Angular Rate Sensors (Gyros)

Motion has six degrees of freedom: translations in three orthogonal directions and rotations around three orthogonal axes. The latter three are measured by an angular rate sensor, also known as a gyroscope or, simply, a gyro. A gyro is based on Newton's second law, just like an accelerometer. When rotation is added to Newton's equations a mathematical term appears that describes a virtual force called the Coriolis force. Converting rotation to Coriolis force is the basis of gyro operation. A primary or a seed motion is needed in a gyro; the Coriolis force is the result of two orthogonal motions and is orthogonal to both of them.

In MEMS gyros the primary motion cannot be continuous rotation as in conventional ones due to a lack of good bearings in MEMS. Instead, mechanical oscillation is used as the primary motion. When the oscillating gyro is subjected to angular rate orthogonal to the direction of the primary motion, an undulating Coriolis force results. This creates a secondary oscillation orthogonal to the primary one and to the axis of the angular rate and at the frequency of the primary oscillation. The amplitude of this coupled oscillation is the measure of the angular rate, and in Murata Electronis Oy's gyro it is detected capacitively.

Murata Electronics Oy's one-axis gyros are based on the most robust and sound design principles available. They eliminate most of the spurious responses and susceptibility to vibration that plague many MEMS gyro designs. Murata has been able to patent these innovative gyros for both horizontal and vertical sensing axes. They are used in automotive and other high precision gyros.

Murata Electronics Oy's three-axis gyro is based on a single complex oscillation mode as the primary motion for all three axes. Each axis is sensed separately. The interface electronics is based on a novel concept of phase detection, which has enabled the smallest circuit size among consumer grade gyros. These gyros are used in user interface control and optical image stabilization.
 

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