A Passive Compliant Gough-Whitehall-Stewart Mechanism for Peg-Hole Disassembly

Abstract

The insertion of a cylindrical peg into a cylindrical hole is often used by robotics researchers as a model for studying assembly operations. This is because many assembly operations can be represented as the mating of a male cylindrical object into a matching female object. The device was an inverted Gough-Whitehall-Stewart mechanism where the six legs were springs instead of actuators. This paper presents a modified version of the device where the legs do not meet in pairs at the platform but at points located remotely from it. This gives the device the properties of a remote-compliance-centre (RCC) mechanism, which has been shown to be effective for precise peg-hole assembly tasks. However, unlike currently available RCC mechanisms, which can only withstand high compressive forces, the proposed compliant device can resist both compressive and tensile forces, which makes it applicable to assembly as well as disassembly operations. Using small motion approximations, the paper derives the compliance matrix of the mechanism and determines the location at which it is diagonal, proving that the compliance centre is situated away from the platform. A sensitivity analysis has confirmed the correctness of the small motion assumptions and the RCC properties of the new compliance device.