In-pivot hybrid stepper motor for ball screw cam elevator mechanism for reduced-head hard disk drive
An approach to a reduced-head hard disk drive (HDD) involves an actuator elevator subsystem that includes a ball screw cam assembly with a hybrid permanent magnet (PM)-variable reluctance (VR) stepper motor disposed therein, to rotate the cam screw, which vertically translates an actuator arm assembly so that a corresponding pair of read-write heads can access different magnetic-recording disks of a multiple-disk stack. A suitably configured hybrid stepper motor can provide 200 full steps/rev for a 3.8 mm translation. Thus, to meet or surpass a step resolution of 6 μm/μstep or 0.5625°/μstep, the hybrid stepper motor would only need to be operated at 4 micro-step mode in order to achieve a 0.45°/μstep or 0.00475 mm/μstep, which enables a smoother motion since the available holding torque at the 4 th micro-step provides sufficient torque margin to overcome load torque, frictional torque, and detent torque.
1. An actuator system for a reduced-head hard disk drive (HDD), the actuator system comprising:
a ball screw cam assembly;
a head-stack assembly (HSA) translatably coupled with the cam assembly;
a permanent magnet (PM)-variable reluctance (VR) hybrid stepper motor disposed within and affixed to a screw of the cam assembly, and configured to drive rotation of the screw to drive translation of the HSA along an axis of the screw; and
a fixed shaft around which the hybrid stepper motor is positioned;
wherein the hybrid stepper motor is rotatable about the fixed shaft to drive the rotation of the screw, the hybrid stepper motor comprising:
a plurality of ring-shaped permanent magnets (PMs),
a stack of electrical steel lamination rings interposed between each adjacent pair of the PMs,
wherein the PMs and the lamination rings are affixed to an inner diameter of the screw and collectively operate as a rotor of the hybrid stepper motor,
a stator, disposed within the rotor, comprising a stack of electrical steel laminations configured with a plurality of main poles each having a plurality of teeth, and
a coil wound on each of the main poles.
2. The actuator system of claim 1 , wherein:
the plurality of ring-shaped PMs comprises at least three (3) PMs in a stacked formation; and
the stack of lamination rings comprises a stack of lamination rings between each of the at least three PMs.
3. The actuator system of claim 1 , wherein:
the plurality of PMs comprises five (5) PMs disposed in a stacked formation; and
the stack of lamination rings comprises four (4) stacks of lamination rings, with one stack positioned between each of the adjacent PMs;
wherein the five PMs are all unidirectionally axially magnetized.
4. The actuator system of claim 1 , wherein the stator consists of eight (8) main poles, with each main pole consisting of five (5) teeth.
5. The actuator system of claim 4 , wherein each of the lamination rings of the rotor consists of fifty (50) teeth.
6. The actuator system of claim 5 , wherein at least one stack of the lamination rings is assembled one-half (½) tooth pitch offset from another stack of the lamination rings.
7. A hard disk drive comprising the actuator system of claim 6 .
8. The actuator system of claim 1 , wherein the cam assembly and the disposed hybrid stepper motor are configured as an actuator pivot cartridge in a HDD.
9. The actuator system of claim 1 , wherein the ball screw cam assembly comprises:
a hollow screw comprising at least three starts,
a ball bearing assembly comprising a same number of balls as starts, wherein each ball rides in a corresponding start, thereby forming a plane on which the balls ride perpendicular to the axis of the screw.
10. The actuator system of claim 1 , further comprising:
one or more proximity sensors coupled with the HSA; and
a magnetic encoder strip positioned in close proximity to the one or more proximity sensors, and configured to provide a magnetic field for sensing by the one or more proximity sensors.
11. A hard disk drive comprising the actuator system of claim 10 .
12. A hard disk drive comprising the actuator system of claim 1 .
13. A permanent magnet (PM)-variable reluctance (VR) hybrid stepper motor configured to rotate about a fixed shaft, the hybrid stepper motor comprising:
a plurality of ring-shaped permanent magnets (PMs);
a stack of electrical steel lamination rings interposed between each adjacent pair of the PMs;
wherein the PMs and the lamination rings collectively operate as a rotor of the hybrid stepper motor;
a stator, disposed within the rotor, comprising a stack of electrical steel laminations configured with a plurality of main poles each having a plurality of teeth; and
a coil wound on each of the main poles.
14. The permanent magnet (PM)-variable reluctance (VR) hybrid stepper motor of claim 13 , wherein:
the plurality of PMs comprises five (5) PMs disposed in a stacked formation; and
the stack of lamination rings comprises four (4) stacks of lamination rings, with one stack positioned between each of the adjacent PMs;
wherein the five PMs are all unidirectionally axially magnetized.
15. The permanent magnet (PM)-variable reluctance (VR) hybrid stepper motor of claim 13 , wherein the stator consists of eight (8) main poles, with each main pole consisting of five (5) teeth.
16. The permanent magnet (PM)-variable reluctance (VR) hybrid stepper motor of claim 15 , wherein each of the lamination rings of the rotor consists of fifty (50) teeth.
17. The permanent magnet (PM)-variable reluctance (VR) hybrid stepper motor of claim 16 , wherein at least one stack of the lamination rings is assembled one-half (½) tooth pitch offset from another stack of the lamination rings.
18. A hard disk drive (HDD) head-stack assembly (HSA) pivot assembly comprising the PM-VR hybrid stepper motor of claim 13 disposed within a ball screw cam assembly and configured to drive rotation of the cam assembly to drive vertical translation of the HSA.
19. A method for vertically translating a head-stack assembly (HSA) in a hard disk drive (HDD) to access multiple magnetic-recording disks, the method comprising:
driving a permanent magnet (PM)-variable reluctance (VR) hybrid stepper motor disposed within a ball screw cam assembly comprising a screw, thereby rotating the screw about a coaxial fixed shaft;
allowing a planar multi-ball bearing assembly that is coupled with the HSA to translate vertically in response to rotating the screw; and
while the bearing assembly is translating, sensing the vertical position of the HSA.
20. A reduced-head hard disk drive (HDD), comprising:
recording means for storing digital information;
reading/writing means for reading from and writing to the recording means;
means for moving the reading/writing means to access portions of the recording means;
a permanent magnet (PM)-variable reluctance (VR) hybrid stepper motor rotating means for rotating cam means about a fixed shaft for translating the reading/writing means from one recording means to another recording means; and
means for sensing a vertical position of the reading/writing means.