JP2008185917A - Optical scanner - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an optical scanner capable of correcting a scanning line shape without being affected by a space region formed between electrodes while generation of a high level electromagnetic radiation noise is suppressed. <P>SOLUTION: The optical scanner includes: an electrooptical crystalline structure 3 that deflects a luminous flux scanned by a polygon mirror 1 in a subscanning direction by voltage application; and a controller 36 that controls the voltage applied to the electrooptical crystalline structure 3 with a prescribed timing independent from an image writing signal. The electrooptical crystalline structure 3 is composed of; a nearly rectangular parallelepiped EO crystal 31 having a property in which a refractive index varies by a voltage application; a common electrode P0 mounted on one face right-angled to the subscanning direction in the EO crystal 31; and electrodes P1-P5 that are mounted on the other face right-angled to the subscanning direction and that are arranged along the main scanning direction so as to form spaces B1-B4. When the luminous flux scanned by the polygon mirror 1 is projected to each space, the projection line of the luminous flux cuts across at least one of the two electrodes forming each space. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to an optical scanning device that is provided in an image forming apparatus such as a laser printer and forms an image of laser light emitted from a light source on a photosensitive member.

  Conventionally, an optical scanning device is used as a writing system of an image forming apparatus such as a printer, a digital copying machine, or a facsimile. The optical scanning method is not limited to the conventional single beam scanning method, and a multi-beam scanning method in which the same scanned surface is simultaneously scanned with a plurality of light spots has been adopted.

  The photosensitive surface to be scanned is not limited to a single photoconductor, but a plurality of photoconductors are arranged along the path of the recording medium to which the toner image is transferred, and the toner images formed on each photoconductor are recorded in common There is a tandem color image forming apparatus that transfers images onto a sheet to obtain a synthetic image.

  Ideally, the scanning line that is the movement locus of the light spot on the surface to be scanned is linear in the main scanning direction (longitudinal direction of the photosensitive member). However, due to factors such as the characteristics of optical parts used in the optical scanning device and assembly accuracy, it is almost impossible to realize an ideal scanning line, and the actual scanning line has a bend and an inclination.

  If the scan line is bent or tilted, there is almost no practical problem in forming a monochromatic image by the single beam scanning method. This is because, in a single color image formed by the single beam scanning method, a minute bend in the scanning line is not actually visually recognized.

  Even in the multi-beam scanning method, if there is only one surface to be scanned, there is almost no influence on the image if the scanning lines have the same shape even if the scanning lines are bent or inclined. A problem with the multi-beam scanning method is when the scanning line spacing of a plurality of scanning lines changes. When the scanning line interval changes depending on the main scanning position, density unevenness occurs, resulting in streaks in the sub-scanning direction. When this streak occurs, the image quality is significantly reduced.

  In addition, when forming a color image with a tandem image forming apparatus, if the scanning lines on each photoconductor are not bent or tilted, color misregistration and color unevenness will occur in the superimposed color image. The image quality is impaired.

  The method of adjusting the light spot position can be corrected by adjusting the condensing position of the light spot that scans the surface to be scanned in the sub-scanning direction. Various proposals have also been made.

  For example, in an image forming apparatus of a tandem system, an electro-optical element that deflects laser light is arranged on the optical path of each laser light emitted from a plurality of optical scanning devices. Then, the amount of deviation of each color image is detected by the amount of deviation detection means, and the voltage applied to each electro-optic element is continuously changed according to the exposure timing of main scanning so that the amount of deviation falls within a predetermined range. And a method of correcting the tilt of the laser beam has been proposed (see, for example, Patent Document 1).

In a multi-beam scanning type or tandem type image forming apparatus, a liquid crystal deflecting element array arranged in the main scanning direction is arranged between the light deflecting means and the surface to be scanned. Then, a method has been proposed in which the converging position of the light spot on the surface to be scanned is adjusted in the sub-scanning direction to correct the bending of the scanning line, and further, the change in the light intensity of the light spot accompanying the correction is corrected. (For example, refer to Patent Document 2).
Japanese Patent Laid-Open No. 10-186255 JP 2004-045840 A

  However, in the above conventional method, it is necessary to continuously change the voltage applied to the electro-optical element according to the exposure timing, and the voltage to be applied is usually changed in synchronization with the image writing clock. In general, since the voltage applied to the electro-optic element is high and the image writing clock is high frequency, generation of high level electromagnetic radiation noise caused by driving high voltage at high frequency cannot be suppressed. In order to satisfy various standards of the optical scanning device, it is necessary to take measures against normal electromagnetic radiation noise caused by an image writing clock, and to take measures against high level electromagnetic radiation noise, a large amount of labor and cost are required.

  Further, in the other conventional methods described above, it is necessary to correct the amount of light with respect to the transmittance change due to the deflection angle of the laser beam, and the laser beam is formed between the electrodes because the laser beam sequentially passes through a number of transparent electrodes that are in close contact with each other. The scanning line shape cannot be corrected in the gap region.

  An object of the present invention is to provide an optical scanning device capable of correcting a scanning line shape without being affected by a gap region formed between electrodes while suppressing generation of high-level electromagnetic radiation noise. is there.

  In order to achieve the above object, the present invention provides a light source, a light deflection unit that scans a light beam emitted from the light source in a main scanning direction, a front light deflection unit, and an irradiation position of the scanned light beam. An electro-optic crystal structure that is disposed in the optical path between the photosensitive member forming the electrostatic latent image and deflects the light beam scanned by the light deflecting means in the sub-scanning direction by applying a voltage, and independent of the image writing signal Control means for controlling a voltage applied to the electro-optic crystal structure at a predetermined timing, and the electro-optic crystal structure has a substantially rectangular parallelepiped-shaped electro-optic crystal having a characteristic that a refractive index changes by voltage application. A common electrode attached to one surface of the electro-optic crystal perpendicular to the sub-scanning direction, and at least one gap attached to the other surface perpendicular to the sub-scanning direction. A plurality of electrodes arranged along the main scanning direction so as to form a light beam, and when the light beam scanned by the light deflection unit is projected onto the gap portion, the projection line of the light beam It traverses at least one of the two electrodes forming the part.

  According to the present invention, the control means controls the voltage applied to the electro-optic crystal structure at a predetermined timing independent of the image writing signal, and the electro-optic crystal structure has a characteristic that the refractive index changes with voltage application. A substantially rectangular parallelepiped electro-optic crystal, a common electrode attached to one surface of the electro-optic crystal perpendicular to the sub-scanning direction, and the other surface perpendicular to the sub-scanning direction. And a plurality of electrodes arranged along the main scanning direction so as to form at least one gap, and when the light beam scanned by the light deflecting means is projected onto the gap, the projection line of the light flux is Since at least one of the two electrodes forming the gap is crossed, the shape of the scanning line is corrected without being affected by the gap area formed between the electrodes while suppressing the generation of high-level electromagnetic radiation noise. It is possible.

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.
[Optical scanning device: FIG. 1]
FIG. 1 is a plan view schematically showing a configuration of an optical scanning device according to an embodiment of the present invention.

In FIG. 1, reference numeral 1 denotes a polygon mirror (also referred to as a rotating polygon mirror; light deflecting means). The polygon mirror 1 is a laser beam (light beam) emitted from a semiconductor laser 10 (light source) and imaged linearly by a collimator lens (not shown) and a cylindrical lens (not shown) in a main scanning direction (with a photoconductor). Scan in the longitudinal direction of a certain photosensitive drum. A scanning lens 2 forms an image of the laser beam scanned by the polygon mirror 1 as a predetermined spot on the surface to be scanned of the photosensitive drum 4. An electro-optic crystal structure 3 is disposed in the optical path between the polygon mirror 1 and the photosensitive drum 4 and deflects the light beam scanned by the polygon mirror 1 in the sub-scanning direction by applying a voltage.
[Electro-optic crystal structure: FIG. 2]
2A and 2B are diagrams schematically showing the configuration of the electro-optic crystal structure 3, wherein FIG. 2A is a block diagram and FIG. 2B is a plan view.

  2A and 2B, the electro-optic crystal structure 3 includes a substantially elongated electro-optic crystal (hereinafter referred to as “EO crystal”) 31 and both end faces perpendicular to the sub-scanning direction. And a pair of electrode portions 32 and 33 attached to the power source, and a power source (not shown) for applying a voltage between the electrode portions. The electrode portion 33 is configured by a common electrode P0 attached to one surface of the EO crystal 31 that is perpendicular to the sub-scanning direction, and the electrode portion 32 is perpendicular to the sub-scanning direction of the EO crystal 31. It comprises a plurality of electrodes P1 to P5 that are attached to the other surface and arranged along the main scanning direction so as to form a plurality of gaps B1 to B4. Since the number of electrodes is sufficiently smaller than the number of pixels in the main scanning direction (for example, about 7500 pixels in the case of 600 dpi), high-frequency noise corresponding to an image writing clock is generated even when a voltage is applied in a time division manner. There is no. D0 to D5 are driver circuits for applying a predetermined voltage to the electrodes P0 to P5. Reference numeral 34 denotes a control unit that controls a voltage applied between the pair of electrode units 32 and 33, and reference numeral 36 denotes a storage unit such as a memory that stores scanning line shape data and correction information corresponding to the scanning line shape data. The correction information is, for example, voltage data applied to the common electrode P0 and the plurality of electrodes P1 to P5 corresponding to the scanning line shape data.

  The pair of electrode portions 32 and 33 forms an electric field in the direction perpendicular to the path of the light beam passing through the EO crystal 31 inside the EO crystal 31. By applying a predetermined voltage to the pair of electrode portions 32 and 33 to generate an electric field in the EO crystal 31, a high-speed response of 1 μs or less (1 MHz or more) is exhibited. The electro-optic crystal structure 3 guides the light beam to the polygon mirror 53 by this high-speed electro-optic effect.

  An electro-optic crystal is a transparent crystal having a characteristic that its refractive index changes when a voltage is applied. The EO crystal 31 is a material made of, for example, K (potassium), Ta (tantalum), Nb (niobium), and O (oxygen), and is characterized by being capable of high-speed and wide-angle scanning. The EO crystal 31 may be a material made of Li (lithium), Nb (niobium), and O (oxygen).

  The positions of the semiconductor laser 10, the collimator lens, the cylindrical lens, the polygon mirror 1, the scanning lens 2, the optical crystal structure 3, and the photosensitive drum 4 are fixed. Therefore, the irradiation position of the laser beam on the photosensitive drum 4 also changes according to the change in the deflection angle of the laser beam. That is, the irradiation position of the laser beam on the photosensitive drum 4 changes according to the change in the voltage applied to the electro-optical element 3. Further, the EO crystal 31 largely deflects the light beam passing through the EO crystal 31 in the direction of the electric field in accordance with an increase in voltage applied to both ends thereof. Thereby, the scanning line shape on the surface to be scanned 4 is changed.

  The controller 34 applies a constant voltage (or ground) to the common electrode P0 via the driver circuit D0. At the same time, a plurality of electrodes P1 to P5 facing the common electrode P0 are supplied with voltages calculated individually based on the scanning line shape data stored in the storage means 101 and correction data corresponding to the scanning line shape data. Apply through circuits D1-D5.

  Here, no voltage is applied to the regions of the gaps B1 to B4, and the electric field strength generated in the EO crystal 31 in each of the regions of the gaps decreases in inverse proportion to the square of the distance from the adjacent electrode. The distance between adjacent electrodes (the width of the gap) in the plurality of electrodes P1 to P5 varies depending on the applied voltage, and the higher the applied voltage, the larger the interelectrode distance needs to be.

  In the present embodiment, gaps B1 to B4 are formed between the plurality of electrodes P1 to P5, and the plurality of electrodes P1 to P5 are separated by a predetermined distance according to the maximum voltage to be applied. Arranged. Further, each of the gaps B1 to B4 has a bent shape along the traveling direction of the laser beam (FIG. 2B). Thereby, when the laser beam L2 is projected onto the gap B1, the projection line of the laser beam L2 crosses at least one of the electrodes P1 and P2. Similarly, the projection line of the laser beam L3 crosses at least one of the electrodes P2 and P3, the projection line of the laser beam L4 crosses at least one of the electrodes P3 and P4, and the projection line of the laser beam L5. Crosses at least one of the electrodes P4 and P5, respectively.

  FIG. 3 is a diagram for explaining a method of correcting the scanning lines formed on the photosensitive drum 4 in FIG.

  In FIG. 3, the laser beam deflected by the polygon mirror 1 is scanned onto the photosensitive drum 4 via the scanning lens 2. At this time, the scanning line 4-A on the photosensitive drum 4 has a shape bent from the ideal position A in the sub-scanning direction. The control unit 34 calculates voltages V1 to V5 to be applied to the electrodes P1 to P5 based on the scanning linear data and the correction data stored in the storage unit 101, respectively. Then, the voltages V1 to V5 are applied to the plurality of electrodes P1 to P5 through the driver circuits D1 to D5 at a predetermined timing independent of the image writing signal (graph 4-B). The predetermined timing corresponds to, for example, when a predetermined time has elapsed since the start of use of the optical scanning device. In each region corresponding to the electrodes P1 to P5 in the EO crystal 31, an electric field corresponding to the individually calculated voltage is generated, and the laser light passing through the EO crystal 31 is sub-scanned according to the intensity of each electric field. Deflected in the direction. Thereby, the line segments 301a to 301e of the scanning line 4-A are corrected to a position close to the ideal position A like the line segments 306a to 306e of the scanning line 4-C.

  FIG. 4 is a partially enlarged view of the vicinity of the gaps B3 and B4 in FIG.

  In FIG. 4, the laser light L4 passing through the region of the gap B3 crosses at least one of the electrodes P3 and P4, and is thus deflected in the sub-scanning direction by a voltage applied to the electrodes P3 and / or P4. Further, since the laser beam L5 passing through the region of the gap B4 crosses at least one of the electrodes P4 and P5, it is deflected in the sub-scanning direction by the voltage applied to the electrodes P4 and / or P5. Thereby, the inflection point does not occur between the line segment 306c and the line segment 306d, and the line segment 306c and the line segment 306d are smoothly connected. Similarly, the inflection point does not occur between the line segment 306d and the line segment 306e, and the line segment 306d and the line segment 306e are smoothly connected. Since the laser beams L1 and L2 passing through the gaps B1 and B2 are deflected by the same method as described above, the description thereof is omitted.

  Therefore, the scanning line 4-A is corrected to a shape as shown in the scanning line 4-C as a whole. The scanning line 4-A in FIG. 3A has a large bent shape for the sake of explanation. The actual bend and inclination of the scanning line 4-A is about 0.1 mm to 0.2 mm as a whole, and the step of the scanning line in the region of the gaps B1 to B4 between the electrodes is about 0.01 mm. The corrected scanning line 4-C has a substantially linear shape at a position close to the ideal position A.

  According to the present embodiment, the control unit 34 controls the voltage applied to the electro-optic crystal structure 3 at a predetermined timing independent of the image writing signal. The electro-optic crystal structure 3 includes a substantially rectangular parallelepiped EO crystal 31 having a characteristic in which a refractive index changes when a voltage is applied, and a common electrode attached to one surface of the EO crystal 31 that is perpendicular to the sub-scanning direction. Has P0. Furthermore, it has electrodes P1 to P5 attached to the other surface perpendicular to the sub-scanning direction and arranged along the main scanning direction so as to form the gaps B1 to B4. When the light beam scanned by the polygon mirror 1 is projected onto each gap, the projection line of the light beam crosses at least one of the two electrodes forming each gap, thereby suppressing the generation of high-level electromagnetic radiation noise. To do. Furthermore, the shape of the scanning line 4-A can be corrected without being affected by the gaps B1 to B4 formed between the electrodes.

  FIG. 5 is a view showing a modification of the electro-optic crystal structure 3 in FIG. The electro-optic crystal structure in the present modification has the same configuration as that of the above-described embodiment, and the same components are denoted by the same reference numerals and redundant description is omitted, and different parts are described below. explain.

  In FIG. 3, the electro-optic crystal structure 50 includes a pair of electrode portions 52 and 33 attached to both end faces perpendicular to the sub-scanning direction. The electrode part 52 includes a plurality of electrodes P <b> 11 to P <b> 15 arranged to face the electrode part 33. Gaps B11 to B14 are formed between the plurality of electrodes P11 to P15, and the plurality of electrodes P11 to P15 are arranged at a predetermined distance according to the maximum voltage to be applied. Further, each gap portion of the gap portions B11 to B14 has a linear shape having a predetermined angle with respect to the traveling direction of the laser beam. That is, the gap B11 is formed so as not to be parallel to the laser beam L12 passing through the area of the gap B11. Thereby, when the laser beam L12 passing through the region of the gap B11 is projected onto the electrode surfaces of the electrodes P11 and P12, the projection line of the laser beam L12 crosses at least one of the electrode surfaces of the electrodes P11 and P12. Similarly, the projection lines of the laser beams L13 to L15 respectively include at least one of the electrode surfaces of the electrodes P12 and P13, at least one of the electrode surfaces of the electrodes P13 and P14, and at least one of the electrode surfaces of the electrodes P14 and P15. Cross.

  According to this modification, since the gaps B11 to B14 have a linear shape, the scanning line shape can be corrected using the electrodes P11 to P15 having a simple shape.

  Since the scanning line shape is unique to the optical scanning device, it is preferably measured by an image forming apparatus provided with the optical scanning device. However, it is necessary to provide a large number of measuring units corresponding to a large number of electrodes in the image forming apparatus, and there is a problem of arrangement and cost of the measuring units. Since the bending of the scanning line shape does not change greatly from the initial stage, an accurate scanning line shape is measured in advance at a measurement location equal to or more than the number of electrodes in the state of the optical scanning device alone, and the scanning line shape data is stored in the storage unit 36. You can memorize it. Further, the image forming apparatus may be configured to be able to measure the inclination of both ends of the scanning line as necessary.

  In the present embodiment, the scanning line shape data and the correction information are stored in the storage unit 36. However, the present invention is not limited to this, and the scanning line shape data and correction information may be labeled on the optical scanning device main body as numerical values or barcodes. As a result, even when the optical scanning device is replaced due to a failure or the like, the image forming apparatus can automatically read the correction information and correct the scanning line shape.

  In the present embodiment, the correction information stored in the storage unit 36 is voltage data applied to the common electrode P0 and the plurality of electrodes P1 to P5 corresponding to the scanning line shape data. However, the present invention is not limited to this, and correction distance data in the sub-scanning direction corresponding to the scanning line shape data may be used.

  In the present embodiment, the number of electrodes of the electrode portion 32 is five (P1 to P5), but is not limited thereto, and may be 10 to 20, or may be 100 or less. Good.

  In the present embodiment, the EO crystal 31 is a material composed of K, Ta, Nb, and O. However, when an electro-optic crystal having a large electro-optic constant (proportional coefficient of the refractive index change amount by applying an electric field) is used, the EO crystal 31 is applied. The voltage can be reduced to 1/10 or less of the conventional voltage. Thereby, the distance between electrodes can be reduced, and generation of electromagnetic radiation noise can be further suppressed.

  In the present embodiment, the photosensitive drum 4 is scanned by the polygon mirror 1, but the present invention is not limited to this, and a configuration in which the photosensitive drum is scanned by a galvano mirror or MEMS (Micro Electro Mechanical System) may be used.

  Another object of the present invention is to supply a storage medium storing a software program for realizing the functions of the above-described embodiments to an optical scanning device, and the computer (or CPU, MPU, etc.) of the optical scanning device stores the storage medium. This can also be achieved by reading and executing the program code stored in.

  In this case, the program code itself read from the storage medium realizes the functions of the above-described embodiment, and the program code and the storage medium storing the program code constitute the present invention.

  Examples of the storage medium for supplying the program code include a floppy (registered trademark) disk, a hard disk, a magneto-optical disk, a CD-ROM, a CD-R, a CD-RW, a DVD-ROM, a DVD-RAM, and a DVD. An optical disc such as RW or DVD + RW, a magnetic tape, a nonvolatile memory card, a ROM, or the like can be used. Alternatively, the program code may be downloaded via a network.

  By executing the program code read from the computer, not only the functions of the above-described embodiments are realized, but an OS (operating system) operating on the computer based on the instruction of the program code is actually used. It goes without saying that a case where the function of the above-described embodiment is realized by performing part or all of the processing and the processing is included.

  Further, after the program code read from the storage medium is written to a memory provided in a function expansion board inserted into the computer or a function expansion unit connected to the computer, the function expansion is performed based on the instruction of the program code. This includes a case where the CPU or the like provided in the board or the function expansion unit performs part or all of the actual processing, and the functions of the above-described embodiments are realized by the processing.

1 is a plan view schematically showing a configuration of an optical scanning device according to an embodiment of the present invention. It is a figure which shows the structure of an electro-optic crystal structure roughly, (a) is a block diagram, (b) is a top view. FIG. 2 is a diagram illustrating a method for correcting a scanning line formed on the photosensitive drum in FIG. 1. FIG. 4 is a partially enlarged view near gaps B3 and B4 in FIG. 3. FIG. 3 is a diagram showing a modification of the electro-optic crystal structure in FIG. 2.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Polygon mirror 2 Scan lens 3 Electro-optic crystal structure 4 Photosensitive drum 31 Electro-optic crystal 32, 33 A pair of electrode part P0 Common electrode P1-P5 Several electrode D0-D5 Driver circuit 34 Control part 36 Memory | storage part

Claims (5)

An optical path between a light source, a light deflecting unit that scans a light beam emitted from the light source in a main scanning direction, and a photosensitive member that forms an electrostatic latent image at an irradiation position of the scanned light beam. And an electro-optic crystal structure that deflects a light beam scanned by the light deflecting means in the sub-scanning direction by applying a voltage, and is applied to the electro-optic crystal structure at a predetermined timing independent of an image writing signal. Control means for controlling the voltage to be
The electro-optic crystal structure includes a substantially rectangular parallelepiped-shaped electro-optic crystal having a characteristic in which a refractive index changes when a voltage is applied, and a common attached to one surface of the electro-optic crystal that is perpendicular to the sub-scanning direction. An electrode, and a plurality of electrodes attached to the other surface perpendicular to the sub-scanning direction and arranged along the main scanning direction so as to form at least one gap,
An optical scanning device characterized in that, when a light beam scanned by the light deflecting means is projected onto the gap, the projection line of the light beam crosses at least one of the two electrodes forming the gap.   2. The optical scanning device according to claim 1, wherein the control unit applies individual voltages, which are predetermined according to a scanning line shape formed by scanning of the light deflecting unit, to the plurality of electrodes. .   3. The optical scanning device according to claim 1, further comprising storage means for storing shape data of scanning lines formed by scanning of the light deflection means and correction information corresponding to the shape data.   4. The optical scanning device according to claim 3, wherein the correction information is voltage data applied to the common electrode and the plurality of electrodes corresponding to the shape data.   5. The optical scanning device according to claim 1, wherein the electro-optic crystal is made of potassium, tantalum, niobium, and oxygen.

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