An experimental study on Cartesian tracking control of automated excavator system using TDC-based robust control design

The Cartesian control of automated excavators has been noted for its difficulty, especially due to severe nonlinearities in hydraulic actuators that can be hardly observed in electric motors. The nonlinearities tend to become even more severe as the size of an excavator increases and the speed of end-effector becomes faster, which conventional controls have been unable to handle adequately. On the basis of modern robust controls we approached this problem by: adopting time-delay control (TDC) as the baseline control; and enhancing it with compensators on the basis of insights obtained from the plant dynamics. The resulting control law has been applied to straight-line motions of a 13 ton hydraulic excavator with the bucket (end-effector) speed of 0.5 m/sec, a speed level at which skilful operators work. The accuracy achieved was within 3 cm for surfaces with various inclinations and over broad ranges of joint motions, which is far better than that of an expert.