JP2005001126A - Optical writing device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an optical writing optical system which can realize optical writing with the trouble of conventional optical writing optical systems improved. <P>SOLUTION: The optical writing device is configured to be able to carry out optical writing of one line at the same time by a combination of a mirror array capable of controlling a deflection direction by units of mirrors corresponding to pixel sizes, and a light shielding slit. In comparison with the conventional liquid crystal shutter array method, a light/shade switching time is greatly speeding up. Moreover, the use efficiency of light is higher owing to the reflection type than that of a liquid crystal shutter or the like transmission type. Also, high-speed writing is enabled as compared with a raster scan method of scanning by units of pixel. The optical writing optical system which can carry out high-speed writing, has a high use efficiency of light, and can fully be made compact is thus realized. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an optical writing optical system using a mirror array, which is used in an optical writing unit of an image forming apparatus such as a digital copying machine, a printer, or a facsimile.
[0002]
[Prior art]
In an image forming apparatus such as a digital copying machine, a printer, or a facsimile, a latent image is formed by optically writing on a writing medium made of a photoconductor according to image information binarized by a digital optical writing optical system. After forming the image, an image is formed on a recording sheet or the like through the steps of development, transfer, and fixing. Here, representative examples of conventionally known optical writing methods used in the image forming apparatus and their characteristics will be described below.
(1) Optical scanning type (raster scan) writing method: a deflecting light beam from a light source such as a laser diode (LD) is deflected and scanned using a deflector such as a polygon mirror, and then on a photoconductor via an fθ lens or the like. Is scanned at a constant speed (see Patent Document 1).
(2) LED array method: A method in which light emitting diodes (LEDs) are arrayed in a line shape corresponding to the pixel density and condensed on a photosensitive member with a unity imaging element or the like (see Patent Document 2).
(3) Liquid crystal shutter array method: A method in which liquid crystals are arrayed in a line shape corresponding to the pixel density, and each liquid crystal is turned on / off as a shutter to write on the photosensitive member (see Patent Document 3).
[0003]
[Patent Document 1]
Japanese Patent Laid-Open No. 08-160694 [Patent Document 2]
JP 05-050653 A [Patent Document 3]
Japanese Patent Laid-Open No. 06-118743
[Problems to be solved by the invention]
However, the optical scanning type (raster scan) writing method (1) is the most widely used method, which is particularly advantageous for increasing the density and speed, and is a highly reliable method. Since a relatively large space is required for the arrangement of optical components such as these, it is disadvantageous for miniaturization. The LED array method (2) has a small magnification error and is advantageous for miniaturization. However, each LED has a large variation in accuracy, tends to cause unevenness in images, and is a self-luminous element, so it can be printed at high speed. Has a problem of insufficient light quantity. The liquid crystal shutter array method (3) has a small magnification error and is advantageous for miniaturization, but is not suitable for increasing the speed because the liquid crystal shutter speed is insufficient and the light transmittance is also poor. In order to improve this, Japanese Patent Laid-Open No. 7-256923 has been proposed. However, in this proposal, control is performed to switch on and off one line at a time (ON / OFF control for each main scanning row). It is difficult to realize gradation control other than control. In addition, a long reflecting mirror having an elliptical shape or the like is used, but in particular, the influence of reflection at a movable mirror or other places is not taken into consideration.
[0005]
An object of the present invention is to provide an optical writing optical system capable of realizing optical writing in which the problems of the conventional optical writing optical system are improved.
[0006]
[Means for Solving the Problems]
In order to achieve the above object, according to the present invention, in a digital type optical writing apparatus, it is disposed in an optical path from a light source to a writing medium, and is formed to have a size corresponding to a pixel density in the main scanning direction. A mirror array comprising movable mirrors arranged in a line in the main scanning direction and a light-shielding slit having a first slit width equal to or smaller than the pixel size in the sub-scanning direction. Accordingly, the writing is performed on the writing medium by deflecting each movable mirror of the mirror array.
[0007]
Further, the mirror array controls the on state and the off state for each line in each sub-scanning direction by deflecting each movable mirror, and has a mirror PWM control circuit for each mirror. .
[0008]
Further, the PWM control circuit has a control register, and the ON / OFF state can be independently controlled by PWM modulation for each line in the sub-scanning direction according to the register value.
[0009]
Further, the register value of the control register is updated at regular intervals.
[0010]
In addition, a buffer register for writing data to the register of the control register is provided.
[0011]
In addition, a linear light source such as a halogen lamp or a fluorescent tube is used as the light source and a long reflecting mirror having an elliptical shape or the like is used to focus the light beam in the sub-scanning direction as necessary. The light source is integrated with the light source through a slit.
[0012]
In addition, a light absorbing material capable of absorbing light reflected by the mirror when the movable mirror is off is applied or mounted on at least the slit wall surface.
[0013]
Further, the mirror array is provided with the PWM control circuit on the same IC.
[0014]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. FIG. 1 is a perspective view of a principal part showing a schematic configuration of an optical system according to an embodiment of the present invention. In FIG. 1, reference numeral 1 is a mirror array, 2 is a movable mirror constituting the mirror array, 3 is a light-shielding slit, Reference numeral 4 denotes a photoconductor as a writing medium. The illustration of the light source unit is omitted. In FIG. 1, the mirror array 1 is disposed in the optical path from the light source to the photoconductor 4, and is in the main scanning direction (the moving direction of the photoconductor surface is the sub-scanning direction, and the direction orthogonal to this direction is the main scanning direction. The movable mirrors 2 formed at intervals and sizes corresponding to the pixel density in the scanning direction are arranged in a line in the main scanning direction.
[0015]
The micromirror 41 is mounted on the yoke 43 via the support post 42. The yoke 43 is swingably supported by the torsion hinges 44a and 44b while being floated from the silicon substrate 40a. A first electrode 45a and a second electrode 45b are formed in the peripheral direction of the yoke 43, respectively. Since 41 can be mounted by rotating at an arbitrary angle on 42 as required, a mirror array corresponding to one array can be easily realized.
[0016]
As shown in FIG. 2, each of the movable mirrors 2 in the mirror array has the micro mirror 41 twisted by the twisting hinges 44a and 44b by the electrostatic force acting according to the polarity of the voltage applied to the first electrode 45a and the second electrode 45b. While twisting, the surface is swung clockwise or counterclockwise, and the surface is inclined. The voltage supply to the first electrodes 45a and 45b is controlled by a controller (not shown). That is, when no voltage is supplied to the first electrodes 45a and 45b, the movable (micro) mirror 41 maintains a horizontal posture, but when a positive polarity is applied to the first electrode 45a and a reverse polarity is applied to the second electrode 45b, The micromirror 45 is tilted to one side, and the tilt angle is + θ. When a reverse polarity is applied to the first electrode 45a and a positive polarity is applied to the second electrode 45b, the micromirror 45 tilts to the other and operates so that the tilt angle becomes −θ, and the mirror is turned ON / OFF. Operation is realized.
[0017]
A light-shielding slit 3 is disposed between the mirror array 1 and the photosensitive member 4, and a slit portion 3 a of the light-shielding slit 3 opens along the line direction (array direction) of the mirror array 1. The direction perpendicular to the line direction, that is, the slit width W in the sub-scanning direction corresponds to the size of the pixel in the sub-scanning direction. Therefore, the light beam reflected by one movable mirror 2 of the mirror array 1 passes through the slit portion 3a of the light-shielding slit 3 and is irradiated onto the photosensitive member 4, whereby optical writing of one pixel is performed. Here, the light beam L emitted from the light source and incident on each movable mirror 2 of the mirror array 1 is deflected by each movable mirror 2 controlled in accordance with the image data, and therefore, the mirror array 1 and the photosensitive member 4. By installing the light shielding slit 3 between the two, the light can be switched between bright (on) and dark (off) depending on whether or not the light beam passes through the slit portion 3a.
[0018]
Therefore, by applying the image data as a parallel control signal to the PWM control circuit that controls each mirror 2 of the mirror array 1 for each line, the PWM control circuit turns on the mirror in correspondence with the data for each bit. Off-PWM control can be performed to perform optical writing on the photosensitive member 4. Even if the surface of the photoconductor is continuously moved in the sub-scanning direction, the next line data is written to the buffer register at a time during the PWM control of the PWM control circuit, and is read from the buffer register at the end timing of the PWM control. By writing to the control register, the next PWM control can be started, and optical writing can be performed continuously.
[0019]
As described above, in the optical writing optical system of the present invention, the mirror array 1 capable of controlling the deflection direction in units of mirrors having a size corresponding to one pixel, the PWM control circuit for controlling the mirror array 1, and the light-shielding slit 3 are provided. By combination, the data in the control register of the PWM control circuit can be updated simultaneously for one line, and the response speed of each movable mirror 1-2 is faster than that of liquid crystal, etc. Dark switching time is very fast. Moreover, since it is a reflection type, the light utilization efficiency is higher than that of a transmission type such as a liquid crystal shutter. In addition, it is possible to realize gradation control between two line data by PWM control with ON / OFF control, and it is also possible to control to increase the number of lines between lines substantially, so the speed in the sub-scanning direction is not slowed down. In addition, there is an effect that printing in the sub-scanning direction can be realized with high resolution and high gradation without increasing the line data transfer rate.
[0020]
FIG. 3 shows a second embodiment. Reference numerals 101 to 104 denote buffer registers, and in this embodiment, they are also used as shift registers for serial data transfer. The data input terminal 121 is connected to the input terminal 101, and the output terminal 101 is connected to the input terminal 102 through 113. Similarly, 102 output terminals are connected to 103 input terminals through 114. The output terminal 103 is connected to the input terminal 104 through 115. The registers 101 to 104 have data setting clock input terminals, which are connected to the output terminals of 134 2-input NOR gates through 130 signal lines, and one of the input terminals is connected to the 131 CLK signal. The other is connected to 126 data_enable signal input terminals.
[0021]
In this embodiment, for the sake of simplicity, an example in which four PWM control circuits are used will be described. However, in practice, it is normal to consider n (7000 to 9000), and the above embodiment is simply simplified. The detailed description in that case is omitted. Reference numerals 105, 106, 107, and 127 denote PWM control circuits. 113 is a PWM control circuit having 105, 114 is 106, 115 is 107, and the signal line 116 connected to the output terminal 104 is 127. Connected to the register input terminal. As a control clock of the PWM control register input terminal of the PWM control circuit 105, 106, 107, 127, 125 signal LINE_CLK is inverted by the inverter 119, and the inverted signal is connected through the 118 signal line. The data on 113, 114, 115, 116 is latched in the registers of the PWM control circuits 105, 106, 107, 127 at the falling edge of the 125 signal.
[0022]
Reference numerals 108, 109, 110, and 128 are mirror array control registers. The PWM signal output signal lines 122, 123, 124, and 129 of 105, 106, 107, and 127 are connected to control data output terminals, respectively. ing. The outputs of 108, 109, 110, and 128 are connected to a mirror controller (not shown), and are controlled to be in an ON state when H is applied to 108, 109, 110, and 128 and to an OFF state when L.
[0023]
105, 106, 107, 127 and 108, 109, 110, 128 are connected to the VCO output signal PWM_CLK signal line of 111 PLL, and operate in synchronization with the clock. 111 and 112 constitute a PLL, 111 is a PLL main body including a VCO, and 112 is a frequency divider. An output signal of the VCO 111 is connected to an input terminal of the frequency divider 112 and is connected to a reference signal input terminal of the 111 clock. A clock signal of 125 LINE_CLK is input to the clock input terminal 111, and a clock having a duty of approximately 50% of the frequency multiplied by n of the signal applied to 125 is synchronized with the signal of 125 to the signal line 117. Is output. (If an accurate 50% duty clock is required, there is no problem if the clock output signal to the 117 signal line is extracted from the middle of 112 minute cycles.)
[0024]
However, n indicates a frequency division ratio of 112, and the frequency division ratio of 112 can be freely set by setting a frequency division ratio to the external input terminal 133. For example, n = 2 means frequency division by 2, and 4 means frequency division by 4. In that case, the circuit in 112 has a plurality of specific n frequency dividing circuits to be used, and can easily be realized by selecting the output by the data of 133, so that the description of the specific circuit is omitted.
[0025]
Next, the operation will be described. FIG. 4 shows an example of an operation time chart. The video_data input terminal 21 is a 4-bit bus, and 16 types of data from 0 to F are synchronized with 31 clocks, and data corresponding to image data is externally output according to the timing as shown in FIG. It is input from. Since the CLK signal 131 is NORed with the data_enable signal of 126 and is input to the clock terminals of the registers 101, 102, 103, and 104, the data_enable signal of 126 is LOW and in an enable condition, and the CLK signal is changed from H to H. At the falling edge of L, the data is latched in each of the 101 to 104 registers, and when 126 is L, the data is sequentially shifted and transferred toward the 101 to 104 register at every falling of 131 CLK. Operate.
[0026]
Next, when the 126 data_enable signal is H, the shift operation of the registers 101 to 104 is stopped. When the LINE_CLK clock signal of 125 is input at that timing, 105, 106, 107, 127 at the falling edge thereof. The data in the registers 101, 102, 103, and 104 are latched in the input register of the PWM control circuit, and the PWM signal is output from the PWM generation circuit of 105, 106, 107, and 127 every time the PWM_CLK signal of 117 thereafter rises. A logical operation is performed, and the result is output as a PWM signal onto the output signal lines 122, 123, 124, and 129.
[0027]
When 121 is 4-bit data, the PWM can be configured so that the waveforms of the PWM signals from DATA1 to DATA16 in FIG. 4 can be selected. In the case of the embodiment of FIG. 4, the data with video_data of 0000, 0001, 0010, and 0100 is sent to the PWM output terminals of 129, 124, 123, and 122 in the timing of DATA1, DATA2, DATA3, and DATA4 in FIG. 105, 106, 107, 127 operate to be output.
[0028]
In general, the relationship between the data 121 and the output waveform can be designed so that it can be freely selected by changing the logic of the logic circuits 105, 106, 107, and 127 as necessary. Since it can be realized by the method, detailed description of the internal circuit is omitted. These drive circuits are integrated into the ASIC, thereby reducing external noise and simplifying the circuit. The registers 108, 109, 110, and 128 operate so as to latch the signals 122, 123, 124, and 129 every time the PWM_CLK signal of 117 falls, so that one data transfer is performed compared to the conventional example. In (design), it is possible to operate by giving information for four times (four lines) to PWM. Also, the multiplication factor of the PLL is greatly increased (64 or more), the frequency of PWM_CLK of 117 is increased, and the output signal of each PWM control circuit is updated between DATA1 to DATA16 of FIG. By repeatedly outputting any one of the data, it is possible to easily realize variable gradation control by turning the mirror on and off. Specifically, PWM modulation with a frequency of about 15 KHZ or more can be easily realized.
[0029]
FIGS. 5A and 5B are diagrams showing a third embodiment, wherein FIG. 5A is a plan view of the optical writing optical system, and FIG. 5B is a cross-sectional view taken along line AA ′ of FIG. In the figure, reference numerals 1 to 4 are the same constituent members as in FIG. 1, reference numeral 5 is a light source, 6 is a light shielding mirror, 7 is an elliptical long mirror, and 8 is a second light shielding slit. In the present embodiment, a linear light source such as a halogen lamp, a xenon lamp or a fluorescent tube is used as the light source 5, the longitudinal direction of the linear light source 5 is arranged in parallel with the line direction of the mirror array 1, and The light shielding mirror 6 and the elliptical long mirror 7 are arranged around the linear light source 5, and the light shielding mirror 6 and the elliptical long mirror 7 are arranged in the sub-scanning direction (longitudinal direction of the linear light source (line of the mirror array). Since the light beam is focused in a direction orthogonal to the direction (direction) and the second slit 8 is provided to limit the passage of light, this increases the energy efficiency (light utilization efficiency), and reflects light, etc. It is possible to increase the exposure accuracy. In addition, there is an effect that unnecessary light caused by scattered light generated at the end of 7 or the like can be reduced by cutting light that is not focused by the second slit. Further, in the present invention, since a linear light source is used as the light source 5, there is no unevenness due to luminance variations as in the conventional LED system, optical writing without image unevenness can be performed, and the back surface of the slit, etc. Since the light absorber is applied to suppress reflection, it is possible to obtain a certain degree of freedom in the arrangement of the mirror array. However, in order to avoid extraneous light such as scattering by the movable lens from entering the slit, the arrangement of the 1-1 mirror array with respect to the irradiation light lowers the possibility particularly when the lens transitions from ON to OFF. Therefore, it is preferable that the mounting substrate is fixed so that the reflected light at the time of OFF is reflected in a direction (1 ′ in FIG. 5B) reflected with a vector in the linear light source direction.
[0030]
【The invention's effect】
As described above, according to the present invention, in the optical writing optical system according to claim 1, the combination of the mirror array and the light-shielding slit capable of controlling the deflection direction in mirror units corresponding to the size of the pixel, Since one line can be optically written at the same time, the switching time between light and dark is very fast compared to the conventional liquid crystal shutter array method, and it is reflective, so it is lighter than a transmission type such as a liquid crystal shutter. In addition, high-speed writing is possible as compared with the raster scan method in which scanning is performed in units of one pixel. Therefore, it is possible to realize an optical writing optical system that can perform high-speed writing, has high light utilization efficiency, and can be miniaturized sufficiently. Since each column has a PWM control circuit, gradation control other than dither (mirror array ON / OFF duty control) and control to increase the number of lines can be realized, so printing in the sub-scanning direction is easy. Can be realized with high resolution and high gradation. In the optical writing optical system according to the third aspect, a linear light source such as a halogen lamp, a xenon lamp or a fluorescent tube is used as a light source, and a long reflecting mirror having an elliptical shape or the like is used as a light source. By focusing in the scanning direction (a direction orthogonal to the longitudinal direction of the linear light source), the light utilization efficiency can be further increased, and since the linear light source is used as the light source, the luminance as in the conventional LED system is used. In addition, the second slit is provided, and optical writing without image unevenness due to reflection at the slit or the like can be performed. In addition, since it is configured so that the substrate on which the mirror array is mounted and the light source is irradiated at a certain angle, the influence on the control light such as scattered light can be minimized. There is an effect that can be realized with high resolution and high gradation. Also, by configuring the PWM control circuit and its control circuit (FIG. 3) on the same IC on which the mirror array is mounted, it can be used without adding an extra circuit to the outside, and the mounting becomes easy. In addition, there is no need for an external control circuit, which facilitates design, simplifies the circuit, and reduces external noise.
[Brief description of the drawings]
FIG. 1 is a perspective view showing a schematic configuration of an optical system according to an embodiment of the present invention. FIG. 2 is a configuration diagram of a mirror array. FIG. 3 is a block diagram showing a second embodiment. Timing chart [FIG. 5] Schematic configuration diagram showing the third embodiment [Explanation of symbols]
1-1 Mirror array 1-2 Movable mirror 1-3 First light-shielding slit 3a Slit portion 1-4 Photoconductors 1-4 Buffer register (shift register)
5-7, 27 PWM generation circuit 11, 12 PLL circuit 34, 19 Gate circuit 8, 9, 10, 28 DFF
3-5 Linear light source 3-6 Shielding mirror 3-7 Elliptical long mirror 3-8 Second shielding slit

Claims (8)

In a digital optical writing device,
A mirror array in which movable mirrors arranged in an optical path from a light source to a writing medium and having a size corresponding to a pixel density in the main scanning direction are arranged in a line in the main scanning direction;
The first slit width is equal to or smaller than the pixel size in the sub-scanning direction, and includes a light-shielding slit having a width smaller than that,
An optical writing apparatus, wherein writing is performed on the writing medium by deflecting each movable mirror of the mirror array in accordance with image information. The mirror array includes a mirror PWM control circuit for each mirror, wherein each movable mirror is deflected to control an on state and an off state for each line in each sub-scanning direction. 2. The optical writing device according to 1. 3. The PWM control circuit according to claim 2, further comprising a control register, wherein the on / off state can be independently controlled by PWM modulation for each line in the sub-scanning direction according to the register value. The optical writing device described. 4. The optical writing device according to claim 3, wherein the register value of the control register is updated at regular intervals. 5. The optical writing device according to claim 4, further comprising a buffer register for writing data to a register of the control register. A linear light source such as a halogen lamp or a fluorescent tube is used as the light source and a long reflecting mirror such as an elliptical shape is used to focus the light beam in the sub-scanning direction as necessary, and the light passes through the second slit. The optical writing apparatus according to claim 1, wherein the optical writing apparatus is integrated with the light source as a line light source. 3. The optical writing device according to claim 2, wherein a light absorbing material capable of absorbing light reflected by the mirror when the movable mirror is in an off state is applied or mounted on at least the slit wall surface. . 2. The optical writing apparatus according to claim 1, wherein the mirror array includes the PWM control circuit on the same IC.

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