ACCELERATION SENSOR AND MAGNETIC DISK DRIVE APPARATUS

Abstract

An acceleration sensor includes a pair of permanent magnets, each having a surface facing a magnetic field detection sensor, arranged in parallel so that the surfaces of the pair of permanent magnets have different magnetic polarities with each other, a spring member for supporting the pair of permanent magnets to displace the pair of permanent magnets when an external force is applied, and a magnetic field detection sensor mounted in stationary state to face the pair of permanent magnets. The magnetic field detection sensor has at least one pair of multi-layered MR elements, each including a magnetization fixed layer and a magnetization free layer, the magnetization fixed layer being magnetized in a direction parallel to a displacement detection direction. The pair of permanent magnets are arranged so that a longitudinal direction of each permanent magnet is in parallel with the magnetized direction of the magnetization fixed layer.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an oblique view schematically illustrating a whole structure of an example of a magnetic disk drive apparatus with an acceleration sensor assembled therein;

FIG. 2 is an exploded oblique view schematically illustrating a whole structure of an acceleration sensor as a preferred embodiment according to the present invention;

FIG. 3 is an exploded oblique view schematically illustrating structures of a spring member, magnetic field generation members with weights and magnetic filed detection sensors mounted in a housing member of the acceleration sensor shown in FIG. 2;

FIG. 4 is a view schematically illustrating electrical connections on a wiring board, and structures of the magnetic filed detection sensors in the acceleration sensor shown in FIG. 2;

FIG. 5 is a circuit diagram schematically illustrating electrical connection structures of the wiring board and the magnetic filed detection sensors in the acceleration sensor shown in FIG. 2;

FIGS. 6 a, 6b and 6c are equivalent circuit diagrams of the acceleration sensor shown in FIG. 2;

FIG. 7 is a view illustrating characteristics of an MR resistance variation versus an applied magnetic field angle with respect to a lamination plane of a spin valve GMR element;

FIG. 8 is a view illustrating an angle 0 of the magnetic field applied;

FIGS. 9 a and 9b are views illustrating magnetic field components in pinned direction and in free direction when the permanent magnet in the acceleration sensor shown in FIG. 2 slightly inclines;

FIGS. 10 a and 10b are characteristic graphs illustrating change in MR resistance of the spin valve GMR element with respect to magnetic field components in pinned direction and in free direction;

FIG. 11 is an oblique view illustrating position relationship between the permanent magnets and the spin valve GMR element in the acceleration sensor shown in FIG. 2;

FIGS. 12 a, 12b and 12c are sectional views illustrating position relationship between the permanent magnets and the spin valve GMR element in the acceleration sensor shown in FIG. 2 and in another modified acceleration sensor;

FIG. 13 is a characteristic graph illustrating in three-dimension the simulated distribution of magnetic field component in the free direction Hx applied to the spin valve GMR element from the pair of the permanent magnets;

FIG. 14 is a characteristic graph illustrating in three-dimension the simulated distribution of magnetic field component in the perpendicular direction Hz applied to the spin valve GMR element from the pair of the permanent magnets;

FIG. 15 is a characteristic graph illustrating in three-dimension the simulated distribution of magnetic field component in the pinned direction Hy applied to the spin valve GMR element from the pair of the permanent magnets;

FIGS. 16 a and 16b are plane views illustrating structures of spin valve GMR elements in the acceleration sensor shown in FIG. 2 and in another modified acceleration sensor;

FIGS. 17 a and 17b are plane views illustrating the structures of spin valve GMR elements in further two modified acceleration sensors;

FIGS. 18 a, 18b and 18c are oblique views illustrating fundamental operations of a strip-shaped plate spring of a spring member according to the present invention;

FIGS. 19 a and 19b are oblique views illustrating operations of a strip-shaped plate spring having a fulcrum at its center and weight members at its both end sections;

FIGS. 20 a, 20b and 20c are oblique views illustrating operations of the spring member shown in FIG. 2;

FIG. 21 is an exploded oblique view schematically illustrating a whole structure of an acceleration sensor as another embodiment according to the present invention;

FIG. 22 is an exploded oblique view schematically illustrating structures of a spring member, magnetic field generation members with weights and magnetic filed detection sensors mounted in a housing member of the acceleration sensor shown in FIG. 21;

FIG. 23 is a view schematically illustrating electrical connections on a wiring board, and structures of the magnetic filed detection sensors in the acceleration sensor shown in FIG. 21;

FIG. 24 is a circuit diagram schematically illustrating electrical connection structures of the wiring board and the magnetic filed detection sensors in the acceleration sensor shown in FIG. 21;

FIGS. 25 a and 25b are equivalent circuit diagrams of the acceleration sensor shown in FIG. 21; and

FIGS. 26 a, 26b and 26c are oblique views illustrating operations of the spring member shown in FIG. 21.

Claims

1. An acceleration sensor comprising: a pair of permanent magnets each having a surface facing a magnetic field detection sensor, said pair of permanent magnets being arranged in parallel so that said surfaces of the pair of permanent magnets have different magnetic polarities with each other;a spring member for supporting said pair of permanent magnets to displace the pair of permanent magnets when an external force is applied; andthe magnetic field detection sensor mounted in stationary state to face said pair of permanent magnets,said magnetic field detection sensor having at least one pair of multi-layered magnetoresistive effect elements, each including a magnetization fixed layer and a magnetization free layer, said magnetization fixed layer being magnetized in a direction parallel to a displacement detection direction,said pair of permanent magnets being arranged so that a longitudinal direction of each permanent magnet is in parallel with the magnetized direction of said magnetization fixed layer.

2. The acceleration sensor as claimed in claim 1, wherein a center of each multi-layered magnetoresistive effect element is located at the same position in a magnetized direction of said magnetization free layer as a center of each permanent magnet.

3. The acceleration sensor as claimed in claim 1, wherein said at least one pair of multi-layered magnetoresistive effect elements are arranged to face said pair of permanent magnets at a position where no reverse of a component of magnetic field applied from said pair of permanent magnets, in a magnetized direction of said magnetization free layer, occurs.

4. The acceleration sensor as claimed in claim 3, wherein a center of each multi-layered magnetoresistive effect element differs from the position of a center of each permanent magnet, in the magnetized direction of said magnetization free layer.

5. The acceleration sensor as claimed in claim 4, wherein the center of each multi-layered magnetoresistive effect element deviates from the center of each permanent magnet toward a center between the permanent magnets, in the magnetized direction of said magnetization free layer.

6. The acceleration sensor as claimed in claim 1, wherein each multi-layered magnetoresistive effect element has a length in the magnetized direction of said magnetization fixed layer, which is longer than that of said magnetization free layer.

7. The acceleration sensor as claimed in claim 1, wherein said at least one pair of multi-layered magnetoresistive effect elements are arranged near a center of each permanent magnet in the magnetized direction of said magnetization fixed layer.

8. The acceleration sensor as claimed in claim 1, wherein each multi-layered magnetoresistive effect element consists of a plurality of multi-layered magnetoresistive effect layers connected in series, each multi-layered nagnetoresistive effect layer having a linear portion running along a direction perpendicular to the magnetized direction of said magnetization fixed layer.

9. The acceleration sensor as claimed in claim 1, wherein said spring member has at least one strip-shaped plate spring with a fulcrum and support sections separated from said fulcrum for supporting said pair of permanent magnets, said at least one strip-shaped plate spring being configured to produce a bending stress in response to the external force applied so as to displace said pair of permanent magnets.

10. The acceleration sensor as claimed in claim 9, wherein said at least one strip-shaped plate spring consists of two strip-shaped plate springs, and wherein each strip-shaped plate spring has said fulcrum at one end and said support section for supporting said pair of permanent magnets at the other end.

11. The acceleration sensor as claimed in claim 9, wherein said at least one strip-shaped plate spring consists of a single strip-shaped plate spring having said fulcrum at its center and said support sections for supporting said pair of permanent magnets at its both ends.

12. The acceleration sensor as claimed in claim 1, wherein each multi-layered magnetoresistive effect element consists of a giant magnetoresistive effect element or a tunnel magnetoresistive effect element.

13. A magnetic disk drive apparatus with an acceleration sensor comprising: a pair of permanent magnets each having a surface facing a magnetic field detection sensor, said pair of permanent magnets being arranged in parallel so that said surfaces of the pair of permanent magnets have different magnetic polarities with each other;a spring member for supporting said pair of permanent magnets to displace the pair of permanent magnets when an external force is applied; andthe magnetic field detection sensor mounted in stationary state to face said pair of permanent magnets,said magnetic field detection sensor having at least one pair of multi-layered magnetoresistive effect elements, each including a magnetization fixed layer and a magnetization free layer, said magnetization fixed layer being magnetized in a direction parallel to a displacement detection direction,said pair of permanent magnets being arranged so that a longitudinal direction of each permanent magnet is in parallel with the magnetized direction of said magnetization fixed layer.

14. The magnetic disk drive apparatus as claimed in claim 13, wherein a center of each multi-layered magnetoresistive effect element is located at the same position in a magnetized direction of said magnetization free layer as a center of each permanent magnet.

15. The magnetic disk drive apparatus as claimed in claim 13, wherein said at least one pair of multi-layered magnetoresistive effect elements are arranged to face said pair of permanent magnets at a position where no reverse of a component of magnetic field applied from said pair of permanent magnets, in a magnetized direction of said magnetization free layer, occurs.

16. The magnetic disk drive apparatus as claimed in claim 13, wherein each multi-layered magnetoresistive effect element has a length in the magnetized direction of said magnetization fixed layer, which is longer than that of said magnetization free layer.

17. The magnetic disk drive apparatus as claimed in claim 13, wherein said at least one pair of multi-layered magnetoresistive effect elements are arranged near a center of each permanent magnet in the magnetized direction of said magnetization fixed layer.

18. The magnetic disk drive apparatus as claimed in claim 13, wherein each multi-layered magnetoresistive effect element consists of a plurality of multi-layered magnetoresistive effect layers connected in series, each multi-layered magnetoresistive effect layer having a linear portion running along a direction perpendicular to the magnetized direction of said magnetization fixed layer.

19. The magnetic disk drive apparatus as claimed in claim 13, wherein said spring member has at least one strip-shaped plate spring with a fulcrum and support sections separated from said fulcrum for supporting said pair of permanent magnets, said at least one strip-shaped plate spring being configured to produce a bending stress in response to the external force applied so as to displace said pair of permanent magnets.