On the design of fault tolerant parallel manipulators

Methodologies for the design of fault tolerant parallel manipulators are presented based on the failure analysis of manipulators. The investigations concentrate on the architecture and actuator/sensor distribution layouts of parallel manipulators. Failures of parallel manipulators are analyzed at the component level (link and joint failures), subsystem level (branch failure), and system level (parallel device failure). All potential joint and actuator distributions of parallel manipulators are identified, and the results for manipulators with the mobility of three and six are tabulated. The mechanical failures of parallel and serial manipulators are presented and classified based on the component, subsystem and system failures. In addition to the component failures, the failure of parallel manipulators as a result of the loss of degree of freedom, loss of actuation, loss of constraint, special configurations (singularities), as well as branch interference, are discussed. Redundant configurations of parallel manipulators are classified as redundant mobility, redundant sensing, and redundant actuation; all being considered for the performance improvement of these devices. Two criteria are defined for the identification of optimum configurations of parallel manipulators with one redundant actuation. For the considered classes of parallel manipulators, optimum fault tolerant configuration of each class is identified.