MEMS GYROSCOPE By:

Topics Introduction Mechanical Gyroscope Laser based Gyroscope(interference and doppler effect based) Tuning Fork Gyroscope Piezo Gyroscope Application Conclusion

What is a Gyroscope and need Gyroscope is a device which can measure the angular velocity. The bulky version of mechanical gyro was used in analog world, takes more space and subjected to wear and tear. MEMS version can be used in digital world. High sensitivity and robustness has been achieved

Mechanical Gyroscope A spinning-wheel will resist any change in its angular momentum vector relative to inertial space. Hence this system Isolates the Spinning-wheel from outer angular movement

Ring LASER gyroscope-Type I The inertial characteristics of light can also be utilized, by letting two beams of light travel in a loop in opposite directions. If the loop rotates clockwise, the clockwise beam must travel a longer distance before finishing the loop. The opposite is true for the counter-clockwise beam. Combining the two rays in a detector, an interference pattern is formed, which will depend on the angular velocity.

Ring LASER GyroscopeType II _ _ This device is based on doppler effect. Using two laser beam to produces beat frequency. Shown device dimension is in meter, in the next slide MEMS version is explained

Contd_ 1)Varying Offset bias Errors in Doppler based Ring Laser Gyroscope 1)Varying Offset bias 2) Dead-band at very small angular velocity Offset bias happens due to different indexes of refraction of beam pair Dead band is “range of angular velocity for which Gyro gives zero output” . Dead-band is normally centered at very small angular velocity. Dead-band=

Contd_ _ MEMS version of Ring laser Gyro If the size is decreased by a factor of ‘S=10^-4’ then sensitivity goes down by ‘S’ And dead-band is increased by factor (I/S)^2 By the way dead band can be decreased by reducing the wavelength That means we need to decrease wavelength by (S)^2.by doing so wavelength comes in range of Gamma range .which is a dangerous ray.

Tuning Fork gyroscope _ WORKING: To a vibrating tuning fork in y-axis, If angular velocity is given to z-axis then because of Coriolis Force extra vibration comes in x-axis. This vibration is seen only when we are sitting on tuning fork(non inertial frame) ADVANTAGE: High resolution of 100degree/hour is achieved. Very low drift 01 degree/hour. Strong SNR

Contd_ Using comb drive structure we can Realize Tuning Fork Gyro. since coriolis force only can be seen in non-inertial frame ,here the comb drive structure is placed in non inertial frame.

Piezoelectric Gyro _ ADVANTAGE: Single gyro can sense in all the three direction of rotation (by changing the actuation pair). Lower drive voltage. High sensitivity STRUCTURE: All the 6 surfaces of PZT is connected to electrode. WOKING: (analogous to tuning fork gyro) We have 3 pair of electrode. One pair is used to actuate PZT with AC voltage(to vibrate). If this vibrating PZT is put under rotation then voltage comes across either of two pair.

Cont_

Application of Gyroscope _ _ _ 1)Inertial Navigation System: It is measurement of [1] Velocity , position & orientation ACCELEROMETER DATA(acceleration) GYROSCOPE DATA(angular-velocity) INTEGRATOR INTEGRATOR VELOCITY ORIENTATION INTEGRATOR POSITION

Contd_ 2) Gait Phase Detection sensor(GPDS):This system is basically actuator to human-muscle used by paralyzed person. It consist of Gyroscope and force meter. Gyroscope placed in shoe-sole measure the angular velocity which is processed with sensed data of force meter to give stimulation to muscle.

Contd_ _ 3)ANTILOCK BRAKES(ABS):. In vehicles equipped with ABS, your foot should remain firmly planted on the brake pedal , while ABS pump the optimum brakes for you so you can concentrate on steering to safety.

Conclusion

References [1]N. Yazdi, F. Ayazi, and K Najafi, “Micromachined Inertial Sensors”, Proceedings of the IEEE, Vol. 86, No. 8, (1998) 1640-1659. [2]A. Kourepenis et al, “Performance of Small, Low-Cost Rate Sensors for Military and Commercial Applications”, Charles Stark Draper Laboratory releases (1997). [3]N. Barbour and G. Schmidt, “Inertial Sensor Technology Trends,” Proceedings of the 1998 Workshop on Autonomous Underwater Vehicles, 20-21 August, (1998), 55-62. [4] “Design and Analysis of a Micro-gyroscope with Sol-gel Piezoelectric Plate” Smart Material Structures. 1999 Vol. 8. 212-217. He, Nguyen, Hui, Lee, Luong. [5] “Micro-machined Vibrating Gyroscopes: Design and Fabrication” Elliott, Gupta, Reed, Rodriguez. December 6th, 2002. [6] “Design of a Triangle Active Ring Laser 13 m on a Side” Robert W. Dunn Applied Optics 20 September, 1998. Vol. 37, No. 27. 6405. [7] http://img3.custompublish.com/getfile.php/706509.753.qeqfawvevu/INSFFI.pdf?return=www.nornav.org (Norwegian Space Centre)

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