Peg-In-Hole Task Using Impedance Control For T-Flex Demonstration

In the recent past, the Precision Engineering group of the University of Twente developed the T-Flex; a fully flexure-based, six degrees of freedom parallel kinematic manipulator with a large range of motion. The T-Flex is the perfect showpiece to demonstrate the accomplishments of the PE group and the development of flexure- based robotics on fairs and events. To showcase T-Flex’s force sensitivity, reproducibility and accelerations through its workspace, a demonstration is developed around the peg-in-hole problem. As part of the setup, a visually attractive peg and hole are designed and manufactured. The demonstration involves inserting the peg and measuring the hole, followed by a dancing motion to show accelerations and the workspace, and finally re-inserting the peg to display reproducibility. To solve the peg-in-hole problem, an impedance control-based strategy without vision or force feedback is developed. The compliance of the controller varies throughout the demonstration. During phases of interaction with the environment, a soft controller is implemented to limit the interaction forces. To increase the bandwidth of the system during the dancing motion and to improve accuracy during the re-insertion, a stiffer controller is implemented. The stiff controller has a bandwidth of 9 Hz and exhibits a maximum steady-state tracking error in the task space of 45 μm when the set of model parameters is well-trained. Further increase of the controller stiffness is limited by destabilization of the first parasitic eigenmode. The hole measurement procedure shows high reproducibility, and the peg-in-hole task is performed successfully during the observed instances.