Comparison of milligram scale deadweights to electrostatic forces

This paper presents a comparison of milligram scale deadweights to electrostatic forces via an electrostatic sensing & actuating force measurement system. The electrostatic sensing & actuating force measurement system is designed for measuring force below 200 mN with an uncertainty of few nanonewton. The force measurement system consists of three main components: a monolithic flexure stage, a three-electrode capacitor for position sensing and actuating and a digital controller. The principle of force measurement used in this system is a static force balance, i.e. a force to be measured is balanced by a precisely controlled, electrostatic force. Four weights of 1 mg to 10 mg were tested in this comparison. The results of the comparison showed that there exist extra stray electrostatic forces between the test weights and the force measurement system. This extra electrostatic force adds a bias force to the measurement result, and was different for each weight. In principle, this stray electrostatic force can be eliminated by installing a metal housing to isolate the test weight from the system. In the first section, we briefly introduce the electrostatic sensing and actuating force measurement system, and then we describe the experimental setup for the comparison and the results. Finally, we give a discussion and outlook.