The bulk silicon etch process and unique patented ring design enable close tolerance geometrical properties for precise balance and thermal stability and, unlike other MEMS gyros, there are no small gaps to create problems of interference and stiction. Below are two videos, diagrammatically showing the resonance of the silicon MEMS ring.
The first show the gyro powered, but not rotating i. In the second video, the gyro is now subjected to an angular rate input. The net effect of this is to move the vibrating mode around the ring, to an angle which is proportional to the rotational velocity. The rotational velocity can be measured in two ways i by detecting the amount by which the previously nodal points now move — termed open loop measurement or ii by establishing a restoring force which keep the ring vibration mode in the original place on the ring — termed closed loop measurement.
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Ankush Wawoo Follow. Laser ignition in IC Engines. Related Books Free with a 30 day trial from Scribd. MEMS sensors often are smaller, lower power, and lower cost than discrete sensor equivalents. In addition, they can also integrate signal conditioning circuitry in the same semiconductor package. However, there is still a need for additional degrees of freedom to precisely measure movement of the system in harsh environment applications where the end product can be subjected to severe shock, vibration, and violent motion.
This type of abuse can cause undue wear and early failure of the system, incurring high cost in maintenance or downtime. MEMS gyroscopes measure angular rate by means of Coriolis acceleration. The Coriolis effect can be explained as follows, starting with Figure 1. Consider yourself standing on a rotating platform, near the center.
Your speed relative to the ground is shown as the blue arrow lengths. If you were to move to a point near the outer edge of the platform your speed would increase relative to the ground, as indicated by the longer blue arrow. The rate of increase of your tangential speed, caused by your radial velocity, is the Coriolis acceleration. Figure 1. Coriolis acceleration example. A person moving northward toward the outer edge of a rotating platform must increase the westward speed component blue arrows to maintain a northbound course.
The acceleration required is the Coriolis acceleration. This is half of the Coriolis acceleration. The ADXRS takes advantage of this effect by using a resonating mass analogous to the person moving out and in on a rotating platform.
The mass is micromachined from polysilicon and is tethered to a polysilicon frame so that it can resonate only along one direction. Figure 2 shows that when the resonating mass moves toward the outer edge of the rotation, it is accelerated to the right and exerts on the frame a reaction force to the left.
When it moves toward the center of the rotation it exerts a force to the right, as indicated by the green arrows. Figure 2. Demonstration of Coriolis effect in response to a resonating silicon mass suspended inside a frame.
The green arrows indicate the force applied to the structure based on status of the resonating mass. This figure also shows the Coriolis sense fingers that are used to sense displacement of the frame through capacitive transduction in response to the force exerted by the mass.
As the rate of rotation increases, so does the displacement of the mass and the signal derived from the corresponding capacitance change. It should be noted that the gyroscope may be placed anywhere on the rotating object and at any angle, so long as its sensing axis is parallel to the axis of rotation. Figure 4.
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