Electrical generator or motor structure – Dynamoelectric – Linear
Reexamination Certificate
1997-05-30
2001-10-30
Enad, Elvin (Department: 2834)
Electrical generator or motor structure
Dynamoelectric
Linear
C360S078130, C360S100100
Reexamination Certificate
active
06310413
ABSTRACT:
FIELD OF THE INVENTION
The present invention is related to disk drives for storing digital information, and more particularly, to linear actuators for use in a disk drive.
DESCRIPTION OF THE PRIOR ART
Disk drives for storing electronic information are found in a wide variety of computer systems, including workstations, personal computers, and laptop and notebook computers. Such disk drives can be stand-alone units that are connected to a computer system by cable, or they can be internal units that occupy a slot or bay in the computer system. Laptop and notebook computers have relatively small bays in which to mount internal disk drives and other peripheral devices, as compared to the much larger bays available in most workstation and personal computer housings. The relatively small size of peripheral bays found in laptop and notebook computers can place significant constraints on the designer of internal disk drives for use in such computers. Techniques that address and overcome the problems associated with these size constraints are therefore important.
Disk drives of the type that accept removable disk cartridges have become increasingly popular. One disk drive product that has been very successful is the ZIP™ drive designed and manufactured by Iomega Corporation, the assignee of the present invention. ZIP™ drives accept removable disk cartridges that contain a flexible magnetic storage medium upon which information can be written and read. The disk-shaped storage medium is mounted on a hub that rotates freely within the cartridge. A spindle motor within the ZIP™ drive engages the cartridge hub when the cartridge is inserted into the drive, in order to rotate the storage medium at relatively high speeds. A shutter on the front edge of the cartridge is moved to the side during insertion into the drive, thereby exposing an opening through which the read/write heads of the drive move to access the recording surfaces of the rotating storage medium. The shutter covers the head access opening when the cartridge is outside of the drive to prevent dust and other contaminants from entering the cartridge and settling on the recording surfaces of the storage medium.
The ZIP™ drive is presently available for workstations and personal computers in both stand-alone and internal configurations. In order to provide a version of the ZIP™ drive for use in laptop and notebook computers, the size constraints of the peripheral bays of such computers must be considered. In particular, for an internal drive to fit in the majority of laptop and notebook peripheral bays, the drive must be no longer than 135 mm. The height of the drive must be in the range of 12 mm to 15 mm. These dimensions place many constraints on the design of such a drive, and give rise to numerous design problems. The present invention addresses and overcomes one such problem.
Disk drives, for example the ZIP™ drive, often include an actuator assembly to carry read/write heads into engagement with an information storage disk. One type of actuator is a linear actuator that includes a coil mounted to a carriage, an magnetic flux outer return path assembly, two inner return path assembly members, and two actuator magnets that are typically bonded to opposing inner walls of the outer return path. The inner and outer return paths form a flux return path for a magnetic field generated by the magnets. The magnetic flux within the air gap between the magnets and the inner return paths induces a force on the actuator in response to an electric current in the actuator coil, thereby moving the carriage.
Unfortunately, the force generated on the actuator by the magnets and coil substantially diminishes near the ends of the air gap. These end effects may possibly be due to loss of perpendicularity of the magnetic flux relative to the magnet. Regardless of the phenomenon responsible for the end effects, conventional full-size actuator assemblies typically allow for the end effects by limiting the travel of the carriage to the area within the air gap where end effects are minimal. Such limitation on carriage travel requires a longer outer return path to provide the longer air gap. This solution to the end effect problem is feasible in full-size drives because such drives lack a constraint on overall length. However, in laptop and notebook computers such ineffective use on space is problematic. It is desirable to provide a linear actuator for a disk drive that enables the carriage to utilize a greater portion of the air gap.
The linear actuator has a related magnetic problem that is also exasperated by the trend toward smaller disk drives. Magnetic flux from the magnets cannot be confined to a given location or magnetic path because a portion of the flux naturally takes paths that are external to the magnet. The portion of the flux that leaks from the external paths is referred to as leakage or leakage flux. Magnetic leakage is troublesome in magnetic disk drives because the leakage may interfere with the recording or reading of the information, may create shifting in the timing of bits written to the disk, or may even cause bulk erasure of magnetic information.
To ensure proper operation, it is desirable to maintain a magnetic leakage flux limit of approximately 10 Gauss in the Z direction (that is, perpendicular to the plane of the disk) and 3 Gauss in the Y direction (that is, tangential to a circular track on the disk) in the area where the heads access the magnetic information. Conventional disk drives, in which overall drive length is not tightly constrained, may reach such a low level of leakage flux in the area of the magnetic information by locating the magnets far away from the disk and locating the read/write heads at the end of long actuator arms.
This nominally acceptable flux limit at the heads is significantly less than the magnetic flux present in other areas of the actuator assembly, especially near the actuator magnets. For example, the actuator magnets of the ZIP™ drive produce approximately 4,200 Gauss in the air gaps through which the coil translates. Without techniques to limit leakage outside of the return path, the 10 Gauss flux limit in the information reading area requires significant spacing between the actuator magnets and the disk, thereby limiting the potential reduction of overall size of the drive.
Because of the reduced drive length compared with larger drives, a linear actuator of laptop and notebook computer drives must be positioned significantly closer to the magnetic information on the disk. Because the magnets are affixed within the linear actuator, the magnets of these smaller drives must also be closer to the magnetic information. It is desirable to provide a device that diminishes the leakage flux from the actuator magnets in the area of the magnetic information on a magnetic disk, especially in smaller disk drives such as those of laptop and notebook computers.
The foregoing and other objects, features and advantages of the invention will become evident hereinafter.
SUMMARY
A disk drive having a pair of steering magnets that reduce the magnetic leakage flux from the actuator magnets of a linear actuator is provided. The steering magnets are located on each side of the linear actuator substantially parallel to the actuator magnets. Like poles of the steering magnets face inward toward like poles of the actuator magnets. Employing the steering magnets in this manner diminishes the magnetic flux leakage, which is especially important in the portion of the disk over which the read/write heads travel.
Because magnetic leakage flux interferes with reading and recording data, diminishing the leakage flux enables a magnetic disk to operate more closely to the actuator magnets than would otherwise be feasible. Employing the steering magnets according to the present invention therefore permits a reduction in disk drive size because flux leakage may be reduced to a level at which the read/write heads may properly perform.
REFERENCES:
patent: 4080542 (1978-03-01), De Graffenried
patent: 4504879 (1985-03-01), T
Bracken Allen T.
Briggs John C.
Enad Elvin
Iomega Corporation
Jones Judson H.
Woodcock Washburn Kurtz Mackiewicz & Norris LLP
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