A FLEXURE BALANCE WITH ADJUSTABLE RESTORING TORQUE FOR NANONEWTON FORCE MEASUREMENT

Jon R. Pratt, David B. Newell, John A. Kramar

Abstract

The NIST electrostatic force balance compares mechanical probe forces to an SI realization of force derived from measurements of the capacitance gradient and voltage in an electronic null balance. As we approach the nanonewton regime, the finite stiffness of the guiding flexure in the balance becomes a limiting factor. Here, we consider an equal arm balance mechanism constructed using flexure pivots as an alternative to the compound rectilinear spring of the present design. We review how the sensitivity of such mechanisms can be adjusted either by manipulating the center of gravity, or by applying a negative restoring torque using a spring. We examine tradeoffs associated with tuning the stiffness of these mechanisms with regards to tilt sensitivity and various nonideal flexure behaviors. Results obtained with a prototype mechanism are presented.

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IMEKO-TC3-2002-030.pdf

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IMEKO TC

TC3 - Measurement of Force, Mass, Torque, and Gravity

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