An absolute displacement measurement method of simple graphic decimal shift encoding

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