Electrical generator or motor structure – Dynamoelectric – Rotary
Reexamination Certificate
1999-11-15
2001-06-05
Mullins, Burton (Department: 2834)
Electrical generator or motor structure
Dynamoelectric
Rotary
C310S045000, C310S06700R, C360S099080, C384S907000
Reexamination Certificate
active
06242831
ABSTRACT:
BACKGROUND OF THE INVENTION
This invention relates to a reduction in the stiction for spindle motors.
Disc drive data storage devices use rigid discs coated with a medium, e.g. a magnetizable medium, for storage of digital information in a plurality of data tracks. The information is written to and read from the discs using a transducing head mounted on an actuator mechanism which moves the head from track to track across a surface of the disc under control of electronic circuitry. The discs are mounted for rotation on a spindle motor which causes the discs to spin and the surfaces of the disc to pass under the heads.
Spindle motors typically include a rotor that rotates about a fixed shaft. During rotation, the radial pressure of the fluid, e.g., gas (air) or liquid, between the rotor and shaft acts as a hydrodynamic bearing to keep these components apart. For example, in a hydrodynamic gas bearing, the axial and/or radial pressure distribution of air is increased and the rotor rotates on a bearing of air about the fixed shaft. In many applications, a lubricant is located between the shaft and the rotor to reduce wear of the motor's surfaces.
SUMMARY OF THE INVENTION
In one aspect, the invention features a spindle drive motor including a drive mechanism means and a means for reducing stiction.
In another aspect, the invention features a reduced stiction drive mechanism for a spindle drive motor including a shaft and a rotor arranged for relative motion, a lubricant between the shaft and rotor, and a surface energy modifier between the lubricant and at least one of the shaft and rotor. The surface energy modifier has a surface energy effective to reduce stiction.
In another aspect, the invention features a computer disc drive including a spindle drive motor for rotating storage media. The spindle drive motor includes a shaft and a rotor arranged for relative motion, a lubricant between the shaft and rotor, and a surface energy modifier between the lubricant and at least one of the shaft and rotor. The surface energy modifier has a surface energy effective to reduce stiction.
Embodiments may include one or more of the following features. The shaft and the rotor can be spaced apart by about 0.5 to about 20 microns. The surface energy modifier can have a surface energy lower than the surface tension of the lubricant. Preferably, the surface energy modifier can have a surface energy about 2% lower than the surface tension of the lubricant. More preferably, the surface energy modifier can have a surface energy, about 20% to about 50% or more, lower than the surface tension of the lubricant. For example, the surface energy modifier has a surface energy of about 6 to about 14 dynes/cm and the lubricant has a surface tension of about 12 to about 80 dynes/cm. Each of the surface energy modifier and the lubricant, independently, can have a thickness of about 1 nm to about 2000 nm.
The surface energy modifier can be a fluorochemical polymer in a fluorocarbon solvent, e.g., Fluorad or Nye Bar-Type K, isosteric acid, or mixtures thereof. The lubricant can be a fluorinated polyether, a hydrocarbon, an ester, atmosphere moisture, or mixtures thereof.
Liquid lubricants include, but are not limited to, motor lubricants, e.g., fluorinated polyether, hydrocarbons, and esters; motor lubricant contaminants, e.g., hydrocarbon contaminants; atmospheric moisture; or mixtures thereof.
An advantage of embodiments of the invention is that stiction is reduced, thus lowering the starting power requirements of the motor. Stiction is a type of friction that occurs in the null position, i.e., “touch down,” between two moving members, e.g., a motor journal (shaft) and sleeve (rotor). For instance, when a journal is in contact with a sleeve, liquids in the interface, such as lubricants, redistribute themselves, e.g., via capillary action between the sleeve and journal to form menisci around the contacting areas. The pressure inside a meniscus is lower than the pressure outside the meniscus, thereby leading to an additional force, namely, meniscus force, causing the two mating surfaces to be pulled closer together. Thus, in order to restart the motor, the stiction force between the journal and sleeve must be overcome.
Starting torque or power in a spindle motor is governed by many factors, such as the materials used, surface finish, friction coefficient of the surface, environmental condition, etc. In some instances, e.g., humid environments, the starting force or torque will be governed by the stiction between the touch down surfaces and any other materials on the surface, e.g., absorbed moisture and organic materials. Stiction can also result when one or both surfaces are coated with wear-resistant thin films or lubricants.
As stiction increases, the power consumption, i.e., starting torque or starting power, of the spindle motor must also increase so that the spindle motor can overcome the menisci forces. In situations of low power disc drive applications, e.g., portable battery powered laptop type computers, power consumption of the spindle motor cannot be increased and the available starting power may not be sufficient to overcome stiction. This situation renders the spindle drive motor inoperable. The reduced stiction spindle motor decreases the starting power consumption of the spindle motor and lowers the probability that the spindle motor will be inoperable. Reducing power consumption is particularly important in low power disc drive applications in which power conservation is extremely desirable.
Other features of the invention will be apparent from the following description of the preferred embodiments and from the claims.
REFERENCES:
patent: 5366298 (1994-11-01), Toshimitsu et al.
patent: 5575567 (1996-11-01), Brown
patent: 5678929 (1997-10-01), Parsoneault et al.
patent: 5742518 (1998-04-01), Gui et al.
patent: 5815346 (1998-09-01), Kimmal et al.
patent: 5841607 (1998-11-01), Khan et al.
patent: 5997179 (1999-12-01), Khan et al.
patent: 6007896 (1999-12-01), Bhushan
Fluorad™ Technical Information, Fluorochemical Specialties, Fluorad™ Fluorochemical Coating FC-722.
Product Characteristics: NyeBar-Type K.
Fish & Richardson P.C.
Mullins Burton
Seagate Technology Inc.
LandOfFree
Reduced stiction for disc drive hydrodynamic spindle motors does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Reduced stiction for disc drive hydrodynamic spindle motors, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Reduced stiction for disc drive hydrodynamic spindle motors will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2531183