Closed loop compensation of kinematic error in harmonic drives for precision control applications

Harmonic drives are widely used in precision positioning applications because of their unique advantages including near zero backlash, high gear reduction and small weight. However, precision positioning is made difficult by inherent error that exists between input and output, known as kinematic error. The latter is difficult to compensate for because of its nonlinear periodic behavior and dependence on drive type, assembly, and environmental conditions. We present nonlinear PD-type control algorithms to compensate for the kinematic error independent of its form. Dynamic simulation and experimental regulation and tracking results obtained with a dedicated harmonic drive test setup demonstrate the effectiveness of our proposed control strategies