Laser Displacement Sensor Technology Book

Innovative Measurement Accuracy and Stability

A laser beam emitted from the semiconductor laser is applied to the target. The light reflected from the target is collected by the receiver lens and focused on the light-receiving element. When the distance to the target changes, the angle of the reflected light passing through the receiver lens changes, and the light is focused at a different position on the light-receiving element.

The measurement accuracy of the laser sensor utilizing triangulation is greatly affected by the following two factors:
Optical design and Stability of received light intensity and waveform.

With a single receiver lens, the spot diameter formed on the light-receiving element becomes larger when the measuring distance is shorter or longer than the reference distance, due to the lens aberration. When the spot diameter on the light-receiving element becomes larger, the measurement accuracy factors, such as "resolution", "linearity", and "scan resolution", become poorer than those obtained at the reference distance. Consequently, it is necessary to develop an optical design which ensures a constant spot size regardless of the measuring distance.

As described in "1. Basic principle of triangulation", a laser displacement sensor calculates the distance to a target by focusing the light reflected from the target on the light-receiving element. If the light reflected from the target changes due to the color, gloss, surface condition (roughness, tilt) of the target surface, the condition of the beam spot formed on the light-receiving element (received light waveform) also changes. Such a change in the beam spot condition (received light waveform) affects the measurement accuracy of laser displacement sensors.