Optical scanning device and image forming device

Abstract

To reduce the size of an optical scanner.SOLUTION: An optical scanner comprises: a plurality of light source units 3 having a light source 301 having a plurality of light emitting points 301a, 301b that emit light beams, and a holder 303 that holds the light source 301; and a housing 201 that has attachment surfaces 205, 206, 207, 208 that hold a cylindrical part of the holder 303 of the light source unit 3 and an elastic member 211 that urges the holder 303 held by the attachment surfaces 205-208 in a direction of the attachment surfaces, in which the attachment surfaces 205-208 are arranged in a grid-like pattern. The holder 303 has, at one end of the holder 303, projections 304A, 304B that are orthogonal to the central axis of the cylindrical part and extend in directions opposite to each other. The length from the central axis of the cylindrical part of the holder 303 to the leading ends of the projections 304A, 304B is shorter than half the length of the longest straight line, of straight lines connecting the central axes of the cylindrical part of the adjacent holders 303 of the light source unit 3 held by the attachment surfaces 205-208 of the housing 201.SELECTED DRAWING: Figure 5

Description

[Technical field]

[0001] The present invention relates to an optical scanning device and an image forming apparatus equipped with an optical scanning device. [Background technology]

[0002] It is known that an optical scanning device mounted on an electrophotographic image forming apparatus has the following configuration. That is, the optical scanning device includes a laser unit including a laser diode as a light source, a collimator lens, and a holder for holding the laser diode and the collimator lens, and an optical deflector for deflecting the laser light emitted from the laser unit. Furthermore, the optical scanning device includes optical elements such as lenses and mirrors so that the laser light deflected by the optical deflector forms a latent image on the scanned surface. In the case of a color image forming apparatus that forms a color image on a recording material, an optical scanning device having multiple laser diodes mounted in one housing is used. In addition, in order to meet the demands of high image quality and high productivity, a multi-beam laser diode in which one laser diode has multiple light emitting points is used as the light source of the optical scanning device.

[0003] For example, Patent Document 1 proposes a scanning optical device in which four multi-beam laser diodes are mounted in one housing. As described in Patent Document 1, the multi-beam laser diode is attached to the housing after adjusting the interval (hereinafter referred to as the beam pitch) between the scanning positions of the laser light emitted from each light source on the photosensitive drum, which is the surface to be scanned, according to the resolution of the image. The beam pitch of the laser light emitted by the multi-beam laser diode is adjusted by applying a moment to an adjustment protrusion provided on a holder to rotate the laser unit, which is attached to the housing so as to be rotatable approximately around the optical axis of the collimator lens.

[0004] Also, for example, Patent Document 2 proposes a method of holding a laser unit on a housing so that the laser unit can be easily rotated approximately around the optical axis of the lens. In the above-mentioned Patent Document 1, an intermediate member is required between the laser unit and the housing, but in Patent Document 2, an approximately cylindrical laser unit is directly biased against the mounting surface of the housing using an elastic member. The configuration proposed in Patent Document 2 holds the laser unit directly on the housing without an intermediate member, which makes it possible to improve mounting accuracy and reduce product costs. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] JP 2018-132643 A [Patent Document 2] JP 2004-37836 A Summary of the Invention [Problem to be solved by the invention]

[0006] In recent years, with the miniaturization of image forming devices, there is a demand for further miniaturization of optical scanning devices. However, the above-mentioned conventional method of holding a laser unit in a housing has the following problems. The configuration proposed in the above-mentioned Patent Document 1 is such that the two laser units are attached at different positions in the lens optical axis direction, and therefore the configuration is unlikely to contribute to miniaturization of the optical scanning device in the lens optical axis direction.

[0007] In addition, Patent Document 2 does not mention a method for adjusting the beam pitch of the laser light of the laser unit using a multi-beam laser diode, but in order to actually miniaturize the optical scanning device, it is necessary to arrange the laser units closer to each other. However, if the holder of the laser unit that holds the multi-beam laser diode and the collimator lens has an adjustment protrusion, the size of the protrusion and the location of the laser unit are limited due to space. For example, if the adjustment protrusion is shortened, a larger force must be applied to the adjustment protrusion in order to rotate the laser unit. As a result, a large force in a direction different from the direction in which the mounting surface is urged during adjustment is applied to the laser unit, causing the mounting posture to collapse, and there is a risk that the beam pitch cannot be adjusted accurately. In addition, if the urging pressure applied to the mounting surface is increased, the holder of the laser unit may be deformed, and the beam angle of the laser light may change.

[0008] The present invention has been made under these circumstances, and has an object to reduce the size of an optical scanning device. [Means for solving the problem]

[0009] In order to solve the above-mentioned problems, the present invention has the following configuration.

[0010] (1) An optical scanning device that irradiates a scanned surface with a light beam, the optical scanning device comprising: four light source units, each having a light source having a plurality of light emitting points that emit a light beam; and a holder that holds the light source, the holder having a cylindrical portion whose central axis is parallel to the optical axis direction of the light beam; and a housing of the optical scanning device that holds the cylindrical portions of the four light source units, the four light source units being arranged such that a line connecting the centers of the four cylindrical portions forms a rectangle when viewed in the direction of the central axis, each of the four holders has a rectangular shape at one end of the holder in the direction of the central axis, the rectangular shape being 100 mm from the center of the cylindrical portion when viewed in the direction of the central axis. Each othera pair of protrusions extending from the cylindrical portion in a direction away from each other, and each of the four holders is shaped such that the pair of protrusions and the center of the cylindrical portion are aligned in a straight line when viewed in the direction of the central axis; With the four light source units fixed to the housing, Of the four holders, two of the holders whose centers of the cylindrical portions are on one of the two diagonals of the rectangle have straight lines connecting the pair of protrusions and the center of the cylindrical portion that are substantially parallel to the one diagonal, and straight lines connecting the pair of protrusions and the center of the cylindrical portion of the remaining two holders are also substantially parallel to the one diagonal, and the length from the center of the cylindrical portion of the four holders to the tip of one of the pair of protrusions is shorter than half the length of the one diagonal so that the protrusions facing each other between the two holders whose centers of the cylindrical portions are on the one diagonal do not interfere with each other. and each of the four sides of the rectangle is shorter than twice the length from the center of the cylindrical portion of the holder to the tip of one of the pair of protrusions. 1. An optical scanning device comprising:

[0011] (2) An image forming apparatus comprising: an image forming means having a photosensitive drum on which an electrostatic latent image is formed, which develops the electrostatic latent image formed on the photosensitive drum and forms an image on a recording material; and an optical scanning device described in (1), wherein the optical scanning device forms an electrostatic latent image on the photosensitive drum. Effect of the Invention

[0012] According to the present invention, the optical scanning device can be made smaller. [Brief description of the drawings]

[0013] [Figure 1] FIG. 1 is a cross-sectional view showing a configuration of an image forming apparatus according to an embodiment of the present invention. [Diagram 2] FIG. 1 is a cross-sectional view showing a configuration of an optical scanning device according to an embodiment of the present invention. [Diagram 3] FIG. 2 is a perspective view showing the configuration of a laser unit according to the embodiment; [Figure 4] FIG. 1 is a diagram for explaining a method of mounting the laser unit of the embodiment to the housing of the optical scanning device. [Diagram 5] FIG. 1 is a diagram illustrating a laser unit installed in a housing of an optical scanning device according to an embodiment of the present invention. [Figure 6] FIG. 1 is a diagram for explaining a method for adjusting the beam pitch of a laser unit according to an embodiment of the present invention; DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0014] Hereinafter, an embodiment of the present invention will be described in detail with reference to the drawings. EXAMPLES

[0015] [Configuration of image forming device] FIG. 1 is a cross-sectional view showing an example of the configuration of an electrophotographic image forming apparatus 1. In the image forming apparatus, as shown in FIG. 1, four process cartridges PY, PM, PC, and PK are arranged side by side in the horizontal direction. The process cartridges PY, PM, PC, and PK contain toner of yellow (Y), magenta (M), cyan (C), and black (K), respectively. The process cartridge PK has a larger toner capacity than the other process cartridges PY, PM, and PC, and therefore has a larger height (length in the vertical direction in the figure). In addition, the process cartridges PY, PM, PC, and PK each have a photosensitive drum 11 (11a, 11b, 11c, and 11d) as an image carrier and a developing roller 12 (12a, 12b, 12c, and 12d) integrally arranged therein. The developing roller 12 develops an electrostatic latent image formed on the photosensitive drum 11 (on the photosensitive drum) by attaching toner to the electrostatic latent image to form a toner image. 1, the process cartridges PY, PM, PC, and PK have the same configuration. Note that the suffixes a, b, c, and d in the reference numbers correspond to the process cartridges PY, PM, PC, and PK, respectively, and in the following description, the suffixes a, b, c, and d will be omitted except when referring to a member of a specific color.

[0016] An optical scanning device 2 is disposed above the process cartridges PY, PM, PC, and PK in the figure. The optical scanning device 2 irradiates a laser beam (light beam) onto the photosensitive drum 11 of each process cartridge PY, PM, PC, and PK based on image information, and forms an electrostatic latent image on the surface of the photosensitive drum 11. Meanwhile, an intermediate transfer belt unit 20 is disposed below the process cartridges PY, PM, PC, and PK in the figure. The intermediate transfer belt unit 20 is composed of an intermediate transfer belt 21, a driving roller 22, a tension roller 23, and a driven roller 24. As shown in FIG. 1, the intermediate transfer belt 21 is stretched by the driving roller 22, the tension roller 23, and the driven roller 24, and rotates in the direction of the arrow in the figure (clockwise direction).

[0017] 1, the Z axis indicates the sub-scanning direction in which the photosensitive drum 11 rotates, the X axis perpendicular to the Z axis indicates the main scanning direction in which the photosensitive drum 11 is scanned with the laser light from the optical scanning device 2, and the Y axis is an axis perpendicular to the X and Z axes. The X, Y, and Z axes are the same in the following figures.

[0018] A primary transfer roller 25 is disposed below the photosensitive drum 11 of each of the process cartridges PY, PM, PC, and PK in the figure, at a position facing the photosensitive drum 11. The intermediate transfer belt 21 is brought into contact with the photosensitive drum 11 by the primary transfer roller 25, and the toner images on the photosensitive drum 11 of each of the process cartridges PY, PM, PC, and PK are transferred in sequence onto the intermediate transfer belt 21 in a superimposed manner, forming a color image. The drive roller 22 is brought into contact with a secondary transfer roller 26 via the intermediate transfer belt 21, and the color image on the intermediate transfer belt 21 is transferred to a recording material S fed from a paper feed tray 61.

[0019] A fixing unit 30 and a discharge unit 40 are disposed within the image forming apparatus 1. The fixing unit 30 has a fixing film 31 that heats a color image transferred onto the recording material S, and a pressure roller 32 that pressurizes the color image transferred onto the recording material S, and each rotates in the direction of the arrow in the figure to transport the recording material S, thereby fixing the color image onto the recording material S. Meanwhile, the discharge unit 40 has a discharge roller 41 and a discharge roller 42, and discharges the recording material S transported from the fixing unit 30 onto a stacking tray 50 that is provided on the upper surface of the image forming apparatus 1 and has a slope portion 51.

[0020] During image formation, in each of the process cartridges PY, PM, PC, and PK, the photosensitive drum 11 is rotated, and the surface of the photosensitive drum 11 is charged to a uniform potential by a charging roller (not shown). Then, the photosensitive drum 11 charged to a uniform potential is irradiated with laser light (shown by a broken line in the figure) from the optical scanning device 2 according to image information, and exposed. As a result, an electrostatic latent image is formed on the surface of the photosensitive drum 11, and the formed electrostatic latent image is developed by the developing roller 12 to form a toner image of each color. Then, the toner images on the photosensitive drum 11 are transferred in sequence onto the intermediate transfer belt 21 in a superimposed manner, and a color image is formed.

[0021] Meanwhile, the recording material S, which is a recording medium loaded in a paper feed tray 61 of the paper feed device 60, is fed by a paper feed roller 62 rotating in the direction of the arrow in the figure (clockwise direction), and the overlapped recording materials S are separated and conveyed by a separation roller 63. Then, the recording material S is conveyed to a nip portion where the drive roller 22 and the secondary transfer roller 26 abut against each other, and in the nip portion, a color image formed on the intermediate transfer belt 21 is transferred to the conveyed recording material S. Thereafter, the recording material S to which the color image has been transferred is conveyed to a nip portion where the fixing film 31 and the pressure roller 32 of the fixing device 30 abut against each other, and is heated and pressed, so that the transferred color image is fixed to the recording material S. The recording material S to which the color image has been fixed is discharged to a stacking tray 50 by the discharge device 40 and stacked on the inclined portion 51.

[0022] [Configuration of optical scanning device] Fig. 2 is a cross-sectional view showing the configuration of the optical scanning device 2 mounted on the image forming apparatus 1 of Fig. 1. The optical scanning device 2 includes a laser unit (not shown) that emits laser light, an optical deflector SM that deflects the laser light, and an imaging lens and a reflecting mirror that guide the laser light deflected by the optical deflector SM onto the photosensitive drum 11 of each process cartridge PY, PM, PC, and PK. In the optical scanning device 2, as shown in Fig. 2, the optical deflector SM is disposed approximately in the center of a housing (also called an optical box) 201. The optical deflector SM includes a rotary polygon mirror 200 that deflects the laser light incident from the laser unit, a rotor unit 204 that is a drive unit that drives the rotary polygon mirror 200, and a motor drive board 203 on which the rotor unit 204 is mounted.

[0023] 2, on the left side of the optical deflector SM, a first imaging lens N1, a second imaging lens N1a, and a first reflecting mirror M1a, M1b, and a second reflecting mirror M2b that reflect the laser light are arranged. On the other hand, on the right side of the optical deflector SM, a first imaging lens N2, a second imaging lens N2c, and a first reflecting mirror M1c, M1d, and a second reflecting mirror M2c that reflect the laser light are arranged. The optical deflector SM, the imaging lenses, and the reflecting mirrors are arranged integrally inside a housing 201, and a housing cover 202 that seals the opening of the housing 201 is attached to the housing 201, so that the inside of the housing 201 is set to a sealed state.

[0024] 2, a laser unit (not shown) is disposed at the front side of the optical scanning device 2, which emits laser light for forming an electrostatic latent image on the photosensitive drum 11 of each process cartridge PY, PM, PC, and PK, and exposes the photosensitive drum 11. The laser unit is provided corresponding to each photosensitive drum 11 of the process cartridges PY, PM, PC, and PK. The laser light La emitted from the laser unit corresponding to the photosensitive drum 11a of the process cartridge PY is deflected by the rotating polygon mirror 200 of the optical deflector SM and enters the first imaging lens N1. The laser light La transmitted through the first imaging lens N1 is reflected by the first reflecting mirror M1a. The laser light La reflected by the first reflecting mirror M1a passes through the second imaging lens N1a and an exit port provided in the housing cover 202, and scans the photosensitive drum 11a.

[0025] The laser light Lb emitted from the laser unit corresponding to the photosensitive drum 11b of the process cartridge PM is deflected by the rotating polygon mirror 200 of the optical deflector SM and enters the first imaging lens N1. The laser light Lb transmitted through the first imaging lens N1 is reflected by the first reflecting mirror M1b. The laser light Lb reflected by the first reflecting mirror M1b is then reflected by the second reflecting mirror M2b. The laser light Lb reflected by the second reflecting mirror M2b passes through the second imaging lens N1b and an exit port provided in the housing cover 202, and scans the photosensitive drum 11b.

[0026] The laser light Lc emitted from the laser unit corresponding to the photosensitive drum 11c of the process cartridge PC is deflected by the rotating polygon mirror 200 of the optical deflector SM and enters the first imaging lens N2. The laser light Lc transmitted through the first imaging lens N2 is reflected by the first reflecting mirror M1c. The laser light Lc reflected by the first reflecting mirror M1c enters the second imaging lens N2c. The laser light Lc transmitted through the second imaging lens N2c is reflected by the second reflecting mirror M2c, passes through an exit port provided in the housing cover 202, and scans the photosensitive drum 11c.

[0027] The laser light Ld emitted from the laser unit corresponding to the photosensitive drum 11d of the process cartridge PK is deflected by the rotating polygon mirror 200 of the optical deflector SM and enters the first imaging lens N2. The laser light Ld transmitted through the first imaging lens N2 is reflected by the first reflecting mirror M1d. The laser light Ld reflected by the first reflecting mirror M1d passes through the second imaging lens N2d and an exit port provided in the housing cover 202, and scans the photosensitive drum 11d.

[0028] [Laser unit configuration] 3 is a schematic diagram showing the configuration of laser unit 3, which is a light source unit having a light source that emits laser light. Laser unit 3 is composed of a two-beam laser diode (hereinafter referred to as light source) 301 having two light emitting points, a collimator lens 302, and a holder 303. Holder 303 has a generally cylindrical shape with a hollow interior, with collimator lens 302 attached to one end and projections 304A and 304B for position adjustment, which will be described later, extending in a direction perpendicular to the cylindrical axis (the central axis of holder 303, which is a cylindrical portion), at the other end. Note that U-shaped notches are provided at the center of projections 304A and 304B, which are projections, in order to grip laser unit 3 with a tool for adjusting the beam pitch of laser unit 3, which will be described later. Furthermore, a through hole (not shown) for press-fitting light source 301 is provided at the center of the end side where projections 304A and 304B of holder 303 are provided.

[0029] The holder 303 has cylindrical side portions 303A and 303B that come into contact with the mounting surface of the housing 201 that holds the laser unit 3 when the laser unit 3 is installed in the housing 201 of the optical scanning device 2. The light source 301 is pressed into the holder 303 from the front side in the figure in the depth direction and fixed to the holder 303. At this time, the light source 301 is fixed to the holder 303 at a position where the adjustment error of the beam pitch described later is about several degrees (for example, about 2 to 3 degrees). In the figure, the four terminals protruding from the light source 301 in the front direction in the figure are lead terminals 301C of the light source 301. On the other hand, the collimator lens 302 is attached to the end opposite to the end of the holder 303 into which the light source 301 is pressed, and is fixed with an adhesive after the position adjustment with respect to the light source 301 is completed.

[0030] [Installation of the laser unit into the housing] Next, a method of attaching the laser unit 3 to the housing 201 will be described. FIG. 4 is a perspective view illustrating a state in which the laser unit 3 that irradiates the photosensitive drum 11 of the process cartridges PY, PM, PC, and PK with laser light is attached to the housing 201. Four laser units 3Y, 3M, 3C, and 3K shown in FIG. 4 indicate the laser units 3 that irradiate the photosensitive drum 11 of the process cartridges PY, PM, PC, and PK with laser light, respectively. Note that, in order to explain the configuration of the housing 201 in which the laser unit 3 is installed, FIG. 4 shows a state in which the laser unit 3Y is removed from the housing 201, and the laser units 3M, 3C, and 3K are installed in the housing 201. In FIG. 4, the laser unit 3Y has a collimator lens 302 attached to one end of a holder 303, and a light source 301 (not shown) fixed to the end on the side where the protrusions 304A and 304B are provided. In addition, four lead terminals 301C of the light source 301 protrude toward the control board 209. The control board 209 is provided with through holes 210Y, 210M, 210C, and 210K into which the lead terminals 301C of the light sources 301 of the laser units 3Y, 3M, 3C, and 3K are inserted.

[0031] The mounting portion of the housing 201 on which the laser unit 3Y is installed has a trapezoidal shape consisting of two opposing inclined surfaces (mounting surfaces) and a plane connecting the two inclined surfaces (mounting surfaces). In detail, as shown in FIG. 4, in the mounting portion of the housing 201 on which the laser unit 3Y is installed, the mounting portion to which the cylindrical side surface portion 303A of the laser unit 3Y is attached is provided with mounting surfaces 205 and 206. On the other hand, the mounting portion to which the cylindrical side surface portion 303B is attached is provided with mounting surfaces 207 and 208. When the laser unit 3Y is attached to the housing 201, the cylindrical side surface portion 303A of the holder 303 contacts the mounting surfaces 205 and 206, and the cylindrical side surface portion 303B contacts the mounting surfaces 207 and 208. The holder 303 is urged in the directions of the mounting surfaces 205, 206, 207, and 208 of the housing 201 by the elastic member 211 (see FIG. 5 and FIG. 6). Laser unit 3Y is held in housing 201 so that holder 303 can rotate about the cylindrical axis by sliding cylindrical side portions 303A and 303B on mounting surfaces 205, 206, 207, and 208. When laser unit 3Y is attached to housing 201, one of protrusions 304A and 304B abuts against housing 201, thereby positioning laser unit 3Y in the cylindrical axis direction.

[0032] Here, the method of mounting the laser unit 3 to the housing 201 using the laser unit 3Y has been described, but the other laser units 3M, 3C, and 3K are also mounted to the housing 201 in a similar manner. As shown in FIG. 4, the mounting parts are arranged in a lattice pattern, but the positions of the mounting parts of the housing 201 to which the laser units 3 are mounted are different between the laser units 3Y and 3C and the laser units 3M and 3K. The mounting parts (mounting surfaces 205-208) of the housing 201 to which the laser units 3Y and 3C are mounted are provided below the laser units 3Y and 3C in the figure. On the other hand, the mounting parts (mounting surfaces 205-208) of the housing 201 to which the laser units 3M and 3K are mounted are provided above the laser units 3M and 3K in the figure.

[0033] Each laser unit 3 attached to the housing 201 is adjusted so that the beam pitch in the sub-scanning direction, which will be described later, falls within a predetermined range, and then fixed to the housing 201 with an adhesive. After the four laser units 3 are fixed with an adhesive, the control board 209 of the optical scanning device 2 is fixed to the housing 201 with the lead terminals 301C of the corresponding light sources 301 inserted into the through holes 210 provided in the control board 209. Then, the lead terminals 301C of the light sources 301 are joined to the control board 209 by soldering.

[0034] [Laser unit layout] Fig. 5 is a view of the laser units 3 (3Y, 3M, 3C, 3K) attached to the housing 201 viewed from the lead terminal 301C side of the light source 301 with the control board 209 removed in Fig. 4. Note that in Fig. 5, it can be seen that the holder 303 of the laser unit 3 is biased in the directions of the attachment surfaces 205, 206, 207, 208 by the elastic member 211.

[0035] As shown in FIG. 5, by arranging the four laser units 3Y, 3M, 3C, and 3K close to each other in the Z-axis and Y-axis directions, the volume of the housing 201 occupied by the laser units 3 can be reduced, and the optical scanning device 2 can be made smaller. Therefore, in this embodiment, the laser units 3Y, 3M, 3C, and 3K are arranged so that the straight line connecting the centers of the cylindrical axes of the holders 303 of the laser units 3 adjacent to each other in the Z-axis and Y-axis directions forms a square or a rectangle. Furthermore, in FIG. 5, the straight line connecting the protrusions 304A and 304B of each laser unit 3 is inclined around the central axis of the cylindrical portion with respect to the straight line connecting the central axes of the cylindrical portions of the holders 303 of the adjacent laser units 3Y, 3M, 3C, and 3K. In detail, the straight line connecting the protrusions 304A and 304B of each laser unit 3 is arranged in the housing 201 so as to be parallel to the straight line D connecting the centers of the cylindrical axes of the holders 303 of the diagonal laser units 3Y and 3K among the adjacent laser units 3. As a result, the area surrounded by the laser unit 3 can be effectively used as an arrangement area for protrusions 304A and 304B for position adjustment, which will be described later, and the optical scanning device 2 can be made more compact. In addition, in this case, in order to prevent the protrusion 304B of the laser unit 3Y from coming into contact with the protrusion 304A of the laser unit 3K, the following restriction is imposed on the length Lh from the center of the cylindrical axis of the holder 303 of the laser unit 3 to the tips of the protrusions 304A and 304B. In other words, in FIG. 5, if the length from the cylindrical axis center QY of the holder 303 of the laser unit 3Y to the cylindrical axis center QK of the holder 303 of the laser unit 3K is Ld, then the relationship is established in which the length Lh is shorter than 1 / 2 (half) of the length Ld (Lh <Ld / 2)。

[0036] 5, each laser unit 3 is installed in the housing 201 such that the straight line connecting the protrusions 304A and 304B is approximately parallel to a straight line D connecting the centers of the cylindrical axes of the holders 303 of the diagonal laser units 3Y and 3K of the adjacent laser units 3. For example, each laser unit 3 may be installed in the housing 201 such that the straight line connecting the protrusions 304A and 304B is parallel to a straight line connecting the centers of the cylindrical axes of the holders 303 of the diagonal laser units 3C and 3M of the adjacent laser units 3.

[0037] [How to adjust the beam pitch of the light source] Fig. 6 is a schematic diagram for explaining a method for adjusting the beam pitch of the laser unit 3. In Fig. 6, the laser unit 3 is installed on the mounting portion of the housing 201, and is urged in the direction of the mounting portion of the housing 201 by the elastic member 211. In detail, the holder 303 of the laser unit 3 is installed on the housing 201 with the cylindrical side portion 303B in contact with the mounting surfaces 207 and 208 of the housing 201, and the cylindrical side portion 303A (not shown) in contact with the mounting surfaces 205 (not shown) and 206 (not shown) of the housing 201. The elastic member 211 urges the cylindrical side portions 303A and 303B of the holder 303 of the laser unit 3 in the directions of the mounting surfaces 205, 206, 207, and 208 of the housing 201.

[0038] The light source 301 in this embodiment is a multi-beam laser diode having two light emitting points 301A and 301B. After adjusting the beam pitch (spacing between scanning positions) of the laser light emitted from each light emitting point of the light source 301 on the photosensitive drum 11 according to the image resolution, the laser unit 3 is fixed to the housing 201 by an adhesive. The beam pitch is adjusted by rotating the laser unit 3, which is biased by a force Fs by an elastic member 211 to the mounting surfaces 205 (not shown), 206 (not shown), 207, and 208 of the housing 201, around the cylindrical axis of the holder 303. Specifically, U-shaped notches provided in the centers of two adjustment protrusions 304A and 304B arranged opposite to each other, are gripped by an adjustment tool J (hatched circular parts in the figure), and the laser unit 3 is rotated around the cylindrical axis of the holder 303 by the adjustment tool J. In this way, the positions of two light emitting points 301A and 301B of light source 301 fixed by press-fitting into holder 303 are adjusted.

[0039] For example, assume that the positions of the two light emitting points of the light source 301 are positions 301A and 301B in the figure, and the desired positions of the light emitting points are 301A' and 301B'. In this case, the laser unit 3 is rotated in the direction of the arrow in the figure (clockwise direction) using the adjustment tool J to adjust the beam pitch. The rotation moment M of each of the protrusions 304A and 304B when the laser unit 3 is rotated can be calculated as follows. That is, the rotation moment M is calculated by the product of the distance Lj from the cylindrical axis center Q of the holder 303 to the contact point where the adjustment tool J contacts the protrusions 304A and 304B and the force Fj that the adjustment tool J applies to the protrusions 304A and 304B (rotation moment M = distance Lj x force Fj). Also, if the laser unit 3 is made smaller and the protrusions 304A and 304B are shortened, the distance Lj will be shortened, but the required rotation moment M can be obtained by increasing the force Fj accordingly.

[0040] Here, when the laser unit 3 is rotated around the cylindrical axis of the holder 303, friction occurs between the mounting surfaces 205 (not shown), 206 (not shown), 207, 208 and the cylindrical side surface portions 303A (not shown) and 303B of the holder 303. When a force Fj is applied to the projections 304A and 304B using the adjustment tool J, a force that tries to move the laser unit 3 is generated in a direction other than the rotation direction of the holder 303. For example, the force Fj on the projection 304A side generates a force in a direction that moves the holder 303 away from the mounting surface 208. If the biasing force Fs by the elastic member 211 is increased to resist this, the frictional forces between the cylindrical side surface portions 303A and 303B of the holder 303 and the mounting surfaces 205, 206, 207, 208, and between the cylindrical side surface portions 303A and 303B and the elastic member 211 will increase. As a result, the movement of the laser unit 3 in the rotation direction is hindered. However, in this embodiment, when rotating the laser unit 3, the adjustment tool J grips not only the protrusion 304A but also the opposing protrusion 304B, and can apply a force Fj in the opposing directions. Therefore, it is possible to cancel out forces that try to move the laser unit 3 in a direction other than the rotation direction of the holder 303.

[0041] In the laser unit 3 of this embodiment, the projections 304A and 304B for position adjustment are provided to face each other around the cylindrical axis of the holder 303. For example, in order to reduce the size of the laser unit 3, the distance Lj from the cylindrical axis center Q of the holder 303 to the contact point where the adjustment tool J contacts the projections 304A and 304B (or the length Lh from the cylindrical axis center Q of the holder 303 to the tips of the projections 304A and 304B) is shortened. This makes it possible to rotate the laser unit 3 while maintaining the position of the holder 303 biased against the housing 201 by the elastic member 211, even if the force Fj required to rotate the holder 303 increases.

[0042] In FIG. 6, in order to explain the beam pitch adjustment method, the holder 303 of the laser unit 3 is installed on the mounting surfaces 205, 206, 207, and 208 of the housing 201 so that the protrusions 304A and 304B are horizontal, not diagonally as shown in FIG. 5. In FIG. 6, the angle to be adjusted is also shown large in order to easily explain the beam pitch adjustment. In actual beam pitch adjustment, as shown in FIG. 5, the protrusions 304A and 304B are installed in the diagonal direction as shown in FIG. 5, and the adjustment angle of the beam pitch is several degrees, so the angle of the protrusions 304A and 304B hardly changes before and after the beam pitch adjustment.

[0043] As described above, even if the protrusions 304A, 304B provided on the laser unit 3 are miniaturized, the optical scanning device 2 can be miniaturized without deteriorating the beam pitch adjustment accuracy. Note that, in this embodiment, the collimator lens 302 is configured to be attached to the laser unit 3, but the present invention is not limited to this configuration, and the collimator lens 302 may be configured to be bonded and fixed to the housing 201 after the position of the collimator lens 302 relative to the light source 301 is adjusted.

[0044] As described above, according to this embodiment, the optical scanning device can be made smaller. [Explanation of symbols]

[0045] 3 Laser unit 201 Case 205, 206, 207, 208 Mounting surface 211 Elastic members 301 Light source 303 Holder 304A, 304B adjustment protrusion

Claims

1. An optical scanning device that irradiates a surface to be scanned with a light beam, four light source units each including a light source having a plurality of light emitting points for emitting a light beam, and a holder for holding the light source, the holder having a cylindrical portion whose central axis is parallel to the optical axis direction of the light beam; a housing of the optical scanning device that holds the cylindrical portions of the four light source units; Equipped with In an optical scanning device, the four light source units are arranged such that a line connecting the centers of the four cylindrical portions forms a rectangle when viewed in the direction of the central axis, Each of the four holders has a pair of protrusions at one end of the holder in the direction of the central axis, the protrusions extending from the cylindrical portion in directions away from each other from the center of the cylindrical portion when viewed in the direction of the central axis, When viewed in the direction of the central axis, Each of the four holders has a shape in which the pair of protrusions and the center of the cylindrical portion are aligned in a straight line, With the four light source units fixed to the housing, Among the four holders, two of the holders whose centers of the cylindrical portions are on one of the two diagonals of the rectangle have straight lines connecting the pair of protrusions and the center of the cylindrical portion substantially parallel to the one diagonal, and straight lines connecting the pair of protrusions and the center of the cylindrical portion of the remaining two holders are also substantially parallel to the one diagonal, a length from the center of the cylindrical portion of each of the four holders to a tip of one of the pair of protrusions is shorter than half the length of the one diagonal so that the protrusions facing each other between the two holders whose centers of the cylindrical portions are on the one diagonal do not interfere with each other; An optical scanning device, characterized in that the length of each of the four sides of the rectangle is shorter than twice the length from the center of the cylindrical portion of the holder to the tip of one of the pair of protrusions.

2. 2. The optical scanning device according to claim 1, wherein the positioning of each of the four light source units in the optical axis direction is achieved by abutting one of the pair of protrusions with the housing.

3. An optical scanning device as described in claim 1 or 2, characterized in that the light source is fixed to the end side of the holder where the pair of protrusions are provided, and a collimator lens is fixed to the end side opposite the end of the holder in the direction of the central axis.

4. 4. The optical scanning device according to claim 1, wherein the pair of protrusions has a notch at the center of the protrusion.

5. an image forming unit having a photosensitive drum on which an electrostatic latent image is formed, the image forming unit developing the electrostatic latent image formed on the photosensitive drum and forming an image on a recording material; An optical scanning device according to any one of claims 1 to 4; Equipped with The image forming apparatus is characterized in that the optical scanning device forms the electrostatic latent image on the photosensitive drum.

Images