Experiments in load-adaptive control of a very flexible one-link manipulator

Abstract

An adaptive control algorithm based on the Self-Tuning Regulator concept has been experimentally demonstrated on a very flexible one-link robotic manipulator. The very lightly-damped structural resonances of the manipulator coupled with the use of a primary sensor separated from the actuator by flexible structure ( non-collocated sensor and actuator) to give good accuracy in tip positioning make high-performance controllers very sensitive to modeling error. The adaptive controller is able to maintain precise tip position control despite wide variations in end effector load. An identification algorithm is employed which estimates the mass of the tip load. It makes use of a simple parameterization of system transfer functions which is a linear-fractional expression in the mass of the load. The Linear Quadratic Gaussian synthesis procedure is used for control design, a polynomial interpolation to a precalculated table of controller gains is made on-line to implement a controller appropriate to the identified value of load mass. Rate of convergence of the identification algorithm is such that the system is able to adapt to a 40% change in moment of inertia during a single commanded step change in position.