Trajectory Optimization of Robots with Regenerative Drive Systems: Numerical and Experimental Results

In this paper, we investigate energy-optimal control of robots with ultracapacitor-based regenerative drive systems. Based on a previously introduced framework, a fairly generic model is considered for the robot and the drive system. An optimal control problem is formulated to find point-to point trajectories maximizing the amount of energy regenerated and stored in the capacitor. The optimization problem, its numerical solution, and an experimental evaluation are demonstrated using a PUMA manipulator with custom regenerative drives. Power flows, stored regenerative energy, and efficiency are evaluated. Tracking of optimal trajectories is enforced on the robot using a standard robust passivity based control approach. Experimental results show that when following optimal trajectories, a reduction of about 10 - 22% in energy consumption can be achieved for the conditions of the study, relative to the nonregenerative case.