Voice coil motor composite magnet assembly including low-coercivity magnetic material
A voice coil motor (VCM) includes a coil, and on a first side a first yoke having a coil-side facing the coil, a first low-coercivity permanent magnet positioned between the coil and the coil-side of the first yoke and having a yoke-side facing the first yoke and a coil-side opposing the yoke-side, and a first high-coercivity permanent magnet adjoining the coil-side of the first low-coercivity magnet. A second side of the VCM on the opposing side of the coil is similarly configured. The permeance coefficient of such a VCM enables magnetic stability of low-coercivity magnetic materials. Additional high-coercivity permanent magnets may be bonded to the coil-sides of each of the first and second yokes and adjoining the yoke-sides of each of the low-coercivity permanent magnets, if the relative thicknesses of the magnet materials so dictate by design.
1. A voice coil motor (VCM) comprising:
a coil;
a first yoke having a coil-side facing the coil;
a first low-coercivity permanent magnet positioned between the coil and the coil-side of the first yoke and having a yoke-side facing the first yoke and a coil-side opposing the yoke-side;
a first high-coercivity permanent magnet adjoining the coil-side of the first low-coercivity permanent magnet;
a second yoke having a coil-side facing the coil;
a second low-coercivity permanent magnet positioned between the coil and the coil-side of the second yoke and having a yoke-side facing the second yoke and a coil-side opposing the yoke-side; and
a second high-coercivity permanent magnet adjoining the coil-side of the second low-coercivity permanent magnet.
2. The VCM of claim 1 , wherein:
the first low-coercivity permanent magnet is bonded to the coil-side of the first yoke; and
the second low-coercivity permanent magnet is bonded to the coil-side of the second yoke.
3. The VCM of claim 2 , wherein:
the first high-coercivity permanent magnet is bonded to the coil-side of the first low-coercivity permanent magnet; and
the second high-coercivity permanent magnet is bonded to the coil-side of the second low-coercivity permanent magnet.
4. The VCM of claim 1 , further comprising:
a third high-coercivity permanent magnet bonded to the coil-side of the first yoke and adjoining the yoke-side of the first low-coercivity permanent magnet; and
a fourth high-coercivity permanent magnet bonded to the coil-side of the second yoke and adjoining the yoke-side of the second low-coercivity permanent magnet.
5. The VCM of claim 4 , wherein:
the first low-coercivity permanent magnet is bonded to a coil-side of the third high-coercivity permanent magnet; and
the second low-coercivity permanent magnet is bonded to a coil-side of the fourth high-coercivity permanent magnet.
6. The VCM of claim 5 , wherein:
the first high-coercivity permanent magnet is bonded to the coil-side of the first low-coercivity permanent magnet; and
the second high-coercivity permanent magnet is bonded to the coil-side of the second low-coercivity permanent magnet.
7. The VCM of claim 1 , wherein:
each of the first and second high-coercivity permanent magnets has a magnetic normal coercivity (H cn ) greater than ten kilooersted (10 kOe) at ambient temperature; and
each of the first and second low-coercivity permanent magnets has a magnetic normal coercivity (H cn ) less than ten kilooersted (10 kOe) at ambient temperature.
8. A hard disk drive (HDD) comprising:
a plurality of disk media rotatably mounted on a spindle motor;
means for reading from and writing to at least one disk medium of the plurality of disk media; and
a voice coil motor (VCM) assembly configured for moving the means for reading and writing to access portions of the plurality of disk media, the VCM assembly comprising:
a coil,
a first yoke having a coil-side facing the coil,
a first low-coercivity permanent magnet positioned between the coil and the coil-side of the first yoke and having a yoke-side facing the first yoke and a coil-side opposing the yoke-side,
a first high-coercivity permanent magnet adjoining the coil-side of the first low-coercivity permanent magnet,
a second yoke having a coil-side facing the coil,
a second low-coercivity permanent magnet positioned between the coil and the coil-side of the second yoke and having a yoke-side facing the second yoke and a coil-side opposing the yoke-side, and
a second high-coercivity permanent magnet adjoining the coil-side of the second low-coercivity permanent magnet.
9. The HDD of claim 8 , wherein:
the first low-coercivity permanent magnet is bonded to the coil-side of the first yoke; and
the second low-coercivity permanent magnet is bonded to the coil-side of the second yoke.
10. The HDD of claim 9 , wherein:
the first high-coercivity permanent magnet is bonded to the coil-side of the first low-coercivity permanent magnet; and
the second high-coercivity permanent magnet is bonded to the coil-side of the second low-coercivity permanent magnet.
11. The HDD of claim 8 , further comprising:
a third high-coercivity permanent magnet bonded to the coil-side of the first yoke and adjoining the yoke-side of the first low-coercivity permanent magnet; and
a fourth high-coercivity permanent magnet bonded to the coil-side of the second yoke and adjoining the yoke-side of the second low-coercivity permanent magnet.
12. The HDD of claim 11 , wherein;
the first low-coercivity permanent magnet is bonded to a coil-side of the third high-coercivity permanent magnet; and
the second low-coercivity permanent magnet is bonded to a coil-side of the fourth high-coercivity permanent magnet.
13. The HDD of claim 12 , wherein:
the first high-coercivity permanent magnet is bonded to the coil-side of the first low-coercivity permanent magnet; and
the second high-coercivity permanent magnet is bonded to the coil-side of the second low-coercivity permanent magnet.
14. The HDD of claim 8 , wherein:
each of the first and second high-coercivity permanent magnets has a magnetic normal coercivity (H cn ) greater than ten kilooersted (10 kOe) at ambient temperature; and
each of the first and second low-coercivity permanent magnets has a magnetic normal coercivity (H cn ) less than ten kilooersted (10 kOe) at ambient temperature.
15. A method of assembling a voice coil motor (VCM), the method comprising:
forming a first half-assembly by:
bonding a first low-coercivity permanent magnet material to a coil-side of a first yoke, wherein the first low-coercivity permanent magnet material has a yoke-side facing the first yoke and a coil-side opposing the yoke-side;
bonding a first high-coercivity permanent magnet material to the coil-side of the first low-coercivity permanent magnet material; and
magnetically charging the first low-coercivity permanent magnet material and the first high-coercivity permanent magnet material to form a first low-coercivity permanent magnet and a first high-coercivity permanent magnet.
16. The method of claim 15 , further comprising:
forming a second half-assembly according to the method of claim 15 ; and
assembling together the first half-assembly and the second half-assembly.
17. A voice coil motor assembled according to the method of claim 16 .
18. A method of assembling a voice coil motor (VCM), the method comprising:
forming a first half-assembly by:
bonding a first high-coercivity permanent magnet material to a coil-side of a first yoke, wherein the first high-coercivity permanent magnet material has a yoke-side facing the first yoke and a coil-side opposing the yoke-side;
bonding a first low-coercivity permanent magnet material to the coil-side of the first high-coercivity permanent magnet material, wherein the first low-coercivity permanent magnet material has a yoke-side facing the first yoke and a coil-side opposing the yoke-side;
bonding a second high-coercivity permanent magnet material to the coil-side of the first low-coercivity permanent magnet material; and
magnetically charging the first high-coercivity permanent magnet material, the first low-coercivity permanent magnet material, and the second high-coercivity permanent magnet material to form a first high-coercivity permanent magnet, a first low-coercivity permanent magnet, and a second high-coercivity permanent magnet.
19. The method of claim 18 , further comprising:
forming a second half-assembly according to the method of claim 18 ; and
assembling together the first half-assembly and the second half-assembly.
20. A voice coil motor assembled according to the method of claim 19 .