Charles Tally

Simulation of a MEMS Coriolis gyroscope with closed-loop control for arbitrary inertial force, angular rate, and quadrature inputs

A closed-loop control system for a MEMS gyroscope is proposed which greatly restricts the mechanical freedom of the sense mass while accurately measuring the total external force acting upon the sense mass. This is realized by an algorithm which uses the previous three sense mass position measurements to generate a position-, velocity-, and acceleration-dependant feedback force on the sense mass. The feedback force is equal and opposite to the average total external force the sense mass was subject to during the previous three position samples. As the feedback sampling rate increases, so too does the control loops ability to both spatially confine the sense mass and determine the total external force acting on the sense mass. For a 1.05 MHz feedback sampling rate, we achieve a measurement of the external force with less than 5 parts per million error, and constrain the sense mass to displacements of less than 10nm.

Proposed digital, auto ranging, self calibrating inertial sensor

A novel means of measuring inertial force is proposed which converts the spatial displacement measurement of a conventional mass-on-a-spring accelerometer to a time interval measurement by harmonically oscillating the mass-on-a-spring and creating digital triggering events when the mass passes known displacement points. By curve fitting the measured time intervals into the sinusoidal nature of the harmonic oscillator, it is possible to measure acceleration without the need of adjustable parameters (such as bias and scale factor) derived by calibration. Being a function of the accuracy of the time interval measurement, the device sensitivity varies with resonant frequency, clock resolution, and oscillation amplitude. The resonant frequency of the harmonic oscillation and the oscillation amplitude can be adjusted in real time to optimize performance for a specific dynamic range.