Multi-Contact Cartesian Null-Space Impedance Control for the Anthropomorphic Manipulator Without Knowledge of Force Locations

There is still a lack of null-space impedance control defined in Cartesian space that is suitable for multipoint contact and does not require knowledge of the force locations. To address this problem, this letter demonstrates a type of Cartesian null-space impedance control for the anthropomorphic manipulator. First, referring to the definition of the arm-angle, an arm-angle-like null-space Cartesian variable is defined for the Franka Emika Panda manipulator being used. Then, a type of specially constructed Cartesian torque, formed by the external forces exerted on the manipulator body about the line passing through the second joint, is defined. Finally, based on the previous two works, a type of Cartesian null-space impedance control is proposed. This control aims to establish a desired dynamic relationship between the arm-angle-like variable and the specially constructed Cartesian torque. Benefiting from the special configuration of the manipulator, the proposed Cartesian null-space impedance control is suitable for multipoint contact, and can be implemented without requiring knowledge of the locations where the external forces are exerted. Three experiments demonstrate the differences between the proposed null-space impedance control and another kind of null-space impedance control. These experiments also validate the characteristics and illustrate the advantages of the proposed null-space impedance control.