JP2013088791A - Optical scanner, and image forming apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To maintain a uniform distribution of a light amount on a peripheral surface of a photoreceptor drum without applying a special coating on a folding mirror.SOLUTION: An incidence angle θ of a laser beam LB is defined within a range of 40° to 65° relative to a folding mirror 677. Reflectance of the folding mirror 677 relative to an S-polarization component of the laser beam is made higher than reflectance relative to a P-polarization component of the laser beam in a red wavelength region by 3%. Within a range of incidence angle of the laser beam at each position in a main-scanning direction of the folding mirror 677, a difference in the reflectance of the S-polarization component between an incidence at a minimum incidence angle and an incidence at a maximum incidence angle, and a difference in the reflectance of the P-polarization component between an incidence at a minimum incidence angle and an incidence at a maximum incidence angle are both defined as 5% or less. An inclination angle α in a sub-scanning direction of the folding mirror 677 is defined as 20° to 30°, and an inclination angle β in a sub-scanning direction of a dust-proof glass 621 is defined as 5° to 20°.

Description

  The present invention relates to an optical scanning apparatus and an image forming apparatus that form an electrostatic latent image by scanning light emitted from a light source in a main scanning direction of an image carrier.

  For example, an optical scanning device used in an image forming apparatus irradiates a circumferential surface of a uniformly charged photosensitive drum with laser light to form an electrostatic latent image. Such an optical scanning device includes a light source that emits laser light, a polygon mirror that reflects the laser light, an optical component that includes an fθ lens that forms an image of light reflected by the polygon mirror on the peripheral surface of the photosensitive drum, and an optical component. And a folding mirror that reflects the light passing through the photosensitive drum toward the peripheral surface of the photosensitive drum.

  Each surface of the polygon mirror is a mirror surface, and the laser beam is reflected on each surface while rotating to scan in the main scanning direction. After that, the laser light passes through the optical parts and the folding mirror to the peripheral surface of the photosensitive drum. However, if the amount of laser light that scans the peripheral surface of the photosensitive drum varies, the image density becomes uneven and the image quality deteriorates. It is easy to invite. Therefore, in order to obtain a good image quality, it is necessary to suppress variations in the amount of laser light.

  Patent Document 1 describes an optical device in which a special coating is applied so that the reflectance with respect to the P-polarized component of a folding mirror that reflects laser light toward a photosensitive drum becomes a predetermined reflectance. Specifically, by coating the folding mirror so that a large amount of P-polarized component light is reflected with little variation in the reflectance of the folding mirror due to wavelength variation, the variation in the amount of laser light irradiated to the photosensitive drum is suppressed. ing.

JP 2001-215427 A

  However, in the method described in Patent Document 1, a coating process is essential in manufacturing the folding mirror. That is, since the manufacturing process increases, it takes time and cost.

  The present invention has been made to solve the above problems, and an optical scanning device and an image forming device capable of maintaining the uniformity of the light amount distribution on the peripheral surface of the photosensitive drum without specially coating the folding mirror. The object is to provide an apparatus.

  An optical scanning device according to a first aspect of the present invention includes a light source that emits laser light, a deflection unit that deflects the laser beam emitted from the light source and scans the image carrier in a main scanning direction, and the deflection unit. The reflected laser beam is reflected so as to be guided onto the image carrier, and a long plate-like mirror extending in the main scanning direction, the light source, the deflecting means, and the mirror are arranged inside, and the mirror And a housing having a transmission window that transmits the laser beam reflected by the laser beam, an incident angle of the laser beam to the mirror is 40 ° to 60 °, and reflection of the mirror with respect to an S-polarized component of the laser beam The reflectance is 3% or more higher than the reflectance of the mirror with respect to the P deflection component of the laser light, and the difference between the maximum reflectance and the minimum reflectance at each position in the main scanning direction of the mirror with respect to the S deflection component and the previous The difference between the maximum reflectance and the minimum reflectance at each position in the main scanning direction of the mirror with respect to the P deflection component is 5% or less, and the mirror is perpendicular to the optical axis perpendicular to the laser beam incident on the mirror. The mirror is inclined in the sub-scanning direction orthogonal to the main-scanning direction and the reflecting surface of the mirror is inclined by 20 ° to 30 ° so as to face the image carrier, and the transmission window transmits laser light that passes through the transmission window. It is tilted by 5 ° to 20 ° in the sub-scanning direction with respect to the perpendicular to the optical axis.

  According to this configuration, it is possible to correct non-uniformity in the light amount distribution of the laser light irradiated to the image carrier without applying a coating for correcting the light amount distribution on the mirror. That is, variations in the amount of light on the image carrier can be suppressed, and deterioration in image quality can be suppressed. Further, it is possible to reduce the labor and cost of coating the mirror.

  The invention according to claim 2 is the optical scanning device according to claim 1, wherein the light source is a single beam system having one light emitting unit that emits laser light, or a multi-beam system having a plurality of the light emitting units. In the case of the multi-beam method, the plurality of light emitting units are arranged in a row, and an angle between the direction along the row of the light emitting units and the main scanning direction is in a range of 80 ° to 90 °. is there.

  According to this configuration, it is possible to correct nonuniformity in the light amount distribution of the laser light irradiated to the image carrier, regardless of whether the light source is a single beam system or a multibeam system. Since the arrangement conditions of the mirror and the transmission window for the single beam type and multi-beam type light sources can be made common, it is not necessary to assemble different optical scanning devices depending on the light source methods.

  The invention according to claim 3 is the optical scanning device according to claim 1 or 2, wherein the light source emits laser light in a red wavelength region or an infrared wavelength region.

  According to this configuration, the light amount distribution of the laser light irradiated to the image carrier is not uniform regardless of whether the light source emitting laser light in the red wavelength region or the light source emitting laser light in the infrared wavelength region is used. Can be corrected. Since the arrangement conditions of the mirror and the transmission window for the light source that emits the laser light in the red wavelength region and the light source that emits the laser light in the infrared wavelength region can be shared, the optical scanning device varies depending on the difference in the wavelength region of the laser light. There is no need to assemble.

  According to a fourth aspect of the present invention, there is provided an image forming apparatus comprising: an image carrier; and an optical scanning device that irradiates the image carrier with a laser beam based on image data. 3. It is a thing as described in any one of 3.

  According to this configuration, variation in the amount of light on the image carrier can be suppressed, and deterioration in image quality can be prevented.

  According to the present invention, in order to make the light amount distribution uniform even when any one of a plurality of types of light sources that emit laser light in a single-beam method, a multi-beam method, or a red wavelength region or an infrared wavelength region is used. Thus, it is possible to suppress variations in the amount of light on the image carrier and to prevent deterioration in image quality without applying a special coating to the mirror.

  Further, since the installation conditions of the mirror and the transmission window can be made common to a plurality of types of light sources, it is not necessary to assemble different optical scanning devices depending on the light sources, and the labor and cost for assembling the devices can be reduced.

1 is a schematic diagram of an internal structure of an image forming apparatus. The perspective view of an optical scanning device. The figure which showed the main component of the optical scanning device typically. FIG. The graph which showed the ratio of the S polarization component with respect to the P polarization component for every image height when the laser beam which the light source of the single beam system injects into a folding mirror. Sectional drawing when an optical scanning device is seen from the main scanning direction. The graph which showed the reflectance of the S polarization component and the P polarization component when a laser beam injects into the general mirror which has not performed special coating. The graph which showed the reflectance for every image height in the folding mirror of the laser beam which the single beam type light source emitted. The graph which showed the ratio of the S polarization component with respect to the P polarization component for every image height when the laser beam which the light source of the single beam system injects into dustproof glass. The graph which showed the transmittance | permeability of dustproof glass with respect to the P polarization component of a laser beam. The graph which showed the reflectance for every image height in a folding mirror about the laser beam which the multi-beam system light source emitted. The graph which showed the transmittance | permeability of the dust-proof glass with respect to the S polarization component of the laser beam which the light source of the multi-beam system emitted.

  Hereinafter, embodiments for carrying out the present invention will be described with reference to the drawings. FIG. 1 is a diagram schematically showing an internal configuration of an image forming apparatus 1 including an optical scanning device according to the present invention. In the present embodiment, a printer is described as an example of the image forming apparatus 1. However, in addition to this, an image forming apparatus adopting an electrophotographic system such as a copier, a facsimile machine, and a multifunction machine having a plurality of these functions. If it is. The image forming apparatus 1 described in this embodiment is a color printer, but may be a monochrome printer.

  A paper feed cassette 300 that stores a bundle of paper is disposed below the image forming apparatus 1. Further, an openable multi-tray 510 is disposed on the front side of the image forming apparatus 1. The multi-tray 510 is a manual feed tray. The paper conveyed from the paper feed cassette 300 or the multi-tray 510 is guided to a paper conveyance path formed in the image forming apparatus 1, and the image forming unit 410 that forms a toner image on the paper and the toner image is fixed to the paper. It is conveyed to the fixing unit 430. Thereafter, the sheet is discharged onto the discharge tray 23 through the discharge unit 450.

  The sheet conveyance path is based on the multi-tray 510 and has a first sheet feeding conveyance path 530 extending in the vertical direction of the image forming apparatus 1 and a downstream end of the sheet feeding cassette 300 positioned below the first sheet feeding conveyance path 530. And a second sheet feeding / conveying path 310 extending upward. The paper on the multi-tray 510 is drawn into the first paper feed conveyance path 530, and the paper in the paper feed cassette 300 is drawn into the second paper feed conveyance path 310 by the pickup roller 311. The paper drawn into each conveyance path is conveyed to the registration roller pair 320 that sends the paper to the image forming unit 410 in synchronization with the image forming process of the image forming unit 410.

  The sheet conveyance path further includes a section from the registration roller pair 320 to the fixing unit 430, a main conveyance path 330 that guides the sheet, a section from the fixing unit 430 to the discharge unit 450, and a discharge conveyance path 340 that guides the sheet. Including. The image forming unit 410 forms a toner image on a sheet that moves along the main conveyance path 330, and the fixing unit 430 fixes the toner image on the sheet.

  At appropriate positions of the first paper feed conveyance path 530, the second paper feed conveyance path 310, the main conveyance path 330, and the discharge conveyance path 340, conveyance roller pairs 360 for conveying the paper guided to these conveyance paths are arranged. Has been.

  The image forming unit 410 includes a yellow toner container 900Y, a magenta toner container 900M, a cyan toner container 900C, and a black toner container 900Bk. Below these containers, developing devices 10Y, 10M, 10C and 10Bk corresponding to the respective colors of YMCBk are arranged. The image forming unit 410 forms an image on a sheet using toner stored in the toner containers 900Y, 900M, 900C, and 900Bk.

  The image forming unit 410 includes a photosensitive drum 17 that carries toner images of respective colors. Around the photosensitive drum 17, a charger 16, a developing device 10 (10Y, 10M, 10C, and 10Bk), a transfer roller 19, and a cleaning device 18 are disposed.

  The charger 16 uniformly charges the surface of the photosensitive drum 17. The surface of the photosensitive drum 17 after charging is exposed by the optical scanning device 600 to form an electrostatic latent image. The optical scanning device 600 emits laser light to the surface of the charged photosensitive drum 17 based on, for example, an image signal from an external device.

  The developing devices 10Y, 10M, 10C, and 10Bk supply the respective color toners supplied from the toner containers 900Y, 900M, 900C, and 900Bk, respectively, and match the electrostatic latent images formed on the respective photosensitive drums 17. A toner image is formed. The transfer roller 19 forms a nip portion with the photosensitive drum 17 across the intermediate transfer belt 921, and primarily transfers the toner image on the photosensitive drum 17 onto the intermediate transfer belt 921. The cleaning device 18 cleans the peripheral surface of the photosensitive drum 17 after the toner image is transferred.

  The optical scanning device 600 has various optical system devices such as a light source, a polygon mirror, and a folding mirror, and emits light based on an image signal to the peripheral surface of the photosensitive drum 17 to form an electrostatic latent image. The optical scanning device 600 will be described in detail later.

  The intermediate transfer unit 92 includes an intermediate transfer belt 921, a driving roller 922, and a driven roller 923. On the intermediate transfer belt 921, toner images are overcoated from a plurality of photosensitive drums 17 (primary transfer). The overcoated toner image is secondarily transferred to the paper in the secondary transfer unit 98.

  The sheet fed from the registration roller pair 320 is supplied to a transfer nip portion between the intermediate transfer belt 921 and the transfer roller 981 constituting the secondary transfer portion 98. Thereafter, the sheet is sent to the fixing unit 430 while carrying the toner image transferred by the secondary transfer unit 98.

  The fixing unit 430 includes a heating roller 432 and a pressure roller 433 pressed against the heating roller 432. The paper sent out from the secondary transfer unit 98 is sent to the nip portion between the heating roller 432 and the pressure roller 433, and the toner on the paper is fixed to the paper. The fixing unit 430 transports the sheet toward the discharge roller 451 after fixing the toner on the sheet. The discharge roller 451 discharges the conveyed paper to the discharge tray 23.

  Next, the optical scanning device 600 in the present embodiment will be described. FIG. 2 is a perspective view of the optical scanning device 600. In the present embodiment, an example in which four optical scanning devices 600Y, 600M, and Bk corresponding to each color of YMCBk are provided is shown below the image forming unit 410 as shown in FIG. Has been placed.

  In FIG. 2, the optical scanning device 600Y disposed on the leftmost side emits laser light to the photosensitive drum 17 that forms a toner image using yellow toner. Similarly, the optical scanning device 600M is a photosensitive drum 17 for a magenta toner image, the optical scanning device 600C is a photosensitive drum 17 for a cyan toner image, and the optical scanning device 600Bk is a photosensitive drum 17 for a black toner image. Each is irradiated with a laser beam.

  The optical scanning device 600 includes a housing 620 having a substantially rectangular parallelepiped shape. The internal structure of the housing 620 will be described in detail with reference to FIG. 3. In general, a light source that emits laser light, a polygon mirror that reflects the laser light and scans in the main scanning direction, and laser light that reflects the polygon mirror are reflected. An optical component including an fθ lens that forms an image on the peripheral surface of the photosensitive drum 17, a folding mirror that reflects laser light that has passed through the optical component toward the peripheral surface of the photosensitive drum 17, and the like are housed.

  A substantially rectangular dust-proof glass (transmission window) 621 is provided on the upper surface of the housing 620. The dust-proof glass 621 extends in the main scanning direction of the optical scanning device 600 on the upper surface of the housing 620. Laser light from a light source disposed in the housing 620 passes through the dust-proof glass 621 and is irradiated on the peripheral surface of the photosensitive drum 17.

  FIG. 3 is a diagram schematically illustrating main components of the optical scanning device 600, and FIG. 4 is an external view of the light source 68. The optical scanning device 600 includes a light source 68, a collimating lens 678, a cylindrical lens 679, a polygon mirror (deflecting means) 671, a polygon motor 672, an fθ lens 676, and a folding mirror (mirror) 677.

  As the light source 68, for example, a semiconductor laser is used. The light source 68 is a single beam type light source (FIG. 4A) provided with one laser diode (light emitting portion) LD on the front end surface Y, or a plurality of laser diodes (light emitting portions) LD1 and LD2 on the front end surface Y. The light source of any type of a multi-beam type light source (FIG. 4B) provided with

  In the case of the multi-beam type light source 68, the laser diodes LD1 and LD2 are arranged in a line at a constant interval on the front end surface Y, and the normal line G passing through the center among the normal lines with respect to the front end surface Y is used as the rotation axis. And is disposed at a predetermined position of the optical scanning device 600. Specifically, when the laser beams emitted from the laser diodes LD1 and LD2 irradiate the peripheral surface of the photosensitive drum 17, the arrangement direction of the irradiation positions (image forming positions), that is, the laser diodes LD1 and LD2 are connected. The light source 68 is rotated and arranged in the X direction so that the line has a predetermined inclination angle (for example, 80 ° to 90 °) with respect to the main scanning direction. By doing so, the resolution in the sub-scanning direction can be adjusted. Usually, the pitch in the sub-scanning direction is determined according to the specifications of the apparatus, and the pitch in the main scanning direction is determined by this determination.

  4B illustrates a case where two laser diodes are provided as a multi-beam type light source, the number of laser diodes provided in the light source may be two or more.

  The laser diode disposed in the light source 68 mounted on the optical scanning device 600 according to the present invention emits laser light in the red wavelength region (660 nm to 680 nm) or the infrared wavelength region (770 nm to 790 nm). . That is, the optical scanning device 600 includes a total of four light sources of a single beam system using a laser diode in a red wavelength region or an infrared wavelength region, or a multi-beam system light source using a laser diode in a red wavelength region or an infrared wavelength region. It is possible to change the type of light source. Which type of light source is mounted on the optical scanning device 600 is determined at the time of circuit design, and the determined light source is assembled at the time of circuit assembly.

  The collimating lens 678 is disposed in the vicinity of the light source 68 and receives the laser light output from the light source 68 to adjust the beam diameter of the laser light. The cylindrical lens 679 is disposed on the downstream side of the collimating lens 678 when viewed from the traveling direction (arrow) of the laser light, and receives the laser light that has passed through the collimating lens 678 to further adjust the beam diameter of the laser light. The positions of the collimating lens 678 and the cylindrical lens 679 are set on the optical axis of the laser light.

  The polygon mirror 671 is disposed on the downstream side of the cylindrical lens 679 when viewed from the traveling direction of the laser beam. The polygon mirror 671 has, for example, regular hexagonal side surfaces, and the six side surfaces correspond to the reflecting surface 5a. The polygon mirror 671 is rotated at a predetermined speed by the polygon motor 672, and the laser beam that has passed through the cylindrical lens 679 is scanned in the longitudinal direction of the photosensitive drum 17 (that is, the main scanning direction indicated by the arrow D). So that the laser light is deflected. In FIG. 3, since the polygon mirror 671 rotates in the direction of the arrow R, the laser beam is scanned from the left side to the right side on the drum surface of the photosensitive drum 17. That is, the laser light emitted from the light source 68 draws the scanning line SL on the photosensitive drum 17 in the main scanning direction. One scanning line SL is drawn by one reflecting surface 5a. By repeating the drawing of one scanning line SL on the photosensitive drum 17 thus rotating, an electrostatic latent image is drawn along the sub-scanning direction. The sub-scanning direction corresponds to the rotation direction of the photosensitive drum 17.

  The fθ lens 676 is disposed on the downstream side of the polygon mirror 671 in the traveling direction of the laser light, and returns the laser light to the mirror 677 so that the laser light is scanned at a constant speed in the main scanning direction of the photosensitive drum 17. Lead to. The folding mirror 677 is disposed downstream of the fθ lens 676 when viewed from the traveling direction of the laser light, and reflects the laser light output from the fθ lens 676 toward the photosensitive drum 17. The reflected laser light passes through a dustproof glass 621 (not shown in FIG. 3) and irradiates the photosensitive drum 17.

  Due to the size limitation of the optical scanning device 6000, the laser beam is reflected by the folding mirror 677 and guided to the peripheral surface of the photosensitive drum 17, but when the laser beam is reflected by the folding mirror 677, the center of the image height (the folding mirror). A light amount difference is generated between the center portion of 677) and the image height end portion (end portion of the folding mirror 677). For this reason, conventionally, a special coating is applied to the folding mirror 677 to correct the unevenness of the light amount distribution. However, in this case, a coating process is essential in the manufacture of the folding mirror 677, and the manufacturing process is increased, which requires labor and cost.

  Therefore, a method for canceling out the difference in light quantity generated at the center of the image height and the end of the image height without applying a special coating to the folding mirror 677 will be described below. FIG. 5 shows the ratio of the S-polarized component to the P-polarized component for each image height when the laser beam emitted from the single beam type light source is incident on the folding mirror 677, for each tilt angle of the folding mirror 677 in the sub-scanning direction. It is the graph shown in.

  Here, the image height is a value indicating the position of the image on the evaluation surface of the optical system as a distance from the optical axis. In the present embodiment, the image height is on the evaluation surface (of the folding mirror 677). This corresponds to each position in the main scanning direction on the reflecting surface. Therefore, hereinafter, “image height” and “position in the main scanning direction” are used as the same meaning as appropriate.

  Next, “an inclination angle of the folding mirror 677 in the sub-scanning direction” will be described. FIG. 6 is a cross-sectional view of the optical scanning device 600 viewed from the main scanning direction, and an enlarged view A in FIG. 6 is a diagram for explaining an inclination angle of the folding mirror 677 in the sub-scanning direction. The inclination angle of the folding mirror 677 in the sub-scanning direction refers to an angle α between the perpendicular line PL2 with respect to the optical axis of the laser beam LB and the reflecting surface 677a of the folding mirror 677. That is, when the tilt angle when the folding mirror 677 is at the same position as the perpendicular line PL2 of the laser beam LB is 0 °, the reflecting surface 677a of the folding mirror 677 faces the photosensitive drum 17 side from the perpendicular line PL2 (arrow). The angle α when tilted (Y1 direction) is the tilt angle in the sub-scanning direction. Hereinafter, the inclination angle of the folding mirror 677 in the sub-scanning direction is simply referred to as “the inclination angle of the folding mirror 677”.

  And in order to implement | achieve the effect of this invention, there are conditions in the incident angle of the laser beam LB to the folding mirror 677, and the reflectance of the folding mirror 677. The range of the incident angle θ of the laser beam LB with respect to the folding mirror 677 is 40 ° to 65 °. If it demonstrates using FIG. 3, PL1 is a perpendicular with respect to the reflective surface of the folding mirror 677. FIG. The angle θ1 between the perpendicular PL1 and the incident light at the center of the folding mirror 677 is 40 °, and the angle θ2 between the perpendicular PL1 and the incident light at the end of the folding mirror 677 is 65 °. Hereinafter, the incident angle of the laser beam to the folding mirror 67 is collectively referred to as an angle θ.

  The light source 68 uses a laser beam that emits laser light in the red wavelength region or infrared wavelength region. The reflectivity of the folding mirror 677 with respect to the S-polarized component of the laser light in the red wavelength region is the laser light in the red wavelength region. 3% or more higher than the reflectance for the P-polarized light component. Similarly, the reflectivity of the folding mirror 677 for the S-polarized component of the laser light in the infrared wavelength region is 3% or more higher than the reflectivity for the P-polarized component of the laser light in the infrared wavelength region.

  This condition will be described. FIG. 7 is a graph showing the reflectance of the S-polarized component and the P-polarized component when the laser light is incident on a general mirror that is not specially coated (that is, equivalent to the folding mirror 677). As shown in this graph, ΔR, which is the difference between the reflectance of the S-polarized component and the reflectance of the P-polarized component, is always 3% or more. The reflectance of each deflection component can be adjusted by changing the film thickness of the metal layer on the surface constituting the folding mirror 677.

  Further, the reflectance and the incident angle θ2 (maximum incident angle) when the S-polarized component of the laser beam in the red wavelength region at each position in the main scanning direction of the folding mirror 677 is incident at the incident angle θ1 (minimum incident angle, that is, 40 °). That is, the difference Δrs between the reflectance when incident at 65 °) and the difference Δrp between the reflectance when the P-polarized component is incident at the incident angle θ1 and the reflectance of the P-polarized component when incident at the incident angle θ2. Both are 5% or less.

  Similarly, the difference Δrs between the reflectance when the S-polarized component of the laser beam in the infrared wavelength region at each position of the folding mirror 677 in the main scanning direction is incident at the incident angle θ1 and the reflectance when incident at the incident angle θ2. The difference Δrp between the reflectance when the P-polarized component is incident at the incident angle θ1 and the reflectance when the P-polarized component is incident at the incident angle θ2 is set to 5% or less. The horizontal axis of the graph shown in FIG. 7 indicates the image height, and the image height indicates the reflectivity of the laser beam incident at the position in the main scanning direction, that is, from the center to the end of the folding mirror 677. . The reflectance of each deflection component can be adjusted by changing the film thickness of the metal layer constituting the folding mirror 677.

  Returning to FIG. The ratio of the S-polarized light component increases as the polarization component of the laser light incident on the folding mirror 677 increases toward the image height end (away from the center of the folding mirror 677). This tendency becomes more prominent as the inclination angle of the folding mirror 677 increases.

  FIG. 7 is a graph showing the reflectance of the S-polarized component and the P-polarized component when the laser light is incident on a general mirror that is not specially coated. The reflectance of the S-polarized component increases as it goes to the image high end, and the reflectance of the P-polarized component decreases as it goes to the image high end.

  FIG. 8 is a graph showing the reflectivity for each image height (each position in the main scanning direction) in the folding mirror 677 of the light combining the S polarization component and the P polarization component of the laser light. According to FIG. 8, when the inclination angle of the folding mirror 677 is 20 ° to 40 °, the reflectance decreases as it goes to the image height end portion (away from the central portion of the folding mirror 677). When the tilt angle of the folding mirror 677 is 20 ° to 40 °, the ratio of the S-polarized component to the P-polarized component of the laser beam incident on the folding mirror 677 is low as shown in FIG. As a characteristic, the characteristic of the reflection characteristic of the P polarization component shown in FIG. 7 appears.

  On the other hand, when the inclination angle of the folding mirror 677 is 50 ° or more, the reflectance increases as it goes to the image height end (away from the center of the folding mirror 677). When the tilt angle of the folding mirror 677 is 50 ° or more, as shown in FIG. 5, the ratio of the S-polarized component to the P-polarized component of the laser beam incident on the folding mirror 677 is increased, so that the reflection characteristics of the laser beam. As a result, the characteristic of the reflection characteristic of the S-polarized component shown in FIG. 7 appears.

  FIG. 9 shows the ratio of the S-polarized component to the P-polarized component for each image height (each position in the main scanning direction) when the laser beam emitted from the single beam type light source passes through the dust-proof glass 621. It is the graph shown for every inclination-angle in the scanning direction.

  Here, the “tilt angle of the dustproof glass 621 in the sub-scanning direction” will be described with reference to an enlarged view B of FIG. 6. The tilt angle of the dust-proof glass 621 in the sub-scanning direction is defined by the angle PL1 and β2 between the perpendicular PL3 with respect to the optical axis of the laser beam LB reflected by the folding mirror 677 and the incident surface 621a and the exit surface 621b of the laser beam LB in the dust-proof glass 621. (See enlarged view B). In other words, if the incident angle 621a and the exit surface 621b of the dust-proof glass 621 are at the same position as the perpendicular PL3 of the laser beam LB is 0 °, the entrance surface 621a and the exit surface 621b of the dust-proof glass 621 from the perpendicular PL3. The angles β1 and β2 when tilting is the tilt angle in the sub-scanning direction. Note that the angle formed by the perpendicular line PL3 and the incident surface 621a and the exit surface 621b of the dust-proof glass 621 may be either β1 or β2. Hereinafter, the inclination angle of the dustproof glass 621 in the sub-scanning direction is simply referred to as “the inclination angle of the dustproof glass 621”.

  Returning to FIG. Similar to the characteristics of the folding mirror 677 shown in FIG. 5, the polarization component of the laser light transmitted through the dust-proof glass 621 is closer to the image height end (the farther from the center of the dust-proof glass 621), the ratio of the S-polarized component is increased. Increase. This tendency becomes more prominent as the inclination angle of the dust-proof glass 621 increases (30 ° to 40 °). On the contrary, when the inclination angle of the dustproof glass 621 is 5 ° to 20 °, the ratio of the S deflection component is small in the total image height. Therefore, by setting the inclination angle of the dust-proof glass 621 to 5 ° to 20 °, the polarization component of the laser light transmitted through the dust-proof glass 621 is almost only the P-polarized component at the entire image height (each position in the main scanning direction). Can do.

  FIG. 10 is a graph showing the transmittance of the dust-proof glass 621 for the P-polarized component of the laser light. The transmittance of the dust-proof glass 621 with respect to the P-polarized component is low at the center of the image height and increases as it goes to the end of the image height.

  From the characteristics shown above, (1) by setting the inclination angle of the folding mirror 677 to 20 ° to 40 °, the reflectance of the folding mirror 677 with respect to the laser light becomes lower from the center of the image height to the end of the image height. That is, the amount of light after reflection has a characteristic that the image height end side is smaller than the image height center portion. (2) By setting the tilt angle of the dust-proof glass 621 to 5 ° to 20 °, the polarization component of the laser light that passes through the dust-proof glass 621 is almost only the P-polarized component, and further, the dust-proof glass 621 transmits the P-polarized component. The rate increases from the center of the image height to the end of the image height. That is, the amount of light after transmission has a characteristic that the image height end side is larger than the image height center portion.

  In other words, by setting the tilt angle of the folding mirror 677 to 20 ° to 40 ° and the tilt angle of the dust-proof glass 621 to 5 ° to 20 °, the amount of laser light reflected by the folding mirror 677 is imaged from the center of the image height. The phenomenon of decreasing toward the high end portion can be canceled by the characteristic that the amount of light increases from the center of the image height of the dustproof glass 621 toward the end of the image height. In other words, by setting the tilt angle of the folding mirror 677 to 20 ° to 40 ° and the tilt angle of the dust-proof glass 621 to 5 ° to 20 °, the amount of laser light transmitted through the dust-proof glass 621 is almost uniform over the entire image height. It is corrected to. Accordingly, the non-uniformity in the light amount distribution of the laser light applied to the peripheral surface of the photosensitive drum 17 can be corrected without applying a special coating on the folding mirror 677 to make the light amount distribution uniform. Can suppress unevenness.

  The above is a description of the tilt of the folding mirror 677 and the dust-proof glass 621 in the sub-scanning direction and the characteristics of the laser light when the single beam type light source 68 is used. Next, a case where a multi-beam light source 68 is used will be described.

  FIG. 11 is a graph showing the reflectance at each image height (each position in the main scanning direction) of the folding mirror 677 of the light combining the S-polarized light component and the P-polarized light component of the laser light emitted from the multi-beam type light source 68. is there. According to FIG. 11, when the inclination angle of the folding mirror 677 is 20 °, the reflectance increases as it goes to the end of the image height (away from the central portion of the folding mirror 677), and when the inclination angle is 30 °, the reflection angle increases. The reflectance is substantially constant at the image height. On the other hand, when the inclination angle of the folding mirror 677 is 40 ° or more, the reflectance decreases as it goes to the image height end (away from the center of the folding mirror 677).

  Then, by setting the inclination angle of the dust-proof glass 621 to 5 ° to 20 °, the polarization component of the laser light transmitted through the dust-proof glass 621 is almost only the S-polarized component at the entire image height (each position in the main scanning direction). Can do. FIG. 12 is a graph showing the transmittance of the dust-proof glass 621 with respect to the S-polarized component of the laser light emitted from the multi-beam type light source. The transmittance of the dust-proof glass 621 with respect to the S-polarized component decreases as it goes from the image height center to the image height end.

  (3) By setting the inclination angle of the folding mirror 677 to 20 ° to 30 °, the reflectivity of the folding mirror 677 with respect to the laser light increases from the center of the image height to the end of the image height ( (Alternatively, the reflectance becomes almost constant at the entire image height). That is, the amount of light after reflection has a characteristic that the image height end side is larger than the image height center portion. (4) By setting the inclination angle of the dust-proof glass 621 to 5 ° to 20 °, the polarization component of the laser light transmitted through the dust-proof glass 621 is almost only the S-polarized component, and further, the dust-proof glass 621 transmits the S-polarized component. The rate decreases from the center of the image height to the end of the image height. That is, the amount of light after transmission has a characteristic that the image height end side becomes smaller than the image height center portion.

  In other words, by setting the tilt angle of the folding mirror 677 to 20 ° to 30 ° and the tilt angle of the dust-proof glass 621 to 5 ° to 20 °, the amount of laser light reflected by the folding mirror 677 is imaged from the center of the image height. The phenomenon that increases as it goes to the high end can be canceled by the characteristic that the amount of light decreases from the center of the image height of the dust-proof glass 621 to the end of the image height.

  From the above, the tilt angle of the folding mirror 677 for making the light quantity distribution of the laser light irradiated on the peripheral surface of the photosensitive drum 17 substantially uniform regardless of whether the light source of the single beam system or the multi-beam system is used. The angle satisfies the conditions (1) and (3), and the inclination angle of the dust-proof glass 621 is an angle satisfying the conditions (2) and (4). That is, (I) the inclination angle of the folding mirror 677 is 20 ° to 30 °, and (II) the inclination angle of the dustproof glass 621 is 5 ° to 20 °.

  That is, by setting the inclination angles of the folding mirror 677 and the dustproof glass 621 to the angles (I) and (II), the photosensitive drum 17 is irradiated regardless of whether the light source 68 is a single beam system or a multibeam system. It is possible to make the light amount distribution of the laser light almost uniform. That is, variation in the amount of charge of the electrostatic latent image formed on the photosensitive drum 17 is reduced, and unevenness in image density can be suppressed.

  The characteristics of the laser light shown in FIGS. 5 to 8 and 9 to 12 are the same in any laser light in the red wavelength region and the infrared wavelength region. Therefore, by setting the inclination angles of the folding mirror 677 and the dustproof glass 621 to the angles (I) and (II), the light source 68 emits a red wavelength laser beam and an infrared wavelength laser beam. The light quantity distribution of the laser light irradiated onto the photosensitive drum 17 can be made substantially uniform regardless of which light source is used. In addition, since the tilt angles of the folding mirror 677 and the dust-proof glass 621 can be made common to a plurality of types of light sources 68, there is no need to assemble different optical scanning devices 600 depending on the types of the light sources 68, and the labor of assembling the devices can be reduced. Cost can be reduced.

DESCRIPTION OF SYMBOLS 1 Image forming apparatus 17 Photosensitive drum 410 Image forming part 600 Optical scanning apparatus 621 Dust-proof glass 671 Polygon mirror 677 Folding mirror 68 Light source

Claims (4)

A light source that emits laser light;
Deflecting means for deflecting laser light emitted from the light source and scanning the image carrier in the main scanning direction;
Reflecting the laser light deflected by the deflecting means onto the image carrier, a long plate-like mirror extending in the main scanning direction;
A casing having the light source, the deflecting means, and the mirror disposed therein, and having a transmission window that transmits the laser light reflected by the mirror;
The angle of incidence of the laser beam on the mirror is 40 ° to 60 °, and the reflectivity of the mirror with respect to the S-polarized component of the laser beam is greater than the reflectivity of the mirror with respect to the P-polarized component of the laser beam. The difference between the maximum reflectance and the minimum reflectance at each position in the main scanning direction of the mirror with respect to the S deflection component is higher than 3%, and the maximum reflectance at each position in the main scanning direction of the mirror with respect to the P deflection component And the difference in the minimum reflectance is 5% or less, and the mirror is in the sub-scanning direction perpendicular to the main scanning direction with respect to the perpendicular to the optical axis of the laser beam incident on the mirror, and the reflecting surface of the mirror Is inclined by 20 ° to 30 ° so as to face the image carrier, and the transmission window is inclined by 5 ° to 20 ° in the sub-scanning direction with respect to the perpendicular of the optical axis of the laser beam transmitted through the transmission window. It shall be a light scanning device.   The light source is a single beam method having one light emitting unit that emits laser light, or a multi-beam method having a plurality of the light emitting units, and in the case of the multi-beam method, the plurality of light emitting units are arranged in a row 2. The optical scanning device according to claim 1, wherein an angle between a direction along a row of light emitting units and the main scanning direction is in a range of 80 ° to 90 °.   The optical scanning device according to claim 1, wherein the light source emits laser light in a red wavelength region or an infrared wavelength region. An image carrier;
An optical scanning device for irradiating the image carrier with laser light based on image data;
An image forming apparatus according to any one of claims 1 to 3, wherein the optical scanning device is provided.

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