Augmented Virtual Stiffness Rendering of a Cable-driven SEA for Human-Robot Interaction

Human-robot interaction(HRI) is fundamental for human-centered robotics, and has been attracting intensive research for more than a decade. The series elastic actuator(SEA) provides inherent compliance, safety and further benefits for HRI, but the introduced elastic element also brings control difficulties. In this paper, we address the stiffness rendering problem for a cable-driven SEA system, to achieve either low stiffness for good transparency or high stiffness bigger than the physical spring constant, and to assess the rendering accuracy with quantified metrics. By taking a velocity-sourced model of the motor, a cascaded velocity-torque-impedance control structure is established. To achieve high fidelity torque control, the 2-DOF(degree of freedom) stabilizing control method together with a compensator has been used to handle the competing requirements on tracking performance, noise and disturbance rejection,and energy optimization in the cable-driven SEA system. The conventional passivity requirement for HRI usually leads to a conservative design of the impedance controller, and the rendered stiffness cannot go higher than the physical spring constant. By adding a phase-lead compensator into the impedance controller,the stiffness rendering capability was augmented with guaranteed relaxed passivity. Extensive simulations and experiments have been performed, and the virtual stiffness has been rendered in the extended range of 0.1 to 2.0 times of the physical spring constant with guaranteed relaxed passivity for physical humanrobot interaction below 5 Hz. Quantified metrics also verified good rendering accuracy.

基于单向饱和绳索作动器的大型太空望远镜桁架的振动主动控制

由于质量轻、易于折叠展开、光学成像精度高等显著优势,近年来大型薄膜衍射太空望远镜已经成为对地观测领域的研究热点之一.大型太空望远镜在太空中受到外界扰动或在进行姿态调整时,不可避免地会发生一定程度的振动,从而影响对地成像精度.因此,为了满足成像精度要求,有必要采取合适的控制方法来快速抑制太空望远镜的有害振动.本文采用主动绳索作为作动器对大型太空望远镜进行振动主动控制研究.由于绳索存在可受拉不可受压且受拉能力有限的特性,本文在控制设计时考虑了绳索作动器的单向性和饱和性.首先,采用有限元方法建立了薄膜衍射太空望远镜的动力学模型.其次,结合二次线性调节器和bangbang调节器,构造了一个分段代价函数来设计结构的振动主动控制律.接着,采用可控性准则和遗传算法进行了绳索作动器的最优位置布置.最后,通过数值模拟验证了所提出的控制方法的有效性.模拟结果表明,采用本文设计的控制方法可有效抑制太空望远镜的振动,并且给出了满足望远镜成像要求的绳索作动器的最少数量及其位置分布.