Vibrating Structure Gyro (VSG) Principles of Operation
Gyroscopes are instruments which are used to measure angular motion. Vibrating Structure Gyroscopes are solid state devices which provide an output voltage proportional to the rate of turn applied to the sensitive axis.
Main features of Vibrating Structure Gyroscopes
- No moving parts
- Simple construction
- Short start-up time
- Low power requirements
- Low noise
All the vibrating structure devices described here work on the basic principle of detecting coriolis forces. These forces are generated when a moving particle is rotated.
To use the coriolis effect to detect angular rotation, a solid structure is forced to vibrate normally at its resonant frequency. This is achieved by applying an alternating voltage to the primary electrodes. The vibration provides the structure with a linear velocity component. When the structure is rotated, the coriolis forces cause the vibration motion of the structure to be coupled to another vibration mode or plane of the structure. The magnitude of this secondary vibration is proportional to the angular rate of turn.
All gyroscopes in Watson’s VSG model series are of the shell type i.e. cylinders or rings. Figure 1 shows the vibration pattern at the end of the shell. Rotational motion produces coriolis forces which couple the vibration to a point 45 degrees relative to the driven axis. A secondary pickoff is used to determine the vibration at the 45 degree points. The output from the secondary pickoff is proportional to the rate of turn.
Figure 2 Shows the block diagram for the VSG. A primary pick off is used to provide feedback to keep the primary loop frequency at resonance and at a constant amplitude. A second closed loop, comprising a secondary pick off and a secondary drive is used to null the rotated vibration and to provide an output directly proportional to the applied rate. These closed loop techniques greatly improve the performance of the device.