Control Design of Observer-Based Virtual Soft Boundary for a Power-Assist System with Limited Operating Range

Control design of power-assist systems has been widely applied to human-robot interactive systems such as wearable exoskeleton systems, of which the range of motion limitation of human joints in the power-assist systems is essential. This paper presents a virtual soft boundary design for a human-robot cooperation system with a limited operating range. The proposed virtual soft boundary is realized by impedance control and integrated into the power-assist robot arm system; meanwhile, power-assist robot arm systems are typical human-in-the-loop systems, and the control of the power-assist system in performing in accordance with a human’s perception is a significant issue. Therefore, a model-based disturbance observer with a pseudo-derivative feedback feedforward (PDFF) compensator is designed to effectively estimate the human’s torque for an appropriate motor torque command. Experimental results show that the proposed control method can estimate the human torque exerted on the robot arm system to achieve a power-assist system, and the virtual soft boundary can be realized by the impedance control and integrated into the power-assist robot arm system