JP2010000676A - Image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image forming apparatus which can correct image formation by correcting the deformation of an optical system by software. <P>SOLUTION: The image forming apparatus is based on the premise that it includes a polygon mirror which scans a laser beam on a photo conductor drum to form an electrostatic latent image on the photo conductor drum and a light receiving element which receives the laser beam and determines the timing of the scanning of the laser beam. The image forming apparatus further includes a detection means to detect the deviation of the sub-scanning start position in the photo conductor drum of the laser beam based on the light income of the light receiving element and a correction means to correct the deviation based on the detection. Thereby, the deviation of image formation can be corrected by software. Here, the correction means corrects the deviation by controlling the timing to form the electrostatic latent image. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to an image forming apparatus such as a printer, a copier, or a multifunction peripheral.

  2. Description of the Related Art In recent years, image forming apparatuses such as printers, copiers, and multifunction machines have become widespread not only in offices but also in general households. In particular, copiers are installed in stores such as convenience stores so that the public can use them for a fee.

  Many of these image forming apparatuses employ a printing method based on a so-called electrophotographic process. This is because an electrostatic latent image is formed by irradiating the surface of a photosensitive drum as an image carrier with laser light, and toner is attached to the electrostatic latent image by a developing voltage (developing bias). This is an image forming method.

  FIG. 6 is a schematic explanatory view of the optical system that irradiates the laser beam to form such an electrostatic latent image, in which FIG. 6A is a view seen from above, and FIG. 6B. And FIG.6 (c) is the figure seen from the horizontal direction.

  The laser light emitted from the laser light source L is reflected by the polygon mirror P and irradiates the photosensitive drum 109. At this time, the polygon mirror P is rotated by the polygon motor M so that the laser beam scans the surface of the photosensitive drum 109 in the direction of arrow F, and an electrostatic latent image is formed in the main scanning direction of the surface. (FIG. 6A). Since the start position of main scanning on the surface of the photosensitive drum 109 is the start position of image formation, it must be accurately determined. For this reason, a light receiving element R (generally referred to as a “BD element”) is installed in the vicinity of the photosensitive drum 109 and the amount of light received by the light receiving element R is detected, whereby the main scanning start position is accurately determined. We are monitoring to be done.

  On the other hand, the photosensitive drum 109 rotates in the direction of arrow S (FIG. 6B), whereby the laser beam sub-scans the surface of the photosensitive drum 109. In this way, an electrostatic latent image of a planar image is formed on the surface of the photosensitive drum 109.

  By the way, as described above, the polygon mirror P is rotated by the polygon motor M, but thermal expansion occurs in peripheral members (not shown) due to the heat generated by the polygon motor M, and as shown in FIG. The polygon mirror P may tilt. In FIG. 6C, this inclination is exaggerated for explanation.

  When such an inclination occurs, the start position of the sub-scanning is shifted by a distance d as shown in FIG. That is, in FIG. 6C, the photosensitive drum 109 rotates in the direction of the arrow S, so that the start (= writing) of scanning of the laser beam is accelerated (solid arrow A). If this is left unattended, an image cannot be formed at an accurate position on the photosensitive drum 109, and a situation may occur in which the edge of the image is cut off when printing is performed on paper or the like.

Therefore, conventionally, for example, a technique for cooling the polygon motor M by providing a heat exhaust fan or the like has been adopted. Patent Document 1 below discloses a technique for firmly pressing a polygon mirror P against a peripheral member using a step screw and a coil spring.
JP 2002-31365 A

  However, the above prior art has the following problems.

  First, it is conceivable that dust is scattered by the method of providing the exhaust heat fan. If the dust adheres to the photosensitive drum 109, the adhered portion is always soiled and printed, which is inconvenient.

  Next, in the technique of Patent Document 1, since the heat generation of the polygon motor itself cannot be suppressed, it is conceivable that the above-described pressing causes another distortion. If another distortion occurs in the optical system, it also hinders accurate image formation and is inconvenient.

  The present invention has been made in view of such problems, and an object thereof is to provide an image forming apparatus capable of forming an image at an accurate position by correcting distortion of an optical system by software.

  In order to achieve the above object, the present invention employs the following means.

  First, according to the present invention, a polygon mirror that scans a laser beam on a photosensitive drum to form a latent image on the photosensitive drum, and a light receiving device that receives the laser beam and determines the main scanning timing of the laser beam. An image forming apparatus including an element is assumed.

  In such an image forming apparatus, based on the amount of light received by the light receiving element, detection means for detecting a shift in the sub-scanning start position of the laser beam on the photosensitive drum, and the shift based on the detection. And a correcting means for correcting. Thereby, it is possible to correct image formation deviation by software.

  Here, the correction means corrects the shift by adjusting the timing of forming the electrostatic latent image. The correction means corrects the deviation by referring to a correspondence table between the received light amount and the deviation. As a result, the correction can be performed at high speed, so that even a high-speed machine with a high printing speed can be sufficiently applied.

  As described above, in the present invention, the deviation of the sub-scanning start position is corrected by software, so that it is not necessary to develop a new jig or the like, and this deviation can be corrected at low cost.

  Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings for understanding of the present invention. In this embodiment, the present invention is embodied as a digital multi-function peripheral which is a form of an image forming apparatus.

  FIG. 1 is a schematic diagram of the overall configuration of a multifunction peripheral 100 according to the present embodiment. When a user prints a document using the multifunction device, the document is placed on the document table 103, for example, and a printing instruction is given to the operation buttons of the touch panel 300 provided near the document table 103. When the instruction is given, printing is performed by operating the following sections (drive sections).

  In the image reading unit 101, the light emitted from the light source 104 is reflected by the document placed on the document table 103, and is guided by the mirrors 105, 106, and 107 to the image sensor 108 such as a CCD (Charge Coupled Device). The image sensor 108 photoelectrically converts the received light to generate image data of the document. In this manner, the image data of the document is read by the image reading unit 101.

  The photosensitive drum 109 provided in the image forming unit 102 rotates in a predetermined direction at a constant speed, and around the charger drum 110, the exposure unit 111, the developing unit 112, and the transfer, in that order from the upstream side in the rotation direction. A device 113 and the like are arranged. The charger 111 uniformly charges the surface of the photosensitive drum 109. The exposure device 111 irradiates light according to the image data read by the image reading unit 101 to form an electrostatic latent image on the photosensitive drum 109. The developing unit 112 attaches toner to the electrostatic latent image formed by the exposure unit 111 to form a toner image on the photosensitive drum 109. The transfer unit 113 transfers the toner image on the photosensitive drum 109 to a sheet. In this way, the series of processes is performed in the image forming unit 102 by rotating the photosensitive drum 109.

  Further, when performing printing, the image forming unit 102 draws one sheet from any one of the sheet feeding cassettes 114 to the conveyance path L using the pickup roller 115. Each sheet cassette 114 stores sheets of different sizes, and sheets of a size selected by the user according to the application are fed. The sheet pulled out to the conveyance path L is sent between the photosensitive drum 109 and the transfer unit 113 by the conveyance roller 116 and the registration roller 117.

  When the sheet passes between the heating roller 119 and the pressure roller 120 in the fixing device 118, the visible image is fixed to the sheet by heat and a pressing force to the sheet. In order to perform the fixing appropriately, the heat amount of the heating roller is optimally set according to the paper size. The image forming unit 102 discharges the sheet that has passed through the fixing device 118 to the discharge tray 121.

  FIG. 2 is a schematic configuration diagram relating to control of the multifunction peripheral 100 according to the present embodiment.

  The MFP 100 includes a CPU (Central Processing Unit) 201, a RAM (Random Access Memory) 202, a ROM (Read Only Memory) 203, an HDD (Hard Disk Drive) 204, and a driver 205 corresponding to each driving unit in the above printing. They are connected via a bus 206.

  The CPU 201 uses, for example, the RAM 202 as a work area, executes a program stored in the ROM 203, the HDD 204, and the like, and exchanges data and commands with the driver 205 based on the execution result, as shown in FIG. The operation of each driving unit is controlled. Also, each means (shown in FIG. 4) described later other than the above-described drive unit operates as each means when the CPU 201 executes a program.

  FIG. 3 is a structural diagram of the optical system 400 included in the image forming unit 102. The optical system 400 includes a laser light source 20 and a polygon motor M (polygon mirror P) that drives a polygon mirror for causing the laser light from the laser light source 20 to scan on the photosensitive drum 109. Further, an optical lens group 22 as an optical member for uniformly performing the above scanning on the photosensitive drum 109 and a folding mirror 23 as a folding member that reflects the laser light onto the photosensitive drum 109 are provided. It has been.

  These laser light source 20, polygon motor M, optical lens group 22, and folding mirror 23 are integrally fixed to a mold frame called an optical box 24 as a casing.

  The optical box 24 is made of a resin member. The material of the optical box 24 is, for example, a PC-ABS containing 35% of GF (glass fiber), which is lightweight and inexpensive.

  Further, the optical box 24 is supported by a laser scanner stay (L) 25 and a laser scanner stay (R) 26 which are iron cases having a thickness of about 3.2 mm. The two laser scanner stays 25 and 26 are connected to the front and rear side plates, and hold the position of the optical system 400.

  The two laser scanner stays 25 and 26 have the mounting surface of the optical system 400 held to have a flatness of 0.1 or less when the main body is assembled with a jig so that the optical parts are not deformed when the screws 32 are tightened. ing.

  The optical system 400 is positioned by a positioning pin (L) 27 and a positioning pin (R) 28. The positioning pins 27 and 28 are separate parts from the optical box 24. The position of the optical box 24 can be moved in the direction indicated by the arrow 29 in a state where the positioning pins 27 and 28 are positioned at another place, that is, on the jig. As a result, adjustment is made so that the laser beam is incident on the light receiving sensor provided in advance on the jig at the correct irradiation position, and the positioning pins 27 and 28 and the optical box 24 are fixed by the two screws 30. .

  In the present embodiment, irradiation position adjustment is not performed on the main body of the multifunction peripheral 100, but the optical system 400 is adjusted in advance with a jig, and the two positioning holes 31 formed in the laser scanner stays 25 and 26 are formed on the main body. Just plug it in. At this time, however, the positioning hole 31 on the main body of the multifunction peripheral 100 is processed with respect to the position of the photosensitive drum 109 with high accuracy.

  The reason for adopting such a method is that if the optical system 400 is damaged in the market, the optical system 400 may be replaced. The optical system 400 is fixed by four screws 32, and four outer peripheral portions are fixed to the laser scanner stays 25 and 26.

  Since the process of forming an electrostatic latent image on the photosensitive drum 109 by the optical system 400 is the same as the background art (see FIG. 6), the description thereof is omitted.

  Now, as described with reference to FIG. 6C in this background art, the thermal expansion of the peripheral member may occur due to the heat generated by the polygon motor M, and the polygon mirror P may be tilted. If this occurs, the start position of the sub-scanning is shifted by the distance d. That is, in FIG. 6C, the photosensitive drum 109 rotates in the direction of the arrow S, so that the start (= writing) of scanning of the laser beam is accelerated (solid arrow A).

  Although the purpose of the present invention is to correct this deviation, as described above, a light receiving element R (generally referred to as a “BD element”) is installed in the vicinity of the photosensitive drum 109, and this light receiving element R By monitoring the amount of received light, the start position of the main scanning of the laser beam is monitored accurately.

  Therefore, in the present invention, the change in the amount of light received by the light receiving element R is used.

  That is, when the polygon mirror P is not inclined, all of the laser beam is incident on the light receiving element R as schematically shown in FIG. However, when the polygon mirror P is inclined and the start position of the sub-scanning is shifted by the distance d, the incident position of the laser beam on the light receiving element R is also shifted according to the distance d. . Then, as shown in FIG.5 (b), the said laser beam injects only into the part of the light receiving element R and the part enclosed with the dotted line of FIG.5 (b).

  In general, the light receiving element (BD element) R outputs a voltage proportional to the amount of received light. Therefore, when the incident position of the laser beam on the light receiving element R is deviated as described above, the voltage decreases as a linear function of this deviation as shown in FIG.

  Therefore, the timing for forming the electrostatic latent image is corrected late in proportion to this decrease.

  Specifically, as shown in FIG. 4A, the detection means 401 detects the output voltage of the light receiving element R that has received the laser light from the polygon mirror P. Then, the correction means 403 calculates the deviation (= distance d) from the result of this detection and the linear function shown in FIG. Further, the correction unit 403 delays the timing of forming the electrostatic latent image (scanning the laser beam) by the time obtained by dividing this by the rotational speed of the photosensitive drum 109. As a result, it is possible to correct the shift of the sub-scanning start position, and an electrostatic latent image can be formed at an accurate position on the photosensitive drum 109.

  This timing (= deviation) may be calculated based on a linear function as described above, but can also be calculated as follows. That is, since the light receiving element R has a certain resolution, the relationship between the output voltage of the light receiving element R and the timing is previously stored in the ROM 203 or the like as the correspondence table 402 with the resolution as a minimum unit. FIG. 4B is an example of the correspondence table 402. The correcting unit 403 determines the timing (= deviation) with reference to the output of the light receiving element R and the correspondence table 402, and delays the timing for forming the electrostatic latent image. In this way, it is not necessary to calculate the timing every time, and it is possible to correct the shift of the sub-scanning start position at high speed.

  As described above, according to the present invention, the deviation of the sub-scanning start position is corrected by software, so that it is not necessary to develop a new jig or the like, and this deviation can be corrected at low cost.

  In FIG. 5C, the polygon mirror P has been described as being inclined clockwise in the drawing, but this is only an example, and it is naturally conceivable that the polygon mirror P is inclined counterclockwise. Which direction of inclination should be statistically determined as a mechanical tendency of the optical system 400. Needless to say, in the case of tilting counterclockwise, correction should be performed so as to advance the timing of forming the electrostatic latent image.

  The image forming apparatus according to the present invention can form an image at an accurate position at low cost by correcting distortion of the optical system by software. In addition, since the correction can be performed at high speed by referring to the correspondence table, even a high-speed machine with a high printing speed is sufficiently applicable. Therefore, it is useful as a printer, a copying machine, a multifunction machine, or the like.

1 is an overall configuration diagram of an image forming apparatus of the present invention. 1 is a hardware configuration diagram of an image forming apparatus of the present invention. 1 is a structural diagram of an optical system in an image forming apparatus of the present invention. 2 is a software configuration diagram of the image forming apparatus of the present invention. FIG. Explanatory drawing of the relationship between the light reception amount of a light receiving element, and the shift | offset | difference of a subscanning start position. Schematic explanatory drawing of an optical system.

Explanation of symbols

DESCRIPTION OF SYMBOLS 100 Compound machine 109 Photosensitive drum 400 Optical system 401 Detection means 402 Correspondence table 403 Correction means L Laser light source P Polygon mirror M Polygon motor R Light receiving element

Claims (3)

A polygon mirror that scans a photosensitive drum with a laser beam to form an electrostatic latent image on the photosensitive drum, and a light receiving element that receives the laser beam and determines the timing of the main scanning of the laser beam. In the image forming apparatus,
Detecting means for detecting a shift of a sub-scanning start position of the laser beam on the photosensitive drum based on the amount of light received by the light receiving element;
Correction means for correcting the deviation based on the detection;
An image forming apparatus comprising:   The image forming apparatus according to claim 1, wherein the correction unit corrects the shift by adjusting a timing of forming the electrostatic latent image.   The image forming apparatus according to claim 2, wherein the correction unit corrects the shift by referring to a correspondence table between the received light amount and the shift.

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