JP5849598B2 - Optical scanning apparatus and image forming apparatus - Google Patents

Description

  The present invention relates to an optical scanning device provided in an electrophotographic image forming apparatus, and an image of a laser printer, a laser plotter, a digital copying machine, a plain paper facsimile, or a composite machine of these equipped with the optical scanning device. The present invention relates to a forming apparatus.

  In electrophotographic image forming apparatuses used in laser printers, laser plotters, digital copiers, plain paper facsimiles, or multi-function machines, etc., in recent years, colorization and high speed have progressed, and photoconductors that are image carriers. An image forming apparatus compatible with a tandem method having a plurality of (usually four) is widely used. In this tandem image forming apparatus, for example, four photoconductors are arranged side by side along a transfer belt (or intermediate transfer belt) that conveys a recording material, and each photoconductor is charged by a charging unit and then written by a writing unit. A latent image is formed on each photoconductor, and the latent image on each photoconductor is developed and visualized with developers of different colors (for example, yellow, magenta, cyan, and black toners) of the developing means. The color images are transferred onto a recording material (or an intermediate transfer belt) conveyed by a transfer belt so as to form a color image.

  The electrophotographic color image forming apparatus has only one photoconductor, rotates the photoconductor by the number of colors, and sequentially superimposes and transfers the image onto the intermediate transfer member. There is also a so-called one-drum-intermediate transfer method in which the image is formed and transferred onto a recording material in a batch. However, in this method, in the case of one drum with four colors, a photoconductor is formed every time one image is formed. It is necessary to rotate 4 times, and productivity is inferior compared with the tandem system.

  As described above, the tandem image forming apparatus can achieve higher speed than the one-drum-intermediate transfer method, and can improve the productivity of color image formation. However, in the case of a tandem image forming apparatus, the number of light sources of the optical scanning device inevitably increases because optical writing is performed on a plurality of photosensitive members by a writing unit using the optical scanning device (for example, the number of photosensitive members is 4). In one case, usually four light sources are required). As a result, problems such as an increase in the number of parts, a color shift due to a wavelength difference between a plurality of light sources, and an increase in cost occur.

  Further, deterioration of the semiconductor laser is cited as a cause of the failure of the writing unit. Therefore, as the number of light sources increases, the probability of failure increases and the recyclability deteriorates.

  Therefore, an optical scanning device configured to divide one light beam from the light source into two light beams shifted in the main scanning direction by the light beam dividing means and scan two different surfaces to be scanned by one polygon mirror. Has been proposed (see, for example, Patent Document 1). In this prior art, the number of light sources can be reduced by using a general-purpose polygon mirror, and color misregistration caused by wavelength differences among a plurality of light sources can be eliminated.

  However, in such a conventional technique, an element for dividing the light beam is required, so that the number of optical components arranged on the optical path is increased and the layout performance is deteriorated. Further, as means for dividing the light beam, there is means for using the polarization state. However, an optical element capable of changing the polarization state is required around the optical element for dividing the light beam. If a parallel plate-like optical element having no refractive power is arranged in the optical path, the interference of the light beam caused by the internal reflection of the parallel plate occurs, and the transmittance of the optical element fluctuates, so that the light quantity is not stable.

  The present invention has been made to solve the above-described problems of the prior art, and can stably obtain light source power and improve layout while maintaining high-quality image output. An object of the present invention is to provide an optical scanning apparatus and an image forming apparatus capable of performing the above.

The present invention includes a light source, a deflecting unit that deflects a light beam from the light source, an imaging optical system that forms a light beam from the light source in the vicinity of a deflection reflection surface of the deflecting unit as a long line image in the main scanning direction, and a deflecting unit. And a scanning optical system that scans the light beam deflected by the light beam in the main scanning direction, a light beam splitting unit that splits the light beam from the light source is disposed on the optical path from the light source to the deflecting unit. A parallel plate-like optical element that changes the polarization state of the light beam from the light source is arranged on the optical path from the image optical system to the deflecting unit, and the coupling optical system uses the light source and the light beam emitted from the light source as a substantially parallel light beam. Another optical element having a parallel plate shape that changes the polarization state is disposed between the optical element and the other optical element so as to be non-parallel to the plane perpendicular to the optical axis of the coupling optical system. The optical surface and the optical surface of another optical element Characterized in that it is tilted in the opposite direction to the straight surface.

  According to the present invention, light source power can be stably obtained, and layout performance can be improved while maintaining high-quality image output.

1 is a schematic perspective view showing an embodiment of an optical scanning device according to the present invention. 2A and 2B are optical layout diagrams of an optical system before a deflecting unit of the optical scanning device, in which FIG. 1A is a main scanning sectional view, and FIG. 2A and 2B are optical layout diagrams of an optical system before a deflecting unit of the optical scanning device, in which FIG. 1A is a sub-scan sectional view, and FIG. 2B is a parallel optical plate-shaped first optical element and second optical element included in the optical system; It is an enlarged view which shows the inclination of an element. It is a figure explaining the in-plane reflection of the light beam which passes the said optical element, Comprising: (a) is a substantially parallel light beam, (b) is a non-parallel light beam (convergent light beam), (c) is a non-light beam. This is the case of a parallel light beam (divergent light beam). It is a figure explaining the size of the said 1st optical element when arrange | positioning before and after the cylindrical lens which comprises the said optical scanning apparatus, Comprising: (a) is the case where it arrange | positions in the substantially parallel light beam until it injects into a cylindrical lens (B) shows the case where the lens is arranged in a convergent light beam from the cylindrical lens to the deflecting means. It is a figure explaining the size of the said 2nd optical element when arrange | positioning before and after the coupling lens which comprises the said optical scanning apparatus, Comprising: (a) is in the substantially parallel light beam from a coupling lens to a light beam splitting means. When arranged, (b) shows the case where it is arranged in a divergent light beam until it enters the coupling lens. It is a figure explaining integration of the light source of the said optical scanning device, and the said 2nd optical element. When the light source and the second optical element have separate structures, (a) is a sub-scan sectional view of the layout from the light source to the second optical element, and (b) is perpendicular to the optical axis of the light source. It is sectional drawing of a direction. FIG. 6 is a main scanning sectional view from the light source to the deflection unit, where (a) shows an aperture in the optical path on the light source side of the cylindrical lens, and (b) shows an aperture on the deflection unit side of the cylindrical lens. This is a case where it is arranged in the optical path. It is a schematic perspective view which shows another embodiment of the optical scanning device concerning this invention. FIGS. 11A and 11B are optical layout diagrams of an optical system before a deflecting unit of the optical scanning device of FIG. 10, in which FIG. 10A is a main scanning sectional view and FIG. It is a schematic perspective view which shows another embodiment of the optical scanning device concerning this invention. FIG. 12A is an optical layout diagram of an optical system before a deflecting unit of the optical scanning device in FIG. 11, wherein FIG. 11A is a main scanning sectional view, and FIG. 1 is a central sectional view showing an embodiment of an image forming apparatus according to the present invention.

  Embodiments of an optical scanning device and an image forming apparatus according to the present invention will be described below with reference to the drawings.

  First, an optical scanning device according to the present invention will be described.

[Embodiment 1]
FIG. 1 is a schematic perspective view showing an embodiment of an optical scanning device according to the present invention. In the figure, reference numeral 1 is a semiconductor laser array having a plurality of light emitting points as a light source, 2 (2a, 2b) is an incident mirror, 3 is a coupling lens, 4 is a beam splitting means (deflection beam splitter), 5 (5a, 5b) is a cylindrical lens, 6 (6a, 6b) is an aperture stop (aperture), 7 is a deflector (for example, a polygon mirror having four deflection reflecting surfaces), 8 is a scanning lens, and 9 is for optical path folding. , 10 is a photosensitive member as a surface to be scanned, 11 (11a, 11b) is a parallel optical plate-shaped first optical element (λ / 4 plate) capable of changing the polarization state, and 12 is a member for changing the polarization state. A parallel plate-shaped second optical element (λ / 4 plate) that can be formed is shown.

  Here, the polygon mirror 7 is rotated at a constant angular velocity in the direction of the arrow in the drawing by the drive mechanism (not shown) about the rotation axis. Hereinafter, the direction in which the light beam emitted from the semiconductor laser array 1 is deflected and scanned by the polygon mirror 7 is defined as a main scanning direction, and the direction orthogonal to the main scanning direction is defined as a sub-scanning direction.

  The divergent light beam emitted from the semiconductor laser array 1 passes through the λ / 4 plate 12 and is converted into a substantially parallel light beam by the coupling lens 3. The light beam exiting the coupling lens 3 enters the light beam splitting means 4. The light beams from the common light source incident on the light beam dividing means 4 are divided into two, and the light beams emitted from the light beam dividing means 4 become two light beams. The two light beams emitted from the light beam splitting means 4 are converted into line images that are long in the main scanning direction by the cylindrical lens 5 in the vicinity of the deflection reflection surface of the polygon mirror 7, respectively. An aperture 6 for stabilizing the beam diameter on the surface to be scanned (on the surface of the photoconductor 10) is disposed in the light beam that has passed through the cylindrical lens 5 and converged in the sub-scanning direction. The light beam that has passed through the aperture 6 further passes through the λ / 4 plate 11 and becomes a line image that is long in the main scanning direction in the vicinity of the deflection reflection surface of the polygon mirror 7.

  2A and 2B are optical layout diagrams of the optical system before the deflecting means of the optical scanning device, wherein FIG. 2A is a main scanning sectional view and FIG. 2B is a sub-scanning sectional view.

  Of the light beams emitted from the semiconductor laser array 1, the light beam emitted with a substantially p-polarized component with respect to the direction of deflection at the polygon mirror 7 is substantially circularly polarized after passing through the λ / 4 plate 12. When a substantially circularly polarized light beam enters the polarizing beam splitter 4, the p-polarized component is transmitted through the polarizing beam splitter 4, and the s-polarized component is reflected by the reflecting surface of the polarizing beam splitter 4. In this way, the light beam from the semiconductor laser array 1 is divided into two light beams, a p-polarized light beam and an s-polarized light beam, and is incident on the deflection reflection surface of the polygon mirror 7 respectively.

  When the polygon mirror 7 has four deflecting and reflecting surfaces, a returning light beam from the polygon mirror 7 to the semiconductor laser array 1 may be generated. Therefore, it is necessary to provide a λ / 4 plate 11 between the polarization beam splitter 4 and the polygon mirror 7 to cut the return light beam to the semiconductor laser array 1. Similarly, when the polarization direction of the light beam emitted from the semiconductor laser array 1 is s-polarized or other linearly polarized state with respect to the deflection direction of the polygon mirror 7, the light beam is similarly divided into 50% reflected light beam and transmitted light beam. And the return beam can be cut.

  In this embodiment, the semiconductor laser array is used as the light source, so that the polarization state of the light beam emitted from the semiconductor laser array is substantially p-polarized with respect to the deflection direction of the polygon mirror 7. Here, when a single-beam semiconductor laser is used as the light source, the polarization state of a light beam emitted from the semiconductor laser may be substantially an s-polarization state. Even in this case, the above-described effects can be obtained by adopting the same optical arrangement as when the above-described semiconductor laser array is used.

  Here, when the λ / 4 plate 11 is disposed in the optical path from the polarization beam splitter 4 to the cylindrical lens 5, it is necessary to secure an optical path length for disposing the λ / 4 plate 11. As a result, the optical path length is extended as a whole optical system, the layout is deteriorated, and the optical scanning device is enlarged. On the other hand, since the length of the optical path from the cylindrical lens 5 to the deflection scanning surface of the polygon mirror 7 is determined by the focal length of the cylindrical lens 5 set by other optical characteristics, it must have a distance corresponding to the focal length of the cylindrical lens 5. Don't be. Therefore, as shown in FIG. 2B, by arranging the λ / 4 plate 11 in the optical path between the cylindrical lens 5 and the polygon mirror 7, the optical path length of the entire optical system can be shortened and the layout can be reduced. It becomes possible to improve the property.

  Further, the aperture 6 can be integrally formed with the housing 20 so that the λ / 4 plate 11 can be positioned by the aperture 6. As a result, the distance from the aperture 6 to the λ / 4 plate 11 can be made closer than the positioning of the λ / 4 plate 11 to the housing 20 alone, and the optical path length can be further shortened, and the layout property can be reduced. Can be improved.

  FIG. 3 is a diagram for explaining the inclination of a parallel plate optical element. FIG. 4A is a sub-scan sectional view of the optical path from the semiconductor laser array 1 to the polygon mirror 7, and reference numeral 50 indicates a surface perpendicular to the optical axis of the coupling lens 3.

  As shown in FIG. 3B, the λ / 4 plate 11 and the λ / 4 plate 12 are arranged in the front-rear direction of the traveling direction of the light beam so that the light beam returning to the semiconductor laser array 1 is not generated with respect to the surface 50. It is desirable to incline (left and right direction on the paper). When the inclination angle of the λ / 4 plate 11 with respect to the surface 50 is θ, the inclination angle θ ′ of the λ / 4 plate 12 is arranged so as to be opposite to θ with respect to the surface 50, thereby reducing the wavefront aberration. Can be reduced. Further, by arranging the inclination angle θ ′ of the λ / 4 plate 12 to be −θ, the wavefront aberration can be further reduced.

  In the present embodiment, the λ / 4 plates 11 and 12 have inclination angles θ and θ ′ in the sub-scanning direction. However, instead of this, when the λ / 4 plates 11 and 12 have an inclination angle in the main scanning direction, the effect of reducing the wavefront aberration can be obtained similarly.

  FIG. 4 is a diagram illustrating in-plane reflection of a light beam passing through a parallel plate-like optical element. FIG. 5A is a diagram for explaining in-plane reflection when the light beam passing through the parallel plate-like λ / 4 plate 11 is a substantially parallel light beam. All of the light beam incident on the λ / 4 plate 11 is not transmitted, and a part of the light beam is reflected by the exit surface 112, and the reflected light beam is reflected again by the entrance surface 111 and exits from the exit surface 112. When the phases of the light beam that has been transmitted without being reflected and the light beam after being reflected by the exit surface 112 and the incident surface 111 are equal, they are intensified, and when the phase is different by π, they are weakened. In the semiconductor laser array 1 as the light source, the wavelength of the light beam output by the injection current changes, and the optical path length in the medium is proportional to the refractive index depending on the wavelength. Therefore, when the injection current is changed, the wavelength of the light beam emitted from the semiconductor laser array 1 is changed, the refractive index of the medium is changed, and the phase is changed, so that the amount of light fluctuates due to the influence of interference. In this case, the ideal proportional relationship between the injection current and the optical output is lost, which is not preferable.

  However, as shown in FIG. 4B, by arranging the λ / 4 plate 11 so that the light beam passes in the non-parallel light beam (in the convergent light beam), the light beam that has been transmitted without being reflected and emitted. Since the light beams reflected by the surface 112 and the incident surface 111 do not overlap, no interference occurs. Further, as shown in FIG. 5C, even when the λ / 4 plate 12 is arranged so that the light beam passes through the non-parallel light beam (in the divergent light beam), the light beam that has been transmitted without being reflected and emitted. The light fluxes after being reflected by the surface 122 and the incident surface 121 also do not overlap and do not cause interference. Therefore, by arranging the λ / 4 plate 11 so that the light beam passes through the non-parallel light beam, the transmittance of the λ / 4 plate 11 does not change even if the injection current is changed, and the light quantity is secured stably. it can.

  FIG. 5 is a diagram for explaining the size of the λ / 4 plate 11 with respect to the light beam passing through the λ / 4 plate 11. FIG. 6A is a diagram for explaining the size of the λ / 4 plate 11 when the λ / 4 plate 11 is arranged in a substantially parallel light beam emitted from the light beam dividing means 4 and entering the cylindrical lens 5. is there. The λ / 4 plate 11 needs to have a size larger than the beam width. However, as shown in FIG. 5B, by placing the λ / 4 plate 11 in the convergent light beam emitted from the cylindrical lens 5 and reaching the deflecting / reflecting surface of the polygon mirror 7, it passes through the λ / 4 plate 11. The width of the luminous flux to be reduced is reduced, and the λ / 4 plate 11 can be reduced in size.

  FIG. 6 is a diagram for explaining the size of the λ / 4 plate 12 with respect to the light beam passing through the λ / 4 plate 12. FIG. 6A shows a λ / 4 plate 12 in a substantially parallel light beam from a divergent light beam emitted from the semiconductor laser array 1 until it passes through the coupling lens 3 to become a substantially parallel light beam and enters the light beam splitting means 4. It is a figure explaining the size of (lambda) / 4 board 12 when arrange | positioning. The λ / 4 plate 12 needs to be larger than the light beam width. However, as shown in FIG. 5B, by arranging the λ / 4 plate 12 in the divergent light beam emitted from the semiconductor laser array 1 and entering the coupling lens 3, the λ / 4 plate 12 is The width of the light beam passing through is narrowed, and the λ / 4 plate 12 can be downsized.

  FIG. 7 is a diagram for explaining integration of the light source and the second optical element. As shown in the figure, the λ / 4 plate 12 is held by a cap 21 that covers the semiconductor laser array 1. Thus, by integrating the semiconductor laser array 1 and the λ / 4 plate 12 via the cap 21, the λ / 4 plate 12 can be further reduced in size. Further, by adjusting the position and angle of the semiconductor laser array 1 through the cap 21, the semiconductor laser array holding member (not shown) does not directly grip the package of the semiconductor laser array 1 during these adjustments. Deterioration of the semiconductor laser array 1 can be prevented.

  FIG. 8 is a diagram illustrating an example when the light source and the second optical element have separate structures. FIG. 2A is a sub-scanning sectional view of the layout up to the semiconductor laser array 1 and the λ / 4 plate 12. FIG. 2B is a cross-sectional view perpendicular to the optical axis of the semiconductor laser array 1. The semiconductor laser array 1 having a plurality of light emitting points is rotated in an angular direction (γ direction) about the optical axis in order to adjust the distance in the sub-scanning direction between the plurality of light emitting points. By configuring the semiconductor laser array 1 and the λ / 4 plate 12 as separate bodies, even if the angle of the semiconductor laser array 1 is set to a desired state as adjustment of the position and angle of the semiconductor laser array 1, particularly the γ direction. The optical axis of the λ / 4 plate 12 does not deviate from the ideal state.

  FIG. 9 is a main scanning sectional view from the light source to the deflecting means. FIG. 6A is a diagram when the aperture 6 is arranged in the optical path on the semiconductor laser array 1 side with respect to the cylindrical lens 5. When the optical path from the aperture 6 to the polygon mirror 7 becomes longer, the light flux from each light emitting point of the semiconductor laser array 1 has a distance in the main scanning direction. FIG. 5B is a diagram in which the aperture 6 is arranged in the optical path between the cylindrical lens 5 and the polygon mirror 7. When the optical path from the aperture 6 to the polygon mirror 7 is shortened, the light flux from each light emitting point of the semiconductor laser array 1 is shortened in the main scanning direction. By reducing the deviation between the light emitting points in the optical characteristics in the main scanning direction, the beam spot diameter on the surface to be scanned can be stably maintained. Similarly, the deviation on the deflecting / reflecting surface of the polygon mirror 7 is also reduced in the sub-scanning direction, and variations in the beam pitch in the sub-scanning direction due to the axis tilt of the polygon mirror and the polygon mirror receiving portion can be reduced.

  According to the embodiment described above, by arranging the λ / 4 plates 11 and 12 in the non-parallel light flux, the variation in transmittance due to the interference of the in-plane reflection of the λ / 4 plates 11 and 12 is suppressed. The light source power can be obtained stably. Further, by arranging the λ / 4 plate 12 in a non-parallel light beam, the λ / 4 plate 12 can be reduced in size and layout. Furthermore, wavefront aberration can be reduced by disposing the λ / 4 plates 11 and 12 non-parallel to the plane perpendicular to the light beam. Furthermore, by integrating the semiconductor laser array 1 and the λ / 4 plate 12, it is possible to reduce the size and layout of the λ / 4 plate 12.

[Embodiment 2]
FIG. 10 is a schematic perspective view showing another embodiment of the optical scanning device according to the present invention. In the figure, reference numeral 1 is a semiconductor laser array as a light source, 2 is an incident mirror, 3 is a coupling lens, 4 is a beam splitting means (deflection beam splitter), 5 (5a, 5b) is a cylindrical lens, and 6 (6a, 6b). ) Is an aperture stop (aperture), 70 is a deflector (for example, a polygon mirror having six deflecting reflecting surfaces) as a deflecting means, 8 is a scanning lens, 9 is a mirror for turning back an optical path, and 10 is a photosensitive as a surface to be scanned. , 13 is a parallel plate-shaped first optical element (λ / 2 plate) capable of changing the polarization state, 12 is a parallel plate-shaped second optical element (λ / 4 plate) capable of changing the polarization state, Respectively.

  The divergent light beam emitted from the semiconductor laser array 1 passes through the λ / 4 plate 12 and is converted into a substantially parallel light beam by the coupling lens 3. The light beam exiting the coupling lens 3 enters the light beam splitting means 4. The light beams from the common light source incident on the light beam dividing means 4 are divided into two, and the light beams emitted from the light beam dividing means 4 become two light beams. The two light beams emitted from the light beam splitting means 4 are converted into line images that are long in the main scanning direction by the cylindrical lens 5 in the vicinity of the deflection reflection surface of the polygon mirror 70, respectively. An aperture 6 for stabilizing the beam diameter on the surface to be scanned is disposed in the light beam that passes through the cylindrical lens 5 and is converged in the sub-scanning direction. That is, the light beam from the cylindrical lens 5 passes through the aperture 6 and becomes a line image that is long in the main scanning direction in the vicinity of the deflection reflection surface of the polygon mirror 70.

  Here, in the optical path between the aperture 6 and the polygon mirror 70, λ // is set so that the polarization state is advantageous on the optical path of the light beam in the polarization state which is disadvantageous for the optical element whose reflectance and transmittance change depending on the polarization state. Two plates 13 are provided.

  11A and 11B are optical layout diagrams of the optical system before the deflecting means (polygon mirror 70) of the optical scanning device, where FIG. 11A is a main scanning sectional view and FIG. 11B is a sub-scanning sectional view.

  In FIG. 11A, among the light beams emitted from the semiconductor laser array 1, the light beam emitted with a substantially p-polarized component with respect to the deflection direction at the polygon mirror 70 passes through the λ / 4 plate 12. It becomes a substantially circular polarization state. When a substantially circularly polarized light beam enters the polarizing beam splitter 4, the p-polarized component is transmitted through the polarizing beam splitter 4, and the s-polarized component is reflected by the reflecting surface of the polarizing beam splitter 4. Each of the light beams is divided into two light fluxes, a p-polarized light beam and an s-polarized light beam, and the λ / 2 plate 13 is disposed only in the optical path of the s-polarized light beam to make the p-polarized light beam. Are incident on the reflecting surface of the polygon mirror 70, respectively.

  In this embodiment, by using a semiconductor laser array as a light source, the polarization state of the light beam emitted from the semiconductor laser array is substantially p-polarized with respect to the deflection direction at the polygon mirror 70. Note that when a single-beam semiconductor laser is used as the light source, the polarization state of the light beam emitted from the semiconductor laser may be substantially the s-polarization state. Even in this case, the same effect as described above can be obtained by the arrangement described above.

  In FIG. 11B, when the λ / 4 plate 11 is disposed in the optical path from the polarization beam splitter 4 to the cylindrical lens 5, it is necessary to ensure the optical path length for disposing the optical element. As a result, the optical path length is extended as a whole optical system, the layout is deteriorated, and the optical scanning device is enlarged. On the other hand, the length of the optical path from the cylindrical lens 5 to the deflection scanning surface of the polygon mirror 70 is determined by the focal length of the cylindrical lens 5 set by other optical characteristics. As a result, the distance must be equal to the focal length of the cylindrical lens 5. Therefore, by arranging the λ / 2 plate 13 in the optical path between the cylindrical lens 5 and the polygon mirror 70, the optical path length of the entire optical system can be shortened, and the layout can be improved.

  In the present embodiment, when a six-sided polygon mirror is used, the incident angle is set so that no return light beam is generated. Therefore, it is not necessary to consider the influence of the return light beam. Even when a four-sided polygon mirror is used, if the layout does not generate a return beam, or if the system configuration is such that the light source does not emit light at the timing when the return beam is generated, the configuration of this embodiment is used. be able to.

  According to the embodiment described above, the λ / 4 plate 13 is arranged on the optical path of the light beam in the deflected state which is disadvantageous for the optical element whose reflectivity and transmittance change depending on the deflected state so that the deflected state is advantageous. By doing so, the loss of light source power can be reduced. As a result, the light source power can be stably obtained.

[Embodiment 3]
FIG. 12 is a schematic perspective view showing still another embodiment of the optical scanning device according to the present invention. In the figure, reference numeral 1 is a semiconductor laser array as a light source, 3 is a coupling lens, 40 is a beam splitting means (deflection beam splitter), 5 (5a, 5b) are cylindrical lenses, 61 is an aperture stop (aperture), 77 Is a deflector as a deflecting means (for example, a phase difference polygon mirror having four deflecting reflecting surfaces and overlapping in the sub-scanning direction with a phase difference of π / 2), 8 a scanning lens, and 9 an optical path folding , 10 is a photosensitive member as a surface to be scanned, 11 is a parallel plate-shaped first optical element (λ / 4 plate) capable of changing the polarization state, and 12 is a parallel plate shape capable of changing the polarization state. Each of the second optical elements (λ / 4 plate) is shown.

  The divergent light beam emitted from the semiconductor laser array 1 passes through the λ / 4 plate 12 and is converted into a substantially parallel light beam by the coupling lens 3. The light beam exiting the coupling lens 3 enters the light beam splitting means 40. The light beams from the common light source incident on the light beam dividing means 40 are divided into two, and the light beams emitted from the light beam dividing means 40 become two light beams. The two light beams emitted from the light beam splitting means 40 are converted into line images that are long in the main scanning direction in the vicinity of the deflection reflection surface of the polygon mirror 77 by the cylindrical lens 5. A λ / 4 plate 11 is provided in the light beam that has passed through the cylindrical lens 5 and is converged in the sub-scanning direction perpendicular to the main scanning direction, and the converged light beam that has passed through the λ / 4 plate 11 has a surface on the surface to be scanned. An aperture 61 is provided for stabilizing the beam diameter. That is, the light beam that has passed through the aperture 61 becomes a line image that is long in the main scanning direction in the vicinity of the deflection reflection surface of the phase difference polygon mirror 77.

  13A and 13B are optical layout diagrams of the optical system before the deflecting means (phase difference polygon mirror 77) of the optical scanning device of this embodiment, where FIG. 13A is a main scanning sectional view, and FIG. 13B is a sub-scanning sectional view. It is.

  In FIG. 13A, when the phase difference polygon mirror 77 is used as the deflecting means, a returning light beam from the phase difference polygon mirror 77 to the semiconductor laser array is always generated. Therefore, it is necessary to provide a λ / 4 plate 11 between the polarizing beam splitter 40 and the polygon mirror 77 to cut the returning light beam to the semiconductor laser array 1.

  In FIG. 13B, a light beam emitted from the semiconductor laser array 1 is emitted with a substantially p-polarized component with respect to the deflection direction of the phase difference polygon mirror 77, and a light beam in a substantially p-polarized state is a λ / 4 plate. After passing through 12, it becomes a substantially circular polarization state. When a substantially circularly polarized light beam enters the polarizing beam splitter 40, the s-polarized component is transmitted through the polarizing beam splitter 40 with respect to the deflection direction of the phase difference polygon mirror 77, and the p-polarized component is reflected on the reflecting surface of the polarizing beam splitter 40. Reflected. Each of the light beams is divided into two light beams, an s-polarized light beam and a p-polarized light beam, and then passes through the λ / 4 plate 11 and then enters the reflection surface of the phase difference polygon mirror 77. By arranging the λ / 4 plate 11, the returning light beam from the phase difference polygon mirror 77 to the semiconductor laser array 1 is emitted by the light beam dividing means 40 in the direction where the semiconductor laser array 1 is not arranged.

  In the present embodiment, the semiconductor laser array is used as the light source, so that the polarization state of the light beam emitted from the semiconductor laser array is substantially p-polarization state with respect to the deflection direction of the phase difference polygon mirror 77. Here, when a single-beam semiconductor laser is used as the light source, the polarization state of a light beam emitted from the semiconductor laser may be substantially an s-polarization state. Even in this case, the above-mentioned effects can be obtained by arranging the same optical arrangement as when the above-described semiconductor laser array is used.

  Further, when a λ / 4 plate is provided in the optical path from the polarization beam splitter 40 to the cylindrical lens 5, it is necessary to secure an optical path length for providing an optical element. As a result, the optical path length is extended as a whole optical system, the layout is deteriorated, and the optical scanning device is enlarged. On the other hand, the length of the optical path from the cylindrical lens 5 to the deflection scanning surface of the phase difference polygon mirror 77 is determined by the focal length of the cylindrical lens 5 set by other optical characteristics. As a result, the distance must be equal to the focal length of the cylindrical lens 5. Therefore, by arranging the λ / 4 plate 11 in the optical path between the cylindrical lens 5 and the phase difference polygon mirror 77, the optical path length of the entire optical system can be shortened, and the layout can be improved. Become.

  According to the embodiment described above, by arranging the λ / 4 plate 11 in the optical path between the cylindrical lens 5 and the phase difference polygon mirror 77, the layout can be improved.

[Embodiment 4]
Next, an embodiment of an image forming apparatus according to the present invention will be described. The image forming apparatus includes each unit to be described later, and performs optical writing from a light scanning device as an optical writing device to a photoconductor as an image carrier, and an electrostatic latent image is formed on the surface of the photoconductor by electrophotography. Form.

  FIG. 14 is a central sectional view showing an embodiment of an image forming apparatus according to the present invention. A laser printer as an image forming apparatus includes an optical scanning device 900, an image forming station, a transfer belt 906, a paper feed tray 907, a paper feed roller 908, a registration roller pair 909, a fixing roller 910, a paper discharge tray 911, and a paper discharge roller 912. Etc. Here, the optical scanning device 900 is the optical scanning device according to the present invention described above.

  Here, four image forming stations corresponding to the respective colors of yellow, magenta, cyan, and black are arranged in parallel in the moving direction of the transfer belt 906. Each image forming station basically has the same configuration except that the toner color is different. The yellow, magenta, cyan, and black toner images from the respective image forming stations are sequentially transferred onto the transfer belt 906 at the appropriate timing, and are superimposed to form a color (multicolor) image.

The image forming station attaches the charged toner to the electrostatic latent image recorded by the photosensitive drum 901, the charging charger 902 that charges the surface of the photosensitive drum 901 to a high voltage, and the optical scanning device 900, and visualizes the image. A developing roller 903, a toner cartridge 904 for supplying toner to the developing roller 903, a cleaning case 905 for scraping and storing toner remaining on the surface of the photosensitive drum 901, and the like. The photosensitive drum 901 is a cylindrical member, and a photosensitive layer is formed on the surface thereof. That is, the surface of the photoconductive drum 901 is the surface to be scanned. The photosensitive drum 901 rotates clockwise on the paper surface, and a charging charger 902, a developing roller 903, and a cleaning case 905 are arranged along this rotation direction.

  The optical scanning device 900 scans the surface of the photosensitive drum 901 charged by the charging charger 902 with a light beam modulated based on image information from a higher-level device (for example, a personal computer), and the surface of the photosensitive drum 901 is scanned. A latent image corresponding to the image information is formed. The latent image formed here moves in the direction of the developing roller 903 as the photosensitive drum 901 rotates.

  Recording paper is stored in the paper feed tray 907. A paper feed roller 908 is disposed in the vicinity of the paper feed tray 907. The paper feed roller 908 takes out the recording paper one by one from the paper feed tray 907 and conveys it to the registration roller pair 909. The registration roller pair 909 temporarily holds the recording paper taken out by the paper supply roller 908 and directs the recording paper to a gap between the photosensitive drum 901 and a transfer charger (not shown) in accordance with the rotation of the photosensitive drum 901. And send it out.

  A voltage having a polarity opposite to that of the toner is applied to the transfer charger in order to electrically attract the toner on the surface of the photosensitive drum 901 to the recording paper. With this voltage, the toner image on the surface of the photosensitive drum 901 is transferred to the recording paper. The recording sheet transferred here is sent to the fixing roller 910.

  In the fixing roller 910, heat and pressure are applied to the recording paper, whereby the toner is fixed on the recording paper. The recording paper fixed here is sent to the paper discharge tray 911 via the paper discharge roller 912 and sequentially stacked on the paper discharge tray 911.

The surface of the photosensitive drum 901 is neutralized by a neutralizing unit (not shown), and after the residual toner is removed by the cleaning case 905, the surface of the photosensitive drum 901 returns to the position facing the charging charger 902 again.

  According to the embodiment described above, by using the optical scanning device according to the present invention as the optical scanning device 900, the light source power can be stably obtained, the layout is improved, and the high-quality image output is performed. Can be maintained.

  The embodiment described above is an example of a full-color tandem image forming apparatus having a four-station configuration. Instead, the above-described effect can be obtained by applying the optical scanning device of the present invention as an optical writing device even in a tandem image forming apparatus of 5 stations or more and a monochrome machine.

DESCRIPTION OF SYMBOLS 1 Light source 4 Light beam splitting means 7 Deflection means 8 Scanning lens 10 Photoreceptor 11 1st optical element 12 2nd optical element

JP 2008-257169 A

Claims (11)

A light source;
Deflecting means for deflecting a light beam from the light source;
An imaging optical system that forms a light beam from the light source as a long line image in the main scanning direction in the vicinity of the deflection reflection surface of the deflection unit;
A scanning optical system that scans the light beam deflected by the deflecting means in the main scanning direction;
In an optical scanning device comprising:
On the optical path from the light source to the deflecting means, a light beam splitting means for splitting the light flux from the light source is disposed,
On the optical path from the imaging optical system to the deflecting means, a parallel plate-like optical element that changes the polarization state of the light beam from the light source is disposed ,
Another optical element in the form of a parallel plate that changes the polarization state is disposed between the light source and a coupling optical system that makes the light beam emitted from the light source substantially parallel.
The optical element and the other optical element are installed non-parallel to a plane perpendicular to the optical axis of the coupling optical system;
An optical scanning device , wherein an optical surface of the optical element and an optical surface of the other optical element are arranged to be inclined in the opposite direction with respect to the perpendicular surface . A light source;
Deflecting means for deflecting a light beam from the light source;
An imaging optical system that forms a light beam from the light source as a long line image in the main scanning direction in the vicinity of the deflection reflection surface of the deflection unit;
A scanning optical system that scans the light beam deflected by the deflecting means in the main scanning direction;
In an optical scanning device comprising:
On the optical path from the light source to the deflecting means, a light beam splitting means for splitting the light flux from the light source is disposed,
On the optical path from the imaging optical system to the deflecting means, a parallel plate-like optical element that changes the polarization state of the light beam from the light source is disposed ,
Another optical element in the form of a parallel plate that changes the polarization state is disposed between the light source and a coupling optical system that makes the light beam emitted from the light source substantially parallel.
The optical element and the other optical element are installed non-parallel to a plane perpendicular to the optical axis of the coupling optical system;
An optical scanning device characterized in that an optical surface of the optical element and an optical surface of the other optical element are arranged symmetrically with respect to the perpendicular surface . The optical scanning device according to claim 1 or 2 ,
An optical scanning device, wherein the light source and the another optical element are integrated. The optical scanning device according to claim 1 or 2 ,
The light source has a plurality of light emitting points;
The optical scanning device, wherein the light source and the another optical element are configured separately. A light source;
Deflecting means for deflecting a light beam from the light source;
An imaging optical system that forms a light beam from the light source as a long line image in the main scanning direction in the vicinity of the deflection reflection surface of the deflection unit;
A scanning optical system that scans the light beam deflected by the deflecting means in the main scanning direction;
In an optical scanning device comprising:
On the optical path from the light source to the deflecting means, a light beam splitting means for splitting the light flux from the light source is disposed,
On the optical path from the imaging optical system to the deflecting means, a parallel plate-like optical element that changes the polarization state of the light beam from the light source is disposed ,
Another optical element in the form of a parallel plate that changes the polarization state is disposed between the light source and a coupling optical system that makes the light beam emitted from the light source substantially parallel.
The optical scanning device according to claim 1, wherein the optical element and the another optical element are wave plates that give a phase difference of approximately π / 2 . The optical scanning device according to claim 5 .
The optical element and the other optical element are installed non-parallel to a plane perpendicular to the optical axis of the coupling optical system;
An optical scanning device, wherein an optical surface of the optical element and an optical surface of the other optical element are arranged to be inclined in the opposite direction with respect to the perpendicular surface. The optical scanning device according to claim 5 .
The optical element and the other optical element are installed non-parallel to a plane perpendicular to the optical axis of the coupling optical system;
An optical scanning device characterized in that an optical surface of the optical element and an optical surface of the other optical element are arranged symmetrically with respect to the perpendicular surface. In the optical scanning device according to any one of claims 1 to 7 ,
The light source has a plurality of light emitting points;
An optical scanning device, wherein an aperture is disposed on an optical path from the imaging optical system to the deflecting means. The optical scanning device according to claim 8 .
An optical scanning device, wherein the aperture is formed integrally with a housing. The optical scanning device according to any one of claims 1 to 9 ,
The light beam splitting unit divides a light beam according to a polarization state. An image forming apparatus that performs optical writing from an optical writing device to an image carrier and forms an electrostatic latent image on the image carrier by electrophotography,
The optical writing device, an image forming apparatus which is a light scanning apparatus according to any one of claims 1 to 10.