A spherical encoder for real-time measurements of three-DOF wrist orientations

The need for simultaneous measurement of more-than-one degrees-of-freedom (DOF) motions of an object can be found in numerous applications such as robotic assembly, precision machining, optical tracking, wrist actuators, and active joysticks. Conventional single-axis encoders, though capable of providing high-resolution linear or angular measurements, require additional mechanical linkages that often introduce frictions, backlashes, and singularities. In this paper, a non-contact optical sensor for three-DOF orientation measurement is present. Unlike other contemporary designs, which often require a specific pattern to be drawn on a surface, this optical sensor presented here relies only on microscope features on natural surfaces to detect incremental motions. Here we offer a detailed description of the design and the development of a dual-sensor system capable of measuring three-DOF motions in real time. The analysis that is essential for optimizing the sensor design has been validated experimentally.