JPH08309565A - Laser plotting device - Google Patents

Abstract

PURPOSE: To provide a vector scanning type laser plotting device capable of expressing gradation. CONSTITUTION: CPU 6 calculates the length of a minute line segment to be plotted in each pixel constituting a matrix, from gradation data contained in plotting data stored in RAM 8. Then, it forms for each pixel the X address data showing the starting point of the minute line segment to be plotted in each pixel area and the Y address data; it further forms the Y address data showing the ending point using the length of the minute line segment already determined. After that, positional signals are generated from these address data and outputted to FIFO 12, 15. As a result, a deflection mirror is driven through a D/A converter 13, 16 and an amplifier 14, 17 with the minute line segment plotted in each pixel area on a recording medium. Since the minute line segment is short in length, dots are formed in each pixel with their size corresponding to the value of the gradation data.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a laser drawing apparatus for forming an image on a recording medium by irradiating the recording medium with a laser beam for processing or coloring.

[0002]

2. Description of the Related Art A laser drawing apparatus generates a laser beam by a gas laser, a solid-state laser or a semiconductor laser,
The laser beam is irradiated as a convergent beam onto a recording medium, and the recording medium is processed or colored to form an image. This laser drawing apparatus is classified into a system that raster-scans a laser beam and a system that scans a vector.

In a raster scanning type laser drawing apparatus, it is most common to move a laser beam by a polygon scanner or a rotary drum to perform raster scanning, but a type of stopping the laser beam for each pixel is also known. ing. In the former raster scanning type laser drawing apparatus, one pixel is a set of dots, and the number of dots is changed according to the gradation of the pixel, that is, the gray level, thereby expressing the halftone of the image, that is, the image. The gradation expression of is realized. However, in this method, in order to increase the resolution of the image, the size of the pixel must be sufficiently small even if the number of dots in one pixel is large, and the size of one dot must be extremely small. I have to. As a result, it is necessary to use an expensive optical system for converging the laser beam, and since the number of pixels increases, the amount of digital data representing an image becomes huge, which is also uneconomical.

As one measure to solve this problem, Japanese Patent Application No. 5-264165 discloses a method of expressing gradation by pulse width modulation, pulse number modulation or pulse density modulation. In addition, digital / analog (D
A / A) power modulation method is also known in which a laser output is controlled using a converter, and this method is put to practical use in a laser printer.

On the other hand, in the latter method of stopping the scanning for each pixel, gradation is expressed by stopping the laser beam at each pixel position and changing the irradiation time of the laser light at each pixel position. And the laser light heating type thermal transfer device (LIM
T) (published in "Video Information" issued in October 1993).

This apparatus uses a commercially available optical deflector designed to perform vector scanning as a basic operation and its control unit, while performing raster scanning by a simple method by a control command of the control unit. , Time-modulate the laser,
That is, recording is performed for each pixel by performing pulse width modulation. Basically, raster scanning is performed, but since the laser beam is moved from pixel to pixel, the vector scanning element is also included.

FIG. 9 is a timing chart showing an example of the operation. (A) shows changes in the irradiation position of the laser beam in the X (Y, Z) directions, and (B) shows control pulses for turning the laser on and off. The irradiation position of the laser beam moves in the period TA1 and then stops at the position of a predetermined pixel in the period TA2. During that period, the control pulse is at a high level in the period TA3, and the laser beam is emitted. By changing the width of the control pulse, the irradiation time changes and the gray level of this pixel changes.

However, in the laser drawing apparatus that performs these raster scans, all image information is treated as bitmap data, and images composed of line segments such as characters and line drawings are not distinguished from gradation images. However, there is a drawback that the digital error is likely to appear in the drawing. In the latter method of performing raster scanning by stopping the laser beam for each pixel, even if the optical deflector is controlled to stop in order to stop the laser beam, the deflector actually stops and remains stationary. Since it takes time, the laser irradiation cannot be started immediately after the stop control, and the scanning is stopped during the irradiation of the laser light, so that the drawing speed is slow and the drawing takes time.

In contrast to such a raster scanning type laser drawing apparatus, a laser drawing apparatus that performs vector scanning scans a recording medium with a laser beam in an arbitrary direction while irradiating the recording medium with a laser beam and linearly scans the recording medium. Minutes are drawn to form an image. A laser is not used as a device for drawing by vector scanning, but an XY plotter is well known, and is widely used as an output device of a computer for graphic output. Further, in an electron beam drawing apparatus for manufacturing a semiconductor photomask, direct writing, and reticle creation, vector scanning is similarly performed to draw a figure.

As a laser drawing device for vector-scanning a laser beam, there is a beam exposure device such as a laser beam recording device for printing out on a recording paper. This beam exposure device, on a recording medium such as a photosensitive material or a photosensitive drum,
An energy beam such as a laser beam or a charged particle beam is irradiated, and the beam irradiation position on the recording medium is moved by the beam deflector based on the graphic data from the host computer to draw a graphic on the recording medium. .

Therefore, such a vector-scanning type laser drawing device is basically good at drawing geometrical figures and line drawings composed of line segments, and therefore characters can be easily printed with a skeleton font. Can draw. Also, for characters of other fonts, the outline of the character is drawn by vector scanning,
By filling the inside, characters with smooth outlines can be reproduced. Then, in the vector scanning method, since the figure is drawn as a group of line segments, the figure is represented by the position information of the start point and the end point of each line segment that constitutes it, and as a result,
The amount of image data required for drawing is much smaller than that in the raster scanning method.

[0012]

Although the vector scanning type laser drawing apparatus has such a large feature, there has been no one capable of expressing gradation, so that the range of use is limited. . Therefore, an object of the present invention is to provide a vector scanning type laser drawing apparatus capable of expressing gradation.

[0013]

To achieve the above object, the present invention two-dimensionally deflects a laser beam generated by a laser light source by an optical deflector and draws a line segment on a recording medium to form an image. In a laser drawing apparatus to be formed, a gradation vector conversion means for determining the length of a minute line segment for each pixel based on gradation data representing the gray level of each pixel in a matrix form an image, and this gradation A minute line segment drawing means for drawing a minute line segment having the length determined by the vector converting means into each pixel area on the recording medium by controlling the optical deflector. .

According to the present invention, the minute line segment drawing means is
The minute line segment is drawn such that the midpoint of the minute line segment coincides with the center of the pixel region. The present invention is also characterized in that the minute line segment drawing means randomly sets the position of the minute line segment in the pixel area for each pixel area. The present invention is also characterized in that the minute line segment drawing means draws the minute line segment such that the starting point of the minute line segment is at a predetermined position in the pixel region. The present invention is also characterized in that the minute line segment drawing means draws the minute line segment such that an end point of the minute line segment is at a predetermined position in the pixel region. According to the present invention, when the laser beam is deflected by the optical deflector to draw the minute line segment, when the optical deflector is instructed to start moving the laser beam and a designated time has elapsed. The minute line segment drawing means includes a laser light source control means for turning on the laser light source, turning off the laser light source when a specified time elapses when the optical deflector is instructed to end the movement of the laser beam. It is characterized by

According to the present invention, the drawing data including the pixel size, the total number of pixels in the X direction, the total number of pixels in the Y direction, and the gradation data is input, and the gradation vector conversion means outputs the drawing data among the drawing data. The gradation line data is used to determine the length of the minute line segment, and the minute line segment drawing means determines the pixel size, the total number of pixels in the X direction, and the total number of pixels in the Y direction of the drawing data. Is used to determine the position of the starting point and the ending point of the minute line segment.

[0016]

The gradation vector conversion means determines the length of the minute line segment for each pixel based on the gradation data representing the gray level of each of the matrix-shaped pixels forming the image. Then, the minute line segment drawing means draws the minute line segment having the length determined by the gradation vector conversion means in each pixel area on the recording medium by controlling the optical deflector.

The light spot formed on the recording medium by the laser beam has a certain spread because the laser beam cannot be completely converged. Further, the recording medium responds to the irradiation of the laser beam with a certain delay. For these reasons, when the length of the minute line segment is sufficiently short, the drawing result is not a line segment but a dot having a substantially circular shape. The diameter of the dot is almost proportional to the length of the minute line segment to be drawn.

Therefore, by drawing the minute line segment as described above, a dot having a size corresponding to the gradation data is drawn in each pixel area, and the gradation is expressed by the size of the dot. It becomes possible. That is, it is possible to realize gradation expression of an image by a laser drawing device that performs vector scanning.

[0019]

EXAMPLES Next, examples of the present invention will be described. Figure 2
FIG. 1 is a schematic plan view showing an example of a laser drawing apparatus according to the present invention. This laser drawing apparatus 25 includes a laser block 1 as a laser light source, and the laser block 1 has a plurality of semiconductor lasers and a condensing optical system, and generates a laser beam 2 focused on a recording medium. Reference numeral 3 is a folding mirror in which a dielectric multilayer film is coated on the surface of the glass substrate, and the laser beam 2 from the laser block 1 is bent at a right angle on a horizontal plane. Deflection mirrors 4 and 5 composed of plane mirrors
Constitutes an optical deflector for two-dimensionally moving a light spot formed by the laser beam 2 on a recording medium (not shown) arranged below the deflection mirror 5.

A deflection actuator (not shown) is attached to each of the deflecting mirrors 4 and 5, and the laser beam 2 from the folding mirror 3 is first deflected.
When the mirror 4 is oriented in the neutral direction, the laser beam 2 is bent 90 degrees on the horizontal plane and is incident on the deflection mirror 5. Then, the mirror 4 swings about the vertical axis by the actuator, the incident position of the laser beam 2 on the deflection mirror 5 changes, and the light spot moves in the X direction on the recording medium.

Laser beam 2 incident on the deflection mirror 5
When the mirror 5 is oriented in the neutral direction, is bent vertically downward and enters the recording medium. When the mirror 5 swings about the horizontal axis by the actuator, the laser beam 2 is deflected in the Y direction, the incident position on the recording medium changes, and the light spot moves in the Y direction on the recording medium. To do. In the above-mentioned focusing optical system which constitutes the laser block 1, the laser beam 2 is reflected by these mirrors 3-5.
After being reflected by the recording medium, the light is focused on the recording medium.

This laser drawing apparatus further comprises the deflection actuator and a control device (not shown in FIG. 2) for controlling the on / off of the laser block 1, the details of which are shown in the block diagram of FIG. This control device has a central processing unit (CPU) 6, a ROM 7 in which program data for operating the CPU 6 and various parameters necessary for control are stored, work data, and drawing data, as main components. , And a RAM 8 for temporarily storing work parameters.

As elements directly related to the control of the deflection actuator of the deflection mirror 4, an X-axis FIFO buffer memory (hereinafter simply referred to as FIFO) 12 for temporarily storing a digital position signal, and a digital signal from the FIFO 12 are provided. The X-axis D / A converter 13 for converting into an analog signal, and the X-axis amplifier 14 for amplifying the output signal of the D / A converter 13 and supplying it to the deflection actuator of the deflection mirror 4 as an analog position signal are provided.

On the other hand, as elements directly related to the control of the deflection actuator of the deflection mirror 5, a Y-axis FIFO 15 for temporarily storing a digital position signal and a Y-axis D / A converter for converting a digital signal from the YFIFO 15 into an analog signal. 16, a Y-axis amplifier 17 that amplifies the output signal of the D / A converter 16 and supplies it to the deflection actuator of the deflection mirror 5 as an analog position signal. The offset control unit 18 supplies a DC voltage to each of the amplifiers 14 and 17 to add it to the analog position signal so that the drawing area on the recording medium can be shifted on the recording medium as necessary. It is provided.

Further, this control device has a laser block 1
The laser control unit 19 that outputs the on / off control signal of the semiconductor laser of the laser block 1 in synchronization with the deflection operation by the position signals from the FIFOs 12 and 15 and the timing of this control signal And a delay circuit 20 for controlling to compensate the operation delay of the actuator (thus, the deflecting mirrors 4 and 5).
The delay circuit 20 controls the laser block 1 after the timing control.
The on / off control signal is output to each semiconductor laser of
They are supplied to each semiconductor laser through a laser control port (not shown).

In addition to the above-mentioned elements, this control device has a GP-IB interface 9 for communication with an external device,
A liquid crystal display 10 for displaying the operating state of the device, a power control SSR 11 for controlling an accident prevention circuit (not shown), a status control unit 21 for monitoring the condition of the device setting switch, the deflection actuator, or the recording medium conveying device, and A card transportation control unit 22 that controls transportation of the recording medium is provided.

The CPU 6 and the ROM 7 in which a predetermined program is stored constitute the gradation vector conversion means of the present invention, and the CPU 6, the ROM 7 in which the predetermined program is stored, the FIFOs 12, 15 and the D / A converter. 13, 16, amplifiers 14, 17, laser control unit 19,
Further, the delay circuit 20 constitutes the minute line segment drawing means of the present invention.

Next, the operation of the laser drawing apparatus having such a structure will be described. Below, first, as a basic operation,
The conventional drawing operation by vector scanning will be described, and then the drawing operation when performing gradation expression will be described in detail. When vector-format drawing data created by a host computer (not shown) is input via the GP-IB interface 9, the CPU 6 receives it and stores it in the RAM 8. This drawing data is basically the laser on / off for turning the laser light source on / off.
Command and laser off command, and X address data and Y address data for controlling the drawing position. More specifically, one set of drawing data corresponding to one line segment includes a laser off command, X address data and Y address data indicating the start point of the line segment, as shown in FIG. Data, laser on
Command, X address data and Y address data indicating the end point of the line segment, and laser off command, and these commands and data are R in this order.
Stored in AM.

When executing drawing, the CPU 6 is a RAM
The drawing data is sequentially read out from the CPU 8 and the address data is processed by the CPU 6 based on the conversion program stored in the ROM 7.
The FI is performed by converting the address data into digital X position signals and Y position signals which respectively represent the positions in the drawing area.
The data is stored in the FOs 12 and 15, respectively. On the other hand, the command is supplied to the laser control unit 19.

As a result, for example, one line segment is drawn as follows. First, the laser control unit 19 outputs a low-level on / off control signal to turn off all the semiconductor lasers of the laser block 1 based on the laser off command. This signal is supplied to each laser semiconductor through the delay circuit 20, and each semiconductor laser stops emitting light.

After that, the FIFOs 12 and 15 respectively
Digital X position signals and Y position signals representing the start points of the line segments are sequentially output to the D / A converters 13 and 16, and the D / A converters 13 and 16 convert each position signal into an analog position signal. Output to the amplifiers 14 and 17. The amplifiers 14 and 17 amplify these position signals to a predetermined level and supply them to the deflection actuators of the deflection mirrors 4 and 5. as a result,
The angles of the deflection mirrors 4 and 5 are determined by the X position signal and the Y
The angle changes according to the value of the position signal, and the position of the light spot formed on the recording medium when the laser beam 2 is incident moves to the position of the starting point of the line segment to be drawn.

Next, the laser control section 19 turns on the laser.
Since all the semiconductor lasers of the laser block 1 are turned on based on the command, a high-level on / off control signal is output while synchronizing with the position signals output from the FIFOs 12 and 15. This signal is supplied to each laser semiconductor by the delay circuit 20 after a predetermined on-delay time has elapsed, each semiconductor laser emits light, and the laser block 1 generates the laser beam 2. The emission of the semiconductor laser is delayed here because it takes a certain time for the deflection mirrors 4 and 5 to reach the designated angle. Due to the above delay, the laser beam 2 is incident on each mirror and is deflected when the angle of the deflecting mirrors 4 and 5 reaches the angle accurately specified by the position signal.

After that, each of the FIFOs 12 and 15 sequentially outputs the X position signal and the Y position signal indicating the position of the end point of the line segment to the D / A converters 13 and 16, and the D / A converters 13 and 16 are output.
Converts each position signal into an analog position signal and the amplifier 1
Output to 4 and 17. The amplifiers 14 and 17 amplify these position signals to a predetermined level and supply them to the deflection actuators of the deflection mirrors 4 and 5. As a result, the angle of each deflection mirror 4, 5 changes to an angle according to the value of each X position signal and each Y position signal, and the position of the light spot formed on the recording medium by the laser beam 2 is drawn. The line segment is moved to the end point of the line segment to be drawn, and the line segment is drawn on the recording medium.

The laser controller 19 then turns off the laser.
Since all the semiconductor lasers of the laser block 1 are turned off based on the command, the low level on / off control signal is output again while synchronizing with the position signals output from the FIFOs 12 and 15. This signal is supplied to each laser semiconductor after a predetermined off-delay time has elapsed by the delay circuit 20, and each semiconductor laser stops emitting light,
Drawing of one line segment by vector scanning is completed. Here, the reason why the emission stop of the semiconductor laser is delayed is to cope with the mechanical delay of the deflection mirrors 4 and 5 described above.

The above is the operation for drawing one line segment, but when drawing a polygonal line or a curve consisting of a plurality of line segments, the drawing data is as shown in FIG. A portion of the X and Y address data representing the end point of the line segment is replaced by a plurality of X and Y address data representing the end point of each continuous line segment. Therefore, in this case, after the drawing is started from the start point position of the line drawing, the light spot is sequentially moved to the end position of each line segment while each semiconductor laser is in the ON state, and the line drawing is drawn.

Next, the drawing operation for gradation expression will be described in detail. First, the format of drawing data will be described with reference to FIG. When performing gradation expression, drawing data for drawing one rectangular (including square) image includes pixel size data, the number of pixels in the X axis direction (the number of pixels in one line), and the pixels in the Y axis direction. It is composed of a number (the number of lines of one image), a gradation drawing start command, a drawing start X address, a drawing start Y address, a gradation data string, and a gradation drawing end command.

The pixel size data determines the pixel size, and thus the pixel density. The area of one image is determined by the number of pixels in the X axis direction and the number of pixels in the Y axis direction. The drawing position of the image on the recording medium is designated by the drawing start X address and the drawing start Y address. Specifically, these addresses represent the upper left position of the rectangular image on the recording medium. The gradation data string represents the gray level of each pixel. The gradation data are arranged in the order from left to right and from top to bottom of the image. Therefore, the first gradation data is for the pixel at the upper left corner of the image, and the final gradation data is for the pixel at the lower right corner of the image. In the gradation drawing start command and the gradation drawing end command, this drawing data is not the data for drawing by the normal vector scanning shown in FIGS. It indicates that the data is for.

It is also possible to use the drawing data in the format shown in FIG. 3A or 3B even when the gradation expression is performed. However, when performing gradation expression, since one minute line segment is drawn for each pixel,
In the format shown in FIG. 3A, the ASCI is set for each pixel.
When the I code requires 32 bytes of data, and the total number of pixels in one image is about several tens of kilodots to several hundreds of kilodots, the drawing data is enormous at 1 megabyte or more.

On the other hand, in the case of the format shown in FIG. 3C, for example, when each pixel is represented by 256 gradations,
If the data is described in binary format (binary number 00 to FF), it will be 3 bytes even if it is converted into ASCII code and the terminator is included per pixel. Therefore, the scale of the drawing data is reduced to 1/10 or less as compared with the format of FIG.

Drawing data for gradation expression created in the format of FIG. 3C is sent from the host computer to GP-I.
When input through the B interface 9, the CPU 6
Receives it and stores it in RAM 8. Since the input drawing data includes the gradation drawing start command and the gradation drawing end command, the CPU 6 recognizes that this drawing data is for drawing by performing gradation expression. Then, the CPU 6 operates based on a control program stored in the ROM 7, and in the gradation data string included in the drawing data, the pixel area at the upper left corner from the first gradation data (hereinafter, simply referred to as pixel The length of the minute line segment to be drawn inside is calculated. That is,
When the value of the gradation data is small, the length of the minute line segment is decreased in proportion to the value of the gradation data. Conversely, when the value of the gradation data is large, the length of the minute line segment is decreased. It is increased in proportion to the value of gradation data.

Next, the CPU 6 generates X address data representing the starting point of the minute line segment to be drawn in the pixel and Y address data, and further uses the length of the minute line segment already obtained, Y address data representing the end point is generated and is temporarily stored in the RAM 8 as drawing data of a minute line in the format shown in FIG. 3A together with the laser off command and the laser on command. The CPU6
When the address data of the starting point of the minute line segment is generated, the position of the starting point is determined so that the midpoint of the minute line segment coincides with the center of the pixel. Also, when deciding the starting point of a minute line segment,
It is necessary to know the position of the pixel, which is the pixel size data, X, included in the drawing data stored in the RAM 8.
It is calculated by the number of pixels in the axial direction, the number of pixels in the Y-axis direction, the drawing start X address, and the drawing start Y address.

The following operation is the same as the operation when drawing is performed by the raster scanning described above. That is, CPU
6 draws out the drawing data of the minute line segment from the RAM 8, and the CPU 6 stores the address data in the ROM 7
It operates based on the conversion program stored in the CPU, converts the X address data and the Y address data into digital X position signals and Y position signals, respectively, and then FI
Store in FO12,15. On the other hand, the command is supplied to the laser control unit 19.

As a result, the minute line segment is drawn in the pixel by vector scanning as described above. Since the drawing by the vector scanning of the line segment has already been described in detail, it is omitted here. The CPU 6 performs such an operation for all pixels in the order of the gradation data string. As a result, a minute line segment having a length corresponding to the value of the corresponding gradation data is drawn in each pixel. By the way, the light spot formed on the recording medium by the laser beam has a certain spread because the laser beam cannot be completely converged. Also,
The recording medium responds to the irradiation of the laser beam with a certain delay. For these reasons, when the length of a minute line segment is sufficiently short, the drawing result is not a line segment but a substantially circular dot. The diameter of the dot is almost proportional to the length of the minute line segment to be drawn.

Therefore, for example, as shown in FIGS. 4A to 4H, circular dots having different diameters are drawn in each pixel 50 according to the value of the gradation data. It should be noted that in the figure, the values of the gradation data are large in the order of (A) to (H), and therefore the gray level is high. An image having gradation is formed on the recording medium by the dots of various sizes. That is, it is possible to realize gradation expression of an image by a laser drawing device that performs vector scanning.

FIGS. 5A to 5C are graphs showing gradation expression characteristics of the laser drawing apparatus of this embodiment. These graphs draw dots using coloring materials,
Area ratios, average densities, and maximum densities of dots for various gray levels are measured and plotted. The vertical axis represents the area ratio, average density, and maximum dot density, and the horizontal axis represents grayness.

The area ratio ((A) of FIG. 5) is low in a region having a low gray level, and the increase rate increases as the gray level increases.
When the gray level approaches the maximum value, it tends to be saturated. This corresponds to the dots becoming thicker from around the intermediate gray level, and the cause is that the drawing area increases due to the thermal history of the dots drawn in adjacent pixels compared to the case of a single dot. is there.

Maximum density of recording dots ((C) of FIG. 5)
Shows a steep rise in the low gray range and a saturation tendency in the middle range. Average density ((B) in Figure 5)
Is a macroscopic density over the entire drawing area including the density of the undrawn area, reflecting both the area ratio characteristics and the maximum density characteristics of dots. The tonality characteristic shows that the area ratio characteristic and the maximum density characteristic of the dots complement each other to show an excellent linear characteristic.

In the above embodiment, the midpoint of the minute line segment drawn in each pixel is made to coincide with the center of the pixel. However, taking advantage of vector scanning, the inside of the pixel of the minute line segment is utilized. The drawing position can be changed randomly for each pixel. In such a case, the positions of the dots in the pixels change for each pixel, and the matrix dot array, that is, the mesh dot array can be made inconspicuous. Specifically, when the CPU 6 determines the address of the starting point of each minute line segment, a random number may be generated to randomly change the address of the starting point within a certain range.

Further, instead of randomly changing the starting point position, the mesh dot array can be made inconspicuous more easily as follows. That is, when the CPU 6 determines the position of the starting point of the minute line segment in each pixel, the position must be aligned with one side of the pixel, for example, the left end. Figure 6
(A) to (H) show the dots drawn in the pixels with different gray levels when the minute line segment is drawn in this way. (A) is the case where the grayness is the lowest, and (H) is the case where it is the highest.

When an image is expressed in gradation by this method and, for example, a pixel having a high gray level and a pixel having a low gray level are adjacent to each other, the distance between the centers of the dots increases as the difference in gray level increases. Become. If the dots of (A) and the dots of (H) in FIG. 6 are adjacent to each other, the distance between the centers of the dots is greatly separated by about 1.5 pixels, and therefore, the light area and the dark area of the image are large. The difference between and will be expressed more clearly. Therefore, the contour of the image is emphasized, and the image can be clearly expressed. The same effect can be obtained not only by matching the start point of the minute line segment with the side of the pixel but also by matching the end point of the minute line segment with the side of the pixel.

The drawing of the minute line segment expressing each gray level will be described in more detail. FIG. 7 is a timing chart showing the relationship between the length of a minute line segment to be drawn and the on-time of the semiconductor laser. In the figure, the horizontal axis represents time, the vertical axis of the uppermost graph represents the position of the light spot, and the other axes represent the level of the on / off control signal.

The gray levels 1 to 8 correspond to the gray levels represented by the dots in FIGS. 4 or 6 (A) to (H), respectively. For easy understanding, the positions of the starting points of the minute line segments are all the same, and the delay of the on / off control signal is ignored. The time T0 corresponds to the starting point of the minute line segment, and the position of the light spot to be formed on the recording medium coincides with the starting point position P0 at this time. When scanning is started by the operation of the actuator, the on / off control signal simultaneously becomes high level, each semiconductor laser is turned on, the laser beam 2 is generated, and the irradiation of the laser beam to the recording medium is started.

The distance traveled by the light spot by scanning depends on the gray level, and in the case of the lowest gray level 1, when the position P1 is reached, the operation of the deflector is stopped,
The light spot stops moving. At that time, time T
At 1, the on / off control signal becomes low level, and the laser light irradiation is also stopped. As a result, the smallest dot as shown in FIG. 4 or 6A is drawn.
Further, when the gray level is 2, the scanning is stopped when the position P2 is reached, and at that time (T2), the on / off control signal becomes low level and the irradiation of the laser beam is also stopped. Further, when the gray level is 8, the light spot is up to the position P8,
Therefore, it moves by a distance equal to the width of the pixel,
~ T8) The laser beam is irradiated to draw the largest dot as shown in FIG. 4 or 6H.

In this embodiment, the start timing of the deflecting mirrors 4 and 5 basically coincides with the laser-on timing, and the stop timing of the deflecting mirrors 4 and 5 basically coincides with the laser-off timing. Therefore, the semiconductor laser is turned on and laser irradiation is performed while the light spot is moving. Therefore, the moving distance of the light spot,
That is, the length of the minute line segment and the irradiation time of the laser light are in a proportional relationship.

Further, in this embodiment, the ratio of each gray level is set to be an integer. For example, if the length of a minute line segment expressing the gray level n (n is a positive integer) is 1, the gray level 1
Is 1 / n, the length of the minute line segment of gray level 2 is 2 / n, and the length of the minute line segment of gray level n-1 is (n-1) / n. Become.

Incidentally, the irradiation timing of the laser light is actually for correcting the operation delay of the deflecting mirror and its actuator as described above. The timing chart of FIG. 8 is a diagram for explaining this correction. The upper part of this timing chart shows the position signal SP supplied to the deflection actuator of the deflection mirror 4 or 5 and the angle change PD of the deflection mirror 4 or 5, and the vertical axis shows the voltage and the angle. The lower three stages each show an on / off control signal, and the vertical axis shows the level.

At time T0, the position signal is supplied to the actuator, and its value increases with time. When such a position signal is supplied to the actuator, the deflection mirrors 4 and 5 start operating after the delay time TD has elapsed due to the operation delay, and after the change of the position signal stops, the delay time TD decreases. Stops operation after a certain period of time. Therefore,
In order to draw a minute line segment correctly, the on / off control signal S1 is supplied to the semiconductor laser, and the time T is not the time T0 when the position signal is input but the time T when the time TD has elapsed.
In No. 1, it is necessary to start the irradiation of laser light. Further, it is necessary to stop the laser light irradiation not at the time T2 when the change of the position signal ends but at the time T3 when the operation of the deflection mirrors 4 and 5 ends.

Further, by utilizing such a correction function, it is possible to shift the control signal like the on / off control signal S2 to intentionally delay the irradiation timing of the laser light. For example, the control signal When the laser light irradiation period is set to be longer than the operation period of the deflection mirrors 4 and 5 as in S3,
Since the density increases even if the length of the minute line segment remains the same, it is possible not only to change the length of the minute line segment to change the gray level, but also to change the gray level depending on the irradiation time to increase the number of gradations. it can.

Further, by adjusting and fixing the delay time TD when the laser is turned on and the delay time TD when the laser is turned off to different values, the density of the entire image can be adjusted, and the sensitivity fluctuation of the recording medium can be adjusted. It is effective for correction of.

[0060]

As described above, in the laser drawing apparatus of the present invention, the gradation vector conversion means uses the gradation data representing the gray level of each matrix-shaped pixel forming an image, and the gradation vector conversion means minutely calculates each pixel. Determine the length of the line segment. Then, the minute line segment drawing means draws the minute line segment having the length determined by the gradation vector conversion means in each pixel area on the recording medium by controlling the optical deflector.

The light spot formed on the recording medium by the laser beam has a certain spread because the laser beam cannot be completely converged. Further, the recording medium responds to the irradiation of the laser beam with a certain delay. For these reasons, when the length of the minute line segment is sufficiently short, the drawing result is not a line segment but a substantially circular dot. The diameter of the dot is almost proportional to the length of the minute line segment to be drawn.

Therefore, by drawing the minute line segment as described above, a dot having a size corresponding to the gradation data is drawn in each pixel area, and the gradation is expressed by the size of the dot. It becomes possible. That is, it is possible to realize gradation expression of an image by a laser drawing device that performs vector scanning.

[Brief description of drawings]

FIG. 1 is a block diagram showing a control device constituting a laser drawing apparatus according to the present invention.

FIG. 2 is a schematic plan view showing an example of a laser drawing apparatus according to the present invention including the control device of FIG.

FIG. 3 is an explanatory diagram showing a format of drawing data used in the laser drawing apparatus of FIG.

4 is an explanatory diagram showing the relationship between the gray level expressed by the laser drawing apparatus of FIG. 1 and the size of dots drawn in each pixel.

FIG. 5 is a graph showing the results obtained by measuring the relationship between the gray level when an image having gradation is drawn by the laser drawing apparatus of FIG. 1, and the area ratio, average density, and maximum dot density, respectively. Is.

6 is an explanatory diagram showing the relationship between the gray level expressed by the laser drawing apparatus in FIG. 1 and the positions of dots drawn in each pixel.

FIG. 7 is a timing chart showing the relationship between the movement of a light spot on a recording medium and a laser on / off control signal.

FIG. 8 is a timing chart showing the relationship between the position signal supplied to the deflection actuator, the movement of the deflection mirror, and the laser on / off control signal.

FIG. 9 is a timing chart for explaining gradation expression in a conventional laser drawing apparatus.

[Explanation of symbols]

 1 Laser Block 2 Laser Beam 3 Mirror 4, 5 Deflection Mirror 6 CPU 7 ROM 8 RAM 9 GP-IB Interface 10 Liquid Crystal Display 12 X Axis FIFO Buffer Memory 13 X Axis D / A Converter 14 X Axis Amplifier 15 Y Axis FIFO buffer memory 16 Y-axis D / A converter 17 Y-axis amplifier 18 Offset control unit 19 Laser control unit 20 Delay circuit 21 Status control unit 22 Card transport control unit 25 Laser drawing device 50 pixels

Claims (7)

[Claims] 1. A laser drawing apparatus for two-dimensionally deflecting a laser beam generated by a laser light source by an optical deflector to draw a line segment on a recording medium to form an image. A gradation vector conversion unit that determines the length of a minute line segment for each pixel based on gradation data that represents the gray level of each pixel, and a minute line segment of the length determined by this gradation vector conversion unit. A minute line segment drawing means for controlling the optical deflector to draw in each pixel area on the recording medium. 2. The laser drawing apparatus according to claim 1, wherein the minute line segment drawing means draws the minute line segment such that a midpoint of the minute line segment coincides with a center of the pixel region. 3. The laser drawing apparatus according to claim 1, wherein the minute line segment drawing means randomly sets the position of the minute line segment in the pixel area for each pixel area. 4. The minute line segment drawing means sets the starting point of the minute line segment to a predetermined position in the pixel region,
The laser drawing apparatus according to claim 1, wherein the minute line segment is drawn. 5. The minute line segment drawing means sets an end point of the minute line segment at a predetermined position in the pixel region,
The laser drawing apparatus according to claim 1, wherein the minute line segment is drawn. 6. When the laser deflector deflects the laser beam to draw the minute line segment, when the optical deflector is instructed to start moving the laser beam and a designated time elapses. The minute line segment drawing means includes a laser light source control means for turning on the laser light source, turning off the laser light source when a specified time elapses when the optical deflector is instructed to end the movement of the laser beam. The laser drawing apparatus according to any one of claims 1, 2, 3, 4, and 5. 7. Drawing data including a pixel size, the total number of pixels in the X direction, the total number of pixels in the Y direction, and gradation data is input, and the gradation vector conversion means includes the floor among the drawing data. The length of the minute line segment is determined using key data, and the minute line segment drawing means uses the pixel size, the total number of pixels in the X direction, and the total number of pixels in the Y direction of the drawing data. The minute line segment is drawn.
4. The laser drawing apparatus according to any one of 4, 5, and 6.