Simulation and Experimental Studies of Gear Backlash and Stick-Slip Friction in Hydraulic Excavator Swing Motion

Abstract

Inherent to any heavy-duty hydraulic machine operation with a large number of interconnected components are nonidealities such as gear backlash, friction and leakage. The swing motion of the operator’s cabin in an excavator is a typical example. In this paper we conduct a study comprising experimental, mathematical and simulation components to determine the degree to which these nonlinearities affect the performance of such machines. The inclusion of the conventional model of backlash in the simulation of the excavator swing motion is shown to be inefficient and unnecessary in terms of computation time and the final results. A new model which combines the fluid-flow and the gear train dynamics is developed. The study of contact and non-contact cases brings about proper sets of static and dynamic equations which efficiently simulate this phenomenon for the class of excavator machines under consideration. The inclusion of stick-slip friction model in the simulation shows two effects. Firstly, it causes a noticeable time-delay at the beginning of the swing motion. Secondly, it results in an overshoot during velocity control experiments. It is also shown that dry friction and leakage (cross-port or external) are as significant as gear backlash in determining the pressure patterns in the connecting hydraulic lines and, therefore, should not be overlooked, especially when the excavator cabin is brought to a stop. Often, this is the most important state event when accurate positioning is crucial. The simulation results are qualitatively supported by the experimental evidence. The experiments were performed on an instrumented teleoperated Caterpillar 215B excavator.