Twisted string actuation is an actuation concept which uses the twisting motion of strings to convert the rotational motion of a motor into a linear motion. By replacing the heavy, high friction, and high-cost gearheads with light, silent, compliant, and low-cost strings, twisted string actuators (TSAs) can provide powerful tendon-based transmission, making it a unique solution for human-robot interactive tasks. Despite such advantages, TSAs exhibit highly nonlinear force/displacement characteristics when compared to conventional geared motors, thus limiting their performance in bidirectional joints. In order to implement TSAs in a bidirectional joint, two motors had to be used to compensate for the nonlinearities, which eventually increased the control complexity, weight, and overall cost of the robotic system. In addition, TSAs show poor durability, which also limits its applicability. To address these issues, a high-performance bidirectional joint has been proposed by implementing optimized TSAs with lubrication, and a variable radius pulley (VRP). By implementation of specially designed TSAs, we achieved 1) extended service time of the strings. Furthermore, by replacing the conventional circular pulley with a VRP, we achieved 2) improved range of motion; 3) increased payload; and 4) better tracking performance, even with a single motor.

中文翻译：

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双向钢丝绳和可变半径皮带轮的高度耐用双向接头

扭转弦致动是一种利用弦的扭转运动将电动机的旋转运动转换成线性运动的致动概念。通过用轻便，静音，柔顺和低成本的弦代替沉重，高摩擦和高成本的齿轮箱，扭弦促动器（TSA）可以提供强大的基于腱的传动，使其成为人机交互的独特解决方案任务。尽管具有这些优点，但与传统的齿轮电动机相比，TSA仍表现出高度非线性的力/位移特性，因此限制了它们在双向接头中的性能。为了在双向关节中实现TSA，必须使用两个电动机来补偿非线性，这最终会增加机器人系统的控制复杂性，重量和总成本。此外，TSA的耐久性差，这也限制了其适用性。为了解决这些问题，已经提出了一种高性能双向接头，方法是实施优化的带润滑的TSA和可变半径皮带轮（VRP）。通过实施特殊设计的TSA，我们实现了1）延长弦的使用寿命。此外，通过用VRP代替传统的圆形皮带轮，我们实现了2）改善了运动范围；3）增加有效载荷；和4）更好的跟踪性能，即使使用单个电动机也是如此。通过用VRP代替传统的圆形皮带轮，我们实现了2）改善了运动范围；3）增加有效载荷；和4）更好的跟踪性能，即使使用单个电动机也是如此。通过用VRP代替传统的圆形皮带轮，我们实现了2）改善了运动范围；3）增加有效载荷；和4）更好的跟踪性能，即使使用单个电动机也是如此。