sábado, 24 de julio de 2010

Ring Gyroscope


This Ring Gyroscope is constructed from an outer ring, eight semicircular support springs, drive, sense and control electrodes, see Figure 1. The Gyroscope has two identical elliptically-shaped flexural-modes of that are of equal frequency and separated by a 45 degree angle, see Figure 2. The ring is excited electrostatically into the primary flexural mode, and held at a fixed amplitude. As device is subjected to rotation around its normal axis, Coriolis force causes energy to be transferred from the primary mode to the secondary mode, causing the secondary mode amplitude to increase. This amplitude change is sensed capacitively.

Figure 2: The first and second modes of the gyroscope. (a) first flexural mode, and (b) second flexural mode located 45 degrees apart from the first. Both modes have the same frequency.


Architect can be used to build a fully parametric 3D model of the Gyroscope using beams and electrodes from the Parameterized ElectroMechanical (PEM) parts library. Figure 3 shows the schematic of the Gyroscope. In the schematic, a sub-assembly has been used to represent the eight springs in the gyroscope. This makes it easier to construct and understand the schematic. Figure 3a shows the top level schematic while figure 3b shows the lower level hierarchical element. The semicircular support spring is modeled using a combination of 'Arc beam' and 'Beam' components from the PEM parts library.

Figure 3: Hierarchical Ring Gyroscope schematic in Architect, (a) top level schmatic  and (b) lower level hierarchical elements

Figure 4 shows the frequency response of the Gyroscope, generated via a small signal ac analysis. The frequency at which the Gyroscope has flexural modes is 27.085 KHz. The simulation time for this analysis is ~1 second on a 2 GHz laptop. Figure 5 shows an animation of the flexural mode shape at the resonant frequency, created using Scene3D.

Note that process variations can cause asymmetry in the ring structure which will lead to separation of the modes. Architect can help you understand the separation in resonances with process variation.
Figure 4: Small signal ac analysis result showing the displacement magnitude response at 27087 Hz

Figure 5: Animation showing first flexural mode. For clarity, the displacement is scaled up by a factor of 5000

Nombre: Lenny D. Ramirez C.
Asignatura: CRF
Dirección: http://www.coventor.com/mems/applications/Ring_gyroscope.html
Ver blogg: http://lennyramirez-crf3.blogspot.com/

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