JPH11311881A - Laser plotting device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a laser plotting device capable of preventing delicate change in color tone or the like. SOLUTION: In this device 1, in order to control the light quantity of razor beams LF by sampling/holding a light quantity detection result S3, by a formation unit of an electrostatic latent image, or by plural units of the formation units, the device is made so as possible to control the light quantity of the baser beams LF with the higher accuracy the heretofore. Consequently, in the color image, the the device is made possible to prevent the delicate change or the like of the color tone to that extent, and possible to prevent the delicate change of a gradation in the black-and-white image.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention is used in an image forming apparatus such as a printer, a copying machine, a facsimile or the like for forming an image on a transfer member such as paper or a plastic sheet. The present invention relates to a laser drawing apparatus for creating an image.

[0002]

2. Description of the Related Art Conventionally, image forming apparatuses such as printers, copiers, and facsimile machines create an electrostatic latent image on a photoreceptor using a laser drawing device and fix a toner image based on the electrostatic latent image on paper or the like. It has been made to be. Further, in a color image forming apparatus, electrostatic latent images for magenta, cyan, yellow, and black are formed, and toner images based on these electrostatic latent images are superimposed and fixed on paper or the like. Has been made.

[0003] Such a laser drawing apparatus varies the amount of a laser beam in accordance with image data, and forms this type of electrostatic latent image by raster-scanning the charged laser beam with the laser beam. Further, at the time of this raster scanning, the light amount of the laser beam is sampled at the timing of starting the scanning of each line, and the light amount of the laser beam is controlled using the sampling result. Thus, the image forming apparatus is configured to prevent a change in the amount of laser light, form an image with a desired gradation, and further form an image with a desired color tone.

[0004]

By the way, when a color image with a high gradation created by this type of image forming apparatus is observed in detail, the color tone may be slightly changed particularly in a halftone (halftone). It is considered that if this problem can be solved, a color image with higher precision can be provided.

Accordingly, an object of the present invention is to provide a laser drawing apparatus capable of preventing subtle changes in color tone and the like.

[0006]

SUMMARY OF THE INVENTION The present invention is applied to a laser drawing apparatus for forming an electrostatic latent image on a photosensitive member by scanning a photosensitive member with a laser beam. In this laser drawing apparatus, a light amount detection unit that detects a light amount of a laser beam and outputs a light amount detection result, and samples and holds a light amount detection result for each unit of forming an electrostatic latent image or for each of a plurality of units. , Sample and hold means for outputting a sample and hold result, and control means for controlling the amount of laser beam based on the sample and hold result.

According to the present invention having such a configuration, the light amount of a laser beam is detected for each unit of forming an electrostatic latent image or for each of a plurality of units, and the light amount of the laser beam is controlled by a feedback loop. It is possible to control the light amount of the laser beam with higher precision than in the case where the control is performed in line units, thereby controlling the gradation and color tone of the electrostatic image with higher precision. And subtle changes in color tone and the like are prevented.

[0008]

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

(1) Configuration of Embodiment FIG. 1 is a block diagram showing a laser drawing apparatus of a color printer according to an embodiment of the present invention. The image forming apparatus using the laser drawing apparatus 1 is a laser beam LF.
The electrostatic latent images for magenta, cyan, yellow, and black are sequentially formed on the photosensitive drum 2 by the scanning. Further, the toner images of the respective colors due to the electrostatic latent images are superimposed on an intermediate transfer member (not shown), and these toner images are fixed on a sheet material such as paper.

That is, as shown by the arrow A, the laser drawing apparatus 1 rotates the polygon scanner mirror 3 at a predetermined rotation speed by the driving motor 4, and converts the laser beam LF emitted from the laser diode 5 into the polygon scanner mirror. Reflects at 3. Thereby, the laser drawing apparatus 1 repeatedly scans the laser beam LF in a predetermined angular range. The laser drawing device 1 is configured to perform the laser beam LF reflected by the polygon scanner mirror 3.
To the photosensitive drum 2 via the mirror 6 and an fθ lens (not shown). Here, as shown by an arrow B, the photosensitive drum 2 rotates at a predetermined rotation speed and is charged by a charging mechanism disposed on a side preceding the laser beam irradiation position. Accordingly, the laser drawing apparatus 1 raster-scans the surface of the photoconductor drum 2 with the laser beam LF, and forms an electrostatic latent image on the photoconductor drum 2 according to the light amount of the laser beam LF.

The timing generator 7 outputs various reference signals which are used as operating references for the laser writing apparatus 1. That is, the timing generator 7 includes a clock CK and a laser beam LF for forming a reference for a unit of drawing an electrostatic latent image.
Horizontal synchronization signal HS specifying the timing of the start of each scan
Outputs YNC or the like. At this time, the timing generator 7 generates and outputs these reference signals based on the rotation timing of the polygon scanner mirror 3 detected via the beam detector B.

The built-in diode chip of the laser diode 5 is driven by a drive circuit 8, and emits laser beams LF and LB from both end faces of the diode chip. The laser diode 5 emits a laser beam LF, which is a so-called front beam, of the two laser beams LF and LB toward the polygon scanner mirror 3.

The photodetector 9 is a light-receiving element for monitoring the amount of light incorporated in the laser diode 5, and receives a laser beam LB, which is a so-called rear beam, of the two laser beams LF and LB. Monitor result S2 in which current value changes according to light amount
Is output.

The current-voltage conversion circuit (IV conversion) 10 converts the monitor result S2 output from the photodetector 9 into a current-voltage signal, and converts a monitor signal S3 whose signal level changes in accordance with the light amount of the laser beam LF (LB). Output.

The sample and hold circuit 11 samples and holds the monitor signal S3 based on the sample and hold signal SH output from the drawing control circuit 12, and outputs the sample and hold result.

The differential amplifier circuit 13 outputs the sample-hold result and the drawing signal S4 output from the drawing control circuit 12.
Is generated, and the error signal is amplified by a predetermined gain and output. The drive circuit 8 includes the differential amplifier 1
The laser diode 5 is driven by the output signal of 3.

As a result, the laser diode 5, the driving circuit 8, the photodetector 9, the current-voltage conversion circuit 10,
The sample hold circuit 11 and the differential amplifier circuit 13 form a feedback loop, and the sample hold signal SH
And the amount of laser beam LF is controlled so that the detected amount of laser beam becomes the amount of light determined by the drawing signal S4.

The drawing control circuit 12 includes a clock CK output from the timing generator 7, a horizontal synchronizing signal HS
Based on the YNC, a drawing signal S4 is output in accordance with drawing information D1 output from an image generation circuit (not shown), and an electrostatic image corresponding to the drawing information D1 is formed on the photosensitive drum 2.

Here, as shown in FIG. 2, the drawing control circuit 1
2 switches the signal level of the drawing signal S4 according to the drawing information D1 in units of a plurality of periods of the clock CK (four periods in FIG. 2, hereinafter referred to as a dot forming period). Correspondingly, one dot as a unit for forming an electrostatic latent image is formed (FIG. 2A to FIG. 2A).
(C)). Further, the drawing control circuit 12 switches the signal level of the drawing signal S4 in multiple steps according to the drawing information D1,
As a result, an electrostatic image is formed with a plurality of gradations, and a color image with various colors and gradations can be formed from the electrostatic image with the plurality of gradations.

Further, the drawing control circuit 12 raises the signal level of the sample-and-hold signal SH for one clock cycle at the start of each dot-forming cycle. The monitor result S2 of the laser beam light amount is sampled and held at the start timing of the formation cycle, and the light amount of the laser beam is controlled based on the sample hold result (FIGS. 2D and 2E).

(2) Operation of Embodiment In the above configuration, the laser writing apparatus 1 controls the laser diode 5 via the differential amplifier circuit 13 and the drive circuit 8 by the drawing signal S4 output from the drawing control circuit 12. When driven, the laser beam LF output from the laser diode 5 is guided to the charged photosensitive drum 2 via the polygon scanner mirror 3, the mirror 6, and the like. Thereby, in the laser drawing apparatus 1, on the photosensitive drum 2,
An electrostatic latent image is formed, and in the image forming apparatus, the magenta, cyan, yellow, and black electrostatic latent images are sequentially formed on the photosensitive drum 2 in this manner, and are formed on the intermediate transfer member. The toner images by these electrostatic latent images are superimposed,
The color image is fixed on the desired paper.

In forming a color image in this way, in the laser drawing apparatus 1, the laser beam LB emitted from the back side of the laser diode chip is received by the photodetector 9, where the light amount of the laser beam LF is detected. Is done. Further, after the monitor result S2, which is the detection result, is subjected to current-voltage conversion, it is sampled and held by the sample and hold circuit 11, and an error signal between the sample and hold result and the drawing signal S4 is detected by the differential amplifier circuit 13. The light amount of the laser beam LF is controlled based on the result of monitoring the light amount of the laser beam.

In controlling the light amount of the laser beam, a monitor signal S3 output from the current-voltage conversion circuit 10 with reference to a sample hold signal SH whose signal level rises during one clock cycle of the start of each dot formation cycle. Is sampled and held for each dot formation cycle. As a result, the laser beam LF can be provided with remarkably higher accuracy than in the case of the conventional light amount control in units of lines.
Can be controlled.

As a result, in each of the electrostatic latent images for magenta, cyan, yellow, and black formed on the photosensitive drum 2, the gradation can be controlled with higher accuracy than in the past. Accordingly, a subtle change in color tone or the like is prevented in a color image created from these electrostatic latent images.

(3) Effects of the Embodiment As described above, according to the embodiment, the light amount of the laser beam LF is controlled by sampling and holding the light amount detection result in the dot formation cycle, thereby achieving the conventional line. The light amount of the laser beam LF can be controlled with remarkably high precision as compared with the case of controlling the light amount in units, and a subtle change in color tone or the like can be prevented.

(4) Other Embodiments In the laser writing apparatus according to the above-described embodiment, an example will be described in which the light amount detection result is sampled and held for each dot formation cycle which is a unit for forming an electrostatic latent image. However, the present invention is not limited to this. If the light amount can be controlled with sufficient accuracy for practical use, the light amount detection result may be sampled and held for each of a plurality of forming units.

Further, in the laser writing apparatus according to the above-described embodiment, an example has been described in which the amount of the laser beam LB emitted from the back surface of the laser diode 5 is monitored. The present invention can be widely applied to the case where the light amount of the laser beam LF emitted to the side is monitored.

Further, in the laser drawing apparatus according to the above-described embodiment, an example in which a color image is formed has been described. However, the present invention is not limited to this, and can be widely applied to a case where a monochrome image is formed.

[0029]

As described above, the present invention controls the light amount of the laser beam by sampling and holding the light amount detection result for each unit of forming an electrostatic latent image or for each of a plurality of units of the formation unit. The light amount of the laser beam can be controlled with higher precision than in the past, which makes it possible to prevent subtle changes in color tone and the like in color images, and in grayscale images in black and white images. Subtle changes can be prevented.

[Brief description of the drawings]

FIG. 1 is a block diagram showing a laser drawing apparatus according to an embodiment of the present invention.

FIG. 2 is a signal waveform diagram for explaining an operation of the laser drawing apparatus of FIG. 1;

[Explanation of symbols]

1 ... laser drawing device, 2 ... photoconductor drum, 5 ...
Laser diode, 9 Photo detector, 11
…… Sample hold circuit, 12… Drawing control circuit, 1
3 ... Differential amplifier circuit

Claims (1)

[Claims] 1. A laser writing apparatus for scanning a photosensitive member with a laser beam to form an electrostatic latent image on the photosensitive member, comprising: a light amount detecting means for detecting a light amount of the laser beam and outputting a light amount detection result; A sample and hold unit that samples and holds the light amount detection result and outputs a sample and hold result for each unit of forming the electrostatic latent image or for each of the plurality of formation units; and the laser based on the sample and hold result. A laser writing apparatus comprising: a control unit that controls a light amount of a beam.