High sensitivity accelerometer operating on the border of stability with digital sliding mode control

We propose a novel sliding mode control (SMC), implemented on FPGA, for robust stabilization and high sensitivity operation of a capacitive micro-accelerometer on the pull-in border of stability. SMC feedback enforces a maximum sensitivity position of the proof mass in a normally unstable equilibrium, while the value of the external acceleration is extracted from the “chattering” noise bitstream produced by the controller action. Experimental results show a stabilization of the proof mass at the pull-in position and a measurement of small accelerations. The proposed technique, implemented in LabView and FPGA hardware, represents a promising alternative for the digital control of capacitive MEMS devices, with a lighter implementation footprint than common sigma-delta approaches used for inertial sensors.