JP5743539B2 - Image forming apparatus - Google Patents

Description

  The present invention relates to an image forming apparatus that forms an image using an electrophotographic method, and more particularly to an image forming apparatus having a configuration for correcting the inclination of an image.

  2. Description of the Related Art Conventionally, in an image forming apparatus using electrophotography, a photosensitive member is charged by a charging device, and an electrostatic latent image is formed by irradiating the photosensitive member with laser light modulated according to image information. Then, a toner image obtained by developing the electrostatic latent image with a developing device is transferred to a recording medium such as a sheet material to form an image.

  If the moving direction of the light beam forming the electrostatic latent image on the photosensitive member has an inclination of a predetermined angle or more, the output image is inclined. Further, in the case of a color image forming apparatus, there is a problem of so-called color misregistration (positional misregistration) in which images of each color do not match when the images of each color are superimposed.

  To solve these problems, the movement direction of the light beam on the photoconductor is detected using detection sensors provided on both sides outside the image forming area of the photoconductor, and light on the photoconductor is detected based on the detection result. An image forming apparatus that corrects the tilt of a beam has been proposed (see Patent Document 1). According to Patent Document 1, it is possible to suppress deterioration in image quality due to the inclination of the moving direction of the light beam on the photoconductor.

JP 2006-264173 A

  However, even if the relative positional relationship between the photosensitive member and the two detection sensors is adjusted with high accuracy during the assembly of the image forming apparatus, the relative positional relationship between the two detection sensors is shifted due to the influence of the temperature rise in the apparatus. As a result, the detection accuracy of the moving direction of the light beam is lowered, and the correction accuracy is lowered.

  In order to solve the above-described problem, the image forming apparatus according to the present exemplary embodiment is rotated by a driving unit and emits a light beam from a light source in order to expose the photosensitive member. An image forming unit that forms an image on the photoconductor by scanning the light beam so that the light beam moves on the photoconductor, and a pattern image formed by the detection mark or the image forming unit. A first detection means for detecting, a second detection means for detecting the detection mark or the pattern image at a position different from the first detection means in the rotational axis direction of the photosensitive member, and the pattern image is detected. Thus, the first detection unit and the second detection unit are formed on the photoconductor based on a generation timing difference between detection signals generated by the first detection unit and the second detection unit. The pattern based on a difference in generation timing of detection signals generated by the first detection means and the second detection means by detecting the detection mark, and an adjustment means for adjusting the orientation of the image to be detected. And correction means for correcting the generation timing difference between detection signals generated by the first detection means and the second detection means by detecting an image, respectively.

  According to the present invention, the orientation of the image formed on the photoconductor even when the relative positional relationship between the first detection unit and the second detection unit for detecting the moving direction of the light beam on the photoconductor is broken. Can be adjusted with high accuracy.

1 is a schematic diagram of an image forming apparatus according to an embodiment. FIG. 3 is a schematic cross-sectional view showing an internal configuration of the optical scanning device and a photosensitive drum exposed by the optical scanning device. FIG. 3 is a control block diagram of the image forming apparatus according to the present embodiment. FIG. 2 is a diagram illustrating a photosensitive drum and a potential sensor for detecting a surface potential on the photosensitive drum provided in the image forming apparatus according to the present embodiment. The figure which shows the structure with which the lens with which an optical scanning device is equipped and a lens is rotated. The figure which shows the relative position fluctuation | variation of an electric potential sensor. The conceptual diagram which shows the inclination detection method of a scanning line. The conceptual diagram which shows the inclination detection method of a scanning line. A control flow executed when the CPU 300 performs tilt correction.

Example 1
FIG. 1 is a schematic cross-sectional view of an embodiment of an image forming apparatus according to the present embodiment. In this embodiment, a color image forming apparatus will be described as an example, but the embodiment may be a monochrome image forming apparatus.

  In FIG. 1, the image forming apparatus 100 includes four image forming units (image forming units) 101Y, 101M, 101C, and 101Bk that form images according to colors. Here, Y, M, C, and Bk represent yellow, magenta, cyan, and black, respectively. The image forming units 101Y, 101M, 101C, and 101Bk form images using yellow, magenta, cyan, and black toners, respectively.

  The image forming units 101Y, 101M, 101C, and 101Bk are provided with photosensitive drums 102Y, 102M, 102C, and 102Bk as photosensitive members. Around the photosensitive drums 102Y, 102M, 102C, and 102Bk, charging devices 103Y, 103M, 103C, and 103BK, optical scanning devices (laser scanners) 104Y, 104M, 104C, and 104Bk, and developing devices 105Y, 105M, 105C, and 105Bk are provided. It has been. In addition, drum cleaning devices 106Y, 106M, 106C, and 106Bk are disposed around the photosensitive drums 102Y, 102M, 102C, and 102Bk. The optical scanning devices 104Y, 104M, 104C, and 104Bk include casings 200Y, 200M, 200C, and 200Bk (installation means) for installing polygon mirrors and lenses, which will be described later.

  As shown in FIG. 1, the charging position, the exposure position, the charging position by the charging device 103Y, the exposure position by the optical scanning device 104, the detection position of the potential sensor 309, and the developing device 105 in this order from the upstream of the rotation of the photosensitive drum 102Y. The order of development position.

  Further, a reference mark (home position mark, hereinafter referred to as HP mark) is provided at a predetermined position of the photosensitive drum on the side end surfaces of the photosensitive drums 102Y, 102M, 102C, and 102Bk. The image forming apparatus 100 includes home position sensors 311Y, 311C, 311M, and 311Bk (hereinafter referred to as HP sensors) for detecting the HP mark. Further, as shown in FIG. 4 described later, potential sensors 309Y and 310Y for detecting the potential of the surface of the photosensitive drum are provided around the photosensitive drum 102Y. Similarly, a plurality of potential sensors for detecting the potential of the photosensitive drum surface are also provided around 102M, 102C, and 102Bk.

  An endless belt-like intermediate transfer belt 107 is disposed below the photosensitive drums 102Y, 102M, 102C, and 102Bk. The intermediate transfer belt 107 is stretched around a driving roller 108 and driven rollers 109 and 110, and rotates in the direction of the arrow in the figure during image formation. In addition, primary transfer devices 111Y, 111M, 111C, and 111Bk are provided at positions facing the photosensitive drums 102Y, 102M, 102C, and 102Bk via the intermediate transfer belt 107 (intermediate transfer member). The primary transfer devices 111Y, 111M, 111C, and 111Bk transfer the toner images on the photosensitive drums 102Y, 102M, 102C, and 102Bk to the intermediate transfer belt 107.

  The image forming apparatus 100 also includes a secondary transfer device 114 for transferring the toner image on the intermediate transfer belt 107 to the recording medium S, and a fixing device 115 for fixing the toner image on the recording medium S.

  Here, an image forming process executed by the image forming apparatus 100 having such a configuration will be described. Since the image forming process in each image forming unit is the same, the image forming process in the image forming unit will be described using the image forming unit 101Y, and the description of the image forming process in the image forming units 101M, 101C, and 101Bk will be omitted. To do.

  First, the photosensitive drum 102Y is charged by the charging device of the image forming unit 101Y. Laser light (light beam) emitted from a light source described later based on the image data is deflected by a polygon mirror described later, and the spot of the laser light moves (scans) on the charged photosensitive drum 102Y (on the photosensitive member). . As a result, an electrostatic latent image is formed in the main scanning direction on the photosensitive drum 102Y (the rotational axis direction of the photosensitive drum 102Y). Since the photosensitive drum 102Y rotates during exposure, an electrostatic latent image is also formed in the sub-scanning direction of the photosensitive drum 102Y (the rotational direction of the photosensitive drum 102) by repeating the scanning of the laser beam. Thereafter, the electrostatic latent image is developed as a yellow toner image by the developing device 105Y.

  The yellow, magenta, cyan, and black toner images formed on the photosensitive drums 102Y, 102M, 102C, and 102Bk of each image forming unit are transferred to the intermediate transfer belt 107 by the primary transfer devices 111Y, 111M, 111C, and 111Bk, respectively. The As a result, the toner images of the respective colors are superimposed on the intermediate transfer belt 107.

  When the transfer of the four-color toner image to the intermediate transfer belt 107 is completed, the four-color toner image on the intermediate transfer belt 107 is transferred from the manual feed cassette 116 or the paper feed cassette 117 to the secondary transfer position by the secondary transfer device 114. Is transferred (secondary transfer) onto the recording medium S that has been conveyed to the recording medium S. The recording medium S is conveyed by a feeding roller, a conveying roller, and a registration roller in a manual feeding cassette (multi-purpose tray) 117 so as to match the movement timing of the toner image on the intermediate transfer belt 107. Then, the toner image on the recording medium S for which the secondary transfer has been completed is heated and fixed by the fixing device 115 and discharged to the paper discharge unit 118, and a full color image is obtained on the recording medium S.

  The photosensitive drums 102Y, 102M, 102C, and 102Bk that have completed the transfer are prepared for subsequent image formation after the residual toner is removed by the drum cleaning devices 106Y, 106M, 106C, and 106Bk.

  Next, the optical scanning devices 104Y, 104M, 104C, and 104Bk will be described with reference to FIG. Since the configuration of each optical scanning device is the same, subscripts Y, M, C, and Bk indicating colors are omitted. FIG. 2 is a perspective view schematically showing a member housed in the housing of the optical scanning device 104 and the photosensitive drum 102 corresponding to the optical scanning device in a flat shape.

  In the optical scanning device 104, a light source 201 (for example, a semiconductor laser) that emits laser light (light beam) is attached to the housing 200. In FIG. 2, only a part of the housing 200 is shown, but the housing 200 corresponds to the outer frame of the optical scanning devices 104Y, 104M, 104C, and 104Bk shown in FIG. A polygon mirror 203 described below, a polygon mirror driving motor 207 serving as a polygon mirror driving unit, and various lenses are accommodated. The light source 201 includes a collimator lens and an aperture stop that convert laser light into parallel light. The laser light emitted from the light source 201 passes through a cylindrical lens 202 having a predetermined refractive power disposed on the optical path, is deflected by the polygon mirror 203, and the laser light becomes scanning light. Laser light converted into scanning light by the polygon mirror 203 is guided onto the photosensitive drum 102 by a toric lens 204 and an imaging lens 205. In FIG. 2, the description of the folding mirror that reflects the laser beam deflected by the polygon mirror 203 toward the photosensitive drum 102 is omitted for the sake of simplicity.

  On the photosensitive drum 102, a spot of laser light emitted from the semiconductor laser 201 deflected to the polygon mirror 203 that is driven to rotate moves on the photosensitive drum 102 (main scanning). The photosensitive drum 102 is rotationally driven, and image writing is performed in the sub-scanning direction (rotating direction of the photosensitive drum) by turning back the main scanning.

  As shown in FIG. 2, the image forming apparatus 100 or the optical scanning device 104 is provided with a beam detector 206 (hereinafter referred to as BD 206) which is a laser light detecting means. The BD 206 is installed at a position corresponding to the outside of the image forming area of the photosensitive drum 102, and generates a scanning timing signal (BD signal) by detecting the reflected laser light. The timing for emitting laser light from the light source 201 within one scanning period is controlled based on the BD signal.

  FIG. 3 is a diagram illustrating a control block of the image forming apparatus 100. Each unit provided in the image forming apparatus 100 is controlled by the CPU 300. Control programs and control data are stored in memories such as the ROM 301 and the RAM 302, and the CPU 300 performs sequence control of the image forming apparatus based on the control programs and control data.

  The CPU 300 controls the transfer device 313 including the charging device 103, the developing device 105, the primary transfer device 111, the intermediate transfer belt 107, the secondary transfer device 114, and the like based on the control program and control data. Further, the CPU 300 drives the lens driving motor 304 by transmitting a control signal to the lens driving motor driver 303 which is a lens rotating means, thereby adjusting the position of the imaging lens 205. Further, the photosensitive drum driving motor 306 is driven by transmitting a control signal to the photosensitive drum driving motor driver 305, and acceleration / deceleration control and constant speed control are executed so that the photosensitive drum rotates at a predetermined rotation speed during image formation. .

  The CPU 300 emits a light beam from the light source 201 by transmitting a control signal based on the image data to the laser driver 307. Further, by transmitting a control signal to the polygon mirror drive motor driver 308, the polygon mirror drive motor 207 is driven, and the polygon mirror 203 is controlled to rotate at a predetermined rotation speed. The CPU 300 controls the rotation speed of the polygon mirror 203 by comparing the period of the BD signal input from the BD 206 to the CPU 300 and the reference period data, and based on the period of the BD signal, the reference period, and the comparison result, the polygon mirror drive motor. A control signal is transmitted to the driver 308.

  The image forming apparatus 100 includes a first potential sensor 309, a second potential sensor 310, and a home position sensor (HP sensor) 311 described later. Detection signals are transmitted from the first potential sensor 309, the second potential sensor 310, and the HP sensor 311 to the CPU 300, respectively. The CPU 300 recognizes that each sensor has generated a detection signal when the detection signal is input to the CPU 300.

  The image forming apparatus 100 includes a crystal oscillator 312 that generates a clock signal having a predetermined frequency, and the CPU 300 receives the reference clock signal. The CPU 300 executes various controls according to the reference clock signal.

  The image forming apparatus 100 forms an electrostatic latent image pattern or a toner pattern as a pattern image on the photosensitive drum 102, and the pattern image is detected by the first potential sensor 309 and the second potential sensor 310, thereby scanning lines. Is detected (moving direction of the light beam on the photosensitive drum).

  FIG. 4A is a diagram showing the photosensitive drum 102. A photosensitive layer 400 is formed on the surface of the photosensitive drum 102 by vacuum film formation or coating. As shown in FIG. 4A, the photosensitive drum 102 is provided with a first detection mark 401 and a second detection mark 402. Details of the detection mark will be described later. Further, by exposing the charged photosensitive drum 102 with laser light, a first electrostatic latent image pattern 403 and a second electrostatic latent image pattern 404 are formed on the photosensitive drum 102 as pattern images. The first electrostatic latent image pattern and the second electrostatic latent image pattern may be formed on the photosensitive drum during the same scan.

  4B and 4C show the photosensitive drum 102 provided in the image forming apparatus 100 and a first potential sensor 309, a second potential sensor 310, and an HP sensor 311 for detecting the surface potential on the photosensitive drum 102. FIG. FIG. 4B is a diagram illustrating an example of an image forming apparatus in which the first detection mark 401 and the second detection mark 402 are provided on the image forming area in the rotation axis direction of the photosensitive drum. FIG. 4C shows an example of an image forming apparatus in which the first detection mark 401 and the second detection mark 402 are provided outside the image forming area in the rotation axis direction of the photosensitive drum. By adopting the configuration shown in FIG. 4B, the size of the photosensitive drum in the direction of the rotation axis can be suppressed. Therefore, the apparatus can be downsized as compared with the configuration shown in FIG. On the other hand, in the configuration of FIG. 4C, control for forming an image by avoiding the detection mark is unnecessary, and therefore, control at the time of image formation can be simplified as compared with the configuration of FIG. 4B. it can.

  As shown in FIGS. 4B and 4C, a first potential sensor 309 and a second potential sensor 310 for detecting the potential on the surface of the photosensitive drum 102 are provided in the vicinity of the photosensitive drum 102. . The first potential sensor 309 and the second potential sensor 310 are provided on the downstream side of the irradiation position where the photosensitive drum 102 is irradiated with laser light in the rotation direction of the photosensitive drum 102 and on the upstream side of the developing device 105. (Refer to FIG. 1) It is set slightly apart (several μm to several tens μm) from the surface of the photosensitive drum 102. The first potential sensor 309 is provided on one end side of the photosensitive drum in the rotation axis direction of the photosensitive drum 102, and the second potential sensor 310 is provided on the other end side.

  As shown in FIG. 4B, the photosensitive drum 102 is provided with a home position mark (reference mark, hereinafter referred to as HP mark 405) for detecting the reference position. The HP mark 405 is provided on the side end surface of the photosensitive drum 102, and the image forming apparatus 100 is provided with an HP sensor 311 which is a third detection unit for detecting the HP mark. When the HP mark 405 passes the detection position of the HP sensor 311, the HP sensor outputs an HP signal to the CPU 300.

  As shown in FIG. 4B, the electrostatic latent image pattern 403 (first pattern image) is at a position corresponding to the first potential sensor 309, and the electrostatic latent image pattern 404 (second pattern image) is It is formed at a position corresponding to the detection position of the second potential sensor 310. The first electrostatic latent image pattern 403 passing through the detection position of the first potential sensor 309 and the second electrostatic latent image pattern 404 passing through the detection position of the second potential sensor 310 while the photosensitive drum 102 rotates. Are formed during one or a plurality of identical scanning periods.

  A signal output from each potential sensor is input to the CPU 300. Since the electrostatic latent image patterns 403 and 404 are exposed regions, the electrostatic latent image patterns 403 and 404 are regions having a potential different from the charged potential. Therefore, when the first electrostatic latent image pattern 403 passes the detection position of the first potential sensor 309 and the second electrostatic latent image pattern 404 passes the detection position of the second potential sensor 310, the first potential sensor 309 and The second potential sensor 310 outputs an analog signal having a waveform different from that when the charged potential region passes the detection position.

  The CPU 300 uses the first potential sensor 309 and the second potential sensor 310 in response to the first electrostatic latent image pattern 403 and the second electrostatic latent image pattern 404 passing through the detection position of the potential sensor. The inclination of the scanning line is detected based on the generation timing difference of the generated detection signal (pulse signal). For example, when the scanning line has no inclination, there is no difference in the pulse generation timing. On the other hand, when there is an inclination of the scanning line, the first electrostatic latent image pattern 403 and the second electrostatic latent image pattern 404 formed in the same scanning cycle have different passing timings through the corresponding potential sensors. Therefore, a difference occurs in the pulse generation timing. The CPU 300 obtains the scan line tilt correction amount from the generation timing difference and adjusts the position of the lens serving as the scan line tilt adjusting means so that the scan line tilt is reduced based on the correction amount. The motor driver 303 is controlled.

  In the present embodiment, a description is given of a configuration in which the inclination of the scanning line is detected using a potential sensor and the relative position of the potential sensor described later is described as an example, but similar detection may be performed using an optical sensor. . When an optical sensor is used, a toner pattern (visible image) is formed on the photosensitive drum 102 as a pattern image instead of an electrostatic latent image pattern. In this case, the detection marks 401 and 402 are provided on the photosensitive drum as marks having a light reflectance different from that of the photosensitive layer of the photosensitive drum 102.

  Scan line inclination detection will be described. The CPU 300 starts counting the reference clock signal by the internal counter in response to the HP sensor 311 detecting the HP signal. The CPU 300 stores the count value CNT3 in the RAM 302 in response to the first potential sensor 309 generating the pulse signal, and the count value CNT4 in response to the second potential sensor 310 generating the pulse signal. The data is stored in the RAM 302. The CPU 300 detects the inclination of the scanning line based on (Equation 1) CNT = CNT3-CNT4. In the present embodiment, in FIG. 4A, a case where the scanning line rises to the right is assumed to be a positive inclination, and a case where the scanning line falls to the right is assumed to be a negative inclination.

  Next, a configuration for correcting the inclination of the scanning line and an inclination correction operation will be described. FIG. 5A is a diagram illustrating the configuration of a drive unit that corrects the position of the imaging lens 205 in order to correct the inclination of the scanning line.

  In FIG. 5A, 501 is a stepping motor, 502 is a lead screw-shaped motor shaft, 503 is a head for pushing the imaging lens 205, 504 is a head stay, 505 is a pole for guaranteeing straight movement of the stay, Reference numeral 506 denotes a spring for urging the imaging lens 205 toward the head 503, and reference numeral 507 denotes a rotation fulcrum when the imaging lens 205 is rotated.

  Hereinafter, the operation of the drive unit will be described. When the stepping motor 501 rotates at a predetermined rotation speed or a predetermined angle, the stay 504 is pushed by the lead screw 502, the stay 504 moves up and down along the pole 505, and the imaging lens is formed by the head 503 attached to the stay 504. 205 is pushed, and the imaging lens 205 rotates around the rotation fulcrum 507. At this time, the imaging lens 205 rotates while being held by the spring 506 and the head 503, and is fixed by the spring 506 at a position where the movement of the head 503 is stopped. By moving the imaging lens 205 around the rotation fulcrum 507 shown in the figure, the image position in the image forming unit becomes a rotation fulcrum 507 (an axis parallel to the optical axis of the imaging lens 205 as shown in FIG. 5B described later). ) Can be adjusted. Therefore, by changing the position of the imaging lens 205 so as to correct the amount of misalignment, optical scanning is performed at a desired position, and color misregistration due to image tilt is corrected.

  FIG. 5B is a diagram for explaining a change in the inclination of the scanning line when the imaging lens 205 shown in FIG. 5A is moved. When the imaging lens 205 is at the position indicated by 511 in FIG. 5A, the inclination of the scanning line becomes an angle indicated by 521 in FIG. When the imaging lens 205 is at a position indicated by 512 in FIG. 5A, the inclination of the scanning line becomes an angle indicated by 522 in FIG. 5B. When the imaging lens 205 is at a position indicated by 513 in FIG. 5A, the inclination of the scanning line becomes an angle indicated by 523 in FIG. 5B. By setting the position of the imaging lens 205 to an appropriate position, the inclination of the scanning line can be corrected so as not to cause a color shift.

  The CPU 300 transmits to the lens driving motor driver 303 a control signal corresponding to the driving angle based on the inclination direction of the scanning line (which is positive or negative) and the count value.

  Note that the scan line inclination correction method is not limited to this. For example, as disclosed in Japanese Patent Application Laid-Open No. 06-183056, an apparatus provided with a reflection mirror that guides light deflected by a polygon mirror to a photosensitive drum in an optical scanning apparatus can be obtained by adjusting the position of the reflection mirror. Scan line inclination correction can be performed. Further, as disclosed in Japanese Patent Application Laid-Open No. 2007-279238, scanning on a photosensitive drum is performed by correcting image data used in each scanning cycle based on a correction amount when an image is formed on a recording medium. The inclination of the line is not corrected, but the inclination of the image formed on the photosensitive drum can be corrected. That is, the image formation direction can be made closer to the ideal image formation direction.

  Here, the problem in the method of correcting the inclination of the scanning line by detecting the electrostatic latent image pattern or detecting the laser beam will be described. The temperature of the interior of the image forming apparatus to which the potential sensor is attached rises due to heat generated by various drive motors during image formation. Along with this, the housing of the image forming apparatus thermally expands (deforms), and the position of the potential sensor fluctuates, thereby destroying the relative positional relationship between the two potential sensors. In addition, a change in the position of the potential sensor due to vibration or the like is one factor that destroys the relative positional relationship between the two potential sensors.

  FIG. 6A shows a diagram when two potential sensors are in an ideal positional relationship. As shown in FIG. 6A, the first potential sensor 309 and the second potential sensor 310 are adjusted at the time of assembling the apparatus so that both sensors are located on a one-dot chain line. If this state is maintained, the pulse generation timing when the first potential sensor 309 and the second potential sensor 310 detect the electrostatic latent image pattern is the same. On the other hand, as shown in FIG. 6B, the relative positional relationship between the first potential sensor 309 and the second potential sensor 310 may be lost in the rotation direction of the photosensitive drum. In this case, as shown in FIG. 6 (b), the difference in the generation timing of the pulses generated by the both potential sensors in response to the detection of the electrostatic latent image pattern, although the scanning line is not inclined. Will occur. Although the CPU 300 should not correct the inclination originally, the CPU 300 executes the inclination correction control of the scanning line so as to correct the pulse generation timing difference, and as a result, the inclination of the scanning line increases.

  In response to such a problem, in the image forming apparatus 100 according to the present embodiment, detection marks (first detection mark 401 and second detection mark 402) are provided on the photosensitive drum 102, and the detection marks are detected. Thus, the relative positional relationship between the first potential sensor 309 and the second potential sensor 310 is detected from the difference in pulse generation timing generated by each of the first potential sensor 309 and the second potential sensor 310. Then, by detecting the difference between the generation timing and the first electrostatic latent image pattern 403 and the second electrostatic latent image pattern 404, the generation timing difference of the pulse included in the detection signal generated by both potential sensors is detected. . This generation timing difference is corrected by the relative positional relationship between the two potential sensors. As a result, the inclination of the scanning line (or the inclination of the image) can be corrected based on the data from which the relative position shift between the two potential sensors is removed, so that the inclination of the image can be suppressed.

  Returning to FIG. 4, the detection mark will be described. A photosensitive layer 400 is formed on the surface of the photosensitive drum 102 by vacuum film formation or coating. Further, the first detection mark 401 and the second detection mark 402 are formed on both ends of the photosensitive drum 102 in the rotation axis direction so as to be included in the photosensitive layer 400. Although the first detection mark 401 and the second detection mark 402 are in the region of the photosensitive layer 400, the photosensitive layer is not formed, and the conductive base material of the photosensitive drum 102 is exposed. Since the photosensitive drum 102 is electrically grounded, the potentials of the first detection mark 401 and the second detection mark 402 are zero even when charging is performed by the charging device 10. When the photosensitive drum 102 is manufactured, the first detection mark 401 is formed by forming the photosensitive layer 400 on the surface of the photosensitive drum in a state where the positions corresponding to the first detection mark 401 and the second detection mark 402 are masked. The second detection mark 402 is formed. The first detection mark 401 and the second detection mark 402 are formed so as to be positioned on a line parallel to the rotation axis of the photosensitive drum 102 (on the one-dot chain line in FIG. 4A).

  As described above, the photosensitive drum 102 is provided with the HP mark 405 for detecting the reference position. When the HP mark 405 passes the detection position of the HP sensor 311, the HP sensor 311 outputs an HP signal to the CPU 300. The HP mark 405 is provided on the photosensitive drum 102 so that the generation timing of the HP signal is different from the generation timing of the detection signal generated by the both potential sensors.

  The CPU 300 controls the light source 201 so that the electrostatic latent image patterns 403 and 404 are formed on the rotating photosensitive drum 102 so as not to overlap the detection mark. The CPU 300 controls the light source 201 so that the timing at which the laser light is emitted from the light source for forming the electrostatic latent image patterns 403 and 404 is formed a predetermined time after the HP signal is generated (FIG. 7 ( b) and the timing of the drive signal in FIG. 8B). This predetermined time is determined based on the diameter of the photosensitive drum 102 and the rotational speed of the photosensitive drum 102 at the time of image formation.

  Since the CPU 300 is configured to detect the detection mark and the electrostatic latent image pattern with the same potential sensor, it is necessary to distinguish which one is generated by detecting the pulse signal. Therefore, the width of the detection mark and the width of the electrostatic latent image pattern in the rotation direction of the photosensitive drum 102 are made different. For example, if the light source is a semiconductor laser having two light emitting elements, and the detection mark width matches the width of 1000 scan lines, the electrostatic latent image pattern is formed by 250 scans (500 scan lines). If the rotational speed of the photosensitive drum 102 is constant, the pulse width output from the potential sensor differs between when the detection mark is detected and when the electrostatic latent image mark is detected. The CPU 300 determines whether the pulse output from the potential sensor is a pulse corresponding to the detection mark or a pulse corresponding to the electrostatic latent image pattern from the different pulse widths. In this embodiment, the relationship of (detection mark width)> (electrostatic latent image pattern width) is used, but the relationship of (detection mark width) <(electrostatic latent image pattern width) may be used.

  The CPU 300 starts counting the reference clock signal in response to the HP sensor 311 generating the HP signal. Then, the CPU 300 stores the count value CNT1 of the internal counter in the RAM 302 in accordance with the rise of the pulse output from the first potential sensor 309 that has detected the first detection mark 401. Similarly, the count value CNT 2 of the internal counter is stored in the RAM 302 in response to the pulse output from the second potential sensor 310 being input to the CPU 300 by detecting the second detection mark 402. At this time, the difference between CNT1 and CNT2 represents the relative positional relationship in the photosensitive drum rotation direction of both potential sensors. That is, when the difference count value between CNT1 and CNT2 is “0”, there is no deviation in the relative positional relationship. In the case of CNT1-CNT2 <0, the first potential sensor 309 is positioned upstream of the second potential sensor 310 in the photosensitive drum rotation direction. In the case of CNT1-CNT2> 0, the first potential sensor 309 is positioned downstream of the second potential sensor 310 in the photosensitive drum rotation direction.

The CPU 300 stores the count value CNT3 of the internal counter in the RAM 302 in response to the first potential sensor 309 generating a pulse signal by detecting the electrostatic latent image pattern. Similarly, the count value CNT4 of the internal counter is stored in the RAM 302 in response to the second potential sensor 310 generating a pulse signal by detecting the electrostatic latent image pattern. Then, the CPU 300 calculates the count value CNT corresponding to the scan line tilt direction and the scan line tilt based on the following calculation formula.
(Formula 2) CNT = (CNT3-CNT4)-(CNT1-CNT2)

  FIG. 7 illustrates scanning line tilt detection when the first potential sensor 309 is positioned upstream of the second potential sensor 310 in the rotational direction of the photosensitive drum 102 and the scanning line tilts to the right. FIG. As shown in FIG. 7A, since the inclination of the scanning line is lowering to the right, the electrostatic latent image pattern 403 is formed ahead of the electrostatic latent image pattern 404 in the photosensitive drum rotation direction.

  FIG. 8 illustrates scanning line tilt detection when the first potential sensor 309 is located downstream of the second potential sensor 310 in the rotational direction of the photosensitive drum 102 and the scanning line tilts upward. FIG. As shown in FIG. 8A, since the inclination of the scanning line rises to the right, the electrostatic latent image pattern 404 is formed ahead of the electrostatic latent image pattern 403 in the photosensitive drum rotation direction.

  7B and 8B, the CPU 300 starts counting the reference clock in response to the HP signal (HP sensor output) being output from the HP sensor 311. Then, the CPU 300 stores the count value CNT1 in the RAM 302 in response to the first potential sensor 309 generating the pulse 401 ′ for the detection mark 401. Further, the CPU 300 stores the count value CNT3 in the RAM 302 in response to the first potential sensor 309 generating the pulse 403 'for the electrostatic latent image pattern 403.

  The CPU 300 stores the count value CNT2 in the RAM 302 in response to the second potential sensor 310 generating a pulse 402 ′ for the detection mark 402. Further, the CPU 300 stores the count value CNT4 in the RAM 302 in response to the second potential sensor 310 generating the pulse 404 ′ for the electrostatic latent image pattern 404.

In FIG. 7B, here, the respective count values are assumed to be CNT1 = 5, CNT2 = 8, CNT3 = 12, and CNT4 = 18 for convenience. Substituting these count values into (Equation 2),
(Formula 3) CNT = (CNT3-CNT4)-(CNT1-CNT2) =-3
It becomes. This CNT = −3 (time difference) is a count value corresponding to the inclination amount of the scanning line. That is, the scanning line has a downward slope and is inclined by an amount corresponding to | −3 |.

In FIG. 8B, here, for convenience, CNT1 = 8, CNT2 = 5, CNT3 = 20, and CNT4 = 12,
(Formula 4) CNT = (CNT3-CNT4)-(CNT1-CNT2) = + 5
It becomes. This CNT = 5 is a count value corresponding to the amount of inclination of the scanning line. In other words, the scanning line has a downward slope and is inclined by an amount corresponding to | +5 |.

  The CPU 300 uses the result obtained by multiplying the count value CNT by a coefficient corresponding to the rotation speed of the drum as the inclination correction amount, or uses the correction table in which the inclination correction amount corresponds to the count value CNT, and the inclination correction amount of the scanning line. Get. The CPU 300 controls the lens drive motor driver 303 described above in accordance with the tilt correction amount (drive motor control amount).

  Next, a control flow executed when the CPU 300 performs tilt correction will be described with reference to FIG.

  The CPU 300 executes tilt correction at a predetermined timing. The predetermined timing refers to the case where the image forming apparatus is turned on, the apparatus returns from the sleep state, the unit is replaced, the cumulative number of formed images reaches the predetermined number, the continuous image forming number reaches the predetermined number. When the number of sheets is reached, it is at least one timing among the cases where the temperature in the image forming apparatus fluctuates by a predetermined temperature or more. Further, the CPU 300 may execute tilt correction in response to a user instruction. The inclination correction is performed when the photosensitive drum rotates at a constant speed.

  First, the CPU 300 controls the charging device to charge the photosensitive drum 102 (step S901). Thereafter, counting of the reference clock is started in response to the generation of the HP signal (step S902). Further, the laser driver 307 is controlled to form an electrostatic latent image pattern in response to the generation of the HP signal (step S903). Subsequently, the CPU 300 obtains the above CNT1 and CNT2 from the count value of the reference clock signal and stores them in the RAM 302 (step S904).

  After step S904, the CPU 300 calculates a count value corresponding to the inclination amount of the scanning line based on (Equation 2) (step S905), and obtains an inclination correction amount from the count value obtained in step S905 (step S906). Then, the CPU 300 drives the lens driving motor driver 303 based on the tilt correction amount (step S907), and ends the tilt correction.

  With the configuration described above, the relative positional relationship between potential sensors is detected, and the detection result is reflected in the inclination correction of the scanning line. Line inclination correction can be performed.

102 Photosensitive drum 300 CPU
309 First potential sensor 310 Second potential sensor 401 First detection mark 402 Second detection mark

Claims (11)

A photoconductor which is rotationally driven by a driving means and provided with a detection mark;
Image forming means for forming an image on the photoconductor by emitting a light beam from a light source to expose the photoconductor and scanning the light beam so that the light beam moves on the photoconductor; ,
First detection means for detecting a pattern image formed by the detection mark or the image forming means;
Second detection means for detecting the detection mark or the pattern image at a position different from the first detection means in the rotation axis direction of the photosensitive member;
By detecting the pattern image, the orientation of the image formed on the photoconductor is adjusted based on a generation timing difference between detection signals generated by the first detection unit and the second detection unit. Adjusting means;
By detecting the detection mark, the first detection unit detects the pattern image based on a generation timing difference between detection signals generated by the first detection unit and the second detection unit, respectively. And an image forming apparatus comprising: a correction unit that corrects the generation timing difference between detection signals generated by the second detection units.   The detection mark includes a first detection mark and a second detection mark, the first detection mark is provided at a position passing through a detection position of the first detection means, and the second detection mark is The image forming apparatus according to claim 1, wherein the image forming apparatus is provided at a position that passes a detection position of the second detection unit.   The image forming apparatus according to claim 2, wherein the first detection mark and the second detection mark are provided on a line parallel to the rotation axis. The image forming unit includes a developing unit that develops an electrostatic latent image formed on the photoconductor as a toner image by exposing the photoconductor;
The image forming apparatus according to claim 1, wherein the first detection unit and the second detection unit are optical sensors that detect a toner pattern formed on the photoconductor as the pattern image. .   The image according to claim 1, wherein the first detection unit and the second detection unit are potential sensors that detect an electrostatic latent image pattern formed on the photoconductor as the pattern image. Forming equipment. The image forming unit includes a developing unit that develops an electrostatic latent image formed on the photoconductor by exposing the photoconductor as a toner image, and a transfer unit that transfers the toner image to a recording medium.
In the rotational axis direction of the photoconductor, the first detection mark and the second detection mark are provided outside an area where a toner image to be transferred to the recording medium is formed, and sandwich the area. The image forming apparatus according to claim 2, wherein the image forming apparatuses are provided on different sides.   The image forming apparatus according to claim 4, wherein the detection mark is a region having a reflectance different from a region of the photosensitive layer on which an electrostatic latent image based on image data is formed on the photosensitive member. Control means for emitting a light beam from the light source based on image data, and third detection means for detecting a reference mark provided on the photoconductor for detecting a reference position of the photoconductor,
The control means detects the reference mark so that the pattern image and the detection mark do not overlap, and forms the pattern image based on the timing at which the third detection means generates a detection signal. the image forming apparatus according to any one of claims 1 to 7, wherein the controlling the emission timing of the light beam from the light source. The image forming unit includes a control unit that emits the light beam from the light source, and the control unit is configured such that a width of the pattern image in a rotation direction of the photosensitive member is different from a width of the detection mark. the image forming apparatus according to any one of claims 1 to 8, wherein the controller controls the light source. The adjustment unit detects the pattern image so that a difference in generation timing of detection signals generated by the first detection unit and the second detection unit becomes a predetermined time difference on the photoconductor. the image forming apparatus according to any one of claims 1 to 9, characterized in that the adjusting means for adjusting the moving direction of the light beam. A lens for guiding the scanned light beam to the photoreceptor;
The adjusting means includes lens rotating means for rotating the lens about an axis parallel to the optical axis of the lens in order to adjust the moving direction of the light beam on the photoconductor. The image forming apparatus according to claim 10 .

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