Magnetic parking device for disk drive

A magnetic parking device for retaining an actuator in a disk drive over a landing zone. A magnetically permeable capture member is provided on the drive actuator and a magnetic parking member for capturing and magnetically retaining the capture member to park the transducer is provided adjacent the drive actuator. The magnetic parking member includes a permanent magnet and a magnetic field containing member having a slot (or air gap) formed therein. The magnetic field containing member and permanent magnet form a magnetic circuit with a magnetic flux with the slot in the magnetic field containing member allowing a portion of the magnetic flux to extend beyond the physical confines of the magnetic field containing member to provide a capture region for the capture member. When the actuator moves into a position where the transducer is over a landing zone, the capture member enters the capture region adjacent the air gap and becomes part of the magnetic circuit formed by the magnetic field containing member and the permanent magnet. A bucking coil is provided, arranged about the magnet, for passing a current to generate a magnetic field with polarity opposite that provided by the permanent magnet to neutralize the magnetic field to release the actuator from the parked state.

CROSS-REFERENCE TO RELATED APPLICATIONS
 THIN LINE MICRO HARD DISK ARCHITECTURE, Ser. No. 07/527,590, filed May 23,
 1990, now abandoned, inventors Frederick Mark Stefansky, Bernard A. Rusik,
 Glade N. Bagnell, Steve Speckmann, assigned to the assignee of the present
 application;
 LATCH MECHANISM FOR DISK DRIVES, Ser. No. 07/464,696, filed Sep. 18, 1989,
 now U.S. Pat. No. 4,979,062, inventors Frederick Mark Stefansky and Glade
 N. Bagnell, assigned to the assignee of the present application;
 MAGNETIC KING DEVICE FOR DISK DRIVE, U.S. Pat. No. 5,178,300, inventor
 Frederick Mark Stefansky, assigned to the assignee of the present
 application;
 VOICE COIL ACTIVATED DISK DRIVE KING DEVICE WITH MAGNETIC BIAS, U.S.
 Pat. No. 4,985,793, issued Jan. 15, 1991, inventor Kurt Anderson, assigned
 to the assignee of the present application;
 DISK DRIVE SOFTWARE SYSTEM ARCHITECTURE, Ser. No. 07/790,008, now
 abandoned, which is a file wrapper continuation of Ser. No. 07/488,386,
 now abandoned, which is a file wrapper continuation of Ser. No.
 07/057,806, filed Jun. 2, 1987, now abandoned, inventors John P. Squires,
 Thomas A. Fiers and Louis J. Shrinkle, assigned to the assignee of the
 present application;
 DISK DRIVE SOFTWARE SYSTEM ARCHITECTURE UTILIZING IMBEDDED REAL TIME
 DIAGNOSTIC MONITOR, U.S. Pat. No. 4,979,055, issued Dec. 18, 1990,
 inventors John P. Squires, Thomas A. Fiers and Louis J. Shrinkle, assigned
 to the assignee of the present application.
 DISK DRIVE SYSTEM CONTROL ARCHITECTURE, U.S. Pat. No. 4,979,056, inventors
 John P. Squires, Thomas A. Fiers and Louis J. Shrinkle, issued Dec. 18,
 1990, assigned to the assignee of the instant application.
 Each of the above-mentioned applications is hereby specifically
 incorporated by reference.
 BACKGROUND OF THE INVENTION
 1. Field of the Invention
 The present invention relates to parking devices which position and retain
 the head(s) of a disk drive over a selected portion of a hard (or fixed)
 disk when the disk drive is not in use.
 2. Description of the Related Art
 Developments in personal computers, portable computers and lap top
 computers have prompted reductions in the size and increases in the memory
 capacity of disk drives. Factors which hamper the incorporation and use of
 fixed or hard disks in lap-top computers include the size, weight, and
 power consumption of hard disk drives. The desire to operate portable
 computers on battery supplied power, and the reduction of the life of the
 batteries by each power consuming component of a computer, have prompted
 efforts to reduce the power consumed by disk drives intended for use in
 portable computers.
 Conventional hard disk drives often incorporate a device for parking the
 head(s) of the drive. As used in this patent, the terms "park" and
 "parking" refer to the maintaining the position of the head(s) over a
 selected portion (usually a "landing zone" at the inside or outside
 diameter) of the disk (or disks). The heads are supported by an actuator,
 and parking the heads also means parking the actuator by fixing the
 position of the actuator which supports the heads.
 In conventional disk drives, a head "flies" over the surface of a disk,
 riding on the stream of air created by the rotation of the disk. When the
 disk stops rotating, for example, when power is turned off, the head lands
 on the disk. If the head lands on a portion of the disk which is used to
 store data, there is a possibility that the disk, and thus the data stored
 on the disk, will be damaged. Thus, retaining the heads over non-data
 portions of the disk is crucial. Parking the head(s) is particularly
 important in portable computers, in which the disk drive may be
 continually subject to large physical shocks during transportation.
 Non-operational physical shocks, for example, shocks experienced during
 transportation or shipping of portable computers, may cause the heads to
 "slap" against the disk, possibly causing a loss of data if the head slaps
 against a data-carrying portion of the disk. Parking the head assures that
 the head will land on a landing zone--i.e., a non-data storage portion of
 the disk--and will be held in a position over the landing zone during the
 power-down period.
 Various types of parking (or latching) devices have been used to lock the
 actuator arm positioned by a voice coil in a selected position when the
 disk drive is not operating. Many parking devices incorporate a latch
 which physically engages the actuator arm. In such devices, a spring is
 utilized to bias a pivoting latch arm to a parked position and an
 electromagnet to release the latch during operation of the drive. In one
 type of latch configuration, an electromagnet is used to release the
 latch. The use of an electromagnet generally requires the continual use of
 electrical power to maintain the latch in the unlatched position. Further,
 an electromagnet generates heat which is not desirable in a disk drive or
 any other area in a computer.
 Air activated parking devices rely on the air flow generated by the
 rotating disks to release a spring biased latch arm. Air activated parking
 devices pose the problem of interference with the air flow necessary for
 the heads to fly properly. Further, the amount of force generated by the
 air flow is related to the surface area of the disks, and as disks are
 reduced in size, the amount of air flow may be insufficient to release a
 latch mechanism.
 Solenoids have also been used to release latch arms which are spring
 biased. As with an electromagnet, a solenoid requires a constant supply of
 electrical current, and the residual magnetism of the plunger must be
 overcome by the biasing force.
 Such parking devices often utilize pivoting latch arms which often present
 design, manufacturing, and operational problems related to, for example,
 balancing the latch arm to provide proper functioning of the latch for all
 orientations of the disk drive. A latch which does not operate properly
 for all orientations of the disk drive is not suitable for use in a
 portable or lap-top computer.
 Reliability of electromagnetic parking devices which attract a permeable
 member requires overcoming any residual magnetism in the permeable member,
 prompting the use of larger bias springs. However, larger spring forces
 demand greater electrical power to energize an electromagnet which
 reliably overcomes the spring force.
 Purely magnetic parking devices park the actuator by the attraction by a
 magnet of a magnetically permeable portion of the actuator. Such parking
 devices have provided direct contact between the magnetically permeable
 portion of the actuator and the magnet. The primary drawback of a magnetic
 latch of this type is that the rotational movement of the actuator is
 adversely affected by the attraction of the magnetically permeable portion
 of the actuator and the magnet, thereby creating problems with the track
 following and seek functions. Further, an extremely large force is
 required to release the actuator from the magnet.
 SUMMARY OF THE INVENTION
 An object of the present invention is to provide a parking device which
 magnetically captures (or parks) the actuator of a disk drive.
 A further object of the present invention is to provide a parking device
 which requires an minimum amount of space in the disk drive.
 Another object of the present invention is to provide a parking device
 which parks the actuator without relying on physical latching of the
 parking device and the actuator.
 Another object of the present invention is to provide a magnetic parking
 device wherein a magnetic field is concentrated in an interactive region
 where the magnetic field captures an actuator and leakage of the magnetic
 field outside of the interactive region is confined to a limited area.
 Another object of the present invention is to provide a magnetic parking
 device which does not utilize any moving parts other than the actuator
 arm.
 Another object of the present invention is to provide a magnetic parking
 device which has a greater retention force than prior latch mechanisms
 utilizing non-physical latching schemes.
 These and other objects of the invention are provided in a magnetic parking
 device in accordance with the present invention. Such a parking device is
 useful in, for example, a disk drive having a data storage medium, a
 transducer for reading information from and writing information to the
 data storage medium, and an actuator for selectively positioning the
 transducer with respect to the data storage medium. A magnetically
 permeable capture member is provided on the drive actuator and a magnetic
 parking means for capturing and magnetically retaining the capture member
 to park the transducer is provided adjacent the drive actuator. The
 magnetic parking means may include a permanent magnet and a magnetic field
 containing member having a slot (or air gap) formed therein. The magnetic
 field containing member and permanent magnet form a magnetic circuit with
 a magnetic flux substantially contained within the magnetic field
 containing member. The slot in the magnetic field containing member allows
 a portion of the magnetic flux to extend beyond the physical confines of
 the magnetic field containing member to provide a capture region for the
 capture member. When the actuator moves into a position where the
 transducer is over a landing zone, the capture member enters the capture
 region adjacent the air gap and becomes part of the magnetic circuit
 formed by the magnetic field containing member and the permanent magnet. A
 bucking coil is provided, arranged about the magnet, for passing a current
 to generate a magnetic field with polarity opposite that provided by the
 permanent magnet to neutralize the magnetic field to release the actuator
 from the parked state.

DESCRIPTION OF THE PREFERRED EMBODIMENT
 The magnetic parking device of the present invention will be described with
 reference to the preferred embodiments thereof.
 A disk drive including a magnetic parking device according to the present
 invention will be described with reference to FIGS. 1-8. The disk drives
 described herein include, for example, one or more hard disks with
 magnetic coating and utilize Winchester technology. The disk drives may
 utilize various numbers of disks and a corresponding number of heads and
 the teachings of the invention are not limited in the particular
 embodiment of the disk drives disclosed herein. Further, the disk drives
 described herein may utilize other types of disks, for example, optical
 disks, and other read/write technologies, for example, lasers.
 A disk drive 30, including a magnetic parking device in accordance with a
 first embodiment of the present invention, will be described with
 reference to FIGS. 1, 2 and 3. For purposes of describing the magnetic
 parking device of the present invention, disk drive 30 will be described
 in broad terms. Details of disk drives which may use a magnetic parking
 device such as those taught herein in place of other latching devices are
 disclosed in above-identified, co-pending application Ser. No. 527,590,
 which is hereby incorporated by reference.
 Disk drive 30 has a baseplate 32 for supporting internal components of the
 drive and external electronic circuitry. The internal components may be
 identified in three inter-related groups: disk 34 mounted by hub 35 to a
 spin motor (not shown), actuator assembly 36 for positioning head(s) 38
 with respect to disk 34, and header assembly 40 including header 42,
 bracket 44, and flex circuit 46. A cover (not shown) is sealably attached
 to base plate 32 by mounting screws (not shown) and with gasket 31 placed
 between base plate 32 and the cover to provide a controlled, sealed
 internal environment.
 Disk 34, which is rotated by the spin motor, includes specified inside and
 outside diameters 58 and 60, respectively, and a landing zone (or non-data
 area) 61 located, in one embodiment, adjacent to inside diameter 58.
 Landing zone 61 may be any selected portion of disk 34; however, a portion
 of disk 34 adjacent to inside diameter 58 or outside diameter 60 is
 usually selected.
 A printed circuit assembly (or control means, not shown), may be attached
 to the bottom of base plate 32. The control means provides signals to the
 drive components to selectively store and retrieve data on disk 34. Header
 42 carries electrical signals from the printed circuit assembly 62 to the
 controlled, internal environment. Disk drive 30 may have an assembled
 length of about 5.15 inches, a width of about 4 inches, and a total
 height, including the printed circuit assembly, of about 0.75 inches.
 Actuator assembly 36 includes pivotable actuator arm 50, having first arm
 portion 50a. Heads 38, located on opposite sides of the pivot point of the
 actuator arm 50, are mounted on load beam(s) 64 at first end 50a of
 actuator arm 50. Actuator coil 52 is mounted on actuator sub-arms 50-1,
 50-2 at a second end of actuator arm 50. Actuator assembly 36 includes a
 voice coil type actuator motor utilizing a magnet structure 54 for
 supporting magnet 56. The components of magnet structure 54, described in
 further detail below, are formed of magnetically permeable material to
 provide returns for the magnetic flux generated by magnet 56. Magnet
 structure 54 and actuator coil 52 are arranged so that a current in coil
 52, in the presence of the magnetic fields created by magnet 56, creates a
 force which pivots actuator arm 50. Likewise, currents passing in opposite
 directions in coil 52 create torques in opposite directions. The pivoting
 of actuator arm 50 positions head 38 at selected locations with respect to
 disk 34.
 The structure and operation of actuator assembly 36 will be explained with
 reference to FIGS. 1-4. The function of the actuator assembly 36 is to
 selectively position heads 38 over individual tracks on disk(s) 34 by
 pivoting actuator arm assembly 50. Head 38 is supported on actuator arm 50
 by a load beam 64 and a flexure (not shown) provided between load beam 64
 and heads 38. A bearing assembly 66 is inserted in actuator arm 50 to
 provide rotational movement about a pivot point at the approximate center
 of bearing assembly 66. Actuator arm 50, including all of the components
 attached thereto, is precisely balanced, i.e., equal amounts of weight are
 provided on either side of the pivot point so that the positioning of
 heads 38 is less susceptible to linear shock and vibration.
 Magnet structure 54, in conjunction with coil 52, comprises a voice coil
 assembly. Magnet structure 54 includes top and bottom plates 68, 70, arm
 72, support structure 74, and bipolar magnet 56 attached to top plate 68.
 Top plate 68, bottom plate 70, and support structure 74 are formed of
 magnetically permeable material. Top and bottom plates 68, 70 in
 conjunction with arm 72 and support structure 74 function as returns for
 the magnetic flux provided by bipolar magnet 56. It is important that
 there are no air gaps in the areas adjoining arm 72, support structure 74
 and either top plate 68 or bottom plate 70; any air gap would create a
 discontinuity in the return, greatly reducing the strength of the magnetic
 field.
 Magnet 56 includes regions 56a and 56b providing first and second magnetic
 fields B.sub.1, B.sub.2, between magnet 56 and bottom plate 70. First and
 second magnetic fields B.sub.1, B.sub.2, are encompassed in closed
 magnetic field loops including various portions of top plate 68, bottom
 plate 70, arm 72, and support structure 74. By containing magnetic fields
 B.sub.1 and B.sub.2 in returns, the magnetic field intensity of each field
 is increased in the region between the respective magnet 56 and bottom
 plate 70. The strength of the magnetic field in the support structure
 region is directly related to the torque which the voice coil exerts on
 the actuator arm 50, and thus the rotational velocity of actuator arm 50
 and the seek times for the drive.
 Crash stops are provided to limit the pivoting movement of actuator arm 50
 so that heads 38 travel only between the inside and outside diameters 58,
 60 of disk 34. The outside diameter crash stop may be provided by crash
 stop post 33. When the pivoting motion of actuator arm 50 places heads 38
 at the inside diameter 58 of disk 34, capture member 100, mounted on a
 portion of the actuator latch arm 55, contacts a portion of support
 structure 74, thereby acting as the inside diameter crash stop.
 A flex circuit 46 carries electrical signals from header 42 to heads 38 and
 actuator assembly 36. The reverse flex circuit 46 may be separated into
 three portions. A first portion carries current to actuator coil 52; and a
 second portion is a ground plane separating the current carrying portion
 from the third, data-carrying portion. The data carrying portion provides
 signals to heads 38 for recording information on disk 34 and carries
 signals from the heads 38 to the printed circuit assembly (not shown), via
 header 42, when reading data from disk 34. The ground plane portion
 prevents interference with the relatively weak data signals which would
 otherwise be caused by the larger currents necessary for actuator coil 52
 passing through the first portion of the reverse flex circuit 46.
 Flex circuit 46 is designed to exert only a minimal amount of rotational
 force (torque) on actuator arm 50. Any torque exerted on actuator arm 50
 by any means other than the voice coil assembly affects the function of
 actuator assembly 36 in positioning heads 38 with respect to disk 34,
 particularly the track following and seek functions described in the
 above-identified co-pending Applications, Ser. Nos. 057,806 and 058,289.
 The force provided by the voice coil assembly must be controlled to
 compensate for the force exerted by flex circuit 46. A motor flex circuit
 48 is provided for transmitting DC signals to spin motor 35 from header
 assembly 40, to selectively rotate disk 34.
 A magnetic parking device for parking heads 38, i.e., locking actuator arm
 50 in an orientation where heads 38 are positioned, for example, at the
 inside diameter 58 of disk 34, will be described with reference to FIGS.
 2-8.
 With particular reference to FIGS. 2-4, a magnetic parking device in
 accordance with the present invention includes a magnetically permeable
 capture member 100 mounted on actuator latch arm 55.
 Magnetically permeable capture member 100 may be formed of cold drawn steel
 having a nonmagnetic electroless nickel finish, or magnetic stainless
 steel, requiring no nickel finish. In one embodiment, capture member 100
 generally has a "T" shape, including a cylindrical center portion 101
 engaging disc-portion 103. Disc-portion 103 includes face 102; it is
 important that face 102 be manufactured to have a smooth, planar surface
 for engaging tabs 74a and 74b, so that no air gaps are present between the
 three surfaces when in abutment. Such air gaps would substantially reduce
 the magnetic retaining force (described below) provided by the magnetic
 flux (arcs 82) through capture member 100.
 As will be appreciated by those skilled in the art, any number of schemes
 may be utilized to mount capture member 100 on latch arm 55. In one
 embodiment, capture member 100 is adhesively secured in a groove in latch
 arm 55. Alternatively, the magnetically permeable capture member may be
 surrounded by rubber grommet, and actuator latch arm 55 provided with a
 hooked end portion to secure capture member 100 and rubber grommet. In yet
 another embodiment, shown in FIG. 6, capture member 100 may be provided
 through a bore on a portion of actuator arm 50 and secured by a snap ring
 (132).
 As shown in FIGS. 2-4, support structure 74 is provided between one portion
 of top plate 68 and bottom plate 70 to provide structural rigidity, in
 conjunction with arm 72, for magnet structure 54. In addition, as shown
 particularly in FIG. 4, magnet 90 is provided in a portion of support
 structure 74. Specifically, first and second pins 76a, 76b are positioned
 through bores in support structure 74, and magnet 90 is positioned between
 pins 76a, 76b. Bucking coil 85 is provided about pins 76a, 76b and magnet
 90. Support structure 74 may be cast of a solid piece of stainless steel
 or magnesium, or may be assembled from separately cast portions, although
 precaution must be taken to ensure no air gaps exist between the assembled
 portions. Tabs 74a and 74b of support structure 74 define an air gap 80
 having a length L, and gap width W, where W equals approximately 0.012
 inch. Magnet 90 is preferably a 30 Oersted neodymium iron boron magnet
 which generates a magnetic field B.sub.3 and forms a magnetic circuit with
 the support structure 74, including tabs 74a and 74b. The resulting
 magnetic circuit has a magnetic flux which circulates in the direction of
 the magnetic field B.sub.3 and forms a closed loop circuit with a flux
 path passing through pins 76a, 76b and structure 74, including tabs 74a,
 74b.
 When the magnetic flux generated by magnet 90 encounters air gap 80 in the
 magnetic circuit, the magnetic field flux lines pass from tab 74a through
 air gap 80 to tab 74b in across the width W of air gap 80. Due to the
 phenomenon known as "fringing," the flux extends outward a small distance
 into a region adjacent tabs 74a and 74b, shown by example as flux line 82.
 Magnetically permeable capture member 100 is mounted on actuator latch arm
 55 and moves along axis A, as shown in FIG. 3. The elevation and location
 of capture member 100 is selected so that the center of face portion 102
 of capture member 100 engages tabs 74a and 74b of the approximate center
 of air gap 80 when actuator arm 50 is rotated to position heads 38 over
 landing zone 61. When magnetic capture member 100 is positioned outside of
 the magnetic flux 82, capture member 100 is non-permeated and remains
 outside the influence of magnetic field B.sub.3 and the flux 82 fringing
 about air gap 80. When the control means causes actuator assembly 36 to
 pivot actuator arm 50 to position heads 38 over landing zone 61,
 magnetically permeable capture member 100 is brought into contact with
 tabs 74a and 74b.
 Due to the permeability of capture member 100, when actuator arm 50 is
 positioned such that member 100 contacts tabs 74a and 74b, capture member
 100 switches to a permeated state and becomes a component of the magnetic
 circuit formed by support structure 74, magnet 90, and tabs 74a and 74b.
 Specifically, as shown in FIG. 4, magnetic flux (82) fringing about air
 gap 80 permeates magnetic capture member 100. Capture member 100 thus
 becomes an integral part of the magnetic circuit created by magnet 90 and
 is retained in position abutting tabs 74a and 74b with a force which is
 approximately ten times greater than that of previously known magnetic
 latches.
 As shown in FIG. 5, the strength of the latch force is dependent upon the
 width "W" of gap 80. FIG. 5 is a graph of the latch force, in inch-ounces
 vs. the width "W" of gap 80. As shown therein, the smaller the width of
 gap 80 the greater the magnitude of the latching force of the parking
 device. FIG. 5 depicts scaled measurements of the torque required by
 actuator 50 to overcome the latch force provided at varying gap widths W.
 The "computed/act(ual) volts" indicia represents the force derived by
 measuring the amount of voltage which must be applied to actuator coil 52
 to remove actuator 50 from the latched position and computing the torque
 in accordance with well-known principles. The "gram gauge" indicia is
 measured directly by coupling a gram gauge to actuator arm 50 and, with
 capture member 100 abutting tabs 74a, 74b, applying a force to the gram
 gauge which is adequate to release arm 50 from the latched positioned.
 It should be noted that the fringing flux (82) about gap 80 creates a
 relatively small "capture zone". Because the amount of fringing is kept to
 a minimum, little interference with the movement of actuator arm 50 and
 the positioning of head(s) 38.
 In order to disengage actuator assembly 36 from the parked state,
 compensation must be made for the greater retaining force provided by the
 capture member 100 and tabs 74a, 74b. Bucking coil 85 is thus provided to
 neutralize the magnetic force B.sub.3, and hence flux 82, provided by
 permanent magnet 90. Coil 85 is coupled to the control means via header
 assembly 40. Under the direction of the control means, a current is passed
 through bucking coil 85 in a direction to generate a magnetic field of
 opposite polarity to that of magnetic field B.sub.3 to neutralize the
 magnetic flux circuit provided by magnetic field B.sub.3. Preferably, such
 current is provided for only a split second (for example, 0.10 second,)
 while the control means simultaneously causes actuator assembly 36 to
 pivot actuator arm 50 to move capture member 100 along axis A in a
 direction away from tabs 74a and 74b until such time as capture member 100
 is clear of flux 82.
 In one embodiment of the invention, magnet 90 is provided to be slidably
 receivable in the cylindrical area between pins 76a, 76b. In this
 embodiment, if magnet 90 has a diameter of approximately 0.100 inch and a
 length of approximately 0.065 inch, bucking coil 85 may be formed of 1100
 turns of RSTSL insulated copper wire about pins 76a, 76b. Typically, disk
 drive 30 is powered by a 5 volt power supply. This provides a bucking coil
 85 generating 203 Ampere turns, assuming a wire resistance of 27 ohms.
 As shown in FIG. 6, assuming the aforementioned dimensions for magnet 90
 and bucking coil 85, the amount of voltage applied to coil 85 is shown vs.
 (1) the "latch torque" i.e., the retentive force that the magnetic parking
 device, including tabs 74a and 74b, exerts on capture member 100 and
 actuator body 50 in terms of the torque required to remove body 50 from a
 latched position; and (2) the "actuator torque," defined as the torque
 provided by actuator body 50 assuming the specified voltage level is also
 provided through actuator coil 52. Thus, at 0 volts, the latch torque is
 approximately 1.1 in-ounce, while the actuator torque is 0 in-ounce. As
 the voltage in coil 85 and actuator coil 52 increases, the respective
 indicia converge and eventually cross at approximately 3 volts. As can be
 seen, the bucking coil generating a magnetic field of opposite polarity to
 B.sub.3 thus a provides counteractive force to release actuator body 50
 away from tabs 74a, 74b.
 An alternative embodiment of capture member 100 is shown in FIGS. 7 and 8.
 In FIG. 8, tabs 74a and 74b have been rotated approximately 90.degree. so
 that the width W of air gap 80 is now parallel to the length of actuator
 arm 55. FIGS. 7 and 8 detail a capture member 110 which is pivotably
 mounted on actuator arm 55 about an axis 112. Preferably, a bore 114 is
 provided in latch arm 55 and capture member 110 is provided through a
 rubber grommet 116 and secured to latch arm 55 by pin 118. This allows
 capture member 110 pivot about axis 112 to more accurately align its face
 against tabs 74a and 74b. Capture member 110 also includes a recess
 portion 120 which straddles air gap 80 when capture member 110 abuts tab
 74a and 74b. The air gap is provided to limit the amount of flux passing
 through capture member 110 by limiting the contact portion of member 110
 to portions 110a and 110b. As the path of the flux passing through capture
 member 110 generally takes an arcuate path, the deletion of the portion
 comprising recess portion 120 also allows the face of capture member 110
 to more securely abut tabs 74a and 74b.
 Control electronics suitable for use in accordance with the disk drive
 described herein are described in U.S. Pat. No. 4,979,056. To control
 bucking coil 85, circuitry for controlling the bucking coil to release the
 actuator coil may be included in the control electronics. A block
 representation of such circuitry is shown in FIG. 9.
 In FIG. 9, a microprocessor (.mu.P) is shown coupled to a digital-to-analog
 converter 200 and a programmable latch 210 via an address bus 230.
 Digital-to-analog converter 200 is set by the microprocessor to position
 the actuator by directing the current in actuator coil 52. As will be
 generally understood by those skilled in the art, the microprocessor can
 control the output of digital-to-analog converter 200 and the state of
 latch 210 by directly writing to their address on bus 230. As noted above,
 the actuator will be in the latched state when the capture member 100
 contacts tabs 74a, 74b. When the actuator is to be unlatched, the
 microprocessor sets the state of the latch to 1 which drives transistors
 215 and 225 to energize bucking coil 85, while simultaneously driving
 current to actuator coil 52 at full current so as to rapidly move the
 actuator and pull capture member 100 away from capture member 74. As noted
 above, this operation takes about 0.10 second.
 The many features and advantages of the disk drive of the present
 invention, including the magnetic latch device incorporated therein, will
 be apparent to those skilled in the art from the description of the
 preferred embodiments, the drawings, and the claims. Numerous variations
 are possible as will be apparent to those skilled in the art. Such
 variations are intended to be within the scope of the invention as defined
 by the specification and the following claims are intended to cover all
 the modifications and variations falling within the scope of the
 invention.