JP6439925B2 - 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 includes an optical scanning device for scanning the surface of a photosensitive drum with a laser beam and forming a latent image on the surface of the drum.

  The optical scanning device includes a light source, an optical deflector, a scanning optical system, and the like. Laser light emitted from the light source is deflected by an optical deflector and then guided to a drum through a scanning optical system.

  In addition, the optical scanning device includes synchronization detecting means for receiving light before starting writing as synchronizing light in order to determine a writing start timing when writing image information on the drum surface.

  For example, Patent Document 1 includes a light beam limiting unit in an optical path between an optical deflector and a writing position synchronization signal detection unit, and a plurality of light beams deflected by the same deflection surface of the optical deflector The light beams are incident on the light beam limiting unit with different light amounts due to different ratios of kicking in the light beam, and the light beam limiting unit has a plurality of light beams that reach the writing position synchronization signal detection unit that is emitted from the light beam limiting unit in the main scanning section. The writing position synchronization signal detecting means deflected by the same deflection surface of the optical deflector is made smaller than the width of each of the plurality of light beams deflected by the deflecting surface of the optical deflector entering the light flux restricting means. While the plurality of arriving light beams are incident on the writing position synchronizing signal detecting means, the widths of the plurality of light beams reaching the writing position synchronizing signal detecting means deflected by the same deflection surface of the optical deflector are always aligned. Scanning optical system is disclosed having a capability.

  Further, Patent Document 2 discloses an imaging optical element having a function of condensing a deflected light beam by a deflector on a surface to be scanned and speeding up optical scanning on the surface to be scanned, and deflecting and scanning by the deflector. A detection unit that detects the position where the beam is scanned and the beam is scanned, and a part of the beam guided to the detection unit by the deflector causes vignetting by the deflector. An optical scanning device is disclosed in which a light-shielding plate that shields a part of a light flux that causes vignetting is placed.

  Further, in Patent Document 3, only the portion of the light beam reflected and deflected at the end of the deflection surface in the optical path between the deflection means and the write position synchronization signal detection means is reflected and deflected at the edge of the deflection surface. A scanning optical device provided with a light beam limiting means for limiting the above is disclosed.

  However, the conventional optical scanning apparatus does not consider the positional deviation of the synchronization light in the main scanning direction.

The present invention includes a light source having at least one light emitting unit, a light deflector having a plurality of reflecting surfaces and deflecting light emitted from the light source, and a surface to be scanned with light deflected by the light deflector. A scanning optical system that guides light to the scanning surface, synchronization detection means that receives light deflected by the optical deflector to determine the scanning start timing of the surface to be scanned, an opening, and the optical deflector And a light limiting unit that limits light at least in the main scanning direction, and the light source emits light having a P-polarized component stronger than an S-polarized component with respect to the reflecting surface. The light from the light source is partially left by the optical deflector toward the light restricting means, and the opening has a length in the sub-scanning direction orthogonal to the main scanning direction. communicating toward the center in the direction to one of the peripheral portion It is to have optical scanning device and an other peripheral part continuously larger portion flows from the center and to larger parts in the main scanning direction.

  According to the optical scanning device of the present invention, the synchronization detection accuracy can be maintained even if the synchronization light is misaligned in the main scanning direction.

1 is a diagram for describing a schematic configuration of a color printer 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 the positional relationship of an optical system before a deflector, and an optical deflector. It is FIG. (1) for demonstrating the width din of the light which injects into an optical deflector. It is FIG. (2) for demonstrating the width din of the light 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 synchronous detection signal and a light source drive signal. It is a figure for demonstrating the relationship between a synchronous detection and a write start position. It is a figure for demonstrating the output waveform of a synchronous detection sensor. It is a figure for demonstrating the dispersion | variation in the output waveform of a synchronous detection sensor. It is a figure for demonstrating the write start position when there exists dispersion | variation in the output waveform of a synchronous detection sensor. It is a figure for demonstrating the incident light and reflected light with respect to a rotating polygon mirror in the timing which the light deflected by the optical deflector heads to a synchronous detection sensor. The incident light and the reflected light with respect to the rotary polygon mirror at the timing when the light deflected by the optical deflector goes to the position where the image height is -163.5 mm (scanning start position in the scanning area of the photosensitive drum) will be described. FIG. It is a figure for demonstrating the incident light and reflected light with respect to a rotating polygonal mirror in the timing which the light deflected with the optical deflector heads to the position whose image height is -150 mm. FIG. 6 is a diagram for explaining incident light and reflected light with respect to a rotary polygon mirror at a timing when light deflected by an optical deflector goes to a position where the image height is 0 mm (a central position of a scanning area of a photosensitive drum). is there. It is a figure for demonstrating the incident light and reflected light with respect to a rotating polygon mirror in the timing which the light deflected with the optical deflector heads to the position where +150 mm of image height. In order to explain the incident light and the reflected light on the rotary polygon mirror at the timing when the light deflected by the optical deflector goes to the position where the image height is +163.5 mm (the scanning end position in the scanning area of the photosensitive drum) FIG. When light is incident on the deflecting / reflecting surface with S-polarized light and when light having a P-polarized component stronger than the S-polarizing component is incident on the deflecting / reflecting surface when the optical deflector is not “damaged” It is a figure for demonstrating the relationship between image height of this and light quantity. It is a figure for demonstrating the light quantity distribution in a to-be-scanned surface in case light enters with a S polarization with respect to a deflection | deviation reflective surface. It is a figure for demonstrating the light quantity distribution in a to-be-scanned surface when the light whose P polarization component is stronger than an S polarization component injects into a deflection | deviation reflective surface. When a light source has single LD comprised from one light emission part, it is a figure for demonstrating the light inject | emitted from this light source and injecting into a light limiting member. When a light source has 2ch-LD array comprised from two light emission parts, it is a figure for demonstrating the light inject | emitted from this light source, and injecting into a light limiting member. It is a figure for demonstrating the opening part of an aperture plate. It is a figure for demonstrating the opening part of the conventional light limiting member. Explains the light intensity distribution of the light incident on the aperture plate when the light source has a single LD and the single LD is arranged so that the light emitted from the light source becomes S-polarized light with respect to the deflecting reflection surface. It is a figure for doing. Light intensity of light that has passed through the opening of the aperture plate when the light source has a single LD and the single LD is arranged so that the light emitted from the light source becomes S-polarized light with respect to the deflecting reflection surface It is a figure for demonstrating distribution. It is a figure for demonstrating the light intensity distribution of the light which passed the opening part of the aperture plate when the light source which has single LD is rotated only the angle (gamma) centering | focusing on the advancing direction of light. It is a figure for demonstrating the light intensity distribution of the light which passed the opening part of the aperture plate when the light source which has 2ch-LD array is rotated only the angle (gamma) centering | focusing on the advancing direction of light. It is a figure for demonstrating the mode of the light before and behind passage of a light limiting member in case the position shift regarding the main scanning corresponding | compatible direction does not generate | occur | produce in the light which injects into a light limiting member. 34A to 34C illustrate the relationship between the state of light before and after passing through the opening of the light limiting member and the positional shift in the main scanning corresponding direction in the light incident on the light limiting member. It is a figure for doing. It is a figure for demonstrating Example 1 of the opening part of a light limiting member. It is a figure for demonstrating the example 2 of the opening part of a light limiting member. It is a figure for demonstrating the example 3 of the opening part of a light limiting member. It is a figure for demonstrating a synchronous optical system. It is a figure for demonstrating the surface tilt correction function of a synchronous optical system. It is a figure for demonstrating the case where a synchronous optical system is arrange | positioned between a light limiting member and a synchronous detection sensor. It is a figure for demonstrating the case where a synchronous optical system is arrange | positioned between the 1st scanning lens and the light limiting member. It is a figure for demonstrating the case where a synchronous detection sensor is provided in the position of the light source side with respect to the scanning area | region regarding the main scanning direction. In FIG. 42, it is a figure for demonstrating the incident light and reflected light with respect to a rotary polygon mirror in the timing which the light deflected by the optical deflector heads for a synchronous detection sensor.

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

  The color printer 2000 is a tandem color printer that superimposes four colors (black, cyan, magenta, and yellow) to form a multicolor image, and includes four photosensitive drums (K1, C1, M1, and Y1). ) Four drum charging devices (K2, C2, M2, Y2), four developing devices (K4, C4, M4, Y4), four drum cleaning devices (K5, C5, M5, Y5), four transfer devices (K6, C6, M6, Y6), optical scanning device 2010, belt charging device 2030, belt separation device 2031, belt neutralization device 2032, conveyor belt 2040, belt cleaning device 2042, fixing device 2050, paper feed roller 2054, registration roller A pair 2056, a paper discharge roller 2058, a paper feed tray 2060, a communication control device 2080, and the above-described units. A printer control device 2090 for Batch controlled.

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

  The printer control device 2090 notifies the optical scanning device 2010 of multi-color image information received from the host device via the communication control device 2080.

  The photosensitive drum K1, the drum charging device K2, the developing device K4, the drum cleaning device K5, and the transfer device K6 are used as a set and constitute an image forming station that forms a black image.

  The photosensitive drum C1, the drum charging device C2, the developing device C4, the drum cleaning device C5, and the transfer device C6 are used as a set and constitute an image forming station that forms a cyan image.

  The photosensitive drum M1, the drum charging device M2, the developing device M4, the drum cleaning device M5, and the transfer device M6 are used as a set and constitute an image forming station that forms a magenta image.

  The photosensitive drum Y1, the drum charging device Y2, the developing device Y4, the drum cleaning device Y5, and the transfer device Y6 are used as a set and constitute an image forming station that forms a yellow image.

  Each photosensitive drum has a photosensitive layer formed on the surface thereof. Each photoconductor drum rotates in the direction of the arrow in the plane in FIG.

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

  The optical scanning device 2010 converts the light modulated for each color based on the multicolor image information (black image information, magenta image information, cyan image information, yellow image information) from the printer control device 2090 to the corresponding charging. Irradiate each of the surfaces of the photosensitive drums. Thereby, a latent image corresponding to the image information is formed on the surface of each photosensitive drum. That is, the surface of each photoconductive drum is a surface to be scanned. Each photosensitive drum is an image carrier. Therefore, hereinafter, the surface of each photosensitive drum is also referred to as a scanned surface or an image surface. The latent image formed here moves in the direction of the corresponding developing device as the photosensitive drum rotates. The configuration of the optical scanning device 2010 will be described later.

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

  The developing device K4 causes a black toner to adhere to the latent image formed on the surface of the photosensitive drum K1 to make it visible.

  The developing device C4 causes cyan toner to adhere to the latent image formed on the surface of the photosensitive drum C1 to make it visible.

  The developing device M4 causes a magenta toner to adhere to the latent image formed on the surface of the photosensitive drum M1 to make a visible image.

  The developing device Y4 causes yellow toner to adhere to the latent image formed on the surface of the photosensitive drum Y1 to make it visible.

  An image (hereinafter, also referred to as “toner image” for convenience) attached with toner by each developing device moves in the direction of the corresponding transfer device as the photosensitive drum rotates.

  Recording paper is stored in the paper feed tray 2060. A paper feed roller 2054 is disposed in the vicinity of the paper feed tray 2060, and the paper feed roller 2054 takes out the recording paper one by one from the paper feed tray 2060 and conveys it to the registration roller pair 2056. The registration roller pair 2056 sends the recording paper toward the conveyance belt 2040 at a predetermined timing.

  The yellow, magenta, cyan, and black toner images are sequentially transferred onto a recording sheet on the conveying belt 2040 by a corresponding transfer device at a predetermined timing, and are superimposed to form a color image. Then, this recording sheet is sent to the fixing device 2050.

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

  Each drum cleaning device 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.

  The belt charging device 2030 charges the surface of the conveyance belt 2040. As a result, the recording paper is electrostatically attracted to the surface of the conveyance belt 2040.

  The belt separation device 2031 releases the adsorption of the recording paper that is electrostatically adsorbed on the conveyance belt 2040.

  The belt neutralizer 2032 neutralizes the surface of the conveyor belt 2040.

  The belt cleaning device 2042 removes foreign matters adhering to the surface of the conveyance belt 2040.

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

  2 to 5 as an example, the optical scanning device 2010 includes four light sources (2200a, 2200b, 2200c, 2200d), four coupling lenses (2201a, 2201b, 2201c, 2201d), four openings. Plate (2202a, 2202b, 2202c, 2202d), four cylindrical lenses (2204a, 2204b, 2204c, 2204d), optical deflector 2104, four first scanning lenses (2105a, 2105b, 2105c, 2105d), eight foldings Mirror (2106a, 2106b, 2106c, 2106d, 2107a, 2107b, 2107c, 2107d), 4 second scanning lenses (2108a, 2108b, 2108c, 2108d), 4 dust-proof glasses (2109a, 2109b, 2 09c, 2109d), the light limiting member 2114, and a like synchronization detection sensor 2115, soundproof glass 2120, and not shown in the scanning controller. These are assembled at predetermined positions of the optical housing 2300.

  In this specification, 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 rotary polygon mirror in the optical deflector 2104. Is described as the Z-axis direction. 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 four light sources (2200a, 2200b, 2200c, 2200d) individually correspond to the four photosensitive drums (K1, C1, M1, Y1). Here, the light source 2200a corresponds to the photosensitive drum K1, the light source 2200b corresponds to the photosensitive drum C1, the light source 2200c corresponds to the photosensitive drum M1, and the light source 2200d corresponds to the photosensitive drum Y1.

  The light emitted from the light source 2200a is also referred to as “light La”, and the light emitted from the light source 2200b is also referred to as “light Lb”. The light emitted from the light source 2200c is also referred to as “light Lc”, and the light emitted from the light source 2200d is also referred to as “light Ld”.

  The optical system arranged between the light source and the optical deflector 2104 is called “pre-deflector optical system”.

  The coupling lens 2201a, the aperture plate 2202a, and the cylindrical lens 2204a are pre-deflector optical systems for the light La.

  The coupling lens 2201b, the aperture plate 2202b, and the cylindrical lens 2204b are pre-deflector optical systems for the light Lb.

  The coupling lens 2201c, the aperture plate 2202c, and the cylindrical lens 2204c are pre-deflector optical systems for the light Lc.

  The coupling lens 2201d, the aperture plate 2202d, and the cylindrical lens 2204d are a pre-deflector optical system for the light Ld.

  Each coupling lens makes light emitted from a corresponding light source substantially parallel light. Each aperture plate has an aperture and shapes the light through the corresponding coupling lens. Each cylindrical lens condenses the light that has passed through the opening of the corresponding aperture plate in the Z-axis direction. The light passing through each cylindrical lens is directed to the optical deflector 2104.

  The optical deflector 2104 has a two-stage rotating polygon mirror. Each rotary polygon mirror is formed with seven mirror surfaces, and each mirror surface is also referred to as a “deflection reflection surface” hereinafter. In the first-stage (lower) rotating polygon mirror, the light La via the cylindrical lens 2204a and the light Lc via the cylindrical lens 2204c are deflected, respectively. In the second-stage (upper) rotating polygon mirror, the cylindrical lens The light Lb via 2204b and the light Ld via the cylindrical lens 2204d are respectively deflected.

  Here, the light La and the light Lb are deflected to the −X side of the optical deflector 2104, and the light Lc and the light Ld are deflected to the + X side of the optical deflector 2104. Each rotary polygon mirror rotates in the direction of the arrow in the plane in FIG.

  The optical deflector 2104 is accommodated in an airtight container for soundproofing. The sealed container has a window through which light from each cylindrical lens and light deflected by the optical deflector 2104 pass, and the window is covered with a soundproof glass 2120.

  An optical system disposed between the optical deflector 2104 and the photosensitive drum is called a “scanning optical system”.

  The first scanning lens 2105a, the folding mirror 2106a, the folding mirror 2107a, and the second scanning lens 2108a are scanning optical systems for the light La.

  The first scanning lens 2105b, the folding mirror 2106b, the folding mirror 2107b, and the second scanning lens 2108b are scanning optical systems for the light Lb.

  The first scanning lens 2105c, the folding mirror 2106c, the folding mirror 2107c, and the second scanning lens 2108c are scanning optical systems for the light Lc.

  The first scanning lens 2105d, the folding mirror 2106d, the folding mirror 2107d, and the second scanning lens 2108d are scanning optical systems for the light Ld.

  Each first scanning lens is an fθ lens, and each second scanning lens is a long toroidal lens. The optical system composed of the first scanning lens and the second scanning lens in each scanning optical system is also called a “scanning imaging optical system”. Note that the scanning imaging optical system can also be composed of a single lens.

  The light La deflected by the optical deflector 2104 is irradiated onto the photosensitive drum K1 via the first scanning lens 2105a, the folding mirror 2106a, the folding mirror 2107a, the second scanning lens 2108a, and the dust-proof glass 2109a, and the light spot Is formed.

  The light Lb deflected by the optical deflector 2104 is irradiated to the photosensitive drum C1 through the scanning lens 2105b, the folding mirror 2106b, the folding mirror 2107b, the second scanning lens 2108b, and the dust-proof glass 2109b, thereby forming a light spot. Is done.

  The light Lc deflected by the optical deflector 2104 is irradiated onto the photosensitive drum M1 through the scanning lens 2105c, the folding mirror 2106c, the folding mirror 2107c, the second scanning lens 2108c, and the dust-proof glass 2109c, thereby forming a light spot. Is done.

  The light Ld deflected by the optical deflector 2104 is applied to the photosensitive drum Y1 through the scanning lens 2105d, the folding mirror 2106d, the folding mirror 2107d, the second scanning lens 2108d, and the dust-proof glass 2109d, thereby forming a light spot. Is done.

  The light spot on each photoconductive drum moves in the longitudinal direction (main scanning direction) of the photoconductive drum 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). Here, the size of the scanning area in the main scanning direction is 327 mm. That is, the image height of the scanning region is −163.5 mm to +163.5 mm.

  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. Hereinafter, with respect to the main scanning direction, the central portion of the scanning region is also referred to as “central image height”, and both end portions of the scanning region are also referred to as “peripheral image height”.

  Here, as shown in FIG. 7, in a plane orthogonal to the rotation axis of the rotary polygon mirror (here, XY plane), an axis that passes through the rotation center of the rotary polygon mirror and is parallel to the X axis is a “reference axis”. And In the XY plane, an angle formed by the optical axis of each pre-polarizer optical system and the reference axis is denoted as θin. Further, as shown in FIGS. 8 and 9, the width of the light incident on the optical deflector 2104 when orthogonally projected on the XY plane is expressed as din. Here, din = 2.8 mm.

  A diameter of a circle (see FIG. 10) inscribed in the rotary polygon mirror is D. Here, D = 13 mm. Therefore, when orthogonal projection is performed on the XY plane, the width of the light incident on the optical deflector 2104 is smaller than the length of the deflection reflection surface in the main scanning corresponding direction. Further, when it is necessary to distinguish the seven deflecting reflecting surfaces, they are referred to as surface 1, surface 2, surface 3, surface 4, surface 5, surface 6, and surface 7 counterclockwise.

  The light limiting member 2114 has an opening, and is light Ld deflected by the optical deflector 2104, and the light before the start of scanning is incident thereon. Details of the light limiting member 2114 will be described later. The synchronization detection sensor 2115 receives light that has passed through the opening of the light limiting member 2114 and outputs a signal corresponding to the amount of received light to the scanning control device. Hereinafter, a signal output from the synchronization detection sensor 2115 is also referred to as a “synchronization detection signal”. Further, the light deflected by the optical deflector 2104 and directed to the synchronization detection sensor 2115 is also referred to as “synchronous light”.

  The scanning control device determines the writing start timing on the four photosensitive drums based on the synchronization detection signal from the synchronization detection sensor 2115.

  FIG. 11 shows a timing chart of the synchronization detection signal and the light source drive signal when the light source has a single LD composed of one light emitting unit. Since the rotary polygon mirror rotates at an equiangular speed, the synchronization detection signal changes from a low level to a high level at regular intervals. The scanning control device outputs a light source driving signal corresponding to the writing information after a predetermined time t1 has elapsed from the rising timing of the synchronization detection signal.

  Therefore, in each scanning line, as shown in FIG. 12 as an example, writing is always started from the same position in the main scanning direction.

  Here, as shown in FIG. 13 as an example, the scanning control apparatus considers that the synchronization detection signal is received when the signal level of the synchronization detection signal is equal to or higher than a certain threshold value v0. Therefore, the scanning control device determines that the timing at which the signal level of the synchronization detection signal becomes the threshold value v0 is the rising timing of the synchronization detection signal. Hereinafter, the detection of the rising edge of the synchronization detection signal by the scanning control device is also referred to as “synchronization detection”.

  By the way, if the output waveform when the synchronization detection sensor 2115 receives the synchronization light is different, the rising timing of the synchronization detection signal is different as shown in FIG. 14 as an example. Therefore, when the rising timing of the synchronization detection signal is different for each scanning line, the timing of the synchronization detection is different for each scanning line. As shown in FIG. 15 as an example, the writing is started for each scanning line. The position will be different. That is, the print position is shifted in the main scanning direction.

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

  FIG. 16 shows incident light and reflected light (synchronous light) with respect to the rotating polygon mirror at the timing when the light deflected by the optical deflector 2104 is directed to the synchronous detection sensor 2115. At this time, not all of the light incident on the optical deflector 2104 is reflected by the surface 1 of the rotary polygon mirror, but the light incident on the optical deflector 2104 is reflected by the surfaces 1 and 2. ing. Therefore, the width dout of the light (synchronous light) reflected by the surface 1 of the rotary polygon mirror and traveling toward the synchronous detection sensor 2115 is smaller than the width din of the light incident on the optical deflector 2104. That is, at this time, in the optical deflector 2104, a part of the incident light is “erased”. Here, dout = 1.4 mm.

  FIG. 17 shows the timing when the light deflected by the optical deflector 2104 travels to the position where the image height on the corresponding photosensitive drum is −163.5 mm (that is, the scanning start position in the scanning area of the corresponding photosensitive drum). FIG. 2 shows incident light and reflected light with respect to the rotating polygon mirror. At this time, not all of the light incident on the optical deflector 2104 is reflected by the surface 1 of the rotary polygon mirror, but the light incident on the optical deflector 2104 is reflected by the surfaces 1 and 2. ing. Therefore, the width dout of the light reflected by the surface 1 of the rotary polygon mirror toward the scanning start position of the corresponding photosensitive drum is smaller than the width din of the light incident on the optical deflector 2104. That is, at this time, in the optical deflector 2104, a part of the incident light is “erased”.

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

  FIG. 18 shows incident light and reflected light with respect to the rotary polygon mirror at the timing when the light deflected by the optical deflector 2104 is directed to the position where the image height on the corresponding photosensitive drum is −150 mm. . At this time, all of the light incident on the optical deflector 2104 is set to be reflected by the surface 1 of the rotary polygon mirror. Therefore, the width dout of the light reflected by the surface 1 of the rotary polygon mirror toward the position where the image height on the corresponding photosensitive drum is −150 mm is the same as the width din of the light incident on the optical deflector 2104. In other words, at this time, the optical deflector 2104 does not “jump” incident light.

  In FIG. 19, the rotation of the light deflected by the optical deflector 2104 at the timing toward the position where the image height on the corresponding photosensitive drum is 0 mm (that is, the center position of the scanning area of the corresponding photosensitive drum). The incident light and the reflected light for the polygon mirror are shown. At this time, all of the light incident on the optical deflector 2104 is set to be reflected by the surface 1 of the rotary polygon mirror. Therefore, the width dout of the light reflected by the surface 1 of the rotary polygon mirror and traveling toward the center position of the scanning region of the corresponding photosensitive drum is the same as the width din of the light incident on the optical deflector 2104. In other words, at this time, the optical deflector 2104 does not “jump” incident light.

  FIG. 20 shows incident light and reflected light with respect to the rotary polygon mirror at the timing when the light deflected by the optical deflector 2104 is directed to the position where the image height on the corresponding photosensitive drum is +150 mm. At this time, all of the light incident on the optical deflector 2104 is set to be reflected by the surface 1 of the rotary polygon mirror. Therefore, the width dout of the light reflected by the surface 1 of the rotary polygon mirror toward the position where the image height on the corresponding photosensitive drum is +150 mm is the same as the width din of the light incident on the optical deflector 2104. In other words, at this time, the optical deflector 2104 does not “jump” incident light.

  In FIG. 21, the light deflected by the optical deflector 2104 is directed to the position where the image height on the corresponding photosensitive drum is +163.5 mm (that is, the scanning end position in the scanning area of the corresponding photosensitive drum). The incident light and the reflected light with respect to the rotating polygon mirror are shown. At this time, not all of the light incident on the optical deflector 2104 is reflected by the surface 1 of the rotary polygon mirror, but the light incident on the optical deflector 2104 is set to be reflected by the surface 1 and the surface 7. ing. Therefore, the width dout of light reflected by the surface 1 of the rotary polygon mirror toward the scanning end position of the corresponding photosensitive drum is smaller than the width din of light incident on the optical deflector 2104. That is, at this time, in the optical deflector 2104, a part of the incident light is “erased”.

  At this time, the angle between the traveling direction of the light reflected by the surface 1 of the rotary polygon mirror and the reference axis is defined as θe. “Θs + θe” is an angle corresponding to a so-called scanning angle of view. Θs and θe are also called “scanning half angle of view”.

  As described above, in this embodiment, the light deflected by the optical deflector 2104 is directed to the synchronization detection sensor 2115, and the image height on the corresponding photosensitive drum is less than −150 mm from the position of −163.5 mm. At the timing toward the range and the timing toward the range where the image height on the corresponding photosensitive drum exceeds +150 mm to the range of +163.5 mm, a part of the incident light is “erased” by the optical deflector 2104 and corresponds. At the timing when the image height on the photosensitive drum moves from the position of −150 mm to the range of the position of +150 mm, the incident light is set so as not to be “erased” by the optical deflector 2104.

  By the way, there are an underfilled type and an overfilled type as a method of making light incident on 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 main scanning direction (see, for example, JP-A-2005-92129). In this case, all of the incident light is guided to the photosensitive drum.

  In the OF type, the width of the incident light is larger than the length of the deflecting / reflecting surface in the main scanning correspondence direction (see, for example, JP-A-10-206778 and JP-A-2003-279877). In this case, ambient light in the incident light is not guided to the photosensitive drum.

  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 the deflecting reflection surface in the main scanning-corresponding direction. It was necessary to reduce the number of surfaces in the mirror or increase the inscribed circle in the rotating polygon mirror.

  However, if the number of surfaces is reduced, there is a disadvantage that the number of rotations of the rotary polygon mirror must be increased. On the other hand, when the inscribed circle is increased, the windage loss of the rotary polygon mirror increases, and there is a disadvantage that the power consumption increases.

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

  In the optical scanning device 2010 in the present embodiment, the rotary polygon mirror can be made smaller than the conventional UF type optical scanning device, and the scanning angle of view is made larger than that of the conventional OF type optical scanning device. be able to.

  In the following, at the timing when the light reflected by the rotary polygon mirror is directed to the center of the scanning area as in the optical scanning device 2010 in the present embodiment, all of the light incident on the rotary polygon mirror is received by one deflecting reflection surface. A type that reflects light incident on the rotating polygon mirror at a plurality of deflecting reflecting surfaces at the timing when the light reflected and reflected by the rotating polygon mirror is directed to at least one end of the scanning region. Is also referred to as “scan end OF type”.

  Note that light emitted from light sources other than the light source 2200d and traveling toward the corresponding scanning region is set to be a “scanning end OF type” similarly to the light emitted from the light source 2200d.

  In FIG. 22, when only the S-polarized light is incident on the deflecting reflecting surface and the light having a P-polarized component stronger than the S-polarizing component is incident on the deflecting reflecting surface. For each of the cases, an example of the light quantity ratio at each image height with respect to the central image height of the light irradiated to the surface to be scanned through the scanning optical system when there is no “damage” by the optical deflector is shown. ing. When light of only S-polarized light is incident on the deflecting / reflecting surface, the light amount is the highest at the center image height and the light amount is the lowest at the peripheral image height. On the other hand, when light having a P-polarized light component stronger than the S-polarized light component is incident on the deflecting reflecting surface, the light amount is highest at the peripheral image height, and the light amount is lowest at the central image height.

  FIG. 23 shows a case where only S-polarized light is incident on the deflecting / reflecting surface and enters the optical deflector, and when there is “deletion” in the optical deflector corresponding to the scanning end OF type, scanning optics is used. The light quantity distribution of the light irradiated to the surface to be scanned through the system is schematically shown.

  FIG. 24 shows a case where light having a P-polarized component stronger than the S-polarized component is incident on the optical deflector with respect to the deflecting / reflecting surface, and “damage” is caused by the optical deflector corresponding to the scanning end OF type. In some cases, the light amount distribution of light irradiated onto the surface to be scanned through the scanning optical system is schematically shown.

  In FIG. 23, the deviation between the image heights of the amount of light on the surface to be scanned is increased due to “deletion” in the optical deflector. On the other hand, in FIG. 24, the deviation between the image heights of the amount of light on the surface to be scanned is small due to the “deletion” in the optical deflector. That is, when the light having a P-polarized light component stronger than the S-polarized light component is incident on the deflecting / reflecting surface, the deviation between the image heights of the light amount on the scanned surface is smaller. It should be noted that, for any light, the light amount decrease at the peripheral image height due to “skeletal” in the optical deflector corresponding to the scanning end OF type is the same.

  Therefore, in this embodiment, when the light source has a single LD (Laser Diode) composed of one light emitting unit, the light incident on the optical deflector 2104 has a P-polarized component rather than an S-polarized component with respect to the deflecting reflection surface. The light emission direction of the light source is set as the rotation axis so that the light becomes stronger, and the light source is rotated around the rotation axis.

  In the conventional optical scanning device, the light source having a single LD is arranged so that the emitted light becomes S-polarized light with respect to the deflecting reflection surface. At this time, the divergence angle of the light emitted from the light source is large in the main scanning corresponding direction and small in the sub scanning corresponding direction.

  In this way, when the light source has a single LD, the light source is rotated with the light emission direction as the rotation axis, and the P-polarized component is made stronger than the S-polarized component with respect to the deflecting reflection surface, and through the scanning optical system. If the unevenness in the amount of light that occurs in the main scanning correspondence direction is set so that the amount of light is higher in the peripheral part than in the center, the amount of light on the surface to be scanned will be caused by “scratching” by the optical deflector corresponding to the scanning end OF type. The image height deviation can be reduced.

  FIG. 25 shows the state of light emitted from the light source and incident on the light limiting member 2114 when the light source 2200d has a single LD. FIG. 26 shows the state of light emitted from the light source and incident on the light limiting member 2114 when the light source 2200d has a 2ch-LD array composed of two light emitting units. Here, the light emitted from the light source 2200d is converted into parallel light by the coupling lens 2201d. Thereafter, unless otherwise specified, the light traveling toward the synchronization detection sensor 2115 is treated as parallel light.

  The light emitted from the light source 2200d is converted into parallel light by the coupling lens 2201d arranged at a position close to the focal length. The focal length of the coupling lens 2201d is shorter when it has a single LD than when it has a 2ch-LD array. In this embodiment, as an example, the focal length fs of the coupling lens 2201d when the light source 2200d has a single LD is 15 mm, and the focal length fm of the coupling lens 2201d when the light source 2200d has a 2ch-LD array is 27 mm. did.

  The light emitted from the coupling lens 2201d is incident on the cylindrical lens 2204d after a part of the light is blocked by the aperture plate 2202d, and is condensed only in the sub-scanning corresponding direction by the cylindrical lens 2204d, that is, corresponding to the main scanning. In the state of a line image that is long in the direction, it passes through the soundproof glass 2120 and enters the optical deflector 2104.

  As shown in FIG. 27 as an example, the opening of each aperture plate is a rectangular opening having a length b in the main scanning correspondence direction and a length in the sub scanning correspondence direction a. Note that the length a, the length b, and the shape of the opening are set so that the beam spot diameter on the surface of the corresponding photosensitive drum becomes a target value.

  When the light reflected by the deflecting reflecting surface and traveling toward the synchronization detecting sensor 2115 is orthogonally projected onto the XY plane, the width of the light becomes narrower than that of the incident light due to the “depression” by the optical deflector 2104. The light passes through the vicinity of the end of the first scanning lens 2105d in the main scanning direction, and is partially shielded by the light limiting member 2114 and reaches the synchronization detection sensor 2115.

  Here, suppose that the shape of the opening of the light limiting member 2114 is a rectangular shape as in the conventional case. For example, as shown in FIG. 28, a rectangular opening having a length in the main scanning correspondence direction of b 'and a length in the sub scanning correspondence direction of a is assumed. Note that the length b 'in the main scanning corresponding direction is determined in consideration of an assembly error and a shape error in each optical element constituting the optical scanning device. For example, paying attention to the principal ray passing through the center of the aperture plate 2202d, it is determined on the basis of the result of calculation of the tolerance accumulation of the positional deviation in the main scanning corresponding direction of the principal ray at the place where the light limiting member 2114 is arranged.

  The light limiting member 2114 is disposed for the purpose of always aligning the light width in the main scanning corresponding direction after passing through the light limiting member 2114. Therefore, there is no need to limit the light in the sub-scanning corresponding direction. Therefore, the length of the opening in the sub-scanning corresponding direction may be sufficiently wide, but here, the length in the sub-scanning corresponding direction is set to a according to the opening of the opening plate.

  FIG. 29 shows the light incident on the aperture plate 2202d when the light source has a single LD and the light source is arranged so that the light emitted from the light source becomes S-polarized light with respect to the deflecting reflection surface. The light intensity distribution is shown. At this time, the light divergence angle at the light source is the largest in the main scanning correspondence direction and the smallest in the sub scanning correspondence direction. The divergence angle related to the main scanning corresponding direction at this time is expressed as “θ⊥”, and the divergence angle related to the sub scanning corresponding direction is expressed as “θ //”. Note that the divergence angle is usually expressed as a full width at half maximum.

  In FIG. 30, when the light source has a single LD and the light source is arranged so that the light emitted from the light source becomes S-polarized light with respect to the deflecting reflection surface, it passes through the opening of the aperture plate 2202d. The light intensity distribution of the light (the part surrounded by the solid line) is shown.

  Since the divergence angle of the single LD is large in the main scanning correspondence direction and the size of the opening of the aperture plate 2202d is also large in the main scanning correspondence direction, the light passing through the opening of the aperture plate 2202d has a wide emission intensity in the main scanning correspondence direction. In the distribution, a part of a region with high light intensity defined by the length b is cut out.

  FIG. 31 shows light (portion surrounded by a solid line) that has passed through the opening of the aperture plate 2202d when the light source having a single LD is rotated by an angle γ with the light emission direction as the rotation axis. The intensity distribution is shown. Here, the angle γ is 82.806 ° as an example. A light source having a single LD rotates the light source by an angle γ, so that the divergence angle in the main scanning correspondence direction becomes smaller than the above θ⊥, and the divergence angle in the sub scanning correspondence direction becomes larger than the above θ //. Become. At this time, the divergence angle in the main scanning corresponding direction and the sub-scanning corresponding direction is defined by three of θ //, θ⊥, and angle γ. If the angle γ is 90 °, the divergence angle in the main scanning correspondence direction is θ //, and the divergence angle in the sub-scanning correspondence direction is θ⊥.

  As described above, in the light source having the single LD, the divergence angle in the main scanning correspondence direction is reduced by the rotation of the light source, but the length of the opening of the opening plate 2202d in the main scanning correspondence direction does not change. The light that has passed through the aperture is a part of the region defined by the length b in the narrow emission intensity distribution in the main scanning corresponding direction.

  Therefore, compared with the case where the light source is not rotationally arranged, a portion having a low light intensity also passes through the opening of the opening plate 2202d. In this case, if the light incident on the light limiting member 2114 has a positional shift in the main scanning corresponding direction, the light intensity of the light that has passed through the light limiting member 2114 changes greatly.

  FIG. 32 shows the light intensity distribution of the light passing through the opening of the aperture plate 2202d when the light source having the 2ch-LD array is rotated by an angle γ with the light emission direction as the rotation axis. . Here, the angle γ is 82.806 ° as an example.

  32 and FIG. 31, when the light source having the 2ch-LD array is used, the light intensity distribution of the light before passing through the opening of the aperture plate 2202d is shown in the portion surrounded by the solid line in the drawing. The ratio is small. Therefore, if the light incident on the light limiting member 2114 is misaligned in the main scanning direction, the light intensity change of the light that has passed through the opening of the light limiting member 2114 is larger than that when a light source having a single LD is used. Become smaller.

  This is because the focal length of the coupling lens corresponding to the light source having the 2ch-LD array is longer than the focal length of the coupling lens corresponding to the light source having the single LD, and therefore corresponding to the main scanning of the opening portion of the aperture plate 2202d. This is because the F value defined by the length b in the direction and the focal length of the coupling lens is smaller when a light source having a 2ch-LD array is used.

  Therefore, a light source having a single LD is used, and the light emission direction of the light source is rotated so that light incident on the optical deflector 2104 is stronger in the P-polarized component than in the S-polarized component with respect to the deflecting reflection surface. If the light is incident on the light restricting member 2114 as a shaft and is misaligned in the main scanning direction, the light intensity change of the light after passing through the opening of the light restricting member 2114 Becomes larger. For this reason, the output change of the synchronization detection sensor 2115 also becomes large, and there is a concern about image deterioration due to the shift of the writing start position on the scanning line.

  FIG. 33 shows the state of light before and after passing through the light limiting member 2114 when the light incident on the light limiting member 2114 has no positional shift in the main scanning correspondence direction. The width of the opening of the aperture plate 2202d in the main scanning correspondence direction is the width b of the light reflected by the deflecting reflection surface and directed to the synchronization detection sensor 2115 due to “skew” in the optical deflector 2104. It enters into the light limiting member 2114 in a state of being smaller than that.

  The light that has passed through the opening of the light restricting member 2114 narrows the width in the main scanning correspondence direction to the length b ′ of the opening of the light restricting member 2114 in the main scanning correspondence direction, and travels toward the synchronization detection sensor 2115.

  34A to 34C show the relationship between the state of the light before and after passing through the opening of the light limiting member 2114 and the positional shift in the main scanning corresponding direction in the light incident on the light limiting member 2114. It is shown. The width of the light passing through the opening of the light limiting member 2114 in the main scanning corresponding direction is always constant even if there is a positional shift in the main scanning corresponding direction.

  In the case of FIG. 34A in which there is no positional shift in the main scanning correspondence direction, the portion cut out in the main scanning correspondence direction by the opening of the light limiting member 2114 (the portion surrounded by the solid line in the drawing) is incident light. The light intensity distribution is a portion having a high light intensity. On the other hand, in the case of FIGS. 34B and 34C in which there is a positional shift in the main scanning corresponding direction, the portion cut out in the main scanning corresponding direction by the opening of the light limiting member 2114 (enclosed by the solid line in the figure). Part) includes a weak part of the light intensity distribution of the incident light.

  Therefore, in the conventional light limiting member having a rectangular opening, if the incident light is misaligned in the main scanning direction, the light intensity change of the light passing through the opening of the light limiting member is reduced. It was difficult. Even if the length b ′ of the opening portion of the conventional light limiting member in the main scanning correspondence direction is reduced, the portion cut out in the main scanning correspondence direction is reduced, and the influence of the positional deviation of the incident light in the main scanning correspondence direction is reduced. Is more strongly received.

  Therefore, in the present embodiment, the shape of the opening of the light limiting member 2114 is such that the opening diameter in the sub-scanning corresponding direction has a region that continuously increases from the center in the main scanning corresponding direction toward the periphery. By prescribing, the change in the intensity of light before and after passing through the opening of the light limiting member 2114 due to the positional deviation of the incident light in the main scanning direction is suppressed, and the image deterioration due to the deviation of the scanning line writing start position is reduced. I let you.

  A specific example of the shape of the opening of the light limiting member 2114 will be described with reference to FIGS. Here, a = 1.64 mm, b = 2.82 mm, b ′ = 1.78 mm, and γ = 82.806 °. The divergence angle θ⊥ in the main scanning correspondence direction of the light source having the single LD arranged so that the light emitted from the light source is S-polarized with respect to the deflecting reflection surface is 21 ° in the full width at half maximum, and the sub scanning correspondence direction. The divergence angle θ // with respect to the full width at half maximum is 7 °.

  The maximum movement amount of the light incident on the light limiting member 2114 in the main scanning corresponding direction is focused on the chief ray passing through the center of the aperture plate 2202d, and the main scanning corresponding direction of the chief ray at the place where the light limiting member 2114 is disposed. It was set to 0.518 mm on the basis of the calculation result of the tolerance accumulation of misalignment. 35 to 37, for convenience, the main scanning corresponding direction in the light limiting member 2114 is the M-axis direction.

  By the way, for the light that has passed through the opening of the light limiting member, the light intensity when the incident light has no positional deviation in the main scanning correspondence direction and the light intensity when the incident light has a positional deviation in the main scanning correspondence direction. When the ratio was calculated, it was 0.883 in the conventional light limiting member having a rectangular opening. In other words, in the conventional light limiting member, the light intensity of the light that has passed through the opening of the light limiting member changes by a maximum of 0.117 because the incident light has a positional shift in the main scanning correspondence direction.

  FIG. 35 shows an example 1 of the opening of the light limiting member 2114. In this example 1, from a rectangle, a portion surrounded by a straight line A (Z = AM + B), a straight line B (Z = −AM + B), and a long side on the + Z side, and a straight line C (Z = AM−B) and a straight line D ( Z = −AM−B) and the length of the opening in the sub-scanning corresponding direction is the center of the main scanning corresponding direction so that light is allowed to pass through only the region excluding the part surrounded by the long side on the −Z side. It continuously increases from ((M, Z) = (0, 0) position) toward the peripheral portion.

  As an example, the coefficient A that is the slope of a straight line is 0.9, and the coefficient B that is an intercept is 0.03. In this case, for the light that has passed through the opening of the light limiting member, the light intensity when the incident light has no positional deviation in the main scanning correspondence direction, and the light intensity when the incident light has a positional deviation in the main scanning correspondence direction, The ratio was 0.909. In other words, the light intensity of the light that has passed through the opening of the light limiting member changes by a maximum of 0.091 due to the positional deviation of the incident light in the main scanning corresponding direction.

FIG. 36 shows an example 2 of the opening of the light limiting member 2114. In this example 2, from a rectangle, the portion surrounded by the curve A (Z = AM ² + B) and the + Z side long side, and the curve B (Z = −AM ² + B) and the −Z side long side are surrounded. The length of the opening in the sub-scanning corresponding direction is from the central part (position (M, Z) = (0, 0)) to the peripheral part in the sub-scanning corresponding direction so that light is allowed to pass through only the region excluding the part. It is continuously increasing toward.

  The curve A and the curve B are expressed by a second-order polynomial. As an example, the coefficient A is 2.5 and the coefficient B is 0.03. In this case, for the light that has passed through the opening of the light limiting member, the light intensity when the incident light has no positional deviation in the main scanning correspondence direction and the light intensity when the incident light has a positional deviation in the main scanning correspondence direction. The ratio was 0.913. In other words, the light intensity of the light that has passed through the opening of the light limiting member changes by a maximum of 0.087 due to the positional deviation of the incident light in the main scanning correspondence direction.

FIG. 37 shows an example 3 of the opening of the light limiting member 2114. In Example 3, from a rectangle, a portion surrounded by a curve A (Z = AM ² + BM ⁴ + C) and a long side on the + Z side, and a curve B (Z = − (AM ² + BM ⁴ + C)) and a −Z side The length of the opening in the sub-scanning corresponding direction is the center in the main-scanning corresponding direction ((M, Z) = (0, 0) so that only the region excluding the portion surrounded by the long side of ) Is continuously increased from the position) toward the periphery.

  Curve A and curve B are expressed by a fourth-order polynomial. As an example, coefficient A is 2.0, coefficient B is 2.4, and coefficient C is 0.03. In this case, for the light that has passed through the opening of the light limiting member, the light intensity when the incident light has no positional deviation in the main scanning correspondence direction and the light intensity when the incident light has a positional deviation in the main scanning correspondence direction. The ratio was 0.914. In other words, the light intensity of the light that has passed through the opening of the light limiting member changes by a maximum of 0.086 due to the positional deviation of the incident light in the main scanning corresponding direction.

  Here, taking the difference between 0.117 and 0.086 gives 0.031, and dividing this by 0.117 gives 0.265. That is, when the light limiting member of Example 3 is used for the opening, the change in the light intensity of the light that has passed through the opening of the light limiting member due to the positional deviation of the incident light in the main scanning correspondence direction is the conventional light. This is an improvement of 26.5% over the limiting member.

  As described above, the light limiting member 2114 of the present embodiment can suppress a change in light intensity due to the positional deviation of the incident light in the main scanning correspondence direction with respect to the light before and after passing through the light limiting member. . Therefore, it is possible to reduce the output change of the synchronization detection sensor 2115 and reduce image deterioration due to the shift of the writing start position of the scanning line.

  When the light source is a multi-beam having a plurality of light emitting units, a synchronization detection signal is not acquired for each light emitting unit, but a synchronization detection signal is acquired for only one arbitrary light emitting unit, and the acquired synchronization detection signal is used as a basis. The write start timing in all the light emitting units is determined. At this time, it is only necessary to set the aperture diameter of the light limiting member 2114 in the main scanning correspondence direction using only the result of the positional deviation in the main scanning correspondence direction of the light emitted from the arbitrary one light emitting unit. Become.

  In this case, compared with the case where the length of the opening portion in the main scanning correspondence direction of the light restriction member 2114 is determined based on the result of the positional deviation of the light emitted from each light emitting portion in the main scanning correspondence direction, the light restriction is performed. The range in which light is blocked by the member 2114 can be narrowed. Therefore, it is possible to suppress a decrease in the output of the synchronization detection sensor 2115 and to prevent deterioration in synchronization detection accuracy due to a decrease in the SN ratio.

  A case where the light source has a 2ch-LD array will be described. One light emitting part of the 2ch-LD array is ch1 and the other light emitting part is ch2. In general, the light source is mounted in a state of being rotated around the axis with the traveling direction of light as a rotation axis so that a desired writing density is realized on the surface to be scanned. Therefore, the light emitted from ch1 and ch2 is deflected toward the synchronization detection sensor 2115 by the optical deflector, and reaches the synchronization detection sensor at different timings.

  Further, the light emitted from ch2 reaches the synchronization detection sensor 2115 earlier than the light emitted from ch1, and the light emitted from ch1 is time Δt after the light emitted from ch2 arrives. It is assumed that the synchronization detection sensor 2115 is reached after elapse. The time Δt is information that can be known at the design stage.

  Here, ch2 is selected as the target light emitting unit for acquiring the synchronization detection signal. Since the rotating polygon mirror rotates at an equal angular speed, the synchronization detection signal rises at regular intervals. When the scanning control device detects a rising edge in the synchronization detection signal, it sends a light source drive signal for ch2 after a predetermined time t1 has elapsed.

  Since it is known in advance that the light emitted from ch1 reaches the synchronization detection sensor 2115 after the time Δt has elapsed since the light emitted from ch2 arrives, the scanning control device sends a light source drive signal to ch2. After the elapse of time Δt, a light source drive signal for ch1 is sent out. In this way, even if the synchronization detection signal is not acquired at ch1, the writing timing of each scanning line can be appropriately set only by the information of the synchronization detection signal at ch2.

  In the present embodiment, the light limiting member 2114 is formed integrally with the optical housing 2300. In this case, the positional accuracy of the light limiting member 2114 can be improved. Since the light blocking member 2114 can narrow the light shielding range, it is possible to suppress a decrease in output of the synchronization detection sensor 2115 and to prevent a decrease in synchronization detection accuracy due to a decrease in the SN ratio.

  As described above, in the optical scanning device according to the present embodiment, four light sources (2200a, 2200b, 2200c, 2200d), four pre-deflector optical systems individually corresponding to the four light sources, and the optical deflector 2104 Four scanning optical systems individually corresponding to the four light sources, a light limiting member 2114 having an opening, a synchronization detection sensor 2115 for receiving synchronization light, and the like are provided.

  Each light source has at least one light emitting unit, and emits light having a P-polarized component stronger than an S-polarized component with respect to the deflecting reflection surface of the optical deflector 2104. Then, the synchronization light emitted from the light source 2200 d and deflected by the optical deflector 2104 passes through the opening of the light limiting member 2114 and is received by the synchronization detection sensor 2115. This synchronizing light is set so that a part thereof is “displaced” when deflected by the optical deflector 2104. In addition, the opening of the light limiting member 2114 has a portion in which the length in the sub-scanning corresponding direction continuously increases from the central portion toward the peripheral portion in the main scanning corresponding direction.

  In this case, the synchronization detection accuracy can be maintained even if the synchronization light is misaligned in the main scanning direction.

  Then, when orthogonal projection is performed on a plane orthogonal to the rotation axis of the rotary polygon mirror (here, the XY plane), the width of the light incident on the rotary polygon mirror is smaller than the length of the deflection reflection surface in the main scanning corresponding direction. In addition, at the timing when the light reflected by the rotary polygon mirror goes to the center of the scanning area, all the light incident on the rotary polygon mirror is reflected by one deflecting reflection surface, and the light reflected by the rotary polygon mirror is scanned. At the timing toward the end of the region, light incident on the rotary polygon mirror is reflected by a plurality of deflection reflection surfaces including the one deflection reflection surface.

  In this case, the surface to be scanned can be optically scanned at high speed with high accuracy without causing an increase in size and cost.

  Since the color printer 2000 includes the optical scanning device 2010, as a result, a high-quality image can be formed at a high speed without causing an increase in size and cost.

  In the above embodiment, as shown in FIG. 38 as an example, a synchronous optical system 2116 having a function of converging light in the main scanning correspondence direction is disposed between the first scanning lens 2105d and the synchronous detection sensor 2115. You may do it. In this case, it is possible to suppress light from protruding from the synchronization detection sensor 2115 in the main scanning corresponding direction. Therefore, the output of the synchronization detection sensor 2115 increases, and a decrease in synchronization detection accuracy due to a decrease in the SN ratio can be suppressed. In addition, the size of the synchronization detection sensor 2115 in the main scanning corresponding direction can be reduced, and the response of the synchronization detection sensor 2115 can be improved.

  At this time, if the synchronization optical system 2116 has a surface tilt correction function, as shown in FIG. 39 as an example, light can be guided to the synchronization detection sensor 2115 even if the rotary polygon mirror is tilted to some extent. This makes it possible to suppress a decrease in the output of the synchronization detection sensor 2115 due to the face-down. Therefore, it is possible to further suppress a decrease in synchronization detection accuracy due to a decrease in the SN ratio.

  As shown in FIG. 40 as an example, the synchronization optical system 2116 may be disposed on the optical path between the light limiting member 2114 and the synchronization detection sensor 2115. As an example, as shown in FIG. It may be disposed on the optical path between the one scanning lens 2105d and the light limiting member 2114.

  In particular, when the synchronization optical system 2116 is disposed on the optical path between the light limiting member 2114 and the synchronization detection sensor 2115, the light limiting member 2114 is disposed between the synchronization optical system 2116 and the optical deflector 2104. It is possible to reliably block light by a desired amount. In this case, it is possible to suppress a decrease in output of the synchronization detection sensor 2115 due to unnecessarily blocking light. Further, the output variation of the synchronization detection sensor 2115 due to the mounting error or the shape error of the light limiting member 2114 can be reduced.

  In the above embodiment, the focal length of the synchronous optical system 2116 is shorter than the focal length of the first scanning lens 2105d. In this case, since the scanning speed of light on the light receiving surface of the synchronization detection sensor 2115 becomes slow, the amount of light received by the synchronization detection sensor 2115 can be increased. Therefore, the output of the synchronization detection sensor 2115 is increased, the SN ratio is improved, and the synchronization detection accuracy can be improved.

  Since the color printer 2000 includes the optical scanning device 2010, as a result, a high-quality image can be formed at a high speed without causing an increase in size and cost.

  In the above embodiment, as shown in FIG. 42 as an example, the synchronization detection sensor 2115 may be arranged on the light source side with respect to the scanning region.

  FIG. 43 shows incident light and reflected light with respect to the rotating polygon mirror at the timing when the light deflected by the optical deflector 2104 is directed to the synchronization detection sensor 2115 in this case. At this time, not all of the light incident on the optical deflector 2104 is reflected by the surface 1 of the rotary polygon mirror, but the light incident on the optical deflector 2104 is set to be reflected by the surface 1 and the surface 7. ing. Therefore, the width dout of the light reflected by the surface 1 of the rotary polygon mirror and traveling toward the synchronization detection sensor 2115 is smaller than the width din of the light incident on the optical deflector 2104. That is, at this time, in the optical deflector 2104, a part of the incident light is “erased”. Here, dout = 1.4 mm.

  In this case, since the light is incident at an acute angle with respect to the deflecting / reflecting surface, even if there is an assembly error or shape error in any one optical element constituting the optical scanning device, the position of the light in the main scanning corresponding direction The amount of deviation can be reduced, and the opening of the light limiting member 2114 can be enlarged. Therefore, the output of the synchronization detection sensor 2115 is increased, the SN ratio is improved, and the synchronization detection accuracy can be improved.

  In the above-described embodiment, the case where the light deflected by the optical deflector 2104 and directed toward both ends of the scanning region is “damaged” by the optical deflector 2104 is not limited to this. The light that is deflected by the deflector 2104 and travels toward one end of the scanning region may be “bounced” by the optical deflector 2104. Even in this case, the rotating polygon mirror can be made smaller than the conventional underfill type optical scanning device.

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

  Moreover, the various numerical values of the specific example in the said embodiment are examples, and are not limited to this.

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

  In the above embodiment, the case of a tandem color printer as the image forming apparatus has been described. However, the present invention is not limited to this. The image forming apparatus may be a monochrome printer. The image forming apparatus may be a copying machine or 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 ... Color printer (image forming apparatus), 2010 ... Optical scanning device, 2104 ... Optical deflector, 2105a-2105d ... First scanning lens, 2106a-2106d ... Folding mirror, 2107a-2107d ... Folding mirror, 2108a-2108d ... First 2 scanning lenses, 2109a to 2109d ... dustproof glass, 2114 ... light limiting member (light limiting means), 2115 ... synchronization detection sensor (synchronization detection means), 2116 ... synchronization optical system, 2120 ... soundproof glass, 2200a-2200d ... light source, 2201a to 2201d ... coupling lens, 2202a to 2202d ... aperture plate, 2204a to 2204d ... cylindrical lens, 2300 ... optical housing, K1, C1, M1, Y1 ... photosensitive drum (image carrier).

Japanese Patent No. 3740339 Japanese Patent No. 2971005 JP 2003-2222811 A

Claims (10)

A light source having at least one light emitting unit;
An optical deflector having a plurality of reflecting surfaces and deflecting light emitted from the light source;
A scanning optical system for guiding the light deflected by the optical deflector to the surface to be scanned;
Synchronization detecting means for receiving the light deflected by the optical deflector to determine the scanning start timing of the surface to be scanned;
An aperture, and is disposed between the optical deflector and the synchronization detection unit, and includes an optical limiting unit that limits light at least in the main scanning direction,
The light source emits light having a P-polarized component stronger than an S-polarized component with respect to the reflective surface,
The light from the light source is partly left by the optical deflector and is directed to the light limiting means.
The opening has a length in the sub-scanning direction orthogonal to the main scanning direction that continuously increases from the central portion in the main scanning direction toward one peripheral portion and the central portion in the main scanning direction. An optical scanning device having a portion that continuously increases toward the other peripheral portion . In the opening length in the sub scanning direction, toward the other of the peripheral portion from the central portion toward the central portion on one of the peripheral portion and the continuously larger portion in the main scanning direction in the main scanning direction The portion that is continuously enlarged is that at least one edge of these portions can be approximated by an even-order polynomial whose origin is the center of the opening in the main scanning direction and depends only on the position in the main scanning direction. The optical scanning device according to claim 1. The width of the light incident on the optical deflector is smaller than the length of the reflecting surface of the optical deflector in the direction corresponding to the main scanning direction,
At the timing when the light deflected by the optical deflector is directed toward the center of the scanning area on the scanned surface, all the light incident on the optical deflector is reflected by one reflecting surface,
At the timing when the light deflected by the optical deflector is directed to at least one end of the scanning region, the light incident on the optical deflector is reflected by the one reflecting surface and the reflecting surface adjacent to the one reflecting surface. the optical scanning device according to claim 1 or 2, characterized in that it is reflected by the. The light source has a plurality of light emitting units,
4. The optical scanning device according to claim 1, wherein the synchronization detection unit corresponds to one of the plurality of light emitting units. 5.   5. The light according to claim 1, further comprising a synchronization optical system that is disposed between the optical deflector and the synchronization detection unit and converges light in the main scanning direction. Scanning device.   The optical scanning apparatus according to claim 5, wherein the synchronization optical system has a conjugate relationship between the reflection surface and the synchronization detection unit when deflecting light toward the synchronization detection unit.   7. The optical scanning device according to claim 5, wherein the synchronization optical system is disposed between the light limiting unit and the synchronization detection unit.   The optical scanning device according to claim 5, wherein a focal length of the synchronous optical system in the main scanning direction is shorter than a focal length of the scanning optical system in the main scanning direction.   The optical scanning device according to claim 1, wherein the synchronization detection unit is disposed at a position on the light source side with respect to a scanning region with respect to the main scanning direction. 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 light modulated by image information.

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