Design, fabrication, and calibration of a micro-load cell for micro-resistojet development

In this paper, a micro-load cell utilized for the thrust measurement of a micro-resistojet is described. To improve the degree of completion of the micro-resistojet during the development process, a concept of a micro-load cell, which enables sufficient performance evaluation under space environmental conditions, was proposed through minimization and simplification of a thrust measurement stand. The piezoresistive sensing method was applied to this load cell, which was composed of a membrane, strain gauges, and a built-in Wheatstone bridge. The membrane size was designed using large-deflection theory so that the load cell could exhibit linear characteristics within the measurement range. A polysilicon strain gauge with a high gauge factor was used for the piezoresistor. The strain gauge also had very low sensitivity to temperature, allowing accurate measurement of the membrane deflection caused by thrust without requiring an additional compensation circuit. Four strain gauges were placed to form a full-bridge circuit at the edge of the membrane. The load cell was then realized by a microelectromechanical system fabrication process. The fabricated load cell was calibrated using a three-axis precision moving stage and a commercial load cell. As a result, the load cell output signal was linear in the measurement range of 1-7 mN and the measured sensitivity of the sensor was 1.566 31 × 10^-4 V/mN. The calculated nonlinearity was within 1% in the measurement range.