HIGH SPEED MAGNETISABLE DISK CONTACT RECORDING AND READING SYSTEM

Abstract: A high speed magnetisable disk contact recording and reading system comprising a recording disk (10) including a substrate with a coating (15) thereon of a magnetisable material having a relatively low thermal conductivity, a magnetic recording and reading transducer (17) in physical contact with the recording disk (10), and means (21) to produce relative motion between the magnetisable recording disk and said transducer. According the invention the system is characterised in that the transducer comprises a substrate of a single crystal material having a relatively high thermal conductivity, a relatively low friction coefficient and a high surface energy, whereby an attractive force is exerted between the recording medium said transducer so that the transducer is maintained in contact with the recording medium during said relative motion and high density recorded data can be reliably written on and sensed from the recording medium.

Description: This invention relates in general to magnetic recording and reading systems and, in particular, to a magnetisable disk recording and reading system in which the magnetic transducer is in contact with the recording medium at operating speed. It has been recognised since the early days of moving magnetic storage systems that contact recording and reading is desirable. R. L. Wallace, Jr. established the space loss relationship in his paper "The Reproduction of Magnetically Recorded Signals", Bell System Technical Journal, October, 1951, pp 1145-1173. This paper defines the spacing loss (i.e. loss of read signal amplitude) in terms of the distance d between the magnetic read head and the surface of the recording medium and the wavelength of the recorded signal. Although contact is known to be a key factor in audio and video tape recording systems as well as system using floppy disks, in contrast, contact recording systems for high performance moving magnetic storage systems using a rigid recording medium such as a disk have not been widely used. The reason for this is that, in a moving magnetic recording system using a recording disk, the transducer must be capable of running on the same track on the disk for extended periods of time without damage to the recording medium. The contact recording systems for high speed moving magnetic recording that have been built have had the problem of excessive wear of both the magnetic transducer and the magnetisable recording medium. US-A-4,225,892 discloses a magnetoresistive read head which is deposited onto a single crystal sapphire substrate which has a particular crystallographic orientation as the wear surface. IBM Technical Disclosure Bulletin, Vol. 27, No. 1B, June 1984 at page 496, discloses a ferrite magnetic read/write head having at least one surface to form a smooth pore-free surface. The unexamined published Japanese patent application 57-207408 discloses the use of a single crystal corundum as a substrate for a magnetic read/write head. US -A- 3,919,717 shows a wear resistant surface for magnetic read/write heads comprising diamond particles in a matrix of a softer material such as rhodium, for example. None of the above documents discloses a contact recording system having the physical characteristics required to hold the read/write transducer in contact with the recording medium without external force during high speed recording and sensing operations. The object of this invention is to provide an improved contact recording system for a high speed moving magnetic storage and reading system in which high density data can be reliably recorded and read without excessive wear to either the magnetic transducer or the recording medium. The present invention relates to a high speed magnetisable disk contact recording and reading system comprising a recording disk including a substrate with a coating thereon of a magnetisable material, a magnetic recording and reading transducer in physical contact with the recording disk, and means to produce relative motion between the magnetisable recording disk and the transducer. According to the invention the system is characterised in that the recording disk has a relatively low thermal conductivity, a relatively low surface energy and a relatively high temperature as compared with the thermal conductivity, the surface energy and the temperature of the transducer, the transducer comprises a substrate of a single crystal material, and the coefficient of friction as between the recording disk and the transducer is relatively low, whereby when the recording disk is moving relative to the transducer an attractive force is exerted between the recording disk and the transducer so that the transducer is maintained in contact with the recording disk during the relative motion and high density data can be reliably recorded on and read from the recording disk. In order that the invention may be more readily understood, an embodiment will now be described with reference to the accompanying drawings, in which Fig. 1 is a simplified block diagram of a magnetic recording and reading disk file embodying the present invention, Fig. 2 is an enlarged top view showing the slider in Fig. 1 in greater detail, Fig. 3 is a side view of the slider illustrated in Fig. 2 in contact with the recording disk illustrated in Fig. 1, with the disk shown in section, Fig. 4 is a side view of the slider with an alternative embodiment of the recording medium shown in section, Fig. 5 is a three dimensional view of an alternative embodiment of the slider, Fig. 6 is a bottom view of a further embodiment of the slider, Fig. 7 is a side view of the slider illustrated in Fig. 6 sectioned along lines 7-7 of Fig. 6, and Fig. 8 is a diagrammatic side view of another embodiment of the slider, in contact with the recording medium. The present invention is described in a magnetic recording disk storage file as shown diagrammatically in Fig. 1. At least one rigid rotatable disk, such as disk 10, is supported on a spindle 11 and rotated by a disk drive motor 12. A magnetisable recording medium 15 on each disk is in the form of an annular pattern of concentric data tracks having an inside diameter 13 and an outside diameter 14, as shown on disk 10. At least one slider 16 is positioned in contact with the magnetisable recording medium 15, and each slider 16 supports one or more read/write heads 17. The slider 16 is attached to an actuator arm 18 by means of a suspension unit 19. The suspension unit 19 provides a slight spring force which biases the slider 16 against the disk surface 20. The actuator arm 18 is attached to an accessing mechanism such as a voice coil motor (VCM) 21, for example. The VCM is a coil movable within a fixed magnetic field, and the direction and velocity of the coil movement is controlled by the current supplied thereto. As the disk 10 rotates, the slider 16 is moved radially in and out so that the head 17 may access different portions of the disk surface 20 for recording data therein or for reading data previously recorded therein. The above description of a magnetic recording disk storage file, and the accompanying illustration of it in Fig. 1 are for representative purposes only. It should be apparent that disk files may contain a large number of disks and VCMs and that each actuator arm may support a number of sliders. The arrangement being described of a contact recording magnetic recording disk storage file is fully applicable to any such movable storage apparatus, provided it is of the type in which the sliders are in contact with the storage medium when at operating speed. The various components of the disk storage file are controlled in operation by signals generated by a control unit 22 which includes internal clock signals, logic control circuits, storage and a microprocessor. The control unit 22 generates control signals to control various disk storage file operations, such as motor control signals on line 23 and position control signals on line 24. The control signals on line 24 provide the desired current profile to move the selected slider 16 optimally to the desired track on the associated disk 10. The READ and WRITE signals are communicated to and from read/write head 17 by means of a recording channel 25. In the arrangement being described, as shown in Fig. 2, the slider 16 is positioned so that it is in contact with the recording medium at normal operating speed produced by relative motion, at a predetermined rate, between slider 16 and the surface 20 of the magnetic recording medium 15 in the direction indicated by arrow 26. The magnetic read/write head 17 preferably comprises a magnetic head formed by thin film deposition techniques such as the thin film transducer described in US-A-4,190,872, for example. The magnetic read/write head 17 is deposited on a surface 28 of the slider 16 which is substantially normal to the surface of the slider which is in contact with the recording medium. It is a feature of the arrangement being described that the slider remains in direct contact with the disk surface even when the relative motion between the slider and the disk surface reaches speeds of 20 metres per second or greater. This is accomplished by an attractive force that is strong enough to overcome the force of the film of air which is moving with the disk surface which tends to force the slider away from the disk surface. The attractive force is believed to be produced by a phenomenon known as contact electrification, although others have attempted to explain the operation based on Van der Waal's force. These phenomena have been known for years although they are not well understood in their detailed workings. However, by the use of specific material characteristics for the slider and disk, it has been shown that direct and continuous contact between slider and disk surface can be ensured without causing excessive wear to either the magnetic transducer slider or the recording medium. Contact electrification works on the principle that, when two materials are rubbed together, electrical charge is usually transferred from one material to the other. When two insulators are involved, as in the present case, the electrical charge transfer is by way of an ion transfer from one insulator to the other. It is also believed that a temperature difference can result in charge transfer. If the temperatures of the two insulators differ, the two currents resulting from the ionic transfer will not balance unless the two thermionic currents alter. This results in the following relationship: where Δ T = T₂ - T₁ Δ U = U₂ - U₁ and T₁, T₂ are the temperatures of the two insulators and U₁, U₂ are the surface energies of the two insulators. Δ U is the energy difference and this factor is proportional to the attractive force generated between the two insulators. In the present case, the materials characteristics are chosen so that the temperature of the surface of the slider which is in contact with the recording medium is lower than that of the recording medium. Should the materials characteristics be chosen so that the temperature of the surface of the slider is the greater, then greater wear and possibly destructive wear of the slider would occur. According to the arrangement being described, as shown in Figs. 2-4, the slider 16 is made from a single crystal material having a high thermal conductivity, a low friction coefficient with the material of the disk surface, high surface energy and a material that is electrically non-conductive. The slider material will be maintained in direct contact with the disk surface during normal operation of the disk storage file due to the attractive force between the slider 16 and the disk surface 20. In a specific embodiment, slider 16 is made from a single crystal diamond cut so that its crystalline orientation is <110> for the surface 27 which is in contact with the disk surface 20. Another suitable material is a single crystal cubic boron nitride. These materials have properties, when operated in contact with a magnetisable disk of the type described in greater detail below, which result in contact being maintained between slider and disk surface without causing excessive wear of either slider or disk surface. The properties for the single crystal material include high thermal conductivity, a low friction coefficient, a high surface energy, and a high hardness. The thermal conductivity enables the slider material to maintain a lower temperature than the surface of the magnetisable medium. The low friction coefficient prevents wear of the surface of the magnetisable medium which is in contact with the slider. The high surface energy prevents the slider surface from picking up contamination which may be present in the system and the hardness prevents plastic deformation and wear of the slider. The single crystal diamond material was chosen since its thermal conductivity is high (ten times higher than single crystal sapphire) at room temperature, its friction coefficient is low (four times lower than single crystal sapphire), its surface energy is high (six times higher than single crystal sapphire), and its hardness is high (four and one-half times harder than single crystal sapphire). The comparisons are given to single crystal sapphire since this material is the most attractive, by its characteristics, of any of the materials disclosed in the prior art references discussed at the beginning of this description. The other materials discussed there would therefore be even less suitable for the arrangement being described than the single crystal sapphire material. The single crystal material chosen should have a surface energy above 5000 ergs/cm2, a high thermal conductivity, a friction coefficient lower than .1, and a hardness above 3500 kg/mm². Single crystal diamond and single crystal cubic boron nitride are two materials which have the desired characteristics. As illustrated in Figure. 2, slider 16 is formed in the shape of an isosceles triangle with the apex of the triangle along the line of relative motion, which may be 3600 RPM, or greater, between the slider and the surface of the recording medium. The magnetic read/write head is formed on the trailing end of slider 16 with respect to the direction of relative motion. The triangular shape of the slider and the position of the slider counteract any tendency for the slider to be moved off-track by the film of air which is moving with the disk surface. The recording medium comprises a substrate having a magnetisable coating thereon. In the specific embodiment shown in Fig. 3, the recording medium 30 is a particulate magnetisable material. The recording medium 30 comprises a substrate 32 made of an aluminium alloy, for example, having a particulate magnetisable coating 34 thereon. The magnetisable coating 34 comprises magnetisable particles in an epoxy-resin binder, and the coating may also have alumina particles, if desired. The material of the magnetisable coating 34 is cured and buffed to a chosen surface finish and a small quantity of a liquid lubricant is deposited on the surface 36 of the recording medium. It was unexpected that a non-overcoated particulate coating 34 could be used in a contact recording system with the slider 16 in contact with surface 36 without exhibiting excessive wear. It is apparent that an overcoated particulate magnetisable coating may alternatively be used, if desired. In the embodiment shown in Fig. 4, the recording medium 40 is a thin film magnetisable disk. The recording medium 40 comprises a substrate 42 made of an Al-Mg alloy, for example, an undercoat 44 of a material such as chromium, for example, a magnetisable coating 46 of a cobalt based alloy, for example, and a protective overcoat 48 of a material such as carbon. The slider 16 is positioned in contact with the surface 49 of the recording medium 40 under normal operating conditions of the disk storage file without producing excessive wear. In a specific embodiment a triangular shaped slider comprising a single crystal diamond 3 mm on a side and 1 mm thick was operated in contact with a carbon overcoated recording medium, and an attractive force of 18 grams was generated. It is not necessary to have a slider which is made of a single material in all cases provided that the material which contacts the surface of the recording medium has sufficient thickness to provide the required wear and thermal characteristics. One embodiment of a composite slider is shown in Fig. 5. In this embodiment the slider 50 comprises a thin sheet 52 of a single crystal material which forms the surface 54 which is in contact with the recording medium. The thin sheet 52 of single crystal material is bonded to a slider body 56 which is made of a suitable material such as a ceramic comprising a mixture of Al₂O₃ and TiC. The suspension unit 19 is attached to the slider body 56, and the magnetic read/write head 17 is formed on surface 58 of the slider 50. If desired, a non-conductive coating 59 such as alumina, for example, may be deposited on surface 58 prior to deposition of the magnetic transducer 17. In a further embodiment of the slider shown in Figs. 6 and 7, the slider 60 comprises a triangular shaped slider body 62 of a suitable material such as stainless steel, having a plurality of contacting members 64 which contact the recording medium and a magnetic read/write transducer 68. Contacting members 64 are bonded to the slider body 62 and each member 64 is made from a single crystal material having characteristics as stated above. The total area of the contacting members 64 is chosen compared to the area of pole tip area 67 of the transducer 68 so that sufficient attractive force can be generated to maintain slider 60 in contact with the recording medium during normal operation of the disk file. The magnetic read/write transducer 68 is centrally located relative to the contacting members 64. In this case the transducer is formed of a suitable magnetic material such as a ferrite material and the transducer 68 is bonded in position in central opening 69 in slider body 62. A further embodiment of a slider 70 is shown in Fig. 8 along with a magnetic read/write transducer 71 in which the slider body 72 comprises a first single crystal material such as sapphire, for example, upon which is deposited an epitaxially grown layer 74 of single crystal material. It has been found that a layer having a thickness of about 250 Angstroms units (250 x 10⁻¹⁰m) can provide the characteristics required to ensure contact between the surface 76 of slider 70 and the recording medium 78.

Claims: A high speed magnetisable disk contact recording and reading system comprising a recording disk (10) including a substrate with a coating (15) thereon of a magnetisable material, a magnetic recording and reading transducer (17) in physical contact with said recording disk (10), and means (12, 21) to produce relative motion between said magnetisable recording disk and said transducer (17), characterised in that said recording disk (10) has a relatively low thermal conductivity, a relatively low surface energy and a relatively high temperature as compared with the thermal conductivity, the surface energy and the temperature of said transducer (17), said transducer (17) comprises a substrate of a single crystal material, and the coefficient of friction as between said recording disk (10) and said transducer (17) is relatively low, whereby when said recording disk (10) is moving relative to said transducer (17) an attractive force is exerted between said recording disk and said transducer so that said transducer is maintained in contact with said recording disk during the relative motion and high density data can be recorded on and read from said recording disk. A recording and reading system as claimed in claim 1 characterised in that said single crystal material comprises a single crystal diamond. A recording and reading system as claimed in claim 2 characterised in that said single crystal diamond is cut so that its crystalline orientation is <110>. A recording and reading system as claimed in claim 1 characterised in that said single crystal material comprises a single crystal of cubic boron nitride. A recording and reading system as claimed in claim 1 characterised in that said single crystal material has a friction coefficient with said recording disk (10) lower than .1 and a surface energy above 5000 ergs/cm2. A recording and reading system as claimed in any one of the preceding claims characterised in that said recording disk (10) comprises a particulate magnetisable disk. The recording and reading system as claimed in any one of claims 1 to 5 characterised in that said recording disk (10) comprises a thin film magnetisable disk.

Inventors: BREZOCZKY, BLASIUS, HOPNER, EMIL
Applicants: INTERNATIONAL BUSINESS MACHINES CORPORATION
Application year: 1988
Main classification: G11B5
IPC codes: G11B5