Abstract
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.
Highlights
The concept of a power-assist system, which was first discussed by the Cornell Aeronautical Laboratory in 1968 [1], was a concept with the purpose of assisting people with disabilities by using a wearable exoskeleton
The control design of power-assist techniques is essential for the human-robot interactive system
Control design of power-assist devices is regarded as an essential technique for dealing with physical human-robot interaction (pHRI) because of its compliance design, and it has recently been investigated in several service robots, such as power-assisted wheelchairs [5], cycle ergometers for stroke rehabilitation [8], walking assisted robots [9], ankle rehabilitation robotic devices [10], and so on
Summary
The concept of a power-assist system, which was first discussed by the Cornell Aeronautical Laboratory in 1968 [1], was a concept with the purpose of assisting people with disabilities by using a wearable exoskeleton. The control design of power-assist techniques is essential for the human-robot interactive system. Using model-based observers instead of force sensors has been recommended for estimating the human propel efforts of power-assist systems [5,6,8,16], in which only the excitation signal (i.e., the current input of a servo motor) and a measurable feedback signal (i.e., the motor position output information) are necessary for the presented observer. Various power assist human-robot systems, especially in wearable exoskeletons, are performed in accordance with the user’s joint motion. The virtual soft boundary realized by the impedance control is integrated with the disturbance estimation to achieve the compliant operation of the power assist human-robot system, constrained by the ROM of the human joints.
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