Modeling and experimental characterization of an active MEMS based force sensor

Abstract

Active force sensors are based on the principle of force balancing using a feedback control. They allow, unlike passive sensors, the static characterization of forces without interference of the sensor mechanical properties on the estimated stiffness of the object to be studied. This capability is fundamental when dealing with the mechanical characterization of samples Q1 having a wide range of stiffness. This paper deals with the modeling and the experimental characterization of a new active MEMS based force sensor. This sensor includes Q2 folded-flexure type suspensions and a differential comb drive actuation allowing a linear force/voltage relationship. A control oriented electromechanical model is proposed and validated experimentally in static and dynamic operating modes using a stroboscopic measurement system. This work is a first step towards new MEMS active force sensor with high resonant frequency (>2kHz) and high linear measurement force range (50 µN). The advantage of this structure is to be able to change the sensor operating point without changing the sensor dynamics. Thus simplifying the control law. Modifying the operating point allows performing an accurate self positioning of the probe Q3 in close proximity to the surface to be studied.

Modeling and Experimental Characterization of an Active MEMS Based Force Sensor

“…The non linearity error is lower than 0.4 µm once measurement artifacts have been removed, this error can be due to image noise or outside vibrations. Experimental results differ by a factor 2 from the ones presented in [18] because of a faulty amplifier in the original setup which introduced an amplification 2 times higher than expected.…”