JPH0532824Y2 - - Google Patents

Description

[Detailed description of the invention] (Field of industrial application) The present invention provides highly accurate synchronization detection in optical beam recording devices, particularly in optical beam scanning devices that scan a recording medium with multiple optical beams. About what made it possible.

(Prior art) In recent years, various printing and copying devices such as printers and copiers that use laser beams have become popular, and the demand for faster scanning and higher resolution is increasing year by year. . Improving the scanning speed by increasing the speed of optical deflectors such as polygon scanners and galvanometer mirrors is effective to some extent as a means of achieving these demands, but there are mechanical limits to increasing the speed of optical deflectors. Therefore, recently, a multi-beam system that simultaneously deflects a plurality of beams has been attracting attention as a means of increasing the scanning speed without increasing the speed of the optical deflector.

FIG. 5 is an explanatory diagram of the configuration of a conventionally used light beam scanning device. This scanning device includes a light source unit 1 consisting of a laser diode array (LD array) capable of simultaneously outputting a plurality of light beams;
A collimating lens 2 converts the light emitted from the light source unit 1 into a parallel beam, an optical deflector 3 as a rotating polygon mirror that repeatedly performs main scanning by irradiating the light beam onto the recording medium 7, and the optical deflector 3. An imaging lens 4 that forms an image of a scanning beam irradiated with a beam onto a recording medium with a predetermined spot diameter and a predetermined beam pitch.
and a folding mirror 5 disposed at the tip of the scanning line to guide the plurality of scanning beams to the photodetector 6.
and a photodetector 6 that receives part of the light transmitted through the imaging lens 4 that is incident through the reflection mirror 5.

In the light beam scanning device having such a configuration, the light emitted from the light source 1 is repeatedly scanned in the main scanning direction I by the rotation of the optical deflector 3, and the recording medium 7 is scanned at right angles to the main scanning direction. By rotating or translating in a certain direction, the light beam raster scans the recording medium 7.

By emitting a plurality of light beams from the light source 1, it is possible to record a plurality of lines in one main scan. Therefore, while the sub-scanning speed can be increased by a multiple of the number of light beams, there is an advantage that there is no need to change the pixel clock that modulates and drives the light beams.

The photodetector 6 is a synchronization detection means for detecting that the light beam has arrived at a predetermined position and starting modulation control of the light beam. This makes it possible to achieve synchronization of recorded images even when

By the way, in the multi-beam system as described above, various configurations have been proposed for realizing synchronous detection.

As a multi-beam system, for example, a system in which multiple beams are emitted so as to be arranged in a line in the sub-scanning direction can be considered. The scanning locus of each light beam in the sub-scanning direction on the recording medium 7 needs to correspond to the pitch of the writing density, but there is a limit to the emission pitch of the laser diode array as a light source.
In high-density scanning of about 300 dpi or higher, it is difficult to realize fine emission pitches. From this point of view, the pitch on the image plane is narrowed to obtain the required pitch by tilting the LD array with a pitch larger than the actually required pitch in the sub-scanning direction at a predetermined angle. There is.

However, when such a configuration is adopted, there is a difference in the time at which each light beam reaches the photodetector, so a measure to eliminate this difference is required.

As a synchronization detection method in such cases,
For example, as shown in FIGS. 6a and 6b, there is a method of arranging a number of photodetectors corresponding to the number of light beams each having a small light receiving area. Here, Figure 6a
6 shows a case in which the photodetectors are arranged in a line along the sub-operation direction, and FIG. 6b shows a case in which the photodetectors are arranged in a diagonal line at a predetermined angle with the sub-operation direction. However, in such a configuration, the positional relationship between each photodetector needs to be set appropriately and with high precision, and the light receiving area needs to be set small due to the arrangement spacing of each photodetector. However, there are problems in that the sensitivity decreases and it becomes difficult to obtain a signal with a sufficiently high S/N ratio.

As another method for synchronous detection, Japanese Patent Application Laid-Open No. 57-67375 discloses a method in which a light shielding plate having a slit extending in the sub-scanning direction is provided between a light source and a photodetector to separate the incoming light beams.

FIG. 7 is an explanatory diagram showing this basic principle, in which a plurality of light beams B1 to B4 are tilted by a predetermined angle θ with respect to a line A-A perpendicular to the main scanning direction, and a photodetector is provided with an aperture width ds. A slit S is provided,
Modulation synchronization is achieved by the output of the light beam passing through this slit S.

However, in this modulation synchronization method,
Since it is not possible to use a slit width ds larger than the beam spacing da determined by the arrangement pitch of the LD array and the required spot diameter, the amount of light received by the photodetector is severely limited. especially,
As the scanning speed increases, there is a risk that the amount of light will be insufficient and the accuracy of synchronization detection will deteriorate.

For this, the distance between adjacent light beams da
It is conceivable to increase the distance db between the centers of adjacent beams by setting a large value, but this may lead to various inconveniences in the optical system design, such as increasing the area of the polarization plane of the optical polarizer. There is.

If the emphasis is on simplifying the design of the optical system while considering cost and performance, it is preferable that the tilt angle of the LD array be as small as possible, and even when the da between the light beams is small, the angle of inclination of the LD array should be sufficiently high. It has been desired to develop a synchronization detection means that can demonstrate accuracy.

(Purpose of the invention) The present invention has been made in view of the above, and an object of the present invention is to provide a light beam scanning device that accurately separates and detects multiple light beams that arrive with small time differences and performs synchronous control. The purpose is

(Structure of the invention) In order to achieve the above object, the light beam scanning device of the present invention is a light beam scanning device that records an image by scanning a recording medium with a plurality of light beams at different timings. a plurality of photodetectors each detecting the arrival of a plurality of light beams, and a synchronization control means for sequentially controlling turning off of each light beam when each of the plurality of photodetectors detects a plurality of corresponding light beams, The recording start timing of each of the plurality of light beams is controlled according to output signals from a plurality of photodetectors.

Hereinafter, the light beam scanning device of the present invention will be explained in detail.

FIG. 1 is an explanatory diagram of the configuration of an embodiment of the present invention, and the same parts as in FIG. 5 are denoted by the same reference numerals.
Duplicate explanations will be omitted.

The embodiment of the present invention shown in FIG.
It is different from the conventional example in that it is composed of PD3...PDn.

The gist of the present invention is that in order to separate and detect light beams that arrive close to each other, the light beams are blinked by each photodetector arranged corresponding to each light beam and a synchronization control circuit to be described later. The problem lies in the fact that it is controlled.

As the photodetector 6, for example, one in which a plurality of photodiodes are arranged, one in which an optical system is arranged on the light-receiving surface side, or one using a split-type photodiode can be practically used.

In the following description, a case will be described in which there are three light beams.

FIG. 2 is an explanatory diagram illustrating the state in which each light beam arrives at each of the photodetectors PD1, PD2, and PD3 over time. As shown in the figure, each light beam arrival position B1, B forms a light beam array tilted by a predetermined angle θ with respect to the line A-A perpendicular to the scanning direction I.
2 and B3 sequentially transition from time t ₀ to times t ₁ to t ₃ as scanning is performed by rotation of the optical deflector 5.

When the deflector 3 starts steady rotation, each detector
Each light beam B1 for PD1, PD2, PD3,
The time interval between the incidences of B2 and B3 is approximately constant.
Therefore, each beam passes through photodetectors PD1, PD2, PD
It is possible to predict in advance the timing of scanning over 3 and turn on the beam just before scanning. Each of the beams B1, B2, and B3 is controlled to be turned off by being detected by the corresponding photodetector PD1, PD2, and PD3, respectively.

At the position _t0 in FIG.
in preparation for the incident. At the position _t2 , the first beam B1 is incident on the corresponding first photodetector PD1 and outputs the detection signal SPD1 (described later in the explanation of FIGS. 3 and 4), and at the same time, the first beam Turn off B1. When the three beams are further scanned in the main scanning direction and reach the position _t2 , the second beam B2 is incident on the second photodetector PD2 and outputs the detection signal SPD2. Lights out. Further, when the third beam B3 reaches the position t ₃ , the third beam B3 is incident on the third photodetector PD3, outputs the detection signal SPD3, and at the same time turns off the third beam B3.

The rising portion (incidence start portion) of each signal of SPD1 to SPD3 obtained in this way accurately represents the timing of incidence of each beam B1 to B3 to each photodetector PD1 to PD3, as will be described later. These signals can be used as timing signals for write system sequence control.

The configuration and operation procedure of a synchronous control circuit for realizing the setting of lighting timing for separating and detecting a plurality of light beams, which is a feature of the present invention, will be explained with reference to FIGS. 3 and 4. Each scanning beam B1-B3
is sequentially applied to each photodetector PD1 according to the rotation of the deflector 3.
When the light enters PD3 and the deflector starts rotating stably, the output signals from each photodetector PD1 to PD3 become approximately constant intervals.

In the example in Figure 3, the output from the previous line is
Based on the SPD1 signal, the timing control circuit 54 outputs a timing signal by predicting in advance the timing at which the first beam B1 will be incident on the photodetector 51 (PD1) in the next line. Based on this timing signal, each blanking signal generating section 55 to 57 turns on each BEAM1 to 3, and each
Turn on LD61, LD62, and LD63. Each LD6
1, the beams B1 to B3 outputted by the lighting of LD62 and LD63 are scanned, and the first of these is scanned.
When the beam B1 reaches the first photodetector 51, the photodetector 51 outputs the SPD1 signal to the blanking signal generator 55 and turns BEAM1 off. Therefore, the first LD 61 is turned off.

In this state, next, the second photodetector 52
When the second beam B2 is detected by the (PD2), the SPD2 outputs the second blanking signal generator 5.
6 and turns off the second LD 62.

Further, when only the third beam B3 is illuminated and enters the third photodetector, the SPD3 signal output from the third photodetector 53 is input to the third blanking signal generator 57 and LD63
Turn off the light.

As described above, these signals SPD1 to SPD3 are used as timing signals 1 to 3 for image writing control.

The first to third LD driving units 58 to 60 repeatedly turn on and off in accordance with the respective signals BEAM1 to BEAM3, and in the image writing area (the part where the photoreceptor is scanned) receive the video signal and LD61
to 63 to form a latent image on the photoreceptor according to the video signal.

Next, to explain the above operation with reference to FIG. 4, first, each signal is
BEAM1 to BEAM3 become High, and each LD61
~LD63 lights up. 1st from 1st LD61
BEAM
1 becomes Low, and the LD61 is turned off. Furthermore,
The output BEAM2 from the second blanking signal generator 56 becomes Low due to the output signal SPD2 from the second photodetector 52, and the LD 62 is turned off. Furthermore, the output signal from the third photodetector 53
The SPD3 causes the output BEAM3 from the third blanking signal generator 57 to go low, and the LD63
is turned off.

By realizing the above-described operation, the plurality of beams B1 to B3 can be accurately separated and detected.

The advantage of the present invention, which has the above configuration and operates, is that it is possible to accurately synchronize detection even for multiple beams that are scanned close to each other, and it is possible to eliminate dot deviation (image deviation) in the main scanning direction. It is possible to obtain high-quality image output without any problems.

(Effects of the invention) As explained above, in the present invention, a plurality of photodetectors corresponding to each light beam are arranged, and each light beam is turned on only when it passes through the corresponding photodetector. The light is turned off when the light passes through the photodetector, making it possible to accurately synchronize detection even for multiple beams that are scanned close to each other at minute intervals, and It is possible to obtain high-quality image output without dot shift (image shift).

Therefore, even when the scanning pitch in the sub-scanning direction is narrowed, high-speed scanning can be performed without causing insufficient light quantity, and high resolution can be achieved.

[Brief explanation of the drawing]

Figure 1 is an explanatory diagram of the configuration of one embodiment of the present invention;
The figure is an explanatory diagram illustrating the state in which each light beam that arrives at each photodetector enters each photodetector over time. Figures 3 and 4 show lighting timing for separating and detecting multiple light beams. A configuration explanatory diagram of a synchronization control circuit for realizing the settings and a timing chart showing the operating procedure. Fig. 5 is a schematic configuration explanatory diagram of a conventional optical beam scanning device. Figs. FIG. 7 is an explanatory diagram of a conventional example in which a plurality of light beams are provided corresponding to each beam. FIG. 7 is an explanatory diagram showing a state in which a light beam passes through a slit immediately in front of a photodetector in a conventional example. 1... Light source unit, 2... Collimating lens, 3... Light deflector, 4... Imaging lens, 6...
Photodetector, 7... Recording medium, 9... Slit plate (light amount regulating means), 10... Slit (light transmitting portion), 51, 52, 53... Photodetector, 54...
Timing control section.

Claims (1)

[Claims for Utility Model Registration] A light beam scanning device that records an image by scanning a plurality of light beams on a recording medium at different timings, comprising a plurality of photodetectors that respectively detect the arrival of each of the light beams; When the plurality of photodetectors detect a plurality of corresponding light beams, sequentially turning off each light beam is controlled, and each of the light beams is recorded in accordance with an output signal from each of the photodetectors. A light beam scanning device characterized by comprising a synchronous control means for synchronously controlling start timing.