A Comparison of the Capacity for Precise Motion Control Between Hinged Joints and Flexure Joints

Abstract

Hinged joints are ubiquitous in machine and mechanism design where components must rotate relative to one another. Their simplicity and reliability, coupled with limited alternatives, make them an obvious choice. However, the propensity of such joints to exhibit unpredictable discontinuities in their operation can limit the precision with which a mechanism incorporating such a joint can be controlled. In particular, almost all hinged joints experience some degree of both backlash and stiction. An alternative to hinged joints in many applications may be the use of large-displacement flexure-link joints. The use of flexure joints in micro-mechanisms is already an established practice, but their use in joints with large angular displacements (e.g. 30 degrees) is far less common. Such joints are inherently non-linear, and introduce more complex motion than simple hinges, but they offer the considerable advantage of highly predictable behaviour, without the exhibition of discontinuities. These characteristics open the way to increased mechanism precision and repeatability, and consequent new possibilities in machine design. This work makes a comparison of the precision which can be achieved when controlling similar mechanisms employing each of i) a realistic hinged joint, and ii) a large-displacement flexure-link joint. The modeling techniques used to represent each mechanism are discussed, and a series of results are presented illustrating the performance and prospects for precision motion of each system.