Task coordinate frame-based contouring control of an excavator with sliding mode observer and prescribed performance

In this paper, a contouring control algorithm is developed for surface flattening tasks of an excavator regardless of lumped disturbances/uncertainties and system nonlinearities. The task coordinate frame (TCF) is adopted to decouple the contouring error from the tracking error, which allows different treatments on each error component. Moreover, a sliding mode observer (SMO) is proposed to effectively estimate both unmeasurable joint velocities and lumped disturbances and uncertainties. To integrate these techniques into the main controller, backstepping control and the barrier Lyapunov function (BLF) are introduced to guarantee the system stability and prescribed contouring performance. Finally, simulations with different operating conditions are conducted to validate the effectiveness of the proposed contouring control method with a mini-excavator model.