FPGA-based velocity estimation for control of harmonic drives

FPGA (Field Programmable Gate Array) devices have emerged as a new type of reconfigurable high-performance computing hardware. Despite their successful applications in a variety of areas, FPGA devices are just about to find their way into the control systems. In this paper, a general velocity estimation solution for on-chip FPGA implementation is presented. Possessing the advantages of both frequency count and period count methods, the proposed solution automatically covers a wide range of velocities. It behaves as a period counter at low velocities and also behaves as a frequency counter at high velocities. Remarkably, the division operation required by most period count methods is averted by using an accumulator to ease the FPGA-based implementation. The developed velocity estimation solution is experimentally compared to a classic frequency count method in terms of both velocity signal smoothness and position tracking control accuracy. Experimental results also reveal that the position control accuracy of harmonic drives is more sensitive to the velocity phase-lag than to the velocity smoothness.