Agni-V’s test flight on 31st January, 2015 put India into an elite group of countries possessing an intercontinental ballistic missile system. It is the country’s most formidable nuclear missile till now since it brings the whole of China and much more within its strike envelope. One of the key components which gives the 50 tonne missile the ability of reaching the target point within few meters of the designated point is the Ring Laser Gyro based Inertial Navigation System (RINS) and the most modern and accurate Micro Navigation System (MINS). These gyroscopes were the crux of the lecture organized by the R&D Dept. of VCE.
Figure 1 :RING LASER GYROSCOPE
On the 30th of July, 3rd year students of ECE department had the opportunity of listening Dr M. Sree Ramana speak on the topic of navigation sensors. Mr. P.Venkat, member of R&D and also a professor of ECE dept. introduced Dr Ramana who is a scientist ‘E’ from RCI Hyderabad and had been a former lecturer at Vasavi college, working in the physics department for 2 years. Dr Ramana briefed the students on topics which were currently the main focus of many researchers throughout the country and in what aspect the students could get a know-how on them.
Dr Ramana discussed on two main sensors used for navigation namely accelerometer and gyroscope. He spoke in depth on gyroscope, his primary area of research which included their working, different classes of gyroscopes and the ongoing research on them, particularly in India.
Given below are some of the topics on which Dr Ramana shed light on.
Gyroscope:
A gyroscope is useful for measuring or maintaining orientation. A gyroscope is a spinning wheel or disc in which the axis of rotation is free to assume any orientation by itself. When rotating, the orientation of this axis is unaffected by tilting or rotation of the mounting, according to the conservation of angular momentum.
Hemispherical Resonator Gyroscope:
The nature of the beats which may be heard when a vibrating shell in the form of a cylinder or other surface of revolution has imparted to it a rotatory motion about its axis.
If we select a wine glass which when struck gives, under ordinary circumstances, a pure and continuous tone, we shall on twisting it round hear beats, thus showing that the nodal meridians do not remain fixed in space. And if the observer will turn himself rapidly round, holding the vibrating glass all the time, beats will again be heard, showing that the nodal meridians do not rotate with the same angular velocity as the glass and observer. If the glass be attached to a revolving turntable it is easy to count the number of beats during a certain number of revolutions of the table, and it will thus be found that the gravest tone gives about 2.4 beats per revolution. As this type of vibration has 4 nodes we should bear 4 beats per revolution if these nodes were to rotate with the glass.
Based on this concept hemispherical resonator gyroscope is invented, 1mm thickness of glass is taken which is made of fused silica, it is coated with gold and an electrode which is also coated with gold is taken which is placed beside this by applying the voltage between this coated glass and electrode vibrations produced and there will be many electrodes for this glass, while changing in direction the capacitance between glass and these electrodes will be changing so that the angle will be calculated.
Ring laser gyroscope:
This gyroscope is mainly depends on Sagnac’s experiments. The Sagnac effect manifests itself in a setup called a ring interferometer. A beam of light is split and the two beams are made to follow the same path but in opposite directions. To act as a ring the trajectory must enclose an area. On return to the point of entry the two light beams are allowed to exit the ring and undergo interference. The relative phases of the two exiting beams, and thus the position of the interference fringes, are shifted according to the angular velocity of the apparatus. This arrangement is also called a Sagnac interferometer.
These beams fall on the photographic plates, where the output is based on the light beams interference, by using the angle deflection.
Atom interferometer sensor and fiber optic gyroscope were also discussed during the lecture. Afterwards there was a QnA session where Dr Ramana cleared doubts which were raised by some of the students relating to sensors. After the session ended Dr Ramana was presented a memento by Dr M. Satyam, professor of ECE Dept.
Written By:
Pruthvi Raj (B.E. 3/4- ECE-A)
Edited By:
Imran Ahmed (ECE-A 3/4)