JP2014142432A - Optical scanner and image forming apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a compact optical scanner without reducing synchronization detection accuracy.SOLUTION: An opening in an opening plate 2202a is formed so that an opening width in a sub-scanning direction is smaller at both ends than a center part in a main-scanning direction. In orthogonal projection on a plane orthogonal to a Z axis, a width of a light flux made incident on an optical deflector 2104 is smaller than a length in the main-scanning direction of one polarized reflection surface of an optical deflector 2104. When the light flux deflected by the optical deflector 2104 travels toward a synchronization detection sensor 12, a part of the light flux made incident on the optical deflector 2104 is blocked (vignetting) by the optical deflector 2104.

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 beam is widely used. This image forming apparatus generally includes an optical scanning device, and scans the surface of a photosensitive drum with a laser beam using an optical deflector (for example, a polygon mirror), and a latent image ( Electrostatic latent image).

  The optical scanning device includes a synchronization detection sensor that receives the light deflected by the optical deflector at a predetermined timing before or after the end of writing in one scan, and outputs an output signal of the synchronization detection sensor. Based on this, the writing start timing in one scanning line is obtained.

  For example, Patent Document 1 discloses a light source, a deflector, an imaging mirror, a detection unit that receives a light beam deflected and scanned by the deflector and detects a position where the light beam is scanned, and guides the light beam to the detection unit. In an optical scanning device having a detection imaging optical element, the effective diameter of the detection imaging optical element is made smaller than the incident light beam diameter, and the light intensity distribution of the light beam after passing through the detection imaging optical element is mainly An optical scanning device is disclosed which has a substantially line-symmetric shape centered on a light beam.

  Patent Document 2 discloses a first optical system that shapes a light beam emitted from a light source and forms an image as a linear light beam that is long in the main scanning direction, and a deflecting surface in the vicinity of the imaging position of the first optical system. And deflecting and scanning the incident light beam in the main scanning direction, and forming an image of the light beam reflected and deflected by the deflecting device on the surface to be scanned, and the deflection surface of the deflection unit and the surface to be scanned And a writing position synchronization signal detecting means for controlling the timing of the scanning start position on the surface to be scanned using a light beam reflected and deflected at the end of the deflecting surface. In the scanning optical device, the optical path between the deflecting means and the writing position synchronization signal detecting means limits only the portion of the light beam reflected and deflected at the end of the deflecting surface that is reflected and deflected at the end of the deflecting surface. Scanning optical device characterized by providing light beam limiting means It has been disclosed.

  In recent years, with the development of information equipment, the demand for printers and copiers in small offices (small offices) and home offices has increased. Accordingly, there has been an increasing demand for downsizing of the image forming apparatus. Therefore, downsizing is also important for the optical scanning device constituting a part of the image forming apparatus.

  However, with the devices disclosed in Patent Document 1 and Patent Document 2, it is difficult to achieve both downsizing and high synchronization detection accuracy.

  The present invention is an optical scanning device that scans a surface to be scanned along a main scanning direction with a light beam, and includes a light source, an opening member having an opening for shaping the light beam from the light source, and an opening of the opening member. A rotating polygon mirror that receives the light beam that has passed through, a scanning optical system that guides the light beam deflected by the rotating polygon mirror to the scanned surface, and a light receiving device that receives the light beam reflected by the rotating polygon mirror And 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 width of one reflecting surface of the rotary polygon mirror, The size of the aperture of the aperture member in the direction corresponding to the sub-scanning direction orthogonal to the main scanning direction is smaller at both ends than the center in the direction corresponding to the main scanning direction, and the rotation axis of the rotary polygon mirror Orthographically projected onto a plane perpendicular to , The width of the light beam toward the light receiver is a small optical scanning device than the width of the light beam incident on the rotating polygon mirror.

  According to the optical scanning device of the present invention, it is possible to reduce the size without reducing the synchronization detection accuracy.

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 inscribed circle and inscribed circle radius of a rotary polygon mirror. It is a figure for demonstrating angle (theta) in which the advancing direction of the light beam which injects into an optical deflector and the X-axis direction make. It is a figure for demonstrating the width din of the light beam which injects into an optical deflector. It is a figure for demonstrating angle (theta) p which the advancing direction of the light beam which goes to a synchronous detection sensor, and the X-axis direction make. It is a figure for demonstrating the surface 1-surface 7 in a rotary polygon mirror. It is a figure for demonstrating a rotary polygon mirror, an incident light beam, and a synchronous light beam in the timing which the light beam deflected by the optical deflector goes to a synchronous detection sensor. It is a figure for demonstrating a rotary polygon mirror, an incident light beam, and a scanning light beam in the timing which a scanning light beam heads to the scanning start position in a scanning area | region. It is a figure for demonstrating a rotary polygon mirror, an incident light beam, and a scanning light beam in the timing which a scanning light beam heads to the center position of a scanning area | region. It is a figure for demonstrating a rotary polygon mirror, an incident light beam, and a scanning light beam in the timing which a scanning light beam heads to the scanning end position in a scanning area | region. It is a figure for demonstrating an example of the light quantity distribution of the conventional synchronous light beam. FIG. 16A and FIG. 16B are diagrams for explaining a conventional aperture plate, respectively. FIG. 17A to FIG. 17D are diagrams for explaining examples of the aperture plate in the present embodiment, respectively. It is a figure for demonstrating an example of the light quantity distribution of the synchronous light beam in this embodiment. In this embodiment, it is a figure for demonstrating an example of the light quantity distribution of a synchronous light beam when a light-shielding member is removed.

  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 as an image forming apparatus 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 has 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 or the like, and data communication via a public line.

  The printer control device 2090 includes a CPU, a ROM described in a program written in code readable by the CPU, various data used when executing the program, a RAM as a working memory, an analog data An A / D conversion circuit for converting the data into digital data. 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. Here, the surface of each photosensitive drum is a surface to be scanned. Each photosensitive drum is rotated in the direction of the arrow in the plane of FIG. 1 by a rotation mechanism (not shown).

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

  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, 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.

  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), a synchronization detection optical system 11, a synchronization detection sensor 12, a light shielding plate 13, 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 shapes the light beam La via the coupling lens 2201a.

  The aperture plate 2202b has an aperture and shapes the light beam Lb via the coupling lens 2201b.

  The aperture plate 2202c has an aperture and shapes the light beam Lc via the coupling lens 2201c.

  The aperture plate 2202d has an aperture and shapes the light beam Ld via the coupling lens 2201d.

  When it is not necessary to distinguish the four aperture plates, they are collectively referred to as “aperture plate 2202”.

  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 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) rotating polygon mirror, the light beam Lb via the cylindrical lens 2204b and the light beam Lc via the cylindrical lens 2204c are respectively deflected, and in the second-stage (upper) rotating polygon mirror, the cylindrical lens. The light beam La via 2204a and the light beam Ld via the cylindrical lens 2204d are arranged so as to be deflected. Each rotating polygon mirror has an inscribed circle radius A (see FIG. 6) of 16 mm.

  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 photoconductive drum moves in the longitudinal direction of the photoconductive drum as the corresponding rotary polygon mirror rotates. The moving direction of the light spot at this time is the “main scanning direction”, and the rotation direction of the photosensitive drum is the “sub scanning direction”.

  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 12 is disposed at a position where the light beam deflected by the optical deflector 2104 is incident at a predetermined timing before the start of writing or after the end of writing in one scan. The synchronization detection sensor 12 outputs a signal (photoelectric conversion signal) having a level corresponding to the amount of received light to the scanning control device. Based on the output signal of the synchronization detection sensor 12, the scanning control device obtains the writing start timing on each photosensitive drum.

  The synchronization detection optical system 11 is disposed between the optical deflector 2104 and the synchronization detection sensor 12, and guides the light beam deflected by the optical deflector 2104 to the synchronization detection sensor 12. With respect to the main scanning corresponding direction, the focal length of the synchronization detection optical system 11 is set to be shorter than the focal length of the scanning optical system. In this case, the movement speed of the light spot on the light receiving surface of the synchronization detection sensor 12 is slower than the movement speed of the light spot on the scanned surface, and the S / N in the output signal of the synchronization detection sensor 12 is increased. be able to. Note that the synchronization detection optical system 11 may be composed of one optical element or a plurality of optical elements.

  The light use efficiency of the synchronization detection optical system 11 is set to be higher than the light use efficiency of the scanning optical system. In this case, the S / N in the output signal of the synchronization detection sensor 12 can be further increased.

  The light shielding plate 13 is disposed between the optical deflector 2104 and the synchronization detection optical system 11 and shields one end portion of the light beam deflected by the optical deflector 2104 in the main scanning corresponding direction.

  As shown in FIG. 7, when orthogonally projected onto a plane orthogonal to the Z-axis direction, an angle formed between the traveling direction of the light beam emitted from the light source and incident on the optical deflector 2104 and the X-axis direction is expressed as θin. . Here, θin = 55 ° is set.

  Further, as shown in FIG. 8, the width of the light beam that has passed through the opening of the aperture plate when orthogonally projected onto a plane orthogonal to the Z-axis direction is denoted as din. This light beam enters the optical deflector 2104. Here, din = 4 mm is set. din is smaller than the width (length in the main scanning correspondence direction) of one deflecting / reflecting surface.

  Further, as shown in FIG. 9, when orthogonally projected onto a plane orthogonal to the Z-axis direction, the angle between the traveling direction of the light beam deflected by the optical deflector 2104 and directed to the synchronous detection sensor 12 and the X-axis direction is θp. Is written. Here, θp = 45 ° is set.

  Further, when it is necessary to distinguish the seven deflecting reflecting surfaces in each rotary polygon mirror, as shown in FIG. 10, surface 1, surface 2, surface 3, surface 4, surface 5, surface 6 and surface 7.

  Next, a light beam emitted from the light source 2200A and incident on the optical deflector 2104 (hereinafter abbreviated as “incident light beam”), a light beam deflected by the optical deflector 2104 and directed toward the synchronization detection sensor 12 (hereinafter, referred to as “incident light beam”). , Abbreviated as “synchronous luminous flux”). Here, it is assumed that the light beam reflected by the surface 1 of the rotary polygon mirror goes to the synchronization detection sensor 12.

  FIG. 11 shows the incident light beam and the synchronous light beam at the timing when the light beam reflected by the surface 1 is directed to the synchronization detection sensor 12. At this time, not all of the incident light beam is incident on the surface 1 of the rotary polygon mirror, but a part of the incident light beam is set to be incident on the surface 7. Therefore, when orthogonal projection is performed on a plane orthogonal to the Z-axis direction, the width dp of the synchronous light beam is smaller than the width din of the incident light beam. That is, at this time, in the optical deflector 2104, one side end portion of the incident light beam is removed to become a synchronous light beam. Hereinafter, the removal of a part of the incident light beam is also referred to as “vignetting”.

  Here, the light shielding plate 13 is disposed so that the light beam reflected in the vicinity of the boundary between the surface 1 and the surface 7 included in the synchronous light beam is shielded. That is, the light shielding plate 13 restricts the “vignetting” side of the synchronous light flux.

  Subsequently, a light beam deflected by the optical deflector 2104 and directed to the scanning region of the corresponding photosensitive drum (hereinafter, abbreviated as “scanning light beam”) will be described.

  FIG. 12 shows the incident light beam and the reflected light beam at the timing when the scanning light beam moves toward the scanning start position in the scanning region. At this time, not all of the incident light beam is incident on the surface 1 of the rotary polygon mirror, but a part of the incident light beam is set to be incident on the surface 7. Therefore, the width ds of the scanning light beam toward the scanning start position is smaller than the width din of the incident light beam in the main scanning corresponding direction. That is, at this time, in the optical deflector 2104, a part of the incident light beam is “vignetted”. The angle θs formed by the traveling direction of the scanning light beam toward the scanning start position and the X-axis direction is 36 °.

  FIG. 13 shows the incident light beam and the reflected light beam at the timing when the scanning light beam is directed toward the center position of the scanning region. At this time, all of the incident light beam enters the surface 1 of the rotary polygon mirror. Therefore, the width dc of the scanning light beam toward the center position of the scanning region in the main scanning corresponding direction is the same as the width din of the incident light beam. That is, at this time, the optical deflector 2104 has no “vignetting” of the incident light beam.

  FIG. 14 shows the incident light beam and the reflected light beam at the timing when the scanning light beam moves toward the scanning end position in the scanning region. At this time, not all of the incident light beam is incident on the surface 1 of the rotary polygon mirror, but a part of the incident light beam is set to be incident on the surface 2. Therefore, in the main scanning correspondence direction, the width de of the scanning light beam toward the scanning end position is smaller than the width din of the incident light beam. That is, at this time, in the optical deflector 2104, a part of the incident light beam is “vignetted”. The angle θe formed by the traveling direction of the scanning light beam toward the scanning end position and the X-axis direction is −36 °.

  | Θs | + | θe | is an angle corresponding to a so-called scanning angle of view, and is 72 ° here. 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 one 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 in the scanning area in the main scanning direction. It is the other end.

  The scanning control device increases the light output of the light source higher than usual just before the timing when the light beam deflected by the optical deflector 2104 is directed to the synchronization detection sensor 12 so that the light amount of the synchronous light beam is larger than the light amount of the scanning light beam. Then, immediately after the synchronization is detected, the light output of the light source is returned to normal. Thereby, S / N in the output signal of the synchronous detection sensor 12 can be further increased.

  For the light beam emitted from the light source 2200B, the relationship between the incident light beam and the scanning light beam is set in the same manner as in the case of the light beam emitted from the light source 2200A described above.

  By the way, there are an underfilled type and an overfilled type as a method of making a laser beam incident on an optical deflector. 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 one deflecting / reflecting surface in the main scanning direction (see, for example, JP-A-2005-92129). In this case, all of the incident light is reflected by one deflecting reflection surface.

  In the OF type, the width of incident light is larger than the length of one deflecting / reflecting surface in the main scanning correspondence direction (see, for example, JP-A-10-206778). In this case, incident light is simultaneously incident on a plurality of deflecting and reflecting surfaces.

  In the conventional UF type optical scanning device, in order to cope with high-speed image formation and high pixel density, it is necessary to increase the length of one deflecting reflection surface in the main scanning-corresponding direction. It was necessary to reduce the number of mirror surfaces in the rotating polygon mirror or increase the inscribed circle radius in the rotating polygon mirror.

  However, if the number of mirror surfaces in the rotating polygon mirror is reduced, there is a disadvantage that the number of rotations of the rotating polygon mirror must be increased. On the other hand, when the inscribed circle radius in the rotary polygon mirror is increased, there is a disadvantage that the windage loss of the rotary polygon mirror increases and the power consumption increases. Although it is conceivable to increase the number of light emitting units in the light source and increase the number of beams deflected by one deflecting reflection surface, the drive circuit of the light source increases in size and increases in cost as the number of light emitting units increases. .

  Further, in the conventional OF type optical scanning device, it is necessary to use a rotating polygonal mirror having 10 or more mirror surfaces in order to cope with high-speed image formation and high pixel density. However, there is a disadvantage that the size of the optical scanning device is increased. Further, since a part of the light beam is not used, there is a disadvantage that the light use efficiency is low.

  In the present embodiment, when the light beam deflected by the optical deflector 2104 scans the scanning region, a part of the incident light beam is transmitted by the optical deflector 2104 only at the timing toward the scanning start position and the timing toward the scanning end position. “Vignetting” is set.

  Therefore, in the optical scanning device 2010 according to the present embodiment, the rotary polygon mirror can be made smaller than the conventional UF type optical scanning device. In this case, it becomes possible to rotate the rotary polygon mirror at a high speed without increasing the power consumption. Further, it is not necessary to increase the number of light emitting units, and an increase in the size of the light source driving circuit can be avoided. Therefore, it is possible to cope with high-speed image formation and high pixel density without increasing the cost.

For example, instead of a rotating polygon mirror having an inscribed circle radius of 18 mm and having 6 mirror surfaces, a rotating polygon mirror having an inscribed circle radius of 16 mm and having 7 mirror surfaces can be used. In this case, if the windage loss is the same, the scanning speed can be increased by about 1.5 (≈ (18/16) ² × (7/6)) times.

  If the rotational speed of the rotary polygon mirror is the same, the size of the rotary polygon mirror can be reduced, so that the durability of the rotary polygon mirror can be improved and the amount of heat generated can be reduced.

  Further, in the optical scanning device 2010 in the present embodiment, 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.

  In this embodiment, the synchronous light beam is a light beam in which a part of the incident light beam is “vignetted” by the optical deflector. In this case, it is possible to further reduce the size of the rotary polygon mirror.

  By the way, in the conventional optical scanning device, when a part of the incident light beam is “sparkled” by the optical deflector as a synchronous light beam, variations in the distance from the rotation center to each mirror surface in the rotary polygon mirror, two adjacent Due to variations in the angles formed by the mirror surfaces, the amount of the synchronized light beam may vary greatly from mirror surface to mirror surface (see FIG. 15). Δp 0 in FIG. 15 is a difference between the peak light amount of the synchronous light beam reflected by the surface 1 and the peak light amount of the synchronous light beam reflected by the surface 2.

  In the present embodiment, even if the distance from the center of rotation to each mirror surface varies due to the aperture plate 2202 and the light shielding plate 13 or the angle formed by two adjacent mirror surfaces varies, the amount of the synchronous light flux varies from mirror surface to mirror surface. The difference is suppressed.

  FIG. 16A shows an example of an aperture plate used in a conventional UF type optical scanning device. The opening of the opening plate has a rectangular shape. FIG. 16B shows an example of an aperture plate used in a conventional OF type optical scanning device. The opening of the aperture plate has a shape in which the length (opening width) in the sub-scanning corresponding direction is larger at both end portions in the main scanning corresponding direction than the central portion in the main scanning corresponding direction.

  FIGS. 17A to 17D show examples of the aperture plate 2202 in the present embodiment. The opening of the aperture plate 2202 has a shape in which the length (opening width) in the sub-scanning corresponding direction is smaller at both end portions in the main scanning corresponding direction than in the central portion in the main scanning corresponding direction.

  FIG. 18 shows an example of the light amount distribution of the synchronous light beam in the present embodiment. In this case, in the rotating polygon mirror, even if the distance from the center of rotation to each mirror surface varies or the angle formed by two adjacent mirror surfaces varies, it is possible to prevent the amount of synchronized light flux from being different for each mirror surface. can do. Δp1 in FIG. 18 is a difference between the peak light amount of the synchronous light beam reflected by the surface 1 and the peak light amount of the synchronous light beam reflected by the surface 2, and is extremely smaller than the above Δp0.

  FIG. 19 shows an example of the light quantity distribution of the synchronized light beam when the light shielding plate 13 is removed in the present embodiment. In FIG. 19, Δp2 is a difference between the peak light amount of the synchronous light beam reflected by the surface 1 and the peak light amount of the synchronous light beam reflected by the surface 2, and is larger than the above Δp1 but considerably smaller than the above Δp0.

  As is clear from the above description, in the optical scanning device 2010 according to the present embodiment, the aperture plate 2202 constitutes the aperture member of the present invention, and the synchronization detection sensor 12 constitutes a light receiver. Further, the light blocking plate 13 constitutes a limiting member, and the synchronization detection optical system 11 constitutes a light receiving optical system.

  As described above, according to the optical scanning device 2010 according to the present embodiment, two light sources (2200A, 2200B), four pre-deflector optical systems, an optical deflector 2104, four scanning optical systems, and a synchronous detection optical system. 11, a synchronization detection sensor 12, a light shielding plate 13, a scanning control device, and the like.

  Each pre-deflector optical system has an aperture plate 2202 that shapes the light beam emitted from the light source. The opening of the aperture plate 2202 has a shape in which the opening width in the sub-scanning corresponding direction is smaller at both ends than in the center in the main scanning corresponding direction.

  Further, in this embodiment, when orthogonal projection is performed on a plane orthogonal to the rotation axis of the optical deflector 2104, the width din of the light beam incident on the optical deflector 2104 is the width of one deflection reflection surface of the optical deflector 2104 ( Smaller than the length in the main scanning direction.

  In the present embodiment, at the timing when the light beam deflected by the optical deflector 2104 is directed to the synchronization detection sensor 12, a part of the incident light beam is set to be “vignetted” by the optical deflector 2104.

  Further, in the present embodiment, when the light beam deflected by the optical deflector 2104 scans the scanning region, a part of the incident light beam is only at the timing toward the scanning start position and the timing toward the scanning end position. Is set to “vignetting”.

  In the present embodiment, the light shielding plate 13 that restricts the “vignetting” side of the synchronous light flux is provided.

  Further, in this embodiment, when orthogonal projection is performed on a plane orthogonal to the rotation axis of the optical deflector 2104, the angle formed by the light beam traveling toward the synchronization detection sensor 12 and the light beam incident on the optical deflector 2104 is directed toward the scanning region. The angle is smaller than the angle formed between the light beam and the light beam incident on the optical deflector 2104.

  In this case, (1) the rotating polygon mirror can be reduced, (2) the scanning angle of view can be increased, and (3) it is possible to suppress the amount of the synchronous light flux from being different for each mirror surface. Therefore, it is possible to reduce the size of the optical scanning device without reducing the synchronization detection accuracy.

  In the present embodiment, the focal length of the synchronization detection optical system 11 is shorter than the focal length of the scanning optical system in the main scanning corresponding direction. Further, the light use efficiency of the synchronization detection optical system 11 is larger than the light use efficiency of the scanning optical system. The light output of the light source at the timing when the light beam deflected by the optical deflector 2104 goes to the synchronization detection sensor 12 is more than the light output of the light source at the timing when the light beam deflected by the optical deflector 2104 goes to the scanning region. large.

  In this case, the synchronization detection accuracy can be further improved.

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

  In the above embodiment, the case where din is 4 mm has been described, but the present invention is not limited to this.

  In the above embodiment, the case where θin is 55 ° has been described. However, the present invention is not limited to this.

  Moreover, although the said embodiment demonstrated the case where (theta) p was 45 degrees, it is not limited to this.

  Moreover, although the said embodiment demonstrated the case where the radius of the circle | round | yen inscribed to each rotary polygon mirror was 16 mm, it is not limited to this.

  Moreover, although the said embodiment demonstrated the case where the mirror surface of 7 surfaces was formed in each rotary polygon mirror, it is not limited to this.

  In the above embodiment, when the light beam deflected by the optical deflector 2104 scans the scanning region, a part of the incident light beam is light only at one of the timing toward the scanning start position and the timing toward the scanning end position. The deflector 2104 may be set to “vignetting”.

  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 the 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. 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.

  DESCRIPTION OF SYMBOLS 11 ... Synchronous detection optical system (light-receiving optical system), 12 ... Synchronous detection sensor (light receiver), 13 ... Light-shielding plate (restriction member), 2000 ... Multi-function device (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), 2200A, 2200B ... light source, 2201a, 2201b, 2201c. 2201d, coupling lenses, 2202a, 2202b, 2202c, 2202d, aperture plates (opening members), 2204a, 2204b, 2204c, 2204d, cylindrical lenses.

Japanese Patent No. 2971005 JP 2003-222811 A

Claims (10)

An optical scanning device that scans a surface to be scanned along a main scanning direction with a light beam,
A light source;
An opening member having an opening for shaping the light beam from the light source;
A rotating polygonal mirror on which the light beam that has passed through the aperture of the aperture member is incident;
A scanning optical system for guiding the light beam deflected by the rotary polygon mirror to the surface to be scanned;
A light receiver on which the light beam reflected by the rotary polygon mirror is incident;
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 width of one reflecting surface of the rotary polygon mirror,
The size of the opening of the opening member in the direction corresponding to the sub-scanning direction orthogonal to the main scanning direction is smaller at both ends than the center with respect to the direction corresponding to the main scanning direction,
An optical scanning device in which a width of a light beam directed to the light receiver is smaller than a width of a light beam incident on the rotary polygon mirror when orthogonally projected onto a plane orthogonal to the rotation axis of the rotary polygon mirror.   The limiting member which restrict | limits the light beam which is arrange | positioned on the optical path between the said rotary polygon mirror and the said light receiver, and goes to the said light receiver regarding the direction corresponding to the said main scanning direction is provided. Optical scanning device. When orthogonally projected on a plane orthogonal to the rotation axis of the rotary polygon mirror, the light beam directed to the light receiver is a light beam from which one end is removed by the rotary polygon mirror,
The optical scanning device according to claim 2, wherein the restricting member restricts the removed side of the light flux toward the light receiver.   When orthogonally projected onto a plane orthogonal to the rotation axis of the rotary polygon mirror, the angle formed by the light beam traveling toward the light receiver and the light beam incident on the rotary polygon mirror is such that the light beam directed toward the scanned surface and the rotary polygon mirror are The optical scanning device according to claim 1, wherein the optical scanning device is smaller than an angle formed by a light beam incident on the light beam.   When orthogonally projected onto a plane orthogonal to the rotation axis of the rotary polygon mirror, the width of the light beam directed to at least one of the scan start position and the scan end position on the scanned surface is greater than the width of the light beam incident on the rotary polygon mirror. The optical scanning device according to claim 1, wherein the optical scanning device is also small. A light receiving optical system disposed on an optical path between the rotary polygon mirror and the light receiver;
6. The optical scanning device according to claim 1, wherein a focal length of the light receiving optical system is shorter than a focal length of the scanning optical system with respect to a direction corresponding to the main scanning direction.   The light output of the light source at the timing when the light beam deflected by the rotary polygon mirror goes to the light receiver is the light output of the light source at the timing when the light beam deflected by the rotary polygon mirror goes to the scanned surface. The optical scanning device according to claim 1, wherein the optical scanning device is also larger. A light receiving optical system disposed on an optical path between the rotary polygon mirror and the light receiver;
The optical scanning device according to claim 1, wherein the light use efficiency of the light receiving optical system is greater than the light use efficiency of the scanning optical system.   The optical scanning device according to claim 1, wherein the light receiver is a synchronization detection sensor for detecting a writing start timing to the surface to be scanned. At least one image carrier;
An image forming apparatus comprising: the optical scanning device according to claim 1, wherein the at least one image carrier is scanned with a light beam modulated by image information.

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