JP2015004714A - Optical scanner and image forming apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a more compact and high-speed optical scanner without reducing image quality.SOLUTION: In detecting synchronization by means of a synchronization detection sensor 2115B, a light flux which has been emitted from a light source 2200B and has not started scanning is made incident on a surface 1 of a rotary polygon mirror and a surface 6 adjacent to the surface 1 simultaneously. The light flux reflected by the surface 1 is received by the synchronization detection sensor 2115B. In orthogonal projection on a plane orthogonal to a Z-axis, an angle formed by a traveling direction of adjacent surface ghost light, which is a light flux reflected by the surface 6, and a reference axis direction is set to be smaller than an angle formed by an incident direction of the light flux emitted from the light source 2200B and made incident on the rotary polygon mirror and the reference axis direction.

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 recording, an image forming apparatus using a laser is widely used. Generally, this image forming apparatus scans the surface of a photosensitive drum (hereinafter also referred to as “photosensitive drum”) with a laser beam, and forms light on the surface of the photosensitive drum. A scanning device is provided.

  The optical scanning device includes a light source, a pre-deflector optical system, a rotary polygon mirror, and a scanning optical system. The laser light emitted from the light source enters the rotary polygon mirror via the pre-deflector optical system, is deflected by the reflecting surface of the rotary polygon mirror, and is then guided to the photosensitive drum via the scanning optical system. . The reflection surface of the rotary polygon mirror is also called a “deflection reflection surface”.

  There are an underfilled type and an overfilled type as a method of making laser light enter the rotary polygon mirror. Hereinafter, for convenience, the underfilled type is also referred to as “UF type” and the overfilled type is also referred to as “OF type”.

  In the UF type, the width of incident light is smaller than the length of the deflecting / reflecting surface in the direction corresponding to the main scanning direction (see, for example, Patent Document 1). In this case, all of the incident light is guided to the photosensitive drum.

  In the OF type, the width of incident light is larger than the length of the deflection reflection surface in the direction corresponding to the main scanning direction (see, for example, Patent Document 2). In this case, ambient light in the incident light is not guided to the photosensitive drum.

  In recent years, there has been an increasing demand for further downsizing and speeding up of image formation for image forming apparatuses. Therefore, further downsizing and speeding up of the optical scanning device are required.

  However, in the conventional optical scanning device, it has been difficult to further reduce the size and speed without causing deterioration in image quality.

  The present invention provides an optical scanning device that scans a scanning region of a surface to be scanned along a main scanning direction with a light beam emitted from a light source and reflected by a rotating polygon mirror having a plurality of reflecting surfaces. A light receiving device in which a light beam before scanning is simultaneously incident on a reflection surface and a second reflection surface adjacent to the first reflection surface, and a light beam reflected by the first reflection surface is incident; When orthogonally projected onto a plane orthogonal to the rotation axis, the angle formed by the traveling direction of the light beam reflected by the first reflecting surface and the incident direction of the light beam incident on the rotating polygon mirror is reflected by the rotating polygon mirror. The traveling direction of the light beam reflected by the second reflecting surface is greater than the angle formed by the traveling direction of the light beam toward the scanning area and the incident direction of the light beam incident on the rotating polygon mirror, and is incident on the rotating polygon mirror. Than the incident direction of the luminous flux An optical scanning device, characterized in that the angle with respect to the axial direction perpendicular to the direction small.

  According to the optical scanning device of the present invention, it is possible to further reduce the size and increase the speed without degrading the image quality.

1 is a diagram for explaining a schematic configuration of a multifunction peripheral according to an embodiment of the present invention. FIG. FIG. 2 is a diagram (part 1) for explaining the configuration of the optical scanning device in FIG. 1; FIG. 3 is a second diagram for explaining the configuration of the optical scanning device in FIG. 1; FIG. 3 is a third diagram for explaining the configuration of the optical scanning device in FIG. 1; FIG. 4 is a fourth diagram for explaining the configuration of the optical scanning device in FIG. 1; It is a figure for demonstrating the scanning start position and scanning end position in a scanning area | region. It is a figure for demonstrating angle (theta) in which the advancing direction (incident direction) of the light beam which injects into an optical deflector, and a reference axis direction make. It is a figure for demonstrating the light beam width din of the light beam which injects into an optical deflector. It is a figure for demonstrating the inscribed circle of a rotary polygon mirror. It is a figure for demonstrating the incident light beam and synchronous light beam Ld with respect to a rotating polygon mirror in the timing which the light beam inject | emitted from the light source 2200B and deflected with the optical deflector heads to the synchronous detection sensor 2115B. It is a figure for demonstrating the incident light beam and reflected light beam with respect to a rotary polygon mirror in the timing which the light beam inject | emitted from the light source 2200B and deflected with the optical deflector heads to the scanning start position in the scanning area | region of a photosensitive drum. . It is a figure for demonstrating the incident light beam and reflected light beam with respect to a rotary polygon mirror in the timing which the light beam inject | emitted from the light source 2200B and deflected with the optical deflector heads to the center position of the scanning area | region of a photosensitive drum. It is a figure for demonstrating the incident light beam and reflected light beam with respect to a rotary polygon mirror in the timing which the light beam inject | emitted from the light source 2200B and deflected with the optical deflector heads to the scanning end position in the scanning area | region of a photosensitive drum. . It is a figure for demonstrating a scanning angle of view. It is a figure for demonstrating the relationship between | (theta) in | + | (theta) BD | and the surface number N of a rotary polygon mirror. FIG. 16A to FIG. 16C are diagrams for explaining the first specific example. FIG. 17A to FIG. 17C are diagrams for explaining the comparative example 1, respectively. The traveling direction of the adjacent surface ghost light and the incident direction of the light beam incident on the optical deflector 2104 at the timing at which the light beam before the start of scanning emitted from the light source 2200B and deflected by the optical deflector 2104 is received by the synchronization detection sensor 2115B. It is a figure for demonstrating the relationship between a scanning area | region. It is a figure for demonstrating the incident light beam and the synchronous light beam La with respect to a rotating polygon mirror in the timing which the light beam inject | emitted from the light source 2200A and deflected with the optical deflector heads to the synchronous detection sensor 2115A. It is a figure for demonstrating the incident light beam and reflected light beam with respect to a rotary polygon mirror in the timing which the light beam inject | emitted from 2200A and deflected with the optical deflector heads to the scanning start position in the scanning area | region of a photosensitive drum. . It is a figure for demonstrating the incident light beam and reflected light beam with respect to a rotary polygon mirror in the timing which the light beam inject | emitted from 2200A and deflected with the optical deflector heads to the center position of the scanning area | region of a photosensitive drum. It is a figure for demonstrating the incident light beam and reflected light beam with respect to a rotating polygon mirror in the timing which the light beam inject | emitted from 2200A and deflected with the optical deflector heads to the scanning end position in the scanning area | region of a photosensitive drum. . The traveling direction of the adjacent surface ghost light and the incident direction of the light beam incident on the optical deflector 2104 at the timing when the light beam emitted from the light source 2200A and deflected by the optical deflector 2104 is received by the synchronization detection sensor 2115A. It is a figure for demonstrating the relationship between a scanning area | region. 24A to 24C are diagrams for explaining the specific example 2. FIG. FIG. 25A to FIG. 25C are diagrams for explaining the comparative example 2. FIG.

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

  The multifunction machine 2000 has functions of a copying machine, a printer, and a facsimile machine, and includes a main body device 1001, a reading device 1002, an automatic document feeder 1003, and the like.

  The main body device 1001 is a tandem multicolor printer that forms a full-color image by superimposing four colors (black, cyan, magenta, and yellow), and includes an optical scanning device 2010 and four photosensitive drums (2030a and 2030b). , 2030c, 2030d), four cleaning units (2031a, 2031b, 2031c, 2031d), four charging devices (2032a, 2032b, 2032c, 2032d), four developing rollers (2033a, 2033b, 2033c, 2033d), intermediate transfer A belt 2040, a transfer roller 2042, a fixing roller 2050, a paper feed roller 2054, a paper discharge roller 2058, a paper feed tray 2060, a paper discharge tray 2070, a communication control device 2080, and a printer control device 2090 that comprehensively controls the above components. It is equipped with a.

  The reading device 1002 is disposed on the upper side of the main body device 1001 and reads a document. That is, the reading device 1002 is a so-called scanner device. The image information of the document read here is sent to the printer control device 2090 of the main body device 1001.

  The automatic document feeder 1003 is disposed on the upper side of the reading device 1002 and sends out the set document toward the reading device 1002. This automatic document feeder 1003 is generally called an ADF (Auto Document Feeder).

  The communication control device 2080 controls bidirectional communication with a host device (for example, a personal computer) via a network and the like, and bidirectional communication with other devices via a public line.

  The printer control device 2090 includes a CPU, a program written in a code decipherable by the CPU, a ROM storing various data used when executing the program, a RAM as a working memory, an analog signal An A / D conversion circuit for converting the signal into a digital signal. Then, the printer control device 2090 sends image information from the reading device 1002 or image information via the communication control device 2080 to the optical scanning device 2010.

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

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

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

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

  Each photosensitive drum has a photosensitive layer formed on the surface thereof. 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.

  The optical scanning device 2010 is charged correspondingly by light modulated for each color based on multi-color image information (black image information, cyan image information, magenta image information, yellow image information) from the printer control device 2090. Each surface of the photosensitive drum is scanned. Thereby, a latent image corresponding to the image information is formed on the surface of each photosensitive drum. That is, here, the surface of each photosensitive drum is a surface to be scanned, and each photosensitive drum is an image carrier. 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.

  By the way, in each photosensitive drum, an area scanned with light is called a “scanning area”, and an area in which image information is written in the scanning area is an “effective scanning area”, “image forming area”, “ This is called “effective image area”. In addition, the direction parallel to the rotation axis of each photosensitive drum is referred to as “main scanning direction”, and the rotation direction of the photosensitive drum is referred to as “sub-scanning direction”.

  As each developing roller rotates, toner from a corresponding toner cartridge (not shown) 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 to make it visible. Here, the toner-attached image (toner image) moves in the direction of the intermediate transfer belt 2040 as the photosensitive drum rotates.

  The yellow, magenta, cyan, and black toner images are sequentially transferred onto the intermediate 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. The paper feed roller 2054 takes out the recording paper one by one from the paper feed tray 2060. The recording paper is sent out toward the gap between the intermediate transfer belt 2040 and the transfer roller 2042 at a predetermined timing. As a result, the color image on the intermediate 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.

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

  2 to 5 as an example, the optical scanning device 2010 includes two light sources (2200A, 2200B), four coupling lenses (2201a, 2201b, 2201c, 2201d), and four aperture plates (2202a, 2202b, 2202c, 2202d), four cylindrical lenses (2204a, 2204b, 2204c, 2204d), an optical deflector 2104, four scanning lenses (2105a, 2105b, 2105c, 2105d), eight folding mirrors (2106A, 2106B, 2107a, 2107b, 2107c, 2107d, 2108a, 2108d), two synchronization detection sensors (2115A, 2115B), two synchronization optical systems (2116A, 2116B), and a scanning control device (not shown). These are assembled at predetermined positions of the optical housing.

  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 rotation axis of the optical deflector 2104 is defined as the Z-axis direction. To do. In the following, for convenience, in each optical member, a direction corresponding to the main scanning direction is abbreviated as “main scanning corresponding direction”, and a direction corresponding to the sub scanning direction is abbreviated as “sub scanning corresponding direction”.

  The light source 2200A and the light source 2200B are arranged at positions separated from each other in the X-axis direction. Each light source has two light emitting portions, and emits two light beams that are separated from each other at least in the Z-axis direction.

  Here, of the two light beams emitted from the light source 2200A, the light beam on the + Z side is referred to as “light beam La”, and the light beam on the −Z side is referred to as “light beam Lb”. Of the two light beams emitted from the light source 2200B, the light beam on the + Z side is referred to as “light beam Ld”, and the light beam on the −Z side is referred to as “light beam Lc”.

  The coupling lens 2201a is disposed on the optical path of the light beam La 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 Lb emitted from the light source 2200A, and makes the light beam a substantially parallel light beam. The coupling lens 2201c is disposed on the optical path of the light beam Lc emitted from the light source 2200B, and makes the light beam a substantially parallel light beam. The coupling lens 2201d is disposed on the optical path of the light beam Ld emitted from the light source 2200B, and makes the light beam a substantially parallel light beam.

  The cylindrical lens 2204a is disposed on the optical path of the light beam La via the coupling lens 2201a, and condenses the light beam in the Z-axis direction. The cylindrical lens 2204b is disposed on the optical path of the light beam Lb via the coupling lens 2201b, and condenses the light beam in the Z-axis direction. The cylindrical lens 2204c is disposed on the optical path of the light beam Lc via the coupling lens 2201c, and condenses the light beam in the Z-axis direction. The cylindrical lens 2204d is disposed on the optical path of the light beam Ld via the coupling lens 2201d, and condenses the light beam in the Z-axis direction.

  The aperture plate 2202a has an aperture and shapes the light beam La via the cylindrical lens 2204a. The aperture plate 2202b has an aperture and shapes the light beam Lb via the cylindrical lens 2204b. The aperture plate 2202c has an opening, and shapes the light beam Lc via the cylindrical lens 2204c. The aperture plate 2202d has an aperture and shapes the light beam Ld via the cylindrical lens 2204d.

  The light beam that has passed through the opening of each aperture plate enters the optical deflector 2104.

  The optical system disposed on the optical path between each light source and the optical deflector 2104 is also referred to as “pre-deflector optical system”.

  The optical deflector 2104 has a two-stage rotating polygon mirror. Each rotary polygon mirror is formed with six mirror surfaces, and each mirror surface is a deflection reflection surface. In the first stage (lower stage) rotary polygon mirror, the light beam Lb and the light beam Lc are respectively deflected. In the second stage (upper stage) rotary polygon mirror, the light beam La and the light beam Ld are respectively deflected. ing. Each rotary polygon mirror rotates in the direction of the arrow within the plane in FIG.

  Here, the light beam La and the light beam Lb are deflected to the + X side of the optical deflector 2104, and the light beam Lc and the light beam Ld are deflected to the −X side of the optical deflector 2104.

  The scanning lens 2105 a and the scanning lens 2105 b are disposed on the + X side of the optical deflector 2104, and the scanning lens 2105 c and the scanning lens 2105 d are disposed on the −X side of the optical deflector 2104.

  The scanning lens 2105a and the scanning lens 2105b are stacked in the Z-axis direction, the scanning lens 2105a faces the second-stage rotary polygon mirror, and the scanning lens 2105b faces the first-stage rotary polygon mirror. The scanning lens 2105c and the scanning lens 2105d are stacked in the Z-axis direction, the scanning lens 2105c is opposed to the first-stage rotary polygon mirror, and the scanning lens 2105d is opposed to the second-stage rotary polygon mirror.

  The light beam La deflected by the optical deflector 2104 is irradiated onto the photosensitive drum 2030a through the scanning lens 2105a, the folding mirror 2106A, the folding mirror 2107a, and the folding mirror 2108a.

  The light beam Lb deflected by the optical deflector 2104 is applied to the photosensitive drum 2030b through the scanning lens 2105b, the folding mirror 2106A, and the folding mirror 2107b.

  The light beam Lc deflected by the optical deflector 2104 is applied to the photosensitive drum 2030c through the scanning lens 2105c, the folding mirror 2106B, and the folding mirror 2107c.

  The light beam Ld deflected by the optical deflector 2104 is irradiated onto the photosensitive drum 2030d through the scanning lens 2105d, the folding mirror 2106B, the folding mirror 2107d, and the folding mirror 2108d.

  The light spot on each photosensitive drum moves along the main scanning direction as the rotary polygon mirror rotates. The photosensitive drum 2030a and the photosensitive drum 2030b perform optical scanning in the −Y direction, and the photosensitive drum 2030c and the photosensitive drum 2030d perform optical scanning in the + Y direction (see FIG. 6).

  Therefore, when orthogonally projected onto a plane orthogonal to the Z axis, the angle formed between the traveling direction of the light beam deflected by the optical deflector 2104 and directed to the synchronization detection sensor 2115A and the incident direction of the light beam incident on the optical deflector 2104 is The angle is smaller than the angle formed between the traveling direction of the light beam deflected by the deflector 2104 toward the scanning region and the incident direction of the light beam incident on the optical deflector 2104.

  On the other hand, when orthogonally projected onto a plane orthogonal to the Z axis, the angle formed by the traveling direction of the light beam deflected by the optical deflector 2104 toward the synchronization detection sensor 2115B and the incident direction of the light beam incident on the optical deflector 2104 is The angle is larger than the angle formed between the traveling direction of the light beam deflected by the deflector 2104 toward the scanning region and the incident direction of the light beam incident on the optical deflector 2104.

  The optical system disposed on the optical path between the optical deflector 2104 and each photosensitive drum is also called a “scanning optical system”.

  The synchronization detection sensor 2115A is disposed at a position where the light beam La deflected by the optical deflector 2104 and the light beam before writing to the photosensitive drum 2030a enters. Hereinafter, the light beam entering the synchronization detection sensor 2115A is also referred to as “synchronous light beam La”.

  The synchronization optical system 2116A is disposed on the optical path of the synchronization light beam La between the optical deflector 2104 and the synchronization detection sensor 2115A, and condenses the synchronization light beam La.

  The synchronization detection sensor 2115B is disposed at a position where the light beam Ld deflected by the optical deflector 2104 and the light beam before writing on the photosensitive drum 2030d enters. Hereinafter, the light beam entering the synchronization detection sensor 2115B is also referred to as “synchronous light beam Ld”.

  The synchronization optical system 2116B is disposed on the optical path of the synchronization light beam Ld between the optical deflector 2104 and the synchronization detection sensor 2115B, and condenses the synchronization light beam Ld.

  Each synchronization detection sensor outputs a signal corresponding to the amount of received light to the scanning control device. Based on the output signal of the synchronization detection sensor 2115A, the scanning control device obtains timing for starting writing to the photosensitive drum 2030a and the photosensitive drum 2030b. Further, the scanning control device obtains the writing start timing to the photosensitive drum 2030c and the photosensitive drum 2030d based on the output signal of the synchronization detection sensor 2115B.

  As shown in FIG. 7, when orthogonally projected onto a plane orthogonal to the Z-axis direction, the angle formed between the traveling direction (incident direction) of the light beam emitted from the light source and incident on the optical deflector 2104 and the reference axis direction is Indicated as θin. The reference axis is an axis that passes through the rotation center of each rotary polygon mirror and is parallel to the direction orthogonal to the main scanning direction. Therefore, here, the reference axis direction is the same as the X-axis direction.

  Further, as shown in FIG. 8, when orthogonally projected onto a plane orthogonal to the Z-axis direction, the width of the light beam that has passed through the aperture of each aperture plate is denoted as din. This light beam enters the optical deflector 2104. Here, din is set to be 3.8 mm. din is smaller than the width (length in the main scanning correspondence direction) of one deflecting / reflecting surface.

  The diameter of a circle (see FIG. 9) inscribed in each rotary polygon mirror is 18 mm. Therefore, in each rotary polygon mirror, the length of the perpendicular line drawn from the rotation center to each deflection reflection surface is 9 mm. Further, in each rotary polygon mirror, when it is necessary to distinguish six deflecting reflecting surfaces, they are referred to as surface 1, surface 2, surface 3, surface 4, surface 5, and surface 6 in the direction opposite to the rotational direction (FIG. 9). reference).

  Next, a light beam emitted from the light source 2200B and incident on the optical deflector 2104 and a light beam deflected by the optical deflector 2104 will be described with reference to FIGS. Here, it is assumed that the light beam reflected by the surface 1 of the rotary polygon mirror goes to the scanning area of the synchronization detection sensor 2115B and the corresponding photosensitive drum.

  FIG. 10 shows the incident light beam and the synchronous light beam Ld with respect to the rotary polygon mirror at the timing when the light beam deflected by the optical deflector 2104 is directed to the synchronization detection sensor 2115B. At this time, not all of the light beam incident on the optical deflector 2104 is incident on the surface 1 of the rotary polygon mirror, but a part of the light beam incident on the optical deflector 2104 is set to be incident on the surface 6. . That is, at this time, in the optical deflector 2104, a part of the incident light flux is “scratched”.

  At this time, the angle between the traveling direction of the light beam reflected by the surface 1 of the rotary polygon mirror and the reference axis direction is denoted as θBD.

  FIG. 11 shows the incident light beam and the reflected light beam with respect to the rotary polygon mirror at the timing when the light beam deflected by the optical deflector 2104 moves toward the scanning start position in the scanning region of the corresponding photosensitive drum. At this time, not all of the light beam incident on the optical deflector 2104 is incident on the surface 1 of the rotary polygon mirror, but a part of the light beam incident on the optical deflector 2104 is set to be incident on the surface 6. . Therefore, the width ds of the light beam reflected by the surface 1 of the rotary polygon mirror and traveling toward the scanning start position of the corresponding photosensitive drum is smaller than the width din of the light beam incident on the optical deflector 2104. That is, at this time, in the optical deflector 2104, a part of the incident light flux is “scratched”.

  At this time, an angle formed between the traveling direction of the light beam reflected by the surface 1 of the rotary polygon mirror and the reference axis direction is expressed as θs.

  FIG. 12 shows the incident light beam and the reflected light beam with respect to the rotary polygon mirror at the timing when the light beam deflected by the optical deflector 2104 is directed to the center position of the scanning area of the corresponding photosensitive drum. At this time, all the light beams incident on the optical deflector 2104 are set to be incident on the surface 1 of the rotary polygon mirror. Therefore, the width dc of the light beam reflected by the surface 1 of the rotary polygon mirror and going to the center position of the scanning region of the corresponding photosensitive drum is the same as the width din of the light beam incident on the optical deflector 2104. That is, at this time, the optical deflector 2104 does not “jump” the incident light beam.

  FIG. 13 shows the incident light beam and the reflected light beam with respect to the rotary polygon mirror at the timing when the light beam deflected by the optical deflector 2104 moves toward the scanning end position in the scanning region of the corresponding photosensitive drum. At this time, not all the light beams incident on the optical deflector 2104 are incident on the surface 1 of the rotary polygon mirror, but a part of the light beams incident on the optical deflector 2104 are set to be incident on the surface 2. . Therefore, the width de of the light beam reflected by the surface 1 of the rotary polygon mirror and traveling toward the scanning end position of the corresponding photosensitive drum is smaller than the width din of the light beam incident on the optical deflector 2104. That is, at this time, in the optical deflector 2104, a part of the incident light flux is “scratched”.

  At this time, an angle formed between the traveling direction of the light beam reflected by the surface 1 of the rotary polygon mirror and the reference axis direction is expressed as θe.

  | Θs | + | θe | is an angle corresponding to a so-called scanning angle of view (see FIG. 14). Further, | θs | and | θe | are called “scanning half angle of view”.

  Here, the scanning start position in the scanning area of the photosensitive drum is the −Y side end of the scanning area in the main scanning direction, and the scanning end position in the scanning area of the photosensitive drum is the scanning area in the main scanning direction. + Y side end.

  Here, as shown in FIG. 15, the light beam from the light source 2200B is incident on the first deflection reflection surface and the second deflection reflection surface of the rotary polygon mirror having one interior angle α, and the second deflection reflection is performed. Consider a case where the light beam reflected by the surface becomes the synchronous light beam Ld and the incident direction of the light beam from the light source 2200B is orthogonal to the second deflecting / reflecting surface. At this time, the light beam reflected by the second deflecting / reflecting surface becomes return light to the light source 2200B. For convenience, | θin | + | θBD | is A.

  In this case, the following equation (1) is established.

  α + β + A + 90 = 360 (1)

  The angle β in FIG. 15 is expressed by the following equation (2).

  β = (180−A) / 2 (2)

  Further, when the rotary polygon mirror has N deflecting reflection surfaces, the angle α in FIG. 15 is expressed by the following equation (3).

  α = (180 × (N−2)) / N (3)

  Substituting the above equations (2) and (3) into the above equation (1) yields the following equation (4).

  A = 720 / N (4)

  In other words, when the value of | θin | + | θBD | is 720 / N, the light beam “kept” by the optical deflector 2104 returns to the light source 2200B. Therefore, it is necessary that | θin | + | θBD | ≠ 720 / N.

  In order to increase the scanning angle of view, it is preferable that | θin | and | θBD | Therefore, in the present embodiment, the following equation (5) is set to be satisfied. At this time, the angle formed between the traveling direction of the light beam “cleared” by the optical deflector 2104 and the reference axis direction is smaller than θin.

  | Θin | + | θBD |> 720 / N (5)

  Further, in the present embodiment, the following equation (6) is set so as to prevent the light beam “squeezed” by the optical deflector 2104 from going to the scanning region. At this time, the angle formed between the traveling direction of the light beam “cleared” by the optical deflector 2104 and the reference axis direction is larger than θe.

  | ΘBD | + | θe | <720 / N (6)

  Specific example 1 is shown in FIGS. 16 (A) to 16 (C). In this specific example 1, | θin | = 70 °, | θBD | = 60 °, | θs | = 50 °, | θe | = 50 °.

  At this time, 720 / N = 120, | θin | + | θBD | = 130 °, | θBD | + | θe | = 110 °, and the above expressions (5) and (6) are satisfied.

  In addition, at the timing when the light beam deflected by the optical deflector 2104 is directed to the synchronization detection sensor 2115B, the light that has been “scratched” by the optical deflector 2104, that is, unnecessary light that has been reflected by the adjacent deflecting reflection surface (hereinafter referred to as “light”). The angle θg formed by the traveling direction of the “adjacent surface ghost light” and the reference axis direction is 60 °. That is, there is a relationship of θe <θg <θin, and the adjacent surface ghost light does not become return light to the light source or travel to the scanning region.

  By the way, by arranging the synchronization detection sensor 2115B so that the following expression (7) is satisfied, the above expressions (5) and (6) can be satisfied.

  720 / N− | θin | <| θBD | <720 / N− | θe | (7)

  The comparative example 1 is shown by FIG. 17 (A)-FIG. 17 (C). In Comparative Example 1, | θin | = 55 °, | θBD | = 50 °, | θs | = 40 °, and | θe | = 40 °.

  At this time, 720 / N = 120, | θin | + | θBD | = 105 °, | θBD | + | θe | = 90 °, and although the above equation (6) is satisfied, the above equation (5) is satisfied. Is not satisfied.

  Further, at the timing when the light beam deflected by the optical deflector 2104 is directed to the synchronization detection sensor 2115B, the angle θg formed by the traveling direction of unnecessary light (adjacent surface ghost light) reflected by the adjacent deflecting reflection surface and the X axis. Is 70 °. That is, θg> θin.

  In the first specific example, compared to the first comparative example, | θs | and | θe | can be increased, and the optical path length from the optical deflector 2104 to the photosensitive drum can be shortened. As a result, the optical scanning device can be reduced in size.

  When the adjacent surface ghost light becomes the return light to the light source, the light amount control of the light source becomes unstable. Further, when the adjacent surface ghost light is reflected at an angle larger than the incident angle, the scanning angle of view becomes small, and the optical path length from the optical deflector 2104 to the photosensitive drum becomes long.

  In FIG. 18, in this embodiment, the traveling direction and light of the adjacent surface ghost light at the timing when the light beam before the start of scanning emitted from the light source 2200B and deflected by the optical deflector 2104 is received by the synchronization detection sensor 2115B. The relationship between the incident direction of the light beam incident on the deflector 2104 and the scanning area is shown.

  Next, a light beam emitted from the light source 2200A and incident on the optical deflector 2104 and a light beam deflected by the optical deflector 2104 will be described with reference to FIGS. Here, it is assumed that the light beam reflected by the surface 1 of the rotary polygon mirror goes to the scanning area of the synchronization detection sensor 2115A and the corresponding photosensitive drum.

  FIG. 19 shows the incident light beam and the synchronous light beam La on the rotary polygon mirror at the timing when the light beam deflected by the optical deflector 2104 goes to the synchronization detection sensor 2115A. At this time, not all of the light beam incident on the optical deflector 2104 is incident on the surface 1 of the rotary polygon mirror, but a part of the light beam incident on the optical deflector 2104 is set to be incident on the surface 6. . That is, at this time, in the optical deflector 2104, a part of the incident light flux is “scratched”.

  FIG. 20 shows the incident light beam and the reflected light beam with respect to the rotary polygon mirror at the timing when the light beam deflected by the optical deflector 2104 goes to the scanning start position in the scanning region of the corresponding photosensitive drum. At this time, not all of the light beam incident on the optical deflector 2104 is incident on the surface 1 of the rotary polygon mirror, but a part of the light beam incident on the optical deflector 2104 is set to be incident on the surface 6. . Therefore, the width ds of the light beam reflected by the surface 1 of the rotary polygon mirror and traveling toward the scanning start position of the corresponding photosensitive drum is smaller than the width din of the light beam incident on the optical deflector 2104. That is, at this time, in the optical deflector 2104, a part of the incident light flux is “scratched”.

  FIG. 21 shows the incident light beam and the reflected light beam with respect to the rotary polygon mirror at the timing when the light beam deflected by the optical deflector 2104 goes to the center position of the scanning area of the corresponding photosensitive drum. At this time, all the light beams incident on the optical deflector 2104 are set to be incident on the surface 1 of the rotary polygon mirror. Therefore, the width dc of the light beam reflected by the surface 1 of the rotary polygon mirror and going to the center position of the scanning region of the corresponding photosensitive drum is the same as the width din of the light beam incident on the optical deflector 2104. That is, at this time, the optical deflector 2104 does not “jump” the incident light beam.

  FIG. 22 shows the incident light beam and the reflected light beam with respect to the rotary polygon mirror at the timing when the light beam deflected by the optical deflector 2104 moves toward the scanning end position in the scanning region of the corresponding photosensitive drum. At this time, not all the light beams incident on the optical deflector 2104 are incident on the surface 1 of the rotary polygon mirror, but a part of the light beams incident on the optical deflector 2104 are set to be incident on the surface 2. . Therefore, the width de of the light beam reflected by the surface 1 of the rotary polygon mirror and traveling toward the scanning end position of the corresponding photosensitive drum is smaller than the width din of the light beam incident on the optical deflector 2104. That is, at this time, in the optical deflector 2104, a part of the incident light flux is “scratched”.

  The incident angle | θin | of the light beam emitted from the light source 2200A and incident on the optical deflector 2104 is the same as the incident angle | θin | of the light beam emitted from the light source 2200B and incident on the optical deflector 2104. Therefore, in the case of the specific example 1, the incident angle | θin | of the light beam emitted from the light source 2200A and incident on the optical deflector 2104 is also 70 °. And | θs | = 50 ° and | θe | = 50 °.

  In FIG. 23, in this embodiment, the traveling direction and light of the adjacent surface ghost light at the timing at which the light beam before the start of scanning emitted from the light source 2200A and deflected by the optical deflector 2104 is received by the synchronization detection sensor 2115A. The relationship between the incident direction of the light beam incident on the deflector 2104 and the scanning area is shown.

  By the way, in the conventional UF type optical scanning device, it is necessary to increase the length of the deflecting reflection surface in the direction corresponding to the main scanning direction in order to cope with the high speed of image formation and the high density of the pixel density. For this reason, it is necessary to reduce the number of faces in the rotating polygon mirror or increase the diameter of the inscribed circle in the rotating polygon mirror.

  However, if the number of surfaces is reduced, there is a disadvantage that the number of rotations of the rotary polygon mirror must be increased. On the other hand, when the diameter of the inscribed circle is increased, the windage loss of the rotary polygon mirror increases and there is a disadvantage that the power consumption increases. It is conceivable to increase the number of light sources and increase the number of beams deflected by one deflecting / reflecting surface. However, as the number of light sources increases, the drive circuit of the light source increases in size, resulting in an increase in cost.

  Further, in the conventional OF type optical scanning device, it is necessary to use 10 or more rotating polygonal mirrors in order to cope with high-speed image formation and high pixel density, so the scanning angle of view becomes small. There is a disadvantage that the optical scanning device is increased in size. Moreover, since the peripheral part of the light beam is not used, there is a disadvantage that the light utilization efficiency is low.

  In the optical scanning device 2010 in this embodiment, (1) the rotating polygon mirror can be made smaller than the conventional UF type optical scanning device. Therefore, it becomes possible to rotate the rotary polygon mirror at a high speed without increasing the power consumption. Further, it is possible to cope with a high-speed image formation and a high pixel density without increasing the number of light sources, that is, without increasing the cost.

  Further, in the optical scanning device 2010 in this embodiment, (2) the scanning angle of view can be made larger than that of the conventional OF type optical scanning device. Therefore, it is possible to cope with an increase in image formation speed and an increase in pixel density without causing an increase in size.

  As described above, the optical scanning device 2010 according to the present embodiment includes the two light sources (2200A, 2200B), the pre-deflector optical system, the optical deflector 2104 having a rotating polygon mirror, and the two synchronization detection sensors (2115A, 2115B) and a scanning optical system.

  The angle formed between the traveling direction of the light beam reflected by the rotating polygon mirror and traveling toward the synchronization detection sensor 2115B and the incident direction of the light beam emitted from the light source 2200B and incident on the rotating polygon mirror is reflected by the rotating polygon mirror and travels toward the scanning region. It is larger than the angle formed by the traveling direction of the light beam and the incident direction of the light beam emitted from the light source 2200B and entering the rotary polygon mirror.

  When the synchronization detection by the synchronization detection sensor 2115B is performed, the light beam emitted from the light source 2200B before the start of scanning is the surface 1 (first reflection surface) of the rotary polygon mirror and the surface 6 (second reflection surface) adjacent to the surface 1. It is set so that the light beam incident on the reflection surface and reflected by the surface 1 is received by the synchronization detection sensor 2115B.

  Further, when the synchronization detection is performed by the synchronization detection sensor 2115B, when an orthogonal projection is performed on a plane orthogonal to the Z-axis, the angle formed between the traveling direction of the adjacent surface ghost light that is the light beam reflected by the surface 6 and the reference axis direction is The angle is set to be smaller than the angle formed between the incident direction of the light beam emitted from the light source 2200B and incident on the rotary polygon mirror and the reference axis direction.

  Then, the angle | θin | formed by the incident direction of the light beam emitted from the light source 2200B and incident on the optical deflector 2104 and the reference axis direction, and the traveling direction of the light beam reflected by the rotary polygon mirror and toward the synchronization detection sensor 2115B, and the reference axis The angle | θBD | made with the direction is set so as to satisfy the above expression (5). At this time, | θBD | is set so that the above expression (6) is satisfied with respect to the angle | θe | formed by the traveling direction of the light beam reflected by the rotary polygon mirror and toward the scanning end position and the reference axis direction. ing.

  In this case, part of the light beam reflected by the rotary polygon mirror can be prevented from returning to the light source 2200B during the synchronization detection by the synchronization detection sensor 2115B. Further, at the time of synchronization detection by the synchronization detection sensor 2115B, it is possible to suppress a part of the light beam reflected by the rotary polygon mirror from going to the corresponding photosensitive drum. Furthermore, the scanning angle of view can be increased. Therefore, according to the optical scanning device 2010, it is possible to further reduce the size and increase the speed without degrading the image quality.

  Further, at the timing when the light beam deflected by the optical deflector 2104 is directed to the center of the scanning area of the corresponding photosensitive drum, all the light beams incident on the rotary polygon mirror are reflected by one deflecting reflection surface, and light At the timing when the light beam deflected by the deflector 2104 is directed to each end of the scanning area of the corresponding photosensitive drum, the light beam incident on the rotary polygon mirror is applied to the one deflection reflection surface and the one deflection reflection surface. It is set so as to be reflected by another adjacent deflecting reflecting surface.

  In this case, the rotary polygon mirror can be reduced in size and the scanning field angle can be further increased.

  Since the multifunction machine 2000 includes the optical scanning device 2010, as a result, it is possible to reduce the size and increase the speed without degrading the image quality.

  In the above-described embodiment, the case where the incident light beam is “kept” by the optical deflector 2104 at both the timing toward the scanning start position and the timing toward the scanning end position in the scanning region has been described. However, the present invention is not limited to this. Instead, the incident light beam may be “kept” by the optical deflector 2104 at either the timing toward the scanning start position or the timing toward the scanning end position in the scanning region.

  Moreover, although the said embodiment demonstrated the case where the diameter of the circle | round | yen inscribed in a rotating polygon mirror was 18 mm, it is not limited to this. The diameter of a circle inscribed in the rotary polygon mirror can be set according to the required scanning half angle of view.

  Moreover, although the said embodiment demonstrated the case where the mirror surface of 6 surfaces was formed in the rotating polygon mirror, it is not limited to this. For example, seven mirror surfaces may be formed on the rotary polygon mirror.

  24A to 24C show a specific example 2 in a case where seven mirror surfaces are formed on the rotary polygon mirror. In the second specific example, | θin | = 60 °, | θBD | = 50 °, | θs | = 40 °, and | θe | = 40 °.

  At this time, 720 / N≈102.9, | θin | + | θBD | = 110 °, | θBD | + | θe | = 90 °, and the above expressions (5) and (6) are satisfied. .

  Further, at the timing when the light beam deflected by the optical deflector 2104 is directed to the synchronization detection sensor 2115B, the angle θg formed by the traveling direction of unnecessary light (adjacent surface ghost light) reflected by the adjacent deflecting reflection surface and the X axis. Is 52.9 °. That is, there is a relationship of θe <θg <θin, and the adjacent surface ghost light does not become return light to the light source 2200B or travel to the scanning region.

  25 (A) to 25 (C) show a comparative example 2 in the case where seven mirror surfaces are formed on the rotary polygon mirror. In Comparative Example 2, | θin | = 55 °, | θBD | = 40 °, | θs | = 30 °, and | θe | = 30 °.

  At this time, 720 / N≈102.9, | θin | + | θBD | = 95 °, | θBD | + | θe | = 70 °, and the above expression (6) is satisfied, but the above (5 The formula is not satisfied.

  Further, at the timing when the light beam deflected by the optical deflector 2104 is directed to the synchronization detection sensor 2115B, an angle formed between the traveling direction of unnecessary light (adjacent surface ghost light) reflected by the adjacent deflection reflection surface and the reference axis direction. θg is 92.9 °. That is, θg> θin.

  In the second specific example, | θs | and | θe | can be made larger than in the second comparative example, and the optical path length from the optical deflector 2104 to the photosensitive drum can be shortened. As a result, the optical scanning device can be reduced in size.

  In the above embodiment, a monolithic edge emitting laser array or a surface emitting laser array may be used as the light source.

  Moreover, although the said embodiment demonstrated the case where two light sources each having two light emission parts were used, it is not limited to this. For example, four light sources each having one light emitting unit may be used. Alternatively, two light sources each having one light emitting unit may be used, and a light beam emitted from each light source may be divided into two.

  In the above-described embodiment, the case where the image forming apparatus is a multifunction peripheral has been described. However, the present invention is not limited to this. The image forming apparatus may be a single copying machine, a printer, and a facsimile machine.

  Further, the image forming apparatus may directly irradiate a laser beam to a medium (for example, paper) that develops color with laser light.

  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 photographic paper 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.

  2000 ... MFP (image forming apparatus), 2010 ... optical scanning device, 2030a, 2030b, 2030c, 2030d ... photosensitive drum (image carrier), 2104 ... optical deflector, 2105a, 2105b, 2105c, 2105d ... scanning lens ( Part of scanning optical system), 2115A ... synchronization detection sensor, 2115B ... synchronization detection sensor (light receiver), 2116A ... synchronization optical system, 2116B ... synchronization optical system, 2200A, 2200B ... light source, 2201a, 2201b, 2201c, 2201d ... Coupling lenses, 2202a, 2202b, 2202c, 2202d ... aperture plates, 2204a, 2204b, 2204c, 2204d ... cylindrical lenses.

JP 2005-92129 A JP-A-10-206778

Claims (6)

In an optical scanning device that scans a scanning region of a surface to be scanned along a main scanning direction by a light beam emitted from a light source and reflected by a rotary polygon mirror having a plurality of reflecting surfaces,
Light flux before the start of scanning is simultaneously incident on the first reflecting surface of the rotary polygon mirror and the second reflecting surface adjacent to the first reflecting surface,
A light receiver on which the light beam reflected by the first reflecting surface is incident;
When orthogonally projected onto a plane orthogonal to the rotation axis of the rotary polygon mirror,
The angle formed between the traveling direction of the light beam reflected by the first reflecting surface and the incident direction of the light beam incident on the rotating polygon mirror is determined by the traveling direction and the rotation of the light beam reflected by the rotating polygon mirror toward the scanning region. It is larger than the angle formed by the incident direction of the light beam incident on the polygon mirror,
The optical scanning is characterized in that the traveling direction of the light beam reflected by the second reflecting surface is smaller in angle with respect to the axial direction perpendicular to the main scanning direction than the incident direction of the light beam incident on the rotary polygon mirror. apparatus. The rotating polygon mirror has N reflecting surfaces;
Using the angle θin formed between the incident direction of the light beam incident on the rotary polygon mirror and the axial direction, the angle θBD formed between the traveling direction of the light beam reflected by the first reflecting surface and the axial direction is | θin. 2. The optical scanning device according to claim 1, wherein | + | θBD |> 720 / N is satisfied. When orthogonally projected onto a plane orthogonal to the rotation axis of the rotary polygon mirror,
The angle formed by the reflection direction of the light beam traveling toward the scanning end position of the scanning region with the rotating polygon mirror and the incident direction of the light beam incident on the rotating polygon mirror is the rotation of the light beam toward the scanning start position of the scanning region. Smaller than the angle formed by the reflection direction of the polygon mirror and the incident direction of the light beam incident on the rotary polygon mirror,
Using the angle θe formed by the reflection direction of the light beam traveling toward the scanning end position of the scanning region with the rotary polygon mirror and the axial direction, the angle θBD becomes | θBD | + | θe | <720 / N. The optical scanning device according to claim 2, wherein the optical scanning device is satisfied.   4. The optical scanning device according to claim 3, wherein an angle formed between a traveling direction of a light beam reflected by the second reflecting surface and the axial direction is larger than the angle θe. At the timing when the light beam reflected by the rotary polygon mirror is directed toward the center of the scanning region, all of the light beam incident on the rotary polygon mirror is reflected by one reflection surface,
At the timing when the light beam reflected by the rotary polygon mirror is directed to at least one end of both ends of the scanning region, the light beam incident on the rotary polygon mirror is combined with the one reflecting surface and the one 5. The optical scanning device according to claim 1, wherein the optical scanning device is reflected by another reflecting surface adjacent to the reflecting surface. An image carrier;
An image forming apparatus comprising: an optical scanning device according to claim 1 that scans the image carrier with a light beam modulated by image information.

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