SIMULATION AND EXPERIMENTAL STUDIES OF GEAR BACKLASH AND STICK-SLIP FRICTION IN HYDRAULIC EXCAVATOR SWING MOTION

Inherent to any heavy-duty hydraulic machine operation with a large nu mber of interconnected components are nonidealities such as gear backl ash, 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 c omprising experimental, mathematical and simulation components to dete rmine 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 ineffic ient and unnecessary in terms of computation rime and the final result s. A new model which combines the fluid-flow, and the gear train dynam ics is developed. The study of contact and non-contact cases brings ab out proper sets of static and dynamic equations which efficiently simu late this phenomenon for the class of excavator machines ur?der consid eration. The inclusion of stick-slip friction model in the simulation shows two effects. Firstly, it causes a noticeable time-delay at the b eginning of the swing motion. Secondly, it results in an overshoot dur ing velocity control experiments. It is also shown that dry friction a nd leakage (cross-port or external) are as significant as gear backlas h in determining the pressure patterns in the connecting hydraulic lin es and, therefore, should not be overlooked, especially when the excav ator cabin is brought to a stop. Often, this is the most important sta te event when accurate positioning is crucial. The simulation results are qualitatively supported by the experimental evidence. The experime nts were performed on an instrumented teleoperated Caterpillar 215B ex cavator.