JP2012098454A - Image forming apparatus and control method therefor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To correct a magnification ratio of a primary scanning direction without using a large number of optical detection parts.SOLUTION: An apparatus includes: an optical detection part 140S1 for detecting a light beam at one end in a primary direction; a storage part 160 for pre-correlating a detection interval (scanning time in the primary scanning direction) of a light beam between two points including a primary scanning range of an image carrier on each face of a rotating polygon mirror with a detection interval (one-end scanning time) of a light beam at one point nearby the primary scanning range, and storing the correlation result: a measurement part 150 for measuring the detection interval (one-end scanning time) of a light beam on each face of the rotating polygon mirror detected at the optical detection part; a reflection surface specification part 170 for specifying a correspondence of scanning direction scanning time on each face of the rotating polygon mirror on the basis of a correlation, for each of the rotating polygon mirror, between the stored one-end scanning time and measured one-end scanning time; and a correction part 180 for correcting a positional interval of exposure dots of image data for each face of the rotating polygon mirror by using the specified scanning direction scanning time for each face.

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 laser beam from a light source with a rotary polygon mirror and writing on a recording medium such as a photoconductor. The present invention relates to image forming magnification correction.

  As an image forming apparatus, image formation of one line in the main scanning direction is performed with a light beam 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 for one page. One that performs image formation is known.

  As an example, an electrophotographic image forming apparatus scans a laser beam modulated in accordance with image data in the main scanning direction, and rotates in the sub-scanning direction in parallel with this. Above, an image is formed by the laser beam. In this case, the laser beam is modulated with image data on the basis of a clock signal (write clock) called a dot clock.

  In addition, in order to perform image formation at high speed, a light source such as two or three or more laser diodes (LD) is provided, and laser beams from the plurality of light sources are used in the main scanning direction according to the image data. An image forming apparatus that forms an image for one page by repeating image formation for each line in the sub-scanning direction is known. Such a multi-beam type image forming apparatus is disclosed in, for example, Japanese Patent Laid-Open No. 63-124664.

  In such an image forming apparatus, a deviation in the main scanning direction may occur due to a subtle error of each reflecting surface of the polygon mirror.

  FIG. 11 is an explanatory diagram schematically showing a deviation in the main scanning direction. Here, when performing scanning of a plurality of lines simultaneously in the sub-scanning direction using a plurality of laser beams for speeding up as described above, even when polygon mirrors having the same number of reflection surfaces are used, the number of polygon mirror surface cycles In the main scanning direction deviation generated in (3), the spatial frequency in the sub-scanning direction decreases according to the number of laser beams, and the situation becomes easy to be visually recognized. That is, the sub-scanning direction period of the main scanning direction shifts in accordance with the number of laser beams (the number of lines), resulting in a situation where the spatial frequency is lowered and is easily recognized.

  In order to achieve high image quality with such a multi-beam type image forming apparatus, the main scanning direction start position (starting end) and the main scanning direction end position (termination end) of a plurality of laser beams are aligned. It is important to eliminate the deviation in the main scanning direction between the beams.

  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.

  First, in order to obtain main-scanning direction magnification correction data, it is necessary to provide a light detection unit on the start side and the end side of the laser beam to detect fluctuations in the main-scanning direction scanning time. Since the light detector on the start end is generally provided to determine the main scanning exposure start position, it is necessary to add a light detector on the end. That is, by using two light detection units, there is a problem that the number of parts of the device increases.

  Second, since the main scanning direction magnification correction data has different data for each reflection surface of the polygon mirror, it is necessary to accurately take correspondence between the main scanning direction magnification correction data and each reflection surface of the polygon mirror. For this reason, it is necessary to provide a high-speed compatible sensor that recognizes each reflection surface of the polygon mirror rotating at several tens of thousands of revolutions per second and a processing circuit.

  The present invention has been made to solve the above-described problem, and has an object to perform magnification correction in the main scanning direction without using a surface detection sensor of a polygon mirror and two light detection units in the main scanning direction. To do.

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

  (1) The present invention scans a light beam modulated in accordance with 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 carrier and the light beam. An image forming apparatus that forms an image by exposing the surface of the image carrier by driving the image carrier to move relative to the surface of the image carrier, the light source generating the light beam and a plurality of rotating reflecting surfaces. A rotating polygon mirror that scans the light beam in the main scanning direction, a light detection unit that detects the light beam at one end of the starting end side or the terminal end side in the main scanning direction, and each reflecting surface of the rotating polygon mirror The light beam detection interval between two points including the main scanning range of the image carrier (scanning direction in the main scanning direction) and the detection interval of the light beam at one point near the main scanning range (one-end scanning time) And related in advance A storage unit that stores the data, a measurement unit that measures a detection interval (one-end scanning time) of the light beam at the light detection unit for each reflection surface of the rotary polygon mirror, and the measurement unit that measures the measurement time. The correspondence of the scanning time in the main scanning direction is specified for each reflecting surface of each rotating polygon mirror according to the correlation for each reflecting surface of each rotating polygon mirror between the one end scanning time and the one end scanning time stored in the storage unit. The exposure dot position interval of the image data is adjusted for each reflecting surface of the rotary polygon mirror using the reflecting surface specifying unit and the scanning time in the main scanning direction of each reflecting surface specified by the reflecting surface specifying unit. And a correction unit.

  According to the present invention, a light beam modulated according to image data is scanned in the main scanning direction of the image carrier, and the image carrier and the light beam are relatively moved in the sub-scanning direction orthogonal to the main scanning direction. A method for controlling an image forming apparatus that exposes the surface of the image carrier to form an image by driving it so as to move the image, and includes a main scanning range of the image carrier for each reflecting surface of the rotary polygon mirror. The light beam detection interval between the points (scanning direction in the main scanning direction) and the detection interval of the light beam at one point in the vicinity of the main scanning range (one-end scanning time) are associated in advance and stored in the storage unit, The light beam is scanned in the main scanning direction on the image carrier by a plurality of reflecting surfaces of a rotating polygon mirror, and the light beam is at one end in the main scanning direction so as to include the main scanning range of the image carrier. The light detector And detecting the light beam detection interval (one-end scanning time) by the measuring unit for each reflecting surface of the rotary polygon mirror, and measuring the one-end scanning time and the memory measured by the measuring unit. In accordance with the correlation for each reflecting surface of the rotating polygon mirror with the one-end scanning time stored in the part, the correspondence of the scanning time in the main scanning direction is specified by the reflecting surface specifying unit for each reflecting surface of the rotating polygon mirror, Using the scanning time in the main scanning direction of each reflecting surface specified by the reflecting surface specifying unit, the exposure dot position interval of the image data is adjusted for each reflecting surface of the rotary polygon mirror, and the magnification in the main scanning direction It is characterized by correcting.

  (2) Further, according to the present invention, in the above (1), the storage unit has a magnification in the main scanning direction such that the scanning length is constant for each reflecting surface of the rotary polygon mirror as the main scanning direction scanning time. Is stored in advance, and the correction unit adjusts the exposure dot position interval of the image data for each reflecting surface of the rotary polygon mirror using the magnification correction data. Then, the magnification in the main scanning direction is corrected.

  (3) Further, according to the present invention, in the above (2), the storage unit obtains the magnification correction data from the section scanning time measured in advance by dividing the main scanning range of the image carrier into a plurality of sections. Magnification correction data configured by the section-specific magnification correction data is stored, and the correction unit exposes the image data by using the magnification correction data of each reflecting surface specified by the reflecting surface specifying unit. The dot position interval is adjusted for each reflecting surface of the rotary polygon mirror in a plurality of sections in the main scanning direction to correct the magnification in the main scanning direction.

  (4) Further, according to the present invention, in the above (1) to (3), the correction unit uses a write clock frequency used when the light beam is modulated by the image data as the adjustment of the exposure dot position interval. It is characterized by adjusting.

  (5) Also, in the present invention, in the above (1) to (4), the light source has a function of generating a plurality of light beams aligned in the sub-scanning direction, and the plurality of light beams are respectively It is modulated according to image data adjacent in the sub-scanning direction.

  (6) In the invention (1) to (5), the light detection unit performs detection on a start end side on an extension line of a main scanning position on the image carrier. .

  (7) Moreover, this invention is provided with the control part which changes the rotation speed of the said rotary polygon mirror according to image formation conditions in said (1)-(6), The said control part is the said rotary polygon mirror. Control is performed so that the specification by the reflecting surface specifying unit is performed in a state where the number of rotations is controlled to the lowest.

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

  In the present invention, first, with respect to each reflecting surface of the rotary polygon mirror, the detection interval (scanning time in the main scanning direction) of the light beam between two points including the main scanning range of the image carrier, and one point in the vicinity of the main scanning range. The light beam detection interval (one-end scanning time) is stored in the storage unit in advance in association with the factory shipment or adjustment.

  Then, the light beam is scanned in the main scanning direction on the image carrier by the plurality of reflecting surfaces of the rotating polygon mirror, and the light beam is detected at one end in the main scanning direction so as to include the main scanning range of the image carrier. The detection interval (one-end scanning time) of the light beam in the light detection unit is measured by the measurement unit, and the correlation between the one-end scanning time measured by the measurement unit and the one-end scanning time stored in the storage unit Accordingly, the correspondence of each reflecting surface of the rotary polygon mirror with respect to the scanning time in the main scanning direction is specified by the reflecting surface specifying unit, and the main scanning direction scanning time of each reflecting surface specified by the reflecting surface specifying unit is used. The magnification in the main scanning direction is corrected by adjusting the exposure dot position interval for each reflecting surface of the rotary polygon mirror.

  Note that the main scanning direction scanning time stored in the storage unit may be a variation in each main surface in the main scanning direction scanning time, or magnification correction data generated based on this variation.

  Thus, without using the surface detection sensor of the rotating polygon mirror and the two light detection units in the main scanning direction, each reflecting surface of the rotating polygon mirror and the correction information (based on the scanning time variation in the main scanning direction on each reflecting surface). It becomes possible to perform magnification correction in the main scanning direction while taking correspondence with the magnification correction data.

  Also, magnification correction data is stored that is composed of magnification correction data for each section obtained from a section scanning time measured in advance by dividing the main scanning range of the image carrier into a plurality of sections. Using the magnification correction data of the surface, the exposure dot position interval of the image data is adjusted for each reflecting surface of the rotary polygon mirror in a plurality of sections in the main scanning direction to correct the magnification in the main scanning direction. As a result, when performing magnification correction in the main scanning direction, it is possible to appropriately maintain the pixel position at each position in the main scanning direction as well as the coincidence between the start end and the end.

1 is a block diagram illustrating a configuration (during operation) of an image forming apparatus according to a first embodiment of the present invention. 1 is a block diagram illustrating a configuration (during measurement) of an image forming apparatus according to a first embodiment of the present invention. 3 is a flowchart illustrating an operation of the image forming apparatus according to the first embodiment of the present invention. 3 is a time chart illustrating an operation of the image forming apparatus according to the first embodiment of the present invention. FIG. 6 is an explanatory diagram illustrating characteristics during operation of the image forming apparatus according to the first embodiment of the present invention. 3 is a time chart illustrating an operation of the image forming apparatus according to the first embodiment of the present invention. FIG. 6 is an explanatory diagram for explaining an operation of the image forming apparatus. FIG. 6 is an explanatory diagram for explaining an operation of the image forming apparatus. It is a block diagram which shows the structure (at the time of measurement) of the image forming apparatus of 2nd embodiment of this invention. 6 is a flowchart illustrating an operation of the image forming apparatus according to the second embodiment of the present invention. FIG. 6 is an explanatory diagram for explaining an operation of the image forming apparatus.

  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 modulated according to image data in the main scanning direction of the image carrier, and the image carrier and light in a 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 preliminary operation and the normal operation of the image forming apparatus are the image forming apparatus control method.

[Configuration of First Embodiment (1)]
Hereinafter, the electrical configuration of the first embodiment of the image forming apparatus 100 according to the first embodiment will be described in detail with reference to FIG. In this embodiment, the description will focus on the structural requirements necessary for correcting the deviation in the main scanning direction of exposure by a laser 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 correlates the one-end scanning time (or one-end scanning time variation) measured by the light detection unit 140S1 described later and the one-end scanning time (or one-end scanning time variation) stored in the storage unit 160. Accordingly, with respect to the main scanning direction scanning time (main scanning direction scanning time fluctuation or magnification correction data) stored in the storage unit 160, the correspondence of each reflective surface of the polygon mirror 120 is specified by the reflective surface specifying unit 170, and the reflective surface is specified. The exposure dot position interval of the image data is adjusted for each reflecting surface of the polygon mirror 120 using the main scanning direction scanning time (main scanning direction scanning time variation or magnification correction data) of each reflecting surface specified by the unit 170. The control in correcting the magnification in the main scanning direction is performed.

  The operation unit 105 is an operation input unit for inputting various instructions regarding image formation by the operator, and the content of the instruction input is transmitted from the operation unit 105 to the control unit 101. When a thick paper having a thickness larger than that of a normal recording paper is designated from the operation unit 105 as a paper type used for image formation, the control unit 101 sets the image forming speed to an image forming speed lower than the normal speed. Perform switching control.

  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 LD drive circuit 110D 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 supplies the laser diode 110 with a light emission drive signal modulated according to image data. To do. When a plurality of laser beams aligned in the sub-scanning direction modulated according to image data adjacent in the sub-scanning direction are generated by the laser diode 110, a corresponding light emission drive signal is generated to generate the laser diode 110. To supply.

  The polygon mirror 120 is a rotating polygon mirror that scans the surface of the photosensitive member with a laser beam in the main scanning direction by a plurality of rotating reflecting surfaces. The polygon motor 120M is a rotation driving means that receives the polygon driving signal and rotates the polygon mirror 120 at a predetermined rotation 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 optical system 130 includes a cylindrical lens, a collimator lens, and the like for performing optical processing on the laser 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 photosensitive member surface. Various optical members such as an f-θ lens.

  The photosensitive member 140 is an electrostatic latent image corresponding to image data by exposure of a laser beam scanned in the main scanning direction by rotation of the polygon mirror 120 and rotation in the sub-scanning direction perpendicular to the main scanning direction. Is a photosensitive member as an image carrier on which a toner image is formed by developing the electrostatic latent 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, and the fixing of the toner image on the recording paper are generally used as an image forming apparatus. Therefore, the description is omitted.

  The photosensitive member driving unit 140M is a photosensitive member rotation driving unit that rotates the photosensitive member 140 in the sub-scanning direction at a predetermined rotational speed. The photoconductor driving unit 140M drives the photoconductor 140 so that the photoconductor rotation speed corresponds to the image forming speed determined by the control unit 101.

  The light detection unit 140S1 is a sensor that detects a light beam on the main scanning start end side on the extended line of the main scanning position on the photosensitive member 140, and the detection result is transmitted to the measurement unit 150 described later. The light detection unit 140S1 only needs to detect the light beam at one end on the start side or the end side in the main scanning direction. However, the light detection unit 140S1 is arranged on the start end side in order to align the exposure start position on the photoconductor 140. It is desirable that

  The light detection unit 140S1 disposed on the start end side is called an SOS (Start Of Scan) sensor, and is described as SOS in the drawing.

  Further, in the image forming apparatus 100, the light detection unit is not provided on the main scanning end side. However, as described later, in the measurement jig, the light detection unit 240S1 on the main scanning start side and the light on the main scanning end side are used. A detection unit 240S2 is provided.

  The measuring unit 150 is a detection point (one end scanning time) of the light beam scanned by the rotation of the polygon mirror 120 at the start end side light detection unit 140S1 as one point in the vicinity of the main scanning range, or a polygon mirror for one end scanning time. 120 is a measuring means for measuring variation (one-end scanning time variation) on each reflecting surface.

  The storage unit 160 stores magnification correction data for correcting the magnification in the main scanning direction so that the scanning length is constant for each reflection surface of the polygon mirror 120 at the time of factory shipment by the magnification correction data generation unit 260 described later. It is a storage means for generating and storing.

  The reflection surface specifying unit 170 includes a one-end scanning time (or one-end scanning time variation) of the polygon mirror 120 measured by the measuring unit 150 when the image forming apparatus is used, and a one-end scanning time of the polygon mirror 120 previously measured at the time of factory shipment ( Alternatively, the specifying means for specifying the correspondence between the magnification correction data corresponding to the scanning time in the main scanning direction of the polygon mirror 120 measured in advance at the time of shipment from the factory and each reflecting surface of the polygon mirror 120 in accordance with the correlation with the one-end scanning time fluctuation). It is. The reflection surface specifying unit 170 eliminates the need for a surface detection sensor for the polygon mirror 120.

  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 magnification correction data when generating the write clock, and adjusts the exposure dot position interval of the image data to correct the magnification in the main scanning direction. The correction part which adjusts is comprised. Note that the writing clock generation unit 180 as the correction unit can correct the magnification in the main scanning direction by adjusting the exposure dot position interval of the image data by various methods such as PLL and frequency modulation.

  Note that the write clock generation unit 180 adjusts the exposure dot position interval of the image data for each reflection surface of the polygon mirror 120 using the magnification correction data of each reflection surface specified by the reflection surface specification unit 170, and The magnification in the scanning direction is corrected.

  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 laser beams aligned in the sub-scanning direction modulated according to image data adjacent in the sub-scanning direction, the corresponding image data is output to the LD drive circuit 110D. The

[Configuration (1) of the first embodiment]
FIG. 2 is a block diagram showing a configuration when magnification correction data for correcting the magnification in the main scanning direction so as to make the scanning length constant for each reflection surface of the polygon mirror 120 is generated in advance at the time of factory shipment. .

  Here, the same components as those in FIG. Further, in FIG. 2, the part that was 1X0 in FIG. 1 is assigned a number of 2X0 to indicate that it is related.

  In order to obtain magnification correction data used when correcting the magnification in the main scanning direction so that the main scanning length is constant for each reflecting surface of the polygon mirror 120, the exposure unit A centering on the polygon mirror 120 is used as a measurement jig. It shows the state of wearing.

  The measurement jig includes a light detection unit 240S1 arranged at a position corresponding to the light detection unit 140S1 on the main scanning start end side on the extension line of the main scanning position of the image forming apparatus 100, and the main scanning position of the image forming apparatus 100. Of the scanning time (main scanning direction scanning time) of the predetermined distance or the main scanning direction scanning time from the detection results of the light detection unit 240S2 and the light detection units 240S1 and 240S2 arranged at the position corresponding to the main scanning end side on the extension line The polygon mirror 120 measures the time difference (main scanning direction scanning time fluctuation) of each reflecting surface, the main scanning direction scanning time measured by the measuring section 250 or the main scanning direction scanning time fluctuation based on the polygon mirror 120. A magnification correction data generation unit 260 that generates magnification correction data when correcting the magnification in the main scanning direction so that the main scanning length is constant for each reflection surface. Ete is configured. Various means (not shown) such as an operation unit, a display unit, a measurement control unit, and an interface may be provided.

  The light detection unit 240S1 disposed on the start end side is referred to as an SOS (Start Of Scan) sensor and is denoted as SOS in the drawing, and the light detection unit 240S2 disposed on the end side is an EOS (End Of Scan). It is called a sensor and is described as EOS in the figure.

  In addition, the measurement unit 250 is the light detection unit 240S1 on the start end side, and the detection interval (one end scanning time) of the light beam scanned by the rotation of the polygon mirror 120, or each reflection surface of the polygon mirror 120 for this one end scanning time. Variation (one-end scanning time fluctuation) is measured.

  The magnification correction data generated by the magnification correction data generation unit 260 is magnification correction data for correcting the magnification in the main scanning direction so that the scanning length is constant for each reflection surface of the polygon mirror 120.

  The generated magnification correction data or main scanning direction scanning time fluctuation is stored in the storage unit 160 in a state associated with the one-end scanning time or the one-end scanning time fluctuation, and is used at the time of image formation.

[Pre-operation of the first embodiment]
Hereinafter, the magnification correction data acquisition operation (preliminary operation) will be described with reference to the flowchart of FIG.

  First, as this preliminary operation, in order to acquire magnification correction data used when correcting the magnification in the main scanning direction so that the main scanning length is constant for each reflection surface of the polygon mirror 120, the polygon mirror 120 is the center. An operation in a state where the exposure unit A is mounted on the measurement jig (see FIG. 2) will be described.

  Note that the magnification correction data acquisition operation with the exposure unit A mounted on the measurement jig is performed when adjustment is performed in a manufacturing factory or an adjustment facility (hereinafter referred to as factory shipment). That is, before the image forming apparatus 100 is normally used, a magnification correction data acquisition operation is executed in advance.

  First, when viewed from the exposure unit A, the light detection unit 240S1 of the measurement jig is positioned at the position where the light detection unit 140S1 of the image forming apparatus 100 should be, and on the extension line of the main scanning position of the image forming apparatus 100. The exposure unit A is mounted on the measurement jig so that the light detection unit 240S2 comes to a position corresponding to the main scanning end side (step S101 in FIG. 3). In addition, when the exposure unit A is mounted on the measurement jig in advance, it is desirable that the alignment and the like have been completed on the measurement jig side in advance so that each light detection unit comes to a predetermined position. Further, the magnification correction data generation unit 260 and the storage unit 160 are connected so that the magnification correction data generated by the magnification correction data generation unit 260 is stored in the storage unit 160. Note that an interface, a connector, or the like (not shown) may be used.

  Then, with the exposure unit A mounted on the measurement jig as described above, the control unit 101 controls the polygon mirror 120 to rotate at a predetermined rotational speed. At this time, there may be some instruction from the measurement jig side, and when the measurement jig and the exposure unit A are connected, the control unit 101 automatically starts rotating the polygon mirror 120. Also good.

  In this state, the measuring unit 250 scans in the main scanning direction (the time difference in which the light detection unit 240S1 on the start side and the light detection unit 240S2 on the end side detect the light beam) and the one end scanning time (on the start side). The time difference at which the light detector 240S1 detects the light beam is measured (step S102 in FIG. 3).

  4A shows the detection result of the light detection unit 240S1 when the polygon mirror 120 rotates, FIG. 4B shows the detection result of the light detection unit 240S2 when the polygon mirror 120 rotates, and FIG. The reflection surface at the time of polygon mirror 120 rotation is shown.

  In addition, since the surface detection sensor is not used in 1st embodiment, since the absolute surface number of the reflective surface of the polygon mirror 120 cannot be managed, the reflective surface number in prior operation | movement is represented as #a, #b, ..., The reflection surface numbers in normal operation are represented as #A, #B,.

  Here, the time from the detection result of the light detection unit 240S1 (FIG. 4A) to the detection result of the light detection unit 240S2 (FIG. 4B) is a main scanning direction scanning time Tse (xy). Note that x represents the reflection surfaces #a to #f of the polygon mirror 120, and y represents the number of rotations from the start of measurement. In order to reduce the error, data for a predetermined number of rotations, for example, data for 500 rotations is acquired and then averaged for each reflecting surface.

  In addition, regarding the variation in the respective reflecting surfaces of the polygon mirror 120 with respect to the scanning time in the main scanning direction (main scanning direction scanning time fluctuation), the average value of the scanning times in the main scanning direction of all the reflecting surfaces is set as a reference (deviation 0%). Then, the deviation from the average value of the scanning time in the main scanning direction of each reflecting surface is obtained (see FIG. 5A).

  When a plurality of rotation speeds of the polygon mirror 120 can be selected, the control unit 101 performs control so that the above measurement is performed with the polygon mirror 120 controlled to the lowest rotation speed. This is because the lower the number of rotations of the polygon mirror 120, the more prominently the deviation in the main scanning direction at each reflecting surface of the polygon mirror 120 appears.

  Here, the time from the detection result of the light detection unit 240S1 (FIG. 4A) to the next detection result of the light detection unit 240S1 (FIG. 4A) is defined as one-end scanning time Tss (xy). . Note that x represents the reflection surfaces #a to #f of the polygon mirror 120, and y represents the number of rotations from the start of measurement. In this case as well, in order to reduce the error, data for a predetermined number of rotations, for example, data for 500 rotations is acquired and then averaged for each reflecting surface.

  As for the variation in the respective reflecting surfaces of the polygon mirror 120 for this one-end scanning time (one-end scanning time fluctuation), one end of each reflecting surface is based on an average value of one-end scanning times of all reflecting surfaces as a reference (deviation 0%). A deviation from the average value of the scanning time is obtained (see FIG. 5B).

  Then, the measurement unit 250 notifies the magnification correction data generation unit 260 of the main scanning direction scanning time or main scanning direction scanning time variation and the one end scanning time variation or one end scanning time variation of each reflecting surface of the polygon mirror 120.

  The magnification correction data generation unit 260 corrects the magnification in the main scanning direction so that the scanning length is constant on each reflecting surface of the polygon mirror 120 from the main scanning direction scanning time or the fluctuation in the main scanning direction scanning time. Is generated (step S103 in FIG. 3).

  Then, the magnification correction data generation unit 260 associates the magnification correction data of each reflection surface of the polygon mirror 120 with the one end scanning time or the one end scanning time variation of each reflection surface of the polygon mirror 120 and stores it in the storage unit 160 (see FIG. 3 in step S104).

  For example, as shown in FIGS. 5 (a) and 5 (b), the #a to #f reflecting surfaces are stored in 01h to 06h of the storage unit 160 as magnification correction data or main scanning direction scanning time variation, and the one end scanning time or The #a to #f reflecting surfaces are stored in 11h to 16h of the storage unit 160 as the one-time scanning time fluctuation.

  Here, when the magnification correction data and the one-end scanning time or the magnification correction data and the one-end scanning time variation are stored in the storage unit 160, the control unit 101 stops the rotation of the polygon mirror 120, and obtains the magnification correction data acquisition operation. To complete.

  Thereafter, the exposure unit A is removed from the measurement jig and placed at a predetermined position of the image forming apparatus 100 (step S105 in FIG. 3).

[Normal operation of the first embodiment]
Hereinafter, the normal operation of the image forming apparatus 100 of the first embodiment will be described with reference to the flowchart of FIG.

  This normal operation refers to the image forming apparatus 100 in which the magnification correction data is stored in the storage unit 160 by performing the magnification correction data acquisition operation in advance by the above-described preliminary operation (steps S101 to S105 in FIG. 3). It is meant to be used for forming.

  When the power of the image forming apparatus 100 is turned on or the standby state such as the sleep mode is released, the control unit 101 performs the following control. First, the control unit 101 initializes each unit of the image forming apparatus 100 and activates the polygon motor 120M to rotate at a predetermined rotational speed via the polygon motor drive circuit 120D (step S201 in FIG. 3). Each unit of the image forming apparatus 100 includes toner density control of the developer of the developing device, fixing temperature control of the fixing device, and the like. At least the polygon mirror 120 that is rotationally driven by the polygon motor 120M has a predetermined number of rotations. When it reaches, the process proceeds to the following process.

  Here, the control unit 101 gives an instruction to the LD drive circuit 110D to cause the LD 110 to emit light, and the polygon mirror 120 scans the light beam. Further, the control unit 101 controls each unit so as to perform the following operation.

  The measurement unit 150 measures the detection interval (one-end scanning time) of the light beam scanned by the rotation of the polygon mirror 120 by the light detection unit 140S1 on the start end side as one point near the main scanning range (step in FIG. 3). S202).

  FIG. 4D shows a measurement flag which becomes H level when the rotation of the polygon mirror 120 is stably measured, and FIG. 4E shows the detection of the light detection unit 140S1 when the polygon mirror 120 is rotated. A result is shown and FIG.4 (f) shows the reflective surface at the time of polygon mirror 120 rotation. In the first embodiment, since the surface detection sensor is not used, the absolute surface number of the reflection surface of the polygon mirror 120 cannot be managed. Therefore, the reflection surface numbers are represented as #A, #B,. .

  Here, the time from the detection result of the light detection unit 140S1 (FIG. 4E) to the next detection result of the light detection unit 140S1 (FIG. 4E) is defined as one-end scanning time Tss (XY). X represents the reflection surfaces #A to #F of the polygon mirror 120, and Y represents the number of rotations from the start of measurement. In this case, in order to reduce the error, data for a plurality of predetermined rotations, for example, data for 500 rotations is acquired and then averaged for each reflecting surface.

  As for the variation in the respective reflecting surfaces of the polygon mirror 120 for this one-end scanning time (one-end scanning time fluctuation), one end of each reflecting surface is based on an average value of one-end scanning times of all reflecting surfaces as a reference (deviation 0%). A deviation from the average value of the scanning time is obtained (see FIG. 5C).

  After measuring as described above, the measurement unit 150 notifies the reflection surface specifying unit of the measurement result.

  And the reflective surface specific | specification part 170 reads the difference (FIG.5 (b)) for every reflective surface of the one end scanning time fluctuation | variation measured at the time of factory shipment beforehand from the memory | storage part 160, and the one end obtained by measuring with the measurement part 150 Comparison is made with the difference of the scanning time variation for each reflecting surface (FIG. 5C).

  In the first embodiment, the polygon mirror 120 does not include a surface detection sensor for identifying each reflection surface, and therefore there is no absolute surface number for each reflection surface. That is, #a to #f in the horizontal axis direction in FIG. 5B are convenient surface numbers at the time of preliminary operation, and #A to #F in the horizontal axis direction in FIG. This is a convenient face number.

  Therefore, from the pattern (difference difference of each reflecting surface) of each reflecting surface with one-end scanning time variation, the surface numbers #a to #f at the time of the preliminary operation in FIG. 5B and the image in FIG. 5C. Matching of the surface numbers #A to #F at the time of formation is obtained using pattern matching or the like.

  In this example, as shown in FIGS. 6A and 6B, the reflection surfaces #a, #b, #c, #d, #e, and #f during the pre-operation and the reflection surfaces #C, It is determined by the reflecting surface specifying unit 170 that #D, #E, #F, #A, and #B match (step S203 in FIG. 3).

  Even if the rotational speed of the polygon mirror 120 in the measurement at the time of shipment from the factory is different from the rotational speed of the polygon mirror 120 when the image forming apparatus is used, the above-described pattern of deviation in the main scanning direction of each reflecting surface is rough. Since the shapes are similar, the reflecting surface can be specified by pattern matching or the like.

  When the image forming apparatus 100 can select a plurality of rotation speeds of the polygon mirror 120, the control unit 101 specifies the reflection surface specifying unit 170 with the polygon mirror 120 controlled to the lowest rotation speed. Control to do. This is because the lower the number of rotations of the polygon mirror 120, the more prominently the amount of deviation in the main scanning direction when the image forming apparatus is used.

  The control unit 101 reads magnification correction data of each reflection surface measured in advance from a predetermined address in the storage unit according to the reflection surface specified in this way (see FIG. 6C), and uses it at the time of image formation. This is applied to each reflecting surface of the polygon mirror 120 in the middle, and the correction unit controls the exposure dot position interval of the image data for each reflecting surface of the polygon mirror 120 to correct the magnification in the main scanning direction (FIG. 3). Middle step S204).

  Then, the control unit 101 reads out the magnification correction data of each reflecting surface measured in advance from the storage unit 160 and applies the magnification correction data to the write clock in a state in which the clock frequency is adjusted by the write clock generation unit 180. The generated image is applied to the LD drive circuit 110D and the image processing unit 190, and the exposure dot position interval of the image data is adjusted so as to eliminate the main scanning direction deviation from the start end to the end. The formation is executed (step S205 in FIG. 3).

  As described above, in this embodiment, the magnification correction data for correcting the magnification in the main scanning direction is generated in advance in association with the one-time scanning time and stored in the storage unit 160 and measured by the measurement unit during image formation. In accordance with the correlation between the one-end scanning time and the one-end scanning time stored in the storage unit, the reflection surface specifying unit specifies the correspondence of each reflection surface of the rotary polygon mirror with respect to the main scanning direction scanning time stored in advance, By correcting the magnification in the main scanning direction using the main scanning direction scanning time of each specified reflecting surface, the polygon is detected without using the surface detection sensor of the polygon mirror 120 and the two light detection units in the main scanning direction. It becomes possible to perform magnification correction in the main scanning direction while taking correspondence between each reflection surface of the mirror 120 and correction information (magnification correction data based on fluctuations in scanning time in the main scanning direction on each reflection surface).

[Second Embodiment]
FIG. 7A shows the deviation in the main scanning direction when one laser beam is scanned on each reflecting surface of the six-sided polygon mirror 120. Also, FIG. 7B shows how the deviation state changes according to each position in the main scanning direction by converting the deviation in the main scanning direction of each reflecting surface of the polygon mirror 120 having the same six surfaces into the vertical axis direction. It is explanatory drawing which shows this profile typically. The characteristic of the tilt of the deviation state in FIG. 7B represents the difference in flatness of each reflecting surface.

  For example, the first surface (# 1) and the third surface (# 3) in FIG. 7B are substantially equal in the main scanning direction, but have different profiles in the middle of the main scanning direction. For this reason, when # 1 and # 3 are uniformly reduced, the pixel positions at the start and end of the main scanning direction are aligned, but the pixel positions are not aligned near the middle in the main scanning direction.

  For this reason, even if the start end and the end end are aligned by correcting the magnification in the main scanning direction, the pixel positions are not aligned in the sub-scanning direction at the intermediate portion in the main scanning direction. As a result, depending on the type of image, as shown in FIG. 8, there may occur a phenomenon in which a moire-like portion is generated around the intermediate portion in the main scanning direction, or a vertical line is distorted.

[Configuration of Second Embodiment]
FIG. 9 is a block diagram showing a configuration when performing an operation for obtaining magnification correction data (preliminary operation) in the second embodiment. Here, the same components as those in the first embodiment shown in FIG.

  In order to obtain magnification correction data used when correcting the magnification in the main scanning direction so that the main scanning length is constant for each reflecting surface of the polygon mirror 120, the exposure unit A centering on the polygon mirror 120 is used as a measurement jig. It shows the state of wearing.

  As the measurement jig, an image forming apparatus is provided between the light detection unit 240S1 on the main scanning start side on the extension line of the main scanning position of the image forming apparatus 100 and the light detection unit 240S2 disposed on the main scanning end side. A plurality of photodetecting portions 241S1 to 241S5 are arranged at the same position as the main scanning range of 100 photoconductors 140.

  In addition to the one-end scanning time by the light detection unit 240S1 and the main scanning direction scanning time by the light detection units 240S1 and 240S2, the measurement unit 250 performs scanning in the main scanning direction for each section based on the detection results of the light detection units 241S1 to 241S5. Measure time.

  In addition to the magnification correction data in the main scanning direction described in the first embodiment, the magnification correction data generation unit 260 generates magnification correction data for each section according to the detection results of the light detection units 241S1 to 241S5.

  Here, a specific example is given of the case where the magnification correction data for each of four sections is obtained by five sensors of the light detection units 241S1 to 241S5. The generated section-by-section magnification correction data is stored in the storage unit 160 together with the magnification correction data, and is used at the time of image formation.

[Pre-operation of the second embodiment]
This pre-operation is an operation in a state where the exposure unit A centering on the polygon mirror 120 is mounted on the measurement jig (see FIG. 9), and is basically the same as the first embodiment. Hereinafter, the difference between the magnification correction data acquisition operation (preliminary operation) and the operation of the first embodiment will be described.

  First, the exposure unit A is mounted on the measurement jig so that the light detection units 241S1 to 241S5 are arranged at the same position as the main scanning range of the photoconductor 140 of the image forming apparatus 100 (step S301 in FIG. 10).

  Here, in addition to the measurement of the one-end scanning time by the light detection unit 240S1 and the measurement of the scanning time in the main scanning direction by the light detection units 240S1 and 240S2, the measurement unit 250 uses the detection results of the light detection units 241S1 to 241S5 based on the detection results. The section scanning time obtained by dividing the scanning direction scanning time for each section is measured (step S302 in FIG. 10).

  Then, the magnification correction data generation unit 260, in addition to the generation of magnification correction data in the main scanning direction described in the first embodiment, magnification correction for each section according to the section scanning time that is the detection result of the light detection units 241S1 to 241S5. Data is generated (step S303 in FIG. 10). That is, in the second embodiment, not only the magnification correction data from the start to the end but also the magnification correction data configured by the magnification correction data for each section obtained from the above section scanning time is generated.

  Then, the magnification correction data generation unit 260 associates the magnification correction data including the above-described magnification correction data for each section with the one end scanning time or the one end scanning time variation of each reflection surface of the polygon mirror 120 and causes the storage unit 160 to store the data (see FIG. 10 step S304).

  When the magnification correction data including the magnification correction data for each section and the one-time scanning time are stored in the storage unit 160, the control unit 101 stops the rotation of the polygon mirror 120 and completes the magnification correction data acquisition operation. Thereafter, the exposure unit A is removed from the measurement jig and installed at a predetermined position of the image forming apparatus 100 (step S305 in FIG. 10).

[Normal operation of the second embodiment]
This normal operation is basically the same as in the first embodiment. Hereinafter, the difference between the normal operation of the second embodiment and the operation of the first embodiment will be described.

  When the image forming apparatus 100 is in an operating state, the control unit 101 initializes each part of the image forming apparatus 100 and starts up the polygon motor 120M to rotate at a predetermined rotational speed via the polygon motor driving circuit 120D (see FIG. 10 in step S401).

  When the polygon mirror 120 reaches a predetermined number of rotations, the measurement unit 150 detects the detection interval (one end of the light beam) scanned by the rotation of the polygon mirror 120 by the light detection unit 140S1 on the start end side as one point near the main scanning range. (Scanning time) is measured, and the measurement result is notified to the reflecting surface specifying unit (step S402 in FIG. 10).

  Then, the reflecting surface specifying unit 170 reads out the difference between the reflecting surfaces of the one-end scanning time variation measured in advance at the time of shipment from the storage unit 160 and measures the one-end scanning time variation obtained by the measuring unit 150 for each reflecting surface. Compared with the difference, the correspondence of the reflecting surface is specified (step S403 in FIG. 10).

  The control unit 101 reads magnification correction data of each reflection surface measured in advance from a predetermined address in the storage unit according to the reflection surface specified in this way (see FIG. 6C), and uses it at the time of image formation. This is applied to each reflecting surface of the polygon mirror 120 in the middle, and the correction unit controls the exposure dot position interval of the image data for each reflecting surface of the polygon mirror 120 to correct the magnification in the main scanning direction (FIG. 10). Middle step S404).

  The control unit 101 reads the magnification correction data and the magnification correction data for each section measured in advance from the predetermined address of the storage unit according to the reflection surface specified in this way, and is in use at the time of image formation. 10 is applied to each reflecting surface of the polygon mirror 120, and the correction unit controls the exposure dot position interval of the image data for each reflecting surface of the polygon mirror 120 to correct the magnification in the main scanning direction (in FIG. 10). Step S404).

  Then, the control unit 101 reads the magnification correction data / magnification correction data for each section measured in advance from the storage unit 160, and adjusts the clock frequency by applying the magnification correction data / magnification correction data for each section. The write clock generation unit 180 generates a write clock in the above-described state and applies the write clock to the LD drive circuit 110D and the image processing unit 190, so that the main scanning direction shift is not limited to the coincidence of the start end to the end, and the main scan Image formation is performed with the exposure dot position interval of the image data adjusted so as to eliminate even the middle portion of the range (step S405 in FIG. 10).

  As described above, in this embodiment, the magnification correction data for correcting the magnification in the main scanning direction is generated in advance in association with the one-time scanning time and stored in the storage unit 160 and measured by the measurement unit during image formation. In accordance with the correlation between the one-end scanning time and the one-end scanning time stored in the storage unit, the reflection surface specifying unit specifies the correspondence of each reflection surface of the rotary polygon mirror with respect to the main scanning direction scanning time stored in advance, By correcting the magnification in the main scanning direction using the main scanning direction scanning time of each specified reflecting surface, the polygon is detected without using the surface detection sensor of the polygon mirror 120 and the two light detection units in the main scanning direction. It becomes possible to perform magnification correction in the main scanning direction while taking correspondence between each reflection surface of the mirror 120 and correction information (magnification correction data based on fluctuations in scanning time in the main scanning direction on each reflection surface).

  In the above embodiment, the magnification correction data constituted by the magnification correction data for each section obtained from the section scanning time measured in advance by dividing the main scanning range into a plurality of sections is stored, and the polygon mirror 120 is stored. When adjusting the magnification in the main scanning direction by adjusting the respective reflecting surfaces in a plurality of sections in the main scanning direction and correcting the magnification in the main scanning direction, not only the coincidence between the start and end but also the main end It is possible to appropriately maintain the pixel position at each position in the scanning direction. As a result, the pixel position deviation at the intermediate portion in the main scanning direction shown in FIG. 8 is eliminated.

  In the above description of the second embodiment, the main scanning range is divided into four sections by the five sensors of the light detection units 241S1 to 241S5. However, the present invention is not limited to this numerical value. Various modifications are possible for the section.

  In the second embodiment, the light detection units 240S1 and 240S2 of the measurement jig may be omitted, and the one-end scanning time and the main scanning direction scanning time may be obtained using the light detection units 241S1 to 241S5.

  Further, in the above description of the second embodiment, the light detection units 241S1 to 241S5 are evenly arranged to measure the section scanning time. However, the present invention is not limited to this. For example, it is possible to arrange the light detection unit so that a specific area such as the vicinity of the center is fine and other areas are rough. Thereby, it is possible to correct the magnification in the main scanning direction with high accuracy for a specific region.

<Other embodiment (1)>
In the above embodiment, an electrophotographic image forming apparatus using a laser 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 laser beam, and good results can be obtained.

<Other embodiment (2)>
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 laser 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 laser 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 of the exposure units A.

DESCRIPTION OF SYMBOLS 100 Image forming apparatus 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 140S1 Photodetection part 150 Measurement part 160 Storage part 180 Write clock generation part 190 Image processing unit 240S1, 240S2 Light detection unit 241S1 to 241S5 Light detection unit 250 Measurement unit 260 Magnification correction data generation unit

Claims (8)

A light beam modulated in accordance with image data is scanned in the main scanning direction of the image carrier, and the image carrier and the light beam are relatively moved in a sub-scanning direction orthogonal to the main scanning direction. An image forming apparatus that forms an image by exposing the surface of the image carrier by driving,
A light source for generating the light beam;
A rotating polygon mirror that scans the light beam in the main scanning direction on the image carrier by a plurality of rotating reflecting surfaces;
A light detection unit for detecting the light beam at either one of the start end side and the end end side in the main scanning direction;
The light beam detection interval (main scanning direction scanning time) between two points including the main scanning range of the image carrier on each reflecting surface of the rotary polygon mirror and the light beam at one point in the vicinity of the main scanning range. A storage unit for storing the detection interval (one-end scanning time) in advance in association with each other,
A measuring unit that measures a detection interval (one-end scanning time) of the light beam at the light detection unit for each reflecting surface of the rotary polygon mirror;
The main scanning is performed on each reflecting surface of the rotating polygon mirror according to the correlation of each reflecting surface of the rotating polygon mirror between the one end scanning time measured by the measuring unit and the one end scanning time stored in the storage unit. A reflecting surface identifying unit that identifies the correspondence of the direction scanning time;
A correction unit that adjusts the exposure dot position interval of the image data for each reflecting surface of the rotary polygon mirror using the scanning time in the main scanning direction of each reflecting surface specified by the reflecting surface specifying unit;
An image forming apparatus comprising: The storage unit stores, as the scanning time in the main scanning direction, magnification correction data generated in advance to correct the magnification in the main scanning direction so that the scanning length is constant for each reflecting surface of the rotary polygon mirror. And
The correction unit corrects the magnification in the main scanning direction by adjusting the exposure dot position interval of the image data for each reflection surface of the rotary polygon mirror using the magnification correction data.
The image forming apparatus according to claim 1. The storage unit includes, as the magnification correction data, magnification correction data constituted by section-by-section magnification correction data obtained from a section scanning time measured in advance by dividing the main scanning range of the image carrier into a plurality of sections. Remember,
The correction unit uses the magnification correction data of each reflecting surface specified by the reflecting surface specifying unit to determine the exposure dot position interval of the image data for a plurality of sections in the main scanning direction for each reflecting surface of the rotary polygon mirror. The image forming apparatus according to claim 2, wherein the magnification in the main scanning direction is corrected by adjusting separately. The correction unit adjusts a writing clock frequency used when modulating the light beam by the image data as the adjustment of the exposure dot position interval.
The image forming apparatus according to claim 1, wherein the image forming apparatus is an image forming apparatus. The light source has a function of generating a plurality of light beams aligned in the sub-scanning direction;
The plurality of light beams are each modulated according to image data adjacent in the sub-scanning direction,
The image forming apparatus according to claim 1, wherein the image forming apparatus is an image forming apparatus. The light detection unit performs detection on a start end side on an extension line of a main scanning position on the image carrier.
The image forming apparatus according to claim 1, wherein the image forming apparatus is an image forming apparatus. A controller that changes the rotational speed of the rotary polygon mirror according to image forming conditions;
The control unit is controlled to perform the specification by the reflective surface specifying unit in a state where the control is performed at the lowest rotational speed of the rotary polygon mirror.
The image forming apparatus according to claim 1, wherein the image forming apparatus is an image forming apparatus. A light beam modulated in accordance with image data is scanned in the main scanning direction of the image carrier, and the image carrier and the light beam are relatively moved in a sub-scanning direction orthogonal to the main scanning direction. A method of controlling an image forming apparatus for performing image formation by exposing the surface of the image carrier by driving,
The light beam detection interval (main scanning direction scanning time) between two points including the main scanning range of the image carrier on each reflecting surface of the rotary polygon mirror and the light beam at one point in the vicinity of the main scanning range. Is stored in the storage unit in advance in association with the detection interval (one-end scanning time),
The light beam is scanned in the main scanning direction on the image carrier by a plurality of reflecting surfaces of a rotating polygon mirror,
The light beam is detected by a light detection unit at one end in the main scanning direction so as to include the main scanning range of the image carrier,
Measure the light beam detection interval (one-end scanning time) at the light detection unit with respect to each reflecting surface of the rotary polygon mirror,
The main scanning is performed on each reflecting surface of the rotating polygon mirror according to the correlation of each reflecting surface of the rotating polygon mirror between the one end scanning time measured by the measuring unit and the one end scanning time stored in the storage unit. The correspondence of the direction scanning time is specified by the reflecting surface specifying unit,
Using the scanning time in the main scanning direction of each reflecting surface specified by the reflecting surface specifying unit, the exposure dot position interval of the image data is adjusted for each reflecting surface of the rotary polygon mirror, and the magnification in the main scanning direction Correct,
An image forming apparatus control method.

Images