Disc drive spindle motor with rotor isolation and controlled resistance electrical pathway from disc to ground

• US 5,729,404 A
• Filed: 03/06/1996
• Issued: 03/17/1998
• Est. Priority Date: 09/30/1993
• Status: Expired due to Term

• Current Assignee: Seagate Technology LLC (Seagate Technology Holdings Plc)
• Original Assignee: Seagate Technology plc (Seagate Technology Holdings Plc)
• Inventors: Dunfield, John C., Jue, Clifford T., Kloeppel, Klaus, Pelstring, Robert M., MacLeod, Donald J., Kazmierczak, Frederick F., Raffetto, Michael
• Primary Examiner(s): Renner, Craig A.
• Application Number:
  US08/611,285
• Time in Patent Office: 741 Days
• Field of Search: 360/99.08, 360/98.07, 360/99.04, 360/97.02, 369/72, 361/212, 361/220
• US Class Current: 360/99.08
• CPC Class Codes: G11B 17/02 Details
• CPC Class Codes: G11B 19/2009 Turntables, hubs and motors for disk drives; Mounting of motors in the drive means for clamping of disk to turntable G11B17/022 and subgroups
• CPC Class Codes: G11B 25/043 using rotating discs
• CPC Class Codes: H02K 11/40 Structural association with grounding devices

Abstract

A disc drive for storing and retrieving data from at least one memory storage disc includes a drive base and a spindle motor. The spindle motor includes a rotor hub, a shaft, a bearing unit. The bearing unit rotatably supports the rotor hub about an axis. A controlled resistance electrical pathway is established from the rotor hub to ground to control disc potential and to prevent excess static charge buildup. In one embodiment, the spindle motor includes structural elements made of a conducting plastic having a controlled resistance to establish a controlled resistance electrical pathway from the rotor hub to ground. In a second embodiment, the shaft of the spindle motor includes a conductive contact button electrically connected to the shaft and operatively coupled with a contact shield electrically grounded by an electrical conductor having a controlled resistance. In another embodiment, the spindle motor includes a rod made of conductive material extending from an electrically grounded contact shield and received within the shaft. An electrical pathway between the shaft and the rod is established by a conducting fluid between the rod and the shaft. Alternatively, the electrical pathway from the shaft to the rod is established by a conducting unit. The conducting unit includes a seal, a magnetic conductive material, and a ferro-fluid. The seal is positioned within the shaft. The magnetic conductive material is coupled to the rod. The ferro-fluid is supported between the seal and the magnetic conductive material.

Claims

1. A disc drive spindle motor for rotatably driving at least one memory storage disc confronting at least one magnetoresistive head having a sensing current, the spindle motor comprising:

a drive base at ground;

a rotor hub for supporting said at least one memory storage disc above the base;

means for rotatably supporting the rotor hub above the drive base while electrically insulating the rotor hub from the base to prevent electrical short circuiting between the magnetoresistive head and ground; and

means establishing a controlled resistance electrical pathway from the rotor hub to ground for draining static charge from the disc to the ground at a rate such that static charge remaining on the disc maintains the disc above ground potential during all periods in which the disc is rotating and the magnetoresistive head is in electrical contact with the rotating disc without thereby short circuiting the sensing current to ground through the electrical pathway.

2. The motor of claim 1 wherein the base includes an interface surface which engages the means for rotatably supporting, the means for rotatably supporting includes a high resistivity material formed on the interface surface for electrically insulating the rotor hub from the base.

3. The motor of claim 2 wherein the high resistivity material is a hard anodized metallic layer formed upon the interface surface.

4. The motor of claim 2 wherein the high resistivity material is an epoxy coating applied to the interface surface.

5. The motor of claim 2 wherein the means for rotatably supporting includes a bearing sleeve fixedly coupled to the base, wherein the high resistivity material formed on the interface surface of the base engages the bearing sleeve.

6. The motor of claim 1 wherein the means for rotatably supporting includes a layer of high resistivity material formed on an interface surface of the means for rotatably supporting, wherein the high resistivity material engages the base.

7. The motor of claim 6 wherein the high resistivity material includes an epoxy coating deposited upon the interface surface of the means for rotatably supporting.

8. The motor of claim 1 wherein the means establishing the controlled resistance electrical pathway includes:

a shaft electrically coupled to the rotor hub and defining an inner bore;

a contact shield extending below the shaft;

an electrical conductor electrically grounding the contact shield, the electrical conductor having a controlled resistance for draining static charge from the disc to ground at a rate such that remaining static charge on the disc maintains the disc above ground potential during all periods in which the magnetoresistive head is in electrical contact with the rotating disc without thereby short circuiting the sensing current to ground through the electrical conductor;

a rod made of conductive material extending from the contact shield and received within the inner bore of the shaft; and

means for providing an intermediate electrical pathway from the shaft to the rod while permitting the shaft to rotate about the rod.

9. The motor of claim 8 wherein the means for providing the intermediate electrical pathway from the shaft to the rod includes:

a seal positioned within the inner bore;

a magnetic conductive material coupled to the rod; and

a conductive ferro-fluid between the seal and the magnetic conductive material.

10. The motor of claim 8 wherein the means for providing the intermediate electrical pathway from the shaft to the rod includes:

a conducting liquid electrically connecting the shaft to the rod.

11. The motor of claim 10 wherein the conducting liquid comprises mercury.

12. The motor of claim 1 wherein the means establishing the controlled resistance electrical pathway includes:

a shaft electrically coupled to the rotor hub and defining an inner bore;

a contact shield extending below the shaft;

a rod made of a conducting plastic having a controlled resistance, the rod extending from the contact shield and received within the inner bore of the shaft, wherein the controlled resistance controls disc potential by draining static charge from the disc to ground at a rate such that remaining charge on the disc maintains the disc above ground potential during all periods in which the magnetoresistive head is in electrical contact with the rotating disc without thereby short circuiting the sensing current to ground through the rod; and

means for providing an intermediate electrical pathway from the shaft to the rod while permitting the shaft to rotate about the rod.

13. The motor of claim 1 wherein the means for rotatably supporting includes bearing means coupled to the base for supporting the rotor hub, at least a portion of the bearing means being made of a high resistivity material for electrically isolating the rotor hub from the base to prevent electrical short circuiting through the bearing means between the magnetoresistive head and ground.

14. The motor of claim 13 wherein the bearing means includes a first race coupled to the base, a second race coupled to the rotor hub, and ball bearings rotatably supported between the first and second races, the ball bearings being made of the high resistivity material for electrically isolating the rotor hub from the base to prevent electrical short circuiting through the bearing means between the magnetoresistive head and ground.

15. The motor of claim 1 including a shaft rigidly mounted to the base, the means for rotatably supporting includes bearing means coupled to the shaft for supporting the rotor hub, at least a portion of the bearing means being made of a high resistivity material for electrically isolating the rotor hub from the base to prevent electrical short circuiting through the bearing means between the magnetoresistive head and ground.

16. The motor of claim 15 wherein the bearing means includes a first race coupled to the shaft, a second race coupled to the rotor hub, and ball bearings rotatably supported between the first and second races, the ball bearings being made of the high resistivity material for electrically isolating the rotor hub from the base to prevent electrical short circuiting through the bearing means between the magnetoresistive head and ground.

17. The motor of claim 1 wherein the means for rotatably supporting the rotor hub includes

an interface surface made of a high resistivity electrically insulating material supported on the base electrically insulating the base from the rotor hub,

and wherein the means establishing the controlled resistance electrical pathway includes

a shaft electrically coupled to the rotor hub and defining an inner bore,

a contact shield extending below the shaft,

a rod made of conductive material extending from the contact shield and received within the inner bore of the shaft,

means for providing an intermediate electrical pathway from the shaft to the rod while permitting the shaft to rotate about the rod, and

an electrical conductor electrically grounding the contact shield, the electrical conductor including controlled resistance means for draining static charge from the disc to ground at a rate such that remaining static charge on the disc maintains the disc above ground potential during all periods in which the magnetoresistive head is in electrical contact with the rotating disc without thereby short circuiting the sensing current to ground through the electrical conductor.

18. The motor of claim 17 wherein the means for providing the intermediate electrical pathway from the shaft to the rod includes:

a seal positioned within the inner bore;

a magnetic conductive material coupled to the rod; and

a conductive ferro-fluid between the seal and the magnetic conductive material.

19. The motor of claim 17 wherein the means for providing the intermediate electrical pathway from the shaft to the rod includes:

a conducting liquid electrically connecting the shaft to the rod.

20. The motor of claim 19 wherein the conducting liquid comprises mercury.

21. The motor of claim 1 wherein the means establishing the controlled resistance electrical pathway includes

a shaft electrically coupled to the rotor hub and defining an inner bore;

a contact shield extending below the shaft;

a rod made of a conducting plastic having a controlled resistance for draining static charge from the disc to ground at a rate such that remaining static charge on the disc maintains the disc above ground potential during all periods in which the magnetoresistive head is in electrical contact with the rotating disc without thereby short circuiting the sensing current to ground through the rod; and

means for providing an intermediate electrical pathway from the shaft to the rod while permitting the surface to rotate about the rod.

22. The motor of claim 1 wherein the rotor hub has an axis and the means for rotatably supporting the rotor hub comprises;

a shaft coupled to the rotor hub and extending along the axis, the shaft being made of a high resistivity material for electrically isolating the rotor hub from the base to prevent electrical short circuiting between the magnetoresistive head and ground through the shaft, and

a plurality of ball bearing units coupled to the rotor hub and spaced along the axis between the shaft and the rotor hub, wherein the ball bearing units wholly support rotation of the rotor hub about the axis.

23. The motor of claim 22 wherein the high resistivity material is a ceramic material.

24. The motor of claim 22 wherein the means establishing the controlled resistance electrical pathway includes:

an electrically conductive ferro-fluid seal between the shaft and the rotor hub; and

an electrical conductor electrically connecting the ferro-fluid seal to ground, the electrical conductor having a controlled resistance for draining static charge from the disc to the ground at a rate such that remaining static charge on the disc maintains the disc above ground potential during all periods in which the magnetoresistive head is in electrical contact with the rotating disc without thereby short circuiting the sensing current to ground through the electrical conductor.

25. The disc drive spindle motor of claim 22 wherein the shaft is fixedly coupled to the drive base along the axis and wherein the plurality of ball bearing units are coupled between the shaft and the rotor hub for supporting rotation of the rotor hub about the axis.

26. The motor of claim 22 wherein the shaft is fixedly coupled to the base and extending concentrically within the rotor hub, the motor including

a high resistivity isolator secured to the shaft, the isolator having a resistance large enough to prevent electrical short circuits between the magnetoresistive head and ground through the shaft,

and wherein the means establishing the controlled resistance electrical pathway includes

an electrically conductive ferro-fluid seal between the rotor hub and the high resistivity isolator;

and

means secured to the electrically conductive ferro-fluid seal for providing a controlled resistance electrical pathway to ground for draining static charge from the disc to the ground at a rate such that remaining static charge on the disc maintains the disc above ground potential during all periods in which the magnetoresistive head is in electrical contact with the rotating disc without thereby short circuiting of the sensing current to ground through the electrical pathway.

27. The motor of claim 22 wherein the shaft is fixedly coupled to the base and extending concentrically within the rotor hub, wherein the means establishing the controlled resistance electrical pathway includes:

a high resistivity isolator secured to the shaft for providing a controlled resistance electrical pathway to ground for draining static charge from the disc to the ground at a rate such that remaining static charge on the disc maintains the disc above ground potential during all periods in which the magnetoresistive head is in electrical contact with the rotating disc without thereby short circuiting of the sensing current to ground through the electrical pathway, and

an electrically conductive ferro-fluid seal between the rotor hub and the high resistivity isolator.

28. The motor of claim 1 wherein the means establishing the controlled resistance electrical pathway includes

a shaft electrically coupled to the rotor hub and defining an inner bore;

a conducive contact shield extending below the shaft;

a conducive rod extending from the contact shield and received within the inner bore of the shaft;

a coherent electrically conductive liquid above the rod between the rod and the shaft, wherein the coherency of the liquid maintains the liquid above the rod and wherein the liquid provides an electrical pathway from the shaft to the rod while permitting the shaft to rotate about the rod; and

an electrical conductor electrically grounding the contact shield, the electrical conductor having a controlled resistance for draining static charge from the disc to ground at a rate such that remaining static charge on the disc maintains the disc above ground potential during all periods in which the magnetoresistive head is in electrical contact with the rotating disc without thereby short circuiting the sensing current to ground through the electrical conductor.

29. The motor of claim 28 wherein the conductive liquid comprises mercury.

30. The motor of claim 1 wherein the means establishing the controlled resistance electrical pathway includes

a shaft electrically coupled to the rotor hub and defining an inner bore;

a conductive contact shield extending below the shaft;

an electrical conductor electrically grounding the contact shield;

a rod having a controlled resistance for draining static charge from the disc to the ground at a rate such that remaining static charge on the disc maintains the disc above ground potential during all periods in which the magnetoresistive head is in electrical contact with the rotating disc without thereby short circuiting the sensing current to ground through the rod; and

a coherent electrically conductive liquid above the rod between the rod and the shaft, wherein the coherency of the liquid maintains the liquid above the rod and wherein the liquid provides an electrical pathway from the shaft to the rod while permitting the shaft to rotate about the rod.

31. The motor of claim 1 wherein the means establishing the controlled resistance electrical pathway includes

a shaft electrically coupled to the rotor hub and defining an inner bore;

a rod received within the inner bore of the shaft, wherein the rod is made of a conducting plastic having a controlled resistance for draining static charge from the disc to ground at a rate such that remaining static charge on the disc maintains the disc above ground potential during all periods in which the magnetoresistive head is in electrical contact with the rotating disc without thereby short circuiting of the sensing current to ground through the rod; and

means for providing an electrical pathway from the shaft to the rod while permitting the shaft to rotate about the rod.

32. The motor of claim 31 wherein the means establishing the controlled resistance electrical pathway further includes a conductive contact shield extending below the shaft and an electrical conductor electrically grounding the contact shield.

33. The motor of claim 30 wherein the conducive liquid comprises mercury.

34. The motor of claim 1 wherein the means rotatably supporting includes

a shaft fixedly coupled to the drive base, the rotor hub encircling the shaft, and

a plurality of ball bearing units between the shaft and the rotor hub for wholly supporting rotation of the rotor hub about the shaft,

the shaft being made of a high resistivity material for electrically isolating the rotor hub from the base to prevent electrical short circuiting between the magnetoresistive head and ground through the shaft;

and further wherein the means establishing the controlled resistance electrical pathway includes

an electrically conductive ferro-fluid seal between the shaft and the rotor hub; and

an electrical conductor electrically connecting the ferro-fluid seal to ground, the electrical conductor having a controlled resistance for draining static charge from the disc to the ground at a rate such that remaining static charge on the disc maintains the disc above ground potential during all periods in which the magnetoresistive head is in electrical contact with the rotating disc without thereby short circuiting of the sensing current to ground through the electrical conductor.

35. The motor of claim 34 wherein the high resistivity material is a ceramic material.

36. A disc drive spindle motor for rotatably driving at least one memory storage disc confronted by a magnetoresistive head having a sensing current, the spindle motor comprising:

a drive base;

a rotor hub for supporting the at least one memory storage disc above the base;

means for rotatably driving the rotor hub about an axis;

a shaft electrically connected to the rotor hub, the shaft being made of a conductive material;

a contact shield electrically connected to ground;

bearing means coupled to the contact shield for supporting the rotor hub, at least a portion of the bearing means being made of a high resistivity material for electrically isolating the rotor hub from the base to prevent electrical short circuiting through the bearing means between the magnetoresistive head and ground;

a contact button having a contact area electrically connected to the shaft and operably coupled to the contact shield, wherein the contact area is made of a conducting plastic having a controlled resistance for draining static charge through the contact button and the contact shield from the disc to the ground at a rate such that static charge remaining on the disc maintains the disc above ground potential during all periods in which the disc is rotating and the magnetoresistive head is in electrical contact with the rotating disc without thereby short circuiting the sensing current to ground through the contact button.

37. The motor of claim 36 wherein the contact shield comprises:

a plate having an outer periphery and a central portion integrally extending below the periphery and spring biased to contact the contact area of the contact button to operably couple the contact shield to the contact area.

38. The motor of claim 36 wherein the shaft further defines an inner bore and wherein the contact button is received within the inner bore to electrically connect the contact area to the shaft.

39. A disc drive spindle motor for rotatably driving at least one memory storage disc in confrontation with at least one magnetoresistive head having a sensing current, the spindle motor comprising:

a drive base;

a rotor hub for supporting the at least one memory storage disc above the base;

a shaft coupled to the rotor hub;

a bearing sleeve encircling at least a portion of the shaft;

a contact shield within the bearing sleeve and below the shaft;

an electrical conductor electrically connecting the contact shield to ground;

a bearing unit coupled between the shaft and the bearing sleeve, the bearing unit including;

an outer race coupled to the bearing sleeve;

an inner race coupled to the shaft; and

a bearing ball rotatably supported between the inner race and the outer race to rotatably support the shaft concentrically within the bearing sleeve wherein the bearing ball is made of a high resistivity material for electrically isolating the rotor hub from the base to prevent electrical short circuiting through the bearing unit between the magnetoresistive head and ground; and

means establishing a controlled resistance electrical connection between the shaft and the contact shield for draining static charge through the controlled resistance electrical connection and the electrical conductor from the disc to the ground at a rate such that static charge remaining on the disc maintains the disc above ground potential during all periods in which the disc is rotating and the magnetoresistive head is in electrical contact with the rotating disc without thereby short circuiting the sensing current to ground through the electrical connection, while permitting the shaft to rotate above the contact shield.

40. The motor of claim 39 wherein the means establishing the controlled resistance electrical connection includes:

a conductive contact button protruding from the shaft; and

means for urging the contact button and the contact shield into contact with each other.

41. A disc drive spindle motor for rotatably driving at least one memory storage disc, the spindle motor comprising:

a drive base;

a rotor hub for supporting the at least one memory storage disc above the base;

a shaft coupled to the rotor hub, wherein the shaft defines an inner bore;

a bearing sleeve encircling the shaft and coupled to the drive base;

a bearing unit coupled between the bearing sleeve and the shaft, the bearing unit including;

an outer race coupled to the bearing sleeve;

an inner race coupled to the shaft; and

a bearing ball rotatably supported between the inner race and the outer race to rotatably support the shaft relative to the bearing sleeve;

a contact shield fit within the bearing sleeve and extending below the shaft to seal contaminates from the bearing unit within the bearing sleeve, the contact shield having a raised periphery abutting the outer race of the bearing unit and a depressed central portion integrally extending below the raised periphery and spaced from the inner race and the shaft to permit the inner race and the shaft to rotate;

an electrical connector electrically grounding the contact shield; and

a conducting mechanism received within the inner bore of the shaft and electrically connecting the shaft to the depressed central portion of the contact shield, wherein the conducting mechanism has a controlled resistance small enough to control disc potential and impede static charge buildup.