Position Accommodation and Compliance Control for Robotic Excavation

Abstract

A robotic excavator must be able to operate in all three states of manipulator motion: free space, contact, and exertion of a force against an environment. A position accommodation control scheme is ideally suited for this task. The position accommodation method described in this study uses a position controller to track a predefined trajectory in the absence of a force at the excavator bucket. If a force is detected, the measured force is used, through a compliance controller, to modify the commanded trajectory. This allows for better control of the complete excavation cycle. This paper describes a rheological method for modeling the soil–bucket interaction force and how that method must be modified to suit the unique case of excavation. Results for both a fixed and variable spring set-point are shown, illustrating the difference between a purely position controlled robot and one using a position accommodation/compliance controller, when used to dig a level trench.