Biologically Inspired Joint Stiffness Control

Exploiting sensorimotor stochasticity for learning control of variable impedance actuators

“…Because forces produced through springs with linear tension to force characteristics tend to cancel out in an antagonistic setup, an increase in the tension of both springs (i.e., co-contraction) does not change the stiffness of the system. Commercially available springs usually have linear tension to force characteristics and consequently most antagonistic SEA require relatively complex mechanical structures to achieve a nonlinear tension to force curve [8], [14]. These mechanisms typically increase construction and maintenance effort but also can complicate the system identification and controllability, for example, due to added drag and friction properties.…”

Teleoperation of Pneumatic Artificial Muscles Based on Joint Stiffness of Master Device

“…에서는 관절의 강성과 위치를 동시에 조절하는 공압인공근육 이하 (Pneumatic Artificial Muscle; PAM), (5,6) 가변강성 구동기 등 (variable stiffness) (7,8) 이 적용되고 있다 그리고 마스터장치에 있어서 . 도 기존의 각도변위 덧붙여 인간근육의 강성까지 전달해야 하는 필요성을 충족하기 위해 근전도센 서 근육경도센서 등 ,…”

Variable-stiffness joints with embedded force sensor for high-performance wearable gait exoskeletons

“…Dynamic control of joint stiffness is crucial for humans to adapt to changes in environmental conditions [38]. Muscles in biological systems modulate the stiffness and position of the joint achieving high adaptability, force transmission and significant reduction of energy expenditure [15].…”

“…Joint compliance is a function of muscular co-contraction given that an increase in a muscle's activation increases the number of parallel elastic elements used by the muscle, which raises the muscle's stiffness. To emulate this behavior, the elastic elements must have a nonlinear force-length relationship [38]. This allows the joint to have a great range of variable rigidity, if both muscles act at the same time an isometric action (without motion) takes place and the joint achieves high rigidity, if only one muscle is activated the joint will be moved to one side, if both muscles are deactivated the joint will show a free motion only with the rigidity of the tissues that compose the muscles.…”

“…In this case, the need for feedback is removed, but the joint stiffness becomes a constant function of the mechanical elements used in the robotic device and is therefore not controllable. A more advanced version of this implementation uses variable stiffness elastic elements to dynamically control joint compliance [38].…”