Considering Boundary Conditions in the Design of Compliant Mechanisms With Desired Force Profiles

Compliant mechanisms can be designed to exhibit a variety of force–deflection curves. Demonstrating a specific force behavior is an integral part of many of their applications. In this work, we select several fundamental force profiles and present compliant mechanisms that can achieve them. These force profiles are predicted using mathematical models that assume specific boundary conditions. When creating physical mechanisms, it can be often difficult to create ideal boundary conditions, particularly for mechanisms that experience axial forces. This is demonstrated first through a cantilever beam, which exhibits a linear force profile and experiences no axial forces so its boundary conditions and expected force profile are relatively easy to achieve. A more complicated case that does experience compressive axial forces—a mirrored parallel-guiding mechanism—is then examined to demonstrate its greater difficulty in achieving ideal boundary conditions. The effects of nonideal boundary conditions are then systematically explored to determine how altering specific boundary conditions from a mirrored parallel-guiding mechanism significantly alters its force profile. We also demonstrate how achieving specific force profiles is affected by factors that are difficult to control, including a small difference in force application location. Using these methods, a designer can select a compliant mechanism to achieve a specific force profile and can better predict how the force profile is affected by testing and boundary conditions.