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").

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[edit] Theory of operation

Consider two proof masses vibrating in plane (as in the MEMS gyro) at frequency \scriptstyle\omega_r. Recall that the Coriolis effect induces an acceleration on the proof masses equal to \scriptstyle a_c = -2(v\times\Omega), where \scriptstyle v is velocity and \scriptstyle\Omega is the angular rate of rotation. The in-plane velocity of the proof masses is given by: \scriptstyle X_{ip} \omega_r \cos(\omega_r t), if the in-plane position is given by \scriptstyle X_{ip} \sin(\omega_r t). The out of plane motion \scriptstyle y_{op}, 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}}
\scriptstyle m is the mass of the proof mass
\scriptstyle k_{op} is the spring constant in the out of plane direction
\scriptstyle\Omega is magnitude of a rotation vector in the plane of and perpendicular to the driven proof mass 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.

The tuning fork gyro is not a new concept. F.W.Meredith took out a patent for such a device in 1942 when he was working at the Royal Aircraft Establishment (RAE). Further development was carried out at the RAE in the late 1950s by Messrs G.H.Hunt and A.E.W.Hobbs who demonstrated a performance of less than 1 °/h (3×10-4 °/s) drift.[2]

[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.[3]

[edit] MEMS gyroscope

Relatively inexpensive (less than US$10 per part as of 2009) vibrating structure gyroscopes using MEMS technology are available. These can be implemented as the tuning fork resonator, vibrating wheel or (planar) wine glass resonator.[4]

[edit] Applications

[edit] Spacecraft orientation

The oscillation can also be induced and controlled in the vibrating structure gyroscope for the positioning 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 yaw sensors can be built around vibrating structure gyroscopes. These are used to detect error states in yaw compared to a predicted response when connected as an input to electronic stability control systems in conjunction with a steering wheel sensor.[5] Advanced systems could conceivably offer rollover detection based on a second VSG but it is cheaper to add longitudinal and vertical accelerometers to the existing lateral one to this end.

[edit] Entertainment

The Nintendo Game Boy Advance game WarioWare: Twisted! uses a piezoelectric gyroscope to detect rotational movement. The Sony SIXAXIS PS3 controller uses a single MEMS gyroscope to measure the sixth axis (yaw). The Nintendo Wii MotionPlus accessory uses multi-axis MEMS gyroscopes to augment the motion sensing capabilities of the Wii Remote.[6]

[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.[7]

[edit] References

  1. ^ "NEC TOKIN's ceramic piezo gyros". http://www.nec-tokin.com/english/product/piezodevice2/ceramicgyro.html. Retrieved 2009-05-28. 
  2. ^ Collinson, R.P.G. Introduction to Avionics, Second edition, Kluwer Academic Publishers: Netherlands, 2003, p.235
  3. ^ "Inertial Sensors - Angular Rate Sensors". http://www.hsg-imit.de/index.php?id=41&L=1. Retrieved 2009-05-28. 
  4. ^ William S. Watson (19 September 2006). "Improved Vibratory Gyro Pick-off and Driver Geometry". http://www.watson-gyro.com/files/gyro_technology_report.pdf. Retrieved 2009-05-28. 
  5. ^ "The Falling Box (Video)". http://www.bosch-esperience.co.uk/uk/language1/flash/videos/the_falling_box.html. Retrieved 2009-05-28. 
  6. ^ InvenSense (15 July 2008). "InvenSense IDG-600 Motion Sensing Solution Showcased In Nintendo's New Wii MotionPlus Accessory". Press release. http://www.invensense.com/news/071508.html. Retrieved 2009-05-28. 
  7. ^ Steven Nasiri. "A Critical Review of MEMS Gyroscopes Technology and Commercialization Status". http://www.invensense.com/shared/pdf/MEMSGyroComp.pdf. Retrieved 2009-05-28. 

[edit] External links

Retrieved from "http://en.wikipedia.org/wiki/Vibrating_structure_gyroscope#MEMS_gyroscope"
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