JP2000203083A - Image forming apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent deterioration of an image due to deterioration of linearity at a start position for writing an image in a sub-scanning direction. SOLUTION: There is disclosed an image forming apparatus wherein a plurality of optical beams from a light source device are scanned by a scanning means, then a photosensitive body is scanned with the optical beams from the scanning means in parallel in the main scanning direction and the plurality of the beams are detected by a single synchronism detector. The apparatus further comprises tuning means 15, 16 that measure an interval of synchronism detection signals with respect to the plurality of optical beams and control linearity of the plurality of optical beams in the sub-scanning direction at the position of synchronism detecting.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image forming apparatus such as a copying machine, a printer, a facsimile, etc., which writes an image by scanning a photosensitive member in parallel in a main scanning direction with a plurality of light beams.

[0002]

2. Description of the Related Art Conventionally, in an image forming apparatus such as a copying machine, a printer, a facsimile or the like, which writes an image by scanning a photosensitive member in a main scanning direction with a light beam, a single laser beam from a single laser light source is used. Scanning is performed by a scanning means including a polygon mirror, and the laser beam from the polygon mirror scans the photoconductor in the main scanning direction and moves the photoconductor in the sub-scanning direction to expose the photoconductor to form an image. Then, the laser beam from the polygon mirror is detected by the synchronization detector, and the laser light source is modulated with the image signal in synchronization with the synchronization detection signal from the synchronization detector, and the image writing position on the photosensitive member (in the main scanning direction). (Exposure start position).

In an image forming apparatus using such a single laser light source, when high performance is required, it is necessary to increase the rotation speed of the polygon mirror or the frequency of the image signal. However, there are limitations on the number of rotations of the polygon mirror and the frequency of the image signal, and it has not always been possible to form an image at a desired speed. Therefore, using a light source device having a plurality of laser light sources, a plurality of laser beams from the plurality of laser light sources are scanned by a scanning means comprising a polygon mirror, and the photoconductor is scanned in the main scanning direction by the plurality of laser beams from the polygon mirror. There has been proposed a multi-beam type image forming apparatus that scans in parallel.

In this multi-beam type image forming apparatus, since the amount of information that can be processed simultaneously increases, the rotation speed of the polygon mirror and the frequency of the image signal can be reduced, and a stable image can be formed at high speed. It becomes possible to do. In a multi-beam type image forming apparatus, each laser light source is shifted in position, a plurality of laser beams from a polygon mirror are detected by one synchronization detector, and a synchronization detection signal for each laser beam is obtained. A method of modulating a plurality of laser beams with an image signal in synchronization with a synchronization detection signal for the laser beam has also been proposed.

[0005]

In the method of detecting a plurality of laser beams from a polygon mirror with one synchronous detector, the line synchronous position accuracy of each laser light source (each laser beam is detected by a single synchronous detector) If there is a variation in the accuracy of the detected position), this leads to a deterioration in the linearity of the image writing position in the sub-scanning direction (a deterioration in the linearity of the image writing position in the sub-scanning direction by each laser beam).
The image deteriorates.

An object of the present invention is to provide an image forming apparatus capable of adjusting the linearity of an image writing position in the sub-scanning direction to prevent image deterioration. Another object of the present invention is to provide an image forming apparatus capable of adjusting the linearity of an image writing position in the sub-scanning direction by simple means to prevent image deterioration.

[0007]

In order to achieve the above object, according to the first aspect of the present invention, a plurality of light beams from a light source device are scanned by a scanning means, and each of the plurality of light beams from the scanning means is scanned by the plurality of light beams. An image is written by scanning the photoconductor in parallel in the main scanning direction, and a plurality of light beams from the scanning means are detected by a single synchronization detector at a predetermined synchronization detection position, and a synchronization detection signal from the synchronization detector is detected. An image forming apparatus that separates the synchronization detection signal for each light beam and modulates the plurality of light beams with an image signal in synchronization with the synchronization detection signal for each light beam. And an adjusting means for adjusting the linearity of the plurality of light beams in the sub-scanning direction at the synchronization detection position based on the measured intervals.

According to a second aspect of the present invention, in the image forming apparatus according to the first aspect, there is provided a delay unit for delaying a synchronization detection signal for each of the light beams, and a delay time of the delay unit is adjusted by the interval. To adjust the linearity of the plurality of light beams in the sub-scanning direction at the synchronization detection position.

[0009]

FIG. 3 shows a laser writing apparatus comprising a scanning optical system as exposure means according to an embodiment of the present invention. In this embodiment, the number of laser light sources that generate a laser beam as a light beam is two, but this does not limit the present invention in any way.
The number of a and 1b may be three or more. The laser light source 1 is composed of, for example, two semiconductor lasers (hereinafter, referred to as LDs) and is assembled so as to be shifted in position. The two LDs 1a and 1b are modulated by an image signal in synchronism with a synchronization detection signal by LD modulation circuits 12a and 12b as modulation means, respectively, as described later, so that a laser beam modulated by the image signal is emitted. Emit.

The LDs 1a and 1b and the collimating lens 2 constitute a light source device, and the laser beams from the LDs 1a and 1b are collimated by the collimating lens 2. The laser beams a and b from the collimating lens 2 are linearly incident on a reflecting surface of a rotary polygon mirror 4 composed of a polygon mirror as a scanning means via a cylindrical lens 3 and deflected by the polygon mirror 4. This polygon mirror 4
Is driven to rotate by the motor 5 and scans the laser beam in the main scanning direction.

The two laser beams from the polygon mirror 4 pass through an fθ lens 6 serving as an imaging lens, are reflected by mirrors 7 and 8,
It is irradiated to 0. The photoconductor 10 moves in the sub-scanning direction at an exposure position by being rotated by a driving unit (not shown) using, for example, a photoconductor drum, and is uniformly charged by a charging unit (not shown). The laser beam from 9 is irradiated and exposed. The photoreceptor may be a photoreceptor belt or the like.

The photosensitive drum 10 scans the dust-proof glass 9 from the dust-proof glass 9 by scanning the polygon mirror 4 with a laser beam.
The image is written and an electrostatic latent image is formed by repeatedly scanning the two laser beams in parallel in the main scanning direction. The electrostatic latent image on the photosensitive drum 10 is developed by a developing unit into a toner image, and is transferred to paper or the like by a transfer unit. The single synchronization detector 11 outputs f from the polygon mirror 4 at a predetermined synchronization detection position outside the image writing area.
It detects two laser beams incident through the θ lens 6 and outputs a synchronization detection signal.

FIG. 1 shows a part of this embodiment, and FIG. 2 shows the operation timing of this embodiment. A sync separation circuit 13 serving as a sync separation unit is a single sync detector 1 that detects two laser beams a and b from the two LDs 1a and 1b that are displaced in the main scanning direction at a sync detection position.
1, a synchronization detection signal is input, and the synchronization detection signal from the synchronization detector 11 is separated into synchronization detection signals A and B for each of the laser beams a and b.

The LD control circuit 14 as a control means sends an image signal to the LD modulation circuit 12a by a first pixel clock synchronized with the synchronization detection signal A for the laser beam a from the synchronization separation circuit 13, and sends the image signal to the LD modulation circuit 12a. Modulates the LD1a with the image signal and turns it on,
The laser beam modulated by the image signal is emitted from the LD 1a.

The LD control circuit 14 sends an image signal to the LD modulation circuit 12b by a second pixel clock synchronized with the synchronization detection signal B for the laser beam b from the synchronization separation circuit 13, and the LD modulation circuit 12b By modulating the LD 1b with the image signal, the LD 1b emits a laser beam modulated with the image signal. Therefore, the image writing position in the main scanning direction by the two laser beams a and b on the photosensitive drum 10 is determined by the synchronization detection signals A and B for the laser beams a and b, respectively.

The counter 15 serving as a time measuring means is cleared at the edge, for example, at the falling edge of the synchronization detection signal A with respect to the laser beam a from the synchronization separation circuit 13, and is synchronized with the pixel clock (first pixel) synchronized with the synchronization detection signal A. Clock) CLK is counted to measure the interval between the synchronization detection signal A for the laser beam a and the synchronization detection signal B for the laser beam b. The register 16 includes the synchronization separation circuit 13
The count value of the counter 15 is read at the edge of the synchronization detection signal B with respect to the laser beam b, for example, at the rising edge (or at the falling edge).

Based on the count value read by the register 16 and the pixel density of the image forming apparatus of this embodiment (the pixel density of an image formed by the image forming apparatus of this embodiment), two laser beams a at the synchronization detection position are determined. , B in the main scanning direction can be calculated. The count value read by the register 16 is displayed by display means (not shown), or is stored in the register 16 by arithmetic means (not shown).
The distance (interval) in the main scanning direction between the two laser beams a and b at the synchronization detection position is calculated from the read count value and the pixel density of the image forming apparatus according to the present embodiment, and the result is displayed by a display unit (not shown). Is displayed.

The operator determines the distance (interval) between the two laser beams a and b at the synchronization detection position in the main scanning direction based on the count value displayed by the display means and the pixel density of the image forming apparatus of this embodiment. The distance (interval) in the main scanning direction between the two laser beams a and b at the synchronization detection position displayed by the calculation and the calculation result or displayed by the display means.
By operating the adjusting device, the LD1 is operated by the adjusting device.
One or both of a and 1b are shifted so that the distance (interval) between the two laser beams a and b in the main scanning direction at the synchronization detection position is reduced (so that the image writing position is aligned in the sub-scanning direction). Thus, the two laser beams a and b are adjusted so as to be coincident with each other in the sub-scanning direction, and the linearity of the image writing position in the sub-scanning direction is adjusted, thereby preventing image deterioration.

This embodiment is an embodiment of the first aspect of the present invention, in which a plurality of light beams from a light source device comprising LDs 1a and 1b and a collimating lens 2 are scanned by a scanning means comprising a polygon mirror 4. An image is written by scanning the photoreceptor 10 in parallel in the main scanning direction with a plurality of light beams from the scanning means, and a plurality of light beams from the scanning means are applied to one synchronization detector 11 at a predetermined synchronization detection position. , And separates a synchronization detection signal for each light beam from the synchronization detection signal from the synchronization detector 11,
In an image forming apparatus that modulates the plurality of light beams with an image signal in synchronization with the synchronization detection signal for each of the light beams, an interval between the synchronization detection signals for the plurality of light beams is measured, and the synchronization detection is performed based on the measured interval. The counter 15, the register 16, the adjusting means including the display means and the adjusting device for adjusting the linearity of the plurality of light beams in the sub-scanning direction at the position are provided, so that the linearity of the image writing position in the sub-scanning direction is adjusted. Then (the image writing position is adjusted), the synchronization detection accuracy of each light beam at the synchronization detection position can be improved, and image deterioration can be prevented.

FIG. 4 shows a part of another embodiment of the present invention. In this embodiment, delay circuits 17 and 18 as delay means are inserted between the sync separation circuit 13 and the LD control circuit 14 in the above embodiment, and each of the laser beams a and b from the sync separation circuit 13 The synchronization detection signals A and B are input to the LD control circuit 14 after being delayed by the delay circuits 17 and 18, respectively.

The delay circuit 17 has a delay time set by the set value 1, and delays the synchronization detection signal A for the laser beam a from the sync separation circuit 13 by the delay time. The delay circuit 18 has a delay time set by the setting value 2, and delays the synchronization detection signal B for the laser beam b from the synchronization separation circuit 13 by the delay time.
The set value 1 and the set value 2 are each arbitrarily changed and set by an operator by a setting circuit (not shown).

The image writing position in the main scanning direction by the two laser beams a and b on the photosensitive drum 10 is determined by the synchronization detection signals A and B for the laser beams a and b, respectively, and the set value 1 and the set value 2 are set. Fluctuates depending on the combination of. The operator calculates the distance (interval) between the two laser beams a and b in the main scanning direction at the synchronization detection position based on the count value displayed by the display unit and the pixel density of the image forming apparatus of the present embodiment. The setting circuit is operated to set value 1 and setting value 2 according to the calculation result or the distance (interval) between the two laser beams a and b at the synchronization detection position displayed by the display means in the main scanning direction. Either or both of the two laser beams a and b at the synchronization detection position are reduced in distance (interval) in the main scanning direction (so that the image writing position is aligned in the sub-scanning direction).
By shifting, the two laser beams a and b are adjusted so as to coincide with each other in the sub-scanning direction to adjust the linearity of the image writing position in the sub-scanning direction, thereby preventing image deterioration. Therefore, the adjusting device can be omitted.

This embodiment is an embodiment of the invention according to claim 2, and in the image forming apparatus according to claim 1, a delay circuit 17 as delay means for delaying a synchronization detection signal for each light beam; 2. The image forming apparatus according to claim 1, further comprising: adjusting a delay time of the delay unit according to the interval to adjust linearity of the plurality of light beams in the sub-scanning direction at the synchronization detection position. Similarly, by adjusting the linearity of the image writing position in the sub-scanning direction (adjusting the image writing position), it is possible to improve the synchronization detection accuracy of each light beam at the synchronization detection position and prevent image deterioration. In addition, the linearity of the image writing position in the sub-scanning direction can be adjusted by simple means to prevent image deterioration.

That is, in the above embodiment, a high-performance adjusting device is required to adjust the linearity of the image writing position in the sub-scanning direction at the stage of assembling the laser light source. The adjustment device is not required, and the deterioration of the image can be prevented by adjusting the linearity of the image writing position in the sub-scanning direction only by adjusting the delay time of the delay circuits 17 and 18. In the present embodiment, the operator may adjust the delay times of the delay circuits 17 and 18 by changing the resistances or capacitors constituting the delay circuits 17 and 18.

[0025]

As described above, according to the first aspect of the present invention, with the above-described configuration, it is possible to adjust the linearity of the image writing position in the sub-scanning direction and prevent the image from deteriorating.

According to the second aspect of the present invention, with the above configuration, it is possible to adjust the linearity of the image writing position in the sub-scanning direction by a simple means to prevent the image from deteriorating.

[Brief description of the drawings]

FIG. 1 is a block diagram showing a part of an embodiment of the present invention.

FIG. 2 is a timing chart showing operation timings of the embodiment.

FIG. 3 is a perspective view showing the laser writing device of the embodiment.

FIG. 4 is a block diagram showing a part of another embodiment of the present invention.

[Explanation of symbols]

 1a, 1b LD 2 Collimating lens 4 Polygon mirror 10 Photoconductor 11 Synchronization detector 12a, 12b LD modulation circuit 13 Synchronization separation circuit 14 LD control circuit 15 Counter 16 Register 17, 18 Delay circuit.

Claims (2)

[Claims] An image is written by scanning a plurality of light beams from a light source device by a scanning means, and scanning the photosensitive member in parallel in the main scanning direction with the plurality of light beams from the scanning means. A plurality of light beams from a plurality of light beams are detected at a predetermined synchronization detection position by one synchronization detector, and a synchronization detection signal for each light beam is separated from a synchronization detection signal from the synchronization detector, and synchronization detection for each light beam is detected. In an image forming apparatus that modulates the plurality of light beams with an image signal in synchronization with a signal, an interval of a synchronization detection signal with respect to the plurality of light beams is measured, and the plurality of light beams at the synchronization detection position are measured based on the interval. An image forming apparatus comprising an adjusting unit for adjusting linearity of a beam in a sub-scanning direction. 2. An image forming apparatus according to claim 1, further comprising delay means for delaying a synchronization detection signal for each of said light beams, wherein a delay time of said delay means is adjusted according to said interval and at said synchronization detection position. Wherein the linearity of the plurality of light beams in the sub-scanning direction is adjusted.