JP4524116B2 - Image forming apparatus - Google Patents

Description

  The present invention relates to an image forming apparatus, and more particularly to an image forming apparatus that forms an image by scanning a light beam on an image carrier.

  In general, in an image forming apparatus using a light beam scanning device, a light beam is modulated by image data, and a polygon mirror is rotated so as to be deflected at a constant angular velocity in a main scanning direction. It is configured to correct and scan on the photoreceptor.

  Here, in general, in an image forming apparatus, particularly when a plastic lens is used as an fθ lens, the shape and refractive index of the plastic lens change due to a change in environmental temperature, a change in internal temperature, and the like. When the change is made in this way, the scanning position on the image surface of the photosensitive member changes, an image magnification error in the main scanning direction occurs, and a high-quality image may not be obtained.

  Further, in a conventional image forming apparatus that forms a plurality of color images using a plurality of light beams and lenses, there is a possibility that a high-quality image cannot be obtained if a color shift occurs due to a magnification error of each light beam. is there. When a light beam scanning device in which the scanning directions of the respective light beams are reversed is used, the magnification error becomes a color shift as it is, so that the image quality is deteriorated.

  For this reason, there is a technique disclosed in Patent Document 1 previously filed by the present applicant in order to correct an image magnification error and a color shift caused by a change in environmental temperature, a change in in-machine temperature, and the like.

In Patent Document 1, a light beam is detected by at least two sensors, a passage time interval between the sensors is measured by a predetermined clock count, and a written image is set so that the result matches a preset reference count value. The main scanning magnification is corrected by changing the frequency, and a new reference count value is acquired and updated at the corrected image frequency.
Accordingly, an object of the present invention is to obtain a high-quality image that always maintains the same magnification and a high-quality image without color misregistration without being affected by the change in the scanning position due to the temperature change.
JP 2002-160398 A

However, in the case of the above-described Patent Document 1, it is sufficient to turn on the light beam before the beam passes through the start side sensor and the end side sensor. However, when measuring during image formation, the light beam is turned on. The flare light caused by the light may affect the image, and considering the life of the LD, it is preferable that the lighting time is as short as possible.
In addition, when the writing image frequency is changed to correct the magnification, when the lighting timing of the light beam is controlled using a counter that operates, the lighting start position with respect to the sensor position changes, and the light beam is detected by the sensor. It may not be possible.

The present invention has been made in view of such a situation, and eliminates unnecessary lighting of a light beam when measuring a time difference, prevents deterioration in image quality, and extends the life of an LD. An object is to provide an apparatus.
Another object is to provide an image forming apparatus capable of reliably detecting a light beam for measuring a time difference.

In order to achieve such an object, an image forming apparatus according to the present invention includes a light emitting source that emits a light beam, a deflecting unit that deflects the light beam output from the light emitting source in a main scanning direction by a plurality of deflecting surfaces, First and second light beam detecting means for detecting the light beam deflected by the means, and the first light beam detecting means detects the light beam and outputs a start side synchronization detection signal . Measures the time difference between the detection of the light beam and the output of the end-side synchronization detection signal, and obtains the magnification error detection means for obtaining the magnification error in the main scanning direction from the time difference, and the magnification error detection means. an image forming apparatus having a control means for correcting the image magnification, and the start-side synchronization detection signal is input by changing the frequency of the pixel clock based on the obtained magnification error A counter for counting the pixel clocks from the time it is reset by the line synchronizing signal output from the scanning line synchronization signal generator, the and the second set value when the count value of the counter reaches a first set value Each of the light emitting sources is turned on at the time of arrival, and during the image formation, after the start side synchronization detection signal is output, the count value of the counter reaches the second set value according to the image data. and a lighting control unit that Ru lights the light-emitting source, the first set value can detect the first light beam detecting means a light beam, and be a value set so that there is no influence of the flare light the second set value is the second light beam detecting means to detect the light beam, and a set value so that there is no influence of the flare light, the control means varying the frequency of the pixel clock And changes the first setting value and the second setting value in accordance with.

A table storing the frequency of the pixel clock and the first and second setting values in association with each other; and the control means is configured to store the first setting value and the second setting based on the table. It is preferable to change the value.
The lighting control unit preferably turns off the light emitting source when the first light beam detecting unit detects the light beam and when the second light beam detecting unit detects the light beam. .
The lighting controller turns off the light emitting source when the count value of the counter reaches a third set value when no light beam is detected by the first or second light beam detecting means. It is preferable to make it.

As described above, according to the present invention, it is possible to eliminate useless lighting of a light beam when measuring a time difference, to prevent deterioration of image quality, and to extend the life of a light emitting source.
In addition, the light beam for measuring the time difference can be reliably detected.

  Next, an image forming apparatus according to the present invention will be described in detail with reference to the drawings.

FIG. 1 shows an outline of the configuration around the light beam scanning device 10 and the photoconductor 20 in the image forming apparatus as the first embodiment of the present invention.
In the light beam scanning device 10 described above, the LD light beam that is turned on by image data is converted into a parallel light beam by a collimator lens (not shown), passes through a cylinder lens (not shown), and is rotated by a polygon motor. 11, passes through the fθ lens, passes through the BTL, is reflected by the mirror, and scans on the photoconductor 20. 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 photoconductor 20, a charger, a developing unit, a transfer unit, a cleaning unit, and a static eliminator are provided, and an image is formed on a recording sheet by charging, exposure, development, and transfer, which are normal electrophotographic processes. . Although not shown, the image on the recording paper is fixed by the fixing device.
In the present embodiment, the polygon mirror 11 has six surfaces.

FIG. 2 shows the image formation control unit and the light beam scanning device 10 in the image forming apparatus as the present embodiment.
A synchronization detection sensor 1 (13a) and a synchronization detection sensor 2 (13b) for detecting a light beam are provided at both ends in the main scanning direction of the light beam scanning device 10, and the light beam transmitted through the fθ lens 14 is mirror 1 (15a). ), Reflected by the mirror 2 (15b), condensed by the lens 1 (16a) and the lens 2 (16b), and incident on the synchronization detection sensor 1 (13a) and the synchronization detection sensor 2 (13b). ing.

  As the light beam passes over the sensor, the synchronization detection sensor 1 (13a) outputs a start-side synchronization detection signal XDETP, and the synchronization detection sensor 2 (13b) outputs an end-side synchronization detection signal XEDETP to detect a magnification error. Input to the unit 32. The magnification error detector 32 measures the time from the falling edge of the start side synchronization detection signal XDETP to the falling edge of the end side synchronization detection signal XEDETP, compares it with the reference time difference, and outputs correction data corresponding to the difference to the printer. It is generated by the control unit 31 and sent to the pixel clock generation unit 33, and the image magnification is corrected by changing the pixel clock frequency.

The synchronization detection signal XDETP is also sent to the pixel clock generator 33. The pixel clock generation unit 33 generates a pixel clock PCLK that is synchronized with the synchronization detection signal XDETP, and sends it to the synchronization detection lighting control unit 34 and the LD control unit 35.
The synchronization detection signals XDETP and XEDETP are also sent to the synchronization detection lighting control unit 34. The synchronization detection lighting control unit 34 first turns on the LD forced lighting signal BD to forcibly light the LD in order to detect the synchronization detection signal XDETP, but after detecting the synchronization detection signal XDETP, the synchronization detection signal XDETP is detected. The LD is turned on at a timing at which the synchronization detection signals XDETP and XEDETP can be reliably detected without causing flare light by the XDETP and the pixel clock PCLK, and the LD is turned off when the synchronization detection signals XDETP and XEDETP are detected. A signal BD is generated and sent to the LD control unit 35.

The LD control unit 35 controls the lighting of the laser in accordance with the image signal synchronized with the synchronous detection forced lighting signal BD and the pixel clock PCLK. Then, a laser beam is emitted from the LD unit 12, deflected to the polygon mirror 11, passes through the fθ lens 14, and scans on the photoconductor 20.
The polygon motor control unit 36 controls the rotation of the polygon motor at a specified number of rotations based on a control signal from the printer control unit 31.

FIG. 3 shows a configuration of the magnification error detection unit 32.
A time difference counting unit and a comparison control unit are provided, and the time difference counting unit is configured by a counter and a latch. The counter is cleared by the start side synchronization detection signal XDETP, counted up by the clock VCLK, and the count value is latched at the falling edge of the end side synchronization detection signal XEDETP. Then, the count value (time difference: T) is compared with a preset reference time difference T 0 by the comparison control unit, and the difference data (magnification error data) is obtained and sent to the printer control unit 31. The printer control unit 31 calculates a set value of the pixel clock frequency from the magnification error data and sends it to the pixel clock generation unit 33 as correction data.
For reference time difference: T0, for example, six planes are measured in advance and set as an average value.

The pixel clock generation unit 33 includes a reference clock generation unit 331, a VCO (Voltage Controlled Oscillator) clock generation unit 332, and a phase synchronization clock generation unit 333.
FIG. 4 shows the configuration of the VCO clock generator 332 (PLL circuit: Phase Locked Loop). A reference clock signal FREF from the reference clock generator 331 and a signal obtained by dividing VCLK by N by a 1 / N divider are shown. The phase comparator compares the falling edges of both signals and outputs an error component at a constant current. Then, unnecessary high-frequency components and noise are removed by an LPF (low-pass filter), which is sent to the VCO. The VCO outputs an oscillation frequency depending on the output of the LPF. Accordingly, the frequency of VCLK can be varied by varying the frequency of FREF and the frequency division ratio N by correction data from the printer control unit 31.

  The phase synchronization clock generation unit 333 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. Therefore, the frequency of VCLK is varied by the correction data from the printer control unit 31, and the frequency of the pixel clock PCLK is thereby varied. By changing the frequency of PCLK, the overall magnification of the image can be changed.

FIG. 5 shows a configuration of the synchronization detection lighting control unit 34.
The synchronization detection lighting control unit 34 is divided into a main scanning line synchronization signal generation unit, a main scanning counter, a start side lighting control unit, an end side lighting control unit, and an OR circuit, and a main scanning line synchronization signal generation unit. Generates a line synchronization signal for operating the main scanning counter.

The main scanning counter is a counter that resets with a line synchronization signal and counts up with a pixel clock PCLK.
The start side lighting control unit compares the counter value of the main scanning counter with the set value 1 from the printer control unit 31, outputs the result, the comparison result from the comparator, and the start side synchronization detection signals XDETP to XDETP. And a lighting signal generation unit that generates an LD lighting signal for detection.

  The end side lighting control unit compares the counter value of the main scanning counter with the set value 2 from the printer control unit 31 and outputs the result, the comparison result from the comparator and the end side synchronization detection signal XEDETP to XEDETP And a lighting signal generation unit that generates an LD lighting signal for detection.

  The OR circuit is a circuit that ORs the start side lighting signal and the end side lighting signal. Further, each lighting signal generation unit has a function of turning on / off each lighting signal by the control signals 1 and 2 from the printer control unit 31.

FIG. 6 shows the LD lighting timing in this embodiment.
By setting the set value 1 = B and the set value 2 = A to the synchronization detection lighting control unit 34 shown in FIG. 5, the LD is lit at the timing shown in FIG. As described above, the values of A and B are set to values that have no flare light influence and can reliably detect the synchronization detection signals XDETP and XEDETP. Since LD is turned off after XDETP and XEDETP are detected, the LD is turned off from the time XEDETP is detected until the counter value = B and after the time XDETP is detected until the counter value = A.
During image formation, the LD is lit along with the image data from the detection of XDETP until the counter value = A.

As described above, the image forming apparatus according to the present embodiment has a function that can turn on / off each lighting signal using the control signals 1 and 2 from the printer control unit 31, so that the time difference can be reduced. It is possible to easily turn on the LD for detecting the end-side synchronization detection signal XEDETP only at the time of measurement, and turn off the other lights.
For this reason, deterioration of image quality can be prevented and the life of the LD can be extended.

  Next, an image forming apparatus according to a second embodiment of the present invention will be described. In the image forming apparatus according to the present embodiment, the light beam scanning device 10 and the image formation control unit are the same as those in the first embodiment described above, and the lighting timing setting value is made variable as the image magnification is corrected. Is.

FIG. 7 shows the LD lighting timing in this embodiment. In this embodiment, in order to correct the image magnification, when the pixel clock is varied, the setting value 1 and the setting value 2 of the LD lighting timing are variable.
For example, when the pixel clock frequency is lowered (when delayed) to correct the image magnification, the counter values A and B may be behind the position (timing) of the synchronization detection signal. Therefore, the set value is also changed (A-α, B-β) by the amount of changing the frequency, and the LD is always turned on from the substantially same position (timing) with respect to the sensor position.

If a frequency variable table is created and stored in advance, a table of lighting timing setting values corresponding to the frequency variable table is also created and stored in advance, and a setting value corresponding to the set frequency may be used. . Alternatively, the setting value may be obtained by calculation every time the frequency is changed without creating a table in advance.
According to the present embodiment, it is possible to more reliably detect the light beam that measures the lighting time difference.

  Next, an image forming apparatus as a third embodiment of the present invention will be described. In the image forming apparatus according to the present embodiment, the image forming apparatus, the light beam scanning device 10, and the image formation control unit are the same as those in the first and second embodiments, and the light beam is turned off at a preset timing. It is what you do.

FIG. 8 shows the LD lighting timing in this embodiment. In the present embodiment, when the synchronization detection signal cannot be detected due to some trouble, the LD is turned off by the synchronization detection lighting control unit 34. FIG. 8 shows a case where the end-side synchronization detection signal XEDETP cannot be detected. Normally, the LD is turned off by detection of XEDETP, but if it cannot be detected, a counter value is set in advance. When the set value reaches C, the LD is turned off.
This set value may be set to a value that is surely behind XEDETP in consideration of the variable range of the frequency. As in the second embodiment, the set value may be changed according to the frequency. Also good. The latter can shorten the lighting time.

As described above, according to the present embodiment, by turning off the light beam at a preset timing, it is possible to prevent deterioration in image quality even when an abnormality occurs and to extend the life of the LD.
In addition, by making the set value of the extinction timing variable along with the correction of the image magnification, it is possible to reliably prevent the deterioration of the image quality even in the event of an abnormality, and to extend the life of the LD.

  Next, an image forming apparatus as a fourth embodiment of the present invention will be described. In the image forming apparatus according to the present embodiment, the light beam scanning device 10 and the image formation control unit are the same as those in the first to third embodiments described above, and color is obtained using one photosensitive drum and an intermediate transfer belt. In this configuration, image formation is performed.

FIG. 9 conceptually shows the main part of the color image forming apparatus as the present embodiment.
In the color image forming apparatus according to this embodiment, optical writing is performed according to image data, and an electrostatic latent image is formed on the photosensitive member 20 as a latent image carrier. The photosensitive drum, which is the photosensitive member 20, rotates counterclockwise. Around the photosensitive drum, a photosensitive member cleaning unit, a static eliminator, a charger, a developing unit (BK developing device, C developing device, M developing device, Y developing device). ), An intermediate transfer belt as a carrier is disposed. The developing unit includes a developing sleeve that rotates so that the developer faces the photoconductor 20 in order to develop the electrostatic latent image, a developing paddle (not shown) that rotates to pump up and stir the developer, and the like. It is prepared for.

An image forming operation in this embodiment will be described. Here, the order of the developing operations is BK, C, M, and Y, but is not limited to this.
When the printing operation is started, optical writing and latent image formation by the light beam scanning device 10 are first started based on the BK image data. In order to enable development from the leading edge of the BK latent image, before the leading edge of the latent image reaches the developing position of the BK developing device, the developing sleeve starts rotating and the BK latent image is developed with BK toner. Thereafter, the developing operation of the BK latent image area is continued, but the development inoperative state is set when the trailing edge of the BK latent image passes the BK developing position. This is completed at least before the leading edge of the C latent image by the next C image data arrives.

The BK toner image formed on the photoconductor 20 is transferred to the surface of an intermediate transfer belt that is driven at the same speed as the photoconductor 20. This belt transfer is performed by applying a predetermined bias voltage to the belt transfer bias roller while the photoconductor 20 and the intermediate transfer belt are in contact with each other. On the intermediate transfer belt, toner images of BK, C, M, and Y that are sequentially formed on the photoreceptor 20 are sequentially aligned on the same surface to form a belt transfer image by superimposing four colors, and then collectively onto the recording paper. Transcription.
In the photoconductor 20, the process proceeds to the C process after the BK process, and then continues to the M process and the Y process.

The intermediate transfer belt is wound around a drive roller, a belt transfer bias roller, and a driven roller, and is driven and controlled by a drive motor (not shown).
The belt cleaning unit includes a blade, a contact / separation mechanism, and the like, and prevents the blade from coming into contact with the belt by the contact / separation mechanism while the BK image, C image, M image, and Y image are transferred to the belt. Yes.

  The paper transfer unit includes a paper transfer bias roller, a contact / separation mechanism, and the like. The paper transfer bias roller is usually separated from the surface of the intermediate transfer belt, but a four-color superimposed image formed on the surface of the intermediate transfer belt. Is pressed by the contact / separation mechanism when transferring the image to the recording paper, and a predetermined bias voltage is applied to transfer the image onto the recording paper.

The recording paper is fed in accordance with the timing when the leading end of the four-color superimposed image on the intermediate transfer belt surface reaches the paper transfer position. The image thus transferred onto the recording paper is fixed by a fixing unit (not shown).
Also in this embodiment, the above-described means according to the first to third embodiments may be used.
As described above, according to the image forming apparatus as the present embodiment, it is possible to provide a one-drum image forming apparatus that can obtain the effects of the above-described embodiments.

Next, an image forming apparatus according to a fifth embodiment of the present invention will be described.
In the image forming apparatus according to the present embodiment, the configurations and operations of the first to third embodiments described above are performed in four colors of yellow (Y), magenta (M), cyan (C), and black (BK). In order to form a color image by superimposing images, the image forming unit (photosensitive member 20, developing unit, charging unit, transfer unit) and four sets of light beam scanning devices are realized.

FIG. 10 shows a four-drum type color image forming apparatus as this embodiment.
The first color image is formed on the recording paper conveyed in the direction of the arrow by the transfer belt, and then the second color, the third color, and the fourth color are transferred in this order, whereby the four color images are superimposed. The image is formed on the recording paper, and the image on the recording paper is fixed by a fixing device (not shown). The image forming unit for each color is provided with a charger, a developing unit, a transfer unit, a cleaning unit (not shown), and a static eliminator around the photoconductor 20, and charging and exposure, which are normal electrophotographic processes. Then, an image is formed on the recording paper by development and transfer.
Also in this embodiment, each of the means described above according to the first to third embodiments can be applied to four sets of light beam scanning devices.
As described above, according to the image forming apparatus as the present embodiment, it is possible to provide a four-drum type image forming apparatus that can obtain the effects of the above-described embodiments.

  As described above, according to each of the above-described embodiments, the light emission source that is controlled to be turned on according to the image data, the deflection unit that deflects the light beam output from the light emission source in the main scanning direction by the plurality of deflection surfaces, A light beam detecting means for detecting the light beam deflected by the deflecting means at two locations on the main scanning line, and one light beam detecting means detects the light beam and then the other light beam detecting means is the light beam. An image forming apparatus comprising a means for measuring a time difference until detection of a light and a means for correcting an image magnification in the main scanning direction from the measured time difference, for detecting a light beam at two locations on the main scanning line Since each light beam lighting timing can be variably controlled independently, it is possible to eliminate unnecessary light beam lighting when measuring the time difference, prevent degradation of image quality, and extend the life of the LD. It is possible to provide an image forming apparatus that can reliably detect the light beam for measuring the difference.

Each of the above-described embodiments is a preferred embodiment of the present invention, and various modifications can be made without departing from the spirit of the present invention.
For example, the image forming apparatus according to each embodiment of the present invention may be of various types, and may be applied to a copying machine such as monochrome, single color, and full color, a printer, a FAX, and a printing machine.

1 is a diagram illustrating an outline of a configuration around a light beam scanning device 10 and a photosensitive member 20 in an image forming apparatus as a first embodiment of the present invention. 2 is a block diagram illustrating an image formation control unit and a light beam scanning device 10 in the image forming apparatus. FIG. 3 is a block diagram illustrating a configuration of a magnification error detection unit 32. FIG. 3 is a block diagram showing a configuration around a VCO clock generation unit 332; FIG. It is a block diagram which shows the structure of the lighting control part 34 for a synchronous detection. It is a wave form diagram which shows LD lighting timing in 1st Embodiment. It is a wave form diagram which shows LD lighting timing in 2nd Embodiment. It is a wave form diagram which shows LD lighting timing in 3rd Embodiment. It is a figure which shows notionally the principal part of the color image forming apparatus of 1 drum system as 4th Embodiment. It is a figure which shows notionally the principal part of the color image forming apparatus of 4 drum systems as 5th Embodiment.

Explanation of symbols

10 Light beam scanning device 11 Polygon mirror (deflection means)
12 LD unit (light source)
13 Synchronization sensor (light beam detection means)
14 fθ lens 15 mirror 16 lens 20 photoconductor (image carrier)
31 Printer control unit (control means)
32 Magnification error detector (time difference measuring means)
33 pixel clock generation unit 331 reference clock generation unit 332 VCD clock generation unit 333 phase synchronization clock generation unit 34 synchronization detection lighting control unit 35 LD control unit 36 polygon motor control unit

Claims (4)

A light source emitting a light beam;
Deflection means for deflecting the light beam output from the light emitting source in the main scanning direction by a plurality of deflection surfaces;
First and second light beam detecting means for detecting the light beam deflected by the deflecting means;
The first light beam detection means detects the light beam and outputs a start side synchronization detection signal until the second light beam detection means detects the light beam and outputs an end side synchronization detection signal. A magnification error detecting means for measuring a time difference and obtaining a magnification error in the main scanning direction from the time difference;
Control means for correcting the image magnification by changing the frequency of the pixel clock based on the magnification error obtained by the magnification error detecting means;
An image forming apparatus comprising:
A counter that counts the pixel clock from the time when the start side synchronization detection signal is reset by a line synchronization signal output from a main scanning line synchronization signal generator ;
When the count value of the counter reaches the first set value and when the count value reaches the second set value, the light emission source is turned on, and the start side synchronization detection signal is output during image formation. , and a said count value is said second set value lighting control unit Ru is lit the light emitting source in accordance with image data until a counter,
The first set value is a value set so that the first light beam detecting means can detect the light beam and is not affected by flare light, and the second set value is the second light beam. It is a value set so that the detection means can detect the light beam and there is no influence of flare light ,
The image forming apparatus, wherein the control unit changes the first set value and the second set value in accordance with a change in the frequency of the pixel clock. A table for storing the frequency of the pixel clock and the first and second setting values in association with each other;
The image forming apparatus according to claim 1, wherein the control unit changes the first set value and the second set value based on the table.   The lighting control unit turns off the light emission source when the first light beam detection unit detects a light beam and when the second light beam detection unit detects a light beam. The image forming apparatus according to claim 1.   The lighting control unit turns off the light emitting source when the count value of the counter reaches a third set value when the light beam is not detected by the first or second light beam detecting unit. The image forming apparatus according to claim 3.

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