Rotational inductive accelerometer

• US 6,318,176 B1
• Filed: 03/24/2000
• Issued: 11/20/2001
• Est. Priority Date: 03/26/1999
• Status: Expired due to Fees

• Current Assignee: Seagate Technology LLC (Seagate Technology Holdings Plc)
• Original Assignee: Seagate Technology LLC (Seagate Technology Holdings Plc)
• Inventors: Ratliff, Ryan Todd, Misso, Nigel Frank, McKenzie, Lealon Ray
• Primary Examiner(s): MOLLER, RICHARD ALAN
• Application Number:
  US09/535,026
• Time in Patent Office: 606 Days
• Field of Search: 735/143.1, 324/200, 324/207.11, 324/162, 340/669, 340/683, 360/69, 318/560
• US Class Current: 73/514.31
• CPC Class Codes: G01P 15/0888 for indicating angular acceleration
• CPC Class Codes: G01P 15/11 by inductive pick-up

Abstract

An inductive rotational accelerometer for assisting in servo control of a hard disc drive using a torsional mass-spring system in combination with an inductance sensitive circuit to detect and measure the rotational vibrations imposed on a hard disc drive. The inductive rotational accelerometer includes a frame member coupled to the disc drive, the frame member supporting a pin on which is disposed a rotational mass. The rotational mass supports conductive blocks which with the rotational mass and the frame member provide a path for inductance.

Claims

1. An apparatus for detecting and measuring rotational vibration of a disc drive comprising:

a top frame member having a cross bar, the top frame member being coupled to the disc drive;

a bottom frame member having two lower side-posts and a bottom cross bar, the bottom cross bar being coupled to the disc drive and coupling the two lower side-posts, wherein each side post has an uppermost end;

a pin having a top end and a bottom end, the top end being coupled to the cross bar of the top frame member and the bottom end being coupled to the cross bar of the bottom frame member;

a rotational mass disposed on the pin so as to surround the pin, wherein the rotational mass has a moment of inertia;

first and second ferro-magnetic blocks disposed on a surface of the rotational mass facing the bottom frame member, each of the ferro-magnetic blocks being suspended above one of the uppermost ends of the two side-posts of the bottom frame member to define an air gap therebetween, the ferro-magnetic blocks having a surface area that overlaps the side-posts, the surface area that overlaps the side-posts changing in size when the rotational mass experiences angular acceleration relative to the bottom frame member, the ferro-magnetic blocks with the rotational mass and the bottom frame member providing a path for magnetic flux; and

a wire coil disposed around one of the side-posts of the bottom frame member, the coil being electrically coupled to an inductance meter for measuring a change in the inductance of the wire coil caused by a change in the magnetic flux through the path when the surface area of the conductive blocks that overlaps the side-posts changes in size.

2. The apparatus of claim 1 wherein the ferro-magnetic blocks are shaped such that a cross section of the ferro-magnetic blocks in a plane perpendicular to the length of the pin matches a similarly defined cross section of the lower side-posts of the bottom frame member.

3. The apparatus of claim 1 wherein the ferro-magnetic blocks are disposed on the rotational mass so that the blocks are separated from each other by a distance equal to a distance separating the two lower side-posts of the bottom frame member.

4. The apparatus of claim 1 wherein the inductance meter is a tuned oscillator comprising an inductance sensing circuit for producing a voltage output proportional to rotational acceleration of the hard disc drive.

5. The apparatus of claim 1 further comprising a second wire coil disposed around the second side post of the bottom frame member, the coil being electrically coupled to an inductance meter.

6. The apparatus of claim 1 wherein the rotational mass is shaped as a disc.

7. The apparatus of claim 1 wherein the ferro-magnetic blocks are soft iron.

8. The apparatus of claim 1 wherein the rotational mass is centered on the pin.

9. The apparatus of claim 1 wherein the top frame member, bottom frame member, and rotational mass are steel and the pin is mechanically pressed through the rotational mass.

10. An apparatus for detecting and measuring rotational vibration and acceleration of a disc drive to assist in servo control comprising:

(a) a ferro-magnetic rotational mass connected to a frame member by a mounting means, the mounting means being capable of torsional movement, the rotational mass characterized by a moment of inertia, the frame member being mounted to the disc drive,

(b) a ferro-magnetic block disposed on the rotational mass, the ferro-magnetic block acting with the rotational mass and the frame member to define a path for magnetic flux, the path for magnetic flux characterized at at least one point by a cross sectional area defined by an area that the ferro-magnetic block overlaps the frame member, the cross sectional area changing in size when the apparatus experiences rotational acceleration,

(c) a wire coil around the frame member, the wire coil being electrically connected to a means for measuring a change in inductance of the coil caused by rotational acceleration.

11. The apparatus of claim 10 wherein the mounting means is a pin.

12. The apparatus of claim 10 further comprising a second wire coil around the frame member, the second wire coil being electrically connected to a means for measuring the inductance of the second wire coil.

13. The apparatus of claim 10 wherein the rotational mass is shaped as a disc.

14. The apparatus of claim 10 wherein the ferro-magnetic block is soft iron.

15. An apparatus for detecting and measuring rotational vibration and acceleration of a disc drive to assist in servo control comprising:

a ferro-magnetic rotational mass connected to a frame member by a mounting means, the mounting means being capable of torsional movement, the rotational mass characterized by a moment of inertia, the frame member being mounted to the disc drive and a ferro-magnetic block disposed on the rotational mass, the ferro-magnetic block acting with the rotational mass and the frame member to define a path for magnetic flux wherein the path for magnetic flux is characterized at at least one point by a cross sectional area defined by an area that the ferro-magnetic block overlaps the frame member; and

means mounted on the frame member for measuring inductance.

16. The apparatus of claim 15 wherein the mounting means is a pin.

17. The apparatus of claim 15 wherein the means for measuring inductance is a wire coil wrapped around the frame member.

18. The apparatus of claim 15 further comprising a second wire coil wrapped around the frame member, the second wire coil being electrically connected to a means for measuring inductance of the second wire coil.

19. The apparatus of claim 15 wherein the rotational mass is shaped as a disc.

20. The apparatus of claim 15 wherein the ferro-magnetic block is soft iron.