High speed high accuracy active force transducer

Abstract

A force transducer and method of measuring an applied force such as a weight of material, comprising a balance beam, said balance beam being supported at a preset position on a base at a fulcrum between its two ends, a voice coil actuator comprising an electrically conductive coil and a magnet, the coil being mounted on the base and the magnet being mounted on one side of the fulcrum of the balance beam, a counterbalance mounted on the second side of the fulcrum of the balance beam whereby said balance beam is generally unresponsive to low frequency vibration at the base, a beam position sensor for detecting beam movement from its preset position by a force applied to the beam, a control system associated with the sensor and coil and responsive to the sensor for supplying an electric current through the coil in an amount sufficient to maintain the magnet and thereby the beam at the present position, and a current detector for measuring the amount of current so supplied and thereby the amount of the applied force. According to one embodiment, the conductive coil and magnet are located on the same side as the object to be weighed. A force concentration assembly may further concentrate the force to be weighed to a small-area on said balance beam. According to another embodiment, a double-beam force transducer is provided in which force of an object to be weighed is applied to a pair of balance beams.