JP2008216512A - Optical scan apparatus, image formation apparatus and optical deflector manufacturing method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an optical scan apparatus improved in scan speed and scan precision. <P>SOLUTION: In the optical deflector, the mean length RSm of profile elements of a cross section of the deflection surface of a polygon mirror 104 in the sub scan direction is set to be less than to spacing b between spots of the adjacent light beams formed in the sub scan direction of the deflection surface. This makes it possible to prevent a variation in the shape of the spots of the light beams due to the undulation (unevenness) of the deflection surface of the polygon mirror 104. As a result, it is able to accurately scan a face to be scanned in a short time, particularly in the case where many light beams are simultaneously scanned, effectively suppress a decrease of the granularity of images because the dot size composing finally formed images is kept constant. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to an optical scanning device, an image forming apparatus, and a deflector manufacturing method, and more specifically, an optical scanning device that scans a surface to be scanned with a light beam, an image forming apparatus including the optical scanning device, and the light The present invention relates to a method of manufacturing a deflector used in a scanning device.

  Conventionally, as an image forming apparatus that forms an image using the Carlson process, for example, a surface of a rotating photosensitive drum is scanned with a plurality of light beams to form a latent image on the surface of the photosensitive drum. There is known an image forming apparatus that forms an image by fixing a toner image obtained by visualizing the image on a sheet as a recording medium. In recent years, this type of image forming apparatus is often used for simple printing as an on-demand printing system, and demands for higher image density and faster image output are increasing.

  In general, as a method for speeding up image output, it is conceivable to increase the printing speed by increasing the rotational speed of a rotating polygon mirror or the like that deflects a light beam and the rotational speed of a photosensitive drum. However, when the rotational speed of the rotary polygon mirror is increased, there is an inconvenience that noise and vibration from the drive system increase and the amount of heat generation also increases. Further, since high-speed image output has a trade-off relationship with high-density image, there is a disadvantage that the image quality is lowered as the rotational speed of the polygon mirror is increased.

  Therefore, as a method for simultaneously achieving higher image density and higher image output speed, an image forming apparatus has been proposed in which a light source is multi-beamed and a photosensitive drum is scanned with a plurality of light beams at one time (for example, Patent Document 1). The image forming apparatus described in Patent Document 1 deflects diverging light from a vertical cavity surface emitting laser (VCSEL) having a plurality of light emitting points as a light beam light source by a polygon mirror at once. By doing so, the photosensitive drum can be simultaneously scanned with a plurality of light beams.

  In addition, as a measure to increase the speed in a multicolor image forming apparatus, a plurality of miniaturized rotating polygon mirrors are firmly connected to each other so that there is little noise even at high speed rotation, and the displacement of the rotating polygon mirrors due to acceleration and temperature changes is also reduced. There has been proposed a deflector that hardly causes color misregistration, that is, hardly causes color misregistration (see, for example, Patent Document 2). Provided is a multicolor image forming apparatus capable of forming a high-density image at high speed by suppressing color misregistration by combining the above-described surface-emitting laser array and a deflector having a plurality of rotary polygon mirrors. be able to.

  However, when the light beam from the multi-beam light source is deflected by a conventional deflector, the spot shape between the light beams varies due to the shape of the deflecting surface, and scattered light is generated. There is. Specifically, if there is waviness (unevenness) on the deflection surface around the incident position of the light beam, the spot effect will be non-uniform between the light beams due to the lens effect, resulting in degradation of the graininess of the image. End up. In particular, in a color image forming apparatus that forms an image by superimposing a plurality of color toner images, dot displacement occurs for each color, resulting in image quality deterioration such as a decrease in color reproducibility.

  In general, the deflecting surface of the deflector is formed by mirror cutting, and fine cutting traces usually remain on the deflecting surface. Therefore, in an optical scanning device that uses a multi-beam having a wider deflection reflection field than a single beam, the light beam may be scattered by cutting marks on the deflection surface, and a ghost may occur in the image.

Japanese Patent No. 3227226 JP 2005-92129 A

  The present invention has been made under such circumstances, and a first object thereof is to provide an optical scanning apparatus capable of improving the scanning speed and the scanning accuracy.

  A second object of the present invention is to provide an image forming apparatus capable of forming an image with high accuracy.

  A third object of the present invention is to provide a deflector manufacturing method for manufacturing a deflector capable of improving the scanning speed and scanning accuracy of a scanning device.

  From the first aspect, the present invention scans the surface to be scanned in the main scanning direction by deflecting at least three or more light beams separated in the sub-scanning direction by a deflector rotating around a predetermined axis. In the optical scanning device, the spot of the light beam is formed such that an average length of cross-sectional curve elements in the sub-scanning direction of the deflecting surface of the deflector is formed on the deflecting surface adjacent to the sub-scanning direction It is an optical scanning device characterized by being smaller than the interval of.

  According to this, the average length of the cross-sectional curve elements in the sub-scanning direction orthogonal to the main scanning direction of the deflecting surface of the deflector is smaller than the interval between the spots of the light beams formed adjacent to the deflecting surface. Therefore, the surface to be scanned can be accurately scanned in a short time without being affected by the surface waviness of the deflection surface.

  According to a second aspect of the present invention, there is provided a deflector manufacturing method for manufacturing a deflector used in the optical scanning device of the present invention, wherein a rough deflection surface is formed on the deflector; Cutting the rough deflection surface by rotating a cutting member that cuts the rough deflection surface around a rotation axis perpendicular to the shaft while moving the shaft at a predetermined speed in the axial direction. And the size of the entire irradiation range of the light beam incident on the deflection surface in the sub-scanning direction is a value obtained by dividing the movement distance of the deflector per minute by the number of rotations of the cutting member per minute. This is a smaller deflector manufacturing method.

  According to this, the size of the entire irradiation range of the light beam incident on the deflection surface in the sub-scanning direction is obtained by dividing the movement distance of the deflector per minute by the number of rotations of the cutting member per minute. It is smaller than the value. Therefore, it is possible to form a deflection surface in which the influence of light beam scattering is avoided, and in an optical scanning device using this deflector, it is possible to improve the scanning speed and scanning accuracy.

  According to a third aspect of the present invention, there is provided an image forming apparatus for forming an image by fixing a toner image formed on the basis of a latent image obtained from information relating to an image to a recording medium. An optical scanning device of the invention; a photosensitive member on which a latent image is formed by the optical scanning device; a developing unit that visualizes a latent image formed on a surface to be scanned of the photosensitive member; and a visible image formed by the developing unit An image forming apparatus comprising: transfer means for fixing the converted toner image to the recording medium.

  According to this, the image forming apparatus includes the optical scanning device of the present invention. Therefore, the surface to be scanned can be scanned with high accuracy in a short time, and as a result, an image can be formed with high accuracy in a short time.

  According to a fourth aspect of the present invention, a toner image formed based on a latent image for each color obtained from information on a multicolor image is superimposed and fixed on a recording medium, whereby a multicolor image is obtained. An image forming apparatus to be formed, the optical scanning device of the present invention; a plurality of photoreceptors on which latent images corresponding to respective colors are formed by the optical scanning device; and a scanning surface of each of the plurality of photoreceptors An image forming apparatus comprising: a developing unit that visualizes the formed latent image; and a transfer unit that superimposes and fixes the toner images for each color visualized by the developing unit on the recording medium.

  According to this, the image forming apparatus includes the optical scanning device of the present invention. Therefore, it is possible to scan the surface to be scanned with high accuracy in a short time, and as a result, it is possible to form a multicolor image with high accuracy in a short time.

  Hereinafter, an embodiment of the present invention will be described with reference to FIGS. FIG. 1 shows a schematic configuration of an image forming apparatus 10 according to an embodiment.

  The image forming apparatus 10 is, for example, a tandem color printer that prints a multicolor image by superimposing and transferring black, yellow, magenta, and cyan toner images on plain paper (paper). As shown in FIG. 1, the image forming apparatus 10 includes an optical scanning device 100, four photosensitive drums 30A, 30B, 30C, and 30D, a transfer belt 40, a paper feed tray 60, a paper feed roller 54, a first resist. A roller pair 56, a second registration roller pair 52, a fixing roller 50, a paper discharge roller 58, a control device (not shown) that controls the above-described units centrally, and a substantially rectangular parallelepiped housing 12 that accommodates the above components. ing.

  The housing 12 is formed with a paper discharge tray 12a on which the printed paper is discharged on the upper surface, and the optical scanning device 100 is disposed below the paper discharge tray 12a.

  The optical scanning device 100 scans the photosensitive drum 30A with a light beam of a black image component modulated based on image information supplied from a host device (such as a personal computer), and cyan for the photosensitive drum 30B. The light beam of the image component is scanned, the light beam of the magenta image component is scanned on the photosensitive drum 30C, and the light beam of the yellow image component is scanned on the photosensitive drum 30D. The configuration of the optical scanning device 100 will be described later.

  The four photosensitive drums 30A, 30B, 30C, and 30D are cylindrical members each having a photosensitive layer having a property that becomes conductive when irradiated with a light beam. Below the scanning device 100 are arranged at equal intervals along the X-axis direction.

  The photosensitive drum 30A is disposed at the −X side end inside the housing 12 with the Y-axis direction as the longitudinal direction, and is rotated clockwise in FIG. 1 (the direction indicated by the arrow in FIG. 1) by a rotation mechanism (not shown). It is like that. In the vicinity thereof, a charging charger 32A is arranged at the 12 o'clock (upper) position in FIG. 1, a toner cartridge 33A is arranged at the 2 o'clock position, and a cleaning case 31A is arranged at the 10 o'clock position. .

  The charging charger 32A is arranged with a predetermined clearance with respect to the surface of the photosensitive drum 30A with the longitudinal direction as the Y-axis direction, and charges the surface of the photosensitive drum 30A with a predetermined voltage.

  The toner cartridge 33A includes a cartridge main body filled with black image component toner, a developing roller charged with a voltage having a polarity opposite to that of the photosensitive drum 30A, and the toner filled in the cartridge main body is passed through the developing roller. The toner is supplied to the surface of the photosensitive drum 30A.

  The cleaning case 31A includes a rectangular cleaning blade whose longitudinal direction is the Y-axis direction, and is arranged so that one end of the cleaning blade is in contact with the surface of the photosensitive drum 30A. The toner adsorbed on the surface of the photosensitive drum 30A is peeled off by the cleaning blade as the photosensitive drum 30A rotates, and is collected in the cleaning case 31A.

  The photosensitive drums 30B, 30C, and 30D are sequentially arranged at a predetermined interval on the + X side of the photosensitive drum 30A, and are rotated clockwise (in the direction indicated by the arrow) in FIG. 1 by a rotation mechanism (not shown). ing. Around the periphery, charging chargers 32B, 32C, and 32D, toner cartridges 33B, 33C, and 33D, and cleaning cases 31B, 31C, and 31D are arranged in the same positional relationship as the above-described photosensitive drum 30A.

  The charging chargers 32B to 32D are configured similarly to the charging charger 32A described above, and charge the surfaces of the photosensitive drums 30B to 30D with a predetermined voltage.

  Each of the toner cartridges 33B to 33D includes a cartridge main body filled with cyan, magenta, and yellow image component toners and a developing roller that is charged with a voltage having a polarity opposite to that of the photosensitive drums 30B to 30D. The toner thus supplied is supplied to the surfaces of the photosensitive drums 30B to 30D via the developing roller.

  The cleaning cases 31B to 31D are configured in the same manner as the cleaning case 31A and function in the same manner.

  Hereinafter, the photosensitive drum 30A, the charging charger 32A, the toner cartridge 33A, and the cleaning case 31A are collectively referred to as a first station, and the photosensitive drum 30B, the charging charger 32B, the toner cartridge 33B, and the cleaning case 31B are collectively referred to as a second station, The photosensitive drum 30C, the charging charger 32C, the toner cartridge 33C, and the cleaning case 31C are collectively referred to as a third station, and the photosensitive drum 30D, the charging charger 32D, the toner cartridge 33D, and the cleaning case 31D are collectively referred to as a fourth station. .

  The transfer belt 40 is an endless annular member, a driven roller 40a disposed below the photosensitive drum 30A, a driven roller 40c disposed below the photosensitive drum 30D, and a position slightly lower than these driven rollers 40a and 40c. The upper end surface is wound around the driving roller 40b disposed in the contact roller 40b so as to be in contact with the lower end surfaces of the photosensitive drums 30A, 30B, 30C, and 30D. The drive roller 40b rotates counterclockwise (in the direction indicated by the arrow in FIG. 1) by rotating counterclockwise in FIG. A transfer charger 48 to which a voltage having a polarity opposite to that of the above-described charging chargers 32A, 32B, 32C, and 32D is applied is disposed near the + X side end of the transfer belt 40.

  The paper feed tray 60 is disposed below the transfer belt 40. The paper feed tray 60 is a substantially rectangular parallelepiped tray, and a plurality of sheets 61 to be printed are stacked and stored therein. A rectangular paper feed port is formed near the + X side end of the upper surface of the paper feed tray 60.

  The paper feed roller 54 takes out the paper 61 one by one from the paper feed tray 60 and guides it to a gap formed by the transfer belt 40 and the transfer charger 48 via a registration roller 56 composed of a pair of rotating rollers.

  The fixing roller 50 is composed of a pair of rotating rollers. The fixing roller 50 overheats and pressurizes the paper 61 and guides it to the paper discharge roller 58 via the registration roller 52.

  The paper discharge roller 58 includes a pair of rotating rollers, and sequentially stacks the derived paper 61 on the paper discharge tray 12a.

  Next, the configuration of the optical scanning device 100 will be described. 2 and 3, the optical scanning device 100 includes a polygon mirror 104, an fθ lens 105, a reflection mirror 106B, a reflection mirror 106A, and an fθ lens 105 that are sequentially arranged in the −X direction of the polygon mirror 104. , A toroidal lens 107B sequentially disposed in the −X direction of the reflection mirror 108B, the reflection mirror 108A, the toroidal lens 107A, and an fθ lens 305 disposed in the + X direction of the polygon mirror 104. A scanning optical system including a reflecting mirror 306C, a reflecting mirror 306D, a reflecting mirror 308C disposed below the fθ lens 305, a reflecting mirror 308D sequentially disposed in the + X direction of the reflecting mirror 308C, and a toroidal lens 307C; Station and second An incident optical system 200A that makes the light beam that scans the station enter the polygon mirror 104 and two incident optical systems 200B that make the light beam that scans the third station and the fourth station enter the polygon mirror 104 I have.

  As representatively shown in the incident optical system 200B of FIG. 2, the incident optical systems 200A and 200B include a light source unit 201, a light beam splitting prism 202, a set of liquid crystal elements 203A and 203B, a set of cylinder lenses 204A, 204B is provided.

  FIG. 4 shows the configuration of the light source unit 201 together with the light beam splitting prism 202 and the like. As shown in FIG. 4, the light source unit 201 includes a rectangular plate-like substrate 150 whose longitudinal direction is the x-axis direction, a laser array 152, a branch mirror 153, A coupling lens 154, a converging lens 156, and a light receiving element 157 are provided.

  4 and 5, the laser array 152 is a surface-emitting type semiconductor laser array in which light sources are arranged as secondary sources, and is centered on the y axis with respect to the substrate 150 (from the front of FIG. 5). It is fixed in a state where it is rotated by an angle γ in the clockwise direction. As shown in FIG. 5, 32 light emitting sources (VCSELs) arranged in a matrix of 4 rows and 8 columns with d between rows and columns are formed on the surface of the laser array 152 on the -y side. . As a result, 32 lines are simultaneously scanned for each station in one scan. If the sub-scan magnification of the entire optical system is βs, the line pitch is p, and the number of columns of the matrix is n, the angle γ is expressed by the following equation (1).

  sinγ = (cosγ) / n = p / d · βs (1)

  Further, instead of fixing the laser array 152 in a state rotated by the rotation angle γ as described above, the row direction of the light emission source forms an angle γ with respect to the main scanning direction at the stage of the processing process of the laser array 152. In this manner, each light emitting source may be formed.

  Returning to FIG. 4, the branch mirror 153 is disposed on the −y side of the light source unit 201, transmits the light beam emitted from the laser array 152, and branches a part thereof in the + x direction.

  The converging lens 156 focuses the light beam branched in the + x direction by the branch mirror 153 onto the light receiving element 157.

  The beam splitting prism 202 divides the light beam incident from the laser array 152 through the coupling lens 154 into two parts in the vertical direction and emits the light beam at a predetermined interval in the sub-scanning direction.

  The light source unit 201 configured as described above is driven by a control device (not shown) based on image information. Further, the intensity of each light beam from each light source of the laser array 152 is determined by sequentially driving each light source before scanning the writing area on the surface to be scanned (photosensitive drum surface). The output signal is monitored and controlled to have a preset intensity.

  Returning to FIG. 2, the liquid crystal elements 203 </ b> A and 203 </ b> B are arranged adjacent to the vertical direction of the exit surface of the beam splitting prism 202, and deflect the light beam in the sub-scanning direction according to a voltage signal from a control device (not shown). To do.

  The cylinder lenses 204A and 204B are arranged adjacent to each other in the vertical direction corresponding to each light beam divided into two by the light beam splitting prism 202, and one of them is attached so as to be rotatable around the optical axis. The focal line can be adjusted to be parallel. Then, each incident light beam is condensed on the polygon mirror 104. The cylinder lenses 204A and 204B have a positive curvature at least in the sub-scanning direction, and once converge the beam on the reflection surface of the polygon mirror 104, the deflection points and the photosensitive elements are detected by the toroidal lenses 107A to 107D described later. A surface tilt correction optical system having a conjugate relationship in the sub-scanning direction with the surfaces of the drums 30A to 30D is formed.

  The polygon mirror 104 is composed of a pair of regular quadrangular columnar members having light beam deflection surfaces formed on the side surfaces, and the respective members are arranged adjacent to each other in the vertical direction in a state of being shifted by 45 degrees from each other. Yes. Then, it is rotated at a constant angular velocity in the direction of the arrow shown in FIG. 2 by a rotation mechanism (not shown). Therefore, the light beam branched into two in the vertical direction by the light beam splitting prism 202 of the incident optical systems 200A and 200B and condensed on the deflection surface of the polygon mirror 104 is deflected by the upper and lower deflection surfaces of the polygon mirror 104. Thus, the light is incident on the photosensitive drum alternately.

  FIG. 7 shows a light beam spot formed on one of the eight deflection surfaces of the polygon mirror 104. As shown in FIG. 7, the spots of the light beams respectively emitted from the 32 light emitting sources formed on the laser array 152 are a and b adjacent to each other in the main scanning direction and the sub-scanning direction. The size of the illumination range of the light beam in the main scanning direction is A, and the size in the sub-scanning direction is B.

  Usually, the deflecting surface of a deflector such as a polygon mirror has an uneven shape of the order of 0.1 μm, and the spot diameter after deflection increases depending on the location where the incident light beam is deflected (position within the deflecting surface). And shrinkage may occur. For example, in FIG. 7, the spots sp1 and sp2 of the light beam incident on the deflection surface of the polygon mirror 104 are indicated by black circles, and the spots sp1 and sp2 after being reflected by the deflection surface are indicated by white circles. As shown in FIG. 7, the spots sp1 and sp2 have substantially the same shape on the deflection surface of the polygon mirror 104, but the light beam reflected at a position that is convex with respect to the reflection direction on the deflection surface. The spot sp1 ′ of LB1 becomes larger than the spot sp2 ′ of the light beam LB2 reflected at a position that is concave with respect to the reflection direction. This is because the light beam reflected at the convex position with respect to the reflection direction is diverged and the light beam reflected at the concave position with respect to the reflection direction is converged. Therefore, in the polygon mirror 104 according to the present embodiment, the average length RSm of the cross-sectional curve elements in the sub-scanning direction of the deflection surface is set to be equal to or less than the distance b between adjacent spots in the sub-scanning direction (RSm ≦ b). Thus, it is possible to prevent the spot diameters from varying between a plurality of light beams.

  RSm is defined in JIS B 0601: 2001, and is the average of the length Xsi of the contour curve element at the reference length shown in FIG. This RSm is expressed by the following equation (2). However, according to JIS B 0601: 2001, the evaluation is performed using a stylus-type surface roughness measuring instrument. Therefore, according to the resolution of the measuring instrument, the expression (2) has an Xsi of 2.5 μm or more. However, even if Xsi is 2.5 μm or less, equation (2) is considered to hold. For example, the measurement resolution by the optical scanning type white light interferometry is about 0.1 μm, and the equation (2) holds even when Xsi is about 0.1 μm.

  The fθ lenses 105 and 305 have an image height proportional to the incident angle of the light beam, and move the image surface of the light beam deflected at a constant angular velocity by the polygon mirror 104 at a constant speed with respect to the Y axis.

  The reflection mirrors 106A, 106B, 306C, and 306D have the longitudinal direction as the Y-axis direction, fold back the light beam that passes through the fθ lenses 105 and 305, and guide the light beams to the toroidal lenses 107A, 107B, 307C, and 307D, respectively.

  2 and 3, the toroidal lens 107A is stably supported by a support plate 110A whose longitudinal direction is the Y-axis direction and both ends are fixed to the housing 12, and is folded back by the reflection mirror 106A. The formed light beam is imaged on the surface of the photosensitive drum 30A through the reflection mirror 108A having the longitudinal direction in the Y-axis direction.

  The toroidal lenses 107B, 307C, and 307D have a longitudinal direction as the Y-axis direction, one end (+ Y side) is fixed to the housing 12, and the other end (−Y side) is a drive mechanism that includes, for example, a rotary motor and a feed screw mechanism. 112B, 312C, and 312D (not shown in FIG. 2, refer to FIG. 3) are stably supported by support plates 110B, 310C, and 310D, respectively. The light beams folded back by the reflecting mirrors 106B, 306C, and 306D are imaged on the surfaces of the photosensitive drums 30B, 30C, and 30D via the reflecting mirrors 108B, 308C, and 308D having the Y-axis direction as the longitudinal direction, respectively. To do.

  Photodetectors 141A and 141B are arranged in the vicinity of + Y side (light beam incident side) end portions of the toroidal lenses 107A and 107B, respectively, and in the vicinity of the −Y side (light beam incident side) end portions of the toroidal lenses 107C and 107D. Are respectively provided with photodetection sensors 141C and 141D. Further, light detection sensors 142A and 142B are arranged near the −Y side end portions of the toroidal lenses 107A and 107B, respectively, and light detection sensors 142C and 142D are arranged near the + Y side end portions of the toroidal lenses 107C and 107D, respectively. ing. For example, the light detection sensors 141A to 141D and 142A to 142D output signals that are turned on while the light beam is incident and turned off otherwise.

  Next, the operation of the image forming apparatus 10 including the optical scanning device 100 configured as described above will be described. When image information is supplied from a host device or the like, a plurality of light beams emitted from the light source unit 201 of the incident optical system 200A are divided into two in the vertical direction by the light beam splitting prism 202 and transmitted through the liquid crystal elements 203A and 203B, respectively. Thus, after the position correction in the sub-scanning direction is performed, the light is condensed on the deflection surface of the polygon mirror 104 from the cylinder lenses 204A and 204B. Then, the light beam deflected by the polygon mirror 104 enters the fθ lens 105.

  The upper light beam incident on the fθ lens 105 is reflected by the reflection mirror 106B and incident on the toroidal lens 107B. Then, the light is condensed on the surface of the photosensitive drum 30B by the toroidal lens 107B via the reflection mirror 108B. The lower light beam incident on the fθ lens 105 is reflected by the reflection mirror 106A and enters the toroidal lens 107A. Then, the light is condensed on the surface of the photosensitive drum 30B by the toroidal lens 107A via the reflection mirror 108A. The polygon mirror 104 has a phase difference of 45 degrees between the upper and lower deflection surfaces as described above. Accordingly, the scanning of the photosensitive drum 30B by the upper light beam and the scanning of the photosensitive drum 30A by the lower light beam are in the −Y direction in synchronization with the signals output from the light detection sensors 141A, 141B, 142A, 142B, respectively. It will be performed alternately toward.

  On the other hand, a plurality of light beams emitted from the light source unit 201 of the incident optical system 200B are divided into two in the vertical direction by the light beam splitting prism 202 and transmitted through the liquid crystal elements 203A and 203B, thereby correcting the position in the sub-scanning direction. Then, the light is condensed on the deflection surface of the polygon mirror 104 from the cylinder lenses 204A and 204B. Then, the light beam deflected by the polygon mirror 104 enters the fθ lens 305.

  The upper light beam incident on the fθ lens 305 is reflected by the reflection mirror 306C and incident on the toroidal lens 307C. Then, the light is condensed on the surface of the photosensitive drum 30C by the toroidal lens 307C via the reflection mirror 308C. The lower light beam incident on the fθ lens 305 is reflected by the reflection mirror 306D and incident on the toroidal lens 307D. Then, the light is condensed on the surface of the photosensitive drum 30D by the toroidal lens 307D via the reflection mirror 308D. The polygon mirror 104 has a phase difference of 45 degrees between the upper and lower deflection surfaces as described above. Therefore, the scanning of the photosensitive drum 30C by the upper light beam and the scanning of the photosensitive drum 30D by the lower light beam are performed in the + Y direction in synchronization with the signals output from the light detection sensors 141C, 141D, 142C, and 142D, respectively. Will be performed alternately.

  The photosensitive layers on the respective surfaces of the photosensitive drums 30A, 30B, 30C, and 30D are charged with a predetermined voltage by the charging chargers 32A, 33B, 33C, and 32D, so that charges are distributed at a constant charge density. As described above, when each of the photosensitive drums 30A, 30B, 30C, and 30D is scanned, the photosensitive layer where the light beam is condensed has conductivity, and the potential is almost zero in that portion. Become. Therefore, by scanning the photosensitive drums 30A, 30B, 30C, and 30D rotating in the directions of the arrows in FIG. 1 with the light beams modulated based on the image information, the respective photosensitive drums 30A, 30B, and 30C are scanned. , 30D can form an electrostatic latent image defined by the charge distribution.

  When electrostatic latent images are formed on the surfaces of the photosensitive drums 30A, 30B, 30C, and 30D, the developing rollers of the toner cartridges 33A, 33B, 33C, and 33D shown in FIG. Toner is supplied to each surface of 30D. At this time, since the developing rollers of the toner cartridges 33A, 33B, 33C, and 33D are charged with a voltage having a polarity opposite to that of the photosensitive drums 30A, 30B, 30C, and 30D, the toner adhering to the developing rollers is the photosensitive drums 30A, 30B, and 30D. It is charged with the same polarity as 30C and 30D. Therefore, the toner does not adhere to the portions of the surfaces of the photosensitive drums 30A, 30B, 30C, and 30D where the electric charges are distributed, and the toner adheres only to the scanned portions, whereby the photosensitive drums 30A, 30B, and 30C. , A toner image in which the electrostatic latent image is visualized is formed on the surface of 30D.

  As described above, the respective toner images formed at the first station, the second station, the third station, and the fourth station based on the image information are transferred while being superimposed on the surface of the transfer belt 40, It is transferred by the transfer charger 48 to the surface of the paper 61 taken out from the paper feed tray 60 and fixed by the fixing roller 50. Then, the sheet 61 on which the image is formed in this manner is discharged by a discharge roller 58 and sequentially stacked on the discharge tray 12a.

  As described above, according to the optical scanning device 100 according to the present embodiment, the deflection surface of the polygon mirror 104 has the average length RSm of the sectional curve elements in the sub-scanning direction adjacent to the deflection surface in the sub-scanning direction. It is smaller than the distance b between the spots of the formed light beam. Therefore, it is possible to avoid the spot shape of each light beam from becoming non-uniform due to the influence of surface waviness on the deflection surface, and to scan the surface to be scanned with high accuracy in a short time. In particular, when the number of light beams scanned at a time is large, the size of the dots constituting the finally formed image is constant, so that deterioration of graininess is effectively avoided.

  Various methods for forming the deflection surface of the polygon mirror 104 are conceivable. An example will be described with reference to FIGS. FIG. 9 is a perspective view showing a schematic configuration of the main part of the cutting machine 500 for processing the deflection surface of the polygon mirror 104 together with the polygon mirror 104, and FIG. 10 is a cutting machine 500 in FIG. FIG. Here, as shown in FIG. 9, a description will be given of a case where a mirror surface is formed on a rough deflection surface disposed above among rough shapes in which a rough shape of the polygon mirror 104 is formed.

  9 and 10, the cutting machine 500 has a disk-like member 501 that rotates about an axis L parallel to the X-axis and a center of the axis L by the rotation of the disk-like member 501. And a fixing device 503 having a holding portion 503a for holding the polygon mirror 104 so that the rotation axis thereof is parallel to the Z axis.

  In this cutting machine 500, for example, while feeding the fixing device 503 of the cutting machine 500 little by little in the vertical direction (Z-axis direction), the disk-like member 501 is rotated to cut the cutting tool 502, for example, with a broken line in FIG. The entire deflection surface is rotated by rotating the deflection surface of the polygon mirror 104 in a direction substantially parallel to the Y axis by the cutting tool 502 along the indicated path and rotating at a rotational speed R [rpm] per minute. Cutting. Thereby, on the deflection surface, a plurality of cutting surfaces having a longitudinal direction formed by a single cutting substantially as the main scanning direction are formed adjacent to each other in the sub-scanning direction.

  Here, “substantially parallel to the Y axis” means that the locus of the cutting blade of the cutting tool 502 when the cutting tool 502 rotates about the axis L is substantially parallel to the Y axis at the portion where the deflection surface is cut. It means that For example, if the radius of rotation of the cutting tool 502 is relatively large compared to the size of the deflection surface of the polygon mirror 104 in the sub-scanning direction, for example, about 5 to 10 times, the cutting tool 502 moves substantially linearly at the cutting portion. You can think that you are doing.

  FIG. 11 is an enlarged image of the deflecting surface formed by the cutting machine 500 by the scanning white interference method. As shown in FIG. 11, it can be seen that a plurality of cutting surfaces 104c are generated in a direction substantially parallel to the main scanning direction (Y-axis direction). In a multi-beam compatible optical scanning device having a deflected reflection field wider than a single beam, the deflected reflection field is formed across a plurality of cutting surfaces, so that the light beam is scattered at the end of the cutting surface 104c, and a ghost is generated. May occur. Therefore, in this embodiment, the cutting direction of the deflection surface of the polygon mirror 104 is substantially parallel to the main scanning direction, and the cutting interval c in the sub scanning direction shown in FIG. Cutting of the deflection surface of the polygon mirror 104 is performed so as to be larger than B (see FIG. 6) (c> B).

  As a result, when the light beams are incident on the polygon mirror 104, each light beam is incident on the same cutting surface of the deflection surface, and scattering of the light spot at the end of the cutting surface can be prevented. For example, in the laser array 152 of the present embodiment, the irradiation range B in the sub-scanning direction on the deflection surface is 15 μm, so the cutting interval of the deflection surface of the polygon mirror 104 is 20 μm.

  Further, assuming that the cutting rotation speed of the cutting tool 502 around 1 minute is R [rpm] and the moving speed of the deflection surface of the polygon mirror 104 in the main scanning direction is q [mm / min], the cutting interval c [mm] is expressed by the following equation. It is indicated by (3).

c = (60 / p) × (q / 60) = q / p (3)

  Therefore, when the distance B between the most distant spots in the sub-scanning direction is smaller than c, that is, when the relationship of B <q / p is satisfied, it is possible to avoid light beam scattering at the cutting surface edge. It becomes.

  Further, the image forming apparatus 10 according to the present embodiment includes the optical scanning device 100. Therefore, scanning with a light beam having a uniform spot shape is possible, and as a result, an image can be formed with high accuracy.

  Moreover, in the said embodiment, although the laser array 152 was used as the light source, this invention is not limited to this, The same effect can be acquired if it is a monolithic light source formed.

  In the above-described embodiment, the image forming apparatus 10 that forms a multicolor image including the plurality of photoconductors 30A to 30B has been described. The present invention can also be applied to an image forming apparatus that forms a monochrome image by scanning with a beam.

  In the above embodiment, the case where the optical scanning device 100 of the present invention is used in a printer has been described. However, the image forming apparatus other than the printer, for example, a copier, a facsimile, or a multifunction machine in which these are integrated. Is preferred.

1 is a diagram illustrating a schematic configuration of an image forming apparatus 10 according to an embodiment of the present invention. 1 is a perspective view showing an optical scanning device 100. FIG. 1 is a side view showing an optical scanning device 100. FIG. 2 is a perspective view illustrating a schematic configuration of a light source unit 201. FIG. 2 is a plan view showing a laser array 152. FIG. FIG. 4 is a diagram showing a light beam spot formed on a deflection surface of a polygon mirror 104. It is a figure for demonstrating the dispersion | variation in the spot diameter resulting from deflecting a light beam. It is a figure for demonstrating the average length of a cross-sectional curve element. 1 is a perspective view showing a cutting machine 500. FIG. It is sectional drawing which shows the cutting machine 500. FIG. It is an enlarged image by the scanning white interferometry of a deflection surface.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 10 ... Image forming apparatus, 12 ... Housing, 30A-30B ... Photosensitive drum, 40 ... Transfer belt, 50 ... Fixing roller, 45 ... Position shift detection apparatus, 100 ... Optical scanning device, 104 ... Polygon mirror, 104c ... Cutting surface, 105, 305... Fθ lens, 106A, 106B, 108A, 108B, 306C, 306D, 308C, 308D... Reflection mirror, 107A, 107B, 307C, 307D ... Toroidal lens, 201. 202B ... Liquid crystal element, 204A, 204B ... Cylinder lens, 141A, 141B, 141C, 141D, 142A, 142B, 142C, 142D ... Photodetection sensor, 152 ... Laser array, 500 ... Cutting machine, 501 ... Disc-shaped member, 502 ... cutting tool, 503 ... fixed Location, 503a ... holding unit.

Claims (8)

In an optical scanning device that scans a surface to be scanned in a main scanning direction by deflecting at least three or more light beams separated in the sub-scanning direction by a deflector rotating around a predetermined axis,
The average length of the cross-sectional curve element in the sub-scanning direction of the deflecting surface of the deflector is smaller than the distance in the sub-scanning direction of the spot of the light beam formed adjacent to the deflecting surface. An optical scanning device. The deflecting surface of the deflector is formed by mirror cutting with the cutting direction as the main scanning direction,
2. The optical scanning device according to claim 1, wherein a cutting width in the sub-scanning direction in the cutting process is larger than a size in a sub-scanning direction of a whole irradiation range of the light beam incident on the deflection surface. The deflector includes a pair of rotary polygon mirrors that are formed with a plurality of deflection surfaces and rotate about the axis.
3. The optical scanning device according to claim 1, wherein each of the pair of rotary polygon mirrors is arranged in the axial direction in a state in which phases of the deflection surfaces are different from each other.   The optical scanning device according to any one of claims 1 to 3, further comprising a light source in which a plurality of light emitting points respectively emitting the light beams are arranged at equal intervals in the sub-scanning direction.   The optical scanning device according to claim 4, wherein the light source is a surface-emitting light source. A deflector manufacturing method for manufacturing the deflector according to any one of claims 1 to 5,
Forming a rough deflection surface on the deflector;
A cutting step of cutting the rough deflection surface by rotating a cutting member for cutting the rough deflection surface around a rotation axis perpendicular to the shaft while moving the deflector in the axial direction at a predetermined speed. And including
The size in the sub-scanning direction of the entire irradiation range of the light beam incident on the deflection surface is larger than a value obtained by dividing the movement distance per minute of the deflector by the number of rotations per minute of the cutting member. Small deflector manufacturing method. An image forming apparatus that forms an image by fixing a toner image formed based on a latent image obtained from information about an image to a recording medium,
An optical scanning device according to any one of claims 1 to 5;
A photoreceptor on which a latent image is formed by the optical scanning device;
Developing means for visualizing a latent image formed on the surface to be scanned of the photoreceptor;
An image forming apparatus comprising: a transfer unit that fixes the toner image visualized by the developing unit to the recording medium. An image forming apparatus for forming a multicolor image by superimposing and fixing a toner image formed on the basis of a latent image for each color obtained from information on a multicolor image on a recording medium,
An optical scanning device according to any one of claims 1 to 5;
A plurality of photosensitive members on which latent images corresponding to the respective colors are formed by the optical scanning device;
Developing means for visualizing latent images formed on the scanned surfaces of the plurality of photoconductors;
An image forming apparatus comprising: a transfer unit configured to superimpose and fix the toner image of each color visualized by the developing unit on the recording medium.