How Gyroscope Capacitors Works?

[Carl Fredrik Ahl]

Hi,

In this video (



Look from 3:30) they show how they use capacitors in gyroscopes. I wonder how these capacitors operate with the masses of the gyroscope.

[Strange]

Not sure what your question as the explanation in the video seems quite clear: when the device is rotated, the Coriolis force causes the vibrating system to deform which moves the two capacitor plates and changes the capacitance.

There is a more detailed description here (of a slightly different structure) which includes videos showing animations of the change in the movement of the vibrating part when it is rotated: https://www.siliconsensing.com/technology/mems-gyroscopes/

[Carl Fredrik Ahl]

1 hour ago, Strange said:

Not sure what your question as the explanation in the video seems quite clear: when the device is rotated, the Coriolis force causes the vibrating system to deform which moves the two capacitor plates and changes the capacitance.

There is a more detailed description here (of a slightly different structure) which includes videos showing animations of the change in the movement of the vibrating part when it is rotated: https://www.siliconsensing.com/technology/mems-gyroscopes/

Thx! I meant how the capacitor gets the different charges depending on how far away the masses are.

[Strange]

So the capacitance is proportional to the area of the plates (which in this case doesn't change) and inversely proportional to how far apart the plates are. (In other words, the closer together they are, the higher the value of the capacitance.)

One of the plates is the vibrating mass that you can see in the video. The other plate is fixed on the surface of the silicon underneath the mass. As the gyroscope rotates, the vibrating mass is forced downwards (by the Coriolis force) making the gap between the plates smaller and hence increasing the capacitance. The other mass moves up, making the capacitance smaller.

There are various ways of measuring the value of the capacitance and I don't know what they use in this circuit. Typically, you measure the time it takes to charge the capacitor or the frequency of a resonant circuit containing the capacitor.

[Carl Fredrik Ahl]

On 11/30/2018 at 6:38 PM, Strange said:

Typically, you measure the time it takes to charge the capacitor or the frequency of a resonant circuit containing the capacitor.

Can you explain this in more detail please? I don't understand how the capacitor get charged. I understand everything else.

[Strange]

53 minutes ago, Carl Fredrik Ahl said:

Can you explain this in more detail please? I don't understand how the capacitor get charged. I understand everything else.

Well, I don't know much more detail I'm afraid. There will be circuitry on the chip as well as the mechanical structures. They will control the vibration of the mechanism and, presumably, charge the capacitors to measure the changing capcatince value. But I don't know exactly how they do that (without trying to find a detailed data sheet of the device).