Читать книгу Whole-Angle MEMS Gyroscopes - Doruk Senkal, Andrei M. Shkel - Страница 17

Degenerate mode gyroscopes utilize two symmetric modes for detecting angular rotation. For an ideal degenerate mode gyroscope, these two modes have identical stiffness and damping; for this reason typically an axisymmetric or – symmetric structure is used, such as a ring, disk, wineglass, etc. Degenerate mode gyroscopes are commonly employed in two primary modes of instrumentation: (i) force‐to‐rebalance (FTR) (rate) mechanization and (ii) whole‐angle mechanization.

In FTR mechanization, an external force is applied to the vibratory element that is equal and opposite to the Coriolis force being generated. This is a rate measuring gyroscope implementation, where the magnitude of externally applied force can be used to detect angular velocity. The main benefit of this mode of operation is to boost the mechanical bandwidth of the resonator, which would otherwise be limited by the close to zero drive‐sense separation () of the degenerate mode gyroscope.

In the whole‐angle mechanization, the two modes of the gyroscope are allowed to freely oscillate and external forcing is only applied to null the effects of imperfections such as damping and asymmetry. In this mode of operation the mechanical element acts as a “mechanical integrator” of angular velocity, resulting in an angle measuring gyroscope, also known as a Rate Integrating Gyroscope (RIG).

Whole‐angle gyroscope architectures can be divided into three main categories based on the geometry of the resonator element: (i) lumped mass systems, (ii) ring/disk systems, and (iii) micro‐wineglasses. Ring/disk systems are further divided into three categories: (i) rings, (ii) concentric ring systems, and (iii) disks. Whereas, micro‐wineglasses are divided into two categories according to fabrication technology: surface micro‐machined and bulk micro‐machined wineglass gyroscope architectures, Figure 1.2 [2].

String and bar resonators can also be instrumented to be used as whole‐angle gyroscopes, even though these types of mechanical elements are typically not used at micro‐scale due to limited transduction capacity. In principle, any axisymmetric elastic member can be instrumented to function as a whole‐angle gyroscope.