A Study of Force-Free Control Framework for Industrial Manipulator Tasks Based on High-Pass Filter

Force-free control (FFC) allows for flexible manipulator motion in response to external forces, making it a vital component of human-robot interaction (HRI). Manual intervention may cause uneven forces on the manipulator or frequencies close to the natural frequency, and mechanical resonance can occur due to the inertia of the manipulator and adjustable equivalent stiffness of the controller. This paper proposes an FFC approach for industrial manipulators using a six-axis force/torque sensor (F/T sensor), implemented through a three-layer control architecture, consisting of motion control layer, Admittance Control layer and force decoupling layer. To mitigate the effects of mechanical resonance, a high-pass filter (HPF) is integrated with the F/T sensor and its impact is investigated. Experimental validation is conducted using both a simulation model and an industrial manipulator. Test results indicate that the proposed FFC architecture enables the manipulator not only to interact smoothly with external forces, but also to distinguish load forces at different frequencies and potentially address the issue of mechanical resonance between the manipulator and the applied load forces.