Gyroscopes are a kind of rotation sensors which measure the angular rate–how quickly an object turns. The rotation is typically measured in degrees per second of change and in reference to one common axis. Typical rotation sensing applications or functions involve tracking or measuring movement of head or body rotation, precision instrumentation, Personal Navigation Devices (PND),Vehicular stability control systems etc. The main application of rotation sensor is a device called gyroscope used in missiles. The gyroscopes are installed in the missiles to keep a track of the direction of motion of the missile. The analog signal output from the gyroscopes is plots of time vs. angular rotation. 1.1. Types of Gyroscopes
Gyroscopes are of 3 types
1.1.1. Ring Laser Gyroscopes
The Ring Laser Gyros (RLG) can be used as the stable elements (for one degree of freedom each) in an inertial guidance system. The advantage of using a RLG is that there are no moving parts. Compared to the conventional spinning gyro, this means there is no friction, which in turn means there will be no inherent drift terms. Additionally, the entire unit is compact, lightweight and virtually indestructible, meaning it can be used in aircraft. The basic principle of operation is that a single RLG can measure any rotation about its sensitive axis. This implies that the orientation in inertial space will be known at all times. The elements that measure actual accelerations can therefore be resolved into the appropriate directions. The input laser beam is split into two beams that travel the same path but in opposite directions: one clockwise and the other counter-clockwise. The beams are recombined and sent to the output detector. In the absence or rotation, the path lengths will be the same and the output will be the total constructive interference of the two beams. If the apparatus rotates, there will be a difference (to be shown later) in the path lengths travelled by the two beams, resulting in a net phase difference and destructive interference. The net signal will vary in amplitude depending on the phase shift, therefore the resulting amplitude is a measurement of the phase shift, and consequently, the rotation rate. 1.1.2 Fiber Optic Gyroscopes
A fibre optic gyroscope (FOG) senses changes in orientation, thus performing the function of a mechanical gyroscope. However its principle of operation is instead based on the interference of light which has passed through a coil of optical fibre which can be as long as 5 km. The development of diode (semiconductor) lasers and low-loss single-mode optical fibre in the early 1970s for the telecommunications industry enabled Sagnac effect fibre optic gyros to be developed as practical devices. Many optical gyroscopes implemented so far use Sagnac effect, which states that an optical path difference induced by counter propagating beams in a rotating reference frame is proportional to the absolute rotation. FOGs are used in inertial navigational systems for guided missiles. An FOG can be a navigational aid in remotely operated vehicles and autonomous underwater vehicles. 1.1.3. MEMS Gyroscopes
Inexpensive vibrating structure gyroscopes manufactured with MEMS technology (Micro Electronic Mechanical Systems) have become widely available. These are packaged similarly to other integrated circuits and may provide either analog or digital outputs. In many cases, a single part includes gyroscopic sensors for multiple axes. Some parts incorporate both a gyroscope and an accelerometer, in which case the output has six full degrees of freedom. A vibrating structure gyroscope is a type of gyroscope that functions much like the halteres of an insect. The underlying physical principle is that a vibrating object tends to continue...
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