JP6217966B2 - Optical scanning apparatus and image forming apparatus - Google Patents

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 increasing the cost and degrading the image quality.

The present invention provides an optical scanning device that scans a scanning region in 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, and the light beam reflected by the rotating polygon mirror is At the timing toward the center of the scanning area, all of the light beam incident on the rotary polygon mirror is reflected by one reflecting surface, and the light beam reflected by the rotary polygon mirror is at least one of both ends of the scanning area. At the timing toward the end on the side, a part of the light beam incident on the rotary polygon mirror is reflected by the one reflecting surface, and the rest is reflected by another reflecting surface adjacent to the one reflecting surface, An opening member having an opening on an optical path between a light source and the rotary polygon mirror is provided, and the opening is at a first position and an end that are a central portion with respect to a first direction corresponding to the main scanning direction. Between the second position The opening width in the second direction perpendicular to the first direction is reduced from the third position to the second position, the opening width a in the second direction at the first position, and the second position and the opening width b of the second direction at a position between the second direction of the opening width c in the third position, possess b <a ≦ c, the relationship reflected by the rotating polygon mirror The light beam emitted from the light source and incident on the other reflecting surface at a timing when the emitted light beam travels to at least one end of both ends of the scanning region, and the third position in the opening and the third position An optical scanning device that passes between the second position and the second position .

  According to the optical scanning device of the present invention, it is possible to further reduce the size and increase the speed without increasing the cost and 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 relationship between a rotary polygon mirror and an incident light beam 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 relationship between a rotary polygon mirror and an incident light beam in the timing which the light beam inject | emitted from the light source 2200A and deflected with the optical deflector heads to the scanning start position in a scanning area | region. It is a figure for demonstrating the relationship between a rotary polygon mirror and an incident light beam in the timing which the light beam inject | emitted from the light source 2200A and deflected with the optical deflector goes to the center position of a scanning area | region. It is a figure for demonstrating the relationship between a rotary polygon mirror and an incident light beam in the timing which the light beam inject | emitted from the light source 2200A and deflected with the optical deflector heads to the scanning end position in a scanning area | region. It is a figure for demonstrating a scanning angle of view. It is a figure for demonstrating the deflection range and peripheral part by an optical deflector. It is a figure for demonstrating the opening part of an aperture plate. It is a figure for demonstrating the inflection part in the opening part of an opening plate. FIG. 18A to FIG. 18C are diagrams for explaining modifications of the aperture plate, respectively. It is a figure for demonstrating the relationship between the light beam which is "kept" by the optical deflector in an incident light beam, and the opening part of an aperture plate. It is a figure for demonstrating the relationship between the light quantity fall inclination and the opening width of an opening part. It is a figure for demonstrating the light quantity fall in case an opening part is a hexagon shape, and the light quantity fall in case an opening part is a rectangular shape. FIG. 22A and FIG. 22B are diagrams for explaining a light beam passage region “squeezed” by the optical deflector when the opening has a hexagonal shape. FIG. 23A and FIG. 23B are diagrams for explaining light beam passage areas “squeezed” by the optical deflector when the opening has a rectangular shape. It is a figure for demonstrating the relationship between average light quantity fall inclination (% / mm) and d / D about a hexagonal shaped opening part. FIG. 25A is a diagram for explaining the opening shape when d / D = 0 in FIG. 24, and FIG. 25B shows the opening shape when d / D = 1 in FIG. It is a figure for demonstrating. It is a figure for demonstrating the average light quantity fall inclination (% / mm). It is a figure for demonstrating the relationship between beam spot diameter depth (mm) and d / D about the opening part of a hexagonal shape. It is a figure for demonstrating the calculation result of average light quantity fall inclination (au) about a hexagonal shaped opening part. It is a figure for demonstrating the calculation result of beam spot diameter depth (au) about the opening part of a hexagonal shape. It is a figure for demonstrating the relationship between d / D and average light quantity fall inclination (au) and beam spot diameter depth (au) about a hexagonal shaped opening part. It is a figure for demonstrating the calculation result of a compatibility index | exponent about the hexagonal shape opening part. It is a figure for demonstrating the relationship between a compatibility index | exponent and d / D about the hexagonal-shaped opening part. It is a figure for demonstrating the calculation result of average light quantity fall inclination (au) about an oval-shaped opening part. It is a figure for demonstrating the calculation result of beam spot diameter depth (au) about an oval-shaped opening part. It is a figure for demonstrating the relationship between average light quantity fall inclination (au) and beam spot diameter depth (au), and d / D about an oval-shaped opening part. It is a figure for demonstrating the calculation result of a compatibility index | exponent about an oval-shaped opening part. It is a figure for demonstrating the relationship between compatibility index | exponent and d / D about an oval-shaped opening part.

  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”. Further, the direction parallel to the rotation axis of each photosensitive drum is referred to as “main scanning direction”, and the rotational direction of each 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 so as to be visualized. 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 2300.

  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 aperture plate 2202a has an aperture and regulates the size of the light beam La via the coupling lens 2201a. The aperture plate 2202b has an aperture and regulates the size of the light beam Lb via the coupling lens 2201b. The aperture plate 2202c has an aperture and regulates the size of the light beam Lc via the coupling lens 2201c. The aperture plate 2202d has an aperture and regulates the size of the light beam Ld via the coupling lens 2201d.

  The cylindrical lens 2204a is disposed on the optical path of the light beam La that has passed through the opening of the aperture plate 2202a, 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 that has passed through the opening of the aperture plate 2202b, 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 that has passed through the opening of the aperture plate 2202c, 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 that has passed through the opening of the aperture plate 2202d, and condenses the light beam in the Z-axis direction.

  The light beam that has passed through each cylindrical lens 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 rotating polygon mirror is formed with seven 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).

  The scanning start position in the scanning region of the photosensitive drum 2030a and the photosensitive drum 2030b is the + Y side end of the scanning region in the main scanning direction, and the scanning end position is the −Y side end of the scanning region in the main scanning direction. Part.

  The scanning start position in the scanning region of the photosensitive drum 2030c and the photosensitive drum 2030d is the −Y side end of the scanning region in the main scanning direction, and the scanning end position is the + Y side end of the scanning region in the main scanning direction. Part.

  The position in the main scanning direction in the scanning area on the surface to be scanned is called the image height. In the following, with respect to the main scanning direction, the center position of the scanning region is also referred to as “center image height”, and both ends of the scanning region are also referred to as “peripheral image height”. In general, the image height is expressed by coordinates where the central image height is zero. For example, when the length of the scanning region in the main scanning direction is 340 mm, the central image height is 0 mm, the peripheral image height on one side is +170 mm, and the peripheral image height on the other side is −170 mm.

  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. Here, θin = 62 ° is set. 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, 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. Here, din is set to be 3.6 mm. din is smaller than the length of one deflecting / reflecting surface in the main scanning direction (hereinafter also referred to as “width of the deflecting / reflecting surface”). That is, in this embodiment, as in the conventional UF type, when orthogonally projected onto a plane orthogonal to the Z-axis direction, the width din of the light beam incident on the optical deflector 2104 is larger than the width of one deflection reflection surface. small.

  The diameter of a circle (see FIG. 9) inscribed in each rotary polygon mirror is 26 mm. Therefore, in each rotating polygonal mirror, the length of the perpendicular drawn from the center of rotation to each deflecting reflecting surface is 13 mm. Further, in each rotary polygon mirror, when it is necessary to distinguish the seven deflection reflection surfaces, the surfaces 1, 2, 3, 4, 5, 6, and 7 are provided in the direction opposite to the rotation direction. (See FIG. 9).

  Next, a light beam emitted from the light source 2200A and incident on the optical deflector 2104 (hereinafter, also simply referred to as “incident light beam”) and a light beam deflected by the optical deflector 2104 will be described with reference to FIGS. To do. 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. 10 shows an incident light beam and a synchronous light beam La with respect to the rotary polygon mirror at a timing when the light beam emitted from the light source 2200A and deflected by the optical deflector 2104 is directed 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 7. . That is, at this time, in the optical deflector 2104, a part of the incident light flux is “scratched”.

  In FIG. 11, the incident light beam and the reflected light beam with respect to the rotary polygon mirror at the timing when the light beam emitted from the light source 2200A and deflected by the optical deflector 2104 is directed to the scanning start position in the scanning region of the corresponding photosensitive drum. It is shown. 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 7. . 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”. Here, ds is 3.3 mm.

  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 represented as θs. Here, | θs | is 37 °.

  In FIG. 12, the incident light beam and the reflected light beam with respect to the rotary polygon mirror at the timing when the light beam emitted from the light source 2200A and deflected by the optical deflector 2104 is directed to the center position of the scanning region of the corresponding photosensitive drum. It is shown. 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.

  In FIG. 13, the incident light beam and the reflected light beam with respect to the rotary polygon mirror at the timing when the light beam emitted from the light source 2200A and deflected by the optical deflector 2104 moves toward the scanning end position in the scanning region of the corresponding photosensitive drum. It is shown. 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”. Here, de is 3.3 mm.

  At this time, the 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 represented as θe. Here, | θe | is 37 °.

  | Θs | + | θe | is an angle corresponding to a so-called scanning angle of view (see FIG. 14), and is 74 ° here. | Θs | and | θe | are also called “scanning half angle of view”.

  Further, the luminous flux emitted from the light source 2200B and incident on the optical deflector 2104 is set in the same manner as the luminous flux emitted from the light source 2200A.

  That is, at the timing when the light beam emitted from the light source 2200B and deflected by the optical deflector 2104 is directed to the synchronization detection sensor 2115B, a part of the incident light beam is “scratched” by the optical deflector 2104.

  Further, at the timing when the light beam emitted from the light source 2200B and deflected by the optical deflector 2104 is directed to the scanning start position in the scanning region of the corresponding photosensitive drum, a part of the incident light beam is “disposed by the optical deflector 2104. "

  Further, at the timing when the light beam emitted from the light source 2200B and deflected by the optical deflector 2104 is directed to the center position of the scanning area of the corresponding photosensitive drum, there is no “deletion” of the incident light beam by the optical deflector 2104. .

  Further, at the timing when the light beam emitted from the light source 2200B and deflected by the optical deflector 2104 is directed to the scanning end position in the scanning region of the corresponding photosensitive drum, a part of the incident light beam is “disposed by the optical deflector 2104”. "

  By the way, in the conventional UF type optical scanning device, by increasing the number of light sources and using the so-called multi-beam writing method, the image forming speed and the pixel density can be increased without increasing the rotational speed of the rotary polygon mirror. It is possible to increase the density. However, an increase in the number of light sources leads to an increase in the size of the drive circuit, and the cost of the light source unit is significantly increased. In the optical scanning device, the cost ratio of the light source unit is high, which is a serious problem for providing the optical scanning device at a low cost. In particular, an optical scanning device corresponding to a full color machine requires a plurality of light sources corresponding to different colors such as yellow, magenta, cyan, and black, and the number of light sources further increases.

  Further, in the conventional OF type optical scanning device, the rotational speed of the rotating polygon mirror is reduced by reducing the width of the deflecting reflecting surface without increasing the inscribed circle diameter of the rotating polygon mirror and increasing the number of deflecting reflecting surfaces. The image forming speed and the pixel density can be increased without increasing the image quality. However, in this case, since the angle that can be deflected by the deflecting / reflecting surface is narrow, the optical path length from the deflecting / reflecting surface to the scanned surface becomes long in order to secure a desired writing width in the main scanning direction on the scanned surface. As a result, the size of the optical scanning device increases. Further, since the light beam incident on the optical deflector is cut out and scanned, the amount of light decreases from the center image height toward the peripheral image height.

  Until now, various technologies for speeding up image formation and increasing the pixel density have been disclosed. However, along with increasing the speed of image formation and the pixel density, downsizing, cost reduction, and optical characteristics have been improved. It was difficult to satisfy all of the maintenance.

  In addition, miniaturization of the rotating polygon mirror is effective for increasing the speed of image formation and increasing the pixel density. However, usually, if the inscribed circle diameter of the rotary polygon mirror is reduced without changing the number of the deflecting reflecting surfaces, the width of the deflecting reflecting surface is reduced and the deflectable angle is narrowed. That is, the scanning angle of view becomes narrow.

  In the present embodiment, the configuration is such that only in the peripheral portion within the deflection range by the optical deflector 2104 (see FIG. 15), a part of the incident light beam is “scratched” by the optical deflector 2104 to become a reflected light beam. Even if the width of the deflecting / reflecting surface is small, the scanning angle of view is not narrowed. In the following, in order to avoid complications, a range in which a part of the incident light beam is “displaced” by the optical deflector 2104 within the deflection range by the optical deflector 2104 is simply referred to as “deflection range”. " In FIG. 15, the peripheral portion is the “squeeze range”.

  In place of the rotating polygonal mirror having an inscribed circle diameter of 32 mm to 36 mm, a rotating polygonal mirror having an inscribed circle diameter of 26 mm can be used. That is, it is possible to reduce the size of the rotary polygon mirror without narrowing the scanning field angle. Thereby, a windage loss can be reduced. Furthermore, by reducing the weight of the rotary polygon mirror, the diameter of the bearing can be reduced, and the frictional force can be reduced.

  Therefore, in the optical scanning device 2010 of the present embodiment, 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. In addition, it is possible to cope with an increase in image formation speed and pixel density without causing an increase in size.

  By the way, in the present embodiment, the width of the deflection reflection surface can be made smaller as the above-mentioned “squeezing range” becomes larger toward the inner side of the scanning region. However, if the “squeezing range” is large, the reduction in the amount of light at the end of the scanning area becomes a level that cannot be ignored.

  Therefore, in the present embodiment, the aperture plate included in the pre-deflector optical system suppresses the inclination of the light amount decrease due to the “deletion” in the optical deflector 2104 without significantly reducing the beam spot diameter depth. Yes.

  FIG. 16 shows an example of an aperture plate that can be used in this embodiment. The opening of the opening plate has two features. The first feature is that the opening width in the sub-scanning corresponding direction becomes narrow at the end in the main scanning corresponding direction. Hereinafter, in order to avoid complexity, the opening width in the sub-scanning corresponding direction is also simply referred to as “opening width”. A second feature is that there is an inflection (see FIG. 17) between the center and the end in the main scanning direction. The inflection portion is a position where the opening width starts to become narrower toward the end portion, and the opening width of the inflection portion is set to be equal to or larger than the opening width in the central portion. That is, the area between the inflection part and the end part is an area where the opening width is narrowed. Hereinafter, this region is also referred to as a “width reduction region”.

  Here, with respect to the main scanning corresponding direction, the length from the center to the end is D, the length from the center to the inflection is L, and the length from the inflection to the end is d. Further, regarding the sub-scanning corresponding direction, the opening width at the center is a, the opening width at the inflection portion is c, and the opening width at the end is b.

  18 (A) to 18 (C) show other examples of an aperture plate in which the aperture has the above two characteristics.

  When a part of the incident light beam is “cleared” by the optical deflector 2104, the light beam “cleared” by the optical deflector 2104 corresponds to the main scanning at the opening of the aperture plate as shown in FIG. It is a light beam that passes in the vicinity of one side end in the direction. When the rotary polygon mirror is rotated, the region through which the light beam “squeezed” by the optical deflector 2104 passes through the aperture plate.

  If the light quantity distribution in the main scanning correspondence direction of the light beam passing through the opening of the aperture plate is a normal distribution and the light quantity in the vicinity of the end of the light beam is uniform, the breakage of the light beam that is “squeezed” by the optical deflector 2104 The area and the amount of decrease in the amount of light on the surface to be scanned are substantially proportional. Each differential amount has the same relationship. The amount of change in the cross-sectional area is related to the opening width of the opening. Therefore, as shown in FIG. 20 as an example, the opening width of the opening and the slope of the light amount decrease are also approximately proportional.

  FIG. 21 shows the end of the scanning region when a hexagonal aperture plate (see FIG. 16) is used and when a rectangular aperture plate is used as a conventional example. This shows how the amount of light decreases. Note that the vertical axis in FIG. 21 is a light amount when the light amount at an image height of 0 mm is 100%, and this is referred to as a light amount ratio (%).

  When a hexagonal aperture plate is used, for example, when the direction in which the light beam deflected by the optical deflector 2104 travels slightly changes from an image height of 151 mm to an image height of 151 + δ mm, the optical deflector 2104 If the aperture width of the portion through which the increased luminous flux passes among the “squeezed” luminous flux is 1.0 mm (see FIG. 22A), the light amount decreasing slope at the image height of 151 mm (slope of arrow A in FIG. 21). Is -0.29 (% / mm).

  Further, when a hexagonal aperture plate is used, for example, when the direction in which the light beam deflected by the optical deflector slightly changes from an image height of 160 mm to an image height of 160 + δ mm, the optical deflector If the aperture width of the portion through which the increased luminous flux passes among the “squeezed” luminous flux is 1.6 mm (see FIG. 22B), the light amount decreasing slope at the image height of 160 mm (slope of arrow B in FIG. 21). Is -0.43 (% / mm).

  On the other hand, when an aperture plate having a rectangular opening is used, for example, when the direction in which the light beam deflected by the optical deflector slightly changes from an image height of 151 mm to an image height of 151 + δ mm, If the aperture width of the portion through which the increased luminous flux passes among the luminous fluxes that are “squeezed” is 1.6 mm (see FIG. 23A), the light amount decrease slope at the image height of 151 mm (the slope of the arrow C in FIG. 21) is -0.43 (% / mm).

  When an aperture plate having a rectangular opening is used, for example, when the direction in which the light beam deflected by the optical deflector slightly changes from an image height of 160 mm to an image height of 160 + δ mm, The aperture width of the portion through which the increased luminous flux passes among the luminous fluxes that are “squeezed” is also 1.6 mm (see FIG. 23B), and the light amount decrease slope at the image height of 160 mm (the slope of the arrow D in FIG. 21) is − 0.43 (% / mm). In other words, when an aperture plate having a rectangular opening is used, the gradient of the light amount decrease is substantially constant, and the light amount decreases with a relatively steep inclination.

  As described above, when the opening width of the end portion of the opening in the main scanning direction is reduced, the inclination of the light amount decrease is reduced, and the influence of “skipping” can be mitigated.

  FIG. 24 shows the relationship between the average light amount decrease gradient on the surface to be scanned and d / D. When d / D is 0, the opening has a rectangular shape (see FIG. 25A), and when d / D is 1.0, the opening has a rhombus shape (see FIG. 25B). is there. In addition, as shown in FIG. 26 as an example, the average light amount decrease slope is a light amount ratio at an image height at which “deletion” starts, where an area where “deletion” occurs in the scanning region is an averaging range. It is calculated from the light amount ratio at the peripheral image height. For example, if the image height at which "Kere" starts is M1, the light quantity ratio at the image height M1 is p1, the peripheral image height is M2, and the light quantity ratio at the peripheral image height M2 is p2, (p2-p1) / The value calculated by (M2−M1) is defined as the average light amount decrease slope. According to FIG. 24, it can be seen that as the value of d / D increases, the average light quantity decrease slope decreases significantly.

  FIG. 27 shows the relationship between the beam spot diameter depth on the surface to be scanned and d / D. The larger the value of d / D, the shallower the beam spot diameter. This is because, when the same beam spot diameter is set as a target value, if the value of d / D is increased, the size of the opening in the main scanning direction increases, and the light beam that has passed through the opening becomes longer in the main scanning direction. This is because the light beam is more strongly converged in the optical system.

  Here, the absolute value of the average light amount decrease slope was obtained, and numerical conversion (unit: au) with the maximum value being 1 was performed. The result is shown in FIG. The beam spot diameter depth was also converted numerically (unit: au) with a maximum value of 1. The result is shown in FIG.

  FIG. 30 shows the relationship between the average light amount decrease gradient (au) and the beam spot diameter depth (au) and d / D.

  According to FIG. 30, by adjusting the value of d / D, the light intensity decrease gradient is reduced without greatly reducing the beam spot diameter depth when an aperture plate having a rectangular opening is used. It is possible. Moreover, it is possible to increase the beam spot diameter depth while keeping the light amount decrease slope small, as compared with the case where an opening plate having a rhombus shape is used.

  That is, by using the aperture plate having the above-mentioned two features for the aperture, it is possible to simultaneously satisfy the securing of the beam spot diameter depth and the reduction of the light amount decrease gradient.

  By the way, since the “defocused range” is physically determined, it is necessary to reduce fluctuations in the amount of light and the beam spot diameter in the “defocused range”. Therefore, in order to satisfactorily reduce the influence of “deletion” in the optical deflector 2104, the light beam “deleted” by the optical deflector 2104 in the incident light beam may pass through the width reduction region in the opening. preferable.

  For example, if the value of d is 0.5 mm smaller than the value of L at the opening, the beam spot diameter depth is about 0.9 mm shallower than when the opening is rectangular, but conversely the value of d is When it is 0.5 mm larger than the value of L, the beam spot diameter depth becomes shallower by about 3.0 mm than when the opening has a rectangular shape. This is due to the fact that the value of d / D is relatively increased when the value of d is greater than the value of L. Therefore, it is preferable to use an aperture plate having an aperture configured in a range of d <L, on the assumption that the beam spot diameter depth is not greatly reduced compared to when the aperture is rectangular.

  The smaller the amount of decrease in the amount of light, the more the influence of “defocusing” in the optical deflector 2104 can be suppressed, and the greater the beam spot diameter depth, the smaller the focus shift when forming an image on the surface to be scanned. Therefore, the difference between the beam spot diameter depth (au) and the average light intensity decrease slope (au) is taken and standardized so that the maximum value is 100 is defined as the “compatibility index”. (See FIG. 31).

  FIG. 32 is a graph of FIG. According to this, by providing the width reduction region in the opening, the compatibility index becomes larger than when the shape of the opening is rectangular.

  In a region where the compatibility index is large, it is possible to suppress the average light amount decrease slope while suppressing a large decrease in the beam spot diameter depth. Therefore, as shown in FIG. 32, an aperture plate having an aperture in the range of 0.2 <d / D <0.4, which is a region with a high compatibility index, is balanced in terms of maintaining optical characteristics. Thus, the advantages of the present invention can be most effectively extracted.

  In this way, by providing a width-reduced region in the opening, it is possible to suppress the decrease in the beam spot diameter depth compared to the rectangular opening, and to reduce the amount of light due to the incident light beam being “jagged” by the optical deflector. Can be kept small.

  Further, FIG. 33 shows the result of the above-described numerical conversion (unit: au) of the average light amount decrease slope when the shape of the opening is an ellipse (see FIG. 18A). FIG. 34 shows the result of the numerical conversion (unit: au) for the beam spot diameter depth. In this case, the opening where d / D = 0 is a rectangular opening, and the opening where d / D = 1 is an elliptical opening.

  FIG. 35 shows the relationship between the average light amount decrease slope (au), the beam spot diameter depth (au), and d / D. FIG. 36 shows the calculation result of the compatibility index when the shape of the opening is an ellipse. FIG. 37 shows the relationship between the compatibility index and d / D. Also in this case, the aperture plate having the aperture in the range of 0.2 <d / D <0.4, which is a region having a high compatibility index, is balanced in terms of maintaining optical characteristics, and is superior to the present invention. Sex can be most effectively extracted.

  Further, as shown in FIGS. 18B and 18C, by making the opening width in the inflection part larger than the opening width in the center part, the overall length of the opening part in the main scanning correspondence direction is made smaller. It is possible to further increase the beam spot diameter depth.

  As described above, the optical scanning device 2010 according to this embodiment includes two light sources (2200A, 2200B), a pre-deflector optical system, an optical deflector 2104 having a rotating polygon mirror, a scanning optical system, and the like. ing.

  When orthogonal projection is performed on a plane orthogonal to the rotation axis of the rotary polygon mirror, the width of the light beam incident on the rotary polygon mirror is smaller than the width of the deflection reflection surface. At the timing when the light beam reflected by the rotary polygon mirror goes to the center of the scanning area, all the light beams incident on the rotary polygon mirror are reflected by one deflecting reflection surface, and the light beam reflected by the rotary polygon mirror is scanned. At the timing toward both ends of the region, a part of the light beam incident on the rotary polygon mirror is reflected by one deflection reflection surface, and the rest is reflected by another reflection surface adjacent to the one deflection reflection surface.

  The pre-deflector optical system includes an aperture member having an aperture that regulates the size of the light beam emitted from the light source. The aperture is centered with respect to the main scanning correspondence direction (first direction). The opening width in the sub-scanning corresponding direction (second direction) gradually decreases from the inflection part (third position) provided between the first position) and the end part (second position) toward the end part. There is a relationship of b <a ≦ c between the opening width a at the central portion, the opening width b at the end portion, and the opening width c at the inflection portion.

  In this case, in the optical scanning device, the rotary polygon mirror can be reduced in size and the scanning angle of view can be increased without degrading the quality of the latent image formed on each photosensitive drum. Therefore, the optical scanning device can be further reduced in size and speed without increasing the cost and degrading the quality of the image (latent image).

  Since the multi-function device 2000 includes the optical scanning device 2010, as a result, it is possible to further reduce the size and speed without increasing the cost and degrading the quality of the output image.

  In the above-described embodiment, the incident light beam is “kicked” by the optical deflector 2104 at both the timing when the light beam deflected by the optical deflector 2104 goes to the scanning start position and the scanning end position in the scanning region. However, the present invention is not limited to this. The incident light beam is light at either the timing when the light beam deflected by the optical deflector 2104 is directed to the scanning start position or the scanning end position in the scanning region. It may be “kicked” by the deflector 2104.

  Moreover, although the said embodiment demonstrated the case where the diameter of the inscribed circle of a rotary polygon mirror was 26 mm, it is not limited to this.

  Moreover, although the said embodiment demonstrated the case where seven mirror surfaces were formed in the rotating polygon mirror, it is not limited to this.

  Moreover, although the case where din was 3.6 mm was demonstrated in the said embodiment, it is not limited to this, What is necessary is just that din is smaller than the width | variety of a deflection | deviation reflective surface.

  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, an image forming apparatus that directly irradiates laser light onto a medium (for example, paper) that develops color with laser light 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 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, 2115A ... Synchronization detection sensor, 2115B ... Synchronization detection sensor, 2116A ... Synchronization optical system, 2116B ... Synchronization optical system, 2200A, 2200B ... Light source, 2201a, 2201b, 2201c, 2201d ... Coupling lens, 2202a, 2202b, 2202c, 2202d ... Opening plate (opening member), 2204a, 2204b, 2204c, 2204d... Cylindrical lens.

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

Claims (6)

In an optical scanning device that scans a scanning region in a main scanning direction with a light beam emitted from a light source and reflected by a rotary polygon mirror having a plurality of reflecting surfaces,
At the timing when the light beam reflected by the rotary polygon mirror goes to the center of the scanning area, 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, a part of the light beam incident on the rotary polygon mirror is reflected by the one reflection surface. The remainder is reflected by another reflecting surface adjacent to the one reflecting surface;
An opening member having an opening on an optical path between the light source and the rotary polygon mirror;
The opening is directed from a third position provided between a first position as a central portion and a second position as an end portion toward the second position with respect to a first direction corresponding to the main scanning direction. , The opening width in the second direction perpendicular to the first direction is reduced,
Between the opening width a in the second direction at the first position, the opening width b in the second direction at the second position, and the opening width c in the second direction at the third position. , b <a ≦ c, the relationship possess,
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 emitted from the light source and incident on the other reflecting surface is incident on the opening. An optical scanning device passing between the third position and the second position . The opening is L> d, using a length L from the first position to the third position and a length d from the third position to the second position with respect to the first direction. The optical scanning device according to claim 1 . The opening portion has a length d from the third position to the second position and a length D from the first position to the second position with respect to the first direction, and 0.2 <d / 3. The optical scanning device according to claim 1, wherein D <0.4. In both ends of the scanning area, an optical scanning apparatus according to any one of claims 1 to 3, wherein the spot diameter of the light beam are equal. When orthogonally projected onto a plane orthogonal to the rotation axis of the rotary polygon mirror, the width of the light beam incident on the rotary polygon mirror is smaller than the length of the reflecting surface of the rotary polygon mirror in the direction corresponding to the main scanning direction the optical scanning device according to any one of claims 1 to 4, characterized in that. An image carrier;
An image forming apparatus including an optical scanning device, a according to any one of claims 1 to 5 for scanning the image carrier by the light beam modulated by image information.

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