JPS6148083B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field] The present invention relates to a scanning device capable of detecting the shape of a spot light scanned by a deflector.

[Prior art]

Scanning devices that use spot light to move a light beam along a predetermined scanning line on a scanning surface by a scanning optical system including a deflector and a scanning lens are applied to image writing devices and image reading devices.
In these devices, from the point of view of resolution, the problem is whether the spot size is a predetermined size or not. Therefore, when writing or reading an image, it is necessary to detect whether the spot size is a predetermined size or not.

Various methods for detecting the size of this spot have been proposed in the past. For example, APPLIED
OPTICS VOl.15, No.6, June 1976, No. 1427
5 shows a method of cutting a stationary spot with a knife edge vibrating in one direction, detecting the light intensity of the spot in each cutting state with a photodetector, and detecting the size of the spot from this detection signal. It is shown.

The reason why the spot size can be detected from the detection signal is basically that the detection signal shows changes from the beginning of the knife edge spot cutting to the end of the cutting.
This is because if the moving speed of the knife edge is constant, the time at which this detection signal changes corresponds to the diameter of the spot. Therefore, by measuring the time during which this detection signal changes, the size of the spot can be measured. In this document, the detection signal is differentiated by a finer circuit, the differentiated signal is displayed on an oscilloscope, and the displayed waveform is observed.

However, when this method is applied to the above-mentioned scanning device, a special method is used to obtain a stationary spot, for example, a beam splitter is placed between the scanning lens and the deflector, and the scanning beam is Requires a method of obtaining another stationary beam and utilizing the stationary spot provided by this stationary beam, and requires an oscillating knife edge.
It has various drawbacks such as.

Also, the device in the literature cannot detect the state of the spot along two directions. Therefore, when an elliptical spot is required, or when turning light with different divergence angles in the vertical and horizontal directions, such as light from a semiconductor laser, into a circular spot light using an anamorphic imaging optical system, it is possible to This device was inconvenient when it was desired to detect the condition of a spot.

On the other hand, in the above-mentioned scanning device, the timing at which each scanning line starts scanning on the scanning surface may vary in the scanning direction if the manufacturing precision of the deflector (for example, in the case of a rotating polygon mirror, the division precision of each surface) is poor. Displaced against
It appears as so-called jitters. This jitter becomes a particularly important problem when displaying or writing high-precision images by adding a signal to a light beam. One way to prevent this is to eliminate the angle error of the polygon mirror, but it is extremely difficult to create a polygon mirror with high precision when the polygon mirror has a large number of faces. Therefore, instead of increasing the manufacturing precision of a deflector such as a rotating polygon mirror, a method is known in which a part of the scanning beam is taken out as an information light beam to determine the timing for starting scanning. This timing signal is referred to herein as a scan start signal for a desired scan width.

[Summary of the invention]

The present invention has been made in view of the above points.
SUMMARY OF THE INVENTION Accordingly, it is an object of the present invention to provide a device capable of detecting a scan start signal and a scan spot along two directions with a simple configuration. and,
This purpose is to provide a scanning apparatus that converts a light beam from a light source into a spot light moving along a predetermined scan line on a scanning surface by a scanning optical system including a polarizer and a scan lens. A knife edge is provided on a line other than the scanning width, and a plurality of photodetectors arranged along a direction intersecting the scanning line detect changes in the light intensity of the spot light cut by the knife edge. , by constantly or selectively connecting the photodetector to a circuit for detecting the shape of the spot light, and by constantly or selectively connecting the photodetector to a scan start signal circuit for the desired scan width. will be achieved.

[Example] The present invention will be described below with reference to the accompanying drawings.

FIG. 1 is a diagram showing an optical layout of a first embodiment in which the device of the present invention is applied to a laser beam writing device. In the figure, 1 is a laser light source, 2 is an optical modulator that performs optical modulation according to a signal from the control circuit 3,
4 is a beam expander, A is an anamorphic optical system for obtaining an elliptical spot, 5 is a rotating polygon mirror, and 6 is a scanning lens such as an fθ lens. The rotating polygon mirror 5 and the scanning lens 6 convert the stationary parallel beam from the beam expander 4 into an elliptical scanning spot that moves along the scanning line in the scanning plane. Note that the scanning plane is usually located at a position separated by the focal length of the scanning lens 6. 7 is a photosensitive material placed on the scanning surface. 8 is a photodetector placed on the scanning surface. This photodetector is responsive to the wavelength of the laser light source. For example, if the light from the laser light source is invisible light such as infrared rays, the photodetector needs to be responsive to infrared rays. 9
is a straight knife edge. Details of this knife edge and photodetector are shown in FIG. That is, on the back side of the knife edge 9 there are photodetector elements 71, 72, 7 consisting of three elements.
3 is placed. The photodetector elements 71, 72, and 73 are arranged in a direction perpendicular to, or intersecting, the moving direction of the spot. The outputs of these photodetector elements 71, 72, and 73 are introduced into three series of electric circuits to be described later. Returning to FIG. 1 again, 10 is a moving beam directed toward the photodetector 8, and 11 is a moving beam directed toward the photosensitive material 7. Reference numeral 12 denotes three differentiators to which signals from the photodetector 8 are input. As shown in FIG. 2, this differentiator 12 is composed of three amplifiers 13 and a differentiating circuit 14 including a capacitor and a resistor. The output from this differentiator 12 is displayed on three oscilloscopes 15. Therefore, by observing each of the three waveforms displayed on the oscilloscope 15, the shape of the spot can be determined. That is, the spots having shapes A, B, and C shown in FIG. 7 will now be explained.
In this case, it is assumed that a spot in the shape of A is desired. When the spots A, B and C cross the knife edge 9, each light receiving element 71, 72, 7
As shown in FIG. 8, the output of No. 3 is as shown in FIG.
The rising outputs 71a, 72a, 73a are the same.
In the case of (b), the rise is somewhat worse than in (a), but there is a difference in the output between the light receiving elements. In case of C, this rise becomes even worse,
The difference in output between each light receiving element becomes even larger. In this way, by viewing the rising signals of each light receiving element independently, information corresponding to the spot diameters in the main scanning direction and the sub-scanning direction can be obtained.

FIG. 9 is a result of differentiating the output shown in FIG. 8. By observing this differential waveform, the state of the spot can be recognized more clearly.

If it is determined from the waveform displayed on the oscilloscope that the spot shape is not the predetermined shape, adjust the focus of the anamorphic optical system A or the scanning lens 6 while observing the oscilloscope to obtain the desired spot shape. Is possible.

Furthermore, in the embodiment shown in FIG. 1, the photodetector 8 is used as a photodetector for obtaining a scan start signal of a desired scan width.

The output from photodetector 8 is input to detector 16 . Incidentally, at this time, the output of the photodetector 8 may be input to the differentiating circuit 12 at the same time.

Also, the circuit 1 can be switched by a switch (not shown).
6 and 12 may be input. However, in the former case, the spot shape can be measured for each scan, but in the latter case, the spot shape cannot be measured all the time.

This detector 16 is connected to a comparator 17 as shown in FIG.
and a reference voltage source 1 that provides a reference level to the comparator.
It is composed of 8. This detector 16 converts the detection signal of the photodetector 8 into a 0.1 level digital signal. The output from the comparator 17 is input to the control circuit 3.

This control circuit 3 is constructed as shown in FIG. Information from the computer 21 is input in a predetermined format to the interface circuit 22 of the apparatus, either directly or via a storage medium such as a magnetic tape or magnetic disk. Various instructions from the computer are sent to the instruction execution circuit 24.
is decrypted and executed. Data is stored in the data memory 23 in fixed amounts. In the case of character information, the data format is given as a binary code, and in the case of graphic information, it is data in units of pixels that make up the figure, or data of lines that make up the figure (so-called vectors). data). These modes are specified in advance of the data, and the instruction execution circuit 24 controls the data memory 23 and line data generator 26 to process the data according to the specified mode.
control. The line data generator 26 generates final data for one scan line.
That is, when data is given as a character code, the character pattern is read out from the character generator 25, and the character pattern of one line of text is lined up and buffered, or the character code of one line is buffered and sequentially sent to the character generator 25. Character patterns are read out and data for modulating laser light for one scan line is sequentially created.
Even when the data is graphic information, the data is converted into scan line data to create data for sequentially modulating the laser beam for one line scan. Data for one scan line is alternately inputted to line buffers 1 and 2, which are comprised of shift registers and the like, each having a number of bits equal to the number of pixels for one scan line, under the control of a buffer switch control circuit.

Furthermore, the data in line buffer 1 and line buffer 2 are sequentially read out one bit at a time for one scan line using the beam detection signal from the detector 16 shown in FIG. 1 as a trigger signal, and are applied to the modulator control circuit. While one reflective surface scans the recording surface, one scan line's worth of data stored in the line buffer is applied to the modulator 2.
A bright and dark pattern of scan lines is provided on the recording surface 7. Data is read out alternately from line buffers 27 and 28 under the control of a buffer switch control circuit 29. These temporal relationships are shown in FIG. That is, while reading from one line buffer, writing is occurring to the other line buffer. By this method, when the polygonal rotating mirror sweeps over the recording surface 7 and the interval between one reflecting surface and the next reflecting surface is very short, all data can be applied to the modulator 2. While scanning one scan line, the recording medium is moved in a direction perpendicular to the scan line by an appropriate scan line interval. In this way, the figure desired by the user is displayed on the recording surface.
Alternatively, text information can be output. What you need to be careful about here is to turn on the light when outputting information, and turn on the light when not outputting information.
In a recording system that is turned off, the modulator control circuit must have a function to control the modulator so that the light beam is turned on and off in accordance with the output signal of the detector 16, regardless of the presence or absence of information. That's what it means. That is, in order to obtain a photodetection signal from the detector 16, when the scanning light beam approaches the knife edge 9, the light beam must be turned on unconditionally.

Furthermore, after the scanning beam passes through the knife edge 10, it is necessary to turn off the light beam immediately and turn on the light only when there is information to be output, and the modulator control circuit plays this role. . This timing relationship is shown in FIG. a is detector 1
The photodetection signal obtained from 6, b is the signal to turn the light on or off regardless of the presence or absence of information to be written, c is the information to be written, and d is the signal to actually turn the light beam on or off. b and c.
It becomes an OR output signal.

Next, a spot detection device will be described in which light from a semiconductor laser is converted into a circular spot using an anamorphic optical system.

In the embodiment shown in FIG. 1, a laser light source that emits parallel light was assumed, but the
The second embodiment shown in the figure differs from this in that it uses a semiconductor laser that emits diverging light.

An optical system that generally uses a semiconductor laser as a light source.
When trying to obtain a light spot, since the light emitting surface of the semiconductor laser is rectangular, the focus position must be in the direction parallel to the light emitting surface (the layer direction of the P-N junction) and in the direction perpendicular to it. are different.
FIG. 11 is an explanatory diagram of this diagram, and if the semiconductor laser 50 is placed in the coordinate system as shown in the figure, its light emitting surface 5
Beyond 1, energy diverges at different orientation angles in the y and z directions. When the transverse mode of the laser is a completely single mode, these divergence angles θy and θz match the spread due to diffraction using the size of the light emitting surface as an aperture. In this case, the shape of the wavefront is such that it is considered to diverge from point 0 in the y direction as shown in FIG. 11b,
In the z direction, it forms a shape that is considered to diverge from point 0'. In other words, if the transverse mode of the laser is completely single mode, and if a spot is created by focusing it on one point with a lens, the points where the image can be sharpest are located at different positions in the y and z directions. become. Therefore, when an image scanning system is constructed using such a light source, the focus position will be different in the main scanning direction and the sub-scanning direction, and it is not possible to obtain a good image by simply focusing only in the main scanning direction. Can not.

In the second embodiment shown in FIG. 10, the knife edge shown in FIG. 7 placed at a position corresponding to the recording surface (or display surface) and the photodetector 8 are moved across the spot, and the light receiving element placed after the knife edge is It was possible to obtain a good spot on the recording surface from the rising signal.

FIG. 10 is a perspective view showing a second embodiment of the present invention. That is, the light emitted from the semiconductor laser 50 is collimated by an anamorphic collimator lens 52 and deflected by a deflector 53 such as a galvano mirror. The deflected light beam passes through the imaging lens 5
4, an image is formed on the recording surface 55. At this time, the light beam deflected by the deflector 53 first crosses the knife edge 9 and is detected by the light receiving element 8.

The following operations are the same as those in the first embodiment, and will therefore be omitted.

[Brief explanation of the drawing]

Fig. 1 is a diagram showing an embodiment in which the device of the present invention is applied to a laser beam writing machine, Fig. 2 is a diagram showing details of the differentiator shown in Fig. 1, and Fig. 3 is a diagram showing the details of the differentiator shown in Fig. 1. FIG. 4 is a block diagram of the write control circuit of the device shown in FIG. 1, and FIG.
Figure 6 is a time chart of the block diagram in Figure 4, Figure 7 is a diagram explaining the details of the knife edge and photodetector in Figure 1, and Figure 8 is a diagram for explaining the details of the photodetector in Figure 1. Figure 9 is an output diagram obtained by differentiating the output shown in Figure 8, Figure 10 is a diagram showing a laser beam writing device that uses the emitted light of a semiconductor laser as a light source, and Figure 11 is a diagram showing the output of a semiconductor laser. FIG. 3 is a diagram showing characteristics of emitted light. In the figure, 1... Laser light source, 2... Modulator, 3
...Control circuit, 4...Beam expander, 5
... Polycon, 6 ... Scanning lens, 7 ... Scanning surface, 8 ... Photodetector, 9 ... Knife edge, 10
... Spot state detection light, 11 ... Writing beam, 12 ... Differentiator, 15 ... Synchronoscope, 16 ... Detector, A ... Anamorphic optical system, 71, 72, 73 ... Photodetector element be.

Claims (1)

[Claims] 1. In a scanning device that converts a light beam from a light source into a spot light that moves along a predetermined scanning line on a scanning surface by a scanning optical system including a deflector and a scanning lens, a scanning width other than the desired scanning width on the predetermined scanning line is provided. A knife edge is provided on the line, and a plurality of photodetectors are arranged along a direction intersecting the scanning line for detecting changes in the amount of light of the spot light cut by the knife edge. Scanning characterized in that a detector is constantly or selectively connected to a circuit for detecting the shape of the spot light, and the photodetector is always or selectively connected to a scan start signal circuit for the desired scan width. Device.