CA1210045A - Brushless direct current motor with inverted magnet cup - Google Patents
Brushless direct current motor with inverted magnet cupInfo
- Publication number
- CA1210045A CA1210045A CA000439877A CA439877A CA1210045A CA 1210045 A CA1210045 A CA 1210045A CA 000439877 A CA000439877 A CA 000439877A CA 439877 A CA439877 A CA 439877A CA 1210045 A CA1210045 A CA 1210045A
- Authority
- CA
- Canada
- Prior art keywords
- motor
- shaft
- housing
- assembly
- spindle hub
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Expired
Links
Classifications
-
- G—PHYSICS
- G11—INFORMATION STORAGE
- G11B—INFORMATION STORAGE BASED ON RELATIVE MOVEMENT BETWEEN RECORD CARRIER AND TRANSDUCER
- G11B19/00—Driving, starting, stopping record carriers not specifically of filamentary or web form, or of supports therefor; Control thereof; Control of operating function ; Driving both disc and head
- G11B19/20—Driving; Starting; Stopping; Control thereof
- G11B19/2009—Turntables, hubs and motors for disk drives; Mounting of motors in the drive
-
- H—ELECTRICITY
- H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
- H02K—DYNAMO-ELECTRIC MACHINES
- H02K15/00—Methods or apparatus specially adapted for manufacturing, assembling, maintaining or repairing of dynamo-electric machines
- H02K15/16—Centering rotors within the stator; Balancing rotors
- H02K15/165—Balancing the rotor
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- Engineering & Computer Science (AREA)
- Manufacturing & Machinery (AREA)
- Power Engineering (AREA)
- Brushless Motors (AREA)
Abstract
ABSTRACT OF THE DISCLOSURE
A brushless direct current motor with the rotating magnet cup permanently attached to the spindle hub. After attachment, the combination spindle hub and magnet cup are affixed to the shaft and the resulting subassembly is dynamically balanced. The motor using this balanced subassembly can be assembled with no balancing required after assembly. The motor can also be disassembled for repair and reassembled without disturbing the dynamic balance The motor is especially useful for disk drive applications.
A brushless direct current motor with the rotating magnet cup permanently attached to the spindle hub. After attachment, the combination spindle hub and magnet cup are affixed to the shaft and the resulting subassembly is dynamically balanced. The motor using this balanced subassembly can be assembled with no balancing required after assembly. The motor can also be disassembled for repair and reassembled without disturbing the dynamic balance The motor is especially useful for disk drive applications.
Description
) Title: A BRU.S~ S DIRECT CURRENT
- MOTOR WITH INVERTED MAGNET
C~IP
Inventors: hichard A. Wilkinson, Jr.
William C. Hunt BACKCROUND OF THE INYENrION
This invention relates to a brushless direct current motor, and more particularly to a brushless direct current motor designed for use with rotating dis~ systems. Even more particularly, the iDvention relates to a brushless direct current motor wherein all of the rotating components can all be balanced as a unit in one balancing operation.
The use of brushless direct current motors in electronic equipment with rotating oomponents, such as a magnet1c disk storage system, has become common. There are two reason~ for this: (1) the speed of rotat$on of such devices must be precisely controlled, and the brushless direct current motor, with its electronic control system, allows accurate speed control to be easily accomplished; and
- MOTOR WITH INVERTED MAGNET
C~IP
Inventors: hichard A. Wilkinson, Jr.
William C. Hunt BACKCROUND OF THE INYENrION
This invention relates to a brushless direct current motor, and more particularly to a brushless direct current motor designed for use with rotating dis~ systems. Even more particularly, the iDvention relates to a brushless direct current motor wherein all of the rotating components can all be balanced as a unit in one balancing operation.
The use of brushless direct current motors in electronic equipment with rotating oomponents, such as a magnet1c disk storage system, has become common. There are two reason~ for this: (1) the speed of rotat$on of such devices must be precisely controlled, and the brushless direct current motor, with its electronic control system, allows accurate speed control to be easily accomplished; and
(2) the brushless direct current motor can be made an integral part of ths ~ech~nical support structure, thereby saving both space and cost.
In some uses of the brushle~s direct current motor~ the rotating components of the motor must be balanced to an acceptable level. If the correct leYel of balanoe is not aohieved, the electronic equipment using the motor may not function as desired, or the life of the motor may be shortened because of the stresses placed on the bearings from the wobble intnoduced by the imb~lance.
~2~ 5 Balancing of brushless direct current motors is accomplished in the prior art by individually balancing aach rotating component of the motor. The components are then assembled and the assembled unit 1s checked for the correct balance. Quite often, additional balancing is required.
If the motor should ever have to be ~ls~ss~mbled, e.g., because of maintenance of the motor or the overall system in which the motor is used, additional balancing may be required when the motor is reassembled. This is bec~l~e the individual components of the motor will probably not re~ssP~hle exactly as they were before disassembly. Two approachas have been used in the prior art to avoid this additional b~l~n~ing step: (1) the individual motor components may be fabricated to very tight tolerances, thereby ensuring that proper balance wlll be obtained regardless Or how the components are reassembled; or (2) keying pins and matching alignment holes may be selectively placed in the co~ponents, thereby maint~;~ln~ a fixed relationship between the components each time reassembly occurs. While the use of tight tolerances and keying pins and Al~L -nt holes helps ensure that a motor can be re~q~ ~led without needing rebalancing, these approache3 also disadvantageously add significantly to the cost of the motor. What i9 needed therefore is a low co~t, simple brushle^~s direct current motor design wherein maint~inln~ the desired balance of the rotating compon~nts ls no longer a problem.
SUMMARY OF THE INVENTION
It is an objective of the present invention to provide a brushless direct current motor whose rotating components can be balanced prior to assembly into the motor and which do not need additional balancing after motor assemblyO
It is another objective or the present in~ention to provide such a motor that can be disassembled, if necessary, and reassembled without the need of balancing after re~ssp~hly~
The invention meets these and other objectives through a brushless direct current motor design wherein all the rotating components can be assembled as a subassembly. This subassembly is then b~l~nced and assembled into the stationary components of the motor. Consequently, the rotating components, being in balance prior to assembly into the stationary components, and having no additicnal parts added, require no further balancing after assembly with the stationary components.
Further, because the rotating components of the motor are designed as a balanced subassembly, there is never a need to dlsassemble the subassembly. Thuq, whenever dis~q~ bly of the motor i3 required, the balanced subassembly can be readily removed from, and re-installed into, the stationary components of the motor, yet the balanoed subassembly never requires rebalancing.
The rotating components included in the balanced subassembly of the present invention comprise a shaft, a spindle hub (on which the rotating di3k or disks may be mounted), and a cup assembly (wherein permanent magnetics are mounted). Unlike the prior art, wherein traditional design practice teaches that the cup assembly must be mounted at one end of the shaft using a cup adapter, and the spindle hub must be mounted at the other end of the shaft, the present invention provides a unique subassembly wherein the cup assembly and spindle hub may be advantageously mounted to the same end of the shaft Once assembled and balanced, therefore, thi~ subassembly need never be disassembled.
Thus, in accordance with one broad aspect of the inven-tion, there is provided an improved, low cost, compact brushless direct current motor for use in a disk drive device comprising:
a housing having motor windings selectively spaced around an outer surface thereof, and means for mounting said housing to a disk drive device;
a shaft rotatably mounted in an opening extending through said housing, said rotatable mounting being realized with at least two non-resilient friction reducing bearings respectively placed at each end of said shaft and at corresponding ends of said opening in said housing;
a spindle hub affixed to a first end of said shaft, an upper side of said spindle hub being adapted for engagement with the center of the disk to be driven by said motor; and a magnet cup attached to said spindle hub, said magnet cup including at least one permanent magnet, said magnet cup bei.ng positioned within the periphery of said spindle hub such that said magnet maintains a selected juxtaposed, non-touching, relationship with an outer surface of said motor windings.
In accordance with another broad aspect of the inven-tion there is provided a method of manufacturing a compact, low cost brushless direct current motor for use in a disk drive de-vice, said motor including a housing, stationary windings affixed to an outer surface of said housing so as to lie sub-stantially in a plane orthogonal to a central longitudinal axis of said housing, a shaft, a spindle hub, and a magnet cup having an inside diameter greater than the diameter of said housing and windings, said method comprising the steps of:
(a) selectively spacing a plurality or permanent magnets around the inner periphery of said magnet cup;
~! - ~a"
P~ 5 ~ b) attaching said spindle hub to a first end of said shaft;
(c) attaching said magnetic cup to the shaft side of said spindle hub, thereby forming a first assembly comprised of said shaft, hub, and magnet cup;
(d) dynamically balancing said first assembly about a central longitudinal axis of said shaft; and (e~ rotatably and non-elastically mounting said first assembly in said housing such that the longitudinal axes of said housing and shaft coincide and maintain such relationship during operation of said motorr whereby the magnets of said magnet cup may rotate substantially in the same plane as said motor windings without coming in physical contact with said windings.
` 3b BRIEF DESCRIPTION OF THE DRA~INGS
The above and other object$ves, advantages and fea~ures of the present invention will become more apparent from the ~ollowing description of the preferred embodiment, which is described with reference to the following drawings, wherein:
FIGURE l is a cross-sectional drawing of a brushless direct current motor of the prior art, showing the rotating components that may require balancing and how they are assembled with the stationary components of the motor; an~
FIGURE 2 is a cross-sectional drawing of a brushless direct current motor desi~ned according to of the present invention, showing the same detail as FIGURE l.
DESCRIPTION OF THE PR~FERRED EMBODIMENT
The following is a description oP the be~t presently contemplated mode of carrying out the present invention. This description is given only ~or the purpose of describing the general prlnciples of the present invention and should not be taken in a limiting sense. The true scope of the invention can be ascertained by referring to the appended claims.
In order to bettér appreciate the features and advantages of the present invention1 it will first be instructive to describe in more detail a conventional brushless direct currert ~otor 2S used in the prior art ~or disk drive applications. Such a motor is shown in the cros~-sectional view of FIGURE l. The rotating components of the ~otor consist of the shaft lO, spindle hub ll, cup adapter 12, and rotating magnet cup 13. Mounted on the inner edge o~ the rotating ~2~
ma~net cup 13 are a plurallty of permanent magnets, shown in the fieure as solid rectangles 14 and 15.
The stationary components of the motor consist of the spindle housing l6 with a plurality of motor magnets, ~hown in the figure as rectangles 17 and 18, arranged around the periphery. These magnets re usually electro-magnets that are excited by applying a direct current of a desired polarity to coil win~ing~ associated wlth the magnets.
The Ahaft 10 of the rotating components is supported in the spindle housing 16 of the stationary component3 by the ball-bearings 20-27. The ball-bearings can be considered to be part of either the rotating components, the stationary components, or part of neither since typically the inner races ~supports for the bearings) 26-27 rotate with the ~haft 10, the outer race3 24-25 are stationary against She spindle housing 16, and the ball-bearings 20-23 rotate as necessary between the inner and outer races to 3upport the load of the rotatin~ components. While ball-bearings are ~hown in the figure, lt is not uncom~on ~or any appropriate rotational bearing mech~n1~ , e.g., roller bearing, ball-bearings, tapered pin bearings, etc., to be used.
The splndle ho~sing 16 of the stationary components is attached to the mount 30 of the mechanical structure o~ the equipment in which the motor is being used. The manner of mounting is not important to the present invention.
It i~ noted that ln a traditional direct current motor, (not a brushless motor), the magnets are part of the stationary portion o~
the motor. These magnets may be permanent or electro-magnets which are excited by the application of the proper direct current through coils built into the motor housing. The motor w1ndinEs are part of the rotating portion of the motor. Dir~ct current is supplied to the windings tbrough a commutator, i.e., slotted, insulated segments of copper (or other conductive material), which is made part of the rotating shaft, through carbon brushes which rub against the commutator. Pairs of segments of the commutator are electrically connected to individual pairs of motor windings. Electrical currents ln a pair of motor windings create a magnetic field which oppose~ the magnetic f`ield oP the fixed magnets in the stationary part of the motor, thus creatin~ tor~ional ~orces that cause the shaft to rotate. A~ the shaft, and therefore the commutator, rotate~ a different pair of motor w;n~ines receive the current from the commutator, thereby allowing the torsional forces, and hence shaft rotation to continue. Traditional direct current motors are heavy and bulky, and precise speed control i~ difficult to achieve.
~ n contrast, the motor windin~.q of a brushless dirsct current motor are part o~ the stationary component of the motor and the permanent magnet are part of` the rotating components. In order to develop the most torque, the permanent magnets are typically spaced radlally ~rom the center line of the shaft as far a~q possible.
Hence, a magnet cup assembly 13, as shown in FIGURF 1, i employed to place the magnets at a r-~il radial spacing, rather than merely attaching the magnets to the side of the shaft 10. Thus in FIGURE
1, the permanert magnets 14-15 are placed a r~ distance from the centerline of the shaft 10 and opposite the motor w1n~ngq 17-18. Direct current is electronically switched to the appropriate pair of motor win~in~ to create a magnetic force which causes the permanent magnet~, and therefore all the rotating components of the motor, to rotate.
Advantageously, the rotational speed of the brushless motor can easily be measured. For example, a slotted plate could be made part of the rotating portion of the motor. As the slots of such a plate pas~ between a light source and a photosensitive diode, a pulse train whose frequency is proportional to the rotational speed of the motor is created. This pulse train can be used to control the switching of current to the motor windings and thus accurately control the speed of the motor.
Therefore, the ability to precisely control the speed of a bru3hleqs direct current motor allow~ such motors to be used ln many applicatlons where a conventional direct current motor would not be acceptable, such as in a disk drive device. Such appllcations also require, however, a precise balance oP the rotating components. As explained earlier, while it i9 possible to precisely balance a motor such as that shown in FIG~RE 1, this balance will be lost if the motor i~ disassembled. To explain further, the shaft 10 and spindle hub 11 (see FIGURE 1) are fabricated from separate pieces of metal.
The spindle hub 11 is then attached permanently, e.g~, by means of an interference fit, to the shaft 10. The resultant sl'h~q~embly is then dynamically b~l~nced. This balancing is typically done by spinning the object at the desired speed, and measuring the amount of imbal~nce, for example with a ~trobe light. The object iY
stopped and an amount of material, estimated to be equal to the imbalance, is removed from the proper area of the object, usually by machinln~ or drilling the surface. The object is again spun and any imbalance is again determined. This process is repeated until the amount of r~m~ining imbalance i3 within a predetermined limit.
The cup adapter 12 and rotating magnet cup 13 must be balanced in a similar manner. ~hen all the rotating components 10-15 are balanced, the rotating components re assembled with the stationary components, and a complete motor assembly is realized. Depending upon the amount of imbalance allowed by the application 7 the resulting oomplete motor assembly may require additional balancing.
Also, as explained previously, i~ the motor should ever have to disassembled, a strong po~sibility exist~, dependent upon the care and cost expended in ~abricating the rotating parts, that upon reassembly balano$ng will again be required.
FIGURE 2 is a cross-sectional drawlng of a brushless direct current motor configured acaording to the present invention. As can b~ seen ~rom the figure, a rotating ~agnet cup 43~ along with the permanent magnet~ 44~45, are attached to a ~pindle hub 11 instead of to the opposite end of the shaft 10 (as taught in the prior art), and the ~otor windings ~7~48 are located at the spindle hub end of a spindle housing 46. The magnets 44-45 (which may be a single doughnut shaped core piece that is selectively magnetized, or a plurality of individual magnetized pieces) are mounted in the cup 43 so as to ma1ntain a selected juxtaposed relationship (depending upon th~ rotational position of the shaft~ an outer sur~ace of the motor windings 47-48. The shaft 10 rotates about an axis 50~ A disk 52, typically having a center hole 54 therein, engages the spindle hub 11 when the motor is used for disk drive application these ~eatures of the invention advantageously allow all the rotating components o~ the motor, i.e., the shaft 10, the spindle hub 11, rotating magnet cup l13, and permanent magnets 44-45 to be manufactured using conventional manu~acturing practices. No additional costs are incurred just because the components are going to be balanced. The rotating components are then assembled into a single compact subassembly. This subassembly is then balanced in the manner described above. The b~l~nced subassembly can then be installed into the stationary component~ of the ~otor.
a unique feature of the present invention i9 that once the rotating components are jolned together in a 3ubassembly, there is never a need to disassemble them. Thus~ once balanced, the rotating suba~sembly can be installed, and removed and reinstalled., in the motor without requiring additional balancing. This feature signi~icantly reduces the cost of manu~acturing and maintaining the motor assembly because only one subassembly need be balanced, and t~at need only be ~ nced one time.
While seemingly a simple change, placing the rotating magnetic cup 13, permanent magnets 14-159 and motor w~ndlng~ 17-18 at the spindly hub end o~ the motor housing as shown in FIGURE 2 represents a significant advance in the art. Prior art disk drive brushless motors known ~o applicants have all placed the magnetic cup 13 at the opposite end of the shaft from the spindle in order to more evenly distribute the motor inert~a along the length of the shaft.
Such inertia distribution is neces~ry, as taught in the art, in order to properly distribute the rotational shaft stresses along the ~ull length of the sha~t and in order to maintain a moment of inertia that is more or less centered within the motor housing. The inventors herein where the first to recogni~e that coupling most of the motor inertia to one end of the ~haft as shown in FIGURE 2 does not create a problem as the prior art teachings wo~ld suggest It is believed that the reason ~or this is that achieving an~
maintaining a proper dynamic balance, in a simple and inexpensive manner as is done with the configuration of the PreSent invention, results in much less wear and strain of the type that would otherwise make uneven motor inertia distribution ti.e., most of the motor inertia coupled to one end of the sha~t) significant. In any event, the result~ obtained to date by u~ing the motor configuraSion shown in FIGU~E 2 have been surprisingly and unexpectedly good.
Accordlngly, because of the advantages it provides, the present invention is planned for use in many of the dlsk drive products manufactured by the inventors' employer.
In some uses of the brushle~s direct current motor~ the rotating components of the motor must be balanced to an acceptable level. If the correct leYel of balanoe is not aohieved, the electronic equipment using the motor may not function as desired, or the life of the motor may be shortened because of the stresses placed on the bearings from the wobble intnoduced by the imb~lance.
~2~ 5 Balancing of brushless direct current motors is accomplished in the prior art by individually balancing aach rotating component of the motor. The components are then assembled and the assembled unit 1s checked for the correct balance. Quite often, additional balancing is required.
If the motor should ever have to be ~ls~ss~mbled, e.g., because of maintenance of the motor or the overall system in which the motor is used, additional balancing may be required when the motor is reassembled. This is bec~l~e the individual components of the motor will probably not re~ssP~hle exactly as they were before disassembly. Two approachas have been used in the prior art to avoid this additional b~l~n~ing step: (1) the individual motor components may be fabricated to very tight tolerances, thereby ensuring that proper balance wlll be obtained regardless Or how the components are reassembled; or (2) keying pins and matching alignment holes may be selectively placed in the co~ponents, thereby maint~;~ln~ a fixed relationship between the components each time reassembly occurs. While the use of tight tolerances and keying pins and Al~L -nt holes helps ensure that a motor can be re~q~ ~led without needing rebalancing, these approache3 also disadvantageously add significantly to the cost of the motor. What i9 needed therefore is a low co~t, simple brushle^~s direct current motor design wherein maint~inln~ the desired balance of the rotating compon~nts ls no longer a problem.
SUMMARY OF THE INVENTION
It is an objective of the present invention to provide a brushless direct current motor whose rotating components can be balanced prior to assembly into the motor and which do not need additional balancing after motor assemblyO
It is another objective or the present in~ention to provide such a motor that can be disassembled, if necessary, and reassembled without the need of balancing after re~ssp~hly~
The invention meets these and other objectives through a brushless direct current motor design wherein all the rotating components can be assembled as a subassembly. This subassembly is then b~l~nced and assembled into the stationary components of the motor. Consequently, the rotating components, being in balance prior to assembly into the stationary components, and having no additicnal parts added, require no further balancing after assembly with the stationary components.
Further, because the rotating components of the motor are designed as a balanced subassembly, there is never a need to dlsassemble the subassembly. Thuq, whenever dis~q~ bly of the motor i3 required, the balanced subassembly can be readily removed from, and re-installed into, the stationary components of the motor, yet the balanoed subassembly never requires rebalancing.
The rotating components included in the balanced subassembly of the present invention comprise a shaft, a spindle hub (on which the rotating di3k or disks may be mounted), and a cup assembly (wherein permanent magnetics are mounted). Unlike the prior art, wherein traditional design practice teaches that the cup assembly must be mounted at one end of the shaft using a cup adapter, and the spindle hub must be mounted at the other end of the shaft, the present invention provides a unique subassembly wherein the cup assembly and spindle hub may be advantageously mounted to the same end of the shaft Once assembled and balanced, therefore, thi~ subassembly need never be disassembled.
Thus, in accordance with one broad aspect of the inven-tion, there is provided an improved, low cost, compact brushless direct current motor for use in a disk drive device comprising:
a housing having motor windings selectively spaced around an outer surface thereof, and means for mounting said housing to a disk drive device;
a shaft rotatably mounted in an opening extending through said housing, said rotatable mounting being realized with at least two non-resilient friction reducing bearings respectively placed at each end of said shaft and at corresponding ends of said opening in said housing;
a spindle hub affixed to a first end of said shaft, an upper side of said spindle hub being adapted for engagement with the center of the disk to be driven by said motor; and a magnet cup attached to said spindle hub, said magnet cup including at least one permanent magnet, said magnet cup bei.ng positioned within the periphery of said spindle hub such that said magnet maintains a selected juxtaposed, non-touching, relationship with an outer surface of said motor windings.
In accordance with another broad aspect of the inven-tion there is provided a method of manufacturing a compact, low cost brushless direct current motor for use in a disk drive de-vice, said motor including a housing, stationary windings affixed to an outer surface of said housing so as to lie sub-stantially in a plane orthogonal to a central longitudinal axis of said housing, a shaft, a spindle hub, and a magnet cup having an inside diameter greater than the diameter of said housing and windings, said method comprising the steps of:
(a) selectively spacing a plurality or permanent magnets around the inner periphery of said magnet cup;
~! - ~a"
P~ 5 ~ b) attaching said spindle hub to a first end of said shaft;
(c) attaching said magnetic cup to the shaft side of said spindle hub, thereby forming a first assembly comprised of said shaft, hub, and magnet cup;
(d) dynamically balancing said first assembly about a central longitudinal axis of said shaft; and (e~ rotatably and non-elastically mounting said first assembly in said housing such that the longitudinal axes of said housing and shaft coincide and maintain such relationship during operation of said motorr whereby the magnets of said magnet cup may rotate substantially in the same plane as said motor windings without coming in physical contact with said windings.
` 3b BRIEF DESCRIPTION OF THE DRA~INGS
The above and other object$ves, advantages and fea~ures of the present invention will become more apparent from the ~ollowing description of the preferred embodiment, which is described with reference to the following drawings, wherein:
FIGURE l is a cross-sectional drawing of a brushless direct current motor of the prior art, showing the rotating components that may require balancing and how they are assembled with the stationary components of the motor; an~
FIGURE 2 is a cross-sectional drawing of a brushless direct current motor desi~ned according to of the present invention, showing the same detail as FIGURE l.
DESCRIPTION OF THE PR~FERRED EMBODIMENT
The following is a description oP the be~t presently contemplated mode of carrying out the present invention. This description is given only ~or the purpose of describing the general prlnciples of the present invention and should not be taken in a limiting sense. The true scope of the invention can be ascertained by referring to the appended claims.
In order to bettér appreciate the features and advantages of the present invention1 it will first be instructive to describe in more detail a conventional brushless direct currert ~otor 2S used in the prior art ~or disk drive applications. Such a motor is shown in the cros~-sectional view of FIGURE l. The rotating components of the ~otor consist of the shaft lO, spindle hub ll, cup adapter 12, and rotating magnet cup 13. Mounted on the inner edge o~ the rotating ~2~
ma~net cup 13 are a plurallty of permanent magnets, shown in the fieure as solid rectangles 14 and 15.
The stationary components of the motor consist of the spindle housing l6 with a plurality of motor magnets, ~hown in the figure as rectangles 17 and 18, arranged around the periphery. These magnets re usually electro-magnets that are excited by applying a direct current of a desired polarity to coil win~ing~ associated wlth the magnets.
The Ahaft 10 of the rotating components is supported in the spindle housing 16 of the stationary component3 by the ball-bearings 20-27. The ball-bearings can be considered to be part of either the rotating components, the stationary components, or part of neither since typically the inner races ~supports for the bearings) 26-27 rotate with the ~haft 10, the outer race3 24-25 are stationary against She spindle housing 16, and the ball-bearings 20-23 rotate as necessary between the inner and outer races to 3upport the load of the rotatin~ components. While ball-bearings are ~hown in the figure, lt is not uncom~on ~or any appropriate rotational bearing mech~n1~ , e.g., roller bearing, ball-bearings, tapered pin bearings, etc., to be used.
The splndle ho~sing 16 of the stationary components is attached to the mount 30 of the mechanical structure o~ the equipment in which the motor is being used. The manner of mounting is not important to the present invention.
It i~ noted that ln a traditional direct current motor, (not a brushless motor), the magnets are part of the stationary portion o~
the motor. These magnets may be permanent or electro-magnets which are excited by the application of the proper direct current through coils built into the motor housing. The motor w1ndinEs are part of the rotating portion of the motor. Dir~ct current is supplied to the windings tbrough a commutator, i.e., slotted, insulated segments of copper (or other conductive material), which is made part of the rotating shaft, through carbon brushes which rub against the commutator. Pairs of segments of the commutator are electrically connected to individual pairs of motor windings. Electrical currents ln a pair of motor windings create a magnetic field which oppose~ the magnetic f`ield oP the fixed magnets in the stationary part of the motor, thus creatin~ tor~ional ~orces that cause the shaft to rotate. A~ the shaft, and therefore the commutator, rotate~ a different pair of motor w;n~ines receive the current from the commutator, thereby allowing the torsional forces, and hence shaft rotation to continue. Traditional direct current motors are heavy and bulky, and precise speed control i~ difficult to achieve.
~ n contrast, the motor windin~.q of a brushless dirsct current motor are part o~ the stationary component of the motor and the permanent magnet are part of` the rotating components. In order to develop the most torque, the permanent magnets are typically spaced radlally ~rom the center line of the shaft as far a~q possible.
Hence, a magnet cup assembly 13, as shown in FIGURF 1, i employed to place the magnets at a r-~il radial spacing, rather than merely attaching the magnets to the side of the shaft 10. Thus in FIGURE
1, the permanert magnets 14-15 are placed a r~ distance from the centerline of the shaft 10 and opposite the motor w1n~ngq 17-18. Direct current is electronically switched to the appropriate pair of motor win~in~ to create a magnetic force which causes the permanent magnet~, and therefore all the rotating components of the motor, to rotate.
Advantageously, the rotational speed of the brushless motor can easily be measured. For example, a slotted plate could be made part of the rotating portion of the motor. As the slots of such a plate pas~ between a light source and a photosensitive diode, a pulse train whose frequency is proportional to the rotational speed of the motor is created. This pulse train can be used to control the switching of current to the motor windings and thus accurately control the speed of the motor.
Therefore, the ability to precisely control the speed of a bru3hleqs direct current motor allow~ such motors to be used ln many applicatlons where a conventional direct current motor would not be acceptable, such as in a disk drive device. Such appllcations also require, however, a precise balance oP the rotating components. As explained earlier, while it i9 possible to precisely balance a motor such as that shown in FIG~RE 1, this balance will be lost if the motor i~ disassembled. To explain further, the shaft 10 and spindle hub 11 (see FIGURE 1) are fabricated from separate pieces of metal.
The spindle hub 11 is then attached permanently, e.g~, by means of an interference fit, to the shaft 10. The resultant sl'h~q~embly is then dynamically b~l~nced. This balancing is typically done by spinning the object at the desired speed, and measuring the amount of imbal~nce, for example with a ~trobe light. The object iY
stopped and an amount of material, estimated to be equal to the imbalance, is removed from the proper area of the object, usually by machinln~ or drilling the surface. The object is again spun and any imbalance is again determined. This process is repeated until the amount of r~m~ining imbalance i3 within a predetermined limit.
The cup adapter 12 and rotating magnet cup 13 must be balanced in a similar manner. ~hen all the rotating components 10-15 are balanced, the rotating components re assembled with the stationary components, and a complete motor assembly is realized. Depending upon the amount of imbalance allowed by the application 7 the resulting oomplete motor assembly may require additional balancing.
Also, as explained previously, i~ the motor should ever have to disassembled, a strong po~sibility exist~, dependent upon the care and cost expended in ~abricating the rotating parts, that upon reassembly balano$ng will again be required.
FIGURE 2 is a cross-sectional drawlng of a brushless direct current motor configured acaording to the present invention. As can b~ seen ~rom the figure, a rotating ~agnet cup 43~ along with the permanent magnet~ 44~45, are attached to a ~pindle hub 11 instead of to the opposite end of the shaft 10 (as taught in the prior art), and the ~otor windings ~7~48 are located at the spindle hub end of a spindle housing 46. The magnets 44-45 (which may be a single doughnut shaped core piece that is selectively magnetized, or a plurality of individual magnetized pieces) are mounted in the cup 43 so as to ma1ntain a selected juxtaposed relationship (depending upon th~ rotational position of the shaft~ an outer sur~ace of the motor windings 47-48. The shaft 10 rotates about an axis 50~ A disk 52, typically having a center hole 54 therein, engages the spindle hub 11 when the motor is used for disk drive application these ~eatures of the invention advantageously allow all the rotating components o~ the motor, i.e., the shaft 10, the spindle hub 11, rotating magnet cup l13, and permanent magnets 44-45 to be manufactured using conventional manu~acturing practices. No additional costs are incurred just because the components are going to be balanced. The rotating components are then assembled into a single compact subassembly. This subassembly is then balanced in the manner described above. The b~l~nced subassembly can then be installed into the stationary component~ of the ~otor.
a unique feature of the present invention i9 that once the rotating components are jolned together in a 3ubassembly, there is never a need to disassemble them. Thus~ once balanced, the rotating suba~sembly can be installed, and removed and reinstalled., in the motor without requiring additional balancing. This feature signi~icantly reduces the cost of manu~acturing and maintaining the motor assembly because only one subassembly need be balanced, and t~at need only be ~ nced one time.
While seemingly a simple change, placing the rotating magnetic cup 13, permanent magnets 14-159 and motor w~ndlng~ 17-18 at the spindly hub end o~ the motor housing as shown in FIGURE 2 represents a significant advance in the art. Prior art disk drive brushless motors known ~o applicants have all placed the magnetic cup 13 at the opposite end of the shaft from the spindle in order to more evenly distribute the motor inert~a along the length of the shaft.
Such inertia distribution is neces~ry, as taught in the art, in order to properly distribute the rotational shaft stresses along the ~ull length of the sha~t and in order to maintain a moment of inertia that is more or less centered within the motor housing. The inventors herein where the first to recogni~e that coupling most of the motor inertia to one end of the ~haft as shown in FIGURE 2 does not create a problem as the prior art teachings wo~ld suggest It is believed that the reason ~or this is that achieving an~
maintaining a proper dynamic balance, in a simple and inexpensive manner as is done with the configuration of the PreSent invention, results in much less wear and strain of the type that would otherwise make uneven motor inertia distribution ti.e., most of the motor inertia coupled to one end of the sha~t) significant. In any event, the result~ obtained to date by u~ing the motor configuraSion shown in FIGU~E 2 have been surprisingly and unexpectedly good.
Accordlngly, because of the advantages it provides, the present invention is planned for use in many of the dlsk drive products manufactured by the inventors' employer.
Claims (4)
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:
1. An improved, low cost, compact brushless direct cur-rent motor for use in a disk drive device comprising:
a housing having motor windings selectively spaced around an outer surface thereof, and means for mounting said housing to a disk drive device;
a shaft rotatably mounted in an opening extending through said housing, said rotatable mounting being realized with at least two non-resilient friction reducing bearings respectively placed at each end of said shaft and at corresponding ends of said opening in said housing;
a spindle hub affixed to a first end of said shaft, an upper side of said spindle hub being adapted for engagement with the center of the disk to be driven by said motor; and a magnet cup attached to said spindle hub, said magnet cup including at least one permanent magnet, said magnet cup being positioned within the periphery of said spindle hub such that said magnet maintains a selected juxtaposed, non-touching, relationship with an outer surface of said motor windings.
a housing having motor windings selectively spaced around an outer surface thereof, and means for mounting said housing to a disk drive device;
a shaft rotatably mounted in an opening extending through said housing, said rotatable mounting being realized with at least two non-resilient friction reducing bearings respectively placed at each end of said shaft and at corresponding ends of said opening in said housing;
a spindle hub affixed to a first end of said shaft, an upper side of said spindle hub being adapted for engagement with the center of the disk to be driven by said motor; and a magnet cup attached to said spindle hub, said magnet cup including at least one permanent magnet, said magnet cup being positioned within the periphery of said spindle hub such that said magnet maintains a selected juxtaposed, non-touching, relationship with an outer surface of said motor windings.
2. The motor as defined in claim 1 wherein said shaft, spindle hub, and magnet cup are assembled into a first assembly and dynamically balanced about a center axis of said shaft prior to mounting said first assembly into said housing.
3. The motor as defined in claim 2 wherein said first assembly may be selectively detached from said housing, whereby said motor may he disassembled for maintenance or other purposes and reassembled without having to disassemble said first assembly, and further whereby said first assembly need not be dynamically balanced subsequent to an initial balancing operation.
4. A method of manufacturing a compact, low cost, brushless direct current motor for use in a disk drive device, said motor including a housing, stationary windings affixed to an outer surface of said housing so as to lie substantially in a plane orthogonal to a central longitudinal axis of said housing, a shaft, a spindle hub, and a magnet cup having an inside diameter greater than the diameter of said housing and windings, said method comprising the steps of:
(a) selectively spacing a plurality or permanent magnets around the inner periphery of said magnet cup;
(b) attaching said spindle hub to a first end of said shaft;
(c) attaching said magnetic cup to the shaft side of said spindle hub, thereby forming a first assembly comprised of said shaft, hub, and magnet cup;
(d) dynamically balancing said first assembly about a central longitudinal axis of said shaft; and (e) rotatably and non-elastically mounting said first assembly in said housing such that the longitudinal axes of said housing and shaft coincide and maintain such relationship during operation of said motor, whereby the magnets of said magnet cup may rotate substantially in the same plane as said motor windings without coming in physical contact with said windings.
(a) selectively spacing a plurality or permanent magnets around the inner periphery of said magnet cup;
(b) attaching said spindle hub to a first end of said shaft;
(c) attaching said magnetic cup to the shaft side of said spindle hub, thereby forming a first assembly comprised of said shaft, hub, and magnet cup;
(d) dynamically balancing said first assembly about a central longitudinal axis of said shaft; and (e) rotatably and non-elastically mounting said first assembly in said housing such that the longitudinal axes of said housing and shaft coincide and maintain such relationship during operation of said motor, whereby the magnets of said magnet cup may rotate substantially in the same plane as said motor windings without coming in physical contact with said windings.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| US43798882A | 1982-11-01 | 1982-11-01 | |
| US437,988 | 1982-11-01 |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1210045A true CA1210045A (en) | 1986-08-19 |
Family
ID=23738763
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA000439877A Expired CA1210045A (en) | 1982-11-01 | 1983-10-27 | Brushless direct current motor with inverted magnet cup |
Country Status (3)
| Country | Link |
|---|---|
| EP (1) | EP0124547A1 (en) |
| CA (1) | CA1210045A (en) |
| WO (1) | WO1984001863A1 (en) |
Families Citing this family (10)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US4779165A (en) * | 1981-09-07 | 1988-10-18 | Papst-Motoren Gmbh & Co. Kg | Disk storage drive |
| CH670323A5 (en) * | 1985-03-30 | 1989-05-31 | Papst Motoren Gmbh & Co Kg | |
| USRE34412E (en) * | 1981-09-07 | 1993-10-19 | Papst-Motoren Gmbh & Co. Kg | Disk storage drive having motor drive with non-corrodible hub |
| GB2142786B (en) * | 1983-05-23 | 1986-12-31 | Data General Corp | Disc drive system |
| DE3419814C1 (en) * | 1984-05-26 | 1985-11-28 | GMN Georg Müller Nürnberg GmbH, 8500 Nürnberg | Motor spindle for magnetic disk storage |
| GB2218856B (en) * | 1985-03-30 | 1990-02-28 | Papst Motoren Gmbh & Co Kg | Disk store drive |
| CA2027225A1 (en) * | 1989-10-27 | 1991-04-28 | Donald James Macleod | Spindle motor assembly for disc drives |
| US5223756A (en) * | 1993-01-04 | 1993-06-29 | Gec-Marconi Electronic Systems Corp. | Self-aligning motor assembly |
| FR2782856B1 (en) * | 1998-09-02 | 2002-01-18 | Peugeot | ELECTRIC MOTOR INTENDED TO BE COUPLED TO A TRANSMISSION, ESPECIALLY OF A MOTOR VEHICLE |
| EP1730834A1 (en) * | 2004-01-29 | 2006-12-13 | Koninklijke Philips Electronics N.V. | Method of balancing an suction unit comprising a ventilator and an electric motor |
Family Cites Families (5)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US3458740A (en) * | 1965-12-02 | 1969-07-29 | Victor Company Of Japan | Motor of outer rotor type |
| US3596121A (en) * | 1969-09-10 | 1971-07-27 | Robbins & Myers | Electric induction motor |
| US4117359A (en) * | 1974-01-30 | 1978-09-26 | Teldix Gmbh | Bearing and drive structure for spinning turbine |
| DE2417818C2 (en) * | 1974-04-11 | 1983-03-31 | Teldix Gmbh, 6900 Heidelberg | Electric machine |
| GB1604121A (en) * | 1977-04-08 | 1981-12-02 | Sony Corp | Dc motors |
-
1983
- 1983-10-13 EP EP19830903358 patent/EP0124547A1/en not_active Withdrawn
- 1983-10-13 WO PCT/US1983/001613 patent/WO1984001863A1/en not_active Application Discontinuation
- 1983-10-27 CA CA000439877A patent/CA1210045A/en not_active Expired
Also Published As
| Publication number | Publication date |
|---|---|
| EP0124547A1 (en) | 1984-11-14 |
| WO1984001863A1 (en) | 1984-05-10 |
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| MKEX | Expiry |