Position control in the presence of unknown output backlash

Backlash is a troublesome nonlinearity present in many practical systems. In position and speed control systems, it can lead to steady state errors and limit cycles. In this paper, the problem of accurately controlling the position of a mechanical load (e.g., an antenna) with an electric motor in the presence of gear backlash is considered. A control scheme is proposed which ensures good transient, as well as steady state, performance of the system. Using motor position and speed feedback, the linear part of the system is controlled to yield a specified transient and steady state performance. Using an additional feedback signal from the motor and load positions, a slower loop ensures steady-state accuracy in the presence of backlash at the output. Simulations are presented to show the efficacy of the control scheme. The proposed control scheme does not require knowledge of the dead-band width of the backlash characteristic.