FPGA-based adaptive friction compensation for precision control of harmonic drivers

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 FPGA-based adaptive friction compensation scheme with a FPGA-based velocity estimator is reported for the first time. The FPGA device allows the LuGre friction model to be effectively implemented and updated at a clock rate. A parameter adaptation mechanism automatically accommodates the parameter uncertainties. To avert the need of having a division computation, which is extremely difficult if not impossible for a FPGA device to perform, a specially designed accumulator is used to create the velocity signal necessarily required for high-precision position tracking control. The developed technology is experimentally tested on a harmonic drive coupled with a brushless motor. The ratio of the maximum position tracking error to the maximum velocity reaches 0.00034 (s) - an unprecedented number in the precision control of harmonic drives.