Disk storage device having a three-phase brushless DC underhub configured spindle motor

Abstract

A disk memory drive includes a brushless drive outer rotor motor having an internal space and a stator with windings. The outer rotor coaxially encircles the stator and a substantially cylindrical air gap is defined between the stator and the rotor. The rotor includes permanent magnets and a hub fixedly connected with the magnet. A disk mounting section is provided on the hub for accommodating at least one storage disk positioned in a clear space, the mounting section being adapted to extend through a central aperture of the storage disk. The windings and the magnets interacting with the windings are disposed for at least half of the axial longitudinal dimension thereof within a space surrounded by the disk mounting section of the hub. Bearings rotatably mount the rotor and the hub.

What is claimed is:  
     
       1. A disk memory drive comprising: a brushless drive motor having an internal space defined therein and a stator including winding means defining magnetically active parts of the drive motor and having a given axial extension, the motor having an outer rotor with an inner circumference, an outer circumference and an open end coaxially encircling the stator and a substantially cylindrical air gap defined between the stator and the rotor, the rotor including a separate non ferromagnetic hub and a soft iron ring element interiorly of said hub and radially located means forming a permanent magnet interiorly of said ring having a predetermined axial extension fixedly connected therewith for magnetic interaction with said winding means; a disk mounting section provided on the outside of said hub for accommodating at least one storage disk for location in a clean chamber surrounding said rotor when the drive motor is mounted for operation, the disk mounting section on the hub along its axial length being adapted to extend through a central aperture of the storage disk, the winding means and the magnet means interacting therewith being disposed for at least half of the axial extension thereof within a space surrounded by the disk mounting section of the hub; and first and second axially separated bearing means having inner and outer races on a shaft rotatably mounting the rotor and the hub on the shaft, the motor also including rotating means interacting with stationary means for determining the rotational position of the rotor, the internal space of said motor, which includes the internal portions thereof with the bearing means, being sealed off against the clean chamber when the drive motor is mounted for operation, a disk-shaped ring member being located with precision at the open end of the rotor between the inner circumference of the rotor and the outer race of one of the axially separated bearing means, and means stationary containing leads establishing electrical connection between the internal space and the outside of the motor. 
     
     
       2. A disk memory drive according to  claim 1 , wherein said rotating means interacting with said stationary means comprises rotational position indicator means which includes permanent magnet poles disposed on the disk-shaped ring member for rotation therewith and wherein the rotational position sensor means is sensitive to magnetic fields and interacts with the permanent magnet poles. 
     
     
       3. A disk memory drive according to  claim 2 , wherein the shaft is a stationary shaft. 
     
     
       4. A disk memory drive according to  claim 3  wherein the rotational position sensor means is mounted on a printed circuit board opposite the disk-shaped member ring. 
     
     
       5. A disk memory drive according to  claim 4 , further including electronic commutation devices for the electromagnetization of the stator also being mounted on the printed circuit board. 
     
     
       6. A disk memory drive according to  claim 4 , wherein the printed circuit board is supported on a flange fixed to the stationary shaft. 
     
     
       7. A disk memory drive according to  claim 3 , further including a magnetic shield means at least circumferentially surrounding the stator for shielding a clean chamber containing the disk from the magnetic flux of the stator and wherein the stationary shaft is of constant diameter and the outer rotor includes a bell-shaped housing with a substantially closed end and a substantially open end, the stator together with the magnetic shield being firmly mounted to the stationary shaft, the inner race of each bearing being firmly mounted on the stationary shaft on either axial side of the stator, the upper bearing being positioned inwardly adjacent of the closed end of the bell-shaped outer rotor, and the lower bearing being positioned adjacent the open end of the bell-shaped outer rotor. 
     
     
       8. A disk memory drive according to  claim 2 , wherein the internal space of the motor is sealed by means of a cover located at the open end of the outer rotor, the cover also serving as a bearing mounting flange, and the rotational position indicator means being mounted on the outside of the motor cover with respect to the sealed inner space of the motor. 
     
     
       9. A disk memory drive according to  claim 2 , wherein the outer rotor includes an outer rotor casing of ferromagnetic material, the outer rotor serving also as the hub, the rotational position indicator being mounted on a lower part of the hub outside the sealed inner space of the motor. 
     
     
       10. A disk memory drive according to  claim 2 , further comprising a bearing mounting flange having projections in the actual axial direction that project into the disk-shaped ring member, and a labyrinth seal located between the projections and the ring member formed by a combination of cylindrical and radially flat gaps having only dimensions of normal clearances between moving parts. 
     
     
       11. A disk memory drive according to  claim 10 , wherein the projections on the bearing mounting flange are rectangular in section and extend axially. 
     
     
       12. A disk memory drive according to  claim 10 , wherein the ring member on which part of the bearing race is mounted is substantially flush in the axial direction with the mounting flange, the ring member being inserted in the outer rotor casing that forms the hub. 
     
     
       13. A disk memory drive having a brushless drive motor, comprising a stator having a predetermined axial extension, a coaxially positioned outer rotor encircling the stator and defining therebetween a substantially cylindrical air gap, the rotor having an inner circumference and an outer circumference and a predetermined axial extension, a cylindrically shaped permanent magnet having a predetermined axial extension disposed adjacent the air gap on the inner circumference of the rotor to rotate therewith and magnetically interact with the stator, a ferromagnetic hub on the outer circumference of the rotor firmly fixed to the motor magnet, the hub radially surrounding the predetermined axial extension of said permanent magnet and being provided on its outer circumference with a disk mounting section which can extend through the central opening in a storage disk to mount at least one storage disk thereon, a shaft having first and second axially separated bearing means mounted thereon rotatably mounting the rotor with hub on the shaft, and seals located axially outside of the axial extension of the first and second bearing means for sealing the space therebetween. 
     
     
       14. A disk memory drive according to  claim 13 , wherein the shaft is a stationary shaft. 
     
     
       15. A disk memory drive according to  claim 14 , wherein the seals are magnetic liquid seals. 
     
     
       16. A disk memory drive according to  claim 14 , wherein the seals are labyrinth seals. 
     
     
       17. A disk memory drive according to  claim 14 , wherein the stationary shaft projects axially externally of the upper and lower seals. 
     
     
       18. A disk memory drive according to  claim 14 , wherein the labyrinth seal is formed of a member having a substantially L-shaped cross section, being mounted on and extending radially from the stationary shaft, the short leg of the L-shaped member extending axially outwardly. 
     
     
       19. A disk memory drive according to  claim 16 , further including a ring member of L-shaped cross section being provided on the rotor and being opposite and complementary to the stationary mounted L-shaped member, the longer leg of the L-shaped member on the rotor extending inwardly toward the stationary shaft with only a clearance dimension separating the two parts. 
     
     
       20. A disk memory drive according to  claim 16 , wherein the stationary L-shaped a member lies inboard axially and is substantially encompassed by the rotating L-shaped ring, a flat radial labyrinth gap being formed radially between the respective short legs of the L-shaped members. 
     
     
       21. A disk storage device, comprising in combination: 
       
         a housing for providing an environment that is not maintained substantially contaminant free;  
       
       
         at least one rotatable storage disk that is provided in said environment for rotation about an axis, said at least one disk having a central opening;  
       
       
         at least one data head that is provided in said environment and that allows information to be read from said at least one storage disk;  
       
         a brushless DC motor for rotating said at least one storage disk about said axis, said brushless DC motor including a stator concentric with said axis, a stator winding disposed on said stator that has at least first, second, and third phase windings that are Y connected, each of said phase windings including at least two non - overlapping stator coils, said brushless DC motor further including a shaft aligned on said axis, at least one bearing affixed to said shaft, and a rotor that is mounted for rotation about said axis relative to said stator, said rotor having a permanent magnetic ring that has at least four permanent magnets of alternating polarity and that is mounted on a magnetically conductive member in a manner such that a generally cylindrical air gap is defined between adiacent surfaces of said stator and said permanent magnetic ring;    
       
         a circuit that generates first, second, and third control signals that are offset by approximately  120 ° electrical from one to the next and that are generally representative of the position of said rotor with respect to said stator, each one of said control signals being at a first potential during an interval of approximately  180 ° electrical and being at a second potential during a next following interval of approximately  180 ° electrical;  
       
       
         said circuit applying first, second, and third drive voltages to said first, second, and third phase windings to thereby supply current to the coils in each one of said phase windings in a cyclical sequence as a function of said first, second, and third control signals to cause said rotor to rotate about said axis;  
       
       
         wherein first, second, and third induced voltages are induced in said first, second, and third phase windings by the rotation of said permanent magnetic ring with respect to said phase windings, each one of said induced voltages being offset by approximately  120 ° electrical from one to the next and, in passing through zero, being alternatively positive for an interval of at most  180 ° electrical and negative for an interval of at most  180 ° electrical, the sum of said first, second, and third induced voltages being approximately equal to zero for every relative position between said rotor and said stator;  
       
       
         wherein the changes of state of said first, second, and third control signals are in a fixed relationship with the zero-crossovers of said first, second, and third induced voltages so that said circuit generates said first, second, and third drive voltages without changing the approximate duration of said first, second, and third control signals;  
       
         wherein said circuit causes the duration of said first, second, and third drive voltages to be approximately equal to the duration of said first, second, and third control signals so that overlapping currents are generated in said three - phase winding thereby allowing said motor to provide generally smoother torque; and    
       
         wherein said brushless DC motor is mounted in said environment so that the space of said environment that is occupied by said at least one storage disk is axially separated from the space of said environment that is occupied by said permanent magnetic ring in a direction along said axis.  
       
     
     
       22. The disk storage device of  claim 21  wherein said central opening is smaller than at least one of the distances specified in a group consisting of: the inner diameter of said permanent magnetic ring, the outer diameter of said permanent magnetic ring, the inner diameter of said magnetically conductive member, and the outer diameter of said magnetically conductive member.  
     
     
       23. The disk storage device of  claim 21  wherein said magnetically conductive member provides at least a portion of a magnetic return path for said permanent magnetic ring.  
     
     
       24. The disk storage device of  claim 21  wherein said shaft is rotatable about said axis.  
     
     
       25. The disk storage device of  claim 21  wherein said rotor comprises an external rotor.  
     
     
       26. The disk storage device of  claim 21  wherein said permanent magnetic ring coaxially surrounds the Portion of said stator that forms said generally cylindrical air gap.  
     
     
       27. The disk storage device of  claim 21  further comprising at least two rotor position detectors that are mounted stationary with respect to said stator.  
     
     
       28. The disk storage device of  claim 27  wherein said rotor position detectors comprise Hall effect sensors.  
     
     
       29. The disk storage device of  claim 28  wherein said Hall sensors are positioned with respect to said stator to cause the changes of state of said first, second, and third control signals to substantially coincide with the zero- crossovers of said first, second, and third induced voltages.    
     
     
       30. The disk storage device of  claim 29  wherein at least one of said control signals changes state at approximately the same time as the zero- crossover of a corresponding one of said induced voltages.    
     
     
       31. The disk storage device of  claim 21  wherein the changes of state of said first, second, and third control signals substantially coincide with the zero- crossovers of said first, second, and third induced voltages.    
     
     
       32. The disk storage device of  claim 31  wherein at least one of said control signals changes state at approximately the same time as the zero- crossover a corresponding one of said induced voltages.    
     
     
       33. The disk storage device of  claim 21  wherein at least one of said control signals changes state at approximately the same time as the zero- crossover of a corresponding one of said induced voltages.    
     
     
       34. The disk storage device of  claim 21  further comprising a hub member for supporting said at least one disk said hub member having a cylindrical portion that extends through the central opening of said at least one storage disk.  
     
     
       35. The disk storage device of  claim 34  wherein said hub member is contiguous with a portion of said rotor.