Selective flotation mechanism for a pendulous accelerometer proof mass

• US 3,998,106 A
• Filed: 06/30/1975
• Issued: 12/21/1976
• Est. Priority Date: 06/30/1975
• Status: Expired due to Term

• Current Assignee: Kearfott Guidance and Navigation Corporation
• Original Assignee: Singer Company (SVP Holdings Ltd.)
• Inventors: William, Albert
• Primary Examiner(s): Gill, James J.
• Application Number:
  US05/591,434
• Time in Patent Office: 540 Days
• Field of Search: 73/515, 73/516 R, 73/517 B, 73/503
• US Class Current: 73/514.06
• CPC Class Codes: G01P 1/006 used for thermal compensation
• CPC Class Codes: G01P 15/132 with electromagnetic counterbalancing means

Abstract

The proof mass of a pendulous accelerometer is floated in a liquid metal such as mercury which has high surface tension and non-wetting characteristics within a specially designed cavity such that neutral bouyancy conditions are achieved for all principle axes except the input axis.

Claims

1. In a pendulous accelerometer in which a proof mass is supported by means rotatable about a pivot axis in response to an acceleration along a sensing axis, said proof mass contained within a casing to which said support means are attached and movable within said casing, the improvement comprising said proof mass having a central section of a larger cross-section and two end sections of smaller cross-sections and a liquid metal filling the gaps between said smaller end sections of said proof mass and said casing so as to support said proof mass for neutral buoyancy along all axes except the sensing axis.

2. Apparatus according to claim 1 wherein the gap between said larger central portion and said casing, at the point where said gap is contiguous to the gaps surrounding said smaller end portions is of a size which will not permit the entry of said liquid metal therein because of the surface tension of said liquid metal.

3. Apparatus according to claim 2 and further including a channel through the center of said proof mass along said sensing axis.

4. Apparatus according to claim 3 wherein said center section and said end sections are both of a cylindrical cross section with their cylindrical axes on said sensing axis.

5. Apparatus according to claim 4 wherein the length of each of said smaller end sections in the direction of said sensing axis is l₁, the radius of each of said end sections is r, the mass of said proof mass is M and the density of said liquid metal is ρ

, and wherein said device satisfies the equation;

M = 2π

r² l₁ ρ

.

6. Apparatus according to claim 3 wherein said liquid metal is mercury.

7. Apparatus according to claim 3 and further including means for filling said gaps with said liquid metal.

8. Apparatus according to claim 3 and further including means to take up expansion of said liquid metal due the temperature changes.

9. Apparatus according to claim 8 wherein said means comprise an expansion bellows.