodiment, Y, M,
The exposure of the organic photosensitive layer of the photosensitive drum 10 by the C and K exposure units 12 is performed from the inside of the photosensitive drum 10 through a transparent substrate. Therefore, the exposure of the images corresponding to the second, third and fourth colors can form an electrostatic latent image without being shielded by the previously formed toner image. Exposure may be performed from outside the drum 10.

On the other hand, the recording paper as a transfer material is sent out from a paper feed cassette 15 as a transfer material storage means by a feed roller (no code) and fed by a feed roller (no code) to a timing roller 16. Transported to

The recording paper is fed to the transfer area in synchronization with the color toner image carried on the photosensitive drum 10 by the driving of the timing roller 16. In the transfer area, a transfer unit 14A as a transfer unit to which a voltage having a polarity opposite to that of the toner (positive polarity in the present embodiment) is applied.
Thereby, the color toner images on the peripheral surface of the photosensitive drum 10 are collectively transferred to the recording paper.

The recording paper to which the color toner image has been transferred is neutralized by a paper separation AC static eliminator 14B as transfer material separating means, separated from the photosensitive drum 10, and conveyed to a fixing device 17 as fixing means. You. Then, the fixing device 17
In this case, heat and pressure are applied between a fixing roller 17a having a heater (not shown) therein and a pressure roller 17b, so that the toner adhered to the recording paper is fixed, and the recording paper is discharged. And discharged to a tray on the upper part of the apparatus.

After the transfer, the toner remaining on the peripheral surface of the photosensitive drum 10 is further rotated and cleaned by a cleaning device 19 or a cleaning blade (not shown) made of rubber material in contact with the photosensitive drum 10. It is scraped into the device 19. The photosensitive drum 10 from which the residual toner has been removed by the cleaning device 19 is uniformly charged by the uniform charger 11Y, and enters the next image forming cycle.

Next, the LED array 1 of the exposure unit 12
The configuration of the lighting control 2a will be described with reference to FIG. 3, which is a block diagram of a control circuit serving as a control unit.

In the following description, the exposure units 12 (Y), 12 (M), 12 (C), 12
Since (K) is the same, the symbols of Y, M, C, and K are omitted as in the exposure unit 12. In addition, LED
The array 12a has an A4 size of 300 dpi (dots / dot).
In order to form a latent image of 2 inches, the LED 121 is moved in the main scanning direction in the order of 1, 2,..., N,.
Although 560 are physically arranged, they are not shown in this order for convenience in FIG. 3 (however, the number assigned to each LED 121 in FIG. 3 is the end in the physically arranged state). First). Further, in the present embodiment, as a method of controlling the lighting of the LED array 12a, 2560 LEDs 121 are divided into 40 light emitting blocks (hereinafter, simply referred to as blocks), and the lighting of each block is sequentially controlled, so-called dynamic lighting. The control method is adopted. That is, a part (one in the present embodiment) of the 40 blocks (64 LEDs)
121) is controlled to be lit, and the blocks to be lit are sequentially changed so that L
The lighting control of all the LEDs 121 of the ED array 12a is performed. By adopting this dynamic lighting control method, the first and second shift registers 25 and 26 and the LE
The number of D lighting circuits 28 can be reduced to promote cost reduction.

The first memory 21 as a first storage means is a means for storing image data of an image to be formed. In the present embodiment, the first memory 21 is a page memory configured of a random access memory (RAM) in order to cope with high-speed operation and storing image data of at least one page (for each color). The image data stored in the first memory 21 is obtained by subjecting an image signal sent from a separate computer to image processing such as masking processing and gradation processing as appropriate, for each color (stored in each developing device 13). In this embodiment, since each pixel is represented by multi-values, the data is multi-valued data for expressing the gradation of an image.

The second memory 22, which is the second storage means, is a storage means for storing individual correction data of the plurality of LEDs 121. The second memory 22 is a read-only memory (ROM), and stores at least data corresponding to one line (in the number of LEDs 121) in the main scanning direction in correspondence with each LED 121. is there. The correction data stored in the second memory 22 is 2
Even if the same voltage and current are applied to each of the 560 LEDs 121 due to various factors, their exposure intensity (emission intensity)
(Individual difference) in the image, which leads to a deterioration in quality such as density unevenness and uneven line width and color unevenness in the formation of a latent image. This is data for correcting unevenness of the exposure intensity of each of the 2560 LEDs 121 measured in advance, since the expression becomes remarkable when expressed in (multi-gradation). The second memory 22 may be a rewritable PROM (for example, an EPROM that erases data with ultraviolet rays, but an EEPROM that electrically erases data, in order to cope with the aging of each LED 121). Is preferable).

The memory controller 23 includes a first memory 2
A controller that controls reading of data stored in the first and second memories. The memory controller 23 stores in the first memory 21 which line (position in the sub-scanning direction) of the image data for one page and data of which pixel (position in the main scanning direction) in one line. Functions as a reading circuit. Further, the memory controller 23 functions as a circuit for reading out data of any pixel (position in the main scanning direction) of the correction data for one line from the second memory 22. The data read from the first memory 21 and the second memory 22 by the memory controller 23 are data corresponding to each other,
That is, data having the same pixel (position in the main scanning direction) in one line is read.

Therefore, the memory controller 23
Image data corresponding to a predetermined pixel on a predetermined line of the image data having a plurality of lines stored in the first memory 21 is transferred to the first shift register 25 at the subsequent stage and stored in the second memory 22. The correction data of the predetermined pixel (at the same position as the pixel read from the first memory 21) of the correction data being transferred is transferred to the second shift register 26 at the subsequent stage.

The memory controller 23 reads and transfers data in synchronization with a clock signal, and sequentially reads and transfers the next data based on the clock signal. As will be described later, a block designating signal is input from the block designating circuit 30 to the memory controller 23 to read and transfer pixels (positions in the main scanning direction) corresponding to the block designated by the block designating signal. Done.

The first shift register 25 includes a first memory 2
This is a shift register that sequentially shifts image data (print data) sequentially transferred from 1 as pulse width modulation data (hereinafter referred to as PWM data) in synchronization with a clock signal. Also, the second shift register 26
The correction data sequentially transferred from the second memory 22 is converted into intensity modulation (that is, exposure intensity is changed by changing a current applied to the LED 121) data (hereinafter, referred to as current value data) in synchronization with a clock signal. This is a shift register for sequentially shifting. In this embodiment, the lighting control is speeded up by controlling the lighting by sharing the correction data of the LED 121 with the intensity modulation by printing the print data representing the gradation of the image by pulse width modulation (PWM). The handling and the circuit configuration are simplified, and a latent image is formed without lowering the gradation. However, the sharing between PWM and intensity modulation is not limited to this. Note that pulse width modulation has the meaning of modulating the exposure width, that is, the area of the latent image, and intensity modulation has the meaning of modulating the exposure intensity, that is, the potential of the latent image.

In this embodiment, 64 LEDs 121 are included in one block in the dynamic lighting control system.
The first and second shift registers 25 and 26 are configured to sequentially shift the PWM data and the current value data of 64 pixels in order to perform the lighting control of.

The timing control circuit 27 includes an LED 121
Is a circuit for controlling the time during which the lamp can be turned on. The timing control circuit 27 counts 64 clock signals after print data and correction data are transferred from the first and second memories 21 and 22, that is, the first and second memories 21 and 22.
When it is determined that the print data and the correction data for 64 pixels have been transferred to the two shift registers 25 and 26, an instruction to turn on the LED 121 is given by a lighting signal.
Before counting the next 64 clocks,
That is, before the print data and correction data for the next 64 pixels are transferred, the LED 121 is turned on by the lighting signal.
Turn off the lights. Then, the timing control circuit 27
When an instruction to turn off the LED 121 is issued by the lighting signal, a signal is sent to the delay circuit 32 to be described later so as to send a signal for selecting the next block. Note that the lighting instruction of the lighting signal transmitted from the timing control circuit 27 to the LED lighting circuit 28 is an instruction for enabling lighting, and the lighting time and the exposure intensity of each LED 121 are determined by the subsequent stages. It is controlled by the LED lighting circuit 28.

The LED lighting circuit 28 is a circuit for controlling the lighting time of the LED 121 and the exposure intensity. That is, the LED lighting circuit 28 has a circuit for 64 pixels for the dynamic lighting system, like the first and second shift registers. Then, the LED lighting circuit 28
The PWM data and current value data for the 64 pixels of the first and second shift registers 25 and 26 are stored in registers (not shown) in the respective LED lighting circuits 28 in response to a lighting instruction by a lighting signal from the timing control circuit 27. ) Is latched (temporarily stored), and the 64 LEDs (for 64 pixels) selected by the + side driving circuit 29 described later are stored in the LED 12 based on the latched PWM data and current value data.
1 controls the lighting time and exposure intensity.

The + drive circuit 29 is provided with an LED lighting circuit 28.
Is a circuit that selects the 64 LEDs 121 controlled by the LED and supplies power from the LED power supply (no symbol) to the selected 64 LEDs 121. This +
The side drive circuit 29 divides the 2560 LEDs 121 into 40 blocks, so one of the 40 blocks is selected and the one block (64 LEDs) is selected.
121). The + drive circuit 29 is connected to the LED lighting circuit 2 via the LED 121.
8, the power supplied from the + drive circuit 29 is controlled by the individual LED based on the lighting time and the exposure intensity controlled by the LED lighting circuit 28.
It will be consumed at 121. As the block selected by the + drive circuit 29, a block specified by a block specifying signal output from a block specifying circuit 30 (via a delay circuit 32) described later is selected.

The block designating circuit 30 uses the 256
Forty blocks obtained by dividing the zero LED 121 (hereinafter, referred to as 40 blocks)
For convenience, 64 L from the end of 2560 LEDs 121
.., Block 40 for each ED 121). The block designating circuit 30 has a third memory 31 which is a third storage means in which the order of the designated block among the forty blocks is stored. The block designating circuit 30 sends a block designation signal for designating a part (one) block based on the order stored in the third memory 31 to the memory controller 23 and the delay circuit 3.
Output to 2. The block designating signal is configured to output a block designating signal for designating the next block in the order stored in the third memory 31 when the clock signal is counted 64 times. .

The order in which the third memory 31 is stored from an operation unit (not shown) of the color image forming apparatus or from an input terminal by a service person or an assembler using an input device such as a personal computer. Is provided so that the setting can be changed. For this reason, each of the LEs of the LED array 12 a
D121 is not arranged in a straight line in the main scanning direction,
The order stored in the third memory 31 can be corrected each time the displacement of the exposure unit 12 due to the inclination of the attachment of the exposure unit 12 (LED array 12a) itself. That is, when performing dynamic lighting control, it is possible to arbitrarily set a block for controlling lighting. Therefore, by setting the order stored in the third memory 31 to an order corresponding to the displacement of the exposure unit 12, that is, an order for correcting the displacement of the exposure unit 12, image shift and deterioration of image quality are achieved. Can be prevented, and a good image can be formed.

The delay circuit 32 is a circuit for delaying the block designation signal output from the block designation circuit 30 when outputting the signal to the + drive circuit 29. That is, based on the block designating signal output from the block designating circuit 30, the memory controller 23 reads out all (64 pixels) of image data and correction data corresponding to the pixels of the block indicated by the block designating signal. , First, second
This is for delaying until the transfer to the shift registers 25 and 26 is completed to synchronize the block selection by the + drive circuit 29 and the latch of the LED lighting circuit 28. The block designating signal input to the delay circuit 32 is a signal output from the timing control circuit 27 after the timing control circuit 27 outputs an instruction to turn off the LED 121 (the input block designating signal is The signal is output to the + drive circuit 29 based on the instruction signal output to the drive circuit 29).

The operation of the lighting control of the LED array 12a by the control circuit will be described with reference to FIG. 4 which is a timing chart and FIG. 5 which schematically shows the lighting timing of each block. In this description, in order to correct the displacement of the exposure unit 12, the blocks that are controlled to be lit so as to be turned on are performed in the order of block 3, block 2, block 1, block 4, block 5,. is there.

First, a one-line division signal is input, and based on this signal, the line pixel selection circuit 24, the timing control circuit 27, the + side drive circuit 29, and the block designation circuit 30 are initialized. . That is, the pixel selected by the memory controller 23 is set to read the first pixel in one line, the lighting signal from the timing control circuit 27 instructs to turn off (Lo), and the block selection signal enters the defragmented state. Therefore, all the LEDs 121 are not lit because the power from the LED power supply cannot be supplied and the lighting signal instructs turning off. In the initialization of the block designating circuit 30, a block designating signal for designating the first block (block 3 in the present embodiment) in the order stored from the third memory 31 is output.

The pixel corresponding to the block 3 designated by the block designation signal (129th pixel in this embodiment) of the image data stored in the first memory 21 is synchronized with the clock signal by the memory controller 23. ) Are sequentially read out (transmitted) as image data from the pixels, and PW is stored in the first shift register 25.
M data is sequentially transferred to the first shift register 25.
Then, the transferred PWM data is sequentially shifted in synchronization with the clock signal. At the same time, the correction data corresponding to the image data to be transferred is read out from the second memory 22 in synchronization with the clock signal, and similarly to the PWM data,
The current value data is sequentially transferred to the second shift register 24 and sequentially shifted by the second shift register 26 in synchronization with the clock signal.

The timing control circuit 27 counts the clock of the clock signal, and when the count value reaches 64, 64 PWM data and current value data are transferred to the first and second shift registers 25 and 26, respectively. And the lighting signal output from the LED lighting circuit 28 is
It is changed to a lighting instruction (Hi). Before the timing control circuit 27 counts the clock signal to 64 (while the lighting signal is outputting the light-off instruction (Lo)), the block designating signal (block 3) is sent to the delay circuit 32.
Is output to the + drive circuit 29. As a result, the block designating signal for designating the block 3 is output from the delay circuit 32 to the + drive circuit 29, and the + drive circuit 29 sets the block selection signal 3 to Hi and supplies power to the LED 121 of the block 3.

Therefore, when the lighting signal from the timing control circuit 27 changes to a lighting instruction, LE
The D lighting circuit 28 includes first and second shift registers 25 and 26.
Are latched in a register provided therein, and the LEDs 121 of 1 to 64 are turned on for an exposure time based on the PWM data at an exposure intensity based on the current value data. Let it.

The timing control circuit 27 sends the lighting signal to a light-off instruction (Lo) before the next 64 print data and correction data are all transferred to the first and second shift registers 25 and 26. ), And the delay circuit 32 outputs a signal for outputting the block designating signal for designating the next block (block 2 in this embodiment) output from the block designating circuit 30 to the + drive circuit 29. Send out.

On the other hand, the block designating circuit counts the clock of the clock signal continuing at the same timing, and when the count value reaches 64, the next block (this embodiment) is stored in the order stored in the third memory. In the embodiment, a block designating signal for designating the block 2) is output. Then, in the memory controller 23, in synchronization with the clock signal, the image data is sequentially transferred from the 65th pixel corresponding to the block 2 designated by the block designation signal among the image data stored in the first memory 21. Read (transmitted) as print data,
The PWM data is sequentially transferred to the shift register 25 as PWM data, and the transferred PWM data is sequentially shifted in the first shift register 25 in synchronization with a clock signal.

At the same time, the correction data corresponding to the image data to be transferred is read out from the second memory 22 in synchronization with the clock signal, and, like the PWM data, sequentially stored in the second shift register 26 as current value data. The data is transferred and sequentially shifted by the second shift register 26 in synchronization with the clock signal. Thus, the first and second shift registers 25,
The data of the pixels (129th to 192nd) corresponding to the block 3 of 26 are rewritten, but since they are latched in the register of the LED lighting circuit 28, 129 to 1
The lighting time and exposure intensity of the 92 LEDs 121 do not change.

Also, in the timing control circuit 27, after the count value of the previous clock signal reaches 64, the count value is reset and the count is subsequently started. The same operation as is performed.

By repeating such an operation for 40 blocks, 2560 LEDs 1 arranged in the main scanning direction are arranged.
Lighting control is sequentially performed on all 40 blocks obtained by dividing 21, and one line of exposure (latent image formation) is performed. That is, as shown in FIG. 5, the exposure of the block 3, the exposure of the block 2, the exposure of the block 1, and the exposure of the block 4 are performed at a maximum of about 80 μm (corresponding to 300 dpi) with respect to the moving direction of the photosensitive drum 10. Exposure, exposure of block 5,... Exposure of block 40 are performed at intervals of about 2 μm,
One line of exposure (latent image formation) is performed.

When the image data and the correction data for one line are transferred from the first and second memories 21 and 22,
The same operation as described above is further performed for the second line based on the one-line separation signal. In this case,
From the first memory 21, the image data of the pixel (129th pixel) corresponding to the block 3 of the second line is read, but the correction data stored in the second memory 22 and the correction data stored in the third memory 31 are stored. The order in which they are performed has no relation to the line (sub-scanning direction), so that the correction data corresponding to the pixel corresponding to block 3 (the 129th pixel) is read. By repeating this operation for 3508 lines, an A4 size image (latent image) can be formed on the photosensitive drum 10 at 300 dpi.

As described above, in the present embodiment, the exposure unit 12 (LED array 12a) including a plurality of blocks arranged in the main scanning direction and exposing the image forming body to light is provided.
In contrast, while controlling only a predetermined (one in the present embodiment) block of the plurality of blocks to be lit,
In the so-called dynamic lighting control, which controls the exposure unit 12 (LED array 12a) by sequentially changing the blocks to be turned on, the blocks to be turned on are stored in the third memory 31. Based on the stored order of the blocks to be turned on,
change. Thereby, even if the exposure unit 12 is displaced, it is possible to easily prevent the image from being shifted and the image quality from being lowered. From another point of view, the setting of the order of the blocks to be turned on / off can be changed, so that the blocks to be turned on / off can be selected in an arbitrary order. Even if this is the case, it is possible to easily prevent the image from shifting and the image quality from deteriorating.

In this embodiment, a plurality of LEs
The individual correction data of D121 is stored in the second memory 22, and the image data stored in the first memory 21 and the correction data stored in the second memory 22 of the LED 121 corresponding to the position of the image data in the main scanning direction are stored. Based on the data and
Since the light emission of each LED 121 is controlled, high-quality image formation free from color unevenness and density unevenness, particularly corresponding to a large number of gradations, can be performed without increasing the amount of data stored in the second memory 22 and at high speed. Can be done with

[0058]

As described above in detail, according to the present invention, even if the exposure unit 12 is displaced, it is possible to easily prevent the image from being displaced and the image quality from being lowered.

[Brief description of the drawings]

FIG. 1 is a cross-sectional configuration diagram of a color image forming apparatus.

FIG. 2 is a perspective view of an exposure unit.

FIG. 3 is a block diagram of a control circuit for lighting control.

FIG. 4 is a timing chart for lighting control.

FIG. 5 is a diagram schematically showing lighting timing of each light-emitting block.

[Explanation of symbols]

 REFERENCE SIGNS LIST 10 photoconductor drum (image forming body) 12 exposure unit (exposure means) 21 first memory 22 second memory 25, 26 shift register 27 timing control circuit 28 LED lighting circuit 29 + side drive circuit 30 block designation circuit 31 third memory (Storage means) 32 Delay circuit 121 Light emitting diode (Light emitting element)

Claims (3)

[Claims] An exposure unit that includes a plurality of light-emitting blocks arranged in a main scanning direction and performs exposure on an image forming body; and controls only a part of the plurality of light-emitting blocks to be lit. And a control unit for controlling the exposure unit by sequentially changing the light-emitting blocks to be turned on and off, wherein the image forming body and the exposure unit are orthogonal to the main scanning direction. By relatively moving in the sub-scanning direction
In an image forming apparatus for forming an image on the image forming body, the image forming apparatus includes a storage unit that stores an order of light-emitting blocks that are controlled to be lit, and the control unit includes a light-emitting block that is controlled to be lit.
Based on the order stored in the storage means,
An image forming apparatus, wherein the exposure unit is controlled by changing. 2. The image forming apparatus according to claim 1, wherein the order stored in the recording unit can be changed. 3. An exposure means comprising a plurality of light-emitting blocks arranged in the main scanning direction for exposing an image forming body, and controlling only some of the plurality of light-emitting blocks to be lighted. And a control unit for controlling the exposure unit by sequentially changing the light-emitting blocks to be turned on and off, wherein the image forming body and the exposure unit are orthogonal to the main scanning direction. By relatively moving in the sub-scanning direction
An image forming apparatus for forming an image on the image forming body, wherein the order of the light-emitting blocks controlled to be turned on by the control means can be changed.