The operation and mechanization of the hemispherical resonator gyroscope

Abstract

The Hemispherical Resonator Gyro (HRG) is unique in the area of high accuracy inertial sensors. One of its very first selected applications was on the Cassini mission to Saturn, its Rings, and Moons. Since that time it has been the chosen gyro technology for precision space missions both military and commercial. For these missions the HRG has been mechanized to operate in the Whole Angle (WA) mode when operation under high dynamic rates is required. However when high sensitivity and very precise angular measurements are at a premium the same HRG is switched to a Force To Rebalance (FTR) mode. In this FTR mode the gyro operates at low rates thus sacrificing the inherent high rate capability of the HRG. It should be noted that a third mechanization can be implemented that gives the same high rate capability as the WA mode and at the same time capable of the sensitivity that is inherent in the FTR mode. This mode is known as the Whole Angle Tracking (WAT) mode. To implement this mode changes to electronics, that are responsible for the readout and control of the gyro, are required. This paper will outline these mechanization changes and also show that a reduction in the electronics that support the HRG is possible. Because electronic noise characteristics plays a very large role in noise sensitivity of the gyro, a reduction of control electronics should lead to an improvement of the noise characteristics of the complete HRG sensor. Mechanization of this WAT mode is presented together with simulation of the mechanization that demonstrates both the high rate and high precision sensitivity of the gyroscope. It should be noted that the WAT mode actually has been implemented and tested when exposed to laboratory and extreme environmental conditions. Finally, D.D Lynch plainly demonstrated in one of his paper Ref (2) that “size does matter” when considering the performance of the HRG. In the quest for high precision using HRG technology accordingly this paper will outline geometry of a type HRG and mechanization changes will give precision performance that is very competitive with that used in HRG applications today, but at greatly reduced production costs. A low cost technique proposes “glass blowing” and, or “glass moldings” which are being actively pursued today in many establishments with excellent results. Incorporating these techniques is discussed in the design of a new HRG to meet both space and terrestrial applications. The introduction of “Glass blowing” allows geometry changes to be made so that the HRG is not the only geometric candidate. Accordingly the term Shell Resonator Gyroscopes, SRG, is introduced to cover these other geometries.