Impedance Control of a Spherical Motor with a Complementary H2 - H∞ Paradigm

This paper presents a robust impedance control method for a spherical motor to ensure compliant manipulations of robots with unstructured environment. By defining a controlled variable in terms of impedance error, the proposed control method allows for rendering the desired impedance on the spherical motor by driving the impedance error to zero. Featured with a complementary $H_{2}-H_{\infty}$ scheme, the proposed controller ensures the optimal performance of the system impedance while also guarantees the robustness in presence of system uncertainties. The proposed method has been validated with numerical simulations in the context of a contact process between a robotic wrist driven by a spherical motor and unstructured environment. The results demonstrate that the robotic wrist is capable of precisely rendering desired impedance when interacting with external objects and compliant manipulations can be guaranteed in omni-direction in joint space.