JP6584087B2 - Scanning optical device - Google Patents

Description

  The present invention relates to an optical deflector that deflects a light beam and a scanning optical device that includes a plurality of optical system parts including a detection unit that detects the timing at which the light beam passes.

  A scanning optical device used in a conventional image forming apparatus such as a laser printer optically modulates a laser beam emitted from a light source in accordance with an image signal, and the light modulated laser beam is an optical deflector formed of, for example, a rotating polygon mirror. Deflection scanning. The laser beam that has been deflected and scanned is guided to a BD sensor as a light detection means (light receiving element) in order to control the timing of the scanning start position on the surface to be scanned. Thereafter, the image is formed in a spot shape on the photosensitive recording medium surface by a scanning lens such as an imaging optical system having fθ characteristics, and optical scanning is performed. The optical scanning start timing is a predetermined time after the synchronization signal is generated based on the detection of the laser beam by the BD sensor.

  Patent Document 1 discloses a configuration in which the BD sensor as described above is mounted on a circuit board.

Patent No.4109878

  In the configuration of Patent Document 1, the element of the BD sensor is mounted through-hole. However, in recent years, an element for surface mounting is used as a light receiving element such as a BD sensor in order to reduce the size and cost of the apparatus. Is considered. When the light receiving element is surface-mounted, a through hole for fitting the element into the substrate is provided, and the light entering the through hole can be received by the light receiving element.

  However, in the case where the through hole is provided in the substrate as described above, when the light passes through the through hole, the light reflected by the inner wall surface of the through hole is incident on the light receiving portion of the light receiving element depending on the position and orientation of the light. In some cases, erroneous detection may occur.

  In view of the above problems, an object of the present invention is to suppress erroneous detection of a light receiving element.

The present invention for solving the above-described problems includes a light source, a deflecting unit that deflects a light beam emitted from the light source, a substrate including a through hole to which the light source is attached, a light receiving unit, and the substrate. has a mounting light-receiving member, wherein the light receiving member, in the optical scanning device for receiving the light beam entering into the through-hole while moving to the deflected scanning direction by the deflecting means, accommodating the polarization means The substrate has an optical box attached to the outside, the light receiving member is mounted on the surface of the substrate away from the deflecting means, and the light receiving unit is centered on the light receiving member with respect to the scanning direction. downstream from, and is deflected by said deflecting means, said light beam reflected by the inner wall of the through hole and is arranged at a position not incident, the light receiving member of the downstream side of the light receiving member in the scanning direction Gap between the substrate and wherein the larger upstream.

  ADVANTAGE OF THE INVENTION According to this invention, it can suppress that a light receiving element detects erroneously.

1 is a schematic sectional view of an image forming apparatus. 1 is a schematic perspective view of an optical scanning device. The partial perspective view of the BD sensor vicinity of an optical scanning device. (A) The perspective view which shows the relationship between the BD sensor in the state before mounting of a BD sensor, and the board | substrate with which it is mounted, (b) Between the BD sensor in the state after mounting of BD sensor, and the board | substrate with which it is mounted The perspective view which shows a relationship. The scanning sectional view which illustrated laser beam L which enters a BD sensor. FIG. 4 is a scanning sectional view illustrating a laser beam L reflected at a point B. FIG. 6 is a schematic cross-sectional view of another form of optical scanning device.

<First Embodiment>
[Image forming apparatus]
FIG. 1 is a diagram illustrating an image forming apparatus 101. An optical scanning device 100 to be described later is installed on the optical bench 103. The optical bench 103 is a part of the housing of the image forming apparatus 101. The image forming apparatus 101 includes an image forming unit, such as a process cartridge 108, a sheet feeding unit 104 on which a transfer material P is placed, a sheet feeding roller 105, a transfer roller (transfer unit) 106, and a fixing device (fixing unit). 107 is provided. The process cartridge 108 includes a photosensitive drum (photosensitive member) 8 that is an image carrier, a charging roller 108a, and a developing roller 108b. The transfer roller 106 and the photosensitive drum 8 are in contact with each other to form a transfer nip.

  The surface of the photosensitive drum 8 is charged by the charging roller 108a while rotating around the rotation axis, and then the optical scanning device 100 emits laser light and scans the surface to form a latent image. Thereafter, toner is adhered to the surface by the developing roller 108b, and the latent image becomes a toner image developed by the toner.

  On the other hand, the transfer material P is fed from the paper feed unit 104 by the paper feed roller 105, and the toner image formed on the photosensitive drum 8 is transferred by the transfer roller 106. Thereafter, the toner image on the transfer material P is fixed to the transfer material P by heat and pressure in the fixing device 107. The transfer material P on which the toner is fixed is output to the outside of the image forming apparatus 101 by the paper discharge roller 110.

[Optical scanning device]
Next, the optical scanning device 100 will be described. FIG. 2 is a schematic perspective view of the optical scanning device 100. FIG. 3 is a perspective view of the vicinity of the BD sensor 6 of the optical scanning device 100. The semiconductor laser unit 1 is formed by unitizing a semiconductor laser 1a (not shown) as a light source for emitting a laser beam L and its drive circuit 1b. A laser beam L emitted from the semiconductor laser 1 a passes through a lens 2 having a collimator lens function and a cylindrical lens function, and an aperture stop 3, and a plurality of laser beams L formed on a rotating polygon mirror (polygon mirror) 4 of the deflecting unit 5. Incident on one of the reflective surfaces 12. The polygon mirror 4 is rotationally driven in the direction of the arrow by a motor provided in the deflecting means 5 and changes the direction of the reflecting surface 12 to continuously change the direction in which the laser beam L is reflected, thereby deflecting the laser beam L. . When the polygon mirror 4 is in a certain rotational phase, the laser beam L reflected by the reflecting surface 12 is transmitted through the BD lens 14 and collected, and enters the light receiving unit 10 of the BD sensor 6 as a light receiving member (light receiving element). When the polygon mirror 4 is in another rotational phase, the laser beam L enters the fθ lens (scanning lens) 7 and enters the photosensitive surface (scanned surface) that is the surface of the photosensitive drum 8. The optical members (semiconductor laser unit 1, lens 2, aperture stop 3, deflecting means 5, BD sensor 6, fθ lens 7) described above are positioned and supported by the optical box 9 and fixed.

[Scanning of photosensitive drum with laser light]
Next, a method for scanning the photosensitive drum 8 with laser light by the optical scanning device 100 will be described. The laser beam L emitted from the semiconductor laser 1a of the semiconductor laser unit 1 is converted into substantially parallel light or convergent light in the main scanning direction by the lens 2 and converged light in the sub-scanning direction. Next, the laser beam L passes through the aperture stop 3 and is limited in its beam width, and forms an image on the reflecting surface 12 of the polygon mirror 4 in the form of a focal line extending long in the main scanning direction. Then, the reflection direction of the laser beam L on the reflecting surface 12 is continuously changed by the rotation of the polygon mirror 4, and the laser beam L is deflected. When the polygon mirror 4 is in a predetermined rotational phase, the reflected laser beam L is incident on the surface of the optical box 9 or the BD sensor 6 near the BD sensor 6 to form a circular spot S1. As the polygon mirror 4 rotates, the spot S1 of the laser beam L moves in the direction of the broken line arrow in FIG. At this time, the BD sensor 6 outputs a BD signal when the amount of light received by the light receiving unit 10 exceeds a predetermined threshold. Based on the timing at which the BD signal is output, the light emission start timing (image writing) based on the image data is determined.

  When the polygon mirror 4 further rotates a predetermined amount, the reflected laser beam L passes through the fθ lens 7 and enters the surface of the photosensitive drum 8. The fθ lens 7 focuses the laser beam L and forms it as a spot image on the surface of the photosensitive drum 8. While the polygonal mirror 4 further rotates by a predetermined amount after the laser beam L starts to enter the fθ lens 7, the laser beam L continues to be incident on the surface of the photosensitive drum 8 through the fθ lens 7. The spot image moves in the scanning direction corresponding to the rotation direction of the polygon mirror 4. The scanning direction is parallel to the rotational axis direction of the photosensitive drum 8. The fθ lens 7 is designed at an imaging position of the laser beam L such that the spot image of the laser beam L moves in the scanning direction at a constant speed on the surface of the photosensitive drum 8.

  While the spot image of the laser beam L moves on the surface of the photosensitive drum 8 in the scanning direction, a driving current is supplied to the light source of the semiconductor laser unit 1 based on a laser driving signal (VIDEO signal) corresponding to image data to be formed. Is supplied and the light source is turned on. As a result, a latent image corresponding to the image data in the scanning direction is formed by scanning (main scanning) with the laser beam L.

  In addition to the rotation of the polygon motor 4 described above, the photosensitive drum 8 rotates around the rotation axis, so that the spot image of the laser beam L moves relative to the photosensitive drum surface 8 in a direction perpendicular to the scanning direction ( (Sub scan). By rotating the polygon mirror 4 and the photosensitive drum 8 as described above, a two-dimensional latent image corresponding to image data is scanned and formed on the surface of the photosensitive drum 8 with the laser beam L.

  The BD signal output process and the subsequent scanning process using the laser beam L on the photosensitive drum 8 described above are performed for each reflection surface 12 as the polygon mirror 4 rotates.

[Positioning of BD sensor 6]
4A and 4B are perspective views showing the relationship between the BD sensor 6 and the substrate 20 on which the BD sensor 6 is mounted (assembled). FIG. 4A is a state before the BD sensor 6 is mounted, and FIG. Shown later. The moving direction (scanning direction) of the spot S1 of the laser beam L on the surface of the BD sensor 6 is defined as the X direction, and the direction parallel to the surface of the substrate 20 and orthogonal to the scanning direction X is defined as the Y direction.

  Since the semiconductor laser 1a and the BD sensor 6 are mounted on the substrate 20, the substrate 20 includes a drive control circuit for the semiconductor laser 1a and a BD signal output circuit. A through hole 21 is provided on the substrate 20, and the terminal array 23 is soldered to the pad 22 of the substrate 20, so that the BD sensor 6 is surface-mounted on the substrate 20. Note that the terminal row 23 may be soldered to the pad 22 in a state in which at least a part of the BD sensor 6 is inserted and fitted into the hole 21. The pads 22 of the substrate 20 are arranged so as to overlap the terminal rows 23 when the BD sensor 6 is fitted into the holes 21. Further, the pad 22 is longer than the terminal row 23 on the front end side in the Y direction. Cream solder is applied to the pad 22 in advance, and the BD sensor 6 is fixed to the substrate 20 with solder by flowing it through a reflow furnace in a state where the terminal row 23 of the component and the pad 22 overlap each other.

  When the substrate 20 is flowed through the reflow furnace, the cream solder applied to the pad 22 melts, and the self-alignment in which the BD sensor 6 moves in the X direction so that the terminal row 23 and the pad 22 overlap each other due to the surface tension of the melted cream solder. Occur. By self-alignment due to surface tension, even if the BD sensor 6 is displaced in the X direction, the BD sensor 6 moves in the X direction and moves to the center position of the pad 22 to determine the position. Furthermore, since the pad 22 has a shape that is slightly longer than the terminal row 23 in the Y direction, the surface tension of the solder can be increased and the self-alignment can be further stabilized. The terminal row 23 is arranged on two sides parallel to the X direction of the BD sensor 6, and the positions thereof are axisymmetric with respect to a center line parallel to the X direction passing through the center of the BD sensor 6. For this reason, a moment to rotate the BD sensor 6 on the surface of the substrate 20 hardly occurs, and stable self-alignment occurs.

As described above, the BD sensor 6 is mounted with high accuracy at the position of the pad 22 on the substrate in the X direction. Here, the X direction is a direction in which the light beam scans the BD sensor, and the position of the BD sensor 6 is mounted with high accuracy, whereby the image writing timing is accurately determined. Further, self-alignment hardly occurs in the Y direction. Therefore, the positioning of the BD sensor 6 in the Y direction is determined by restricting the positions of two sides parallel to the X direction of the BD sensor 6 with the holes 21 and fitting the BD sensor 6 itself into the holes 21. .
[Prevents stray light on BD sensor 6]
FIG. 5 is a view of the AA section as a scanning section of the laser beam L deflected by the polygon mirror 4 shown in FIG. 4B as viewed from above, and shows the laser beam L incident on the BD sensor 6. It is a thing. As described above, since the BD sensor 6 is surface-mounted on the mounting surface 24 of the substrate 20 on which the semiconductor laser 1 a is mounted, the laser beam L is normal to the light receiving unit 10 that is a light receiving surface parallel to the mounting surface 24. Incident at an angle θ1 with respect to the direction. Since the hole 21 of the substrate 20 is formed by pressing from the mounting surface 24 side of the substrate 20 with a mold, the inner wall surface of the hole 21 has an inclination of an angle θ2 with respect to the normal direction of the mounting surface 24. Arise.

  The laser beam L scans in the X direction (from right to left in the figure), and the hole 21 is wide open on the side that the laser beam L passes after passing through the light receiving unit 10 (downstream in the X direction of the light receiving unit 10). . The size of the downstream portion of the hole 21 in the X direction of the light receiving unit 10 will be described. If the innermost wall surface of the hole 21 is the end surface 25 on the most downstream side in the scanning direction, the light reflected by the end surface 25 after the laser beam L has passed through the light receiving unit 10 is incident on the light receiving unit 10, and based on that, the BD There is a possibility that the sensor 6 outputs a BD signal. In particular, since the light receiving unit 10 of the present embodiment is disposed on the downstream side in the X direction with respect to the center of the BD sensor 6, the light receiving unit 10 is close to the end surface 25 and is easily incident on the light reflected by the end surface 25. In order to suppress such erroneous detection of the BD sensor 6, the shape of the hole 21 is set so that the light reflected by the end face 25 does not enter the light receiving unit 10.

  A point closest to the polygon mirror 4 in the end face 25 is a point B. Point B is a reflection point at which the reflected laser beam L is closest to the light receiving unit 10 side. Also, let t be the length of a perpendicular drawn from the light receiving unit 10 to the back surface 26 of the substrate 20 that is parallel to the mounting surface 24 including the point B.

FIG. 6 is a view of the AA cross section as a scanning cross section of the laser beam L deflected by the polygon mirror 4 shown in FIG. Shows how it reflects. Like the incident light beam to the light receiving unit 10, the laser light incident at an incident angle θ1 with respect to the vertical direction of the light receiving unit 10 takes an angle θ1 + 2 · θ2 in consideration of the angle θ2 inside the hole. Therefore, the distance D1 from the point B in the X direction when the laser beam reflected at the point B reaches the same height as the light receiving unit 10 is t · tan (θ1 + 2 · θ2).
For this reason, if the distance D between the light receiving unit 10 and the point B in the X direction satisfies the following expression (1), the laser light reflected at the point B does not enter the light receiving unit 10.
D> t · tan (θ1 + 2 · θ2) (1)
Assuming that the angle of the light beam reflected at the reflection point B with respect to the direction orthogonal to the X direction is θ (= θ1 + 2 · θ2), Equation (1) can be replaced as follows.
D> t · tan θ Formula (1) ′
As described above, if the distance D satisfies the expression (1), the laser beam L reflected at the point B does not enter the light receiving unit 10, so that the laser light velocity L reflected at the end face 25 of the hole 21 of the substrate 20 is It does not enter the light receiving unit 10. In the present embodiment, the position of the BD sensor 6 in the X direction is determined as a position where the distance D satisfies the expression (1). Thereby, the light reflected by the inner wall surface of the hole 21 can be prevented from entering the light receiving unit 10 of the BD sensor 6.

Second Embodiment
FIG. 7 is a schematic perspective view of the optical scanning device 100 of the second embodiment. This embodiment is different from the first embodiment in that the BD lens 14 is not provided. When the polygon mirror 4 is in a certain rotational phase, the laser beam L reflected by the reflecting surface 12 is incident on the light receiving portion of the BD sensor 6 without passing through a lens or the like. In the case of the configuration of the present embodiment that does not include the BD lens 14, the spot S1 of the laser beam L at the position of the BD sensor 6 is larger than the configuration of the first embodiment with the BD lens 14. For this reason, when the laser beam L is reflected by the inner wall surface of the hole 21 and enters the light receiving unit 10, the BD sensor 6 may detect a relatively large light amount. Therefore, it is more effective to configure so as to satisfy the formula (1).

6 BD sensor 10 light receiving portion 20 substrate 21 hole 22 pad 23 terminal row 25 end face

Claims (6)

A light source, a deflecting means for deflecting a light beam emitted from the light source, a substrate including a through hole to which the light source is attached, a light receiving member including a light receiving unit and mounted on the substrate, In the optical scanning device that receives the light beam entering the through hole while the light receiving member is deflected by the deflection unit and moves in the scanning direction,
An optical box containing the polarizing means and having the substrate mounted on the outside;
The light receiving member is mounted on the surface of the substrate on the side away from the deflecting means;
The light receiving portion is disposed downstream of the center of the light receiving member with respect to the scanning direction, and at a position where the light beam deflected by the deflecting unit and reflected by the inner wall of the through hole does not enter .
An optical scanning device characterized in that a gap between the light receiving member on the downstream side of the light receiving member and the substrate in the scanning direction is larger than the upstream side . When the light beam deflected by the deflecting unit is viewed in a scanning cross section, a point disposed on the most downstream side in the scanning direction among the inner walls of the through hole and closest to the deflecting unit is a reflection point, The distance between the reflection point and the light receiving unit in the scanning direction is D, the distance between the reflection point and the light receiving unit in the direction orthogonal to the scanning direction is t, and the light flux reflected at the reflection point is in the scanning direction. If the angle with respect to the orthogonal direction is θ,
D> t · tan θ
The optical scanning device according to claim 1, wherein:   The optical scanning device according to claim 1, wherein the light source is mounted on the substrate.   The said light-receiving part outputs a signal based on having received the said light beam, The said light source light-emits based on the timing when the said signal was output, The Claim 1 thru | or 3 characterized by the above-mentioned. Optical scanning device.   The deflecting unit includes a reflecting surface, deflects the light beam by continuously changing a direction in which the light beam is reflected by the reflecting surface, and the light beam reflected by the reflecting surface does not pass through the lens. The optical scanning device according to claim 1, wherein the optical scanning device is incident on the light receiving unit.   The optical scanning device according to claim 1, wherein the light receiving member is mounted on the substrate in a state in which at least a part is inserted into the through hole.

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