Research on a Long-Range and Single-Track Absolute Displacement Sensor With Simple Graphic Shift Coding

In terms of reducing the coding complexity and manufacturing difficulty caused by the increase in coding density of the fractional encoding parts in absolute displacement measurement, a simple graphic shift coding method that increases the grid spacing of the incremental code and cancels the small coding value was proposed in this article. First, the displacement measurement is converted into the time difference measurement using the orthogonal modulation of light intensity. Increase the size of the gate distance to reduce the amount of encoded data without reducing the sensor resolution. Then, the decimal place of the absolute code channel is replaced by the pixel array of the image sensor, and the fractional part of the absolute code channel is canceled. Furthermore, with shift coding of pattern variations, the proposed method realizes a cursor shift coding which can be cycled for a plurality of times, solving the problem of increasing encoding density caused by the increase in cursor encoding range effectively. Based on the above principle, a prototype has been developed that achieves
$\mu \text{m}$
-level measurement accuracy with mm-level encoding pitch, further reducing the absolute encoding density for long-distance measurements, and has an effective range of 530 mm. Finally, the practical numerical results demonstrate that the measurement error of the sensor is
$\pm 0.1~\mu \text{m}$
within a short period of 0.6 mm, the absolute measurement repetition accuracy can be up to
$\pm 0.2~\mu \text{m}$
, and the measurement precision is
$\pm 2~\mu \text{m}$
in the whole range.