JP2023118469A - image forming device - Google Patents

Abstract

To reduce expansion and contraction of an image due to eccentricity or the like of a rotary shaft of a photoreceptor.SOLUTION: Exposing means has a plurality of light emitting elements arranged along an intersecting direction intersecting with a rotating direction of a photoreceptor and forms an electrostatic latent image by exposing a surface of the photoreceptor at least for each one line by light outputted from the plurality of light emitting elements. Developing means develops the electrostatic latent image with toner to form a toner image. Conveying means is arranged to oppose to the photoreceptor, and conveys a sheet onto which the toner image is to be transferred. Control means corrects a line interval for forming the electrostatic latent image so as to offset change in movement speed of the surface of the photoreceptor due to variations in distance from the rotary shaft of the photoreceptor to the surface of the photoreceptor.SELECTED DRAWING: Figure 12

Description

The present invention relates to an image forming apparatus.

2. Description of the Related Art An electrophotographic printer that forms a latent image by exposing a photosensitive drum using an exposure head having LEDs (light emitting diodes) and organic ELs (electroluminescence) is known. The latent image formed on the photoreceptor drum is developed into a toner image, and the toner image is transferred from the photoreceptor drum to a sheet on the transfer belt. At this time, if the moving speed of the surface of the photosensitive drum and the moving speed of the surface of the transfer belt do not match, the reproducibility of the image may deteriorate. Japanese Unexamined Patent Application Publication No. 2002-200001 proposes a mechanical mechanism for reducing expansion and contraction (density unevenness) of an image caused by a misalignment between the rotating shaft of a photosensitive drum and the driving shaft of a motor.

JP-A-5-341589

By the way, the cause of image density unevenness is other than the misalignment between the rotating shaft of the photosensitive drum and the driving shaft of the motor. For example, the rotating shaft that holds the photoreceptor drum may deviate from the center of the photoreceptor drum (eccentricity). In this case, the distance (radius of the cross section) from the rotation axis to the surface of the photoreceptor drum varies for each rotational phase of the photoreceptor drum. As a result, the speed of movement of the surface of the photosensitive drum and the speed of movement of the surface of the transfer belt do not match, resulting in image density unevenness. A similar phenomenon can occur when the cross-sectional shape of the photosensitive drum is not a perfect circle. SUMMARY OF THE INVENTION Accordingly, it is an object of the present invention to reduce image density unevenness caused by the eccentricity of the rotating shaft of a photoreceptor.

The present invention, for example,
a photoreceptor having a rotating shaft and driven to rotate about the rotating shaft;
charging means for uniformly charging the photoreceptor;
a plurality of light emitting elements arranged along a direction crossing the rotation direction of the photoreceptor, and exposing the surface of the photoreceptor at least one line at a time with light output from the plurality of light emitting elements; an exposure means for forming an electrostatic latent image with
a developing means for developing the electrostatic latent image with toner to form a toner image;
a transfer means for transferring the toner image from the photoreceptor to a transfer body;
and a control means for controlling the exposure means,
The control means forms the electrostatic latent image so as to offset a change in moving speed of the surface of the photoreceptor caused by a change in the distance from the rotational axis of the photoreceptor to the surface of the photoreceptor. Provided is an image forming apparatus characterized by correcting the line spacing of .

According to the present invention, image density unevenness caused by the eccentricity of the rotating shaft of the photoreceptor can be reduced.

Diagram for explaining an image forming apparatus Diagram explaining the exposure head Diagram explaining the exposure head Diagram explaining the exposure head A diagram for explaining a plurality of light-emitting elements forming a light-emitting element group. A diagram for explaining density unevenness caused by the eccentricity of the rotating shaft. A diagram for explaining density unevenness caused by the eccentricity of the rotating shaft. Diagram for explaining the image processing unit FIG. 5 is a diagram for explaining emission control signals related to exposure of one line; FIG. 4 is a diagram for explaining an electrostatic latent image formed on the peripheral surface of a photoreceptor drum; A diagram for explaining a light emission control signal involved in exposure for one page. Diagram explaining how to compensate for peripheral speed fluctuations Diagram explaining how to measure correction data Diagram for explaining the control signal generator Diagram for explaining arrangement of exposure head, optical sensor and transfer position Diagram explaining reading of correction data Diagram explaining correction results Timing chart showing various signals involved in correction

Hereinafter, embodiments will be described in detail with reference to the accompanying drawings. In addition, the following embodiments do not limit the invention according to the scope of claims. Although multiple features are described in the embodiments, not all of these multiple features are essential to the invention, and multiple features may be combined arbitrarily. Furthermore, in the accompanying drawings, the same or similar configurations are denoted by the same reference numerals, and redundant description is omitted.

<Image forming apparatus>
FIG. 1 shows an image forming apparatus 1 which is an electrophotographic copier. However, the image forming apparatus 1 may be realized as a monochrome printer, a full-color printer, a facsimile communication device, and a multi-function machine.

The scanner unit 100 is a document reading device that illuminates a document placed on a document table, optically reads the document image, converts the reading result into an electric signal, and creates image data. The printer engine 103 forms a toner image on the sheet P. FIG. A printer engine 103 rotates the photosensitive drum 102 . The charger 107 charges the surface of the photoreceptor drum 102 so that the surface of the photoreceptor drum 102 has a uniform potential. The exposure head 106 exposes the surface of the photoreceptor drum 102 with light corresponding to image data to form an electrostatic latent image on the surface of the photoreceptor drum 102 . The developing device 108 adheres toner to the electrostatic latent image formed on the photosensitive drum 102 to form a toner image. Further rotation of the photoreceptor drum 102 causes the toner image to reach the transfer nip. At the transfer nip, the sheet P is conveyed while being nipped between the photosensitive drum 102 and the transfer belt 111 . Thereby, the toner image is transferred from the photosensitive drum 102 to the sheet P. FIG.

The printer engine 103 has four image forming units 101C, 101M, 101Y, and 101K corresponding to toner colors CMYK (cyan, magenta, yellow, and black). The four image forming units 101C, 101M, 101Y, and 101K transfer toner images of different colors onto the sheet P, thereby forming a full-color image on the sheet P. FIG.

The feeding unit 105 is designated in advance among the feeding devices 109a and 109b provided in the main body of the image forming apparatus 1, the feeding device 109c provided outside the main body, and the manual feed type feeding device 109d. The sheet P is fed from the feeding device. The fed sheet P is conveyed to registration rollers 110 . The registration roller 110 conveys the sheet P so that the timing at which the toner image arrives at the transfer nip coincides with the timing at which the sheet P arrives. The transfer belt 111 conveys the sheet P onto which the toner image has been transferred to the fixing device 104 .

The fixing device 104 fixes the toner image onto the sheet P by applying pressure and heat to the toner image and the sheet P. FIG. A paper discharge roller 112 discharges the sheet P to the outside of the image forming apparatus 1 .

<Exposure head>
FIG. 2A is a perspective view of the exposure head 106 that exposes the photosensitive drum 102. FIG. FIG. 2B is a schematic cross-sectional view of the photosensitive drum 102 and the exposure head 106. FIG. The exposure head 106 has a light emitting element group 201 , a printed circuit board 202 , a rod lens array 203 and a housing 204 . Light emitted from the light emitting element group 201 mounted on the printed circuit board 202 is condensed by the rod lens array 203 and irradiated onto the surface of the photosensitive drum 102 . The printed circuit board 202 and rod lens array 203 are fixed to the housing 204 .

The exposure head 106 is individually assembled and adjusted. The adjustment work includes spot size adjustment (focus adjustment) at the condensing position and light amount adjustment. In focus adjustment, the mounting position of the rod lens array 203 is adjusted so that the distance between the rod lens array 203 and the light emitting element group 201 is a predetermined value. In the light amount adjustment, the plurality of light emitting elements included in the light emitting element group 201 are sequentially caused to emit light one by one, and each light emitting element is adjusted so that the light amount condensed through the rod lens array 203 becomes a predetermined light amount. A drive current is adjusted.

<Structure of Light Emitting Element Group>
FIG. 3A shows a non-mounting surface 301 of the printed circuit board 202. FIG. Although no light emitting element is mounted on the non-mounting surface 301, other electronic components such as a connector 305 are mounted. The connector 305 is connected to a cable (power line and signal line) that conveys various signals such as a clock signal to the printed circuit board 202 .

As shown in FIG. 3B, the light emitting element group 201 is mounted on the mounting surface 302 of the printed board 202 . The mounting surface 302 is the surface opposite to the non-mounting surface 301 . The light emitting element group 201 has m light emitting element arrays 300-1 to 300-m arranged in a zigzag pattern. The light emitting element arrays 300-1 to 300-m may be collectively referred to as the light emitting element array 300. FIG.

As shown in FIG. 3C, a plurality of light emitting elements 350 are arranged along the longitudinal direction of the light emitting element array 300 in each of the light emitting element arrays 300-1 to 300-m.

As shown in FIG. 3B, the light emitting element array 300 is arranged in two columns. A light emitting element array 300-1, a light emitting element array 300-3, . . . , a light emitting element array 300-m-1 are provided in the first row. A light emitting element array 300-2, a light emitting element array 300-4, . . . , a light emitting element array 300-m are provided in the second row.

As shown in FIG. 3C, the distance between two adjacent light emitting elements 350 in a certain light emitting element array 300 is L. As shown in FIG. A distance L is a longitudinal distance of the light emitting element array 300 . At 1200 dpi resolution, L=about 21.16 μm. This is a distance corresponding to one pixel at 1200 dpi. The distance between the right end light emitting element 350 of the i-th light emitting element array 300-i and the left end light emitting element 350 of the i+1-th light emitting element array 300-i+1 is also L. i is any integer from 1 to m−1. As shown in FIG. 3C, in the lateral direction of the light emitting element array 300, the distance S between the right end light emitting element 350 of the light emitting element array 300-i and the left end light emitting element 350 of the light emitting element array 300-i+1 is about 105 μm. This corresponds to a distance of 5 pixels at 1200 dpi. Note that the distances L and S are only examples.

<Structure of Light Emitting Element Array>
FIG. 4 is a plan view of the light emitting element array 300. FIG. The X direction indicates the longitudinal direction of the photoreceptor drum 102 . The Y direction indicates the direction of rotation of the photosensitive drum 102 . The light emitting element array 300 has a light emitting substrate 402 , a light emitting section 404 including a plurality of light emitting elements 350 mounted on the light emitting substrate 402 , and WB pads 408 mounted on the light emitting substrate 402 . WB is an abbreviation for wire bonding. The light emitting substrate 402 incorporates a circuit section 406 for controlling the light emitting section 404 . Circuit portion 406 includes both analog drive circuitry (analog portion) and digital control circuitry (digital portion). Power supply to the circuit section 406 and signal input/output to/from the light emitting element array 300 are performed through the WB pad 408 .

<Light emitting part>
FIG. 5 shows a light-emitting element array that constitutes the light-emitting section 404 . The light emitting section 404 has n light emitting elements 350 arranged in a line. The plurality of light emitting elements 350 are arranged at a predetermined pitch (distance L=21.16 μm) in the X direction.

In FIG. 5, W1 is the length of the light emitting element 350 in the X direction. d1 is the distance between two adjacent light emitting elements 350 in the X direction. W2 is the length of the light emitting element 350 in the Y direction. The length W2 is determined in consideration of the scanning speed and resolution in the Y direction. As an example, the lengths W1 and W2 are 20.9 μm, and the adjacent distance d1 is 0.26 μm.

<Photosensitive drum and transfer belt>
FIGS. 6A to 6C are diagrams for explaining the photosensitive drum 102 and the transfer belt 111. FIG. Sheet P is not shown for simplicity of illustration. Also, the transfer process is described assuming that the toner image is transferred from the photosensitive drum 102 to the transfer belt 111, but in reality, the toner image is transferred from the photosensitive drum 102 to the sheet P on the transfer belt 111. . However, the transfer belt 111 may function as an intermediate transfer member, and the toner image may be transferred from the transfer belt 111 to the sheet P.

The electrostatic latent image formed on photoreceptor drum 102 by exposure head 106 is developed into a toner image by developer 108 . A white square on the surface of the photoreceptor drum 102 indicates one line of electrostatic latent image and toner image formed by the exposure head 106 . A black square on the surface of the transfer belt 111 indicates a toner image for one line transferred onto the transfer belt 111 .

FIG. 6A shows an ideal state in which the rotating shaft 601 holding the photoreceptor drum 102 is at the center of the photoreceptor drum 102 . The transfer belt 111 rotates at a constant speed. The photosensitive drum 102 also rotates at a constant angular velocity. Further, the moving speed of the surface of the transfer belt 111 (hereinafter referred to as peripheral speed) and the peripheral speed of the photosensitive drum 102 match (constant speed state). The exposure head 106 exposes each line at regular intervals in the sub-scanning direction to form an electrostatic latent image. A developer 108 develops the electrostatic latent image with toner. As a result, the toner image is transferred to the transfer belt 111 at line intervals as expected.

FIG. 6B shows a case (first case) in which the rotating shaft 601 is displaced from the center of the photosensitive drum 102 . In particular, the surface section with the shortest distance from the rotating shaft 601 to the surface of the photosensitive drum 102 is in contact with the transfer belt 111 . The transfer belt 111 rotates at a constant speed. The photosensitive drum 102 also rotates at a constant angular velocity. The exposure head 106 exposes each line at regular intervals in the sub-scanning direction to form an electrostatic latent image. A developer 108 develops the electrostatic latent image into a toner image. In this case, the toner image is transferred to the transfer belt 111 at line intervals wider than the assumed interval. When the distance between the rotating shaft 601 and the surface of the photoreceptor drum 102 is shorter than the assumed distance, the peripheral speed of the photoreceptor drum 102 is relatively low. In other words, the peripheral speed of the photosensitive drum 102 is lower than the peripheral speed of the transfer belt 111 . Therefore, the line spacing on the transfer belt 111 becomes relatively wide.

FIG. 6C shows a case (second case) in which the rotating shaft 601 is displaced from the center of the photosensitive drum 102 . In particular, the surface section with the longest distance from the rotating shaft 601 to the surface of the photosensitive drum 102 is in contact with the transfer belt 111 . In this case, the toner image is transferred to the transfer belt 111 at line intervals narrower than the assumed line interval. When the distance between the rotating shaft 601 and the surface of the photoreceptor drum 102 is longer than the assumed distance, the peripheral speed of the photoreceptor drum 102 becomes relatively high. That is, the peripheral speed of the photosensitive drum 102 is higher than the peripheral speed of the transfer belt 111 . Therefore, the line spacing on the transfer belt 111 becomes relatively narrow.

FIG. 7 shows the influence on the toner image due to the displacement of the rotating shaft 601 that holds the photosensitive drum 102 . When the rotary shaft 601 is displaced from the center of the photoreceptor drum 102, the relative speed of the surface of the photoreceptor drum 102 with respect to the transfer belt 111 increases or decreases.

The upper half of FIG. 7 shows changes in relative velocity of the photosensitive drum with respect to the transfer belt 111 . The vertical axis indicates relative velocity. The horizontal axis indicates elapsed time from the start of printing. Normally, when forming one toner image on the sheet P, the photosensitive drum 102 rotates a plurality of times. That is, the relative speed changes many times when forming one toner image. As a result, when image data of uniform density is printed, or when a plurality of main scanning lines are printed at regular intervals in the sub-scanning direction, the line spacing narrows or widens.

The lower half of FIG. 7 shows the print result. In the section where the relative speed is high, the line spacing in the sub-scanning direction becomes narrow, so the image becomes darker (higher density). Conversely, in sections where the relative speed is low, the line spacing in the sub-scanning direction increases, so the image becomes lighter (lower density). Such local expansion and contraction of the image in the sub-scanning direction causes density unevenness in the image.

<Image processing part>
FIG. 8 shows the internal configuration of the image processing unit 800. As shown in FIG. The image processing unit 800 has an image processing circuit 801 , a control signal generation unit 802 , a PS conversion unit 803 and a memory 804 . The image processing unit 800 is assumed to be realized by a hardware circuit such as FPGA (Field Programmable Gate Array) or ASIC (Application Specific Integrated Circuit). However, part or all of the image processing unit 800 may be implemented by a processor such as a CPU executing a control program.

The image processing circuit 801 applies predetermined image processing to the image data input from the scanner unit 100 to generate image data for output. Predetermined image processing is, for example, color space conversion (RGB→YMCK), trimming, scaling, or density conversion.

A control signal generation unit 802 generates a light emission control signal from the image data output from the image processing circuit 801 . A light emission control signal is a signal for controlling the light emitting element group 201 in the exposure head 106 . Examples of light emission control signals include a timing signal Lsync_in and light emission data Data. The light emission data Data may be called lighting data or lighting signal. The timing signal Lsync_in is a signal that serves as a reference for the exposure timing of each line. The timing signal Lsync_in is generated based on the page top signal Top sent from the printer control unit (not shown) and the home position signal (hereinafter referred to as HP signal) input from the optical sensor 805 . The light emission data Data is a signal generated based on image data output from the image processing circuit 801 . A page top signal Top is a signal indicating the beginning of one page. The HP signal is a signal that indicates the absolute reference (home position) of the rotation phase of the photosensitive drum 102 .

The PS converter 803 is an interface circuit that transmits the light emission control signal output from the control signal generator 802 to the exposure head 106 . In this embodiment, it is assumed that the image processing unit 800 and the exposure head 106 are separated, and the light emission control signal is transmitted via the serial communication cable 807 . Therefore, the PS converter 803 converts the light emission data Data and the timing signal Lsync_in from parallel signals to serial signals.

The exposure head 106 has an SP conversion section 806 . The SP converter 806 is connected to the PS converter 803 via a serial communication cable 807 . The SP conversion unit 806 converts the serial signal transmitted from the PS conversion unit 803 into the original parallel signal (light emission data Data and timing signal Lsync_in). After that, the SP conversion unit 806 supplies the light emission data Data and the timing signal Lsync_in to the light emitting element group 201 .

The memory 804 stores a correction value (correction data) for correcting deviation of the peripheral speed of the photosensitive drum 102 with respect to the peripheral speed of the transfer belt 111 . The control signal generator 802 corrects the transmission timings of the light emission data Data and the timing signal Lsync_in based on the correction data. As a result, density unevenness caused by the eccentricity of the rotating shaft 601 of the photosensitive drum 102 is reduced.

<Exposure for one line and emission control signal>
FIG. 9 shows the relationship between the light emission data Data, which is the light emission control signal, and the timing signal Lsync_in. Here, the clock signal clk is also described. The clock signal clk is the most fundamental signal that operates various integrated circuits and serves as a reference for other signals.

The timing signal Lsync_in serves as a reference signal for exposure start timing in the main scanning direction. As shown in FIG. 9, the timing signal Lsync_in is synchronous with the clock signal clk. At time t1, the timing signal Lsync_in is enabled "0" for a period of time corresponding to one cycle of the clock signal clk. As a result, the light emission data Data is continuously output from time t2 corresponding to the next cycle.

The light emission data Data is a 1-bit signal that controls whether the plurality of light emitting elements 350 forming the light emitting element group 201 are turned on or off. When forming a white image, the light emission data Data is "0" so that the light emitting element 350 does not emit light. When forming a black image, the light emission data Data is "1" so that the light emitting element 350 emits light.

The number of light emission data output in one cycle of the timing signal Lsync_in is the same as the number m of the light emitting elements 350 forming the light emitting element group 201 . From time t1 when the timing signal Lsync_in for the first line is enabled to time t2, a front margin is formed in the main scanning direction. Light emission data Data of "0" are output for the number of pixels corresponding to the front margin.

From time t2 to time t3, one line's worth of light emission data Data of "0" or "1" is output for each pixel. From time t3 to time t4, a trailing blank is formed in the main scanning direction. That is, the light emission data Data of "0" are output by the number of pixels corresponding to the rear margin.

A period from time t4 to time t5 is a period corresponding to the interval (line interval) between the first line and the second line. At time t5, the timing signal Lsync_in is enabled again to start the exposure of the second line.

After that, from time t5 to time t6, the front margin of the second line is formed (light emission data Data is 0). From time t6 to time t7, one line of light emission data Data of "0" or "1" according to the image data of the second line is output.

An electrostatic latent image for one page is formed on the photosensitive drum 102 by repeating the series of processes as described above.

FIG. 10 shows an electrostatic latent image formed on the photosensitive drum 102 based on the light emission data Data and the timing signal Lsync_in shown in FIG. t1 to t7 shown in FIG. 10 coincide with t1 to t7 in FIG.

The horizontal direction of the photosensitive drum 102 in FIG. 10 represents the main scanning direction. The positions p1 to p2 of the photosensitive drum 102 represent the width of the short side of the A4 sheet. The light emitting element group 201 has a plurality of light emitting elements 350 (eg, LEDs) exposed along the short side direction of the A4 sheet from positions p1 to p2.

The vertical direction of the photosensitive drum 102 in FIG. 10 represents the sub-scanning direction. The photosensitive drum 102 rotates around the rotating shaft 601 at a constant angular velocity. At time t1, the timing signal Lsync_in for the first line is enabled. In order to form the front margin in the main scanning direction from time t1 to time t2, the image data of a plurality of pixels corresponding to the front margin are set to "0". As a result, the light emitting element 350 facing the front blank in the light emitting element group 201 does not emit light. From time t2 to time t3, one line of light emission data Data of "0" or "1" is output. As a result, the light emitting element 350 in the light emitting element group 201 facing the image section for one line is turned on or off according to the light emission data Data. In order to form the rear margin in the main scanning direction from time t3 to time t4, the image data of a plurality of pixels corresponding to the rear margin are set to "0". As a result, the light emitting element 350 facing the rear blank in the light emitting element group 201 does not emit light.

After that, the exposure of the second line is started from time t5. Here, the period from time t4 to time t5 corresponds to the line interval. During the period from time t4 to time t5, sub-scanning of the exposure head 106 is realized by rotating the photosensitive drum 102 . That is, the exposure position of the light emitting element group 201 moves from the first line to the second line on the photosensitive drum 102 . At time t5, timing signal Lsync_in is enabled to start the exposure of the second line.

From time t5 to time t6, the front margin of the second line is formed in the same manner as the first line. From time t6 to time t7, the image of the second line is formed in the same manner as the image of the first line. By repeating such exposure processing, an electrostatic latent image for one page is formed on the photosensitive drum 102 .

When the peripheral speed of the photosensitive drum 102 is slower than the peripheral speed of the transfer belt 111, it is necessary to lengthen the time corresponding to the line interval (the time from time t4 to time t5). On the other hand, when the peripheral speed of the photosensitive drum 102 is faster than the peripheral speed of the transfer belt 111, it is necessary to set a longer time corresponding to the line interval.

<Exposure for one page and light emission control signal>
FIG. 11 shows the relationship between the exposure for one page and the light emission control signal. At time t1, a page top signal Top is input to the control signal generator 802 from the printer controller (the printer controller 1400 shown in FIG. 14). A page top signal Top_in is generated at time t2. Although the page top signal Top_in is not shown in FIG. 8, it corresponds to the page top signal Top delayed by the internal delay time. The page top signal Top_in is an internal signal in the control signal generation unit 802, and is a signal for starting the output of the light emission control signal for each page. When the page top signal Top_in is enabled at time t2, the timing signal Lsync_in is enabled. As a result, the exposure of the uppermost line of the sheet P can be started. Note that the page top signal Top_in is enabled (set to "0" in the embodiment) for a period of time corresponding to one cycle of the clock signal clk.

At time t2, timing signal Lsync_in is enabled, but each page is provided with a top margin. Therefore, the image data from time t2 to time t3 are all "0". At time t3, exposure processing (actually non-exposure) of a plurality of lines corresponding to the upper margin ends.

From time t3 to time t4, exposure processing of a plurality of lines corresponding to an image section is performed. The light emission data Data is continuously output in synchronization with the timing signal Lsync_in. After that, from time t4 to time t5, all image data become "0", and a margin (bottom margin) is formed at the bottom of the page. Note that the last line of the plurality of lines forming the bottom margin corresponds to the exposure timing of the bottommost line of the sheet P. FIG. Therefore, at time t5, the output of the timing signal Lsync_in and the light emission data Data is stopped.

Time t5 to time t7 correspond to the distance (page interval) from the trailing edge of the sheet P of the preceding first page to the leading edge of the sheet P of the succeeding second page. The page top signal Top of the next page is enabled at time t6, and the page top signal Top_in is also enabled at time t7. An upper margin is formed from time t7 to time t8. After that, the same exposure processing as that for the first page is performed for the second page.

A page top signal Top_in for the second page is also generated based on the page top signal Top. The printer control unit monitors the status of each unit that performs image reading, image formation, fixing, and feeding/conveyance based on the rotational speed of the photosensitive drum 102, the rotational speed of the transfer belt 111, the operation timing of the registration rollers 110, and the like. there is Based on the monitoring result, the printer control unit 1400 generates a page top signal Top so that the entire image forming apparatus 1 can maintain harmony and operate smoothly.

<Correction of Line Spacing to Reduce Density Unevenness>
As already described, when the rotary shaft 601 is displaced from the center of the photoreceptor drum 102, the relative velocity of the surface of the photoreceptor drum 102 with respect to the surface of the transfer belt 111 does not become zero, resulting in uneven density. Therefore, a correction method for reducing density unevenness will be described below.

FIG. 12A shows a correction method when the peripheral speed of the photosensitive drum 102 is lower than the peripheral speed of the transfer belt 111 . Since the rotating shaft 601 is offset from the center of the photosensitive drum 102 , the surface portion of the photosensitive drum 102 where the distance between the rotating shaft 601 and the surface of the photosensitive drum 102 is the shortest is in contact with the transfer belt 111 . Therefore, the peripheral speed of the photosensitive drum 102 becomes relatively low. In order to transfer a plurality of lines of toner onto the transfer belt 111 at the expected line spacing, the line spacing of the electrostatic latent image on the photosensitive drum 102 should be set to be narrower than the specified spacing. As a result, the line spacing of the toner image transferred onto the transfer belt 111 becomes the expected line spacing.

FIG. 12B shows a correction method when the peripheral speed of the photosensitive drum 102 is higher than the peripheral speed of the transfer belt 111 . Since the rotating shaft 601 is offset from the center of the photoreceptor drum 102 , the surface portion of the photoreceptor drum 102 with the longest distance from the rotating shaft 601 is in contact with the transfer belt 111 . Therefore, the peripheral speed of the photosensitive drum 102 is relatively high. In order to transfer a plurality of lines of toner onto the transfer belt 111 at the expected line spacing, the line spacing of the electrostatic latent image on the photosensitive drum 102 should be set wider than the specified spacing. As a result, the line spacing of the toner image transferred onto the transfer belt 111 becomes the expected line spacing.

The memory 804 stores correction data (correction values) for correcting the line spacing. The control signal generator 802 corrects the line spacing by controlling the output timings of the light emission data Data and the timing signal Lsync_in based on the correction data. Specifically, when exposing a surface section where the peripheral speed of the photosensitive drum 102 decreases, the control signal generator 802 shortens the time corresponding to the line interval. That is, the control signal generation unit 802 narrows the line spacing of the electrostatic latent image on the photosensitive drum 102, thereby correcting the line spacing of the toner image transferred onto the transfer belt 111 to the expected line spacing. .

On the other hand, when exposing a surface section where the peripheral speed of the photosensitive drum 102 increases, the control signal generator 802 lengthens the time corresponding to the line interval. That is, by widening the line spacing of the electrostatic latent image on the photosensitive drum 102, the line spacing of the toner image transferred to the transfer belt 111 is corrected to the expected line spacing.

<Correction data>
As an example, the correction data is acquired in the assembly process of the image forming apparatus 1 and stored in the nonvolatile memory 804 . Specifically, while the rotating shaft 601 of the photoconductor drum 102 is rotating at a constant angular velocity, the peripheral velocity of the photoconductor drum 102 is measured for each predetermined rotation angle (rotation phase). For example, the peripheral speed is measured once. When the photosensitive drum 102 is a perfect circle and the rotating shaft 601 is at the center, the difference between the peripheral speed (ideal value) of the photosensitive drum 102 and the measurement result is stored in the memory 804 as correction data. For example, correction data is expressed as a signed percentage.

When exposing a surface section where the difference between the ideal and the measured peripheral velocity is -1%, the line spacing in that surface section is reduced by 1%. When exposing a surface section where the difference between the ideal and the measured peripheral velocity is +5%, the line spacing in that surface section is increased by 5%.

FIG. 13 is a side view of the photosensitive drum 102. FIG. A plurality of optical marks (encoder memory 1301) are printed on the surface of the photosensitive drum 102 at regular intervals using paint or the like. The interval between two adjacent encoder memories 1301 is, for example, 0.1 mm. mm is an abbreviation for millimeter. Furthermore, an HP mark 1302 is printed at one location on the surface of the photosensitive drum 102 . HP is an abbreviation for home position. The HP mark 1302 serves as an absolute reference for the rotation angle (rotation phase) when the photosensitive drum 102 is rotating.

Next, a method for measuring the peripheral speed of the photosensitive drum 102 at intervals of a predetermined angle (eg, 1 degree) will be described. The photosensitive drum 102 continues to rotate at a constant angular velocity during printing. As an example, it is assumed that the photoreceptor drum 102 rotates once every 3.6 seconds. In order to measure the peripheral velocity for each degree of rotation, it is sufficient to measure how many mm the surface moves in 0.01 seconds. Encoder memories 1301 are printed on the surface of the photosensitive drum 102 at intervals of 0.1 mm. Therefore, the optical sensor 805 installed facing the surface of the photosensitive drum 102 counts the number of encoder memories 1301 passing through the optical sensor 805 every 0.01 seconds. For example, assume that 10 encoder memories 1301 pass in 0.01 seconds. In this case, the peripheral speed of the photosensitive drum 102 when the rotating shaft 601 rotates once is 100 mm/sec.

In this way, the peripheral speed is measured once with the HP mark 1302 as a reference. Furthermore, by subtracting the measured value of each peripheral speed from the ideal value, the correction data for each degree based on the HP mark 1302 is calculated. As described above, the correction data is expressed as a plus/minus ratio (percentage). For example, assume the ideal peripheral velocity is 100 mm/sec and the measured peripheral velocity is 105 mm/sec. In this case the measured value is only 5% higher than the ideal value. Therefore, the correction data stored in memory 804 is +5%. If the ideal peripheral velocity is 100 mm/sec and the measured peripheral velocity is 104 mm/sec, the correction data is +4%. If the ideal peripheral velocity is 100 mm/sec and the measured peripheral velocity is 97 mm/sec, the correction data is -3%. Thus, if the correction data is a positive value, the line interval is corrected to increase. If the correction data is a negative value, the line spacing is corrected to decrease.

Correction data is stored at a specific address in memory 804 . That is, the address is associated with the rotational phase relative to the HP mark 1302 . This makes it possible to easily and accurately acquire correction data corresponding to a specific rotational phase.

At an address 0000h of the memory 804, correction data for one rotation from the HP mark 1302 is stored. At address 0001h, correction data during rotation from 1 degree to 2 degrees is stored. At address 0002h, correction data during rotation from 2 degrees to 3 degrees is stored. In this manner, the correction data for each rotation phase with the HP mark 1302 as a reference is stored in the memory 804 in order. According to this storage method, the correction data for the rotation from 359 degrees to the HP mark 1302 is stored at address 0167h.

For example, correction data is stored as 8-bit data. The 1st bit of the 8 bits is a sign bit indicating plus/minus. The remaining 7 bits indicate a numerical value (%). A sign bit of "1" indicates plus and a sign bit of "0" indicates minus. For example, correction data indicating that the peripheral speed is about 0.1% higher is expressed as 10000001b (81h). Correction data indicating that the peripheral speed is about 10% slower is expressed as 01100100b (64h). By using such a method of expression, it is possible to correct the difference in peripheral speed from -12.7% to +12.7%.

By increasing the number of bits of the correction data, even higher precision correction becomes possible. Further, by increasing the number of encoder memories 1301, narrowing the interval between the encoder memories 1301, and narrowing the measurement intervals (angular velocities), highly accurate correction becomes possible.

<Details of correction method using correction data>
FIG. 14 is a diagram showing the internal configuration of control signal generation section 802 . The Top_in generation circuit 1401 generates a page top signal Top_in delayed by the internal delay time from the page top signal Top input from the printer control unit 1400 and outputs it to the Lsync generation circuit 1402 . The Lsync generation circuit 1402 recognizes the start of data output for each page based on the fall of the page top signal Top_in, and periodically generates the timing signal Lsync. Timing signal Lsync may be referred to as a line synchronization signal. The output period of the timing signal Lsync is, for example, the sum of the time for causing the light emitting element 350 of the light emitting element group 201 to emit light and the delay time corresponding to the ideal line interval. That is, the timing signal Lsync is output at equal intervals (constant cycle).

Timing signal Lsync is output to output circuit 1405 and line counter 1403 . A line counter 1403 is reset by the HP signal from the optical sensor 805 and counts the line number with reference to the home position. The output circuit 1405 generates the timing signal Lsync_in based on the correction data read out from the memory 804 and the count value of the line counter 1403 . That is, the output circuit 1405 corrects the output timing of the timing signal Lsync_in based on the timing at which the timing signal Lsync is input, based on the correction data. As a result, the line spacing is corrected based on the correction data.

The address counter 1404 sets the counted address in the memory IF 1408 . IF is an abbreviation for interface. The memory IF 1408 reads the correction data from the address indicated by the address counter 1404 and sets it in the output circuit 1405 .

A margin control circuit 1406 controls the sizes of the top, bottom, left, and right margins of each sheet P. FIG. For example, the margin control circuit 1406 creates margin data based on margin information set by the user or the like, and outputs the margin data to the light emission control circuit 1407 . The margin data indicates the number of lines in the top margin, the number of lines in the bottom margin, the number of pixels in the front margin of each line, and the number of pixels in the rear margin. The light emission control circuit 1407 sets the light emission data Data of the pixels to be blank to 0 based on the blank data.

The light emission control circuit 1407 creates light emission data Data by adding margins based on the margin data to the image data output from the image processing circuit 801 . The light emission data Data is adjusted to match the number of light emitting elements 350 in the light emitting element group 201, and is output based on the timing signal Lsync_in. The light emission data Data is adjusted to match the number of lines forming one page, and is output based on the timing signal Lsync_in.

FIG. 15 shows the positional relationship between the exposure head 106 and the optical sensor 805. As shown in FIG. A contact point (transfer position) between the transfer belt 111 and the photosensitive drum 102 is defined as 0 degree. The optical sensor 805 is installed at a position of 240 degrees in the rotation direction of the photosensitive drum 102 . The exposure head 106 is installed at a position of 270 degrees. The photosensitive drum 102 is controlled to rotate at a constant angular velocity (eg, one rotation in 3.6 seconds). When the rotating shaft 601 of the photoreceptor drum 102 is not displaced, the peripheral speed of the photoreceptor drum 102 matches the peripheral speed of the transfer belt 111 . An HP mark 1302 is printed on the surface of the photosensitive drum 102 . When the optical sensor 805 detects passage of the HP mark 1302, the optical sensor 805 outputs "1" as the HP signal.

It is assumed in FIG. 15 that the axis of rotation 601 is displaced upwards. When the HP mark 1302 coincides with the detection position of the optical sensor 805, the point where the photoreceptor drum 102 and transfer belt 111 are in contact is the point where the peripheral speed of the photoreceptor drum 102 is the slowest. The point on the opposite side of 180 degrees from that point is the point where the peripheral speed of the photosensitive drum 102 is the fastest. Since the exposure timing (line interval) of the exposure head 106 is corrected based on the correction data, density unevenness of the toner image on the transfer belt 111 is reduced.

FIG. 16 is a diagram for explaining correction data read from the memory 804. As shown in FIG. The print start signal is a signal indicating that the image forming apparatus 1 starts a print operation in response to a copy or print instruction input by the user. A period in which the print start signal is "1" indicates that the image forming apparatus 1 is in a printing state. When the print start signal becomes "1", power is supplied to the printer engine 103, and rotation of the photosensitive drum 102 is started.

The synchronization start signal is a trigger signal for synchronizing reading of correction data from the memory 804 with the rotation of the photosensitive drum 102 after the rotation of the photosensitive drum 102 is started. After the synchronous start signal becomes "1", reading of the correction data from the memory 804 is started at the timing (time t1) when the HP signal is first input.

The peripheral speed of the photosensitive drum 102 in FIG. 16 repeatedly changes between 105 mm/sec and 95 mm/sec. The period of change of this peripheral speed is 3.6 seconds. This corresponds to the time from time t2 to time t4. It is assumed that the ideal peripheral velocity of the photosensitive drum 102 is 100 mm/sec. Therefore, the correction data takes values from +5% to -5%.

When the HP mark 1302 passes the optical sensor 805 at time t1, the HP signal becomes "1". Using time t1 as a reference, the time when the photosensitive drum 102 rotates 60 degrees is t2. The time difference from time t1 to time t2 is 0.6 seconds. At time t2, the peripheral speed of the photosensitive drum 102 becomes the fastest. The time when the photoreceptor drum 102 further rotates 180 degrees from there is t3. The time difference from time t2 to time t3 is 1.8 seconds. The peripheral speed becomes the slowest at time t3. The time when the photosensitive drum 102 rotates 180 degrees from there is t4. At time t4, the peripheral speed becomes the fastest again.

"Memory address A" and "Correction data A" in FIG. 16 indicate the memory address and the correction data assuming that the positions of the exposure head 106 and the optical sensor 805 match. . When the HP signal becomes "1" at time t1, the memory IF 1408 reads the correction data at address 0000h specified as the address of the memory 804. FIG. The address counter 1404 counts up by 1 every 0.01 seconds from 0000h to 0167h. As a result, the correction data synchronized with the rotational phase of the photoreceptor drum 102 is read with reference to the timing at which the HP mark 1302 passes the optical sensor 805 .

At time t5, the address counter 1404 counts up to address 0167h. At time t6, the count value of the address counter 1404 returns to 0000h. Address counter 1404 may be designed to automatically wrap from address 0167h to 0000h. As a result, the timing at which the address becomes 0000h coincides with the timing at which the optical sensor 805 detects the HP mark 1302 . As a result, appropriate correction data corresponding to the rotational phase of the constantly rotating photosensitive drum 102 is repeatedly read out.

For example, at time t2, the peripheral speed is 105 mm/sec, so the correction data (=+5%) stored at address 003bh in memory 804 is read. At time t3, since the peripheral speed is 95 mm/sec, the correction data (=-5%) stored at address 00EFh of memory 804 is read.

It is assumed that the timing of detecting the HP mark 1302 and the timing of reading the correction data from the memory 804 coincide with the position of the exposure head 106 and the position of the optical sensor 805 . However, in practice, as shown in FIG. 15, the exposure head 106 may be arranged at a position 30 degrees ahead of the optical sensor 805 . In this case, the generation of the light emission control signal and the reading of the correction data need to be executed at the timing considering the position of the optical sensor 805 and the position of the exposure head 106 .

At time t7 when the photoreceptor drum 102 rotates 30 degrees from time t1 when the optical sensor 805 detects the HP mark 1302, readout of correction data is started from the address 0000h of the memory 804. FIG. The time difference from time t1 to time t7 is 0.3 seconds. Thereafter, from time t7 to time t8, the memory IF 1408 reads the correction data while counting up one dress every 0.01 seconds to address 0167h. At time t9, the count value returns to 0000h. It should be noted that the address counter 1404 is designed to start counting up with address 0149h as the initial value at time t1.

As described with reference to FIGS. 14 and 9, the control signal generator 802 adds a blank portion to the image data input from the image processing circuit 801 to generate the light emission data Data. Also, the control signal generator 802 outputs the image data of each line in synchronization with the timing signal Lsync_in. The length of each cycle of timing signal Lsync_in is adjusted using correction data input from memory 804 . Thereby, the length of the line interval is appropriately corrected. Specifically, output circuit 1405 uses line counter 1403 to adjust the length of each cycle of timing signal Lsync_in.

The line counter 1403 is reset when the HP signal is input. That is, the count value becomes 0. Furthermore, the line counter 1403 counts up by one each time the timing signal Lsync is input.

A count value of the address counter 1404 is supplied to the memory IF 1408 and used as a read address of the memory 804 . In the arrangement of the exposure head 106 and the optical sensor 805 as shown in FIG. 15, the count value of the address counter 1404 is set to 329 (0149h) by the HP signal. After that, the address counter 1404 counts up by 1 every 0.1 seconds. In the next cycle when the count value reaches 359 (0167h), the HP signal is input again and the address counter 1404 is set to 329 (0149h). Thereafter, the address counter 1404 repeatedly counts up to 359 (0167h) every 0.1 seconds.

By the way, the number of lines exposed in 0.1 second is determined according to the resolution in the sub-scanning direction. In this example, it is assumed that 30 lines are exposed during 0.1 seconds. From the time when the optical sensor 805 detects the HP mark 1302 until 0.1 seconds have passed, the line spacing of the 1st to 30th lines is corrected based on the correction data read from the address 0149h of the memory 804. be done. From the 31st line to the 60th line, the line spacing is corrected based on the correction data read from the address 014Ah. By repeating this, the line spacing for the line to be exposed is corrected based on appropriate correction data.

As described above, the output circuit 1405 receives signals at equal intervals every time that is the sum of the lighting time of the light emitting element 350 and the delay time corresponding to the ideal line interval. The output circuit 1405 corrects the line spacing by multiplying the ideal line spacing by the correction data, and outputs the timing signal Lsync_in according to the corrected line spacing. That is, the output circuit 1405 outputs the timing signal Lsync_in at the timing according to the correction data, using the input timing signal Lsync as a reference.

FIGS. 17A to 17F are diagrams for explaining the results of line spacing correction. A plurality of lines parallel to the main scanning direction are formed at different positions in the sub scanning direction. Note that the image data output from the image processing circuit 801 has a constant line interval in the sub-scanning direction.

FIG. 17A shows the timing signal Lsync_in output without correcting the line interval. FIG. 17B shows a toner image formed on the transfer belt 111 without correcting the line spacing. In surface sections t1, t3, and t5 where the peripheral speed of the photosensitive drum 102 is faster than the peripheral speed of the transfer belt 111, the image on the transfer belt 111 is dark. On the other hand, in the surface sections t2, t4, and t6 where the peripheral speed of the photosensitive drum 102 is relatively slow, the image on the transfer belt 111 becomes light.

FIG. 17C shows the timing signal Lsync_in corrected for the line interval. In the surface sections t1, t3, and t5 where the peripheral speed is high, the timing signal Lsync_in is corrected based on the correction data so that the line interval is widened. On the other hand, in the surface sections t2, t4, and t6 where the peripheral speed is slow, the timing signal Lsync_in is corrected based on the correction data so that the line spacing becomes narrower.

However, in this embodiment, the contact position between the photosensitive drum 102 and the transfer belt 111 and the position of the exposure head 106 are different by about 90 degrees. Therefore, as shown in FIG. 17D, the timing signal Lsync_in is output at a timing earlier by 0.9 seconds.

As a result, as shown in FIG. 17(E), an electrostatic latent image (toner image) whose line spacing has been corrected is transferred to the transfer belt at a timing rotated by about 90 degrees (0.9 seconds) from the exposure timing. Reach 111.

Finally, as shown in FIG. 17F, an image is formed on the transfer belt 111 at ideal line intervals.

Next, the correction of density unevenness caused by the eccentricity of the rotary shaft 601 and the output of the light emission control signal when printing one page will be described in detail with reference to FIG. At time t 1 , the print start signal becomes “1” and power is supplied to the printer engine 103 . At time t2, the synchronous start signal becomes "1". After that, the first HP signal is input at time t3.

The page top signal Top is input at time t4, and the page top Top_in is output at time t5 delayed by the internal delay time. Output of the timing signals Lsync and Lsync_in is started in synchronization with the page top Top_in.

From time t5 to time t6, light emission data Data (=0) of the number of lines corresponding to the upper margin is output. From time t6 to time t8, light emission data Data of 0 or 1 is output. From time t8 to time t9, light emission data Data (=0) for the number of lines corresponding to the bottom margin is output. That is, printing of one page is completed at time t9.

While forming an image of one page, the line spacing for each line is corrected according to correction data synchronized with the rotation phase of the photosensitive drum 102 . As a result, the line spacing of the toner image transferred onto the transfer belt 111 is maintained at a constant spacing.

When the print job is completed in one page, the output of the timing signal Lsync_in stops, and the synchronization start signal and the print start signal become "0". On the other hand, if there is a next page, the page top signal Top is input again at time t10. A page top signal Top_in is output at time t11 when a time corresponding to the page interval has elapsed from time t10. After that, the printing operation for the second and subsequent pages is repeated in the same manner as for the first page.

According to this embodiment, density unevenness caused by the eccentricity of the rotating shaft 601 that holds the photosensitive drum 102 is corrected. In this example, the correction data stored in memory 804 was the ratio of the measured circumferential velocity to the ideal circumferential velocity. However, the correction data may be other values. For example, the correction data may be the time difference between the ideal line spacing and the measured line spacing. Further, the correction data may be the time itself indicating the line interval corrected in advance.

In this embodiment, a method for correcting density unevenness caused by the eccentricity of the rotating shaft 601 is described. However, even if the cross-sectional shape of the photosensitive drum 102 is not a perfect circle, the correction method of this embodiment can be applied. This is because there is no difference between the two in that the peripheral speed changes according to the rotational phase of the photosensitive drum 102 .

<Technical Concept Derived from Examples>
[Viewpoint 1]
The photoreceptor drum 102 is an example of a photoreceptor that has a rotating shaft 601 and is driven to rotate about the rotating shaft 601 . The charger 107 functions as a charging unit that uniformly charges the photoreceptor. The exposure head 106 is an example of exposure means having a plurality of light-emitting elements 350 arranged along a direction crossing the rotation direction of the photosensitive member. The exposure head 106 exposes the surface of the photosensitive member at least one line at a time with light emitted from the plurality of light emitting elements 350 to form an electrostatic latent image. The developing device 108 functions as developing means for developing the electrostatic latent image with toner to form a toner image. The transfer belt 111 conveys the sheet P onto which the toner image is transferred, and functions as a conveying unit arranged to face the photosensitive member.

A control signal generation unit (processor) 802 functions as control means for controlling the exposure means. The control signal generation unit 802 forms an electrostatic latent image so as to offset changes in the moving speed of the surface of the photoreceptor caused by the eccentricity of the rotating shaft 601 of the photoreceptor (or the fact that the cross-sectional shape is not circular). Correct the line spacing of If the rotating shaft 602 of the photoreceptor is eccentric or the cross-sectional shape of the photoreceptor is not perfectly circular, the distance from the rotating shaft 601 to the peripheral surface of the photoreceptor varies, and the peripheral speed changes for each rotational phase of the photoreceptor. Resulting in. This causes partial expansion and contraction of the image in the sub-scanning direction and uneven density that periodically repeats in the sub-scanning direction. According to this embodiment, the line spacing is corrected so as to cancel out variations in peripheral speed. As a result, image density unevenness caused by the eccentricity of the rotating shaft 601 of the photoreceptor is reduced.

[Viewpoint 2]
The control signal generator 802 relatively narrows the line spacing in the rotational phase in which the distance from the rotating shaft 601 to the surface is relatively short. The control signal generator 802 relatively widens the line interval in the rotation phase in which the distance from the rotation axis 601 to the surface is relatively long. As a result, density unevenness in the image may be reduced.

[Viewpoint 3]
The control signal generator 802 relatively narrows the line spacing in the rotation phase in which the moving speed of the surface of the photosensitive member is lower than the moving speed of the surface of the conveying means. The control signal generator 802 relatively widens the line spacing in the rotational phase in which the moving speed of the surface of the photoreceptor increases more than the moving speed of the surface of the conveying means. As a result, density unevenness in the image may be reduced.

[Viewpoint 4]
The non-volatile memory 804 is an example of storage means that stores a correction value for correcting line spacing. The control signal generator 802 may correct the line spacing using the correction value read from the storage means. Density unevenness caused by the eccentricity of the rotating shaft 601 is reproducible. Therefore, density unevenness is reduced by using correction values obtained in advance.

[Viewpoint 5]
The correction value may be acquired in the assembly process of the image forming apparatus 1 and written in the storage means. This is because the eccentricity of the rotating shaft 601 is determined in the process of assembling the image forming apparatus 1 .

[Viewpoint 6]
The optical sensor 805 is an example of detection means for detecting the rotational phase of the photosensitive member. The control signal generation unit 802 may read out from the storage means a correction value corresponding to the rotation phase detected by the detection means, and use the correction value to correct the line spacing for each rotation phase. The absolute rotational phase of the photoreceptor can be found by using the detection means. Therefore, it becomes possible to use a correction value associated with the absolute rotational phase of the photoreceptor, and density unevenness can be reduced with higher accuracy.

[Viewpoint 7]
The photoreceptor may have a reference mark (eg, HP mark 1302) provided on the surface of the photoreceptor to indicate the rotational phase reference of the photoreceptor. The detection means is configured to, when detecting the reference mark, output a detection signal indicating that the reference mark has been detected to the control means. The control signal generator 802 may recognize the rotation phase of the photoreceptor based on the detection signal. Although HP mark 1302 has been described as an optical mark detectable by optical sensor 805, this is only an example. For example, magnetic marks (eg, coils, magnets) detectable by magnetic sensors such as Hall elements may be employed. Alternatively, an encoder that detects the absolute rotational phase of rotating shaft 601 may be employed.

[Viewpoint 8]
The reference mark may be a mark fixed on the surface of the photoreceptor during the manufacturing process of the photoreceptor. Examples of fixing methods include pasting, printing (laser engraving, printing with paint), engraving, and the like.

[Viewpoint 9]
The address counter 1404 is an example of an address counter that counts up based on the detection signal. The control signal generator 802 may read out the correction value corresponding to the rotational phase from the storage area indicated by the count value of the address counter via the memory IF 1408 . This will enable accurate acquisition of the correction value corresponding to the rotational phase.

[Viewpoint 10]
The address counter 1404 is set to an initial count-up value according to the difference in rotation angle between the exposure position of the exposure means and the detection position of the detection means in the rotation direction of the photosensitive member. For example, the initial value may be set to 0149h as shown in FIG.

[Viewpoint 11]
The Lsync generation circuit 1402 and the output circuit 1405 function as generation means for generating a timing signal indicating exposure start timing for each line. The control signal generation unit 802 functions as correction means for correcting the line interval by correcting the timing of outputting the timing signal based on the correction value.

[Viewpoint 12]
The line counter 1403 is an example of a line counter that counts the timing signal for each line generated by the generation means with reference to the start signal indicating the start of one page. The control signal generator 802 may correct the timing of outputting the timing signal based on the count value of the line counter and the correction value.

[Viewpoint 13]
As shown in FIG. 17(D), the timing signal corrected by the correction means corresponds to the difference in rotation angle between the exposure position of the exposure means in the rotation direction of the photoreceptor and the contact position of the sheet with respect to the photoreceptor. It is output earlier than the timing.

[Viewpoint 14]
The correction value may be changed every predetermined number of lines. That is, a common (same) correction value may be applied to a predetermined number of lines. As described above, a correction value may be stored in the memory 804 for each rotation angle of the photosensitive drum 102 . In this case, a plurality of main scanning lines are drawn by exposure on the circumferential surface of the photosensitive drum 102 corresponding to a rotation angle of 1 degree. Therefore, the speed at which the line counter 1403 counts up by one is faster than the speed at which the address counter 1404 counts up by one. As a result, a common (same) correction value is applied to a predetermined number of lines. However, if the storage area of the memory 804 has enough space, one correction value may be prepared for one main scanning line.

[Viewpoint 15]
The light emission control circuit 1407 is an example of output means for outputting image data for lighting a plurality of light emitting elements based on the timing signal.

[Viewpoint 16]
The conveying means (eg, transfer belt 111) may be an endless belt that is driven to rotate. Although the toner image is transferred from the photosensitive drum 102 to the sheet P in FIG. 1, this is merely an example. A toner image may be transferred from the photosensitive drum 102 onto the sheet P onto an intermediate transfer member (eg, an intermediate transfer belt).

The invention is not limited to the embodiments described above, and various modifications and variations are possible without departing from the spirit and scope of the invention. Accordingly, the claims are appended to make public the scope of the invention.

102: photoreceptor drum, 107: charger, 106: exposure head, 108: developer, 111: transfer belt, 802: control signal generator

Claims (16)

a photoreceptor having a rotating shaft and driven to rotate about the rotating shaft;
charging means for uniformly charging the photoreceptor;
a plurality of light emitting elements arranged along a direction crossing the rotation direction of the photoreceptor, and exposing the surface of the photoreceptor at least one line at a time with light output from the plurality of light emitting elements; an exposure means for forming an electrostatic latent image with
a developing means for developing the electrostatic latent image with toner to form a toner image;
a conveying means for conveying a sheet onto which the toner image is transferred and arranged to face the photoreceptor;
and a control means for controlling the exposure means,
The control means forms the electrostatic latent image so as to offset a change in moving speed of the surface of the photoreceptor caused by a change in the distance from the rotational axis of the photoreceptor to the surface of the photoreceptor. An image forming apparatus characterized by correcting a line interval between lines. The control means is
In a rotation phase in which the distance from the rotation axis to the surface is relatively short, the line spacing is relatively narrowed,
In a rotation phase in which the distance from the rotation axis to the surface is relatively long, the line spacing is relatively widened;
2. The image forming apparatus according to claim 1, wherein: The control means is
relatively narrowing the line spacing in a rotation phase in which the speed of movement of the surface of the photoreceptor is lower than the speed of movement of the surface of the conveying means;
relatively widening the line interval in a rotation phase in which the speed of movement of the surface of the photoreceptor is higher than the speed of movement of the surface of the conveying means;
2. The image forming apparatus according to claim 1, wherein: further comprising storage means for storing a correction value for correcting the line spacing;
4. The image forming apparatus according to claim 1, wherein the control means corrects the line spacing using the correction value read from the storage means. 5. The image forming apparatus according to claim 4, wherein the correction value is acquired in an assembly process of the image forming apparatus and written into the storage means. further comprising detection means for detecting a rotation phase of the photoreceptor;
The control means reads the correction value corresponding to the rotation phase detected by the detection means from the storage means, and corrects the line spacing for each rotation phase using the correction value. The image forming apparatus according to claim 4 or 5. The photoreceptor has a reference mark provided on the surface of the photoreceptor that indicates a reference of the rotation phase of the photoreceptor,
When the detection means detects the reference mark, the detection means is configured to output a detection signal indicating that the reference mark has been detected to the control means,
7. An image forming apparatus according to claim 6, wherein said control means is configured to recognize the rotational phase of said photosensitive member based on said detection signal. 8. The image forming apparatus according to claim 7, wherein the reference mark is a mark fixed on the surface of the photoreceptor during the manufacturing process of the photoreceptor. further comprising an address counter that counts up with reference to the detection signal;
9. The image forming apparatus according to claim 7, wherein said control means reads said correction value corresponding to said rotational phase from a storage area indicated by a count value of said address counter. The address counter sets an initial count-up value according to a difference in rotation angle between the exposure position of the exposure means in the rotation direction of the photoreceptor and the detection position of the detection means in the rotation direction of the photoreceptor. 10. The image forming apparatus according to claim 9, wherein: further comprising generating means for generating a timing signal indicating exposure start timing for each line;
11. The apparatus according to any one of claims 4 to 10, wherein said control means includes correction means for correcting said line interval by correcting the timing of outputting said timing signal based on said correction value. Image forming device. further comprising a line counter for counting the timing signal for each line generated by the generating means with reference to a start signal indicating the start of one page;
12. The image forming apparatus according to claim 11, wherein said correction means corrects the timing of outputting said timing signal based on the count value of said line counter and said correction value. The timing signal corrected by the correction means is output earlier by a timing corresponding to a difference in rotation angle between the exposure position of the exposure means in the rotation direction of the photoreceptor and the contact position of the sheet with respect to the photoreceptor. 13. The image forming apparatus according to claim 12, wherein: 14. The image forming apparatus according to claim 12, wherein the correction value is changed every predetermined number of lines. 15. The image forming apparatus according to claim 12, further comprising output means for outputting image data for lighting the plurality of light emitting elements based on the timing signal. The image forming apparatus according to any one of claims 1 to 15, wherein the conveying means is an endless belt that is driven to rotate.