A highly sensitive multi-dimensional motion measurement system using a spherical reflector

A new measurement system is proposed that can detect three-degree-of-freedom ( three-DOF) translational motions of an object with high sensitivity. Its measurement method is based on an optical lever technique using a spherical reflector. The spherical reflector is mounted on an object whose motion is to be measured. It reflects each laser beam, generated from two laser sources, in two different directions, depending on the motion of the object of interest. The reflected beam is then detected by two PSDs. Since each PSD is a two-dimensional sensor, the information on the 3D position of the spherical reflector can be acquired, thus enabling us to measure the three-DOF translational motions of the object. The relationship between the 3D position of the spherical reflector and the outputs of two PSDs is modelled through ray tracing. To verify the principle and effectiveness of the proposed method, a series of experiments were performed and the performance indices were evaluated, such as sensitivity, resolution, measurement error and crosstalk. In experiments, the resolution of each sensing direction is approximately 0.16 mu m and the measurement error and crosstalk between sensing channels are within +/- 0.1 mu m. The experimental results show that the proposed system can be an effective means of measuring three- DOF translational motions of arbitrary objects with high sensitivity.