Compliant Activatable Neutrally Stable Joint

Abstract

Active materials are a type of material that can respond to external stimuli and change their physical properties as a response. Neutrally stable compliant mechanisms are a class of compliant mechanisms that use the flexibility of their members to deform and maintain that deformed configuration without requiring external work. In order to make a compliant mechanism neutrally stable, pre-stress is required. In most cases, this pre-stress is applied when the neutrally stable compliant mechanisms are being made. Therefore, neutrally stable compliant mechanisms are always in a zero-stiffness state. In this research, a new Compliant Active Neutrally Stable joint (CANS-J) is developed in which this pre-stress can be turned on and off using active materials. This means that the joint can switch between a stiff state and a zero-stiffness state. This change in the stiffness is realized by a Flexinol SMA wire. A Flexinol wire can contract when it is heated. This active behavior of the Flexinol wire is used to turn on and off the pre-stress when required. Results show that the CANS-J shows behavior which is close to neutral stability in the active state with a significant range of motion. The CANS-J can for instance be used to transport a satellite with solar panels to its orbit around the world. During transportation the solar panels are folded for which the joints are required to be in a stiff state. In orbit, the solar panels are unfolded for which the joints are required to have zero stiffness.