JPS61269563A - Device for correcting feeding pitch error - Google Patents

Abstract

PURPOSE:To correct uneven recording by applying main scanning and sub scanning while applying flicker exposure control to spots arranged in sub scanning direction independently so as to detect a feeding pitch error in the sub scanning direction of the spots thereby controlling the diameter of each spot based on the detected value. CONSTITUTION:A rotary drum 1 is driven by a main scanning motor 2 and an exposure head 3 is fed in the sub scanning direction by a feeding mechanism comprising a sub scanning motor 4 and a feeding screw 5. An output pulse of a rotary encoder 7 fitted to the drum 1 forms a sub scanning position command pulse (a), the pulse (a) and a real position feedback pulse (b) from a linear scale 10 are compared to drive the motor 4. An acoustooptic modulator (AOM) driver 12 receives an error signal (c) from a driver 11 and an on/off dot signal (d) from a computer 13 to control the AOM in the head 3 so as to change the diameter of a beam spot at each channel. Thus, the recording uneveness on a photosensitive member produced due to a feeding pitch error in the sub scanning direction is corrected.

Description

Detailed Description of the Invention (Industrial Application Field) The present invention relates to a device, such as a raster plotter, which records an image on a photosensitive material by performing main and sub-scanning while controlling blinking exposure of a light spot. In particular, the present invention relates to an apparatus for correcting recording unevenness on a photosensitive material caused by a feed pitch error in the sub-scanning direction of such an apparatus.

(Prior art and its problems) In order to record images with high precision in raster printing, each micropixel divided into equal bits in the main and sub-scanning directions must be detected by a light beam spot. It is necessary to perform blinking exposure without pitch unevenness, and for this reason, various methods have been proposed to improve the pitch precision in the main scanning direction and the sub-scanning direction. For example, as a method of changing the pitch stacking in the sub-scanning direction, exposure-U and a method of reducing the absolute feed error have been commonly used. However, there is naturally a limit to the improvement in viscosity and performance of such a feed mechanism. Furthermore, although it has been conventionally practiced to detect the feed pitch and control the servo system, tracking errors occur due to delays in the mechanical system.

For these reasons, slight "unevenness" may occur in the feed pitch in the sub-scanning direction. Otherwise, the beam spot in the main scanning direction of the recorded image will meander.As a result, the width of the recorded image line will not be constant.

In particular, in the multi-beam simultaneous exposure method, it is necessary to expose a minute spot by dividing the sub-scan feed pitch of one main scan by the number of 11 beams, and in many cases, a highly detailed image is required. The burnout pitch error due to the sub-scanning feed pitch error is much more significant than in other cases. Also, when recording the exposure of the front side of a PWB (printed wiring board) on film, it is necessary to avoid uneven spots. If the recorded line width does not reach the intended thickness, many PWBs will be found to be defective during inspection after manufacturing. In order to reduce defects, it is desirable that the recorded line width be as thick as intended.

(Objective of the Invention) Therefore, the object of the present invention is to solve the problems of the prior art described above, and to create a system of such a size that no gap is created between the beams when a feed pitch error occurs in the sub-scanning direction. To provide a feed pitch error correction device which selects beam spots 1, aligns the beam spots substantially in a straight line, and provides a required line width.

(Means for Achieving the Object) In order to achieve the above object, the feed pitch error correction device according to the present invention includes means for detecting the feed pitch error in the sub-scanning direction of the light spot, and a means for detecting the feed pitch error in the sub-scanning direction of the light spot. The device is configured to include a means for controlling the diameter of the light spot, and the gap between the light spots caused by the feed pitch error is eliminated by making the beam larger, thereby correcting recording unevenness on the sensitive material. That's what I do.

(Embodiment) FIG. 1 is a block diagram showing an embodiment of a feed pitch error correction device according to the present invention. This feed pitch error correction device is applied to, for example, a rotating drum type raster plotter not shown in FIG.

In FIG. 2, a rotating drum 1 is rotationally driven by a main scanning motor 2, and an exposure head 3 is sent in the sub-scanning direction by a feeding mechanism consisting of a layer 4 and a feed screw 5. In this case, if a synchronous motor is used as the main scanning motor 2, the number of rotations of the drum 10 will vary in proportion to the frequency variation of the power supply, so if the sub-scanning motor 4 is rotated at a constant speed, the film 6F will be printed with f41J. The image is expanded or contracted in the sub-scanning direction, and an absolute \1 error occurs. Therefore, the output pulse of the rotary cylinder 7 attached to the rotating drum 1 is passed through the PlU circuit 8 and the frequency divider 9 to create the sub-scanning position command pulse a.
In comparing this sub-scanning position command pulse a with the actual position feedback pulse b indicating the actual sub-scanning position from the linear scale 10, the sub-scanning motor 4 is driven by the motor driver 11, and the rotational speed in the main scanning direction is The feed speed in the sub-scanning direction is synchronized. The exposure head 3 is, for example, a 10-channel multi-beam type head, and responds to drive signals from the AOM driver 12 to zero out dots for 10 channels arranged in the sub-scanning direction.
In addition to controlling the N10FF, it is configured to enable power control for each channel. The AOM driver 12 is
In response to an error signal C (described later) from the motor driver 11 and an 0N10FF dot signal d from the computer 13 that performs image processing, an 80M (acousto-optic modulator) (not shown) in the exposure head 3 is controlled. Create a signal for

In FIG. 1, the first counter 14 multiplies the position command pulse a from the frequency divider 9 in FIG. Accumulate.

Deception logic -] The unit (ALU) 16 is the first and second
After receiving the contents of the link 14.15, the first counter 1
The number of tuna counted on the second counter 15 is reduced from the first counter of 4, and the bundle is sent to the D/Am converter 17.

D/A:] The output value of the converter 17 represents the error of the actual sub-scanning position with respect to the sub-scanning position command, and this error signal C and the rotational speed of the sub-scanning motor 4 are detected. 18 is input to a differential amplifier 19, and the rotation speed of the sub-scanning motor 4 is controlled by its output. By forming a velocity loop like this,
-, the sub-scanning motor 4 rotates so that the error is zero.

Immediately, the output value of the D/A converter 17 is a constant value, but in reality, there are screw pitch errors and feed load fluctuations, so the output value of the D/A converter 17 is Le A voltage containing slight fluctuations corresponding to bits 1 to 1 is generated. This voltage fluctuation width can be suppressed to a certain extent by increasing the gain of the speed loop and the gain of the position loop (the loop including the linear scale 10 and ALU 16) by t-J within the stability region of the system. , it is impossible to say anything. Therefore, if this continues, the beam interval will not be constant, and the width of the image line of the recorded image, especially the image line parallel or nearly parallel to the main scanning direction, will become uneven.

Therefore, the output signal of the D/A converter 17 (error signal C
), each 1ch from the computer 13 in FIG.
The following correction is performed on the 0N10FF dot signal d of ~10ch. That is, the 0N10FF dot signal d of the odd channel. For DO, the product of the error signal C and the inverted signal C is obtained by the multiplier 20, and the multiplication output is input to each odd channel AOM driver 21. In addition, even-numbered channel 0N10FF dot i・
For the signal dEVEN, the non-inverted signal C of the error signal C
' is calculated by the multiplier 22, and the multiplication output is input to each even channel AOM driver 23. Each AOM driver 21, 23 creates a signal for driving 80M (not shown) in the exposure head 3 of FIG. 2 in response to an input signal. In response to this drive offset, the power of each channel's output beam is controlled to be strong or weak, and the diameter of the beam spot (light spot) changes for each channel accordingly.

In FIG. 1, the odd channel line 24 and the even channel line 25 are shown comprehensively, and the odd channel line 24 (actually G, Llc
There are 5 channels: h, 3ch, 5ch, 7ch, and 9ch, and the even channel line 22 is actually 2ch, 4ch.
There are five channels: -ch, 6ch, 8ch, and 10ch.

FIG. 3 is an explanatory diagram showing how the beam spot diameter changes with respect to the output value of the D/A converter 17, which is calculated by 1q during the above-described correction. For odd channels, D/
As the output value of the Aml inverter 17 increases, the beam diameter decreases, and in even channels, the D/A
The beam spot diameter increases as the output value of the converter 17 increases. At the intersection of both straight lines, the positional error is U-shaped, and the beam spots are large enough to overlap sufficiently.

FIG. 4 shows how images are connected in the sub-scanning direction when such correction is performed. Figure 4 shows ICh~10c
This shows the trajectory of the beam from n-1 rotation to n+1 rotation when all 0N10FF dot signals up to h are turned on, and it oscillates slightly around the correct trace trajectory l (that is, it contains errors). While being scanned on the actual trace locus l', each beam sbot t-S is
The diameter is continuously changed according to the relationship shown in FIG. It will be easily understood that the beam spots are aligned substantially linearly in the main scanning direction without any gaps at the joints between the respective scans (dotted line portions in the figure). In addition, since the relationship of increase/decrease in spot diameter with respect to error is reversed between odd and even channels, 1ch~
Even between the 10 channels, there is no gap between the beer channels. An example of how the dot diameter changes in the image obtained in this manner is shown in FIG. Figure 5 (a
) and (b) exaggerate the changes in the beam power of even and odd channels, respectively, and the changes in the image output of the film at that time.

FIG. 6 is a timing chart showing signals of each part in FIG. 1. The output signal (error signal) of the D/A converter 17 shown in (C) is obtained by the sub-scanning position command pulse (a) and the actual position feedback pulse (b). For example, if the 0N10FF dot signal of the even channel is as shown in (d) and the 0N10FF dot signal of the odd channel is as shown in (f), the signal input to the even channel AOM driver 23 is (e ), and the signal input to the odd channel AOM driver 21 is corrected as (0). When the number of beam spots is odd, one of the odd beam spots is controlled in the same way as for the even spots. As a result, the beam spots at both ends are controlled in an inverse relationship.

Incidentally, in the embodiment shown in FIG. 2 described above, all channels were corrected, but if the line width of each scanning line and the line width calculated by the computer are in an integer relationship, the correction shown in FIG. As shown, by only correcting lch and l0ch (beam spots at both ends), no gap is created between the beams, and a straight line in the main scanning direction is retained. In such a case, for channels 2 to 9, the multiplier 26 multiplies each 0N10FF dot signal by a fixed value to keep the beam power constant.

FIG. 8 is an explanatory diagram showing the change in the beam spot diameter with respect to the output value of the D/A converter 17 when such control is performed.
The trajectory of the beam up to the +i rotation is as shown in FIG. Unlike FIG. 4, the beam spot diameters of channels 2 to 9 do not change, but the positional errors are not that large, so gaps between channels 1 and 2 and between channels 9 and 10 can be prevented from occurring. Furthermore, at the joints between the scans (the dotted line portions in the figure), the beam spots are neatly aligned as in FIG. 4.

FIG. 10 shows an example of a change in the dot diameter of an image obtained in this way, (a) and (b).

(C) is 10ch, lch, 2ch to 9ch respectively
It shows the change in beam power and the change in the image output of Noilm at that time. In 2Ch-9Ch, the diameter of the driver 1 of the output image remains unchanged. In addition, FIG. 11 is a timing chart 1 showing the signals of each part of the 7th part.
− is. Unlike the case in Figure 6, 0 of 2Ch to 9Ch
The N10FF dot signal (h) is only multiplied by a constant value in the multiplier 26 (that is, it is corrected), and the
Each AOM driver 270 input signal from Ch to 9Ch (i)
given as.

Although the case where the sub-scanning feed is continuous has been described in detail using the embodiment, it goes without saying that the present invention can also be applied to the case where the sub-scanning feed is carried out in steps for each scanning line.

(Effects of the Invention) As explained above, according to the present invention, the feed pitch error of the light spot in the sub-scanning direction is detected and the diameter of the light spot is controlled based on the error. Even when there is unevenness in the feed pitch in the scanning direction, the beam spots are aligned substantially linearly in the main scanning direction without gaps between the beams, and the image line width is constant. Furthermore, in manufacturing the PWB, by controlling the line width within a certain value, the manufacturing accuracy of the PWB is improved, and the accuracy in comparative defect inspection is improved.

[Brief explanation of drawings]

1 and 7 are block diagrams showing one embodiment of the present invention, FIG. 2 is a mechanical schematic diagram of a rotating drum type raster plotter to which this invention is applied, and FIGS. 3 and 8 are block diagrams showing one embodiment of the present invention. An explanatory diagram showing changes in beam spot diameter,
FIGS. 4 and 9 are explanatory diagrams showing how lines are connected in the sub-scanning direction in each embodiment, FIGS. 5 and 10 are explanatory diagrams that do not show the film image output of each channel, and FIGS. FIG. 11 is a timing chart 1- showing the signals of the respective parts of FIG. 1 and FIG. 7, respectively. 4... Sub-scanning motor 10... Linear scale 14.15... Counter 16... Arithmetic logic unit (ALU) 17... D/
A converter 20.22, 26.29... Multiplier 12.21.23.27.30... AOM driver

Claims (4)

[Claims] (1) In an apparatus that records a desired image on a photosensitive material by performing main scanning and sub-scanning while independently blinking exposure control of at least one light spot arranged in the sub-scanning direction, A means for detecting a feed pitch error in the scanning direction and a means for controlling the diameter of a light spot based on the detected feed pitch error are provided to correct recording unevenness on the sensitive material due to the feed pitch error. Features: Feed pitch error correction device. (2) The feed pitch error correction device according to claim 1, wherein the relationship between the increase and decrease in the diameter of the light spot with respect to the change in the value of the feed pitch error is controlled in an opposite relationship for the light spots at both ends. (3) The feed pitch error correction device according to claim 1 or 2, wherein there is a plurality of light spots, and the diameter of all the light spots is controlled. (4) The feed according to claim 3, wherein the relationship between the increase and decrease in the diameter of the light spot with respect to the change in the value of the feed pitch error is reversed between odd-numbered light spots and even-numbered light spots. Pitch error correction device.