Rigid disk drive with secured shaft

Abstract: A disk drive includes a fastening structure to secure a shaft between parallel walls which will secure and locate the shaft without inducing a distortion of the walls. One end of the shaft is secured to the adjacent wall and the other end of the shaft is secured through a wall opening using an annular slug 43 and a deformable washer 45 which is compressed by a bolt 41 attached axially to the shaft end to cause the deformed washer to engage the surfaces defining the wall opening 32. The uniform axisymmetric expansion of the washer does not affect the position of the shaft and the radial force secures the shaft end without influencing the structure of the casting.

Description: Field of the Invention The invention relates to rigid disk drives for data storage and particularly to the securing of non-rotatable shafts between opposed walls thereof. Background In the design of rigid disk drives, a common problem occurs when the axis of rotation of the disk stack and the pivot axis of the head carrier (the rotary actuator) shift relative to one another causing track misregistration (TMR). TMR may be a result of vibrations or thermally induced movements of the components. These characteristics are inherent in disk drives that use a plate type base casting design. The base casting bends during operation of the disk drive causing relative movement between the respective axes of rotation, or centrelines, of the disk stack and actuator. This can be particularly problematic for disk drives in which the positions of the data transducer heads that transfer data to and from the disk surfaces are governed by the position of a servo head that reads position information signals from a dedicated servo surface (often on the uppermost disk surface). When TMR is excessive, the data head on the disk most remote from the servo disk may not be properly aligned to the same track as the servo head, resulting in "write fault errors". Other disk file designs are known in which TMR problems are reduced by rigidly attaching the top and bottom of the spindle shaft and the actuator to parallel opposed wall portions of a clamshell-like two part housing. It is also known to rigidly attach spindle shaft ends to opposite walls of a single piece box casting. Disclosure of the Invention When the disk file base casting is designed as either a clamshell or a box casting, the relative movement between the two shafts is minimized due to the stiffness of the structure. However, the rigid attachment of both shaft ends to the box-type base casting structure can cause physical distortion of the casting structure. Furthermore, the box casting design also creates a problem because the inside of the box cannot be easily machined to allow close tolerance mounting of the major components. Accordingly, the invention provides a rigid disk drive including: two substantially parallel opposed wall portions between which a disk spindle assembly and a rotary actuator are mounted; a non-rotatable shaft for rotatably supporting at least one of said disk spindle assembly and said rotary actuator, said shaft extending perpendicularly in an axial direction from one of said opposed wall portions to the other; a first securing means for securing one end of said shaft to one of said opposed wall portions; an opening in the other of said opposed wall portions which is substantially aligned with said shaft and said first securing means; and a second securing means for securing the other end of said shaft to said other opposed wall portion via said opening, said second securing means including a deformable washer disposed in said wall opening, and compressive retaining means connected to said shaft for compressing and deforming said deformable washer into contact with the wall surface surrounding said opening whereby said shaft is retained in said other wall portion. Since this is achieved without applying a force that urges said substantially parallel opposed wall portions towards or away from one another, deformation of the wall portions due to the attachment of the shaft is avoided. In a preferred embodiment, said second securing means further includes an annular slug member located at said other shaft end with a frusto conical peripheral surface facing away from said other shaft end, and said deformable washer has a mating frusto conical inner surface that engages said slug frusto conical surface. Said compressive retaining means comprises a bolt which passes through said annular slug and said washer, and is received in a threaded axial opening said other shaft end. Said deformable washer is formed of a low yielding metal or an elastomer. In a further preferred embodiment, both of said opposed wall portions are part of a single piece box-frame. However, it will be noted that the invention is also applicable to disk drives having two piece clamshell housings. Although as described below, the invention is applied to a shaft supporting a rotary actuator, a similarly attached shaft might also be used to support the disk stack assembly. In either case, the method of attachment of the components within a box-type frame does not require such close tolerancing as the prior art, whilst at the same time avoiding physical distortion of the frame structure. Brief Description of the Drawings Fig. 1 is a schematic side section of a prior art disk drive wherein the disk stack and actuator are mounted on a base plate; Fig. 2 is a schematic side section of a disk drive according to the present invention; Fig. 3 shows further detail of the upper end of the actuator shaft in the disk drive of Fig. 2. Detailed Description Fig. 1 illustrates a prior art disk drive assembly wherein a disk drive assembly 10 and rotary actuator 11 are supported on a base casting 12. The disk assembly 10 rotates about a centreline or axis 13 and the rotary actuator pivots about the centreline or axis 14. The proper operation of the disk drive is dependent upon the distance between and the parallelism of the centrelines 13 and 14. These can be varied by forces applied to the base or by thermal changes that induce bending of the base or non-uniform expansion. With high density storage designs, wherein track densities have been increasing from 500 tracks per inch to more than 2000 tracks per inch (along with corresponding increases in the linear bit densities), the magnitude of deformation that induces errors in the reading or writing of data becomes progressively less. This is particularly true for systems with a dedicated servo disk surface in which the positioning of a servo head on the dedicated servo surface must ensure that all of the data heads on the corresponding data disk surfaces are correctly aligned with the appropriate track centreline (or cylinder). One method of reducing alignment problems between the centrelines of the disk stack and actuator in a disk drive is to use a design in which there are plate members to support each end of the disk assembly shaft and the actuator shaft. The centreline distance and parallelism can be more accurately maintained when both ends of the pair of shafts are supported and constrained. This is most effectively accomplished using a box-frame construction, as shown in Fig. 2, wherein both of the substantially parallel, shaft-supporting walls 21 and 22 are formed from a single piece box-type frame casting 20. A shaft 26 is captured at opposite ends by opposed casting walls 21 and 22 respectively and supports the spindle assembly 35 that carries and rotates the data storage disks 36. The rotary actuator 37 pivots about shaft 24 and supports head suspension assemblies 38 (two of which are shown) for movement from one concentric track to another concentric track on disks 36 when driven by a voice coil motor 39. In a design where the shafts 24 and 26 are supported at both ends, it is important to ensure that positive attachment of the shafts 24, 26 at both ends does not induce distortion forces that are similar to the distortions that the design has sought to overcome, such as the clamping of a cover or rigid attachment of subassemblies. It is required that the shafts be confined at each end, but not influence or otherwise distort the supporting wall members 21, 22 or base structure so as to cause deformation. The box-frame design creates a further problem because the inside surfaces of the box cannot be easily machined to allow close tolerance mounting of the major components. The most accurate way to machine surfaces inside the box to mount the components is to bore a large clearance hole 32 (see Fig 2) with bore diameter B through one base casting supporting wall 21, and then make a spot faced surface 33 of the same or smaller diameter on the opposite wall 22. Wall 22 has an increased thickness boss 27 through which an opening 28 is made to receive screw 30 and an enlarged counterbore C is formed to receive the head diameter D of screw 30. The spot faced surface 33 is at the inner surface of boss 27 and aligned with the opening 32 in supporting wall 21. The top of the actuator shaft 24 must have enough clearance E designed into it to allow assembly of the components. This clearance creates a problem since there is not only a large bored hole 32 in the top of the casting which makes mounting more difficult, but there is also a significant amount of clearance E between the top of the actuator shaft and the inside surface of the casting wall. The attachment structure and method of the present invention is designed to securely fasten the top of the actuator shaft 24 without influencing (distorting) wall 21 or the structure of cast base 20. Once the shaft 24 is attached to the bottom wall 22 of base casting 20 using the screw 30 through the counterbored clearance hole, a slug 43 with a tapered upper peripheral surface 44 is placed on top of shaft 24. Next a washer 45, made of a low yield strength metal or an elastomer, with a mating tapered surface 46 is placed over the top of slug 43. Finally, screw 41 is threaded into the top of the shaft 24 to compress the washer 45 over the tapered surface 44 of slug 43, causing the washer to expand against the surface defining the base casting wall opening 32. This secures the top of the shaft 24 without adversely influencing the structure of the box-type base casting 20, and effectively seals the opening through which the fastener was installed.

Claims: A rigid disk drive including: two substantially parallel opposed wall portions (21, 22) between which a disk spindle assembly (10) and a rotary actuator (11) are mounted; a non-rotatable shaft (24) for rotatably supporting at least one of said disk spindle assembly and said rotary actuator, said shaft extending perpendicularly in an axial direction from one of said opposed wall portions to the other; a first securing means for securing one end of said shaft to one of said opposed wall portions (22); an opening (32) in the other of said opposed wall portions (21) which is substantially aligned with said shaft and said first securing means; and a second securing means for securing the other end of said shaft to the said other opposed wall portion (21) via said opening; the disk drive being characterised in that: said second securing means includes a deformable washer (45) disposed in said wall opening and compressive retaining means connected to said shaft for compressing and deforming said deformable washer into contact with the wall surface surrounding said opening whereby said shaft is retained in said other wall portion. A rigid disk drive as claimed in claim 1, wherein said second securing means further includes an annular slug member (43) located at said other shaft end with a frusto conical peripheral surface (44) facing away from said other shaft end, and said deformable washer (45) has a mating frusto conical inner surface (46) that engages said slug frusto conical surface. A rigid disk drive as claimed in claim 2, wherein said compressive retaining means comprises a bolt (41) which passes through said annular slug and said washer, and is received in a threaded axial opening in said other shaft. A rigid disk drive as claimed in any preceding claim, wherein said deformable washer is formed of a low yielding metal or an elastomer. A rigid disk drive as claimed in any preceding claim, wherein said first securing means comprises a hole through said one opposed wall portion (22), a faced surface (33) on said one opposed wall portion surrounding said hole, and a bolt (30) axially aligned with said one shaft end and received in a threaded axial opening in said one shaft end to fixedly retain said shaft against said faced surface on said one opposed wall portion. A rigid disk drive as claimed in any preceding claim, wherein both of said opposed wall portions are part of a single piece box-frame. A rigid disk drive as claimed in any preceding claim in which said shaft supports said rotary actuator.

Inventors: BOIGENZAHN JEFFREY FRED, BRATVOLD DARRELL EUGENE, RIGOTTI JAMES MICHAEL, TUFTY LYLE RICK, BOIGENZAHN, JEFFREY FRED, BRATVOLD, DARRELL EUGENE, RIGOTTI, JAMES MICHAEL, TUFTY, LYLE RICK
Applicants: IBM, INTERNATIONAL BUSINESS MACHINES CORPORATION
Application year: 1990
Main classification: G11B19
IPC codes: G11B21, G11B19, G11B25