Control Section Design of a Multicomponent Microforce Measurement System

This paper presents a discussion of a new approach to the problem of measuring small forces in the presence of a large tare load with emphasis on the analysis and design of the force balance servo system. The object under study is suspended by an air bearing, and the applied forces, in the plane perpendicular to the direction of the tare load, are nulled by a two-dimensional servo system with force readout supplied by measuring the required servo motor currents. Each servo loop consists of a position sensor, a compensating network, a power amplifier, and a servo motor. The criteria governing selection of these components are discussed, and detailed design information is presented. The system was found to have excellent repeatability, linearity better than 1 percent, and cross coupling between dimensions less than 1 percent.