| 摘要 |
<p>PURPOSE:To enhance S/N of sensor output by fixing a light receiving window with an optical filter which blocks the YAG laser light and transmits the detection light for a sensor thereby eliminating noise due to laser from the detection signal. CONSTITUTION:When a liquid crystal mask 2 exhibits a constant transmittance, the image mark being put on a work 2 exhibits uniform quality. Transmittance of the mask 2 can be altered by varying the image indicating voltage. By taking advantage thereof, a light emitting element 5 and a light receiving element 6 are connected electrically with a controller 7. The controller 7 receives an emitted light R1 and a received light R2 thus grasping the transmittance of the mask 2 and then regulates the indicating voltage of the mask 2 such that the measured transmittance will be equal to a reference transmittance. Consequently, the image marking quality is sustained constant. The optical filter blocks the light L of a YAG laser 1 but transmits the detection light R of sensor. Since the intensity of light R2 received from the element 5 is invariant, erroneous function is eliminated in the drive control and the image marking quality is sustained at high level.</p> |
