Buckling-induced instability in topology optimization of compliant constant-force mechanisms

Compliant constant-force mechanisms are compliant mechanisms that provide a nearly constant force over a prescribed deflection range. Topology optimization is an effective method for compliant constant-force mechanism design. However, instabilities caused by buckling often cause the optimization algorithm to fail to converge. This study analyzes the causes of buckling -induced instability and proposes methods to avoid this instability. A mechanism with three torsional springs is proposed, and its three force-displacement curves are analyzed. These bifurcated force-displacement curves cause the optimization algorithm to be unstable. Several topology optimization models with buckling constraints are proposed for designing compliant constant-force mechanisms. Their effects are tested and analyzed in numerical examples with different target constant forces and constant-force strokes. Almost all optimization results have three hinges, corresponding to a proposed mechanism with three torsion springs. A slight change in their initial design causes a large change in the force-displacement curve, which eventually leads to buckling-induced instability. This instability can be avoided by constraining the buckling load calculated at the configuration near the start of the constant-force stroke.

Automated summary

This study analyzes the causes of buckling-induced instability and proposes methods to avoid this instability. By proposing a mechanism with three torsional springs and using topology optimization models with buckling constraints, stable compliant constant-force mechanisms can be designed.