JPH0247622A - Light beam scanner - Google Patents

Abstract

PURPOSE:To uniform the line pitch of a main scanning on a recording material by operating a moving means according to a position shift detected by a position shift detecting means, and providing a control means which performs control so that a light beam aligned with a reference line. CONSTITUTION:When a reflecting surface slants, the light beam does not pass on the reference line, but is deviated and moved. Consequently, the position shift can be detected from the degree of this deviation. The control means 16 outputs a signal to the moving means 44 according to the detected position shift to move a subscanning optical system 26. When the subscanning optical system 26 is moved, a light beam passing through the subscanning optical system 26 is moved in a subscanning direction in parallel, consequently, the light beam is aligned with the reference line. Consequently, the fitting of the optical system for surface tilt correction is facilitated, and the pitch of scanning track lines of light beams by the respective reflecting surfaces of a polygon mirror is uniformed.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to a light beam scanning device, and particularly to a light beam that reads or records information by a light beam reflected by a rotating polygon mirror having a plurality of reflecting surfaces. Relating to a scanning device.

[Prior art]

Generally, a light beam emitted from a laser is irradiated onto the image,
In a light beam device that reads the transmitted or reflected light, or in a light beam scanning device that irradiates a recording material with a light beam and records an image, the recording light beam from a laser is composed of a rotating polygon mirror, etc. The scanning optical system allows
The irradiation direction is continuously deflected. That is, the angle of incidence of the recording light beam on the polygon mirror is changed by the rotation of the polygon mirror, thereby deflecting the direction of reflection. The light beam reflected by the polygon mirror is
For example, in the case of a light beam scanning device, a recording medium placed on a fixed recording stage is irradiated with light, and an image is recorded. This recording medium is one in which the recording layer in the irradiated area changes its transmittance by melting or evaporating, for example, and like conventional silver halide photosensitive materials,
It is possible to check the recorded state at the same time as writing (light beam irradiation) without performing any development processing after recording an image (see Japanese Patent Laid-Open No. 153025/1983).
.

However, in such a structure, the accuracy of the polygon mirror's reflective surface greatly affects the main scanning line pitch, and if so-called surface tilt occurs, the pitch of the main scanning lines recorded on the recording material becomes uneven, resulting in the image being distorted. This will cause a disturbance. Furthermore, since the polygon mirror is mechanically rotated, the reflective surface may become tilted due to dimensional errors in the rotational drive system or wear over time, which also causes surface inclination.

In order to solve this problem, it has been proposed to correct the light beam reflected by the reflecting surfaces using an optical system so that the trajectories of the scanning lines from each reflecting surface of the polygon mirror match (face tilt correction) -28666, Utility Model 53
(Refer to Publication No.-91845). In addition, when implementing the technology described in the above-mentioned publication, a short focus lens (for example, a toric lens) that requires high quality and is difficult to manufacture is required, so the present applicant has proposed the technique described in Japanese Patent Publication No. 60-52409. disclose that long focal length cylindrical lenses can be used that are relatively inexpensive. According to these publications, an optical system is interposed between the polygon mirror and the recording material to eliminate the surface tilt.

[Problem to be solved by the invention]

However, when an optical system is installed between the polygon mirror and the recording material to correct the surface tilt, the amount of surface tilt (
Since the position of the optical system is fixed even though the deflection angle range differs depending on each reflecting surface, it is necessary to correct the surface tilt of all reflecting surfaces. For this reason, high precision is required when installing the optical system.
There are problems in that it is troublesome to assemble, has a large number of parts, and the device itself is large. Particularly, when the numerical aperture of the converging optical system is large and the converged laser spot system is required to have an accuracy of several micrometers, the above-mentioned problem occurs conspicuously.

In consideration of the above facts, the present invention allows easy installation of an optical system for surface tilt correction, and allows the scanning locus of the light beam by each reflecting surface of the polygon mirror to be approximately straight.
It is an object of the present invention to obtain a beam scanning device that can make the main scanning line pitch on a recording material uniform.

[Means to solve the problem]

A light beam scanning device according to the present invention includes: a deflecting means for deflecting a light beam in the main scanning direction; a sub-scanning optical system disposed on the irradiation locus of the light beam and deflecting the light beam in the sub-scanning direction; a moving means for moving the sub-scanning optical system so as to move in parallel in the sub-scanning direction, a branching means for branching the light beam that has passed through the sub-scanning optical system, and a reference line corresponding to the movement locus of the main scanning. positional deviation detection means for detecting a positional deviation between the light beam and the actual movement trajectory of the light beam;
and control means for operating the moving means based on the positional deviation detected by the positional deviation detection means and controlling the light beam to match the reference line.

[Effect]

In the present invention, for example, an afocal optical system of an infinite focus system is disposed as a sub-scanning optical system on the irradiation locus of the light beam,
The light beam that has passed through this afocal optical system is irradiated onto the positional deviation detection means. The positional deviation detection means detects the positional deviation between the reference line that coincides with the main scanning direction of the light beam and the actual movement locus of the light beam, and if the main scanning is performed with high accuracy, the light beam Since it passes on this reference line, it can be determined that there is no positional shift. On the other hand, if the reflective surface is tilted, the light beam will not pass over the reference line, but will be biased to one side.

Therefore, positional deviation can be detected based on the degree of this bias.

The control means outputs a signal to the moving means based on the detected positional deviation to move the sub-scanning optical system. When the sub-scanning optical system is moved, the light beam passing through the sub-scanning optical system is translated in parallel in the sub-scanning direction, so that the light beam coincides with the reference line.

By performing this for each reflecting surface, the light beam always passes approximately on the reference line, and the surface tilt is corrected.

In this way, since the sub-scanning optical system is moved according to the degree of inclination of the reflective surface, there is no need to use a fixed type optical system that is difficult to manufacture, and it can be easily assembled.

Note that as the moving means, a piezoelectric element that can change an electrical quantity such as a voltage into a mechanical quantity to slightly move the surface can be applied. Preferred materials include some piezoelectric materials that are durable against mechanical action, such as barium titanate and its analog PZT (lead zirconate).

〔Example〕

Since the content of the present invention remains the same whether it is applied to a reading device using a light beam or a recording device, the following description will be made using a recording device.

FIG. 1 shows a schematic diagram of a light beam scanning device 10 according to this embodiment. In this embodiment, two lasers for light beam irradiation are provided, one of which is used as the writing laser 12 and the other as the reading radar 14. These lasers 12 and 14 are arranged in parallel and emit a light beam (indicated by a dashed line Bm in FIG. 1) in response to a signal from the control section 16. The writing light beam Bmw emitted from the writing laser 12 is supplied to the optical modulator 18, where it is modulated, passes through the gicroic mirror 20, and is irradiated onto the polygon mirror 22, which is a rotating polygonal mirror. It looks like this. On the other hand, the reading light beam Bmr is reflected by the mirror 24 in the direction of the guichroic mirror 20, and the optical axis of the reading light beam Bmr is made to coincide with the writing light beam Bmw by the guichroic mirror 20. Therefore, the polygon mirror 22 is irradiated with a combined light beam Bm, which is a combination of the writing light beam Bmw and the reading light beam Bmr, through the lens 26, which is a sub-scanning optical system. In this embodiment, this lens 26 constitutes an afocal system, which is an infinite focal system such as a telescope that does not have a light-gathering power.

The polygon mirror 22 has a plurality of reflective surfaces 22A, and is rotated via a rotation shaft 23 by rotation of a drive motor (not shown).

The rotation of the polygon mirror 22 serves to continuously change the angle of incidence of the composite light beam Bm incident within a predetermined angle range.

The combined light beam Bm reflected from the polygon mirror 22 passes through the optical system 27 and is split by the beam splitter 28.
Only the reading light beam Bmr is reflected and separated from the writing light beam Bmw passing through the beam splitter 28.

The lens 26 is held by an inner holder 42, and this inner holder 42 is held by an outer holder 46 via a piezoelectric element 44 in the left-right direction in FIG. 1 (sub-scanning direction). By applying a predetermined voltage to the piezoelectric element 44, the surface of the piezoelectric element 44 can be slightly moved to change the relative position between the inner holder 42 and the outer holder 46. Thereby, the angle of the lens 26 is changed, and the incident light beam can be moved.

The writing light beam Bmw that has passed through the beam splitter 28 is irradiated onto the recording surface of the roll-shaped recording medium 36 placed in the recording stage 40 via a converging optical system 38 to perform main scanning. ing. Recording medium 36
is wound up from one roller to the other roller at a constant speed, thereby performing sub-scanning. In addition,
In this embodiment, the recording medium 36 is a roll-shaped film, but it may be a so-called microfiche that records a plurality of images on the sheet-shaped recording medium 36.

On the other hand, the reading light beam Bmr separated from the writing light beam Bmw by the beam splitter 28 is converged by a converging optical system 30, and is irradiated onto a photodetection sensor 32, which is a positional deviation detection means. The photodetection sensor 32 is configured with photoelectric conversion elements 34 arranged in two rows (hereinafter, the row on the left side of the paper in Figure 1 will be referred to as the first row 34A, and the row on the right side will be referred to as the second row 34B). The light beam Bmr is sequentially scanned in accordance with the scanning by the polygon mirror 22 from the top to the bottom in the vertical direction in FIG.

The line between the first column 34A and the second column 34B is a reference line BS, which indicates the normal scanning position of the reading light beam Bmr. That is, when the reading light beam Bmr passes on this reference line BS, the first row 34A and the second row
The output values of the respective corresponding photoelectric conversion elements 34 in the column 34B are made to be the same. In addition, if the actual reading light beam Bmr deviates from this reference line (for example, line P in FIG. 1), the column on the deviated side (first column 34A)
The output value of the photoelectric conversion element 34 becomes larger, and the output values of the photoelectric conversion element 34 are different from each other.

The output value of the photoelectric conversion element 34 in the first row 34A is supplied to the positive side input terminal of the operational amplifier 48, and the output value of the photoelectric conversion element 34 in the second row 34B is supplied to the negative side input terminal of the operational amplifier 48. It is now possible to do so. As a result, the output terminal of the operational amplifier 48 outputs an electric signal corresponding to the output difference between the first column 34A and the second column 34B. The output terminal of this operational amplifier 48 is connected to the control section 16.

The control unit 16 includes a CPU 50, a RAM 52, a ROM 54,
The microcomputer 60 is equipped with a human output port 56 and a bus 58 such as a data bus or a control bus that connects these ports.
The operational amplifier 48 is connected through a /D converter 62, the writing laser 12 is connected through a driver 64, and the reading laser 14 is connected through a driver 66.

The RAM 52 of the microcomputer 60 stores a characteristic map (see FIG. 2) showing the relationship between the output electrical signal from the operational amplifier 48 and the amount of deviation of the scanning line with respect to the reference line BS.
is memorized, and this map determines the operational amplifier 4.
The amount of deviation is determined according to the output electrical signal from 8. Further, the CPU 50 calculates the amount of movement of the lens 26 from this amount of deviation.

Further, a piezoelectric element 44 is connected to the human output boat 56 via a driver 68, and a voltage value corresponding to the amount of movement calculated by the CPU 50 is supplied to the piezoelectric element 44.

The operation of this embodiment will be explained below with reference to the flowchart of FIG.

First, in step 100, the polygon mirror 22 is rotated, and the process proceeds to step 102, where the irradiation of the reading light beam Bmr from the reading laser 14 is started. 20 and the polygon mirror 2 via the lens 26
2. The polygon mirror 22 is rotated at a constant speed by a signal from the control section 16, so that the angle of incidence of the reading light beam Bmr is changed within a predetermined range, and the direction of the reflected light is deflected accordingly.

This reflected light reaches a photodetection sensor 32 via an optical system 27, a beam splitter 28, and a converging optical system 30. The optical system 27 may be omitted. In the photodetection sensor 32, the photoelectric conversion element 34 (FIG. 1) converts the reading light beam Bm
When light reception of r starts (step 104), the control unit 1
In step 6, it is determined that writing (image recording) is to be started after a predetermined time from the time of light reception (step 106).

Here, when the image recording timing comes (the position of the polygon mirror 22 becomes the main scanning start position), step 108
Then, in step 112, the recording medium 3G starts moving at a constant speed, and then, in step 112, the writing laser 12 starts irradiating the writing light beam Bmw. After the writing light beam Bmw is modulated by the optical modulator 18, it passes through the gicroic mirror 20 and enters the polygon mirror 22. The light beam reflected from the polygon mirror 22 is a composite light beam B of the writing and reading light beams.
m, but these are separated by a beam splitter 28 installed downstream of the polygon mirror 22,
Only the writing light beam F3mw travels straight and is irradiated onto the recording medium 36 to perform main scanning.

On the other hand, the reading light beam Bmr is scanned along the photoelectric conversion element 34 in correspondence with the main scanning. In this case, if it passes over the reference line BS, the output values of the left and right photoelectric conversion elements in FIG. 1 at the current scanning point are the same, and the output from the operational amplifier read in the next step 114 is 0. becomes.

Thereby, it can be determined that main scanning to the recording medium 36 is being performed accurately.

Here, the light beam reflected by the reflective surface 22A is
Due to the inclination of the reflective surface 22A, the roughness of the reflective surface 22A, etc., the light beams reflected by all the reflective surfaces 22A do not follow the same scanning locus, and depending on the reflective surface 22A, they may shift in the sub-scanning direction.

In this embodiment, this positional shift is determined according to the output value of the operational amplifier 48. That is, if the reading light beam deviates from the reference line BS, the amounts of light received by the photoelectric conversion elements 34 on the left and right sides of the scanning line in FIG. 1 differ. For example, if the first imaginary line is the actual scanning trajectory line, the first row 3
The output of the 4A photoelectric conversion element 34 is greater than the output of the second row photoelectric conversion element 34, and the output values supplied to the positive input terminal and the negative input terminal of the operational amplifier 48 are different. The operational amplifier 48 outputs a value corresponding to this output difference.

The output electrical signal from the operational amplifier 48 is sent to the A/D converter 6.
2, the signal is A/D converted and supplied to the input/output port 56 (step 114). Here, in the CPU 50, RA
The amount of deviation is determined based on a characteristic map (see FIG. 2) showing the relationship between the output electrical signal from the operational amplifier 48 stored in M52 and the amount of deviation of the scanning line from the reference line (step 116). In this case, as mentioned above, the operational amplifier 4
When the output of 8 is 0, the deviation amount is 0. Next, in step 118, the P line is changed to the reference line BS according to this amount of deviation.
The amount of movement of the lens 26 for upward correction is calculated, and a predetermined voltage is applied to the piezoelectric element 44 based on the calculation result (step 120).

As a result, the relative positions of the inner holder 42 and the outer holder 46 are deflected, and the lens 26 is positioned downward as shown in the imaginary line in FIG. The light beam is moved as shown in the imaginary line. When this light beam is reflected by the polygon mirror 22, it can be made to coincide with the proper light beam at the incident position of the optical system 27. Note that if the amount of deviation is 0, the applied voltage is 0, and the lens 26 is not actually moved.

In the next step 122, it is determined whether recording of one image has been completed, and if not, step 114
Move to the following steps 114.116.118.12
Repeat 0. Also, when recording of one image is finished,
This routine ends.

In this way, since the surface tilt of each reflective surface 22A is constantly corrected, the main scanning locus recorded on the recording medium 36 does not shift in the sub-scanning direction, and image unevenness can be prevented. Further, since the lens 26 is moved to correct the surface tilt, there is no need to use a fixed type lens that is difficult to manufacture and expensive, and ease of assembly is improved.

Furthermore, the number of parts can be reduced, and the device itself can be made more compact.

In this embodiment, the lens 26 is replaced by the polygon mirror 22.
Although it is arranged upstream of the polygon mirror 22, it may be arranged downstream of the polygon mirror 22. However, when disposed downstream of the polygon mirror 22, the light beam moves in the main scanning direction, so a large lens that covers the movement range is required.

〔Effect of the invention〕

As explained above, in the light beam scanning device according to the present invention, the optical system for surface tilt correction can be easily installed, and the line pitch of the scanning locus of the light beam by each reflecting surface of the polygon mirror can be made uniform. It has this excellent effect.

[Brief explanation of the drawing]

Fig. 1 is a schematic diagram of the optical beam recording device according to this embodiment, Fig. 2 is a characteristic map showing the relationship between the output electrical signal from the operational amplifier and the amount of deviation of the scanning line with respect to the reference line, and Fig. 3 is a control map. It is a flowchart. 10... Light beam scanning device, 12... Writing laser, 14... Reading laser, 16... Control unit, 22, 26, 34, 36, 44, polygon mirror lens, Photoelectric conversion element, ・Recording medium, ・Piezoelectric element.

Claims (1)

[Claims] (1) Deflection means for deflecting the light beam in the main scanning direction;
a sub-scanning optical system disposed on the irradiation locus of the light beam and deflecting the light beam in the sub-scanning direction; a moving means for moving the sub-scanning optical system so that the light beam moves in parallel in the sub-scanning direction; a branching means for branching the light beam that has passed through the sub-scanning optical system; a positional deviation detection means for detecting a positional deviation between a reference line corresponding to the main scanning movement trajectory and the actual movement trajectory of the light beam; A light beam scanning device comprising: control means for controlling the moving means to operate the moving means based on the positional deviation detected by the positional deviation detection means so as to make the light beam coincide with a reference line.