| 摘要 |
Interferometers are known for measuring the displacement of an object 6 with an accuracy of a fraction of 1 mu m, having digital display, and forward/reverse motion discrimination. To avoid the use of a special frequency stabilised laser source producing oppositely polarised beams of different frequencies, an interferometer is provided having a simple laser source 1, in which an interference line pattern is formed on a detection system 20 having a moving grating-like structure whose grating period corresponds to the period of the interference pattern. The effect of a moving grating is provided by a detection system comprising a linear array of photodiodes in which sequential activation of interjacent groups of photodiodes by a ring counter moves an effective grating pattern along the array. By counting the number of periods in the output signal of the detection system, changes in the measuring arm b of the interferometer can be measured with high accuracy. The interferometer may assist in measuring and controlling the movement of an optical recording head (Figure 7). <IMAGE> |
