JP4636891B2 - Image forming apparatus - Google Patents

Description

  The present invention relates to an image forming apparatus that forms an image using image data of a small amplitude differential signal, and more particularly to EMI reduction and image degradation prevention associated therewith in the image forming apparatus.

  In recent years, in image forming apparatuses, printing speed has been increased and resolution has been increased. As a result, the transfer rate of image data has also been increased, and radiation noise associated with high-speed signal transfer using cables has been reduced. A method of transmitting between substrates using an amplitude differential signal (LVDS) is adopted.

  As a transmission technique using this LVDS, for example, the inventions disclosed in Patent Documents 1 to 3 are known. Among them, Patent Document 1 discloses an output unit and an input circuit of an output circuit when a signal is transmitted by a cable between printed wiring boards mounted on an electronic device that handles high-speed digital signals using an IC for an LVDS interface. Impedance components are coupled between the signal lines that transmit the differential signal pair at the input section of the input section, and the impedance between the signal lines of each impedance component is approximately four times the odd mode impedance (Zodd) of each line of the transmission cable. An invention is disclosed in which data transmission is performed using a small-amplitude differential signal and an accident that causes a problem when laser light is generated based on the data is prevented.

As a related invention, for example, the invention disclosed in Patent Document 2 or 3 is also known.
JP 2002-354053 A JP 2000-299706 A Japanese Patent Laid-Open No. 2002-237853

  By the way, when an impedance component such as an RC filter is inserted into the LVDS line as in the invention described in Patent Document 1, the signal waveform naturally becomes dull. Noise generation can be further suppressed, but when this signal is used as a laser lighting signal, the faster the signal, the greater the effect on lighting time, and the shorter the lighting time, the more the image density. It degrades and affects the image.

  Further, further EMI (unnecessary electromagnetic wave) countermeasures are required for higher printing speed and higher resolution. Of course, it is necessary to be strong against noise received from the outside, and to prevent deterioration in image quality.

  The present invention has been made in view of such a background, and an object of the present invention is to enable an enhanced EMI countermeasure against an increase in printing speed and resolution.

In order to solve the above-mentioned object, the first means of the present invention comprises a rotating or moving image carrier on which a latent image is formed by irradiating a light beam output from a light source, and the latent image. A PWM signal for generating a PWM signal for controlling the lighting time of the light emitting source in an image forming apparatus comprising: a developing unit that visualizes the image; and a transfer unit that transfers the visualized image onto a recording sheet. A generation unit; a control unit that converts the PWM signal into a small amplitude differential signal and sends it to an image data line; and a drive unit that drives the light emitting source according to the small amplitude differential signal in the image data line; A capacitor inserted between the image data line and GND,
The PWM signal generation unit has a difference in lighting time that is shorter when the capacitor is inserted than when the capacitor is not inserted, with respect to the lighting time of the light source with respect to the pulse width in the PWM signal. In order to correct this, the PWM signal is corrected by changing the pulse width to be wide .
The second means is characterized in that, in the first means, the transfer means transfers the visualized image onto the recording paper conveyed by a member that rotates or moves .
The third means is characterized in that, in the first means, the transfer means transfers the visualized image onto an intermediate transfer medium that rotates or moves once, and then transfers the image onto the recording paper .
According to a fourth means, in the first means, the PWM signal generating unit has the same lighting time for the light emitting source with respect to the pulse width in the PWM signal as the lighting time when the capacitor is not inserted. The pulse width is set in advance .
According to a fifth means, in the first means, the PWM signal generator includes a conversion table for correcting the PWM signal by changing the pulse width, and the conversion table includes a pulse in the PWM signal. Regarding the lighting time of the light emitting source with respect to the width, a pulse width that is the same as the lighting time when the capacitor is not inserted is set in advance .
Sixth means, in any one of the first means to the fifth means, the cable including the image data line is characterized by a twisted pair wire.

According to the present invention, faster print speeds, thereby enabling more enhanced EMI protection for high resolution.

  Embodiments of the present invention will be described below with reference to the drawings.

1. First Embodiment FIG. 1 is a schematic configuration diagram showing a main part of an image forming apparatus according to a first embodiment of the present invention. In FIG. 1, a light beam scanning device (optical unit) 1 configured as an optical unit includes a laser diode (hereinafter referred to as LD) that is turned on in accordance with image data, and a laser beam (hereinafter referred to as light beam) emitted from the LD. (Also referred to as) a collimating lens (not shown) that converts L into a parallel beam, a cylinder lens (not shown) that focuses in a line parallel to the sub-scanning direction, and a polygon mirror 101 that receives light from the cylinder lens and deflects the light. A polygon motor 102 that rotationally drives the polygon mirror 101 at a high speed, an fθ lens 103 that converts a constant angular velocity scan into a constant velocity scan, a BTL lens 104, and a mirror 105. With such a configuration, the light beam L emitted from the LD is converted into a parallel beam by a collimator lens (not shown), is deflected by the polygon mirror 101 that is rotated by the polygon motor 102 through the cylinder lens, and passes through the fθ lens 103 and the BTL 104. Then, the light is reflected by the folding mirror 105 and scanned on the photosensitive member 106. BTL is an abbreviation for Barrel Toroidal Lens, and performs focusing in the sub-scanning direction (condensing function and position correction in the sub-scanning direction (surface tilt, etc.)).

  Around the photosensitive member 106, a charger 107, a developing unit 108, a transfer unit 109, a cleaning unit 110, and a static eliminator 111 are arranged to form an image forming unit, and charging, which is a normal electrophotographic process, An image is formed on the recording paper P by exposure, development, and transfer. Then, the image on the recording paper P is fixed by a fixing device (not shown).

  FIG. 2 is a schematic configuration diagram illustrating a light beam scanning device, an image formation control unit, and an optical unit in the image forming apparatus. In this figure, a peripheral control system is added to the plan view of the laser beam scanning device 1 of FIG. 1 as viewed from above. As a control system, a printer control unit 201, a pixel clock generation unit 202, a magnification error detection unit 203, a synchronization detection lighting control unit 204, an LD drive unit 205, a polygon motor drive control unit 206, and a correction data storage unit 207 are provided. ing. The pixel clock generator 202 further includes a reference clock generator 2021, a VCO (Voltage Controlled Oscillator) clock generator 2022, and a phase-synchronized clock generator 2023. Further, a synchronization detection sensor 123 that detects the light beam L on the scanning start side in the main scanning direction of the light beam scanning apparatus 1 is provided. Thereby, the light beam L emitted from the LD unit 120, reflected by the polygon mirror 101 and transmitted through the fθ lens 103 is reflected by the mirror 121, collected by the lens 122, and incident on the synchronization detection sensor.

  In this configuration, when the light beam L passes over the synchronization detection sensor 123, a synchronization detection signal XDETP is output from the synchronization detection sensor 123 and sent to the pixel clock generation unit 202 and the synchronization detection lighting control unit 204.

  The pixel clock generation unit 202 generates a pixel clock PCLK synchronized with the synchronization detection signal XDETP, and sends the pixel clock PCLK to the LD control unit 205 and the synchronization detection lighting control unit 204. As described above, the pixel clock generation unit 202 includes the reference clock generation unit 2021, the VCO clock generation unit 2022, and the phase synchronization clock generation unit 2023.

FIG. 3 is a block diagram showing the configuration of the VCO clock generator (PLL circuit: PhaseLocked Loop) 2022. The VCO clock generator 2022 inputs the reference clock signal FREF from the reference clock generator 2021 and the signal obtained by dividing VCLK by N by the 1 / N divider 20221 to the phase comparator 20222. The phase comparison of the falling edge of the signal is performed, and the error component is output at a constant current. Then, an unnecessary high frequency component and noise are removed by an LPF (low pass filter) 20223 and sent to the VCO 20224. The VCO 20224 outputs an oscillation frequency depending on the output of the LPF 20223. Therefore, the frequency of VCLK can be changed by changing the frequency of FREF and the frequency division ratio: N from the printer control unit 201.
The phase synchronization clock generation unit 2023 generates a pixel clock PCLK from VCLK set to a frequency eight times the pixel clock frequency, and further generates a pixel clock PCLK synchronized with the synchronization detection signal XDETP. Further, the frequency of VCLK can be changed by changing the frequency of FREF and the frequency division ratio: N from the printer control unit 201, and thus the frequency of the pixel clock PCLK can also be changed. Then, the overall magnification of the image can be changed by changing the frequency of the pixel clock PCLK.

  The synchronization detection lighting control unit 204 first turns on the LD forced lighting signal BD to forcibly light the LD in order to detect the synchronization detection signal XDETP. However, after detecting the synchronization detection signal XDETP, the synchronization detection signal XDETP is detected. With the XDETP and the pixel clock PCLK, the LD is turned on at a timing at which the synchronization detection signal XDETP can be reliably detected without causing flare light. The data is sent to the LD control unit 205.

  The LD control unit 205 generates LD lighting data synchronized with the pixel clock PCLK from the synchronous detection forcible lighting signal BD and the input image data, converts it into LVDS, and sends it to the LD driving unit 1201 of the LD unit 120. Send (see FIG. 4). The LD driving unit 1201 controls the lighting of the LD according to the LD lighting data with the light amount set by the printer control unit 201. Then, a laser beam is emitted from the LD unit 120, deflected by the polygon mirror 101, passes through the fθ lens 103, and scans on the photosensitive member 106. The polygon motor control unit 206 controls the rotation of the polygon motor so as to maintain a prescribed number of rotations based on a control signal from the printer control unit 201.

  FIG. 4 is a diagram showing the configuration of the LD unit 120. As is well known, the LD 1202 includes an LD (laser diode) 1202 and a PD (photodiode) 1203. The LD driving unit 1201 controls the LD current Id so as to keep the monitor voltage Vm of the PD 1203 constant in order to turn on the LD 1202 with the light amount instructed from the printer control unit 201 (APC operation: auto power control). When changing the amount of light, the voltage Vm is changed by an instruction (control signal) from the printer control unit 201, and the LD current Id is controlled so as to keep the set voltage Vm constant. Also, the LD 1202 is ON / OFF controlled in accordance with image data (LD lighting data) sent from the LD control unit 1201.

  FIG. 5 is an explanatory diagram showing a method for transmitting image data (LD lighting data). In this embodiment, an inductor 215 is used as a filter. That is, the LVDS driver 2051 and the LD driving unit 1201 in the LD control unit 205 are connected by the cable 210, and an inductor 215 is provided as a filter in the previous stage of the cable 210. As a result, the LD lighting data output from the LVDS driver 2051 in the LD control unit 205 is sent to the LD driving unit 1201 in the LD unit 120 via the inductor 215. A signal sent from the LBDS driver 2051 is a small-amplitude differential signal and is terminated on the LD driving unit 201 side. In this embodiment, the inductor 215 is used as a filter, but the present invention is not limited to this.

2. Second Embodiment In this embodiment, an RC filter 216 is used instead of the inductor 215 as shown in FIG. 6 as a filter in the first embodiment. Note that the RC filter 216 may be configured only with a capacitor.

  FIG. 7 is a diagram showing the influence on the optical pulse due to the insertion of the filter (capacitor, inductor) in FIG. 5 and FIG. Even if the input data to the LVDS driver 2051 is the same, the actual lighting time (light pulse width) varies depending on the presence or absence of a capacitor. When a capacitor is inserted, the smaller the input data (the shorter the pulse width), the greater the influence on the LD lighting time.

  It is assumed that the LD control unit 205 includes a PWM signal generation unit that controls the lighting time of the LD, and a 16-division PWM signal can be generated. When the image data input to the LD control unit 205 is 1 bit (binary), the LD lighting data (pulse width data) is determined by the control signal from the printer control unit 201. In this case, there is no problem as long as the data is not affected by the insertion of the capacitor. However, when using the affected data, the data should be changed in advance to obtain the same LD lighting time as before the insertion of the capacitor. . For example, it is assumed that 10/16 pulse data is used before inserting a capacitor and an LD lighting time of 12.5 nS is obtained. If it is narrowed to 10.0 nS due to insertion of a capacitor, to obtain 12.5 nS, if 11/16 pulse data is necessary, the data is changed from 10/16 to 11/16 pulse data.

  The same applies to the case where the image data input to the LD control unit 205 is 2 bits (4 values). In the case of 2 bits, there are four types of data of “00”, “01”, “10”, and “11”, and the PWM signal is determined by setting from the printer control unit 201 for each of them. Since '00' has no data, the pulse data is changed for other data so that there is no change in the LD lighting time due to the insertion of the capacitor. The same applies to image data of 3 bits or more.

  Then, the changed pulse data is signal-converted by the LVDS driver 2051 and sent to the LD driving unit 1201 via a filter, for example, an RC filter 216, to light the LD.

  FIG. 8 is a diagram showing an example of the input data conversion table. For example, assuming that the LD control unit 205 includes a PWM signal generation unit that controls the lighting time of the LD and can generate a 16-divided PWM signal, a conversion table 211 as shown in FIG. 8 is created in advance from the characteristics of FIG. Keep it. When 17-value image data is input to the LD control unit 205, the pulse data is converted by the conversion table 211, the signal is converted by the LVDS driver 2051, and sent to the LD drive unit 1201 through a filter to light the LD.

  Since the pulse is narrowed by inserting the capacitor, as a result, in the example of FIG. 8, the number of gradations is reduced from 17 values to 14 values, but the image density in the highlight portion (low gradation portion) can be ensured.

  In the example shown in FIG. 6, the LVDS driver 2051 and the LD driving unit 1201 are connected by the cable 210. However, for example, a twisted pair wire 212 can be used instead of the cable 210 as shown in FIG. When the twisted pair wire 212 is used in this way, EMI countermeasures are further strengthened, and deterioration in image quality can be prevented.

  The other parts are configured in the same way as in the first embodiment and function in the same way. The image data transmission method is also the same as in the first and second embodiments.

3. Third Embodiment FIG. 10 is a schematic configuration diagram showing a four-drum type image forming apparatus according to a third embodiment. The image forming apparatus includes four image forming units (photosensitive members) for forming a color image in which four color images of yellow (Y), magenta (M), cyan (C), and black (BK) are superimposed. 106, a developing unit 108, a charger 107, a transfer unit 109, a cleaning unit 110 (not shown), and four sets of optical units (laser beam scanning device 1). Accordingly, the four image forming apparatuses shown in FIG. 1 are arranged side by side, the first color image is formed on the recording paper P conveyed in the direction of the arrow by the transfer belt B, and then the second color, the third color, By transferring the images in the order of the fourth color, a color image in which the four color images are superimposed is formed on the recording paper, and the image on the recording paper is fixed by a fixing device (not shown).

  The transfer belt B is stretched between the rollers R and is driven by a conveyance motor M. As for the optical unit, four sets shown in FIG. 2 are provided. Since the configuration and control of each optical unit 1 are the same as those in the first embodiment described above, description thereof is omitted. Also in the image forming apparatus of this configuration, the image data (LD lighting data) transmission method described in the first and second embodiments can be applied. In this case, since the light beam scanning device is provided independently for each color, the power transmission is performed for each color.

  Other parts not specifically described are configured in the same manner as the first and second embodiments described above and function in the same manner.

  As described above, according to these embodiments, the following effects can be obtained.

1) Since a filter is inserted on the image data line of the small amplitude differential signal and signal transmission is performed, EMI countermeasures can be further strengthened.

2) Since the image data is corrected by changing the data input to the control unit that generates the small-amplitude differential signal for the change in the image data due to the filter insertion, it is possible to prevent the image quality from being deteriorated.

3) Since correction is performed using the conversion table, it is possible to prevent deterioration in image quality without being affected by input data.

4) Since the image data of the small-amplitude differential signal is transmitted using the twisted pair line, the countermeasure against EMI is further strengthened and the deterioration of the image quality can be prevented.

1 is a schematic configuration diagram illustrating a main part of an image forming apparatus according to a first embodiment of the present invention. 1 is a schematic configuration diagram illustrating a light beam scanning device, an image formation control unit, and an optical unit in an image forming apparatus according to a first embodiment. FIG. 3 is a block diagram showing a configuration of a VCO clock generation unit in FIG. 2. It is a figure which shows the structure of LD unit in FIG. It is explanatory drawing which shows the transmission method of image data (LD lighting data). It is explanatory drawing which shows the transmission method of the image data (LD lighting data) which concerns on 2nd Embodiment. It is a figure which shows the influence on the optical pulse by the filter (capacitor, inductor) insertion in FIG.5 and FIG.6. It is a figure which shows an example of an input data conversion table. It is explanatory drawing which shows the other example of the transmission method of image data (LD lighting data). FIG. 5 is a schematic configuration diagram illustrating a four-drum image forming apparatus according to a third embodiment.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Light beam scanning device 106 Photosensitive drum 107 Charging device 108 Developing unit 109 Transfer device 110 Cleaning unit 111 Electric discharge 120 LD unit 123 Synchronization detection sensor 201 Printer control unit 202 Pixel clock generation unit 204 Synchronization detection lighting control unit 205 LD control Unit 206 polygon motor control unit 210 cable 212 twisted pair wire 215 inductor 216 RC filter 1201 LD drive unit 1202 LD
1203 PD
2051 LVDS driver

Claims (6)

A rotating or moving image carrier on which a latent image is formed by irradiating a light beam output from a light source, developing means for visualizing the latent image, and the visualized image In an image forming apparatus comprising a transfer means for transferring onto a recording paper ,
A PWM signal generating section for generating a PWM signal for controlling the lighting time of the light emitting source, a control section for converting the PWM signal into a small amplitude differential signal and sending it to an image data line , and the small signal in the image data line A drive unit for driving the light emitting source according to an amplitude differential signal, and a capacitor inserted between the image data line and GND,
The PWM signal generation unit has a difference in lighting time that is shorter when the capacitor is inserted than when the capacitor is not inserted, with respect to the lighting time of the light source with respect to the pulse width in the PWM signal. In order to correct the image, the PWM signal is corrected by changing the pulse width to be widened . The image forming apparatus according to claim 1, wherein said transfer means, images forming device you characterized in that transferred to the recording sheet being conveyed by the rotating or moving member of the visualized image. The image forming apparatus according to claim 1, wherein the transfer means, after transferring to an intermediate transfer medium to once rotate or move the visualized image, images characterized in that transferred onto the recording Forming equipment. 2. The image forming apparatus according to claim 1, wherein the PWM signal generation unit has a pulse width that is the same as a lighting time when the capacitor is not inserted, with respect to a lighting time of the light emission source with respect to a pulse width in the PWM signal. images forming device you characterized in that There are preset. 2. The image forming apparatus according to claim 1, wherein the PWM signal generation unit includes a conversion table for correcting the PWM signal by changing the pulse width, and the conversion table corresponds to a pulse width in the PWM signal. wherein the lighting time of the light emitting source, inserted when not lighting time that the pulse width becomes the same are set in advance with the images forming apparatus wherein said capacitor. The image forming apparatus according to any one of claims 1 to 5, the cable including the image data line images forming device you being a twisted pair line.

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