Collaborative robots must simultaneously be safe enough to operate in close proximity to human operators and powerful enough to assist users in industrial tasks such as lifting heavy equipment. The requirement for safety necessitates that collaborative robots are designed with low-powered actuators. However, some industrial tasks may require the robot to have high payload capacity and/or long reach. For collaborative robot designs to be successful, they must find ways of addressing these conflicting design requirements. One promising strategy for navigating this tradeoff is through the use of static balancing mechanisms to offset the robot's self weight, thus enabling the selection of lower-powered actuators. In this paper, we introduce a novel, 2 degree of freedom static balancing mechanism based on spring-loaded, wire-wrapped cams. We also present an optimization-based cam design method that guarantees the cams stay convex, ensures the springs stay below their extensions limits, and minimizes sensitivity to unmodeled deviations from the nominal spring constant. Additionally, we present a model of the effect of friction between the wire and the cam. Lastly, we show experimentally that the torque generated by the cam mechanism matches the torque predicted in our modeling approach. Our results also suggest that the effects of wire-cam friction are significant for non-circular cams.

翻译：协作机器人必须同时满足两个要求：一是足够安全，能够与操作人员近距离协作；二是具备足够动力，协助用户完成提升重型设备等工业任务。安全性要求协作机器人的执行器采用低功率设计，然而某些工业任务可能需要机器人具有高负载能力和/或长臂展。成功的协作机器人设计必须解决这些相互冲突的设计需求。应对这一权衡的一种有前景的策略是采用静态平衡机构来抵消机器人自身重量，从而允许选择低功率执行器。本文提出一种基于弹簧加载绕线凸轮的新型二自由度静态平衡机构，同时介绍了一种基于优化的凸轮设计方法，该方法可保证凸轮保持凸形、确保弹簧不超过其伸长极限，并最小化标称弹簧常数未建模偏差的敏感性。此外，我们建立了钢丝与凸轮之间摩擦效应的模型。最后，通过实验证明凸轮机构产生的扭矩与我们建模方法预测的扭矩相吻合，实验结果表明钢丝-凸轮摩擦效应对非圆形凸轮的影响显著。