WO1983001861A1

WO1983001861A1 - Contaminant purging in a magnetic disc drive

Info

Publication number: WO1983001861A1
Application number: PCT/US1982/000387
Authority: WO
Inventors: Systems Corporation Dma; William A. Pollock
Original assignee: DMA Systems Corp
Current assignee: DMA Systems Corp
Priority date: 1981-11-16
Filing date: 1982-04-01
Publication date: 1983-05-26
Anticipated expiration: 1984-05-16
Also published as: JPS58501880A; DE8237134U1; EP0093714A1; EP0093714A4; GB2121591A; BR8207975A; GB8317983D0

Abstract

Dans une unité de disque magnétique (10) comprenant un disque (12) possédant une surface magnétique et maintenu en rotation sur une broche (11), un moteur de broche (13) pour l'entraînement de la broche, une tête de transducteur (14), une structure de support de tête (15) servant à déplacer la tête le long de la surface du disque, et un circuit de commande de vitesse (22) pour commander la vitesse du moteur de broche, le procédé ci-décrit permet la purge des substances contaminantes et le chargement de la tête. Le moteur de broche (13) est actionné à une vitesse sensiblement supérieure à la vitesse normale de fonctionnement et de l'air filtré circule entre la tête (14) et la surface du disque. La tête est chargée et vole sur la surface du disque et la vitesse du moteur de broche est ensuite réduite à la vitesse normale de fonctionnement.In a magnetic disk drive (10) comprising a disk (12) having a magnetic surface and held in rotation on a spindle (11), a spindle motor (13) for driving the spindle, a transducer head ( 14), a head support structure (15) for moving the head along the surface of the disk, and a speed control circuit (22) for controlling the speed of the spindle motor, the method herein allows purging contaminants and loading the head. The spindle motor (13) is operated at a speed substantially above normal operating speed and filtered air is circulated between the head (14) and the disc surface. The head is loaded and flies over the disc surface and the spindle motor speed is then reduced to normal operating speed.

Description

CONTAMINANT PURGING IN A MAGNETIC DISC DRIVE BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a method for contaminant purging and head loading in a magnetic disc drive and, more particularly, to a head cleaning and loading cycle which improves the purging air flow and provides for better head load reliability.

2. Description of the Prior Art Magnetic disc storage systems are widely used to provide large volumes of relatively low-cost, computer-accessible memory or storage. A typical disc storage device has a number of discs coated with a suitable magnetic material mounted for rotation on a common spindle and a set of transducer heads carried in pairs on elongated supports for insertion between adjacent discs, the heads of each pair facing in opposite directions to engage opposite faces of adjacent discs. The support structure is coupled to a positioner motor, the positioner motor typically including a coil mounted within a magnetic field for linear movement and oriented relative to the discs to move the heads radially over the disc surfaces to thereby enable the heads to be positioned over any annular track on the surfaces. In normal operation, the positioner motor, in response to control signals from the computer, positions the transducer heads radially for recording data signals on, or retrieving data signals from, a pre-selected one of a set of concentric recording tracks on the discs.

The transducer heads are supported above the disc surfaces by a film of air to prevent contact therebetween which might otherwise damage one or both members. Modern magnetic disc drives incorporate rigid substate discs, the surfaces of which are polished to a high finish so that the heads can reliably fly on the air bearing. Systems are presently being developed wherein the heads fly above the disc recording surfaces at heights of less than 20 microinches.

Magnetic disc drives typically incorporate filtered air systems to control cleanliness of the head flying environment. However, regardless of the care taken to maintain cleanliness of the head flying environment, the probability remains high that contamination particles may be present and that such particles may become deposited on either the heads or the disc surfaces. This is especially the case in removable media disc drives wherein a disc pack or cartridge is removed from the disc drive. The presence of these lodged particles may affect the flight attitude of the heads and thereby reduce their ability to record and retrieve data from the disc surfaces. In the extreme, the presence of disc contamination may cause a crash of a flying head, causing destruction of the head and/or disc. Accordingly, it is very common in disc pack drives or disc cartridge drives to incorporate a purging cycle wherein the disc is brought up to rotational speed and some period of time is spent with the disc rotating in the presence of a filtered air flow before the heads are moved into proximity with the disc.

In existing technology, the heads are normally started and stopped in contact with the disc. In the case of a removable disc drive, this would require loading the heads onto a stationary disc which is undersirable from the standpoint of head and disc damage. Furthermore, since the removable disc normally must be placed in the drive and spun for 15 to 60 seconds in a clean air environment to sweep dust and contaminants from the disc surface and since the disc then must be stopped so the heads can be loaded, this technique is further undesirable from the standpoint of start-up time.

QVPI_ A solution to this problem is to load the heads onto the spinning disc, thus eliminating the stop and restart cycle. Unfortunately, the air bearing surfaces of present heads are not especially designed for the landing of heads on a moving surface. This is due to the transient behavior of the air bearing and the need to decelerate the mass of the head during loading. The problem is acute on small diameter disc drives where surface speeds are lower and the air bearing has less design margin to support transient loads without allowing head-to-disc contact.

As a result of the above, when a head is loaded onto a spinning disc, there is a possibility that the head will contact the disc surface momentarily at the instant of load. This contact may damage the head or the media and may also generate- additional contamination problems. This is especially true if the contaminant purging cycle has been ineffective. Accordingly, there is a need for a method for making the purge cycle more efficient and for reducing the probability of head contact upon load.

SUMMARY OF THE INVENTION

According to the present invention, there is provided a method and means for making the purge cycle more efficient while simultaneously reducing the probability of head contact upon load. This is accomplished by rotating the magnetic discs more rapidly than normal during the contaminant-purging and head-loading operations and then reducing the speed to normal for head read/write operations. The higher speed improves the purging of dust and loose surface particles due to the increased centrifugal force and air flow across the disc surfaces. The higher speed also increases the flying height of the heads and the force the air bearings can support, making it easier to load the heads onto the moving discs without head-to-disc contact.

According to a preferred embodiment of the invention, the clean air blower fan is mounted directly on the disc rotating spindle and a rotating magnet, brushless, DC spindle motor is employed. This combination allows for simple spindle speed control so that the spindle may be run at a speed significantly above normal operating speed during the purge and head-load cycle. The higher spindle speed improves the purging air flow by turning the air and disc faster and provides for better head load reliability by increasing the air bearing stiffness during head load.

Briefly, in a disc drive including a disc having a magnetic surface and supported for rotation on a spindle, a spindle motor for driving the spindle, a transducer head, a head support structure, a drive motor for moving the head along the disc surface, and control electronics for controlling the speed of the spindle motor, there is disclosed a method for contaminant purging and head loading comprising the steps of: operating the spindle motor at a speed significantly above the normal operating speed; circulating filtered air past the head and the disc surface; loading and flying the head on the disc surface; and reducing the spindle motor speed to the normal operating speed. It is therefore an object of the present invention to increase the efficiency of the purge cycle in a magnetic disc drive. It is a feature of the present invention to achieve this object by rotating the magnetic disc more rapidly than normal during the contaminant purging operation. A further feature is the mounting of the clean air blower fan on the disc rotating spindle. An advantage to be derived is the greater efficiency of the purge cycle. A further advantage is the improvement of the purging of dust and loose surface particles due to the increased centrifugal force and air flow across the disc surface. A still further advantage is the increasing of the air bearing stiffness during head load.

It is another object of the present invention to reduce the probability of head contact upon load. It is a feature of the present invention to achieve this object by increasing the air bearing stiffness during head load by increasing the disc speed during the head loading operation. An advantage to be derived is the increase in the flying height of the head during head load. A further advantage is to increase the force the air bearing can support. A still further advanatage is the reduction in the likelihood of head contact upon load. Still other objects, features, and attendant advantages of the present invention will become apparent to those skilled in the art from a reading of the following detailed description of the preferred embodiment constructed in accordance therewith, takin in conjunction with the accompanying drawings wherein like numerals designate like or corresponding parts in the several figures and wherein: BRIEF DESCRIPTION OF THE DRAWINGS

FIGURE 1 is a generalized block diagram of the electronic control system of a typical magnetic disc drive_? FIGURE 2 is a simplified perspective view of a typical magnetic disc drive showing the air flow system thereof, as modified by the teachings of the present invention; and

FIGURE 3 is a generalized block diagram of the manner in which the system of FIGURE 1 may be operated to perform the present method.

OMP DESCRIPTION OF THE PREFERRED EMBODIMENT

Referring now to the drawings and, more particularly, to FIGURE 1 thereof, there is shown the components of a conventional magnetic disc drive, generally designated 10, which includes a spindle 11 supporting one or more magnetic discs 12. As is well known in the art, discs 12 may either be fixed to spindle 11 or user-replaceable. Spindle 11 is driven by a spindle motor 13 which rotates discs 12 about an axis defined by spindle 11.

Modern magnetic disc drives incorporate rigid substrates for discs 12. As is well known in the art, these substrates have a magnetic material coated on either one or both surfaces thereof to enable data to be magnetically recorded thereon. Data is recorded on the disc surfaces by signals applied to magnetic transducers 14, typically referred to as "heads". In a typical disc drive, a head support structure 15 is provided, structure 15 typically including, for each disc 12, a support arm 16, all of which arms 16 are connected to a common carriage 17. Carriage 17 is physically coupled to a positioner coil 18 of a linear positioner motor 19 which, in response to the application of positioning signals thereto, is capable of linearly moving support structure 15 in the direction of arrows 20. Support structure 15 is mounted relative to discs 12 so that heads 14 may move radially with respect to the recording surfaces of discs 12. That is, support structure 15 can be moved linearly to enable heads 15 to be selectively positioned over any one of a plurality of annular recording tracks defined on the disc recording surfaces.

While motor 19 has been described as being a linear motor, since such is the preferred embodiment of the present invention, it need not be such. Other types of motors are well known for moving support

OMPI structure 15 with respect to the recording surfaces of discs 12, such as swing arms, lead screw types, and the like, and the present invention is equally applicable to such other types. Magnetic disc drive 10 is typically controlled by signals from control electronics 21, typically a programmed microprocessor. Control electronics 21 controls the speed of spindle motor 13 via spindle speed control circuit 22 and controls the radial position of heads 14 via a linear motor control circuit 23. The output of speed control circuit 22 is applied to spindle motor 13, whereas the output of linear motor control circuit 23 is applied to coil 18 of linear motor 19. All of the above components of drive 10 are well known to those skilled in the art.

In normal operation, that is, when heads 14 are writing data onto or reading the data from the surfaces of discs 12, heads 14 will be loaded. When heads 14 are loaded, it simply means that a spring force is acting upon heads 14, generally through support arms

16, to urge heads 14 towards the surfaces of discs 12. This force is counteracted by an air cushion caused by the rapid rotation of discs 12 so that heads 14 actually fly immediately above the disc recording surfaces as long as discs 12 are rotating at a certain speed. In magnetic disc drives, the heads may fly at distances less than 50 microinches above the disc surfaces and drive systems are presently being developed wherein the heads may fly at distances of less than 20 microinches above the disc surfaces. Magnetic disc drives, such as disc drive 10, typically incorporate filtered air systems to control the cleanliness of the head flying environment. Such a filtered air system is shown in FIGURE 2. That is, in FIGURE 2, portions of magnetic disc drive 10 are positioned within a housing, generally designated 30, which is preferably divided into two compartments, 31 and 32. Extending into compartment 31, from the bottom thereof, is spindle 11 so that discs 12 may be mounted thereon within compartment 31. In the present embodiment, the lower disc 12 is fixed to spindle 11 whereas the upper disc 12 is removable. Heads 14, mounted at the ends of support arras 16, may extend into compartment 31 to be loaded on discs 12. On the other hand, arms 16 and heads 14 may be retracted into compartment 32 through openings 33 in a dividing wall 34 between compartments 31 and 32 when it is desired to remove discs 12. Doors (not shown) may be used to seal opening 33 so as not to expose heads 14 to the outside environment during disc removal. Motor 19 would also be positioned within compartment 32. Dirty air is conducted from compartment 31 via conduits 35 under power of a blower fan 36. This dirty air is conducted via a conduit 37 through an air filter 38 and then via a conduit 39 back to compartment 32. Regardless of the care taken to maintain cleanliness of the head flying environment within compartments 31 and 32, the probability remains high that contamination particles may be present and that such particles may become deposited on either heads 14 or the surfaces of discs 12. This is especially the case in removable media disc drives where a disc-pack cartridge is removed from disc drive 10. The presence of these lodged particles may affect the flight attitude of heads 14 and thereby reduce their ability to record and retrieve data from the disc surfaces. In the extreme, the presence of disc contamination may cause a crash of a flying head 14, causing destruction of head 14 or discs 12.

According to the present invention, clean air blower fan 36 is mounted directly on spindle 11 and a rotating magnet, brushless, DC spindle motor 13 is employed. This combination allows for simple spindle speed control so that magnetic discs 12 may be rotated more rapidly than normal during the contaminant-purging and head-loading operations. That is, and referring now to FIGURE 3, the generalized block diagram of magnetic disc drive 10 is modified so that control electronics 21 has two outputs, on lines 41 and 42, which are coupled to spindle speed control circuit 22. The output on line 42 signals spindle speed control 22 to cause spindle motor 13 to rotate at its normal speed. The signal on line 41 signals speed control 22 to cause spindle motor 13 to rotate at a significantly higher speed. In a typical example, the rotational speed is servo controlled, typically at 3600 RPM. By simply increasing the demand speed of speed control circuit 22, or by allowing motor 13 to run open loop (speed limited by its power supply only and not by the servo controller) , a speed of 4800 RPM, for example, could be obtained in most systems for use during the purge and load cycles. The speed need not be accurately controlled at this high speed since no reading or writing is done at this time. Furthermore, since the cycle is short in duration, the motor servo controller and drive cooling need not be rated for continuous duty at the higher speed.

In any event, this higher speed improves the purging of dust and loose surface particles due to the increased centrifugal force and air flow across the disc surface. Furthermore, by mounting blower fan 36 on spindle 11, there is also an increased air flow at this time. Still further, it is the teaching of the present invention to load heads 14 onto discs 12 with discs 12 rotating at the higher speed. The higher spindle speed provides for better head load reliability by increasing the air bearing stiffness during head load. That is, the higher speed increases the flying height of heads 14 and the force the air bearings can support, making it easier to load heads 14 onto the moving discs 12 without head-to-disc contact. After a period of time of anywhere from 15 to 60 seconds at this higher speed, control electronics 21 signals spindle speed control circuit 22 over line 42 to cause spindle motor 13 to reduce its speed to the normal operating speed. Since the heads are loaded at this time, there is a significantly lesser likelihood of head-to-disc contact and normal flying operation can proceed.

It can therefore be seen that in accordance with the present invention there is provided a method and means for making the purge cycle more efficient while simultaneously reducing the probability of head contact upon load. This is accomplished by rotating discs 12 more rapidly than normal during the contaminant purging and head loading operations and then reducing the speed to normal for head read/write operations. The higher speed improves the purging of dust and loose surface particles due to the increased centrifugal force and air flow across the disc surface. The higher speed also increases the flying height of the head and the force the air bearing can support, making it easier to load the heads onto the moving disc without head-to-disc contact.

While the invention has been described with respect to the preferred physical embodiment constructed in accordance therewith, it will be apparent to those skilled in the art that various modifications and improvements may be made without departing from the scope and spirit of the invention. Accordingly, it is to be understood that the invention is not to be limited by the specific illustrative embodiment, but only by the scope of the appended claims.

Claims

I CLAIM:

1. In a disc drive including a disc having a magnetic surface supported for rotation on a spindle, a spindle motor for driving said spindle, a transducer head, a head support structure, a drive motor for moving said head along the disc surface, control means for controlling the speed of said spindle motor, and' a clean air circulating system including a blower and a purging filter, a method comprising the steps of: operating said spindle motor at a speed significantly above its normal operating speed for a predetermined period of time; circulating filtered air past said head and said disc surface; and reducing said spindle motor speed to said normal operating speed.

2. In a disc drive according to claim 1, wherein said blower is a variable speed blower, a method comprising the step of: operating said blower at a speed significantly above its normal operating speed when said spindle motor is operating at its above-normal speed; and reducing said blower speed to its normal operating speed when the speed of said spindle motor is reduced.

3. In a disc drive according to claim 2, a method further comprising the step of: mounting said blower on said spindle.

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OMPI

4. In a disc drive according to claim 1, 2 or 3, a method wherein said spindle motor is a rotating magnet, brushless, DC motor.

5. In a disc drive according to claim 1, 2 or 3, a method further comprising the step of: loading and flying said head on said disc surface.

6. In a disc drive according to claim 5, a method wherein said head is loaded and caused to fly on said disc surface with said spindle motor operating at said speed significantly above its normal operating speed.