WO1998036408A2

WO1998036408A2 - A magnetic structure urging an actuator assembly toward a home position

Info

Publication number: WO1998036408A2
Application number: PCT/US1998/002671
Authority: WO
Inventors: A. David Michael; Brian P. Murphy; William D. Robertson
Original assignee: Quantum Corporation
Priority date: 1997-02-18
Filing date: 1998-02-13
Publication date: 1998-08-20
Also published as: WO1998036408A3; AU6323998A

Abstract

A method in a disk drive (300) having a permanent magnet (302), a data storage disk, and an actuator assembly (304) coupled to a transducer (308), for spinning down the data storage disk. The actuator assembly is coupled to an actuator motor (310) which is configured, when on, for positioning with a first torque the actuator assembly (304) such that the transducer (308) is disposed over data storage zones of the data storage disk. The method includes moving, using a ferromagnetic structure coupled to the actuator assembly, the actuator assembly to a home position. The home position represents a position of the transducer assembly in which the transducer is disposed over a designated parking area of the data storage. The ferromagnetic structure is configured to be magnetically attracted toward the permanent magnet with a magnetic force which urges the actuator assembly toward the home position with a second torque lower than the first torque. The method further includes holding, using the second torque, the actuator assembly in the home position when the actuator motor is off. Additionally, the method includes applying dynamic braking, using a spindle motor coupled to the data storage disk, to stop the data storage disk from spinning.

Description

IMPROVED ACTUATOR HOLDING MECHANISM AND METHODS THEREFOR

BACKGROUND OF THE INVENTION

The following co-pending U.S. patent applications are incorporated herein by reference for all purposes:

"Pressure Differential Latch For A Disk Drive," (Attorney's Docket No. Q96- 1011-US1), filed on November 13, 1995, U.S. Serial No. 08/557,584 (hereinafter S/N 08/557,564).

The present invention relates to hard disk drives. More particularly, the invention relates to apparatus and methods for positioning an actuator assembly at the home position and for ensuring that the actuator assembly is held at the home position during disk drive spin down.

Hard disk drives have long been employed for storing data in computer systems. To facilitate discussion, Fig. 1 is a generalized schematic of the relevant components of a hard disk drive 100, representing for example a typical hard disk drive for use in a computer. As shown in Fig. 1, hard disk drive 100 includes one or more data storage disks 102, each of which may have one or both disk surfaces 104 coated or deposited with a medium capable of storing data, e.g., a magnetic or magneto-optical medium. Disk 102 is disposed on a spindle motor 106, which rotates disk 102 at a predetermined rate of rotation during use.

For ease of discussion, the remaining discussion is made with reference to a single disk 102, and more particularly to the upper disk surface 104 of disk 102. It should be understood, however, that the concepts discussed herein apply equally well to both the upper and lower disk surfaces of a data storage disk, and to disk drives having multiple data storage disks, some of which may be commonly mounted on the same spindle.

An actuator assembly 108 is configured to exert a biasing force to hold a transducer 110 against disk surface 104 of disk 102. When spindle motor 106 is at rest, transducer 110 rests on disk surface 104. When disk 102 is rotated by spindle motor 106 during operation, its rotation creates an air bearing or cushion on disk surface 104. In accordance with well known Winchester disk principles, this air bearing overcomes the biasing force supplied by actuator assembly 108 and permits transducer 110 to "fly" at a predefined height above disk surface 104 to record data into or to read data off the recording medium on disk surface 104.

Disk surface 104 is typically divided into a multiplicity of data storage zones, e.g., sectors. To access the individual data storage zones on disk surface 104, an actuator motor 112, typically in the form of a voice coil motor (VCM), is employed to position actuator assembly 108 and transducer 110 between inner diameter (ID) 114 and outer diameter (OD) 116 of disk 102 (by pivoting actuator assembly 108 around bearing bore 111). The radial motion of transducer 110 across disk surface 104, in combination with the rotation of disk 102, allows transducer 110 to be positioned over any data storage zone on disk surface 104.

It is generally desirable to minimize contact between transducer 110 and disk surface 104. This is because excessive sliding of dragging of transducer 110 on the disk surface may lead to premature erosion or wear and ultimately to failure of the transducer itself. More importantly, erosion of disk surface 104 may occur where transducer 110 physically slides or drags against the thin recording film on the disk surface.

If the disk surface erosion occurs in a data storage zone, data loss may occur. Even if there is no sliding or dragging, the stiction force between the smooth transducer and the smooth data storage zones of the disk surface may prevent the transducer, once in contact with the smooth disk surface, from being separated therefrom and from becoming airborne again the next time the disk starts up.

To prevent transducer 110 from coming into contact with the data storage zones on disk surface 104, transducer 110 is arranged to position over and to park on a designated parking area 118 on disk surface 104 when there is an insufficient air bearing above the disk surface to allow transducer 110 to be airborne. For example, when disk 102 slows down, spindle motor 106 may be used as a generator to generate power to actuator motor 112, allowing actuator motor 112 to urge actuator assembly 108 to its "home" position, i.e., the position where transducer 110 is positioned over designated parking area 118. Once disk 102 stops spinning, transducer 110 may be parked on designated parking area 118 which may, in some cases, be textured to reduce the aforementioned stiction force.

To ensure that actuator assembly 108 stays in its home position and not jolted therefrom by impact when disk 102 stops spinning, a latching mechanism may be provided. The latching mechanism engages to lock actuator assembly 108 in its home position and releases it only when disk 102 spins up again. In general, these latching mechanisms may be actuated by the air flow within disk drive 100, by a solenoid, by magnetic forces, and the like.

Air actuated latching mechanisms, an implementation of which is described in detail in the aforementioned co-pending patent application S/N 08/557,584, unlatch when the air flow created by the spinning disk acts upon an air vane. To facilitate discussion, Fig. 2 illustrates a simplified top view of disk drive 100 of Fig. 1, including an air- actuated latching mechanism 202. To facilitate ease of comprehension, components having substantially similar functions are referenced using the same reference number throughout the figures herein. Latching mechanism 202 includes an air vane 204, which is biased toward wall 206 of disk drive 100, e.g., via a spring. When disk 102 spins at its normal rotation rate (e.g., about 7,200 RPM in some models), an air flow is created within disk drive 100, e.g., in the counter-clockwise direction in the example of Fig. 2. The air flow acts on air vane 204 to overcome the biasing force and moves air vane 204 away from wall 206. As air vane 204 moves away from wall 206, actuator 108 is unlatched and may be freely moved by actuator motor 112 to position transducer 110 over the data storage zones. Latching mechanism 202 is shown in its unlatched position in Fig. 2.

As the spinning disk slows down, the amount of air flow within disk drive 110 decreases, and less force is available to act on air vane 204 to keep latching mechanism 202 unlatched. As mentioned earlier, spindle motor 106 may be employed during this time as a generator to provide power to actuator motor 112, thereby allowing actuator motor 112 to bring actuator assembly 108 to its home position, e.g., to bring transducer 110 over annular parking area 118. When the disk slows down sufficiently (e.g., to about 3,000 to 5,000 RPM in some models), the biasing force returns air vane 204 toward wall 206 to allow latching mechanism 202 to engage and lock actuator assembly 108 in its home position. For example, when latching mechanism 202 is latched, structure 208 engages an extension portion 210 of actuator assembly 108 to prevent transducer 110 from moving away from annular parking area 118. As long as latching mechanism 202 remains latched, actuator assembly 108 cannot be moved from its home position even if disk drive 100 subsequently experiences an impacting force.

Although the above arrangement is capable of providing protection for the data storage zones of storage disk 102, the aforementioned transducer erosion problem still persists. During spin down, spinning disk 102 may take a long time, e.g., up to 30 seconds in some drives, to come to rest. Consequently, transducer 110 may be dragged across the surface of parking area 118 for an extended period of time, which exacerbates the transducer erosion problem. To reduce erosion, it is therefore desirable to shorten the spin down period, i.e., to quickly stop the rotation of disk 102.

It is known that the spin down period may be shortened through the use of dynamic braking. During dynamic braking, the windings of spindle motor 106 are shorted together to create a back electromotive force (EMF). The back EMF created then brings spindle motor 106 and disk 102 to a quick stop. The mechanisms involved in dynamic braking are well known to those skilled and are not repeated here to avoid unnecessarily obscure the invention. However, when dynamic braking is employed, spindle motor 106 is unavailable for use as a generator to generate power to actuator motor 112. Consequently, the force holding actuator assembly 108 in its home position is cut off when dynamic braking commences.

If disk 102 has not sufficiently spun down to allow latching mechanism 202 to engage and lock actuator assembly 108 in its home position, an impact on the disk drive during this time may cause the actuator assembly 108 and transducer 110 to move out of parking area 118, i.e., toward OD 116 and over the data storage zones of disk 102. This is because spindle motor 106 is no longer available to generate power (as a generator) to actuator motor 112 during this time to enable actuator motor 112 to keep actuator assembly 108 at its home position. Even if there is no jolt, actuator assembly 108 may be urged out of its home position by, for example, windage on actuator assembly 108 or by the bias force applied by a flex circuit (e.g., flexible conductor-bearing strip or bundle) coupling to transducer 110. As discussed earlier, this situation is highly undesirable as it may allow transducer 110 to crash land on a data storage zone when disk 102 comes to a stop.

The above-discussed problem is particularly acute for disk drives which are designed to be "hot-swapped." During hot-swapping, the disk drive may be pulled off the computer while running. As mentioned earlier, the spindle motor may be employed to generate power to the actuator motor to allow it to quickly retract the actuator assembly over the designated parking area. Dynamic braking may subsequently take place to quickly stop the disk from spinning. However, if the disk drive experiences an impact during this time (a probable event during hot-swapping), the actuator assembly may be jarred from the home position. Once out of the parking area, the transducer 110 may subsequently crash land on the data storage zones of the disk and may cause data loss and/or damage to the drive. In view of the foregoing, there are desired improved apparatus and methods for positioning the actuator assembly in the home position and for keeping the actuator assembly in the home position during disk drive spin down.

SUMMARY OF THE INVENTION

The invention relates, in one embodiment, to a disk drive having a permanent magnet, a data storage disk, and an actuator assembly coupled to a transducer. The actuator assembly is coupled to an actuator motor which is configured, when on, for positioning with a first torque the actuator assembly such that the transducer is disposed over data storage zones of the data storage disk. The disk drive includes a ferromagnetic structure fixedly coupled to the actuator assembly. The ferromagnetic structure is configured to be magnetically attracted toward the permanent magnet with a magnetic force. The magnetic force urges the actuator assembly toward a home position with a second torque lower than the first torque. The actuator assembly, when the actuator motor is off, is held by the second torque in the home position, wherein the home position represents a position of the transducer assembly in which the transducer is disposed over a designated parking area of the data storage disk.

In another embodiment, the invention relates to a method for manufacturing a disk drive. The method includes providing an actuator motor having a permanent magnet. The method further includes rotatably coupling an actuator assembly to the actuator motor. The actuator assembly has a transducer coupled thereto. The method also includes providing a data storage disk, the data storage disk being disposed under the transducer to permit the transducer to access data on a first surface of the data storage disk, wherein the actuator motor is configured, when on, for positioning with a first torque the actuator assembly such that the transducer is disposed over data storage zones of the data storage disk.

Additionally, the method includes coupling a ferromagnetic structure to the actuator assembly. The ferromagnetic structure is configured to be magnetically attracted toward the permanent magnet with a magnetic force which urges the actuator assembly toward a home position with a second torque lower than the first torque. The actuator assembly, when the actuator motor is off, is held by the second torque in the home position. The home position represents a position of the transducer assembly in which the transducer is disposed over a designated parking area of the data storage disk. In yet another embodiment, the invention relates to a method in a disk drive having a permanent magnet, a data storage disk, and an actuator assembly coupled to a transducer, for spinning down the data storage disk. The actuator assembly is coupled to an actuator motor which is configured, when on, for positioning with a first torque the actuator assembly such that the transducer is disposed over data storage zones of the data storage disk. The method includes moving, using a ferromagnetic structure coupled to the actuator assembly, the actuator assembly to a home position. The home position represents a position of the transducer assembly in which the transducer is disposed over a designated parking area of the data storage. The ferromagnetic structure is configured to be magnetically attracted toward the permanent magnet with a magnetic force which urges the actuator assembly toward the home position with a second torque lower than the first torque.

The method further includes holding, using the second torque, the actuator assembly in the home position when the actuator motor is off. Additionally, the method includes applying dynamic braking, using a spindle motor coupled to the data storage disk, to stop the data storage disk from spinning.

These and other advantages of the present invention will become apparent upon reading the following detailed descriptions and studying the various figures of the drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

To facilitate discussion, Fig. 1 is a generalized schematic of the relevant components of a typical hard disk drive.

Fig. 2 illustrates a simplified top view of the disk drive of Fig. 1, including an air- actuated latching mechanism.

Fig. 3 A illustrates, in accordance with one embodiment of the present invention, a simplified top view of the relevant components of a disk drive, including the inventive magnetic holding mechanism.

Fig. 3B illustrates, in one embodiment, a simplified top view of the disk drive of

Fig. 3 A when the actuator assembly is urged by the actuator motor to move outside of its home position. Fig. 3C illustrates, in one embodiment, another simplified top view of the disk drive of Fig. 3 A when the actuator assembly is urged by the actuator motor to move further outside of its home position.

Fig. 4 depicts, in one embodiment, the relative distances between the ferromagnetic structure and the permanent magnet as the actuator assembly is rotated out of its home position.

Fig. 5 illustrates a graph, shown in relative scale, of the torque acting on the actuator assembly versus the distance between the ferromagnetic structure and the permanent magnet.

Fig. 6 illustrates, in accordance with one embodiment of the present invention, a side view of an actuator assembly for a disk drive, including an aperture for receiving the ferromagnetic structure.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The present invention will now be described in detail with reference to a few preferred embodiments thereof as illustrated in the accompanying drawings. In the following description, numerous specific details are set forth in order to provide a thorough understanding of the present invention. It will be apparent, however, to one skilled in the art, that the present invention may be practiced without some or all of these specific details. In other instances, well known process steps have not been described in detail in order to not unnecessarily obscure the present invention.

In accordance with one aspect of the present invention, there is provided an magnetic hold mechanism for returning the actuator assembly to its home position when the drive spins down. The inventive magnetic hold mechanism is preferably configured to continue providing a magnetic holding force to keep the actuator assembly in the home position when power to the actuator motor is no longer available. By way of example, the inventive magnetic hold mechanism preferably continues to hold the actuator assembly in the home position (thereby keeping the transducer in the designated parking area) when dynamic braking is applied, during which time the spindle motor is not available for use as a generator to supply power to the actuator motor. In this manner, the invention permits the use of dynamic braking to quickly stop the spinning disk while ensuring that the actuator assembly cannot be moved from its home position, whether by a jolt on the disk drive, windage on the actuator assembly, biasing force due to the flexing circuit, or the like.

In one embodiment of the present invention, the magnetic hold mechanism includes a ferromagnetic structure coupled to the actuator assembly. The ferromagnetic structure is appropriately positioned so as to create a magnetic attraction force between the ferromagnetic structure and the permanent magnet of the actuator motor. When so positioned, the ferromagnetic structure exerts a biasing torque on the actuator assembly to urge the actuator assembly toward the home position.

To further illustrate the foregoing, Fig. 3A illustrates, in accordance with one embodiment of the present invention, a simplified top view of the relevant components of a disk drive 300 (a portion of which is shown), including a ferromagnetic structure 302. With reference to Fig. 3 A, disk drive 300 includes an actuator assembly 304, which is rotatable about a bearing bore 306. Actuator assembly 304 is movable by an actuator motor (lower half only is shown to simplify the illustration) to position a transducer 308 over the data storage zones of the disk surface. Depending on the storage medium employed, transducer 308 is appropriately selected to facilitate writing data to and reading data from the storage medium disposed on the disk surface. In the example of Fig. 3 A, the actuator motor takes the form of a voice coil motor (VCM), of which lower permanent magnet 310 is shown disposed under the actuator forks (the upper VCM magnet has been removed to improve clarity).

As shown in Fig. 3A, actuator assembly 304 is at its home position, i.e., the position wherein transducer 308 is disposed over a designated parking area on the disk. For ease of discussion, the designated parking area represents in the example of Fig. 3 A the annular area adjacent to the inner diameter (ID) of the disk although other areas may well be specified. A crash stop 312 is provided to prevent transducer 308 from crashing into the disk spacer rings disposed at the inner portion of the disks. Crash stop 312 engages a portion 314 on actuator assembly 304 to stop the rotation of actuator assembly 304 as it is rotated counter-clockwise around bearing bore 306 on its way to its home position.

A ferromagnetic structure 302 is coupled to actuator assembly 304 as shown in Fig. 3 A. Ferromagnetic structure 302, together with permanent magnet 310, forms a magnetic hold mechanism to hold actuator assembly 304 at its home position. Advantageously, the magnetic attraction force between ferromagnetic structure 302 and permanent magnet 310 exists irrespective whether power is supplied to the actuator motor. In the embodiment of Fig. 3 A, ferromagnetic structure 302 takes the form of an iron-containing (e.g., stainless steel) ball inserted into an aperture in the coil fork of actuator assembly 304 although, as discussed later in connection with Fig. 6, ferromagnetic structure 302 may assume any suitable form and shape, including rod, and may be coupled to any suitable position on actuator assembly 304.

Ferromagnetic structure 302 is preferably sized and positioned on actuator assembly 304 such that the resultant magnetic attraction force is capable of overcoming substantially any torque that may bias actuator assembly 304 out of its home position when power to the actuator motor is cut off. For example, it is preferable that the resultant magnetic attraction force be greater than forces acting on the actuator assembly 304 due to windage, even when the disks are spinning at or near their maximum operational speed (as in the early stage of disk spin down).

Additionally, the resultant magnetic attraction force is preferably greater than the biasing torque from by any flex circuit coupled to transducer 308, which may otherwise bias actuator assembly 304 away from its home position. Furthermore, the resultant magnetic attraction force is preferably higher than an expected torque acting on actuator assembly 304 in the direction away from its home position when disk drive 300 experiences an impact. However, the resultant magnetic attraction force must not be so high as to require the actuator motor, when power is furnished to it, to supply an undue amount of torque to overcome the magnetic attraction force in order to position actuator assembly 304 over the various data storage zones. In one embodiment for example, the magnitude of the torque acting on the actuator assembly by the inventive magnetic hold mechanism is about 1/1,000 to about 1/10,000 the magnitude of the torque supplied by the actuator motor during reading or writing.

The fact that the magnetic hold mechanism continually hold actuator assembly

304 in its home position when power to the actuator motor is cut off offers great advantages. For example, the invention ensures that actuator assembly 304 is still held at its home position even when the spindle motor (not shown in Fig. 3 A) is employed as a dynamic brake mechanism and is not available to generate power to the actuator motor. Furthermore, the invention permits dynamic braking to be applied sooner since there is little risk that actuator assembly 304 may wander due to windage from the rapidly rotating disks. Early dynamic braking shortens the spin down period, which in turn reduces the time transducer 308 is dragged across the disk surface when the disks are spinning at non- flying speeds. In fact, if ferromagnetic structure 302 and/or permanent magnet 310 are appropriately sized and/or positioned relative to each other, the resultant magnetic attraction force may be relied on to bring actuator assembly 304 to its home location when power to the disk drive is cut off. In this case, there may be no need to employ the spindle motor as a generator, i.e., dynamic braking may commence immediately to further shorten the spin down period and reduce transducer wear. Of course, the use of the actuator motor as a parking mechanism is not precluded in any of the disclosed embodiments, if desired.

If a latch mechanism is employed, e.g., the air-actuated latch mechanism discussed earlier in connection with Fig. 2, the invention advantageously allows actuator assembly 304 to be held in its home position until the latch mechanism can engage to lock actuator assembly 304 in the home position. In the air-actuated latch embodiment, the magnetic hold mechanism comprising ferromagnetic structure 302 and permanent magnet 310 advantageously keeps actuator assembly 304 in its home position (even when no power is furnished to the actuator motor) until the disk spins down sufficiently to allow the air-actuated latch mechanism to latch.

Since the spindle motor is immediately available for use as a dynamic brake, the spin down period may be quite short, which narrows the vulnerability window during which actuator assembly 304 is unlatched (e.g., down to 3-5 seconds in some drives). Of course, the magnetic hold mechanism is preferably configured such that even if the disk drive should experience a jolt during the aforementioned vulnerability window, the resultant magnetic attraction force would be sufficiently high to return actuator assembly 304 to its home position.

The magnetic hold mechanism of the present invention also advantageously exerts a continuous holding torque on actuator assembly 304, which keeps actuator assembly 304 substantially immobile against crash stop 312 at all times. In contrast, prior art latch mechanisms, although effective in holding the transducer in the designated parking area when engaged, typically have a certain amount of tolerance and "play," which may allow some relative motion between the transducer and the parking surface on which it rests. The inventive magnetic hold mechanism, via the continuous magnetic attraction force, advantageously minimizes any relative motion between the transducer and the parking surface, thereby further reducing transducer wear when the disk drive is moved about, e.g., during handling or shipping.

Fig. 3B illustrates, in one embodiment, a simplified top view of disk drive 300 of Fig. 3 A when.actuator assembly 304 is urged by the actuator motor to move outside of its home position, i.e., to position transducer 308 above a data storage zone. Note that in Fig. 3B a magnetic attraction force exists between ferromagnetic structure 302 and permanent magnet 310, which tends to urge actuator assembly 304 toward the home position. As mentioned, the magnetic attraction force therebetween may be (but is not required to be) configured such that it is unnecessary, in one embodiment, to employ the actuator motor to park actuator assembly 304 in its home position.

Further note that the distance between ferromagnetic structure 302 and permanent magnet 310 has increased in Fig. 3B (relative to the distance shown in Fig. 3 A). As can be appreciated by those skilled, the increased distance reduces the magnetic attraction force between magnetic structure 302 and permanent magnet 310, thereby advantageously reducing the amount of torque the actuator motor must furnish to position actuator assembly 304 among the various data storage zones once actuator assembly 304 is moved out of the home position. Due to the reduced magnetic attraction force, less energy is consumed and less heat is generated by the actuator motor during reading or writing.

Fig. 3C illustrates, in one embodiment, a simplified top view of disk drive 300 of

Fig. 3 A when actuator assembly 304 is urged by the actuator motor to move even further outside of its home position, i.e., to position transducer 308 above a data storage zone. Again, a magnetic attraction force exists between ferromagnetic structure 302 and permanent magnet 310, albeit with a lower magnitude than that of Fig. 3B or Fig. 3 A. Nevertheless, actuator assembly 304 is also urged toward the home position by the magnetic attraction force when it is disposed as shown in Fig. 3C.

Fig. 4 depicts, in one embodiment, the relative distances between ferromagnetic structure 302 (in the form of a steel ball in the example of Fig. 4) and permanent magnet 310 as actuator assembly 304 is rotated out of its home position. In Fig. 4, top and bottom magnets 402 and 404 of the actuator motor is shown disposed between a top steel structure 406 and a bottom steel structure 408, which are also associated with the actuator motor. When ferromagnetic structure 302 is in position A (corresponding to the situation in Fig. 3 A wherein the actuator assembly is at its home position), ferromagnetic structure 302 is located in a region of high flux density (represented by the high density of lines between top magnet 402 and bottom magnet 404). Accordingly, a strong magnetic attraction force exists between ferromagnetic structure 302 and the permanent magnet comprising top magnet 402 and bottom magnet 404. This strong magnetic holding force acts to hold the actuator assembly in its home position and to keep the actuator assembly substantially immobile against the crash stop (as discussed earlier in connection with Fig. 3A). When ferromagnetic structure 302 is in position B (corresponding to the situation in Fig. 3B wherein the actuator assembly is moved away a small distance from its home position), ferromagnetic structure 302 is located in a region of lower flux density compared to the flux density at position A. The magnetic attraction force between ferromagnetic structure 302 and the permanent magnet is present, albeit at a lower magnitude than the magnetic attraction force that exists when ferromagnetic structure 302 is in position A. The magnetic attraction force acts to urge ferromagnetic structure 302 (and the actuator assembly which is coupled thereto) to return to position A, i.e., the position wherein the actuator assembly is at its home position.

When ferromagnetic structure 302 is in position C (corresponding to the situation in Fig. 3C wherein the actuator assembly is moved even further away from its home position), ferromagnetic structure 302 is located in a region of even lower flux density compared to the flux densities at positions A and B. Again, the magnetic attraction force between ferromagnetic structure 302 and the permanent magnet is still present. However, this magnetic attraction is even lower in magnitude than the magnetic attraction force that exists when ferromagnetic structure 302 is in either position A or B. The magnetic attraction force acts to urge ferromagnetic structure 302 (and concomitantly the actuator assembly which is coupled thereto) to return to position A, wherein the actuator assembly is at the home position. Preferably, the magnetic hold mechanism is configured such that the magnetic attraction force is capable of returning the actuator assembly to its home from all positions, including from the fully extended position.

To facilitate discussion, Fig. 5 illustrates a graph, shown in relative scale, of the torque acting on the actuator assembly versus the distance between the ferromagnetic structure (e.g., ferromagnetic structure 302) and the permanent magnet. Position A in Fig. 5 corresponds to the situation wherein the ball is at position A in Fig. 4 and the actuator assembly at its home position in Fig. 3 A. As discussed earlier, this corresponds to a relatively short, if any, distance between the ferromagnetic structure and the permanent magnet, and the torque on the actuator assembly is relatively high to hold the actuator assembly in its home position.

Position B in Fig. 5 corresponds to the situation wherein the ball is at position B in

Fig. 4, and the actuator assembly has moved a short distance away from its home position (see Fig. 3B). As discussed earlier, this corresponds to a slightly greater distance between the ferromagnetic structure and the permanent magnet (as shown on the x-axis of the graph of Fig. 4 and in Fig. 3B). The torque on the actuator assembly is relatively lower compared to that associated with position A. However, as shown in Fig. 4, a torque still exists for urging the actuator assembly back to the home position. Position C in Fig. 5 corresponds to the situation wherein the ball is at position C in Fig. 4, and the actuator assembly has moved a further distance away from its home position (see Fig. 3C). As discussed earlier, this corresponds to an even greater distance between the ferromagnetic structure and the permanent magnet (as shown on the x-axis of the graph of Fig. 4 and in Fig. 3C). The torque on the actuator assembly is relatively even lower compared to those associated with positions A and B. However, as shown in Fig. 4, a torque still exists for urging the actuator assembly back to the home position.

Note that the torque tends to be highest in position A, i.e., when the actuator assembly is in its home position, and a high level of torque can more effectively keep the actuator assembly from being moved away from the home position. In the region of positions B and C, the torque is relatively low. The relatively low torque associated with these positions corresponds to the torque experienced by the actuator assembly when the actuator assembly is away from its home position, i.e., while it is positioned by the actuator motor to allow the transducer to access the various data storage zones. Advantageously, less power is required from the actuator motor to overcome the magnetic attraction force of the inventive magnetic hold apparatus during operation. Further, the low level of magnetic attraction force also makes it simpler to compensate for in the control circuitry that controls the actuator motor.

If a return spring had been employed instead of the inventive magnetic hold mechanism, the presence of the spring biasing against the actuator assembly would have resulted in a more cumbersome structure. More importantly, a return spring would disadvantageous^ supply less torque at the home position, where it is most needed to keep the actuator assembly home. The return spring also would supply more torque as the actuator arm is moved away from the home position (in accordance with Hook's law, F = Kx, which is well known). The higher level of torque would require the actuator motor to work harder in positioning the actuator assembly during reading and writing, which is disadvantageous from the control and/or energy consumption perspectives.

It should be borne in mind that line 502 is depicted in Fig. 4 for illustrative purposes, and the exact shape of line 502 for a given disk drive may differ depending on the geometries of the magnet, the ferromagnetic structure, and other structures of the drive. To increase the holding force, the ferromagnetic structure may be repositioned, which has the result of moving points A, B, and C along line 502 of Fig. 4. For example, positioning the ferromagnetic structure closer to the magnet tends to move these points in the direction of increasing torque along line 502. Alternatively, the ferromagnetic structure and/or the permanent magnet may be resized. In general, a smaller ferromagnetic structure tends to move line 502 inward (i.e., toward the origin of the graph) while a larger ferromagnetic structure tends to move line 502 outward. In general, it is desirable to keep the size of the ferromagnetic structure sufficiently large such that the magnetic attraction force is sufficient for keeping the actuator assembly home while the actuator motor is off (i.e., against windage, impact, or the like). Additionally, the size of the ferromagnetic structure should not be so large that it adds an undue mass to the actuator assembly and/or results in an excessively high magnetic attraction force, which interferes with actuator assembly motion. In one embodiment, the ferromagnetic structure is a stainless steel ball weighing about 0.014 grams.

Fig. 6 illustrates, in accordance with one embodiment of the present invention, a side view of actuator assembly 304 for a disk drive having five disks (inserted during use between the six actuator arms shown). Actuator assembly 304 of Fig. 6 includes a bore 602 arranged to receive one or more ferromagnetic structures (e.g., steel balls or rods). In one embodiment, the exact size and shape of the suitable ferromagnetic structure(s) and its position on the actuator assembly may be determined empirically. In general, bore 602 may be located on any suitable location on actuator assembly 304 including, for example, at alternative location 604. At location 604, for example, the bore may be arranged to receive a vertical ferromagnetic rod, or any number of ferromagnetic balls, or any other ferromagnetic structure(s) of a suitable size and shape.

As can be appreciated from the foregoing, the present invention results in a highly compact and elegant mechanism capable of holding the actuator assembly at its home position even when power to the actuator motor is cut off. As discussed earlier, this ensures that the transducer is kept in the designated parking area and does not crash land over the data storage zones of the disk. By eliminating the need for the actuator motor to continue holding the actuator assembly in its home position until the latch mechanism (e.g., the air-actuated latch mechanism) engages, the invention advantageously permits dynamic braking to be apply early to reduce transducer wear. Early application of dynamic braking also means that the spin down time is substantially shortened, thereby allowing the latching mechanism to be engaged sooner. The early engagement of the latching mechanism in turn captures and locks the actuator assembly early, thereby substantially reducing the potentiality for errant transducer landings, particularly for disk drives that are hot-swapped.

Furthermore, the inventive magnetic hold mechanism results in a high holding torque when most needed (i.e., when the actuator assembly is in the home position). The holding torque advantageously decreases, as discussed in connection with Figs. 4 and 5, when the actuator assembly is positioned by the actuator motor for reading and writing.

While this invention has been described in terms of several preferred embodiments, there are alterations, permutations, and equivalents which fall within the scope of this invention. For example, while the inventive magnetic hold mechanism has been described with reference to an air-actuated latching mechanism in one embodiment, the presence of an air-actuated latching mechanism is not required to derive advantages from the invention. Additionally or alternatively, it is contemplated that the inventive magnetic hold mechanism may well be employed with drives that use other types of latching mechanisms, e.g., solenoid latches, air vane latches, inertia latches, and the like.

Furthermore, although the invention has been described in connection with a rotational actuator motor to facilitate ease of discussion, it is contemplated that the inventive magnetic hold mechanism may also be applied to drives employing linearly actuated actuator motors. Still further, although the permanent magnet has been discussed herein as part of the actuator motor, it is contemplated that a separate magnet, e.g., one not associated with the actuator motor, may also be employed to provide the required magnetic attraction force. It should also be noted that there are many alternative ways of implementing the methods of the present invention. It is therefore intended that the following appended claims be interpreted as including all such alterations, permutations, and equivalents as fall within the true spirit and scope of the present invention.

Claims

What is claimed is:

1. A disk drive comprising:

a data storage disk;

an actuator assembly having a transducer mounted on one end thereon, said actuator assembly being coupled to an actuator motor configured, when on, for positioning with a first torque said actuator assembly such that said transducer is positioned over data storage zones of said data storage disk;

an actuator motor having a magnet therein,

a ferromagnetic structure fixedly coupled to the other end of said actuator assembly, said ferromagnetic structure being configured to be magnetically attracted toward said magnet with a magnetic force, said magnetic force urging said actuator assembly toward a home position with a second torque lower than said first torque, said actuator assembly, when said actuator motor is off, is held by said second torque in said home position, said home position representing a position of said transducer assembly in which said transducer is disposed over a designated parking area of said data storage disk.

2. The disk drive of claim 1 wherein said actuator motor represents a voice coil motor.

3. The disk drive of claim 1 wherein said actuator assembly is held against a crash stop in said home position, said transducer, when said actuator assembly is held against said crash stop, is held substantially immobile against said crash stop to reduce wear on said transducer.

4. The disk drive of claim 1 wherein said second torque is sufficient to bias said actuator assembly to said home position when said actuator motor is off irrespective of whether said data storage disk spins at a first speed or at a second speed, said first speed representing a speed at which said data storage disk spins while data on said data storage disk is accessed, said second speed representing a speed slower than said first speed.

5. The disk drive of claim 4 wherein said first speed is about 7,200 revolutions per minute.

6. The disk drive of claim 1 further comprising:

an air-actuated latch for latching said actuator assembly in said home position when said data storage disk stops spinning.

7. The disk drive of claim 1 wherein said ferromagnetic structure is disposed within an aperture in said actuator assembly.

8. The disk drive of claim 1 wherein said ferromagnetic structure represents a steel ball disposed within an aperture in said actuator assembly.

9. The disk drive of claim 1 wherein a magnitude of said second torque is between about 1/1,000 and 1/10,000 of a magnitude of said first torque.

10. The disk drive of claim 1 wherein said magnet and said ferromagnetic structure are configured such that a first magnetic attraction force between said magnet and said ferromagnetic structure when said actuator assembly is in said home position is greater than a second magnetic attraction force between said magnet and said ferromagnetic structure when said actuator assembly is in a position for accessing data on said data storage disk.

11. A method for manufacturing a disk drive, comprising: providing a baseplate;

mounting spindle motor on the baseplate;

rotatably mounting a data storage disk to the spindle motor;

rotatably mounting an actuator assembly to the baseplate;

mounting a transducer to one end of the actuator assembly such that the transducer may be rotatably positioned over a surface of the disk;

mounting an actuator motor to the baseplate, in close proximity to the other end of the actuator assembly, the actuator motor providing a first torque from a magnet defined therein, the first torque for biasing the actuator assembly to position the transducer over a data storage area of the disk; and

coupling a ferromagnetic structure to said other end of the actuator assembly, said ferromagnetic structure being magnetically attracted toward said magnet with a magnetic force, said magnetic force urging said actuator assembly toward a home position with a second torque lower than said first torque, said actuator assembly, when said actuator motor is off, is secured over a designated parking area of said data storage disk by said second torque.

12. The method of claim 11 wherein said actuator motor represents a voice coil motor.

13. The method of claim 11 wherein said actuator assembly is held against a crash stop in said home position, said transducer, when said actuator assembly is held against said crash stop, is held substantially immobile against said crash stop to reduce wear on said transducer.

14. The method of claim 11 wherein said second torque is sufficient to bring said actuator assembly to said home position when said actuator motor is off irrespective of whether said data storage disk spins at a first speed or at a second speed, said first speed representing a speed at which said data storage disk spins while data on said data storage disk is accessed, said second speed representing a speed slower than said first speed.

15. The method of claim 11 further comprising:

providing an air-actuated latch, said air-actuated latch being configured for latching said actuator assembly in said home position when said data storage disk stops spinning, said air-actuated latch being configured for releasing said actuator assembly, thereby allowing said actuator assembly to be moved from said home position while said data storage disk spins.

16. The method of claim 11 wherein said ferromagnetic structure is disposed within an aperture in said actuator assembly.

17. The method of claim 11 wherein a magnitude of said second torque is between about 1 / 1 ,000 and 1/10,000 of a magnitude of said first torque.

18. The method of claim 11 wherein said magnet and said ferromagnetic structure are configured such that a first magnetic attraction force between said magnet and said ferromagnetic structure when said actuator assembly is in said home position is greater than a second magnetic attraction force between said magnet and said ferromagnetic structure when said actuator assembly is in a position for accessing data on said data storage disk.

19. In a disk drive having a magnet, a data storage disk, and an actuator assembly coupled to a transducer, said actuator assembly being coupled to an actuator motor configured, when on, for positioning with a first torque said actuator assembly such that said transducer is disposed over data storage zones of said data storage disk, a method for spinning down said data storage disk, comprising:

moving, using a ferromagnetic structure coupled to said actuator assembly, said actuator assembly to a home position, said home position representing a position of said transducer assembly in which said transducer is positioned over a designated parking area of said data storage, said ferromagnetic structure being magnetically attracted toward said permanent magnet with a magnetic force, said magnetic force urging said actuator assembly toward said home position with a second torque lower than said first torque;

holding, using said second torque, said actuator assembly in said home position when said actuator motor is off; and

applying dynamic braking, using a spindle motor coupled to said data storage disk, to stop said data storage disk from spinning.

20. The method of claim 19 wherein said data storage disk is spun down without employing said spindle motor as a generator to enable said actuator motor to hold said actuator assembly at said home position.

21. The method of claim 19 further comprising latching, using an air-actuated latch, said actuator assembly at said home position when said data storage disk rotates at a first speed lower than a second speed employed while accessing data on said data storage disk.