JP2010134358A - Optical scanner, image forming apparatus, and laser drawing device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an optical scanner, which is compact, can suppress noise light rays regardless to the scanning position of scanning light and can stably suppress occurrence of ghost light rays, and to provide an image forming apparatus and a laser drawing device. <P>SOLUTION: The optical scanner includes: a light source unit that outputs a luminous flux composed of linearly polarized light; a deflector 14 that deflects the luminous flux from the light source unit; and a scanning optical system that includes a polarization switching means composed of liquid crystal elements 411, 412, alternately switching between (1) a first polarized state in which an electric field vector is parallel to the deflection plane and (2) a second polarized state in which an electric field vector varies in accordance with the deflection angle, each time of scanning of the luminous flux deflected by the deflector, and polarization splitting means 161, 162 changing the exiting direction of the luminous flux in accordance with the polarization state, and that individually condenses the luminous flux deflected by the deflector 14 onto a corresponding surface to be scanned. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to an optical scanning apparatus, an image forming apparatus, and a laser drawing apparatus. More specifically, the present invention relates to an optical scanning apparatus that scans a surface to be scanned with a light beam, and an image forming apparatus and a laser drawing apparatus including the optical scanning apparatus.

  In image recording by electrophotography, an image forming apparatus using a laser is widely used. In this case, the image forming apparatus includes an optical scanning device, and scans laser light using an optical deflector (for example, a polygon mirror) in the axial direction of a photosensitive drum (hereinafter referred to as “photosensitive drum”). A general method is to form a latent image on the surface of the photosensitive drum by rotating the photosensitive drum.

  In recent years, colorization and speeding-up have progressed in image forming apparatuses, and tandem type image forming apparatuses having a plurality of (usually four) photosensitive drums have become widespread. Each of the plurality of photosensitive drums corresponds to, for example, four colors (black, cyan, magenta, and yellow), and each photosensitive drum is modulated with an image signal corresponding to each color by an optical scanning device. An electrostatic latent image is formed by scanning with a light beam. These electrostatic latent images are developed with toners of corresponding colors, and each toner image is transferred onto a transfer paper so that a full color image can be formed. The following are examples of conventional optical scanning devices.

  For example, Patent Document 1 discloses two laser light sources that emit laser beams that are linearly polarized in directions perpendicular to each other and that are modulated by a signal to be recorded, and two laser beams that are emitted from these laser light sources. Polarized light combining means for combining, deflecting means for deflecting the combined laser light in the main scanning direction, and polarized light separating means for separating the combined laser light deflected by the deflecting means into separate spots on the scanning recording surface; A recording device is disclosed.

  Patent Document 2 discloses a single laser light source, information control means for giving different information to two polarized light beams of laser light from the light source, and the amount of polarization based on information from the information control means. A polarization control means for scanning, a scanning means for scanning and irradiating a polarization-controlled light onto a predetermined irradiation surface, a separating means for splitting the scanned light into two lights according to the polarization state, and a scanning means An optical scanning device having an optical rotation control means for optically controlling laser light according to an incident angle at which light is incident on a separation means is disclosed.

  Patent Document 3 discloses a light source, an optical deflector having a plurality of deflection reflection surfaces in the sub-scanning direction, and a light beam that divides a light beam from the light source into a plurality of light beams incident on each of the plurality of deflection reflection surfaces. An optical scanning device is disclosed that includes a dividing diffractive optical element and a scanning optical system that condenses a light beam deflected by an optical deflector onto a surface to be scanned.

JP-A-60-32019 JP-A-7-144434 2007-279670

  However, in the recording apparatus disclosed in Patent Document 1, the electric field vector of P-polarized light that should be transmitted through the polarized light separation means may not be parallel to the transmission axis of the polarization separation surface. There is a disadvantage that a part of the light is reflected by the polarized light separating means.

  In the optical scanning device disclosed in Patent Document 2, when a magneto-optical element is used as the optical rotation control means, there is a disadvantage that the cost is increased. In addition, the power consumption increases with the optical rotation control, and heat is generated. Furthermore, the optical rotation angle is likely to change as the environment such as temperature changes, and it is difficult to stably manage the performance.

  Further, the optical scanning device disclosed in Patent Document 3 has a disadvantage that it is difficult to reduce the thickness of an optical changer such as a polygon mirror because it has multi-stage deflecting / reflecting surfaces.

  The present invention has been made under such circumstances, and a first object thereof is to suppress noise light regardless of the scanning position of scanning light by equally suppressing noise from P-polarized light in the entire scanning range. Therefore, an object of the present invention is to provide an optical scanning device that is small and that can stably suppress the generation of ghost light.

  A second object of the present invention is to provide an image forming apparatus capable of forming a small and high quality image while suppressing the cost by mounting the optical scanning device according to the present invention.

  A third object of the present invention is to provide a laser drawing apparatus capable of drawing a small and high-quality image while suppressing the cost by mounting the optical scanning device according to the present invention.

An optical scanning device according to the present invention includes a light source unit that outputs a light beam composed of linearly polarized light,
A deflector for deflecting a light beam from the light source unit;
Each time the light beam deflected by the deflector is scanned, (1) a first polarization state in which the electric field vector is parallel to the deflection surface, and (2) a second polarization state in which the electric field vector changes in accordance with the deflection angle. Polarization switching means comprising a liquid crystal element that switches between, and polarization separation means that switches the emission direction of the light beam in accordance with the polarization state, and individually the light beams deflected by the deflector on the corresponding scanned surface And a scanning optical system for condensing light.

  An image forming apparatus according to the present invention includes a plurality of image carriers and at least one optical scanning device that scans the plurality of image carriers with a light beam including image information. The optical scanning device according to the present invention. It is an optical scanning device.

  A laser drawing apparatus according to the present invention is a laser drawing apparatus that includes an optical scanning device that scans an object with laser light, and a drawing control device that controls the optical scanning device, and draws an image on the object, The optical scanning device is an optical scanning device according to the present invention.

  According to the optical scanning device of the present invention, it is possible to suppress noise light regardless of the scanning position of the scanning light, and to stably suppress generation of ghost light, despite being small.

  According to the image forming apparatus according to the present invention, since the optical scanning device according to the present invention is provided, it is possible to form a high-quality image as a result, despite the small size and low cost.

  According to the laser drawing apparatus according to the present invention, since the optical scanning apparatus according to the present invention is provided, it is possible to draw a high-quality image as a result, despite the small size and low cost.

  Embodiments of an optical scanning apparatus, an image forming apparatus, and a laser drawing apparatus according to the present invention will be described below with reference to FIGS.

  FIG. 1 shows a schematic configuration of a color printer 2000 as an image forming apparatus according to an embodiment of the present invention. The color printer 2000 is a tandem multicolor printer that forms a full-color image by superimposing images of four colors (black, cyan, magenta, and yellow), and includes four photosensitive drums (parallelly arranged). 2030a, 2030b, 2030c, 2030d), around each photosensitive drum, a cleaning unit (2031a, 2031b, 2031c, 2031d), a charger (2032a, 2032b, 2032c, 2032d), a developing roller (2033a, 2033b). , 2033c, 2033d), toner cartridges (2034a, 2034b, 2034c, 2034d), and other units for performing the electrophotographic process are arranged.

  An optical scanning device 2010 is arranged above the four photosensitive drums, and scans each photosensitive drum with a laser beam modulated by an image signal corresponding to each color. Therefore, the surface of each photosensitive drum is a surface to be scanned by the laser beam. The optical scanning device 2010 is a device that executes an exposure process in the electrophotographic process. Below each photosensitive drum, a transfer belt 2040, a fixing roller 2050, a paper feed tray 2060, a paper feed roller 2054, and a registration roller pair 2056 are arranged. Above the optical scanning device 2010, a paper discharge roller 2058 and a paper discharge tray 2070 are disposed, and a communication control device 2080 and a printer control device 2090 that controls the above-described units in an integrated manner are provided.

  The communication control device 2080 controls bidirectional communication with a host device (for example, a personal computer) via a network or the like.

  The photosensitive drum 2030a, the charging charger 2032a, the developing roller 2033a, the toner cartridge 2034a, and the cleaning unit 2031a are integrated into an image forming station (hereinafter referred to as “K station” for convenience) that forms a black image. Construct).

  The photosensitive drum 2030b, the charging charger 2032b, the developing roller 2033b, the toner cartridge 2034b, and the cleaning unit 2031b are separate units, and are also referred to as an image forming station (hereinafter referred to as “C station” for convenience) that forms a cyan image. Construct).

  The photosensitive drum 2030c, the charging charger 2032c, the developing roller 2033c, the toner cartridge 2034c, and the cleaning unit 2031c are further separate units, and form an magenta image (hereinafter, “M station” for convenience). (Also called).

  The photosensitive drum 2030d, the charging charger 2032d, the developing roller 2033d, the toner cartridge 2034d, and the cleaning unit 2031d are further separate units, and form an yellow image forming station (hereinafter referred to as “Y station” for convenience). (Also called).

  Each photosensitive drum has a photosensitive layer formed on the surface thereof. That is, the surface of each photosensitive drum is a surface to be scanned, and each photosensitive drum also functions as an image carrier. Each photosensitive drum is rotated in a direction indicated by an arrow (clockwise) in a plane parallel to the paper surface in FIG. 1 by a rotation mechanism (not shown). Further, in this specification, in the XYZ three-dimensional orthogonal coordinate system, the direction along the longitudinal direction of each photosensitive drum is described as the Y-axis direction, and the direction along the arrangement direction of the four photosensitive drums is described as the X-axis direction.

  Each charging charger uniformly charges the surface of the corresponding photosensitive drum. Based on the multicolor image information (black image information, cyan image information, magenta image information, yellow image information) from the host device, the optical scanning device 2010 applies a light beam modulated for each color to the corresponding charged light beam. Irradiate each surface of the photosensitive drum. As a result, on the surface of each photoconductive drum, the charge disappears only in the portion irradiated with light, and a latent image corresponding to the image information is formed on the surface of each photoconductive drum. The latent image formed here moves in the direction of the corresponding developing roller as the photosensitive drum rotates. The configuration of the optical scanning device 2010 will be described later.

  The toner cartridge 2034a stores black toner, and this toner is supplied to the developing roller 2033a. The toner cartridge 2034b stores cyan toner, and this toner is supplied to the developing roller 2033b. The toner cartridge 2034c stores magenta toner, and this toner is supplied to the developing roller 2033c. The toner cartridge 2034d stores yellow toner, and this toner is supplied to the developing roller 2033d.

  On the surface of each developing roller, the toner from the corresponding toner cartridge is thinly and uniformly applied as each developing roller rotates. Then, when the toner on the surface of each developing roller comes into contact with the surface of the corresponding photosensitive drum, the toner moves only to a portion irradiated with light on the surface and adheres to the portion. In other words, each developing roller causes toner to adhere to the latent image formed on the surface of the corresponding photosensitive drum so as to be visualized. Here, the toner-attached image (hereinafter referred to as “toner image” for convenience) moves in the direction of the transfer belt 2040 as the photosensitive drum rotates.

  The yellow, magenta, cyan, and black toner images are sequentially transferred onto the transfer belt 2040 at a predetermined timing, and are superimposed to form a color image.

  Recording paper is stored in the paper feed tray 2060. A paper feed roller 2054 is disposed in the vicinity of the paper feed tray 2060, and the paper feed roller 2054 takes out the recording paper one by one from the paper feed tray 2060 and conveys it to the registration roller pair 2056. The registration roller pair 2056 sends the recording sheet toward the transfer belt 2040 at a predetermined timing. As a result, the color image on the transfer belt 2040 is transferred to the recording paper. The recording sheet on which the image has been transferred is sent to a fixing roller 2050, where heat and pressure are applied to the recording sheet, and toner is fixed on the recording sheet. The recording paper on which the toner image is fixed is sent to the paper discharge tray 2070 via the paper discharge roller 2058 and is sequentially stacked on the paper discharge tray 2070.

  Each cleaning unit removes toner (residual toner) remaining on the surface of the corresponding photosensitive drum. The surface of the photosensitive drum from which the residual toner has been removed returns to the position facing the corresponding charging charger again.

Next, the configuration of the optical scanning device 2010 will be described.
As shown in FIG. 2 and FIG. 3 as an example, the optical scanning device 2010 includes two light source units (LU1, LU2), two cylindrical lenses (121, 122), a polygon mirror 14, two fθ lenses (151). 152), two liquid crystal elements (411, 412), two polarizing beam splitters (161, 162), two reflecting mirrors (171, 172), a plurality of folding mirrors (18a, 18b1, 18b2, 18c1, 18c2, 18d) It has four anamorphic lenses (19a, 19b, 19c, 19d) and a scanning control device (not shown). In the following, for convenience, the direction corresponding to the main scanning direction is abbreviated as “main scanning corresponding direction”, and the direction corresponding to the sub scanning direction is abbreviated as “sub scanning corresponding direction”.

  The light source unit LU1 includes a laser light source 101 and a collimator lens 111 as shown in FIG. 4 as an example. It is assumed that the light source 101 outputs polarized light (S-polarized light) in which the electric field vector reflected by the deflection reflection surface of the polygon mirror 14 as an optical deflector is parallel to the deflection surface. The collimating lens 111 is disposed on the optical path of the light beam (LB1) from the light source 101, and makes the light beam from the light source 101 substantially parallel light.

  The light source unit LU2 includes a laser light source 102 and a collimating lens 112 as shown in FIG. 5 as an example. Assume that S-polarized light is output from the light source 102 in the same manner as the light source 101. The collimating lens 112 is disposed on the optical path of the light beam (LB2) from the light source 10b, and makes the light beam from the light source 102 substantially parallel light.

  Returning to FIG. 2, the cylindrical lens 121 converges the light beam from the light source unit LU <b> 1 in the Z-axis direction and forms a long line image in the main scanning direction in the vicinity of the deflection reflection surface of the polygon mirror 14. The cylindrical lens 122 converges the light beam from the light source unit LU2 in the Z-axis direction, and forms a long line image in the main scanning direction in the vicinity of the deflection reflection surface of the polygon mirror 14.

  In this embodiment, the polygon mirror 14 has mirrors on four side surfaces, and each mirror surface is a deflection reflection surface. The polygon mirror 14 rotates at a constant speed around an axis parallel to the Z-axis direction, and deflects a light beam from each cylindrical lens at a constant angular velocity in a plane parallel to a plane including the X-axis and the Y-axis. In the arrangement example shown in FIG. 2, the light beam from the cylindrical lens 121 is deflected to the −X side of the polygon mirror 14, and the light beam from the cylindrical lens 122 is deflected to the + X side of the polygon mirror 14. The beam bundle surface formed with time by the light beam deflected by the deflecting / reflecting surface of the polygon mirror 14 is called a “deflecting surface” (see JP-A-11-202252).

  The fθ lens 151 is disposed on the −X side of the polygon mirror 14 and on the optical path of the light beam from the cylindrical lens 121 deflected by the polygon mirror 14.

  In FIG. 3, a liquid crystal element 411 is disposed on the −X side of the fθ lens 151. The liquid crystal element 411 is disposed on the optical path of the light beam (here, the light beam LB1) via the fθ lens 151, and the S-polarized light of the light beam LB1 is incident on the liquid crystal element 411 as shown in FIG. Yes. The liquid crystal element 411 includes a first polarization state (LBb: S-polarized light) in which the electric field vector is parallel to the deflecting surface and a second polarization state (LBa: P-polarized light) in which the electric field vector changes according to the deflection angle. ) To switch the direction of the electric field vector. In the first polarization state described here, since the incident S-polarized light is emitted as it is, the liquid crystal element 411 does not actively control the polarization state. The P-polarized light in the second polarization state refers to linearly polarized light whose electric field vector is in a direction parallel to the normal of the polarization separation surface of the polarization beam splitter 161 and the plane formed by incident light. It should be noted that the electric field vector plane is inclined from the plane including the X axis and the Z axis according to the incident angle to the polarization beam splitter 161.

  In FIG. 3, a polarizing beam splitter 161 is disposed on the optical path of the light beam via the liquid crystal element 411 on the −X side of the liquid crystal element 411. The polarization beam splitter 161 has a polarization separation surface that transmits the P-polarized light and reflects the S-polarized light in the −Z direction. In this embodiment, as shown in FIG. 6, the light beam LBa emitted as P-polarized light through the liquid crystal element 411 passes through the polarizing beam splitter 161, and the light beam LBb emitted as S-polarized light is converted into the polarized beam splitter. 161 is reflected in the −Z direction.

  In FIG. 3, the light beam (here, the light beam LBa) that has passed through the polarization beam splitter 161 is irradiated onto the surface of the photosensitive drum 2030a via the folding mirror 18a and the anamorphic lens 19a, thereby forming a light spot. This light spot moves in the longitudinal direction of the photosensitive drum 2030a as the polygon mirror 14 rotates. That is, the photosensitive drum 2030a is scanned. The moving direction of the light spot at this time is the “main scanning direction” on the photosensitive drum 2030a, and the rotational direction of the photosensitive drum 2030a is the “sub-scanning direction” on the photosensitive drum 2030a.

  Thus, the fθ lens 151, the liquid crystal element 411, the polarizing beam splitter 161, the folding mirror 18a, and the anamorphic lens 19a are scanning optical systems corresponding to “K station”, that is, a station for forming a black image.

  On the other hand, the light beam reflected in the −Z direction by the polarization beam splitter 161 (here, the light beam LBb) is reflected by the reflection mirror 171 in the −X direction, and then passes through the folding mirror 18b1, the folding mirror 18b2, and the anamorphic lens 19b. The surface of the photoconductor drum 2030b is irradiated to form a light spot. This light spot moves in the longitudinal direction of the photosensitive drum 2030b as the polygon mirror 14 rotates. That is, the photosensitive drum 2030b is scanned. The moving direction of the light spot at this time is the “main scanning direction” on the photosensitive drum 2030b, and the rotational direction of the photosensitive drum 2030b is the “sub-scanning direction” on the photosensitive drum 2030b.

The fθ lens 151, the liquid crystal element 411, the polarizing beam splitter 161, the reflection mirror 171, the folding mirror 18 b 1, the folding mirror 18 b 2, and the anamorphic lens 19 b are a scanning optical system corresponding to a “C station”, that is, a station for forming a cyan image. It is.
As described above, the fθ lens 151, the liquid crystal element 411, and the polarization beam splitter 161 are shared by the two image forming stations.

  Returning to FIG. 2, the fθ lens 152 is arranged on the optical path of the light beam from the cylindrical lens 122 deflected by the polygon mirror 14 on the + X side of the polygon mirror 14. On the X side of the fθ lens 152, a liquid crystal element 412 is disposed on the optical path of a light beam (here, the light beam LB2) that passes through the fθ lens 152. As shown in FIG. 7, the S-polarized light of the light beam LB2 enters the liquid crystal element 412. The liquid crystal element 412 includes a first polarization state (LBd: S polarization) in which the electric field vector is parallel to the deflection surface on the time axis, and a second polarization state (LBc: P polarization) in which the electric field vector changes according to the deflection angle. ) To switch the direction of the electric field vector. Here, it is necessary to note that the P-polarized light of LBc is inclined from the plane including the X axis and the Z axis according to the incident angle to the polarization beam splitter 162 in the same manner as in the case of LBa.

  On the X side of the liquid crystal element 412, a polarization beam splitter 162 is disposed on the optical path of the light beam that passes through the liquid crystal element 412. The polarization beam splitter 162 has a polarization separation surface that transmits P-polarized light and reflects S-polarized light in the −Z direction. Here, as shown in FIG. 7, the light beam LBc emitted as P-polarized light through the liquid crystal element 412 passes through the polarization beam splitter 162, and the light beam LBd emitted as S-polarized light is −Z by the polarization beam splitter 162. Reflected in the direction.

  Returning to FIG. 3, the light beam reflected in the −Z direction by the polarization beam splitter 162 (here, the light beam LBc) is reflected in the + X direction by the reflection mirror 172, and then the folding mirror 18c1, the folding mirror 18c2, and the anamorphic lens 19c. Irradiates the surface of the photoconductor drum 2030c through the, thereby forming a light spot. This light spot moves in the longitudinal direction of the photosensitive drum 2030c as the polygon mirror 14 rotates. That is, the photosensitive drum 2030c is scanned. The moving direction of the light spot at this time is the “main scanning direction” on the photosensitive drum 2030c, and the rotational direction of the photosensitive drum 2030c is the “sub-scanning direction” on the photosensitive drum 2030c.

  Thus, the fθ lens 152, the liquid crystal element 412, the polarizing beam splitter 162, the reflection mirror 172, the folding mirror 18c1, the folding mirror 18c2, and the anamorphic lens 19c correspond to an “M station”, that is, a station for forming a magenta image. This is a scanning optical system of the scanning optical system.

  On the other hand, the light beam that has passed through the polarization beam splitter 162 (here, the light beam LBd) is irradiated onto the surface of the photosensitive drum 2030d through the folding mirror 18d and the anamorphic lens 19d, thereby forming a light spot. This light spot moves in the longitudinal direction of the photosensitive drum 2030d as the polygon mirror 14 rotates. That is, the photosensitive drum 2030d is scanned. The moving direction of the light spot at this time is the “main scanning direction” on the photosensitive drum 2030d, and the rotational direction of the photosensitive drum 2030d is the “sub-scanning direction” on the photosensitive drum 2030d.

The fθ lens 152, the liquid crystal element 412, the polarization beam splitter 162, the folding mirror 18d, and the anamorphic lens 19d are scanning optical systems corresponding to the “Y station”, that is, the station for forming a yellow image.
As described above, the fθ lens 152, the liquid crystal element 412, and the polarization beam splitter 162 are shared by the two image forming stations. Each folding mirror is provided so that the optical path lengths at the respective image forming stations are equal to each other.

In this embodiment, the fθ lenses 151 and 152 are provided between the polygon mirror 14 and the liquid crystal element. The P-polarized light path and the S-polarized light path almost overlap each other in the Z-axis direction, so that the fθ lens can be made thin.
FIG. 8 shows a polarizing beam splitter and a light beam incident on the polarizing beam splitter. The light beam LB (L) and the light beam LB (R) are light beams directed toward the end portion of the effective scanning region of the photosensitive drum, and the light beam LB (C) is a light beam directed toward the central portion of the effective scanning region of the photosensitive drum. is there.

Table 1 shows the results of measuring noise light when a P-polarized light and an S-polarized light are incident on the commercially available polarizing beam splitter (Meles Griot, broadband polarizing cube beam splitter) with different deflection angles. Show. The definition of the noise light is the intensity ratio of the reflected light from the polarization beam splitter to the incident light for P-polarized light, and the intensity ratio of the transmitted light from the polarized beam splitter to the incident light for S-polarized light. Although the noise light intensity varies depending on the film design of the polarization separation surface of the polarizing beam splitter, generally, as shown in Table 1, it is more conspicuous when p-polarized light is incident than when s-polarized light is incident.

  FIG. 9 shows a polarization beam splitter whose polarization separation surface is inclined by 45 ° with respect to the deflection surface (see FIG. 8), and an incident surface (a surface formed by the polarization separation surface and the incident light beam) with respect to the deflection angle. The relationship of the angle (polarization rotation angle) formed by the electric field vector of P-polarized light is shown in a graph. At the deflection angle of 0 °, the electric field vector is in the plane of incidence, so the polarization rotation angle is 0 °, and at the deflection angle of 35 °, the polarization rotation angle is 20.7 °. That is, a light component with a deflection angle of 0 ° (corresponding to the light beam LB (C) in FIG. 8) does not generate a reflection component due to polarization separation, but the image height as in the light beams LB (L) and LB (R) in FIG. Is partially reflected by the polarization rotation. This is a cause of noise light. In order to avoid this, the polarized light incident on the polarization beam splitter may be rotated in the reverse direction in advance. For example, when the deflection angle is 35 °, the polarization rotation amount is easily predicted to be 20.7 ° as described above.

  FIG. 10 is a graph showing the results of verifying this. When the polarization direction was rotated when the deflection angle was 35 °, it was confirmed from the calculation and the result of the actual measurement that the reflectance decreased most at 20.7 °. Therefore, it is only necessary to prepare a polarization switching means that transmits the S-polarized light as it is, compensates the polarization rotation angle for the P-polarized light, and rotates the polarized light in the reverse direction.

FIG. 13 shows the configuration of the liquid crystal element 41 (common to the liquid crystal elements 411 and 412) as the polarization switching means used in this embodiment and the incident light flux. The liquid crystal element 41 is provided at a pair of transparent substrates 4101a and 4101b, transparent electrodes 4102a and 4102b formed on each transparent substrate, a nematic liquid crystal layer 4104 sandwiched between the substrates, and both interfaces of the liquid crystal layer. The alignment films 4103a and 4103b are configured.
In the liquid crystal element, the incident light beam is changed in accordance with (1) the first polarization state in which the electric field vector is parallel to the deflection surface and (2) the electric field vector in accordance with the deflection angle for each scan accompanying the rotation of the polygon mirror 14. And switch between the second polarization state that changes. This switching is performed by controlling and controlling the drive voltage by the driver 4105 in synchronization with the rotation of the polygon mirror 14.

  FIG. 14 shows the direction of alignment treatment (rubbing) applied to the alignment film. The alignment treatment of the alignment film 4103a on the light beam incident side is set in the Y direction in the drawing, that is, parallel to the deflection surface. The alignment film 4103b on the light beam exit side is rubbed in the Z direction, that is, in the direction perpendicular to the deflection surface, in the vicinity of the position where the light beam is parallel to the normal direction of the alignment film surface (denoted as C in the figure). As the position moves away from this position to the + Y side (denoted as R in the figure), the rubbing direction rotates clockwise from the + Z direction, and as the position moves away from the -Y side (denoted as L in the figure), it moves away from the + Z direction. The rubbing direction rotates clockwise. This rotation direction is a direction parallel to the incident surface formed by the light beam that exits the position of the alignment film and enters the polarization beam splitter 162 with the polarization splitting surface normal line in the polarization beam splitter 162.

  FIG. 15 is a diagram schematically showing the molecular direction of the liquid crystal molecules 4104 sandwiched between the alignment films 4103a and 4103b, and shows a state where no voltage is applied. (L), (C), and (R) in FIG. 15 indicate positions corresponding to L, C, and R in FIG. 15 schematically showing the configuration of the alignment film. The dotted line in the horizontal direction is a line indicating the reference position in the thickness direction (X direction) of the liquid crystal layer. The liquid crystal molecules 4104 are twisted between the alignment films 4103a and 4103b, but the twist angles differ depending on the locations (L), (C), and (R). The twist angle can be continuously changed depending on the location by changing the rubbing direction shown in FIG.

  Due to the twisted structure of the liquid crystal molecules, the incident light beam is emitted with a predetermined optical rotation when no voltage is applied to the liquid crystal. This is (2) “second polarization state in which the electric field vector changes according to the deflection angle”. FIG. 17 is a graph showing an example of calculating the electric field vector direction to be set with respect to the deflection angle. The electric field vector direction is indicated by a rotation angle from the Z-axis direction. Note that the liquid crystal molecules shown here are in a state parallel to the alignment film surface, but providing a slight pretilt should not be problematic in terms of optical function, and should be appropriately set depending on the operability when an electric field is applied.

  FIG. 16 is a diagram schematically showing the liquid crystal molecule direction in a state where a voltage is applied to the liquid crystal. In all places, the liquid crystal molecules orient the molecular long axis in the direction of the electric field. In this state, the incident light beam is transmitted without receiving optical rotation. This is (1) “first polarization state in which the electric field vector is parallel to the deflection surface”.

  In this way, by controlling the voltage applied to the liquid crystal element, the liquid crystal molecule direction can be switched between the state shown in FIG. 15 and the state shown in FIG. 16. It is possible to switch between a first polarization state parallel to the deflection surface and (2) a second polarization state in which the electric field vector changes according to the deflection angle.

  FIG. 18 shows the transparent electrode structure of the liquid crystal element, and FIG. 19 shows the timing of the on / off operation of these electrodes. The transparent electrode 4102a shown in FIG. 18 is always grounded, and the voltage of the transparent electrode 4102b is controlled in synchronization with scanning.

The polarizing beam splitter as the deflection separation means can be composed of, for example, a dielectric multilayer film, a wire grid, etc., but since the manufacturing process is advantageous for increasing the area, the polarization beam splitter is preferably composed of a dielectric multilayer film. preferable.
By configuring the polarization beam splitter as described above, it is possible to efficiently remove noise light that has been a problem in conventional optical scanning devices using a dielectric multilayer film.
The substrate that supports the polarization separation surface can be made of glass or transparent resin. In addition, the polarization separation surface can be protected from dirt and scratches by adopting a structure in which the polarization separation surface is sandwiched between the substrates from both sides.

  The scanning control device has a light source control circuit corresponding to each light source. The light source control circuit corresponding to the light source 101 shown in FIG. 4 is mounted on the circuit board of the light source unit LU1. A light source control circuit corresponding to the light source 102 shown in FIG. 5 is mounted on the circuit board of the light source unit LU2.

  As is clear from the above description, in the optical scanning device 2010 according to the present embodiment, the polarization beam splitter is configured by the polarization beam splitter. Also, an fθ lens (151 and 152), a liquid crystal element (411 and 412), a polarization beam splitter (161 and 162), a reflection mirror (171 and 172), and a folding mirror (18a, 18b1, 18b2, 18c1, 18c2, and 18d). And the anamorphic lenses (19a, 19b, 19c, 19d) constitute a scanning optical system.

  As described above, the optical scanning device 2010 according to the present embodiment includes a light source unit that outputs an S-polarized light beam, a polygon mirror 14 that deflects each light beam from the light source unit at a constant angular velocity within a deflection surface, and For each scan, the light beam deflected by the polygon mirror 14 is subjected to (1) a first polarization state in which the electric field vector is parallel to the deflection surface, and (2) a second state in which the electric field vector changes according to the deflection angle. A liquid crystal element that switches between the polarization states, and a scanning optical system that includes a polarization beam splitter and individually collects each light beam deflected by the polygon mirror 14 on the surface of the corresponding photosensitive drum. According to the present embodiment configured as described above, it is possible to obtain an optical scanning device capable of stably suppressing generation of ghost light while avoiding high cost.

  Further, since the fθ lens and the polarization beam splitter are shared by the two image forming stations, it is possible to reduce the size of the optical scanning device corresponding to the tandem type image forming apparatus.

  According to the color printer 2000 as the image forming apparatus according to the present embodiment, the optical scanning apparatus according to the above embodiment that can stably suppress generation of ghost light while avoiding high cost. Since the optical scanning device 2010 is provided, it is possible to obtain a small-sized image forming apparatus capable of forming a high-quality image while avoiding high costs.

  In the above embodiment, as an example of the liquid crystal element as the polarization switching means, the alignment film is aligned in the alignment treatment direction, the liquid crystal molecules are bend-aligned under no electric field, and the alignment film is at least one of the alignment films. It is possible to use a liquid crystal element in which the light beam that exits the position of the light beam and enters the polarization separation means is in a direction parallel to the incident surface formed between the polarization separation means and the normal line of the polarization separation surface. Since the entire configuration of the liquid crystal element is equivalent to the configuration of FIG.

  FIG. 23 is a diagram illustrating an alignment process (rubbing) performed on the alignment film. In FIG. 23, both the alignment film 4103a ′ on the light beam incident side and the alignment film 4103b ′ on the light beam output side are in the vicinity of a position where the light beam is parallel to the normal direction of the alignment film surface (see FIG. 14). In the middle C), the rubbing process is performed in the Z direction, that is, in the direction perpendicular to the deflection surface, and the rubbing direction rotates clockwise from the + Z direction as the position moves away from this position to the + Y side (denoted R in the figure). The rubbing direction rotates counterclockwise from the + Z direction as the position moves away from the −Y side (denoted by L in the drawing). This rotation direction is a direction parallel to an incident surface formed by a light beam that exits the position of each alignment film and is incident on the polarization beam splitter 162 between the polarization beam splitter 162 and the polarization separation surface normal line. .

  FIG. 24 is a diagram schematically showing the molecular direction of the liquid crystal molecules 4104 sandwiched between the alignment films 4103a ′ and 4103b ′, and shows a state where no voltage is applied. 24, (L), (C), and (R) indicate positions substantially corresponding to L, C, and R shown in FIG. The dotted line in the horizontal direction is a line indicating the reference position in the thickness direction (X direction) of the liquid crystal layer. The liquid crystal molecules 4104 are bend-aligned between the alignment films 4103a 'and 4103b', and the average direction is the optical axis direction of the liquid crystal at that position. The optical axis direction varies depending on the locations (L), (C), and (R), and is continuously changed by the change in the rubbing direction shown in FIG.

  Due to the bend alignment, in the state where no voltage is applied to the liquid crystal, the incident light beam is emitted with the phase modulation of λ / 2 and the electric field vector direction rotated. The phase of λ / 2 can be designed according to the liquid crystal layer thickness, the ordinary light refractive index and extraordinary light refractive index of the liquid crystal material, and the incident angle. The rotation angle in the electric field vector direction may be determined by the rubbing direction with respect to the optical axis direction with respect to the incident electric vector direction. This is (2) “second polarization state in which the electric field vector changes according to the deflection angle”. The electric field vector direction to be set with respect to the deflection angle is the same as the calculation result shown in FIG.

  FIG. 25 is a diagram schematically showing the liquid crystal molecule direction in a state where a voltage is applied to the liquid crystal element. The direction of the liquid crystal molecules in this case is the same as that in FIG.

  An alignment state of a liquid crystal element in which one side alignment film is formed of a vertical alignment film and the opposite side alignment film is aligned in a certain direction in the surface is known as a so-called OCB mode (for example, JP-A-08-328045). reference). One feature of the OCB mode is that liquid crystal molecules are aligned in a bowed state (bend alignment). In the OCB mode, a high-speed operation is possible as compared with the normal twisted nematic mode. Unlike the OCB mode, the liquid crystal element of the present invention has a structure in which the in-plane alignment processing direction is changed depending on the location. However, like the OCB mode, high-speed operation is possible.

  In the above embodiment, as an example, the voltage application timing may be set differently depending on the scanning position. FIG. 20 shows a transparent electrode structure for driving with such a setting. In FIG. 20, the transparent electrode on the incident light side is divided into five in the scanning direction. Reference numerals 4102b1 to 4102b5 indicate five divided transparent electrodes. FIG. 21 shows the timing of the on / off operation of these electrodes. At least at the timing when the light beam passes, for example, at the point indicated by a circle in FIG. 21, the liquid crystal molecules need to be in a predetermined alignment state, but it is not necessary in other periods. Therefore, the alignment state of the liquid crystal may be switched using a time other than the time when the light beam passes. With such a configuration, it is possible to use an inexpensive nematic liquid crystal as a liquid crystal material without using a liquid crystal having high-speed response such as a ferroelectric liquid crystal. The electrode 4102a facing the divided electrode is always kept in a grounded state as a common electrode.

  Moreover, in the said Example, you may integrate a polarizing beam splitter and a liquid crystal element as an example. FIG. 22 shows a configuration example thereof. The transparent substrate 41 in FIG. 22 is substituted by the polarization beam splitter 16. Thereby, it is possible to simplify the assembly process and the adjustment process in the optical scanning device.

The effects that can be obtained by the above embodiment are listed below.
By separating the linearly polarized light reflected from the deflector by the polarization separation means for each scan, it is possible to perform two or more optical scans at different positions with a single rotating polygon mirror type optical deflector, and miniaturization And it is useful for cost reduction.
In the conventional polarization separation means, the electric field vector of P-polarized light is not parallel to the transmission axis of the polarization separation surface at the position where the light beam is incident with a large deflection angle, and a part of the electric field vector is reflected without being completely transmitted. However, according to the above-described embodiment of the present invention, noise light can be reduced by correcting with the polarization switching means formed of a liquid crystal element.
Since a latent image can be formed on two photoconductors with one light source, the number of light sources can be reduced.

The polarization separation performance can be improved over the entire scanning light.
By setting the liquid crystal alignment direction on the light beam incident side to be perpendicular or parallel to the deflection surface, it is possible to effectively rotate the light while preventing elliptical polarization.
By setting the liquid crystal alignment direction on the light beam incident side to be perpendicular or parallel to the deflection surface, a phase of λ / 2 is effectively formed while preventing elliptical polarization, and the electric field vector direction is rotated in a predetermined direction. be able to.
Since the liquid crystal response time can be set low, the applied voltage can be reduced and the material life can be increased.

  In the conventional optical scanning device not provided with the polarization switching means, for example, a wire grid deflection beam splitter is preferable to the dielectric multilayer film deflection beam splitter because of less noise light. However, the wire grid deflection beam splitter has a large reflected wavefront aberration, and it has been difficult to ensure imaging performance on the surface to be scanned. By providing the polarization switching means as in the embodiment of the present invention, it is possible to sufficiently suppress noise even if a dielectric multilayer film deflecting beam splitter is used, and to improve the wavefront aberration.

By making the optical path lengths of the plurality of scanning lights equal, the same optical scanning lens can be used, the optical system layout design becomes easy, and the component cost can be reduced. Further, since the distance from the optical scanning device to the photosensitive member can be shortened, the optical scanning device can be downsized.
Images can be written on a plurality of photoconductors using one light source and one deflector, and the optical scanning device and the image forming device can be reduced in size and cost.

  According to the liquid crystal element and the polarization beam splitter integrated into one structure, the number of interfaces can be reduced, so that wavefront aberration can be reduced. Cost reduction can be achieved by sharing parts. Positioning when incorporated in an optical scanning device is facilitated.

  FIG. 11 shows a second embodiment of the optical scanning device according to the present invention. In FIG. 11, two fθ lenses are arranged so as to overlap each other on both sides of the polygon mirror 14. Liquid crystal elements 411 and 412 and polarizing beam splitters 171 and 172 are arranged between the polygon mirror 14 and the fθ lenses 15a and 15b on one side and between the fθ lenses 15c and 15d on the opposite side of the polygon mirror 14. Therefore, in this embodiment, the fθ lens 15a for the light beam LBa, the fθ lens 15b for the light beam LBb, the fθ lens 15c for the light beam LBc, and the fθ lens 15d for the light beam LBd are required. According to this embodiment, the shape of each fθ lens can be a lens shape suitable for the polarization state of the light beam, the optical path length, the imaging position, and the scanning length.

  The embodiment of the image forming apparatus described so far has been the color printer 2000 having four photosensitive drums, but is not limited to this. For example, a printer having two photosensitive drums may be used. In this case, one light source unit is used.

  FIG. 12 shows a schematic configuration of a laser drawing apparatus 3000 according to the third embodiment. The laser drawing device 3000 has a table on which the optical scanning device 2010 and the drawing object 3100 are placed, a table device 3010 that can move the table in the XY plane, and a host device (for example, a personal computer). And a drawing control device 3020 for controlling the optical scanning device 2010 and the table device 3010 on the basis of the image information. The optical scanning device 2010 scans the surface of the drawing target 3100 with a laser beam modulated by the image signal. An image can be written on the surface of the drawing object 3100 by moving the drawing object 3100 in the XY plane by the table device 3010 while performing this scanning. Whether or not the written image is visualized is arbitrary, and when it is visualized, the means is arbitrary.

  As described above, since the laser drawing apparatus according to the above embodiment includes the optical scanning device according to the present invention and performs drawing by the optical scanning, the effect obtained by the optical scanning device according to the present invention is obtained as a result. be able to. That is, it is possible to obtain a laser drawing apparatus capable of drawing a small and high quality image while avoiding high cost.

  Further, since the optical scanning device according to the present invention can simultaneously scan with a plurality of light beams, it can draw at a high speed using the plurality of light beams.

As described above, according to the optical scanning device of the present invention, it is possible to perform high-precision optical scanning by stably suppressing generation of ghost light while avoiding high costs. Can do.
In addition, according to the image forming apparatus of the present invention, the optical scanning device according to the present invention is provided, and an image is formed by the optical scanning. An image can be formed.
According to the laser drawing apparatus of the present invention, since the optical scanning device according to the present invention is provided and drawing is performed by the optical scanning, a small and high-quality image is drawn while avoiding high costs. be able to.

1 is a front view illustrating a schematic configuration of a color printer which is an example of an image forming apparatus according to the present invention. It is a top view which shows the Example of the optical scanning device based on this invention. It is a front view of the optical scanning device. It is a top view which shows one light source unit in the said optical scanning device. It is a top view which shows another light source unit in the said optical scanning device. It is a front view which shows the liquid crystal element, polarization beam splitter, and reflection mirror which are used for the said optical scanning device. It is a front view which shows another liquid crystal element, a polarization beam splitter, and a reflective mirror which are used for the said optical scanning device. It is a perspective view which shows the polarization beam splitter used for the said optical scanning device, and the light beam incidence to this polarization beam splitter. It is a graph which shows the relationship between the deflection angle at the time of making the polarization | polarized-light which has an electric field vector perpendicular | vertical to a deflecting surface inject into a polarization beam splitter, and a change rotation angle. It is a graph which shows the relationship between the deflection angle at the time of making the said polarized light inject into a polarizing beam splitter, and the light intensity of reflected light. It is a top view which shows another Example of the optical scanning device based on this invention. 1 is a front view schematically showing an embodiment of a laser drawing apparatus according to the present invention. It is a schematic diagram which shows the example of the liquid crystal element applicable to this invention. It is a schematic diagram which shows the example of the rubbing direction of the orientation film of the liquid crystal element used for this invention. It is a schematic diagram which shows an example of the liquid crystal molecular state in an example of the liquid crystal element used for this invention. It is a schematic diagram which shows another example of the liquid crystal molecular state in an example of the said liquid crystal element. It is a graph which shows the example which calculated the electric field vector direction which should be set with respect to the deflection angle of a liquid crystal element. It is a schematic diagram which shows the schematic structure of the transparent electrode of the liquid crystal element which can apply this invention, and the example of the driver for a liquid crystal drive. It is a timing chart which shows the time change of ON / OFF operation of the transparent electrode of the above-mentioned liquid crystal element. It is a schematic diagram which shows another example of the schematic structure of the transparent electrode of the liquid crystal element which can apply this invention, and the driver for a liquid-crystal drive. It is a timing chart which shows the time change of ON / OFF operation of the transparent electrode of the above-mentioned liquid crystal element. It is a model diagram which shows the example of the integrated structure of the liquid crystal element and polarization beam splitter which can be applied to this invention. It is a schematic diagram which shows another example of the rubbing direction of the alignment film of the liquid crystal element used for this invention. It is a schematic diagram which shows an example of the liquid crystal molecular state in another example of the liquid crystal element used for this invention. It is a schematic diagram which shows another example of the liquid crystal molecular state in another example of the said liquid crystal element.

Explanation of symbols

10a to 10d Light source 14 Polygon mirror (optical deflector)
151,152 fθ lens (part of scanning optical system)
161, 162 Polarization beam splitter (polarization separation element)
171 and 172 Reflective mirrors 19a to 19d Anamorphic lens (part of scanning optical system)
2000 Color printer (image forming device)
2030a to 2030d Photosensitive drum 2010 Optical scanning device 3000 Laser drawing device 3010 Table device 3020 Drawing control device LU1 Light source unit LU2 Light source unit 41 Liquid crystal element 4101a, 4101b Transparent substrate 4102a, 4102b Transparent electrode 4103a, 4103b Alignment film 4104 Liquid crystal molecule 4105 Liquid crystal molecule 4105 Device driver

Claims (11)

An optical scanning device that scans a plurality of scanned surfaces with a light beam,
A light source unit that outputs a light beam composed of linearly polarized light;
A deflector for deflecting a light beam from the light source unit;
Each time the light beam deflected by the deflector is scanned, (1) a first polarization state in which the electric field vector is parallel to the deflection surface, and (2) a second polarization state in which the electric field vector changes in accordance with the deflection angle. Polarization switching means comprising a liquid crystal element that switches between, and polarization separation means that switches the emission direction of the light beam in accordance with the polarization state, and individually the light beams deflected by the deflector on the corresponding scanned surface And a scanning optical system for condensing light. The liquid crystal element includes a pair of transparent substrates, a transparent electrode formed on each transparent substrate, a nematic liquid crystal layer sandwiched between these substrates, and an alignment film provided on both side interfaces of the liquid crystal layer. Have
The alignment film corresponds to the deflection angle of the light beam, and is subjected to alignment processing in a different direction for each light beam incident position. A voltage higher than the liquid crystal saturation voltage is applied when the first polarization state is set, and when the second polarization state is set. 2. The optical scanning device according to claim 1, wherein no voltage is applied or a voltage within a range in which liquid crystals are aligned in the alignment direction of the alignment film is applied.   The alignment treatment direction of the alignment film is a direction in which liquid crystal molecules are substantially parallel to the alignment film surface under no electric field, and the alignment film provided at the liquid crystal layer interface on the light beam incident side is parallel to the deflection surface or The alignment film provided at the liquid crystal layer interface on the light beam exit side in the vertical direction is such that the light beam that exits the position of the alignment film and enters the polarization separation means is the polarization separation surface normal line in the polarization separation means. 3. The optical scanning device according to claim 2, wherein the direction is parallel to an incident surface formed between the two.   The alignment treatment direction of the alignment film is that the liquid crystal molecules are bend aligned under no electric field, and at least in one alignment film, the light beam that exits the position of the alignment film and enters the polarization separation means 3. The optical scanning device according to claim 2, wherein the optical scanning device has a direction parallel to an incident surface formed with respect to the polarization splitting surface normal.   The optical scanning device according to claim 2, wherein the voltage application timing to the alignment film is set to be different depending on the scanning position.   6. The optical scanning device according to claim 1, wherein the polarization separation means is a dielectric multilayer film deflecting beam splitter.   7. The optical scanning device according to claim 1, wherein the scanning optical system includes at least one folding mirror that makes each optical path length from the deflector to the plurality of scanned surfaces equal to each other.   8. The optical scanning device according to claim 1, wherein the one side substrate of the liquid crystal element is constituted by a polarization separation means.   9. An image forming apparatus having an image carrier and forming an image by executing an electrophotographic process on the image carrier, wherein the exposure process is performed among the electrophotographic processes. An image forming apparatus comprising the above-described optical scanning device.   The optical scanning device has a plurality of image carriers, and the optical scanning device can scan the plurality of image carriers with a plurality of light fluxes including image information, and color images are formed by superimposing images formed on the image carriers. The image forming apparatus according to claim 9, wherein the image forming apparatus is capable of forming an image.   An apparatus for scanning with the laser beam in the laser drawing apparatus for drawing an image on the object, comprising: an optical scanning device for scanning the object with laser light; and a drawing control device for controlling the optical scanning device. A drawing apparatus comprising the optical scanning device according to any one of claims 1 to 8.

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