sábado, 24 de julio de 2010

Dual Mass Gyroscope


This dual mass gyroscope consists of two perforated proof masses supported by a system of suspension elements. Attached to the ends of each proof mass are interdigitated comb-finger capacitors. The comb capacitors are used for electrostatically driving the proof masses in anti-phase in a mode parallel to the substrate (the x direction). Rotation about the in-plane y-axis induces a Coriolis force, which deflects the proof masses in opposite directions, perpendicular to the substrate. Beneath the plates are deposited metal electrodes that are biased with a DC voltage. The proof mass motion in the z direction, resulting from the rotation of the gyroscope, induces current flow on the electrodes, which is then measured. Figure 1 shows the 3-D model of the gyroscope.

Figure 1: 3D model of the dual mass gyroscope. For clarity, the model has been scaled factor of 2 in the Z direction


In this example, Architect is employed to build a fully parametric, 3-D model of the gyroscope using plates, beams, electrodes and comb-finger elements from the Parameterized Electromechanical (PEM) parts library. Figure 2 shows the Architect schematic of the gyroscope.

Figure 2: Architect schematic of dual mass gyroscope

The perforated proof masses are modeled using components labeled "Rigid Plate". Similarly, the electrodes beneath the proof masses, which sense the proof mass motion, are modeled by components labeled "Electrode". The comb drives on either side of the two proof masses are modeled by "Straight Comb" components. The suspension elements for the proof masses are modeled using a combination of "Box-beam" and "Beam" components. Note that the Architect PEM parts library has a variety of beam-like suspensions structures, and a single "Box-Beam" element could therefore be used instead of using four rectangular "Straight" beams.

Figure 3a shows the simulated displacement of the proof mass in the x and z direction over a period of 50ms. Figure 3b shows the first 5ms only. The simulation starts from the steady state, computed with a small signal AC analysis. The excitation voltages applied to the comb-drives vibrates the proof masses in the x direction at a frequency of 16.987 KHz. Angular velocity applied about y direction, after 1ms, induces a Coriolis force that causes proof mass motion in the z direction. This motion is sensed by measuring the difference in capacitance, "Delta Cap" in the output plot, between the two sensing electrodes. After 25ms the rotation rate about the y axis returns to zero, and the output signal decreases to a steady-state value. In this simulation modal (Rayleigh) damping models are used for the beam and velocity damping values used for the plate. The fully coupled electro-mechanical 50ms simulation takes about 1 hr to run on a 2 GHz processor.

Figure 3a: Gyroscope transient simulation showing input rotation about y, sense capacitance "delta cap", (right) mass displacement "x" and "z".

Figure 3b: Gyroscope transient simulation from (a) with response from 0 to 5.0ms.

Figure 4: Animation of transient simulation. For clarity, the fixed electrodes and the comb drives are transparent and the thickness scaled by 2. The displacement in Z is also scaled by a factor of 1,00,000 to allow the movement of the gyroscope to be resolved.

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

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