JP2012163867A - Optical scanner and image forming apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an optical scanner that reduces manufacturing costs without an increase in size and deterioration in scan accuracy.SOLUTION: A light-source device includes a light-receiving element for a monitor that receives a light flux emitted backward from a light source. The light-source device further includes a synchronization detection sensor that receives a light flux reflected by a polygon mirror through a mirror of an optical system disposed before a deflector, and a synchronization detection sensor that receives a light flux reflected by a polygon mirror not through the mirror of the optical system disposed before the deflector. A scan control device performs APC based on the output signal of the light-receiving element for a monitor, and performs synchronization detection based on the output signals of the respective synchronization detection sensors. Timing in which an X incident angle and a Y incident angle to the deflective reflection surface are 0° falls in the range between timing of the APC and timing of the synchronization detection.

Description

  The present invention relates to an optical scanning apparatus and an image forming apparatus, and more particularly to an optical scanning apparatus that scans a surface to be scanned with a light beam and an image forming apparatus including the optical scanning apparatus.

  In electrophotographic image forming apparatuses used in laser printers, laser plotters, digital copying machines, plain paper facsimiles, or multi-function machines including these, in recent years, colorization and speeding up have progressed, and photoconductors that are image carriers. A tandem type image forming apparatus having a plurality of drums (usually four) is widely used.

  In this tandem image forming apparatus, for example, four photosensitive drums are provided along the transfer belt or the intermediate transfer belt. Each photosensitive drum is charged by a corresponding charging unit, and then a latent image is formed by the optical scanning device. The latent images on the respective photosensitive drums are developed with a developer (for example, yellow, magenta, cyan, and black toners) having different colors from each other by a corresponding developing unit to be visualized. Each visualized image is transferred to a transfer belt or an intermediate transfer belt and superimposed to form a multicolor image.

  An image forming apparatus having only one photosensitive drum is also conceivable as an electrophotographic color image forming apparatus. In this case, when forming a multicolor image by superimposing the four colors, it is necessary to perform latent image formation on the photosensitive drum, visualization, and transfer to the intermediate transfer member four times in time series. And productivity is inferior compared to the tandem method.

  As described above, the tandem image forming apparatus can improve the productivity of multi-color image formation, but requires a plurality of light sources corresponding to the number of photosensitive drums, and accordingly, the number of parts increases. There are inconveniences such as color shift and cost increase due to wavelength difference between light sources.

  Further, the cause of the failure of the optical scanning device is the deterioration of the semiconductor laser as the light source. For this reason, when the number of light sources increases, there is a disadvantage that the probability of failure increases and the recyclability decreases.

  Accordingly, an optical scanning device having a smaller number of light sources than the number of photosensitive drums has been devised as an optical scanning device used in a tandem image forming apparatus.

  For example, in Patent Document 1, a plurality of scanned surfaces to be optically scanned are arranged in parallel to each other with a common optical deflector interposed therebetween, and the optical deflector deflects a light beam by rotating a deflection reflection surface. A light that is configured so that the rotation axis of the deflection reflection surface and the deflection reflection surface are parallel, and the two scanned surfaces sandwiching the optical deflector are optically scanned by the light beam from one light source. A scanning device is disclosed.

  Further, Patent Document 2 discloses a light source that is modulated and driven, a deflecting unit having a plurality of stages of reflecting mirrors on a common rotation axis, and a reflection from different stages of the deflecting unit by dividing a beam from the common light source. A beam splitting unit that makes the beam split into the mirror incident; a plurality of scanned surfaces; a scanning optical system that guides the beam scanned by the deflecting unit to the scanned surface; and a light receiving unit that detects the beam scanned by the deflecting unit There is disclosed an optical scanning apparatus that scans different scanned surfaces by beams divided from a common light source means.

  Patent Document 3 discloses a light source that is modulated and driven, a deflecting unit having four reflecting mirrors, a scanning optical system that guides a beam scanned by the deflecting unit to a surface to be scanned, and between the light source and the deflecting unit. And an optical beam splitting unit that splits the beam from the light source and enters each split beam toward the deflecting unit with a phase difference of approximately π / 2.

  However, in the optical scanning device disclosed in Patent Document 1, the number of deflecting and reflecting surfaces is two at the maximum, and it is difficult to increase the speed.

  Further, in the optical scanning device disclosed in Patent Document 2, the deflecting means has a plurality of multi-surface reflecting mirrors, and it is necessary to shift the phases of the multi-surface reflecting mirrors at each stage, resulting in an increase in cost. . In addition, the surface tilt of the reflecting mirror is different for each stage, and the surface accuracy is also different, which may reduce the quality of the image output from the image forming apparatus.

  In addition, the optical scanning device disclosed in Patent Document 3 has a disadvantage that the angle of view becomes narrow and the size is increased.

  The present invention has been made under such circumstances, and a first object of the invention is to provide an optical scanning device capable of reducing the price without causing an increase in size and a decrease in scanning accuracy. .

  A second object of the present invention is to provide an image forming apparatus capable of reducing the price without causing an increase in size and a decrease in image quality.

  From a first viewpoint, the present invention is an optical scanning device that scans a plurality of scanned surfaces with a light beam in the main scanning direction, and includes an illumination system that emits the plurality of light beams and a plurality of deflecting and reflecting surfaces. An optical deflector for deflecting a plurality of light beams emitted from the illumination system, a scanning optical system for individually guiding the plurality of light beams deflected by the optical deflector to a corresponding scanned surface, and an emission from the illumination system A light amount control device that controls the light amount of a plurality of light fluxes, and a synchronization detection device that receives at least one light flux deflected by the optical deflector and obtains a write start timing on a corresponding scanned surface, An optical scanning device characterized in that the timing of the light amount control by the light amount control device and the timing of the synchronization detection by the synchronization detection device sandwich the timing at which the incident angle to the deflection reflection surface is 0 °. is there

  According to this, it is possible to reduce the price without causing an increase in size and a decrease in scanning accuracy.

  According to a second aspect of the present invention, there is provided an image comprising: a plurality of image carriers; and an optical scanning device according to the present invention that individually scans the plurality of image carriers with a light beam modulated according to image data. Forming device.

  According to this, it is possible to reduce the price without causing an increase in size and a decrease in image quality.

1 is a diagram for describing a schematic configuration of a color printer according to an embodiment of the present invention. FIG. It is a perspective view for demonstrating the structure of the optical scanning device in FIG. It is a figure for demonstrating a light source device. It is a figure for demonstrating the effect | action of a half mirror. It is a figure for demonstrating the optical system before a deflector. FIG. 6A and FIG. 6B are diagrams for explaining oblique incidence. It is a figure for demonstrating a scanning optical system. It is FIG. (1) for demonstrating the optical path of the two light beams deflected by the deflection | deviation reflective surface of a polygon mirror. It is FIG. (2) for demonstrating the optical path of the two light beams deflected by the deflection | deviation reflective surface of a polygon mirror. It is FIG. (3) for demonstrating the optical path of the two light beams deflected by the deflection | deviation reflective surface of a polygon mirror. FIG. 11A and FIG. 11B are timing charts for explaining the driving operation of each light source in the scanning control device. It is a timing chart for demonstrating the modification of the drive operation of the light source in a scanning control apparatus. FIG. 10 is a diagram for explaining an arrangement position of a synchronization detection sensor 2206. It is a figure for demonstrating the optical path of the return light of the light beam LBa and the light beam LBd which injected into the deflection | deviation reflective surface with XY incident angle 0 degree. It is a figure for demonstrating the optical path of the return light of the light beam LBa and the light beam LBd which injected into the deflection | deviation reflective surface with XY incident angle -1 degree. It is a timing chart for demonstrating the timing of APC and a synchronous detection in the conventional optical scanning device. It is the figure which expanded a part of FIG. It is a timing chart when t2 is made shorter than t1. It is a figure for demonstrating the effective scanning area | region corresponding to FIG. 20A and 20B are timing charts for explaining the timing of APC and synchronization detection in this embodiment, respectively. It is the figure which expanded a part of FIG. It is the figure which compared this embodiment and the prior art about the writable time. 10 is a timing chart in the case where the writing start timing on the photosensitive drum 2030d is obtained based on the result of synchronization detection on the photosensitive drum 2030a. It is a figure for demonstrating the case where each light beam is horizontally incident on the deflection | deviation reflective surface of a polygon mirror. It is a figure for demonstrating the scanning optical system corresponding to FIG. It is FIG. (1) for demonstrating the modification of the optical system before a deflector. It is FIG. (2) for demonstrating the modification of the optical system before a deflector. It is FIG. (3) for demonstrating the modification of the optical system before a deflector.

  Hereinafter, an embodiment of the present invention will be described with reference to FIGS. FIG. 1 shows a schematic configuration of a color printer 2000 according to an embodiment.

  The color printer 2000 is a tandem multi-color printer that forms a full-color image by superimposing four colors (black, cyan, magenta, and yellow), and includes an optical scanning device 2010, four photosensitive drums (2030a, 2030b, 2030c, 2030d), four cleaning units (2031a, 2031b, 2031c, 2031d), four charging devices (2032a, 2032b, 2032c, 2032d), four developing rollers (2033a, 2033b, 2033c, 2033d), 4 Toner cartridges (2034a, 2034b, 2034c, 2034d), transfer belt 2040, transfer roller 2042, fixing device 2050, paper feed roller 2054, registration roller pair 2056, paper discharge roller 2058, paper feed tray 2 60, the discharge tray 2070 includes a communication control unit 2080, and a printer control device 2090.

  The communication control device 2080 controls bidirectional communication with a host device (for example, a personal computer) via a network or the like.

  The printer control device 2090 includes a CPU, a ROM described in a program written in code readable by the CPU, various data used when executing the program, a RAM as a working memory, an analog data An AD conversion circuit for converting the signal into digital data. The printer control device 2090 controls each unit in response to a request from the host device, and sends image information from the host device to the optical scanning device 2010.

  The photosensitive drum 2030a, the charging device 2032a, the developing roller 2033a, the toner cartridge 2034a, and the cleaning unit 2031a are used as a set and form an image forming station (hereinafter also referred to as “K station” for convenience) that forms a black image. Constitute.

  The photosensitive drum 2030b, the charging device 2032b, the developing roller 2033b, the toner cartridge 2034b, and the cleaning unit 2031b are used as a set and form an image forming station (hereinafter also referred to as “C station” for convenience) that forms a cyan image. Constitute.

  The photosensitive drum 2030c, the charging device 2032c, the developing roller 2033c, the toner cartridge 2034c, and the cleaning unit 2031c are used as a set, and form an image forming station (hereinafter also referred to as “M station” for convenience) that forms a magenta image. Constitute.

  The photosensitive drum 2030d, the charging device 2032d, the developing roller 2033d, the toner cartridge 2034d, and the cleaning unit 2031d are used as a set, and form an image forming station (hereinafter also referred to as “Y station” for convenience) that forms a yellow image. Constitute.

  Each photosensitive drum has a photosensitive layer formed on the surface thereof. That is, the surface of each photoconductive drum is a surface to be scanned. Each photosensitive drum is rotated in the direction of the arrow in the plane of FIG. 1 by a rotation mechanism (not shown).

  Each charging device uniformly charges the surface of the corresponding photosensitive drum.

  Based on the multicolor image information (black image information, cyan image information, magenta image information, yellow image information) from the higher-level device, the optical scanning device 2010 charges the light flux modulated for each color correspondingly. Irradiate each surface of the photosensitive drum. As a result, on the surface of each photoconductive drum, the charge disappears only in the portion irradiated with light, and a latent image corresponding to the image information is formed on the surface of each photoconductive drum. The latent image formed here moves in the direction of the corresponding developing device as the photosensitive drum rotates. The configuration of the optical scanning device 2010 will be described later.

  The toner cartridge 2034a stores black toner, and the toner is supplied to the developing roller 2033a. The toner cartridge 2034b stores cyan toner, and the toner is supplied to the developing roller 2033b. The toner cartridge 2034c stores magenta toner, and the toner is supplied to the developing roller 2033c. The toner cartridge 2034d stores yellow toner, and the toner is supplied to the developing roller 2033d.

  As each developing roller rotates, the toner from the corresponding toner cartridge is thinly and uniformly applied to the surface thereof. Then, when the toner on the surface of each developing roller comes into contact with the surface of the corresponding photosensitive drum, the toner moves only to a portion irradiated with light on the surface and adheres to the surface. In other words, each developing roller causes toner to adhere to the latent image formed on the surface of the corresponding photosensitive drum so as to be visualized. Here, the toner-attached image (toner image) moves in the direction of the transfer belt 2040 as the photosensitive drum rotates.

  The yellow, magenta, cyan, and black toner images are sequentially transferred onto the transfer belt 2040 at a predetermined timing, and are superimposed to form a multicolor image.

  Recording paper is stored in the paper feed tray 2060. A paper feed roller 2054 is disposed in the vicinity of the paper feed tray 2060, and the paper feed roller 2054 takes out the recording paper one by one from the paper feed tray 2060 and conveys it to the registration roller pair 2056. The registration roller pair 2056 feeds the recording paper toward the gap between the transfer belt 2040 and the transfer roller 2042 at a predetermined timing. As a result, the color image on the transfer belt 2040 is transferred to the recording paper. The recording sheet transferred here is sent to the fixing device 2050.

  In the fixing device 2050, heat and pressure are applied to the recording paper, thereby fixing the toner on the recording paper. The recording paper fixed here is sent to a paper discharge tray 2070 via a paper discharge roller 2058 and is sequentially stacked on the paper discharge tray 2070.

  Each cleaning unit removes toner (residual toner) remaining on the surface of the corresponding photosensitive drum. The surface of the photosensitive drum from which the residual toner has been removed returns to the position facing the corresponding charging device again.

  Next, the configuration of the optical scanning device 2010 will be described.

  As shown in FIG. 2 as an example, the optical scanning device 2010 includes a light source device 2200, two coupling lenses (2201A and 2201B), two aperture plates (2202 and 2205), a half mirror HM, and four cylindrical lenses ( 2204a, 2204b, 2204c, 2204d), two mirrors (M1, M2), polygon mirror 2104, two scanning lenses (2105A, 2105B), and eight folding mirrors (2106a, 2106b, 2106c, 2106d, 2107a, 2107b, 2107c). 2107d), two synchronization detection sensors (2206, 2111), an ND filter 2110, a scanning control device (not shown), and the like. These are assembled at predetermined positions of an optical housing (not shown).

  As an example, the light source device 2200 includes two light sources (2200A, 2200B) as shown in FIG. Each light source is an edge-emitting semiconductor laser and is mounted on a common circuit board (not shown). Further, two monitor light receiving elements (not shown) for individually receiving the light beams emitted backward from the respective light sources are mounted on the circuit board. Each monitor light-receiving element outputs a signal corresponding to the amount of received light to the scanning control device.

  The coupling lens 2201A is disposed on the optical path of the light beam emitted from the light source 2200A, and makes the light beam a substantially parallel light beam.

  The coupling lens 2201B is disposed on the optical path of the light beam emitted from the light source 2200B, and makes the light beam a substantially parallel light beam.

  Hereinafter, the light beam emitted from the light source 2200A is also referred to as a light beam LB1, and the light beam emitted from the light source 2200B is also referred to as a light beam LB2.

  The aperture plate 2202 has two apertures. The + Z side aperture shapes the light flux through the coupling lens 2201A, and the −Z side aperture shapes the light flux through the coupling lens 2201B.

  The half mirror HM is disposed on the optical path of the light beam LB1 and the light beam LB2 that have passed through the openings of the aperture plate 2202. As shown in FIG. 4 as an example, the half mirror HM has a dividing surface that divides an incident light beam into a transmitted light beam and a reflected light beam. The dividing surface is set so that the ratio of the light amount of the transmitted light beam and the light amount of the reflected light beam is 1: 1. Note that the setting of the dividing surface is determined according to the characteristics of the optical system arranged between the half mirror HM and the photosensitive drum so that the amount of light on the surface of each photosensitive drum is substantially equal. It may be different from the form.

  Here, the light beam LB1 transmitted through the half mirror HM is referred to as a light beam LBa, and the light beam LB2 transmitted through the half mirror HM is referred to as a light beam LBb. The light beam LB2 reflected by the half mirror HM is referred to as a light beam LBc, and the light beam LB1 reflected by the half mirror HM is referred to as a light beam LBd.

  Furthermore, when it is not necessary to distinguish between the light beam LBa and the light beam LBb, they are collectively referred to as “HM transmitted light beam”. When it is not necessary to distinguish between the light beam LBc and the light beam LBd, they are collectively referred to as “HM”. Also referred to as “reflected light flux” (see FIG. 5).

  The cylindrical lens 2204a is disposed on the optical path of the light beam LBa emitted from the half mirror HM, and condenses the light beam in the vicinity of the deflection reflection surface of the polygon mirror 2104 in the Z-axis direction via the mirror M1.

  The cylindrical lens 2204b is disposed on the optical path of the light beam LBb emitted from the half mirror HM, and condenses the light beam in the vicinity of the deflection reflection surface of the polygon mirror 2104 in the Z-axis direction via the mirror M1.

  The cylindrical lens 2204c is disposed on the optical path of the light beam LBc emitted from the half mirror HM, and condenses the light beam in the vicinity of the deflection reflection surface of the polygon mirror 2104 in the Z-axis direction via the mirror M2.

  The cylindrical lens 2204d is disposed on the optical path of the light beam LBd emitted from the half mirror HM, and condenses the light beam in the vicinity of the deflection reflection surface of the polygon mirror 2104 in the Z-axis direction via the mirror M2.

  The optical system disposed between the light source and the polygon mirror 2104 is also called a pre-deflector optical system.

  The polygon mirror 2104 has a four-sided mirror, and each mirror serves as a deflection reflection surface. The polygon mirror 2104 rotates at a constant speed clockwise around an axis parallel to the Z-axis direction, and the light beam LBa from the cylindrical lens 2204a, the light beam LBb from the cylindrical lens 2204b, the light beam LBc from the cylindrical lens 2204c, and the cylindrical lens. The light beam LBd from 2204d is deflected at a constant angular velocity in a plane orthogonal to the Z axis.

  The light beam LBa and the light beam LBb via the mirror M1 are incident on the same deflecting and reflecting surface located on the + X side of the rotation axis of the polygon mirror 2104.

  The light beam LBc and the light beam LBd via the mirror M2 are incident on the same deflecting and reflecting surface located on the −X side of the rotation axis of the polygon mirror 2104.

  In plan view, the angle formed between the light beam that has entered the polygon mirror 2104 via the mirror M1 and the light beam that has passed through the mirror M2 is approximately 90 ° (see FIG. 5).

  The light beam LBa and the light beam LBd are incident on the deflecting / reflecting surface from a direction inclined to the + Z side with respect to a plane orthogonal to the Z axis (a plane parallel to the XY plane) (see FIGS. 6A and 6B). ).

  The light beam LBb and the light beam LBc are incident on the deflecting / reflecting surface from a direction inclined to the −Z side with respect to a plane orthogonal to the Z-axis (a plane parallel to the XY plane) (FIGS. 6A and 6B). reference).

  In the following, when the light beam enters the deflecting / reflecting surface, it is referred to as “oblique incidence” to be incident from a direction inclined in the sub-scanning corresponding direction with respect to the surface orthogonal to the rotation axis, and is orthogonal to the rotation axis. Incident from a direction parallel to the surface is called “horizontal incidence”. The incident angle at the time of oblique incidence is referred to as “oblique incidence angle”.

  In addition, the configuration including the light source set so that the light beam is obliquely incident on the deflecting reflection surface and the pre-deflector optical system is also referred to as an “oblique incident optical system”.

  In this case, a general-purpose polygon mirror can be used as the optical deflector, and the size (height) in the Z-axis direction can be reduced, so that the cost can be reduced.

  The light beam LBa and the light beam LBb are deflected to the + X side of the polygon mirror 2104. Further, the light beam LBc and the light beam LBd are deflected to the −X side of the polygon mirror 2104.

  The scanning lens 2105A is disposed on the optical path of the light beam LBa deflected by the polygon mirror 2104 and the light beam LBb.

  The scanning lens 2105B is disposed on the optical path of the light beams LBc and LBd deflected by the polygon mirror 2104.

  The folding mirror 2106a is disposed on the optical path of the light beam LBa via the scanning lens 2105A, and folds the optical path of the light beam in the −X direction.

  The folding mirror 2107a is disposed on the optical path of the light beam passing through the folding mirror 2106a, and folds the optical path of the light beam in a direction toward the photosensitive drum 2030a.

  Therefore, the light beam LBa deflected by the deflecting / reflecting surface is irradiated onto the photosensitive drum 2030a through the scanning lens 2105A, the folding mirror 2106a, and the folding mirror 2107a, thereby forming a light spot (see FIG. 7). This light spot moves in the longitudinal direction of the photosensitive drum 2030a in accordance with the vibration of the deflecting reflection surface. The moving direction of the light spot at this time is the “main scanning direction” on the photosensitive drum 2030a, and the rotational direction of the photosensitive drum 2030a is the “sub-scanning direction” on the photosensitive drum 2030a.

  The folding mirror 2106b is disposed on the optical path of the light beam LBb via the scanning lens 2105A, and folds the optical path of the light beam in the −X direction.

  The folding mirror 2107b is disposed on the optical path of the light beam passing through the folding mirror 2106b, and folds the optical path of the light beam in the direction toward the photosensitive drum 2030b.

  Therefore, the light beam LBb deflected by the deflecting / reflecting surface is irradiated onto the photosensitive drum 2030b through the scanning lens 2105A, the folding mirror 2106b, and the folding mirror 2107b, thereby forming a light spot (see FIG. 7). This light spot moves in the longitudinal direction of the photosensitive drum 2030b with the vibration of the deflecting reflection surface. The moving direction of the light spot at this time is the “main scanning direction” on the photosensitive drum 2030b, and the rotational direction of the photosensitive drum 2030b is the “sub-scanning direction” on the photosensitive drum 2030b.

  The folding mirror 2106c is disposed on the optical path of the light beam LBc via the scanning lens 2105B, and folds the optical path of the light beam in the + X direction.

  The folding mirror 2107c is disposed on the optical path of the light beam that passes through the folding mirror 2106c, and folds the optical path of the light beam in a direction toward the photosensitive drum 2030c.

  Therefore, the light beam LBc deflected by the deflecting / reflecting surface is irradiated onto the photosensitive drum 2030c through the scanning lens 2105B, the folding mirror 2106c, and the folding mirror 2107c, thereby forming a light spot (see FIG. 7). This light spot moves in the longitudinal direction of the photosensitive drum 2030c with the vibration of the deflecting reflection surface. The moving direction of the light spot at this time is the “main scanning direction” on the photosensitive drum 2030c, and the rotational direction of the photosensitive drum 2030c is the “sub-scanning direction” on the photosensitive drum 2030c.

  The folding mirror 2106d is disposed on the optical path of the light beam LBd via the scanning lens 2105B, and folds the optical path of the light beam in the + X direction.

  The folding mirror 2107d is disposed on the optical path of the light beam passing through the folding mirror 2106d, and folds the optical path of the light beam in a direction toward the photosensitive drum 2030d.

  Therefore, the light beam LBd deflected by the deflecting / reflecting surface is irradiated onto the photosensitive drum 2030d through the scanning lens 2105B, the folding mirror 2106d, and the folding mirror 2107d, thereby forming a light spot (see FIG. 7). This light spot moves in the longitudinal direction of the photosensitive drum 2030d with the vibration of the deflecting reflection surface. The moving direction of the light spot at this time is the “main scanning direction” on the photosensitive drum 2030d, and the rotational direction of the photosensitive drum 2030d is the “sub-scanning direction” on the photosensitive drum 2030d.

  The optical system arranged on the optical path between the polygon mirror and the photosensitive drum is also called a scanning optical system.

  Here, the scanning optical system of the K station is composed of the scanning lens 2105A and the two folding mirrors (2106a, 2107a).

  Further, the scanning optical system of the C station is composed of the scanning lens 2105A and the two folding mirrors (2106b, 2107b).

  That is, the scanning lens 2105A is shared by the two stations.

  Further, the scanning optical system of the M station is constituted by the scanning lens 2105B and the two folding mirrors (2106c, 2107c).

  The scanning optical system of the Y station is composed of the scanning lens 2105B and the two folding mirrors (2106d, 2107d).

  That is, the scanning lens 2105B is shared by the two stations.

  Here, the number of deflection reflection surfaces in the polygon mirror 2104 is four, and the HM reflected light beam and the HM transmitted light beam are incident on different deflection reflection surfaces. The angle formed by the HM reflected light beam and the HM transmitted light beam incident on the polygon mirror 2104 is set to be approximately 90 ° in plan view. Therefore, the light beam LBa and the light beam LBd, and the light beam LBb and the light beam LBc do not simultaneously scan the effective scanning areas on the corresponding photosensitive drums.

  For example, as shown in FIG. 8, when the light beam LBa reflected by the deflection reflection surface of the polygon mirror 2104 goes to the writing start position on the photosensitive drum 2030a, the light beam LBd reflected by the deflection reflection surface of the polygon mirror 2104. Is directed to a position on the + Y side of the writing end position on the photosensitive drum 2030d.

  Further, as shown in FIG. 9, when the light beam LBa reflected by the deflecting reflection surface of the polygon mirror 2104 is directed to the center (image height 0) position of the effective scanning area of the photosensitive drum 2030a, the deflection of the polygon mirror 2104 is performed. The light beam LBd reflected by the reflecting surface is directed in the + Y direction.

  Further, as shown in FIG. 10, when the light beam LBa reflected by the deflecting / reflecting surface of the polygon mirror 2104 goes to the writing end position of the effective scanning area of the photosensitive drum 2030a, it is reflected by the deflecting / reflecting surface of the polygon mirror 2104. The emitted light beam LBd is directed to a position on the −Y side of the writing start position on the photosensitive drum 2030d.

  As described above, when the light beam LBa reflected by the deflecting / reflecting surface of the polygon mirror 2104 scans the effective scanning area of the photosensitive drum 2030a, the light beam LBd reflected by the deflecting / reflecting surface of the polygon mirror 2104 is photosensitive. It does not go into the effective scanning area of the body drum 2030d.

  On the contrary, when the light beam LBd reflected by the deflecting / reflecting surface of the polygon mirror 2104 scans the effective scanning area of the photosensitive drum 2030d, the light beam LBa reflected by the deflecting / reflecting surface of the polygon mirror 2104 is It does not go into the effective scanning area of the drum 2030a.

  Similarly, when the light beam LBb reflected by the deflecting / reflecting surface of the polygon mirror 2104 is scanning the effective scanning area of the photosensitive drum 2030b, the light beam LBc reflected by the deflecting / reflecting surface of the polygon mirror 2104 is It does not go into the effective scanning area of the drum 2030c.

  Further, when the light beam LBc reflected by the deflecting / reflecting surface of the polygon mirror 2104 scans the effective scanning area of the photosensitive drum 2030c, the light beam LBb reflected by the deflecting / reflecting surface of the polygon mirror 2104 is It does not go into the effective scanning area in 2030b.

  Note that the angle formed between the HM reflected light beam and the HM transmitted light beam incident on the polygon mirror 2104 may be slightly deviated from 90 ° in plan view.

  Therefore, the light beam LBa and the light beam LBd are modulated in the same manner as one light beam when emitted from the light source 2200A. However, when the light beam LBa scans the effective scanning area in the photosensitive drum 2030a, the scanning control device is used. When the light source 2200A is driven so that a light beam modulated according to black image information is emitted, and the light beam LBd scans the effective scanning area on the photosensitive drum 2030d, the scanning control device The light source 2200A is driven so that a light beam modulated in accordance with information is emitted (see FIG. 11A).

  Similarly, the light beam LBb and the light beam LBc are subjected to the same modulation as one light beam when emitted from the light source 2200B. However, when the light beam LBb scans the effective scanning area on the photosensitive drum 2030b, scanning control is performed. The apparatus drives the light source 2200B so that a light beam modulated in accordance with cyan image information is emitted, and when the light beam LBc scans the effective scanning area on the photosensitive drum 2030c, the scanning control device The light source 2200B is driven so that a light beam modulated in accordance with image information is emitted (see FIG. 11B).

  In addition, when the transmittance and reflectance of the optical element are relatively different between the stations, if the light emission amount of the light source at the time of writing is the same, the light amount of the light beam reaching the photosensitive drum is relatively different. End up. Therefore, in this case, the light emission amounts of the light sources at the time of writing may be different from each other so that the light amounts of the light beams reaching the respective photosensitive drums are equal to each other.

  FIG. 12 shows an example in which the light emission amount of the light source 2200A when writing to the photosensitive drum 2030a is different from the light emission amount of the light source 2200A when writing to the photosensitive drum 2030d.

  By the way, in the image forming apparatus, the light amount of the light beam that scans the photosensitive drum changes with a change in temperature or with time, and there is a possibility that density unevenness may occur in the finally output image (output image). Therefore, in order to suppress this, in an optical scanning device, usually, a part of a light beam emitted from a light source is received by a monitor light receiving element, and the output level of the light source is controlled based on the result. Control) is being implemented.

  At this time, if ghost light is incident on the monitor light-receiving element, the amount of light detected by the monitor light-receiving element increases, which may promote uneven density in the output image.

  In the present embodiment, APC of each light source is performed based on the output signal of the light receiving element for monitoring of each light source in the scanning control device. In plan view, when the incident angle of the light beam on the deflecting / reflecting surface is 0 °, the deflecting / reflecting surface faces the light source direction. If APC is performed at this time, the light reflected by the deflecting reflecting surface returns to the light source side, and the amount of light detected by the light receiving element for monitoring increases. Therefore, in the present embodiment, APC is set so as not to be performed at the timing when the incident angle of the light beam on the deflecting reflection surface becomes 0 ° in plan view. Hereinafter, in order to distinguish from the oblique incident angle, for convenience, the incident angle of the light beam on the deflecting / reflecting surface in the XY plane is referred to as “XY incident angle”.

  Next, in order to know the timing for starting writing, synchronous detection for detecting a light beam before being started to be deflected by the polygon mirror 2104 and going outside the effective scanning area of the photosensitive drum will be described. The two synchronization detection sensors (2206, 2111) are sensors used for synchronization detection, and output a signal corresponding to the amount of received light to the scanning control device.

  In this embodiment, on the −Y side of the polygon mirror 2104, a synchronization detection sensor can be arranged outside the effective scanning area of the photosensitive drum to perform synchronization detection. However, on the + Y side of the polygon mirror 2104, Since incident light passes through the vicinity of the effective scanning area of the body drum, there is no room for arranging the synchronization detection sensor.

  In other words, among the light deflected by the polygon mirror 2104, there is a spatial margin for arranging the synchronization detection sensor on the optical path of the light deflected farther from the incident light. On the optical path of the light deflected to the near side, there is no spatial margin for arranging the synchronization detection sensor.

  Therefore, in this embodiment, the photosensitive drum 2030a is detected by using light reflected by the polygon mirror 2104 and returning to the mirror M1. Specifically, synchronous detection is performed using light that is incident on the deflecting / reflecting surface with an XY incident angle of −1 °, reflected by the deflecting / reflecting surface, and returned to the mirror M1.

  The synchronization detection sensor 2206 is light that is incident on the deflecting / reflecting surface with an XY incident angle of -1 °, reflected by the deflecting / reflecting surface, and returned to the mirror M1 and reflected by the split surface of the half mirror HM. It arrange | positions on the optical path of light (refer FIG. 13). The aperture plate 2205 is disposed between the half mirror HM and the synchronization detection sensor 2206. Note that the synchronization detection sensor 2206 is disposed at a position where it does not receive the light that is incident on the deflection reflection surface at an XY incident angle of 0 ° and is reflected by the deflection reflection surface in plan view.

  For example, the light beam LBa incident on the deflection reflection surface with an XY incident angle of -1 °, reflected by the deflection reflection surface, and returned to the mirror M1 returns to the half mirror HM via the cylindrical lens 2204a. The light beam returned to the half mirror HM is divided into a light beam traveling toward the light source 2200B and a light beam traveling toward the synchronization detection sensor 2206.

  Light beams traveling toward the synchronization detection sensor 2206 are incident on the synchronization detection sensor 2206 after light unnecessary for synchronization detection is removed by the aperture plate 2205.

  Here, the reason why not the light incident on the deflecting reflection surface with the XY incident angle of 0 ° but the light incident with the XY incident angle of −1 ° is used as the light for synchronization detection will be described.

  If light incident on the deflecting reflection surface with an XY incident angle of 0 ° is used for synchronization detection, for example, when performing synchronization detection on the photosensitive drum 2030a, as shown in FIG. 14, the XY incident angle of the light beam LBa is shown. Is coincident with the timing when the XY incident angle of the light beam LBd is 0 °. In this case, the optical path of the return light beam LBa reflected by the deflection reflection surface and reflected by the split surface of the half mirror HM and the return light beam LBd reflected by the deflection reflection surface and transmitted through the split surface of the half mirror HM. These optical paths overlap. That is, only the return light of the light beam LBa cannot be received by the synchronization detection sensor 2206. Accordingly, accurate synchronization detection on the photosensitive drum 2030a cannot be performed.

  On the other hand, when light incident on the deflecting reflecting surface with an XY incident angle of -1 ° is used for synchronous detection, as shown in FIG. 15 as an example, it is reflected by the deflecting reflecting surface and reflected by the split surface of the half mirror HM. The optical path of the return light of the reflected light beam LBa is different from the optical path of the return light of the light beam LBd reflected by the deflection reflection surface and transmitted through the split surface of the half mirror HM. Therefore, by arranging the aperture plate 2205 and the synchronization detection sensor 2206 on the optical path of the return light beam LBa reflected by the split surface of the half mirror HM, only the return light beam LBa is received by the synchronization detection sensor 2206. Can do. Accordingly, accurate synchronization detection on the photosensitive drum 2030a can be performed.

  Based on the output signal of the synchronization detection sensor 2206, the scanning control device performs synchronization detection on the photosensitive drum 2030a, and determines the writing start timing on the photosensitive drum 2030a. The scanning control device determines the writing start timing on the photosensitive drum 2030b based on the writing start timing on the photosensitive drum 2030a.

  Returning to FIG. 2, the synchronization detection sensor 2111 is disposed outside the effective scanning area of the photosensitive drum 2030d, is deflected by the polygon mirror 2104, and receives the light beam LBd before the start of writing without passing through the mirror of the optical system before the polarizer. . The ND filter 2110 is arranged on the optical path of the light beam that is deflected by the polygon mirror 2104 and travels toward the synchronization detection sensor 2111. The ND filter 2110 is set so that the amount of light received by the synchronization detection sensor 2111 substantially matches the amount of light received by the synchronization detection sensor 2206. The scanning control device performs synchronization detection on the photosensitive drum 2030d based on the output signal of the synchronization detection sensor 2111, and determines the writing start timing on the photosensitive drum 2030d. Then, the scanning control device determines the writing start timing on the photosensitive drum 2030c based on the writing start timing on the photosensitive drum 2030d.

  In the two synchronization detection sensors, since the ranges of the received light amounts are substantially the same, the scanning control device can share a circuit for performing synchronization detection. Thereby, the number of parts can be reduced and the cost can be reduced.

  Next, timing for performing APC and synchronization detection will be described. For convenience, the timing at which the light beam enters the deflection reflection surface at an XY incident angle of 0 ° is abbreviated as “XY incident angle of 0 ° timing”. The time from the end of writing to the XY incident angle 0 ° timing is t1, and the time from the XY incident angle 0 ° timing to the writing start is t2.

  In the conventional optical scanning device, as shown in FIG. 16 as an example, the timing of APC and synchronization detection is on the same side with respect to the timing of the XY incident angle of 0 °.

  In this case, t1 = t2 is set as shown in FIG. 17 in which a part of FIG. 16 is enlarged. Here, useless time exists only for time t2.

  Therefore, as an example, it is conceivable to shorten t2 as shown in FIG. In this case, the writing start timing is earlier than in the case of FIG. 17, and as shown in FIG. 19 as an example, the main scanning direction between the two photosensitive drums facing each other with the polygon mirror interposed therebetween. Deviation occurs in the effective scanning area. This shift is a color shift in the output image. Therefore, the effective writing area that can actually be used for image formation is an area in which two effective scanning areas overlap in the main scanning direction. Therefore, in order to maximize the effective writing area, it is necessary to set t1 = t2.

  In this embodiment, as shown in FIG. 20 as an example, the timing of APC and synchronization detection is set so as to sandwich the timing of 0 ° XY incident angle. In this case, as shown in FIG. 21 in which a part of FIG. 20 is enlarged, it is possible to reduce t1 and t2 while maintaining t1 = t2.

  Therefore, in this embodiment, as shown in FIG. 22 as an example, the time available for writing can be made longer than in the conventional example. Therefore, in this embodiment, the angle of view of the scanning optical system can be made wider than that of the conventional example, and as a result, the optical scanning device can be reduced in size.

  Here, the synchronization detection is performed after the APC, but the present invention is not limited to this, and the APC may be performed after the synchronization detection.

  As described above, according to the optical scanning device 2010 according to the present embodiment, the light source device 2200, the pre-deflector optical system, the polygon mirror 2104, the four scanning optical systems, the two synchronization detection sensors (2206, 2111), and the like. I have.

  The light source device 2200 has two light sources, and the pre-deflector optical system divides the light beams from the two light sources and emits the four light beams toward the polygon mirror 2104.

  The APC timing and the synchronization detection timing sandwich the timing at which the XY incident angle on the deflecting reflecting surface becomes 0 °.

  In this case, the price can be reduced without increasing the size and reducing the scanning accuracy.

  The color printer 2000 according to the present embodiment includes the optical scanning device 2010. As a result, it is possible to reduce the price without causing an increase in size and a decrease in image quality.

  In the above-described embodiment, the case where light incident at an XY incident angle of −1 ° is used as light used for synchronization detection is not limited to this, and only the return light of the light beam LBa is used. It is only necessary that the synchronization detection sensor 2206 can receive light.

  In the above embodiment, the writing start timing on the photosensitive drum 2030d may be obtained based on the result of synchronous detection on the photosensitive drum 2030a five images before, as shown in FIG. 23 as an example.

  A black image and a yellow image to which writing is performed successively use light beams deflected by different deflection reflection surfaces. Therefore, the result of synchronization detection on the immediately preceding photoconductor drum 2030a cannot be used for synchronization detection on the photoconductor drum 2030d. Therefore, the result of synchronization detection in the photoconductor drum 2030a five images before having the same deflection reflection surface is used to determine the writing start timing in the photoconductor drum 2030d. In this case, the writing start timing on the photosensitive drum 2030d can be obtained with high accuracy without the synchronization detection sensor 2111.

  Further, the synchronization detection sensor 2111 and the ND filter 2110 are not necessary, and the number of parts can be further reduced.

  In addition, since it is not necessary to ensure the timing at which the light beam enters the synchronization detection sensor 2111, the sizes of t1 and t2 can be made smaller than those in the above embodiment, and a wider angle of view can be achieved.

  In the above-described embodiment, the case where each light beam incident on the polygon mirror 2104 is obliquely incident on the deflecting / reflecting surface is described. However, the present invention is not limited to this. (See FIG. 24). In this case, as shown in FIG. 25, a scanning lens 2105a and a scanning lens 2105b are used instead of the scanning lens 2105A, and a scanning lens 2105c and a scanning lens 2105d are used instead of the scanning lens 2105B. In the polygon mirror 2104, the dimension (height) in the Z-axis direction of the deflecting / reflecting surface is larger than that in the above embodiment.

  A scanning lens 2105a is disposed on the optical path of the light beam LBa deflected by the polygon mirror 2104, and a scanning lens 2105b is disposed on the optical path of the light beam LBb. A scanning lens 2105c is disposed on the optical path of the light beam LBc deflected by the polygon mirror 2104, and a scanning lens 2105d is disposed on the optical path of the light beam LBd.

  Even in this case, the same effect as the above-described embodiment can be obtained.

  In the above-described embodiment, the case where two light sources are provided and the light beam emitted from each light source is divided into two by the half mirror HM has been described. As an example, as illustrated in FIGS. You may have two light sources (2200a, 2200b, 2200c, 2200d). In this case, the half mirror HM, the mirror M1, and the mirror M2 are unnecessary. Further, instead of the coupling lens 2201A and the coupling lens 2201B, a coupling lens 2201a, a coupling lens 2201b, a coupling lens 2201c, and a coupling lens 2201d are used. Further, instead of the aperture plate 2202, an aperture plate 2202a, an aperture plate 2202b, an aperture plate 2202c, and an aperture plate 2202d are used.

  Even in this case, the angle of view of the scanning optical system can be made larger than the conventional one by setting the timing of the APC and the synchronization detection with the XY incident angle of 0 °, and the optical scanning device can be reduced in size. Can be achieved.

  In the above embodiment, the toner image is transferred from the photosensitive drum to the recording paper via the transfer belt. However, the present invention is not limited to this, and the toner image is directly transferred to the recording paper. Also good.

  In the above embodiment, the color printer 2000 is described as the image forming apparatus. However, the present invention is not limited to this, and may be, for example, an optical plotter or a digital copying apparatus.

  Further, an image forming apparatus using a silver salt film as the image carrier may be used. In this case, a latent image is formed on the silver salt film by optical scanning, and this latent image can be visualized by a process equivalent to a developing process in a normal silver salt photographic process. Then, it can be transferred to a photographic paper as a transfer object by a process equivalent to a printing process in a normal silver salt photographic process. Such an image forming apparatus can be implemented as an optical plate making apparatus or an optical drawing apparatus that draws a CT scan image or the like.

  Further, an image forming apparatus using a color developing medium (positive photographic paper) that develops color by the heat energy of a beam spot as an image carrier may be used. In this case, a visible image can be directly formed on the image carrier by optical scanning.

  In short, if it is an image forming apparatus provided with the optical scanning device 2010, it is possible to reduce the price without causing an increase in size and a decrease in image quality.

  As described above, the optical scanning device of the present invention is suitable for reducing the price without causing an increase in size and a decrease in scanning accuracy. The image forming apparatus according to the present invention is suitable for reducing the price without causing an increase in size and a decrease in image quality.

2000 ... Color printer (image forming apparatus), 2010 ... Optical scanning device, 2030a to 2030d ... Photosensitive drum (image carrier), 2104 ... Polygon mirror (optical deflector), 2105A, 2105B ... Scanning lens (of the scanning optical system) 2105a to 2105d ... scanning lens (part of scanning optical system), 2106a to 2106d ... folding mirror (part of scanning optical system), 2107a to 2107d ... folding mirror (part of scanning optical system), 2110 ND filter (dimming member), 2111 ... synchronization detection sensor (second synchronization detection sensor), 2200A, 2200B ... light source, 2200a-2200d ... light source, 2201A, 2201B ... coupling lens (part of illumination system), 2201a to 2201d ... coupling lens (part of illumination system) 2202 ... aperture plate 2202a to 2202d ... aperture plate, 2204a to 2204d ... cylindrical lens (part of illumination system), 2205 ... aperture plate, 2206 ... synchronization detection sensor, HM ... half mirror (beam splitting member), M1, M2 ... mirror (light guide) Element).

Japanese Patent Laid-Open No. 2002-23085 JP 2006-284822 A JP 2008-257169 A

Claims (8)

An optical scanning device that scans a plurality of scanned surfaces in the main scanning direction with a light beam,
An illumination system that emits a plurality of luminous fluxes;
An optical deflector having a plurality of deflecting reflecting surfaces and deflecting a plurality of light beams emitted from the illumination system;
A scanning optical system for individually guiding a plurality of light beams deflected by the optical deflector to a corresponding scanned surface;
A light amount control device for controlling the light amounts of a plurality of light beams emitted from the illumination system;
A synchronization detecting device that receives at least one light beam deflected by the optical deflector and obtains a write start timing on a corresponding scanned surface;
The optical scanning device according to claim 1, wherein the light amount control timing by the light amount control device and the synchronization detection timing by the synchronization detection device sandwich a timing at which an incident angle to the deflection reflection surface becomes 0 °.   2. The optical scanning device according to claim 1, wherein the plurality of light beams incident on the optical deflector are incident obliquely with respect to a sub-scanning direction orthogonal to the main scanning direction.   The illumination system guides the light beam splitting member that splits the light beam emitted from one light source into two light beams and the two light beams split by the light beam splitting member to different deflecting and reflecting surfaces of the optical deflector. The optical scanning device according to claim 1, further comprising a light guide member.   The optical scanning device according to claim 3, wherein the synchronization detection device includes a synchronization detection sensor that receives a light beam reflected by the optical deflector through the light guide member.   5. The optical scanning device according to claim 4, wherein the synchronization detection device obtains writing start timings on the plurality of scanned surfaces based on output signals of the synchronization detection sensor.   The synchronization detection device includes: a second synchronization detection sensor that receives a light beam reflected by the optical deflector without passing through the light guide member; and a gap between the optical deflector and the second synchronization detection sensor. The optical scanning device according to claim 4, further comprising a dimming member disposed on the optical path.   The optical scanning device according to claim 1, wherein the plurality of deflection reflection surfaces are four deflection reflection surfaces. A plurality of image carriers;
An image forming apparatus comprising: the optical scanning device according to claim 1, wherein the plurality of image carriers are individually scanned with a light beam modulated according to image data.