Repetitive control to reduce speed ripple caused by strain wave gearing

A strain wave gearing, also known as a harmonic drive gear, is frequently used in robotics actuators. Transmission error of the gear produces a speed ripple when the actuator operates. Since the transmission error of the strain wave gearing is a periodical function, it produces a speed ripple with defined and discrete frequencies. We show that at these conditions it is possible to use a repetitive control to reduce the speed ripple. To attain the system´s stability, it is important to provide a sufficient damping. A significant reduction of the speed ripple was confirmed, and some experimental results are shown