JP2011056916A - Driving device, optical scanner, and image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To faithfully reproduce gradation property in the case of writing respective pixels in the image data inputted by a writing element. <P>SOLUTION: A writing controller 20, on the basis of inputted image data, forms a switching signal showing presence/absence of writing for every pixel of the image data and, on the basis of the switching signal, outputs a light source driving signal that drives a light source LD for writing by each pixel. The writing controller 20 makes the driving signal overshoot for every pixel driving the light source LD. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a driving device, an optical scanning device, and an image forming apparatus.

  Conventionally, when writing each pixel in the input image data by driving a light source such as a laser diode or VCSEL (Vertical-Cavity Surface-emitting Laser), the rise of the light source In order to improve the speed, it is known to cause an overshoot in the driving current of the light source (see Patent Document 1).

  However, the above-described prior art does not always cause overshoot for each pixel in the drive current to the light source. For example, when the driving current is a pulse width modulation signal and the gradation is reproduced with the size of the pulse width, when the pulse width continues with the same maximum width as the period of one pixel, the first rising portion is displayed. Only overshoot occurs. In such a case, the linearity of the light quantity with respect to the pulse width is lost, and the gradation cannot be faithfully reproduced.

  The present invention has been made in view of the above, and a driving device capable of faithfully reproducing gradation when writing each pixel in input image data by a writing element. An object of the present invention is to provide an optical scanning device and an image forming apparatus.

  In order to solve the above-described problems and achieve the object, the driving device of the present invention includes a generating unit that generates a switching signal indicating whether or not writing is performed for each pixel of the image data based on the input image data. Output means for driving a write element that writes data for each pixel based on the switching signal, and the output means drives the drive for each pixel that drives the write element. It is characterized by overshooting the signal.

  An optical scanning device of the present invention scans irradiation light of a light source that blinks based on a driving signal output from the driving device according to any one of claims 1 to 3 and the driving device for each pixel. And optical scanning means for performing writing.

  According to another aspect of the present invention, there is provided an image forming apparatus including: the optical scanning device according to claim 4; an image carrier on which the optical scanning device performs writing; And image forming means for forming the image.

  According to the present invention, when writing each pixel in the input image data by the writing element, there is an effect that the gradation can be faithfully reproduced.

FIG. 1 is a block diagram illustrating a configuration of a color image forming apparatus according to the present embodiment. FIG. 2 is a diagram illustrating optical scanning of the color image forming apparatus. FIG. 3 is a diagram illustrating a configuration of the write control unit. FIG. 4 is a diagram showing the relationship between the gradation of one pixel and the PWM width. FIG. 5 is a diagram illustrating a conventional light source drive signal and the light source drive signal of the present embodiment. FIG. 6 is a diagram illustrating a conventional light source drive signal and the light source drive signal of the present embodiment. FIG. 7 is a diagram illustrating the relationship between the PWM width and the light amount. FIG. 8 is a diagram illustrating a configuration of a write control unit according to a modification.

  Exemplary embodiments of a driving device, an optical scanning device, and an image forming apparatus according to the present invention will be explained below in detail with reference to the accompanying drawings. FIG. 1 is a block diagram showing a configuration of a color image forming apparatus 1 according to the present embodiment.

  As shown in FIG. 1, the color image forming apparatus 1 is of an electrophotographic tandem type, and roughly, there are four drum-shaped photosensitive drums 2Y (yellow) and 2C (cyan) which are image carriers. , 2M (magenta), 2K (black), and toner images formed by developing the electrostatic latent images on the photosensitive drums 2Y, 2C, 2M, 2K by the developing units 3Y, 3C, 3M, 3K. Then, the images are sequentially transferred onto the intermediate transfer belt 5L as a transfer medium by the primary transfer devices 4Y, 4C, 4M, and 4K, and the images on the intermediate transfer belt 5L are collectively transferred onto the sheet P as a transfer body by the secondary transfer device 6L. It uses an indirect transfer method for transferring.

  The intermediate transfer belt 5L is an endless belt and is stretched by a plurality of rollers 10L to 13L. The intermediate transfer belt 5L is rotated at a constant speed by a motor (not shown) connected to any one of the rollers 10L to 13L. It is driven in the moving direction (sub-scanning direction) D1. The intermediate transfer unit is configured by the intermediate transfer belt 5L and the drive unit (motor and rollers 10L to 13L, etc.) of the intermediate transfer belt 5L. On the upper side of the intermediate transfer belt 5L, there are four photosensitive drums 2K, 2M, 4M for the respective colors of black, magenta, cyan and yellow along the rotation direction D1 of the intermediate transfer belt 5L. 2C and 2Y are respectively arranged in parallel.

  For the circulation of the photosensitive drums 2K, 2M, 2C, 2Y, the charging devices 7K, 7M, 7C, 7Y, the developing units 3K, 3M, 3C, 3Y, the primary transfer devices 4K, 4M, 4C, 4Y, Cleaning devices 8K, 8M, 8C, and 8Y constituted by blades, brushes, and the like, and neutralizing devices 9K, 9M, 9C, and 9Y are provided, respectively.

  The primary transfer devices 4K, 4M, 4C, and 4Y are disposed to face the photosensitive drums 2K, 2M, 2C, and 2Y, respectively, with the intermediate transfer belt 5L interposed therebetween. That is, the intermediate transfer belt 5L is rotated while being sandwiched between the primary transfer devices 4K, 4M, 4C, and 4Y and the photosensitive drums 2K, 2M, 2C, and 2Y.

  The photosensitive drums 2K, 2M, 2C, and 2Y are rotationally driven in the rotation direction D2. At this time, the charging devices 7K, 7M, 7C, and 7Y charge the surfaces of the photosensitive drums 2K, 2M, 2C, and 2Y to a predetermined polarity. Is done. Next, the light beam scanning device 16L irradiates the charged surfaces of the photosensitive drums 2K, 2M, 2C, and 2Y with a light beam (for example, laser light) that flickers according to the light source drive signal output from the writing control unit 20. As a result, electrostatic latent images are formed on the photosensitive drums 2K, 2M, 2C, and 2Y. The electrostatic latent images formed in this manner are developed into toner images of respective colors by the developing units 3K, 3M, 3C, and 3Y, and are visualized.

  The black, magenta, cyan, and yellow toner images developed on the photosensitive drums 2K, 2M, 2C, and 2Y are sequentially superimposed on the surface of the intermediate transfer belt 5L by the action of the primary transfer devices 4K, 4M, 4C, and 4Y. In this state, the image is transferred and a full-color composite color image is formed.

  The photosensitive drums 2K, 2M, 2C, and 2Y are cleaned by the cleaning devices 8K, 8M, 8C, and 8Y after the toner images remaining on the photosensitive drums 2K, 2M, 2C, and 2Y are removed. , 9M, 9C, 9Y.

  The secondary transfer device 6L is disposed to face the roller 12L with the intermediate transfer belt 5L interposed therebetween. Between the roller 12L (intermediate transfer belt 5L) and the secondary transfer device 6L, the paper P fed from a paper feeding unit (not shown) is fed at a predetermined timing under the control of the controller 30. . When the paper P is fed in the paper transport direction D3 between the roller 12L (intermediate transfer belt 5L) and the secondary transfer device 6L, the composite color image carried on the intermediate transfer belt 5L is transferred to the secondary transfer device 6L. By the action, it is transferred to the paper P at a time.

  Thereafter, the composite color image on the paper P is fixed by heat and pressure by the fixing device 14L, and is discharged onto a paper discharge tray (not shown). On the other hand, the transfer residual toner adhering to the surface of the intermediate transfer belt 5L after the transfer of the composite color image is removed by the cleaning device 15L.

  The writing control unit 20 is a CPU (Central Processing Unit) or a plurality of ASICs (Application Specific Integrated Circuits), and outputs a light source driving signal (driving signal) to the light beam scanning device 16L under the control of the controller 30. Thus, the beam is emitted from the light beam scanning device 16L described above.

  The controller 30 includes a CPU, a ROM (Read Only Memory), a RAM (Random Access Memory), and the like. The CPU expands a program stored in the ROM in a work area of the RAM and sequentially executes the program. The operation of the color image forming apparatus 1 such as image formation is centrally controlled.

  The synchronization sensor 40 detects the beam irradiated by the light beam scanning device 16L, and outputs a synchronization signal for synchronizing the timing of outputting the light source drive signal to the writing control unit 20 according to the detection result.

  Here, beam irradiation (light scanning) by the light beam scanning device 16L will be described. FIG. 2 is a diagram illustrating light scanning by the light beam scanning device 16L. As shown in FIG. 2, the light beam scanning device 16L includes a light source LD, a polygon mirror LM, and an optical member LL.

  The light source LD may be a laser diode, VCSEL, LED (Light Emitting Diode), EL (Electro Luminescence), or the like. The polygon mirror LM is a rotary polygon mirror whose rotation is controlled under the control of the writing control unit 20, and deflects the beam irradiated by the light source LD. The optical member LL is an fθ lens or the like, and scans (scans) the beam deflected by the polygon mirror LM to the synchronization sensor 40 and the photosensitive drums 2Y, 2C, 2M, and 2K. For this reason, every time the beam for one line is scanned by the deflection of the polygon mirror LM, the beam is incident on the synchronization sensor 40. The synchronization sensor 40 detects the incidence of this beam, thereby detecting the incidence of each beam. A synchronization signal indicating the scanning timing is output to the writing control unit 20.

  The controller 30 outputs image data to be formed on the paper P to the writing control unit 20 together with a start signal indicating the start of image formation. The image data to be formed is image data for which copying or printing has been instructed. Specifically, when the color image forming apparatus 1 is a multifunction device including a touch panel, a key operation unit, a scanner, a communication interface (all not shown), etc., in response to an instruction input from the touch panel, the key operation unit, or the like. There are image data of a document read by the scanner and image data input from an external device via a communication interface.

  The writing control unit 20 starts the operation in response to the start signal from the controller 30, and then transmits a light source driving signal obtained by modulating the image data input from the controller 30 at a predetermined timing (one line or a plurality of lines). Output to the light source LD for each scan). Specifically, the writing control unit 20 converts the image data input from the controller 30 into a light source drive signal that drives the light source LD in units of pixels included in one line in accordance with the synchronization signal from the synchronization sensor 40. Modulate and output to the light source LD. Accordingly, the light beam scanning device 16L scans the beam that the light source LD blinks in accordance with the above-described light source drive signal, thereby generating an image corresponding to the image data input from the controller 30 with the photosensitive drums 2Y, 2C, An electrostatic latent image is formed on 2M and 2K. That is, the writing control unit 20 is a driving device that outputs a light source driving signal for driving the light beam scanning device 16L based on the input image data.

  Next, the write control unit 20 will be described in detail. FIG. 3 is a diagram illustrating a configuration of the write control unit 20. As shown in FIG. 3, the write control unit 20 includes a TG 21, a raster conversion unit 22, a γ conversion unit 23, an overshoot correction unit 24, DACs 25 and 26, and an amplifier 27.

  The TG 21 (Timing Generator) generates a clock signal (pixel synchronization signal) for synchronizing processing in units of one pixel and outputs the clock signal to the raster conversion unit 22, the γ conversion unit 23, and the overshoot correction unit 24. The raster conversion unit 22 converts input data (image data) from the controller 30 into a raster format that can be scanned according to the number of beams (number of pixels). The data converted into the raster format is output to the γ conversion unit 23 and the overshoot correction unit 24 as a switching signal indicating ON / OFF of writing in units of pixels in accordance with the timing of the synchronization signal and the pixel synchronization signal. That is, the raster conversion unit 22 is a generation unit that generates a switching signal indicating whether or not image data is written for each pixel based on input image data.

  The γ conversion unit 23 performs pulse width modulation on the switching signal output from the raster conversion unit 22 based on the image data input to the writing control unit 20 and indicating the gradation level for each pixel in the pulse width. (PWM: Pulse Width Modulation, hereinafter referred to as PWM) signal. The PWM signal converted by the γ converter 23 is output to the DAC 25 in accordance with the timing of the pixel synchronization signal. Note that the γ conversion unit 23 may perform γ conversion on the input image data to perform contrast adjustment, and convert the image data into a PWM signal.

  FIG. 4 is a diagram showing the relationship between the gradation of one pixel and the PWM width. While the switching signal output from the raster conversion unit 22 is turned on / off for each pixel, the PWM signal is provided with a pixel synchronization as shown in FIG. The PWM width is changed in the range of 0 to 100% in the period of one pixel by the signal. In the illustrated example, the period for one pixel is divided into ten, and the gradation from white to solid black is expressed in 11 steps by the PWM width. For example, when the PWM width is 10%, it means that the lighting period of the light source LD per pixel is 1/10.

  The overshoot correction unit 24 outputs to the DAC 25 a correction signal for generating an overshoot waveform in the PWM signal when the switching signal is ON. Specifically, this correction signal is a PWM signal corresponding to the overshoot waveform. The correction signal may be output at any time as long as it is within the period of one pixel when the switching signal is ON. For example, not only the timing of causing an overshoot at the first rise, but also the timing of causing an overshoot in the central portion of the pixel. Further, the correction signal may be output several times as long as it is within the period of one pixel when the switching signal is ON. The timing and number of times of outputting such a correction signal may be appropriately changed according to the characteristics of the light source LD.

  The DACs 25 and 26 are digital-analog conversion circuits. The DAC 25 converts the input PWM signal into a switching current having an amplitude corresponding to the light amount setting and a pulse width corresponding to the PWM signal. The DAC 26 converts the input correction signal into an overshoot current that is a waveform overshooted from the amplitude corresponding to the light amount setting.

  The amplifier 27 amplifies a current obtained by adding the switching current output from the DAC 25 and the overshoot current output from the DAC 26, and generates a light source driving signal for driving the light source LD. That is, the configuration including the overshoot correction unit 24, the γ conversion unit 23, the DACs 25 and 26, and the amplifier 27 outputs a light driving signal for writing for each pixel based on the switching signal to the light source LD, and the light source LD. This is output means for overshooting the light drive signal for each pixel to be driven.

  FIG. 5 is a diagram illustrating a conventional light source drive signal and the light source drive signal of the present embodiment. In FIG. 5, the upper part illustrates a conventional light source driving signal, and the lower part illustrates a light source driving signal of the present embodiment. As shown in FIG. 5, when pixels with a PWM width of 100% are continuous, the conventional light source drive signal has an overshoot only at the first rise because an overshoot occurs in response to the switching current pulse. And overshoot did not occur for the subsequent pixels. On the other hand, in the light source drive signal of this embodiment, since overshoot occurs for each pixel, overshoot occurs not only at the first rise but also at the rise of all pixels.

  FIG. 6 is a diagram illustrating a conventional light source drive signal and the light source drive signal of the present embodiment. More specifically, the conventional light source when the PWM width is 90% and the PWM width is 100%. It is a figure for comparing a drive signal and the light source drive signal of this embodiment. FIG. 7 is a diagram illustrating the relationship between the PWM width and the light amount.

  As shown in FIG. 6, when the PWM width is 90%, overshoot occurs in the light source drive signal for each pixel. However, when the PWM width is 100%, overshoot for each pixel does not occur in the conventional light source drive signal. Therefore, as shown in FIG. 7, conventionally, the integrated light quantity of the light source LD per pixel may be larger under the condition when the PWM width is 90% than when the PWM width is 100%. In some cases, it is impossible to faithfully reproduce the gradation of the image.

  On the other hand, in the light source drive signal of this embodiment, as shown in FIG. 6, overshoot occurs for each pixel even when the PWM width is 100%. Therefore, in this embodiment, as shown in FIG. 7, the integrated light quantity of the light source LD per pixel changes linearly with respect to the change in the PWM width, so that the gradation of the image can be faithfully reproduced. it can.

<Modification>
Here, a modified example of the write control unit 20 will be described. FIG. 8 is a diagram illustrating a configuration of the write control unit 20a according to the modification. In the writing control unit 20a according to the modification, the PWM signal rises for each pixel by preventing the PWM width of the PWM signal from becoming 100% in the period of one pixel by the pixel synchronization signal. Yes.

  Specifically, as illustrated in FIG. 8, the write control unit 20 a includes a γ conversion unit 23 a instead of the γ conversion unit 23 described above. The γ conversion unit 23a converts the switching signal into a PWM signal so that the PWM width of the PWM signal does not become 100% in the period of one pixel by the pixel synchronization signal. Specifically, the pulse width falls at the end of a period of at least one pixel by converting the PWM width to 100% and converting it to 99%. Note that the fall period at the end of the above period is set as short as possible in order to faithfully reproduce the gradation of the image.

  The overshoot correction unit 24 receives the PWM signal from the γ conversion unit 23a, and outputs a correction signal for causing an overshoot in response to the rise of the PWM signal. In the PWM signal output from the γ conversion unit 23a, the pulse falls at the end of the period of at least one pixel. Therefore, if the gradation of the pixel is not 0%, the pulse for each pixel has a rise. . Therefore, if the gradation of the pixel is not 0%, the overshoot correction unit 24 outputs a correction signal for each pixel, and the write control unit 20a supplies a light source drive signal that overshoots for each pixel to the light source LD. Can be output.

  In the modification, for example, when a light source drive signal is output to the light source LD so as to form a black solid (PWM width equivalent to 100%) on the paper P, the light source drive signal includes a pulse at the end of the period of one pixel. Although the falling period occurs, the influence on the gradation can be sufficiently reduced as compared with the case where the overshoot for each pixel disappears.

  In the above embodiment, the color image forming apparatus 1 that performs image formation by electrophotography is illustrated, and the writing element that performs writing for each pixel has been described as the light source LD. However, the image forming method of the color image forming apparatus 1 is not limited to the electrophotographic method, and may be an ink jet method or a thermal transfer method as long as it uses a writing element that performs writing for each pixel. Therefore, the writing element is not limited to the light source LD, and may be a piezoelectric element for ejecting ink for each pixel, a thermal head for performing thermal transfer for each pixel, or the like.

  The color image forming apparatus 1 according to the above embodiment is applied to a multi-function machine having at least two functions among a copy function, a printer function, a scanner function, and a facsimile function, a copier, a printer, a scanner device, a facsimile device, and the like. However, the aspect is not particularly limited.

1 Color Image Forming Apparatus 2Y, 2C, 2M, 2K Photosensitive Drum 16L Light Beam Scanning Device 20, 20a Write Control Unit 21 TG
22 Raster converter 23, 23a γ converter 24 Overshoot corrector 25, 26 DAC
27 Amplifier 30 Controller 40 Synchronization sensor LD Light source LM Polygon mirror LL Optical member P Paper

JP 2008-213246 A

Claims (5)

Generating means for generating a switching signal indicating the presence or absence of writing for each pixel of the image data based on the input image data;
An output means for outputting a driving signal for driving a writing element for writing for each pixel based on the switching signal;
With
The output device overshoots the drive signal for each pixel that drives the writing element. The output means converts the switching signal into a pulse waveform signal for driving the writing element; and
A correction signal generation unit that generates a correction signal for adding an overshoot waveform to the pulse waveform signal according to the switching signal, and an output that outputs the drive signal by adding the correction signal to the pulse waveform signal The drive device according to claim 1, further comprising a unit.   The output means is a pulse waveform signal for driving the writing element, a conversion unit for converting the switching signal into a pulse waveform signal including a pulse falling period at the end of a period of at least one pixel, A correction signal generation unit that generates a correction signal for adding a shoot waveform to the pulse waveform signal in response to a rising edge of the pulse waveform signal, and outputs the drive signal by adding the correction signal to the pulse waveform signal The drive unit according to claim 1, further comprising: an output unit configured to output the output unit. The drive device according to any one of claims 1 to 3,
An optical scanning unit that performs writing for each pixel by scanning irradiation light of a light source that blinks based on a driving signal output by the driving device;
An optical scanning device comprising: An optical scanning device according to claim 4,
An image carrier on which the optical scanning device performs writing; and
Image forming means for forming an image by transferring an image written on the image carrier to paper;
An image forming apparatus comprising:

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