JP5505870B2 - 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. In this case, the image forming apparatus includes an optical scanning device, deflects laser light emitted from a light source using an optical deflector, and rotates the surface of a photosensitive drum (hereinafter referred to as “photosensitive drum”) as an axis. A method of rotating a photosensitive drum while scanning in the direction (main scanning direction) to form a latent image on the surface of the photosensitive drum is common.

  2. Description of the Related Art In recent years, in an image forming apparatus, output images have become multicolored, and a tandem type image forming apparatus having a plurality (usually four) photosensitive drums has become widespread.

  In order to obtain the writing start timing for each photosensitive drum, at least one synchronization detection optical system is provided.

  For example, Patent Document 1 and Patent Document 2 disclose an optical system that receives a light beam deflected by an optical deflector with a photodetector for synchronous detection without using a scanning lens.

  However, in the optical systems disclosed in Patent Document 1 and Patent Document 2, if a plurality of light sources and a photodetector for synchronization detection are to be mounted on the same substrate, the deflection angle at the optical deflector is increased. That is, it is necessary to reduce the number of faces of the polygon mirror. In order to maintain the same period even if the number of surfaces is reduced, it is necessary to increase the speed in inverse proportion to the number of surfaces. Polygon mirrors that support high-speed rotation are expensive and have the disadvantage of increasing the cost of the optical scanning device.

  Further, if the light that has passed through the scanning lens is directly received by the synchronous detection mounted on the same substrate as the plurality of light sources, the substrate becomes large, and the optical scanning device and the image forming apparatus become large. There was an inconvenience.

  The present invention has been made under such circumstances, and a first object of the present invention is to provide an optical scanning device that can be reduced in price and size without causing a decrease in synchronization detection accuracy. is there.

  A second object of the present invention is to provide an image forming apparatus that can be reduced in price and size without degrading image quality.

  According to a first aspect of the present invention, there is provided an optical scanning device that scans a plurality of scanned surfaces in the main scanning direction with light beams, respectively, and a plurality of light sources; parallel to the sub-scanning direction orthogonal to the main scanning direction An optical deflector that rotates a deflecting reflection surface around a certain axis and deflects light beams from the plurality of light sources; and includes at least one scanning lens and a plurality of folding mirrors, and the plurality of the deflected light beams by the optical deflector A scanning optical system for condensing the light beams from the light sources on the corresponding scanned surfaces; a light receiver disposed on the same substrate as the plurality of light sources; and the optical deflector among the plurality of folding mirrors Including a synchronization detection mirror that reflects the light beam folded near the end farther from the plurality of light sources in the folding mirror having the shortest optical path length in a direction toward the light receiver. An optical scanning apparatus comprising a; and a single synchronization detecting system for force.

  According to this, it is possible to reduce the price and the size without causing a decrease in the synchronization detection accuracy.

  According to a second aspect of the present invention, there are provided a plurality of image carriers; and the optical scanning device of the present invention that scans the plurality of image carriers with a light beam modulated according to corresponding image information. An image forming apparatus provided.

  According to this, it is possible to reduce the price and reduce the size without degrading the image quality.

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 describing a configuration of an optical scanning device 2010A in FIG. FIG. 3 is a diagram (No. 2) for describing a configuration of an optical scanning device 2010A in FIG. FIG. 5 is a diagram for explaining a scanning direction on the surface of a photosensitive drum by the optical scanning device 2010A. FIG. 6 is a diagram (No. 1) for describing a synchronization detection system of the optical scanning device 2010A. FIG. 10 is a diagram (No. 2) for describing a synchronization detection system of the optical scanning device 2010A. It is a figure for demonstrating the arrangement position and attitude | position of each optical element of a synchronous detection system. It is a figure for demonstrating the twist in a synchronous light beam. It is a figure for demonstrating elimination of the twist in a synchronous light beam. FIGS. 10A to 10C are diagrams for explaining the relationship between the photoreceptor pitch and the scanning optical system, respectively. FIG. 11A and FIG. 11B are diagrams for explaining comparative examples of the relationship between the photoreceptor pitch and the scanning optical system, respectively. It is a figure for demonstrating the enlargement of a circuit board. FIG. 13A is a diagram for explaining the height d1 of the deflecting reflection surface in the case of oblique incidence, and FIG. 13B is a diagram for explaining the height d2 of the deflecting reflection surface in the case of horizontal incidence. FIG. FIG. 3 is a diagram (part 1) for describing a configuration of an optical scanning device 2010B in FIG. 1; FIG. 3 is a second diagram for explaining the configuration of the optical scanning device 2010B in FIG. 1; FIG. 10 is a diagram for explaining a scanning direction on the surface of a photosensitive drum by the optical scanning device 2010B. FIG. 6 is a diagram (No. 1) for describing a synchronization detection system of the optical scanning device 2010B. FIG. 6 is a diagram (No. 2) for describing a synchronization detection system of the optical scanning device 2010B. FIG. 10 is a diagram (No. 1) for describing a modification of the optical scanning device 2010A. FIG. 10 is a second diagram illustrating a modification of the optical scanning device 2010A. FIG. 14 is a diagram (No. 1) for describing a synchronization detection system in a modification of the optical scanning device 2010A. FIG. 10 is a diagram (No. 2) for describing a synchronization detection system in a modification of the optical scanning device 2010A. It is a figure for demonstrating the optical scanning device corresponding to a counter scanning system.

  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 as an image forming apparatus according to an embodiment.

  The color printer 2000 is a tandem multicolor printer that forms a full-color image by superimposing four colors (black, cyan, magenta, and yellow), and includes two optical scanning devices (2010A, 2010B), four Photosensitive drums (2030a, 2030b, 2030c, 2030d), four cleaning units (2031a, 2031b, 2031c, 2031d), four charging devices (2032a, 2032b, 2032c, 2032d), and four developing rollers (2033a, 2033b, 2033c, 2033d), four toner cartridges (2034a, 2034b, 2034c, 2034d), transfer belt 2040, transfer roller 2042, fixing device 2050, paper supply roller 2054, registration roller pair 2056, paper discharge low 2058, the paper feed tray 2060, a discharge tray 2070, and a like communication control unit 2080, and a printer control device 2090.

  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 includes a CPU, a ROM described in a program written in code readable by the CPU, various data used when executing the program, a RAM as a working memory, an analog data An AD conversion circuit for converting the signal into digital data. The printer control device 2090 controls each unit in response to a request from the host device, and sends image information from the host device to each optical scanning device.

  The photosensitive drum 2030a, the charging device 2032a, the developing roller 2033a, the toner cartridge 2034a, and the cleaning unit 2031a 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. Configure.

  The photosensitive drum 2030b, the charging device 2032b, the developing roller 2033b, the toner cartridge 2034b, and the cleaning unit 2031b 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. Configure.

  The photosensitive drum 2030c, the charging device 2032c, the developing roller 2033c, the toner cartridge 2034c, and the cleaning unit 2031c are used as a set, and form an image forming station (hereinafter also referred to as “M station” for convenience) that forms a magenta image. Configure.

  The photosensitive drum 2030d, the charging device 2032d, the developing roller 2033d, the toner cartridge 2034d, and the cleaning unit 2031d 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. Configure.

  Each photosensitive drum has a photosensitive layer formed on the surface thereof. That is, the surface of each photoconductive drum is a surface to be scanned. Each photosensitive drum is rotated in the direction of the arrow in the plane of FIG. 1 by a rotation mechanism (not shown).

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

  The optical scanning device 2010A irradiates the surface of the photosensitive drum 2030a charged by the charging device 2032a with a light beam modulated based on the black image information from the printer control device 2090, and cyan from the printer control device 2090. The surface of the photosensitive drum 2030b charged by the charging device 2032b is irradiated with a light beam modulated based on the image information.

  The optical scanning device 2010B irradiates the surface of the photosensitive drum 2030c charged by the charging device 2032c with the light beam modulated based on the magenta image information from the printer control device 2090, and also outputs the yellow beam from the printer control device 2090. The surface of the photosensitive drum 2030d charged by the charging device 2032d is irradiated with a light beam modulated based on the image information.

  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 configurations of the optical scanning device 2010A and the optical scanning device 2010B will be described later.

  The toner cartridge 2034a stores black toner, and the toner is supplied to the developing roller 2033a. The toner cartridge 2034b stores cyan toner, and the toner is supplied to the developing roller 2033b. The toner cartridge 2034c stores magenta toner, and the toner is supplied to the developing roller 2033c. The toner cartridge 2034d stores yellow toner, and the toner is supplied to the developing roller 2033d.

  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 (toner image) moves in the direction of the transfer belt 2040 as the photosensitive drum rotates.

  The yellow, magenta, cyan, and black toner images are sequentially transferred onto the transfer belt 2040 at a predetermined timing, and are superimposed to form a multicolor image.

  Recording paper is stored in the paper feed tray 2060. A paper feed roller 2054 is disposed in the vicinity of the paper feed tray 2060, 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 feeds the recording paper toward the gap between the transfer belt 2040 and the transfer roller 2042 at a predetermined timing. As a result, the color image on the transfer belt 2040 is transferred to the recording paper. The recording sheet transferred here is sent to the fixing device 2050.

  In the fixing device 2050, heat and pressure are applied to the recording paper, thereby fixing the toner on the recording paper. The recording paper fixed here is sent to a paper discharge tray 2070 via a paper discharge roller 2058 and is sequentially stacked on the paper discharge tray 2070.

  Each cleaning unit removes toner (residual toner) remaining on the surface of the corresponding photosensitive drum. The surface of the photosensitive drum from which the residual toner has been removed returns to the position facing the corresponding charging device again.

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

  As shown in FIG. 2 and FIG. 3 as an example, the optical scanning device 2010A includes two light sources (2200a, 2200b), two coupling lenses (2201a, 2201b), two aperture plates (2202a, 2202b), 2 Two cylindrical lenses (2204a, 2204b), polygon mirror 2104A, deflector side scanning lens 2105A, three folding mirrors (2106a, 2106b, 2107a), two image plane side scanning lenses (2108a, 2108b), and two dustproofs Glass (2110a, 2110b), a scanning control device 12 and the like are provided. These are assembled at predetermined positions of the optical housing 2300A (not shown in FIG. 2, see FIG. 3).

  In this specification, in the XYZ three-dimensional orthogonal coordinate system, the direction along the longitudinal direction of each photosensitive drum is described as the Y-axis direction, and the direction parallel to the rotation axis of the polygon mirror is described as the Z-axis direction. In the following, for convenience, the direction corresponding to the main scanning direction is abbreviated as “main scanning corresponding direction”, and the direction corresponding to the sub scanning direction is abbreviated as “sub scanning corresponding direction”.

  The light source 2200a and the light source 2200b are arranged at positions separated from each other in the Z-axis direction. Each light source includes a semiconductor laser array having a plurality of light emitting portions having an oscillation wavelength of 659 nm.

  The light source 2200a and the light source 2200b are mounted on the same circuit board 11. The scanning control device 12 is formed as an IC chip and mounted on the circuit board 11.

  The coupling lens 2201a is disposed on the optical path of a light beam emitted from the light source 2200a (hereinafter also referred to as “light beam LBa”), and makes the light beam a substantially parallel light beam.

  The coupling lens 2201b is disposed on the optical path of a light beam emitted from the light source 2200b (hereinafter also referred to as “light beam LBb”), and makes the light beam a substantially parallel light beam.

  The aperture plate 2202a has a rectangular or elliptical aperture, and shapes the light beam LBa via the coupling lens 2201a.

  The aperture plate 2202b has a rectangular or elliptical aperture, and shapes the light beam LBb via the coupling lens 2201b.

  The cylindrical lens 2204a forms an image of the light beam LBa that has passed through the opening of the aperture plate 2202a in the vicinity of the deflection reflection surface of the polygon mirror 2104A in the Z-axis direction.

  The cylindrical lens 2204b focuses the light beam LBb that has passed through the opening of the aperture plate 2202b in the vicinity of the deflection reflection surface of the polygon mirror 2104A in the Z-axis direction.

  An optical system including the coupling lens 2201a, the aperture plate 2202a, and the cylindrical lens 2204a is a pre-deflector optical system of the K station.

  An optical system including the coupling lens 2201b, the aperture plate 2202b, and the cylindrical lens 2204b is a pre-deflector optical system of the C station.

  The polygon mirror 2104A has a six-sided mirror that rotates counterclockwise around an axis passing through the center thereof, and each mirror serves as a deflection reflection surface. That is, the polygon mirror 2104A has six deflecting reflecting surfaces.

  Here, the light beams from the respective cylindrical lenses are incident on the same deflecting / reflecting surface located on the + X side with respect to the rotation center of the polygon mirror 2104A.

  At this time, the light beam LBa from the cylindrical lens 2204a is incident on the deflecting / reflecting surface from a direction inclined 2.5 ° to the + Z side with respect to a plane (XY plane) orthogonal to the rotation axis of the polygon mirror 2104A. Further, the light beam LBb from the cylindrical lens 2204b is incident on the deflecting / reflecting surface from a direction inclined 2.5 ° to the −Z side with respect to a plane (XY plane) orthogonal to the rotation axis of the polygon mirror 2104A. That is, the values (absolute values) of the angle θa and the angle θb in FIG. 2 are 2.5 °.

  Hereinafter, when the light beam is incident on the deflecting / reflecting surface, it is referred to as “oblique incidence” to be incident from a direction inclined with respect to a plane orthogonal to the rotation axis of the polygon mirror 2104A, and the rotation axis of the polygon mirror 2104A. Incident from a direction parallel to a plane orthogonal to is called “horizontal incidence”. The angles θa and θb are referred to as “oblique incident angles”.

  The deflector-side scanning lens 2105A is disposed on the optical path of the light beam LBa and the light beam LBb deflected by the polygon mirror 2104A. The deflector-side scanning lens 2105A is a resin lens having a refractive index of 1.527153 with respect to light having a wavelength of 658 nm. Further, the deflector side scanning lens 2105A has power only in the main scanning corresponding direction, and does not have power in the sub scanning corresponding direction.

  The folding mirror 2106a is disposed on the optical path of the light beam LBa via the deflector-side scanning lens 2105A, and folds the optical path of the light beam LBa in the −X direction.

  The folding mirror 2107a is disposed on the optical path of the light beam LBa folded by the folding mirror 2106a, and folds the optical path of the light beam LBa in a direction toward the photosensitive drum 2030a.

  The image plane side scanning lens 2108a is disposed on the optical path of the light beam LBa folded by the folding mirror 2107a.

  Therefore, the light beam LBa deflected by the polygon mirror 2104A is irradiated onto the photosensitive drum 2030a via the deflector side scanning lens 2105A, the folding mirror 2106a, the folding mirror 2107a, the image plane side scanning lens 2108a, and the dustproof glass 2110a. A light spot is formed. This light spot moves in the + Y direction as the polygon mirror 2104A rotates (see FIG. 4). That is, scanning is performed on the photosensitive drum 2030a so as to approach the two light sources. The moving direction of the light spot at this time is the “main scanning direction” on the photosensitive drum 2030a, and the rotational direction of the photosensitive drum 2030a is the “sub-scanning direction” on the photosensitive drum 2030a.

  The folding mirror 2106b is disposed on the optical path of the light beam LBb via the deflector-side scanning lens 2105A, and folds the optical path of the light beam LBb in a direction toward the photosensitive drum 2030b.

  The image plane side scanning lens 2108b is disposed on the optical path of the light beam LBb folded by the folding mirror 2106b.

  Therefore, the light beam LBb deflected by the polygon mirror 2104A is irradiated onto the photosensitive drum 2030b through the deflector side scanning lens 2105A, the folding mirror 2106b, the image plane side scanning lens 2108b, and the dustproof glass 2110b, thereby forming a light spot. Is done. This light spot moves in the + Y direction as the polygon mirror 2104A rotates (see FIG. 4). That is, scanning is performed on the photosensitive drum 2030b in a direction approaching the two light sources. The moving direction of the light spot at this time is the “main scanning direction” on the photosensitive drum 2030b, and the rotational direction of the photosensitive drum 2030b is the “sub-scanning direction” on the photosensitive drum 2030b.

  Incidentally, a scanning area in the main scanning direction in which image information is written on each photosensitive drum is called an “effective scanning area”, an “image forming area”, or an “effective image area”.

  The optical system disposed on the optical path between the polygon mirror 2104A and each photosensitive drum is also called a scanning optical system.

  In this embodiment, the K station scanning optical system is composed of the deflector side scanning lens 2105A, the two folding mirrors (2106a, 2107a), the image plane side scanning lens 2108a, and the dustproof glass 2110a.

  Further, the scanning optical system of the C station is composed of the deflector side scanning lens 2105A, the folding mirror 2106b, the image plane side scanning lens 2108b, and the dust-proof glass 2110b.

  That is, the deflector side scanning lens 2105A is shared by the two stations.

  Each image plane side scanning lens has power mainly in the sub-scanning corresponding direction and has a surface tilt correction function. Therefore, it can be said that each image plane side scanning lens has the strongest power in the scanning scanning system in the sub-scanning corresponding direction.

  By the way, the optical scanning device 2010A further includes a synchronization detection system having a synchronization detection mirror 13, a condenser lens 14, and a light receiver 15, as shown in FIGS.

  The light receiver 15 is mounted on the circuit board 11. That is, the light source 2200a, the light source 2200b, the scanning control device 12, and the light receiver 15 are mounted on the same circuit board 11. As a result, the number of substrates can be reduced, and the cost can be reduced and the optical scanning device can be reduced in size.

  At this time, it is preferable that the light receiver 15 is provided between the plurality of light emitting units in the sub-scanning corresponding direction. In this case, the height in the sub-scanning corresponding direction can be reduced, and the circuit board 11 can be reduced in size.

  The synchronization detection mirror 13 is a light beam LBa which is deflected by the polygon mirror 2104A, passes through the deflector-side scanning lens 2105A, and is folded by the folding mirror 2106a. Reflects in the direction toward. The folding mirror 2106a is a folding mirror having the shortest optical path length from the polygon mirror 2104A among the plurality of folding mirrors. Hereinafter, for convenience, the light beam received by the light receiver 15 is also referred to as “synchronous light beam”.

  The condenser lens 14 is disposed on the optical path of the synchronous light beam reflected by the synchronization detection mirror 13 and condenses the synchronous light beam near the light receiving surface of the light receiver 15.

  The incident optical surface of the condensing lens 14 has a curvature radius in the direction corresponding to the main scanning and a curvature radius in the direction corresponding to the sub-scanning both of 55 mm. Further, the exit optical surface of the condenser lens 14 has a radius of curvature of ∞ (infinite) in the main scanning direction and -24 mm in the sub-scanning direction. The condensing lens 14 has a refractive index of 1.487553 with respect to light having a wavelength of 658 nm.

  The light receiver 15 outputs an electrical signal corresponding to the amount of received light. The output signal of the light receiver 15 is called a “tip synchronization signal”. The scanning control device 12 determines the writing start timing in each station based on the tip synchronization signal.

  An arrangement example of the deflector side scanning lens 2105A, the folding mirror 2106a, and the synchronization detection system is shown in FIG.

  The synchronous light flux via the condenser lens 14 is incident on the light receiver 15 with an incident angle α (see FIG. 5) of about 13 ° with respect to the XY plane. Thereby, it can suppress that the light reflected by the surface of the light receiver 15 returns to the light source 2200a. If the synchronous light beam enters the light receiver 15 at an incident angle of 0 °, the light reflected by the surface of the light receiver 15 returns to the light source 2200a, which may make the oscillation of the semiconductor laser in the light source 2200a unstable. However, if the incident angle of the synchronous light beam is too large, the synchronous light beam protrudes from the light receiving surface of the light receiver 15, and the amount of light received by the light receiver 15 is reduced, which may lead to so-called insufficient sensitivity. Therefore, the incident angle α of the synchronous light beam is preferably 5 ° to 18 °.

  Here, since the synchronous light beam is optically folded by the folding mirror closest to the polygon mirror 2104A and then separated, the light receiver 15 can be disposed at a position close to the two light sources, and the circuit board 11 Downsizing can be promoted.

  Further, when the optical path length from the deflection point on the deflection reflecting surface to the synchronization detecting mirror 13 is Lm, and the optical path length from the deflection point to the light receiver 15 is L, the following equation (1) is set. ing.

  If Lm is smaller than (1/3) L, the synchronization detection mirror 13 is too close to the deflection point, and the deflection angle necessary for separating the synchronization beam is increased, and the number of deflection reflection surfaces is reduced. The inconvenience of having to do so arises.

  Further, if Lm is larger than (1/2) L, the optical path length to the folding mirror 2107a becomes too long, resulting in an inconvenience that the optical scanning device is increased in size.

  Here, L = 270.4 mm and Lm = 103.1 mm, which satisfy the above formula (1). For this reason, it is possible to achieve both reduction in size and increase in the degree of freedom of layout.

  By the way, when the light beam is obliquely incident on the deflecting / reflecting surface, the light beam deflected by the deflecting / reflecting surface is twisted and incident on the deflector-side scanning lens 2105A, and the wavefront aberration is increased. In particular, the light beam directed to the vicinity of the end (peripheral image height) in the effective scanning region is significantly deteriorated, and so-called “thickening of the beam spot diameter” occurs. Since the synchronous light beam is a light beam that goes to the outside of the effective scanning region, the twist is further large.

  Therefore, in the present embodiment, as shown in FIG. 8 as an example, the marginal rays passing through the synchronization detection mirror 13 and the scanning beam (longitudinal direction) of the synchronization beam passing through the center of the synchronization beam. The angle β formed by the connected axes is about 2 degrees. This is due to the wavefront twist due to the oblique incidence.

  On the other hand, on the condenser lens 14 and the light receiver 15, the angle γ formed by the direction corresponding to the main scanning and the axis connecting the marginal rays passing through the center of the synchronizing beam and in the scanning direction (longitudinal direction) of the synchronizing beam is It is about 0.6 degrees (see FIG. 9).

  Here, the synchronization detection mirror 13 is folded back in the + Z direction with respect to the sub-scanning corresponding direction. That is, assuming that the eccentric angles of the folding mirror 2106a and the synchronization detection mirror 13 in the sub-scanning corresponding direction are βM1 and βDM, respectively, | βM1 | <| βDM |. As a result, it is possible to reduce the increase in beam spot diameter due to the wavefront twist peculiar to the oblique incidence optical system, and to reduce the diameter of the synchronous light flux. Therefore, more accurate synchronization detection can be performed.

  In this embodiment, the optical path of the light beam LBa that has passed through the deflector-side scanning lens 2105A is folded back to the photosensitive drum side (−Z side) by the folding mirror 2106a within the sub-scanning section (XZ plane). In this case, the applicability to the change of the interval between the two photosensitive drums (also referred to as “drum pitch”) is increased, and the light flux is also applied to the space on the photosensitive drum side (−Z side) of the polygon mirror 2104A in the sub-scan section. (See FIGS. 10A to 10C). Therefore, for example, it is possible to cope with an image forming apparatus having a narrower drum pitch.

  As an example, as shown in FIG. 11A, the optical path of the light beam LBa that has passed through the deflector-side scanning lens 2105A is moved away from the photosensitive drum within the sub-scan section (XZ plane) by the folding mirror 2106a. When folded back to the (+ Z side), the optical path of the light beam LBa folded back by the folding mirror 2107a is directed to the photosensitive drum 2030a, so that it passes through the XY plane including the deflection point (hereinafter referred to as “reference plane”) twice. To do. Near the reference plane, there are a deflector-side scanning lens 2105A and a polygon mirror 2104A. Since the optical path of the light beam LBa needs to avoid the deflector-side scanning lens 2105A and the polygon mirror 2104A, the degree of freedom with respect to the optical path layout becomes low (see FIG. 11B). For this reason, the folding by the folding mirror 2106a is preferably folded back to the photosensitive drum side (−Z side). In FIG. 11B, a part of the deflector-side scanning lens 2105A and the polygon mirror 2104A exist on the optical path of the light beam LBa, and cannot be used for an image forming apparatus with a drum pitch of P4.

  Also, if the light beam that has passed through the vicinity of the + Y side end portion of the deflector-side scanning lens is directly received by the light receiver, an increase in the size of the circuit board is caused as shown in FIG.

  In the present embodiment, since the two light beams are incident obliquely on the deflecting / reflecting surface, the length (height) of the deflecting / reflecting surface in the Z-axis direction is shortened compared to the case where it is incident horizontally. (See FIGS. 13A and 13B). In addition, if the length (height) of the deflecting / reflecting surface in the Z-axis direction is long, there are inconveniences that machining costs increase, windage loss during operation increases, and energy consumption increases and noise increases. .

  In the present embodiment, since the light beams from different stations are simultaneously deflected by the same deflecting / reflecting surface, it is possible to suppress color misregistration caused by variations in surface accuracy among the six deflecting / reflecting surfaces. Furthermore, even if two stations share one synchronization detection system, the accuracy of the respective write start positions can be maintained high.

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

  As shown in FIG. 14 and FIG. 15 as an example, the optical scanning device 2010B includes two light sources (2200c, 2200d), two coupling lenses (2201c, 2201d), two aperture plates (2202c, 2202d), 2 Two cylindrical lenses (2204c, 2204d), polygon mirror 2104B, deflector side scanning lens 2105B, three folding mirrors (2106c, 2106d, 2107c), two image plane side scanning lenses (2108c, 2108d), and two dustproofs Glass (2110c, 2110d), a scanning control device 22 and the like are provided. These are assembled at predetermined positions of the optical housing 2300B (not shown in FIG. 14, see FIG. 15).

  That is, the configuration is the same as that of the optical scanning device 2010A described above. The optical members are arranged in the same positional relationship as the optical scanning device 2010A.

  A light beam emitted from the light source 2200c (hereinafter, also referred to as “light beam LBc”) is obliquely incident on the polygon mirror 2104B through the coupling lens 2201c, the aperture plate 2202c, and the cylindrical lens 2204c.

  A light beam emitted from the light source 2200d (hereinafter, also referred to as “light beam LBd”) is incident obliquely on the polygon mirror 2104B via the coupling lens 2201d, the aperture plate 2202d, and the cylindrical lens 2204d.

  The oblique incident angle θc and the oblique incident angle θd are both 2.5 °.

  The light beam LBc deflected by the polygon mirror 2104B is applied to the photosensitive drum 2030c through the deflector-side scanning lens 2105B, the folding mirror 2106c, the folding mirror 2107c, the image-side scanning lens 2108c, and the dust-proof glass 2110c, and the light spot Is formed. This light spot moves in the + Y direction as the polygon mirror 2104B rotates (see FIG. 16). That is, scanning is performed on the photosensitive drum 2030c in a direction approaching two light sources. The moving direction of the light spot at this time is the “main scanning direction” on the photosensitive drum 2030c, and the rotational direction of the photosensitive drum 2030c is the “sub-scanning direction” on the photosensitive drum 2030c.

  The light beam LBd deflected by the polygon mirror 2104B is applied to the photosensitive drum 2030d through the deflector-side scanning lens 2105B, the folding mirror 2106d, the image-side scanning lens 2108d, and the dust-proof glass 2110d, thereby forming a light spot. Is done. This light spot moves in the + Y direction as the polygon mirror 2104B rotates (see FIG. 16). That is, scanning is performed on the photosensitive drum 2030d in a direction approaching the two light sources. The moving direction of the light spot at this time is the “main scanning direction” on the photosensitive drum 2030d, and the rotational direction of the photosensitive drum 2030d is the “sub-scanning direction” on the photosensitive drum 2030d.

  Here, the scanning optical system of the M station is composed of the deflector side scanning lens 2105B, the two folding mirrors (2106c, 2107c), the image plane side scanning lens 2108c, and the dustproof glass 2110c.

  The deflecting side scanning lens 2105B, the folding mirror 2106d, the image plane side scanning lens 2108d, and the dust-proof glass 2110d constitute a Y station scanning optical system.

  That is, the deflector-side scanning lens 2105B is shared by the two stations.

  As an example, the optical scanning device 2010B includes a synchronization detection system having a synchronization detection mirror 23, a condenser lens 24, and a light receiver 25, as shown in FIGS.

  The light source 2200c, the light source 2200d, the scanning control device 22, and the light receiver 25 are mounted on the same circuit board 21. As a result, the number of substrates can be reduced, and the cost can be reduced and the optical scanning device can be reduced in size.

  The synchronization detection mirror 23 is a light beam LBc that is deflected by the polygon mirror 2104B, passes through the deflector-side scanning lens 2105B, and is folded by the folding mirror 2106c. Is reflected in the direction toward the light receiver 25. The folding mirror 2106c is a folding mirror having the shortest optical path length from the polygon mirror 2104B among the plurality of folding mirrors.

  In addition, the synchronization detection mirror 23 is arranged so that the twist caused by the oblique incidence is eliminated in the synchronization light beam when being received by the light receiver 25, similarly to the synchronization detection mirror 13 in the optical scanning device 2010A. Has been.

  The condenser lens 24 is a lens equivalent to the condenser lens 14 and is disposed on the optical path of the synchronous light beam reflected by the synchronization detection mirror 23, and condenses the synchronous light beam near the light receiving surface of the light receiver 25. To do. The synchronous light beam via the condenser lens 24 enters the light receiver 25 with an incident angle of about 13 °.

  The light receiver 25 outputs an electrical signal (tip synchronization signal) corresponding to the amount of received light. The scanning control device 22 determines the writing start timing in each station based on the tip synchronization signal.

  Therefore, the optical scanning device 2010B has the same advantages as the optical scanning device 2010A.

  As described above, according to each optical scanning device according to the present embodiment, two light sources, two pre-polarizer optical systems, a polygon mirror, two scanning optical systems, a single synchronous detection system, and a scanning control device And so on.

  The two light sources, the scanning control device, and the light receiver are mounted on the same circuit board. Each deflecting / reflecting surface of the polygon mirror rotates so as to scan the surface of the photosensitive drum in a direction in which the light beam approaches the two light sources.

  Of the two light beams deflected by the polygon mirror, the light beam is folded by the folding mirror having the shortest optical path length from the polygon mirror, and is folded in the vicinity of the end portion farther from the two light sources in the folding mirror. The synchronized light beam is used as a synchronous light beam, and the synchronous light beam is reflected in the direction toward the light receiver by the synchronization detection mirror.

  In this case, it is possible to mount the two light sources and the light receiver of the synchronization detection system on the same circuit board without increasing the size of the circuit board, and the number of boards can be reduced. Moreover, the freedom degree regarding the layout of the optical path of a synchronous light beam can be improved. Therefore, it is possible to reduce the price and reduce the size without deteriorating the synchronization detection accuracy.

  Furthermore, it is possible to easily cope with a plurality of types of image forming apparatuses having different photoreceptor pitches. That is, it has high versatility.

  Further, even if the light beam is incident on the deflecting / reflecting surface obliquely, a decrease in synchronization detection accuracy due to the twist of the light beam peculiar to the oblique incidence can be suppressed.

  In addition, among the deflector-side scanning lens and the image plane-side scanning lens of the scanning optical system, the light beam that has passed through only the deflector-side scanning lens is incident on the synchronization detection system as a synchronous light beam. In this case, even if the incident position of the synchronous light flux in the sub-scanning corresponding direction is different from the design position due to the assembly error, it is possible to suppress a decrease in the synchronization detection accuracy.

  The color printer 2000 according to the present embodiment includes the optical scanning device 2010A and the optical scanning device 2010B. As a result, the price and size can be reduced without degrading the image quality. .

  In the above embodiment, the case where the light beam from each pre-deflector optical system is obliquely incident on the deflecting / reflecting surface of the polygon mirror has been described. However, the present invention is not limited to this. May be incident horizontally on the deflecting / reflecting surface of the polygon mirror (see FIGS. 19 and 20).

  Also in this case, of the two light beams deflected by the polygon mirror, the light beam is folded by the folding mirror having the shortest optical path length from the polygon mirror, and the end of the folding mirror far from the two light sources A light beam folded in the vicinity is used as a synchronous light beam, and the synchronous light beam is reflected by a synchronization detection mirror in a direction toward the light receiver (see FIGS. 21 and 22).

  In the above embodiment, the case where the synchronous light beam is a light beam before the start of writing has been described. However, the present invention is not limited to this, and the synchronous light beam may be a light beam after the completion of writing. In this case, each deflecting and reflecting surface of the polygon mirror rotates so as to scan the surface of the photosensitive drum in a direction in which the light beam moves away from the two light sources. At this time, the signal output from the photo detector of the synchronization detection system is called “rear end synchronization signal”.

  Moreover, although the said embodiment demonstrated the case where a deflector side scanning lens did not have power in a subscanning corresponding | compatible direction, it is not limited to this. Even if the optical surface of the deflector-side scanning lens has power in the sub-scanning corresponding direction, the light beam that has passed through the portion having no power in the sub-scanning corresponding direction near the end in the main scanning direction may be used as the synchronous light beam. .

  In the above embodiment, instead of the optical scanning device 2010A and the optical scanning device 2010B, a single optical scanning device corresponding to a so-called counter scanning method may be used (see FIG. 23).

  In the above embodiment, the toner image is transferred from the photosensitive drum to the recording paper via the transfer belt. However, the present invention is not limited to this and may be directly transferred to the recording paper.

  The semiconductor laser array of each light source in the above embodiment may be a vertical cavity surface emitting laser array.

  Moreover, although the said embodiment demonstrated the case where each light source had several light emission part, not only this but each light source may have only one light emission part.

  In the above embodiment, the color printer 2000 is described as the image forming apparatus. However, the present invention is not limited to this, and may be, for example, an optical plotter or a digital copying apparatus.

  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 a photographic paper as a transfer object 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.

  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 short, if the image forming apparatus is provided with the optical scanning device 2010A (or the optical scanning device 2010B), it is possible to reduce the price and size without degrading the image quality.

  In the above embodiment, the case where the image forming apparatus has four photosensitive drums has been described. However, the present invention is not limited to this. The image forming apparatus may have a plurality of photosensitive drums.

  As described above, the optical scanning device according to the present invention is suitable for reducing the cost and size without causing a decrease in synchronization detection accuracy. The image forming apparatus according to the present invention is suitable for reducing the price and size without degrading the image quality.

  DESCRIPTION OF SYMBOLS 11 ... Circuit board, 13 ... Mirror for synchronous detection, 14 ... Condensing lens (part of synchronous detection system), 15 ... Light receiver, 21 ... Circuit board, 23 ... Mirror for synchronous detection, 24 ... Condensing lens (synchronization) Part of the detection system), 25: light receiver, 2000: color printer (image forming apparatus), 2010A: optical scanning apparatus, 2010B ... optical scanning apparatus, 2030a to 2030d ... photosensitive drum (image carrier), 2104A ... polygon Mirror (optical deflector), 2104B... Polygon mirror (optical deflector), 2105A, 2105B... 2106b ... Folding mirror 2106c ... Folding mirror (Folding mirror with the shortest optical path length from the optical deflector), 2106d ... Folding Ra, 2107a, 2107c ... folding mirror, 2108a~2108d ... image-side scanning lens (second scanning lens), 2200a to 2200d ... light source.

Japanese Patent No. 3205263 Japanese Patent No. 4366074

Claims (10)

An optical scanning device that scans a plurality of scanned surfaces with a light beam in the main scanning direction,
With multiple light sources;
An optical deflector that rotates a deflection reflection surface about an axis parallel to the sub-scanning direction orthogonal to the main scanning direction, and deflects light beams from the plurality of light sources;
A scanning optical system including at least one scanning lens and a plurality of folding mirrors, and condensing the light beams from the plurality of light sources deflected by the optical deflector on the corresponding scanned surfaces;
A light receiver disposed on the same substrate as the plurality of light sources, and an end portion near the end farther from the plurality of light sources in the folding mirror having the shortest optical path length from the optical deflector among the plurality of folding mirrors. And a single synchronization detection system that includes a synchronization detection mirror that reflects the folded light beam in a direction toward the light receiver and outputs a synchronization signal of the scanning. The deflection reflection surface rotates so that the surface to be scanned is scanned in a direction in which a light beam approaches the plurality of light sources,
2. The optical scanning device according to claim 1, wherein the light beam reflected by the synchronization detection mirror is a light beam before writing is started. The deflecting reflection surface rotates so that the surface to be scanned is scanned in a direction in which the light beam moves away from the plurality of light sources,
2. The optical scanning device according to claim 1, wherein the light beam reflected by the synchronization detection mirror is a light beam before writing is completed.   4. The optical scanning device according to claim 1, wherein light beams from the plurality of light sources are obliquely incident on the deflection reflection surface in the sub-scanning direction.   The light beam reflected by the synchronization detection mirror passes through a portion of the scanning lens of the scanning optical system that has no power in the sub-scanning direction, and is folded back by a folding mirror having the shortest optical path length from the optical deflector. The optical scanning device according to claim 1, wherein the optical scanning device is a light beam. The scanning optical system includes at least one first scanning lens having no power in the sub-scanning direction, and a plurality of second scanning lenses having power in the sub-scanning direction,
The light beam reflected by the synchronization detection mirror passes only the at least one first scanning lens among the at least one first scanning lens and the plurality of second scanning lenses, and is emitted from the optical deflector. 6. The optical scanning device according to claim 1, wherein the optical beam is a light beam folded by a folding mirror having the shortest optical path length.   The light beam that is folded back by the folding mirror having the shortest optical path length from the optical deflector and travels toward the corresponding scanned surface passes through one of the plurality of second scanning lenses and is collected on the corresponding scanned surface. 7. The optical scanning device according to claim 6, wherein the optical scanning device is illuminated.   8. The light according to claim 1, wherein the folding mirror having the shortest optical path length from the optical deflector folds the light flux in a direction approaching the surface to be scanned with respect to the sub-scanning direction. Scanning device.   The optical path length from the deflection point on the deflection reflection surface to the synchronization detection mirror is not less than 1/3 times and not more than 1/2 times the optical path length from the deflection point to the light receiver. Item 9. The optical scanning device according to any one of Items 1 to 8. A plurality of image carriers;
An image forming apparatus comprising: the optical scanning device according to claim 1, wherein the plurality of image carriers are scanned with a light beam modulated according to corresponding image information.

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