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

Definitions

• This invention relates to a brushless direct current motor, and more particularly to a brushless direct current motor designed for use with rotating disk systems. Even more particularly, the invention 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 rotating components of the motor must be balanced to an acceptable level. If the correct level of balance is not achieved, 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 introduced by the imbalance. Balancing of brushless direct current motors is accomplished in the prior art by individually balancing each rotating component of the motor. The components are then assembled and the assembled unit is checked for the correct balance. Quite often, additional balancing is required.
• 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 balanced 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 additional parts added, require no further balancing after assembly with the stationary components.
• the rotating components of the motor are designed as a balanced subassembly, there is never a need to disassemble the subassembly.
• the balanced subassembly can be readily removed from, and re-installed into, the stationary components of the motor, yet the balanced 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 disk or disks may be mounted), and a cup assembly (wherein permanent magnetics are mounted).
• a shaft a spindle hub (on which the rotating disk or disks may be mounted)
• a cup assembly wherein permanent magnetics are mounted.
• 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, this subassembly need never be disassembled.
• FIGURE 1 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;
• FIGURE 2 is a cross-sectional drawing of a brushless direct current motor designed according to of the present invention, showing the same detail as FIGURE 1.
• FIG. 1 a conventional brushless direct current motor as used in the prior art for disk drive applications.
• Such a motor is shown in the cross-sectional view of FIGURE 1.
• the rotating components of the motor consist of the shaft 10, spindle hub 11, cup adapter 12, and rotating magnet cup 13.
• Mounted on the inner edge of the rotating magnet cup 13 are a plurality of permanent magnets, shown in the figure as solid rectangles 14 and 15.
• the stationary components of the motor consist of the spindle housing 16 with a plurality of motor magnets, shown 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 windings associated with the magnets.
• the shaft 10 of the rotating components is supported in the spindle housing 16 of the stationary components 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 shaft 10, the outer races 24-25 are stationary against the spindle housing 16, and the ball-bearings 20-23 rotate as necessary between the inner and outer races to support the load of the rotating components. While ball-bearings are shown in the figure, it is not uncommon for any appropriate rotational bearing mechanism, e.g., roller bearing, ball-bearings, tapered pin bearings, etc., to be used.
• the spindle housing 16 of the stationary components is attached to the mount 30 of the mechanical structure of the equipment in which the motor is being used.
• the manner of mounting is not important to the present invention.
• the magnets are part of the stationary portion of 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 windings are part of the rotating portion of the motor. Direct current is supplied to the windings through 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.
• the motor windings of a brushless direct current motor are part of the stationary component of the motor and the permanent magnets are part of the rotating components.
• the permanent magnets are typically spaced radially from the center line of the shaft as far as possible.
• a magnet cup assembly 13 as shown in FIGURE 1, is employed to place the magnets at a maximum radial spacing, rather than merely attaching the magnets to the side of the shaft 10.
• the permanent magnets 14-15 are placed a maximum distance from the centerline of the shaft 10 and opposite the motor windings 17-18. Direct current is electronically switched to the appropriate pair of motor windings to create a magnetic force which causes the permanent magnets, and therefore all the rotating components of the motor, to rotate.
• the rotational speed of the brushless motor can easily be measured.
• a slotted plate could be made part of the rotating portion of the motor. As the slots of such a plate pass 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.
• the ability to precisely control the speed of a brushless direct current motor allows such motors to be used in many applications where a conventional direct current motor would not be acceptable, such as in a disk drive device. Such applications also require, however, a precise balance of the rotating components. As explained earlier, while it is possible to precisely balance a motor such as that shown in FIGURE 1, this balance will be lost if the motor is disassembled.
• the shaft 10 and spindle hub 11 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 subassembly is then dynamically balanced.
• This balancing is typically done by spinning the object at the desired speed, and measuring the amount of imbalance, for example with a strobe light.
• the object is stopped and an amount of material, estimated to be equal to the imbalance, is removed from the proper area of the object, usually by machining or drilling the surface.
• the object is again spun and any imbalance is again determined. This process is repeated until the amount of remaining imbalance is within a predetermined limit.
• the cup adapter 12 and rotating magnet cup 13 must be balanced in a similar manner. When 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, the resulting complete motor assembly may require additional balancing. Also, as explained previously, if the motor should ever have to disassembled, a strong possibility exists, dependent upon the care and cost expended in fabricating the rotating parts, that upon reassembly balancing will again be required.
• FIGURE 2 is a cross-sectional drawing of a brushless direct current motor configured according to the present invention.
• a rotating magnet cup 43 along with the permanent magnets 44-45, are attached to a spindle hub 11 instead of to the opposite end of the shaft 10 (as taught in the prior art), and the motor windings 47-48 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 maintain a selected juxtaposed relationship (depending upon the rotational position of the shaft) an outer surface 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 applications.
• a unique feature of the present invention is that once the rotating components are joined together in a subassembly, there is never a need to disassemble them. Thus, once balanced, the rotating subassembly can be installed, and removed and reinstalled., in the motor without requiring additional balancing. This feature significantly reduces the cost of manufacturing and maintaining the motor assembly because only one subassembly need be balanced, and that need only be balanced one time.

Applications Claiming Priority (2)

Publications (1)

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• 1983
  • 1983-10-13 WO PCT/US1983/001613 patent/WO1984001863A1/en not_active Application Discontinuation
  • 1983-10-13 EP EP19830903358 patent/EP0124547A1/de not_active Withdrawn
  • 1983-10-27 CA CA000439877A patent/CA1210045A/en not_active Expired

Non-Patent Citations (1)

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