Design of an engaging-disengaging compliant mechanism by using bistable arches

TL;DR

The paper addresses enabling switchable stiffness in compliant mechanisms by introducing an engaging-disengaging compliant mechanism (EDCM) built from bistable arches with a locking element. It develops analytical design relations for central and side arches, using the switching force $f_s$ and travel $u_{tr}$ with the key condition $f_s l^3/(E I h_{mid})=1486.57$ and $u_{tr}/h_{mid}=1.98$, then validates the design through ABAQUS FEA with $E=2.4$ GPa Onyx and a 3D-printed prototype. The final mechanism, featuring four EDCMs with two side arches and a central arch, achieves substantial rigidity in the locked state while allowing easy toggle to the unlocked state, supported by FEA and experimental prototyping. This approach enables practical deployment of engaging-disengaging behavior in segments of existing compliant mechanisms and offers potential applications in biomechanical assays, shock/isolation, and metamaterial fabrics.

Abstract

Compliant mechanisms utilise elastic deformation of their segments to transmit motion or force. The utility and behaviour of specific compliant mechanisms can be enhanced by introducing an engaging and disengaging ability with its elastic segments. Towards this, we present an engaging-disengaging compliant mechanism (EDCM) that can switch its stiffness between infinite and zero. The design of the EDCM is based on bistable arches and a locking mechanism. We describe its working, identify its design parameters, and use analytical expressions to arrive at its dimension. The design is verified by detailed finite element analysis and experiments on a 3D-printed prototype. Three alternate designs that lead us to the final mechanism are also briefly discussed.

Figures (12)

• Figure 1: EDCM engages and disengages to (b) transfer and (c) not transfer motion between points A and B.
• Figure 2: EDCM with (a) EDCMS in locked state (b)EDCMS in free state
• Figure 3: Preliminary designs: Fig. 3 a-c show the first design which is able to resist deformation only for small loads. Fig. 3 d-e show the second design, which reduces the resistance for the clip return but has imperfect locking due to its geometry. Fig. 3 f-g show the third design, in which the resistance for return was further reduced.
• Figure 4: The labelled schematic of the final mechanism.
• Figure 5: The stable states of Final design. (a) The first stable state of the mechanism when the lock is switched off, (b) The first stable state of the mechanism in which any deformation is resisted as the lock is switched on, and (c) The second stable state.