Passivity-Based Impedance Control With Energy-Aware and Safety Null Space Compliance for 7-DOF Redundant Robots

Under the premise of ensuring the safety of the primary task, the proper utilization of the null space of redundant robots can significantly improve human-robot collaboration efficiency, such as in medical surgery or industrial assembly cases. However, the uncertainty of the operation could potentially precipitate unsafe robotic behavior. To guarantee the overall safety of the system, an energy-aware impedance control scheme with safety null space compliance is proposed. The controller employs Cartesian space stiffness shaping and damping injection to bound the system's energy and power, ensuring safe interaction behaviors. Redundancy is then exploited to handle human-robot interaction behavior by using the designed null space impedance controller while constraining the range of elbow motion. Furthermore, two separate energy tanks are introduced to bolster passivity, with each tank regulated to varying levels and power flows to adapt to the specific requirements of their respective tasks. Three human-robot collaborative experiments with a Franka Research 3 robot are conducted to demonstrate the effectiveness of the proposed approach in enhancing safety and passivity, showcasing its potential in human-robot collaborative manipulation tasks.