A major field of industrial robot applications deals with repetitive tasks that alternate between operating points. For these so-called pick-and-place operations, parallel kinematic manipulators (PKM) are frequently employed. These tasks tend to automatically run for a long period of time and therefore minimizing energy consumption is always of interest. Recent research addresses this topic by the use of elastic elements and particularly series elastic actuators (SEA). This paper explores the possibilities of minimizing energy consumption of SEA actuated PKM performing pick-and-place tasks. The basic idea is to excite eigenmotions that result from the actuator springs and exploit their oscillating characteristics. To this end, a prescribed cyclic pick-and-place operation is analyzed and a dynamic model of SEA driven PKM is derived. Subsequently, an energy minimizing optimal control problem is formulated where operating trajectories as well as SEA stiffnesses are optimized simultaneously. Here, optimizing the actuator stiffness does not account for variable stiffness actuators. It serves as a tool for the design and dimensioning process. The hypothesis on energy reduction is tested on two (parallel) robot applications where redundant actuation is also addressed. The results confirm the validity of this approach.

翻译：工业机器人应用的一个重要领域涉及在操作点之间交替进行的重复性任务。对于这类所谓的拾放操作，并联运动机械臂（PKM）被广泛采用。此类任务通常需要长时间自动运行，因此最小化能耗始终是关注的焦点。近期研究通过引入弹性元件，特别是串联弹性驱动器（SEA）来探讨这一课题。本文研究了在执行拾放任务的SEA驱动PKM中实现能耗最小化的可能性。其基本思想是激发由驱动器弹簧产生的本征运动，并利用其振荡特性。为此，本文分析了预设的周期性拾放操作，推导了SEA驱动PKM的动力学模型。随后，构建了一个能量最小化的最优控制问题，其中同时优化了操作轨迹与SEA刚度。需说明的是，此处优化驱动器刚度并非针对可变刚度驱动器，而是作为设计与尺寸确定过程的工具。该能耗降低假设在两个（并联）机器人应用案例中进行了验证，其中也涉及冗余驱动问题。结果证实了该方法的有效性。