JP2008181104A - Optical scanning device and image forming device equipped with the optical scanning device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an optical scanning device capable of accurately correcting an image forming position, while improving beam detection accuracy, and to provide an image forming device that is equipped with the optical scanning device. <P>SOLUTION: The optical scanning device comprises a laser diode for emitting a diffusion laser beam; an electro-optical crystal member that is disposed in the optical path between the laser diode and a polygon mirror and deflects the beam outputted from the laser diode in the subscanning direction by application of a voltage; a BD sensor and two light detection sensors that detect the beam deflected in the subscanning direction; and a scanning control part 60 that, based on the results of the detection by the BD sensor and two light detection sensors, controls the irradiation position of the beam outputted from the laser diode on a photosensitive drum. The BD sensor and the two light detection sensors are disposed at the central portion and the two end portions of an image region, in the main scanning direction corresponding to an electrostatic latent image formed on the photosensitive drum. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to an optical scanning device mounted on an image forming apparatus using electrophotographic process technology and an image forming apparatus including the same.

  Conventionally, in an electrophotographic image forming apparatus, generally, laser light emitted by driving a semiconductor laser in accordance with input image data is deflected and scanned by a rotary polygon mirror (polygon mirror) rotated by a scanner motor. The photosensitive member is irradiated. Thus, a latent image is formed, developed into a toner image, and the toner image is transferred onto a recording medium to form an image.

  In such an image forming apparatus, optical components such as a reflection mirror and an fθ lens are provided between the polygon mirror and the photosensitive member. This fθ lens has optical characteristics such as a laser beam condensing function and a distortion aberration correcting function that guarantees temporal linearity of scanning, so that the laser beam that has passed through the fθ lens The combined scanning is performed on the body at a constant speed in a predetermined direction.

  However, since this fθ lens has a characteristic deviation from a design value due to variations in molding or the like, depending on the position of the laser beam irradiated onto the photoconductor in the main scanning direction (longitudinal direction of the photoconductor), Color shift and color unevenness due to magnification error and writing position shift occur.

  That is, the laser beam is provided between the polygon mirror and the photosensitive member during one main scanning section in which a polygon mirror mounted on the scanner motor is driven to rotate and irradiated with laser light to scan one line. Pass through the fθ lens. For this reason, due to the deviation in the characteristics of the fθ lens, the laser light irradiated onto the photoreceptor is displaced from the ideal image forming position. In addition, the laser beam may deviate from the ideal image forming position due to the refractive index distribution of the optical component and the deterioration of surface accuracy due to environmental fluctuations in the image forming apparatus.

  There has been proposed a technique for detecting a deviation from the ideal image forming position and reducing the deviation.

  For example, in Patent Document 1, a mirror that reflects laser light that has passed through an fθ lens and guides it to a photoconductor, and writing of laser light in the main scanning direction, which is the longitudinal direction of the photoconductor, is provided outside both ends of the mirror. A photo detector for detecting a reference sync signal is provided. And the structure which calculates / correct | amends the deviation | shift with ideal time based on the detection signal of this photodetector is proposed.

Further, in Patent Document 2, a beam splitter that separates laser light that has passed through a scanning lens into transmitted light and reflected light, and detection means for detecting a scanning position provided downstream of the beam splitter are provided. Then, a configuration has been proposed in which reflected light from the beam splitter is imaged on the surface of the photosensitive member, and the transmitted light is guided to detection means.
JP 2005-181694 A Japanese Patent Laid-Open No. 62-143554

  However, with the configuration in which the photodetectors are provided outside both ends of the mirror as in Patent Document 1, it is possible to detect and correct the overall magnification deviation. However, the amount of deviation from the ideal length from the image center to the image writing position, or the amount of deviation from the ideal length from the image center to the writing end position, which occurs due to, for example, partial temperature rise of the lens, changes. In such a case, it is impossible to accurately detect the deviation. Therefore, there is a problem that the shift cannot be accurately corrected.

Further, in the configuration in which the transmitted light is imaged on the surface of the photosensitive member and the reflected light is guided to the detection unit as in Patent Document 2 described above, it is possible to detect the scanning timing in the image forming area. However, since the laser beam is separated into transmitted light and reflected light by the beam splitter, even if the amount of deviation is corrected, it is greatly affected by the surface accuracy of the beam splitter and the mirror shake caused by vibration, and the image forming position is accurately determined. There is a problem that it cannot be corrected. Further, since the amount of light is halved by the separation, the amount of scanning light for scanning the photosensitive member and the amount of transmitted light for detecting the shift amount cannot be sufficient. For this reason, there also exists a problem of deterioration of detection accuracy.
An object of the present invention is to provide an optical scanning device capable of accurately correcting an image forming position while improving detection accuracy of a light beam, and an image forming device including the same.

  In order to solve this problem, an optical scanning device of the present invention includes a light source that emits a light beam, and light that deflects the light beam emitted from the light source and scans the photosensitive member with the deflected light beam in the main scanning direction. A scanning unit, an electro-optic crystal structure disposed in an optical path between the light source and the plurality of light detection units, and deflecting a light beam emitted from the light source in a sub-scanning direction by applying a voltage; and in the sub-scanning direction A plurality of light detecting means for detecting the deflected light beam, and the plurality of light detecting means are provided in an image forming region in a main scanning direction corresponding to an electrostatic latent image formed on the photosensitive member. The outputs of the plurality of light detection means are used for controlling the irradiation position of the light beam on the photoconductor in the main scanning direction.

  Here, the electro-optic crystal structure is disposed in an optical path between the light source and the optical scanning unit. The plurality of light detection means include three light detection means, each of the three light detection means being at a position away from the optical path of the light flux to the photoconductor in the sub-scanning direction, and the image forming area It is provided in the center part and both ends. Further, the three light detecting means are timings at which light beams deflected in the sub-scanning direction by the electro-optic crystal structure and scanned in the main scanning direction by the light scanning means pass through the three light detecting means, respectively. Is detected. The electro-optic crystal structure is an electro-optic crystal having a characteristic that a refractive index changes when a voltage is applied, and further includes voltage control means for controlling a voltage applied to the electro-optic crystal. Further, the voltage control means has a pair of electrode portions attached to the electro-optic crystal, and the pair of electrode portions has a path direction of a light beam passing through the electro-optic crystal inside the electro-optic crystal. An electric field in the sub-scanning direction is formed at a right angle to the direction. The electro-optic crystal contains potassium, tantalum, niobium and oxygen. The electro-optic crystal structure corresponds to the next one unit image from the end of the electrostatic latent image formation corresponding to one unit image when the image forming apparatus performs image processing in units of a plurality of sheets. Before the start of electrostatic latent image formation, the light beam emitted from the light source is deflected in the sub-scanning direction. Further, the apparatus further includes a light beam drive control means for controlling driving of the light beam emitted from the light source in response to a signal for controlling the ON / OFF time of the light beam.

  The image forming apparatus of the present invention is an image forming apparatus having an optical scanning device, wherein the optical scanning device deflects a light source that emits a light beam and a light beam emitted from the light source. An optical scanning unit that scans the photosensitive member with a light beam in the main scanning direction and an optical path between the light source and the plurality of light detecting units, and deflects the light beam emitted from the light source in the sub-scanning direction by applying a voltage. An electro-optic crystal structure, and a plurality of the light detection means for detecting the light beam deflected in the sub-scanning direction, the plurality of light detection means corresponding to an electrostatic latent image formed on the photoconductor Provided in an image forming area in the main scanning direction, and the outputs of the plurality of light detecting means are used for controlling the irradiation position of the light beam on the photoconductor in the main scanning direction.

  Here, the electro-optic crystal structure is an electro-optic crystal having a characteristic that a refractive index changes when a voltage is applied, and further includes voltage control means for controlling a voltage applied to the electro-optic crystal. The apparatus further includes a photoconductor that forms an electrostatic latent image at the irradiation position of the light beam by scanning the deflected light beam. Further, the electro-optic crystal structure corresponds to the next one unit image from the end of the electrostatic latent image formation corresponding to one unit image when the image forming apparatus performs image processing in units of a plurality of sheets. Until the start of electrostatic latent image formation, the light beam emitted from the light source is deflected in the sub-scanning direction. Scanning control means for controlling the irradiation position in the main scanning direction of the light flux on the photosensitive member by generating a signal for controlling the ON / OFF time of the light flux based on the detection results of the plurality of light detection means; And a light beam driving control means for controlling the driving of the light beam emitted from the light source in response to a signal for controlling the ON / OFF time of the light beam.

  ADVANTAGE OF THE INVENTION According to this invention, the optical scanning device which can correct | amend an image formation position correctly, improving the detection accuracy of a light beam, and an image forming apparatus provided with the same can be provided.

  That is, the electro-optic crystal structure is disposed in the optical path between the light source and the light deflecting unit, and deflects the light beam emitted from the light source in the sub-scanning direction by applying a voltage. A plurality of light detection means are provided in an image region corresponding to the electrostatic latent image formed on the photoconductor, and the control means is configured to control the light flux on the photoconductor based on the detection results of the plurality of light detection means. The irradiation position in the main scanning direction is controlled. Therefore, it is possible to perform high-precision light beam detection that is not affected by the loss of light quantity, and to accurately correct the dot position deviation in the image area, thereby accurately detecting the image forming position while improving the detection accuracy. It can be corrected.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

<Configuration Example of Image Forming Apparatus with Optical Scanning Device>
1A and 1B are diagrams schematically showing a configuration of an image forming apparatus on which an optical scanning device according to a first embodiment of the present invention is mounted, FIG. 1A is a perspective view, and FIG. 1B is a cross-sectional view. FIG.

  1A and 1B, the image forming apparatus 100 irradiates the photosensitive drum 15 with laser light so that an electrostatic latent image corresponding to input image data is formed on the photosensitive drum 15 described later. A scanning device 90 is provided.

<First Configuration Example of Optical Scanning Device>
The optical scanning device 90 includes a laser diode (corresponding to a light source) 1 that emits diffused laser light in response to a signal from a laser (LD) drive control unit 82 corresponding to a light beam drive control unit. Further, a collimator lens 13 that converts the diffused laser light emitted from the laser diode 1 into a substantially parallel light beam is provided. In addition, a cylindrical lens 6 that changes the light beam converted by the collimator lens 13 in the sub-scanning direction and makes the light beam enter an electro-optic crystal described later is provided. Further, a polygon mirror 2 that scans the light beam and a reflection member 18 that reflects the light beam scanned by the polygon mirror 2 in the direction of the photosensitive drum 15 described later are provided. An electrostatic latent image is formed on the photosensitive drum 15 at the irradiation position of the light beam reflected by the reflecting member 18 corresponding to the turning on and off of the laser light based on the image data.

  The electro-optic crystal structure 12 is disposed in the optical path between the cylindrical lens 6 and the polygon mirror 2 and deflects the light beam emitted from the laser diode 1 in the sub-scanning direction by applying a voltage. Here, the sub-scanning direction is a direction perpendicular to the traveling direction of the light beam passing through the electro-optic crystal structure 12, and corresponds to the sub-scanning direction shown in FIG. 1B. Further, a beam detection sensor (hereinafter referred to as a BD sensor) 17 and light detection sensors 75a and 75b for detecting the light beam deflected in the sub-scanning direction, and the light beam scanned by the polygon mirror 2 are exposed via the reflection member 18. And an fθ lens 14 that forms an image on the drum 8. A condensing lens 76 for condensing a light beam on each sensor surface is disposed upstream of each optical path of the BD sensor 17 and the light detection sensors 75a and 75b.

  The optical scanning device 90 includes a voltage control unit 19 that is electrically connected to the electro-optic crystal structure 12 and controls a voltage applied to the electro-optic crystal structure 12. The LD drive control unit 82 also controls the irradiation position on the photosensitive drum 15 of the light beam emitted from the laser diode 1 based on the detection results of the BD sensor 17 and the light detection sensors 75a and 75b. The output signal is controlled.

  The BD sensor 17 also detects a horizontal synchronization signal (BD signal) that serves as a writing reference for the photosensitive drum 15 in the main scanning direction.

(Configuration example of electro-optic crystal structure 12)
FIG. 2 is a perspective view schematically showing the configuration of the electro-optic crystal structure 12 in FIG.

  As shown in FIG. 2, the electro-optic crystal structure 12 includes a rectangular parallelepiped electro-optic crystal (hereinafter referred to as “EO crystal”) 41 having a light incident surface 201 a and an exit surface 201 b. In addition, electrodes 74a and 74b corresponding to a pair of electrode portions attached to both end faces perpendicular to the sub-scanning direction and a power source (not shown) for applying a voltage between the pair of electrodes 74a and 74b are provided. The electrodes 74a and 74b are formed in a linear strip shape with a relatively narrow electrode width d and length L. For example, Au is used as the material of the electrodes 74a and 74b, but other conductive materials may be used. The manufacturing method is based on vacuum deposition.

  The pair of electrodes 74a and 74b form an electric field in the vertical direction (sub-scanning direction in FIG. 2, vertical direction in FIG. 1B) inside the EO crystal 41 with respect to the path of the light beam passing through the EO crystal 41.

  In a state where no voltage is applied to the electrodes 74a and 74b, the EO crystal 41 does not have a lens action, and the incident beam incident on the incident surface 201a is not deflected and is emitted from the exit surface 201b toward the polygon mirror 5 as it is. .

  By applying a voltage of 2 to 5 kV at the maximum to the pair of electrodes 74a and 74b to generate an electric field in the electro-optic crystal 41, an electric field distribution is generated. For example, it is deflected by 3 degrees. The electro-optic crystal structure 12 uses the high-speed and wide-angle electro-optic effect to cause the light beam to be separated from the reflecting member 18 in the sub-scanning direction via the polygon mirror 5 and the light detection during non-image formation. Guided to sensors 75a and 75b.

Here, the electro-optic crystal is a crystal having a characteristic that the refractive index changes when a voltage is applied. The EO crystal 21 is formed of an electro-optic crystal made of potassium, tantalum, niobium and oxygen. For example, an electro-optic crystal such as KTN (KTaNbO ₃ : potassium tantalate niobate, KTa _1-x Nb _x O ₃ ) crystal. KTN crystals can be handled in the same way as ordinary optical glass, have good workability, and can easily ensure surface accuracy in cutting and polishing. The light transmittance of the KTN crystal shows an internal transmittance of 95% or more per meter from the laser wavelength of infrared to the entire visible light range, and birefringence is also small. Furthermore, the water absorption rate of the KTN crystal is less than that of ordinary glass, and is extremely small compared to a resin or the like.

  In addition, it is known that the internal refractive index of a KTN crystal changes when an electric field is applied to the inside. When electrodes are installed at both ends of the KTN crystal (voltage = V on one side and voltage = 0 on the other) and an electric field is generated inside, the refractive index is also affected by the distribution of the electric field inside It is known that the light travels while changing its direction. The KTN crystal is characterized by being capable of high-speed and wide-angle scanning.

  As the voltage applied to both ends of the EO crystal 41 increases, the path of the light beam passing through the EO crystal 41 is largely deflected in the electric field direction (sub-scanning direction in this example). In the present invention, this phenomenon is used to change the path when transmitting the laser beam.

(Configuration example of voltage control unit 19)
The voltage control unit 19 includes a control power source 70, a power source drive control unit 71 that controls driving of the control power source 70, and switching means 72 that switches a voltage applied to the electro-optic crystal structure 12. The voltage is selectively applied to the electro-optic crystal structure 12. Although the deflection angle by the electro-optic crystal structure 12 in this example is 3 degrees, it is changed to an appropriate value according to the position where the BD sensor 17 and the light detection sensors 75a and 75b are arranged.

(Example of arrangement of each sensor)
The BD sensor 17 and the light detection sensors 75a and 75b are provided at the first irradiation position (dot position), the center irradiation position, and the last irradiation position of the light beam scanned on the photosensitive drum 15. That is, it corresponds to the central portion and both end portions in the image forming area corresponding to the electrostatic latent image formed on the photosensitive drum 15. The BD sensor 17 and the light detection sensors 75a and 75b are arranged at equal intervals with respect to the longitudinal direction (axial direction) of the photosensitive drum, that is, the main scanning direction that is the longitudinal direction of the reflecting member 18, with the light detection sensor 75a as the center. Yes. Thereby, it is possible to suppress deterioration in detection accuracy of the light beam to be scanned for correcting the image forming position due to the influence of the aberration or the like of the fθ lens 14.

(Configuration Example of Scanning Control Unit 60)
The scanning control unit 60 includes a dot position deviation detection unit 80 that detects deviations in dot positions at the center and both ends of the image forming area based on the detection signals of the BD sensor 17 and the light detection sensors 75a and 75b. Further, a modulation / image data processing unit 81 that executes image data processing and outputs a signal for controlling the light emission timing of the laser diode 1 so as to correct the dot position shift detected by the dot position shift detection unit 80; Is provided. The modulation / image data processing unit 81 outputs a signal for controlling the light emission timing of the laser diode 1 to the LD drive control unit 82.

<Operation example of this optical scanning device>
Laser light emitted from the laser diode 1 is converted into a substantially parallel light beam via the collimator lens 13. Thereafter, the substantially parallel light flux passes through the cylindrical lens 6 and is condensed in the sub-scanning direction. The light beam that has passed through the cylindrical lens 6 passes through the electro-optic crystal structure 12 and is irradiated to the polygon mirror 2 that is rotationally driven by the polygon motor 3.

  The light beam applied to the polygon mirror 2 is deflected and scanned and guided to the fθ lens 14. Since there is no deflection by the electro-optic crystal structure 12 within the image formation time, the light beam that has passed through the fθ lens 14 is reflected by the reflecting member 18 and forms an image on the photosensitive drum 15, and the main scanning direction is constant in the main scanning direction. Scan with. An electrostatic latent image is formed on the photosensitive drum 15 by scanning the light beam, that is, a scanning operation.

  On the other hand, when a voltage is applied to the EO crystal 41 at a predetermined timing outside the image formation time, the EO crystal 41 is deflected by 2 to 3 degrees in the sub-scanning direction. It is guided to the light detection sensors 75a and 75b. The BD sensor 17 and the light detection sensors 75a and 75b detect the passage timing of the light beam scanned by the polygon mirror 2. Note that when the image forming apparatus 100 executes image processing for a plurality of sheets, the following operation is performed. That is, the electro-optic crystal structure 12 is a laser diode between the end of the electrostatic latent image formation corresponding to one unit image and the start of the electrostatic latent image formation corresponding to the next one unit image. The light beam emitted from 1 is deflected in the sub-scanning direction. Thereby, even when images are output continuously, it is possible to appropriately correct the deviation of the dot position in the main scanning direction, and it is possible to form an electrostatic latent image with high positional accuracy.

  The BD sensor 17 is disposed above the reflecting member 18 and in the vicinity of the end of the reflecting member 18 on the scanning start side. The BD sensor 17 detects a light beam deflected in the sub-scanning direction by the electro-optic crystal structure 12 and deflected and scanned in the main scanning direction by the polygon mirror 2. Specifically, when the laser diode 1 is forcibly lit at a time corresponding to the start of scanning of the light beam applied to the photosensitive drum 15, the BD sensor 17 is deflected and scanned by the polygon mirror 2 during the forcible lighting period of the laser diode 1. Detect the luminous flux. Then, a beam detect signal (hereinafter referred to as a BD signal) serving as a reference signal for writing start timing in image formation for each main scan is output to a dot position deviation detection unit 80 described later.

  The light detection sensor 75a is disposed above the reflection member 18 and substantially at the center of the reflection member 18, and the light detection sensor 75b is disposed above the reflection member 18 and near the end of the reflection member 18 on the scanning end side. Yes. The light detection sensors 75a and 75b detect light beams deflected in the sub-scanning direction by the electro-optic crystal structure 12 and deflected and scanned in the main scanning direction by the polygon mirror 2. Specifically, the light detection sensors 75 a and 75 b detect the light beam deflected and scanned by the polygon mirror 2 during the forced lighting period of the laser diode 1. A signal corresponding to the writing intermediate timing in image formation for each main scan (hereinafter simply referred to as “intermediate timing signal”) and a signal corresponding to the writing end timing (hereinafter simply referred to as “end timing signal”) Output to the misalignment detector 80.

  The BD signal, the intermediate timing signal, and the end timing signal output from the BD sensor 17 and the light detection sensors 75a and 75b are calculated by the dot position shift detection unit 80 and input to the modulation / image data processing unit 81, respectively. Is done. Then, the modulation / image data processing unit 81 corrects the dot position deviation in the main scanning direction of the image data. Specifically, based on the BD signal, the intermediate timing signal, and the end timing signal, a shift amount from the theoretical distance of the distance from the first dot position to the center dot position of the image data (hereinafter referred to as a first shift amount). Is calculated. Also, a deviation amount from the theoretical distance of the distance from the center dot position of the image data to the last dot position (hereinafter referred to as a second deviation amount) is calculated. Then, the calculated first shift amount is compared with the second shift amount. The first dot position and the last dot position of the image data are changed so that the difference between the first shift amount and the second shift amount is 0 or minimum. Thereafter, a signal indicating the light emission timing of the laser diode 1 is output to the LD drive control unit 82 based on the corrected dot position change, and the LD drive control unit 82 is controlled to change the light emission timing of the laser diode 1. Thereby, the deviation in the main scanning direction from the theoretical dot position in the image forming area corresponding to the electrostatic latent image formed on the photosensitive drum 15 is corrected.

(Configuration Example of Scanning Control Unit 60)
FIG. 3 is a block diagram showing an internal configuration of the scanning control unit 60 in FIG.

  The scanning control unit 60 is a circuit capable of correcting a shift in the printing position of the main scanning line by modulating the image clock. As shown in FIG. 3, the scanning control unit 60 includes a dot position deviation detection unit 80 and a modulation / image data processing unit 81.

  The dot position deviation detection unit 80 includes a main scanning interval dk detection circuit 1. The main scanning interval dk detection circuit 1 detects each sensor distance as a main scanning interval from the BD signal, the intermediate timing signal, and the end timing signal output from the BD sensor 17 and the light detection sensors 75a and 75b. Then, a main scanning interval signal 2 indicating the detected interval value is output. The main scanning interval signal 2 is input to the main scanning interval dk measuring circuit 3, and the main scanning interval dk measuring circuit 3 converts the main scanning interval signal 2 into a main scanning interval measuring signal 4 which is time data. The main scanning interval measurement signal 4 is supplied to the error ratio γk calculation circuit 13.

  The error ratio γk calculation circuit 13 calculates a ratio between a value indicated by the main scanning interval measurement signal 4 and a characteristic of the fθ lens 14 in advance and a predetermined value 12 preset in the predetermined value d storage circuit 11. The ratio is output as an error ratio signal 14. The error ratio signal 14 is stored in the error ratio γk storage circuit 15. This error ratio γk is a value related to the shift amount.

  The error ratio signal 14 stored in the error ratio γk storage circuit 15 is input to the modulation / image data processing unit 81. The modulation / image data processing unit 81 modulates the frequency of a preset image clock based on the value indicated by the error ratio signal 14 and outputs it as the image clock 18.

  Next, the configuration of the modulation / image data processing unit 81 will be described. As shown in FIG. 3, the modulation / image data processing unit 81 includes a reference clock generation unit 20, a scaling coefficient setting register 22, an auxiliary pixel generation circuit 24, an initial period setting register 26, and a modulation clock control circuit 30. And a modulation clock generation circuit 28.

  The reference clock generator 20 generates a reference clock signal 21 having an arbitrary frequency. In the scaling factor setting register 22, a scaling factor (αk) 23 for changing the cycle ratio of the reference clock signal 21 is set and held in accordance with the error ratio γk (and the following number of segments).

  The auxiliary pixel generation circuit 24 generates an auxiliary pixel period 25 based on the reference clock signal 21 and the scaling coefficient 23. The magnification in the main scanning direction is corrected by the auxiliary pixel period 25. That is, due to the optical system of the polygon mirror 2 and the fθ lens 14 in FIG. 1 and the environmental change, the width or dot interval of dots formed on the photosensitive drum 15 in the main scanning direction is not uniform. Therefore, using the auxiliary pixel period 25, the frequency of the image clock 18 in one scanning section is corrected so that the dot width or dot interval is uniform.

(Example of displacement correction by rotation of polygon mirror)
In the case of a rotational scanning system such as the polygon mirror 2, the scanning speed tends to increase at both ends of the photosensitive drum 15 in the main scanning direction, and conversely, the scanning speed is low at the central portion of the photosensitive drum 15 in the main scanning direction. Tend to be. Accordingly, the dot width or dot interval on the photosensitive drum 15 is corrected by increasing the frequency of the image clock 18 near both ends of the photosensitive drum 15 and decreasing the frequency of the image clock 18 in the center of the photosensitive drum 15. Can be made uniform.

  Here, for example, assuming that the period of the reference clock signal 21 is τref, the magnification coefficient 23 is αk, and the auxiliary pixel period 25 is Δτ, Δτ is expressed by the following equation (1).

Δτ = αk × τref (1)
Here, the scaling coefficient 23 (αk) is set to a value such that the auxiliary pixel period 25 (Δτ) is sufficiently shorter than the period of the image clock 18.

  In the initial period setting register 26, an initial value 27 (τvdo) of the period of the image clock 18 output from the image clock generation unit 17 is set and held.

  The modulation clock control circuit 30 divides one line scanned in the main scanning direction into segments composed of an arbitrary number of pixels, forms a plurality of segments, and makes the period of the image clock 18 in each segment constant. To do.

(Operation Example of Modulation Clock Control Circuit 30)
FIG. 4 is a diagram showing a relationship between a part of the segments formed by the modulation clock control circuit 30 in FIG. 2 and the period of the image clock 18 in each segment.

  In FIG. 4, the modulation clock control circuit 30 receives a BD signal 29 that is a signal serving as a writing reference output from the BD sensor 17. Then, the modulation clock control circuit 30 generates a modulation clock control signal 33 for the first segment (segment 0) and outputs it to the modulation clock generation circuit 28. Upon receiving this modulation clock control signal 33, the modulation clock generation circuit 28 outputs the image clock 18 having the initial period 27 (τvdo) held in the initial period setting register 26. For the next segment (segment 1), the modulation clock control circuit 30 generates a modulation clock control signal 33 for the next segment (segment 1) and outputs it to the modulation clock generation circuit 28. Upon receiving this modulation clock control signal 33, the modulation clock generation circuit 28 performs modulation having a period represented by the following equation (2) based on the initial period 27 (= τvdo) and the auxiliary pixel period 25 (= Δτ). A clock τ1 is generated. Then, the modulation clock τ1 is output as the image clock 18.

τ1 = τvdo + Δτ
= Τvdo + (α1 × τref) (2)
Here, α1 is a scaling factor for segment 1.

  Similarly, for a further next segment (segment 2), the modulation clock control circuit 30 outputs a modulation clock control signal 33 for the further next segment (segment 2) to the modulation clock generation circuit 28.

  Upon receiving this modulation clock control signal, the modulation clock generation circuit 28 uses the initial period 27 (= τvdo) and the auxiliary pixel period 25 to generate a modulation clock τ2 having a period represented by the following equation (3). . Then, the modulation clock τ 2 is output as the image clock 18.

τ2 = τvdo + (α1 × τref) + (α2 × τref) (3)
Here, α2 is a scaling factor for segment 2.

  Further, the modulation clock τn for the other segments after the segment 2 is generated in the same procedure as described above, and the modulation clock τn is output as the image clock 18.

  As described above, the modulation clock control circuit 30 outputs the plurality of image clocks 18 corresponding to each segment from the modulation clock generation circuit 28 within one main scanning line.

(Example of multi-stage variable within one segment)
5A and 5B are diagrams showing the relationship between the segment and the period of the image clock 18 in the segment when the image clock 18 in one segment is varied in multiple stages. FIG. 5A shows a case where the initial segment is variable, and FIG. 5B shows a case where the initial segment is fixed. Hereinafter, a segment period control method when frequency modulation is performed in one segment will be described with reference to FIGS. 5A and 5B.

(1) When Initial Segment (Segment 0) is Variable Assume that the initial period is τvdo, the number of pixels per segment is n, the scaling factor (segment 1) is α1, and the reference clock period is τref. In this case, Δτa (period per pixel in segment 0) and ΔT0 (total period of segment 0) are expressed by the following equations (4) and (5).

Δτa = (α1 × τref) / n (4)
ΔT0 = τvdo + {n × (n + 1) / 2} × {(α1 × τref) / n}
= Τvdo + (n + 1) / 2 × (α1 × τref) (5)
(2) When Initial Segment (Segment 0) is Fixed Assuming that the initial period is τvdo, the total period ΔT0 of segment 0 is expressed by the following equation (6).

ΔT0 = n × τvdo
On the other hand, when the scaling factor (segment 2) is α2 and the reference clock period is τref, Δτb (period per pixel in segment 1) and ΔT1 (total period of segment 1) are expressed by the following equation (6): It is represented by the formula (7).

Δτb = (α2 × τref) / n (6)
ΔT1 = τvdo + {n × (n + 1) / 2} × {(α2 × τref) / n}
= Τvdo + (n + 1) / 2 × (α2 × τref) (7)
Further, for each segment after segment 1, the period Δτb per pixel and the total period ΔTn (n ≧ 2) of each segment can be expressed by the same formula.

  The image data 107 and the image clock 18 calculated above are input to a PWM (Pulse Width Modulation) generator 105. The PWM generator 105 generates a pulse for controlling the ON / OFF time of the laser within one clock in accordance with the calculated image clock 18 and the image data 107, and outputs the pulse to the laser drive controller 82. The emission of the light beam from 1 is controlled.

<Procedure example of magnification control processing in main scanning direction of optical scanning device>
FIG. 6 is a flowchart showing magnification control processing in the main scanning direction, which is executed by the optical scanning device 90 in FIG.

  In FIG. 6, when a request for starting magnification control in the main scanning direction is received at a predetermined timing outside the image formation time, a voltage is applied to the pair of electrodes 74a and 74b attached to the EO crystal 41 (step S600). ). At almost the same time, the laser is turned on and the polygon motor 3 is rotated, and the scanning light is deflected in the sub-scanning direction by the EO crystal 41 and guided to the position toward the BD sensor 17 and the light detection sensors 75a and 75b. Thereby, three-point synchronous measurement of the scanning light is performed, and the scanning light count value is read based on each timing signal transmitted from the BD sensor 17 and the light detection sensors 75a and 75b (step S601).

  Thereafter, the count value read in step S601 is converted into a magnification error in the main scanning direction from the ideal timing (step S602), and whether or not the magnification error in the main scanning direction is within an allowable range (shown as Eth). Determination is made (step S603). When the magnification error in the main scanning direction is within the allowable range (≦ Eth), this process is terminated, and the image forming apparatus enters an image forming operation waiting state.

  On the other hand, when the main scanning magnification error is outside the allowable range (> Eth), that is, when a dot position shift has occurred, it is determined whether or not the polygon mirror 2 is operating normally by detecting a polygon lock signal or the like. Determination is made (step S604). When the operation of the polygon mirror 2 is abnormal, an error display for displaying a service man call or the like on the operation unit is performed (step S605).

  When the operation of the polygon mirror 2 is normal, the modulation / image data processing unit 81 performs modulation / image data processing (step S606), and outputs an image data signal based on the corrected image clock (step 6907). The image forming standby state is entered, and this process is terminated.

(Effects of the first embodiment)
According to the present embodiment, the electro-optic crystal structure 12 is disposed in the optical path between the cylindrical lens 6 and the polygon mirror 2, and the luminous flux emitted from the laser diode 1 is applied in the sub-scanning direction by applying a voltage. To deflect. The BD sensor 17 and the light detection sensors 75a and 75b are provided at the center and both ends of the image forming area corresponding to the electrostatic latent image formed on the photosensitive drum 15. Then, the scanning control unit 60 controls the irradiation position of the light flux on the photosensitive drum 15 in the main scanning direction based on the detection results of the BD sensor 17 and the light detection sensors 75a and 75b. Therefore, since the deviation of the light beam can be detected without branching the light beam halfway, highly accurate light beam detection that is not affected by the loss of the light amount can be executed. At the same time, it is possible to accurately correct the dot position shift in the image forming area, and thus to accurately correct the image forming position while improving the detection accuracy.

  In addition, the light flux emitted from the light source is not separated by a half mirror as in the prior art, but the deviation of the light flux can be detected using the total light flux. Therefore, even when a light source having a small maximum output, such as a VCSEL, is used, highly accurate light flux detection can be executed.

  In addition, by using a KTN crystal as the electro-optic crystal structure 12, the KTN crystal has a light transmittance of 95% or more per meter from the infrared wavelength of the laser to the entire visible light range. . In addition, since the birefringence is small, the light flux can be detected with high accuracy.

  Further, when detecting the deviation, since all the light beams are deflected and incident in the direction of the BD sensor 17 and the light detection sensors 75a and 75b, light emission at the time of deviation detection scans the photosensitive drum as in the light beam separation method. There is no fear of doing it.

  In addition, it is not necessary to arrange a light detection sensor at a position (in this example, outside of the reflecting member 18 in the main scanning direction) that is largely deviated from the image forming region in the main scanning direction, and the apparatus can be downsized. .

  In the present embodiment, the light detection sensors 75a and 75b are arranged at the above-described positions, but the present invention is not limited to this. You may arrange | position in positions other than a position. Three or more light detection sensors may be installed at equal intervals along the main scanning direction. Thereby, it is possible to correct the main scanning magnification with higher accuracy.

  In the present embodiment, three detection sensors (BD sensor 17 and light detection sensors 75a and 75b) for detecting a light beam deflected in the sub-scanning direction are arranged, but the present invention is not limited to this. Three or more light detection sensors may be arranged in an image region in which a light beam deflected and scanned in the sub-scanning direction can be detected. By increasing the number of light detection sensors, it is possible to accurately correct the image forming position while improving the detection accuracy.

<Second Configuration Example of Optical Scanning Device>
FIG. 7 is a plan view schematically showing the configuration of the optical scanning device according to the second embodiment of the present invention. The configuration of the second embodiment is the same as that of the first embodiment, and the same components are denoted by the same reference numerals and redundant description is omitted, and different portions are described below. To do.

  In FIG. 7, the optical scanning device 700 includes a light detection reflecting member 717 that reflects the light beam deflected in the sub-scanning direction by the electro-optic crystal structure 12 in a predetermined direction. In addition, a BD sensor 717 and light detection sensors 775a and 775b that detect the light beam reflected by the light detection reflection member 717 are provided. In the BD sensor 717, the optical path length from the deflection point of the light beam at the polygon mirror 2 to the light receiving surface of the BD sensor 717 is substantially the same as the optical path length from the deflection point of the light beam at the polygon mirror 2 to the surface of the photosensitive drum 15. It is arranged at the position. The light detection sensors 775a and 775b also have an optical path length from the deflection point of the light beam at the polygon mirror 2 to the light receiving surface of the light detection sensor 775a and 775b, from the deflection point of the light beam at the polygon mirror 2 to the surface of the photosensitive drum 15. The optical path length is approximately the same as the optical path length. Thereby, the dot position shift on the surface of the photosensitive drum 15 can be detected with higher accuracy, and the correction accuracy of the image data in the main scanning direction can be further improved.

<Third Configuration Example of Optical Scanning Device>
FIG. 8 is a plan view schematically showing the configuration of the optical scanning device according to the third embodiment of the present invention. The configuration of the third embodiment is the same as that of the first embodiment, and the same components are denoted by the same reference numerals and redundant description is omitted, and different portions are described below. To do.

  In FIG. 8, the optical scanning device 800 includes a BD sensor 801 disposed in substantially the same plane as the polygon mirror 2 in the sub-scanning direction. In addition, the light detection sensors 802a, 802b, and 802c are provided above the reflecting member 18 and disposed in the vicinity of the scanning start side end portion, the substantially central portion, and the scanning end side end portion of the reflecting member 18. Specifically, the light detection sensor 802a is disposed inside the first irradiation position (position A in the drawing) of the light beam scanned on the photosensitive drum 15, and the light detection sensor 802c is the light beam scanned on the photosensitive drum 15. Is arranged inside the last irradiation position (position B in the figure). Thereby, all the light detection sensors can be arranged inside both ends of the reflecting member 18 in the main scanning direction, and the apparatus can be miniaturized.

<Another configuration example of the optical scanning device>
In the above embodiment, the electro-optic crystal structure 12 is disposed in the optical path between the cylindrical lens 6 and the polygon mirror 2, but is not limited thereto.

  As shown in FIG. 9, it may be disposed in the optical path between the polygon mirror 2 and the fθ lens 14. In this case, the electro-optic crystal structure 900 has a substantially long EO crystal extending in the main scanning direction, and deflects the light beam scanned in the main scanning direction by the polygon mirror 2. Further, the electro-optic crystal structure may be disposed at any position in the optical path between the laser diode 1 and the polygon mirror 2, in the incident side optical path to the polygon mirror 2 or on the exit side from the polygon mirror 2. You may arrange | position in any position in an optical path.

  In the above embodiment, the light beam changed by the polygon mirror 2 scans the photosensitive drum 15. However, the configuration is not limited to this, and a configuration in which a photosensitive drum is scanned using a galvano mirror or a MEMS (Micro Electro Mechanical System) may be used.

1 is a perspective view schematically showing a configuration of an image forming apparatus in which an optical scanning device according to a first embodiment of the present invention is mounted. 1 is a cross-sectional view schematically illustrating a configuration of an image forming apparatus in which an optical scanning device according to a first embodiment of the present invention is mounted. It is a perspective view which shows roughly the structure of the electro-optic crystal structure of this embodiment. It is a block diagram which shows the internal structure of the scanning control part in this embodiment. It is a figure which shows the relationship between a part of segment formed with the modulation | alteration clock control circuit in FIG. 3, and the period of the image clock in each segment. When an initial segment is variable, it is a figure which shows the relationship between the segment and the period of the image clock in this segment in the case of varying the image clock in one segment in multiple stages. When an initial segment is fixed, it is a figure which shows the relationship between a segment and the period of the image clock in this segment in the case of varying the image clock in one segment in multiple stages. . 6 is a flowchart illustrating a procedure example of main scanning magnification control processing executed by the image forming apparatus according to the present exemplary embodiment. It is a top view which shows roughly the structure of the optical scanning device concerning the 2nd Embodiment of this invention. It is a top view which shows roughly the structure of the optical scanning device concerning the 3rd Embodiment of this invention. It is a top view which shows roughly the structure of the optical scanning device using the modification of an electro-optic crystal structure.

Claims (14)

A light source that emits a luminous flux;
An optical scanning means for deflecting a light beam emitted from the light source and scanning the photosensitive member in the main scanning direction with the deflected light beam;
An electro-optic crystal structure that is disposed in an optical path between the light source and a plurality of light detection means, and deflects a light beam emitted from the light source in a sub-scanning direction by applying a voltage;
A plurality of the light detection means for detecting a light beam deflected in the sub-scanning direction,
The plurality of light detection means are provided in an image forming area in a main scanning direction corresponding to an electrostatic latent image formed on the photoconductor, and an output of the plurality of light detection means is a light flux on the photoconductor An optical scanning device used for controlling the irradiation position in the main scanning direction.   The optical scanning device according to claim 1, wherein the electro-optic crystal structure is disposed in an optical path between the light source and the optical scanning unit.   The plurality of light detection means includes three light detection means, and each of the three light detection means is located in a sub-scanning direction from a light path of a light beam to the photoconductor, and is within the image forming area. The optical scanning device according to claim 1, wherein the optical scanning device is provided at a central portion and both end portions.   The three light detecting means detect the timing at which the light beams deflected in the sub-scanning direction by the electro-optic crystal structure and scanned in the main scanning direction by the light scanning means pass through each of the three light detecting means. The optical scanning device according to claim 3. The electro-optic crystal structure is an electro-optic crystal having a characteristic that a refractive index changes when a voltage is applied,
The optical scanning device according to claim 1, further comprising voltage control means for controlling a voltage applied to the electro-optic crystal. The voltage control means has a pair of electrode parts attached to the electro-optic crystal,
6. The pair of electrode portions form an electric field in a sub-scanning direction perpendicular to a traveling direction of a light beam passing through the electro-optic crystal inside the electro-optic crystal. Optical scanning device.   The optical scanning device according to claim 5, wherein the electro-optic crystal contains potassium, tantalum, niobium, and oxygen.   When the image forming apparatus performs image processing in units of a plurality of sheets, the electro-optic crystal structure has an electrostatic capacity corresponding to the next unit image from the end of the electrostatic latent image formation corresponding to the unit unit image. The optical scanning device according to claim 1, wherein the light beam emitted from the light source is deflected in a sub-scanning direction until the start of latent image formation.   2. The optical scanning apparatus according to claim 1, further comprising a light beam drive control unit that controls driving of the light beam emitted from the light source in response to a signal for controlling an ON / OFF time of the light beam. An image forming apparatus having an optical scanning device,
The optical scanning device is
A light source that emits a luminous flux;
An optical scanning means for deflecting a light beam emitted from the light source and scanning the photosensitive member in the main scanning direction with the deflected light beam;
An electro-optic crystal structure that is disposed in an optical path between the light source and a plurality of light detection means, and deflects a light beam emitted from the light source in a sub-scanning direction by applying a voltage;
A plurality of the light detection means for detecting a light beam deflected in the sub-scanning direction,
The plurality of light detection means are provided in an image forming area in a main scanning direction corresponding to an electrostatic latent image formed on the photoconductor, and an output of the plurality of light detection means is a light flux on the photoconductor An image forming apparatus used for controlling the irradiation position in the main scanning direction. The electro-optic crystal structure is an electro-optic crystal having a characteristic that a refractive index changes when a voltage is applied,
The image forming apparatus according to claim 10, further comprising a voltage control unit that controls a voltage applied to the electro-optic crystal.   The image forming apparatus according to claim 10, further comprising a photoconductor that forms an electrostatic latent image at an irradiation position of the light beam by scanning the deflected light beam.   When the image forming apparatus performs image processing in units of a plurality of sheets, the electro-optic crystal structure has a static image corresponding to the next unit image from the end of electrostatic latent image formation corresponding to the unit image. 13. The image forming apparatus according to claim 12, wherein the light beam emitted from the light source is deflected in the sub-scanning direction until the start of the electrostatic latent image formation. Scanning control means for controlling the irradiation position of the light flux on the photosensitive member in the main scanning direction by generating a signal for controlling the ON / OFF time of the light flux based on the detection results of the plurality of light detection means;
The image forming apparatus according to claim 10, further comprising: a light beam driving control unit that controls driving of the light beam emitted from the light source in response to a signal for controlling an ON / OFF time of the light beam. .

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