Thin-Volume Image-Type Angular Displacement Measurement Based on Point Light Reflection

Image-type angular displacement measurement technology based on image recognition algorithm is a high-performance displacement measurement technology with high robustness and fault tolerance. In our previous research, using parallel light sources to illuminate the grating disk can achieve high measurement resolution and measurement accuracy. However, due to the optical path height of the transmission displacement measurement, the measurement volume cannot be further reduced in the axial direction. Therefore, a thin-volume image-type displacement measurement (IDM) was proposed here based on point light reflection. First, to reduce the volume of the measuring optical path, a reflective imaging optical path was designed using a point light. Second, to improve robustness of reflective imaging displacement measurements, an absolute encoding method was proposed based on Manchester encoding. Third, based on the encoding pattern used, a decoding and subdivision algorithm was derived. Finally, the resulting method was verified by experimentation. In these experiments, the axial height of the test measuring optical path was only 6 mm. Based on Manchester encoding, the method achieved more than 25-bit measurement resolution and $3.11^{\prime \prime }$ error standard deviation when the grating encoder at 86 mm. This research greatly reduced the optical path volume of angular displacement measurements, providing a technical basis for thin-volume and high-performance photoelectric displacement measurement.