JP2013088589A - Optical scanner, and image forming apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To maintain uniformity in light amount distribution on a photoreceptor drum even if a light source is replaced with a light source that emits a laser beam having a different wavelength, or a light source that employs a different method.SOLUTION: For each thickness of a metal layer that constitute a reflection surface of a polygon mirror, reflectances of an S-polarization component and a P-polarization component of a laser beam in a red wavelength region and an infrared wavelength region are measured respectively at each position in a main-scanning direction of the reflection surface. A thickness when a difference between the measured maximum reflectance and minimum reflectance is equal, and the sum of differences between the maximum reflectance and the minimum reflectance becomes the minimum value is adopted as a thickness of the metal layer.

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 the main scanning direction of an image carrier using a polygon mirror.

  The optical scanning device used in the electrophotographic image forming apparatus has a light source and a polygon mirror, and the laser beam emitted from the light source is reflected by the polygon mirror that is rotationally driven to perform main scanning of the photosensitive drum. By scanning in the direction, an electrostatic latent image is formed on 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. In order to irradiate the photosensitive drum with a sufficient amount of laser light, the mirror surface needs to have optimum reflection characteristics for the laser light, such as the reflectance of the polygon mirror being uniform in the main scanning direction ( (See Patent Documents 1 to 4).

JP-A-6-51223 JP 2001-337285 A JP 2007-156248 A JP 2009-25738 A

  In general, a polygon mirror is made of aluminum, plastic, glass, or the like, and increases the reflectivity or prevents oxidation (rust) by applying a vapor deposition film or an anodized film to the mirror surface. . Further, the reflectance of the laser beam at the mirror surface is generally optimized only for the laser beam having a predetermined wavelength. In other words, the reflectance of the mirror surface is adjusted so that the light quantity distribution on the photosensitive drum is uniform when the laser beam having a predetermined wavelength is reflected on the mirror surface and irradiated onto the photosensitive drum.

  For this reason, when a polygon mirror that is optimized only for a laser beam of a predetermined wavelength is irradiated with a laser beam of a wavelength other than the predetermined wavelength, the reflection characteristics of the mirror surface will be different, so the light quantity distribution on the photosensitive drum is uniform. Therefore, an image with good image quality cannot be formed. That is, the polygon mirror optimized only for laser light having a predetermined wavelength cannot be used with a light source that emits laser light having a wavelength other than the predetermined wavelength. Also, with respect to a single beam type light source composed of one light emitting unit and a multi-beam type light source composed of a plurality of light emitting units, the reflection characteristics of the mirror surface differ depending on each light source. It was difficult to share the light source of the system.

  The present invention has been made to solve the above problems, and can maintain the uniformity of the light amount distribution on the photosensitive drum even when the light source emits laser light of a different wavelength or is replaced with a light source of a different method. An object of the present invention is to provide an optical scanning device and an image forming apparatus that can be used.

  The optical scanning device according to the first aspect of the present invention 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. A light source that is mounted by rotating at a predetermined angle around the optical axis of the unit, and a deflecting unit that has a mirror surface and reflects the laser light emitted from the light source on the mirror surface to scan in the main scanning direction. When the difference between the maximum reflectance and the minimum reflectance at each position in the main scanning direction on the mirror surface of the laser beam is a characteristic difference, the film thickness of the metal layer constituting the mirror surface is the single beam The film thickness is such that the difference in characteristics of the laser light emitted from the light source of the system and the characteristic difference of the laser light emitted from the light source of the multi-beam system are equal, or the sum of the two characteristic differences is minimized.

  According to this configuration, the reflectance distribution of the laser beam at each position in the main scanning direction of the mirror surface can be suppressed substantially uniformly regardless of whether the light source is a single beam system or a multi-beam system. That is, even if the optical scanning device is configured by using either a single beam type or a multi-beam type light source, variations in the amount of light on the irradiation target can be suppressed.

  Invention of Claim 2 is the optical scanning device of Claim 1, Comprising: The said light emission part radiate | emits the laser beam of a red wavelength range or an infrared wavelength range, The film thickness of the said metal layer Is a single beam system, and the light emitting part emits laser light in the red wavelength region. The light source emits laser light in the infrared wavelength region. The characteristic difference of the laser light emitted from the light source, which is a multi-beam method, wherein the light emitting part emits the laser light in the red wavelength region, the characteristic difference of the laser light emitted from the light source, and the light emitting part Among the characteristic differences of laser light emitted from a light source that emits laser light in the infrared wavelength region, at least two characteristic differences are equal and the sum of the four characteristic differences is minimum, or the four characteristic differences Sum the film thickness becomes minimum.

  According to this configuration, the distribution of the reflectance of the laser beam at each position in the main scanning direction of the mirror surface is almost uniform regardless of whether the single-wavelength or multibeam-type light sources in the red wavelength region and the infrared wavelength region are used. Can be suppressed. In other words, even if any of the light sources is used to configure the optical scanning device, variations in the amount of light on the irradiation target can be suppressed.

  Therefore, the same optical scanning device can be shared by four types of light sources of a single beam system or a multi-beam system using laser diodes in the red wavelength region and the infrared wavelength region, thereby reducing the assembly process and cost of the device. be able to.

  The invention according to claim 3 is the optical scanning device according to claim 1, wherein the metal layer has a film thickness different from a characteristic difference of an S-polarized component of laser light in a red wavelength region, laser light in a red wavelength region. Of the P-polarized light component, the S-polarized light component difference of the laser light in the infrared wavelength region, and the P-polarized component property difference of the laser light in the infrared wavelength region, The film thickness is such that the sum of the four characteristic differences is minimum or the sum of the four characteristic differences is minimum.

  The ratio of the S-polarized component and the P-polarized component is different between the laser beam emitted from the single-beam type light source and the laser beam emitted from the multi-beam type light source. Therefore, the characteristic difference of the S polarization component of the laser light in the red wavelength region, the characteristic difference of the P polarization component of the laser light in the red wavelength region, the characteristic difference of the S polarization component of the laser light in the infrared wavelength region, A film in which the characteristic difference of the P-polarized component of the laser beam is measured, and the film thickness of the mirror metal layer is equal to at least two characteristic differences and the sum of the four characteristic differences is the smallest or the sum of the four characteristic differences is the smallest Even if the ratio of the S-polarization component and the P-polarization component of the laser light changes by setting the thickness (that is, using either a single-beam or multi-beam light source in the red wavelength region or infrared wavelength region). The distribution of the reflectance of the laser beam at each position of the mirror surface in the main scanning direction can be suppressed almost uniformly. In other words, even if any of the light sources is used to configure the optical scanning device, variations in the amount of light on the irradiation target can be suppressed.

  A fourth aspect of the present invention is the optical scanning device according to the first or second aspect, wherein the multi-beam type light source has the plurality of light emitting units arranged in a line and is arranged along the row of the light emitting units. The angle between the direction and the main scanning direction is in the range of 80 ° to 90 °.

  According to this configuration, it is possible to adjust the resolution in the sub-scanning direction that is a direction orthogonal to the main scanning direction (the number of dots that can be irradiated with laser light within a predetermined range along the sub-scanning direction in the irradiation target).

  According to a fifth 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. 4. It is a thing as described in any one of 4.

  According to this configuration, since the light amount distribution of the laser light reflected by the deflecting unit is substantially uniform, it is possible to suppress variations in the light amount on the image carrier. Therefore, even if the light source mounted on the optical scanning device is different, it is possible to prevent image quality deterioration.

  According to the present invention, the light scanning device is mounted with any one of a plurality of types of light sources having a light emitting unit that emits laser light in a single-beam method or a multi-beam method, or in a red wavelength region or an infrared wavelength region. However, the reflectance of the laser beam in the main scanning direction of the mirror surface can be made substantially uniform. Therefore, no matter what kind of light source is used, variation in the amount of light on the image carrier can be suppressed, and deterioration in image quality can be suppressed.

  In addition, the same optical scanning device can be shared by four types of light sources of single beam type or multi-beam type using laser diodes in the red wavelength region and infrared wavelength region, thereby reducing the assembly process and cost of the device. be able to.

1 is a schematic diagram of an internal structure of an image forming apparatus. The schematic diagram which shows the state which irradiated the laser beam on the reflective surface of the polygon mirror. The block diagram which shows the irradiation control system of a laser beam. FIG. Reflection at each position in the main scanning direction of the reflecting surface with respect to the thickness of the metal layer on the reflecting surface when using a single-beam type light source and a multi-beam type light source that have laser diodes emitting laser light in the red wavelength region A graph showing the difference between the maximum reflectance and the minimum reflectance. The main scanning direction of the reflective surface relative to the thickness of the metal layer on the reflective surface when using a single-beam light source and a multi-beam light source that have laser diodes that emit laser light in the red wavelength region and infrared wavelength region The graph which showed the difference of the maximum reflectance of the reflectance in each position, and the minimum reflectance.

  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 including an optical scanning device according to the present invention. In this embodiment, a printer is described as an example of an image forming apparatus. However, in addition to this, an image forming apparatus that employs an electrophotographic system, such as a copier, a facsimile machine, or a multifunction machine having a plurality of these functions. I just need it. The image forming apparatus described in this embodiment is a color printer, but may be a monochrome printer.

  The image forming apparatus 1 is a tandem color printer including image forming units 2 (2M, 2C, 2Y, and 2K) for each color of magenta (M), cyan (C), yellow (Y), and black (K). is there. Each of the image forming units 2M, 2C, 2Y, and 2K includes a developing device 3, a charger 5, an optical scanning device 6, a toner supply unit 7, a cleaner 21, and a primary transfer roller 9.

  The toner supply unit 7 stores magenta, cyan, yellow, and black toners. The developing device 3 supplies the toner supplied from the toner supply unit 7 to the photosensitive drum (image carrier) 4.

  The photosensitive drum 4 is located below a transfer belt 8 described later and is disposed in contact with the outer surface of the transfer belt 8. From the upstream side in the rotation direction B of the transfer belt 8, a magenta photosensitive drum 4, a cyan photosensitive drum 4, a yellow photosensitive drum 4, and a black photosensitive drum 4 are arranged in parallel. The photosensitive drum 4 is made of a-Si (amorphous silicon) or the like and rotates in the clockwise direction (A direction in the figure) in FIG.

  A primary transfer roller 9 is disposed through the transfer belt 8 in a state where the primary transfer roller 9 is in contact with the inner surface of the transfer belt 8 at a position facing the photosensitive drum 4. The primary transfer roller 9 is a roller that is driven to rotate by the rotation of the transfer belt 8, nips the transfer belt 8 with the photosensitive drum 4, and transfers the toner images of the respective colors formed on the photosensitive drum 4 to the transfer belt 8. A primary transfer portion T for primary transfer is configured. In the primary transfer portion T, the toner images of the respective colors are transferred onto the transfer belt 8 in a multiple manner. As a result, a color toner image is formed on the transfer belt 8.

  The charger 5 uniformly charges the peripheral surface of the photosensitive drum 4. The optical scanning device 6 has a polygon mirror (deflecting means) 28 for guiding laser light based on image data transmitted from an external device to the peripheral surface of the photosensitive drum 4. The polygon mirror 28 scans the circumferential surface of each photosensitive drum 4 in the main scanning direction while rotating by a motor 32 described later, and forms an electrostatic latent image on each circumferential surface. The main scanning direction is a direction in which laser light is scanned in the longitudinal direction of the photosensitive drum 4. The polygon mirror 28 is shared between the plurality of photosensitive drums 4.

  The developing device 3 supplies toner to the photosensitive drum 4. As a result, toner adheres to the electrostatic latent image, and a toner image is formed on the photosensitive drum 4. The cleaner 21 is disposed on the peripheral surface of each photosensitive drum 4 and removes residual toner and the like on the peripheral surface.

  The transfer belt 8 is arranged above the row of the photosensitive drums 4 and is stretched between the driven roller 10 and the driving roller 11 so that the outer surface is in contact with the peripheral surface of the photosensitive drum 4. It is installed. Further, the transfer belt 8 is urged upward by a tension roller 19. The driving roller 11 rotates in response to a driving force from a driving source (not shown) to drive the transfer belt 8 to rotate. The driven roller 10 is driven to rotate by the rotation of the transfer belt 8. As a result, the transfer belt 8 rotates in the B direction (counterclockwise direction).

  Further, the transfer belt 8 is in a state where a portion wound around the driving roller 11 is bent, and the toner image primarily transferred to the transfer belt 8 is secondarily transferred to the paper P in this bent portion. Secondary transfer position P1. At the secondary transfer position P1, a secondary transfer roller 18 facing the driving roller 11 with the transfer belt 8 interposed therebetween is provided. The secondary transfer roller 18 forms a nip with the driving roller 11, and secondarily transfers the toner image on the outer surface of the transfer belt 8 onto the paper P passing through the nip.

  A pair of registration rollers 17 is disposed below the secondary transfer position P1. The registration roller 17 transports the paper P toward the secondary transfer position P1 at an appropriate timing and corrects the oblique feeding of the paper P.

  Above the secondary transfer position P1, there is provided a fixing device 14 that performs a fixing process on the paper P on which the secondary transfer of the toner image has been performed at the secondary transfer position P1. The fixing device 14 includes a heating roller 14a and a pressure roller 14b, and this pair of rollers forms a fixing nip portion NP. When the paper P passes through the fixing nip NP, the heating roller 14a heats the paper P, and the pressure roller 14b presses the paper P, so that the second-transferred toner image is fixed on the paper P. To do.

  A paper feed cassette 12 that stores a bundle of paper is disposed below the optical scanning device 6. Between the paper feed cassette 12 and the secondary transfer position P1, a paper transport path 13 for guiding the paper P from the paper feed cassette 12 to the secondary transfer position P1 is provided. The registration roller 17 described above is disposed in the sheet conveyance path 13. In addition to the registration rollers 17, a plurality of roller pairs for guiding the paper P are disposed at appropriate positions in the paper transport path 13.

  The heating roller 14 a and the pressure roller 14 b convey the paper P toward the discharge roller pair 151 after passing through the fixing nip NP. On the upper surface of the image forming apparatus 1, a discharge unit 16 that discharges the paper P that has been subjected to the fixing process by the fixing device 14 is formed, and between the discharge unit 16 and the fixing device 14, the paper P Is provided with a paper discharge path 15. The paper P is conveyed to the paper discharge path 15 by driving the discharge roller pair 151 and is discharged to the discharge unit 16.

  FIG. 2 is a schematic diagram showing a state in which the reflection surface (mirror surface) 282 of the polygon mirror 28 is irradiated with the laser beam LB. FIG. 3 is a block diagram showing a laser light irradiation control system. FIG. 4 is an external view of the light source 31. In FIG. 3, optical components such as a collimator lens and an fθ lens are not shown.

  The laser light generation unit 30 includes a light source 31 that emits laser light LB, a drive circuit that drives the light source 31, and the like.

  As the light source 31, for example, a semiconductor laser is used. As the light source provided in the optical scanning device 6 in the present invention, a single-beam type light source (FIG. 4A) having one laser diode LD on the front end surface Y, or a plurality of laser diodes 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 31, the laser diodes LD1 and LD2 are arranged in a line on the front end surface Y at a constant interval, 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 arranged at a predetermined position of the optical scanning device 6. Specifically, when the laser beams emitted from the laser diodes LD1 and LD2 irradiate the peripheral surface of the photosensitive drum 135, the arrangement direction of the irradiation positions (imaging positions) connects the laser diodes LD1 and LD2. The light source 31 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.

  Further, the laser diode disposed in the light source 31 mounted on the optical scanning device 6 in 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). . In other words, the optical scanning device 6 has a total of 4 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 6 is determined at the time of circuit design, and the determined light source is assembled at the time of circuit assembly.

  The polygon mirror 28 rotates around the rotation shaft 281 in the direction of the arrow R <b> 1 by driving the motor 32, and reflects the laser light LB generated by the laser light generation unit 30. The polygon mirror 28 has, for example, regular hexagonal side surfaces, and the six side surfaces correspond to the reflection surface 282.

  The exposure control unit 303 controls the laser light generation unit 30 to irradiate the laser beam LB and draw an electrostatic latent image on the photosensitive drum 4. That is, the exposure control unit 303 sends the image data stored in the storage unit 301 to the laser beam generation unit 30 while rotating the polygon mirror 28 by the motor 32, and causes the laser beam generation unit 30 to emit the laser beam LB. . The laser beam LB emitted from the light source 31 irradiates the rotating polygon mirror 28, is deflected by the reflecting surface 282, and draws the scanning line SL on the photosensitive drum 4 in the main scanning direction D1. One scanning line SL is drawn by one reflecting surface 282. By repeating the drawing of one scanning line SL on the photosensitive drum 4 thus rotating, an electrostatic latent image is drawn along the sub-scanning direction. The sub-scanning direction corresponds to the rotation direction R2 of the photosensitive drum 4.

  As illustrated in FIG. 3, the timing signal generation unit 305 includes a BD (Beam Detect) sensor 27 and a BD signal conversion unit 29. The laser beam LB is repeatedly scanned in the main scanning direction D1 within a scanning range longer than the dimension of the photosensitive drum 4 in the main scanning direction D1. The BD sensor 27 is installed in a position where the laser beam LB is received before the laser beam LB starts scanning the photosensitive drum 4 in the scanning range.

  The BD sensor 27 is a photo sensor, and receives the laser beam LB reflected by the reflecting surface 282 and outputs the received light signal to the BD signal conversion unit 29. The BD signal conversion unit 29 shapes the received light signal into a rectangular wave timing signal BD, and outputs the timing signal BD to the exposure control unit 303.

  The timing signal BD is a reference signal for aligning the writing position in the main scanning direction D1 when an electrostatic latent image is drawn on the photosensitive drum 4. The exposure control unit 303 instructs the laser light generation unit 30 to emit the laser light LB with reference to the timing signal BD.

  The reflectance of the laser beam LB at the reflecting surface 282 needs to be adjusted so that the light amount distribution when the laser beam LB is imaged on the photosensitive drum 4 is uniform. This is because if the amount of the laser beam LB varies on the photosensitive drum 4, color unevenness occurs in the formed image, causing image quality deterioration. Since the optical scanning device 6 can be replaced with a plurality of types of light sources, the reflective surface 282 is configured to make the reflectance at each point in the main scanning direction on the reflective surface 282 as uniform as possible, regardless of which type of light source is used. Adjust the characteristics. By doing so, it is possible to suppress variations in the amount of laser light LB on the photosensitive drum 4 regardless of which light source is used.

  As a means for adjusting the reflectance of the reflecting surface 282, a method of changing the film thickness of the metal layer formed on the reflecting surface 282 is used. As a method for deriving the optimum film thickness, for each film thickness of the metal layer, the reflectance of the S-polarized component of the laser beam in the red wavelength region and the laser beam in the infrared wavelength region at each position of the reflecting surface 282 in the main scanning direction. The reflectance of the S-polarized light component is measured, and the difference between the maximum value and the minimum value of the reflectance at each position in the main scanning direction for each film thickness (hereinafter, this difference is referred to as “characteristic difference”) is calculated. The film thickness when the characteristic difference between the S-polarized component and the P-polarized component is equal or the sum of the two characteristic differences is minimum is set to an optimum film thickness that can suppress the light amount distribution.

  Here, the reason why the reflectance of the S-polarized component and the P-polarized component of the laser light is used to derive the optimum film thickness will be described. The light component when the laser light is incident on the reflecting surface 282 can be divided into an S-polarized component and a P-polarized component. The ratio of the S-polarized light component and the P-polarized light component differ between the laser light emitted from the single-beam light source and the laser light emitted from the multi-beam light source. Further, in the case of a multi-beam type light source, the above-mentioned ratio differs if the angle (tilt angle) at which the line connecting the laser diodes LD1 and LD2 intersects the main scanning direction is different.

  Therefore, the reflectances of the S-polarized component and the P-polarized component of the laser light in the red wavelength region are measured, and the respective characteristic differences are calculated. Since the laser light is classified into an S-polarized component and a P-polarized component, the calculated characteristic difference can be obtained even if the ratio of the S-polarized component and the P-polarized component of the laser light changes, that is, a single beam method or a multi-beam method. This is the same regardless of which light source is used. Therefore, the respective characteristic differences are calculated from the reflectance of the S-polarized component and the P-polarized component of the laser light in the red wavelength region, and the film thickness when the two characteristic differences are equal or the sum of the two characteristic differences is minimized is The film thickness is also optimum for each of the single-beam and multi-beam light sources that emit laser light in the red wavelength region.

  FIG. 5 is a graph showing the characteristic difference between the S-polarized component and the P-polarized component of the laser light in the red wavelength region with respect to the thickness of the metal layer. The graph L1 is a graph of the S polarization component, and the graph L2 is a graph of the P polarization component.

  As shown in FIG. 5, the film thickness that minimizes the graph L1 is 190 nm. On the other hand, the film thickness that minimizes the graph L2 is 140 nm or 310 nm. However, even when the graph L1 is minimum (0.5%) when the film thickness is 190 nm, the reflectance indicated by the graph L2 is 5.5%, and the reflectance varies when a multi-beam type light source is used. Will come out. Similarly, even when the graph L2 is the minimum (1.2%) when the film thickness is 140 nm, the reflectance indicated by the graph L1 is 7%, and the reflectance varies when a single-beam light source is used. It will come out.

  Therefore, the film thickness at the intersection of the graph L1 and the graph L2, that is, the film thickness when the characteristic difference between the S-polarized component and the P-polarized component is equal, and the film thickness when the sum of the characteristic differences is the minimum (each graph When there is no intersection point, the film thickness when the sum of the two characteristic differences is minimum is employed. In the case of FIG. 5, the film thickness at the intersection of the graph L1 and the graph L2 is 163 nm and 268 nm. Of these two points, the film with the smaller sum of the characteristic differences is the film thickness 163 nm.

  Therefore, by setting the thickness of the metal layer of the reflective surface 282 to 163 nm, the main scanning direction of the reflective surface 282 can be used regardless of whether the single-beam or multi-beam light source that emits laser light in the red wavelength region is used. Thus, the reflectance distribution at each of the positions can be suppressed uniformly, and the uniformity of the light amount distribution on the photosensitive drum 4 can be maintained.

  FIG. 6 is a graph showing the characteristic difference between the S-polarized component and the P-polarized component of the laser light in the red wavelength region and the S-polarized component and the P-polarized component of the laser light in the infrared wavelength region with respect to the film thickness of the metal layer. Graph L1 is an S polarization component in the red wavelength region, graph L2 is a P polarization component in the red wavelength region, graph L3 is an S polarization component in the infrared wavelength region, and graph L4 is a P polarization component in the infrared wavelength region.

  When determining the film thickness of the metal layer for four types of light sources, at least two graphs intersect, and the film thickness when the sum of the four characteristic differences in the film thickness at the intersecting point is the minimum (the graph When there is no intersection, the film thickness when the sum of the four characteristic differences is minimum is employed. In the case of FIG. 6, the film thickness meeting the above condition is 190 nm.

  By setting the thickness of the metal layer of the reflecting surface 282 to 190 nm, the amount of light in the main scanning direction due to the change in the ratio of the S-polarized component and the P-polarized component (by changing the single beam method / multi-beam method). Since the influence on the uniformity of the distribution can be reduced, it is possible to reflect any of the four types of light sources of the single beam system or the multi-beam system that emit laser light in the red wavelength region and the infrared wavelength region. The distribution of reflectance at each position in the main scanning direction of the surface 282 can be suppressed uniformly, and the uniformity of the light amount distribution on the photosensitive drum 4 can be maintained.

  As described above, the reflectance on the reflecting surface 282 of the polygon mirror 28 is measured for four types of light sources of the single beam type or the multi-beam type using laser diodes in the red wavelength region and the infrared wavelength region. By setting the metal layer of the surface 282 to a film thickness that suppresses the variation in reflectance of the reflecting surface 282 in the main scanning direction, the variation in the amount of light on the photosensitive drum 4 can be suppressed regardless of the type of light source used. Deterioration can be suppressed.

  Further, in the optical scanning device 6, it is possible to mount four types of light sources of a single beam system or a multi-beam system using laser diodes in the red wavelength region and the infrared wavelength region with a single polygon mirror 28. Therefore, parts etc. can be made common and an assembly process and cost can be reduced.

DESCRIPTION OF SYMBOLS 1 Image forming apparatus 2 Image forming part 4 Photosensitive drum 6 Optical scanning device 28 Polygon mirror 281 Rotating shaft 282 Reflecting surface 27 BD sensor 29 BD signal conversion part 30 Laser light generation part 31 Light source 32 Motor 303 Exposure control part 305 Timing signal generation Part

Claims (5)

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. In the case of the multi beam method, the light beam is rotated by a predetermined angle around the optical axis of the light emitting unit. A light source attached
A deflecting unit that has a mirror surface and reflects the laser light emitted from the light source on the mirror surface to scan in the main scanning direction;
When the difference between the maximum reflectance and the minimum reflectance at each position in the main scanning direction on the mirror surface of the laser light is a characteristic difference, the film thickness of the metal layer constituting the mirror surface is An optical scanning device in which the characteristic difference between the laser beams emitted from the single-beam type light source and the characteristic difference between the laser beams emitted from the multi-beam type light source are equal or the sum of the two characteristic differences is minimized. .   The light emitting unit emits laser light in a red wavelength region or an infrared wavelength region, and the film thickness of the metal layer is a single beam method, and the light emitting unit emits laser light in a red wavelength region. Characteristic difference of laser light emitted from the laser beam, single beam method and the light emitting part emits laser light in the infrared wavelength region. Difference in characteristics of laser light emitted from a light source that emits laser light in the wavelength region, among the difference in characteristics of laser light emitted from a light source that emits laser light in the infrared wavelength region in the multi-beam method, 2. The optical scanning device according to claim 1, wherein at least two of the characteristic differences are equal and the film thickness is such that the sum of the four characteristic differences is minimum or the sum of the four characteristic differences is minimum.   The thickness of the metal layer is the difference in the characteristics of the S-polarized component of the laser light in the red wavelength region, the difference in the properties of the P-polarized component of the laser light in the red wavelength region, and the difference in the properties of the S-polarized component of the laser light in the infrared wavelength region. A film in which at least two of the characteristic differences among the characteristic differences of the P-polarized component of the laser light in the infrared wavelength region are equal and the sum of the four characteristic differences is the smallest or the sum of the four characteristic differences is the smallest The optical scanning device according to claim 1, wherein the optical scanning device is thick.   In the multi-beam type light source, the plurality of light emitting units are arranged in a line, and an angle between a direction along the row of the light emitting units and the main scanning direction is in a range of 80 ° to 90 °. Item 3. The optical scanning device according to Item 1 or 2. 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 4, wherein the optical scanning device is provided.

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