HEAD LOADING/UNLOADING APPARATUS FOR MAGNETIC DISC SYSTEMS

Abstract: Apparatus for loading and unloading a magnetic head assembly on a magnetic recording surface (10) permitting separation of function between load/retract and flying and producing a predictable pitch to the magnetic head assembly in the static condition and no pitch bias in the dynamic flying condition. The present invention improves on the IBM type 3370 by adding to the single piece spring/load beam element (19) a pair of wings (27) which extend laterally on each side thereof and pair of stationary cam members (28) positioned on opposite sides of the element. The arrangement of the torque wings (27) and cams (28) permits unrestricted retraction of the slider (16). The placement of the wings (27) results in a favorable ratio of lift point to load beam bending point and more control of load zone accuracy.

Description: He ad Lo ading/Unlo ad ing appara tus fo r Magne t i c D i s c Sys tems BACKGROUND OF THE INVENTION Field of the Invention The present invention relates to an apparatus for loading and unloading a- agnetic head assembly on a mag¬ netic recording surface and, more particularly, to a loading and retraction apparatus which permits separation of function between load/retract and flying and which produces a predictable pitch to the magnetic head assem¬ bly in the static condition and no pitch bias in the dynamic flying condition. Description of the Prior Art Magnetic disc storage systems are widely used to provide large volumes of relatively low cost computer- accessible memory or storage. A typical disc storage device has a number of discs coated with a suitable magnetic material mounted for rotation on a common spindle and a set of transducer heads carried in pairs o n elongated supports for insertion between adjacent discs, the heads of each pair facing in opposite di¬ rections to engage opposite faces of adjacent discs. The support structure is coupled to a positioner motor, the positioner motor typically including a coil mounted within a magnetic field for linear movement and oriented relative to the discs to move the heads radially over the disc surfaces to thereby enable the heads to be positioned over any annular track on the surfaces. In normal operation, the positioner motor, in response to control signals from the computer, positions the trans¬ ducer heads radially for recording data signals on or retrieving data signals from a preselected one of a set of concentric recording tracks on the discs. As the density at which digital information is recorded on a magnetic recording surface is increased, the gap between the recording head and the magnetic recording surface must be decreased. The smaller the gap and the closer the magnetic head is positioned with respect to the recording surface, the more difficult it becomes to control the mechanical tolerances of the structure mounting the recording head. To overcome these mechanical difficulties, magnetic recording heads are placed in head assemblies adapted for floating on a thin film of air created by the laminar air flow due to the rotation of the recording surface. Modern magnetic disc drives incorporate rigid substrate discs, the sur¬ faces of which are polished to a high finish so that the head can reliably fly on the air bearing. Systems are presently being designed wherein the heads fly above the disc recording surfaces at heights of less than 20 microinches. In such systems, when the recording medium ro¬ tates, the laminar air flow causes the head assembly to be forced away from the medium. Therefore, some urging means, such as a spring, must be provided to overcome this air flow and counterbalance the head assembly, keeping it as close to the recording medium as possible. Furthermore, floating magnetic recording head assemblies are often mounted in gi bal mounting devices in order to allow the angle and position of the magnetic recording head assembly to conform to the air bearing. The above is well known to those skilled in the art. One known and popular magnetic head/arm assembly is the IBM type 3370 which is disclosed' and claimed in U.S. Patent No. 4,167,765 to Robert B. Watross. Accord¬ ing to the IBM design, a magnetic head/arm assembly has a suspension for an air bearing head slider that in¬ cludes a single piece, substantially rectangular flexure with two parallel, flexible, narrow fingers, a relatively stiff cross leg, and a central finger to which the slider is attached. A combined load beam/spring element is formed from a single piece and is fastened to the flexure so as to engage a load protuberance formed with the central finger. The substantially triangular load beam/spring element has flanges formed along a portion of its length to concentrate the resilient spring action at the opposite end of the element while 'providing a stiffening action along the remaining portion of its length. The opposite end is connected to a rigid arm section. The IBM design, as shown in the Watross patent, is not loadable, i.e. it includes no means for removing the head slider from the disc. Since this is often un¬ desirable, the IBM design has been modified by adding a central protrusion which extends downwardly from the bottom thereof and which is activated by a fixed cam which spans the whole structure. This permits the mag¬ netic head assembly to be lifted off of the recording surface upon retraction of the arm assembly. While the IBM type 3370 head assembly is quite popular, several problems are associated with the loadable version thereof. The first is that retraction of the slider is limited in its motion. That is, the fixed cam extends below the load beam, in position to be contacted by the central protrusion which extends down¬ wardly from the bottom thereof. As the load beam is retracted, the central protrusion passes the cam and if the load beam were continued to be retracted, the head slider would contact the fixed cam. Even by placing the central protrusion and the fixed cam as close to the rear of the load beam as possible, retraction of the slider is still significantly limited. As a result, it often occurs that discs strike the head slider upon being inserted into a system, causing damage to the slider. This problem results from an inability to fully retract the head slider. A second problem is a poor ratio of lift point to load beam bending point, resulting in poor load zone tolerances on the disc. That is, because of the neces¬ sity of putting the central protrusion quite close to the rear end of the load beam, slight misalignments of the load beam bending ppint and the fixed cam result in significant movements of the head slider. The result is that a large load zone area on the disc is required and this is undesirable since data is typically not recorded in the loading zone. A still further problem results from the in¬ ability to acceptably control the pitch of the head assembly and to separate the functions during dynamic and static conditions. That is, the loadable version of the IBM design strictly provides for loading and un¬ loading so that the pitch of the head assembly must be controlled separately. One technique for controlling the pitch of a head assembly and separating the functions during dynamic and static conditions is disclosed in U.S. patent No. 4,376,294, entitled Head Loading and Retraction Appara¬ tus for Magnetic Disc Storage Systems, and assigned to DMA Systems Corporation, the assignee of the present in¬ vention. However, the head loading and retraction apparatus disclosed in such patent is not feasible for use with the IBM type 3370 magnetic head/arm assembly. SUMMARY OF THE INVENTION According to the present invention, there is pro¬ vided an apparatus for loading and unloading a magnetic head assembly on a magnetic recording surface which per- mits separation of function between load/retract and flying and which produces a predictable pitch to the magnetic head assembly in the static condition and no pitch bias in the dynamic flying condition. More specifically, the present invention relates to an im- prove ent to an IBM type 3370 magnetic head/arm assem¬ bly which permits the above. The present invention im¬ proves on the IBM type 3370 by adding to the single piece spring/load beam element a pair of wings which extend laterally on each side thereof and a pair of stationary cam members positioned on opposite sides of the element. Each cam member includes a cam surface positioned to be engaged by the wings when the element is retracted. The cams are positioned asymmetrically so as to provide -a static pitch by imparting torque to the element through the wings. On the other hand, the static pitch will disappear when the head is loaded and flying. The arrangement of the torque wings and cams permits unrestricted retraction of the slider. Cam asymmetry may be adjusted to compensate for normal manufacturing tolerance requirements in the head/load beam subassembly and to provide a positive load/un¬ loading pitch, without applying presets to the head flexure. The wings may be placed forward, toward the head, resulting in a more favorable ratio of lift point to the load beam bending point and more control of load zone accuracy which will make more of the disc surface available for recording. Briefly, the present apparatus for supporting a magnetic head assembly adjacent a recording surface for transcribing thereon comprises a rigid arm section, a single piece spring/load beam element joined to the DMPI arm section, the element being substantially resilient adjacent the rigid arm section and substantially rigid for its remaining length to present a loading force at its free end, a magnetic head assembly fastened to the element adjacent to the free end, a pair of wings ex¬ tending laterally on either side of the element, a pair, of stationary cam members positioned on opposite sides of the element, each including a cam surface posi¬ tioned to be engaged by the wings when the element is retracted by the rigid arm section, the cam members being arranged so that a positive attitude pitch rota¬ tion is induced in the magnetic head assembly when the element is retracted. According to the preferred em¬ bodiment of the invention, the cam surfaces are parallel and longitudinally offset whereby one of the wings con¬ tacts one of the cam surfaces before the other of the wings contacts the other of the cam surfaces to induce such positive attitude pitch rotation in the magnetic head assembly. OBJECTS, FEATURES AND ADVANTAGES It is therefore the object of the present inven¬ tion to solve the problems encountered heretofore with the IBM type 3370 magnetic head/arm assembly. It is a feature of the present invention to solve these problems by providing a loading and retraction apparatus for such an assembly which permits separation of function between load/retract and flying. An advantage to be derived is a predictable pitch to the magnetic head assembly in the static condition. A further advantage is no pitch bias in the dynamic flying condition. Still another advantage is unrestricted retraction of the slider. Another advantage is that adjustments are per¬ mitted to compensate for normal manufacturing tolerance requirements in the head/load beam subassembly. Still another advantage is a more favorable ratio of lift point to load beam bend.ing point. Still other objects, features, and attendant ad¬ vantages of the present invention will become apparent to those skilled in the art from a reading of the fol¬ lowing detailed description of the preferred embodiment constructed in accordance therewith, taken in conjunc¬ tion with the accompanying drawings wherein like num¬ erals designate like or corresponding parts in the sev- eral figures and wherein: . _ OMPI ..„ -, BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 is a perspective view of a magnetic disc storage system showing the magnetic head assembly and supporting apparatus in operative position relative to a recording media; Figure 2 is an enlarged top plan view thereof; Figure 3 is a perspective view of the magnetic head assembly and single piece spring/load beam element ? and Figures 4 and 5 are enlarged sectional views taken along the lines 4-4 and 5-5, respectively, in Figure 2. •» DESCRIPTION OF THE PREFERRED EMBODIMENT Referring now to the drawings, there is shown an improved apparatus, generally designated 10, for sup¬ porting a plurality of magnetic head assemblies 11 adja- cent.recording surfaces 12 for transcribing thereon. Recording surfaces 12 are on opposite sides of a disc 13 which typically has a magnetic material coated on both sides thereof to enable data to be magnetically recorded thereon. Disc 13 would be mounted on a spindle (not shown) which is driven by a spindle motor (not shown) which rotates disc 13 about an axis defined by the spindle. In the embodiment of the invention shown in the drawings, disc 13 has recording surfaces 12 on oppo¬ site sides therof and a pair of magnetic head assemblies 11 and associated supporting apparatus is shown. How¬ ever, since the structure on both sides of disc 13 identical, an explanation of the structure and opera¬ tion of the apparatus on one side will suffice to des¬ cribe the structure and operation of the apparatus on the other side thereof. Data is recorded on disc surfaces 12 by signals applied to transducer elements (not shown) mounted within head assemblies 11. Head assemblies 11 are mounted to the free ends of a pair of cantilevered spring/load beam elements 15. As shown in Figure 1, multiple elements/head assemblies can be mounted in facing relationship to transcribe data on the opposite surfaces 12 of discs 13, all of elements 15 being con¬ nected to a common carriage or rigid arm section 16. Rigid arm section 16 is typically physically coupled to a positioner coil (not shown) of a linear positioner motor or stepping motor (not shown) which, in response to the application of positioning signals thereto, is capable of linearly moving head assemblies 11 over sur- faces 12. This permits head assemblies 11 to be selectively positioned over any one of a plurality of annular recording tracks defined on disc recording sur¬ faces 12. In normal operation, that is, when head assem- blies 11 are writing data onto or reading data from surfaces 12 of disc 13, the heads will be loaded. When a head is loaded, it simply means that a spring force is acting upon the head to urge head assembly 11 toward surface 12 of disc 13. This force is counteracted by an air cushion caused by the rapid rotation of disc 13 so that head assemblies 11 actually fly immediately above surfaces 12. In magnetic disc drives, head assemblies 11 may fly at distances of less than 20 microinches above surfaces 12. The present invention is an improvement to the IBM type 3370 magnetic -head/arm assembly which is dis¬ closed and claimed in U.S. patent No. 4,167,765, ref¬ erence to which should be had for a more complete under¬ standing thereof. For the purposes of the present in- vention, the preferred embodiment of a magnetic head/ arm assembly includes suspension element 15 which is made of stainless steel, for example, and is attached by screws 17 to rigid arm section 16, which may be made of aluminum. Suspension element 15 provides a resilient spring section 18 and a triangularly-shaped load beam section 19. Load beam section 19 of element 15 is provided with flanges 20 as a flat load beam flexure. The apex 21 of section 19 applies the load beam force used for loading the air bearing magnetic assembly to disc 13. Magnetic head assembly 11 is fastened to element 15 at its load beam section 19, as described more fully in said U.S. patent No. 4,167,765. As described more fully in said patent, the apex 21 of element 15 contacts a load protuberance on head assembly 11 to apply a loading force to hold the trans¬ ducer in operating position close to disc 13. The load beam section 19, which is the triangular portion of element 15 with the turned upside flanges 20, trans¬ mits the load force to urge head assembly 11 towards disc 13 and also transmits this force to the center of gravity of head assembly 11. The advantages of element 15 is that a lesser number of parts are required. No separate rigid load beam is required to stiffen resilient spring section 18. The rigidness required for the load beam section 19 is included in assembly 10 by the turned-up side flanges 20 of the triangular load beam section 19. Resilient section 18 of element 15 serves as a flexible support for magnetic head assembly 11 while load beam section 19 provides a rigid section as a load beam. According to the present invention, a bent sheet metal part 25 is fastened, preferably by weld points 26, to load beam section 19 of element 15 so as to form a pair of struts or wings 27 which extend laterally on either side of element 15. As shown most clearly in Figure 2, part 25 is placed close to apex 21 of load beam section 19. A pair of stationary cam members 28 are posi¬ tioned on opposite sides of element 15, each cam member 28 including a cam surface 29 which is positioned to be engaged by one of wings 27 when element 15 is retracted by rigid arm section 16. As shown most clearly in Figures 1, 4 and 5, cam members 28 actually have opposed cam surfaces 29 which are engaged by the wings 27 con¬ nected to the upper and lower elements 15. It should be immediately apparent from an exam¬ ination of Figures 1, 2, 4 and 5, that upon retraction of elements 15 by rigid arm section 16, wings 27 will engage cam surfaces 29 to cause retraction of head assemblies 11 from surfaces 12 of disc 13. According to the preferred embodiment of the invention, cam members 28 are arranged so that a positive attitude pitch rotation is induced in magnetic head assemblies 11 when elements 15 are retracted. Also according to the preferred embodiment of the invention, this is achieved by providing identical cam members 28 which are longitudinally offset by a distance X (see Fig. 2) whereby one of wings 27 contacts one of cam surfaces 29 before the other of wings 27 contacts the other of cam surfaces 29. This achieves the desired positive attitude pitch rotation since only one side of head assembly 11 is retracted initially and retraction of this side continues for a short distance before the other side is retracted. This is clearly shown in Figure 5. A similar effect may be obtained by using cams of different thickness. Furthermore, the arrangement of cam members 28 makes it simple to adjust for cam asymmetry to compen¬ sate for normal manufacturing tolerance requirements in the head/load beam subassembly and to provide a positive load/unloading pitch without applying presets to the head flexure. it can therefore be seen that according to the present invention, there is provided an apparatus for loading and unloading a magnetic head assembly on a magnetic recording surface which permits separation of function between load/retract and flying and which pro- duces a predictable pitch to the magnetic head assembly in the static condition and no pitch bias in the dynamic flying condition. The present invention improves on the IBM type 3370 by adding to the single piece spring/load beam element a pair of wings 27 which extend laterally on each side thereof and a pair of stationary cam mem¬ bers 28 positioned on opposite sides of the element. Each cam member 28 includes a cam surface 29 positioned to be engaged by wings 27 when element 15 is retracted. Cams 28 are positioned asymmetrically so as to provide a static pitch by imparting torque to element 15 through wings 27. On the other hand, the static pitch will dis¬ appear when the head is loaded and flying. OMPI It should be particularly noted that the arrange¬ ment of torque wings 27 and cams 28 permits unrestricted retraction of the slider. This prevents damage to the head slider when discs are inserted into a system. Cam asymmetry may be adjusted to compensate for normal manu¬ facturing tolerance requirements in the head/load beam subassembly and to provide a positive load/unloading pitch, without allowing presets to the head flexure. Wings 27 may be placed forward, toward the head, result- ing in a more favorable ratio of lift point to load beam bending point and more control of load zone accuracy which will make more of the disc surface available for recording. While the invention has been described with respect to the preferred physical embodiment constructed in accordance therewith* it will be apparent to those skilled in the art that various modifications and im¬ provements may be made without departing from the scope and spirit of the invention. Accordingly, it is t ' o be understood that the invention is not to be limited by the specific illustrative embodiment, but only by the scope of the appended claims. I claim:

Claims: 1. Apparatus for supporting a magnetic head assembly adjacent a recording surface for transcribing thereon, comprising: a rigid arm section; a single piece spring/load beam element joined to said arm section, said element being substantially resilient adjacent to said rigid arm section and sub¬ stantially rigid for its remaining length to present a loading force at its free end; a magnetic head assembly fastened to said element adjacent to said free end; a pair of wings extending laterally on either side of said element; a pair of stationery cam members positioned on opposite sides of said element each including a cam sur¬ face positioned to be engaged by said wings when said element is retracted by said rigid arm section; said cam members being arranged so that a posi¬ tive attitude pitch rotation is induced in said mag- netic head assembly when said element is retracted. 2. Apparatus according to Claim 1, wherein said cam surfaces are parallel and longitudinally offset whereby one of said wings contacts one of said cam surfaces before the other of said wings contacts the other of said cam surfaces. 3. Apparatus according to Claim 1, wherein said cam surfaces are parallel and vertically offset whereby one of said wings contacts one of said cam surfaces be¬ fore the other of said wings contacts the other of said cam surfaces. ^

Inventors: MCNEIL MICHAEL, MCNEIL, MICHAEL
Applicants: DMA SYSTEMS CORP, DMA SYSTEMS CORPORATION
Application year: 1984
Main classification: G11B21
IPC codes: G11B5