Abstract
Power soft robots—defined as novel robots driven by powerful soft actuators, achieving both powerfulness and softness—are potentially suitable for complex collaborative tasks, and an approach to actuating a power soft robot is the McKibben artificial muscle. This study aims to show the potential of hydraulic artificial muscles to be implemented in a power soft robot with high safety, including higher stability against sudden load separation or impact disturbance, and appropriate dynamic compliance. The stability of a manipulator arm driven by hydraulic muscle actuators is experimentally proven to be higher than that of pneumatic muscle actuators when the stored elastic energy is instantaneously released. Therefore, the hydraulic muscle actuator is a better candidate for actuating a power soft robot. By taking advantage of the incompressible liquid medium and the compliant structure of a hydraulic muscle, a second-order impedance control strategy with a braking method is proposed to improve dynamic compliance without sacrificing the safety features of hydraulic muscles. The results show that the manipulator can be easily shifted by a several-kilogram-level external force and react safely against sudden load change with low angular velocity by the proposed impedance control.
Highlights
It is a general assumption that softness and powerfulness are contrasting concepts; they are independent and can be achieved simultaneously
To improve its dynamic impedance characteristics, we propose a simple impedance control strategy to utilize the features of the hydraulic muscle
By taking advantage of the compliant structure and incompressible liquid medium of a hydraulic muscle, we proposed a simple second-order impedance control to improve the dynamic characteristics of the antagonist joint
Summary
It is a general assumption that softness and powerfulness are contrasting concepts; they are independent and can be achieved simultaneously. The goal of our research is to develop a robot that has both properties: powerfulness and softness. Traditional robots, which use stiff actuators with high power and high accuracy, have already been applied in many industries to accomplish heavy tasks. Novel soft actuators have intrinsic compliance, which is suitable for human–robot interaction. Most of the current soft actuators lack power. For heavy tasks that require interaction with humans, when both high power and high compliance are required, traditional collaborative robots have to be equipped with other safety components and advanced
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