Acceleration estimator for low-velocity and low-acceleration regions based on encoder position data

Acceleration computation based on simple numerical differentiation from an optical encoder signal may be very erroneous, especially in the low-velocity and low-acceleration regions. To overcome this problem, a novel approach to estimating acceleration in these regions is proposed in this paper. This so-called low-acceleration estimator, which is a computer algorithm, is based on the fact that the displacement signal from the encoder is accurate. Since the bandwidth of this estimator is rather limited, it can be used in combination with the traditional numerical differentiation approach in order to cover a wide velocity range. It was shown in various simulations and experiments that this combined acceleration estimator can yield accurate acceleration estimates over a wide range of velocities. Furthermore, when this estimator is applied to a friction compensation system, the effect of low-velocity friction can be reduced significantly by its capability to detect small changes in acceleration caused by friction.