Robust control for mechanical systems with oscillating bases

In this paper, robust control for manipulator robots with oscillating bases, associated with control for robots installed on either vessels or ocean structures, is considered. First, the formulation of this problem is introduced and the disturbance to the robot dynamics due to oscillation of the base is discussed. Then the control design technique, which is mainly based on scaled H_∞ output feedback control and incorporates some other schemes to reduce the nonlinearity such as gravity, centrifugal force, etc., is presented. Once the feedback schemes to reduce nonlinearity are determined and the signals which should be regarded as disturbances are rendered distinct, then the problem becomes one of disturbance attenuation in the presence of structured model uncertainties. To acquire a controller which satisfies the control objectives and to analyze the resulting control system with respect to robustness, the structured singular value μ theory is exploited. One of the advantages which this technique provides is that, if the frequency range of the base oscillation is known in advance, then the controller dose not require observation of the motion of the base at all. Further, robustness to physical parameter perturbations of the robot can be acquired with respect to both stability and performance