Realization of Flexible Motion of Robot Joint with A Novel Permanent Magnetic Spring

Service robots designed to be used in human environments, require different approach than industrial robots, which safety is achieved mainly by decreasing the interaction with humans, require frequent interaction with humans. The compliant system gives the answer to the safety issue. That should have very low stiffness when subjected to a collision force that could cause human injury, otherwise maintain very high stiffness to keep positioning accuracy. In order to achieve this, robot joint equipped with variable stiffness have been studied by many researchers. This paper proposes a variable stiffness mechanism for robot joint using permanent magnetic spring to ensure collision safety and stable contact. The variable-stiffness range of robot joint using permanent magnetic spring is wider than the mechanical ones, in case of no increase in the wire-tension limited by motor's torque. The mechanical properties of the variable stiffness mechanism are studied. The permanent magnetic variable stiffness robot joint was been built, the safety, the variable-stiffness ability, position step response ability were verified by experiments.