Bilateral Teleoperation of a Hydraulic Robotic Manipulator in Contact With Physical and Virtual Constraints

Teleoperated robotic manipulators can be used to remotely operate within hazardous, hard to reach or dangerous environments. In tasks requiring handling of heavy objects with high forces, hydraulic manipulators have remained the most practical solution. Contrary to the previous research on teleoperation of hydraulic manipulators based on linearization and linear control theory, the present study proposes a full-dynamics-based bilateral force-reflected teleoperation, designed between a multiple degrees-of-freedom (n-DOF) electrical master manipulator and an n-DOF hydraulic slave manipulator. The used teleoperation method allows arbitrary motion and force scaling between the n-DOF manipulators, effectively enabling the use of two greatly dissimilar manipulators. The proposed teleoperation system is demonstrated with a full-scale two-DOF hydraulic slave manipulator (having 475 kg payload attached to the tip) in a free-space motion task, and in a constrained motion task including both real and virtual constraints in the environment. Despite the inherent highly nonlinear dynamic behaviour of hydraulic systems and challenges in realizing a bilateral teleoperation, the experimental results demonstrate that the proposed controller for full-dynamics-based teleoperation 1) can rigorously address the system nonlinearities, 2) can realize a high-performance bilateral teleoperation with hydraulic slave manipulators, and 3) is capable to operate in constrained motion with the environment having both real and virtual (i.e., artificially rendered) constraints.