Gyroscopes and Their Types
Gyroscopes are the most important part of an inertial navigation system or any guidance system. Gyroscopes were invented a century ago and have been used as references to know inertial state of a moving body. From Kettering bug to the Apollo spacecraft, the quality of gyro has determined the performance of the overall mission. It has been a factor behind ‘make or break’ of the many missions.
As gyroscopes have evolved so have their applications. Applications as important as monitoring the orientation of an aircraft, to stabilizing the pictures that we click using our cameras, to guiding an unmanned aircraft during flight.
Life without gyroscopes is unimaginable. Gyroscopes are employed in many critical applications like guiding ballistic missiles, guiding the process of building tunnels, fire control systems abound ships, satellite navigation etc.
Gyroscopes have evolved over the period and hence, many technologies on which gyroscopes are based today; though only a few of them find their place in the practical applications. It is interesting to know more about various types of gyroscopes and understanding the way they operate.
The classic gyroscope consists of a spinning wheel or disc which works based on the principle of conservation of angular momentum. The rotation of the spinning axis remains unaffected due to the conservation of the momentum. As the technology evolved, other types of gyroscopes were developed which could provide more accurate and consistent output. Over the period, as potential applications for gyroscopes were identified, need to develop low cost and compact gyroscopes was felt. This lead to the development of MEMS gyroscopes which are compact in size and give adequately good performance.
Following are some of the commonly used types of gyroscopes:
Ring Laser (RLG) and Fiber Optics Gyroscopes (FOG):
Both ring laser and fiber optic type gyroscopes operate based on a common principle, Sagnac effect. Sagnac effect involves splitting a beam of light in two and sending them through different opposite paths and then creating interference between the two beams. The fringe pattern is observed and the rotation of the platform can be calculated based on the fringes.
In a ring laser type gyroscope, the ring is the part of the laser whereas in a fiber optic gyroscope, light from an external laser is passed through a fiber optic cable.
Dynamically tuned Gyroscopes (DTG):
A dynamically tuned gyro is a mechanical gyroscope. It contains a rotor that is held between extremely free pivots. At a particular speed called the tuning speed the rotor is free from torque due to rotation and can be used as a conventional or ideal gyroscope to measure rotation/rotary displacement from gimbal.
The term MEMS stand for micro-electro-mechanical systems. Typically, MEMS sensing structures range from 1 micrometer to 100 micrometers. MEMS gyroscopes use a vibrating element for rate measurement. The underlying principle is, any vibrating body has a tendency to continue vibrating in its plane of vibration. As a consequence, if the orientation of the platform to which a vibrating body is attached is changed, the vibrating body will exert a force on the platform. This force can be measured and can be used to find out the output.
Advantages of MEMS gyroscopes over FOG/RLG:
- Extremely space efficient. Available in the form of chips, so can be fitted on electronic circuits.
- Adequate performance. As the technology is evolving, the performance accuracy of MEMS gyroscopes is also improving.
- No moving components unlike DTG/RLG and hence, completely maintenance free.
- Available at a fraction of the cost of FOG or RLG.