Design and control of a two-degree-of-freedom lightweight flexible arm

This report describes the design and control of a two-joint, two-link flexible arm. Our purpose has been to build an efficient arm in the sense that most of the energy provided by the motors is spent in doing the task (moving the tip mass) instead of moving the arm structure. In order to achieve that, we designed a flexible arm that has most of its mass concentrated on the tip. We wanted also to decouple radial tip motions from angular tip motions. The special mechanical configuration that fulfills all these specifications is described in Section 2. Section 3 describes the control scheme of this arm. An important problem when controlling it was the large Coulomb friction of the motors. A two-nested-loop multivariable controller has been used. The inner loop controls the position of the motors while the outer loop controls the tip position. The resolved acceleration method is generalized to control this flexible arm. The compliance matrix was used to model the oscillations of the structure, and was included in the decoupling/linearizing term of this controller. Experimental results are given in Section 4, and conclusions are drawn in Section 5.