JP4827754B2 - Optical scanning device - Google Patents

Description

  The present invention relates to an optical scanning device provided in an image forming apparatus such as a digital copying machine, a laser printer, a laser plotter, and a laser facsimile.

  In an optical scanning device used in an optical writing unit or the like of an image forming apparatus, a method for increasing the rotational speed of a polygon mirror (rotating polygonal mirror) that is a deflecting means can be cited as a means for improving the recording speed. However, with this method, the durability, noise, vibration, laser modulation speed, and the like of the motor that drives the polygon mirror are problematic, so there is a limit to the improvement in recording speed. In view of this, a multi-beam scanning device has been proposed that improves the recording speed by emitting a plurality of laser beams at a time and simultaneously exposing and scanning a photosensitive drum as an image carrier with a plurality of beams.

  Conventionally, as a kind of multi-beam scanning device, a multi-beam scanning device using a plurality of single semiconductor lasers as light sources and using a light source device that synthesizes a plurality of laser beams emitted from each of them is proposed. However, in such a multi-beam scanning device, it is necessary to combine a plurality of laser beams emitted from semiconductor lasers arranged independently and write them on the photosensitive drum at a predetermined pitch interval. For this reason, it is difficult to maintain a constant pitch interval that requires an accuracy of error ± several microns or less. In order to solve this problem, a method has been proposed in which the pitch interval is maintained by eliminating the influence of temperature variation, temporal variation, and mechanical vibration.

  FIG. 9 is a diagram schematically showing a configuration of a conventional multi-beam scanning apparatus.

  In FIG. 9, the multi-beam scanning device 20 includes two semiconductor lasers 11a and 11b that respectively emit two laser beams, and liquid crystal elements 43a and 43b that deflect each laser beam by a minute angle (several minutes to several tens of minutes). And a beam pitch detection sensor 41 for detecting the pitch interval of the laser light outside the scanning area (outside the image area) of the photosensitive drum 16. The beam pitch detection sensor 41 is disposed at a position optically equivalent to the surface of the photosensitive drum 16.

  In this multi-beam scanning device 20, the two laser beams 21a and 21b emitted from the two semiconductor lasers 11a and 11b and emitted from the coupling lenses 12a and 12b, respectively, are polygon mirrors that are deflectors by the action of the cylindrical lens 13. 14 is formed as a line image (imaged in the sub-scanning direction and long in the main scanning direction) on the deflecting / reflecting surface, and the scanning optical system 15 (first scanning lens 15-1, second scanning lens 15-2). As a result, the surface to be scanned of the photosensitive drum 16 as an image carrier is scanned as a beam spot. Here, “main scanning direction” and “sub-scanning direction” mean a direction in which the beam spot is scanned on the surface to be scanned and a direction orthogonal thereto. The two semiconductor lasers 11a and 11b are controlled by the semiconductor laser control unit 46 corresponding to the image data and modulated by the semiconductor laser driving IC 47, and the photosensitive drum 16 is moved by the two laser beams 21a and 21b. Scan. The liquid crystal elements 43a and 43b realize the deflection of the optical path by utilizing the refractive index distribution in the liquid crystal layer generated by applying a voltage to the elements.

  The multi-beam scanning device 20 controls the deflection angles of the liquid crystal elements 43a and 43b according to the detection result of the beam pitch detection sensor 41, and keeps a predetermined beam pitch interval. A deviation between the detection result of the beam pitch detection sensor 41 and a desired scanning line interval is calculated by the liquid crystal element control unit 44, and based on correction data for correcting the deviation, the liquid crystal element driving IC 45 performs the liquid crystal element 43a, 43b is driven.

In addition to the beam pitch detection sensor 41, when a temperature detection sensor (not shown) for detecting the temperature in the apparatus is provided, the relationship between the temperature change in the apparatus and the change in the scanning line interval can be simulated or experimented in advance. The liquid crystal elements 43a and 43b are controlled / driven using a correction table created based on the relationship between the temperature change in the apparatus and the change in the scanning line interval. Thereby, the scanning line interval can be kept constant (see, for example, Patent Document 1).
JP 2005-292349 A

  However, in the multi-beam scanning apparatus as described above, since the beam pitch is detected at the scanning start position, the beam pitch fluctuates while scanning from the scanning start position to the end position in the main scanning direction (while scanning one line). Cannot be detected. Therefore, when a short-period pitch variation occurs due to mechanical vibration or the like, the beam pitch cannot be kept constant, and the laser beam cannot be irradiated to an accurate position on the photosensitive drum.

  In addition, since the multi-beam scanning device uses a liquid crystal element (approximately several hundred Hz) with a low response frequency for deflecting the laser beam, the pitch variation is corrected even when a pitch variation of 1 kHz or more can be detected. Can not do it. In particular, drive units such as printers and copiers have a large number of rotating bodies (rollers, etc.) of several hundred to several thousand rpm, and vibrations of 1 kHz or more are generated from gears used for the drive mechanism. It is difficult to correct the fluctuation. In addition, in the configuration of the multi-beam scanning device as described above, it is not possible to correct the irradiation position shift caused by the eccentricity of the photosensitive drum.

  An object of the present invention is to provide an optical scanning device capable of irradiating a laser beam at an accurate position on a photosensitive drum.

In order to achieve the above object, an optical scanning device according to the present invention includes a plurality of light sources, a light deflection unit that scans a light beam emitted from the plurality of light sources, a plurality of light sources, and the light deflection unit. A plurality of electro-optic crystal structures that are provided in each of the optical paths and deflect the light beams emitted from the plurality of light sources by applying a voltage, and the positions of the plurality of light sources. A position detection sensor that detects relative positions of the plurality of light sources by detecting fluctuations, and a calculation unit that calculates a relative irradiation position change of the plurality of light sources based on a detection result by the position detection sensor ; And control means for controlling the voltage applied to the plurality of electro-optic crystal structures in accordance with the irradiation position change calculated by the calculating means.

According to the present invention , even when a pitch fluctuation of a short period of 1 ms or less occurs due to mechanical vibration or the like, the electro-optic crystal structure showing a high-speed response is corrected so as to keep the beam pitch of a plurality of light beams constant. Therefore, the light beam can be irradiated to an accurate position.

[Image forming apparatus: FIG. 1]
Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

  FIG. 1 is a cross-sectional view schematically showing a configuration of an image forming apparatus provided with an optical scanning device according to an embodiment of the present invention.

  In FIG. 1, an image forming apparatus 104 includes a printer controller 111 and an optical scanning device 100, and is connected to an external device 117 such as a personal computer that transmits and receives data to and from the image forming apparatus 104. When the code data Dc is input from the external device 117, the code data Dc is converted into image data (dot data) Di by the printer controller 111 in the image forming apparatus 104, and the optical scanning device (multi-beam scanning optical system) 100. Is input. The optical scanning device 100 emits a laser beam 63 modulated in accordance with the image data Di, and the laser beam 63 moves the photosensitive surface of the photosensitive drum 101 in the main scanning direction (the depth direction in the cross-sectional view of FIG. 1, ie, the photosensitive drum). In the longitudinal direction).

  The photosensitive drum 101 is rotated clockwise by the driving force of the motor 115. With this rotation, the photosensitive surface of the photosensitive drum 101 moves with respect to the laser beam 63 in the sub-scanning direction orthogonal to the main scanning direction. Above the photosensitive drum 101, a charging roller 102 for uniformly charging the surface of the photosensitive drum 101 is provided so as to contact the surface. By irradiating the surface of the photosensitive drum 101 charged by the charging roller 102 with the laser beam 63, an electrostatic latent image is formed on the surface of the photosensitive drum 101.

  This electrostatic latent image is developed as a toner image by a developing unit 107 that is positioned downstream of the irradiation position of the laser beam 63 with respect to the rotation direction of the photosensitive drum 101 and is disposed so as to contact the photosensitive drum 101. .

  The toner image developed by the developing unit 107 is transferred onto a sheet 112 as a transfer material by a transfer roller 108 disposed below the photosensitive drum 101. The paper 112 is stored in the paper cassette 109. A paper feed roller 110 is provided at the end of the paper cassette 109, and feeds the paper 112 in the paper cassette 109 into the transport path. As described above, the sheet 112 on which the unfixed toner image has been transferred is conveyed to the fixing device behind the photosensitive drum 101 (left side in FIG. 2) in the conveying direction. The fixing device includes a fixing roller 113 having a fixing heater (not shown) therein and a pressure roller 114 pressed against the fixing roller. The unfixed toner image is fixed. Further, a paper discharge roller 116 is disposed behind the fixing roller 113 in the transport direction, and the paper discharge roller 116 discharges the paper 112 on which the unfixed toner image is fixed out of the image forming apparatus 104.

[Optical scanning device: FIGS. 2 and 3]
2 is a block diagram schematically showing the configuration of the optical scanning device 100 in FIG. 1, wherein (a) is a plan view and (b) is a cross-sectional view. FIG. 3 is a block diagram schematically showing the configuration of the optical scanning device 100 in FIG.

  As shown in FIGS. 2A and 2B and FIG. 3, the optical scanning device 100 includes two laser irradiation devices (light sources) 50a and 50b and light beams (laser light) emitted from the laser irradiation devices 50a and 50b. ) Is provided. In addition, a first fθ lens 54 and a second fθ lens 55 are provided to form an image of the light beam scanned by the polygon mirror 53 on the photosensitive drum 101. Further, the electro-optic crystal structures 60a and 60b are provided in the respective optical paths between the laser irradiation devices 50a and 50b and the polygon mirror 53, and the light beams emitted from the laser irradiation devices 50a and 50b are sub-scanned by applying a voltage. Deflect in the direction. Further, the MEMS acceleration sensors 51a and 51b and the MEMS acceleration sensors 51g and 51f (first ones) which are attached to both ends of the laser irradiation apparatus 50a and the laser irradiation apparatus 50b and detect a relative position variation between the laser irradiation apparatuses 50a and 50b. 1 position detecting means). Further, based on the detection results of the MEMS acceleration sensors 51a, 51b, 51g, 51f and the data table 73 stored in advance, the fluctuation for predicting the relative irradiation position change of the two light beams irradiated from the laser irradiation devices 50a, 50b. A prediction circuit 71 is provided.

The fluctuation prediction circuit 71 includes an arithmetic circuit 70a, an arithmetic circuit 70b, and an arithmetic circuit 70c.
The arithmetic circuit 70a calculates the irradiation position of the light beam irradiated from the laser irradiation device 50a based on the detection results of the acceleration sensors 51a and 51b. The arithmetic circuit 70b calculates the irradiation position of the light beam irradiated from the laser irradiation device 50b based on the detection results of the acceleration sensors 51f and 51g. The arithmetic circuit 70c calculates fluctuations in the irradiation position interval d of the two light beams based on the calculation results of the arithmetic circuits 70a and 70b and the data in the data table 73.

  Further, the optical scanning device 100 includes a MEMS acceleration sensor 51 d that is attached to one end surface of the photosensitive drum 101 and detects a change in the peripheral speed of the photosensitive drum 101. Further, MEMS acceleration sensors 51 c and 51 h attached on the support side plates 52 a and 52 b that support the photosensitive drum 101, and a MEMS acceleration sensor 51 e attached to the side surface of the casing of the optical scanning device 100 are provided. The MEMS acceleration sensors 51 c, 51 d, 51 e, 51 h (second position detection means) detect relative position fluctuations between the photosensitive drum 101 and the optical scanning device 100. The optical scanning device 100 also changes the irradiation position of the two light beams irradiated from the laser irradiation devices 50a and 50b based on the detection results of the MEMS acceleration sensors 51c, 51d, 51e, and 51h and the data table 74 stored in advance. And an arithmetic circuit 70d.

  Further, the optical scanning device 100 determines a correction amount for the irradiation position of the two light beams irradiated from the laser irradiation devices 50a and 50b based on the prediction result of the fluctuation prediction circuit 71 and the calculation result of the calculation circuit 70d. A determination circuit 72 is provided. Furthermore, a control circuit 75 that controls the voltage applied to the electro-optic crystal structures 60a and 60b according to the correction amount determined by the correction amount determination circuit 72 is provided. The control circuit 75 is electrically connected to the electro-optic crystal structures 60a and 60b.

  The laser beams 63a and 63b emitted from the laser irradiation devices 50a and 50b are deflected by a polygon mirror 53 rotated by a driving unit (not shown) and pass through a first fθ lens 54 and a second fθ lens 55 having fθ characteristics. Then, the light enters the mirror 56. The two laser beams 63a and 63b reflected by the mirror 56 in the direction of the photosensitive drum 101 are irradiated to predetermined positions on the photosensitive drum 101 at a distance d in the sub-scanning direction (see FIG. 2B). ). Further, the irradiation position is main-scanned from one end portion (end portion on the support side plate 52a side) of the photosensitive drum 101 to the other end portion (end portion on the support side plate 52b side) as the polygon mirror 53 rotates. Move in the direction. Thereafter, the movement in the main scanning direction from one end portion (end portion on the support side plate 52a side) to the other end portion is repeated again.

The photosensitive drum 101 is rotated (clockwise in FIG. 3) by driving means (not shown). Therefore, the laser beams 63a and 63b emitted from the laser irradiation devices 50a and 50b scan the surface of the photosensitive drum 101 two lines at a time, and the interval between the two lines scanned last time and the two lines scanned this time is constant. Scan while keeping. As a result, the optical scanning device 100 records an image as an electrostatic latent image on the photosensitive drum 101.
[Laser irradiation device: Fig. 4]
FIG. 4 is a cross-sectional view showing the configuration of the laser irradiation apparatus 50a in FIG. The laser irradiation device 50b is basically the same in configuration as the laser irradiation device 50a, and therefore the description thereof is omitted.

  In FIG. 4, the laser irradiation apparatus 50 a includes a long laser irradiation apparatus main body 151. The MEMS acceleration sensor 51a is attached to the side surface of the laser irradiation apparatus main body 151, and is further attached to the end portion on the side where the semiconductor laser 58a is disposed. The MEMS acceleration sensor 51b is attached to the side surface of the laser irradiation apparatus main body 151, and is further attached to the end opposite to the end where the semiconductor laser 58a is disposed.

  The laser irradiation devices 50a and 50b pass the laser light emitted from the semiconductor lasers 58a and 58b through the collimator lenses 59a and 59b and the electro-optic crystal structures 60a and 60b, and then emit the laser light to the outside. The semiconductor laser 58a, the collimator lens 59a, the electro-optic crystal structure 60a, and the MEMS acceleration sensors 51a and 51b constitute a laser irradiation device 50a. Similarly, the semiconductor laser 58b, the collimator lens 59b, the electro-optic crystal structure 60b, and the MEMS acceleration sensors 51f and 51g constitute a laser irradiation device 50b.

  The electro-optic crystal structure 60a is provided in the laser irradiation apparatus main body 151, and is formed on a rectangular parallelepiped electro-optic crystal (hereinafter referred to as “EO crystal”) 65a and both end faces perpendicular to the main scanning direction. A pair of attached electrodes 61a and 62a and a power source (not shown) for applying a voltage between the pair of electrodes 61a and 62a are provided. The pair of electrodes 61a and 62b form an electric field in the direction perpendicular to the path of the light beam passing through the EO crystal 65a inside the EO crystal 65a. By applying a predetermined voltage to the pair of electrodes 61a and 62b to generate an electric field in the EO crystal 65a, a high-speed response of 1 μs or less (1 MHz or more) is exhibited. In this embodiment, the frequency of the fluctuation phenomenon of the irradiation position to be corrected is about several k to several hundred kHz, although it depends on the writing speed of the optical scanning device 100 and the response speed of the MEMS acceleration sensor. It is possible to cope with the response speed of. The electro-optic crystal structure 60 a guides the light beam to the polygon mirror 53 by this high-speed electro-optic effect.

Here, the electro-optic crystal is a transparent crystal having a characteristic that the refractive index changes when a voltage is applied. The EO crystal 65a is a so-called KTN crystal composed of potassium, tantalum, niobium and oxygen, and has a feature that high-speed and wide-angle scanning is possible. The EO crystal 65a is preferably a material selected from the group consisting of lithium niobate (LiNb0 ₃ ), lithium thalate (LiTa0 ₃ ), and barium titanate (BaTi0 ₃ ). Further, the EO crystal 65a largely deflects the light beam passing through the EO crystal 65a in the direction of the electric field in accordance with an increase in voltage applied to both ends thereof.

  The laser irradiation device 50a corrects the irradiation position on the photosensitive drum 101 by deflecting the emission angle of the laser beam in the sub-scanning direction by the EO crystal 65a having the electro-optic effect as described above. The electro-optic crystal structure 60a makes it possible to adjust the emission angle of the laser beam 63a emitted from the semiconductor laser 58a within the range of 63a ′ to 63a ″ in FIG. 4 by utilizing the properties of the EO crystal 65a.

  The MEMS acceleration sensors 51a to 51d and 51e to 51h detect accelerations used for calculating fluctuations in the irradiation position interval d of the laser light on the photosensitive drum 101 and deviations in the irradiation positions.

[Acceleration waveform detected by MEMS acceleration sensor: FIG. 5]
5A and 5B are diagrams showing acceleration waveforms detected by the MEMS acceleration sensors in FIG. 2. FIG. 5A shows a waveform detected by the MEMS acceleration sensor 51e, and FIG. 5B shows a waveform detected by the MEMS acceleration sensor 51d. The detected waveform is shown, and (c) shows the waveform detected by the MEMS acceleration sensor 51c.

  5A to 5C, for example, if the MEMS acceleration sensor 51c mounted on the photosensitive drum 101 detects the acceleration waveform B as shown in FIG. 5B, the surface of the photosensitive drum 101 is detected. The positional deviation of (indicating the deviation between the surface movement in the case of ideally rotating smoothly and the actual movement) is represented by a value obtained by double integration of this acceleration with respect to time t. Further, the fluctuation between the scanning device 100 and the rotation center position of the photosensitive drum 101 is represented by a differential waveform between the acceleration waveform A detected by the MEMS acceleration sensor 51e and the acceleration waveform C detected by the MEMS acceleration sensor 51c. . By adding the positional deviation of the surface of the photosensitive drum 101 thus obtained and the positional fluctuations of the optical scanning device 100 and the photosensitive drum rotating shaft, the deviation amount of the irradiation position of the laser beam can be calculated.

  6A and 6B are diagrams showing acceleration waveforms detected by the MEMS acceleration sensors in FIG. 4. FIG. 6A is an acceleration waveform detected by the MEMS acceleration sensor 51a, and FIG. 6B is an MEMS acceleration sensor 51b. Is an acceleration waveform detected by

  4 and 6 (a) and 6 (b), the fluctuation of the inclination of the optical axis of the laser irradiation apparatus 50a can be obtained from the differential waveform of the acceleration waveforms D and E detected by the MEMS acceleration sensors 51a and 51b. . That is, when the position of the laser irradiation device 50a is changed due to mechanical vibration or the like, the optical axis of the laser light fluctuates so as to be inclined in the (+) or (−) direction (sub-scanning direction) in FIG. , 51b based on the detected waveforms (acceleration waveforms D and E). And the fluctuation | variation of irradiation position space | interval d can be calculated | required by calculating | requiring the relative angle fluctuation | variation of the laser beams 63a and 63b from the fluctuation | variation of the inclination of the optical axis of the laser irradiation apparatuses 50a and 50b calculated | required in this way. .

  The MEMS acceleration sensor 51 used in the present embodiment has a feature that it is miniaturized using the MEMS technology and can respond at high speed. The response frequency of a general acceleration sensor is only several tens to several hundreds Hz, and the response frequency is too low to predict fluctuations in the optical axis of an optical scanning device that writes several thousand lines of laser light per second. On the other hand, the MEMS acceleration sensor can follow a transient vibration phenomenon because the vibrator for detecting acceleration is very small and light. As a result, the MEMS acceleration sensor can realize a high-speed response of several tens of kHz or more, and is optimal for the acceleration sensor of the present invention. Details of the MEMS acceleration sensor will be described below.

  First, MEMS is an abbreviation of “Micro Electro Mechanical System”, and is a technique for forming a micro mechanical structure together with an electric circuit by using an exposure process used in semiconductor manufacturing. By using such MEMS technology, it is possible to manufacture extremely small sensors and actuators in millimeters that have been impossible in the past at an extremely low cost. Therefore, the MEMS acceleration sensor can easily secure a mounting space. Moreover, since the acceleration applied to a to-be-detected body can be detected directly as long as it contacts the to-be-detected body, the range which can be attached is wide. In addition, unlike the prior art, there is no need to provide a stay for holding the beam pitch sensor in a predetermined direction.

Such an acceleration sensor using the MEMS technology has already been widely put into practical use. For example, Japanese Patent Application Laid-Open No. 05-5750, Japanese Patent Application Laid-Open No. 05-34370, Japanese Patent Application Laid-Open No. 06-331648, and the like. The structure is disclosed. The MEMS acceleration sensor disclosed in Japanese Patent Laid-Open No. 06-331648 will be described below.
[Configuration of MEMS acceleration sensor: FIG. 7]
7A and 7B are diagrams schematically showing the configuration of the MEMS acceleration sensor 51, where FIG. 7A is a plan view, and FIG. 7B is a cross-sectional view taken along line JJ in FIG. (C) is a figure explaining the manufacturing method of the MEMS acceleration sensor 51. FIG.

  7A to 7C, 51 indicates a MEMS acceleration sensor (unit acceleration sensor), 81 indicates a glass substrate as an insulating substrate, and a fixing portion 82 made of a silicon material is provided on the glass substrate 81. A movable portion 83 is formed. The fixed portion 82 and the movable portion 83 constitute a detection portion that detects acceleration, and the fixed portion 82 and a support portion 87 of the movable portion 83 described later constitute an output electrode that transmits an output signal of the MEMS acceleration sensor to the outside. To do. Further, the glass substrate 81 is formed with a rectangular recess 81A so that the mass portion 84 provided with the movable comb-like electrode 85 can be displaced in the arrow K direction (direction in which acceleration is applied).

  The fixed portion 82 includes a pair of fixed-side comb-like electrodes 86 as fixed electrodes that are disposed in the vicinity of the end portion of the glass substrate 81 and are provided on inner surfaces facing each other. The pair of fixed-side comb-like electrodes 86 includes a plurality (for example, five) of thin plate-like electrode plates 86 </ b> A that are projected and formed toward a mass portion 84 to be described later.

  The movable portion 83 includes a support portion 87 fixed at two positions on the front and rear sides of the glass substrate 81, a mass portion 84 supported by the support portion 87 via a thin plate-like beam 88, and a movable electrode provided on the mass portion 84. As a pair of movable side comb-like electrodes 85. The pair of movable side comb-like electrodes 85 includes a plurality of (for example, five) thin plate-like electrode plates 85A formed to protrude toward the thin plate-like electrode plate 86A.

  A minute gap is formed between the electrode plate 85A of the movable comb electrode 85 and the electrode plate 86A of the fixed comb electrode 86 in the direction of arrow K in FIG. When receiving acceleration in the direction of arrow K, the amount of minute gap changes. The fixed part 82 and the movable part 83 are connected to an amplifier 89.

  When acceleration in the direction of arrow K is applied to the MEMS acceleration sensor 51, the amount of minute gap between the electrode plate 85A and the electrode plate 86A changes, and the change in the amount of gap is amplified / amplified by the amplifier 89 as a change in capacitance. Output to the outside. The electrode plates 85A and 86A of the MEMS acceleration sensor 51 are electrically connected in parallel, and the acceleration is detected from the total capacitance obtained by adding the capacitance between the electrode plates 85A and 86A. Thereby, detection sensitivity and detection accuracy can be improved.

  Next, a method for manufacturing the MEMS acceleration sensor 51 will be described.

  First, a masking / etching process is performed on a silicon wafer having a diameter of 7.5 to 15.5 (cm) and a thickness of about 300 μm to form a plurality of mass portions 84, an electrode plate 85A, an electrode plate 86A, and a fixing portion 82. In addition, a glass etching process is performed on a disk-shaped glass substrate having the same size as the silicon wafer to form a plurality of recesses 81A.

  Next, the glass substrate and the silicon wafer are anodically bonded, and a plurality of unit acceleration sensors are formed on the glass substrate as shown in FIG. Thereafter, a plurality of acceleration sensors (acceleration sensor group) on the glass substrate are cut into the size of a chip (about several mm square) to produce a plurality of MEMS acceleration sensors 51.

  Thereby, the MEMS acceleration sensor 51 can be manufactured in units of several tens at the same time in one manufacturing process, and can be manufactured in a small size / light weight. It is also possible to simultaneously form the amplifier 89 of FIG. 7A on the glass substrate 81 using a conventional semiconductor manufacturing technique.

[Flowchart showing irradiation position correction processing: FIG. 8]
FIG. 8 is a flowchart showing an irradiation position correction process for correcting the irradiation position of the laser beam.

  In FIG. 8, first, when an instruction to start correction is input by an input unit (not shown) provided in the image forming apparatus 104, the arithmetic circuit 70a in the fluctuation prediction circuit 71 causes a difference waveform between the acceleration sensor 51a and the acceleration sensor 51b. In addition to calculating α, the arithmetic circuit 70b calculates a differential waveform β between the acceleration sensor 51f and the acceleration sensor 51g (step S801).

  Next, the arithmetic circuit 70c in the fluctuation prediction circuit 71 calculates the difference waveform γ between the difference waveform α and the difference waveform β, refers to the data in the data table 73, and applies the laser beam 63a and the laser beam 63b. The variation of the position interval d is calculated (step S802). Here, the data table 73 is a database of the relationship between the detected waveform of the acceleration sensor and the actual angle fluctuation, and is obtained by simulation or experiment and stored in advance.

  On the other hand, the arithmetic circuit 70d calculates a differential waveform δ between the acceleration sensor 51e and the acceleration sensor 51c, and obtains a relative position variation between the optical scanning device 100 and the support side plate 52a that supports the photosensitive drum 101. The arithmetic circuit 70d calculates a differential waveform ε between the acceleration sensor 51e and the acceleration sensor 51h, and obtains a relative position variation between the optical scanning device 100 and the support side plate 52b (step S803). Next, the detected waveforms of the acceleration sensor 51d attached to the photosensitive drum are added to the differential waveforms δ and ε obtained in step S803 (step S804).

  The arithmetic circuit 70d refers to each added waveform calculated in step S804 and the data in the data table 74, and calculates an irradiation position shift amount when the optical scanning device 100 irradiates the photosensitive drum with the laser light (step S70). S805). Here, the data table 74 is a database of the relationship between each added waveform calculated in step S804 and the actual irradiation position deviation, and is obtained by simulation or experiment and stored in advance.

  Next, the correction amount determination circuit 72 applies a voltage to the electro-optic crystal structures 60a and 60b based on the variation of the irradiation position interval d calculated in step S802 and the irradiation position deviation calculated in step S805. That is, the deflection angles of the electro-optic crystal structures 60a and 60b are determined (step S806). The control circuit 75 applies the voltages determined by the correction amount determination circuit 72 to the electro-optic crystal structures 60a and 60b, respectively, and corrects the irradiation positions of the laser beams 63a and 63b (step S807). Thereafter, it is determined whether or not the image forming operation is finished (step S808). If the image forming operation is not finished, the process returns to step S801, and if finished, this process is finished.

  According to the present embodiment, the optical scanning device 100 includes two laser irradiation devices 50a and 50b, a polygon mirror 53 that scans light beams emitted from the laser irradiation devices 50a and 50b, and laser irradiation devices 50a and 50b. Electro-optical crystal structures 60a and 60b that are provided in each optical path between the polygon mirror 53 and deflect light beams emitted from the laser irradiation devices 50a and 50b in the sub-scanning direction by voltage application, and the laser irradiation devices 50a and 50a. The irradiation positions of the laser irradiation apparatuses 50a and 50b based on the detection results of the MEMS acceleration sensors 51a, 51b, 51g and 51f, and the MEMS acceleration sensors 51a and 51b and the MEMS acceleration sensors 51g and 51f that detect the relative position of the 50b. An arithmetic circuit 70c that calculates the variation of the interval d, and between the irradiation positions calculated by the arithmetic circuit 70c and a control circuit 75 that controls the voltage applied to the electro-optic crystal structures 60a and 60b according to the fluctuation of d, even if a short period pitch fluctuation of 1 ms or less occurs due to mechanical vibration or the like. The electro-optic crystal structures 60a and 60b exhibiting a high-speed response of 1 μs or less (1 MHz or more) can be corrected so as to keep the irradiation position interval d of the two light beams constant, so that the laser light is transferred onto the photosensitive drum 101. It is possible to irradiate the exact position of

  The optical scanning device 100 includes MEMS acceleration sensors 51c, 51e, and 51h that detect relative positional fluctuations of the optical scanning device 100 main body and the photosensitive drum 101, and MEMS acceleration sensors that detect changes in the peripheral speed on the surface of the photosensitive drum 101. 51d, based on the detection results of the MEMS acceleration sensors 51c, 51e, 51h and the MEMS acceleration sensor 51d, the arithmetic circuit 70d for calculating the deviation amount of the irradiation position of the laser irradiation devices 50a, 50b, and the arithmetic circuit 70d And a control circuit 75 that controls the voltage applied to the electro-optic crystal structures 60a and 60b in accordance with the amount of deviation of the irradiation position. In addition, the electro-optic crystal structures 60a and 60b can shift the irradiation positions of the laser irradiation devices 50a and 50b. Can positively be, the laser beam can be irradiated in the correct position on the photosensitive drum 101 with.

  In the present embodiment, the electro-optic crystal structure 60 is provided in the optical path between the diaphragm member 3 and the polygon mirror 53, but the present invention is not limited to this, and between the laser diode 1 and the polygon mirror 53. It may be provided in the optical path.

  In the above embodiment, the photosensitive drum 101 is scanned by the polygon mirror 53. However, 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 that implements the functions of the above-described embodiments to a laser scanning apparatus, and the computer (or CPU, MPU, etc.) of the laser scanning apparatus 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 cross-sectional view schematically showing a configuration of an image forming apparatus provided with an optical scanning device according to an embodiment of the present invention. FIG. 2 is a block diagram schematically showing the configuration of the optical scanning device in FIG. 1, wherein (a) is a plan view and (b) is a cross-sectional view. FIG. 2 is a block diagram schematically showing the configuration of the optical scanning device in FIG. 1. It is sectional drawing which shows the structure of the laser irradiation apparatus in FIG. It is a figure which shows the acceleration waveform detected by each MEMS acceleration sensor in FIG. 2, (a) shows the waveform detected by the MEMS acceleration sensor 51e, (b) shows the waveform detected by the MEMS acceleration sensor 51d. (C) shows the waveform detected by the MEMS acceleration sensor 51c. It is a figure which shows the acceleration waveform detected by each MEMS acceleration sensor in FIG. 4, (a) is an acceleration waveform detected by the MEMS acceleration sensor 51a, (b) is detected by the MEMS acceleration sensor 51b. It is an acceleration waveform. It is a figure which shows the structure of a MEMS acceleration sensor roughly, (a) is a top view, (b) is sectional drawing in alignment with line JJ of FIG. 7 (a), (c) is MEMS. It is a figure explaining the manufacturing method of the acceleration sensor 51. FIG. It is a flowchart which shows the irradiation position correction process which correct | amends the irradiation position of a laser beam. It is a figure which shows schematically the structure of the conventional multi-beam scanning apparatus.

Explanation of symbols

DESCRIPTION OF SYMBOLS 100 Optical scanning apparatus 50a, 50b Laser irradiation apparatus 53 Polygon mirror 54 1st f (theta) lens 55 2nd f (theta) lens 60a, 60b Electro-optic crystal structure 51a-51h MEMS acceleration sensor 71 Fluctuation prediction circuit 70a, 70b, 70c, 70d Arithmetic circuit 72 Correction amount determination circuit 75 Control circuit

Claims (6)

Multiple light sources;
Light deflecting means for scanning light beams emitted from the plurality of light sources;
A plurality of electro-optic crystal structures that are provided in each optical path between the plurality of light sources and the light deflecting unit and deflect light beams emitted from the plurality of light sources by voltage application;
A position detection sensor that is attached to each of the plurality of light sources and detects a relative position of the plurality of light sources by detecting a positional variation of each of the plurality of light sources;
An arithmetic means for calculating a relative irradiation position change of the plurality of light sources based on a detection result by the position detection sensor ;
An optical scanning apparatus comprising: a control unit that controls a voltage applied to the plurality of electro-optic crystal structures according to an irradiation position change calculated by the calculation unit. The position detection sensor is an acceleration sensor,
Said computing means, said analyzing each of the detection value of the acceleration sensor, an optical scanning apparatus according to claim 1, wherein computing the relative irradiation position change of said plurality of light sources.   The acceleration sensor includes a detection unit that detects acceleration and an output electrode that transmits an output signal of the detection unit to the outside, and an acceleration sensor that includes a plurality of detection units and a plurality of output electrodes formed by a semiconductor manufacturing process. 3. The optical scanning device according to claim 2, wherein the optical scanning device is formed by cutting the group individually.   The electro-optic crystal structure includes: an electro-optic crystal having a characteristic that a refractive index changes when a voltage is applied; and a voltage control unit that controls a voltage applied to the electro-optic crystal. The optical scanning device described. The voltage control unit has a pair of electrode units attached to the electro-optic crystal,
5. The optical scanning device according to claim 4, wherein the pair of electrode portions form an electric field in a direction perpendicular to a path of a light beam passing through the electro-optic crystal inside the electro-optic crystal.   6. The optical scanning device according to claim 4, wherein the electro-optic crystal is made of potassium, tantalum, niobium and oxygen.

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