SiMMATM accelerometer for inertial guidance and navigation

This paper presents recent accomplishments in SiMMA^TM silicon micromachined accelerometers using vibrating beam accelerometer (VBA) technology, focusing on achieving navigation grade performance with reduced size and lower cost. Guidance and navigation system applications have continued to require smaller, lower-cost accelerometers. High reliability and long term stability in temperature modeled systems are also in demand. Available navigation grade accelerometers cannot meet all of these inertial measurement unit (IMU) requirements. Direct digital system usage of the SiMMA^TM accelerometer output reduces system level IMU cost by eliminating the need for digitizers (or A/D conversion), their analog calibration costs, resolution limitations, and their instability. High performance silicon micromachined vibrating beam SiMMA^TM accelerometers best meet these next-generation IMU accelerometer requirements. The SiMMA^TM accelerometer presented is a silicon micromachined VBA that converts an applied analog acceleration force directly into frequency modulated electronic signals for direct use in digital strapdown systems. Basic theory of operation is presented. New accelerometer development uses a monolithic single proof mass with integrated dual double-ended tuning forks (DETFs), for differential detection and improved common mode performance. Presently, accelerometer and integrated electronics are packaged in a hermetic metal case for long term reliability with gas damping for vibration control. Units have been designed and tested for programs comprising tactical (100 g) through navigation (20 g) range and performance grade applications