Vibrating structure gyroscope

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In science, a vibrating structure gyroscope is a type of gyroscope that functions much like the halteres of insects. Miniaturized devices on this principle can be used as a relatively inexpensive type of Attitude indicator.

The physical principle is very simple: a vibrating object tends to keep vibrating in the same plane as its support is rotated. It is therefore much simpler and cheaper than is a conventional rotating gyroscope of similar accuracy.

In the engineering literature, this type of device is also known as a Coriolis vibratory gyro because as the plane of oscillation is rotated, the response detected by the transducer results from the coriolis term in its equations of motion ("Coriolis force").

1 Theory of Operation
2 Implementations
3 Applications
4 References
5 External links

[edit] Theory of Operation

Consider two proof masses vibrating in plane (as in the MEMS gyro) at frequency $ω r$ . Recall that the Coriolis effect induces an acceleration on the proofmasses equal to $a_c = -2(v\times\Omega)$ , where $v$ is velocity and $Ω$ is the angular rate of rotation. The inplane velocity of the proofmasses is given by: $X i p ω r cos(ω r t)$ , if the in-plane position is given by $X i p sin(ω r t)$ . The out of plane motion $y o p$ , induced by rotation, is given by:

$y_{op} = \frac{F_c}{k_{op}} = \frac{2m\Omega X_{ip} \omega_r \cos(\omega_r t)}{k_{op}}$

m

is the mass of the proofmass

k o p

is the spring constant in the out of plane direction

Ω

is magnitude of a rotation vector in the plane of and perpendicular to the driven proofmass motion

[edit] Implementations

[edit] Piezoelectric gyroscope

A piezoelectric material can be induced to vibrate, and lateral motion due to coriolis force can be measured to produce a signal related to the rate of rotation ^[1].

[edit] Wine glass resonator

Also called the hemispherical resonator gyro, or the HRG. Hemisphere driven to resonance and nodal points measured to indicate rotation.

[edit] Tuning fork gyroscope

A pair of test masses are driven to resonate and their displacement from the plane of oscillation is measured to produce a signal related to the rate of rotation.

[edit] Vibrating wheel gyroscope

A wheel is driven to rotate a fraction of a full turn about its axis. Tilt of the wheel is measured to produce a signal related to the rate of rotation.^[2].

[edit] MEMS gyroscope

Relatively inexpensive (around US$30 per part in quantity as of late 2007) vibrating structure gyroscopes using MEMS technology are available. These can be implemented as the tuning fork resonator, vibrating wheel or (planar) wine glass resonator ^[3].

[edit] Applications

[edit] Spacecraft orientation

The oscillation can also be induced and controlled in the vibrating structure gyroscope for the positionning of spacecraft such as Cassini-Huygens. These small Hemispherical Resonator Gyroscopes made of quartz operate in vacuum. They provide accurate 3 axis positioning of the spacecraft and are highly reliable over the years as they don't have any moving parts.

[edit] Automotive

Automotive roll sensors can be built around vibrating structure gyroscopes. These can be used to detect rollovers, or to supply input to electronic stability control systems.

[edit] Entertainment

The Nintendo Game Boy Advance game WarioWare: Twisted! uses a piezoelectric gyroscope to detect rotational movement.

[edit] Photography

Many Image stabilization systems on video and still cameras employ vibrating structure gyroscopes.

[edit] Hobbies

Vibrating structure gyroscopes are commonly used in radio-controlled helicopters to help control the helicopter's tail rotor or in radio-controlled airplanes to help keep the tail steady during take-off or hand (especially with discus launched gliders) launch.

[edit] Other

The Segway Human Transporter employs a vibrating structure gyroscope made by Silicon Sensing Systems to maintain stability of the operator platform ^[4].

[edit] References

^ NEC ceramic piezo gyros includes animated illustration
^ Watson piezoceramic cup structure gyroscopes
^ White paper - "A Critical Review of MEMS Gyroscopes Technology and Commercialization Status" Steven Nasiri, InvenSense, ca. 2005
^ MEMS gyrocopes Research and Development - upcoming Sensors - HSG-IMIT Home

[edit] External links

New iMEMS Angular-Rate-Sensing Gyroscope John Geen, Analog Devices
Silicon Sensing - Case Study: Segway HT
Theory and Design of Micromechanical Vibratory Gyroscopes Vladislav Apostolyuk

Categories: Gyroscopes

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