Elastic Robot Arm Research Articles

Dual mode control of an elastic robotic arm: non-linear inversion and stabilization by pole assignment

This paper considers control of an elastic robotic arm of two links based on non–linear inversion and pole assignment for stabilization. The design is performed in two steps. First, based on non-linear inversion, a non–linear controller is designed for the trajectory control of the joint angles using joint torquers. 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 the 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 neighbourhood of the final commanded position. Simulation results are presented to show that in the closed–loop system accurate joint angle trajectory tracking and elastic mode stabilization can be accomplished in spite of payload uncertainty in the ...

Control and stabilization of nonlinear uncertain elastic robotic arm

An approach is presented to the control of an uncertain nonlinear flexible robot arm (PUMA-type) with three rotational joints. The third link is assumed to be elastic. A torquer control law, which is a function of the trajectory error, is derived for controlling the joint angles. The knowledge of the system dynamics is not required for the derivation of the controller. This controller includes a reference model to generate command joint angle trajectories, and a dynamic system in the feedback path which requires only joint angle and rate for feedback. The torquer controller asymptotically decouples the elastic dynamics into two subsystems, representing the transverse vibration of the elastic link in two orthogonal planes. For the damping of the elastic vibration, a force control law using modal velocity feedback is synthesized. Simulation results are presented to show that the combination of the torque and force control law accomplishes reference joint angle trajectory tracking and elastic mode stabilization despite the uncertainty in the system. >