Over-actuated Parallel Manipulator Fault Tolerant Control Based On Minimum Difference Oriented Smooth Transition Method

Over-actuated manipulator has capability of fault tolerance. If faulted actuators do not exceed system redundancy number, the manipulator may retain working normally by redistributing driving force with proper fault tolerant policy. Based on the D´Alembert principle and the equivalent force method, a plane 2-DOF over-actuated parallel manipulator dynamics model was established. Furthermore, a dynamics model of manipulator with partial failure was analyzed. The abrupt change of force is defined and fault tolerant force distributing method was further deduced. To reduce the impact of force abrupt change to end effectors, a minimum difference oriented smooth transition method was brought forward. Taking the minimum quadratic sum of force difference as optimization objective, the force is switched with smooth transition function. With real data analysis, the force change ranges of traditional method and minimum difference oriented fault tolerant method were compared. Furthermore, the transition curve with the cubic spline smooth transition function was presented. The result indicated this fault tolerant force distribution method can dramatically improve fault tolerant performance.