Gyroscopes

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

2. Outline • Introduction • History • Basic Principle • Applications • Advantages • Disadvantages • Cost • Works Cited ECE5320 Mechatronics. Assignment#1 Survey on sensors and actuators

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. ECE5320 Mechatronics. Assignment#1 Survey on sensors and actuators

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. ECE5320 Mechatronics. Assignment#1 Survey on sensors and actuators

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 Bohnenberger’s “machine” in an experiment involving the earth’s rotation. • 1905 – 1908. The first gyroscope for marine navigation was developed by German inventor Hermann Anschutz-Kaempfe. ECE5320 Mechatronics. Assignment#1 Survey on sensors and actuators

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. ECE5320 Mechatronics. Assignment#1 Survey on sensors and actuators

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. ECE5320 Mechatronics. Assignment#1 Survey on sensors and actuators

8. 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. ECE5320 Mechatronics. Assignment#1 Survey on sensors and actuators

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. ECE5320 Mechatronics. Assignment#1 Survey on sensors and actuators

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. ECE5320 Mechatronics. Assignment#1 Survey on sensors and actuators

11. Applications • 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. Gyroscopic sensing is an older technology that is continually finding new uses. Some or the more typical applications include: ECE5320 Mechatronics. Assignment#1 Survey on sensors and actuators

12. Gyrocompasses • Gyrocompasses use a spinning rotor to locate true north, however, an additional torque is needed to offset forces exerted by the Earth’s 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 earth’s surface. Being thus constrained the gyroscope continually realigns itself, pointing towards true north. ECE5320 Mechatronics. Assignment#1 Survey on sensors and actuators

13. 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 plant’s orientation. • Combining orientation information with data collected from accelerometers an onboard computer can determine the objects location. ECE5320 Mechatronics. Assignment#1 Survey on sensors and actuators

14. 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. ECE5320 Mechatronics. Assignment#1 Survey on sensors and actuators

15. 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. ECE5320 Mechatronics. Assignment#1 Survey on sensors and actuators

16. 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. ECE5320 Mechatronics. Assignment#1 Survey on sensors and actuators

17. 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. ECE5320 Mechatronics. Assignment#1 Survey on sensors and actuators

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: ECE5320 Mechatronics. Assignment#1 Survey on sensors and actuators

19. 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 ECE5320 Mechatronics. Assignment#1 Survey on sensors and actuators

20. Works Cited • Analog Devices. (2009). iMEMS Gyroscopes. Retrieved February 15, 2009, from Analog Devices: http://www.analog.com/en/mems-and-sensors/imems-gyroscopes/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/science/pdf/forces/Bicycle%20Wheel%20Gyro.pdf ECE5320 Mechatronics. Assignment#1 Survey on sensors and actuators

21. 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 ECE5320 Mechatronics. Assignment#1 Survey on sensors and actuators