GB1284809A - A laser processing apparatus - Google Patents

Abstract

1284809 Photo-electric control systems MITSUBISHI ELECTRIC CORP 11 June 1970 28435/70 Heading G1A [Also in Division G3] In a laser processing apparatus in which a laser beam 2 is focused at a point 4 on a workpiece 5, to form a hole or a slot, and a monitor beam 15 is focused at the same point 4 and after reflection therefrom is focused by an optical system 10, 9, 16, 17 at a point F 0 , a plate 18 containing a pinhole is vibrated in a direction perpendicular to the optic axis of the lens 17 about the point F 0 , thereby modulating the output from a photo-cell 20. This output is amplified and supplied to a phase sensitive detector 22 whose D.C. output drives a servomotor 24 to adjust the distance between the lens 3 and workpiece 5 to restore the focal point 4 to the surface of the workpiece. This restoring movement may be a movement of the lens 3 alone, a movement of the entire assembly 100, or a movement of the workpiece. The monitor light source 14 may be a lamp or a second, low-power laser, after a point on the workpiece has been processed, the workpiece is moved on for the next point to be processed. A second embodiment uses a single pulsed laser to produce both the monitor and processing beams, Fig.3 (not shown). During pulses, the laser beam passes through an aperture in an inclined mirror (26) to process the surface and hence be absorbed thereby. Between pulses, the low power laser output is reflected from this mirror after reflection from the workpiece and focused at the point F 0 . In a further embodiment the low power output from the non-processing end of a laser is divided by a prism (29) to provide two monitor beams, Fig.6 (not shown). These are focused at two points close to and equi-distant from the processing beam. After reflection these two beams are focused at points (F 10 , F 20 ) corresponding to two different pinholes in a vibrating plate, each pinhole having an associated photo-cell (37, 38). The photo-cell outputs are supplied to separate phasesensitive detectors whose outputs are summed and then fed to the servomotor. One of the monitor beams may be dispensed with.