GB2129186A - Disk drive actuator structure - Google Patents

Abstract

An actuator 14 for a disk drive of a memory storage device includes a fixed magnet assembly comprising of a pair of right circular cylindrical magnets 30, 31 (e.g. of ceramic) slip fitted over center pole pieces 34 and an encompassing cylindrical pole structure 27 spaced from the magnets to form a linearly extending annular air gap 37. A pair of right circular cylindrical coils 41 are fixedly attached to a linearly moving carriage 18 containing a series of read/write transducers 22, 23, 24, movable radially of track locations on disk 11. End pole pieces 17, 28 are provided at the ends of the cylindrical pole structure which prevent undesirable magnetic flux from reaching a surface of the disk. Cu tube (46) (Fig. 3) acts as a bucking coil and seals the magnet periphery to inhibit particles faking off into the air stream. Shock absorbers (55, 56) (Fig. 4) are provided. Opposite charge on magnets 30, 31 minimise gauss leakage, as do C members 27. A carriage rail tensioning mechanism is provided. Dimensions/materials are disclosed. <IMAGE>

Description

SPECIFICATION Disk drive actuator structure The present invention generally relates to memory storage devices of the type that include one or more rotating disks. More particularly, the present invention concerns rotating disk memory storage devices that include an actuator assembly which supports transducers adapted to move radially with respect to the rotating disk or disks to read-write magnetic information thereon. The actuator is referred to as a linear actuator since it moves the transducer along a straight line that extends generally radially of the memory storage disk.

The present invention provides a linear actuator particularly useful in magnetic memory storage apparatus of the type known in the art as a Winchester magnetic disk memory storage apparatus. The linear actuator is juxtaposed adjacent the periphery of one or more vertically spaced disks and is designed to rapidly position the transducer or transducers to access the magnetic information recorded on the disk. The transducers normally comprise floating read/write heads. Although the present invention shall be described in connection with a Winchester disk drive type of unit, it will be appreciated that the actuator will be useful in other types of electromagnetic memory storage apparatus such as optical memory storage apparatus wherein an optical transducer or several optical transducers are incorporated in the actuator.

Due to increased track density made possible by recent disk developments, there has been an ongoing attempt to provide an actuator capable of extremely rapid access time into the information stored on the disk and yet miniaturize the apparatus as much as possible. Thus, it is desired to provide an actuator which has sufficiently high magnetic force constants to rapidly decelerate and accelerate the transducer carriage, which holds the carriage steady against vibrations and maintains any magnetic leakage in front of the actuator adjacent the disks at a minimum so as to not adversely affect the magnetic information recorded on the disks. Further, it is desired that the carriage support and drive arrangement be such as to minimize resonance vibrations induced by the required rapid acceleration and deceleration of the carriage. Lower cost fabrication is also sought.

United States Patent 4,280,1 55 discloses a fixed disk drive that includes a flat rectangular baseplate and bowl-shape cover. A magnetic transducer head carriage and positioning assembly (referred to hereafter as a transducer actuator assembly) is mounted to the baseplate adjacent to the periphery of the disks with the transducers being mounted upon flexure arms that project outwardly from the actuator assembly. A motor for rotating the disks is mounted below the baseplate within the housing. The actuator is moved in and out of position with respect to the disks by a stepper motor driving a rack and pinion.

An improvement to the above transducer actuator assembly is disclosed in UK Patent Application No. 8303136 (Serial No. 2117163), filed on 4th February 1 983 with claim to priority from U.S.

Application No.06/352943 of 26th February 1982, and in European Patent Application No. 83200907.0 filed on 18th June 1983 with claim to priority from U.S. Application No. 06/391782 of 24th June 1982. These applications show an electromagnetic means for driving the actuator including dual pairs of rectangular magnets (four magnets in all) with a rectangular coil attached to the actuator carriage and being driven within a rectangular air gap.

Linear positioners are also shown in the U.S.

patents 3,619,673 and 3,666,977. In the '673 patent rectangular permanent magnets are employed with a rectangular coil, connected to a carriage member, being disposed in an air gap between the magnets and central core pole piece.

Current driven through the coil will develop a propelling force on the coil structure sufficient to move it along the central core. The '977 patent shows a similar scheme involving a central core member and a series of individual magnet blocks around the periphery of the core with a moveable multi-turn drive coil in the air gap. The coil is rigidly mounted to a carriage assembly and both move together when current is passed through the coil.

The present invention provides rotating disk memory storage apparatus and disk drive actuators as set out in the claims of this application, to which reference should now be made. The rotating disk memory storage apparatus of the invention can have an improved magnetic transducer actuator assembly having the above-mentioned and other desirable attributes, particularly a highly efficient figure eight magnetic return path.

In certain embodiments, these functions and results are provided by the incorporation of a single pair of circular cylindrical, radially charged magnets floatingly contained within and spaced from generally confining C-cross sectioned pole structures with dual circular coils movable in the air gap therebetween, such coils being affixed to mounting wings on the actuator body or carriage.

Actuation of the coils results in very rapid movement of the actuator and faster access of the transducer to the disks. The actuator assembly may generally comprise a carriage and a pair of transversely spaced electromagnetic motors that exert symetrically disposed motive forces upon the carriage. The carriage may be supported for reciprocating movement between a pair of lower and upper cylindrical guide rods. The carriage of the actuator assembly can include a central body portion and coil support wings extending symmetrically at the side of the central body portion. A pair of rollers may be mounted to the top of the carriage body and a double pair of rollers (front and rear set) may be mounted at the lower end of the carriage body to ride against the upper and lower guide rods, respectively.The actuator carriage may be in juxtaposition with a pair of cylindrical magnets which are affixed to a support structure. An annular air gap is thus formed between the cylindrical magnets and the pole structure surrounding the magnets. Coils are mounted to the wings of the carriage and the coils are positioned within the air gap and are driveable linearly with respect to that air gap and the cylindrical magnets.

Thus, when energised, the electromagnetic actuator generates a high force adapted to rapidly position the transducers extending from the carriage body relative to the disks in the drive unit.

The transducers may be mounted upon multiple flexure arms cantilevered in extending position forward from the carriage body. In the preferred embodiment there is provided a pair of laterally and symmetrically spaced linear motors which together provide the powerful actuation force to achieve rapid access time and stablize the cartridge carriage against vibrations. Due to the particular design of the pole structure the motors can occupy a small radial space and together produce insignificant magnetic leakage in the vicinity of the peripheries of the rotating disks.

An embodiment of the invention will now be described by way of example with reference to the drawings in which, Figure 1 is an exploded isometric view of a linear actuator assembly embodying the present invention, Figure 2 is a fragmentary top plan view of the linear actuator assembly of Figure 1 and part of a disk of a memory storage apparatus, Figure 3 is a rear view of the linear actuator of Figure 1 with its rear pole plate removed, Figure 4 is a cross-sectional view taken on the line for 4-4 in Figure 3, and Figure 5 is a view of the cylindrical magnet utilized in the actuator of Figures 1 to 4.

Referring to Figure 1 a magnetic disk storage apparatus includes a base 10 through which a spindle (not shown) is mounted for rotatively supporting one or more magnetic storage disks 11 and 12. A linear actuator 14 is provided for moving one or more accessing transducers along a linear path that extends generally radially of a rotating disk. The memory storage apparatus is of the type known as a Winchester drive apparatus that includes fixed disks of 5.25 or 8-inch (13.3 or 20.3 cm) diameter with an intended track density on each disk of about 600 to 1200 tracks per inch (234 to 468 per cm). The Winchester drive type of memory storage apparatus is well-known to those skilled in this art. It includes a motor (not shown) for rotating the disk at a high speed and a direct current drive circuit (not shown) that is operably connected to actuator 14.The base 10 is mounted within a closed housing that includes a ventilation system adapted to keep the disk surfaces free of dust. Linear actuator 14 will now be described in detail. The actuator 14 is very compact, occupying a space that extends only about 2 to 3.5 inches (5.1 to 8.9 cm) outwardly from the periphery of the disks and is positioned about 1/8 in to 1 in (0.32 to 2.5 cm) from the edge of disks 11 and 12. The actuator is capable of reciprocating the transducers through a 1 to 1.5 inch (2.5 to 3.8 cm) stroke with practically no stray magnetic leakage in front of the actuator in the vicinity of the peripheries of the rotating disks. Even though the disks are positioned quite close to the permanent magnets of the actuator assembly, the information magnetically recorded on the disk will not be adversely affected by the fields of the magnets.

Actuator 14 comprises a fixed magnet assembly 15 and a moveable transducer/coil assembly 16. When assembled transducer/coil assembly 16 is positioned within the fixed magnet assembly 1 5 and the rear of the linear actuator 14 is closed off by a rear pole plate 17. A carriage 18 is mounted centrally of assembly 16 and includes forward mounting brackets 19 onto which are affixed a series of cantilevered extensions or arms 21 which hold transducers 22-24. In the disk accessing position transducers 22-24 are juxtaposed to particular tracks on disks 11 and 12 where they either read magnetic information or place desirable magnetic information at that particular location. For illustrative purposes only, transducers 22 and 23 access the upper and lower surfaces of disk 11 and transducer 24 accesses the upper surface of disk 12.It is to be understood that an additional transducer assembly would normally access the underside of disk 12 and additional transducers assemblies may be included underneath the illustrated assemblies so as to access additional disk(s) rotating beneath disks 11 and 12.

Fixed magnet assembly 15 includes a pair of circular cylindrical magnets 30 and 31 held in a magnet housing 27. Magnet housing 27 comprises a forward pole plate 28, peripheral pole structure 29 surrounding the circular magnets and the aforesaid rear pole plate 17. Assembly 16 broadly comprises a symmetrical structure comprising a left lobe 32 and a right lobe 33 which each contain the aforesaid circular cylindrical magnets 30 and 31. Magnets 30 and 31 are annular in cross section and are fitted by a slip fit over central pole pieces 34. The slip fit clearance is shown at numeral 35. Spaced from the outer periphery of the circular magnets is the peripheral pole structure 29 which has a thickness 36 which is sufficient to transmit the magnetic lines of flux generated by the electromagnetic motor. The peripheral pole structure 29 is spaced from the exterior periphery of the magnets 30 and 31 to form an air gap 37 therebetween. Air gap 37 extends linearly along the length of the circular magnet and the peripheral pole structure. The air gap 37 (typically 0.150 to 0.180 inches (3.81 to 4.57 mm)) extending linearly of the magnet is of a radial dimension less than the air gaps 37a (typically 0.200 to 0.250 inches (5.08 to 6.35 mm)) formed between the ends of the circular magnet and their juxtaposed forward and rear pole plates (see Fig. 4) so as to insure maximum efficiency and prevent shorting of the magnet to the end plates. Magnets 30 and 31 are generally made out of a ceramic material such as that manufactured by the Crucible Division of Colt Industries. Magnet assembly 1 5 is fixed to base 10 by an attachment 38.

Carriage 18 includes carriage wings 42 onto which are attached a left driving coil 40 and a right driving coil 41. Holding rings or coil forms 43 and 44 are attached to such wings as by screw fastening at an inward edge portion and function to hold the coils in place on the wings. In addition to a mechanical holding force from the rings an adhesive material 45 may attach the coils to wings 42. Driving coils 40 and 41 are right circular cylinders having an inside diameter greater than the diameter of magnets 30 and 31 and an outside diameter less than the inner diameter of the peripheral pole structure 29. The coils are external to the circular magnets. Thus, the coils may freely move within the air gaps 37 formed between the outer periphery of the circular magnets and the peripheral pole structures.The drive coils are identical so that equal forces are applied at both sides of the carriage that are parallel to the linear path of travel of the carriage.

The path is determined by the guide rails 25 and 26 fixed with respect to base plate 10 and the fixed magnet assembly 1 5. The length of the cylindrical magnets in the direction of travel of the carriage is substantially greater than the length of the coils in the transducerlcoil assembly thus providing a long-gap, short-coil type of linear actuator. The symmetrical arrangement of the drive coils and associated pair of circular cylindrical magnets will be understood as effectively comprising two identical electromagnetic motors that act on the cartridge symmetrically at opposite sides to produce balance driving forces.

Base 10 of the memory storage apparatus as well as peripheral pole structure 29, forward pole plate 28 and rear pole plate 17 are cast from a metal of high magnetic permeability such as iron.

The carriage structure 18 including the carriage arm support 20 and cantilevered arms 21 are normally made of cast or machined aluminum.

As can be seen in Figure 3, a right circular cylindrical copper tube 46 is mounted on the exterior periphery of each of the magnets and 31 to form a so-called shorted turn. The shorted turn acts as a bucking coil to quickly saturate the coil and also prevents the disks from becoming contaminated, i.e., it seals or encapsulates the periphery of the magnet so that particles cannot flake off into the air stream. The rear pole plate 17 and front pole plate 28 is integral or in fixed connection with the peripheral pole structure. The gauss field is kept uniform and a very low gauss reading, i.e., about 3 to 4 gauss (0.3 to 0.4 mT) outside of the gap between the disks and the actuator is provided so long as the casing, i.e. the peripheral pole structure and end pole pieces, are not saturated.Due to the spacing about the periphery of the magnets and the driving coil, the driving coil and the magnets are in effect floating within the pole structure.

As shown in Figs. 2 and 3, carriage 18 contains pairs of upper rail rollers 47 and double pairs of lower rail rollers 48 (forward and back) which are in rolling contact with upper rail 25 and lower rail 26, respectively. Roller shafts 50 and 51 on each of the upper and lower rollers, respectively, extend perpendicularly from surfaces of carriage 18.

Carriage wings 42 support the driving coils 40 and 41. A rail tensioning spring mechanism 39 orients the rail structure and creates a tensioning force so that the carriage may move with no vibration linearly with respect to the upper and lower rails.

Figure 3 more clearly shows the gap 37 between the peripheral surfaces of magnets 30 and 31 and the peripheral pole structure 29. It is in this gap 37 in which driving coils 40 and 41 linearly move.

Peripheral pole structure 29 comprises in cross-section a pair of opposed facing C-cross section members 62 and 63. The upper and lower surfaces of carriage wings or extensions 42 normally of aluminum or magnesium material extend between and are spaced from a gap 64 formed by the facing ends 65 and 66 of members 62 and 63. The spacing between the ends 64 and 65 is such as to provide sufficient spacing for the height of the carriage extensions 42 but yet are close enough together to provide for the lines of flux to traverse the gaps between the ends of the C-cross section 64 and 65 to complete the "Figure 8" magnetic path. This path extends from magnet 30, through gap 37 to pole structure 29, then to end pole piece 17, through air gap 37a back to the magnet 30. This path is present in all four quadrants.As can be seen in Figure 3 the shorted turn 46 is a cylindrical tube which may be pressed fit on the magnet outside diameter.

Figure 4 is a side view of the fixed magnet assembly showing the end structure which incorporates front and rear annular shock absorbers 55 and 56. These function as crash stops and also to absorb kinetic energy from the moving elements to the pole structure. This minimizes resonant vibration into the base 10 from any impact of the coils against the front and rear pole pieces. Magnet 30 slip fits on center pole pieces 34 with or without an air gap. Rear pole piece plate 17 is removably affixed to the fixed magnet assembly so that the transducer coil assembly 16 may be easily removed rearwardly from the linear actuator 14. It is contemplated by this invention that an opposite charge may be placed on each of the magnets 30 and 31 so as to minimize gauss leakage. Due to the size of the air gap 37 and the slip fit of the magnets on the center pole pieces 34 mechanical vibration is prevented from being transmitted into base structure 10. Shock absorbers 55 and 56 also dampen magnetic forces. Approximately 80% of the coil is in the effective magnetic gap. The dual cylindrical coils allow for compact design and the entire linear actuator only requires two magnets unlike many of the prior art devices that require four or more magnets for their operation.

Figure 5 is an illustration of the type of magnet that is utilized in this invention. It is a so-called circular cylindrical magnet in which the poles are lined up radially within the cylinder so that north poles 66 and south poles 67 are on the outer and inner walls, respectively, of the right circular cylinder. A typical magnetic structure of this type is designed to create up 1400 to 1800 gauss (0.14 to 0.18 T) in the air gap. For a typical 8-inch (20.3 mm) Winchester type disk drive magnets 30 and 31 are 2.5 inches (6.35 cm) in length, 1/8 inch (2.86 cm) in outside diameter with a 1/2 inch (1.27 cm) internal diameter.

It is critical that in a disk drive that the magnetic field in the area of the rotating disk be less than some maximum value to present erasure or loss of the information stored on the disks.

Typically, this value is 10 (1 mT) gauss maximum.

In accordance with this invention, it has been discovered that the use of the C-shaped peripheral pole structures made of properly chosen materials which pole structures surround cylindrical magnets effectively shield stray flux from the rotating disks and the carriage bearings.

Details of the mounting of transducers on the cantilevered flexure arms and the mounting of the flexure arms on the carriage as well as the specific design of carriage 18 and tensioning spring mechanism 39 are shown in the aforesaid UK Patent Application No.8303136 (Serial No.2117163). Coils 40 and 41 are provided with coil lead wires 57 and 58 which are connected to a conventional direct current drive circuit (not shown). tne present Invention has been described by reference to what is believed to be the most practical embodiment it is understood that the invention may embody other specific forms not departing from the spirit of the invention. It is understood that there are other embodiments which possess the qualities and characteristics which would generally function in the same manner and should be considered within the scope of this invention. The present embodiment should be considered in all respects as illustrative.

Claims (14)

1. A memory storage apparatus comprising a housing, an actuator base plate assembly mounted within the housing, the actuator assembly including a carriage, at least one transducer mounted to the carriage, and electromagnetic means for reciprocating the carriage, a spindle motor mounted to the base plate, at least one rotatable disk operatively connected to the motor within the housing, said transducer being mounted to the carriage so that upon reciprocation of the carriage it is moved to desired track locations on the surfaces of the disk, wherein said electromagnetic means comprises:: a) a longitudinal-extending center pole of high magnetic permeable material, a longitudinalextending circular cylindrical magnet annular in cross-section surrounding said center pole, an exterior pole structure of high magnetic permerable material surrounding said magnet and having an internal circular surface conforming to and spaced from the exterior surface of said magnet to form a substantially annular air gap therebetween; b) a circular-wound coil longitudinally extending in said air gap and spaced from the pole structure internal circular surface and the exterior surface of said magnet; and c) connecting means affixing said coil to said carriage whereby flow of current through said coil moves said coil and carriage together in linear reciprocating motion.

2. An apparatus according to claim 1, including a pair of said electromagnetic means juxtaposed in spaced longitudinally extending positions, said carriage extending between the pair of electromagnetic means.

3. An apparatus according to claim 2, in which the magnets of the electromagnetic means are oppositely charged to minimize gauss leakage.

4. An apparatus according to any preceding claim, in which said connecting means includes horizontal extensions extending from said carriage to which said coils are affixed, the exterior pole structures of each of said pair of electromagnetic means having C-shaped cross-sections facing each other and wherein said carriage extensions extend between and are spaced from a gap formed by facing ends of the C-shape.

5. An apparatus according to claim 4, in which said carriage extensions are of high magnetic permeable material whereby a magnetic path substantially surrounds said magnets shielding stray magnetic flux from said disk.

6. An apparatus according to any preceding claim, including shock absorbing buffer means juxtaposed to the ends of said magnet(s) and abutting interior surfaces of end sections of said exterior pole structure, said buffer means extending into said annular air gap at the longitudinal ends of travel of said coil to dampen magnetic forces and to cushion overmotion of said coil.

7. An apparatus according to any preceding claim, in which or each said magnet is a slipped fit over its respective said center pole.

8. An apparatus according to any preceding claim, in which the or each said magnets floats between its respective said center pole and said coil to prevent mechanical vibration being transmitted to said housing and base plate assembly.

9. A disc drive actuator comprising an actuator assembly including an actuator base, a moveable carriage, means on said carriage to mount a transducer to access a memory storage disk, means attached to said base to guide said carriage in a reciprocating linear motion, and electromagnetic means to move said carriage in reciprocating linear motion and to place said assembly into read-write position with respect to a memory storage disk, wherein said electromagnetic means comprises:: a) a pair of spaced magnet assemblies, each magnet assembly including a center pole piece, an annular cylindrical magnet surrounding said center pole piece and exterior pole structure fixed to said base and substantially surrounding and spaced from the exterior surface of said magnet to form an air gap therebetween; b) a pair of cylindrical coils situate in said air gap and sized to freely move longitudinally of said magnets in reciprocating motion; c) means forming a slot in each of said exterior pole structures, said slots facing each other; and d) means extending through said slots to connect said carriage to said coils.

10. An actuator according to claim 9, in which said pair of exterior pole structures are integral with each other and include an integral front end pole piece apertured to permit movement of said carriage and attached transducer therethrough toward a disk surface.

11. An actuator according to claim 9 or claim 10, including a removal rear end pole piece affixed to the exterior pole structure and aperture to permit movement of part of said carriage away from a disc surface.

12. An actuator according to any one of claims 9 to 11, in which said exterior pole structures are C-shaped in cross-section, with the open parts of the C-shape facing each other and forming said slots.

13. A memory storage apparatus substantially as hereinbefore described with reference to the drawings.

14. A disk drive actuator substantially as hereinbefore described with reference to the drawings.