JP2008216514A - Optical scanning apparatus and image forming apparatus - Google Patents

Abstract

The present invention aims to improve the utilization efficiency of a light beam without increasing the cost of the apparatus.
Light amount control of a light source is performed by monitoring a light beam that does not contribute to scanning among light beams of a light beam. This makes it possible to control the light amount of the light source 10 without reducing the utilization efficiency of the light beam that contributes to scanning. Further, the light beam is guided to the photodetector 18 by the protective member 71. Therefore, it is not necessary to use an element such as a beam splitter for branching the light beam from the light source 10, and the cost of the apparatus can be reduced.
[Selection] Figure 4

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 a light beam, and an image forming apparatus including the optical scanning apparatus.

  Conventionally, as an image forming apparatus that forms an image using the Carlson process, for example, a surface of a rotating photosensitive drum is scanned with a light beam to form a latent image on the surface of the photosensitive drum, and the latent image is visualized. An image forming apparatus that forms an image by fixing a toner image obtained in this manner on a sheet as a recording medium is known. In recent years, this type of image forming apparatus is often used for simple printing as an on-demand printing system, and demands for higher image density and faster image output are increasing.

  In general, as a method for speeding up image output, it is conceivable to increase the printing speed by increasing the rotational speed of a polygon mirror for deflecting a light beam and the rotational speed of a photosensitive drum. However, if the rotational speed of the polygon mirror is increased, noise and vibration from the drive system increase, power consumption increases, and the durability of the apparatus decreases. Further, since high-speed image output has a trade-off relationship with high-density image, there is a disadvantage that the image quality is lowered as the rotational speed of the polygon mirror is increased.

  Therefore, as a method of simultaneously achieving higher image density and higher image output speed, a method has been proposed in which a light source is multi-beamed and a photosensitive drum is scanned with a plurality of light beams at one time (for example, Patent Documents). 1 and Patent Document 2). The methods described in Patent Document 1 and Patent Document 2 are based on a method in which divergent light from a vertical cavity surface emitting laser (VCSEL) having a plurality of light emitting points is collectively deflected on a photosensitive drum. Can be simultaneously scanned with a plurality of light beams.

  In the above-described surface-emitting laser array, the intensity of the light beam cannot be monitored using the rear emission light as is the case with the edge-emitting laser. As in this method, a part of the light beam emitted from the surface emitting laser array is branched by, for example, a beam splitter, and the light beam is monitored by receiving the branched light beam with a light receiving element or the like. is doing. However, in this method, since the intensity of the light beam is reduced by passing through the beam splitter, there is a disadvantage that the utilization efficiency of the light beam used for scanning is lowered. Further, since the beam splitter is relatively expensive, there is a disadvantage that the cost of the entire apparatus becomes high.

  For example, as shown in Patent Document 4, a method of monitoring reflected light reflected by an aperture when shaping a beam shape with an aperture or the like is also conceivable. However, in this method, an element that receives reflected light is considered. There are many restrictions on the placement of

JP-A-2005-250319 JP 2004-287292 A JP-A-8-330661 Japanese Patent Laid-Open No. 2006-179769

  The present invention has been made under such circumstances, and a first object of the present invention is to provide an optical scanning device capable of improving the utilization efficiency of a light beam without causing an increase in cost of the device. There is.

  A second object of the present invention is to provide an image forming apparatus capable of forming an image with high accuracy.

  According to a first aspect of the present invention, there is provided an optical scanning device that scans a surface to be scanned by deflecting a light beam in a main scanning direction by a deflecting unit, and a plurality of light emitting points that emit the light beam include: A light source two-dimensionally arranged in a first direction that forms a predetermined angle with the main scanning direction, and a second direction that is orthogonal to the main scanning direction or the first direction; A light-receiving element that receives at least a part of the light beam; and a light beam that travels in at least a third direction orthogonal to the first direction and the second direction, out of the light beams emitted from the light emitting points. And a protective member that defines a space in which the light source and the light receiving element are disposed.

  According to this, the optical scanning device includes a light source and a light receiving element that receives a light beam emitted from each light emitting point of the light source. Therefore, by monitoring the intensity of the light beam via the signal from the light receiving element, the light beam can be adjusted to a desired intensity, and as a result, the utilization efficiency of the light beam can be improved. . These light sources and light receiving elements are arranged in a space defined by a protective member having a light beam passage portion in the light beam emission direction. Accordingly, it is possible to avoid interference between the light source or the light receiving element and the foreign object when the light source and the light receiving element are assembled.

  From the second viewpoint, the present invention is an image forming apparatus including the optical scanning device of the present invention. According to this, the image forming apparatus includes the optical scanning device of the present invention. Therefore, it is possible to form an image with high accuracy.

  Hereinafter, an embodiment of the present invention will be described with reference to FIGS. FIG. 1 shows a schematic configuration of a printer 200 as an image forming apparatus according to the first embodiment.

  The printer 200 is a color printer that prints an image by transferring a toner image onto plain paper (paper) using a Carlson process. As shown in FIG. 1, the printer 200 includes an optical scanning device 100, a photosensitive drum 201, a charging charger 202, a toner cartridge 204, a cleaning case 205, a paper feed tray 206, a paper feed roller 207, a registration roller pair 208, a transfer roller A charger 211, a fixing roller 209, a paper discharge roller 212, a paper discharge tray 210, and a housing 220 for housing them are provided.

  The housing 220 has a substantially rectangular parallelepiped shape, and openings that communicate with the internal space are formed on the side walls on the + X side and the −X side.

  The optical scanning device 100 is disposed above the housing 220 and scans the surface of the photosensitive drum 201 by deflecting a light beam modulated based on image information in the main scanning direction (Y-axis direction in FIG. 1). To do. The configuration of the optical scanning device 100 will be described later.

  The photosensitive drum 201 is a cylindrical member in which a photosensitive layer having a property that becomes conductive when irradiated with a light beam on the surface thereof. The direction is arranged as a longitudinal direction, and is rotated clockwise in FIG. 1 (direction indicated by an arrow in FIG. 1) by a rotation mechanism (not shown). In the vicinity thereof, the charging charger 202 is disposed at the 12 o'clock (upper) position in FIG. 1, the toner cartridge 204 is disposed at the 2 o'clock position, and the transfer charger 211 is disposed at the 6 o'clock position. A cleaning case 205 is disposed at the hour position.

  The charging charger 202 is disposed with a predetermined clearance with respect to the surface of the photosensitive drum 201, and charges the surface of the photosensitive drum 201 with a predetermined voltage.

  The toner cartridge 204 includes a cartridge body filled with toner of a black image component, a developing roller charged with a voltage having a polarity opposite to that of the photosensitive drum 201, and the toner filled in the cartridge body is passed through the developing roller. To the surface of the photosensitive drum 201.

  The cleaning case 205 includes a rectangular cleaning blade whose longitudinal direction is the Y-axis direction, and is disposed so that one end of the cleaning blade is in contact with the surface of the photosensitive drum 201. The toner adsorbed on the surface of the photosensitive drum 201 is peeled off by the cleaning blade as the photosensitive drum 201 rotates, and is collected in the cleaning case 205.

  The transfer charger 211 is arranged with a predetermined clearance with respect to the surface of the photosensitive drum 201, and a voltage having a polarity opposite to that of the charging charger 202 is applied.

  The paper feed tray 206 is arranged with the + X side end protruding from an opening formed on the + X side wall of the housing 220, and can accommodate a plurality of sheets 213 supplied from the outside. .

  The sheet feeding roller 207 takes out the sheets 213 one by one from the sheet feeding tray 206, and enters a gap formed by the photosensitive drum 201 and the transfer charger 211 via a registration roller pair 208 including a pair of rotating rollers. To derive.

  The fixing roller 209 is composed of a pair of rotating rollers, overheats and pressurizes the paper 61, and guides it to the paper discharge roller 212.

  The paper discharge roller 212 is composed of a pair of rotating rollers and the like, and with respect to the paper discharge tray 210 disposed with the −X side end protruding from the opening formed in the −X side side wall of the housing 220, The sheets 213 sent from the fixing roller 209 are sequentially stacked.

  Next, the configuration of the optical scanning device 100 will be described. FIG. 2 is a diagram showing a schematic configuration of the optical scanning device 100. As shown in FIG. 2, the optical scanning device 100 includes a light source unit 70 and an optical system 102 housed in a rectangular parallelepiped optical housing 101 whose longitudinal direction is the X-axis direction. As shown in FIG. 3, the light source unit 70 is attached to an outer wall surface (hereinafter referred to as an attachment surface) on the −X side of the optical housing 101.

  FIG. 4 is a view of the light source unit 70 viewed from above (+ Z side), and FIG. 5 is a view of the light source unit 70 viewed from the −Y side. 4 and 5, the light source unit 70 includes the light source 10, the protective member 71 (not shown in FIG. 5), the base 72, the casing 74, the substrate 76, the photodetector 18, the condensing element 19, and the cup. The ring lens 11 is included.

  The light source 10 is a surface emitting semiconductor laser array in which, for example, VCSELs are two-dimensionally arranged as light emitting points. In this light source 10, as shown in FIG. 6, 32 VCSELs emitting divergent light on the light emitting surface (the surface on the -X side) are parallel to a straight line L1 that forms an angle θ1 with the Y axis. Are arranged in a matrix of 4 rows and 8 columns with the direction parallel to the Z axis as the column direction. In this embodiment, the VCSEL row interval Dz is 18.4 μm, the column interval Dy is 30 μm, and the interval dz between adjacent light emitting points in the Z-axis direction (sub-scanning direction) of each VCSEL is 2.3 μm ( = Dz / 8).

  The photodetector 18 is disposed on the −Y side of the light source 10 and outputs a signal (photoelectric conversion signal) corresponding to the intensity of the incident light beam.

  The protective member 71 is a container-like member that is open on the −X side and formed with an opening 71a on the + X side, and is emitted from the vicinity of the + Y side end of the light source 10 on the + Y side and the −Y side of the inner wall surface. A reflection surface is formed to reflect at least a part of the light beam and guide it to the photodetector 18. Further, the opening 71a has a shape when projected onto the light emitting surface of the light source 10 is a quadrangle that includes all the VCSELs and has the smallest area, as indicated by a virtual line in FIG. Is formed. In the present embodiment, the shape of the opening 71a is a parallelogram in which two sets of sides are parallel to the straight line L1 and the Z axis, respectively. The reflective portion can be formed by attaching a reflective material such as a mirror to the inner wall surface or depositing aluminum having a high reflectance.

  The condensing element 19 is made of, for example, a lens or a diffraction grating, and is fixed via a support member (not shown) at a position where the light beam traveling in the + X direction from each VCSEL of the light source 10 does not interfere inside the protective member 71. Yes. Then, the light beam incident from the −Y side is condensed near the reflection surface on the −Y side formed on the inner wall surface of the protection member 71.

  As shown in FIG. 4 and FIG. 5, the base 72 has a plate-like main body portion with a circular opening 72b formed in the center, and an annular protrusion formed on the upper surface of the main body portion so as to surround the circular opening 72b. And a lens support portion 72c having a longitudinal direction arranged below the annular convex portion 72a (on the −Z side) as the X-axis direction. A fixed shaft 81 and two rotating shafts 82A and 82B are arranged on the surface of the main body portion of the base 72 on the −X side so as to surround the circular opening 72b.

  The fixed shaft 81 is a cylindrical member having the longitudinal direction arranged on the + Y side of the circular opening 72b as the X-axis direction. For example, the + X side end portion is screwed into the main body portion of the base 72, 72 is fixed.

  The rotary shafts 82A and 82B are arranged on the -Y side of the circular opening 72b. As shown in FIG. 7, the rotation shafts 82A and 82B have a large diameter portion in which an external thread portion is formed on the outer peripheral surface of the -X side end portion. It is a stepped columnar member consisting of two parts, a small diameter part shorter than the thickness, with the longitudinal direction being the X-axis direction. These rotary shafts 82A and 82B are attached to the base 72 so as to be rotatable about an axis parallel to the X axis by inserting a small diameter portion into a circular hole 72d provided in the base 72, for example. Then, by attaching a pin 82a, for example, to a small diameter portion protruding into the recess 72e formed on the surface of the base 72 on the + X side, it is avoided that the base 72 falls off.

  As shown in FIG. 8, the lens support portion 72c is a protrusion having a fan-shaped cross section and a longitudinal direction as the X-axis direction. The upper surface of the lens support portion 72c is curved in a concave shape with a curvature similar to the curvature of the outer periphery of the coupling lens 11, and supports the coupling lens 11 so that its optical axis passes through the center of the circular opening 72b. ing.

  The coupling lens 11 is a lens having a refractive index of about 1.5119, and both of the first surface (light beam incident side surface) and the second surface (light beam emission side surface) are expressed by the following formulas ( 1). However, y is a coordinate in the main scanning direction with the optical axis position as the origin, and the values of the coefficients of the first surface and the second surface are as shown in Table 1 below.

  The optical axis collimation adjustment of the coupling lens 11 is performed by applying a UV curable adhesive in an amount of 300 μm or less to the upper surface of the lens support portion 72c provided on the base 72, as shown in FIG. In addition, the + Y side and the −Y side of the collimating lens 11 are disposed on the upper surface of the lens support portion 72c with the pair of jigs 300A and 300B sandwiched therebetween. Next, while moving the coupling lens 11 in the X-axis direction, the Y-axis direction, the Z-axis direction, and each axis by the jigs 300A and 300B, the focus position is detected using the knife edge method, and the position sensor The coupling lens 11 is adjusted to the optimum position while detecting the position of the optical axis AX. When the adjustment is completed, the UV curable adhesive is irradiated with UV to cure the adhesive.

  The casing 74 is formed by, for example, processing a metal plate, and is a box-like member having the longitudinal direction with the + X side opened as the Y-axis direction, as can be understood from FIGS. 4 and 5. In the casing 74, a pair of rectangular flange portions 74b and 74c are formed at the + X side end portions of the outer wall surfaces on the + Y side and the −Y side, and the flange portions 74b and 74c are formed on the base 72 by screws or the like (not shown), for example. It is fixed to. Further, a protruding portion 74 a having a substantially spherical shape at the + X side end is formed on the inner wall surface on the −X side of the casing 74.

  The substrate 76 is a substrate whose longitudinal direction is the Y-axis direction, and a protective member 71 is attached to the surface on the + X side. The light source 10 and the photodetector 18 described above are mounted on a substrate in a space defined by the substrate 76 and the protection member 71.

  As shown in FIG. 10, the board 10 has an opening 76 a into which the fixed shaft 81 can be inserted and a female screw that is screwed into a male screw portion of a pair of rotating shafts 82 </ b> A and 82 </ b> B around the light source 10. A pair of screwed portions 77A and 77B formed with portions are provided. In the present embodiment, the pair of screwed portions 77A and 77B are, for example, nuts having a stepped D-cut shape, for example, a D-type provided on the substrate from the + X side of the substrate 76 as shown in FIG. It is formed by fitting in the opening.

  4 and 5, the substrate 76 has a fixed shaft 81 inserted into the opening 76a via a pressing spring 83, and a pair of screwed portions 77A and 77B are a pair of rotating shafts. The main body portion of the base 72 is disposed in a state where it is screwed to 82A and 82B, and the central portion of the −X side surface is supported by the + X side end of the projecting portion 74a provided inside the casing 74. So that the center of the light source 10 coincides with the center of the circular opening 72b.

  Accordingly, the −X side of the substrate 76 is constantly urged in the direction of the arrow in FIG. 4 with respect to the protruding portion 74a by the elastic force of the pressing spring 83, so that the contact between the protruding portion 74a and the substrate 76 (hereinafter simply referred to as the substrate). The position of the substrate 76 is defined by three positions, the center point) and the positions of the screwing portions 77A and 77B, and the rotation shafts 82A and 82B are rotated to position the screwing portions 77A and 77B of the substrate 76. Can be adjusted in the X-axis direction to adjust the posture of the light source 10 mounted on the substrate 76. Specifically, as shown in FIG. 3, a tool tip such as a screwdriver is inserted from a circular hole 74d or 74e provided in the casing 74, and the rotary shafts 82A and 82B are rotated to thereby engage the screwing portions 77A, By moving each of 77B by the same distance in the + X direction or the −X direction, the light source 10 can be tilted about the axis parallel to the Z axis with the substrate center point of the substrate 76 as the center, and the threaded portions 77A and 77B. By moving one of them in the + X direction and moving the other in the -X direction, the light source 10 can be tilted about an axis parallel to the Y axis with the substrate center point of the substrate 76 as the center. Note that the tilt adjustment of the light source 10 suppresses, for example, variations in the beam spot diameter of the light beam emitted from the light source 10 before the light source unit 70 is attached to the optical housing 101, so that reduction of the amount of emitted light is most avoided. To do. For convenience of explanation, a tilt around the axis parallel to the Z axis of the light source 10 is defined as α tilt, and a tilt around the axis parallel to the Y axis is defined as β tilt.

  In the light source unit 70 configured as described above, the annular protrusion 72a of the base 72 is fitted into a circular opening (not shown) formed on the mounting surface of the optical housing 101, and the base 72 shown in FIG. As shown in FIG. 3, the screws 84A and 84B are screwed onto the mounting surface of the optical housing 101 through a pair of long holes 72f formed on the + X side and the −X side. On the other hand, it is attached so as to be rotatable about an axis AX parallel to the X axis. The lower side of the base 72 protrudes from the −Y side end of the pressing spring 91 supported by the protruding portion 101a on the + Y side among the pair of protruding portions 101a and 101b provided on the mounting surface of the optical housing 101. The rotational position about the axis AX is defined by being clamped by the + Y side end of the adjustment screw 92 that can move in the Y-axis direction by being screwed into the portion 101b. Thereby, for example, by rotating the adjusting screw 92 and moving in the + Y direction, the light source unit 70 is rotated in the direction indicated by the arrow a, and the adjusting screw 92 is rotated and moved in the −Y direction. Thus, the light source unit 70 can be rotated in the direction indicated by the arrow a ′.

  When actually rotating the light source unit 70 and adjusting the pitch of the light beam, first, the light source unit 70 is temporarily fixed to the optical housing 11 with screws 84A and 84B, and the adjusting screw 92 can be moved. It is located on the most -Y side of the range. Next, the adjusting screw 92 is moved to the + Y side while monitoring the pitch of the light beam in the sub-scanning direction with a measuring instrument (not shown). Then, when the pitch in the sub-scanning direction becomes a predetermined pitch, the movement of the adjusting screw 92 is stopped, and the light source unit 70 is firmly fixed to the optical housing 101 by the screws 84A and 84B.

  Returning to FIG. 2, the optical system 102 includes an aperture 12, a line image forming lens 13, a reflection mirror 14, and a polygon mirror disposed on the −Y side of the reflection mirror 14, which are sequentially disposed on the + X side of the light source unit 70. 15 and a first scanning lens 16 and a second scanning lens 17 which are sequentially arranged on the + X side of the polygon mirror 15.

  The aperture 12 has a rectangular opening having a width of 5.5 mm in the Y-axis direction (main scanning direction) and a width of 1.18 mm in the Z-axis direction (sub-scanning direction), and the center of the opening is a coupling lens. 11 is located on the + X side of the focal position of 11 (at a position 58.2 mm from the second surface of the coupling lens 11).

  The line image forming lens 13 is an anamorphic lens having a first surface having a refractive power in the Z-axis direction (sub-scanning direction) and a second surface having a refractive power in the Y-axis direction (main scanning direction). The light beam that has passed through 12 is condensed onto the polygon mirror 15 via the reflection mirror 14.

  The polygon mirror 15 is a quadrangular prism-shaped member whose upper surface is a square inscribed in a circle having a radius of 7 mm. Deflection surfaces are formed on the four side surfaces of the polygon mirror 15, and are rotated at a constant angular velocity in the direction of the arrow shown in FIG. 2 by a rotation mechanism (not shown). As a result, the light beam incident on the polygon mirror 15 is deflected in the Y-axis direction.

  The first scanning lens 16 has an image height proportional to the incident angle of the light beam, and moves the image surface of the light beam deflected at a constant angular velocity by the polygon mirror 15 at a constant speed with respect to the Y axis. Note that the curvatures of the first surface and the second surface of the first scanning lens 16 are as shown in Table 2 as an example.

  The second scanning lens 17 is arranged with the longitudinal direction as the Y-axis direction, and forms an incident light beam on the surface of the photosensitive drum 201. Note that the curvatures of the first surface and the second surface of the second scanning lens 17 are as shown in Table 3 below as an example.

  Here, the first surface and the second surface of the first scanning lens 16 and the second scanning lens 17 described above are aspherical, and both surfaces have a noncircular arc shape represented by Expression (1) in the main scanning direction. Thus, the curvature Cs (y) in the sub-scanning section (virtual section parallel to the optical axis and the sub-scanning direction) changes in the main scanning direction as indicated by the following equation (2). However, y is a coordinate in the main scanning direction with the optical axis position as the origin, and the values of the coefficients of the first surface and the second surface are as shown in Tables 4 to 7 as an example.

  The optical distances d1, d3, d5, d6, d8, d10 between the elements of the light source unit 70 and the optical system 102 described above, and the sizes d2, d4, d7, d9 of the elements in the optical axis direction are examples. As shown in Table 8 below. Further, by rotating the light source unit 70 about the axis AX with respect to the optical system 102, the pitch in the sub-scanning direction of the light beam condensed on the photosensitive drum 201 by the optical system 102 becomes a predetermined pitch. It is possible to adjust so that.

  Next, the operation of the printer 200 configured as described above will be described. When receiving image information from the host device, the optical scanning device 100 is driven by the modulation data based on the image information, and 32 light beams modulated based on the image information are emitted from the light source unit 70. When this light beam is condensed on the deflection surface of the polygon mirror 15 by the line image forming lens 13 via the aperture 12, it is deflected in the Y-axis direction by the polygon mirror 15. The light beam is incident on the first scanning lens 16 and the deflection speed is adjusted, and then the light beam is condensed on the surface of the photosensitive drum 201 via the second scanning lens 17. At this time, of the light beam emitted from the light source 10, the light beam that has not passed through the opening 71 a of the protection member 71 is reflected by the inner wall surface of the protection member 71, and at least a part of the light beam is emitted. The light is incident on the photodetector 18 through the reflecting portion and the condensing element 19. In the optical scanning device 100, a signal output when a light beam enters the photodetector 18 is constantly monitored, and the light amount of the light beam output from the light source 10 is controlled.

  The photosensitive layer on the surface of the photosensitive drum 201 is charged with a predetermined voltage by the charging charger 202, so that charges are distributed with a constant charge density. Then, when the photosensitive drum 201 is scanned by the light beam deflected by the polygon mirror 15, the photosensitive layer where the light beam is focused comes to have conductivity. It becomes zero. Accordingly, the photosensitive drum 201 rotating in the direction of the arrow in FIG. 1 is scanned with a light beam modulated based on image information, thereby forming an electrostatic latent image defined by the charge distribution on the surface. Is done.

  When an electrostatic latent image is formed on the surface of the photosensitive drum 201, toner is supplied to the surface of each photosensitive drum 201 by the developing roller of the toner cartridge 203. At this time, since the developing roller of the toner cartridge 203 is charged with a voltage having a polarity opposite to that of the photosensitive drum 201, the toner attached to the developing roller is charged with the same polarity as that of the photosensitive drum 201. Therefore, no toner adheres to the portion of the surface of the photosensitive drum 201 where the electric charges are distributed, and the toner adheres only to the scanned portion, so that the electrostatic latent image is visualized on the surface of the photosensitive drum 201. A toner image is formed. The toner image is attached to the sheet 213 by the transfer charger and then fixed by the fixing roller 209 to form an image on the sheet. The paper 213 on which the image is formed in this manner is discharged by the paper discharge roller 212 and sequentially stacked on the paper discharge tray 210.

  As described above, in the optical scanning device 100 according to the present embodiment, among the light beams emitted from the light source 10, at least a part of the light beams that have not passed through the opening 71 a of the protection member 71 are detected by the photodetector 18. The signal obtained by receiving the light is monitored and the light amount of the light beam output from the light source 10 is controlled. Therefore, the light beam can be accurately adjusted to a desired intensity, and as a result, the utilization efficiency of the light beam can be improved. The light source 10 and the photodetector 18 are arranged in a space defined by the protection member 71. Therefore, when the light source 10 and the photodetector 18 are assembled, it is possible to avoid interference between the light source 10 or the photodetector 18 and foreign matters such as tools.

  In the optical scanning device 100 according to the present embodiment, the light beam is guided to the photodetector 18 by the protection member 71. Therefore, it is not necessary to use an element such as a beam splitter for branching the light beam from the light source 10, and the cost of the apparatus can be reduced. Further, since the opening 71a of the protection member 71 also acts as an aperture, as a result, it is possible to suppress variation in spot diameter on the photosensitive drum 201.

  Further, in the optical scanning device 100 according to the present embodiment, based on the signal obtained by receiving the light beam other than the light beam traveling in the + X direction among the light beams emitted from the light source 10 by the photodetector 18, Light amount control is performed. That is, the light amount control of the light source 10 is performed by monitoring a light beam that does not contribute to scanning among the light beams of the light beam. Therefore, it is possible to control the light amount of the light source 10 without reducing the utilization efficiency of the light beam that contributes to scanning. The light source 10, the photodetector 18, and the protection member 71 are attached to a common substrate 76. Therefore, even if α tilt and β tilt are performed, the relative positional relationship of components such as the light source 10 does not change, so that it is possible to control the light amount of the light source 10 with high accuracy at all times.

  Further, in the optical scanning device 100 according to the present embodiment, the light emitting point is adjusted by tilting the substrate 76 accommodated in the light source unit 70 about the substrate center point around the axes parallel to the Z axis and the Y axis. Tilt adjustment (α tilt and β tilt) can be performed while keeping the distance between the two-dimensionally arranged light source 10 and the coupling lens 11 constant. Thereby, it is possible to easily correct the variation in relative position between each light emitting point of the light source 10 and the coupling lens 11, and it is possible to scan the surface of the photosensitive drum 201 with a light beam having a uniform illuminance. . At this time, the magnification | βm | in the main scanning direction is 4.9, the magnification | βs | in the sub-scanning direction is 2.3, and a scanning line interval of 5.3 μm can be obtained on the surface to be scanned, and the resolution is It can be applied to a scanning optical system of 4800 dpi.

  Further, in the present embodiment, as shown in FIG. 6, the distance between the light emitting points (between columns) farthest in the Y-axis direction (main scanning direction) of the light source 10 is in the Z-axis direction (sub-scanning direction). It is larger than the distance between the most distant light emitting points (between rows). Therefore, the variation in the relative position between each light emitting point and the coupling lens 11 can be easily corrected by performing α tilt particularly on the light source 10. Specifically, the beam spot shape of the light beam was as shown in Table 9 below. Note that the image height y is the origin (mm) of the light source 10 in the main scanning direction, dY is the diameter (μm) in the main scanning direction, and dz is the diameter (μm) in the sub-scanning direction.

  Further, in FIG. 11A, when the photosensitive drum 201 is scanned by the optical scanning device 100, the quadrilateral curvature in the main scanning direction with respect to the image height y is indicated by a dotted line, and the field curvature in the sub-scanning direction is indicated by a solid line. It is shown in From this figure, it can be seen that the field curvature in the main scanning direction and the sub-scanning direction converges within a range of ± 1 mm, and the field curvature is well suppressed. In FIG. 11B, the fθ characteristic with respect to the image height y when the optical beam is scanned by the optical system 102 is indicated by a dotted line, and the linearity is indicated by a solid line. From this figure, it can be seen that the fθ characteristic and linearity with respect to all image heights converge in a range of ± 0.5%, which is a favorable result.

  Further, the α tilt and β tilt mechanism of the light source 10 includes a fixed shaft 81, a pressing spring 83 attached to the fixed shaft 81, a pair of rotating shafts 82A and 82B, a protrusion 74a formed on the casing 74, and the like. It is a simple configuration. Therefore, it is possible to avoid an increase in cost of the apparatus.

  The VCSEL is formed in the light source 10 in a matrix of 4 rows and 8 columns. For example, as shown in FIG. 12A, 32 VCSELs are arranged in a matrix of 8 rows and 4 columns. Even when the distance between light emitting points (between columns) farthest in the Y-axis direction (main scanning direction) is smaller than the distance between light emitting points (between rows) farthest in the Z-axis direction (sub-scanning direction) Similarly, by performing β tilt with respect to the light source 10, it is possible to easily correct the variation in relative position between each light emitting point and the coupling lens 11. Furthermore, as shown in FIG. 12B, a light source 10 having light emitting points arranged in a matrix defined by two orthogonal axes can be used with an angle α tilt, for example.

  Further, the aperture 12 of the optical system 102 is disposed at a position closer to the polygon mirror 15 than the focal position on the exit side of the coupling lens 11. Accordingly, the distance between the center lines of the light beams corresponding to the most peripheral light emitting points on the deflection surface of the polygon mirror 15 is shortened, and the images in the Y-axis direction (main scanning direction) and the Z-axis direction (sub-scanning direction). The surface curvature can be improved. Hereinafter, the operation of the aperture 12 will be described with reference to FIGS. 13 (A) to 13 (B).

  FIG. 13A shows the aperture 12 disposed at the rear focal position of the coupling lens 11. When the aperture 12 is arranged at the rear focal position of the coupling lens 11, as shown in FIG. 13A, the light beam spreads on the deflection surface of the polygon mirror 15, particularly from the most peripheral light emitting point. The optical characteristics of the light beam will deteriorate. In this configuration, the most important characteristic is to obtain a desired scanning line interval on the surface to be scanned. In order to improve the spot diameter characteristic of the light beam in the main scanning direction and the sub-scanning direction, FIG. As shown in B), it is necessary to arrange the aperture 12 at a position closer to the polygon mirror 15 than the rear focal position of the coupling lens 11. As a result, the distance between the center lines of the light beams from the light emitting point at the outermost periphery on the deflection surface of the polygon mirror 15 can be shortened, and the field curvature in the main scanning direction and the sub-scanning direction can be improved. As a result, it is possible to obtain a good light beam having no variation in the diameter of the beam spot in the main scanning direction and the sub-scanning direction.

  Further, in the light beam emitted from the light emitting point at the outermost periphery of the light source 10, the center of the opening formed in the aperture 12 and the center of the beam spot do not coincide with each other as shown by a broken line in FIG. The use efficiency of the light beam from the light emitting point at the outermost periphery of the light source is lower than that of the light beam from the light emitting point at the center of the light source. Therefore, in this embodiment, by setting the output from the light emitting point at the outermost periphery of the light source 10 to be high, an optical scanning device having no density unevenness is realized.

  Further, when the optical system 102 is used, the amount of deviation between the path of the light beam emitted from the light emitting point at the outermost periphery of the light source 10 and the optical axis of the coupling lens 11 is larger in the main scanning direction than in the sub scanning direction. growing. However, when the width of the opening provided in the aperture 12 in the sub-scanning direction is larger than the width in the main scanning direction, the light amount variation increases. For example, FIGS. 15A and 15B are diagrams schematically showing the positional relationship of the openings formed in the aperture 12 with respect to the light beam intensity in the main scanning direction. D1, D1 ′, D2, and D2 ′ shown in FIGS. 15A and 15B indicate the ranges of the light beams that pass through the aperture 12, respectively, and the curve L indicates the ranges D1, D1 ′, D2, And integrated in the interval of D2 ′ represent the light quantity of the light beam that has passed through the aperture 12. D1 and D1 'and D2 and D2' have the same size, and D2 and D2 'are larger than D1 and D1'.

  As can be seen from FIGS. 15A and 15B, the rate of change of the light beam quantity when the range changes from D1 to D1 ′ is the light beam quantity when the range changes from D2 to D2 ′. It can be seen that the rate of change of becomes smaller. Therefore, it is necessary to make the aperture width of the aperture 12 in the main scanning direction with a large optical axis deviation larger than the aperture width in the sub-scanning direction. Further, in order to make the magnification in the sub scanning direction smaller than the magnification in the main scanning direction, it is necessary to increase the opening width of the aperture 12 in the main scanning direction and the opening width in the sub scanning direction. The significance of the arrangement on the polygon mirror 15 side is greater than the focal position on the exit side of the ring lens 11.

  The printer 200 according to the first embodiment includes the optical scanning device 100. Therefore, the photosensitive drum 201 can be scanned with a light beam having a uniform illuminance, and as a result, an image can be accurately formed on a sheet.

  In each of the above-described embodiments, the case where the scanning device 100 is used in a single color image forming apparatus (printer) has been described. However, the image forming apparatus corresponds to a color image as illustrated in FIG. It may be a tandem color machine equipped with a photosensitive drum. The tandem color machine shown in FIG. 16 includes a black (K) photosensitive drum K1, a charging device K2, a developing device K4, a cleaning unit K5, a transfer charging unit K6, and a cyan (C) photosensitive drum. C1, charging unit C2, developing unit C4, cleaning unit C5, transfer charging unit C6, magenta (M) photosensitive drum M1, charging unit M2, developing unit M4, cleaning unit M5, and transfer charging unit M6, yellow (Y) photosensitive drum Y1, charger Y2, developing unit Y4, cleaning unit Y5, transfer charging unit Y6, optical scanning device 900, transfer belt 901, fixing unit 902, and the like. I have.

  In this case, in the optical scanning device 900, the plurality of VCSELs in the surface emitting laser array 300 are divided into black, cyan, magenta, and yellow. The light beam from each VCSEL for black is irradiated to the photosensitive drum K1, the light beam from each VCSEL for cyan is irradiated to the photosensitive drum C1, and the light beam from each magenta VCSEL is irradiated to the photosensitive member. The drum M1 is irradiated with a light beam from each VCSEL for yellow so that the photosensitive drum Y1 is irradiated. The optical scanning device 900 may include an individual surface emitting laser array 300 for each color. Further, an optical scanning device 900 may be provided for each color.

  Each photosensitive drum rotates in the direction of the arrow in FIG. 16, and a charger, a developer, a transfer charging unit, and a cleaning unit are arranged in the order of rotation. Each charger uniformly charges the surface of the corresponding photosensitive drum. The surface of the photosensitive drum charged by the charger is irradiated with a beam by the optical scanning device 900, and an electrostatic latent image is formed on the photosensitive drum. Then, a toner image is formed on the surface of the photosensitive drum by the corresponding developing device. Further, the toner images of the respective colors are transferred onto the recording paper by the corresponding transfer charging means, and finally the image is fixed on the recording paper by the fixing means 30.

  In each of the above embodiments, the case where the optical scanning device 100, 100 ′ of the present invention is used in a printer has been described. However, an image forming apparatus other than a printer, for example, a copier, a facsimile, or the like is integrated. It is also suitable for a multifunction machine.

1 is a diagram illustrating a schematic configuration of a printer 200 according to a first embodiment of the present invention. 1 is a diagram illustrating a schematic configuration of an optical scanning device 100. FIG. 1 is a perspective view of an optical scanning device 100. FIG. It is the figure which looked at the light source unit 70 from the + Z side. It is the figure which looked at the light source unit 70 from the -Y side. 2 is a plan view showing a laser array 152. FIG. It is a figure for demonstrating the structure of rotating shaft 82A, 82B. It is the figure which looked at the light source unit 70 from the + X side. It is a figure for demonstrating the optical axis adjustment of the coupling lens. It is the figure which looked at the light source unit 70 from the -X side. FIG. 11A is a diagram illustrating the ellipsoidal curvature in the main scanning direction and the field curvature in the sub-scanning direction with respect to the image height y, and FIG. 11B is a diagram illustrating the fθ characteristic and linearity with respect to the image height y. It is. 12A and 12B are diagrams showing a modification of the light source 10. FIGS. 13A and 13B are diagrams (No. 1 and No. 2) for explaining the operation of the aperture 12. FIG. 6 is a third diagram for explaining the operation of the aperture 12; FIGS. 15A and 15B are diagrams (No. 4 and No. 5) for explaining the operation of the aperture 12. 1 is a diagram illustrating a schematic configuration of an image forming apparatus corresponding to a color image.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 10 ... Light source, 11 ... Coupling lens, 12 ... Aperture, 13 ... Line image formation lens, 14 ... Reflection mirror, 15 ... Polygon mirror, 16 ... 1st scanning lens, 17 ... 2nd scanning lens, 18 ... Photo detector, 19 ... Condensing element, 70 ... light source unit, 71 ... protective member, 71a ... opening, 72 ... base, 72a ... annular projection, 72b ... circular opening, 72c ... lens support, 72d ... round hole, 72e ... concave, 72f ... long hole, 74 ... casing, 74a ... projecting part, 74b, 74c ... flange part, 74d, 74e ... round hole, 76 ... substrate, 76a ... opening, 77A, 77B ... screwing part, 81 ... fixed shaft, 82A , 82B ... rotating shaft, 82a ... pin, 83 ... pressing spring, 84A, 84B ... screw, 91 ... pressing spring, 92 ... adjusting screw, 101 ... optical housing, 102 ... optical system, 101a, 10 b: protrusion, 200 ... printer, 220 ... housing, 201 ... photosensitive drum, 202 ... charging charger, 204 ... toner cartridge, 205 ... cleaning case, 206 ... paper feed tray, 207 ... paper feed roller, 208 ... registration roller pair 209, fixing roller, 210, discharge tray, 211, transfer charger, 212, discharge roller, 213, paper.

Claims (12)

An optical scanning device that scans a surface to be scanned by deflecting a light beam in a main scanning direction by a deflecting unit,
A light source in which a plurality of light emitting points emitting the light beam are two-dimensionally arranged in a first direction that forms a predetermined angle with the main scanning direction and a second direction that is orthogonal to the main scanning direction or the first direction. When;
A light receiving element for receiving at least a part of the light beams respectively emitted from the plurality of light emitting points;
The light source and the light receiving element have a passing portion that allows at least a light beam traveling in a third direction orthogonal to the first direction and the second direction to pass among light beams emitted from the light emitting points. A protective member that defines a space in which the optical scanner is disposed.   The said protection member reflects the light beam which does not pass the said passage part among the light beams of the said light beam, and condenses at least one part of the reflected light beam to the said light receiving element. The optical scanning device described.   The said passing part is a parallelogram opening defined by a set of sides parallel to the first direction and a set of sides parallel to the second direction. 2. The optical scanning device according to 2. An optical element for coupling light beams respectively emitted from the plurality of light emitting points;
The holding member which hold | maintains the said light source, the said light receiving element, the said protection member, and the said optical element so that rotation around the axis | shaft parallel to the said 3rd direction is possible integrally. The optical scanning device according to Item.   5. The optical scanning device according to claim 4, further comprising a rotating unit that rotates the light source and the optical element about an axis substantially parallel to the main scanning direction or a sub-scanning direction orthogonal to the main scanning direction.   When the distance between the light emitting points farthest in the main scanning direction of the light emitting points arranged in two dimensions is longer than the distance between the light emitting points farthest in the sub scanning direction. The optical scanning device according to claim 5, wherein the light source is rotated about an axis substantially parallel to the sub-scanning direction.   When the distance between the light emitting points farthest in the sub-scanning direction of the light emitting points arranged in two dimensions is longer than the distance between the light emitting points farthest in the main scanning direction, 6. The optical scanning device according to claim 5, wherein the light source is rotated about an axis substantially parallel to the main scanning direction. Further comprising a substrate on which the light source, the light receiving element, and the protective member are arranged on one side;
The said rotation means rotates the said board | substrate centering on the point corresponding to the center of the said light source of the surface of the other side of the said board | substrate. The optical scanning device described.   The rotating means includes support means for supporting the center point, positioning means for positioning at least two points other than the center point, and biasing means for pressing the substrate against the support means. The optical scanning device according to claim 8.   On the path of the light beam emitted from the light source, the optical element has an opening that is disposed at a position closer to the deflecting unit than the focal position on the emission side of the optical element and restricts at least the light beam in the main scanning direction of the light beam. The optical scanning device according to claim 1, further comprising a member.   An image forming apparatus comprising the optical scanning device according to claim 1. The image forming apparatus according to claim 11, wherein the image forming apparatus is a multicolor image forming apparatus.

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