JP2012226051A - Image forming apparatus and image forming apparatus control method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To averagely restrain dot displacements in a main scanning direction over the entire main scanning area.SOLUTION: The image forming apparatus comprises: a light source configured to generate a light beam that is emitted according to image data in synchronization with a writing clock; optical scanning means by which the optical beam is scanned in a main scanning direction on an image carrier by a plurality of reflecting faces of a rotary polygon mirror rotated and driven by a rotation drive source; a reflecting face identification part which identifies each reflecting face of the rotary polygon mirror; sub-scanning direction drive means which moves the image carrier and the light beam relative to each other in a sub-scanning direction orthogonal to the main scanning direction; a storage part which stores jitter information of the light beam measured at a plurality of positions in the main scanning direction on each reflecting face of the rotary polygon mirror; and a control part which refers to the jitter information read from the storage part, obtains a correction characteristic approximate in a straight line for dot displacements in a plurality of positions that occur according to the jitter on the respective faces of the rotary polygon mirror, and adjusts the frequency and phase of the writing clock.

Description

  The present invention relates to an image forming apparatus such as a copying machine or a printer that scans a laser beam using an optical scanning unit including a rotary drive source and a rotary polygon mirror, and an image forming apparatus control method.

  The image forming apparatus forms a predetermined number of lines in the main scanning direction with a light beam according to image data, and repeats the formation of a light beam for each predetermined number of lines in the main scanning direction in the sub-scanning direction for one page. A device that forms an image of a minute is known.

  As an example, in an electrophotographic image forming apparatus, a main scanning is performed with a laser beam emitted according to image data using an optical scanning unit comprising a rotary drive source (polygon motor) and a rotary polygon mirror (polygon mirror). In parallel with this, an image is formed by the laser beam on an image carrier (photosensitive member) that rotates in the sub-scanning direction. In this case, a laser beam is emitted according to image data with reference to a clock signal (write clock) called a dot clock.

  By the way, jitter (time-axis fluctuation) occurs in the laser beam scanned on the image carrier due to slight rotation unevenness of the polygon motor and minute reflection surface accuracy error of the polygon mirror, and a phenomenon called so-called short period jitter occurs. appear.

  Due to this short period jitter, a dot position shift in the main scanning direction is periodically generated for each reflection surface of the polygon mirror, and it becomes easy to be visually recognized as image quality degradation such as horizontal stripes due to interference with the screen image.

  Furthermore, in recent years, emphasis is placed on image forming output performance, and since exposure is performed using a plurality of laser beams at the same time, the spatial frequency such as the horizontal stripe described above is lowered, and the visibility is further improved. It may cause more noticeable image quality degradation.

  For example, at a resolution of 1200 dpi (1200 dots / 25.4 mm), a first image forming speed of 420 mm / s in the sub-scanning direction, 6 polygon mirror surfaces, and a polygon motor rotation speed of 24803 rpm, 8 light sources ( Assume an apparatus that uses all of LD_1 to LD_8) and forms a latent image on a photosensitive member with eight laser beams at a time. In this case, the scanning width in the sub-scanning direction for each rotation of the polygon motor is 1200 dpi × 8 lines × 6 surfaces = 1 mm. That is, a short period jitter of one rotation period appears in a 1 mm period, and is in a state where it can be visually recognized very easily.

  In addition, as a technique that can solve such a problem, for example, various solutions are described in the following patent documents.

Japanese Patent Laid-Open No. 2002-267961 Japanese Patent Laid-Open No. 2003-140068

  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 the laser beam are aligned, that is, the main scanning length is unified between the laser beams, and the main scanning is performed. It is important to eliminate the direction shift.

  In the above-mentioned patent document 1, the write clock is adjusted by the SOS (Start Of Scan) signal on the start position side in the main scanning direction and the EOS (End Of Scan) signal on the end position side in the main scanning direction to adjust the main scanning length. Is controlled to be constant. In this case, in addition to the existing SOS sensor, an EOS sensor for obtaining an EOS (End Of Scan) signal on the end position side in the main scanning direction has to be newly added.

  Although the error is eliminated in the portion corresponding to the outer frame of the image by aligning the start and end in the main scanning direction, in the case of the above-mentioned problem of the reflection surface accuracy of the polygon mirror, the intermediate portion between the start and end In some cases, the error remains, and the problems such as the horizontal stripes described above are not basically solved.

  Further, in Patent Document 2, the correction scan clock modulation frequency for each surface of the polygon mirror is provided in a non-volatile memory, and the write clock frequency is changed for each surface of the polygon mirror a plurality of times within one main scan. The length is controlled to be constant. In the case of this Patent Document 2, although there is a description that the write clock is modulated, there is a sufficient amount of information about how to detect short-period jitter or how to calculate correction data. It is not described. In addition, when the write clock is modulated by subdividing the main scan into a plurality of parts, a problem arises that a large-scale circuit and complicated control are required.

  The present invention has been made in order to solve the above-described problem, and the dot position deviation in the main scanning direction when forming an image using an optical scanning unit including a polygon motor and a polygon mirror is limited to a part of the region. It is an object of the present invention to realize an image forming apparatus and an image forming apparatus control method capable of suppressing the average over the entire main scanning region instead.

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

  (1) The invention according to claim 1 is an image carrier on which an image is formed by exposure of a light beam, a light source that generates the light beam that emits light in accordance with image data in synchronization with a writing clock, and rotational driving A light scanning unit that scans the light beam in the main scanning direction on the image carrier by a plurality of reflecting surfaces of a rotating polygon mirror that is rotationally driven by a source; and a reflecting surface identifying unit that identifies each reflecting surface of the rotating polygon mirror A sub-scanning direction driving means for relatively moving the image carrier and the light beam in a sub-scanning direction orthogonal to the main scanning direction, and a plurality of main scanning directions for each reflecting surface of the rotary polygon mirror A storage unit that stores jitter information of the light beam measured at a position, and a plurality of positions that are generated according to the jitter on each surface of the rotary polygon mirror with reference to the jitter information read from the storage unit De DOO positional deviation determined correction characteristic is approximated by a straight line for, characterized in that it comprises a control unit for adjusting a phase of the write clock while changing the frequency of the write clock in accordance with the correction characteristic.

  (2) The invention described in claim 2 is characterized in that, in the above (1), the control unit changes the frequency of the write clock in accordance with a slope of the correction characteristic.

  (3) The invention according to claim 3 is characterized in that, in the above (2), the control unit adjusts the phase of the write clock according to the intercept at the start position in the main scanning direction of the correction characteristic. To do.

  (4) In the invention according to claim 4, in the above (1) to (3), the control unit refers to the jitter information at a plurality of positions read from the storage unit when obtaining the correction characteristic. The dot position deviation at the jitter information measurement position is calculated from the product of the distance from the main scanning start end at the jitter information measurement position and the jitter amount included in the jitter information.

  (5) The invention according to claim 5 is an image carrier on which an image is formed by exposure of a light beam, a light source that generates the light beam that emits light in accordance with image data in synchronization with a writing clock, and rotational driving. A light scanning unit that scans the light beam in the main scanning direction on the image carrier by a plurality of reflecting surfaces of a rotating polygon mirror that is rotationally driven by a source; and a reflecting surface identifying unit that identifies each reflecting surface of the rotating polygon mirror A sub-scanning direction driving means for relatively moving the image carrier and the light beam in a sub-scanning direction orthogonal to the main scanning direction, and a plurality of main scanning directions for each reflecting surface of the rotary polygon mirror A control method of an image forming apparatus, comprising: a storage unit storing jitter information of the light beam measured at a position; and a control unit that controls each unit, wherein the control unit reads from the storage unit Jitter The correction characteristic approximated by a straight line is obtained for the dot position deviation at a plurality of positions generated according to the jitter on each surface of the rotary polygon mirror, and the frequency of the writing clock is determined according to the correction characteristic. The phase of the write clock is adjusted while changing.

  (6) The invention according to claim 6 is characterized in that, in the above (5), the control unit changes the frequency of the write clock in accordance with a slope of the correction characteristic.

  (7) The invention according to claim 7 is characterized in that, in the above (6), the control unit adjusts the phase of the write clock in accordance with the intercept of the correction characteristic at the start position in the main scanning direction. To do.

  (8) In the invention according to claim 8, in the above (5) to (7), the control unit refers to the jitter information at a plurality of positions read from the storage unit when obtaining the correction characteristic. The dot position deviation at the jitter information measurement position is calculated from the product of the distance from the main scanning start end at the jitter information measurement position and the jitter amount included in the jitter information.

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

  In this invention, the jitter information of the light beam measured at a plurality of positions in the main scanning direction for each reflecting surface of the rotary polygon mirror is stored in advance in the storage unit, and the jitter information read from the storage unit is referred to and rotated. Find correction characteristics approximating with a straight line for dot position deviations at multiple positions that occur according to jitter on each face of the polygon mirror, and change the write clock phase and adjust the write clock phase according to the correction characteristics. .

  As a result, it is possible to suppress, on average, not only a part of the area such as the end portion but also the entire main scanning area when the image is formed using the rotary polygon mirror. .

  Note that by changing the write clock frequency according to the inclination of the correction characteristic and adjusting the phase of the write clock according to the intercept of the correction characteristic at the start position in the main scanning direction, the dot position deviation can be reduced to a value such as the end portion. It is possible to suppress the image on the average in an appropriate state over the entire main scanning area as well as the area of the portion.

  In addition, since the jitter information is read from the storage unit and control for correction is executed in accordance with the read jitter characteristics, the optical scanning unit after replacement is replaced even when the optical scanning unit is replaced. Control suitable for the above is executed, and the dot position deviation in the main scanning direction can be minimized without performing any special adjustment operation, and good image quality can be obtained.

1 is a block diagram illustrating a configuration of an image forming apparatus according to an embodiment of the present invention. 1 is a block diagram illustrating a configuration of an image forming apparatus according to an embodiment of the present invention. 1 is a block diagram illustrating a configuration of an image forming apparatus according to an embodiment of the present invention. It is a block diagram which shows the structure of the measuring apparatus of one Embodiment of this invention. It is a flowchart which shows the procedure at the time of measuring the optical scanning means of one Embodiment of this invention. It is a time chart which shows the operation | movement at the time of measuring the optical scanning means of one Embodiment of this invention. It is a time chart which shows the operation | movement at the time of measuring the optical scanning means of one Embodiment of this invention. FIG. 6 is a characteristic diagram illustrating an operation of the image forming apparatus according to the embodiment of the present invention. 6 is a flowchart illustrating an operation of the image forming apparatus according to the embodiment of the present invention. FIG. 6 is a characteristic diagram illustrating an operation of the image forming apparatus according to the 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. FIG. 6 is a characteristic diagram illustrating an operation of the image forming apparatus according to the embodiment of the present invention. FIG. 6 is a characteristic diagram illustrating an operation of the image forming apparatus according to the embodiment of the present invention.

  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 image carrier, 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 image carrier by driving to move the beam relatively. The optical scanning unit to which the present embodiment is applied is an optical scanning unit composed of a rotary drive source (polygon motor) and a rotary polygon mirror (polygon mirror), and is used for scanning a light beam in the image forming apparatus. Is.

[Configuration of image forming apparatus]
The outline of the configuration of the image forming apparatus will be described below.

  The electrical configuration of the image forming apparatus 100 according to the present embodiment will be described in detail with reference to FIG. Here, the image forming apparatus 100 will be described in the state of monochromatic image formation in a state related to the measuring apparatus 200 described later. In the present embodiment, description will be made focusing on the configuration requirements necessary for describing the embodiment. 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 in addition to a normal image forming operation, a plurality of positions in the main scanning direction for each reflection surface of the polygon mirror 121. When the jitter information of the light beam measured in (1) is stored in the storage unit in advance, the jitter information read out from the storage unit is referred to, and a plurality of positions are generated according to the jitter on each surface of the polygon mirror 121. A correction characteristic approximated by a straight line is obtained for the dot position deviation, and control is performed to change the write clock frequency and adjust the write clock phase in accordance with the correction characteristic.

  The laser diode (LD) 110 is a light source that generates a laser beam (light beam) that performs exposure while scanning on the photosensitive member. The laser beam from the laser diode 110 may be a single beam or a plurality of beams.

  The optical scanning unit 120 includes a polygon mirror 121 as a rotary polygon mirror and a polygon motor 122 as a rotation drive source. Here, the polygon mirror 121 is a rotating polygon mirror that scans a laser beam in the main scanning direction on the surface of the photosensitive member by a plurality of rotating reflecting surfaces. The polygon motor 122 is a rotational drive source that receives the polygon drive signal and rotates the polygon mirror 121 at a predetermined rotational speed.

  The surface detection sensor 125 detects the reference mark 120d attached to the polygon mirror 121, generates a surface detection signal for identifying the reflection surface, and transmits the surface detection signal to the reflection surface identification unit 103.

  The optical system 130 includes a cylindrical lens 130a and an f− for performing an optical process so that the laser beam irradiated from the laser diode 110 and reflected by the polygon mirror 121 has a predetermined main scanning speed on the surface of the photoreceptor. These are various optical members such as the θ lens 130b.

  The light detector 145 on the start end side is an SOS sensor for detecting a light beam and obtaining an SOS (Start Of Scan) signal on the main scan start end side on the extended line of the main scan position on the photoconductor 160, and is detected. The result is transmitted to the optical scanning drive control unit 101 b and the reflection surface identification unit 103 in the control unit 101. Here, the light detection unit 145 is detected using the mirror 141 on the main scanning start end side, but the mirror 141 is not necessarily used.

  The print head 150 includes a laser diode 110, an optical scanning unit 120, an optical system 130, a light detection unit 145, and the like, and scans the photosensitive member with a laser beam. Correspondingly provided. In addition, the print head 150 can be configured to be exchanged by inserting / removing the image forming apparatus 100 in a unit form or the like as necessary.

  The storage unit 151 is storage means in which jitter information of the light beam measured at a plurality of positions in the main scanning direction for each reflection surface of the polygon mirror 121 is measured and stored in advance by the measurement apparatus 200 described later.

  The photosensitive member 160 responds to image data by exposure of a laser beam scanned in the main scanning direction by the rotation of the polygon mirror 121 and relative movement of the light beam in the sub-scanning direction perpendicular to the main scanning direction. The photosensitive member is an image carrier on which an electrostatic latent 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, forming the toner image by developing the latent electrostatic image, transferring the toner image onto the recording paper, fixing the toner image on the recording paper, and the like are generally used as the image forming apparatus 100. Since it is typical, the description is omitted.

  The control unit 101 includes a light emission drive control unit 101a, an optical scanning drive control unit 101b, an image processing unit 102, a reflection surface identification unit 103, and a photoconductor drive unit 105.

  Here, the light emission drive control unit 101a is a 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 corresponding to the image data is supplied to the laser diode 110. Supply.

  The optical scanning drive control unit 101 b is a drive signal generation unit that generates a polygon drive signal for rotating the polygon mirror 121 at a predetermined rotation number and supplies the polygon drive signal to the polygon motor 122.

  The optical scanning drive control unit 101b refers to the jitter information read from the storage unit, and corrects the dot position deviation generated at a plurality of positions according to the jitter on each surface of the rotary polygon mirror by a straight line. And the write clock frequency is changed and the phase of the write clock is adjusted according to the correction characteristics.

  In addition, the optical scanning drive control unit 101b supplies the light emission drive control unit 101a with a write clock that has been subjected to frequency change and phase adjustment as described above.

  The image processing unit 102 is an image processing unit that performs various kinds of image processing necessary for image formation on the image data, and outputs necessary data to the light emission drive control unit 101a in synchronization with a write clock.

  The reflection surface identification unit 103 identifies the reflection surface of the polygon mirror 121 in response to the surface detection signal from the surface detection sensor 125 and the detection result from the light detection unit 145, and on what surface from the reference mark 120d. The reflection surface identification result, such as whether or not there is, is transmitted to the optical scanning drive control unit 101b.

  The photoconductor driving unit 105 is photoconductor rotation driving means that rotates the photoconductor 160 in the sub-scanning direction at a predetermined rotation speed. The photosensitive member driving unit 105 drives the photosensitive member 160 so that the number of rotations of the photosensitive member corresponds to the image forming speed determined by the optical scanning drive control unit 101b.

  When the image forming apparatus 100 is a color image forming apparatus that forms a color image by superimposing a plurality of color images, as shown in FIGS. 2 and 3, the print heads 150Y to 150K and the photoconductors 160Y to 160K. Thus, a plurality of units are arranged according to a plurality of colors, and the control unit 101 is configured in common. 2 and 3 exemplify a case where image formation is performed with four colors of yellow Y, magenta M, cyan C, and black K. FIG. Here, the electrostatic latent images formed on the photoconductors 160Y to 160K by the print heads 150Y to 150K are converted into YMCK toner images by the developing units 170Y to 170K, and the respective color toner images are transferred onto the intermediate transfer member 180. Superimposed. The toner image on the intermediate transfer member 180 is transferred to the recording paper from the paper feed tray T in the transfer unit 185, and the toner image on the recording paper is thermally fixed in the fixing unit 190 to form a stable color image. The In such an image forming apparatus 100, each of the print heads 150Y to 150K is provided with the optical scanning means 120 in a state where the characteristics of the main scanning length are aligned as will be described later.

[Configuration of measuring device]
Hereinafter, the measuring apparatus 200 for measuring the print head 150 will be described with reference to FIG.

  In the following embodiments, a measurement procedure by the measurement apparatus 200 is called, but the same measurement and adjustment as described below may be executed by an adjustment apparatus (not shown) that performs various other adjustments.

  Further, the measuring apparatus 200 is configured so as to have characteristics that are mechanically or optically approximate to those of the image forming apparatus 100 in which the print head 150 is used. In addition, the print head 150 is configured to be mounted on the measuring apparatus 200 configured to have characteristics that are mechanically or optically approximate to those of the image forming apparatus 100 as described above.

  Here, the control unit 201 is configured by a CPU, a control program, and the like to control each unit of the measurement apparatus 200, and a plurality of positions in the main scanning direction for each reflection surface of the polygon mirror 121 included in the print head 150. Control is performed so as to obtain jitter information of the light beam measured in step (1).

  The light detection units 245S1 to 245S5 are sensors for obtaining a detection signal by detecting a light beam at a position (virtual photoconductor surface) optically equivalent to the main scanning position range of the photoconductor 160 in the image forming apparatus 100. The detection result is transmitted to the measurement unit 204 in the control unit 201.

  The above-described control unit 201 includes a light emission drive control unit 201a, an optical scanning drive control unit 201b, a reflection surface identification unit 203, and a measurement unit 204.

  Here, the light emission drive control unit 201a is a 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, and the characteristics of the main scanning length on each surface of the polygon mirror 121. Therefore, a light emission drive signal that emits light at the end in the main scanning direction is supplied to the laser diode 110.

  The optical scanning drive control unit 201b generates a polygon drive signal for rotationally driving the polygon mirror 121 at a predetermined rotational speed equivalent to that of the image forming apparatus 100, supplies the polygon drive signal to the polygon motor 122, and receives jitter information obtained by the measurement. Control is performed so as to be stored in the storage unit 151.

  The reflection surface identification unit 203 identifies the reflection surface of the polygon mirror 121 in response to the surface detection signal from the surface detection sensor 125 and the detection result from the light detection unit 145, and on what number surface from the reference mark 120d. The reflection surface identification result, such as whether or not there is, is transmitted to the optical scanning drive control unit 201b.

  The measurement unit 204 refers to the detection results of the light detection units 245S1 to 245S5 on the virtual photoconductor surface, measures the jitter (fluctuation in the time axis direction) in the main scanning by the laser beam on each surface of the polygon mirror 121, and measures the measurement results. Is notified to the optical scanning drive control unit 201b.

〔Measurement procedure〕
Hereinafter, the procedure (measuring operation) for measuring the print head 150 will be described with reference to the flowchart of FIG.

  First, the print head 150 is mounted on the measuring apparatus 200 so as to be the same position as the mounting position of the print head 150 in the image forming apparatus 100 (step S101 in FIG. 5).

  In addition, this installation means performing predetermined installation and connection mechanically and electrically. In addition, when the print head 150 is mounted on the measurement apparatus 200, the measurement apparatus 200 side aligns with the print head 150 in advance so that each of the light detection units 245S1 to 245S5 comes to a predetermined position in the virtual photoconductor surface. It is desirable that is completed.

  Then, in a state where the print head 150 is mounted on the measuring apparatus 200 as described above, the polygon motor 122 is rotated at a predetermined rotation number in accordance with an instruction from the optical scanning drive control unit 201b. In parallel with this, the light emission drive control unit 201a generates a light emission drive signal and gives it to the laser diode 110 to cause the laser diode 110 to emit light on the virtual photoconductor surface (step S102 in FIG. 5).

  Here, the measurement unit 204 measures the time Tmn from the timing of the SOS signal output from the light detection unit 145 to the output (sensor n signal) of the light detection unit 245Sn for the m-th surface of the polygon mirror 121 ( Step S103 in FIG. Here, in the specific example of this embodiment, m is 1-6 and n is 1-5. This numerical value can be appropriately changed according to the image forming apparatus 100 to be used.

  This state is shown in the time chart of FIG. Here, the reflection surface immediately after the surface detection signal from the surface detection sensor 125 (FIG. 6A) indicating the specific surface of the polygon mirror 121 is defined as the first surface (FIG. 6I).

  That is, for the first surface of the polygon mirror 121, the time T11 (FIG. 6 (h)) from the SOS signal (FIG. 6 (b)) to the output of the light detection unit 245S1 (FIG. 6 (c): sensor 1 signal). From the time T12 (FIG. 6 (h)) from the SOS signal to the output (FIG. 6 (d): sensor 2 signal) of the light detection unit 245S2 (FIG. 6 (b)), from the SOS signal (FIG. 6 (b)). Time T13 (FIG. 6 (h)) until the output of the light detection unit 245S3 (sensor 2 signal: FIG. 6 (e)), from the SOS signal to the output of the light detection unit 245S4 (sensor 2 signal: FIG. 6 (f)) The measurement unit 204 measures the time T14 (FIG. 6 (h)), and the time T15 (FIG. 6 (h)) from the SOS signal to the output of the light detection unit 245S5 (sensor 5 signal: FIG. 6 (g)). .

  Similarly, for the second surface of the polygon mirror 121, the time T21 from the SOS signal to the output of the light detection unit 245S1 (sensor 1 signal), and the time from the SOS signal to the output of the light detection unit 245S2 (sensor 2 signal). T22, time T23 from the SOS signal to the output of the light detection unit 245S3 (sensor 2 signal), time T24 from the SOS signal to the output of the light detection unit 245S4 (sensor 2 signal), output from the SOS signal to the light detection unit 245S5 ( The measuring unit 204 measures the time T25 until the sensor 5 signal).

  Similarly, T31,..., T35 are measured on the third surface, T41,..., T45 are measured on the fourth surface, T51,..., T55 are measured on the fifth surface, and T61 is measured on the sixth surface. ,..., T65 is measured by the measuring unit 204.

  Then, the optical scanning drive control unit 201b receiving the measurement result from the measurement unit 204 calculates the short-period jitter for each reflection surface within one rotation for each position of the light detection units 245S1 to S5 (FIG. 5). Middle step S104).

  For example, the short period jitter for the first surface of the polygon mirror 121 at the position of the light detection unit 245S1 is RF11, the short period jitter for the second surface is RF21, the short period jitter for the third surface is RF31, and the fourth surface. The short-period jitter for the fifth surface is RF41, the short-period jitter for the fifth surface is RF51, and the short-period jitter for the sixth surface is RF61.

  Here, when the average value of T11, T21, T31, T41, T51, and T61 is Ave1, RF11 = (T11−Ave1) / Ave1, RF21 = (T21−Ave1) / Ave1, RF31 = (T31−Ave1) / Ave1, RF41 = (T41−Ave1) / Ave1, RF51 = (T51−Ave1) / Ave1, and RF61 = (T61−Ave1) / Ave1.

  Similarly, the short period jitter for the first surface to the sixth surface at the position of the light detection unit 245S2 is RF12 to RF62. Here, when the average value of T12, T22, T32, T42, T52, and T62 is Ave2, RF12 = (T12−Ave2) / Ave2,..., RF62 = (T62−Ave2) / Ave2.

  Similarly, the short-period jitter for the first surface to the sixth surface at the position of the light detection unit 245S3 is RF13 to RF63. Here, when the average value of T13, T23, T33, T43, T53, and T63 is Ave3, RF13 = (T13−Ave3) / Ave3,..., RF63 = (T63−Ave3) / Ave3.

  Similarly, the short-period jitter for the first surface to the sixth surface at the position of the light detection unit 245S4 is RF14 to RF64. Here, when the average value of T14, T24, T34, T44, T54, and T64 is Ave4, RF14 = (T14−Ave4) / Ave4,..., RF64 = (T64−Ave4) / Ave4.

  Similarly, the short-period jitter for the first surface to the sixth surface at the position of the light detection unit 245S5 is RF15 to RF65. Here, when the average value of T15, T25, T35, T45, T55, and T65 is Ave5, RF15 = (T15−Ave5) / Ave5,..., RF65 = (T65−Ave5) / Ave5.

  The optical scanning drive control unit 201b repeatedly calculates and averages the short cycle jitter as described above, for example, about 500 rotations of the polygon mirror 121, thereby averaging the short cycle jitter RFmn. Can be suppressed.

  In this way, a total of 30 pieces of jitter information regarding short-period jitter at five sensor positions on each of the six surfaces are calculated, and the scanning drive control unit 101b sends this jitter information to the storage unit 151 in the print head 150. Store. In the present embodiment, five light detection units 245S1 to 245S5 are arranged in one scan, but it goes without saying that the number is not limited to this. In addition, although the illustrated light detection units 245S1 to 245S5 are arranged at equal intervals, the present invention is not limited to this.

  As described above, the print head 150 in which the jitter information at the positions of the plurality of light detection units 245S1 to 245S5 for each reflection surface of the polygon mirror 121 is written in the storage unit 151 is removed from the measurement apparatus 200 (in FIG. 5). In step S106), the image forming apparatus 100 is mounted as necessary. Then, when the required number of print heads 150 are measured (YES in step S107 in FIG. 5), the above measurement process is terminated.

[Normal operation of image forming apparatus]
Hereinafter, the normal operation of the image forming apparatus 100 of the present embodiment will be described. Here, the image forming apparatus 100 is equipped with the print head 150 in which jitter information at a plurality of positions for each reflection surface of the polygon mirror 121 is written in the storage unit 151 as described above.

  Next, calculation of jitter correction data in the image forming apparatus will be described. In the conventional method, attention is paid only to the jitter on the downstream side of the main scanning, and in this embodiment, this corresponds to the case where attention is paid only to the jitter (RF15, RF25,..., RF65) at the position of the sensor 245S5. .

  For example, when a dot position deviation as shown in FIG. 7 occurs, a dot position deviation on a certain reflecting surface (“before correction” in FIG. 8) is indicated by a broken line with reference to the dot position deviation on the downstream side of the main scanning. Create correction characteristics like this. In this case, since the dot position deviation in the main scanning direction is not linear, the residual (dot position deviation remaining after correction) is zero on the downstream side in the main scanning direction after correction, but the residual remains large at other positions. It is in a state.

  Therefore, in the present embodiment, first, the optical scanning drive control unit 101b reads out jitter information at five locations within the surface of each surface of the polygon mirror 121 (within one scanning) from the storage unit 151 (step S201 in FIG. 9). Then, the main scanning dot position deviation is calculated based on the jitter information read out from the storage unit 151 at five points in each surface (within one scanning) of each surface of the polygon mirror 121 (step in FIG. 9). S202).

  Here, the dot position deviation in the main scanning direction is obtained by the product of the distance from the light detection unit 145 to the light detection units 245S1 to 245S5 and the jitter at each position.

  For example, when the distance from the light detection unit 145 to the light detection units 245S1 to 245S5 is 40 mm, 110 mm, 180 mm, 250 mm, and 320 mm in the order of 245S1 to 245S5, the main scanning dot position deviation at the positions of the light detection units 245S1 to 245S5 Are 40 × RF11, 110 × RF12, 180 × RF13, 250 × RF14, 320 × RF15.

  The optical scanning drive control unit 101b determines the main scanning dot position deviation at each position of the light detection units 245S1 to 245S5 thus obtained, where x is the distance from the light detection unit 145 and y is the main scanning dot position. As a deviation, linear approximation is performed in the form of y = ax + b (step S203 in FIG. 9). Note that this linear approximation may be performed based on the least square method for a plurality of main scanning dot position shifts.

  Further, the optical scanning drive control unit 101b corrects the frequency of the write clock based on the slope component a of the equation y = ax + b, and calculates the phase of the write clock based on the intercept component b (FIG. 9). Step S204).

  Then, the optical scanning drive control unit 101b calculates the above write clock frequency and phase adjustment amount for each reflection surface of the polygon mirror 121 identified by the reflection surface identification unit 103, and performs frequency change and phase adjustment. The written clock is supplied to the light emission drive controller 101a. As a result, the light emission drive control unit 101a executes image formation on each reflection surface of the polygon mirror 121 by applying the above-described write clock frequency and phase adjustment amount (step S205 in FIG. 9).

  Note that the relationship between the slope component a of the equation and the write clock frequency correction amount and the relationship between the intercept component b and the write clock phase adjustment amount are obtained in advance. If the inclination a is on the positive side, the amount of deviation is on the + side, so the main scanning length is shortened by increasing the frequency, and if the intercept b is on the + side, the phase is advanced to eliminate the deviation on the + side. Try to eliminate.

  In this case, FIG. 10 shows a state where the present embodiment is applied to the same dot position deviation as in FIGS. In this case, a dot-and-dash line with reference to dot position shifts at the positions of the plurality of light detection units 245S1 to 245S5 within the main scanning range with respect to a dot position shift on the reflecting surface ("before correction" in FIG. 10). Thus, the correction characteristic of the write clock frequency adjustment by the inclination a and the phase adjustment by the intercept b of y = ax + b is created. In this case, even if the dot position deviation in the main scanning direction is not linear, the correction characteristic is created based on a plurality of points, so that the residual is small on average throughout. . In other words, the dot position shift is not eliminated only in a part of the region such as the end portion, but the dot position shift in the main scanning direction can be minimized and a good image quality can be obtained.

  Here, another specific example is shown. For example, when the dot position deviation as shown in FIG. 11 occurs, the dot position deviation of a certain reflecting surface becomes “before correction” in FIG. In this case, according to the conventional method, a correction characteristic such as a broken line is created with reference to a dot position shift on the downstream side of the main scanning. In this case, since the dot position deviation in the main scanning direction is not linear, after the correction, the residual becomes zero on the downstream side in the main scanning direction, but the residual remains large at other positions. In particular, a large residual is generated near the center in the main scanning direction.

  In this case, FIG. 13 shows a state where the present embodiment is applied to the same dot position deviation as in FIGS. In this case, a dot-and-dash line on the basis of the dot position shifts at the positions of the plurality of light detection units 245S1 to 245S5 within the main scanning range with respect to the dot position shift of the reflecting surface (“before correction” in FIG. 13). Thus, the correction characteristic of the write clock frequency adjustment by the inclination a and the phase adjustment by the intercept b of y = ax + b is created. In this case, even if the dot position deviation in the main scanning direction is not linear, the correction characteristics are created based on a plurality of points, so that there is no extreme difference in the residual, and the residual is entirely It is in a small state on average. That is, the dot position deviation in the main scanning direction can be minimized, and good image quality can be obtained.

  In this embodiment, the correction characteristic to be approximated is obtained, and control is performed based on the slope and intercept of the correction characteristic, so that the control can be simplified.

  Further, as described above, the jitter information is read from the storage unit 151 in the print head 150 and the control unit 101 executes control for correction in accordance with the read jitter characteristic. Even when the printer is replaced, control suitable for the print head 150 after the replacement is executed, and the dot position deviation in the main scanning direction can be minimized without performing any special adjustment work, and a good image quality can be obtained. Obtainable.

<Other embodiment (1)>
In the above embodiment, since the jitter information itself relating to the short period jitter is stored in the storage unit 151, different types of correction data are calculated on the image forming apparatus 100 side as needed, or different correction calculations are performed. Can be performed.

<Other embodiment (2)>
In the above embodiment, an electrophotographic image forming apparatus using laser beam scanning 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 laser beam scanning, 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 160, but the photosensitive member 160 is not limited to the drum type, and may be a belt. In addition, the laser beam and the photoconductor 160 are applied not only to the rotation of the photoconductor 160 in the sub-scanning direction but also to various sub-scanning methods for relatively moving the photoconductor 160 and the laser beam in the sub-scanning direction. can do.

DESCRIPTION OF SYMBOLS 100 Image forming apparatus 101 Control part 101a Light emission drive control part 101b Optical scanning drive control part 103 Reflective surface identification part 110 Laser diode 120 Optical scanning means 121 Polygon mirror 122 Polygon motor 125 Surface detection sensor 130 Optical system 145 Optical detection part (SOS sensor) )
150 Printhead 160 Photoconductor

Claims (8)

An image carrier on which an image is formed by light beam exposure;
A light source that generates the light beam that emits light according to image data in synchronization with a writing clock;
Optical scanning means for scanning the light beam in the main scanning direction on the image carrier by a plurality of reflecting surfaces of a rotary polygon mirror that is rotationally driven by a rotational drive source;
A reflecting surface identifying unit for identifying each reflecting surface of the rotary polygon mirror;
Sub-scanning direction driving means for relatively moving the image carrier and the light beam in a sub-scanning direction orthogonal to the main scanning direction;
A storage unit storing jitter information of the light beam measured at a plurality of positions in the main scanning direction for each reflection surface of the rotary polygon mirror;
With reference to the jitter information read from the storage unit, a correction characteristic approximated by a straight line is obtained for dot position deviation at a plurality of positions generated according to the jitter on each surface of the rotary polygon mirror, and the correction characteristic is And a control unit that changes the frequency of the write clock and adjusts the phase of the write clock in response.
An image forming apparatus comprising: The control unit changes a frequency of the write clock according to a slope of the correction characteristic;
The image forming apparatus according to claim 1. The control unit adjusts the phase of the write clock according to the intercept of the correction characteristic at the start position in the main scanning direction;
The image forming apparatus according to claim 2. The control unit refers to the jitter information at a plurality of positions read from the storage unit when obtaining the correction characteristics, and is included in the jitter information measurement position from the main scanning start end and the jitter information. The dot position deviation at the jitter information measurement position is calculated by a product with the jitter amount.
The image forming apparatus according to claim 1, wherein the image forming apparatus is an image forming apparatus. An image carrier on which an image is formed by light beam exposure;
A light source that generates the light beam that emits light according to image data in synchronization with a writing clock;
Optical scanning means for scanning the light beam in the main scanning direction on the image carrier by a plurality of reflecting surfaces of a rotary polygon mirror that is rotationally driven by a rotational drive source;
A reflecting surface identifying unit for identifying each reflecting surface of the rotary polygon mirror;
Sub-scanning direction driving means for relatively moving the image carrier and the light beam in a sub-scanning direction orthogonal to the main scanning direction;
A storage unit storing jitter information of the light beam measured at a plurality of positions in the main scanning direction for each reflection surface of the rotary polygon mirror;
A control unit for controlling each unit, and a control method for an image forming apparatus comprising:
The control unit refers to the jitter information read from the storage unit, and obtains a correction characteristic that approximates the dot position deviation at a plurality of positions generated according to the jitter on each surface of the rotary polygon mirror by a straight line. Changing the frequency of the write clock according to the correction characteristics and adjusting the phase of the write clock;
An image forming apparatus control method. The control unit changes a frequency of the write clock according to a slope of the correction characteristic;
The image forming apparatus control method according to claim 5. The control unit adjusts the phase of the write clock according to the intercept of the correction characteristic at the start position in the main scanning direction;
The image forming apparatus control method according to claim 6. The control unit refers to the jitter information at a plurality of positions read from the storage unit when obtaining the correction characteristics, and is included in the jitter information measurement position from the main scanning start end and the jitter information. The dot position deviation at the jitter information measurement position is calculated by a product with the jitter amount.
The image forming apparatus control method according to claim 5, wherein the image forming apparatus control method is an image forming apparatus control method.

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