JP2012225960A - Optical scanner and image forming apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an optical scanner which is free from requiring a scan lens, has high versatility and can be reduced in size, while maintaining a stable optical scan.SOLUTION: A pre-deflector optical system A corresponds to two light sources and includes a first liquid crystal element 2206A, a second liquid crystal element 2207A, a first KTN element 2208A, a second KTN element 2209A, etc. In the first liquid crystal element 2206A and the second liquid crystal element 2207A, an applied voltage is controlled so that the image forming position of a luminous flux and NA (numerical aperture) are kept constant in a valid scan range. In the first KTN element 2208A, an applied voltage is controlled so that the position of a light spot in a sub-scan direction on the surface of a photoreceptor drum is a desired position. In the second KTN element 2209A, an applied voltage is controlled so that the light spot is moved at constant speed in the valid scan region on the surface of the photoreceptor drum, in conjunction with a polygon mirror.

Description

  The present invention relates to an optical scanning device and an image forming apparatus, and more particularly to an optical scanning device that scans a surface to be scanned with light, and an image forming apparatus including the optical scanning device.

  In recent years, electrophotographic image forming apparatuses used in laser printers, laser plotters, digital copiers, laser facsimiles, or multi-function machines including these have become more colorized and faster, and photoconductor drums that are image carriers. Tandem type image forming apparatuses having a plurality of (usually four) are widely used.

  As an example, Patent Document 1 discloses an image forming apparatus including an optical scanning device for each photosensitive drum.

  As an example, Patent Document 2 discloses an optical scanning device including a two-stage polygon mirror.

  As an example, Patent Document 3 discloses an optical scanning device in which a plurality of light beams are obliquely incident on a one-stage polygon mirror.

  In a general optical scanning device, a photosensitive device is exposed from an optical deflector depending on the interval between two adjacent photosensitive drums (photosensitive member pitch) and the layout conditions of a developing unit arranged between the photosensitive drum and the optical scanning device. The optical path length to the body drum is determined. Therefore, even with image forming apparatuses having the same specifications, the same optical scanning apparatus cannot be used in image forming apparatuses having different layout conditions.

  In general, a scanning lens is formed by injecting a resin into a mold having a cavity having a shape similar to that of the scanning lens from the viewpoint of manufacturing cost and optical surface shape accuracy. Such a resin scanning lens causes a change in imaging performance due to thermal expansion when the environmental temperature rises due to heat generated by the polygon mirror. For this reason, using a “diffractive optical element” or an “optical system that combines an optical element that has the power to diverge the light beam and an optical element that has the power to converge the light beam”, a device that offsets fluctuations in the light collection position is devised. It was necessary. This increases the cost of the optical scanning device and restricts the arrangement of the optical elements, making it difficult to reduce the size.

  Furthermore, a resin scanning lens generally has birefringence, and light incident on the scanning lens is emitted with its polarization state changed. Therefore, when performing light beam separation using polarized light, a part of the light beam to be transmitted may be reflected in the light beam separation element, and a part of the light beam to be reflected may be transmitted to become ghost light.

  The inventors have conducted various experiments and studies on an optical scanning device that does not use a scanning lens in order to solve the above problems.

  The present invention has been made based on the above-described experiments and studies by the inventors, and has the following configuration.

  According to a first aspect of the present invention, there is provided an optical scanning device that scans a surface to be scanned in a main scanning direction with a light beam, which is disposed on a light source and an optical path of the light beam emitted from the light source. A first light deflector for deflecting an optical path in a plane parallel to the main scanning direction and changing a deflection angle of the deflection in a sinusoidal manner; and a constant around an axis orthogonal to the plane parallel to the main scanning direction. An optical scanning device comprising: a rotary polygon mirror that rotates at an angular velocity; and second light deflecting means that deflects a light beam that has passed through the first light deflecting means.

  According to this, a scanning lens is unnecessary, high versatility, and downsizing can be achieved while maintaining stable optical scanning.

  According to a second aspect of the present invention, at least one image carrier, and the optical scanning device according to the invention for scanning the at least one image carrier with a light beam modulated according to corresponding image information, An image forming apparatus.

  According to this, it is possible to reduce the size without degrading the image quality.

  According to a third aspect of the present invention, there are provided a plurality of image carriers, and the optical scanning device of the present invention that scans the plurality of image carriers with a light beam modulated according to corresponding image information. An image forming apparatus provided.

  According to this, it is possible to reduce the size without degrading the image quality.

1 is a diagram illustrating a schematic configuration of a color printer according to an embodiment of the present invention. It is a figure for demonstrating an optical scanning device. It is a figure for demonstrating the optical system before a deflector. It is a figure for demonstrating the optical path of the light beam deflected by the polygon mirror. It is a block diagram for demonstrating a scanning control apparatus. It is a figure for demonstrating some data stored in the data area of flash memory. It is a figure for demonstrating polarization beam splitter 2205A. It is a figure for demonstrating a 1st KTN element. It is a figure for demonstrating the deflection | deviation of the light by a 1st KTN element. It is a figure for demonstrating a 2nd KTN element. It is a figure for demonstrating the deflection angle of the light beam inject | emitted from a 2nd KTN element. It is a figure for demonstrating the time change of the deflection angle of the light beam inject | emitted from a 2nd KTN element. FIG. 6 is a diagram (No. 1) for explaining the relationship between a deflection angle of a light beam emitted from a second KTN element and a traveling direction of a light beam deflected by a deflecting reflection surface; FIG. 10 is a diagram (No. 2) for explaining the relationship between the deflection angle of the light beam emitted from the second KTN element and the traveling direction of the light beam deflected by the deflecting / reflecting surface. FIG. 11 is a diagram (No. 3) for explaining the relationship between the deflection angle of the light beam emitted from the second KTN element and the traveling direction of the light beam deflected by the deflecting / reflecting surface. It is a figure for demonstrating the linearity in this embodiment of the light beam which scans the surface of a photoconductive drum in a main scanning direction. It is a figure for demonstrating the polarization beam splitter 2205B. It is a figure for demonstrating the surface tilt correction system in the conventional optical scanning device. It is a figure for demonstrating the modification of the optical system before a deflector.

  Hereinafter, an embodiment of the present invention will be described with reference to FIGS. FIG. 1 shows a schematic configuration of a color printer 2000 as an image forming apparatus according to an embodiment.

  The color printer 2000 is a tandem multi-color printer that forms a full-color image by superimposing four colors (black, cyan, magenta, and yellow), and includes an optical scanning device 2010, four photosensitive drums (2030a, 2030b, 2030c, 2030d), four cleaning units (2031a, 2031b, 2031c, 2031d), four charging devices (2032a, 2032b, 2032c, 2032d), four developing rollers (2033a, 2033b, 2033c, 2033d), 4 Toner cartridges (2034a, 2034b, 2034c, 2034d), transfer belt 2040, transfer roller 2042, fixing device 2050, paper feed roller 2054, registration roller pair 2056, paper discharge roller 2058, paper feed tray 2 60, the discharge tray 2070 includes a communication control unit 2080, and a printer controller 2090 for totally controlling the above elements.

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

  The printer control device 2090 includes a CPU, a ROM described in a program written in code readable by the CPU, various data used when executing the program, a RAM as a working memory, an analog data An AD conversion circuit for converting the signal into digital data. Then, the printer control device 2090 sends image information from the host device to the optical scanning device 2010.

  The photosensitive drum 2030a, the charging device 2032a, the developing roller 2033a, the toner cartridge 2034a, and the cleaning unit 2031a are used as a set and form an image forming station (hereinafter also referred to as “K station” for convenience) that forms a black image. Constitute.

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

  The photosensitive drum 2030c, the charging device 2032c, the developing roller 2033c, the toner cartridge 2034c, and the cleaning unit 2031c are used as a set, and form an image forming station (hereinafter also referred to as “M station” for convenience) that forms a magenta image. Constitute.

  The photosensitive drum 2030d, the charging device 2032d, the developing roller 2033d, the toner cartridge 2034d, and the cleaning unit 2031d are used as a set, and form an image forming station (hereinafter also referred to as “Y station” for convenience) that forms a yellow image. Constitute.

  Each photosensitive drum has a photosensitive layer formed on the surface thereof. That is, the surface of each photoconductive drum is a surface to be scanned. Each photosensitive drum is rotated in the direction of the arrow in the plane of FIG. 1 by a rotation mechanism (not shown).

  In the following description, in the XYZ three-dimensional orthogonal coordinate system, the direction along the longitudinal direction of each photosensitive drum is defined as the Y-axis direction, and the direction along the arrangement direction of the four photosensitive drums is defined as the X-axis direction.

  Each charging device uniformly charges the surface of the corresponding photosensitive drum.

  The optical scanning device 2010 has a corresponding charged photosensitive beam by a light beam modulated for each color based on multi-color image information (black image information, cyan image information, magenta image information, yellow image information) from the host device. Each surface of the body drum is scanned. 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 configuration of the optical scanning device 2010 will be described later.

  The scanning direction of the light beam on each photosensitive drum is referred to as “main scanning direction”, and the rotational direction of the photosensitive drum is referred to as “sub-scanning direction”.

  Incidentally, a scanning area in the main scanning direction in which image information is written on each photosensitive drum is called an “effective scanning area”, an “image forming area”, or an “effective image area”. The position coordinates with the origin 0 as the center of the effective scanning area in the main scanning direction are called “image height”.

  Each latent image formed by the optical scanning device 2010 moves in the direction of the corresponding developing roller as the photosensitive drum rotates.

  As each developing roller rotates, the toner from the corresponding toner cartridge is thinly and uniformly applied to the surface thereof. 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 surface. 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”) 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 feeds the recording paper toward the gap between the transfer belt 2040 and the transfer roller 2042 at a predetermined timing. As a result, the color image on the transfer belt 2040 is transferred to the recording paper. The recording paper on which the color image is transferred is sent to the fixing device 2050.

  In the fixing device 2050, heat and pressure are applied to the recording paper, thereby fixing the toner on the recording paper. The recording paper on which the toner 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 device again.

  Next, the configuration of the optical scanning device 2010 will be described.

  As shown in FIG. 2 as an example, the optical scanning device 2010 includes four light sources (2200a, 2200b, 2200c, 2200d), a pre-deflector optical system A, a pre-deflector optical system B, a polygon mirror 2104, two A polarization beam splitter (2105A, 2105B), two folding mirrors (2106A, 2106B), a scanning control device 3022 (not shown in FIG. 2, refer to FIG. 5), and the like. 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”.

  Each light source includes a semiconductor laser. The light source 2200b and the light source 2200c are arranged apart from each other in the X-axis direction, and both emit light beams in the −Y direction. The light source 2200a and the light source 2200d are disposed to face each other with respect to the X-axis direction. The light source 2200a emits a light beam in the + X direction, and the light source 2200d emits a light beam in the -X direction.

  In the following, for convenience, the light beam emitted from the light source 2200a is referred to as “light beam LBa”, the light beam emitted from the light source 2200b is referred to as “light beam LBb”, and the light beam emitted from the light source 2200c is referred to as “light beam LBc”. The light beam emitted from the light source 2200d is referred to as “light beam LBd”.

  The light beam LBa and the light beam LBb are linearly polarized light whose polarization directions are orthogonal to each other. The light beam LBc and the light beam LBd are linearly polarized light whose polarization directions are orthogonal to each other.

  As shown in FIG. 3 as an example, the pre-deflector optical system A includes two aperture plates (2202a and 2202b), a polarizing beam splitter 2205A, a first liquid crystal element 2206A, a second liquid crystal element 2207A, a first KTN element 2208A, And a second KTN element 2209A.

  This pre-deflector optical system A guides the light beam LBa emitted from the light source 2200 a and the light beam LBb emitted from the light source 2200 b to the polygon mirror 2104. Details of the pre-deflector optical system A will be described later.

  As shown in FIG. 3 as an example, the pre-deflector optical system B includes two aperture plates (2202c, 2202d), a polarizing beam splitter 2205B, a first liquid crystal element 2206B, a second liquid crystal element 2207B, a first KTN element 2208B, And a second KTN element 2209B.

  This pre-deflector optical system B guides the light beam LBc emitted from the light source 2200c and the light beam LBd emitted from the light source 2200d to the polygon mirror 2104. Details of the pre-deflector optical system B will be described later.

  As an example, the polygon mirror 2104 has a four-sided mirror with a radius of an inscribed circle of 7 mm. Each mirror in the four-sided mirror is a deflecting reflecting surface. That is, the polygon mirror 2104 has four deflection reflection surfaces (deflection reflection surface 1 to deflection reflection surface 4).

  The polygon mirror 2104 rotates at a constant speed around an axis parallel to the Z-axis direction, and converts the light beams LBa and LBb from the pre-deflector optical system A, and the light beams LBc and LBd from the pre-deflector optical system B, respectively. Deflection is performed at a constant angular velocity in a plane orthogonal to the Z axis.

  The polarization beam splitter 2105A is disposed on the optical path of the light beams LBa and LBb deflected by the polygon mirror 2104, transmits the light beam LBa, and reflects the light beam LBb in the −Z direction (see FIG. 4).

  The light beam LBa that has passed through the polarization beam splitter 2105A is irradiated onto the photosensitive drum 2030a via the folding mirror 2106A.

  The light beam LBb reflected by the polarization beam splitter 2105A is applied to the photosensitive drum 2030b.

  That is, both the light beam LBa and the light beam LBb are reflected only once between the polygon mirror 2104 and the photosensitive drum.

  The polarization beam splitter 2105B is disposed on the optical paths of the light beam LBc and the light beam LBd deflected by the polygon mirror 2104, transmits the light beam LBd, and reflects the light beam LBc in the −Z direction (see FIG. 4).

  The light beam LBc reflected by the polarization beam splitter 2105B is applied to the photosensitive drum 2030c.

  The light beam LBd that has passed through the polarization beam splitter 2105B is irradiated onto the photosensitive drum 2030d through the folding mirror 2106B.

  That is, both the light beam LBc and the light beam LBd are reflected only once between the polygon mirror 2104 and the photosensitive drum.

  4 is an interval between two adjacent photoconductor drums (photoconductor pitch), and A is a distance in the Z-axis direction between the reflection position on the deflecting reflection surface and the surface to be scanned. B is the distance in the X-axis direction between the reflection position on the deflecting reflection surface and the light separation position on the polarization beam splitter.

  As shown in FIG. 5 as an example, the scanning control device 3022 includes a CPU 3210, flash memory 3211, RAM 3212, liquid crystal element voltage application circuit 3213, IF (interface) 3214, pixel clock generation circuit 3215, image processing circuit 3216, writing A control circuit 3219, a light source drive circuit 3221, a KTN element voltage application circuit 3222, and the like are included. Note that the arrows in FIG. 5 indicate the flow of typical signals and information, and do not represent the entire connection relationship of each block.

  An IF (interface) 3214 is a communication interface that controls bidirectional communication with the printer control apparatus 2090. Image information from the host device is supplied via an IF (interface) 3214.

  The flash memory 3211 has a program area and a data area. The program area stores various programs described in codes readable by the CPU 3210, and the data area stores various data ( 6) is stored.

  The RAM 3212 is a working memory.

  The CPU 3210 operates according to a program stored in the flash memory 3211 and controls the entire optical scanning device 2010.

  The pixel clock generation circuit 3215 generates a pixel clock signal. The pixel clock signal can be phase-modulated with a resolution of 1/8 clock.

  The image processing circuit 3216 performs dot processing for each light source after performing predetermined halftone processing on the image data rasterized for each color by the CPU 3210.

  The write control circuit 3219 obtains a write start timing for each station based on an output signal of a tip synchronization detection sensor (not shown). Then, the dot data of each light source is superimposed on the pixel clock signal from the pixel clock generation circuit 3215 in accordance with the writing start timing, and independent modulation data is generated for each light source.

  The light source driving circuit 3221 outputs a driving signal for each light source in accordance with each modulation data from the writing control circuit 3219.

  The liquid crystal element voltage application circuit 3213 individually applies a voltage to each liquid crystal element based on an instruction from the CPU 3210.

  The KTN element voltage application circuit 3222 individually applies a voltage to each KTN element based on an instruction from the CPU 3210.

  Here, details of the pre-deflector optical system A will be described.

  The aperture plate 2202a has an opening disposed on the optical path of the light beam LBa emitted from the light source 2200a, and limits the beam diameter of the light beam to a desired size. The aperture plate 2202b has an opening disposed on the optical path of the light beam LBb emitted from the light source 2200b, and limits the beam diameter of the light beam to a desired size.

  The polarizing beam splitter 2205A is disposed on the + X side of the aperture plate 2202a and on the −Y side of the aperture plate 2202b. The polarization beam splitter 2205A has a polarization separation surface that transmits p-polarized light and reflects s-polarized light in the -Y direction.

  Here, the light beam LBa emitted from the light source 2200a is s-polarized light and the light beam LBb emitted from the light source 2200b is p-polarized light with respect to the polarization separation surface of the polarization beam splitter 2205A.

  Therefore, the light beam LBa that has passed through the aperture of the aperture plate 2202a is reflected in the −Y direction by the polarization beam splitter 2205A, and the light beam LBb that has passed through the aperture of the aperture plate 2202b passes through the polarization beam splitter 2205A. Thereby, the optical paths of the light beam LBa and the light beam LBb emitted from the polarization beam splitter 2205A are substantially the same (see FIG. 7).

  The first liquid crystal element 2206A is disposed on the optical path of the light beams (light beam LBa and light beam LBb) emitted from the polarization beam splitter 2205A.

  The second liquid crystal element 2207A is disposed on the optical path of the light beam (light beam LBa and light beam LBb) via the first liquid crystal element 2206A.

  The first liquid crystal element 2206A and the second liquid crystal element 2207A are liquid crystal elements including ferroelectric liquid crystal, and change the focal length of the pre-deflector optical system A according to the applied voltage.

  Here, the voltages applied to the first liquid crystal element 2206A and the second liquid crystal element 2207A so that the imaging positions and NA (numerical aperture) of the light beams LBa and LBb are kept constant within the effective scanning region. The relationship with the image height is preset and stored in the data area of the flash memory 3211 (see FIG. 6).

  The CPU 3210 refers to the relationship between the voltage applied to the first liquid crystal element 2206A and the second liquid crystal element 2207A stored in the data area of the flash memory 3211 and the image height, and passes through the liquid crystal element voltage application circuit 3213. Thus, the voltage applied to the first liquid crystal element 2206A and the second liquid crystal element 2207A is controlled.

The first KTN element 2208A is an element including a KTN crystal (potassium tantalate niobate, KTa _1-x Nb _x O ₃ ), and is on the optical path of the light flux (light flux LBa and light flux LBb) via the second liquid crystal element 2207A. Has been placed.

  In the first KTN element 2208A, as shown in FIG. 8 as an example, a KTN crystal is sandwiched between two electrodes facing each other in the Z-axis direction.

  The first KTN element 2208A deflects the optical path of the incident light beam with respect to the sub-scanning corresponding direction (here, the same as the Z-axis direction) in accordance with the voltage (referred to as voltage Vz) applied between the two electrodes (FIG. 9). reference).

  Here, based on the surface tilt information of each deflection reflection surface of the polygon mirror 2104, the deflection is performed so that the positions of the light spots on the surfaces of the photosensitive drum 2030a and the photosensitive drum 2030b in the sub-scanning direction become the desired positions. An applied voltage Vz to the first KTN element 2208A is preset for each reflection surface and stored in the data area of the flash memory 3211 (see FIG. 6).

  Then, the CPU 3210 refers to the voltage Vz applied to the first KTN element 2208A for each deflecting / reflecting surface stored in the data area of the flash memory 3211, and supplies the voltage to the first KTN element 2208A via the KTN element voltage application circuit 3222. Control the applied voltage.

  The second KTN element 2209A is an element including the KTN crystal, and is disposed on the optical path of the light beam (light beam LBa and light beam LBb) via the first KTN element 2208A.

  As shown in FIG. 10 as an example, the second KTN element 2209A has a KTN crystal sandwiched between two electrodes facing each other in the X-axis direction.

  The second KTN element 2209A deflects the optical path of the incident light beam in the XY plane according to the voltage (referred to as voltage Vxy) applied between the two electrodes (see FIG. 11).

  Here, it is assumed that the angular velocity of the polygon mirror 2104 in the constant speed rotation is ωp. In addition, the tilt angle of the emission direction of the light beam emitted from the second KTN element 2209A with respect to the Y-axis direction is defined as a deflection angle φ.

This deflection angle φ is fluctuated sinusoidally as shown in FIG. 12 as an example. The maximum value of the deflection angle φ at this time is a [phi] max, the temporal change of the deflection angle φ of the angular velocity omega _D of the deflection angle.

  Here, as an example, as shown in FIG. 13, when the deflection angle φ is 0, the light beam deflected by the deflecting reflecting surface is set to be directed to the position of the image height 0. As an example, as shown in FIGS. 14 and 15, when the absolute value of the deflection angle φ is φmax, the light beam deflected by the deflecting reflection surface is set to be directed toward the end of the effective scanning region. Yes.

  At this time, the linearity Lin of the light beam that scans the surface of the photosensitive drum can be obtained by the following equation (1). Here, t is time, and the timing when the light beam travels to the position where the image height is 0 is 0.

  If the value of linearity Lin calculated from the above equation (1) is 0 within a range of a certain time t, it can be said that optical scanning within that range has high linearity.

In the present embodiment, so that linearity Lin becomes 0 within the range of t corresponding to the effective scanning area, .omega.p, setting the omega _D, and [phi] max. Specifically, as an example, ωp = 6283.185 rps, ω _D = 29326.42 rps, and φmax = 1.945 °. The rps means “radians / second”.

  FIG. 16 shows the calculation result of the above equation (1) at this time. In FIG. 16, the horizontal axis is converted from time t to image height. Moreover, the unit of the linearity on the vertical axis is%. Thus, in this embodiment, it can be said that the linearity within the effective scanning region is high. In FIG. 16, the case where there is no second KTN element is shown by a broken line for comparison.

The angular velocity ωp of the polygon mirror 2104, the angular velocity ω _D of the deflection angle in the second KTN element 2209A, and the maximum value φmax of the deflection angle φ are set in advance and stored in the data area of the flash memory 3211 (see FIG. 6).

Then, the CPU 3210 refers to the angular velocity ω _{D of} the deflection angle and the maximum value φmax of the deflection angle φ in the second KTN element 2209A stored in the data area of the flash memory 3211, and the first value φmax through the KTN element voltage application circuit 3222 is referred to. The voltage applied to the 2KTN element 2209A is controlled.

  In this case, the light spot on the surface of the photosensitive drum 2030a moves at a constant speed in the longitudinal direction of the photosensitive drum 2030a in accordance with the change of the swing angle in the second KTN element 2209A and the rotation of the polygon mirror 2104.

  Similarly, the light spot on the surface of the photosensitive drum 2030b moves at a constant speed in the longitudinal direction of the photosensitive drum 2030b in accordance with the change of the swing angle in the second KTN element 2209A and the rotation of the polygon mirror 2104.

  Next, returning to FIG. 3, the details of the pre-deflector optical system B will be described.

  The aperture plate 2202c has an opening disposed on the optical path of the light beam LBc emitted from the light source 2200c, and limits the beam diameter of the light beam to a desired size. The aperture plate 2202d has an opening disposed on the optical path of the light beam LBd emitted from the light source 2200d, and limits the beam diameter of the light beam to a desired size.

  The polarizing beam splitter 2205B is disposed on the −Y side of the aperture plate 2202c and on the −X side of the aperture plate 2202d. The polarization beam splitter 2205B has a polarization separation surface that transmits p-polarized light and reflects s-polarized light in the -Y direction.

  Here, the light beam LBc emitted from the light source 2200c is p-polarized light and the light beam LBd emitted from the light source 2200d is s-polarized light with respect to the polarization separation surface of the polarization beam splitter 2205B.

  Therefore, the light beam LBc that has passed through the opening of the aperture plate 2202c passes through the polarization beam splitter 2205B, and the light beam LBd that has passed through the opening of the aperture plate 2202d is reflected in the −Y direction by the polarization beam splitter 2205B. Thereby, the optical paths of the light beam LBc and the light beam LBd emitted from the polarization beam splitter 2205B are substantially the same (see FIG. 17).

  The first liquid crystal element 2206B is disposed on the optical path of the light beams (light beam LBc and light beam LBd) emitted from the polarization beam splitter 2205B.

  The second liquid crystal element 2207B is disposed on the optical path of the light beam (light beam LBc and light beam LBd) via the first liquid crystal element 2206B.

  The first liquid crystal element 2206B and the second liquid crystal element 2207B are liquid crystal elements including ferroelectric liquid crystal, and change the focal length of the pre-deflector optical system B according to the applied voltage.

  Here, the voltage applied to the first liquid crystal element 2206B and the second liquid crystal element 2207B so that the imaging position and NA (numerical aperture) of the light beam LBc and the light beam LBd are kept constant within the effective scanning region. The relationship with the image height is preset and stored in the data area of the flash memory 3211 (see FIG. 6).

  The CPU 3210 refers to the relationship between the voltage applied to the first liquid crystal element 2206B and the second liquid crystal element 2207B stored in the data area of the flash memory 3211 and the image height, and passes through the liquid crystal element voltage application circuit 3213. Thus, the voltage applied to the first liquid crystal element 2206B and the second liquid crystal element 2207B is controlled.

  The first KTN element 2208B is an element including the KTN crystal, and is disposed on the optical path of the light beam (light beam LBc and light beam LBd) via the second liquid crystal element 2207B.

  Similar to the first KTN element 2208A, the first KTN element 2208B has a KTN crystal sandwiched between two electrodes facing each other with respect to the Z-axis direction. The first KTN element 2208B has an incident light flux according to the voltage applied between the two electrodes. The optical path is deflected in the sub-scanning corresponding direction (here, the same as the Z-axis direction).

  Here, based on the surface tilt information of each deflection reflection surface of the polygon mirror 2104, the deflection is performed so that the positions of the light spots on the surfaces of the photosensitive drum 2030c and the photosensitive drum 2030d in the sub-scanning direction become the desired positions. The voltage applied to the first KTN element 2208B is preset for each reflecting surface and stored in the data area of the flash memory 3211 (see FIG. 6).

  Then, the CPU 3210 refers to the voltage applied to the first KTN element 2208B for each deflecting / reflecting surface stored in the data area of the flash memory 3211, and applies the voltage to the first KTN element 2208B via the KTN element voltage application circuit 3222. Control the voltage.

  The second KTN element 2209B is an element including the KTN crystal, and is disposed on the optical path of the light beam (light beam LBc and light beam LBd) via the first KTN element 2208B.

  Similar to the second KTN element 2208A, the second KTN element 2209B has a KTN crystal sandwiched between two electrodes facing each other in the X-axis direction. The second KTN element 2209B generates an incident light flux according to the voltage applied between the two electrodes. The optical path is deflected in the XY plane.

Here, similarly to the second KTN element 2208A, in conjunction with the polygon mirror 2104, the angular velocity ω _D and deflection angle of the deflection angle in the second KTN element 2209B so that the light spot scans the surface of the photosensitive drum at a constant speed. The maximum value φmax of φ is set in advance and stored in the data area of the flash memory 3211 (see FIG. 6).

Then, the CPU 3210 refers to the angular velocity ω _{D of} the deflection angle and the maximum value φmax of the deflection angle φ in the second KTN element 2209B stored in the data area of the flash memory 3211, and through the KTN element voltage application circuit 3222, The voltage applied to the 2KTN element 2209B is controlled.

  In this case, the light spot on the surface of the photosensitive drum 2030c moves at a constant speed in the longitudinal direction of the photosensitive drum 2030c in accordance with the change of the swing angle in the second KTN element 2209B and the rotation of the polygon mirror 2104.

  Similarly, the light spot on the surface of the photosensitive drum 2030d moves at a constant speed in the longitudinal direction of the photosensitive drum 2030d in accordance with the change of the swing angle in the second KTN element 2209B and the rotation of the polygon mirror 2104.

  By the way, in this embodiment, as an example, the code S in FIG. 4 is 100 mm, the code A is 70 mm, and the code B is 43 (= 50−7) mm.

  With this positional relationship, when the scanning optical system is arranged between the polygon mirror and the polarization beam splitter as in the conventional optical scanning device, the focal length of the scanning optical system must be smaller than 120 mm. I must. For example, assuming that the focal length of the scanning optical system is 100 mm, considering a scanning optical system that corresponds to the A3 size (writing range: about 300 mm) and satisfies the so-called fθ characteristic, the angle of view is 300 ÷ 100 = 3 rad = 172 °. Thus, such a scanning optical system cannot be practically designed.

  As described above, when the value of the code S and the value of the code A in FIG. 4 are reduced, the angle of view increases. However, there is a limit to the angle of view that can be secured by the scanning optical system disposed between the polygon mirror and the photosensitive drum, and as a result, there is a limit to reducing the value of the code S and the value of the code A. It was.

  Further, in the conventional optical scanning device, as shown in FIG. 18 as an example, the light beam emitted from the light source and made into a parallel light beam is incident on the cylindrical lens, and the deflection mirror surface position of the polygon mirror is related to the sub-scanning corresponding direction. Only imaged. This light beam is deflected by a polygon mirror, enters the scanning lens while diverging, and is condensed on the surface to be scanned. In this case, even if the deflecting / reflecting surface is not parallel to the rotation axis and there is a so-called surface tilt (also referred to as “β tilt”), the light beam is collected at a desired position on the surface to be scanned without being affected by this. Can be made. That is, a surface tilt correction system is configured by the cylindrical lens and the scanning lens.

  However, in the present embodiment, since there is no surface tilt correction system, for example, when the optical path length between the deflecting reflection surface and the surface to be scanned is 120 mm, if the surface tilt is 1 minute, collection on the surface to be scanned is performed. The optical position deviates from the desired position by about 35 μm with respect to the sub-scanning direction. Since the scanning line interval is 21 μm when the writing density is 1200 dpi, this positional deviation is not acceptable.

  Therefore, in the present embodiment, the above-described positional deviation is corrected by the first KTN element 2208A and the first KTN element 2208B.

  As described above, according to the optical scanning device 2010 according to the present embodiment, the four light sources (2200a, 2200b, 2200c, 2200d), the pre-deflector optical system A, the pre-deflector optical system B, the polygon mirrors 2104, 2 Two polarization beam splitters (2105A, 2105B), two folding mirrors (2106A, 2106B), a scanning control device 3022, and the like.

  Each pre-deflector optical system corresponds to two light sources, and includes two aperture plates, a polarizing beam splitter, a first liquid crystal element, a second liquid crystal element, a first KTN element, and a second KTN element.

  The polarization beam splitter combines the light beams that have passed through the openings of the two aperture plates. The applied voltages of the first liquid crystal element and the second liquid crystal element are controlled so that the imaging position of the light beam and the NA (numerical aperture) are kept constant within the effective scanning region. The applied voltage of the first KTN element is controlled so that the position of the light spot on the surface of the photosensitive drum in the sub-scanning direction becomes a desired position. In the second KTN element, the applied voltage is controlled in conjunction with the polygon mirror 2104 so that the light spot moves at a constant speed within the effective scanning area on the surface of the photosensitive drum.

  In this case, a latent image can be accurately formed on the surface of the photosensitive drum without providing a scanning lens between the polygon mirror 2104 and the photosensitive drum. As a result, it is highly versatile and can be downsized while maintaining stable optical scanning.

  Since the color printer 2000 according to this embodiment includes the optical scanning device 2010, as a result, it is possible to reduce the size without degrading the image quality.

In the above embodiment, the case of ωp = 6283185 rps, ω _D = 29326.42 rps, and φmax = 1.945 ° has been described, but the present invention is not limited to this. In short, the second KTN element and the polygon mirror 2104 need only be set so that the light spot moves at a constant speed within the effective scanning area on the surface of the photosensitive drum.

  In the above embodiment, a dichroic mirror that transmits the light beam LBa and reflects the light beam LBb may be used instead of the polarizing beam splitter 2105A by changing the wavelengths of the light beam LBa and the light beam LBb. Similarly, a dichroic mirror that transmits the light beam LBd and reflects the light beam LBc may be used instead of the polarizing beam splitter 2105B by changing the wavelengths of the light beam LBc and the light beam LBd. In this case, since the first liquid crystal element and the second liquid crystal element cannot be shared by two light beams having different wavelengths, as shown in FIG. 19 as an example, in each pre-deflector optical system, The liquid crystal element and the second liquid crystal element are provided for each light beam, and are disposed between the light source and the combining polarization beam splitter.

  In the above embodiment, a oscillating mirror element having a plurality of oscillating micromirrors may be used in place of each second KTN element.

  In the above embodiment, the case where the image forming apparatus is a color printer in which a toner image is transferred from a photosensitive drum to a recording sheet via a transfer belt has been described. However, the present invention is not limited to this. It may be a color printer that is directly transferred to the printer.

  In the above embodiment, a color printer is described as the image forming apparatus. However, the present invention is not limited to this. For example, an optical plotter or a digital copying apparatus may be used.

  Further, an image forming apparatus using a silver salt film as the image carrier may be used. In this case, a latent image is formed on the silver salt film by optical scanning, and this latent image can be visualized by a process equivalent to a developing process in a normal silver salt photographic process. Then, it can be transferred to a photographic paper as a transfer object by a process equivalent to a printing process in a normal silver salt photographic process. Such an image forming apparatus can be implemented as an optical plate making apparatus or an optical drawing apparatus that draws a CT scan image or the like.

  Further, an image forming apparatus using a color developing medium (positive photographic paper) that develops color by the heat energy of a beam spot as an image carrier may be used. In this case, a visible image can be directly formed on the image carrier by optical scanning.

  In short, if the image forming apparatus includes the optical scanning device 2010, it is possible to reduce the size without deteriorating the image quality.

  As described above, the optical scanning device according to the present invention does not require a scanning lens, is highly versatile, and is suitable for downsizing while maintaining stable optical scanning. The image forming apparatus according to the present invention is suitable for downsizing without deteriorating the image quality.

  2000 ... Color printer (image forming apparatus), 2010 ... Optical scanning device, 2030a to 2030d ... Photosensitive drum (image carrier), 2104 ... Polygon mirror (second light deflecting means), 2105A, 2105B ... Polarizing beam splitter (light) Separation member), 2106A, 2106B ... Folding mirror (reflection member), 2200a to 2200d ... Light source, 2205A, 2205B ... Polarizing beam splitter (light synthesis member), 2206A, 2206B ... First liquid crystal element (optical element), 2207A, 2207B ... Second liquid crystal element (optical element), 2208A, 2208B ... 1st KTN element (part of third light deflecting means), 2209A, 2209B ... 2nd KTN element (part of first light deflecting means), 3022 ... Scan control device (A part of the first light deflection unit, a part of the third light deflection unit).

JP 2007-245705 A Japanese Patent No. 4476047 Japanese Patent No. 3869701

Claims (9)

An optical scanning device that scans a surface to be scanned with a light beam in a main scanning direction,
A light source;
A first light deflector disposed on the optical path of the light beam emitted from the light source, deflecting the optical path of the incident light beam in a plane parallel to the main scanning direction, and changing the deflection angle of the deflection sinusoidally; ,
A light having a rotary polygon mirror that rotates at a constant angular velocity about an axis orthogonal to a plane parallel to the main scanning direction, and that deflects the light beam via the first light deflecting means. Scanning device.   2. The optical scanning device according to claim 1, wherein an angular velocity of a deflection angle in the first light deflection unit is larger than an angular velocity of the rotary polygon mirror in the second light deflection unit.   An optical path of an incident light beam is arranged on an optical path between the light source and the second light deflecting unit, and an optical path of an incident light beam is changed based on inclination information of each mirror surface of the rotary polygon mirror with respect to a rotation axis of the rotary polygon mirror. 3. The optical scanning device according to claim 1, further comprising a third light deflecting unit configured to deflect the light in a direction parallel to the rotation axis.   4. The apparatus according to claim 1, further comprising at least two optical elements arranged on an optical path between the light source and the second light deflecting unit and capable of changing a focal length of an optical system. The optical scanning device according to one item.   5. The optical scanning device according to claim 1, wherein the linearity of the light beam that scans the surface to be scanned has an absolute value of 3% or less. The light source emits a first light beam as a first light source,
A second light source that emits a second light flux different from the first light flux;
A photosynthesis member that makes the optical path of the first luminous flux the same as the optical path of the second luminous flux;
The optical scanning device according to claim 1, further comprising: a light separation member that separates the first light beam deflected by the second light deflection unit and the second light beam.   7. The optical scanning device according to claim 6, wherein the first light beam and the second light beam are reflected only once between a corresponding scanned surface and the second light deflecting unit. At least one image carrier;
An image forming apparatus comprising: the optical scanning device according to claim 1, wherein the at least one image carrier is scanned with a light beam modulated according to corresponding image information. A plurality of image carriers;
An image forming apparatus comprising: the optical scanning device according to claim 6 or 7, wherein the plurality of image carriers are scanned with light beams modulated according to corresponding image information.

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