Path tracking for a hydraulic excavator utilizing proportional-derivative and linear quadratic control

This paper presents a three-dimensional path tracking strategy for a hydraulic excavator. It mainly aims to design the controller for allowing the excavator to follow typical working motions of a skillful operator such as leveling and truck loading. The performance of the designed controller is verified through real-time experiments using a 21-ton class excavator in which displacement sensors, electro-proportional pressure reducing valves, and communication devices are incorporated. Basically, proportional-derivative (PD) controller with dead zone compensation is used to control the cylinder displacements and swing angle. In order to enhance the performance, a linear quadratic outer-loop is introduced for boom, arm, and bucket joints, which compensates reference inputs of the nonlinear PD controller. Experiments of individual joints show that the designed outer-loop can provide faster rise time than the nonlinear PD controller itself. Furthermore, experimental results demonstrate the feasibility of the proposed algorithm for achieving autonomous compliant motions of both leveling and truck loading.