JP4923593B2 - Optical scanning device, method for controlling the device, and image forming apparatus using the device - Google Patents

Description

  The present invention relates to an optical scanning apparatus that scans a surface to be scanned with a light beam in a main scanning direction, a control method for the apparatus, and an image forming apparatus that performs image formation using the apparatus.

  In this type of optical scanning device, a light source and a deflector are provided, and the deflected light beam is scanned in the main scanning direction by deflecting the light beam emitted from the light source by the deflector. In addition, in order to reduce the size and speed of the deflector, it has been conventionally proposed to vibrate the deflecting mirror and use it as a deflector (see Patent Document 1). That is, in this apparatus, the deflecting mirror supported by the torsion bar is sine-vibrated, and the light beam emitted from the light source is reflected by the surface of the deflecting mirror, so that the surface to be scanned such as the surface of the latent image carrier The light beam can be scanned in the main scanning direction.

  Further, in the optical scanning device described in Patent Document 1, a scanning optical system having an arc-sin characteristic is used in order to scan the scanning surface with the light beam deflected by the sine-vibrating deflection mirror as described above at a constant speed. Used. That is, the angular velocity of the incident angle of the light beam deflected by the sine-vibrating deflection mirror to the scanning optical system becomes slower as the incident angle increases. Therefore, for example, when a scanning optical system having no distortion characteristic is used, the scanning speed of the light beam on the surface to be scanned becomes slower as the distance (image height) from the optical axis in the main scanning direction increases. Therefore, in order to compensate for a decrease in scanning speed at a position where the image height is large, a scanning optical system having an arc-sin characteristic that scans a light beam with an exit angle larger than the incident angle as the incident angle increases is used. ing.

  Further, in the image forming apparatus using the optical scanning device as described above, a toner image is formed as follows. In other words, the image forming apparatus includes a latent image carrier capable of forming a toner image on the surface thereof, a developing unit, and a charging unit, and for image gradation data representing gradation values for each pixel in multiple stages. Halftone processing is performed to generate pattern data indicating where the toner is to be attached on the surface of the latent image carrier. That is, in such an image forming apparatus, gradation reproduction is realized by changing the area of the toner per unit area. More specifically, when the gradation value is high, the toner area occupied per unit area is increased, while when the gradation value is low, the toner area occupied per unit area is decreased. Reproduction is realized. Therefore, in such an image forming apparatus, by performing halftone processing, the image gradation data representing the gradation value for each pixel in multiple stages is determined to which position on the surface of the latent image carrier the toner is attached. It is converted to the pattern data shown.

  Then, an exposure signal is generated based on the pattern data, and the exposure signal is output to a light source provided in the optical scanning device. As a result, a light beam modulated based on the exposure signal is emitted from the light source, and the modulated light beam is scanned in the main scanning direction by the deflecting mirror surface that vibrates.

  By scanning the modulated light beam as described above, the light beam is irradiated in a spot shape on the surface of the latent image carrier that has been uniformly charged by the charging unit in advance, and the electric charge at the spot is removed. Thus, a spot-like electrostatic latent image (spot latent image) is formed. In this specification, a spot region formed on a surface of a latent image carrier that is irradiated with a light beam is simply referred to as a “spot”. Then, charged toner is attached to the spot latent image formed in this way by the developing unit, and dots are formed at predetermined positions on the surface of the latent image carrier. As a result, a toner image is formed on the surface of the latent image carrier.

JP 2002-182147 A (page 3, page 5, FIGS. 9 and 10)

  However, the surface to be scanned such as the surface of the latent image carrier is irradiated through the scanning optical system having the arc-sin characteristic with the light beam deflected by the sine-vibrating deflection mirror surface as in the above optical scanning device. In this case, the incident angle of the light beam with respect to the surface to be scanned varies depending on the position in the main scanning direction. As a result, the peak value of the light amount distribution of the spot irradiated on the surface to be scanned takes the maximum value near the optical axis of the scanning optical system and decreases as the distance from the optical axis increases in the main scanning direction. Defects sometimes occurred. Such optical scanning defects may cause the following image problems when a low-density image (highlight image) is formed using the optical scanning device.

  As described above, when an image is formed using an optical scanning device, a spot latent image is formed by irradiating a spot on the surface of the latent image carrier (scanned surface) with the optical scanning device, and toner is applied to the spot latent image. To form dots. Therefore, if the above-mentioned optical scanning failure occurs and the peak value of the spot light quantity distribution differs depending on the position in the main scanning direction, the potential distribution of the spot latent image also differs, and the dot formed by toner development of the spot latent image. The size also varies depending on the position in the main scanning direction. In other words, the size of the formed dot becomes maximum near the optical axis of the scanning optical system and may decrease as the distance from the optical axis increases in the main scanning direction. As a result, in spite of trying to form an image having the same density, an image detrimental effect that the image density decreases as the distance from the optical axis of the scanning optical system in the main scanning direction may occur. Such image defects are particularly prominent when a highlight image, which is a low density image, is formed.

  The present invention has been made in view of the above problems, and the above optical scanning in an optical scanning device that deflects a light beam by a sinusoidally oscillating deflecting mirror surface and scans the light beam by a scanning optical system having arc-sin characteristics. It is an object of the present invention to provide a technique that enables good optical scanning by suppressing the occurrence of defects and enables formation of a good highlight image.

  The control method of the optical scanning device according to the present invention includes a light source that emits a light beam, a deflector that deflects the light beam emitted from the light source by a deflecting mirror surface that sinusoidally vibrates, an arc-sin characteristic, and a deflector. And a scanning optical system for guiding the light beam deflected by the scanning surface to the scanning surface, and capable of performing a light scanning operation of scanning the light beam in the main scanning direction and irradiating the scanning surface in a spot shape In order to achieve the above object, an exposure signal obtained by converting pattern data indicating a position where a light beam is irradiated in a spot shape is input to a light source and an optical scanning operation is executed by an optical scanning device. A method of controlling an optical scanning device that irradiates a predetermined position on a surface to be scanned with a light beam in the form of a spot, wherein the principal ray of the light beam deflected by the deflecting mirror surface and the optical axis of the scanning optical system When the angle formed is the deflection angle, the light quantity of the light beam emitted from the light source is based on a light quantity pattern that continuously increases the light quantity of the light beam emitted from the light source as the absolute value of the deflection angle increases. A patch latent image forming step for forming a plurality of latent images as patch latent images at different positions in the main scanning direction on the surface to be scanned, and developing a plurality of patch images by toner developing the plurality of patch latent images A patch developing process, a density detecting process for detecting the density of a plurality of patch images transferred to the transfer medium by a density sensor facing the transfer medium, and a pattern for obtaining a light quantity pattern based on the detection result in the density detecting process And a generation step.

An optical scanning device according to the present invention includes a light source that emits a light beam, a deflector that deflects the light beam emitted from the light source by a deflecting mirror surface that sinusoidally vibrates, an arc-sin characteristic, and a deflector. And a scanning optical system that guides the deflected light beam to the surface to be scanned, and performs an optical scanning operation that scans the light beam in the main scanning direction and irradiates the surface to be scanned in a spot shape. In order to achieve the above object, when the angle formed by the principal ray of the light beam deflected by the deflecting mirror surface and the optical axis of the scanning optical system is defined as the deflection angle, the light amount of the light beam emitted from the light source is And controlling based on a light amount pattern that continuously increases the light amount of the light beam emitted from the light source with an increase in the absolute value of the deflection angle, and a plurality of latent images at different positions in the main scanning direction of the surface to be scanned. Are formed as patch latent images, a plurality of patch images obtained by toner development of a plurality of patch latent images are formed on a transfer medium, and the density of the plurality of patch images is detected by a density sensor facing the transfer medium. The light quantity pattern is obtained based on the above.
In order to achieve the above object, an image forming apparatus according to the present invention includes a latent image carrier, a charging unit that charges the surface of the latent image carrier substantially uniformly, a light source that emits a light beam, A deflector that deflects the light beam emitted from the light source by a deflecting mirror surface that sine vibrates, and a light beam that has an arc-sin characteristic and is deflected by the deflector is guided to the surface of the latent image carrier charged by the charging means. A scanning optical system that emits light, an exposure unit that performs a light scanning operation of irradiating the surface of the latent image carrier in a spot shape by scanning a light beam in the main scanning direction, and a developing unit that develops the electrostatic latent image with toner And a transfer medium onto which an image obtained by developing the toner by the developing means is transferred, and a density sensor facing the transfer medium, and the principal ray of the light beam deflected by the deflection mirror surface and the scanning optical system With the optical axis When the angle is the deflection angle, the amount of light beam emitted from the light source is controlled based on a light amount pattern that continuously increases the amount of light beam emitted from the light source as the absolute value of the deflection angle increases. In addition, a plurality of latent images are formed as patch latent images at different positions in the main scanning direction on the surface of the latent image carrier, and a plurality of patch images obtained by developing the plurality of patch latent images with toner are used as transfer media. It is characterized in that a light quantity pattern is obtained based on the result of transfer and detection of the density of a plurality of patch images by a density sensor.

  In the invention configured as described above (the optical scanning device, the control method of the device, and the image forming apparatus), the light beam emitted from the light source is deflected by the deflecting mirror surface that sinusoidally vibrates. Then, the deflected light beam is guided to the surface to be scanned by the scanning optical system having arc-sin characteristics, and the light beam is scanned in the main scanning direction of the surface to be scanned and irradiated to the surface to be scanned in a spot shape. . Therefore, as described above, the peak value of the light amount distribution of the spot irradiated to the surface to be scanned takes a maximum value near the optical axis of the scanning optical system and decreases as the distance from the optical axis increases in the main scanning direction. In some cases, optical scanning failure occurs.

  On the other hand, the present invention controls the light quantity of the light beam emitted from the light source based on the following light quantity pattern. Here, when the angle formed by the principal ray of the light beam deflected by the deflecting mirror surface and the optical axis of the scanning optical system is defined as the deflection angle, the light quantity pattern is emitted from the light source as the absolute value of the deflection angle increases. This is a pattern that continuously increases the amount of light beam emitted. Therefore, it is possible to alleviate the change in the main scanning direction position of the peak value of the light amount distribution of the spot irradiated on the surface to be scanned and perform a good optical scanning operation. Then, by executing image formation with an optical scanning device capable of executing such a good optical scanning operation, the above-described difference in image density due to the position in the main scanning direction is suppressed, and a good highlight image can be formed. It becomes possible.

  The present invention also provides a patch latent image forming step for forming a plurality of latent images as patch latent images at different positions in the main scanning direction of the surface to be scanned, and a plurality of patch images by toner developing the plurality of patch latent images. A patch developing process for forming a color density, a density detecting process for detecting the density of a plurality of patch images transferred to the transfer medium by a density sensor facing the transfer medium, and a light quantity pattern based on a detection result in the density detecting process. A desired pattern generation step. In other words, by executing these patch latent image forming process, patch developing process, and density detecting process, it is possible to detect a change in the main scanning direction of the peak value of the light amount distribution of the spot irradiated on the scanned surface with high accuracy. ing. Then, the pattern generation process is executed, and the light quantity pattern is obtained from the detection result of such a density detection process. Therefore, it is possible to obtain an optimum light amount pattern, and as a result, it is possible to perform a better light scanning operation, which is preferable. Then, by performing image formation with an optical scanning device capable of performing a better optical scanning operation, the above-described difference in image density due to the position in the main scanning direction can be suppressed with higher accuracy, and a better high- A light image can be formed, which is preferable. At this time, one of the plurality of electrostatic latent images may be formed on the optical axis of the scanning optical system.

Further, the number of the plurality of patch latent images formed in the patch latent image forming step may be two. However, the optical scanning device as described above is often configured symmetrically with respect to the optical axis of the scanning optical system. In such a case, the positions of the two patch images formed by executing the patch latent image forming step and the patch developing step are positions symmetrical in the main scanning direction with respect to the optical axis of the scanning optical system. The densities of these two patch images are approximately the same. On the other hand, the patch latent image forming step may be configured to form two patch latent images at positions asymmetric with respect to the optical axis of the scanning optical system in the main scanning direction. In the invention configured as described above, the densities of the two patch images formed by executing the patch latent image forming process and the patch developing process are different from each other without depending on the symmetry of the apparatus configuration. Therefore, the change in the main scanning direction of the peak value of the light amount distribution of the spot irradiated on the scanning surface can be detected with high accuracy. Therefore, it is possible to obtain an optimum light amount pattern, and as a result, it is possible to perform a better light scanning operation, which is preferable. Then, by performing image formation with an optical scanning device capable of performing a better optical scanning operation, the above-described difference in image density due to the position in the main scanning direction can be suppressed with higher accuracy, and a better high- A light image can be formed, which is preferable. At this time, one of the two patch latent images may be formed on the optical axis of the scanning optical system.

  Also, pattern data may be generated by performing halftone processing on image gradation data in which the gradation value of each pixel is expressed in multiple gradations. At this time, the halftone process generates pattern data so as to increase the irradiation area of the light beam to the cell with a predetermined increase pattern as the gradation value of the image gradation data increases, and the increase pattern is deflected. You may comprise so that it may be constant irrespective of an angle | corner.

  FIG. 1 is a diagram showing an embodiment of an image forming apparatus according to the present invention. FIG. 2 is a block diagram showing an electrical configuration of the image forming apparatus of FIG. In this image forming apparatus, an exposure unit of a laser printer LP-7000C manufactured by Seiko Epson Corporation is replaced with an exposure unit 6 having the same configuration as that of the optical scanning device according to the present invention. is there. In this image forming apparatus, when a print command is given to the main controller 11 from an external device such as a host computer in response to an image formation request from the user, the engine controller 10 responds to the print command from the CPU 111 of the main controller 11. The engine unit EG is controlled to form an image corresponding to the print command on a sheet such as copy paper, transfer paper, paper, and OHP transparent sheet.

  In the engine unit EG, the photosensitive member 2 is provided so as to be rotatable in the arrow direction (sub-scanning direction) in FIG. A charging unit 3 (charging unit), a rotary developing unit 4 (developing unit), and a cleaning unit (not shown) are arranged around the photosensitive member 2 (latent image carrier) along the rotation direction. Yes. A charging controller 103 is electrically connected to the charging unit 3 and applies a predetermined charging bias. By applying this bias, the outer peripheral surface of the photoreceptor 2 is uniformly charged to a predetermined surface potential. Further, the photosensitive member 2, the charging unit 3, and the cleaning unit integrally constitute a photosensitive member cartridge, and the photosensitive member cartridge is integrally detachable from the apparatus main body 5.

  Then, the light beam L is irradiated from the exposure unit 6 (exposure means, optical scanning device) toward the outer peripheral surface (scanned surface) of the photosensitive member 2 charged by the charging unit 3. The exposure unit 6 exposes the light beam L onto the photoconductor 2 in accordance with image data given from an external device to form an electrostatic latent image corresponding to the image data. The configuration and operation of the exposure unit 6 will be described in detail later.

  The electrostatic latent image thus formed is developed with toner by the developing unit 4. That is, in this embodiment, the developing unit 4 is configured as a support frame 40 that is rotatably provided around the axis, and a cartridge that is detachable with respect to the support frame 40, and for yellow that contains toner of each color. A developing unit 4Y, a magenta developing unit 4M, a cyan developing unit 4C, and a black developing unit 4K are provided. Then, based on a control command from the developing device controller 104 of the engine controller 10, the developing unit 4 is driven to rotate, and the developing devices 4Y, 4C, 4M, and 4K are selectively brought into contact with the photoreceptor 2. Alternatively, when positioned at a predetermined developing position facing each other with a predetermined gap, toner is applied to the surface of the photoreceptor 2 from a developing roller 44 provided in the developing unit and carrying toner of a selected color. As a result, the electrostatic latent image on the photoreceptor 2 is visualized with the selected toner color.

  The toner image developed by the developing unit 4 as described above is primarily transferred onto the intermediate transfer belt 71 of the transfer unit 7 in the primary transfer region TR1. The transfer unit 7 includes an intermediate transfer belt 71 that is stretched over a plurality of rollers 72, 73, and the like, and a drive unit (not shown) that rotates the intermediate transfer belt 71 in a predetermined rotation direction by rotationally driving the roller 73. It has.

  In the vicinity of the roller 72, a transfer belt cleaner (not shown), a density sensor 76 (FIG. 2), and a vertical synchronization sensor 77 (FIG. 2) are arranged. Among these, the density sensor 76 is provided facing the surface of the intermediate transfer belt 71 and measures the optical density of the patch image formed on the outer peripheral surface of the intermediate transfer belt 71. The vertical synchronization sensor 77 is a sensor for detecting the reference position of the intermediate transfer belt 71, and is a synchronization signal output in association with the rotational drive of the intermediate transfer belt 71 in the sub-scanning direction, that is, a vertical synchronization signal. It functions as a vertical sync sensor for obtaining Vsync. In this apparatus, the operation of each part of the apparatus is controlled based on the vertical synchronization signal Vsync in order to align the operation timing of each part and to superimpose toner images of each color accurately.

  When transferring a color image to a sheet, each color toner image formed on the photoreceptor 2 is superimposed on the intermediate transfer belt 71 to form a color image and taken out from the cassette 8 one by one. The color image is secondarily transferred onto the sheet conveyed along the conveyance path F to the secondary transfer region TR2.

  At this time, in order to correctly transfer the image on the intermediate transfer belt 71 to a predetermined position on the sheet, the timing of feeding the sheet to the secondary transfer region TR2 is managed. Specifically, a gate roller 81 is provided on the transport path F on the front side of the secondary transfer region TR2, and the gate roller 81 rotates in accordance with the timing of the circumferential movement of the intermediate transfer belt 71. Are sent to the secondary transfer region TR2 at a predetermined timing.

  Further, the sheet on which the color image is formed in this way is conveyed to the discharge tray portion 51 provided on the upper surface portion of the apparatus main body 5 via the fixing unit 9 and the discharge roller 82. When images are formed on both sides of the sheet, the sheet on which the image is formed on one side as described above is switched back by the discharge roller 82. As a result, the sheet is conveyed along the reverse conveyance path FR. Then, it is put again on the transport path F before the gate roller 81. At this time, the image is transferred to the surface of the sheet that is in contact with the intermediate transfer belt 71 and transfers the image in the secondary transfer region TR2. The surface is the opposite of the surface. In this way, images can be formed on both sides of the sheet.

  In FIG. 2, reference numeral 113 denotes an image memory provided in the main controller 11 for storing image data given from an external device such as a host computer via the interface 112, and reference numeral 106 is executed by the CPU 101. A ROM for storing calculation data, control data for controlling the engine unit EG, and the like, and a reference numeral 107 are RAMs for temporarily storing calculation results in the CPU 101 and other data.

  FIG. 3 is a sub-scan sectional view showing a configuration of an exposure unit (optical scanning device, exposure means) provided in the image forming apparatus of FIG. 4 is a main scanning sectional view showing a configuration of an exposure unit (optical scanning device, exposure means) provided in the image forming apparatus of FIG. FIG. 5 is a sub-scan sectional view in which the optical configuration of the exposure unit (optical scanning device, exposure means) is developed. Hereinafter, the configuration and operation of the exposure unit will be described in detail with reference to these drawings.

  The exposure unit 6 has an exposure housing 61. A single laser light source 62 is fixed to the exposure housing 61, and a light beam can be emitted from the laser light source 62. The laser light source 62 is electrically connected to the exposure control unit 102. As will be described in detail later, the exposure control unit 102 is provided with a video signal (exposure signal) generated based on the image data. Therefore, when the exposure control unit 102 controls the laser light source 62 to be turned on / off, a light beam modulated in accordance with the image data is emitted from the laser light source 62. Thus, in this embodiment, the laser light source 62 corresponds to the “light source” of the present invention.

  Further, in the exposure housing 61, a collimator lens 63, a cylindrical lens 64, a deflector 65, a first scanning lens 66, a light beam from a laser light source 62 are scanned and exposed on the surface of the photosensitive member 2. A folding mirror 67 and a second scanning lens 68 are provided. That is, the light beam from the laser light source 62 is shaped into collimated light of an appropriate size by the collimator lens 63 and then incident on the cylindrical lens 64 having power only in the sub-scanning direction Y as shown in FIG. The The collimated light is converged only in the sub-scanning direction Y and is linearly formed in the vicinity of the deflecting mirror surface 651 of the deflector 65.

  The deflector 65 is formed using a micromachining technique in which a micromachine is integrally formed on a semiconductor substrate by applying a semiconductor manufacturing technique, and is constituted by a deflection mirror that resonates and vibrates. That is, in the deflector 65, the light beam can be deflected in the main scanning direction X by the deflecting mirror surface 651 that resonates and vibrates. More specifically, the deflection mirror surface 651 is pivotally supported around a vibration axis (torsion spring) substantially orthogonal to the main scanning direction X and vibrates according to an external force applied from an operating unit (not shown). Vibrates sine around. This actuating unit applies an electrostatic, electromagnetic or mechanical external force to the deflection mirror surface 651 based on a mirror drive signal from a mirror drive unit (not shown) of the exposure control unit 102 to mirror the deflection mirror surface 651. Vibrate at the frequency of the drive signal. Note that any driving method such as electrostatic adsorption, electromagnetic force, or mechanical force may be adopted as the driving method by the operating unit, and since these driving methods are well known, description thereof is omitted here.

  The light beam deflected by the deflecting mirror surface 651 is guided to the outer peripheral surface (scanned surface) of the photosensitive member 2 by the scanning optical system including the first scanning lens 66 and the second scanning lens 68. Such a scanning optical system has an arc-sin characteristic and is configured such that the one-dot chain line in FIG. 4 is the optical axis OA. Further, as described above, the deflection mirror surface 651 vibrates sinusoidally around the vibration axis. Therefore, when the angle formed between the principal ray of the light beam and the optical axis OA is the deflection angle DA, the light beam is applied to the surface of the photosensitive member 2 in the first direction (+ X) or a constant velocity reciprocating scan in the second direction (−X) opposite to the first direction (+ X). The light beam scanned in this way irradiates the surface (scanned surface, latent image carrier surface) of the photosensitive member 2 uniformly charged in advance by the charging unit 3 in a spot shape. Thereby, the electric charge in the spot is removed and a spot latent image is formed. A plurality of such spot latent images are formed according to the image to be formed. Further, the end of the scanning path of the scanning light beam is guided to the horizontal synchronization sensor 60 by the folding mirror 69 on the upstream side in the scanning direction (+ X). The horizontal synchronization sensor 60 detects the light beam for each cycle of the light beam reciprocally scanned in the main scanning direction X, and outputs a horizontal synchronization signal Hsync. Then, the latent image forming operation is controlled based on the horizontal synchronization signal Hsync.

  The spot latent image formed on the surface of the photoreceptor 2 corresponding to the image data of each color by the exposure unit 6 described above is developed by the developing devices 4K, 4Y, 4M, The toner is developed with 4C to form dots (FIGS. 1 and 2). That is, for example, when a spot latent image is formed on the surface of the photoreceptor 2 corresponding to the image data of black K, the developing device 4K having black toner develops the spot latent image with toner at a predetermined development position. Then, black dots are formed on the surface of the photoreceptor 2. The dots of other colors (cyan C, magenta M, yellow Y) are also formed by developing the latent spot images formed in the same procedure with the corresponding color developing devices 4C, 4M, 4Y. The

  Next, signal processing executed in the image forming apparatus according to the present invention will be described. FIG. 6 is a diagram showing signal processing of the image forming apparatus according to the present invention. In this image forming apparatus, when image data is input from an external device such as the host computer 100, the main controller 11 performs predetermined signal processing on the image data. The main controller 11 includes functional blocks such as a color conversion unit 113, an image processing unit 115, two types of line buffers 116A and 116B, a direction switching unit 116C, and a pulse modulation unit 117. Each of these functional blocks may be configured by hardware, or may be realized by software executed by the CPUs 111 and 101.

  In the main controller 11 to which the image data is given from the host computer 100, the color conversion unit 113 converts the RGB gradation data indicating the gradation level of the RGB component of each pixel in the image corresponding to the image data into the corresponding CMYK. Conversion to CMYK gradation data (image gradation data) indicating the gradation level of the component is performed. In this color conversion unit 113, the input RGB gradation data is 8 bits per pixel and one color component (that is, 256 gradations), and the output CMYK gradation data is similarly 8 bits per pixel and one color component (that is, that is). 256 gradations). The CMYK gradation data output from the color conversion unit 113 is input to the image processing unit 115.

  The image processing unit 115 performs halftone processing on the input CMYK gradation data (image gradation data). In such halftone processing, CMYK gradation data expressed in multiple stages of 8 bits per color component per pixel is applied to a light beam at any position on the surface of the photosensitive member 2 (scanned surface, latent image carrier surface). Is converted into halftone gradation data (pattern data) indicating whether or not to be irradiated in a spot shape. As such halftone processing, various conventionally proposed methods can be used. Specifically, for example, a dot concentration type dither method, a dot dispersion type dither method, an error diffusion method, or the like has been proposed in the past. However, in any of the methods, a predetermined increase pattern as the gradation value increases. The gradation is reproduced by changing the dot area ratio per unit area. That is, when the gradation value is low, the dot area ratio is lowered, while when the gradation value is high, the dot area ratio is increased to realize gradation reproduction. In the halftone processing in the present embodiment, it is assumed that the increase pattern is constant regardless of the position of the target pixel in the main scanning direction. In other words, the increase pattern is constant regardless of the deflection angle.

  The above-described exposure control unit 102 receives the video signal (exposure signal) from the pulse modulation unit 117 and controls ON / OFF of the laser light source 62 of the exposure unit 6. The video signal (exposure signal) is emitted from the laser light source 62 of the engine unit EG using the halftone gradation data (pattern data) output from the image processing unit 115 by the pulse modulation unit 117. It is created for pulse width modulation of a beam. On the other hand, as described above, in this embodiment, the light beam is reciprocated in the main scanning direction X by the deflecting mirror surface 651 that resonates and vibrates. In other words, the light beam is reciprocally scanned in the forward path and the backward path whose scanning directions are opposite to each other. Therefore, when the halftone gradation data is input to the pulse modulation unit 117, it is necessary to change the input order of the halftone gradation data input to the pulse modulation unit 117 according to the difference in the scanning direction of the light beam. Therefore, in this embodiment, a forward line buffer 116A and a backward line buffer 116B are provided.

  The halftone gradation data output in this way is input to the direction switching unit 116C, and only the halftone gradation data output from one line buffer is output from the direction switching unit 116C at an appropriate timing based on the direction switching signal. It is output to the pulse modulation unit 117. That is, when the light beam is scanned in the forward direction, a forward signal is supplied to the direction switching unit 116C as a direction switching signal, and the halftone gradation data from the forward line buffer 116A is directed to the pulse modulation unit 117. Is output. On the other hand, when the light beam is scanned in the reverse direction, a reverse direction signal is supplied to the direction switching unit 116C as a direction switching signal, and the halftone gradation data from the reverse direction line buffer 116A is directed to the pulse modulation unit 117. Is output. The halftone gradation data input to the pulse modulation unit 117 in this way is converted into a video signal and then output to the engine controller 10 via a video interface (not shown).

  Then, as described above, the exposure control unit 102 that has received the video signal controls ON / OFF of the laser light source 62 of the exposure unit 6 (optical scanning device), and at the same time, turns on the laser light source 62 to irradiate the light beam. Is controlled as follows. FIG. 7 is a diagram showing the light amount of the light beam emitted from the laser light source 62. In the drawing, the horizontal axis represents the deflection angle, and the vertical axis represents the amount of light beam emitted from the laser light source 62. Here, the deflection angle is an angle DA formed by the principal ray of the light beam deflected by the deflection mirror surface 651 and the optical axis OA (FIG. 4). Also, the first direction (+ DA) and the second direction (−DA) of the deflection angle DA correspond to the first direction (+ X) and the second direction (−X) of the main scanning direction X, respectively. That is, the light beam deflected in the direction in which the deflection angle DA increases in the first direction (+ DA) is scanned in the first direction (+ X) of the main scanning direction X on the surface of the photosensitive member 2, while the deflection angle is increased. The light beam deflected in the direction in which DA increases in the second direction (−DA) is scanned in the second direction (−X) of the main scanning direction X on the surface of the photoreceptor 2.

  As shown in FIG. 7, in the present embodiment, the amount of light beam emitted from the laser light source 62 is continuously increased as the absolute value of the deflection angle DA increases. In the present embodiment, the light beam whose light amount is controlled in this way is irradiated from the laser light source 62 and scanned in the main scanning direction X, and the light beam is irradiated onto the surface of the photoconductor 2 in a spot shape to cause spot latent. An image is formed. The electrostatic latent image thus formed is developed by the developing unit 4 (developing means) to form dots.

  As described above, the image forming apparatus according to the present embodiment deflects the light beam emitted from the laser light source 62 (light source) by the deflection mirror surface 651 that vibrates sinusoidally and has the arc-sin characteristic of the deflected light beam. The light beam is guided to the surface to be scanned by a scanning optical system (in the present embodiment, composed of a “first scanning lens 66” and a “second scanning lens”), so that the light beam is irradiated on the surface of the photoreceptor 2 (the surface to be scanned). An exposure unit 6 (optical scanning device, exposure means) that scans in the main scanning direction X of the scanning surface (latent image carrier surface) and irradiates the surface in a spot shape is used. In such a case, the incident angle of the light beam with respect to the surface of the photoreceptor 2 varies depending on the position in the main scanning direction. As a result, an optical scanning failure may occur in which the peak value of the light amount distribution of the spot irradiated on the surface to be scanned such as the surface of the photoreceptor 2 varies depending on the position in the main scanning direction.

  FIG. 8 is a diagram illustrating a difference in light amount distribution at positions in the main scanning direction. As shown in FIG. 8, the light amount distribution of the spot irradiated on the surface of the photoconductor 2 spreads in the main scanning direction X at a position away from the optical axis OA compared to the vicinity of the optical axis OA of the scanning optical system. Yes. As a result, the peak value of the light amount distribution of the spot may be relatively high in the vicinity of the optical axis OA, whereas an optical scanning defect may occur in which the peak is relatively low at a position away from the optical axis OA. When the optical scanning operation is performed on the surface of the photoreceptor 2 in a state where such optical scanning failure occurs, the following electrostatic latent image is formed.

  FIG. 9 is a diagram illustrating a potential distribution of a spot latent image formed by spots having the light amount distribution of FIG. More specifically, in FIG. 9, after the surface of the photoreceptor 2 is uniformly charged to a predetermined potential V0 by the charging unit 3, spots are irradiated near the optical axis OA and at positions away from the optical axis OA. It is the figure which compared the electric potential distribution of the spot latent image formed in this way. As can be seen from FIG. 9, the peak value ΔV2 of the spot latent image at a position away from the optical axis OA is smaller than the peak value ΔV1 of the spot latent image near the optical axis OA. Here, the “peak value” is the absolute value of the difference between the peak of the potential distribution and the predetermined potential V0. That is, FIG. 9 shows that the peak value of the spot latent image decreases as the distance from the optical axis OA increases.

  FIG. 10 is a diagram schematically showing the light amount distribution and the peak value of the spot latent image. In FIG. 3A, the horizontal axis represents the position in the main scanning direction, the vertical axis represents the peak value of the light amount distribution of the spot, and the optical axis OA is located at the intersection of the vertical axis and the horizontal axis. In FIG. 5B, the horizontal axis represents the position in the main scanning direction, the vertical axis represents the peak value of the spot latent image, and the optical axis OA is located at the intersection of the vertical axis and the horizontal axis. That is, as shown in FIG. 6A, in the image forming apparatus using the exposure unit 6 (optical scanning device, exposure means) having the above-described configuration, the light amount distribution of the spot irradiated on the surface of the photoconductor 2. An optical scanning failure occurs in which the peak value decreases continuously as the distance from the optical axis OA increases. Then, as shown in FIG. 5B, the peak value of the spot latent image formed by irradiating such a spot also decreases continuously as the distance from the optical axis OA increases. As a result, the size of the dots obtained by developing such a spot latent image decreases as the distance from the optical axis OA increases.

  Incidentally, as described above, in the image forming apparatus according to the present embodiment, gradation reproduction is realized by changing the dot area ratio per unit area. Therefore, if the size of the dots decreases as the distance from the optical axis OA decreases, an image detrimental effect occurs in which the formed image density decreases as the distance from the optical axis OA increases. Such image defects are particularly noticeable when a highlight image, which is a low-density image, is formed. In contrast, in the present embodiment, the light quantity of the light beam emitted from the light source is controlled based on the light quantity pattern shown in FIG. That is, as the absolute value of the deflection angle DA increases, the light amount of the light beam emitted from the laser light source 62 is continuously increased. Therefore, it is possible to reduce the change in the main scanning direction position of the peak value of the light amount distribution of the spot irradiated on the surface of the photosensitive member 2 (scanned surface, latent image carrier surface) and execute a good optical scanning operation. It becomes. Then, by executing image formation with an optical scanning device capable of executing such a good optical scanning operation, the above-described difference in image density due to the position in the main scanning direction is suppressed, and a good highlight image can be formed. It becomes possible.

  Incidentally, the optimum pattern of the light amount pattern shown in FIG. 7 differs depending on individual differences of the exposure unit 6 (optical scanning device) or the image forming apparatus. Therefore, the light quantity pattern may be obtained for each solid at the time of factory shipment. However, even if the light quantity pattern is the same solid, the optimum pattern may differ depending on environmental changes such as ambient temperature. Therefore, the light quantity pattern may be obtained as follows.

  FIG. 11 is a flowchart showing the light quantity pattern setting procedure in the present invention. FIG. 12 is a diagram showing the formation position of the patch latent image formed in the setting of the light quantity pattern. First, a patch latent image forming step is executed to cause the above-described exposure unit 6 (optical scanning device, exposure means) to perform an optical scanning operation, so that two patches corresponding to the highlight image are formed on the surface of the photoreceptor 2. The latent images PL1 and PL2 are formed (step S1). At this time, as shown in “Patch latent image formation” in the upper part of FIG. 12, the patch latent image PL1 is formed on the optical axis OA of the scanning optical system, while the patch latent image PL2 is formed in the main scanning direction X from the optical axis OA. Created at a position distant from the first direction (+ X). Thus, in the present embodiment, these two patch latent images PL1 and PL2 are formed at positions that are asymmetric with respect to the optical axis OA in the main scanning direction X.

  Next, a patch development process is performed, and the patch latent images PL1 and PL2 are developed by the development unit 4 to form highlight images PV1 and PV2 (step S2). Then, the highlight images PV 1 and PV 2 formed in this way are primarily transferred onto the surface of the intermediate transfer belt 71. Since the surface of the intermediate transfer belt 71 circulates and moves in a direction D71 substantially orthogonal to the main scanning direction X, the highlight images PV1 and PV2 also move in the direction D71 along with the surface of the intermediate transfer belt. As a result, the density of the highlight images PV1, PV2 is detected by density sensors 76A, 76B provided on the extended lines in the moving direction of the highlight images PV1, PV2 so as to face the surface of the intermediate transfer belt 71 (density detection). Process, step S3). The densities of the highlight images PV1 and PV2 detected in the density detection process are output to the CPU 101, and the CPU 101 obtains an optimal light quantity pattern based on these detection results (pattern generation process, step S4). ). Then, the subsequent optical scanning operation is executed based on the light quantity pattern thus obtained.

  As described above, by executing the light amount pattern setting shown in FIGS. 11 and 12 and detecting the density of the highlight image formed on the surface of the photoreceptor 2, the spot irradiated on the surface of the photoreceptor 2 has. It becomes possible to detect a change in the main scanning direction X of the peak value of the light amount distribution with high accuracy. And it becomes possible to obtain | require an optimal light quantity pattern from this detection result. Further, by using such a highly accurate light quantity pattern, it is possible to execute a better optical scanning operation. Furthermore, by performing image formation with an optical scanning device capable of performing a better optical scanning operation in this way, the difference in image density in the main scanning direction as described above can be suppressed with higher accuracy and better. It is possible to form a highlight image.

  The present invention is not limited to the above-described embodiment, and various modifications other than those described above can be made without departing from the spirit of the present invention. For example, in the above-described embodiment, the present invention is applied to a so-called four-cycle color printer, but the application target of the present invention is not limited to this. That is, the present invention is also applicable to a so-called tandem color printer in which a plurality of image forming stations are arranged in the moving direction of the intermediate transfer belt. The present invention is also applicable to a monochrome printer that performs only monochrome printing.

  In the patch latent image forming step of the above-described embodiment, the patch latent image PL1 of the two patch latent images PL1 and PL2 is formed on the optical axis OA, but the formation position of the patch latent image PL1 is on the optical axis OA. Not limited to. At this time, the two patch latent images PL1 and PL2 are formed at positions that are asymmetric with respect to the optical axis OA in the main scanning direction X. However, the position where the patch latent image is formed is not limited to this. . However, it is preferable that the patch latent images PL1 and PL2 are formed at positions that are asymmetric with respect to the optical axis OA in the main scanning direction X because a better optical scanning operation can be performed. Then, by performing image formation with an optical scanning device capable of performing a better optical scanning operation, the above-described difference in image density due to the position in the main scanning direction can be suppressed with higher accuracy, and a better high- A light image can be formed, which is preferable. The reason for this will be described next.

  As also shown in the present embodiment, the optical scanning device as described above is often configured symmetrically with respect to the optical axis OA of the scanning optical system. In such a case, the positions of the two highlight images PV1 and PV2 formed by executing the patch latent image forming step and the patch developing step are in the main scanning direction X with respect to the optical axis OA of the scanning optical system. When the positions are symmetrical, the densities of these two highlight images PV1 and PV2 are substantially the same. On the other hand, in the patch latent image forming step, when the two electrostatic latent images PL1 and PL2 are formed at positions asymmetric with respect to the optical axis OA of the scanning optical system in the main scanning direction X, the patch latent image The densities of the two highlight images formed by executing the formation process and the patch development process are different from each other without depending on the symmetry of the apparatus configuration. Therefore, the change in the main scanning direction of the peak value of the light amount distribution of the spot irradiated on the scanning surface can be detected with high accuracy. Therefore, it is possible to obtain an optimum light amount pattern, and as a result, it is possible to perform a better light scanning operation, which is preferable. Then, by performing image formation with an optical scanning device capable of performing a better optical scanning operation, the above-described difference in image density due to the position in the main scanning direction can be suppressed with higher accuracy, and a better high- A light image can be formed, which is preferable.

  Further, in the patch latent image forming step of the present embodiment, the two patch latent images PL1 and PL2 are formed. However, the number of patch latent images to be formed is not limited to this. As described above, the peak value of the light amount distribution of the spot irradiated on the surface of the photoreceptor 2 can be changed in the main scanning direction X.

  Further, in the density detection process of the present embodiment, the density of the highlight images PV1 and PV2 after primary transfer onto the surface of the intermediate transfer belt 71 is detected, but the configuration of the density detection process is not limited to this. For example, the density of the highlight images PV1 and PV2 formed on the photosensitive member 2 may be detected, or the density of the highlight images PV1 and PV2 fixed on the sheet may be detected. You may do it.

  In the above embodiment, the vibrating deflection mirror surface 651 is formed by using a micromachining technique. However, the method of manufacturing the deflection mirror surface is not limited to this, and the vibrating deflection mirror surface is used. The present invention can be applied to all so-called image forming apparatuses in which a light beam is deflected to scan the latent image carrier.

  In the above embodiment, the present invention is applied to an image forming apparatus that temporarily forms a color image on an intermediate transfer medium such as an intermediate transfer belt and then transfers the color image to a sheet. The present invention can also be applied to an apparatus that forms a color image by superimposing images directly on a sheet.

  In the above embodiment, the description is given using a printer that prints an image included in the print command on a sheet such as transfer paper or copy paper based on a print command given from an external device such as a host computer. The present invention is not limited to this, and can be applied to all electrophotographic image forming apparatuses including a copying machine and a facsimile apparatus.

  Next, examples of the present invention will be shown. However, the present invention is not limited by the following examples as a matter of course, and it is of course possible to implement the present invention with appropriate modifications within a range that can meet the gist of the preceding and following descriptions. They are all included in the technical scope of the present invention.

  In this example, a 10% density highlight image was formed to obtain a light quantity pattern by the optical scanning apparatus described in “Best Mode for Carrying Out the Invention” and an image forming apparatus using the apparatus. The optical scanning device used in this embodiment can vibrate the deflecting mirror surface at a frequency of 5 KHz. For example, when scanning is performed in only one direction of the main scanning direction X, 600 dpi in the sub-scanning direction Y is possible. When the scanning is performed in both the main scanning direction X, a resolution of 1200 dpi in the sub-scanning direction Y can be realized.

  Next, the halftone process used in forming a 10% density highlight image in this embodiment will be described. Here, the density when no toner is attached to the unit area is 0% density, and the density when the toner is attached to the entire unit area is 100% density. FIG. 13 is a diagram showing a dither matrix used in the halftone process of this embodiment. That is, in this embodiment, CMYK gradation data is converted to halftone gradation data by comparing with a so-called dot concentration type dither matrix. As described in “Best Mode for Carrying Out the Invention”, CMYK gradation data is generated based on image data input from a host computer. In generating the image data, WORD of Microsoft Corporation is used. Was used.

  FIG. 14 is a diagram showing a patch latent image process in this embodiment. FIG. 15 is a diagram showing a pattern generation process in the present embodiment. In this embodiment, the above-described halftone process is executed to form patch latent images PL corresponding to 10% density highlight images at positions A, B, C, and D in FIG. Here, the symbol A is arranged on the optical axis OA, and the symbols B, C, and D are arranged at intervals of 48 mm from the optical axis OA in the first direction (+ X) of the main scanning direction X. . At this time, a constant voltage of 2.0 V was applied to the laser light source 62 regardless of the deflection angle DA. Then, a patch development process is performed on these patch latent images PL to form a highlight image PV on the surface of the photoreceptor 2, and the highlight image PV is subjected to primary transfer and secondary transfer to perform sheet transfer. Transferred to the surface of

Next, the density detection step was executed, and the density of the four highlight images PV formed on the sheet was measured. From Table 1, it can be seen that the highlight image formed on the optical axis OA has the highest density, and the density decreases with distance from the optical axis OA in the main scanning direction X direction. Therefore, a pattern generation process was executed to obtain a light quantity pattern given by the following equation based on the results of Table 1.
Q = 0.5 × (X / 48) +2.0 (1)
However, Q represents a voltage applied to the laser light source 62, and X represents a position in the main scanning direction. Further, the position of the optical axis OA is set to X = 0.

  Next, in order to confirm the effect of the present invention, a patch latent image PL was formed through the same halftone process at the same position as in FIG. 14 using the light quantity pattern obtained in the form of the formula (1). These patch latent images PL were developed, transferred to a sheet and measured for density, and the results were as shown in Table 2. As can be seen from Table 2, by forming a highlight image based on the light quantity pattern obtained in the form of equation (1), the density difference in the main scanning direction X is suppressed as compared with the results in Table 1. It can be seen that good image formation is realized.

1 is a diagram showing an embodiment of an image forming apparatus according to the present invention. FIG. 2 is a block diagram showing an electrical configuration of the image forming apparatus in FIG. 1. FIG. 2 is a sub-scan sectional view showing a configuration of an exposure unit of the image forming apparatus in FIG. 1. FIG. 2 is a main scanning sectional view showing a configuration of an exposure unit of the image forming apparatus of FIG. 1. FIG. 6 is a sub-scan sectional view in which the optical configuration of the exposure unit is developed. FIG. 3 is a diagram illustrating signal processing of the image forming apparatus according to the present embodiment. The figure which shows the light quantity of the light beam irradiated from a laser light source. The figure which shows the difference in the light quantity distribution in the main scanning direction position. The figure which shows the electric potential distribution of a spot latent image. The figure which represented typically the light quantity distribution and the peak value of a spot latent image. The flowchart which shows the setting procedure of the light quantity pattern in this embodiment. The figure which shows the formation position of the patch latent image formed in the setting of a light quantity pattern. The figure which shows the dither matrix used by the halftone process of an Example. The figure which shows the patch latent image formation process in an Example. The figure which shows the pattern production | generation process in an Example.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 2 ... Photoconductor, 6 ... Exposure unit (optical scanning device, exposure means), 62 ... Laser light source (light source), 65 ... Deflector, 66 ... First scanning lens (scanning optical system), 68 ... Second scanning lens ( Scanning optical system), 101 ... CPU, 651 ... deflection mirror surface, L ... light beam, X ... main scanning direction, Y ... sub-scanning direction, OA ... optical axis, PL, PL1, PL2 ... patch latent image, PV, PV1, PV2 ... Highlight image

Claims (7)

A light source that emits a light beam, a deflector that deflects the light beam emitted from the light source by a deflecting mirror surface that sine vibrates, and a surface to be scanned that has an arc-sin characteristic and is deflected by the deflector A scanning optical system that guides the light beam in a main scanning direction and capable of performing a light scanning operation of irradiating the surface to be scanned in a spot shape. By inputting an exposure signal obtained by converting pattern data indicating a position to be irradiated onto the light source to the light source and causing the optical scanning device to execute the optical scanning operation, the light beam is applied to a predetermined position on the scanned surface. A method of controlling the optical scanning device that irradiates in a spot shape,
When the angle formed by the principal ray of the light beam deflected by the deflection mirror surface and the optical axis of the scanning optical system is a deflection angle,
While controlling the light quantity of the light beam emitted from the light source based on a light quantity pattern that continuously increases the light quantity of the light beam emitted from the light source as the absolute value of the deflection angle increases,
A patch latent image forming step of forming a plurality of latent images as patch latent images at positions different from each other in the main scanning direction of the scanned surface;
A patch development step of developing a plurality of patch images by toner developing the plurality of patch latent images;
A concentration detecting step of detecting the density of the transferred plurality of patch images in transcription medium, the concentration sensor facing the transfer medium,
A pattern generation step for obtaining the light amount pattern based on the detection result in the concentration detection step;
An optical scanning device control method comprising:   The method of controlling an optical scanning device according to claim 1, wherein one of the plurality of patch latent images is formed on an optical axis of the scanning optical system.   2. The patch latent image forming step forms two patch latent images as the plurality of patch latent images at positions asymmetric with respect to the optical axis of the scanning optical system in the main scanning direction. Control method of optical scanning device.   4. The method of controlling an optical scanning device according to claim 3, wherein one of the two patch latent images is formed on an optical axis of the scanning optical system. 5. The method of controlling an optical scanning device according to claim 1, wherein the pattern data is generated by performing halftone processing on image gradation data in which gradation values of each pixel are expressed in multiple gradations. Because
The halftone processing is adapted to generate the pattern data to increase the irradiation area of the light beam with an increase of the gradation values of the image gray-scale data to a predetermined increase pattern Dese Le,
The method of controlling an optical scanning device, wherein the increase pattern is constant regardless of the deflection angle. A light source that emits a light beam, a deflector that deflects the light beam emitted from the light source by a deflecting mirror surface that sine vibrates, and a surface to be scanned that has an arc-sin characteristic and is deflected by the deflector An optical scanning device that performs a light scanning operation of scanning the light beam in a main scanning direction and irradiating the surface to be scanned in a spot shape.
When the angle formed by the principal ray of the light beam deflected by the deflection mirror surface and the optical axis of the scanning optical system is a deflection angle,
While controlling the light quantity of the light beam emitted from the light source based on a light quantity pattern that continuously increases the light quantity of the light beam emitted from the light source as the absolute value of the deflection angle increases,
A plurality of latent images are formed as patch latent images at different positions in the main scanning direction on the surface to be scanned, and a plurality of patch images obtained by toner development of the plurality of patch latent images are formed on a transfer medium. An optical scanning device characterized in that the light quantity pattern is obtained based on a result of detection of density of the plurality of patch images by a density sensor facing the transfer medium. A latent image carrier;
Charging means for charging the surface of the latent image carrier substantially uniformly;
A light source that emits a light beam, a deflector that deflects the light beam emitted from the light source by a deflecting mirror surface that sinusoidally vibrates, and a light beam that has an arc-sin characteristic and is deflected by the deflector A scanning optical system that guides light to the surface of the latent image carrier charged by the optical scanning operation, and performs a light scanning operation that scans the light beam in the main scanning direction and irradiates the surface of the latent image carrier in a spot shape. Exposure means;
Developing means for developing the electrostatic latent image with toner;
A transfer medium onto which an image obtained by toner development by the developing means is transferred;
A density sensor facing the transfer medium;
With
When the angle formed by the principal ray of the light beam deflected by the deflection mirror surface and the optical axis of the scanning optical system is a deflection angle,
While controlling the light quantity of the light beam emitted from the light source based on a light quantity pattern that continuously increases the light quantity of the light beam emitted from the light source as the absolute value of the deflection angle increases,
A plurality of patch images obtained by forming a plurality of patch images as patch latent images at positions different from each other in the main scanning direction on the surface of the latent image carrier and developing the plurality of patch latent images with toner are transferred to the transfer medium. The image forming apparatus is characterized in that the light quantity pattern is obtained on the basis of a result of detecting density of the plurality of patch images by the density sensor.

Images