Model-Free Sliding-Mode-Based Detection and Estimation of Backlash in Drives With Single Encoder

Backlash is a frequently encountered problem for various drives, especially those equipped with a single encoder onside of the controlled actuator. This brief proposes a sliding-mode differentiator-based estimation of unknown backlash size while measuring the actuator displacement only. Neither actuator nor load dynamics are explicitly known, while a principal second-order actuator behavior is assumed. We make use of the different perturbation dynamics distinctive for different backlash modes and an unbounded impulse-type perturbation at impact. The latter leads to transient loss of the sliding-mode and allows for detecting an isolated time instant of the backlash occurrence. The proposed method is simple and insensitive to residual system dynamics. The approach is experimentally evaluated on the data collected from a two-inertia system with backlash in the coupling.