Active structural error suppression in MEMS vibratory gyroscopes

Due to restrictive tolerancing, structural imperfections that reduce the performance of fabricated micro devices are typical. While feedback control is normally used to compensate for these imperfections, we show that this is insufficient for suppressing errors without interfering with device performance. The only alternatives are costly and time consuming post processing or the implementation of a dual stage control architecture comprised of a feedforward and feedback control which compensates for errors without interfering with the performance of the device. In this paper, we describe the design and implementation of such a control architecture for structural error suppression in MEMS vibratory gyroscopes. The feedforward portion of the control is used to "trim" large imperfections, while the feedback portion compensates for the remaining non-idealities and perturbations. The architecture includes self-diagnostic capabilities for in situ identification of structural imperfections used to set the feedforward control forces. The realization of this dual stage control architecture is demonstrated in a device using nonlinear electrostatic parallel plate actuators. We demonstrate successful compensation for a device with 10% error in ideal stiffness subjected to a further 1% perturbation during normal operation.