JP2007229963A - Imaging device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an imaging device which removes a synchronous detection device from the opposite surface by generating a synchronous detection signal realtime from the surface without the synchronous detection device, using an output from a reference synchronous detection device, in a writing unit capable of counter scanning. <P>SOLUTION: This imaging device exposes an image to light by simultaneously reflecting a plurality of light beams using different faces of a rotary polygon mirror 13. In addition, the device comprises an opposed synchronous generation device 17 which generates a reference horizontal synchronous signal by detecting a reference light beam among the light beams, a synchronous interval measuring block 18 which measures time interval by repeating the horizontal synchronous signal, and a mean value calculation block 20 which calculates a face unit mean time from a single rotation time of the polygon mirror 13 based on the measurements of the synchronous interval measuring block 18. Further, the timely writing by the light beam other than the reference light beam, is decided from the difference between the measurements per each face of the synchronous interval measuring block 18 and the face unit mean time. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to an image forming apparatus such as a color copying machine or a color printer provided with a writing device that simultaneously reflects and exposes a plurality of light beams on different surfaces of a rotary polygon mirror.

2. Description of the Related Art Conventionally, in an image forming apparatus that performs exposure by simultaneously reflecting a plurality of light beams on different surfaces of a rotary polygon mirror, several techniques have been proposed in order to avoid the occurrence of synchronization position shift and image degradation. (For example, refer to Patent Documents 1 and 2).
Patent Document 1 discloses a configuration for generating a synchronization detection timing of a surface on which no synchronization detection is provided by measuring an interval between first synchronization signals. Also, Patent Document 2 discloses a configuration that generates a timing of a surface that is not provided with synchronization detection by being delayed for a certain period from the synchronization detection.
JP 2004-102276 A JP 2003-200609 A

However, there is no description regarding the rotational speed fluctuation (jitter) of the polygon motor in the above prior art, and there is a problem that the synchronization position shift occurs due to the rotational speed change of the polygon motor and the image is deteriorated.
Therefore, in view of the above-described situation, the object of the present invention is to detect the synchronization of the surface in which the synchronization detection device is not installed in real time using the output of the reference synchronization detection device in the writing unit that performs opposite scanning. An object of the present invention is to provide an image forming apparatus that removes a synchronization detection device on a surface on which a synchronization detection device is not installed by generating a signal.

In order to solve the above-described problem, the invention described in claim 1 is directed to an image forming apparatus that simultaneously reflects and exposes a plurality of light beams on different surfaces of a rotary polygon mirror, and serves as a reference light beam from the light beam. A synchronization signal generating means for detecting a reference horizontal synchronizing signal, a synchronizing interval measuring means for measuring a repetition time interval of the horizontal synchronizing signal, and a surface unit average time from one rotation time of the rotary polygon mirror Average value calculating means for calculating from the measurement result of the synchronization interval measurement means, and a light beam other than the reference light beam from the difference between the measurement result for each surface of the synchronization interval measurement means and the surface unit average time An image forming apparatus that determines the writing start timing is characterized.
According to a second aspect of the present invention, there is provided the image forming apparatus according to the first aspect, wherein the synchronization interval measuring means measures using a high-speed clock that is faster than a pixel clock.
According to a third aspect of the present invention, the high-speed clock is an N-multiplied clock of the pixel clock, and the image forming apparatus according to the first or second aspect adjusts the write-out timing using the high-speed clock.

  According to the present invention, since the polygon mirror rotational speed is reflected in real time, the influence of the speed fluctuation (jitter) of the polygon mirror motor can be eliminated, and the synchronous detection on the opposite side can be performed without degrading the image quality. Since the device can be removed, the cost of the writing unit can be reduced.

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.
FIG. 1 is a schematic view showing an image forming apparatus including a writing unit according to the present invention. In the image forming apparatus A of FIG. 1, LD (laser diode) light from the writing unit 1 is irradiated onto the photoreceptors 2 (K, Y, C, M), and the respective photoreceptors 2 (K, Y, C, M) Generate an electrostatic latent image on top.
The electrostatic latent image is developed by each developing device 5 (K, Y, C, M) to be visualized, and transferred onto the intermediate transfer belt 3 that is rotationally driven by the driving roller 4. The image transferred onto the intermediate transfer belt 3 is transferred by the secondary transfer roller 7 onto the transfer paper S sent via the registration roller 8, and the transfer paper S onto which the image has been transferred is thermally fixed by the fixing device 9. And discharged from the discharge roller 10 to the outside.

FIG. 2 is a schematic top view showing a configuration example inside the writing unit of the present invention. In the configuration example of FIG. 2, an internal configuration of a writing unit having a pair of LD modulation devices is shown.
In the internal configuration of the writing unit 1 shown in FIG. 2, LD light emitted from the LD modulator 11 is reflected by a rotating polygon mirror (rotating polygon mirror) 13 and scanned in the scanning direction shown in the figure.
The scanned LD light passes through the fθ lens 14, undergoes speed conversion, beam shaping, and the like, and then irradiates the photosensitive member 2 shown in FIG. 1 and generates an electrostatic latent image on the photosensitive member 2. . Also, the LD light irradiates the synchronization detection device 15 installed on the start side in the scanning direction, and performs alignment in the scanning direction.
Similarly, the opposing LD modulation device 12 generates an electrostatic latent image on the photosensitive member 2 via the polygon mirror 13 and the fθ lens 16, but there is no synchronization detection device on the scanning line, and it is generated from the synchronization detection device 15. The alignment in the scanning direction is performed according to the timing.

FIG. 3 is a circuit diagram showing a control block for generating a counter-side synchronization signal. FIG. 4 is a diagram showing the interval of the reference synchronization signal.
The reference synchronization signal output from the synchronization detection device 15 shown in FIG. 3 is input to the synchronization interval measurement block 18 in the opposite synchronization generation device (opposite synchronization signal generation means) 17.
The synchronization interval measurement block (synchronization interval measurement means) 18 measures the intervals (t11 to t34) of the reference synchronization signal shown in FIG. 4 and outputs the measurement results to the average value calculation block 19 and the time difference calculation block 20.
An average value calculation block (average value calculation means) 19 sets a reference surface among a plurality of polygon mirror surfaces, calculates an average value (t0 to t2) of synchronization detection for one rotation from the measurement result, and average synchronization A signal I is generated.
Further, an average synchronization signal III is generated by delaying the number of polygon mirror surfaces from the surface generating the reference synchronization signal to the opposite side. The time difference calculation block 20 calculates the difference between the reference synchronization signal and the average synchronization signal III and outputs the result to the synchronization control block 21.
In calculating the difference between the reference synchronizing signal and the average synchronizing signal III, the fluctuation frequency of the jitter by the polygon mirror motor is small and hardly changes by one rotation of the polygon mirror. Therefore, t11 before one rotation of the polygon mirror as shown in FIG. Use -t1. Further, although the average synchronization signal uses a value before one rotation, the reference synchronization signal may be t21-t1 using the current value.

The synchronization control block 21 measures the timing and adds the calculation result of the time difference calculation block 20 to the average synchronization signal III to generate a counter synchronization signal. An N-multiplied clock (hereinafter referred to as N-times clock) 22 shown in FIG. 3 is a clock having a frequency N times the pixel clock.
This N times clock 22 is input to the synchronization interval measurement block 18 and used for interval measurement of the reference synchronization signal. The N-times clock 22 is also input to the synchronization control block 21, and the timing for generating the counter synchronization signal is synchronized with the N-times clock 22 and output.
Since the time measurement of the synchronization detection interval can be accurately obtained and adjusted with an error smaller than one pixel unit, the position error of the synchronization signal on the surface without the synchronization detection device can be suppressed, and the image quality can be improved.

1 is a schematic diagram illustrating an image forming apparatus including a writing unit according to the present invention. The schematic top view which shows the structural example inside the writing unit of this invention. The circuit diagram which shows the control block which produces | generates the synchronizing signal of an opposing side. The figure which shows the space | interval of a reference | standard synchronizing signal.

Explanation of symbols

A image forming apparatus, 13 polygon mirror, 15 synchronization detection apparatus, 17 counter synchronization generation apparatus, 18 synchronization interval measurement block, 19 average value calculation block, 20 time difference calculation block, 21 synchronization control block, 22 N multiplication clock

Claims (3)

  In an image forming apparatus that simultaneously reflects and exposes a plurality of light beams on different surfaces of a rotary polygon mirror, synchronization signal generating means for detecting a reference light beam from the light beam and generating a reference horizontal synchronization signal; A synchronization interval measurement unit that measures a repetition time interval of the horizontal synchronization signal; an average value calculation unit that calculates a surface unit average time from one rotation time of the rotary polygon mirror from a measurement result of the synchronization interval measurement unit; An image forming apparatus for determining a writing timing of a light beam other than the reference light beam from a difference between a measurement result for each surface of the synchronization interval measuring unit and a surface unit average time.   The image forming apparatus according to claim 1, wherein the synchronization interval measurement unit performs measurement using a high-speed clock that is faster than a pixel clock. The image forming apparatus according to claim 1, wherein the high-speed clock is an N-multiplied clock of a pixel clock, and the writing timing is adjusted using the high-speed clock.

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