A no-contact laser sensor based on the Self-Mixing effect for the measurement of rotations

The development of a no-contact sensor based on the Self-Mixing effect for the simultaneous measurement of linear and angular degrees-of-freedom (DOFs) of a moving target is presented. The sensor is made up of three laser diodes with integrated monitor photodiodes and a plane mirror target attached to the moving object. The proposed technique makes the system easier to align with respect to the traditional interferometric systems and no further optical elements are required in the laser head except for the laser chip and its integrated photodiode, thus providing an effective compact and low-cost motion control system. The linear and angular resolutions are 0.7 mum and 0.8 times 10^-3deg, respectively. A series of experiments is performed to test the proposed method by direct comparison with a reference meter system, showing a linear response over a range of 1 m and plusmn 0.4deg. Moreover, the sensor is tested under complex displacement to validate the feasibility of simultaneous measurements of more than one DOF.