JP4911707B2 - Optical scanning apparatus and image forming apparatus - Google Patents

Description

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

  In electrophotographic image recording, an image forming apparatus using a laser is widely used. In this case, the image forming apparatus includes an optical scanning device, and forms a latent image by rotating the drum while scanning laser light using a polygon scanner (for example, a polygon mirror) in the axial direction of the photosensitive drum. Is common. In the field of electrophotography, an image forming apparatus is required to increase image density in order to improve image quality and to increase image output speed in order to improve operability.

  As one of the methods for achieving both high density and high speed, a so-called multi-beam method of simultaneously scanning with a plurality of lights has been considered.

  For example, Patent Document 1 discloses a light source that emits a plurality of light beams, a coupling optical system that couples the plurality of light beams to a subsequent optical system, an optical deflection device that deflects the plurality of light beams in the main scanning direction, A scanning optical system that forms an image of a plurality of light beams deflected by the deflecting device on a surface to be scanned, and the light source is a surface emitting laser in which a plurality of light emitting regions are arranged in a two-dimensional array. A plurality of openings are arranged in one-to-one correspondence with each light emitting region, Dm is the width of the opening in the main scanning direction, and Ds is the sub-scanning of the opening. Width of the direction, βm is the magnification in the main scanning direction of the entire optical system, βs is the magnification in the sub-scanning direction of the entire optical system, ωm is the light spot size in the main scanning direction formed on the surface to be scanned, and ωs is on the surface to be scanned Assuming that the light spot size in the sub-scanning direction is m · | βm | <ωm and Ds · | βs | <ωs, satisfying optical scanning device is disclosed.

JP 2006-350167 A

  In recent years, image forming apparatuses have come to be used for simple printing as on-demand printing systems, and higher-definition image quality is required.

  The present invention has been made under such circumstances, and a first object thereof is to accurately detect a positional deviation in the sub-scanning direction of a light spot formed on a surface to be scanned without incurring an increase in cost. An object of the present invention is to provide an optical scanning device capable of performing the above.

  A second object of the present invention is to provide an image forming apparatus capable of forming a high quality image at high speed without incurring an increase in cost.

According to a first aspect of the present invention, there is provided an optical scanning device that scans a surface to be scanned with light, a light source unit having a plurality of light emitting units; a deflector that deflects light from the light source unit; A scanning optical system for condensing the light deflected by the deflector onto the surface to be scanned; a plurality of lights deflected by the deflector and passing through the scanning optical system are incident while moving in the main scanning direction; in inner, a photodetector comprising at least one light receiving element having the direction of a position perpendicular to the main scanning direction and the first light receiving portion that the space different in the main scanning direction and the second light receiving portion; wherein the The photodetector has a level at which an output of the comparator changes when the at least one light receiving element receives all of the plurality of lights as a reference level, and an output level of the at least one light receiving element is the reference level. Compare with level It includes a comparator for outputting a result, both the size of the first and second light receiving unit includes the entire rectangular virtual region surrounding the plurality of light spots on the light receiving surface of the photodetector is an optical scanning device you being a size that can.

In this specification, the diameter of the light spot refers to the diameter of a region having a light intensity of 1 / e ² or more when the light intensity at the center is 1.

According to this , the light detectors that are incident while the plurality of lights passing through the scanning optical system move in the main scanning direction are arranged in the light receiving surface according to the positions in the direction orthogonal to the main scanning direction. It includes at least one light receiving element having a first light receiving portion and a second light receiving portion having different intervals. The size of each of the first and second light receiving portions is a size that can include the entire quadrangular virtual region surrounding a plurality of light spots on the light receiving surface of the photodetector. Accordingly, it is possible to secure a sufficient amount of light in each light receiving unit, and the photodetector can output a signal having an excellent S / N ratio. As a result, it is possible to accurately detect the positional deviation of the light spot formed on the surface to be scanned in the sub-scanning direction without increasing the cost.

  According to a third aspect of the present invention, in an image forming apparatus that forms an image by optical scanning, the image forming apparatus includes at least one optical scanning apparatus according to the present invention that performs the optical scanning.

  According to this, since at least one optical scanning device of the present invention is provided, as a result, it is possible to form a high-quality image at a high speed without causing an increase in cost.

  Hereinafter, an embodiment of the present invention will be described with reference to FIGS. FIG. 1 shows a schematic configuration of a printer 10 according to an embodiment of the present invention. In this specification, the main scanning direction will be described as the Y-axis direction, the sub-scanning direction as the Z-axis direction, and the direction orthogonal to these will be described as the X-axis direction.

  The printer 10 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 100, four photosensitive drums (30a, 30a, 30b, 30c, 30d), four charging chargers (32a, 32b, 32c, 32d), four developing rollers (33a, 33b, 33c, 33d), and four toner cartridges (34a, 34b, 34c, 34d). ) Four cleaning cases (31a, 31b, 31c, 31d), transfer belt 40, paper feed tray 60, paper feed roller 54, registration roller pair 56, fixing roller 50, paper discharge tray 70, paper discharge roller 58, And a printer control device (not shown) that controls the above-described units in an integrated manner.

  The photosensitive drum 30a, the charging charger 32a, the developing roller 33a, the toner cartridge 34a, and the cleaning case 31a are used as a set and form an image forming station (hereinafter also referred to as “K station” for convenience) that forms a black image. Constitute.

  The photosensitive drum 30b, the charging charger 32b, the developing roller 33b, the toner cartridge 34b, and the cleaning case 31b are used as a set, and form an image forming station (hereinafter also referred to as “C station” for convenience) that forms a cyan image. Constitute.

  The photosensitive drum 30c, the charging charger 32c, the developing roller 33c, the toner cartridge 34c, and the cleaning case 31c are used as a set, and an image forming station (hereinafter also referred to as “M station” for convenience) that forms a magenta image. Constitute.

  The photosensitive drum 30d, the charging charger 32d, the developing roller 33d, the toner cartridge 34d, and the cleaning case 31d are used as a set, and form an image forming station (hereinafter also referred to as “Y station” for convenience) that forms a yellow image. Constitute.

  Each photosensitive drum has a photosensitive layer formed on the surface thereof. That is, the surface of the photosensitive drum is the surface to be scanned. The photosensitive drums are arranged at equal intervals in the X-axis direction with the longitudinal direction as the Y-axis direction. 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 charger uniformly charges the surface of the corresponding photosensitive drum.

  The optical scanning device 100 converts light modulated for each color based on multicolor image information (black image information, cyan image information, magenta image information, yellow image information) from a host device (for example, a personal computer). The surface of the corresponding charged photosensitive drum is irradiated. As a result, on the surface of each photoconductive drum, the charge disappears only in the portion irradiated with light, and a latent image corresponding to the image information is formed on the surface of each photoconductive drum. The latent image formed here moves in the direction of the corresponding developing roller as the photosensitive drum rotates. The configuration of the optical scanning device 100 will be described later.

  Black toner is stored in the toner cartridge 34a, and the toner is supplied to the developing roller 33a. The toner cartridge 34b stores cyan toner, and the toner is supplied to the developing roller 33b. Magenta toner is stored in the toner cartridge 34c, and the toner is supplied to the developing roller 33c. Yellow toner is stored in the toner cartridge 34d, and the toner is supplied to the developing roller 33d.

  As each developing roller rotates, the toner from the corresponding toner cartridge is thinly and uniformly applied to the surface thereof. Then, when the toner on the surface of each developing roller comes into contact with the surface of the corresponding photosensitive drum, the toner moves only to a portion irradiated with light on the surface and adheres to the surface. In other words, each developing roller causes toner to adhere to the latent image formed on the surface of the corresponding photosensitive drum so as to be visualized. Here, the toner-attached image (hereinafter referred to as “toner image” for convenience) moves in the direction of the transfer belt 40 as the photosensitive drum rotates.

  The black, cyan, magenta, and yellow toner images are sequentially transferred onto the transfer belt 40 at a predetermined timing, and are superimposed to form a color image.

  Recording paper is stored in the paper feed tray 60. A paper feed roller 54 is arranged in the vicinity of the paper feed tray 60, and the paper feed roller 54 takes out the recording paper one by one from the paper feed tray 60 and conveys it to the registration roller pair 56. The registration roller pair 56 feeds the recording paper toward the transfer belt 40 at a predetermined timing. As a result, the color image on the transfer belt 40 is transferred to the recording paper. The recording sheet transferred here is sent to the fixing roller 50.

  In the fixing roller 50, heat and pressure are applied to the recording paper, whereby the toner is fixed on the recording paper. The recording paper fixed here is sent to the paper discharge tray 70 via the paper discharge roller 58 and is sequentially stacked on the paper discharge tray 70.

  Each cleaning case 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 of the corresponding charging charger again.

  Next, the configuration of the optical scanning device 100 will be described.

  As shown in FIG. 2 as an example, the optical scanning device 100 includes two light source units (200a, 200b), two aperture plates (201a, 201b), and two light beam splitting prisms (202a, 202b). Four liquid crystal deflecting elements (203a, 203b, 203c, 203d), four cylinder lenses (204a, 204b, 204c, 204d), polygon mirror 104, four fθ lenses (105a, 105b, 105c, 105d) , 8 folding mirrors (106a, 106b, 106c, 106d, 108a, 108b, 108c, 108d), 4 toroidal lenses (107a, 107b, 107c, 107d), 4 light detection sensors (205a, 205b, 205c, 205d), the main controller 210, and the like.

  Each light source unit includes a laser array and a coupling lens that makes light from the laser array substantially parallel light.

  As an example, this laser array is a surface emitting semiconductor laser array in which 32 light emitting units are formed on one substrate. As shown in FIG. 3, a direction corresponding to the main scanning direction (hereinafter, For convenience, it is also referred to as “M direction”) to a direction corresponding to the sub-scanning direction (hereinafter referred to as “S direction” for the sake of convenience). There are four rows of light emitting portion rows in which the light emitting portions are arranged at equal intervals. These four light emitting section rows are arranged at equal intervals in the S direction so that 32 light emitting sections are equally spaced with respect to the S direction. That is, the 32 light emitting units are two-dimensionally arranged along the T direction and the S direction, respectively. In the present specification, the “light emitting portion interval” refers to the distance between the centers of two light emitting portions. Therefore, it is possible to scan each photosensitive drum with 32 lights at the same time.

  Here, for the sake of convenience, the first light emitting unit row, the second light emitting unit row, the third light emitting unit row, and the fourth light emitting unit row are referred to from the top to the bottom in FIG. Further, in order to specify each light emitting unit, for convenience, the eight light emitting units constituting the first light emitting unit row are configured as v1 to v8 and the second light emitting unit row is configured from the left to the right in FIG. The eight light emitting units are designated as v9 to v16, the eight light emitting units constituting the third light emitting unit row are designated as v17 to v24, and the eight light emitting units constituting the fourth light emitting unit row are designated as v25 to v32.

  Returning to FIG. 2, the aperture plate 201a has an aperture and defines the beam diameter of light from the light source unit 200a. The aperture plate 201b has an aperture and defines the beam diameter of light from the light source unit 200b.

  As shown in FIG. 4, each beam splitting prism transmits a half of incident light and reflects the remaining half mirror surface, and parallel to the half mirror surface on the optical path of the light reflected by the half mirror surface. And a mirror surface arranged. That is, each light beam splitting prism splits incident light into two lights that are parallel to each other.

  The light beam splitting prism 202a splits light that has passed through the opening of the aperture plate 201a into two light beams that are parallel to each other at a predetermined interval in the Z-axis direction. The beam splitting prism 202b splits the light that has passed through the opening of the aperture plate 201b into two lights that are parallel to each other at a predetermined interval in the Z-axis direction.

  Each of the liquid crystal deflection elements can slightly tilt the light emission axis with respect to the sub-scanning direction according to the applied potential (see FIG. 5).

  The liquid crystal deflection element 203a is arranged on the optical path of light on the −Z side (hereinafter also referred to as “black light” for convenience) among the two lights from the light beam splitting prism 202a, and subtracts the black light according to the applied voltage. It can be deflected with respect to the scanning direction.

  The liquid crystal deflection element 203b is arranged on the optical path of + Z side light (hereinafter also referred to as “cyan light” for convenience) of the two lights from the light beam splitting prism 202a, and sub-scans the cyan light according to the applied voltage. Can be deflected with respect to direction.

  The liquid crystal deflection element 203c is arranged on the optical path of + Z side light (hereinafter also referred to as “magenta light” for convenience) of the two lights from the light beam splitting prism 202b, and sub-scans the magenta light according to the applied voltage. Can be deflected with respect to direction.

  The liquid crystal deflecting element 203d is arranged on the optical path of the −Z side light (hereinafter also referred to as “yellow light” for convenience) of the two lights from the light beam splitting prism 202b, and subtracts the yellow light according to the applied voltage. It can be deflected with respect to the scanning direction.

  The cylinder lens 204 a is disposed on the optical path of light (black light) via the liquid crystal deflecting element 203 a and converges the black light in the vicinity of the deflection reflection surface of the polygon mirror 104 in the sub-scanning direction.

  The cylinder lens 204b is disposed on the optical path of light (cyan light) via the liquid crystal deflecting element 203b, and converges the cyan light in the vicinity of the deflection reflection surface of the polygon mirror 104 in the sub-scanning direction.

  The cylinder lens 204c is disposed on the optical path of light (magenta light) via the liquid crystal deflecting element 203c, and converges the magenta light in the vicinity of the deflection reflection surface of the polygon mirror 104 in the sub-scanning direction.

  The cylinder lens 204d is disposed on the optical path of light (yellow light) via the liquid crystal deflecting element 203d, and converges the yellow light in the vicinity of the deflection reflection surface of the polygon mirror 104 in the sub-scanning direction.

  The polygon mirror 104 has a four-stage mirror having a two-stage structure, and each mirror serves as a deflection reflection surface. The light from the cylinder lens 204a and the light from the cylinder lens 204d are respectively deflected on the first (lower) deflecting / reflecting surface, and the light and cylinder from the cylinder lens 204b are deflected on the second (upper) deflecting / reflecting surface. It arrange | positions so that the light from the lens 204c may be deflected, respectively. Further, the first-stage deflecting / reflecting surface and the second-stage deflecting / reflecting surface rotate with a phase shift of 45 °, and light scanning is performed alternately in the first and second stages (see FIG. 6). ).

  As an example, as shown in FIG. 7A, when the light deflected by the second-stage deflecting / reflecting surface is scanning light, the light deflected by the first-stage deflecting / reflecting surface has an adverse effect. In addition, as shown in FIG. 7B, when the light deflected by the first-stage deflecting / reflecting surface is scanning light, the light deflected by the second-stage deflecting / reflecting surface has an adverse effect. The light shielding plate SD may be provided so as not to affect.

  The fθ lens 105 a and the fθ lens 105 b are disposed on the −X side of the polygon mirror 104, and the fθ lens 105 c and the fθ lens 105 d are disposed on the + X side of the polygon mirror 104.

  The fθ lens 105a and the fθ lens 105b are stacked in the Z-axis direction, the fθ lens 105a faces the first-stage deflection / reflection surface, and the fθ lens 105b faces the second-stage deflection / reflection surface. Further, the fθ lens 105c and the fθ lens 105d are stacked in the Z-axis direction, the fθ lens 105c faces the second-stage deflection reflection surface, and the fθ lens 105d faces the first-stage deflection reflection surface.

  Therefore, the black light deflected by the polygon mirror 104 enters the fθ lens 105a, the yellow light enters the fθ lens 105d, the cyan light enters the fθ lens 105b, and the magenta light enters the fθ lens 105c.

  Further, each fθ lens has a non-arc surface shape having such a power that the light spot moves at a constant speed in the main scanning direction on the corresponding photosensitive drum surface as the polygon mirror 104 rotates. Yes.

  The black light transmitted through the fθ lens 105a forms a spot image on the photosensitive drum 30a via the folding mirror 106a, the toroidal lens 107a, and the folding mirror 108a (see FIG. 8).

  The cyan light transmitted through the fθ lens 105b forms a spot image on the photosensitive drum 30b via the folding mirror 106b, the toroidal lens 107b, and the folding mirror 108b (see FIG. 8).

  The magenta light transmitted through the fθ lens 105c forms a spot image on the photosensitive drum 30c via the folding mirror 106c, the toroidal lens 107c, and the folding mirror 108c (see FIG. 8).

  The yellow light transmitted through the fθ lens 105d forms a spot image on the photosensitive drum 30d via the folding mirror 106d, the toroidal lens 107d, and the folding mirror 108d (see FIG. 8).

  The folding mirrors are arranged so that the optical path lengths from the polygon mirror 104 to the photosensitive drums coincide with each other, and the incident position and the incident angle of light on the photosensitive drums are equal to each other. ing.

Each light detecting sensor, as shown in FIG. 9, in the light-receiving surface, the main mutual spacing in the scanning direction is _one different first light receiving portion 205 second light receiving portion by the direction of a position perpendicular to the main scanning direction 205 ₂ , an amplifier (AMP) 205 ₃ that amplifies a signal (photoelectric conversion signal) corresponding to the amount of light received from the light receiving element, an output signal level of the amplifier 205 ₃ , and a preset reference level comparing the Vs, and a comparator (CMP) 205 ₄ that outputs the result of the comparison. The output signal of the comparator 205 ₄ is supplied to the main control unit 210. In amplifier 205 _3, the inverted input signal. Therefore, as the amount of light received by the light receiving element is large, the output signal level of the amplifier 205 ₃ decreases.

  These light detection sensors are used to detect a positional deviation amount in the sub-scanning direction of the light spot on the corresponding photosensitive drum (hereinafter also referred to as “sub-scanning deviation amount” for convenience). When detecting the sub-scanning deviation amount, a plurality of light emitting units selected from among the 32 light emitting units constituting the laser array (hereinafter also referred to as “detecting light emitting unit” for convenience) are used. Light (hereinafter also referred to as “detection light” for convenience) enters each light detection sensor while moving in the Y-axis direction.

The reference level Vs, all of the detection light is set to a slightly higher level than the output signal level of the amplifier 205 ₃ when it is received by the light receiving element. Therefore, when the light receiving element has received all of the detection light, the judgment result of the comparator 205 ₄ changes, the output signal of the comparator 205 ₄ changes accordingly.

Here, as shown in FIG. 10 as an example, the first light receiving portion 205 ₁ has a rectangular shape of the light receiving portion, the longitudinal direction is perpendicular to the moving direction of the detection optical in the light receiving plane ing. The second light receiving portion 205 ₂ is a substantially rectangular light receiving portion, of the first light receiving portion 205 ₁ are arranged in the moving direction of the detection light. The second longitudinal direction of the light receiving portion 205 ₂ is inclined by an angle theta with respect to the first longitudinal direction of the light receiving unit 205 ₁ in the light-receiving surface (0 <θ <90 °) .

As shown in FIG. 11A, four light emitting units (v8, v16, v24, v32) arranged in a line along the S direction are selected as the detection light emitting units. To do. In each light emitting part, the interval between two adjacent light emitting parts is equal. The light spot of the detection light on the light receiving surface in this case is shown in FIG. A symbol AR in FIG. 6B indicates a quadrangular virtual region surrounding the light spot of the detection light on the light receiving surface. The detection light is incident on the light sensor while moving in the main scanning direction, as shown in FIG. 12 as an example, when the detection light is received by the first light receiving portion 205 ₁ and the second light receiving portion the output signal of the comparator 205 ₄ when it is received by the 205 ₂ changes.

For example, if the difference between the reference value of time Ts from falling in the output signal of the comparator 205 ₄ to the fall and .DELTA.Ts, following (1) equation relationship between .DELTA.Ts and the sub-scanning shift amount Δh There is. Here, v is the moving speed of the detection light.

  Δh = (v × ΔTs) / tan θ (1)

  Note that the size of each light receiving portion includes the entire quadrangular virtual region (region AR in FIG. 11B) surrounding the light spot of the detection light on the light receiving surface of the light detection sensor. It has the size that can be. However, if it is too large compared to the virtual region, it is difficult to ensure uniformity of sensitivity quality over the entire surface of the light receiving element, resulting in a decrease in yield and an increase in cost.

  Further, the angle θ is suitably 30 ° to 60 °. When the angle θ is smaller than 30 °, the detection sensitivity is lowered. On the other hand, when the angle θ exceeds 60 °, the length H in the direction perpendicular to the main scanning direction with respect to the length D in the main scanning direction of the light receiving surface decreases, and in order to ensure the necessary length H, the length H D becomes large, and the light receiving surface of the light detection sensor enters the image region, and it is necessary to set a wide effective region of the scanning optical system, resulting in a problem that the scanning lens becomes long. It is appropriate to set the length H and the length D to H = 1 to 3 mm and D = 5 mm or less respectively without causing the above problem. It is optimal when the angle θ is 45 °.

Figure 13 shows a portion of the output signal of the comparator 205 ₄ when the polygon mirror 104 is rotating continuously. As the time from the falling of the output signal of the comparator 205 ₄ to the fall is time Ts from the first light receiving portion 205 ₁ to ₂ second light receiving portion 205, the second light receiving portion 205 ₂ from the first light receiving portion 205 There is a time up to ₁ (T _L ). The ratio of Ts to _TL is determined by the scanning width and the rotation speed (scanning speed) of the polygon mirror 104, and is usually Ts: _TL = 1: 200 to 400.

FIG. 14 is a histogram of the plurality of times observed. Main controller 210 stores time measurement data sequentially in a memory (not shown) in order to reduce the influence of time variation due to polygon mirror 104, divides them into two groups, and shortens the time. The Δh is obtained using the average value of the two. As a method of separating the shorter one, there is a method of applying a filter by calculating an intermediate time between Ts and _TL because there is a large difference between the two groups.

  By the way, in the polygon mirror, surface deflection, scratches, dents, and flatness (a degree that does not affect the image) are different for each deflecting reflecting surface, so that light from all deflecting reflecting surfaces is used as in this embodiment. By doing so, detection accuracy can be improved.

It is to be noted that the number of time samples is preferably as long as variation components are taken into consideration, but it is not between the image formation (the time during which the light source of the optical scanning device is controlled to emit light based on the image signal) and the image formation on the next page. It is preferable that the number of times of scanning is within the image forming time (between print pages). Specifically, the number of samples is preferably about 100 to 500. The number of samples is preferably an even multiple of the number of polygon mirror surfaces. This is because the number of samples for one surface of the polygon mirror is 2 (Ts and T _L ), the surface is tilted, and the jitter has a cycle of one rotation of the polygon mirror (the entire circumferential surface).

  The light detection sensor 205a is disposed at a position equivalent to the image plane, after the scanning-completed black light transmitted through the toroidal lens 107a is incident. Therefore, the sub-scanning deviation amount in the photosensitive drum 30a can be detected from the output signal of the light detection sensor 205a.

  The light detection sensor 205b receives cyan light after scanning that has passed through the toroidal lens 107b, and is disposed at a position equivalent to the image plane. Therefore, the sub-scanning deviation amount in the photosensitive drum 30b can be detected from the output signal of the light detection sensor 205b.

  The photodetection sensor 205c receives magenta light after scanning that has passed through the toroidal lens 107c, and is disposed at a position equivalent to the image plane. Therefore, the sub-scanning deviation amount in the photosensitive drum 30c can be detected from the output signal of the light detection sensor 205c.

  The light detection sensor 205d receives yellow light after scanning that has passed through the toroidal lens 107d, and is disposed at a position equivalent to the image plane. Therefore, the sub-scanning deviation amount in the photosensitive drum 30d can be detected from the output signal of the light detection sensor 205d.

  Further, the main controller 210 applies a voltage for correcting the deviation to the liquid crystal deflecting element 203a in accordance with the sub-scanning deviation amount in the photosensitive drum 30a, and in accordance with the sub-scanning deviation amount in the photosensitive drum 30b. A voltage for correcting the deviation is applied to the liquid crystal deflecting element 203b, and a voltage for correcting the deviation is applied to the liquid crystal deflecting element 203c in accordance with the amount of sub-scanning deviation in the photosensitive drum 30c. A voltage for correcting the deviation is applied to the liquid crystal deflection element 203d in accordance with the amount of sub-scanning deviation in the drum 30d.

  As is clear from the above description, in the optical scanning device 100 according to the present embodiment, a deflector is configured by the polygon mirror 104, and four fθ lenses (105a, 105b, 105c, 105d) and eight folding mirrors. (106a, 106b, 106c, 106d, 108a, 108b, 108c, 108d) and four toroidal lenses (107a, 107b, 107c, 107d) constitute a scanning optical system, and light detection sensors (205a, 205b, 205c). , 205d) constitutes a photodetector.

  Further, the main controller 210 constitutes a position correction device.

As described above, according to the optical scanning device 100 according to the present embodiment, the two light source units (200a, 200b) having a plurality of light emitting units, the polygon mirror 104 that deflects light from each light source unit, and the A scanning optical system for condensing the light deflected by the polygon mirror 104 on each photosensitive drum, and four light detection sensors (205a, 205b, 205c, 205d) provided corresponding to the photosensitive drums are provided. ing. Each light detection sensor enters a plurality of lights through the scanning optical system while moving in the main scanning direction, and the interval between the main scanning directions differs depending on the position in the direction orthogonal to the main scanning direction within the light receiving surface. comprising at least one light receiving element having a first light receiving portion 205 ₁ and a ₂ second light receiving portion 205, both the size of the first and second light receiving portion, a square shape surrounding a plurality of light spots on the light receiving surface The size can include the entire virtual region. Thereby, it becomes possible to secure a sufficient amount of light in each light receiving unit, and the light detection sensor can output a signal having an excellent S / N ratio. As a result, it is possible to accurately detect the positional deviation in the sub-scanning direction of the light spot formed on the surface of each photosensitive drum without increasing the cost.

  Further, the main controller 210 applies a voltage for correcting the deviation to the corresponding liquid crystal deflecting element in accordance with the amount of sub-scanning deviation in each photosensitive drum. As a result, color misregistration can be prevented.

  In addition, according to the printer 10 according to the present embodiment, an optical scanning apparatus that can accurately detect a positional deviation in the sub-scanning direction of a light spot formed on the surface of each photosensitive drum without incurring an increase in cost. As a result, it is possible to form a high-quality image at high speed without incurring an increase in cost.

  In the above embodiment, the case where the four light emitting units arranged in a line along the S direction are used as the detection light emitting units has been described. However, the present invention is not limited to this.

  For example, in FIG. 15A, the interval between two adjacent light emitting units is made larger than that in the above embodiment. The light spot of the detection light on the light receiving surface in this case is shown in FIG. In FIG. 16A, the interval between two adjacent light emitting portions is further increased. The light spot of the detection light on the light receiving surface in this case is shown in FIG. Thereby, the lifetime deterioration of the light emission part by a temperature rise can be suppressed. However, in any case, each light receiving portion needs to have a size that can include the entire rectangular virtual area AR surrounding the light spot of the detection light on the light receiving surface of the light detection sensor ( (Refer FIG. 17, FIG. 18).

For example, in the case of a 4 4 light emitting units located in the corner (v1, v8, v25, v32 ) detecting light emitting portion, when the light spot of the detection light passes through the first light receiving portion 205 _1, the output signal of the amplifier 205 _3, reference level Vs, and the output signal of the comparator 205 ₄ is shown in Figure 19. In this case, the reference level Vs is amplifier 205 _third output signal when the amplifier 205 _third output signal level and the light receiving element when the light-receiving element has received four light spots has received three light spots It is set to a level between levels.

  Further, when the amount of light emitted from the light emitting unit is small, more light emitting units may be used as the detection light emitting units. As an example, FIG. 20A shows a case where eight light emitting units are used as detection light emitting units. The light spot of the detection light on the light receiving surface in this case is shown in FIG.

  In addition, the light-emitting portion for detection may be selected so that the size of the virtual area AR becomes small (see FIGS. 21A and 21B). As a result, the light receiving element can be reduced in size and cost.

Also, due to a decrease in the reflectance and transmittance (deterioration with time) of the optical element and a decrease in the rotation speed of the polygon mirror due to a change in the writing density (the polygon mirror rotates at a rotation speed reduced by 50% due to a change from 1200 dpi to 600 dpi). and, as shown in FIG. 22 as an example, the waveform of the output signal of the amplifier 205 ₃ is deformed. In this case, it is possible to fall timing of the output signal of the comparator 205 ₄ shifts, erroneous sub-scanning shift amount is detected. By the way, the fall timing has a correlation with the integrated amount (integrated light amount) of the light amount incident on the light receiving element, and the above deviation can be eliminated by controlling the integrated light amount to be constant.

  The integrated light quantity is optimally controlled to maintain the initial value (factory default setting) set during the manufacturing (assembly) of the optical scanning device, but it does not cause a practical problem with respect to the detection accuracy. As long as it can be controlled within ± 10% of the initial value. That is, the control may be performed within a preset range.

  Specifically, the output signal of the light receiving element is input to a differentiating circuit, and control is performed so that the level of the differentiating circuit output becomes constant. For example, when writing of a black image is completed and light detection is being performed by the light detection sensor 205a (Lk1 in FIG. 6), the output from the differentiation circuit is monitored, and the next light is detected using the monitor result. Immediately before the light detection by the detection sensor 205a (Lk2 in FIG. 6), the drive signal of the light emitting unit is controlled so that the amount of received light per unit time is constant. This control may be performed by the main controller 210 by adding a differentiation circuit to the main controller 210.

Further, in the above-described embodiment, as shown in FIG. 23 as an example, each light detection sensor has a first interval in the main scanning direction that differs depending on the position in the direction orthogonal to the main scanning direction within the light receiving surface. first light-receiving element, the main mutual spacing in the scanning direction is different first light receiving portion 205 ₁₂ second light receiving portion by the direction of a position perpendicular to the main scanning direction with a light receiving portion 205 ₁₁ and the second light receiving section 205 ₂₁ 205 ₂₂ , a first amplifier (AMP1) 205 ₃₁ that amplifies a signal (photoelectric conversion signal) corresponding to the amount of light received from the first light receiving element, and light reception from the second light receiving element. The second amplifier (AMP2) 205 ₃₂ that amplifies a signal (photoelectric conversion signal) according to the amount, the output signal level of the first amplifier 205 _{31 and} the output signal level of the second amplifier 205 ₃₂ Comparison, may have a comparator 205 ₄ and outputting the comparison result. The reference level Vs is not necessary.

In this case, the first light receiving unit 205 ₁₂ is disposed on the detection light moving direction side of the first light receiving unit 205 ₁₁ , and the second light receiving unit 205 ₂₂ is disposed on the detection light of the second light receiving unit 205 ₂₁ . It is arranged on the moving direction side. Then, FIG. 24 as an example output signal of the output signal and comparator 205 ₄ of each amplifier when light is used as detection light from the four light-emitting portions which are arranged in a row along the S direction Is shown in Even in this case, the main controller 210 can similarly determine the sub-scanning deviation amount.

  Moreover, although the case where each laser array has 32 light emitting units has been described in the above embodiment, the present invention is not limited to this, and it is only necessary to have a plurality of light emitting units. A plurality of light emitting units may be arranged one-dimensionally.

  In the above embodiment, a light source unit may be provided for each color. That is, four light source units may be provided.

  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. For example, even if an image forming apparatus other than a printer (a copier, a facsimile, or a multi-function machine in which these are integrated), an image forming apparatus provided with the optical scanning device 100 can be used without increasing costs. Quality images can be formed at high speed.

  Further, an image forming apparatus using a color developing medium (positive photographic paper) that develops color by the heat energy of a beam spot as an image carrier may be used. In this case, a visible image can be directly formed on the image carrier by optical scanning.

  In the above-described embodiment, the case of a multicolor printer has been described as the image forming apparatus. However, the present invention is not limited to this, and the single-color image forming apparatus includes the optical scanning device having the light detection sensor. Therefore, it is possible to form a high-quality image at a high speed without incurring an increase in cost.

  As described above, according to the optical scanning device of the present invention, it is suitable for accurately detecting the positional deviation in the sub-scanning direction of the light spot formed on the surface to be scanned without increasing the cost. Yes. The image forming apparatus according to the present invention is suitable for forming a high-quality image at high speed without incurring an increase in cost.

1 is a diagram illustrating a schematic configuration of a printer according to an embodiment of the present invention. It is a perspective view which shows the optical scanning device in FIG. It is a figure for demonstrating the laser array of each light source unit in FIG. It is a figure for demonstrating each light beam splitting prism in FIG. It is a figure for demonstrating the effect | action of each liquid-crystal deflection | deviation element in FIG. It is a figure for demonstrating the time change of the write light quantity in the light source unit 200a. FIG. 7A and FIG. 7B are diagrams for explaining a light shielding plate, respectively. It is a side view which shows the optical scanning device 100 in FIG. It is a figure for demonstrating a photon detection sensor. It is a figure for demonstrating the light receiving element of a photon detection sensor. FIG. 11A is a diagram for explaining the detection light emitting unit, and FIG. 11B is a diagram for explaining the light spot of the detection light on the light receiving surface. It is FIG. (1) for demonstrating the output signal of a photon detection sensor. It is FIG. (2) for demonstrating the output signal of a photon detection sensor. It is a figure for demonstrating the histogram formation of the fall time interval in the output signal of a photon detection sensor. FIG. 15A is a diagram for explaining a first modification of the detection light emitting unit, and FIG. 15B is a diagram for explaining a light spot of the detection light on the light receiving surface at that time. FIG. 16A is a diagram for explaining a second modification of the detection light emitting unit, and FIG. 16B is a diagram for explaining a light spot of the detection light on the light receiving surface at that time. It is a figure for demonstrating the 1st light-receiving part corresponding to the light emission part for a detection of FIG. 16 (A). It is a figure for demonstrating the 2nd light-receiving part corresponding to the light emission part for a detection of FIG. 16 (A). It is a figure for demonstrating the output signal of the photon detection sensor in FIG. FIG. 20A is a diagram for explaining a third modification of the detection light emitting unit, and FIG. 20B is a diagram for explaining a light spot of the detection light on the light receiving surface at that time. FIG. 21A is a diagram for explaining a fourth modification of the detection light emitting unit, and FIG. 21B is a diagram for explaining a light spot of the detection light on the light receiving surface at that time. It is a figure for demonstrating the change of the waveform in the output signal of amplifier. It is a figure for demonstrating the modification of a photon detection sensor. It is a figure for demonstrating the output signal of the photon detection sensor of FIG.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 ... Printer (image forming apparatus), 30a-30d ... Photosensitive drum (scanned surface), 100 ... Optical scanning device, 104 ... Polygon mirror (deflector), 105a-105d ... f (theta) lens (a part of scanning optical system) ), 106a to 106d ... folding mirror (part of the scanning optical system), 107a to 107d ... toroidal lens (part of the scanning optical system), 108a to 108d ... folding mirror (part of the scanning optical system), 205a to 205d ... light detection sensor (photodetector), 205 ₁ , 205 ₁₁ , 205 ₁₂ ... first light receiving unit, 205 ₂ , 205 ₂₁ , 205 ₂₂ ... second light receiving unit, 205 ₄ ... comparator, 210 ... main controller ( Position correction device, light quantity control device), AR ... virtual region, Vs ... reference level.

Claims (8)

An optical scanning device that scans a surface to be scanned with light,
A light source unit having a plurality of light emitting portions;
A deflector for deflecting light from the light source unit;
A scanning optical system for condensing the light deflected by the deflector onto the surface to be scanned;
A plurality of light beams that are deflected by the deflector and pass through the scanning optical system are incident while moving in the main scanning direction, and in the light receiving surface, the distance in the main scanning direction depends on the position in the direction orthogonal to the main scanning direction. A photodetector including at least one light receiving element having a different first light receiving portion and a second light receiving portion;
The photodetector has a level at which the output of the comparator changes when the at least one light receiving element receives all of the plurality of lights as a reference level, and the output level of the at least one light receiving element is the level of the output. Including a comparator that outputs the result of comparison with the reference level;
Each of the first and second light receiving portions has a size capable of including the entire quadrangular virtual region surrounding a plurality of light spots on the light receiving surface of the photodetector. An optical scanning device. The plurality of light emitting units are two-dimensionally arranged,
2. The optical scanning according to claim 1, wherein the plurality of lights are light from at least three light emitting units of which the interval between two adjacent light emitting units is equal among the plurality of light emitting units. apparatus.   3. The optical scanning device according to claim 1, wherein the second light receiving unit is inclined with respect to the first light receiving unit within a light receiving surface of the photodetector. 4. The plurality of the respective amount of light, the optical scanning apparatus according to the light quantity control device for controlling in a preset range, in any one of claims 1 to 3, further comprising. A liquid crystal deflecting element that is disposed on an optical path of light toward the surface to be scanned and deflects incident light in a sub-scanning direction according to an applied voltage;
2. A position correction device that controls the applied voltage based on an output signal of the photodetector and corrects a positional deviation of the light spot on the scanned surface in the sub-scanning direction. The optical scanning device according to any one of to 4 . The photodetector includes a first light receiving element and a second light receiving element,
The first light receiving portions of the first and second light receiving elements are adjacent to each other in the main scanning direction, and the second light receiving portions of the first and second light receiving elements are adjacent to each other in the main scanning direction. It arrange | positions, The optical scanning device as described in any one of Claims 1-5 characterized by the above-mentioned. In an image forming apparatus that forms an image by optical scanning,
An image forming apparatus comprising the optical scanning apparatus according to any one of the at least one of claims 1 to 6 for performing the optical scanning. The image forming apparatus according to claim 7 , wherein the image is a multicolor image.