Balancing parallel robots throughout their workspace while avoiding the use of balancing masses and respecting design practicality constraints is difficult. Medical robots demand such compact and lightweight designs. This paper considers the difficult task of achieving optimal approximate balancing of a parallel robot throughout a desired task-based dexterous workspace using balancing springs only. While it is possible to achieve perfect balancing in a path, only approximate balancing may be achieved without the addition of balancing masses. Design considerations for optimal robot base placement and the effects of placement of torsional balancing springs are presented. Using a modal representation for the balancing torque requirements, we use recent results on the design of wire-wrapped cam mechanisms to achieve balancing throughout a task-based workspace. A simulation study shows that robot base placement can have a detrimental effect on the attainability of a practical design solution for static balancing. We also show that optimal balancing using torsional springs is best achieved when all springs are at the actuated joints and that the wire-wrapped cam design can significantly improve the performance of static balancing. The methodology presented in this paper provides practical design solutions that yield simple, lightweight and compact designs suitable for medical applications where such traits are paramount.

翻译：在整个工作空间内平衡并联机器人，同时避免使用配重块并满足设计实用性约束是一项难题。医疗机器人对此类紧凑型轻量化设计具有迫切需求。本文探讨了仅利用平衡弹簧在基于任务的灵巧工作空间内实现并联机器人最优近似平衡的难点。尽管可在特定路径上实现完全平衡，但若不增加配重块，仅能实现近似平衡。本文提出了机器人基座最优放置的设计考量，并分析了扭力平衡弹簧布置的影响。通过建立平衡力矩需求的模态表示，我们运用近期关于绕线凸轮机构设计的研究成果，实现了基于任务工作空间内的平衡。仿真研究表明，机器人基座放置会对静平衡实际设计方案的可行性产生不利影响。我们还发现，当扭力弹簧全部安装于驱动关节时，可达到最优平衡效果，且绕线凸轮设计能显著提升静态平衡性能。本文提出的方法体系可提供简洁、轻量化且紧凑的实用设计方案，特别适用于对上述特性有严格要求的医疗应用场景。