A compliant gripper with integrated twisted-coiled polymer muscles
Loke, Siu Chung
Date of Issue2019-07-09
School of Mechanical and Aerospace Engineering
Robotics Research Centre
The field of soft robotics has emerged as a viable complement to conventional industrial robotics. Soft robotics does not displace industrial robots from their traditional roles, but extends the benefits of robotic technology into fields where traditional robots have proven inadequate. The foundation of a robot’s ‘softness’ is derived from its structure and actuation mechanism(s). The twisted coiled polymer (TCP) artificial muscle, discovered in recent years by Haines, has shown promise as a potential solution to the actuation needs of such soft robots. This study aims to characterise the properties and behaviour of TCP actuators, and the precursor fibres used to make them. To that end, a twist insertion rig and a heating element winding device were built to fabricate Joule heated TCP actuators while a tensile actuator test rig was constructed for the characterisation work. An optimal heating element insertion method was identified through testing; the TCPs thus produced are capable of maximal strokes of 27%, matching the best performance of even TCPs without inserted heating elements. In a first such study, the effect of fibre draw ratio on TCP performance was investigated and the results presented. Based on the foundation work conducted, the specifications for a demonstrator which highlights the unique strengths of TCP artificial muscle were laid down. An intrinsically powered compliant gripper design capable of multiple degrees of freedom motions was chosen to demonstrate the close integration of a network of lightweight artificial muscle with an adaptive structure. A breakdown of the design thought process, as well as the analytical basis for the design features which serve as the building blocks for the compliant gripper, is detailed in this report. The compliant gripper was 3D printed in PETG and successfully assembled with the TCP muscles. The gripper comprises a parallel opening/closing jaw and a rotating jaw. The gripper is submitted to gripping tests and the results are presented.