Design modification of parallel manipulators for optimum fault tolerance to joint jam

Fault tolerant manipulators are capable of completing their critical tasks after encountering failure. In this study, modification of parallel manipulators to achieve fault tolerance to active joint jam (lock) was performed by equipping each branch with a backup revolute joint at a pre-assigned location. Upon the detection of failure of an active joint in a branch, the actuation was switched from the failed active joint to the backup joint in the branch. The optimum axis directions of the backup joints were successfully determined from maximizing the manipulability after failure using Lagrange multiplier optimization method.