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

The design and control of an efficient two-joint, two-link flexible arm are described. This efficient arm was designed and built to use most of the energy (provided by the motors) in performing the tasks instead of moving the arm structure. The arm has most of the mass concentrated at the tip and uses a special mechanical configuration to decouple radial tip motions from angular tip motions. An important problem when controlling lightweight flexible arms is the large Coulomb friction of the motors. A two-nested-loop multivariable controller is used to control the lightweight flexible arm with friction in the joints. 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 is used to model the oscillations of the structure and is included in the decoupling/linearizing term of this controller. Experimental results are presented