| Many applications require simultaneous vibration isolation and precision pointing (e.g., telescopes, laser communication, and laser weapons). As a member of the class of parallel kinematic machines, the hexapod provides a platform for accomplishing these tasks. A simultaneous control scheme for a flexure jointed hexapod is developed in this dissertation using acceleration feedback to provide high-frequency vibration isolation, while Cartesian pointing feedback provides low-frequency pointing. This scheme takes advantage of the bandwidths of both acceleration and pointing sensors and provides a broad control bandwidth.; When less than 6 degrees-of-freedom (DOF's) are required (in precision pointing tasks, for example), the kinematic redundancy of the hexapod makes it possible to implement fault-tolerant algorithms. A previous reconfiguration algorithm, based on choosing the same number of "off" degrees-of-freedom (ODOF's) as failed struts, is optimized. Since there are extra ODOF's available, a least-square solution is achieved by picking all the ODOF's, even when the hexapod works at the edge of its workspace.; For 6 DOF active vibration isolation, there is no kinematic redundancy. If one or more struts fail, it will lose the same number of DOF's. A similar algorithm for preserving isolation performance despite strut failures is developed. This algorithm is also capable of isolating vibration in an arbitrary direction.; Finally, all the techniques developed are combined to provide simultaneous, decoupled, fault-tolerant pointing and vibration isolation with a single device. |
