JP2012233931A - Optical scanning device and image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a compact and low-cost optical scanning device without reducing optical performance.SOLUTION: A half mirror HM divides a light flux emitted from each of light sources via a corresponding coupling lens into a transmitted light flux and a reflected light flux. A reflection mirror M1 is arranged on a light path of the light fluxes (LBa, LBb) reflected by the half mirror HM to guide the light fluxes to a deflective reflection surface 1. A half mirror M2 is arranged on a light path of the light flexes (LBc, LBd) having transmitted the half mirror HM to bend the light flux direction. A reflection mirror M3 is arranged on a light path of the light fluxes reflected by the reflection mirror M2 to guide the light fluxes to a deflective reflection surface 2. The reflection mirror M2 and the reflection mirror M3 are arranged so that the lengths, from the light sources, of the light paths of the light fluxes to be incident on the deflective reflection surfaces are the same.

Description

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

  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.

  This tandem type image forming apparatus can improve the productivity of multi-color image formation, but requires a plurality of light sources according to the number of photosensitive drums. There are inconveniences such as color shift and cost increase due to the wavelength difference between them.

  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, Patent Document 1 discloses a light beam splitting unit that splits a beam from a light source between a light source and a deflecting unit, and enters each split beam toward the deflecting unit with a phase difference of approximately π / 2. And an optical scanning device in which the deflecting means has four reflecting surfaces.

  By the way, in the optical scanning device in which the scanning optical system is arranged in two stages in the height direction (direction corresponding to the sub-scanning direction), two light beams separated with respect to the height direction are separated from each other by the polygon mirror. When the light is incident on the deflecting / reflecting surface from a direction parallel to the plane orthogonal to the rotation axis of the polygon mirror (horizontal incidence), the polygon mirrors are stacked in two stages (see FIG. 35A) or height. It was necessary to use a polygon mirror (see FIG. 35B) having a large size in the direction.

  Therefore, the polygon mirror becomes expensive and it is difficult to reduce the cost of the optical scanning device. Further, there is a disadvantage that the power consumption increases when the polygon mirror is rotated at a high speed.

  Therefore, it has been devised that two light beams separated in the height direction are incident (obliquely incident) on the deflecting / reflecting surface of the polygon mirror from a direction inclined with respect to the plane orthogonal to the rotation axis of the polygon mirror. (For example, refer to Patent Document 2).

  In the case of horizontal incidence, as shown in FIG. 36 (A), the scanning optical system, which is an optical system from the deflecting / reflecting surface of the polygon mirror to the surface to be scanned, is “enlarged system” (| S1b in the height direction). / S1a |> 1, for example, | S1b / S1a | = 3 to 10).

  On the other hand, in the case of oblique incidence, at least two scanning lenses in the scanning optical system are configured in order to suppress deterioration of optical performance such as bending of the scanning line on the surface to be scanned, field curvature, and wavefront aberration. There is a need. Therefore, as shown in FIG. 36B, the scanning optical system becomes a “reduction system” or “same magnification system” (about | S2b / S2a | ≦ 0.2 to 1.2) in the height direction. . Further, in order to make the beam spot diameter in the sub-scanning direction on the surface to be scanned the same as in the case of horizontal incidence, it is necessary to set θ2 = θ1. Further, in order to make the light amount of the beam spot on the scanned surface the same as in the case of horizontal incidence, the focal length F2 of the cylindrical lens in the case of oblique incidence is set to be larger than the focal length F1 of the cylindrical lens in the case of horizontal incidence. It is necessary to make it long (F2> F1). For example, when F1 = 50 [mm], it is necessary to set F2 = 150 [mm] or more. As a result, in the case of oblique incidence, the length of the optical path from the cylindrical lens to the deflecting / reflecting surface of the polygon mirror is longer than in the case of horizontal incidence, so the length of the optical path from the light source to the deflecting / reflecting surface is horizontal. Longer than. In this specification, the ratio (d / n) between the distance d traveled by the light beam and the refractive index n of the medium through which the light beam passes is referred to as “the length of the optical path” for convenience. For example, when a light beam travels a distance d1 in a medium having a refractive index n1 and travels a distance d2 in a medium having a refractive index n2, (d1 / n1) + (d2 / n2) is “the length of the optical path”. Become.

  Further, there is a great demand for further downsizing in a relatively small image forming apparatus such as A4 whose maximum output paper size is A4. Therefore, it is necessary to reduce the dimension of the optical scanning device in the image forming apparatus (particularly, the dimension in the direction of the rotation axis of the photosensitive drum in the depth direction). As an example, as shown in FIG. 37, when a large number of reflection mirrors are arranged on the optical path from the light source to the deflecting reflection surface and the optical path from the light source to the deflecting reflection surface is long by bending a large number of optical paths. However, an increase in the size of the optical scanning device can be suppressed. However, at this time, if the optical performance (surface accuracy and reflectance) of the reflecting surface of the reflecting mirror and the assembling accuracy of each reflecting mirror with respect to the optical housing are not good, the beam spot diameter and the scanning line bend on the surface to be scanned. The amount of light deteriorates. Therefore, it is desirable to reduce the number of reflection mirrors as much as possible.

  However, conventionally, when the light beam emitted from the light source is divided into two light beams and incident on the deflecting / reflecting surface obliquely, it has been difficult to achieve further miniaturization without degrading the optical performance. It was.

  From a first aspect, the present invention is an optical scanning device that individually scans a plurality of scanned surfaces with a light beam in a first direction, and the light source and the light beam emitted from the light source are An imaging optical system that collects light in a second direction orthogonal to the direction of the light, and a light beam that divides the light beam that has passed through the imaging optical system into a first light beam that is a transmitted light beam and a second light beam that is a reflected light beam A split member, a first reflection optical system disposed on the optical path of the first light flux from the light flux split member, and a second reflection optical system disposed on the optical path of the second light flux from the light flux split member And six deflecting reflecting surfaces rotating around an axis parallel to the second direction, the first light flux via the first reflecting optical system and the first light passing through the second reflecting optical system. The two light fluxes are inclined with respect to the plane perpendicular to the second direction on the deflecting / reflecting surfaces different from each other. An optical deflector that is incident from the direction and deflects each light beam, and a scanning optical system that guides each light beam deflected by the light deflector to a corresponding scanned surface, the first reflective optical system and Any one of the second reflection optical systems has at least two reflection mirrors, and the at least two reflection mirrors have a distance traveled by the light beam and the light beam with respect to the first light beam and the second light beam. In the optical scanning device, the ratio of the refractive index of the medium passing therethrough is equal to each other in the optical path from the light beam dividing member to the corresponding deflecting / reflecting surface.

  According to a second aspect of the present invention, there are provided a plurality of image carriers, and the optical scanning device of the present invention that scans the plurality of image carriers with a light beam modulated according to corresponding image information. An image forming apparatus provided.

  According to the optical scanning device of the present invention, cost reduction and size reduction can be achieved without degrading optical performance.

1 is a diagram illustrating a schematic configuration of a color printer according to an embodiment of the present invention. It is a figure for demonstrating schematic structure of the optical scanning device in FIG. It is a figure for demonstrating the arrangement state of two light sources, and the light beam inject | emitted from each light source. It is FIG. (1) for demonstrating the half mirror HM. It is FIG. (2) for demonstrating the half mirror HM. It is a figure for demonstrating the optical path of the light beam inject | emitted from 2200A of light sources. It is a figure for demonstrating the optical path of the light beam inject | emitted from the light source 2200B. FIG. 8A and FIG. 8B are diagrams for explaining oblique incidence. It is a figure for demonstrating a scanning optical system. It is a top view of an optical scanning device. It is a figure for demonstrating the example of arrangement | positioning of each optical element of the optical system before a deflector. It is a figure for demonstrating the holder which hold | maintains the reflective mirror M2 and the reflective mirror M3 integrally. FIGS. 13A and 13B are diagrams for explaining the relationship between the incident direction of the light beam to the polygon mirror and the angle of view. It is a figure for demonstrating the optical system before a deflector in the optical scanning device of the modification 1. FIG. It is FIG. (1) for demonstrating half mirror HM2. It is FIG. (2) for demonstrating half mirror HM2. It is a figure for demonstrating the optical system before a deflector in the optical scanning device of the modification 2. FIG. FIG. 18A and FIG. 18B are diagrams for explaining “lifting of the optical path”, respectively. It is a figure for demonstrating the light beam splitting member in the optical scanning device of the modification 2. It is a figure for demonstrating the optical system before a deflector in the optical scanning device of the modification 3. FIG. It is a figure for demonstrating the optical system before a deflector in the optical scanning device of the modification 4. FIG. It is a figure for demonstrating half mirror HM3. It is a figure for demonstrating the optical system before a deflector in the optical scanning device of the modification 5. FIG. It is a figure for demonstrating half mirror HM4. 6 is a diagram for explaining a pre-deflector optical system in the optical scanning device of Comparative Example 1. FIG. 6 is a plan view of an optical scanning device of Comparative Example 1. FIG. 6 is a diagram for explaining a pre-deflector optical system in an optical scanning device of Comparative Example 2. FIG. 10 is a plan view of an optical scanning device of Comparative Example 2. FIG. FIG. 10 is a diagram for explaining inconveniences in the optical scanning device of Comparative Example 2. It is a figure for demonstrating the case of the modification 1 with respect to the comparative example 2. FIG. FIG. 31A is a diagram for explaining an emission axis in a multi-beam light source used in the optical scanning device according to Modification 6. FIG. 31B shows two light emitting units in the multi-beam light source. It is a figure for demonstrating. It is a figure for demonstrating the attachment state of a multi-beam light source. It is a figure for demonstrating the optical path of the two light beams inject | emitted from the multi-beam light source. It is a figure for demonstrating the optical system before a deflector in the optical scanning device of the modification 7. FIG. FIG. 35A and FIG. 35B are diagrams for explaining a polygon mirror corresponding to two light beams separated in the sub-scanning direction. FIG. 36A and FIG. 36B are diagrams for explaining the difference in the optical system when the light beam is horizontally incident on the deflecting reflecting surface and when it is obliquely incident. It is a figure for demonstrating an example of a reflective optical system in case the length of the optical path from a light source to a polygon mirror is long.

  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 as an image forming apparatus 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 roller 2050, paper feed roller 2054, registration roller pair 2056, paper discharge roller 2058, paper feed tray 060, paper ejection tray 2070 includes a communication control unit 2080, and a printer controller 2090 for totally controlling the above elements.

  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 converter 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. Configure.

  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. Configure.

  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. Configure.

  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. Configure.

  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). Here, in the XYZ three-dimensional orthogonal coordinate system, the direction along the longitudinal direction (rotation axis direction) of each photosensitive drum is defined as the Y-axis direction, and the direction along the arrangement direction of the four photosensitive drums is defined as the X-axis direction. explain.

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

  The optical scanning device 2010 is charged with a light beam modulated for each color based on multi-color image information (black image information, cyan image information, magenta image information, yellow image information) from the host device. Each surface of the photosensitive drum is scanned. 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 roller as the photosensitive drum rotates. The configuration of the optical scanning device 2010 will be described later.

  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 color 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 paper on which the color image is transferred is sent to the fixing roller 2050.

  In the fixing roller 2050, heat and pressure are applied to the recording paper, whereby the toner is fixed on the recording paper. The recording paper on which the toner is fixed is sent to the paper discharge tray 2070 via the 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.

  Here, the optical scanning device 2010 will be described.

  As shown in FIG. 2 as an example, the optical scanning device 2010 includes two light sources (2200A and 2200B), two coupling lenses (2201A and 2201B), two cylindrical lenses (2202A and 2202B), a half mirror HM, It includes three reflecting mirrors (M1, M2, M3), a polygon mirror 2104, a scanning optical system A, a scanning optical system B, a scanning control device (not shown), and an optical housing in which these are housed.

  This optical housing has a dimension H1 in the X-axis direction of 400 mm, a dimension H2 in the Y-axis direction of 200 mm, and a dimension H3 in the Z-axis direction (see FIG. 9) of 50 mm.

  In the following, for convenience, the direction corresponding to the main scanning direction is abbreviated as “main scanning corresponding direction”, and the direction corresponding to the sub scanning direction is abbreviated as “sub scanning corresponding direction”.

  Each light source has a semiconductor laser (LD) or a surface emitting laser (VCSEL), and is driven and controlled by a scanning control device.

  The light source 2200A is disposed on the −Z side of the light source 2200B (see FIG. 3).

  The traveling direction of a light beam emitted from the light source 2200A (hereinafter referred to as “light beam LB1”) is the + Y direction when viewed from the Z-axis direction, and is inclined by an angle θa with respect to the XY plane when viewed from the X-axis direction. (See FIG. 3). Here, as an example, θa = −2.5 ° is set.

  The traveling direction of a light beam emitted from the light source 2200B (hereinafter referred to as “light beam LB2”) is the + Y direction when viewed from the Z-axis direction, and is inclined by an angle θb with respect to the XY plane when viewed from the X-axis direction. (See FIG. 3). Here, as an example, θb = + 2.5 ° is set.

  The coupling lens 2201A is disposed on the optical path of the light beam LB1 emitted from the light source 2200A, and makes the light beam a parallel light beam, a weak divergent light beam, or a weak convergent light beam according to the characteristics of the optical system thereafter.

  The coupling lens 2201B is disposed on the optical path of the light beam LB2 emitted from the light source 2200B, and makes the light beam a parallel light beam, a weak divergent light beam, or a weak convergent light beam according to the characteristics of the optical system thereafter.

  The cylindrical lens 2202A is disposed on the optical path of the light beam LB1 via the coupling lens 2201A, and converges the light beam in the Z-axis direction.

  The cylindrical lens 2202B is disposed on the optical path of the light beam LB2 via the coupling lens 2201B, and converges the light beam in the Z-axis direction.

  The focal length of each cylindrical lens is 150 mm.

  The half mirror HM is disposed on the optical path of the light beam LB1 via the cylindrical lens 2202A and the light beam LB2 via the cylindrical lens 2202B.

  As shown in FIG. 4 as an example, the half mirror HM has a multilayer film deposited on one surface of a transparent parallel plate such as glass or resin. The surface on which the multilayer film is deposited is a half mirror surface that divides an incident light beam into a transmitted light beam and a reflected light beam. The half mirror surface is set so that the ratio of the amount of transmitted light and the amount of reflected light is 1: 1. The setting of the half mirror surface is determined in accordance with the characteristics of the optical system arranged between the half mirror HM and the photosensitive drum so that the light amounts on the surfaces of the photosensitive drums are substantially equal. It may be different from the embodiment.

  The half mirror surface is formed so that an angle formed by the transmitted light beam and the reflected light beam (hereinafter also referred to as “separation angle”) is 90 °. Therefore, when viewed from the Z-axis direction, the light beam transmitted through the half mirror HM travels in the + Y direction, and the light beam reflected by the half mirror HM travels in the + X direction.

  Here, the light beam LB1 reflected by the half mirror HM is referred to as a light beam LBa, and the light beam LB1 transmitted through the half mirror HM is referred to as a light beam LBd (see FIG. 5). The light beam LB2 reflected by the half mirror HM is referred to as a light beam LBb, and the light beam LB2 transmitted through the half mirror HM is referred to as a light beam LBc (see FIG. 5).

  As an example, as shown in FIGS. 6 and 7, the reflection mirror M1 is on the optical path of the light beam LBa and the light beam LBb reflected by the half mirror HM, and is + X higher than the rotation center of the polygon mirror 2014 in the X-axis direction. Arranged on the side. The reflection mirror M1 reflects the light beam LBa and the light beam LBb reflected by the half mirror HM in the −Y direction. The light beam LBa and the light beam LBb reflected by the reflection mirror M1 are incident on the same deflection reflection surface located on the + X side of the rotation center of the polygon mirror 2014.

  The light beam LBa and the light beam LBb are imaged in the Z-axis direction in the vicinity of the deflection reflection surface.

  Furthermore, if the scanning optical system is designed so that the deflection reflection surface and the surface to be scanned (the surface of the photosensitive drum) have a conjugate relationship in the sub-scanning corresponding direction (here, the same as the Z-axis direction), the deflection reflection surface It is possible to reduce the amount of occurrence of scanning line pitch unevenness due to “surface tilt”.

  The reflection mirror M2 is disposed on the optical path of the light beam LBc and the light beam LBd transmitted through the half mirror HM, and reflects the light beam LBc and the light beam LBd in the + X direction.

  The reflection mirror M3 is disposed on the −X side of the rotation center of the polygon mirror 2014 in the X axis direction on the optical path of the light beam LBa and the light beam LBb reflected by the reflection mirror M2. The reflection mirror M3 reflects the light beam LBa and the light beam LBb reflected by the reflection mirror M2 in the -Y direction. The light beam LBc and the light beam LBd reflected by the reflection mirror M3 are incident on the same deflecting and reflecting surface located on the −X side of the rotation center of the polygon mirror 2014.

  The light beam LBc and the light beam LBd are imaged in the Z-axis direction in the vicinity of the deflection reflection surface.

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

  The polygon mirror 2104 has a single-stage rotating hexahedral mirror, and each mirror surface serves as a deflection reflection surface. The rotating hexagonal mirror rotates at a constant speed around a central axis parallel to the Z-axis direction, and deflects the incident light flux at a constant angular velocity.

  The light beam LBa is incident on the deflecting / reflecting surface from a direction inclined by an angle θa with respect to the XY plane including the incident position, and the light beam LBb is deflected from a direction inclined by the angle θb with respect to the XY surface including the incident position. It is set to be incident on the reflecting surface (see FIG. 8A).

  The light beam LBc is incident on the deflecting / reflecting surface from a direction inclined by an angle θb with respect to the XY plane including the incident position, and the light beam LBd is deflected from a direction inclined by the angle θa with respect to the XY surface including the incident position. It is set so as to be incident on the reflecting surface (see FIG. 8B).

  Hereinafter, when the light beam enters the deflecting / reflecting surface, it is referred to as “oblique incidence” to be incident from a direction inclined with respect to the surface orthogonal to the rotation axis, and the direction parallel to the surface orthogonal to the rotation axis. Incident from the side is called “horizontal incidence”.

  Each light beam incident on the deflecting / reflecting surface is reflected in a direction inclined with respect to the surface orthogonal to the rotation axis.

  As shown in FIG. 9 and FIG. 10 as an example, the scanning optical system A is arranged on the + X side of the polygon mirror 2104, and includes a first scanning lens 2105A, five folding mirrors (2106a, 2106b, 2107a, 2107b, 2108b). ) Two second scanning lenses (2109a, 2109b).

  The light beam LBa deflected by the polygon mirror 2104 is condensed on the surface of the photosensitive drum 2030a via the first scanning lens 2105A, the folding mirror 2106a, the second scanning lens 2109a, and the folding mirror 2107a.

  The light beam LBb deflected by the polygon mirror 2104 is condensed on the surface of the photosensitive drum 2030b via the first scanning lens 2105A, the folding mirror 2106b, the folding mirror 2107b, the second scanning lens 2109b, and the folding mirror 2108b. .

  The first scanning lens 2105A is shared by the two stations.

  As shown in FIG. 9 and FIG. 10 as an example, the scanning optical system B is disposed on the −X side of the polygon mirror 2104, and includes a first scanning lens 2105B, five folding mirrors (2106c, 2106d, 2107c, 2107d, 2108c) having two second scanning lenses (2109c, 2109d).

  The light beam LBc deflected by the polygon mirror 2104 is condensed on the surface of the photosensitive drum 2030c via the first scanning lens 2105B, the folding mirror 2106c, the folding mirror 2107c, the second scanning lens 2109c, and the folding mirror 2108c. .

  The light beam LBd deflected by the polygon mirror 2104 is condensed on the surface of the photosensitive drum 2030d via the first scanning lens 2105B, the folding mirror 2106d, the second scanning lens 2109d, and the folding mirror 2107d.

  The first scanning lens 2105B is shared by the two stations.

  The light spot on each photoconductor drum moves in the longitudinal direction of each photoconductor drum (rotation axis direction, here, the same as the Y-axis direction) as the polygon mirror 2104 rotates. The moving direction of the light spot on each photosensitive drum is the “main scanning direction”, and the rotating direction of each photosensitive drum is the “sub-scanning direction”.

  Here, writing scanning on the photosensitive drum 2030a and the photosensitive drum 2030d is alternately performed in a time division manner. Similarly, writing scanning on the photosensitive drum 2030b and the photosensitive drum 2030c is alternately performed in a time division manner.

  FIG. 11 shows a specific arrangement example of each optical element in the pre-deflector optical system of the present embodiment. The polygon mirror 2104 has six deflecting reflecting surfaces, and the distance between the opposing deflecting reflecting surfaces is 26 mm.

  Hereinafter, for the sake of convenience, the deflection reflection surface on which the light beams LBa and LBb are incident will be referred to as a deflection reflection surface 1, and the deflection reflection surface on which the light beams LBc and LBd will be incident is referred to as a deflection reflection surface 2.

  The distance in the X-axis direction between the light beam (light beam LBa and light beam LBb) incident on the deflection reflection surface 1 and the light beam (light beam LBc and light beam LBd) incident on the deflection reflection surface 2 is 20 mm.

  When the light beam is obliquely incident on the deflecting / reflecting surface, if the distance between the deflecting / reflecting surface and the rotation axis in the polygon mirror 2104 differs depending on the deflecting / reflecting surface, the interval of the scanning lines on the surface of the photosensitive drum varies ( Scan line pitch unevenness occurs. In the case of a polygon mirror in which the distance between the opposing deflecting reflecting surfaces is 26 mm, the unevenness of the scanning line pitch can be minimized by setting the distance between the two incident light beams to 20 mm.

  The focal length of each cylindrical lens is 150 mm. The distance from the exit surface (strictly speaking, the rear principal point) to the half mirror surface is 70 mm. The distance from the half mirror surface to the reflecting surface of the reflecting mirror M1 is 40 mm, and the distance from the reflecting surface of the reflecting mirror M1 to the deflecting reflecting surface 1 is 40 mm. Therefore, the length of the optical path from each cylindrical lens to the deflecting reflection surface 1 is 150 mm.

  Further, the distance from the half mirror surface to the reflection surface of the reflection mirror M2 is 10 mm, the reflection surface of the reflection mirror M2 to the reflection surface of the reflection mirror M3 is 20 mm, and the distance from the reflection surface of the reflection mirror M3 to the deflection reflection surface 2 is 50 mm. Therefore, the length of the optical path from each cylindrical lens to the deflecting / reflecting surface 2 is 150 mm.

  By the way, in the polygon mirror 2104, with the rotation of the hexagonal mirror, the angle of the deflection reflection surface with respect to the incident light beam changes, and the incident position of the incident light beam changes. Therefore, the length of the optical path from each cylindrical lens to the deflecting / reflecting surface 1 and the length of the optical path from each cylindrical lens to the deflecting / reflecting surface 2 also vary as the hexahedral mirror rotates. Therefore, although the length of the optical path is not a strict value, the magnitude of the fluctuation is small. Therefore, in this specification, the length of the optical path is described as assuming that there is no fluctuation for convenience.

  That is, the lengths of the optical paths from the half mirror surface to the deflecting / reflecting surface of the light beams LBa and LBd are the same. Thereby, even if the cylindrical lens 2202A is arranged on the optical path of the light beam LB1 between the light source 2200A and the half mirror HM, the light beam LBa and the light beam LBd can be similarly imaged in the vicinity of the deflection reflection surface.

  The lengths of the optical paths of the light beam LBb and the light beam LBc from the cylindrical lens 2202B to the deflecting / reflecting surface are the same. Thereby, even if the cylindrical lens 2202B is disposed on the optical path of the light beam LB2 between the light source 2200B and the half mirror HM, the light beam LBb and the light beam LBc can be similarly imaged in the vicinity of the deflection reflection surface.

  Thus, the reflection mirror M2 and the reflection mirror M3 are arranged so that the length of the optical path of the light beam transmitted through the half mirror HM is the same as the length of the optical path of the light beam reflected by the half mirror HM.

  As shown in FIG. 12 as an example, the reflection mirror M2 and the reflection mirror M3 are held by the holder member 10 so that their normal lines are orthogonal to each other, and form a so-called “dach mirror”. In this case, even if there is an error in the assembly posture of the roof mirror, the traveling direction of the light beam incident on the reflecting mirror M2 and the traveling direction of the light beam reflected by the reflecting mirror M3 are always maintained in a parallel relationship.

  In the present embodiment, the outer size of the optical housing can be reduced to 400 mm (X-axis direction) × 200 (Y-axis direction) × 50 mm (Z-axis direction). Thereby, weight reduction and cost reduction can be achieved. Further, as the size is reduced, the natural frequency increases and the vibration amplitude decreases, which is advantageous in terms of vibration resistance.

  When the number of deflecting reflecting surfaces in the polygon mirror is six, the angle formed by the incident direction of the light beam incident on the deflecting reflecting surface and the X axis direction when viewed from the Z axis direction (denoted as “angle φ”). Is preferably 90 ° or 30 °. When the angle φ is other than 90 ° or 30 °, the maximum possible field angle in the scanning optical system A and the maximum possible field angle in the scanning optical system B are not the same. Therefore, it is necessary to match the smaller maximum angle of view, and the width of an image that can be formed is reduced. Further, as shown in FIGS. 13A and 13B, the angle of view can be made wider when the angle φ = 90 ° than when the angle φ = 30 ° (ω1> ω2). Therefore, this is a more preferable configuration.

  From the above, it is preferable that the incident direction of each light beam incident on the deflecting / reflecting surface is parallel to the Y-axis when viewed from the Z-axis direction.

  Next, some modified examples and comparative examples of the pre-deflector optical system will be described. In the following description, differences from the above-described embodiment will be mainly described, and the same or equivalent components as those in the above-described embodiment will be denoted by the same reference numerals, and the description thereof will be simplified or omitted.

<< Modification 1 >>
In Modification 1, as shown in FIG. 14, a half mirror HM2 is used instead of the half mirror HM. As shown in FIGS. 15 and 16 as an example, the half mirror HM2 is a member in which two triangular prisms are joined, and splits an incident light beam into a transmitted light beam and a reflected light beam at the joint portion. It has a half mirror surface.

  Further, a polarizing beam splitter may be used in place of the half mirror HM.

<< Modification 2 >>
In the second modification, as shown in FIG. 17, a light beam splitting member 2203 that splits an incident light beam into two parallel light beams is used instead of the half mirror HM and the reflection mirror M2. The light beam splitting member 2203 is arranged in parallel to the half mirror surface on the optical path of the light beam transmitted through the half mirror surface, and a half mirror surface that transmits a part of the incident light beam and reflects the rest in the + X direction. And a total reflection mirror surface.

  By the way, as shown in FIG. 18A, the light beam incident on the cylindrical lens is converged in the sub-scanning corresponding direction by the action of the cylindrical lens, and forms an image near the deflecting reflection surface.

  Next, as shown in FIG. 18B, consider a case where a parallel plate glass having a thickness d and a refractive index n is arranged in the optical path between the cylindrical lens and the deflecting reflecting surface. At this time, since the optical path in the parallel plate glass “floats”, it is necessary to move the cylindrical lens away from the deflecting / reflecting surface by a distance (1-1 / n) d in order to form an image of the light flux near the deflecting / reflecting surface. is there.

  In the second modification, the light beam LBa forms an image near the deflecting / reflecting surface 1 by the action of the cylindrical lens 2202A. At this time, in order to image the light beam LBd in the vicinity of the deflecting / reflecting surface 2 by the action of the cylindrical lens 2202A, in consideration of the “lift” of the optical path in the light beam splitting member 2203, in FIG. 19, d1 / n + d2 + d3 = 40 mm. There is a need to. Here, since d2 = 20 mm and d3 = d1, the following equation (1) is obtained.

  Here, the refractive index n is 1.51, and d1 = 12.03 mm.

  In this case, a polarization separation surface may be used instead of the half mirror surface.

<< Modification 3 >>
In Modification 3, as shown in FIG. 20, each light source emits a light beam in the + X direction when viewed from the Z-axis direction. The half mirror HM is disposed on the −X side with respect to the reflection mirror M3 in the X-axis direction.

<< Modification 4 >>
In Modification 4, as shown in FIG. 21, a half mirror HM3 is used instead of the half mirror HM. As shown in FIG. 22, the half mirror HM3 has a multilayer film deposited on one side of a parallel plate so that the separation angle is 60 °. Even in this case, by adjusting the positions of the reflecting mirror M2 and the reflecting mirror M3, the length of the optical path of the light beam from the cylindrical lens to the deflecting reflecting surface 1 and the light beam from the cylindrical lens to the deflecting reflecting surface 2 are adjusted. The length of the optical path can be set to 150 mm as in the above embodiment. By the way, in a half mirror in which one side of a parallel plate is a half mirror surface, a multilayer film can be formed relatively easily if the separation angle is about 40 ° to 60 °. Therefore, in this case, the cost of the half mirror can be reduced as compared with the above embodiment.

<< Modification 5 >>
In Modification 5, as shown in FIG. 23, a half mirror HM4 is used instead of the half mirror HM. As shown in FIG. 24, the half mirror HM4 has a multilayer film deposited on one side of the parallel plate so that the separation angle is 50 °. In this case, each light source emits a light beam in a direction inclined by 10 ° with respect to the Y-axis direction when viewed from the Z-axis direction. In this case, the cost of the half mirror can be further reduced as compared with the above embodiment.

<< Comparative Example 1 >>
In Comparative Example 1, as shown in FIG. 25, each light source is arranged at the end on the + Y side and emits a light beam in the −Y direction when viewed from the Z-axis direction. Also in this comparative example 1, the length of the optical path of the light beam from the cylindrical lens to the deflecting / reflecting surface 1 and the length of the optical path of the light beam from the cylindrical lens to the deflecting / reflecting surface 2 are both 150 mm as in the above embodiment. It is. However, in the case of the comparative example 1, as shown in FIG. 26, the dimension in the Y-axis direction in the outer size of the optical housing is larger than that in the above embodiment.

<< Comparative Example 2 >>
In Comparative Example 2, as shown in FIG. 27, each light source is arranged at the end on the −X side and emits a light beam in the + X direction when viewed from the Z-axis direction. The half mirror HM2 is disposed on the + X side with respect to the reflection mirror M3 in the X-axis direction. Also in Comparative Example 2, the length of the optical path of the light beam from the cylindrical lens to the deflecting / reflecting surface 1 and the length of the optical path of the light beam from the cylindrical lens to the deflecting / reflecting surface 2 are both 150 mm as in the above embodiment. is there. As shown in FIG. 28, the outer size of the optical housing can be reduced to 400 mm (X-axis direction) × 200 (Y-axis direction) × 50 mm (Z-axis direction) as in the above embodiment. Is possible.

  By the way, each reflecting mirror is attached to the optical housing by a positioning member. In order to set the beam spot diameter on the surface to be scanned to a predetermined value (for example, about 50 μm to 70 μm), considering the length of the optical path in the scanning optical system, the focal length in the main scanning corresponding direction, etc., the half mirror HM2 The width of the light beam with respect to the direction corresponding to the main scanning of the light beam incident on is 4 mm.

  In this case, in Comparative Example 2, as shown in FIG. 29 as an example, the positioning member may interfere with a part of the light beam. On the other hand, in the second modification, as shown in FIG. 30 as an example, the positioning member does not interfere with the light flux.

  By the way, the price of the half mirror HM2 increases as the outer size increases. Therefore, it is desired that the half mirror HM2 be as small as possible (for example, a dimension of about +2 mm with respect to the light flux width). In this case, since it is difficult to bring the half mirror HM2 into contact with the positioning reference, the position of the half mirror HM2 is adjusted according to the optical path of the light beam, and then fixed to the optical housing by bonding or the like.

<< Modification 6 >>
In the modified example 6, each light source passes through the center of the light source as shown in FIG. 31A as an example, and the direction orthogonal to the exit surface is the exit axis, and as shown in FIG. 31B as an example. And has two light emitting portions formed monolithically. That is, each light source has a so-called two-channel (2ch) multi-beam semiconductor laser. Here, as an example, the distance D between the centers of the two light emitting units is 50 μm.

  Further, as shown in FIG. 32 as an example, each light source is attached to the optical housing in a state where it is rotated by an angle γ around the emission axis so that the interval between the light emitting portions in the Z-axis direction is D · sin γ. Yes. Here, the “light emitting portion interval” refers to the distance between the centers of the two light emitting portions.

  As an example, as shown in FIG. 33, two light beams emitted from the light source 2200A are a light beam LB1-1 and a light beam LB1-2. The light beam LB1-1 reflected by the half mirror HM is defined as a light beam LB1-1a, and the light beam LB1-1 transmitted through the half mirror HM is defined as a light beam LB1-1d. Furthermore, the light beam LB1-2 reflected by the half mirror HM is referred to as a light beam LB1-2a, and the light beam LB1-2 transmitted through the half mirror HM is referred to as a light beam LB1-2d.

  The light beam LB1-1a and the light beam LB1-2a are reflected by the reflection mirror M1, then deflected and reflected to the + X side by the deflection reflection surface 1, and reach the photosensitive drum 2030a via the scanning optical system. The light beam LB1-1d and the light beam LB1-2d are reflected by the reflecting mirror M2 and the reflecting mirror M3, then deflected and reflected to the −X side by the deflecting / reflecting surface 2, and reach the photosensitive drum 2030d via the scanning optical system. .

  Since the polygon mirror 2104 rotates clockwise, the photosensitive drum 2030a performs optical scanning in the −Y direction, and the photosensitive drum 2030d performs optical scanning in the + Y direction.

  The light beam LB1-1a and the light beam LB1-2a are reflected a total of two times by the half mirror HM and the reflection mirror M1. The light beam LB1-1d and the light beam LB1-2d are reflected a total of two times by the reflection mirror M2 and the reflection mirror M3. That is, in the optical path from the light emitting unit to the deflecting / reflecting surface, the difference between the number of times the light beam is incident on the deflecting / reflecting surface 1 and the number of times the light beam is incident on the deflecting / reflecting surface 2 is an even number (here, 0) . Therefore, in both the photosensitive drum 2030a and the photosensitive drum 2030d, the luminous flux obtained by dividing the luminous flux LB1-1 (the luminous flux LB1-1a and the luminous flux LB1-1d) becomes a “preceding beam” in the optical scanning, and the luminous flux LB1- A light beam (light beam LB1-2a and light beam LB1-2d) obtained by dividing 2 becomes a “following beam” in optical scanning. The same applies to two light beams emitted from the light source 2200B (referred to as a light beam LB2-1 and a light beam LB2-2).

  In this case, there are the following advantages.

(1) After a “synchronization signal” for determining the write start timing is detected by a synchronization detection sensor (not shown), the time until the start of writing (delay time) can be shared by all the photosensitive drums. .

(2) For the photosensitive drum 2030a and the photosensitive drum 2030d, the synchronization signal can be detected with the same light beam LB1-1. Further, the synchronization signal can be detected by the same light beam LB2-1 for the photosensitive drum 2030b and the photosensitive drum 2030c.

  Therefore, the control procedure and the control circuit can be simplified. The same applies when an LD array having three or more light emitting portions is used.

<< Modification 7 >>
In the modified example 7, as shown in FIG. 34 as an example, the light beam reflected by the half mirror HM4 is incident on the deflecting / reflecting surface via two reflection mirrors, and the light beam transmitted through the half mirror HM4 is one sheet. The light is incident on the deflecting reflecting surface through the reflecting mirror. That is, between the half mirror HM4 and the polygon mirror 2104, the number of reflecting mirrors arranged on the optical path of the light beam reflected by the half mirror HM4 and the reflection arranged on the optical path of the light beam transmitted through the half mirror HM4. The difference from the number of mirrors is an odd number. From the viewpoint of the number of times of reflection, the difference in the number of reflections of two light beams incident on different deflection reflection surfaces is an even number (here, twice).

  As described above, according to the optical scanning device 2010 according to the present embodiment, the two light sources (2200A, 2200B), the pre-deflector optical system, the polygon mirror 2104, the scanning optical system A, the scanning optical system B, and the scanning control. Equipment.

  The pre-deflector optical system includes two coupling lenses (2201A, 2201B), two cylindrical lenses (2202A, 2202B), a half mirror HM, and three reflection mirrors (M1, M2, M3).

  The half mirror HM divides a light beam emitted from each light source and passing through a corresponding coupling lens into a transmitted light beam and a reflected light beam.

  The reflection mirror M1 is disposed on the optical path of each light beam reflected by the half mirror HM, and guides each light beam to the deflecting reflection surface 1. The reflection mirror M2 is disposed on the optical path of each light beam that has passed through the half mirror HM, and bends the traveling direction of each light beam. The reflection mirror M3 is disposed on the optical path of each light beam reflected by the reflection mirror M2, and guides each light beam to the deflecting reflection surface 2. In addition, the arrangement positions of the reflection mirror M2 and the reflection mirror M3 are adjusted so that the lengths of the optical paths from the light sources of the plurality of light beams incident on the respective deflection reflection surfaces are the same.

  Therefore, according to the optical scanning device 2010, it is possible to reduce the cost and the size without reducing the optical performance.

  It should be noted that the length of the optical path from the light source of the plurality of light beams incident on each deflecting reflection surface may be slightly shifted within a range that does not affect the image quality.

  Further, according to the color printer 2000 according to the present embodiment, since the optical scanning device 2010 is provided, it is possible to reduce the cost and the size without reducing the image quality.

  In the above embodiment, the case where the image forming apparatus is a color printer in which a toner image is transferred from a photosensitive drum to a recording sheet via a transfer belt has been described. However, the present invention is not limited to this. It may be a color printer that is directly transferred to the printer.

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

  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 the image forming apparatus includes the optical scanning device 2010, the cost and size can be reduced without degrading the image quality.

  DESCRIPTION OF SYMBOLS 10 ... Holder, 2000 ... Color printer (image forming apparatus), 2010 ... Optical scanning device, 2030a-2030d ... Photosensitive drum (image carrier), 2104 ... Polygon mirror (optical deflector), 2105A, 2105B ... First scanning Lens (part of the scanning optical system), 2106a to 2106d ... Folding mirror (part of the scanning optical system), 2108b, 2108c ... Folding mirror (part of the scanning optical system), 2107a to 2107d ... Folding mirror (scanning optical system) 2109a to 2109d ... second scanning lens (part of scanning optical system), 2200A, 2200B ... light source, 2201A, 2201B ... coupling lens, 2202A, 2202B ... cylindrical lens, 2203 ... beam splitting member, HM ... Half mirror (beam splitting member), HM2 to HM4 ... H Mirror (light flux splitting member), M1 ... reflecting mirror, M2 ... reflecting mirror, M3 ... reflecting mirror.

JP 2008-257169 A JP 2003-005114 A

Claims (10)

An optical scanning device that individually scans a plurality of scanned surfaces with a light beam in a first direction,
A light source;
An imaging optical system for condensing the light beam emitted from the light source in a second direction orthogonal to the first direction;
A light beam splitting member that splits the light beam that has passed through the imaging optical system into a first light beam that is a transmitted light beam and a second light beam that is a reflected light beam;
A first reflective optical system disposed on an optical path of the first light flux from the light flux splitting member;
A second reflective optical system disposed on the optical path of the second light flux from the light flux splitting member;
The first light flux via the first reflective optical system and the second light flux via the second reflective optical system having six deflecting reflective surfaces rotating about an axis parallel to the second direction An optical deflector that is incident on a different deflecting reflecting surface from a direction inclined with respect to a surface orthogonal to the second direction, and deflects each light beam;
A scanning optical system that guides each light beam deflected by the optical deflector to a corresponding scanned surface, and
Either of the first reflection optical system and the second reflection optical system has at least two reflection mirrors, and the at least two reflection mirrors have a light flux for the first light flux and the second light flux. An optical scanning device in which a ratio of a traveling distance and a refractive index of a medium through which the light beam passes is equal to each other in an optical path from the light beam dividing member to a corresponding deflecting reflection surface.   A reflection mirror that reflects the first light flux in a direction toward the deflecting reflection surface in the first reflection optical system with respect to a third direction orthogonal to both the first direction and the second direction; 2. The optical scanning device according to claim 1, wherein another reflecting mirror is not disposed between the reflecting mirror that reflects the second light beam in a direction toward the deflecting reflecting surface in the two-reflection optical system. .   The first light flux through the first reflective optical system and the second light flux through the second reflective optical system are each viewed from a direction parallel to the first direction when viewed from the second direction. 3. The optical scanning device according to claim 1, wherein the optical scanning device is incident on a deflecting reflection surface.   When viewed from the second direction, the traveling direction of the light beam emitted from the light source is different from the traveling directions of the first light beam and the second light beam incident on the deflection reflection surface by 180 °. The optical scanning device according to claim 3. The light source is a first light source, and a second light source disposed at a position different from the first light source in the second direction,
The light beam splitting member splits a light beam emitted from the second light source into a third light beam that is a transmitted light beam and a fourth light beam that is a reflected light beam,
The third light beam is incident on the different deflecting reflection surfaces through the first reflection optical system, and the fourth light beam is incident on the different deflection reflection surfaces through the second reflection optical system. The optical scanning device according to any one of claims.   The first light flux, the third light flux, and the second light flux and the fourth light flux are incident on the deflecting / reflecting surface from directions inclined in directions opposite to each other with respect to the surface orthogonal to the second direction. The optical scanning device according to claim 5.   7. The difference between the number of reflection mirrors included in the first reflection optical system and the number of reflection mirrors included in the second reflection optical system is an odd number. The optical scanning device according to Item.   The at least two reflecting mirrors are two reflecting mirrors, and are integrated so that the normal lines of the reflecting surfaces of the reflecting mirrors are orthogonal to each other. The optical scanning device according to one item. The first reflection optical system has two reflection mirrors, the second reflection optical system has one reflection mirror,
9. The optical scanning device according to claim 1, wherein the two reflection mirrors of the first reflection optical system are the at least two reflection mirrors. 10. 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 scanned with light beams modulated according to corresponding image information.

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