High accuracy contouring control of an excavator for surface flattening tasks based on extended state observer and task coordinate frame approach

Abstract

In construction, motion control is primary for excavators to complete earth-moving tasks. However, the position tracking performance is strongly affected by system nonlinearity, external disturbances, and model uncertainties during operation. In this paper, a task coordinate frame approach is firstly adopted for an excavator to separate the tracking error into contouring error, tangential error, and orientation error. Based on this transformation, each error component is treated independently according to their priorities. Furthermore, an extended state observer is designed to cope with not only unmeasurable velocities but also lumped disturbances and uncertainties. Finally, these advanced techniques are integrated into the proposed controller by using the backstepping control with the barrier Lyapunov function which is developed to achieve a prescribed performance of the contouring error. The proposed control algorithm guarantees system stability and provides high accuracy contouring performance and acceptable tangential and orientation performances regardless of the presence of lumped disturbances/uncertainties and nonlinearities in the system. Simulation results verify the control effectiveness of the proposed control algorithm in surface flattening tasks compared to previous works. Practitioners can apply the results of the research to not only semi-autonomous operations with unskilled operators but also fully autonomous operations. Future research is necessary to consider the contouring control of excavators with other earth-moving tasks and relating problems in real operating conditions.