JPH0335579A - Maintenance of gas laser beam in highest output - Google Patents

Abstract

PURPOSE:To adjust a mirror automatically each time preceding the drawing of an image by receiving a spectral beam with a photodetector and detecting the intensity of the beam as a digital electric signal, and stopping a motor at the rotational position where the digital electric signal has a maximum value each time the motor is driven successively. CONSTITUTION:A beam B3, which is separated to the intensity of 2-1% of the beam B1 transmitting a half mirror 18, is received with a photodetector 19 and is detected as an analog electric signal. A control part 21 makes two step motors 16a and 16b of an argon ion laser AR perform specified positive and reverse rotations through a motor driver 22 so as to adjust the quantities of screw-in of threaded shafts 15a and 15c for mirror adjustment thereby setting up or setting down a cathode mirror 3a minimum angle regarding the horizontal axis or the vertical axis which crosses the tubular axis of a plasma tube 1. In this process, for digital electric signals which are obtained by use of the photodetector 19 and an A/D convertor 20, the magnitudes of fellow signals going ahead and behind are compared in turn according to the program stored in a ROM, whereby the step motors 16a and 16b are successively controlled to be adjusted to the step positions where the maximum value can be obtained.

Description

[Detailed description of the invention]

[Industrial Field of Application] The present invention relates to a method of maintaining the beam of a gas laser such as an argon ion gas laser at the maximum output power used for drawing ultra-high-definition images on gravure plates and the like. [Prior art] A device that uses gas lasers to write ultra-high-definition images on gravure plates, etc. uses a beam splitter to arrange about 20 wooden laser beams with equal intensity in a single line. The beam is divided into two beams, and each beam is passed through an independently driven multi-type optical modulator and an autofocus lens according to the image data, so that it can be irradiated onto the subject (photosensitive drum or silver halide film wrapped around the drum). The configuration is such that laser exposure is performed while scanning. A gas laser includes a plasma tube, an anode-side mirror provided perpendicularly to the tube axis of the plasma tube outside the Brewster window on the anode side of the plasma tube, and a Brewster window on the cathode side of the plasma tube. A cathode side mirror (rear mirror in the present invention) is provided perpendicularly to the tube axis of the plasma tube outside the star window in the tube axis direction. The semi-fixed mirror mount is supported by a plate so that the posture of the two mirrors can be adjusted, so that the two mirrors can each reciprocate by a slight angle with respect to two mutually orthogonal wheels passing through a plane perpendicular to the tube axis of the plasma tube. There is. Each mirror mounting plate has two on both sides of the bottom and three on one side of the top, corresponding to the arrangement of the three vertices of an isosceles right triangle with the tube axis of the plasma tube as the base. It is semi-fixed with screws, and by adjusting the screwing of the two screws at the two vertices at both ends of the base of the triangle, the position and inclination of the mirror in the tube axis direction of the plasma tube can be precisely adjusted. If this adjustment is made appropriately, the gas laser beam can be maintained at its maximum output. Although this adjustment is performed at the time of product shipment, the user can adjust the screws through the small holes in the casing. [Problems to be Solved by the Invention] The present inventor has developed a laser exposure device (experimental device) that uses an argon ion gas laser to draw ultra-high-definition images on gravure plates, etc., and has conducted experiments over a long period of time. When I went there, I found that I was able to reliably draw ultra-high-definition images such as gravure plates in the morning, but not in the evening, or that I could do it with a small number of people, but I couldn't do it with a large number of people. We investigated the cause and found that it was due to a synergistic effect between the slight change in the output of the gas laser due to changes in room temperature and the low sensitivity of the photoresist film, and the fact that the mirror was slightly distorted due to the vibration of the subject. It turned out to be off. To explain in detail, the distance between the mirrors on both sides of the plasma tube in the tube axis direction and the attitude with respect to the tube axis are slightly shifted due to thermal expansion of the mirror support member, causing a slight change in the output of the gas laser. It does not use a high-sensitivity subject exposure method that wraps silver halide film around a drum.
This is because a direct plate-making method is adopted, in which a precision-polished copper plate roll is coated with a low-sensitivity photosensitive film (alkali-soluble or solvent-soluble sensitizer). This is because there is a synergistic effect in that the size of the beam spot that can be exposed becomes significantly smaller. To explain in detail about (2), even if the device stand is installed to isolate it from external vibrations, vibrations accompanying the rotation of the subject cannot be avoided, and the vibrations cause subtle shifts in the mirror. Therefore, each time when drawing an image using the above laser exposure device, the intensity of the laser beam is measured using a light intensity measuring device, and the screw is inserted through the small hole in the laser casing. It is necessary to properly adjust the position and tilt of both or one of the mirrors in the plasma tube axis direction to maintain the gas laser beam at its maximum output, which makes it difficult to put the laser exposure system into practical use. Can not. The present invention has been devised in view of the above-mentioned points, and provides a method for maintaining a gas laser beam at maximum output by automatically adjusting the mirror instead of manually each time prior to drawing an image. The purpose is to [Means for Solving the Problems] A method for maintaining the beam of the gas laser of the present invention at maximum output. The posture of the mirror mounting plate that supports the rear mirror of the gas laser is adjusted so that the rear mirror of the gas laser can be rotated back and forth by a slight angle about two mutually orthogonal axes passing through a plane perpendicular to the tube axis of the plasma tube. Two of the three screw shafts are sequentially driven by separate motors, and the beam output from the gas laser is split into tiny beams of intensity, and the split beams are received by a light-receiving element. The beam intensity is detected as a digital electric signal, and each time the motor is sequentially driven, the motor is stopped at a rotational position where the digital electric signal has a maximum value.

[Operation] When the gas laser is turned on, a beam of minute intensity is separated from the beam output from the gas laser and is received by a light receiving element.The intensity of the beam is detected as a digital electric signal and enters the control section. One of the two motors returns the corresponding screw shaft to its home position and then rotates forward and backward by a minute predetermined angle.The sequence of digital electrical signals obtained at this time is The control unit compares the magnitude of two digital electrical signals that are inputted one after the other, one after another.
The maximum value is detected, and the one motor is positioned and stopped so that the maximum value is obtained. Similarly, the other screw shaft is rotated forward and backward by a predetermined angle by the other motor, the maximum value of the digital electric signal obtained at that time is detected, and the rotation is performed so that the maximum value is obtained. The other motor is positioned and stopped. Therefore, the rear mirror of the gas laser is sequentially rotated back and forth by a minute angle with respect to two mutually orthogonal axes passing through a plane perpendicular to the tube axis of the plasma tube, and then
The two wheels are maintained in an appropriate reflective position so that the beam output is maximized. This way, no matter what the room temperature is. Since the beam output is automatically adjusted to the maximum each time, the size of the beam spot that can be effectively exposed when drawing ultra-high-definition images on gravure plates coated with low-sensitivity photosensitive films is adjusted automatically. It will always remain constant,
Cells of various sizes formed by a collection of beams are reliably exposed, and ultra-high-definition drawing such as excellent gravure images can be achieved. [Example: Figures 1 to 4] The method of maintaining the gas laser beam of the present invention at the maximum output will be explained using an example in which the method is applied to an argon ion laser output control device. First, the configuration of the argon ion laser will be explained. The argon ion laser AR includes a plasma tube 1, an anode-side mirror 2 provided perpendicularly to the tube axis of the plasma tube 1 outside the Brewster window 1a on the anode side of the plasma tube 1 in the tube axis direction, and A cathode side mirror 3 (rear mirror in the present invention) is provided perpendicularly to the tube axis of the plasma tube l outside the Brewster window 1b on the cathode side of the plasma tube l in the tube axis direction. . The plasma tube 1 is supported by plasma tube support brackets 4 at two places on each side. The plasma tube l and each mirror 2
．． 3, there are a pair of mirror mounting boards 6a and 6b.
is located. The pair of mirrors are mounted on a substrate 6a,
6b is integrally connected by three tie rods 5 having an extremely small coefficient of thermal expansion that extend through and fix the plasma tube support bracket 4, and has a hole through which the beam passes. The three tie rods 5 are provided two on both sides of the lower part and one on one side of the upper part so as to correspond to the arrangement of the three vertices of an isosceles right triangle whose tube axis is the base of the plasma tube l. . For mounting the mirror, the substrate 6a has a small hole 7a in the center on the outside in the tube axis direction, and the anode side mirror 2 is placed in and supported by the small hole 7a. be. The anode side mirror mounting plate 7 is connected and supported to the mirror mounting board 6a by plate springs 8 at three locations near the tie rod 5. Similarly, on the outside of the mirror mounting board 6b in the tube axis direction, there is a cathode mirror mounting plate 10 centered on which the cathode mirror 3 is supported. The cathode side mirror mounting plate 1O is also connected and supported by plate springs 9 at three locations near the tie rod 5 to the plate 6b, which is the mirror mounting base. Furthermore, the anode side mirror is mounted on the outside of the plate 7 in the tube axis direction.
A bracket 11 is provided for mounting the mirror adjustment bolt having a small hole 11a through which the beam passing through the anode side mirror 2 passes, and a bracket 11 for mounting the mirror adjustment bolt on the cathode side is provided on the outside in the tube axis direction of the plate 10. bracket 1
2 and a platen 13 for mounting the motor are installed upright. The mirror adjustment bolts on the anode side are screwed into the screw holes provided on the platen 11 and the mirrors on the anode side are screwed into screw holes provided at positions corresponding to the extension lines of the three tie rods 5 on the plate 7. There are three mirror semi-fixing screws 14a, 14b, and 14c that extend against the mirror substrate 6a to adjust the position and inclination of the anode side mirror 2.
Bracket 1 is used to install the mirror adjustment bolt on the cathode side.
2 and the cathode side mirror 3 are screwed into screw holes provided on the plate 10 at positions corresponding to the extension lines of the three tie rods 5, and the mirror mount is extended against the base plate 6b to attach the cathode side mirror 3. There are three mirror adjustment screw shafts 15a, 15b, and 15c for adjusting the position and inclination of the mirror. Therefore, the mirror adjustment bolt mounting brackets 11 and 12 are positioned and supported so that the mirror semi-fixing screws 14a, 14b, 14c or the mirror adjustment screw shafts 15a, 15b, 15c do not cause slight movement other than screw movement. ing. The mirror semi-fixing screw 14b is a special screw installed in a hole drilled in the mirror mounting board 6a. 23, and a mirror adjustment screw shaft 15.
The mirror holder 6b is also screwed into a special nut 24 installed in a hole drilled in the base plate 6b. The special nuts 23 and 24 are screwed into a sleeve that has threads on its inner and outer surfaces and is passed through a hole drilled in the board, a pair of hemispherical rubber washers that are passed through the sleeve and sandwich the board, and are screwed onto the sleeve. and a nut that clamps and clamps the board together with the flange of the sleeve, and is therefore flexibly attached to the hole drilled in the board. Further, the motor mounting bracket 13
The step motors 16, a, 16b attached to the
The three mirror adjustment screws @h15a, 15b, and 15c which respectively adjust the position and inclination of the cathode side mirror 3 are spline-coupled with the three mirror rA adjustment screw shafts 15a and 15c for rotation. ing. In addition, the code|symbol 17 is a casing. This concludes the explanation of the argon ion laser-AR, and the constituent parts for maintaining the gas laser beam at the maximum output will be explained below. Beam B1 output from argon ion laser-AR
is, for example, a practical beam B2 that is reflected by a half mirror 18 with a reflectance of 98 to 99% so as to change its direction at right angles, is guided to an optical system (not shown), and is used for drawing images in a laser printer or a color scanner, etc.; The beam B3 is separated into beams B3 having an intensity of 2 to 1% of the beam B1 passing through the half mirror 18. The beam B3 is used for beam intensity detection in order to control the beam Bl output from the argon ion laser-AR to a maximum value. The beam B3 is a photodiode or COD
The light is received by a light receiving element 19 such as the like and detected as an analog electrical signal. When the light receiving element 19 is a photodiode, an analog electrical signal corresponding to the light intensity of the beam B3 can be detected, and when the light receiving element 19 is a COD, an analog electrical signal corresponding to the beam aperture can be detected. Not only can a signal be detected, but also an analog electrical signal corresponding to the amount of light can be detected by integrating it. The analog electrical signal output from the light receiving element 19 is converted into a digital electrical signal by the A/D converter 20 and input to the control section 21 . The control unit 21 controls the two step motors 16a and 16b of the argon ion laser-AR via the motor driver 22 according to the program stored in the ROM, first in the order of the motor 16a and then the motor 16b, to the origin position. After the return rotation, the mirror adjustment screw shaft 15a is rotated in a predetermined forward and reverse direction.
, 15c to align the cathode mirror 3 with the horizontal axis (X-axis) perpendicular to the tube axis of the plasma tube 1 and the vertical axis (Y-axis).
The light-receiving element 19
The digital electric signals obtained by the A/D converter 20 are compared in magnitude between successive signals according to a program stored in the ROM in the control unit 21, and the zero flag is detected twice in a row or is short. When the time changes twice, the maximum value is detected as the maximum value, and the larger of the two maximum values when the two motors rotate forward and backward is selected. In this way,
The step motors 16a and 16b are sequentially adjusted and controlled to step positions where the maximum value is obtained. ``Invention 1 Jhl! 1 As explained above, according to the uninvented method for maintaining the gas laser beam at the maximum output, the gas laser beam can be automatically adjusted to the maximum output before use, so it is possible to If you adjust the output before each drawing, no matter what the room temperature is at that time, the room temperature will not change significantly within a short drawing time, so the beam spot can be effectively exposed. Since the size of the beam is always kept constant, it is possible to reliably expose cells of various sizes formed by the collection of beams.This makes it possible to reliably expose cells of various sizes formed by the collection of beams. In addition to making a significant contribution to the practical application of laser exposure equipment that employs this technology, it can also contribute to improving the performance of laser writing equipment that engraves cells on CDs, VDs, etc.

[Brief explanation of drawings]

FIG. 1 is a sectional view of a high-power gas laser device using the method of maintaining the gas laser beam at maximum output according to the present invention, FIG. 2 is a sectional view of main parts, and FIG. FIG. 4 is a sectional view taken along IV-IT in FIG. 1. FIG. AR... Laser l... Plasma tube, 1a, lb... Brewster window, 2... Anode side mirror 3... Cathode side mirror 4, L--plasma tube support bracket, 5... Tie rod , 6a, 6b... Mirror mounting board, 7Il... Anode side mirror mounting plate, 7a◆... Small hole, 8.9... Leaf spring, 10... Cathode side mirror mounting plate, 11◆...Bracket for mirror adjustment bolt installation, 11a...Small hole, 12...Bracket for mirror adjustment bolt installation, 13...Bracket for motor installation, 14a, 14
b, 14ca*a Mirror semi-fixing screw, 15a, 15b, 15c... Mirror semi-fixing screw, 16a, 16b... Step motor 17... Casing, 18... Half mirror 19... Light receiving Element, 20... A/D converter, 21... Control unit. 22...Motor driver 23.24...Special nut.

Claims (1)

[Claims] The attitude of the mirror mounting plate that supports the rear mirror of the gas laser is adjusted so that the rear mirror of the gas laser can be rotated back and forth by a slight angle about two mutually orthogonal axes passing through a plane perpendicular to the tube axis of the plasma tube. Two of the three screw shafts are sequentially driven by separate motors, and the beam output from the gas laser is split into tiny beams, and the split beams are received by a light-receiving element. The beam intensity of the gas laser is detected as a digital electric signal, and each time the motor is sequentially driven, the motor is stopped at a rotational position where the digital electric signal reaches a maximum value. How to maintain output.