A Position Controller for Hydraulic Excavators With Deadtime and Regenerative Pipelines

This paper proposes a position controller for commercial hydraulic excavators. It is constructed by combining a proportional-derivative (PD) controller and a sliding-mode controller as a differential algebraic inclusion and also is integrated with a recently-proposed hydraulic actuator model. The use of the PD control is intended to make the controller insensitive to the deadtime in the hydraulic system, which is typically 0.1 s to 0.6 s in commercial excavators. The use of the sliding-mode controller combined with the actuator model is for handling the saturation of the actuator force, which may happen when the target position is not close enough to the current position and when the relief valves open. Moreover, this paper extends the controller to deal with the effect of the regenerative pipelines, which are embedded in commercial excavators to realize efficient operations but act as a source of disturbance on the controller. This paper also shows an analysis that can be used for tuning the controller parameters. The proposed controller was validated with simulations and experiments using a 13-ton class excavator, in which some set-point control tasks and trajectory-tracking tasks were performed.
Note to Practitioners
—This paper proposes a position controller for hydraulic excavators. The controller was validated with the boom and arm actuators of a 13-ton class commercial excavator, with trajectory-tracking and set-point control tasks. Most of the controller parameters can be set referring to available specifications of the hydraulic circuit, such as the set pressures of the relief valves and the cross-sectional areas of the chambers. There are three parameters (the proportional gain, the derivative gain, and the time constant of the convergence) that should be carefully tuned, but their physical interpretations are relatively straightforward, and they can also be tuned along our guideline using pole locations of a particular transfer function. It has been shown that the proposed controller properly works despite the existence of the deadtime in the hydraulic systems, which are typically 0.1 s to 0.6 s. An extended version of the proposed controller handles the effects of the regenerative pipeline, which exists in some hydraulic systems, e.g., the arm actuator, for efficient operation and is not accounted for in the original version of the controller. The accuracy of the proposed controller will be further improved by combining it with better means to estimate external forces by using additional sensors, such as pressure sensors installed to actuator chambers.