Design Considerations for 3RRR Parallel Robots with Lightweight, Approximate Static-Balancing

TL;DR

This paper presents a method for achieving approximate static balancing of 3RRR parallel robots using torsional springs and wire-wrapped cam mechanisms, optimizing base placement and spring positioning for lightweight medical robot designs.

Contribution

It introduces a novel approach combining modal analysis and cam mechanism design to enhance static balancing without additional masses in lightweight medical robots.

Findings

Optimal spring placement at actuated joints improves balancing.

Wire-wrapped cam mechanisms significantly enhance balancing performance.

Base placement impacts the feasibility of practical balancing solutions.

Abstract

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.