A high-precision linear displacement measurement method based on digital phase shift of a single light source is proposed. This method uses four-channel sine grating modulation with a 90° difference in spatial position to modulate single alternating light source, then obtains four-channel light intensity signals with the same phase in time and differences phases of 90° in space. Two channels of standing wave signals with a time difference of 90° are obtained through micro-control digital phase shift processing. Using these two standing wave signals to synthesize an electric traveling wave signal containing position information. The reference signal and electric traveling wave signal are phase-discriminated by a high-frequency clock to obtain the phase difference, and it is also the position information. The principle of displacement measurement based on space-time modulation of single-alternating light field and the principle of digital phase-shift of micro control are introduced in detail, and the feasibility of the method is verified through experiments. Finally, by analyzing the reasons for the error, the sensor is optimized and designed, and the measurement accuracy of ±0.2μm is achieved in the 100mm range with a 0.6mm grating period.
Aiming at the problem that the coding difficulty of the traditional absolute encoder increases with the increase of the resolution, a novel method of simple graphic decimal shift encoding is proposed. This method uses the coarse code plus precision code to realize high accuracy measurement. The coarse code is obtained by encoding the simple graphic, which is captured by the image sensor. The encoding sequence is received according to the light intensity, and then uses a simple mathematical formula to complete the decoding. And the precision code is defined by time-grating measurement. The optical signal of the sinusoidal light transmitting surface is firstly received by the photocell and then transformed by the circuit to the voltage signal. The precision code is finally obtained by comparing reference signal with the electrical traveling wave signal, which is transformed from the voltage signal. According to the proposed principle, a prototype with a grating pitch of 0.6mm and a range of 530mm was set up. Experimental result shows that the absolute measurement accuracy of ±0.30μm is realized. It also proved that the resolution can be improved to 1nm in the experiment
It is difficult to control consistency of light source and large volume in current linear time-grating displacement sensor with four-channel alternating light field. A novel integrated linear time-grating displacement measurement system with single alternating light field is proposed. Single alternating light field and micro-controlling phase-shift method are used to synthesize a signal of traveling wave. And the measurement of linear displacement is achieved by measuring a difference of zero-crossing time between a signal of traveling wave and a reference signal. Design of structural miniaturization, design of integrated circuit, design of transmitting surface of cosine and design of optimization of existing time-grating displacement sensor are analyzed in detail. According to measuring principle, manufacture of light source and photoelectric receiver are completed, and corresponding experimental platform is built. Experimental results indicate that the measuring errors of optimized sensor are reached within±0.2μm using grating pitch of 0.1mm in the measuring range of 100mm.
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