An FPGA-based integrated signal conditioner for measurement of position, velocity and acceleration of a rotating shaft using an incremental encoder

Digital motion control applications, where electric motors are utilized as actuators, use incremental encoders as feedback devices to sense the rotating shaft position. However, for the controller to implement an accurate tracking of input position or velocity trajectories, and to make the tracking performance robust with respect to unpredictable disturbances like parameter uncertainties and load fluctuations, measurement of velocity and acceleration data is also required. In majority of the existing digital motion control solutions, direct measurement of velocity and acceleration is rarely done. Instead, they are estimated from the discrete position data obtained from the incremental encoder. Well documented velocity and acceleration estimation algorithms exist, and the literature report both simulation and experimental results on the performance of the said algorithms with typical input position trajectories. However, no integral hardware module that uses an incremental encoder to provide position, velocity and acceleration measurement is reported. This paper presents the design and FPGA-based implementation of an integrated signal conditioner that uses the signals coming from an incremental encoder to measure the current position, and then estimate the current velocity and acceleration from it, and its performance on a test-rig. With a fast, industry-standard serial link, the proposed signal conditioner qualifies to be an integrated feedback device in digital motion control applications.