Ring-Based Stiffening Flexure Applied as a Load Cell With High Resolution and Large Force Range

This paper presents the theory of nonlinear (stiffening) flexures applied to a load cell to achieve both large force range and large resolution. Low stiffness at small forces causes high sensitivity while high stiffness at high forces prevents over-straining. With a standard 0.1 μm deflection sensor, the nonlinear load cell may detect 1% changes in force over 5 orders of force magnitude. In comparison, a traditional linear load cell functions over only three orders of magnitude. We physically implement the nonlinear flexure as a ring that increasingly contacts rigid surfaces with carefully chosen curvatures as more force is applied. We analytically describe the load cell performance as a function of its geometry. We describe methods for manufacturing the flexure from a monolithic part or multiple parts. We experimentally verify the theory for two load cells with different parameters.