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Human safety represents the key requirement in physical human-robot interaction (pHRI). However, the majority of current research works focus on the safety evaluation. There is no definite way to design a robot that not only meets the performance but also has inherent safety. A humanoid robot for human joint movement rehabilitation is developed, to fulfill the requirement of both safety and its performance. A nonlinear model of human-robot collision with effective mass and stiffness of robot's end-effecter (EE) is proposed. An important parameter involved in the model is the joint stiffness of the robot, which has an inherent direct effect on the safety. The influence of joint compliance on the modal frequencies is analyzed, and the kinematic performance of the robot is estimated roughly by the lowest order modal frequency. The design method of compliant joint stiffness is put forward, which can balance the safety and kinematics performance requirements. When the compliance is utilized intentionally in joints to improve safety, the question whether or not rigid performance of compliant joint can be achieved or approached by control is arose naturally. Such a challenge is addressed by the cascade control, where outer position loop with link-side position feedback is constructed. Here, restoring torque in the elastic transmission is taken as virtual control that is, in turn, set as the reference command of the inner torque loop. Intuitively, once the virtual control is reproduced as rapidly as possible in the inner torque loop, quasi-rigid performance is exhibited in the outer position loop as if there were no series elasticity in compliant joint. The stability criterion is derived, and the virtual stiffness and dynamic performance are examined. Finally, experiments are performed to validate effectiveness of the suggested control scheme. [ABSTRACT FROM AUTHOR]

This paper introduces a Compliant thin-walled joint (CTWJ) that expands the group of existing compliant joints. The CTWJ design is based on the nonlinear geometry of the zygoptera animal. With a thin-walled structure, the CTWJ allows a considerably large range of motion in the x-and-y axes. In addition, the thin-walled structure is then filled by polydimethylsiloxane material to reinforce the stiffness of the CTWJ. First, design of experiment methodology is used for the sensitive analysis of the width and the thickness to the strain of joint. The range of motion, the strain, the buckling behavior, and the first natural frequency of CTWJ are investigated via finite element analysis and experiments. The behavior of the CTWJ is subsequently compared with the conventional compliant joints to realize the efficient performance of the CTWJ. The results revealed that the CTWJ has a range of motion and strain energy larger than those of traditional compliant joints. Finally, an example of vibration isolator is modeled by using the CTWJ as planar spring. It is believed that the CTWJ has a great potential for the development of compliant mechanisms in terms of large range of motions in mutliple axes. [ABSTRACT FROM AUTHOR]