JP2013020071A - Image forming device and image forming device control method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To properly keep an exposure pixel position in a main scanning direction within a main scanning range corresponding to an image area.SOLUTION: The image forming device comprises: a light source for generating a light beam; a rotary polygon mirror for making the light beam scan in a main scanning direction at a photoreceptor by rotating multiple reflective surfaces; a light decoupling part for decoupling a part of the light beam made to scan on the photoreceptor surface by the rotary polygon mirror; a light detection part arranged at a predetermined position corresponding to the inside of a main scanning range on the photoreceptor surface, for the light beam decoupled by the light decoupling part; and a clock generation part for generating a clock in a state where an exposure pixel position is corrected at the position of the light detection part, on the basis of the detection result of the light detection part.

Description

  BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image forming apparatus such as a copying machine or a printer and a control method thereof, and more particularly to an image forming apparatus having a function of scanning a light beam from a light source with a rotary polygon mirror and writing it on a recording medium such as a photosensitive member. The present invention relates to optimization of exposure pixel position.

  As an image forming apparatus, image formation of one line in the main scanning direction is performed with a light beam emitted according to image data, and image formation of the light beam for each line in the main scanning direction is repeated in the sub-scanning direction. One that forms an image for a page is known.

  As an example, an electrophotographic image forming apparatus scans a light beam emitted in accordance with image data in the main scanning direction, and simultaneously rotates an image carrier (photosensitive drum) that rotates in the sub-scanning direction. The image is formed by the light beam. In this case, a light beam is emitted as image data with reference to a clock signal (write clock) called a dot clock.

  In order to achieve high image quality with such an image forming apparatus, the main scanning direction start position and the main scanning direction end position of a plurality of light beams are aligned, that is, the main scanning direction deviation is eliminated between the light beams. It becomes important. Such deviation in the main scanning direction occurs due to uneven rotation with a period of one rotation or half rotation of the motor, a difference in flatness of each reflecting surface of the polygon mirror, and the like. Even if the deviation in the main scanning direction is slight, it is visually recognized as a horizontal streak or as a vertical line fluctuation, which causes deterioration in image quality.

  For solving such a deviation in the main scanning direction, for example, the following Patent Document 1 describes various solutions.

Japanese Patent Laid-Open No. 2002-267961

  As a result of investigations by the inventors of the present application, it has been found that there is a problem as described below even if adjustment is made to eliminate the deviation in the main scanning direction by the method described in the above patent documents.

  As a first problem, in addition to an SOS sensor for obtaining an SOS (Start Of Scan) signal on the start position side in the main scanning direction, an EOS for obtaining an EOS (End Of Scan) signal on the end position side in the main scanning direction. Sensors need to be added. For this reason, the number of parts of the image forming apparatus, such as the addition of sensors and the addition of processing circuits, is increased, leading to an increase in cost.

  As a second problem, even if the lengths of the main scanning direction from the start to the end can be made uniform by the SOS sensor and the EOS sensor, correction is made at the intermediate portion as shown in FIG. 7 due to the variation in the flatness of the polygon mirror. An error that is not performed remains as partial jitter. That is, the reflecting surfaces of the polygon mirror are not completely flat, and the flatness is different for each reflecting surface. For this reason, it has been found that even if the start and end are aligned by correcting the magnification in the main scanning direction, the pixel positions may not be aligned in the sub-scanning direction at the intermediate portion in the main scanning direction. The inventor of the present application confirms that the above-described horizontal streaks and vertical line fluctuations remain uncorrected in the actual image forming area because this error is different for each reflecting surface of the polygon mirror. It was. In particular, depending on the size of the recording paper and the image, the position away from the SOS sensor and the EOS sensor is used as the end, so that the effect of correcting the length in the main scanning direction by the SOS sensor and the EOS sensor may be reduced. found. In other words, in an image area smaller than the maximum such as an actual A4 or B5 size, a phenomenon may occur in which the start and end are not aligned.

  The present invention has been made to solve the above-described problem, and is not the alignment of the start end to the end in the main scanning direction, but the exposure pixels in the main scanning direction within the main scanning range corresponding to the actual image area. The purpose is to keep the position appropriate.

  That is, the present invention as means for solving the problems is as described below.

  (1) In the present invention, the exposure light beam emitted in accordance with each pixel of the image data is scanned in the main scanning direction of the photosensitive member, and the photosensitive member and the exposure in the sub-scanning direction orthogonal to the main scanning direction. An image forming apparatus or an image forming apparatus control method for forming an image by exposing the surface of the photosensitive member by driving the optical beam so as to move relative to the main light beam, and corresponds to a main scanning range of the surface of the photosensitive member. A light detection unit for detecting the correction light beam at a predetermined position is provided, and correction data for correcting the exposure pixel position of the exposure light beam based on the detection result of the light detection unit is stored in the storage unit in advance. The exposure light beam and a correction light beam emitted at least at a light detection position are generated from a light source, and the exposure light beam is scanned on the photosensitive member in the main scanning direction. And the correction light beam are reflected by a plurality of reflecting surfaces of a rotary polygon mirror, and the correction light beam is detected by a light detection unit disposed at a position corresponding to the main scanning range of the photoreceptor surface, A write clock whose phase is corrected so that the exposure pixel position of the exposure light beam corresponding to the position where the detection result of the light detection unit is obtained is corrected using the correction data stored in the storage unit. It is generated by a write clock generation unit.

  (2) In the above (1), the write clock generation unit uses the correction data stored in the storage unit at the timing when the correction light beam is detected by the light detection unit, and the exposure pixel A write clock whose phase is corrected so as to correct the position is generated.

  (3) In the above (1)-(2), the exposure is performed based on detection results of a reflection surface identification unit for identifying each reflection surface of the rotary polygon mirror, and the reflection surface identification unit and the light detection unit. And a storage unit that stores correction data for correcting the exposure pixel position of the light beam corresponding to each reflection surface identified by the reflection surface identification unit, and the write clock generation unit includes the reflection surface identification The exposure pixel position of the exposure light beam corresponding to the position where the detection result of the light detection unit is obtained is stored in the storage unit for each reflection surface of the rotary polygon mirror identified by the unit. A write clock whose phase is corrected so as to be corrected using the correction data is generated.

  (4) In the above (1) to (3), the write clock generation unit is configured to detect a plurality of m in the main scanning direction from the exposure pixel position of the exposure light beam corresponding to the position where the detection result of the light detection unit is obtained. In the pixel range, when the correction amount is P, a writing clock having a phase corrected by P / m is generated for each pixel.

  (5) In the above (1) to (4), the write clock generation unit corrects the exposure pixel position by changing a phase of the write clock used when the exposure light beam is emitted by the image data. Correction is performed within a range not exceeding one pixel of the image data.

  According to the present invention described above, the following effects can be obtained.

  In the present invention, correction data for correcting the exposure pixel position of the exposure light beam based on the detection result of the light detection unit is stored in the storage unit in advance, and the photosensitive surface is exposed by the plurality of reflecting surfaces of the rotating polygon mirror. When the exposure light beam is scanned in the main scanning direction on the body, the correction light beam is detected at a predetermined position corresponding to the main scanning range of the photosensitive member surface, and is scanned by the rotating polygon mirror together with the exposure light beam. The detection light beam for correction is detected by the light detection unit arranged at a predetermined position corresponding to the main scanning range on the photosensitive member surface, and the detection result of the light detection unit is obtained at the timing when the detection result of the light detection unit is obtained. The phase of the write clock is corrected by the write clock generator so as to correct the exposure pixel position of the exposure light beam corresponding to the determined position. This makes it possible to appropriately maintain the exposure pixel position in the main scanning direction within the main scanning range corresponding to the actual image area, not the coincidence between the start end and the end in the maximum range in the main scanning direction.

  Further, here, correction data that is a detection result of the light detection unit is stored in the storage unit, and the correction data stored in the storage unit is used at the timing when the correction light beam is detected by the light detection unit. Thus, the phase of the write clock can be corrected so as to correct the exposure pixel position of the exposure light beam. This makes it possible to correct the exposure pixel position in the main scanning direction for each predetermined position in the main scanning range corresponding to the actual image area, instead of matching the start and end in the maximum range in the main scanning direction. .

  In addition, by handling correction data according to the identification result of the reflection surface identification unit, for each reflection surface of the rotary polygon mirror, it corresponds to the actual image area, not the coincidence of the start and end in the maximum range in the main scanning direction The exposure pixel position in the main scanning direction can be appropriately maintained within the main scanning range.

  Further, when the correction amount is P in the range from the exposure pixel position of the exposure light beam corresponding to the position where the detection result of the light detection unit is obtained to a plurality of m pixels in the main scanning direction, P / m for each pixel. By generating the write clock with the phase corrected one by one, the influence of the correction of the exposure pixel position is dispersed in the main scanning direction and becomes inconspicuous, and a good image quality can be obtained.

  Further, as the correction of the exposure pixel position, the phase of the writing clock used when emitting the light beam by the image data is corrected within a range of less than one pulse (a range not exceeding one pixel), so that an actual image region is obtained. It is possible to appropriately maintain the exposure pixel position in the main scanning direction within the corresponding main scanning range.

1 is a block diagram illustrating a configuration of an image forming apparatus according to an embodiment of the present invention. 1 is a perspective view illustrating a configuration of an image forming apparatus according to an embodiment of the present invention. 6 is a time chart illustrating an operation of the image forming apparatus according to the embodiment of the present invention. It is explanatory drawing which shows operation | movement of the image forming apparatus of one Embodiment of this invention. It is explanatory drawing which shows operation | movement of the image forming apparatus of one Embodiment of this invention. It is explanatory drawing which shows operation | movement of the image forming apparatus of one Embodiment of this invention. It is explanatory drawing which shows the conventional shift | offset | difference characteristic.

  DESCRIPTION OF EMBODIMENTS Hereinafter, embodiments (embodiments) for carrying out the present invention will be described in detail with reference to the drawings. The image forming apparatus to which the present embodiment is applied scans a light beam emitted according to image data in the main scanning direction of the photoconductor, and in the sub-scanning direction orthogonal to the main scanning direction. The image forming apparatus forms an image by exposing the surface of the photosensitive member by driving to relatively move the surface of the photosensitive member.

[A] Configuration:
Hereinafter, the electrical configuration of the first embodiment of the image forming apparatus 100 of the present embodiment will be described in detail with reference to FIG. In this embodiment, the description will focus on the structural requirements necessary to correct the deviation in the main scanning direction of exposure by the light beam. Therefore, it is common for an image forming apparatus, and well-known constituent elements are omitted.

  The control unit 101 includes a CPU and a control program for controlling each unit of the image forming apparatus 100, and is characterized by performing the following control in addition to a normal image forming operation. That is, the control unit 101 corrects the exposure pixel position of the exposure light beam corresponding to the position where the detection result is obtained based on the detection result of the light beam at a position corresponding to the main scanning range on the photosensitive member surface. Thus, control is performed when the phase of the write clock is corrected.

  The storage unit 103 is a storage unit that stores various types of data and parameters. In this embodiment, the exposure light beam is based on the detection result of the correction light beam at a predetermined position corresponding to the main scanning range on the photoreceptor surface. Correction data for correcting the exposure pixel position is stored in advance.

  The operation unit 105 is an operation instruction input unit for inputting various instructions regarding image formation by the operator, and generates data according to the content of the instruction input and transmits the data to the control unit 101.

  The laser diode (LD) 110 is a light source that generates a light beam for performing exposure while scanning on the photosensitive member. The light beams from the laser diode 110 are an exposure light beam and a correction light beam in the same position or at regular intervals in the main scanning direction and at regular intervals in the sub-scanning direction. The exposure light beam is a light beam emitted according to each pixel of the image data, and the correction light beam is a light beam emitted at least at the light detection position. The correction light beam is used for acquisition of correction data and for synchronization during correction execution. Further, the exposure light beam may be a single beam or a plurality of beams.

  The LD drive circuit 110D is an LD drive source that generates a light emission drive signal for driving the laser diode 110 to emit light and supplies the light emission drive signal to the laser diode 110. The light emission drive signal emitted according to image data is supplied to the laser diode 110. Supply. When the laser diode 110 generates a plurality of light beams aligned in the sub-scanning direction and emitted according to image data adjacent in the sub-scanning direction, a corresponding light emission drive signal is generated and the laser diode 110 is generated. To supply.

  The polygon mirror 120 is a rotating polygon mirror that scans a light beam in the main scanning direction on the surface of the photosensitive member by a plurality of rotating reflecting surfaces. The polygon motor 120M is a rotational drive source that receives the polygon drive signal and rotates the polygon mirror 120 at a predetermined rotational speed.

  The polygon motor drive circuit 120D is a drive signal generation unit that generates a polygon drive signal for rotating the polygon mirror 120 at a predetermined rotational speed and supplies the polygon drive signal to the polygon motor 120M. The polygon motor drive circuit 120D generates a polygon drive signal so that the rotation speed of the polygon motor corresponds to the image forming speed determined by the control unit 101.

  The surface detection sensor 120S detects the surface identification mark 120P attached to the polygon mirror 120, generates a surface detection signal for identifying the reflection surface, and transmits it to the reflection surface identification unit 160. When the exposure pixel position of the exposure light beam is corrected using the detection result of the light detection unit, correction data for each reflection surface is stored in advance, and the surface detection sensor 120S and the reflection surface are corrected at the time of correction. According to the identification unit 160, correction data for each reflecting surface may be read out.

  The optical system 130 includes a cylindrical lens 130a and a collimator lens for optically processing the light beam irradiated from the laser diode 110 and reflected by the polygon mirror 120 so as to have a predetermined main scanning speed on the surface of the photoreceptor. And various optical members such as an f-θ lens 130b.

  The photosensitive member 140 performs electrostatic latent exposure according to image data by exposing a light beam scanned in the main scanning direction by rotation of the polygon mirror 120 and rotating in the sub-scanning direction perpendicular to the main scanning direction. This is a photoconductor as an image carrier on which an image is formed on the surface and the electrostatic latent image is developed to form a toner image. The charging for forming the electrostatic latent image, the toner image formation by developing the electrostatic latent image, the transfer of the toner image onto the recording paper, the fixing of the toner image on the recording paper, etc. Since it is a general device, illustration and description are omitted.

  The photosensitive member driving unit 140D is a photosensitive member rotation driving unit that rotates the photosensitive member 140 in the sub-scanning direction at a predetermined rotational speed. The photosensitive member driving unit 140D drives the photosensitive member 140 so that the number of rotations of the photosensitive member corresponds to the image forming speed determined by the control unit 101 using a motor and a speed change mechanism.

  The start-end-side light detection unit 140S provided on the start end side in the main scan direction is an SOS sensor for obtaining an SOS (Start Of Scan) signal, and on the main scan start end side on the extension line of the main scan position on the photoconductor 140. The sensor detects a light beam via the mirror 140M, and the detection result is transmitted to a reflection surface identification unit 160, a correction data generation unit 170, and a write clock generation unit 180, which will be described later.

  The light branching unit 142M is a light branching unit that reflects the correction light beam out of the light beam scanned in the surface direction of the photoconductor 140 by the polygon mirror 120 from the photoconductor 140 direction toward the correction light detection unit. . Here, the exposure light beam is directed to the photoconductor 140 as it is, and the correction light beam is reflected by the light branching unit 142 and directed to a correction light detection unit described later.

  The correction light detection units 142S1 to 142S3 are correction light detection units arranged in the main scanning range on the surface of the photoconductor 173 for the light beam branched by the light branching unit 142M. Here, a specific example of n = 3 is shown as a plurality of n correction light detection units arranged at a plurality of n different predetermined positions corresponding to the main scanning range on the surface of the photoconductor 173.

  That is, here, the correction light detection unit 142Sn is arranged at different n positions within the main scanning range on the surface of the photoconductor 173. In order to simplify the description, the correction light detection unit in the case where n = 3 is shown, but at least one correction light detection unit may be used, or two or four or more correction light units may be used. You may provide the detection part. In this case, the n-th correction light detector 142Sn is called.

  The reflection surface identification unit 160 identifies the reflection surface of the polygon mirror 120 in response to the surface detection signal from the surface detection sensor 120S and the detection result from the start-end side light detection unit 140S, and what number from the surface identification mark 120P. The reflection surface identification result, such as whether the reflection surface is, is transmitted to the control unit 101.

  The correction data generation unit 170 starts from each scanning time within the main scanning range measured between the start end side light detection unit 140S and the correction light detection units 142S1 to 142S3, or the start end side light detection unit 140S. Based on the scanning times measured in the correction light detection units 142S1 to 142S3, correction data for correcting the exposure pixel position at the position of each correction light detection unit with the writing clock phase is generated.

  The write clock generation unit 180 generates a write pixel clock (hereinafter referred to as a write clock) that is necessary when the LD drive circuit 110D generates a light emission drive signal for driving the laser diode 110 to emit light. The write clock generation unit 180 uses the correction data described above to correct the exposure pixel position of the image data and correct the exposure pixel position in the main scanning direction when generating the write clock. The correction part which correct | amends the phase of is comprised. The write clock generation unit 180 as the correction unit preferably uses a digital delay type clock generation circuit, which will be described later, in order to instantaneously correct the phase of the write clock at a predetermined timing.

  The image processing unit 190 is an image processing unit that performs various kinds of image processing necessary for image formation on the image data, and necessary data is output to the LD drive circuit 110D in synchronization with the write clock. When the laser diode 110 generates a plurality of light beams aligned in the sub-scanning direction that are emitted according to image data adjacent in the sub-scanning direction, the corresponding image data is output to the LD drive circuit 110D. The

  FIG. 2 is a perspective view showing the state of scanning of the light beam and the state of detection by the correction light detectors 142S1 to 142S3 for the configuration shown in FIG. In FIG. 2, the light branching unit 142M emits a plurality of light beams from the laser diode 110, and the one beam is branched as a correction light beam toward the correction light detection units 142S1 to 142S3 by total reflection. Show. Even in the configuration in which a larger number of light beams are emitted from the laser diode 110, one light beam may be branched as a correction light beam by the branching portion 142M.

[B] Operation:
In this embodiment, unlike the conventional frequency change, PLL phase control, and start / end alignment, it is necessary to change the phase of a predetermined amount of write clock at a predetermined timing based on correction data. Therefore, in the write clock generation unit 180 of the present embodiment, using the phase offset function of Direct Digital Synthesizer (DDS) or the digital delay method clock generation circuit proposed by the applicant in Japanese Patent Laid-Open No. 2002-278408, Based on the correction data, the phase of the write clock of a predetermined amount is changed at a predetermined timing.

[B-1] Acquisition of correction data:
Hereinafter, correction data acquisition will be described with reference to the time chart of FIG. Here, FIG. 1 and FIG. 2 illustrate the polygon mirror 120 having six reflecting surfaces, but FIG. 3 shows four polygons for ease of explanation.

  The horizontal axis of the time chart of FIG. 3 indicates the position or main scanning time (FIG. 3A) of the light detection unit, the timing of the clock before correction (FIG. 3B), and the photosensitive member 140. Exposure pixel position before correction (FIGS. 3C to 3F) formed by the light beam, correction data based on detection results by the correction light detection units 142S1 to 142S2 (FIGS. 3G to 3J) , Corrected clock timings (FIGS. 3 (k) to (n)), corrected exposure pixel positions (FIGS. 3 (o) to (r)) formed by the light beam on the photoreceptor 140, which will be described later, For each of these, the position and timing are shown in a corresponding state.

  Here, with respect to the position and timing (time), the scanning of the light beam with respect to the position is directed from the left to the right, and the time and timing are advanced from the left to the right. 3 is described as a time chart in which the horizontal positions are aligned on the sheet of FIG.

  In addition, here, the correction light detection unit 142S1 is illustrated centering on a portion where the correction light detection unit 142S1 is disposed at the first pixel in the main scanning direction image region and the correction light detection unit 142S2 is disposed at the seventh pixel in the main scanning direction image region. (FIG. 3A).

  An example is shown in which dots (pixels) formed on the surface of the photoreceptor 140 by the first surface of the polygon mirror 120 have a predetermined scanning length without misalignment (FIG. 3C). 2 shows an example in which the pixels formed on the surface of the photoconductor 140 by the two surfaces are shorter than a predetermined scanning length with a positional shift (FIG. 3D), and the surface of the photoconductor 140 is formed by the third surface of the polygon mirror 120. An example in which the formed pixels have a predetermined scanning length without misalignment is shown (FIG. 3E), and the pixels formed on the surface of the photoreceptor 140 by the fourth surface of the polygon mirror 120 have misalignment. Shows an example in which the length becomes longer than a predetermined scanning length (FIG. 3F).

  Here, in FIG. 3D and FIG. 3F, the exposure pixel position with no positional deviation is indicated by a broken line, and the difference in position between the broken line and the solid line corresponds to the positional deviation.

  The pixels formed on the surface of the photosensitive member 140 by the first surface to the fourth surface of the polygon mirror 120 having the same characteristics as those in FIGS. 3C to 3F are all 19 pixels in the main scanning direction. In this case, when the exposure pixel positions are controlled to be aligned on the main scanning front end side by a known method according to the SOS signal, the exposure pixel position shifts due to the influence of each reflection surface of the polygon mirror 120, and therefore, as shown in FIG. As described above, the positional deviation is accumulated and increased toward the rear end in the main scanning direction.

  First, as the correction data acquisition operation based on the control of the control unit 101, the laser diode 110 is driven to emit light according to the write clock from the write clock generation unit 180 without performing the correction of the present embodiment described later, and the polygon mirror 120 is moved. The light beam for correction at that time is rotated by a predetermined number of rotations, and the light detection unit 140S and the light detection units for correction 142S1 to 142S3 detect the correction light beam. Here, the correction light beam may be emitted within a range in which at least the start-end side light detection unit 140S and the correction light detection units 142S1 to 142S3 can be irradiated. Further, exposure pixel position alignment on the known main scanning front end side by the SOS signal is performed.

  Therefore, a time T01 from when the correction light beam passes through the start-end side light detection unit 140S until it passes through the correction light detection unit 142S1, and after the correction light beam passes through the correction light detection unit 142S1, The correction data generation unit 170 measures the time T12 until the light detection unit 142S2 passes, and the time T23 until the correction light beam passes the correction light detection unit 142S2 and passes the correction light detection unit 142S3. To do. In this case, counting is performed by preparing a clock faster than the clock of FIG. Then, this count result is compared with the count value of the original error-free state obtained from the position of the correction light detection unit 142S1, thereby calculating the exposure pixel position shift.

  Here, in the time chart shown in FIG. 3, at the position of the correction light detection unit 142S2, the correction data is generated in accordance with the absence of the exposure pixel position deviation (FIG. 3C) by scanning the first surface of the polygon mirror 120. The unit 170 generates correction data with a correction value “0.0” (FIG. 3G). In addition, the correction data generation unit 170 sets the exposure pixel position to 0 in response to the exposure pixel position being shortened by 0.25 clock (25% of one clock) by scanning the second surface of the polygon mirror 120 (FIG. 3D). The correction data of the correction value “+0.25” is generated to extend by 25 clocks (FIG. 3 (h)). The correction data generation unit 170 generates correction data with a correction value “0.0” in accordance with the fact that there is no displacement of the exposure pixel position in the scanning of the third surface of the polygon mirror 120 (FIG. 3 (e)). i)). In addition, the correction data generation unit 170 shortens the exposure pixel position by 0.25 clocks in accordance with the exposure pixel position 0.25 clock expansion (FIG. 3F) by scanning the fourth surface of the polygon mirror 120. Correction data of the correction value “−0.25” is generated (FIG. 3 (j)).

  Then, the control unit 101 refers to the reflection surface identification result by the reflection surface identification unit 160 with respect to the correction data from the correction data generation unit 170 as described above, and stores the correction data in a state associated with the reflection surface identification result. Store in the unit 103.

  The measurement of T01, T12, and T23 described above is repeated several times, and a plurality of measurement results or correction data on the same reflecting surface of the polygon mirror 120 is obtained in either the correction data generation unit 170 or the control unit 101. It is desirable from the viewpoint of error reduction to average the data after removing the maximum and minimum values. Alternatively, averaging may be performed after removing two maximum values and two minimum values.

  As described above, the correction data acquisition operation ends when the control unit 101 stores the correction data in the storage unit 103.

  In the above time chart of FIG. 3, a specific example is shown between the correction light detection unit 142S1 and the correction light detection unit 142S2. However, between the start-end side light detection unit 140S and the correction light detection unit 142S1, The correction data acquisition operation can be similarly performed between the correction light detection unit 142S2 and the correction light detection unit 142S3.

  The correction data acquisition may be executed at the time of adjustment before shipment at the manufacturing factory, or may be executed regularly or irregularly when the image forming apparatus 100 is turned on. Alternatively, it may be executed when an optical component such as the polygon mirror 120 is replaced.

[B-2] Correction operation:
An operation for generating a write clock whose phase is corrected so as to correct the exposure pixel position of the exposure light beam using the above-described correction data when executing image formation will be described. Here, the operation of the write clock generation unit 180 will be described focusing on the phase correction of the write clock executed in parallel with the normal image forming operation. FIG. 5 shows the configuration of a digital delay type clock generation circuit 1810 applied to the write clock generation unit 180 as a specific example.

[B-2-1] Delay signal generation:
The delay chain unit 1813 delays an input signal (reference clock from the reference clock generation unit 1811) to obtain a plurality of delay signals (delayed signal group: FIG. 5 (1)) having slightly different phases. It is. Here, in the delay chain unit 1813, it is preferable that the delay elements are cascaded in a chain shape so that the delay signals having slightly different phases can be generated over about two cycles of the reference clock. Note that the number of subordinate connections of the delay elements may be determined so as to satisfy the accuracy necessary for phase correction of the exposure pixel position. For example, when about two cycles of the reference clock are delayed by a 200-stage delay element, the phase can be corrected in units of about 1/100 (1% of the cycle of the reference clock) with respect to one cycle of the reference clock. .

[B-2-2] Synchronization detection:
The synchronization detection unit 1814 receives the SOS signal that is the detection result of the start-end side light detection unit 140S, and the number of stages of the delay signal (synchronization point SP) that is synchronized with the SOS signal in the delay signal group (FIG. 5 (1)). ) To detect and output the synchronization point information SP and the synchronization stage number NS as synchronization information (FIG. 5 (2)). That is, the synchronization detection unit 1814 includes first synchronization point information SP1 that is first synchronized with the SOS signal and second synchronization with the SOS signal in the delay signal group (FIG. 5 (1)). 2 synchronization point information SP2. Further, the difference between the second synchronization point information SP2 and the first synchronization point information SP1 is obtained as the synchronization stage number NS.

  The plurality of delay signals from the delay chain portion 1813 may vary in delay time for each stage of the delay element due to the influence of temperature change, power supply voltage change, etc. The number of synchronization stages NS is obtained in advance. Since the reference clock from the reference clock generator 1811 has a stable frequency, the delay time Td per delay element is calculated from the time TC for one pulse of the reference clock and the number of synchronization stages NS by Td = It can be accurately obtained as TC / NS.

[B-2-3] Switching control:
The switching control unit 1815 converts the synchronization information from the synchronization detection unit 1814 (FIG. 5 (2)) and the correction data generated by the correction data generation unit 170 and supplied from the control unit 101 (FIG. 5 (3)). Based on this, the number of correction stages is obtained, and a select signal (FIG. 5 (4)) indicating which phase of the delayed signal should be selected from the delay signal group (FIG. 5 (1)) is output.

  The select signal from the switching control unit 1815 is generated in synchronization with the synchronization information, that is, in synchronization with the detection result of the start-end side light detection unit 140S, and is output to the selection unit 1816. As a result, the phase of the write clock is corrected by the clock generation circuit 1810 in synchronization with the detection of the light beam by the start end side light detection unit 140S.

Here, regarding the select stage number SL to be selected by the select signal generated by the switching control unit 1815, when the phase correction amount is E,
SL = SP1 + (NS × E).

[B-2-4] Delay signal selection / write clock output:
The selection unit 1816 receives the select signal (FIG. 5 (4)) from the switching control unit 1815, selects a delay signal having a corresponding phase from the delay signal group (FIG. 5 (1)), and writes the write clock (FIG. 5). (5)) is output.

  For example, when the first synchronization point information SP1 = 50 and the second synchronization point information SP2 = 150, the number of synchronization stages NS = 100.

When the correction data is “0.0”, the select stage number SL is
SL = 50 + (100 × (+0.0)) = 50,
The selection unit 1816 may select the output of the delay element at the 50th stage.

When the correction data is “+0.25”, the select stage number SL is
SL = 50 + (100 × (+0.25)) = 75,
The selection unit 1816 may select the output of the 75th delay element.

When the correction data is “−0.25”, the select stage number SL is
SL = 50 + (100 × (−0.25)) = 25
The selector 1816 may select the output of the 25th delay element.

  In addition, what is necessary is just to calculate using 2nd synchronizing point information SP2, when calculating using 1st synchronizing point information SP1 and the selection stage number SL becomes negative.

  As described above, a number of pulses having different phases are generated in the delay chain unit 1813, and the switching control unit 1815 selects the synchronization information from the synchronization detection unit 1814 and the correction data from the control unit 101. A signal is generated, and a pulse at a desired timing is selected and output based on the select signal by the selection unit 1816. As shown in FIG. 4B, the phase of the write clock is instantaneously detected immediately after the deviation is detected. Correction becomes possible.

  That is, the output of the write clock by the delay signal selection using such synchronization information (first synchronization point information SP1, second synchronization point information SP2, synchronization stage number NS) and correction data is used as the main scanning corresponding to the image area. This is performed by the selection unit 1816 in synchronization with the correction light beam detection by the correction light detection units 142S1 to 142S3 within the range.

  This makes it possible to appropriately maintain the exposure pixel position in the main scanning direction within the main scanning range corresponding to the actual image area, not the coincidence between the start end and the end in the maximum range in the main scanning direction.

  If the correction data from the correction data generation unit 170 is not relative value to the clock cycle but time data expressed in seconds, a select signal is generated using the delay time Td per one delay element. do it.

[B-3] Application of correction data:
An operation for generating a writing clock whose phase is corrected so as to correct the exposure pixel position of the exposure light beam using the above-described correction data when performing image formation will be described in detail. Here, a specific example (1) based on FIG. 4 and a specific example (2) based on FIG. 6 will be described.

[B-3-1] Specific application example of correction data (1):
Here, under the control of the control unit 101, the exposure light beam from the laser diode 110 is emitted according to the image data as a normal image forming operation, and at the same time, the correction light beam is At least the start end side light detection unit 140S and the correction light detection units 142S1 to 142S3 are allowed to emit light within a range that can be irradiated.

  When the correction light beam is detected by the correction light detection unit 142S1, the control unit 101 that has received the detection result also refers to the reflection surface identification result of the reflection surface identification unit 160, and the corresponding reflection surface at that timing. The correction data of the position of the correction light detection unit 142S1 is read from the storage unit 103. The control unit 101 sends the read correction data to the write clock generation unit 180.

  Further, the write clock generation unit 180 receives the detection result of the correction light beam from the correction light detection unit 142S1, enters a clock phase correction possible state in synchronization with this timing, and is sent from the control unit 101. The phase of the write clock is corrected according to the correction data.

  Similarly, in synchronization with the timing at which the correction light beam is detected by the correction light detection unit 142S2 and the correction light detection unit 142S3, the corresponding correction data is read and written by the control unit 101. The correction data is supplied to 180, and the phase of the write clock is corrected by the write clock generation unit 180 based on the correction data.

  As described above, the write clock generation unit 180 corrects “+0.25” at the timing (the seventh pixel in FIG. 3) when the correction light detection unit 142S1 detects the correction light beam on the second surface of the polygon mirror. Since data is supplied from the control unit 101 (FIGS. 3H to 1L), the write clock is delayed by 0.25 clocks in the immediately following clock pulse (FIG. 3L). In FIG. 3 (l), the timing of the write clock before correction is shown by a broken line, and the difference in position between the broken line and the solid line corresponds to the phase correction amount of the write clock. Then, as shown in FIG. 3 (p), by the phase correction of +0.25 clock of the write clock at the eighth pixel, the reduction of 0.25 pixels in the main scanning direction up to the seventh pixel (the broken line and the solid line) The difference is eliminated.

  As described above, in the write clock generation unit 180, “−0.25” is obtained at the timing when the correction light detection unit 142S1 detects the correction light beam on the fourth surface of the polygon mirror (the seventh pixel in FIG. 3). Is supplied from the control unit 101 (FIGS. 3 (j) to (n)), the write clock is advanced by 0.25 clocks immediately after the clock pulse (FIG. 3 (n)). In FIG. 3 (n), the timing of the write clock before correction is indicated by a broken line, and the difference in position between the broken line and the solid line corresponds to the phase correction amount of the write clock. Then, as shown in FIG. 3 (r), by the phase correction of −0.25 clock of the write clock at the 8th pixel, the expansion of 0.25 pixels in the main scanning direction up to the 7th pixel (broken line and solid line) Difference).

  In the specific example of FIG. 3, since the correction data value is “0.0” on the first surface and the third surface of the polygon mirror 120, the phase of the write clock is not substantially corrected.

  As described above, at the time of image formation, the correction light detection units 142S1 to 142S3 used for detection at the time of correction data acquisition are matched with the timing at which the correction light beams reflected by the respective reflecting surfaces of the polygon mirror 120 are detected. Thus, the corresponding correction data is read out by the control unit 101, the correction data is supplied to the write clock generation unit 180, and the phase of the write clock is corrected by the write clock generation unit 180 based on the correction data.

  As a result, the correction light detectors 142S1 to 142S3 are arranged in the main scanning range corresponding to the actual image area, instead of the coincidence of the start end and the end in the maximum range in the main scanning direction. The exposure pixel position in the main scanning direction can be appropriately maintained for each of the 120 reflecting surfaces.

  In the example of FIG. 3, the exposure pixel position shift occurs between the second surface and the fourth surface of the polygon mirror 120 at the second to seventh pixels, but the first surface to the fourth surface of the polygon mirror 120 at the eighth pixel. Are in a complete state. In addition, the exposure pixel position shift due to the difference between the first surface to the fourth surface of the polygon mirror 120 gradually occurs after the ninth pixel, but the exposure pixel position shift is similarly performed by the correction light detection unit 142S3. By performing detection and phase correction of the write clock, it is possible to eliminate the exposure pixel position shift. For this reason, the exposure pixel position shift does not accumulate toward the end in the main scanning direction.

  In other words, when there are 19 pixels formed on the surface of the photoconductor 140 by the first surface to the fourth surface of the polygon mirror 120 in the main scanning direction, the shift detection and the write clock phase correction of this embodiment are performed. Thus, the correction is made within the main scanning range as shown in FIG. 4 (a) and 4 (b) show a simple specific example in which the surface of the polygon mirror 120 extends or contracts in the main scanning direction. However, the surface expands and contracts within one surface depending on the accuracy of the reflecting surface. Exposure pixel misalignment such that the exposure pixel position is mixed, the exposure pixel position misalignment detection and the write clock phase correction are performed by providing three or more correction light detection units in the main scanning direction. Pixel position shift can be eliminated.

  That is, even when the flatness variation (see FIG. 7) of the polygon mirror 120 is different between the reflecting surfaces, according to this embodiment, the correction light detection unit is within the main scanning range corresponding to the actual image area. By arranging 142S1 to 142S3, it is possible to appropriately maintain the exposure pixel position in the main scanning direction for each reflecting surface of the polygon mirror 120 and to eliminate the partial jitter.

  In the above embodiment, the three cases of the correction light detection units 142S1 to 142S3 are shown as specific examples. However, the location and number of the light detection units can be freely set.

  In the above embodiment, since the phase of the writing clock is corrected, it is desirable to correct the writing clock to less than one pulse (a range not exceeding one pixel). Therefore, the number of correction light detection units 142S1 to 142S3 is determined in accordance with the accuracy of the polygon mirror 120 to be used, and correction is made so that the write clock is less than one pulse (a range not exceeding one pixel). Is desirable.

[B-3-2] Specific application example of correction data (2):
FIG. 6A shows a state in which the positional deviation is accumulated and becomes larger toward the rear end in the main scanning direction as in FIG. 4A.

  Here, by applying the exposure pixel position correction according to the application specific example (1) of the correction data described above, the correction light beam is detected at every predetermined position as shown in FIG. 6B. It becomes possible to correct the exposure pixel position.

  In the case of FIG. 6B, the density of the exposure pixel interval before and after the correction may be visually recognized as a streak in the sub-scanning direction.

  Therefore, the write clock generation unit 180 has a phase correction amount in the range of a plurality of m pixels in the main scanning direction from the exposure pixel position of the exposure light beam corresponding to the position where the detection results of the correction light detection units 142S1 to 142S3 are obtained. Is set to P, a write clock with a phase correction of P / m is generated for each pixel.

  In the case of FIG. 6C, m = 3, and the phase is gradually increased like (1/3) P, (2/3) P, (3/3) P in the range of 3 pixels in the main scanning direction. Make corrections. Thereby, m / m, that is, 100% correction is performed on the mth pixel. That is, since the change in density due to the correction of the exposure pixel position is dispersed in the main scanning direction, the difference before and after the correction becomes inconspicuous and a good image quality is obtained.

  Note that m in this case can be determined according to the number of exposed pixels, the phase correction amount P, the conspicuous details of streaks in the sub-scanning direction, and the like. Moreover, the user who browsed the image of FIG.6 (b) or FIG.6 (c) may make it set the value of m from an operation part.

<Other embodiment (1)>
In the specific example of the above-described embodiment, the correction light detection units 142S1 to 142S3 are illustrated, but the number of the correction light detection units is increased in order to cope with the image formation of recording papers having various different sizes. It is desirable.

<Other embodiment (2)>
In the above embodiment, an electrophotographic image forming apparatus using a light beam has been described. However, the present invention is not limited to this. For example, each embodiment of the present invention can be applied to various image forming apparatuses such as a laser imager that exposes photographic paper using a light beam, and good results can be obtained.

<Other embodiment (3)>
In the above embodiment, the photosensitive drum is used as a specific example as the photosensitive member 140, but the photosensitive member 140 is not limited to the drum type, and may be a belt. In addition, the light beam and the photosensitive member 140 may be applied not only to the rotation of the photosensitive member 140 in the sub-scanning direction but also to various sub-scanning methods for relatively moving the photosensitive member 140 and the light beam in the sub-scanning direction. can do. In the case of a color image forming apparatus, the present embodiment may be applied to each color.

DESCRIPTION OF SYMBOLS 100 Image forming apparatus 103 Memory | storage part 105 Operation part 101 Control part 110 Laser diode 110D LD drive circuit 120 Polygon mirror 120M Polygon motor 120D Polygon motor drive part 130 Optical system 140 Photoconductor 140S Light detection part 142S1-142S3 (142Sn) Photodetection part 160 Reflective surface identification unit 170 Correction data generation unit 180 Write clock generation unit 190 Image processing unit

Claims (10)

The exposure light beam emitted according to each pixel of the image data is scanned in the main scanning direction of the photosensitive member, and the photosensitive member and the exposure light beam are relatively moved in the sub-scanning direction orthogonal to the main scanning direction. An image forming apparatus that exposes the surface of the photoreceptor to form an image by being driven to move to
A light source that generates the exposure light beam and a correction light beam that emits light at least at a light detection position;
A rotating polygon mirror that reflects the exposure light beam and the correction light beam so as to scan the exposure light beam in the main scanning direction on the photoreceptor by a plurality of rotating reflecting surfaces;
A light detection unit that is disposed at a predetermined position corresponding to a main scanning range of the photoreceptor surface and detects the correction light beam;
A storage unit that stores in advance correction data for correcting an exposure pixel position of the exposure light beam based on a detection result of the light detection unit;
A write clock whose phase is corrected so that the exposure pixel position of the exposure light beam corresponding to the position where the detection result of the light detection unit is obtained is corrected using the correction data stored in the storage unit. A write clock generator to generate,
An image forming apparatus comprising: The write clock generation unit corrects the phase so as to correct the exposure pixel position using the correction data stored in the storage unit at a timing when the light beam for correction is detected by the light detection unit. Generated write clock,
The image forming apparatus according to claim 1. A reflecting surface identifying unit for identifying each reflecting surface of the rotary polygon mirror;
Correction data for correcting the exposure pixel position of the exposure light beam based on the detection results of the reflection surface identification unit and the light detection unit corresponding to each reflection surface identified by the reflection surface identification unit. A storage unit for storing;
With
The write clock generation unit is configured to expose the exposure light beam corresponding to the position where the detection result of the light detection unit is obtained for each reflection surface of the rotary polygon mirror identified by the reflection surface identification unit. Generating a write clock having a phase corrected so as to correct the pixel position using the correction data stored in the storage unit;
The image forming apparatus according to claim 1 or 2. When the correction amount is set to P in a range of a plurality of m pixels in the main scanning direction from the exposure pixel position of the exposure light beam corresponding to the position where the detection result of the light detection unit is obtained, the write clock generation unit A write clock with a phase corrected by P / m for each pixel is generated.
The image forming apparatus according to claim 1, wherein the image forming apparatus is an image forming apparatus. The write clock generation unit corrects the phase of the write clock used when the exposure light beam is emitted by the image data within a range not exceeding one pixel of the image data as correction of the exposure pixel position. ,
The image forming apparatus according to claim 1, wherein the image forming apparatus is an image forming apparatus. The exposure light beam emitted according to each pixel of the image data is scanned in the main scanning direction of the photosensitive member, and the photosensitive member and the exposure light beam are relatively moved in the sub-scanning direction orthogonal to the main scanning direction. A method of controlling an image forming apparatus for performing image formation by performing exposure on the surface of the photosensitive member by driving to move to
A light detection unit that detects the correction light beam at a predetermined position corresponding to the main scanning range of the photoreceptor surface is provided, and the exposure pixel position of the exposure light beam is corrected based on the detection result of the light detection unit. Correction data is stored in advance in the storage unit,
Generating a light beam for correction and a light beam for correction emitted at least at a light detection position from the light source;
The exposure light beam and the correction light beam are reflected by a plurality of reflecting surfaces of a rotary polygon mirror so that the exposure light beam is scanned in the main scanning direction on the photoreceptor.
The correction light beam is detected by a light detection unit disposed at a predetermined position corresponding to the main scanning range of the photoreceptor surface,
A write clock whose phase is corrected so that the exposure pixel position of the exposure light beam corresponding to the position where the detection result of the light detection unit is obtained is corrected using the correction data stored in the storage unit. Generated by the write clock generator,
An image forming apparatus control method. The write clock generation unit corrects the phase so as to correct the exposure pixel position using the correction data stored in the storage unit at a timing when the light beam for correction is detected by the light detection unit. Generated write clock,
The image forming apparatus control method according to claim 6. Identify each reflective surface of the rotary polygon mirror by a reflective surface identification unit,
Correction data for correcting the exposure pixel position of the exposure light beam based on the detection results of the reflection surface identification unit and the light detection unit corresponding to each reflection surface identified by the reflection surface identification unit. Store in the storage unit,
The write clock generation unit is configured to expose the exposure light beam corresponding to the position where the detection result of the light detection unit is obtained for each reflection surface of the rotary polygon mirror identified by the reflection surface identification unit. Generating a write clock having a phase corrected so as to correct the pixel position using the correction data stored in the storage unit;
8. The image forming apparatus control method according to claim 6-7. When the correction amount is set to P in a range of a plurality of m pixels in the main scanning direction from the exposure pixel position of the exposure light beam corresponding to the position where the detection result of the light detection unit is obtained, the write clock generation unit A write clock with a phase corrected by P / m for each pixel is generated.
9. The image forming apparatus control method according to claim 6-8. The write clock generation unit corrects the phase of the write clock used when the exposure light beam is emitted by the image data within a range not exceeding one pixel of the image data as correction of the exposure pixel position. ,
The image forming apparatus control method according to claim 6, wherein the image forming apparatus control method is an image forming apparatus.

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