High scanning rate (1600 scans/sec) and high accuracy, non-contact measuring systems, the laser scan micrometer (LSM) inspects small, fragile work pieces at a high temperature, even while in motion or vibrating.
A laser beam is directed at a polygonal mirror rotating at high speed in exact synchronism with highly stable pulses from the system clock. The reflected beam is rotating clockwise as it sweeps across the input surface of a collimating lens but changes direction to be always horizontal after the lens’ exit surface as it moves, or scans, downward. This horizontal beam enters the measuring space and, with no workpiece present, reaches a receiver via a condensing lens to produce an output signal. When a simple workpiece (a cylinder, for example) is put into the measuring space the beam will be interrupted for a time during its sweep and this time, as indicated by clock pulses occurring while the receiver signal is absent, is proportional to the workpiece dimension in the downward direction.
Each transition between the receiver detecting the beam and then not detecting the beam, or vice versa, is called an edge and marks the start and/or end of measuring sections called segments, so that the differences in position of these edges define the length of each segment. The edges and segments generated by a workpiece are numbered sequentially by the instrument and are used when writing programs to extract the required dimensional data.