Desired Contact Force Realization in Unknown Environments via Multiple Virtual Dynamics-based Control Framework

Contact task execution in unknown environments is fundamental to robotic applications, requiring three essential capabilities: accurate position tracking, safe contact establishment, and achievement of desired contact force. While our previous study has demonstrated that combining admittance and impedance control in series enables accurate position tracking and safe contact, achieving desired contact force remains challenging due to environmental and robot dynamic uncertainties. This paper presents a novel force control methodology that integrates all three capabilities by introducing an additional admittance layer to the series admittance-impedance control framework. The key idea lies in the conversion of sensor information into continuous virtual object motion through virtual dynamics, enabling seamless transition from position to force tracking control without controller switching. This approach eliminates the need for direct feedback of raw sensor measurements to controllers while ensuring precise contact force achievement regardless of environmental or dynamic uncertainties. The effectiveness of the proposed method is validated through both numerical simulations using a 2-DOF manipulator model and experimental verification on a physical manipulator system.