JP6726046B2 - Image forming device - Google Patents

Description

The present invention relates to an image forming apparatus.

An image forming apparatus of an electrophotographic apparatus can control a sheet conveyance speed according to a type of paper in order to improve the fixing property of an image on various papers (sheets) such as plain paper, thick paper, and coated paper. is there. For example, when forming an image on thick paper, the conveying speed is set to 1/2 of the conveying speed when forming an image on plain paper. When such a conveyance speed control is performed, the rotation speed of the photosensitive drum or the like may be adjusted according to the conveyance speed, while the rotation speed of the polygon mirror may be constant regardless of the conveyance speed. When the rotation speed of the polygon mirror is kept constant irrespective of the sheet conveying speed, the image formation may be performed by not using the reflecting surface of the polygon mirror for each surface but using the reflecting surface for every other surface. .. Patent Document 1 describes an image forming apparatus that uses every other reflective surface of a polygon mirror.

Further, in the electrophotographic image forming apparatus, magnification correction for correcting the magnification in the main scanning direction of the image formed by scanning the light beam (laser light) can be performed. Patent Document 2 describes an image forming apparatus that performs magnification correction of an image formed by laser light deflected by a reflecting surface of a polygon mirror for each reflecting surface. This is because an image can be formed at different magnifications for each reflecting surface that deflects the laser light due to minute deformation or eccentricity of the polygon mirror. In particular, in a multi-beam type image forming apparatus using a plurality of laser beams, an image defect due to a difference in magnification between reflection surfaces is likely to occur.

JP-A-4-249182 JP, 2013-240994, A

As described above, in the image forming apparatus that forms an image in any one of the operation mode in which the reflection surface of the polygon mirror is used for every one surface and the operation mode in which the reflection surface is used for every other surface, any operation mode is used. , It is necessary to perform magnification correction for each reflective surface used. That is, it is necessary to sequentially switch the correction data to be valid for use in the magnification correction in accordance with the switching of the reflecting surface used for image formation. In this case, the order in which the correction data is validated differs depending on whether the reflecting surface of the polygon mirror is used for each surface or for every other surface, so that different control can be performed according to the operation mode. Need to For example, it is necessary to separately prepare a control program for switching the correction data to be validated for each operation mode, and the memory capacity necessary for storing such a program may increase.

The present invention has been made in view of the above problems. The present invention realizes switching of correction data to be effective for image magnification correction in the same procedure when image formation is performed by using the reflecting surface of the rotating polygon mirror for each one surface or each M surface, It is an object of the present invention to provide a technique for performing correction processing based on correction data.

The present invention can be realized, for example, as an image forming apparatus. An image forming apparatus according to an aspect of the present invention includes a light source that emits a light beam for exposing a photoconductor, and a plurality of reflecting surfaces, and is rotationally driven so that the light beam scans the photoconductor. A rotating polygon mirror that deflects the light beam by any one of the plurality of reflecting surfaces in a state where the plurality of reflecting surfaces are used for each reflecting surface in the first mode image formation, In image formation in the second mode, the plurality of reflective surfaces are used for each M reflective surface (M is an integer of 2 or more) and are associated with the rotary polygon mirror and the plurality of reflective surfaces, respectively. In addition, a storage unit that stores a plurality of correction data for correcting the magnification in the scanning direction of the light beam of the image formed using the corresponding reflection surface, and the plurality of storage units stored in the storage unit. The correction data to be validated among the correction data is switched according to the rotation of the rotary polygon mirror in the order in which the plurality of reflecting surfaces are arranged in the rotation direction of the rotary polygon mirror, and the light source is driven based on the valid correction data. A correction unit that performs correction processing on the image data for use in the image processing, and the correction unit sets the correction data to be valid according to the rotation of the rotary polygon mirror even when image formation is performed in the second mode. It is characterized in that it is switched in sequence for each reflecting surface.

According to the present invention, when the image formation is performed by using the reflecting surface of the rotary polygon mirror for each one surface or each M surface, the switching of the correction data that is effective for the magnification correction of the image is realized by the same procedure. However, it becomes possible to perform the correction process based on the correction data.

Sectional drawing which shows the structural example of an image forming apparatus. Perspective view showing a configuration example of the optical scanning unit Block diagram showing an example of the control configuration for the optical scanning unit The figure which shows the example of the conversion table for converting pixel data into drive data. Timing chart showing an example of inserting and removing auxiliary pixels for magnification correction processing FIG. 6 is a diagram showing an example of dot formation positions in the main scanning direction before magnification correction processing. FIG. 6 is a diagram showing an example of dot formation positions in the main scanning direction after magnification correction processing. Timing chart showing the timing of operations related to magnification correction processing Flowchart showing the control procedure of the optical scanning unit by the controller The figure which shows the example of the deviation of the magnification of the image in the main scanning direction ((A), (C)), and the schematic diagram of the image formed when magnification correction processing is not performed ((B), (D)). The figure which shows the example of the visual sensitivity characteristic which shows the relationship between spatial frequency and visual sensitivity.

Hereinafter, modes for carrying out the present invention will be described with reference to the drawings. Note that the following embodiments do not limit the invention according to the claims, and all combinations of the features described in the embodiments are not necessarily essential to the solving means of the invention.

[First Embodiment]
<Image forming apparatus 100>
FIG. 1 is a sectional view showing a hardware configuration of an image forming apparatus 100 according to the first embodiment. The image forming apparatus 100 may be an image forming apparatus that forms a single color image, but here, it is assumed that the image forming apparatus forms a multicolor image using toners (developers) of a plurality of colors. The image forming apparatus 100 may be, for example, any one of a printing apparatus, a printer, a copying machine, a multifunction peripheral (MFP), and a facsimile apparatus. It should be noted that Y, M, C, and K at the end of the reference numerals indicate that the colors of the toners targeted by the corresponding members are yellow, magenta, cyan, and black, respectively. In the following description, reference symbols without Y, M, C, and K at the end are used when it is not necessary to distinguish colors.

The image forming apparatus 100 includes four image forming units (image forming stations) that form images (toner images) using toners of Y color, M color, C color, and K color, respectively. The image forming unit corresponding to each color includes photosensitive drums (photoconductors) 102Y, 102M, 102C, and 102K, respectively. Around the photosensitive drums 102Y, 102M, 102C, 102K, charging units 103Y, 103M, 103C, 103K, optical scanning units (optical scanning devices) 104Y, 104M, 104C, 104K, and developing units 105Y, 105M, 105C, 105K. Are arranged respectively. A drum cleaning unit (not shown) is further arranged around each of the photosensitive drums 102Y, 102M, 102C, and 102K.

An intermediate transfer belt (intermediate transfer member) 107, which is an endless belt, is arranged below the photosensitive drums 102Y, 102M, 102C, and 102K. The intermediate transfer belt 107 is stretched around a driving roller 108 and driven rollers 109 and 110. During image formation, the outer peripheral surface of the intermediate transfer belt 107 moves in the direction of the arrow shown in FIG. 1 as the drive roller 108 rotates. Primary transfer bias blades 111Y, 111M, 111C and 111K are arranged at positions facing the photosensitive drums 102Y, 102M, 102C and 102K via the intermediate transfer belt 107. The image forming apparatus 100 includes a secondary transfer bias roller 112 for transferring a toner image formed on the intermediate transfer belt 107 onto a sheet, and a fixing for fixing the toner image transferred on the sheet to the sheet. And a section 113. The sheet may be referred to as recording paper, recording material, recording medium, paper, transfer material, transfer paper, or the like.

Next, the image forming process from the charging process to the developing process in the image forming apparatus 100 having the above configuration will be described. The image forming process executed by each image forming unit corresponding to each color is the same. Therefore, hereinafter, the image forming process in the image forming unit corresponding to the Y color will be described as an example, and the description of the image forming process in the image forming unit corresponding to the M color, the C color, and the K color will be omitted.

First, the charging unit 103Y of the image forming unit corresponding to the Y color charges the surface of the photosensitive drum 102Y that is rotationally driven. The optical scanning unit 104Y exposes the surface of the photosensitive drum 102Y by emitting a plurality of laser beams (light beams) and scanning the surface of the charged photosensitive drum 102Y with the plurality of laser beams. As a result, an electrostatic latent image is formed on the rotating photosensitive drum 102Y. The electrostatic latent image formed on the photosensitive drum 102Y is developed with the Y-color toner by the developing unit 105Y. As a result, a Y-color toner image is formed on the photosensitive drum 102Y. Further, in the image forming units corresponding to M color, C color, and K color, the M color, C color, and K color are formed on the photosensitive drums 102M, 102C, and 102K by the same process as the image forming unit corresponding to the Y color. Color toner images are formed respectively.

The image forming process after the transfer process will be described below. In the transfer process, first, the primary transfer bias blades 111Y, 111M, 111C, and 111K apply the transfer bias to the intermediate transfer belt 107, respectively. As a result, the four-color (Y, M, C, and K) toner images formed on the photosensitive drums 102Y, 102M, 102C, and 102K are transferred onto the intermediate transfer belt 107 in an overlapping manner.

The toner image composed of four color toners formed on the intermediate transfer belt 107 in an overlapping manner is formed between the secondary transfer bias roller 112 and the intermediate transfer belt 107 as the outer peripheral surface of the intermediate transfer belt 107 moves. Is conveyed to the secondary transfer nip portion of the. The sheet is conveyed from the paper feed cassette 115 to the secondary transfer nip portion at the timing when the toner image formed on the intermediate transfer belt 107 is conveyed to the secondary transfer nip portion. At the secondary transfer nip portion, the toner image formed on the intermediate transfer belt 107 is transferred onto the sheet by the action of the transfer bias applied by the secondary transfer bias roller 112 (secondary transfer).

Then, the toner image formed on the sheet is heated by the fixing unit 113 to be fixed on the sheet. The sheet on which the multicolor image is formed in this manner is discharged to the paper discharge unit 116.

After the transfer of the toner image to the intermediate transfer belt 107 is completed, the toner remaining on the photosensitive drums 102Y, 102M, 102C, and 102K is removed by the drum cleaning unit described above. When the series of image forming processes is completed in this way, the image forming process for the next sheet is started continuously.

<Optical scanning unit 104>
FIG. 2 is a perspective view showing the configuration of the optical scanning unit 104. The optical scanning unit 104 includes a laser light source 201, a collimator lens 202, a polygon mirror (rotary polygon mirror) 203, a polygon motor 204, an fθ lens (scanning lens) 205, a beam detection (BD) sensor 206, and the like. The polygon mirror 203 is a rotary polygon mirror that is rotationally driven, and has a plurality of reflecting surfaces (deflecting surfaces) that are mirror surfaces along the rotation axis thereof. As shown in FIG. 2, the polygon mirror 203 of this embodiment has five reflecting surfaces (A-side, B-side, C-side, D-side, and E-side), but the number of reflecting surfaces is other than five. May be. It is assumed that the laser light emitted from the laser light source 201 is incident on each reflecting surface in the order of the A surface, the B surface, the C surface, the D surface, and the E surface and is deflected as the polygon mirror 203 rotates. That is, the A surface, the B surface, the C surface, the D surface, and the E surface are arranged in the order of the A surface, the B surface, the C surface, the D surface, and the E surface in the rotation direction of the polygon mirror 203. In the present embodiment, the laser light source 201 is an example of a light source that emits a light beam to expose the photosensitive drum 102 (photoconductor). The polygon mirror 203 is an example of a rotary polygon mirror that deflects the light beam on any one of the plurality of reflecting surfaces while rotating so that the light beam scans the photosensitive drum 102.

A laser light source (hereinafter simply referred to as “light source”) 201 is driven by a drive current supplied from a laser driver 310 (FIG. 3). The light source 201 is supplied with a drive current from the laser driver 310, emits light, and emits a laser beam (light beam) having a light amount corresponding to the drive current. The light source 201 includes N (N is a natural number) laser diodes (LDs) as light emitting elements (light emitting points). In the image forming apparatus 100 of the present embodiment, N is an integer of 2 or more, that is, a multi-beam method in which the photosensitive drum 102 is scanned by a plurality of laser beams emitted from a plurality of LDs is adopted. In the following, a case where N=16 and the light source 201 includes 16 LDs LD1 to LD16 will be described as an example.

The collimator lens 202 shapes the laser light emitted from the light source 201 into parallel light. The laser light L1 that has passed through the collimator lens 202 is incident on any one of the plurality of reflecting surfaces of the polygon mirror 203 (A-side, B-side, C-side, D-side, or E-side), and is incident. It reflects on the reflective surface. The polygon mirror 203 is rotationally driven by a polygon motor 204 so as to rotate in the arrow direction of FIG. The polygon mirror 203 is rotationally driven so as to rotate at a constant speed (constant angular speed) while the laser beam scans the surface of the photosensitive drum 102 to form an electrostatic latent image. The polygon mirror 203 reflects the laser light on each reflection surface while rotating so that the incident laser light L1 is deflected at continuous angles.

The laser light deflected by the polygon mirror 203 enters the fθ lens 205. By passing through the fθ lens 205, the laser light is focused on the surface of the photosensitive drum 102 to form a beam spot, and the photosensitive drum 102 is scanned at a constant speed in the main scanning direction. As a result, an electrostatic latent image 210 is formed on the photosensitive drum 102. The main scanning direction is a direction parallel to the surface of the photosensitive drum 102 and orthogonal to the moving direction of the surface of the photosensitive drum 102. The sub-scanning direction is the moving direction of the surface of the photosensitive drum 102 (direction orthogonal to the main scanning direction).

The optical scanning unit 104 includes a BD sensor 206 at a position on the scanning start side of the laser light in the scanning path of the laser light that has passed through the fθ lens 205. The BD sensor 206 is used as an optical sensor for detecting laser light. When the laser light is incident on the BD sensor 206 in each scanning cycle of the laser light, the BD sensor 206 generates and outputs a detection signal (BD signal) indicating that the laser light has been detected. The BD signal can be used as a synchronization signal that serves as a reference for image writing timing in the main scanning direction. The light source 201 is controlled to forcibly emit light during a certain period during which the laser light can be incident on the BD sensor 206 in order to cause the BD sensor 206 to output a BD signal for each scanning cycle of the laser light.

<Control Configuration of Optical Scanning Unit 104>
FIG. 3 is a block diagram showing a control configuration for the optical scanning unit 104. The image forming apparatus 100 includes a controller 300, an image controller 301, a FIFO memory 302, an AND circuit 303, and a magnification control unit 304 as a control configuration for the optical scanning unit 104. The optical scanning unit 104 further includes a laser driver 310 that drives the light source 201, and a memory 311 in addition to the components shown in FIG.

The controller 300 includes a processor (CPU) and controls the entire image forming apparatus 100. The controller 300 controls the rotation speed of the polygon motor 204 by the speed control signal output to the polygon motor 204, and controls the operation sequence of the laser driver 310 by the operation mode signal output to the laser driver 310. The controller 300 controls the operation of the magnification control unit 304 according to the write start timing signal output to the magnification control unit 304, the switching signal, and the magnification correction data. (In the second embodiment, a correction control signal is also used.)

As described above, when the laser light is incident on the BD sensor 206, the BD sensor 206 outputs the BD signal. The BD signal output from the BD sensor 206 is input to the controller 300. The controller 300 generates a write timing signal in synchronization with the input BD signal, and outputs the generated write timing signal to the magnification control unit 304. The controller 300 also generates a switching signal in synchronization with the input BD signal, and outputs the generated switching signal to the magnification control unit 304.

The writing start timing signal of this embodiment is used as a reference for writing start timing of an image (electrostatic latent image) in the sub-scanning direction. The magnification control unit 304 starts reading image data (driving data) from the FIFO memory 302 in order to start image formation on one sheet in response to the input of the writing timing signal from the controller 300. Further, as will be described later, the switching signal of the present embodiment is a signal for instructing switching of magnification correction data to be validated in the magnification control unit 304, and is also used as a reference for image writing timing in the main scanning direction. ..

The magnification control unit 304 controls reading of drive data from the FIFO memory 302, magnification correction processing for the drive data, and output of the corrected drive data to the laser driver 310 based on the write timing signal and the switching signal described above. To do. Therefore, the controller 300 can control the emission timing (lighting timing of each LD) of the laser light from each LD included in the light source 201 driven by the laser driver 310 by the write start timing signal and the switching signal.

The image controller 301 generates image data for forming an image of one scanning line for each scanning line in the main scanning direction based on input image data from an external information device such as a PC or a reading device. The image data of each scan line generated by the image controller 301 is composed of pixel data of a plurality of pixels. For example, in the image forming apparatus having a resolution of 2400 dpi, the image data of each scanning line includes the pixel data of 28062 pixels for the vertical length of 297 mm of the A4 sheet. The pixel data is density data indicating the density of each pixel. For example, each pixel data is composed of 4 bits (16 gradations).

The image controller 301 converts the generated image data of each scanning line into image data for driving the respective light sources 201 (each LD thereof), and outputs the image data. This conversion processing is realized by converting each pixel data included in the image data into a bit pattern corresponding to drive data according to a conversion table as shown in FIG.

FIG. 4 is a diagram showing an example of a conversion table for converting pixel data into drive data, and shows an example of converting 4-bit pixel data into a 16-bit bit pattern that is drive data. For example, in an image forming apparatus having a resolution of 2400 dpi, drive data of 448992 bits is generated from image data of each scanning line with respect to a vertical length of 297 mm of an A4 sheet. The bit data included in the drive data is either ON data for emitting laser light from the LD (lighting the LD) or OFF data for not emitting laser light from the LD (turning off the LD). It is. In the present embodiment, the ON data indicates the value “1” and the OFF data indicates the value “0”. Also, the bit data included in the drive data corresponds to an auxiliary pixel described later. In the present embodiment, since the pixel data of one pixel is converted into the drive data of 16 bits, the auxiliary pixel corresponds to 1/16 pixel.

The image controller 301 inputs the generated drive data of each scanning line to the FIFO memory 302 in the order of generation. The FIFO memory 302 inputs the drive data of each scanning line to the magnification control unit 304 in the input order in synchronization with the read clock (RCLK) supplied from the magnification control unit 304 via the AND circuit 303. For example, the FIFO memory 302 inputs the bit pattern included in the drive data to the magnification control unit 304 by 128 bits in synchronization with RCLK.

Here, the magnification control unit 304 outputs the image clock input from the outside to the FIFO memory 302 as a read clock (RCLK) for reading drive data from the FIFO memory 302. The image clock input to the magnification control unit 304 is generated by an external clock generation unit (oscillator) that generates a pulse signal having a predetermined frequency. The AND circuit 303 outputs a logical sum of the mask signal output from the controller 300 and RCLK output from the magnification control unit 304. For example, when the mask signal is at H (high) level, the RCLK output from the magnification control unit 304 is supplied to the FIFO memory 302. On the other hand, when the mask signal is at L (low) level, the RCLK output from the magnification control unit 304 is not supplied to the FIFO memory 302. Therefore, the controller 300 can control the RCLK from the magnification control unit 304 to the FIFO memory 302 by the mask signal output to the AND circuit 303.

The magnification control unit 304 executes magnification correction processing on the input drive data in order to correct the magnification of the image formed on the photosensitive drum 102 in the main scanning direction. For example, when the magnification control unit 304 executes enlargement processing on the input 128-bit drive data (bit pattern), the same bit as the last bit of the 128-bit drive data is immediately after the last bit. Add (insert). As a result, the drive data after the magnification correction processing becomes 129-bit data. On the other hand, the magnification control unit 304 deletes the last bit of the 128-bit drive data when performing reduction processing on the input 128-bit drive data (bit pattern). As a result, the drive data after the magnification correction process becomes 127-bit data. A specific example of the magnification correction processing by the magnification control unit 304 will be described later with reference to FIGS.

The memory 311 in the optical scanning unit 104 previously stores magnification correction data used for the magnification correction processing by the magnification control unit 304. The magnification correction data is data obtained by measuring the magnification unique to the optical scanning unit 104 during assembly and adjustment of the optical scanning unit 104, and is prepared as data corresponding to the measured magnification. The controller 300 reads out the magnification correction data stored in the memory 311 and stores it in the register 305 in the magnification control unit 304, so that the magnification control unit 304 uses the magnification correction data stored in the register 305. The correction process can be executed. The magnification correction data can be transmitted between the controller 300 and the optical scanning unit 104 using a low-speed serial signal in order to reduce the size and cost of the device.

The magnification correction data is data used for magnification correction processing by the magnification control unit 304 and for correcting the magnification of the image formed on the photosensitive drum 102 in the main scanning direction. In the present embodiment, magnification correction data associated with each reflecting surface of the polygon mirror 203 is prepared as data for correcting the magnification of an image formed by using the corresponding reflecting surface. In the present embodiment, the plurality of magnification correction data stored in advance in the memory 311 are associated with the plurality of reflecting surfaces, respectively, and the magnification of the image formed by using the corresponding reflecting surfaces is corrected. It is an example of a plurality of correction data for performing.

The switching signal output from the controller 300 to the magnification control unit 304 in synchronization with the BD signal is used to switch the magnification correction data to be valid between the plurality of magnification correction data corresponding to the plurality of reflection surfaces of the polygon mirror 203. It is a signal for instructing. The controller 300 uses the switching signal to control the magnification control unit 304 so as to switch the magnification correction data to be validated each time the BD signal is output from the BD sensor 206 according to the rotation of the polygon mirror 203. The magnification control unit 304 switches the magnification correction data to be validated each time a switching signal is output from the controller 300. The magnification control unit 304 uses the validated magnification correction data to perform magnification correction processing on the input drive data. In the magnification correction process of this embodiment, the partial magnification that is the magnification at each position in the main scanning direction is corrected.

The magnification control unit 304 outputs drive data bit by bit in synchronization with an image clock having a constant frequency. The drive data output in synchronization with the image clock is sent to the laser driver 310 as a video signal (PWM signal) that changes between H level and L level. The magnification control unit 304 outputs an H level video signal when outputting “1” as drive data and outputs an L level video signal when outputting “0” as drive data, for example. To do. The video signal output from the magnification control unit 304 is input to the laser driver 310.

The laser driver 310 drives each LD by supplying a drive current to each LD of the light source 201 according to the input video signal. In this embodiment, when an H level video signal is input, the laser driver 310 supplies a drive current to the LD. When a drive current is supplied to the LD, the LD emits laser light. On the other hand, when the L level video signal is input, the laser driver 310 does not supply the drive current to the LD. Since no drive current is supplied to the LD, the LD does not emit laser light. In this way, the laser driver 310 drives the LD by supplying the pulse-width modulated (PWM) drive current to the LD to be driven according to the input video signal. The photosensitive drum 102 is scanned (exposed) by the laser light emitted from each LD driven according to the video signal corresponding to the input image data, so that the electrostatic latent image corresponding to the input image data is formed on the photosensitive drum 102. It is formed.

The controller 300 according to the present embodiment specifies, on the basis of the Hall element signal output from the polygon motor 204, a reflective surface that deflects the laser light emitted from the laser light source 201 among the plurality of reflective surfaces of the polygon mirror 203. It has more functions. The polygon motor 204 is provided with a Hall element (not shown) that detects changes in the magnetic field due to rotation of the rotor of the polygon motor 204. The controller 300 shapes the waveform of the Hall element signal output from the Hall element, and generates an FG signal whose period changes according to the rotation speed of the polygon motor 204. Using the generated FG signal and the BD signal from the BD sensor 206, the controller 300 can detect a single specific surface of the plurality of reflecting surfaces included in the polygon mirror 203. Specifically, the controller 300 can detect the specific surface from the acquired phase difference by acquiring the phase difference between the FG signal and the BD signal. The phase difference may be the phase difference of the FG signal with respect to the BD signal or the phase difference of the BD signal with respect to the FG signal. Note that, as will be described later, the magnification control unit 304 operates to sequentially validate the magnification correction data corresponding to the reflection surface specified by the controller 300.

As described above, the memory 311 or the register 305 of the present embodiment is an example of a storage unit that stores a plurality of correction data (magnification correction data). Further, the magnification control unit 304 sequentially switches the correction data to be validated among the plurality of correction data in accordance with the rotation of the rotary polygon mirror (polygon mirror 203), and performs the correction process on the drive data based on the validated correction data. It is an example of a correction means to perform. The functions of the controller 300 and the magnification control unit 304 may be realized by hardware such as FPGA or ASIC, or may be realized by software. Further, some of the plurality of functions of the controller 300 and the magnification control unit 304 may be realized by hardware and the remaining functions may be realized by software.

<Operation mode of image forming apparatus>
The image forming apparatus 100 switches the sheet conveyance speed for each type of sheet used for image formation in order to secure the fixing property of an image on a sheet having a different thickness (basis weight) (for example, conveyance of plain paper). It has a function of halving the transport speed of thick paper with respect to the speed. In order to realize such a function, the image forming apparatus 100 sets, as an operation mode for image formation, a first mode in which the photosensitive drum 102 is rotated at a first speed, and the photosensitive drum 102 is 1/M of the first speed. It has a second mode of rotating at a second speed (M is an integer of 2 or more) times. As described below, in the first mode image formation, the plurality of reflection surfaces of the polygon mirror 203 are used for each one, and in the second mode image formation, the plurality of reflection surfaces of the polygon mirror 203 are M. Used for each reflective surface.

In the first mode, the sheet transport speed is V _s1 , the rotation speed of the photosensitive drum 102 (the surface speed in the tangential direction of the photosensitive drum) is V _d1 , and the rotation speed of the intermediate transfer belt 107 (the surface speed of the belt surface) is V _b1. The rotation speed of the polygon mirror 203 is set to V _r, and the reflecting surface of the polygon mirror 203 is used as a deflecting surface of the laser light for each surface. That is, the entire surface of the polygon mirror 203 (all reflecting surfaces) is used. In this embodiment, V _s1 =V _d1 =V _b1 and this speed is defined as the first process speed. However, in consideration of transferability from the photosensitive drum 102 to the intermediate transfer belt 107 and from the intermediate transfer belt 107 to the sheet, V _s1 ≈V _d1 ≈V _b1 may be set, that is, by providing a minute difference between these speeds. Good.

In the second mode, the sheet conveyance speed is V _s2 , the photosensitive drum 102 rotation speed is V _d2 , and the intermediate transfer belt 107 rotation speed is V _b2 .
V _s2 =V _s1 /M
V _d2 =V _d1 /M
V _b2 =V _b1 /M
And set. Further, the polygon mirror 203 is rotated at the same rotation speed V _r as in the first mode, and the reflection surface of the polygon mirror 203 is used for each M surface as a deflecting surface of laser light. In this embodiment, V _s2 =V _d2 =V _b2, and this speed is defined as the second process speed. However, considering the transferability from the photosensitive drum 102 to the intermediate transfer belt 107 and from the intermediate transfer belt 107 to the sheet, V _s2 ≈V _d2 ≈V _b2 may be set, that is, by providing a minute difference between these speeds. Good.

In the present embodiment, the first mode is an operation mode for forming an image on plain paper, and the second mode is an operation mode for forming an image on thick paper having a grammage larger than that of plain paper, where M=2. There is. That is, in the second mode, the second process speed is half the first process speed, and the reflecting surface of the polygon mirror 203 is used every other surface (at a distance). The image forming apparatus 100 maintains the rotation speed of the polygon mirror 203 at the same speed V _r regardless of the operation mode (regardless of the process speed). This is because when the rotation speed of the polygon mirror 203 is changed for each operation mode, the output speed of the image data in the main scanning direction (writing speed of the electrostatic latent image) also needs to be changed, and the control by the optical scanning unit 104 is required. This is because it becomes complicated.

<Specific example of magnification correction processing>
Next, a specific example of the magnification correction processing by the magnification control unit 304 will be described with reference to FIGS. 5 to 7, the reflecting surface of the polygon mirror 203 is used as a partition surface (A surface, C surface, E surface, B surface, D surface, A surface,... In this order). A magnification correction process when image formation is performed in the second mode is shown as an example. The magnification control unit 304 performs magnification correction processing for each laser beam (each beam) emitted from each of the LD1 to LD16 of the light source 201.

The main scanning area, which is an area where the laser beam scans in the main scanning direction on the photosensitive drum 102, is divided into a plurality of sub areas (divided areas). In the magnification correction process of this embodiment, the magnification of the image formed by each laser beam in the main scanning direction is corrected for each sub-region. Specifically, the magnification control unit 304 inserts or deletes bits (inserts/extracts auxiliary pixels) into/from the input drive data as described above, and thereby the pixels (dots) formed in each sub-region. ) Position. Note that the auxiliary pixel used for magnification correction has a width of 1/32 of one pixel in the main scanning direction, and as described above, it has ON data for turning on the LD or OFF data for turning off the LD. Equivalent to.

FIG. 5 is a timing chart showing an example of insertion/extraction of auxiliary pixels for magnification correction processing with respect to an image of one line in the main scanning direction formed by laser light corresponding to each LD. FIG. 6 is a diagram showing dot formation positions in the main scanning direction based on the drive data before the magnification correction processing is performed, and FIG. 7 is a main view based on the drive data after the magnification correction processing is performed. It is a figure which shows the formation position of the dot of a scanning direction. In FIG. 5 to FIG. 7, the main scanning area on the photosensitive drum 102 is divided into a plurality of sub areas A0 to A32 based on (the position corresponding to) the BD signal output timing from the BD sensor 206. The 32 continuous areas including the sub-areas A1 to A32 correspond to the image area where the image is formed. In each figure, the left side is the upstream in the main scanning direction, and the right side is the downstream in the main scanning direction.

5 to 7, every other surface of the polygon mirror 203 (that is, the A surface, the C surface, the E surface, the B surface, the D surface, the A surface,... An image is formed on the photosensitive drum 102 in the main scanning direction by the laser light deflected by each reflecting surface (in the order in which the surfaces are arranged). Each position (main scanning position) h (h1 to h33) in the main scanning direction shown in FIGS. 6 and 7 corresponds to an end portion in the sub areas A1 to A32. For example, the sub area A1 is defined as an area from the main scanning position h1 to the main scanning position h2. The laser light scans the photosensitive drum 102 in the direction from the main scanning position h1 to h33. The main scanning positions h1 to h32 correspond to ideal positions of the writing positions in the main scanning direction of the electrostatic latent images of the sub regions A1 to A32 formed by the laser beams emitted from the LDs. Further, the main scanning position h1 also corresponds to an ideal position for the writing start position in the main scanning direction of the electrostatic latent image (image) of one line formed by the laser light emitted from each LD. The sub area A0 corresponds to a non-image area from the position corresponding to the output timing of the BD signal to the main scanning position h1.

Before the magnification correction process is performed, the dot formation positions of the laser beams corresponding to the LD1 to LD16 are displaced from the main scanning positions h1 to h32 (ideal positions) as shown in FIG. The magnification control unit 304 performs a process of inserting/removing the auxiliary pixel in/from the drive data so that the dot formation position by the laser light corresponding to the LD1 to LD16 matches the ideal position as shown in FIG. This is executed as a correction process. As described above, the magnification control unit 304 is formed in each sub area based on the correction value in each of the sub areas A0 to A32 indicated by the magnification correction data read from the memory 311 and stored in the register 305. Correct the image magnification (partial magnification). This makes it possible to match the writing position of the electrostatic latent image in each of the sub regions A1 to A32 with the main scanning positions h1 to h32 corresponding to the ideal position.

As shown in FIGS. 5 and 6, the position in the main scanning direction on the photosensitive drum 102, which is scanned by the deflected laser light, differs for each reflecting surface of the polygon mirror 203. This is because the polygon mirror 203 has minute deformation and eccentricity. Therefore, the magnification control unit 304 needs to perform magnification correction processing by switching the magnification correction data to be used each time the reflecting surface of the polygon mirror 203 that deflects the laser light is switched. Therefore, magnification correction data (magnification correction data corresponding to surfaces A to E) corresponding to each reflection surface of the polygon mirror 203 is stored in the memory 311 in advance. The magnification correction data corresponding to each reflecting surface includes a magnification correction value of each of the sub-regions A0 to A32 corresponding to each of LD1 to LD16. The magnification control unit 304 controls the position and amount of the auxiliary pixel to be inserted/removed in each of the sub areas A0 to A32 according to the magnification correction data corresponding to the reflection surface used as the deflection surface among the plurality of reflection surfaces of the polygon mirror 203. By doing so, magnification correction processing is performed.

The magnification control unit 304 performs magnification correction processing for each reflecting surface of the polygon mirror 203 according to the corresponding magnification correction data as follows. Specifically, when the writing position of the electrostatic latent image (image) is displaced upstream of the main scanning position h1 (ideal position) in the main scanning direction for each laser beam, the magnification control unit 304 An auxiliary pixel of OFF data is inserted in the area A0. This delays the writing start timing of the image of one line corresponding to the target laser beam. As a result, the entire image of one line shifts to the downstream side in the main scanning direction. On the other hand, the magnification control unit 304 deletes the auxiliary pixel from the sub-area A0 when the writing position of the image is shifted downstream of the main scanning position h1 (ideal position) in the main scanning direction for each laser light ( Pull out). As a result, the writing timing of the image of one line corresponding to the target laser beam is advanced. As a result, the entire image of one line shifts to the upstream side in the main scanning direction.

For example, in the example shown in FIG. 6, with respect to the laser light corresponding to LD1 that is deflected by the surface A of the polygon mirror 203, the dot position corresponding to the image writing position is displaced upstream from the main scanning position h1. There is. In this case, the auxiliary pixel is inserted in the sub-region A0, so that the dot position corresponding to the image writing position is corrected to match the main scanning position h1, as shown in FIG. Such processing is also performed on LD2 to LD16. As a result, as shown in FIG. 7, the dot forming position corresponding to the image writing position by the laser light emitted from LD1 to LD16 and deflected by the A surface of the polygon mirror 203 is aligned with the main scanning position h1. Is corrected as follows.

Further, the magnification control unit 304 corrects the magnification of the sub-regions A1 to A32 by inserting and removing auxiliary pixels so that the image writing position in each sub-region matches the main scanning positions h1 to h32 for each laser beam. Here, in the image forming apparatus having a resolution of 2400 dpi, the width of the auxiliary pixel, which is 1/32 of one pixel, is about 0.33 μm. That is, the correction by inserting and removing the auxiliary pixels is performed with a discrete correction amount of about 0.33 μm. However, the amount of magnification correction in each sub-region is a continuous amount. Therefore, the correction residue (that is, the difference between the continuous correction amount and the discrete correction amount) in the sub-region A0 located on the upstream side in the main scanning direction is the sub-region located on the downstream side in the main scanning direction. Will be accumulated. Therefore, the correction value of the magnification included in the magnification correction data can be set so as to prevent the deviation of the dot formation position due to the accumulation of such a residue of the magnification correction.

By such processing, the dot formation positions by the laser light emitted from the LD1 to LD16 and deflected by the A surface of the polygon mirror 203 are corrected so as to be aligned with the main scanning positions h1 to h32. When the reflection surface of the polygon mirror 203 that deflects the laser light is switched to the next reflection surface, the magnification control unit 304 performs the above-described magnification correction processing according to the magnification correction data corresponding to the next reflection surface. In the example shown in FIGS. 5 to 7, since the image formation is performed in the second mode, the reflecting surfaces of the polygon mirror 203 are used every other surface. That is, the C surface is used after the A surface. Therefore, when the reflection surface of the polygon mirror 203 that deflects the laser light is switched from the A surface to the C surface, the magnification control unit 304 validates the magnification correction data corresponding to the C surface by switching the magnification correction data described later. Is used to perform the magnification correction processing.

<Magnification correction processing in each operation mode>
8A and 8B are timing charts showing operation timings related to magnification correction processing when image formation is performed in the first mode and the second mode, respectively. As described above, in the first mode, image formation is performed by using the reflecting surface of the polygon mirror 203 as a deflecting surface of laser light for each surface. In the second mode, image formation is performed by using every other reflection surface of the polygon mirror 203 (at a separation surface) as a deflection surface of laser light. In both the first mode and the second mode, the magnification correction data corresponding to the total reflection surface (A surface to E surface) of the polygon mirror 203 is read from the memory 311 by the controller 300 at the start of the image forming process. Are stored in the register 305.

(First mode)
In the first mode, the controller 300 performs control so that the drive data of one scan line generated by the image controller 201 is supplied to the magnification control unit 304 every time a BD signal is output from the BD sensor 206. I do. Specifically, as shown in FIG. 8A, in the first mode, a constant mask signal at H level is output from the controller 300 to the AND circuit 303. In this case, the image clock output from the magnification control unit 304 to the FIFO memory 302 as RCLK is input to the FIFO memory 302 via the AND circuit 303. As a result, the drive data of each scan line is sequentially read from the FIFO memory 302 and input to the magnification control unit 304. In this way, the image data (driving data) for image formation using the reflecting surface is input to the magnification control unit 304 at a timing for each reflecting surface of the polygon mirror 203.

When the controller 300 starts the image forming process in the first mode, the controller 300 starts outputting the switching signal to the magnification control unit 304. Specifically, the controller 300 first detects a specific surface of the plurality of reflecting surfaces of the polygon mirror 203 based on the Hall element signal output from the polygon motor 204. In the present embodiment, the surface A is the specific surface, but another surface may be defined as the specific surface. The controller 300 starts the output of the switching signal to the magnification control unit 304 so that the corresponding magnification correction data is sequentially validated in order from the reflection surface (A surface) detected as the specific surface. Further, the controller 300 continues to output the switching signal in synchronization with the BD signal while the polygon mirror 203 is operating.

The magnification control unit 304 validates the magnification correction data corresponding to the A surface of the polygon mirror 203 according to the input of the switching signal from the controller 300. Thereafter, the magnification control unit 304 sequentially switches the magnification correction data to be validated for the magnification correction processing among the plurality of magnification correction data stored in the register 305 according to the switching signal input from the controller 300. That is, the magnification control unit 304 switches the magnification correction data to be validated for each reflecting surface of the polygon mirror 203 that deflects the laser light, in the order in which the reflecting surfaces in the rotation direction of the polygon mirror 203 are arranged. As a result, the magnification control unit 304 can perform the magnification correction process on the input drive data using the validated magnification correction data. That is, it becomes possible to perform magnification correction processing using the corresponding magnification correction data in accordance with the switching of the reflecting surface of the polygon mirror 203 that deflects the laser light corresponding to LD1 to LD16. In this way, the magnification control unit 304 of the present embodiment, in the first mode, validates the magnification correction data for the drive data (image data) input at the timing of each reflecting surface of the polygon mirror 203. The magnification correction process is performed based on

(Second mode)
In the second mode, the controller 300 outputs the drive data of one scanning line generated by the image controller 201 every time the BD signal is output from the BD sensor 206 M times (twice in this example). Control to be supplied to. Specifically, as shown in FIG. 8B, in the second mode, the mask signal that switches between the H level and the L level each time the BD signal is output from the BD sensor 206 (in synchronization with the BD signal). Is output from the controller 300 to the AND circuit 303. In this case, the image clock output from the magnification control unit 304 to the FIFO memory 302 is supplied to the FIFO memory 302 while the mask signal is at H level, and to the FIFO memory 302 while the mask signal is at L level. Not supplied. As a result, the drive data of each scanning line is sequentially read from the FIFO memory 302 and input to the magnification control unit 304 so that an image (electrostatic latent image) is formed on the photosensitive drum 102 every other scanning line. To be done. In this way, the image data (driving data) for image formation using the reflecting surface is input to the magnification control unit 304 at every M reflecting surface of the polygon mirror 203 (every other reflecting surface in this example). To be done.

When the controller 300 starts the image forming process in the second mode, the controller 300 starts outputting a switching signal to the magnification control unit 304 by the same operation as in the first mode, and while the polygon mirror 203 is operating, The switching signal continues to be output in synchronization with the BD signal. Therefore, similarly to the first mode, the magnification control unit 304 validates the magnification correction data corresponding to the surface A of the polygon mirror 203 in response to the input of the switching signal, and thereafter validates the magnification correction data that is valid. Will be switched in order. As a result, the magnification control unit 304 can perform the magnification correction process on the input drive data using the validated magnification correction data.

In the second mode, the drive data is sent to the magnification control unit 304 at the timing of scanning the photosensitive drum 102 with the laser light in the main scanning direction every other scanning line by using the partition surface of the polygon mirror 203 as the deflection surface of the laser light. Is entered. In the present embodiment, the drive data for forming an image (electrostatic latent image) using the respective reflecting surfaces in the order of A surface, C surface, E surface, B surface, D surface, and A surface of the polygon mirror 203. It is input to the magnification control unit 304. When the drive data is input, the magnification control unit 304 performs magnification correction processing on the drive data based on the validated magnification correction data.

The magnification control unit 304 switches the magnification correction data to be validated each time the switching signal is input. Further, the magnification control unit 304, when the drive data is input in a state in which any of the magnification correction data is valid, performs the magnification correction processing by the validated magnification correction data on the drive data. To work. On the other hand, the magnification control unit 304 operates so as not to perform the magnification correction process when the drive data is not input in a state where any one of the magnification correction data is valid. As described above, the magnification control unit 304 does not perform the magnification correction process at the timing for each reflecting surface of the polygon mirror 203 when the drive data is not input, and is effective when the image data is input. A magnification correction process is performed on the drive data based on the magnification correction data. That is, the magnification control unit 304 does not perform the magnification correction process each time the drive signal is not input and outputs the valid magnification correction data when the image data is input each time the switching signal is output. Based on the above, the correction processing is performed on the drive data.

Specifically, as shown in FIG. 8B, the magnification control unit 304 first validates the magnification correction data corresponding to the surface A of the polygon mirror 203 according to the input of the switching signal. In this state, the magnification control unit 304 corrects the drive data input to use the A surface by the magnification correction data corresponding to the A surface. After that, when the switching signal is input, the magnification control unit 304 switches from the state in which the magnification correction data corresponding to the A side is enabled to the state in which the magnification correction data corresponding to the B side is enabled. However, since the drive data is not input because the side B is used, the magnification control unit 304 does not perform the magnification correction process based on the magnification correction data corresponding to the side B. Next, when the switching signal is input, the magnification control unit 304 switches from the state in which the magnification correction data corresponding to the B surface is valid to the state in which the magnification correction data corresponding to the C surface is valid. In this state, the magnification control unit 304 corrects the drive data input to use the C plane by the magnification correction data corresponding to the C plane. After that, the magnification control unit 304 repeats such an operation until the image forming process is completed.

As described above, even when the image formation is performed in the second mode, the magnification control unit 304 of the present embodiment makes the magnification correction data to be valid one reflection according to the rotation of the polygon mirror 203, as in the first mode. Switch in order for each face. Therefore, the magnification control unit 304 does not need to switch the magnification correction data in a different procedure for each operation mode of the image forming apparatus 100, and can be realized by the same procedure. Further, the controller 300 does not need to control the magnification control unit 304 differently for each operation mode, and the magnification correction processing in each operation mode can be realized only by controlling the mask signal. Therefore, there is no need to separately prepare a control program (executed by the controller 300) for causing the magnification control unit 304 to switch magnification correction data for each operation mode and store it in the memory. That is, it is possible to prevent the memory capacity required to store such a control program from increasing.

<Control procedure of optical scanning unit 104>
FIG. 9 is a flowchart showing a control procedure of the optical scanning unit 104 by the controller 300 when executing image formation. The processing of each step shown in FIG. 9 may be realized by the CPU in the controller 300 reading and executing the control program stored in the memory, or may be realized by hardware. Although FIG. 9 shows the control for forming an image on one sheet, the control for continuously forming an image on a plurality of sheets is performed by, for example, repeating the processing of S111 to S114. Can be achieved with.

When the image forming apparatus 100 is powered on, the controller 300 reads the magnification correction data stored in the memory 311 in step S101. Further, in S102, the controller 300 stores the magnification correction data read from the memory 311 in the register 305 of the magnification control unit 304. As a result, the magnification correction data respectively corresponding to the surfaces A to E of the polygon mirror 203 are stored in the register 305.

Next, in S103, the controller 300 waits until the image forming process is started, and when the image forming process is started (“YES” in S103), the process proceeds to S104. In S104, the controller 300 starts the rotation of the polygon motor 204. Further, the controller 300 turns on each LD of the light source 201 in S105, and starts the control of the rotation speed of the polygon motor 204 and the sequence control of each LD of the light source 201 in S106.

In S106, the controller 300 generates an operation sequence of the laser driver 310 and outputs an operation mode signal indicating the generated operation sequence to the laser driver 310, thereby performing sequence control of each LD. When the laser light emitted from the turned-on LD is deflected by the rotating polygon mirror 203 and enters the BD sensor 206, the BD sensor 206 outputs a BD signal to the controller 300. The controller 300 controls the rotation speed of the polygon motor 204 using the BD signal output from the BD sensor 206. In S107, the controller 300 waits until the rotation speed of the polygon motor 204 reaches the target speed, and when the rotation speed reaches the target speed (“YES” in S107), the process proceeds to S108.

In S108, the controller 300 detects the specific surface (A surface in this embodiment) of the polygon mirror 203 based on the Hall element signal output from the polygon motor 204. When the controller 300 detects the specific surface (A surface) of the polygon mirror 203, in step S109, the controller 300 starts outputting the switching signal to the magnification control unit 304. Further, in S110, the controller 300 starts outputting a mask signal corresponding to the sheet conveyance speed (that is, a mask signal corresponding to the operation mode of the image forming apparatus 100). Specifically, when the image forming process is performed in the first mode, the output of a constant mask signal is started at the H level. On the other hand, when the image forming process is performed in the second mode, the output of the mask signal that switches between the H level and the L level is started each time the BD signal is output from the BD sensor 206.

After that, the controller 300 starts the conveyance of the sheet from the paper feed cassette 115 in S111, and determines in S112 whether the leading edge of the sheet has reached a predetermined position (for example, the position of the registration roller). When the controller 300 determines that the leading edge of the sheet has reached the predetermined position (“YES” in S112), in S113, the writing timing signal is generated based on the output timing of the BD signal from the BD sensor 206, and the magnification control unit is generated. Output to 304. The magnification control unit 304 starts the output of the image clock (RCLK) to the FIFO memory 302 in response to the input of the write timing signal, and the FIFO memory of the drive data for forming the image on the sheet being conveyed. Reading from 302 is started.

The drive data read from the FIFO memory 302 by RCLK is sequentially input to the magnification control unit 304. The magnification control unit 304 executes a magnification correction process on the input drive data with the magnification correction data made valid according to the switching signal. However, when performing the image forming process in the second mode, as described above, RCLK is not supplied to the FIFO memory 302 while the L level mask signal is being input to the AND circuit 303, and the drive data is magnified. It is not input to the control unit 304. The magnification control unit 304 operates so as not to execute the magnification correction process when the drive data is not input.

The magnification control unit 304 outputs the drive data after the magnification correction processing to the laser driver 310 as a video signal. The laser driver 310 drives each LD of the light source 201 in accordance with the video signal from the magnification control unit 304, so that an electrostatic latent image is formed on the photosensitive drum 102 and an image is formed on the sheet being conveyed. Become. In S114, the controller 300 determines whether or not to end the image forming process, and if the controller 300 determines to end the image forming process (“YES” in S114), the process proceeds to S115. In S115, the controller 300 stops the rotation of the polygon mirror 203, turns off each LD of the light source 201, and ends the processing.

As described above, according to the present embodiment, while switching data to be validated among a plurality of magnification correction data corresponding to a plurality of reflecting surfaces of the polygon mirror 203 by the same procedure regardless of the operation mode, It becomes possible to perform magnification correction processing based on magnification correction data. Accordingly, it is not necessary to separately prepare a control program (executed by the controller 300) for realizing the switching of the magnification correction data in the magnification control unit 304 and store it in the memory for each operation mode. That is, it is possible to prevent the memory capacity required to store such a control program from increasing.

The present embodiment can be modified in various ways. For example, the controller 300 may not perform the process of storing the magnification correction data stored in the memory 311 in the register 305 at the start of the image forming process. In this case, in the second mode, the controller 300 may operate to store the magnification correction data to be validated next in the register 305 according to the switching signal while the magnification correction processing is not performed. Further, in the first mode, the controller 300 operates to store the magnification correction data to be validated next according to the switching signal in the register 305 while the magnification correction processing is being performed on any of the reflecting surfaces. You may. In this case, the memory capacity required for the register 305 can be saved.

[Second Embodiment]
In the first embodiment, the magnification control unit 304 executes magnification correction processing on the input drive data in both the first mode and the second mode. On the other hand, in the second embodiment, the magnification control unit 304 executes the magnification correction processing when the image forming processing is performed in the second mode, and the magnification correction processing when the image forming processing is performed in the first mode. An example of operation so as not to execute will be described. In the following, differences from the first embodiment will be mainly described.

When the magnification control unit 304 does not perform the magnification correction process, the magnification of the image formed by the laser light emitted from each LD of the laser light source 201 depends on the reflection surface of the polygon mirror 203 used as the deflection surface of the laser light. Different magnifications. Here, FIGS. 10A and 10C show the deviation of the magnification in the main scanning direction of the image formed when each reflection surface (A surface to E surface) of the polygon mirror 203 is used as a deflection surface. It is a figure. FIGS. 10A and 10C respectively show cases in which image formation is performed in the first mode and the second mode without performing the magnification correction process. Further, FIGS. 10B and 10D are schematic views of images formed when the image formation is performed in the first mode and the second mode without performing the magnification correction process, respectively. In the multi-beam type image forming apparatus, as shown in FIGS. 10B and 10D, a plurality of laser beams corresponding to LD1 to LD16 are used to scan a plurality of scanning lines for each reflecting surface used as a deflecting surface. Images are formed in parallel in the sub-scanning direction.

As shown in FIGS. 10B and 10D, in the main scanning direction, the image writing position is the same between the scanning lines, whereas the image writing ending position is the reflection used as the deflecting surface. Each side is different. That is, as shown in FIGS. 10A and 10C, the magnification of the image formed varies depending on the reflecting surface used as the deflecting surface. For example, the image of each scanning line corresponding to the A surface and the C surface of the polygon mirror 203 has a relatively large magnification, and thus is formed with a relatively low density. On the other hand, the image of each scanning line corresponding to the B surface and the E surface has a relatively small magnification, and therefore is formed with a relatively high density. In this way, the density of the image changes depending on the magnification of the formed image. This is because the larger the magnification is, the smaller the integrated light amount per unit area irradiated on the photosensitive drum 102 is, and the smaller the magnification is, the larger the integrated light amount per unit area irradiated on the photosensitive drum 102 is.

As shown in FIGS. 10B and 10D, the image density variation caused by such image magnification variation is periodic in the sub-scanning direction in both the first mode and the second mode. It causes uneven density in the image. For example, when an image is formed at a resolution of 2400 dpi, density unevenness of about 0.423 mm pitch occurs on average in the first mode as shown in FIG. 10B. In this case, the density unevenness has a spatial frequency of about 2.36 cycles/mm. On the other hand, as shown in FIG. 10D, in the second mode, density unevenness of about 0.847 mm pitch occurs on average. In this case, the density unevenness has a spatial frequency of about 1.18 cycle/mm. As described above, when the reflecting surface of the polygon mirror 203 is used as a deflecting surface for each surface (first mode) and when the reflecting surface is used every M surfaces (M=2 in this embodiment) as a deflecting surface. In the (second mode), density unevenness having different spatial frequencies occurs in the image.

Here, FIG. 11 is a diagram showing an example of the visual sensitivity characteristic showing the relationship between the spatial frequency and the human visual sensitivity (relative sensitivity). As shown in FIG. 11, the visual sensitivity at a spatial frequency of 2.36 cycles/mm corresponding to the first mode is 0.650, which is a relatively low visual sensitivity. This means that in the image formed in the first mode, the density unevenness as described above is less noticeable to human eyes. On the other hand, the visual sensitivity at a spatial frequency of 1.18 cycle/mm corresponding to the second mode is 0.992, which is relatively high visual sensitivity. This means that in the image formed in the second mode, the density unevenness as described above tends to be noticeable to human eyes. Also, as shown in FIG. 11, the higher the spatial frequency, the lower the visibility sensitivity, and the less visible it is to the human eye.

Therefore, for example, when the optical scanning unit 104 is adjusted at the time of factory shipment so that the spatial frequency of the density unevenness occurring in the image formed in the first mode is as high as possible, in the first mode, the magnification correction process is not performed, and The density unevenness thus generated can be substantially suppressed. On the other hand, when the image is formed in the second mode, the spatial frequency of the density unevenness generated in the formed image changes, and the spatial frequency of the generated density unevenness becomes a spatial frequency that is easily noticeable to human eyes. It can lead to defects. Therefore, even if the above adjustment is performed, it may be necessary to perform the magnification correction process in the second mode.

Therefore, the magnification control unit 304 of the present embodiment does not perform the magnification correction processing when performing the image forming processing in the first mode, and performs the magnification correction processing when performing the image forming processing in the second mode. To do. Specifically, the controller 300 controls whether or not the magnification control unit 304 executes the magnification correction processing depending on whether the image formation processing is performed in the first mode or the image formation processing in the second mode. .. The controller 300 performs such control by the correction control signal output to the magnification control unit 304 as shown in FIG.

When the magnification control unit 304 is instructed not to perform the magnification correction processing by the correction control signal, the magnification control unit 304 outputs the input drive data to the laser driver 310 without performing the magnification correction processing. That is, the magnification control unit 304 outputs the input drive data to the laser driver 310 as a video signal bit by bit in synchronization with the image clock. On the other hand, when the magnification control unit 304 is instructed to perform magnification correction processing by the correction control signal, the magnification based on the validated magnification correction data is applied to the input drive data, as in the first embodiment. Execute the correction process. Further, the magnification control unit 304 outputs the drive data after the magnification correction processing to the laser driver 310 as a video signal bit by bit in synchronization with the image clock.

According to the present embodiment, even when the magnification correction process is not executed in the first mode, it is possible to obtain the same effect as that of the first embodiment. Further, since the magnification correction processing is not performed in the first mode, the processing load required for the magnification correction processing can be reduced.

100... Image forming apparatus, 102... Photosensitive drum, 104... Optical scanning unit, 201... Laser light source, 203... Polygon mirror, 204... Polygon motor, 206... BD sensor , 300... Controller, 304... Magnification control unit, 305... Register, 310... Laser driver

Claims (14)

A light source that emits a light beam for exposing the photoreceptor,
A rotary polygonal mirror having a plurality of reflecting surfaces, wherein the light beam is deflected by any one of the plurality of reflecting surfaces while being rotationally driven so that the light beam scans the photosensitive member. , In the first mode image formation, the plurality of reflection surfaces are used for each one reflection surface, and in the second mode image formation, the plurality of reflection surfaces are provided for each M reflection surface (M is an integer of 2 or more). The rotating polygon mirror used,
A memory that is associated with each of the plurality of reflecting surfaces and that stores a plurality of correction data for correcting the magnification in the scanning direction of the light beam of the image formed using the corresponding reflecting surfaces. Means and
The correction data to be validated out of the plurality of correction data stored in the storage means is switched in the rotation direction of the rotary polygon mirror in the order in which the plurality of reflecting surfaces are arranged in accordance with the rotation of the rotary polygon mirror, and becomes effective. Correction means for performing a correction process on the image data for driving the light source based on the corrected data,
The image forming apparatus, wherein the correction unit sequentially switches the correction data to be validated for each reflecting surface according to the rotation of the rotary polygon mirror even when the image formation is performed in the second mode. In the first mode, image data for image formation using the reflecting surface is input to the correcting means at a timing for each reflecting surface of the rotary polygon mirror.
In the second mode, image data for image formation using the reflecting surface is input to the correcting means at a timing for each M reflecting surface of the rotary polygon mirror.
The image processing apparatus according to claim 1, wherein, in the second mode, when the image data is input, the correction unit performs the correction process on the image data based on the validated correction data. Forming equipment. The correction means is
In the first mode, the correction processing is performed on the image data input at the timing of each reflecting surface of the rotary polygon mirror based on the validated correction data,
In the second mode, when the image data is not input, the correction process is not performed at the timing for each reflecting surface of the rotary polygon mirror, and when the image data is input, the valid correction is performed. The image forming apparatus according to claim 2, wherein the correction process is performed on the image data based on the data. The correction means is
In the first mode, the correction processing is not performed on the image data input at the timing of each reflecting surface of the rotary polygon mirror,
In the second mode, when the image data is not input, the correction process is not performed at the timing for each reflecting surface of the rotary polygon mirror, and when the image data is input, the valid correction is performed. The image forming apparatus according to claim 2, wherein the correction process is performed on the image data based on the data. When detecting a light beam deflected by each of the plurality of reflecting surfaces, a detection unit that outputs a detection signal indicating that the light beam has been detected,
Control means for controlling the correction means so as to switch the correction data to be validated each time the detection signal is output from the detection means in accordance with the rotation of the rotary polygon mirror;
The image forming apparatus according to claim 2, further comprising: The control means outputs a switching signal for instructing switching of the correction data to be validated to the correction means each time the detection signal is output from the detection means,
The image forming apparatus according to claim 5, wherein the correction unit switches the correction data to be validated each time the switching signal is output from the control unit. In the second mode, the correction unit does not perform the correction process each time the switching signal is output from the control unit when the image data is not input, and does not perform the correction process when the image data is input. The image forming apparatus according to claim 6, wherein the correction processing is performed on the image data based on the validated correction data. The image forming apparatus further includes a generation unit that generates image data corresponding to each scanning line scanned by the light beam deflected by the rotating polygon mirror and outputs the image data to the correction unit.
The control means is
In the first mode, each time the detection signal is output from the detection unit, the image data of one scanning line generated by the generation unit is supplied to the correction unit,
In the second mode, each time the detection signal is output from the detection unit M times, the image data of one scanning line generated by the generation unit is supplied to the correction unit. The image forming apparatus according to any one of items 1 to 7. Drive means for driving the rotary polygon mirror,
A signal generating device that generates a signal whose period changes according to the number of rotations of the driving device, and specifies a reflecting surface that deflects the light beam among the plurality of reflecting surfaces based on the signal. ,
9. The correcting unit operates so as to sequentially validate the correction data corresponding to the reflecting surface specified by the specifying unit according to the rotation of the rotary polygon mirror. The image forming apparatus according to item. The rotation speed of the photoconductor in the second mode is 1/M of that in the first mode, and the rotation speed of the rotary polygon mirror is the same as that in the first mode. 10. The image forming apparatus according to any one of 1 to 9. The image forming apparatus according to claim 1, wherein the correction processing corrects a partial magnification of each position of the light beam in the main scanning direction. The photoconductor,
Charging means for charging the photoreceptor,
The electrostatic latent image formed on the photoconductor is developed by scanning the light beam emitted from the light source based on the image data output from the correction unit, and the image to be transferred onto the sheet is exposed by the photosensitizer. The image forming apparatus according to claim 1, further comprising: a developing unit that is formed on the body. A light source that emits a light beam for exposing the photoreceptor,
A rotary polygonal mirror having a plurality of reflecting surfaces, wherein the light beam is deflected by any one of the plurality of reflecting surfaces while being rotationally driven so that the light beam scans the photosensitive member. The rotating polygon mirror, wherein the plurality of reflecting surfaces are used for each one reflecting surface in the first mode image formation, and the plurality of reflecting surfaces are used for every other reflecting surface in the second mode image formation. When,
A memory that is associated with each of the plurality of reflecting surfaces and that stores a plurality of correction data for correcting the magnification in the scanning direction of the light beam of the image formed using the corresponding reflecting surfaces. Means and
The correction data to be validated out of the plurality of correction data stored in the storage means is switched in the rotation direction of the rotary polygon mirror in the order in which the plurality of reflecting surfaces are arranged in accordance with the rotation of the rotary polygon mirror, and becomes effective. Correction means for performing a correction process on the image data for driving the light source based on the corrected data,
The image forming apparatus, wherein the correction unit sequentially switches the correction data to be validated for each reflecting surface according to the rotation of the rotary polygon mirror even when the image formation is performed in the second mode. In the first mode, image data for image formation using the reflecting surface is input to the correcting means at a timing for each reflecting surface of the rotary polygon mirror.
In the second mode, image data for image formation using the reflecting surface is input to the correcting unit at every other reflecting surface of the rotary polygon mirror.
14. The image according to claim 13, wherein, in the second mode, when the image data is input, the correction unit performs the correction process on the image data based on the validated correction data. Forming equipment.