ABSTRACT
Measurement of displacement is important for precise positioning, processing, and testing. Typical optical techniques for the measurement of displacement use equipment such as laser interferometers, linear encoders, and distance meters. This chapter introduces these measurement techniques. Most laser interferometers have the same configuration as the Michelson interferometer. One of the reflecting mirrors of the Michelson interferometer is attached to the object whose displacement is to be measured. The two main types of laser interferometers are the homodyne type and the heterodyne type. In practical use, such as in the manufacturing industries, linear encoders other than laser interferometers are commonly used for positioning. There are several kinds of linear encoders. The magnetic-scale type and the magnet–electric type are the oldest types of linear encoders. Distance measurements are classified into two types. One is the measurement of a value between two points, and the other is a measurement of a change in long length.
