JPS62138827A - Light beam scanning device - Google Patents

Abstract

PURPOSE:To prevent scanning pitch from becoming irregular owing to the surface inclination of a rotary polygon mirror, etc., by controlling a subscanning speed so that deviation is canceled on a scanned body. CONSTITUTION:The scanning deviation quantity signal S5 outputted by a signal processing circuit 23 is inputted to the gate circuit 41 of a control circuit 40. Further, the driving device for an endless belt 18 for subscanning performs driving at a constant speed during the effective main scan of a light beam 11 by a driving circuit 43 which outputs a driving signal S10 on the basis of the subscanning speed setting signal S9 outputted by a subscanning speed setting circuit 42. Then, the scanning deviation quantity signal S5 is inputted to a correcting circuit 44 at specific timing right before the light beam 11 utilized to find it starts making an effective main scan. The correcting circuit 44 corrects the subscanning speed setting signal S9 according to the scanning deviation quantity signal S5 and sends a signal S9' to the driving circuit 43 to compensate scanning deviation, thereby making the scanning line pitch constant.

Description

[Detailed Description of the Invention] (Field of the Invention) The present invention relates to a light beam scanning device, and more specifically, to a light beam scanning device, and more particularly, to a light beam scanning device that prevents occurrence of scanning line pitch unevenness due to surface tilt of a rotating polygon mirror that distorts the light beam. This invention relates to a beam scanning device.

(Technique of invention 1↑, i background and prior art) Conventionally,
The optical beam is deflected by an optical deflector to perform main scanning on the object to be scanned, and the object to be scanned and the light beam are relatively moved in a direction substantially perpendicular to the main scanning direction to perform sub-scanning. The optical beam scanning device using the optical beam scanning device is widely used in practical use, for example, in various scanning recording devices, scanning reading devices, etc.

In such a light beam scanning device, a rotating polygon mirror is often used to direct the light. This rotating polygon mirror is superior in terms of scanning stability compared to other optical deflectors such as a calhanometer mirror.

However, on the other hand, this rotating polygon mirror has a problem in that the degree of parallelism between the rotation axis and the mirror surface differs for each mirror surface, so-called surface inclination. If the rotating polygon mirror is tilted like this, the scanning beam will be deviated on the scanned surface in a direction perpendicular to the main scanning direction (i.e., the sub-scanning direction), resulting in scanning line pitch unevenness. . Various devices for optically correcting such surface tilt have been provided in the past, but such correction devices use expensive optical elements such as cylindrical lenses, so they are inevitably expensive. .

(Object of the Invention) The invention has been made in view of the above-mentioned circumstances, and it is an object of the present invention to provide a light beam scanning method that can prevent the occurrence of scanning line pitch unevenness due to the tilting of the surface of a rotating polygon mirror, etc., and can be formed at low cost. The purpose is to provide a device.

(Structure of the Invention) In the light beam scanning device of the present invention, in the light beam scanning device configured to perform main scanning and sub-scanning of the light beam as described above, the sub-scanning means for performing sub-scanning is controlled at a sub-scanning speed. In addition to making it variable, the scanning deviation of the light beam due to the tilting of the rotating polygon mirror mentioned above, etc.
That is, a scanning deviation amount measuring means that measures the amount of deviation in the sub-scanning direction and outputs a signal indicating the deviation amount, and a sub-scanning speed control signal that corresponds to the signal indicating the deviation amount. The present invention is characterized in that it is provided with a control means for controlling a sub-scanning speed so that the deviation is transmitted to the scanning means and is canceled out on the object to be scanned.

(Actual Test Mode) Hereinafter, the invention will be described in detail based on the drawings and embodiments. FIG. 1 shows a light beam scanning device according to an embodiment of the present invention. A light beam 11 emitted from a light source 10 such as a semiconductor laser or an @e-Ne laser is made into a parallel beam by a collimator lens 12 and then enters a rotating polygon mirror 13 . The optical beam 11 is formed by this rotating polygon mirror 1.
3, is reflected and deflected by a lens 14, is passed through a focusing lens 14, which is usually an f/theta lens, is reflected by a long mirror 15, and is scanned (main scan) over a scanned object 16 in the direction of arrow X. At the same time, the object to be scanned 16 is an endless bell driven by a driving device 17! - 18, the optical beam 11 is conveyed in the direction of the arrow Y, which is substantially perpendicular to the main scanning direction X, and sub-scanning is performed.
Illuminated dimensionally. In the optical scanning recording apparatus described above, the object to be scanned 16 is a recording medium such as a photosensitive film, and in this case, the light beam 11 is modulated based on an image signal. In addition, in the optical scanning reading device, the object to be scanned 16 is a reading medium, and in this case, the emitted light, blown light, or transmitted light from the object to be scanned 16 by irradiation with the light beam 11 is read by a photoelectric reading means. It will be done.

Here, if the rotating polygon mirror 13 has a surface tilt as described above, the optical beam 11 scanning the object to be scanned 16 will be deviated from the scanning reference position in the sub-scanning direction. Scanning 4 for measuring the amount of position>The position measuring means will be explained. Endless belt 18 as shown in FIG.
A slit plate 20 is arranged on the side of the object 16 so as to be scanned by the light beam 11 which is outside the effective scanning area on the object 16 to be scanned. This slit board? As shown in detail in FIG. 2, O has a wedge-shaped slit 21 having an end surface oblique to the main scanning direction X of the light beam 11. Then, on the back side of the temporary 20 to this sleeve 1, the above-mentioned slit 21
In order to be able to detect the light beam 11 passing through both ends of the
First and second photodetectors 22A and 22B are arranged.

These photodetectors 22A and 22B are composed of, for example, photodiodes, phototransistors, etc., and the photodetection signals 31 and 32 outputted from each are inputted to a signal processing circuit 23 as shown in FIG. It has become. As shown in the figure, this signal processing circuit 23 includes a goo-i signal generation circuit 25 that receives the photodetection signals 81 and 32, a counter 26, and a clock signal generation circuit? 7 and latch 2
8 and an arithmetic unit 29.

Hereinafter, scanning width position measurement by the signal processing circuit 23 will be explained with reference to FIG. 4. Before scanning the object to be scanned 16, the front light distribution beam 11 scans the slit plate 20 in the direction of the arrow X in FIG. This 8-light beam 11 is
Slit temporary? When the threshold approaches the slit 21 from above O, the first photodetector 2? 8 and then this first
After being removed from the photodetector 22A, the second photodetector 22B
detected by.

And light beam 11 or slit? 1, the light beam 11 is again blocked by the slit plate 20 and no longer enters the second photodetector 22B. The first thing I want to do is
, second photodetector? 2△, signal processing circuit from 22B? 3, a pulsed photodetection signal 31.82 as shown in FIGS. 4(b) and 4(c) is input.

The gate signal generation circuit 25 of the signal processing circuit 23 is shown in FIG.
As shown in d), a gate indicates the timing from the rise of the photodetection signal S1 to the fall of the photodetection signal S2 (that is, the timing while the light beam 11 crosses the slit 1). Outputs signal S3. Is this gate signal S3 a counter? 6 is input. On the other hand, this counter? 6, from the clock signal generation circuit 27, the fourth
The lock signal CLK is input as shown in Figure (a),
The counter 26 counts this clock signal @CLK while the gate signal @S3 is input. Is the latch 28 a slit for the light beam 11? When the sampling signal S6 is input at a predetermined time after passing through 1 (
(See Figure 4(e)), counter the signal @S4 indicating the above count number? 6 and sends it to the calculation unit 29.

In addition, the counter 26 receives a reset signal S7 (FIG. 4 (f
)) is reset.

The calculation unit 29 calculates the amount of scanning deviation of the light beam 11 based on the clock signal count indicated by the above-mentioned signal S4. In other words, this count corresponds to the time required for the light beam 11 to cross the slit 21, and the count number corresponds to the time required for the light beam 11 to cross the slit 21.
9 calculates the above-mentioned time based on the frequency of the clock signal @CLK given in advance, and the arithmetic unit 29 calculates the light beam based on this time and the scanning speed of the light beam 11 given in advance. slit 21 crossed by 11
Find the length ′. Here, as shown in FIG. 2, for example, one end of the slit 21 of the slit plate 20 is
, and the other end is at an angle θ with respect to the main scanning direction If the length of 1 is L, then Δχ= (L'-L)tanθ.The calculation unit 29 is given in advance, and θ
Based on the value of .DELTA..chi. from the length L, the amount of deviation of the light beam 11 from the reference scanning position is determined, and a signal S5 indicating the amount of deviation is output.

Although the shapes of the ribs 1 to 21 are limited as shown in FIG. 2 to simplify the explanation above, the shape of the slit 21 is not limited to this. That is, it is sufficient that both ends of the slit 21 are formed at an angle to each other, and in that case, the values of L' and Δχ correspond to each other under a predetermined relationship, so that L' can be determined based on this relationship. It is sufficient to find the crucible deviation Δχ from the value.

Furthermore, in order to make the explanation easier to understand, the calculation section 29
is the time required for the light beam 11 to cross the slit 21, the length L', in sequence from the count number of the clock signal CLK.
, then the deviation amount Δχ is calculated.Of course, what is ultimately required is the value of the scanning deviation amount Δχ, and usually a predetermined program is used to calculate the clock signal count number indicating the above-mentioned time. What is necessary is to be able to directly determine the scanning amount Δχ from .

The above signal logic circuit? Scanning deviation quantity signal output from 3 @S
5 is taken into the gate circuit 41 of the control circuit 40 as shown in FIG. Further, as shown in FIG. 3, the driving device 17 for the sub-scanning endless belt 18 is a drive circuit that outputs a drive signal 310 based on the %J scanning speed setting signal S9 output from the sub-scanning speed setting circuit 42. 43, the light beam 11 is driven at a constant speed during effective main scanning. The scanning deviation amount signal S5 obtained for each main scan and taken into the gate circuit 41 is transmitted to the light beam 11 used for obtaining it.
At a predetermined timing just before effective main scanning starts,
The signal is input to the correction circuit 44. Note that the gate circuit 41 obtains the above timing based on the photodetection signal S2 outputted by the second photodetector 22B. While the scanning deviation amount signal S5 is being input, the correction circuit 44 inputs the scanning deviation amount signal @S.
5, the sub-scanning speed setting signal 89 is corrected and sent to the drive circuit 43 as a signal S9'.
The scanning line pitch is made constant by compensating for the position. That is, for example, as shown in FIG. 2, when the scanning deviation is to the front side in the sub-scanning direction, the correction circuit 44 increases the sub-scanning speed, and the amount of increase is determined by the scanning deviation position Δχ. Sub-scanning speed setting signal 8
Correct 9. In this way, by temporarily changing the sub-scanning speed before the main scanning by the light beam 11 starts,
This deviation of the light beam 11 is compensated for, and the scanning line pitch on the scanned object 16 is always kept at a predetermined value. If the scanning deviation is backward in the sub-scanning direction, the sub-scanning speed setting signal S9 is corrected in the opposite direction to the above. Incidentally, changes in the sub-scanning speed controlled in the above manner are shown in FIG. 5 for easy understanding.

In the embodiment described above, the scanning deviation position Δχ is determined for each main scanning of the light beam 11, and the sub-scanning speed is controlled accordingly. Since the scanning deviation amount Δχ is approximately the same value for each mirror surface, the scanning deviation amount Δχ is determined for each mirror surface in advance and stored in the storage means, and the main scanning 1 of the light beam 11 is
Specify the mirror surface every time and store the scanning deviation amount Δ from the above storage means.
It is also possible to read χ and use it for sub-scanning speed control. Roughly speaking, for example, if the main scanning speed is extremely high and
In the circuit shown in the figure, the scanning deviation amount signal S5 is sent to the gate circuit 41 through the delay circuit.
The scanning deviation amount signal $5 may be used for sub-scanning speed control with a one-rotation delay of 3.

In addition, in a device that does not perform steady sub-scanning as described above and performs sub-scanning by pitch-feeding the scanned object 16 between main scans, the above-mentioned pitch is determined based on the scanning offset position signal S5. All you have to do is control the feed speed.

In addition, the scanning deviation measurement means for determining the deviation position of the light beam is not limited to the above-mentioned embodiments, and may be used, for example, to directly measure the deviation by receiving the light beam with a near array sensor. However, the scanning deviation measuring means in the above embodiment can be formed at a lower cost than a device using a near array sensor, which is expensive, and can be formed in parallel with the surface to be scanned. Since the light beam that is focused thereon can be detected by the photodetector, it is possible to measure the scanning deviation position with high precision, which is preferable.

(Effects of the Invention) As explained in detail above, in the light beam constant distortion device of the present invention, even if the light beam is deflected due to the surface tilt of the rotating polygon mirror, the scanning line pitch can be kept constant. , precision scanning becomes available. Moreover, since the device of the present invention does not use a correction optical system consisting of an expensive cylindrical lens or the like, it can be manufactured at low cost.

[Brief explanation of drawings]

FIG. 1 is a schematic perspective view showing a light beam scanning device according to one embodiment of the present invention, FIG. 2 is a plan view showing an enlarged part of the above embodiment device, and FIG. 3 is an electrical diagram of the above embodiment device. FIG. 4 is a timing chart showing the output timing of various signals in the above electric circuit, and FIG. 5 is a graph showing changes in sub-scanning speed in the above embodiment device. Beam 13...Rotating polygon mirror 1
6... Scanned object 17... Drive device 18.
... Endless belt 20 ... Slit plate 21 ...
・Slit 22A, 22B...Photodetector 2
3...Signal processing circuit 25...Gate signal generation circuit 26...Counter 27...Clock signal generation circuit? 8... Latch 29... Arithmetic unit 40... Control circuit 41... Gate circuit 42... Sub-scanning speed setting circuit 43... Drive circuit A4... Correction circuit Sl, S2... Photodetection signal S5... Scanning position mother signal S9... Sub-scanning speed setting signal 89'... Corrected sub-scanning speed setting signal 310...
・Drive signal diagram 3

Claims (2)

[Claims] (1) A light beam deflected by an optical deflector is caused to main scan an object to be scanned, and the object to be scanned and the light beam are relatively moved in a direction substantially perpendicular to the main scanning direction. In the light beam scanning device configured to perform sub-scanning, the sub-scanning means for performing the sub-scanning is formed to be able to change the sub-scanning speed, and the deviation of the light beam in the sub-scanning direction during the main scanning is scanning deviation amount measuring means for measuring the amount of deviation and outputting a signal indicating the deviation amount, and sending a sub-scanning speed control signal corresponding to the signal indicating the deviation amount to the sub-scanning means to 1. A light beam scanning device, further comprising: a control means for controlling a sub-scanning speed so that the light intensity is canceled out on the object to be scanned. (2) The scanning deviation measuring means includes a wedge-shaped slit which is arranged to receive scanning of the light beam at a position outside the effective main scanning area of the light beam, and which intersects with the direction of the main scanning. a slit plate having a slit plate; a photodetector for detecting the light beam through the wedge-shaped slit; and measuring the time required for the light beam to cross the wedge-shaped slit based on the output of the photodetector; The light beam scanning device according to claim 1, further comprising a signal processing circuit that outputs a signal indicating the amount of deviation of the light beam in a direction perpendicular to the scanning direction based on this time. .