Time-energy optimal control of articulated systems with geometric path constraints

A method is presented for optimizing the motions of articulated systems along specified paths, minimizing a time-energy cost function. Using a transformation to path variables, the optimization problem is formulated in a reduced two dimensional state space. The necessary conditions for optimality, stated for the reduced problem, lead to a compact two point boundary value problem that requires the iterations of only one boundary condition. The optimal control obtained for this problem is smooth, as opposed to the typically discontinuous time optimal control. The method is demonstrated numerically for a two link planar manipulator, and experimentally for the UCLA Direct Drive Arm. The smoother time-energy optimal trajectory is shown to result in smaller tracking errors than the time optimal trajectory.