Study on operational space control of a redundant robot with un-actuated joints: experiments under actuation failure scenarios

Abstract

This paper analyzes operational space dynamics for redundant robots with un-actuated joints and reveals their highly nonlinear dynamic impacts on operational space control (OSC) tasks. Unlike conventional OSC approaches that partly address the under-actuated system by introducing rigid grasping or contact constraints, we deal with the problem even without such physical constraints which have been overlooked, yet it includes a wide range of applications such as free-floating robots and manipulators with passive joints or unwanted actuation failure. In addition, as an intuitive application example of the drawn result, an OSC is formulated as an optimization problem to alleviate the dynamics disturbance stemmed from the un-actuated joints and to satisfy other inequality constraints. The dynamic analysis and the proposed control method are verified by a number of numerical simulations as well as physical experiments with a 7-degrees-of-freedom robotic arm. In particular, we consider joint actuation failure scenarios that can be occurred at certain joints of a torque-controlled robot and practical case studies are performed with an actual redundant robot arm.

Joint Reconfiguration after Failure for Performing Emblematic Gestures in Humanoid Receptionist Robot

“…The process that allows the robot system to generate a new motion trajectory for completing the tasks with the remaining actuators is called joint failure recovery. One way to handle the problem of some actuators malfunctioning is designing and developing robots with redundancy mechanisms [4][5][6][7][8]; redundant robots are designed to have more degrees of freedom than required to perform their tasks. These redundant joints can be used to replace the failed joints and allow the robot to complete its tasks under the joint failure condition in many different ways.…”