Dual Mode Control of an Elastic Robotic Arm: Nonlinear Inversion and Stabilization by Pole Assignment

This paper considers control of an elastic robotic arm of two links based on nonlinear inversion and pole assignment for stabilization. The design is done in two steps. First, based on nonlinear inversion, a nonlinear controller is designed for the trajectory control of the joint angles using joint torquers. Although, the inverse controller accomplishes trajectory control of the joint angles, this excites the elastic modes of the arm. In order to damp the elastic oscillations, a stabilizer is designed for a linearized system about the terminal state using pole assignment technique. In the closed-loop system, first the inverse controller acts when a command is given, and the stabilizer automatically switches when the joint angle trajectory enters a specified neighborhood of the final commanded position.