A straight-line motion tracking control of hydraulic excavator system

The Cartesian control of automated excavators has been noted for its difficulty, especially due to severe nonlinearities in hydraulic actuators, which are 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, and conventional controls have been unable to adequately handle nonlinearities to this degree. In a conviction that modern robust controls can resolve this problem, we approached this problem by adopting Time-delay control (TDC) as the baseline control, and by 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 a bucket (end-effector) speed of 0.5 m/s, a speed level at which skilful operators work. The accuracy achieved was mostly within 3 cm for surfaces with various inclinations and over broad ranges of joint motions, which is far better than that of an expert operator. These promising results not only justify our approach to this problem, but also convince us that we now have an effective means for the control of automated excavator systems. (C) 2001 Elsevier Science Ltd. All rights reserved.