Gyroscopes

1
Gyroscopes
Eric Ruben Mechatronics Literature Survey Dept.
of Electrical and Computer Engineering Utah
State University E e.r_at_aggiemail.usu.edu T
801-916-2400
2/17/2009
2
Outline

• Introduction
• History
• Basic Principle
• Applications
• Advantages
• Disadvantages
• Cost
• Works Cited

3
Introduction

• Most everyone has used some form of gyroscope in
  their lifetime. But perhaps they did not
  recognize it.
• Simply put, a gyroscope consists of a rotor that
  is journaled to spin about an axis. Often the
  spinning rotor is gimbaled and allowed to move
  freely. This spinning rotor has some very useful
  physical properties.

• One of these properties can even be seen in a
  simple 7 gyroscope toy. That is, when a rotor
  spins about an axis, that axis tends to want to
  maintain its spacial orientation.

4
Introduction

• A second important property of gyroscopes can be
  observed from the common Bicycle Wheel Gyro
  experiment.

• In the experiment a person sits in a pivoting
  office chair while holding a spinning bicycle
  wheel.

• As the person tilts the spin axis to the left a
  seemingly invisible force begins to pivot his/her
  chair to the left.
• This action is a result of a property called
  precession. This property will be discussed in
  greater detail later.

5
History

• 1817. Johann Bohnenberger created the first know
  gyroscope, calling it simply the machine.
• 1820. Pierre-Simon Laplace recommended the
  machine be used as a teaching aide.
• 1852. Leon Foucault coins the name gyroscope
  when he uses Bohnenbergers machine in an
  experiment involving the earths rotation.
• 1905 1908. The first gyroscope for marine
  navigation was developed by German inventor
  Hermann Anschutz-Kaempfe.

6
History

• 1917. The Chandler gyroscope toy was invented
  by the Chandler Company in Indiana. It is still
  considered a classic American toy.
• 1991. Charles Stark Draper Laboratory
  demostrated one of the first MEMS or Vibratory
  gyroscopes fabricated in silicon.

7
Basic Principle

• Gyroscopes operate on a physical property of
  spinning objects known as precession.

• Precession is the phenomenon observed in the
  bicycle wheel experiment. If an input force is
  applied against the spin axis the wheel will
  resist it by generating an output force
  perpendicular and proportional to the input.

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Basic Principle

• Precession is an interesting property of
  gyroscopes. But how can it be used to create
  useful sensors?
• Gyroscopes can be used to measure orientation,
  tilt (gravity), and external force. Gyroscopes
  are also used to determine the position of a body
  in space, but this often requires the integration
  of additional sensors like accelerometers.
• Some of the more common applications of
  gyroscopes will be discussed here in greater
  detail.

9
Basic Principle

• Gimbals can be used to provide the spinning rotor
  with additional degrees of freedom.

• The gyroscope shown here has both an inner and
  outer gimbal, allowing the rotor to pivot about 2
  different axis.
• This is knows as a two degree-of-freedom (2DOF)
  gyroscope.

10
Basic Principle

• Interestingly, If a 2 DOF gyroscope rotor is left
  spinning with a spin axis orientation other than
  the north celestial pole, the spin axis will
  appear to us on Earth to have rotated every 24
  hours.

• This is due to the law of conservation of angular
  momentum.

11
Applications
Gyroscopic sensing is an older technology that is
continually finding new uses. Some or the more
typical applications include

• Naval navigation systems and stabilizers.
• Aircraft attitude controllers and stabilizers.
• Inertial guidance systems for ballistic missiles.
• Video game controllers.
• Image stabilization systems on video cameras.

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Gyrocompasses

• Gyrocompasses use a spinning rotor to locate true
  north, however, an additional torque is needed
  to offset forces exerted by the Earths rotation
  (discussed earlier).

• Using weights is the most practical method for
  providing the offset torque. Weights force the
  axis of rotation to remain horizontal with
  respect to the earths surface. Being thus
  constrained the gyroscope continually realigns
  itself, pointing towards true north.

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Inertial Navigation Systems

• Most sophisticated aircraft and missile systems
  use INS to determine their location and
  orientation.
• The gyroscope sensor is only one component of the
  INS but it is very important. It provides
  information about the plants orientation.

• Combining orientation information with data
  collected from accelerometers an onboard computer
  can determine the objects location.

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Inclinometers

• Gyroscopes are used extensively in land, air and
  sea vehicles to take high precision tilt
  measurements, much like inertial navigation
  systems only without the accelerometers.
• An good example would be an aircraft that uses 3
  gyroscopes to measure the pitch, roll and yaw.

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MEMS Gyroscopes

• The size, accuracy and cost of MEMS gyroscopes
  makes them an attractive option for many
  applications.
• One common type of MEMS gyroscope is the
  vibrating wheel gyroscope. Vibrating wheels
  operate much like the macroscopic spinning wheel
  gyroscope but use capacitive sensors to determine
  changes in attitude.

• The drawing to the right shows a vibrating wheel
  gyroscope with a z direction spin axis.

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Advantages

• Most MEMS gyroscopes are extremely small,
  lightweight, and inexpensive.
• Sensor resolution depends largely on the spin
  rate of the rotor and can be much higher than
  other force, or tilt sensors.
• A gyrocompass, unlike a magnetic compass,
  indicates true north as opposed to magnetic
  north. This makes gyroscopes the preferred
  sensor for high precision navigation systems.

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Disadvantages

• In general, gyroscopes are a more expensive
  alternative to navigation and tilt sensing.
• A free moving gyroscope is always dependant on
  the rotation of the Earth. For this reason fast
  moving objects moving on a trajectory from east
  to west cannot use gyroscopes for navigation.

18
Cost

• Most applications today use MEMs gyroscopes
  because they are small and relatively
  inexpensive. Here is a comparison of some
  expensive and inexpensive ones

Part Range Sensitivity Supply Current Price
ADXRS610 /- 300 deg/s 6 mV/degs 3.5mA 19.98
ADXRS150 /- 150 deg/s 12.5 mV/degs 6mA 30.36
ADIS6255 /- 80 deg/s .018 deg/secLSB 18mA 56.57
ADIS16120 /- 300 deg/s .2 deg/secmV 95mA 636.55
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Future Work

• Most development being done in gyroscopes as
  sensors is focused on reducing the size and
  improving the precision of MEMS gyroscopes.

• Much of this research is fueled by DARPA and the
  military. The goal is to produce a small, light
  weight, and inexpensive 6-axis Inertial

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Works Cited

• Analog Devices. (2009). iMEMS Gyroscopes.
  Retrieved February 15, 2009, from Analog Devices
  http//www.analog.com/en/mems-and-sensors/imems-gy
  roscopes/products/index.html
• Conventor. (2008, February). Gyroscope
  Application Examples. Retrieved February 15,
  2009, from Conventor http//www.coventor.com/pdfs
  /Gyro_Applications.pdf
• Kaumualii High School. (2004). Bicycle Wheel
  Gyro. Retrieved February 14, 2009, from Kaumualii
  High http//www.kaumualii.k12.hi.us/technology/sc
  ience/pdf/forces/Bicycle20Wheel20Gyro.pdf

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Works Cited

• muRata. (2007). Piezoelectric Vibrating
  Gyroscopes. Retrieved February 15, 2009, from
  Gyrostar http//www.murata.com/catalog/s42e.pdf
• Nasiri, S. (2006, July). A Critical Review of
  MEMS Gyroscopes Technology and Commercialization
  Status. Retrieved Feb 15, 2009, from InvenSense
  http//www.invensense.com/shared/pdf/MEMSGyroComp.
  pdf