JP2014035476A - Optical scanner and color image forming apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reduce warpage of an internal reflection element integrally formed with resin, in an optical scanner and a color image forming apparatus having the internal reflection element.SOLUTION: An internal reflection element integrally formed with resin has a shape in which a sub-scanning cross section is notched by at least one of the following areas: a first area that is around an intersection of extended lines of a first internal reflection surface and a second internal reflection surface; a second area that is around an intersection of extended lines of a first transmission surface and the first internal reflection surface; and a third area that is around an intersection of extended lines of the second internal reflection surface and a second transmission surface.

Description

  The present invention relates to an optical scanning device and a color image forming apparatus.

  Conventionally, an optical scanning device has been used in a laser beam printer (LBP), a digital copying machine, a multifunction printer, and the like. In this optical scanning device, a light beam (light beam) that is light-modulated and emitted from the light source means in accordance with an image signal is periodically deflected by an optical deflector formed of, for example, a rotating polygon mirror (polygon mirror). The deflected light beam is focused in a spot shape on the surface of a photosensitive recording medium (photosensitive drum) by an imaging optical system having fθ characteristics, and image recording is performed by optically scanning the surface.

  In addition, a proposal has been made that a trapezoidal prism is arranged between the optical deflector and the photosensitive drum, and the optical scanning device is made smaller while ensuring the necessary optical path length by folding the optical path (Patent Literature). 1). Usually, in order to fold the optical path, it is common to use a folding mirror in which a thin film such as aluminum or copper is deposited on the surface of a glass substrate. However, when the optical path is folded by a normal folding mirror, the optical scanning device becomes larger by the thickness of the glass substrate itself. The trapezoidal prism proposed in Patent Document 1 does not require an extra space other than the light beam passage region because light travels inside the element (prism).

  Further, since total reflection is performed on the inner surface of the prism, it is not necessary to deposit aluminum, copper, or the like, and there are no problems such as variations in reflectance due to uneven film thickness. Furthermore, since two orthogonal reflecting surfaces are integrally formed, there is an advantage that even if the prism is tilted in the sub-scanning direction, the light emission angle does not change.

  In addition, when a resin scanning lens is used as the imaging optical system, it is intended to align the warp in the longitudinal direction that occurs at the time of manufacture in one direction. A proposal has been made in which a rib projecting in the scanning direction is provided (Patent Document 2).

JP 2001-51221 A JP 2006-91774 A

  In Patent Document 1, since the trapezoidal prism (inner surface reflecting element as the inner surface reflecting means) for turning the optical path is made of glass, there is no process of generating a large warp in the longitudinal direction in the manufacturing process. However, a trapezoidal prism made by repeating a polishing process of a glass base material is difficult and expensive.

  Here, when the trapezoidal prism is made of a resin mold so as to be a resin-made prism, it is expected that a large warp will occur. In an optical scanning device, when a large amount of warpage occurs in the internal reflection element, optical performance deterioration such as magnification deviation in the main scanning direction, curvature of field, bending of the scanning line, and deformation of the spot shape due to twist of wavefront aberration, etc. occur. End up.

  In Patent Document 2, ribs protruding from either one of the upper and lower sides of a scanning lens having a symmetrical shape in the sub-scanning direction are provided, and the ribs are cooled first, thereby causing uneven temperature distribution in the mold. The warp in the longitudinal direction generated for the reason is aligned in one direction. That is, warping is generated in one direction by intentionally making the element itself symmetric with an asymmetric shape. However, although the scanning lenses are aligned in one direction, a desired optical performance cannot be obtained with a scanning lens that is still warped. For this reason, a correction mechanism for correcting the warp is required, and the space for the warp correction mechanism increases the size and cost of the apparatus.

  An object of the present invention is to reduce the warpage of the inner surface reflecting means in the optical scanning device and the color image forming apparatus having the inner surface reflecting means integrally made of resin.

  In order to achieve the above object, a typical configuration of an optical scanning device according to the present invention includes light source means for emitting at least one light beam, and deflecting means for deflecting and scanning the light beam emitted from the light source means on a deflection surface. And an imaging optical system that forms an image on the surface to be scanned with the light beam deflected by the deflecting means, the inner surface reflecting means for folding back the light beam deflected by the deflecting means, And the inner surface reflecting means includes a first transmitting surface on which the light beam deflected by the deflecting unit is incident and a light beam transmitted through the first transmitting surface. A first inner surface reflecting surface that reflects the first inner surface, a second inner surface reflecting surface that reflects the light beam reflected by the first inner surface reflecting surface, and a first light beam that is reflected by the second inner surface reflecting surface. 2 transmission surfaces are integrally made of resin, and the inner surface reflection hand In the sub-scan section, the first region around the intersection when the first inner reflective surface and the second inner reflective surface are extended together, the first transmission surface and the first inner surface. At least one of the second region around the intersection when the reflection surfaces are extended together and the third region around the intersection when the second inner reflection surface and the second transmission surface are extended together. It has a shape in which a region is cut out.

  According to the present invention, in the optical scanning device and the color image forming apparatus having the inner surface reflecting means integrally formed of resin, the warpage of the inner surface reflecting means can be reduced.

(A) is a sub-scan sectional view of the optical scanning device according to the first embodiment of the present invention, and (B) is an enlarged view of a main part in the sub-scan section. (A) is a development view in the main scanning direction corresponding to black of the optical scanning device according to the first embodiment of the present invention, and (B) is a development view in the main scanning direction corresponding to cyan. It is a sub-scan sectional view of an internal reflection element as various internal reflection means. (A) is a figure explaining the internal reflection element of the main scanning direction center part of the optical scanning device concerning the 2nd Embodiment of this invention, (B) is a figure explaining the internal reflection element of the main scanning direction edge part. is there. (A) is a figure explaining the internal reflection element of the main scanning direction center part of the optical scanning device concerning the 3rd Embodiment of this invention, (B) is a figure explaining the internal reflection element of the main scanning direction edge part. is there. (A) thru | or (E) is a figure explaining the modification of this invention. 1 is a diagram illustrating a color image forming apparatus equipped with an optical scanning device according to an embodiment of the present invention.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings.

<< First Embodiment >>
(Color image forming device)
FIG. 7 is a schematic diagram of a main part of a color image forming apparatus equipped with an optical scanning device according to an embodiment of the present invention. The present embodiment is a tandem type color image forming apparatus in which four optical scanning devices (optical imaging optical systems) are arranged in parallel and image information is recorded on a photosensitive drum surface as an image carrier. In FIG. 7, 60 is a color image forming apparatus, 12 is an optical scanning device, 21, 22, 23 and 24 are photosensitive drums as image carriers, 31, 32, 33 and 34 are developing units, and 51 is a conveyor belt. It is. In FIG. 7, there are a transfer device (not shown) for transferring the toner image developed by the developing device to the transfer material, and a fixing device (not shown) for fixing the transferred toner image to the transfer material. doing.

  In FIG. 7, the color image forming apparatus 60 receives R (red), G (green), and B (blue) color signals from an external device 52 such as a personal computer. These color signals are converted into C (cyan), M (magenta), Y (yellow), and B (black) image data (dot data) by a printer controller 53 in the apparatus. These image data are respectively input to the optical scanning device 12. The optical scanning device 12 emits light beams 41, 42, 43, and 44 that are modulated according to each image data, and the photosensitive surfaces of the photosensitive drums 21, 22, 23, and 24 are mainly formed by these light beams. Scanned in the scanning direction.

  The color image forming apparatus according to the present embodiment emits scanning light corresponding to each color of C (cyan), M (magenta), Y (yellow), and B (black) from the optical scanning device 12. Then, image signals (image information) are recorded on the photosensitive drums 21, 22, 23, and 24 in parallel, and a color image is printed at high speed.

  The color image forming apparatus according to the present embodiment uses the light beam based on each image data by the optical scanning device 12 as described above, and converts the latent images of the respective colors onto the corresponding photosensitive drums 21, 22, 23, and 24, respectively. Is formed. Thereafter, a single full color image is formed by multiple transfer onto a recording material.

  As the external device 52, for example, a color image reading device including a CCD sensor may be used. In this case, the color image reading apparatus and the color image forming apparatus 60 constitute a color digital copying machine.

(Optical scanning device)
FIG. 1A is a sub-scan sectional view of the optical scanning device according to the first embodiment of the present invention. FIG. 1B is an enlarged view of a sub-scanning cross section around the inner surface reflection element 7 as inner surface reflection means. FIG. 2A is a main scanning sectional view of the imaging optical system SA through which the light beam RA traveling toward the outer photosensitive drum 8A passes. FIG. 2B is a development view of the main scanning section regarding the imaging optical system SB through which the light beam RB traveling toward the inner photosensitive drum 8B passes.

  In the following description of the present embodiment, the optical axis or axis of the imaging optical system is an axis that passes through the center of the scanned surface and is perpendicular to the scanned surface. The sub-scanning direction (Z direction) is a direction parallel to the rotation axis of the deflecting unit. The main scanning section is a section having the normal in the sub scanning direction. The main scanning direction (Y direction) is the direction in which the light beam deflected and scanned by the deflecting means is projected onto the main scanning section. The sub-scanning cross section is a cross section whose normal is the main scanning direction.

  In FIG. 2, reference numeral 1 denotes light source means for emitting at least one light beam, which is composed of, for example, a semiconductor laser. Reference numeral 2 denotes an aperture stop that shapes the beam shape by limiting the passing light flux. An anamorphic lens 3 converts the divergent light beam emitted from the light source means 1 into weakly convergent light in the main scanning section, and in the main scanning direction on the deflecting surface 5a of the optical deflector (deflecting means) 5 in the sub-scanning section. Is converted into a long line image. The anamorphic lens 3 may be composed of two lenses, a collimator lens that converts weakly convergent light in the main scanning section and the sub-scanning section, and a cylindrical lens that has power only in the sub-scanning direction.

  Each element of the aperture stop 2 and the anamorphic lens 3 constitutes an incident optical system (condensing optical system) LA. The optical deflector 5 is composed of a polygon mirror having four faces with a circumscribed circle diameter of 20 mm, and is rotated at a constant speed in the direction of arrow A in the figure by a driving means (not shown). SA and SB are imaging optical systems having two imaging lenses (plastic lenses) 61 and 62 as imaging optical elements having fθ characteristics and an internal reflection element 7 that bends the optical path of the light beam RB. Yes.

  The imaging optical system SA forms a light beam based on the image information deflected and scanned by the optical deflector 5 in a spot shape on the photosensitive drum surface 8A as the scanned surface in the main scanning section. In addition, the imaging optical system SA performs surface tilt correction by optically conjugating the deflection surface 5a of the optical deflector 5 and the photosensitive drum surface 8A in the sub-scan section. Usually, in the case of an optical deflector (polygon mirror) having a plurality of deflecting surfaces, the tilting angle of the deflecting surface in the sub-scanning direction is different for each deflecting surface. is there.

  Reference numeral 4 denotes a synchronization detection lens for synchronization detection. The synchronization detection light beam is imaged on a slit surface (not shown) provided in the vicinity of the synchronization detection element 9. In the present embodiment, the output signal from the synchronization detection element 9 is detected, and the timing of the scanning start position of image recording on the photosensitive drum surface 8A is adjusted using the obtained synchronization signal. Each element of the synchronization detection lens 4 and the synchronization detection element 9 constitutes one element of the synchronization position detection system. The synchronization position detection system may be provided for each of the four light beams corresponding to the four photosensitive drums. However, in order to reduce the number of parts, the synchronization position detection system is provided only for the light beam RA directed to the photosensitive drum 8A as in the present embodiment, and the remaining light beams. It is also possible to control the scanning start position.

  In the present embodiment, the light beam emitted from the semiconductor laser 1 according to the image information is incident on the deflecting surface 5a from the direction orthogonal to the optical axis of the imaging optical system in the main scanning section. Further, in the sub-scan section, the light is incident obliquely at a predetermined angle (3 ° with respect to the normal line of the deflection surface 5a) in the sub-scanning direction with respect to the deflection surface 5a.

  Then, the light beam RB deflected and scanned by the deflecting surface (polygon mirror surface) 5a of the optical deflector 5 passes through the imaging lenses 61 and 62, the optical path is turned back by the inner surface reflecting element 7 described later, and the photosensitive drum 8B. Has reached. Further, the light beam RA passes through the imaging lenses 61 and 62, passes through the lower side of the inner surface reflection element 7, and then the optical path is folded back by the folding mirror 10A to reach the photosensitive drum 8A.

  The light beams RA and RB that have passed through the imaging lenses 61 and 62 are imaged in a spot shape on the photosensitive drum surfaces 8A and 8B, and the optical deflector 5 is rotated in the direction of the arrow A, thereby Is scanned at an equal speed in the direction of arrow B (main scanning direction). Thus, image recording is performed on the photosensitive drum surfaces 8A and 8B as recording media.

(Internal reflection element)
Here, a trapezoidal prism shown in FIG. 1B or the like that is totally reflected on the inner surface of the element and turns the optical path is defined as an inner surface reflecting element. A light beam RB that travels toward the photosensitive drum 8B on the side of the optical deflector 5 that is physically closer to the photosensitive drum 8A that is physically farthest from the optical deflector 5 is a first transmission surface ( (Incident surface) 71, and is reflected by the first inner surface reflecting surface 72 and the second inner surface reflecting surface 73. Then, after passing through the second transmission surface (emission surface) 74, the optical path is bent by the folding mirror 10B and reaches the photosensitive drum 8B.

  Here, the two inner reflecting surfaces 72 and 73 are configured to face each other so as to be substantially orthogonal (88.5 °) in the sub-scanning section, so that the traveling direction of the light beam is rotated by about 180 degrees. Can be made. In addition, a metal material such as aluminum or copper may be vapor-deposited on the first inner surface reflecting surface 72 and the second inner surface reflecting surface 73. This is advantageous in terms of cost reduction. Here, the total reflection surface is a surface in which the light beam is incident on the inner reflection surface so that all the light beams that scan the entire scanning region are totally reflected by the inner reflection surface.

  In addition, the mold may be simplified if the four optical function surfaces of the first and second transmission surfaces and the first and second inner reflection surfaces are configured as a plane as in this embodiment. If the optical function surface is configured so that there is no refractive power in the main scanning direction (non-power), if the light beam scanning on the optical axis is totally reflected, the light beam scanning off-axis is also totally reflected. To come.

  As shown in FIG. 1B, the angle formed by the sub-scanning direction between the light beam RB and the surface normal of the inner reflection surface (total reflection surface) 72 is α1 = 42.45 °, and the light beam RB and the inner reflection surface ( The angle formed by the sub-scanning direction with respect to the surface normal of the (total reflection surface) 73 is α2 = 46.05 °. Since the internal reflection element 7 is integrally formed of a resin (plastic) material having a refractive index of 1.52781, the total reflection occurs when the incident angle to the reflection surface is 40.88 ° or more.

  If the two internal reflection surfaces (total reflection surfaces) 72 and 73 are configured as substantially orthogonal planes as in this embodiment, the light emission angle does not change even if the internal reflection element is tilted in the sub-scanning direction. It has such an effect.

  Further, as in the present embodiment, the first transmission surface (incident surface) and the second transmission surface (output surface) may be configured as independent mirror surfaces (in FIG. 1B, α3 = 3.0 °). If it is plastic mold molding, it can be produced easily. Furthermore, if it is configured as one mirror surface (plane), the configuration of the mold is simplified, which is advantageous in terms of cost reduction.

(Notched shape)
Here, in the specification of the present application, the notched shape means a shape in which a vertex portion is transformed into a trapezoidal portion in the sub-scanning cross section. In the present embodiment, when the internal reflection element 7 is first viewed in the sub-scan section, a region A (first region) around the intersection where both the first internal reflection surface and the second internal reflection surface are extended is cut. The shape is lacking. This is done for the purpose of reducing the cost of the device by further reducing the thickness in the thickness direction and shortening the molding cycle. Further, a region B (second region) around the intersection where both the first transmission surface and the first inner reflection surface are extended, and a region around the intersection where both the second transmission surface and the second inner reflection surface are extended. Region C (third region) is cut out.

  Thereby, it has the effect of the curvature reduction mentioned later. Specifically, the intersection of the first notch surface 75 and the first inner surface reflecting surface 72 formed when the region A is notched, the first notch surface 75 and the second inner surface reflecting surface 73, The distance from the intersection of HR is set to HR = 3.0 mm. Further, the intersection of the second notch surface 76 and the first transmission surface 71 formed when the region B is notched, and the third notch surface 77 and the second notch formed when the region C is notched. The distance from the intersection with the transmission surface 74 is HL = 12.6 mm.

  Further, the distance between the intersection where both the first transmission surface 71 and the first inner reflection surface 72 are extended and the intersection where both the second transmission surface 74 and the second inner reflection surface 73 are extended is defined as HLo. Then, the distance HLo = 14.59 mm. Then, 12.59 / 14.59 = 0.863, which satisfies the following (Formula 1).

0.65 <HL / HLo <0.95 (Formula 1)
Exceeding the lower limit of (Equation 1) is not good because the distance between each end face of the inner surface reflection element and the light beam is too close and affected by the refractive index distribution. On the other hand, if the upper limit is exceeded, the effect of reducing warpage becomes thin.

  Further, it is desirable that the distance between the end of the inner surface reflection element and the light beam when each region is cut out is at least half of the light beam diameter. For example, as shown in FIG. 1B, the distance between the end of the inner reflection element and the light beam h1 = 2.21 and the light beam diameter w1 = 1.39 on the first notch surface 75. Similarly, h2 = 1.51 and luminous flux diameter w2 = 1.46 at the second notch surface 76, and h3 = 1.17 and luminous flux diameter w3 = 1.20 at the third notch surface 77. .

  If the distance between the end of the inner surface reflection element 7 and the light beam is made smaller than half of the light beam diameter, it is affected by the change in the focus position in the sub-scanning direction due to durability and the influence of the birefringence distribution. As a result, adverse effects such as enlargement of the spot diameter in the sub-scanning direction occur. As in this embodiment, if a margin equal to or greater than the light beam diameter is provided, it is not necessary to be affected by the refractive index distribution and the birefringence distribution.

[Operations and effects of this embodiment]
Next, the effect of reducing warpage of the internal reflection element 7 which is a characteristic part of the present invention will be described. Type A shown in FIG. 3 shows a triangular shape having no notches at three apexes in the sub-scan section. The triangle has a base of 14 mm, a height of 7 mm, and a length of 130 mm in the main scanning direction. Type B has a shape in which regions A, B, and C are cut away from Type A by 2 mm in the sub-scanning direction. Type C has a shape in which two protruding portions are added in the vicinity of region A in the vertical direction in the sub-scanning direction with respect to Type B.

  The angle formed between the inner reflective surface and the first and second transmission surfaces in the region B and the region C of Type A is 45 ° and an acute angle, and the angle formed between the two inner reflective surfaces in the region A is 90 °. In the molding process, first, the cooling of these non-obtuse parts proceeds. When the element is taken out of the mold, the internal reflection element is deformed so as to warp toward the upper bottom side where cooling is delayed from the lower bottom side. This is the mechanism of warpage. Therefore, warping can be suppressed if the element can be cooled evenly, but the internal reflection element having two internal reflection surfaces that are substantially orthogonal to each other is asymmetric in shape, and is inevitably in the element during the molding process. The temperature distribution is attached.

  Therefore, although it is impossible to cool evenly, it is possible to suppress warpage by removing a portion that is rapidly cooled. Further, if the shape of the sub-scanning cross section such as Type C in which protrusions are provided at two locations in the sub-scanning direction in the vicinity of the region A in order to make the shape of the inner reflection element close to a symmetrical shape, the warp is further reduced.

  Regarding the shape of Type B, the intersection of the second cut-out surface and the first transmission surface formed when the region B is cut out, the third cut-out surface formed when the region C is cut out, and the second cut-out surface The distance HL = 10 mm from the intersection with the transmission surface. Further, a distance HLo = 14 mm between an intersection where the first transmission surface and the first inner reflection surface are extended together and an intersection where the second transmission surface and the second inner reflection surface are extended together, 10/14 = 0.714 is satisfied, and (Formula 1) is satisfied.

  Regarding the shape of Type C, the distance between the intersection of the first inner reflection surface and the first cutout surface and the intersection of the second inner reflection surface and the first cutout surface is HR, The total distance of the protruding portions is HT (= HT1 + HT2). Then, HR = 4 mm, HT = 4 mm, and 4/4 = 1.00, which satisfies the following (Formula 2).

0.50 <HT / HR <1.50 (Formula 2)
If the lower limit of (Formula 2) is exceeded, the effect of reducing warpage becomes thin. On the other hand, if the upper limit is exceeded, the area of the inner reflection surface of the inner reflection element becomes narrow, and the light beam cannot be reflected in the entire scanning region, which is not good.

  As another method for reducing the warpage, a method of providing a temperature distribution such that the temperature of the mold on the side where the internal cooling of the internal reflection element proceeds fast is higher than the temperature of the mold on the side where the cooling proceeds slowly. There is. However, if a large temperature distribution is applied in order to eliminate the warpage in an element shape where a large amount of warpage occurs, the amount of thermal expansion differs between the fixed side and the movable side of the mold, resulting in inconvenience due to mold matching and the like. . Therefore, it is important to reduce the warp with the shape of the element as much as possible as in this embodiment.

<< Second Embodiment >>
FIG. 4A is a sub-scanning sectional view on the optical axis (center portion in the main scanning direction) in the vicinity of the inner surface reflection element according to the second embodiment of the present invention. FIG. 4B is a sub-scanning sectional view of the outermost axis (end in the main scanning direction) near the inner surface reflection element. In the present embodiment, similarly to the first embodiment, the light beam emitted from the light source unit is incident on the surface normal of the deflecting surface of the deflecting unit from the sub-scanning oblique direction. In the present embodiment, the light beam transmitted through the first transmission surface is folded back in the + Z direction by the first inner reflection surface.

  This is the same side as the incident direction in the sub-scanning direction of the light emitted from the light source means. In such a case, the off-axis light beam has a higher position in the sub-scanning direction (+ Z direction side) of the light beam that passes through the first transmission surface than the light beam on the optical axis. Similarly, the off-axis light beam has a higher position in the sub-scanning direction (+ Z direction side) of the light beam reflected by the first inner reflection surface than the light beam on the optical axis.

  As the internal reflection element, it is more advantageous for the molding cycle to cut off the extra area through which the luminous flux does not pass as much as possible. For this reason, the notched shape is made different between the end portion in the main scanning direction of the internal reflection element and the central portion in the main scanning direction. That is, the distance HR between the intersection between the first inner reflection surface and the first notch surface and the intersection between the second inner reflection surface and the first notch surface is determined as the main scanning of the inner reflection element. The central part (HRc) in the main scanning direction is made longer than the direction end part (HRe). That is, a larger notch is formed on the axis.

  In addition, as an internal reflection element, it is advantageous for reducing warpage to cut as much as possible an extra region through which the light flux does not pass, and therefore, the intersection of the first transmission surface and the second cut-out surface, The distance between the intersection of the second transmission surface and the third notch surface is changed in the main scanning direction. That is, the notched shape is made different between the end portion in the main scanning direction of the inner surface reflection element and the central portion in the main scanning direction. In other words, the off-axis direction is cut larger so that the distance HL is longer at the center (HLc) in the main scanning direction than at the main scanning direction end (HLe) of the inner surface reflecting element.

  The sub-scanning sectional shape of the internal reflection element at each image height satisfies (Equation 1). For the axial cross section, HLc = 12.59 mm and HLo = 14.59 mm, so HLc / HLo = 0.863. For the outermost axis cross section, HLe = 11.38 mm and HLo = 14.59 mm, so that HLe / HLo = 0.780.

  In the case of an optical system in which the light beam emitted from the light source is incident on the deflecting means in the sub-scanning oblique direction as in this embodiment, the amount of notch is changed in the main scanning direction, and the extra area of the internal reflection element is made as much as possible. By cutting off, the effect of further shortening the molding cycle and reducing warpage can be obtained.

<< Third Embodiment >>
FIG. 5A is a sub-scanning sectional view on the optical axis (center portion in the main scanning direction) in the vicinity of the inner surface reflection element according to the third embodiment of the present invention. FIG. 5B is a sub-scanning cross-sectional view of the outermost axis (end in the main scanning direction) near the inner surface reflection element. In the present embodiment, similarly to the first embodiment, the light beam emitted from the light source unit is incident on the surface normal of the deflecting surface of the deflecting unit from the sub-scanning oblique direction. In the present embodiment, the light beam transmitted through the first transmission surface is folded back in the −Z direction by the first inner reflection surface. This is opposite to the incident direction of the light emitted from the light source means in the sub-scanning direction.

  In such a case, the off-axis light beam has a higher position in the sub-scanning direction (+ Z direction side) of the light beam that passes through the first transmission surface than the light beam on the optical axis. Similarly, the off-axis light beam has a higher position in the sub-scanning direction (+ Z direction side) of the light beam reflected by the first inner reflection surface than the light beam on the optical axis.

  As an internal reflection element, it is more advantageous for the molding cycle to cut off an extra region through which the light beam does not pass. Therefore, the intersection between the first internal reflection surface and the first notch surface, The distance HR between the intersection of the inner reflection surface and the first notch surface is changed in the main scanning direction. That is, the notched shape is made different between the end portion in the main scanning direction of the inner surface reflection element and the central portion in the main scanning direction. That is, the off-axis side is cut out more greatly so that the main scanning direction center portion (HRc) is shorter than the main scanning direction end portion (HRe) of the internal reflection element.

  Further, as an internal reflection element, it is advantageous for reducing warpage to cut as much as possible an extra region through which the light beam does not pass. Therefore, the intersection of the first transmission surface and the second notch surface, The distance between the intersection of the second transmission surface and the third notch surface changes HL in the main scanning direction. That is, the notched shape is made different between the end portion in the main scanning direction of the inner surface reflection element and the central portion in the main scanning direction. In other words, the axially larger portion is cut out so that the central portion (HLc) in the main scanning direction is shorter than the end portion (HLe) in the main scanning direction of the internal reflection element.

  Furthermore, (Formula 1) is also satisfied in the sub-scanning cross-sectional shape of the internal reflection element at each image height. For the axial section, HLc = 16.49 mm and HLo = 20.98 mm, so HLc / HLo = 0.786. For the outermost axis cross section, since HLe = 18.30 mm and HLo = 20.98 mm, HLe / HLo = 0.877.

  In the case of an optical system in which the light beam emitted from the light source is incident on the deflecting means in the sub-scanning oblique direction as in this embodiment, the amount of notch is changed in the main scanning direction, and the extra area of the internal reflection element is made as much as possible. By cutting off, the effect of further shortening the molding cycle and reducing warpage can be obtained.

(Mold and molding method)
In order to mold the resin-made internal reflection element 7 described above, first, a mold is prepared in advance as a shape (concave) complementary to the shape (convex) of the internal reflection element 7. That is, the inner surface reflection element 7 has a shape in which the regions A to C are cut out as described in the above-described embodiment, but the mold is formed as a trapezoidal portion instead of the apex portion in the regions A to C. The resin is poured into such a mold and cooled, and after cooling, the mold is removed, and the integrally formed internal reflection element 7 is taken out.

(Modification)
In the above-described embodiment, the region A (first region), the region B (second region), and the region C (third region) are cut out, but the present invention is not limited to this, and the three Of the two regions, at least one region may be cut out. In the form shown in FIG. 6A, the region A is not cut out, and only the region B and the region C are cut out. In the form shown in FIG. 6B, an upper and lower projecting portion is added to the area A in contrast to the form shown in FIG.

  In the form shown in FIG. 6C, the area A and the area C are not cut out, but only the area B is cut out, and a protruding portion is added to the area C. Further, in the form shown in FIG. 6D, an upper and lower projecting portion is added to the region A with respect to the form shown in FIG. In the form shown in FIG. 6E, the area A and the area B are cut out, and a protruding portion is added to the area C without cutting out the area C.

  In these modifications, as in the above-described embodiment, the internal reflection element has a shape that does not include an acute angle portion in the sub-scanning cross section.

1 ··· Light source means, 5 ··· Optical deflector (deflection means), 61, 62 ·· Imaging lens (imaging optical system), 7 · · Internal reflection element, 71 · · · First transmission surface (incident surface) ), 72... First inner surface reflecting surface, 73... Second inner surface reflecting surface, 74... Second transmitting surface (outgoing surface), Region A .. First region, Region B. , Region C ··· Third region

Claims (13)

Light source means for emitting at least one light beam, deflection means for deflecting and scanning the light beam emitted from the light source means on a deflection surface, and imaging optics for imaging the light beam deflected by the deflection means on the surface to be scanned An optical scanning device having a system,
An inner surface reflecting means for folding the light beam deflected by the deflecting means in an optical path between the deflecting means and the scanned surface;
The inner surface reflecting means includes a first transmitting surface on which the light beam deflected by the deflecting means is incident, a first inner surface reflecting surface that reflects the light beam transmitted through the first transmitting surface, and the first inner surface. The second inner surface reflecting surface that reflects the light beam reflected by the reflecting surface and the second transmission surface from which the light beam reflected by the second inner surface reflecting surface is integrally formed of resin,
The inner surface reflecting means includes a first region around an intersection when the first inner surface reflecting surface and the second inner surface reflecting surface are extended in the sub-scan section, the first transmitting surface, and the first transmitting surface. A second region around the intersection when the first inner reflection surface is extended together and a third region around the intersection when the second inner reflection surface and the second transmission surface are both extended. An optical scanning device having a shape in which at least one region is cut out.   The optical scanning device according to claim 1, wherein the inner surface reflecting means does not include an acute angle portion in the sub-scanning cross section.   3. The projecting portion according to claim 1, wherein the inner surface reflecting means includes a projecting portion projecting in the sub-scanning direction around any one of the first region, the second region, and the third region. The optical scanning device described.   4. The cutout shape is different between a central portion and an end portion in the main scanning direction in any one of the first region, the second region, and the third region. The optical scanning device according to any one of the above. In a first notch surface that is a surface in a shape in which the first region is notched, a second notch surface that is a surface in a shape in which the second region is notched, and in a shape in which the third region is notched The distance between the intersection of the first transmission surface and the second cutout surface and the intersection of the second transmission surface and the third cutout surface with respect to the third cutout surface, which is a surface, is HL, When the distance between the intersection when both the transmission surface and the first inner reflection surface are extended and the intersection when the second transmission surface and the second inner reflection surface are both extended is HLo, the following equation is obtained: The optical scanning device according to claim 1, wherein the optical scanning device is satisfied.
0.65 <HL / HLo <0.95 In the sub-scanning section, an intersection when the first inner reflection surface and the first cutout surface are extended together and an intersection when the second inner reflection surface and the first cutout surface are extended together HR, and the total distance in the sub-scanning direction of the projecting portion projecting in the sub-scanning direction around any one of the first region, the second region, and the third region is HT,
0.50 <HT / HR <1.50
The optical scanning device according to claim 5, wherein: At least one light beam emitted from the light source means is incident on the deflection means from a sub-scanning oblique direction with respect to the surface normal of the deflection surface,
In the sub-scan section, a direction in which the light beam transmitted through the first transmission surface of the inner surface reflection means is reflected by the first inner surface reflection surface, and a direction in which the light beam emitted from the light source means heads toward the deflection means. Are on the same side,
7. The optical scanning device according to claim 6, wherein the HR is longer in a central portion in the main scanning direction than in an end portion in the main scanning direction of the inner surface reflecting means. At least one light beam emitted from the light source means is incident on the deflection means from a sub-scanning oblique direction with respect to the surface normal of the deflection surface,
In the sub-scan section, the direction in which the light beam transmitted through the first transmission surface of the inner surface reflection means is reflected by the first inner surface reflection surface and the direction in which the light beam emitted from the light source means heads toward the deflection means. On the same side,
7. The optical scanning device according to claim 5, wherein the HL has a longer central portion in the main scanning direction than an end portion in the main scanning direction of the inner surface reflecting means. At least one light beam emitted from the light source means is incident on the deflection means from a sub-scanning oblique direction with respect to the surface normal of the deflection surface,
In the sub-scan section, the direction in which the light beam transmitted through the first transmission surface of the inner surface reflection means is reflected by the first inner surface reflection surface and the direction in which the light beam emitted from the light source means heads toward the deflection means. On the other side,
7. The optical scanning device according to claim 6, wherein the HR is shorter in a central portion in the main scanning direction than in an end portion in the main scanning direction of the inner surface reflecting means. At least one light beam emitted from the light source means is incident on the deflection means from a sub-scanning oblique direction with respect to the surface normal of the deflection surface,
In the sub-scan section, the direction in which the light beam transmitted through the first transmission surface of the inner surface reflection means is reflected by the first inner surface reflection surface is opposite to the direction in which the light beam emitted from the light source means is directed to the deflection means. On the side,
7. The optical scanning device according to claim 5, wherein the HL has a shorter central portion in the main scanning direction than an end portion in the main scanning direction of the inner surface reflecting means.   The first transmission surface, the first inner surface reflection surface, the second inner surface reflection surface, and the second transmission surface are surfaces having no refractive power at least in the main scanning direction. The optical scanning device according to any one of 1 to 10.   12. The optical scanning device according to claim 1, wherein the first inner surface reflecting surface and the second inner surface reflecting surface of the inner surface reflecting means are total reflection surfaces.   A color image forming apparatus comprising: the optical scanning device according to claim 1; and a plurality of photosensitive members respectively disposed on the plurality of scanned surfaces.