WO1996007181A1

WO1996007181A1 - Arm for disc drive and method of strengthening

Info

Publication number: WO1996007181A1
Application number: PCT/GB1995/002076
Authority: WO
Inventors: Martin John Michael Murphy
Original assignee: Metal Composite Technology Plc
Priority date: 1994-09-01
Filing date: 1995-09-01
Publication date: 1996-03-07
Also published as: AU4497996A; GB9417601D0

Abstract

A movable arm (13) for carrying a data-reading and/or writing head of a disc drive is reinforced with pre-formed resin composites (1, 2) of channel-shaped cross-section which contain embedded filaments of boron and graphite and are fitted to longitudinal edge regions of the arm to increase its specific stiffness and thereby reduce resonance and reduce the access time.

Description

ARM FOR DISC DRIVE AND METHOD OF STRENGTHENING

The access time of a hard disc drive in a computer is controlled by the maximum acceleration and deceleration of the movable arm carrying the data reading and writing heads and by the damping out of transient vibrations. Assuming that the shape of the arms is optimised (and in practice commercially available arms are of similar, near optimum shape) the access time is determined by the specific stiffness (= tensile modulus/density) of the arm material.

The relevant data and cost factors for four commercially available materials are given in Table 1 belovv:-

TABLE 1

Material Tensile Density Specific Cost modulus (Gpa) (g/cm³) Stiffness Factor

(MNmkg ¹)

6061 (Aluminium) 65.0 2.65 24.5 1.0

ZE41 (Magnesium) 44.1 1.84 24.0 1.0

UL40 (Al-Li) 83.0 2.41 34.4 4.0

MMC particulate 100.0 2.90 34.5 2.0

An object of the present invention is to provide an arm for a disc drive which has a high specific stiffness in relation to its cost.

A further object of the present invention is to provide an arm for a disc drive in which arm responses are damped further. In one aspect the invention provides a movable arm for carrying a data-reading and or data-writing head of a disc drive, the arm material being characterised by added high modulus reinforcing material which increases the specific stiffness of the arm.

Such an arm may be used in a hard disc drive but is not limited to such use; it can also be used in an optical or magneto - optical disc drive for example.

In a preferred embodiment the arm of the present invention has a specific stiffness in excess of 40 (preferably in excess of 45) MNmkg^'1. It is believed that such an arm could be produced with a cost factor (c.f. Table 1) of below 2. This is a significant technical advance.

In another aspect the invention provides a method of increasing the stiffness of a movable arm for carrying a data-reading and/or data-writing head of a disc drive, comprising the step of bonding a composite comprising added high modulus reinforcing material to a surface of said arm.

A further advantage conferred by the increased specific stiffness and reduction in resonance attainable by the present invention is that the arm and its associated data reading/writing head(s) can be positioned more accurately over the desired region of the disc, enabling the data to be stored in a smaller area and thus enabling a large data capacity for a given area of disc and a faster data reading/writing rate. This latter is a particularly pressing requirement in fields such as "video on demand" for example. According to the invention in another aspect there is provided a component having low inertia and high damping, the component being formed of a composition comprising a structural material and incorporating, at least in selected regions particles of reinforcing filler, the portions being at locations such that the resonance is reduced. Preferably the particles are in fibre or filamentary form and are of high modulus material such as boron, graphite, silicon carbide or boron carbide for example.

Provided that it may be fabricated economically the arm may be made of a composition which is a metal matrix composite i.e. a continuous metal phase reinforced with a disperse phase which may or may not be metal. The matrix may be formed of a metal such as aluminium, magnesium, titanium or an alloy based on any of these; the disperse phase may be in particulate, fibre or whisker form and selected from a wide range of material such as silicon carbide, boron carbide, alumina, carbon, boron, sand and other refractory fillers; wires of steel, copper or silver; and the like. A typical metal matrix composite comprises from about 10% to 40% by volume of silicon carbide in a continuous phase or an alloy of aluminium magnesium/silicon or aluminium/copper or aluminium/lithium. Such composites can be made by a wide variety of techniques.

Preferred features are defined in the dependent claims.

A preferred embodiment of the invention is described below by way of example only with reference to the accompanying drawings, wherein:-

Figure 1 is an isometric view of a reinforced arm in accordance with the invention; Figure 2 is a sectional elevation of a clamping assembly used to form the composites 1 and 2 of Figure 1 , and

Figure 3 is a schematic plan view of a hard disc arrangement utilising the arm of Figure 1.

Referring to Figure 1 , the arm 13 has an upright bore 4 defining an axis A about which it swings in use, the bore being sized to receive a standard supporting axle. The arm comprises several forwardly extending fingers F which have generally triangular cut-outs in order to reduce the inertia of the arm, and terminate in cut-outs 3 which are arranged to carry standard magnetic data reading and writing heads (not shown), for a hard disc. The arm is driven by an actuator (not shown) which is coupled to rearwardly extending fingers 5 and 6. The arm is machined from aluminium.

The outer longitudinal edges of the uppermost finger F are shown fitted within respective channel-shaped resin-boron fibre-graphite fibre composites 1 and 2. HY-BOR™ boron/graphite pre-preg, obtainable from Textron Inc. is a suitable material for these composites and typically comprises 0.8 volume fraction of a mixture of boron fibres of 0.102mm (4.0mil) diameter and graphite fibres of 0.003/0.010 mm diameter in an epoxy resin matrix forming the remaining 0.2 volume fraction. When cured, this material has a tensile modulus of 6.02 x 10⁵ MPa (39 msi) and accordingly the composites 1 and 2 greatly stiffen the arm. They are bonded to the finger F by a two-part epoxy adhesive (3M-93230) after preparing the surface of the finger by de-greasing and treatment with an acid etch mix

(Pasagel™, obtainable from Courtaulds).

Although only one finger F is shown fitted with the resin - boron/graphite fibre composites, any or all of the fingers may be stiffened by such composites, which could be fitted to an inner longitudinal edge defined by triangular cut-out in an alternative embodiment.

Although a mixture of boron and graphite fibres is preferred in order to maximise the tensile strength of the composite, other reinforcing fibres can be used, e.g. silicon or silicon carbide fibres. Furthermore, although it is preferred to form a cured preform and bond this to the arm, it is also within the scope of the invention to apply the uncured resin, containing the reinforcing fibres (longitudinally aligned) directly to the arm fingers and to cure the material in situ.

Furthermore, it is within the scope of the invention to cut the fingers F from a laminate of metal (e.g. aluminium) and cured high modulus fibre-reinforced resin (preferably a laminate with the aluminium layer sandwiched between reinforced resin layers to minimise bending due to differential expansion and contraction).

The preferred method of forming the resin-boron/graphite composites 1 and 2 will now be described with reference to Figure 2.

These are prepared using an aluminium former 7 of the same thickness as the finished actuator arm covered with a release ply (not shown) on to the edges of which fibre is laid up in the usual manner. This is then clamped into metal tooling. The tooling consists of two metal face plates 11 which are clamped into position over the flat surface of the lay-up and two end plates 10 inserted into the edges of the assembly. Pressure is applied to all areas of the lay-up. Using shrink tape 9 which on heating to the curing temperature of the resin 150° C applies a hoop stress of the order of 175 kg/cm². After curing, the tooling is removed to reveal a

U-shaped preform of fibre formed along each edge of the former. These are applied to the arm 13 using a post-cure 2 part epoxy adhesive (3M-9323). A room temperature curing adhesive is selected to avoid the problems of distortion.

Several fingers were made using both the preform method as described above and a non-preform method and were tested for integrity and stiffness by applying a force at 90 degrees to the plane of the finger and measuring the deflection produced. In the "non-preform" method the uncured Hybor™ material was applied directly to the dummy finger and cured in situ. A further variant, namely vacuum bagging, was also used as an alternative to the shrink tape and tooling described above in order to apply atmospheric pressure to the assembly. The results are shown in Table 2 below. As can be seen from the results the addition of 1 layer of Hybor™ greatly affects the deflection of the finger. For 0.9mm thick aluminium the control specimen (f) failed whereas a single layer of fibre (A & B) sustained a deflection of 1.65mm (0.065") without breaking. Thicker specimens (1.6mm -C.D&E) reduced the deflection from 1.27mm to 0.76mm (0.050" to 0.030") for 1 layer and 0.51mm (0.020") for 2 layers. It is noticeable that the preform route (specimens G and I) gives improved deflections over the direct lay-ups. This probably is because of the ease of assembling a preform compared with direct lay-ups of fibre onto the finger. TABLE 2

Sample Force Deflection Thickness No. Layers ID

A 22.2N(5lb) 1.65mm (0.065") 0.9mm 1 (Metal tool)

B 1.65mm (0.065") 0.9mm 1 (Metal tool)

C 0.76mm (0.030") 1.6mm 1 (vac bagging)

D 0.51mm (0.020") 1.6mm 2 (vac bagging)

E 1.27mm (0.050") 1.6mm 0

F " Failed below max 0.9mm 0

G 0.64mm (0.025") 1.6mm 1 (Preform)

H 1.52mm (0.060") 0.9mm 1 (vac bagging)

1 0.43mm (0.017") 1.6mm 2 Preform |

Surprisingly, the samples produced by the vacuum bagging method (in which the assembly is placed in a flexible bag which is then evacuated) produced comparable if not slightly better deflections than the metal tool manufactured samples (compare H and A B).

Figure 3 stlows a hard disc drive in accordance with the invention, comprising an arm 13 reinforced with channel - shaped boron/graphite- loaded preformed resin composites 1 and 2 and carrying a read writing head 15. The arm is moved to position the head over a rotating hard disc 12 by an actuator 14.

Claims

1. A movable arm for carrying a data-reading and or data-writing head of a disc drive, the arm material being characterised by added high modulus reinforcing material which increases the specific stiffness of the arm.

2. A movable arm as claimed in Claim 1 , wherein said reinforcing material is graphite and/or boron.

3. A movable arm as claimed in Claim 1 or Claim 2, wherein said reinforcing material is embedded in resin material to form a composite and the composite is bonded to a longitudinal edge region of the arm.

4. A movable arm as claimed in Claim 3, wherein said composite is a preform which is bonded to said longitudinal edge region by an adhesive which is distinct from said resin.

5. A movable arm as claimed in Claim 3 or Claim 4, wherein said composite fits around, and is bonded to, upper and lower surfaces of said longitudinal edge region.

6. A movable arm as claimed in any preceding Claim, wherein said reinforcing material is in filamentary form and is aligned in the longitudinal direction of the arm.

7. A movable arm as claimed in Claim 1 or Claim 2, wherein said reinforcing material is embedded in a layer of resin material and said layer is laminated to a major portion of the surface of the arm.

8. A movable arm as claimed in Claim 7, wherein said arm comprises a laminate of at least three layers including at least one layer of said resin material having embedded reinforcing material and at least one metal layer, said layers being symmetrically disposed so as to balance thermally-induced stresses.

9. A movable arm as claimed in Claim 1 or Claim 2, wherein said arm is tubular and a tubular layer of resin material having embedded reinforcing material is laminated to at least a portion of a tubular surface of the arm.

10. A movable arm as claimed in any preceding Claim having a specific stiffness in excess of 40MNnkg^"1.

11. A disc drive for a magnetic, optical or magneto-optical disc which comprises a movable arm as claimed in any preceding Claim.

12. A method of increasing the stiffness of a movable arm for carrying a data- reading and/data-writing head of a disc drive, comprising the step of bonding a composite comprising embedded high modulus reinforcing material to a surface of said arm.

13. A method as claimed in Claim 12, wherein said composite is a resin composite which is pre-formed into a shape which is complementary to said surface, cured and subsequently bonded to said surface at temperature below the curing temperature of the resin.

14. A method as claimed in Claim 13, wherein said resin composite is pre¬ formed into a channel cross-section around a former and is bonded to a longitudinal edge region of said arm.

15. A method as claimed in any of Claims 12 to 14, wherein said composite is bonded to said surface using an epoxy adhesive.

16. A method as claimed in any of Claims 12 to 15, wherein said reinforcing material is as defined in Claim 2 or Claim 6.