Human-Robot Interaction: Controller Design and Stability

In this paper we derive the control parameter gains required to guarantee a stable human-robot interaction (HRI). One goal in HRI research field is to reduce the robot mechanical impedance and enable humans to easily manipulate the robot. Force feedback is an effective way to reduce robot inertia and friction, but stability is paramount especially when interacting with humans. This paper discusses gains and stability boundaries. The phase response of the open loop transfer function that represents the human robot interaction is used to derive the gains. The environment is modeled as a second-order spring-mass-damper system. The stability boundaries correspond to the region when the phase response of the transfer function becomes greater than -180 degrees at all frequencies. This enables the system to interact stably regardless of the environment second-order system parameters. One of the interesting results is that the virtual spring used to generate the impedance field has nothing to do with the stability condition. The experimental results show the validity of our method.