US Patent 7121642 Drop volume measurement and control for ink jet printing

A system and method is presented for measuring the volume of an ink-jet droplet or the relative volumes of a plurality of ink-jet droplets using their electrical properties. In a preferred embodiment a single small capacitor or an array of capacitors is used to measure the dielectric properties of ink-jet droplets and the absolute drop volumes are derived. In an alternative preferred embodiment the relative differences in drop volumes are determined. A feedback circuit, such as one using lock-in technique, may be used to automatically adjust subsequent drop volumes.