Joint transitions for the remote center of motion constraint: Demonstration on a redundant manipulator

One of the challenges for redundant robotic manipulators is generating a trajectory that goes from an initial configuration to a task configuration. Often, the resolution of kinematic redundancy in trajectory generation problems is accomplished by adding a constraint, or by subjecting the motion to a cost function and searching for an optimal solution. This paper investigates the remote center of motion (RCM) constraint, which specifies an insertion point that a link can rotate about and translate into, but not deviate from. Using the RCM constraint, this paper theoretically and experimentally demonstrates how to create trajectories that enable a KUKA LBR iiwa 7 R800 robotic serial-link manipulator to insert several links into a single-entrance enclosure. Both a Jacobian-based and an optimization-based trajectory generation method are explored by physical demonstration. The maximum positional RCM errors were 1.2 mm and 0.9 mm respectively. The small positional error suggests that both methods are capable of generating trajectories for redundant manipulators that accomplish a task requiring both RCM constraint adherence and multiple link insertions.