Magnetic head assembly for a flexible magnetic disk drive unit

Abstract: A magnetic head assembly for a flexible magnetic disk drive unit has a magnetic recording and retrieving head (22) for carrying out magnetic recording onto and retrieving from a metallic thin-film type flexible magnetic medium (l0) rotating about a center of the medium by coming into contact with the medium at a contact posi­ tion, a first group of non-magnetic supporting pads (3lA, 3lB, 3lC, 3lD) arranged to support a plurality of positions of the flexible magnetic medium (l0) and disposed so as to surround the contact position, and a second group of non-magnetic suppressing pads (47, 48) in contact with a different plurality of positions of the flexible magnetic medium outward of the plurality of supporting positions so that the suppressing pads (47, 48) suppress any undulation of the flexible magnetic medium during rotation of the medium. The support pads and the magnetic recording and retrieving head may be formed with a recess, respectively, for trapping dust and other foreign materials, thereby preventing an accumulation of dust and other foreign materials between the head and the medium.

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a magnetic head assembly for a flexible magnetic disk drive unit. More particularly, it relates to a magnetic head assembly having a magnetic recording and retrieving head or heads brought into contact with a flexible magnetic recording disk consisting of a metallic thin-film type magnetic recording medium for carrying out magnetic recording on and retrieving information from the flexible magnetic disk. 2. Description of the Related Art A flexible magnetic disk drive unit employing a flexible magnetic recording medium, such as a floppy disk unit or a micro-disk unit used as a secondary information storage unit for an electronic computer, is well known. Recently, the demand for high density recording on the flexible magnetic recording medium has increased. To meet this demand, instead of the conventional flexible magnetic medium having a magnetic recording layer coated on the surface of a flexible nonmagnetic base by the use of a conventional binder, there has been proposed a metallic thin-film type flexible magnetic recording medium using, as a magnetic recording layer, a strongly magnetic metallic thin-film or a metallic thin-film formed by a sputtering method, such as a cobalt system alloy film having a perpendicular magnetic anisotropy as disclosed in Japanese Examined Patent Publication No. 58-91 (corresponding to U.S. Patent No. 4,210,946), or Japanese Unexamined Patent Publication No. 61-5404. However, when employing the metallic thin-film as a magnetic recording layer of the flexible magnetic recording medium, a problem arises in that, since a conventional magnetic head assembly having a magnetic read/write head, a magnetic erase head and pressure pads must be subjected to a large frictional resistance when in contact with the metallic thin-film, the magnetic heads as well as the matnetic recording medium are worn and damaged by this friction. As a result, both the magnetic heads and the medium are not sufficiently durable and do not have a long operational life. Particularly, when the conventional flexible magnetic disk drive unit is employed for a magnetic recording on both sides of the flexible magnetic recording medium having the above-mentioned metallic thin-film recording layers on both surfaces thereof, the problem of a sufficient durability, and an additional problem of stability in contact between the magnetic head assembly and both sides of the flexible magnetic recording medium, become more critical and stringent. As a result, the conventional flexible magnetic disk drive unit cannot be practically applied as a double-sided magnetic flexible disk drive unit for the metallic thin-film type magnetic flexible recording medium. Therefore, provision of a practically applicable magnetic head assembly capable of being accommodated in the flexible magnetic disk drive unit for a metallic thin-film type magnetic recording medium is demanded. When the above-mentioned metallic thin-film having a perpendicular magnetic anisotropy is used for forming a magnetic recording layer or layers of a flexible magnetic recording medium, or disk a magnetic read/write head per se must have sufficient durability to ensure a long operational life, and must be highly sensitive during perpendicular magnetic recording and retrieving. Also, a magnetic flexible disk cartridge containing the above-mentioned metallic thin-film type magnetic recording medium therein must be held in a casing in such a manner that stable magnetic recording and retrieving operations can be carried out over a long operational life. SUMMARY OF THE INVENTION Therefore, an object of the present invention is to obviate the problems encountered by the conventional magnetic head assembly for a flexible magnetic recording medium. Another object of the present invention is to provide a flexible magnetic disk drive unit provided with a magnetic head assembly having a long operational life and able to maintain a stable contact between a magnetic head or heads and a single-sided or double-sided metallic thin-film type flexible magnetic recording medium, especially the medium which is susceptible to a perpendicular magnetization. A further object of the present invention is to provide a magnetic recording head including at least a magnetic read/write head having an improved magnetic recording and retrieving sensitivity as well as an excellent and long operation life, and adapted for accommodation in a flexible magnetic disk drive unit for a metallic thin-film type magnetic recording medium. A still further object of the present invention is to provide a flexible magnetic recording disk cartridge having a magnetic flexible disk in a casing in such a manner that the flexible magnetic recording disk is exhibits a longer operational life and better stable recording and retrieving characteristics when is used with the flexible magnetic disk drive unit provided with the magnetic head assembly stated in the afore-mentioned object. JP-A 60-22768 discloses an arrangement of support pads and a recording head for a recording sheet, in which the pads are disposed on the opposite side of the sheet from the recording head and are spaced apart from each other, equidistant from the centre line of the recording head. The support pads have a large radius of curvature to enable the formation of an air film between the pads and the recording sheet, in order to reduce abrasion damage to the sheet while maintaining satisfactory contact with the head. However, the large radius of curvature of the pads requires that the overall size of the arrangement would be too large to be satisfactorily accommodated in a flexible magnetic disk drive unit. JP-A-59-3748 discloses an arrangement in which pressure pads are disposed on the opposite side of a magnetic disk from the head and are in constant sliding contact with the disk. In this arrangement, however, one of the pads presses against the disk in a position facing the head so that the disk is sandwiched between the head and the pad. This means that the contact between the head and the disk is not stable with respect to changes in the head-to-spindle penetration, i.e. the pressure exerted by the head on the disk; from a reference position. In accordance with the present invention, there is provided a flexible magnetic disk drive unit comprising the features of claim 1. According to research and experiments by the present inventors, the metallic thin-film type magnetic recording medium can exhibit an elastic property. This elastic property of the metallic thin-film type magnetic recording medium and the above-mentioned disposition of the plurality of supporting pads on opposed sides of the contact position where contact between the magnetic recording and retrieving head with a flexible magnetic disk takes place, are very effective for establishing a stable contact between the flexible magnetic recording medium and the magnetic recording and retrieving head unit during the recording and retrieving operation, and for overcoming the problems of frictional wear and damage of the magnetic head assembly and the flexible magnetic recording medium. That is, since the flexible magnetic recording medium is elastically flexible, and since the medium is not locally sandwiched by the magnetic recording and retrieving head unit and the supporting pads, the contact between the flexible magnetic recording medium and the magnetic recording and retrieving head unit during the recording and retrieving operation can be lightened. Preferably, the magnetic head assembly for the flexible magnetic disk drive unit further comprises a second pad unit arranged so as to restrict or suppress an undulating motion of the flexible magnetic disk which occurs during the rotational movement of the flexible magnetic disk. The second pad unit includes a plurality of suppressing pads arranged outward of the plurality of supporting pads of the first pad unit with respect to the contact position where contact between the magnetic recording and retrieving head with the flexible magnetic disk takes place, each of the suppressing pads of the second pad unit having an end face thereof arranged so as to be in sliding contact with the flexible magnetic disk while the flexible magnetic disk is rotating. The provision of the suppressing pads effectively reduces any change in mechanical impact force when the magnetic recording and retrieving head unit is in sliding contact with the flexible magnetic recording medium while the medium is rotating. Thus, the durability and operational reliability of the magnetic recording and retrieving head as well as the flexible magnetic recording medium can be enhanced. The metallic thin-film type flexible magnetic recording medium or disk for which the magnetic head assembly according to the present invention is adapted may have a flexible base of an organic polymer film, such as of polyethylene terephthalate film, polyethylene naphthalate film, or polyimide film, a magnetic recording layer applied onto the flexible base which is formed by a strongly magnetic metallic thin-film, such as an iron system thin-film, cobalt system thin-film or nickel system thin-film, and a protective layer. Particularly, the magnetic head assembly according to the present invention may be advantageously used with a perpendicular magnetic recording medium having a perpendicular magnetic recording layer which is susceptible to a perpendicular magnetization and has a high recording density. The perpendicular magnetic recording layer is constituted by an alloy film, such as a cobalt-chrome alloy film, a cobalt-chrome-tantalum alloy film, a cobalt-vanadium alloy film, or a cobalt oxide alloy film, applied onto the flexible base substrate directly or via a high magnetic permeable layer formed by an alloy film, such as a permalloy film, a cobalt-tantalum alloy film, a cobalt-zirconium alloy film, a cobalt-zirconium-niobium alloy film, or a cobalt-zirconium-tantalum alloy film. Preferably, the above-mentioned magnetic recording layer of the perpendicular magnetic recording medium is covered with a 50 through 500 Å thick protective layer to enhance the abrasion resistant property of the magnetic recording medium with which the magnetic head assembly of the present invention is used. The protective layer may be formed by a non-magnetic metallic oxide, such as a cobalt oxide, a silicone oxide, or a copper oxide. The magnetic recording and retrieving head employed in the magnetic head assembly of the present invention may be any known kind of magnetic recording and retrieving head, such as a conventional ring type magnetic head or a perpendicular magnetic head. Namely, the magnetic recording and retrieving head has a main magnetic pole, an excitation coil wound on a magnetic core, and a head slide. Preferably, the magnetic recording and retrieving head has a sliding contact face formed as a spherical surface at an end of the head slide so that the concentration of an impact force on the sliding contact face of the magnetic recording and retrieving head is prevented. The radius of curvature of the spherical surface is set at a value experimentally selected from several millimeters through several hundred millimeters, depending on the flexible magnetic recording mediums to be used. When the recording density of the flexible magnetic recording medium used is more than 50 KFRPI (Kilo Flux Reversal Per Inch), the radius of curvature of the spherical surface of the magnetic recording and retrieving head is preferably set at a value equal to or less than 10 millimeters, and the surface area of the end face of the magnetic recording and retrieving head should be as small an area as at most l millimeter square to several millimeters square, from the point of view of stable magnetic recording and retrieving. Alternatively, the sliding contact face of the end of the head slide may be formed as a cylindrical surface, as employed in the conventional magnetic head for a video tape recorder. The head slide may be made of a conventionally employed material, such as a ferrite system ceramic, a glass system ceramic, or a alumina system ceramic. That is, the material preferably should have a good thermal conductivity and have a sufficient hardness from the point of view of durability. Preferably, the head slide should be formed with at least one recess arranged adjacent to the main magnetic pole for trapping dust and other foreign materials therein during the magnetic recording and retrieving operation with the metallic thin-film type flexible magnetic recording medium. The supporting pads and suppressing pads of the first and second pad units should be strong enough to endure sliding contact with the flexible magnetic recording medium or disk for a long period of time, and be able to exhibit good sliding contact characteristics. Thus, preferably, the configuration of the contact end face should have a circular cross-section along a plane perpendicular to the contacting flexible magnetic recording disk and in parallel with the sliding direction of the first and second pad units. Most preferably, the configuration of the contact end face of the supporting and suppressing pads of the first and second pad units should be spherical, similar to that of conventional button pads. The entire shape of the supporting and suppressing pads of the first and second pad units may be cylindrical, conical, or pyramidal. The suppressing pad of the second pad unit may also have a semi-barrel shape. Both supporting and suppressing pads must be hard and thermally conductive, and preferably may be made of an abrasion resistant material having sufficient strength to support the spinning flexible magnetic recording disk. Thus, a crystallized glass, alumina system ceramics, or a material having a surface hardened by a titanium nitride, may be used for producing the supporting and suppressing pads of the first and second pad units. The supporting pads of the first pad unit are arranged so as to be spaced apart from one another and to be disposed respectively on opposed sides of a contact position where contact between the magnetic recording and retrieving head unit with the spinning flexible magnetic recording disk takes place. At least two supporting pads should be arranged so as to support two separate positions on each side of the above-mentioned contact position. Preferably, the supporting pads of the first pad unit are disposed at a plurality of supporting positions on a circle or concentric circles with a center thereof located at the position where the magnetic recording and retrieving head unit is in contact with the flexible magnetic disk. The plurality of supporting positions should be symmetrically distributed on both sides of a line substantially tangent to a circle having a center corresponding to a rotation center of the flexible magnetic disk and passing through the contact position. The number and disposition of the supporting pads of the first pad unit is determined by the physical characteristics of the flexible magnetic recording medium to be supported. The spacing between two adjacent supporting pads should be determined by taking the elasticity of the flexible magnetic recording medium into consideration. The plurality of supporting pads of the first pad unit may be either individual pad elements or integrally formed as one part. The suppressing pads of the second pad unit are provided to restrict or suppress undulating motion of the flexible magnetic recording medium during the rotation thereof, so that a flat rotational condition of the flexible magnetic recording medium is maintained when the medium comes into contact with the magnetic recording and retrieving head unit. Therefore, the plurality of suppressing pads of the second pad unit are arranged outward of the plurality of the supporting pads of the first pad unit. The plurality of the suppressing pads of the second pad unit are preferably disposed in such a manner that one group of the suppressing pads is located on one side of the contact position where contact between the magnetic recording and retrieving head with the flexible magnetic recording medium takes place, with respect to the rotational direction of the medium, and the other group of the suppressing pads is located on the other side of the above-mentioned contact position. Additional suppressing pads of the second pad unit may be disposed on both sides of the contact position in the radial direction of the flexible magnetic recording medium with respect to the rotational center of the medium, as required. Preferably, the supporting and suppressing pads of the first and second pad units are commonly arranged on a carriage unit for holding the magnetic recording and retrieving head unit, so that the magnetic head assembly of the present invention may be compact, and so that a stable recording and retrieving may be achieved. Alternatively, the suppressing heads of the second pad unit may be separately arranged on either a separate stationary part of the magnetic flexible disk drive unit or the jacket of each flexible magnetic recording medium, to reduce the weight of the carriage unit that must be quickly moved relative to the flexible magnetic recording medium. When the suppressing pads of the second pad unit are arranged on the separate stationary part of the magnetic flexible disk drive unit, they should be disposed so as to be in contact with a plurality of radial positions of an entire recording part of the flexible magnetic recording medium, which appears in the head window of the jacket of the flexible magnetic recording medium, circumferentially on both sides of the contact position where contact between the magnetic recording and retrieving head unit with the flexible magnetic recording medium takes place. The suppressing pads then may be a plurality of button type pads, but preferably, are constituted by a pair of semi-barrel type pads extending continuously and radially of the flexible magnetic recording disk, to permit a stable movement of the magnetic recording and retrieving head unit in the radial direction of the flexible magnetic recording disk by the carriage unit. Since the magnetic head assembly for the flexible magnetic disk drive unit is mainly intended for use with the metallic thin-film type magnetic recording medium or disk having a hard protective layer, the magnetic recording and retrieving head and the supporting and suppressing pads must have hard contact end faces, respectively, so that the durability of both the magnetic head assembly and the magnetic recording medium is enhanced. Thus, the end contact faces of the suppressing pads as well as the supporting pads should have a Vickers hardness equal to or more than 500. When the magnetic recording and retrieving head unit and the first and second pads units are commonly arranged on the carriage unit, at least one of the magnetic recording and retrieving head unit and the first and second pads units should be appropriately held on the carriage unit by an appropriate shock absorbing means and/or spring means, so that a flexible contact between the magnetic recording and retrieving head unit and the flexible magnetic recording medium is established, and so that a replacement of one flexible magnetic recording medium with another flexible magnetic recording medium can be safely carried out. When the magnetic head assembly of the present invention is used with a double-sided flexible magnetic recording medium or disk, the magnetic recording head unit should have a pair of magnetic recording and retrieving heads arranged on both sides of the medium or disk. The first and second pad units also should be arranged on both sides of the medium and disk. With this arrangement, one of the magnetic recording and retrieving heads preferably is arranged at a position at which it can act as a supporting pad with respect to the other magnetic recording and retrieving head. BRIEF DESCRIPTION OF THE DRAWINGS The above and other objects and advantages of the present invention will be made more apparent from the ensuing description of the preferred embodiments with reference to the accompanying drawings wherein: Fig. 1 is a partial cross-sectional view of a metallic thin-film type magnetic recording medium with which a magnetic head assembly can be used; Fig. 2 is a schematic front elevational view of a magnetic head assembly for a flexible magnetic disk drive unit; Fig. 3 is a cross-sectional view taken along the line III-III of Fig. 2; Fig. 4 is a plan view taken along the line IV-IV of Fig. 2; Fig. 5 is a cross-sectional view of a magnetic recording and retrieving head that can be accommodated in the magnetic head assembly of Fig. 2; Fig. 6 is a graphical view of the enveloped curve of the retrieving output signal derived from the magnetic head assembly of Figs. 2 through 4; Fig. 7 is a graphical view of the enveloped curve of the retrieving output signal derived from a magnetic head assembly according to the prior art; Fig. 8 is a graphical view of the relationship between the carrier to noise ratio C/N on the basis of the retrieving output signal and the head-to-spindle penetration of the magnetic recording and retrieving head according to Fig. 2; Figs. 9A and 9B are cross-sectional and plan views of a magnetic head assembly for double-sided recording and retrieving; Fig. 10A is a cross-sectional view of a magnetic head assembly according to an embodiment of the present invention; Fig. 10B is a cross-sectional view of a magnetic head assembly slightly modified from the assembly of Fig. 10A; Fig. 11 is a plan view taken along the line XI-XI of Fig. 10; Fig. 12 is a plan view taken along the line XII-XII of Fig. 10; Fig. 13 is a graphical view of the modulation amount of the flexible magnetic recording disk tested by the magnetic head assembly of Figs. 10 through 12; Fig. 14A is a cross-sectional view of another magnetic head assembly according to the present invention; Fig. 14B is a plan view taken along the line XIV-XIV of Fig. 14A; Fig. 15 is a graphical view of the modulation amount of the flexible magnetic recording disk tested by the magnetic head assembly of Figs. 14A and 14B; Fig. 16 is a graphical view of the modulation amount of the flexible magnetic recording disk tested by the magnetic head assembly of the prior art; Fig. 17 is a plan view of an improved magnetic recording and retrieving head that can be accommodated in the magnetic head assembly of the present invention; Fig. 18 is a cross-sectional view taken along the line XVIII-XVIII of Fig. 17; Fig. 19 is a cross-sectional view taken along the line XIX-XIX of Fig. 18; Fig. 20 is a cross-sectional view taken along the line XX-XX of Fig. 17; Fig. 21 is a perspective view of a further improved magnetic recording and retrieving head that can be accommodated in the magnetic head assembly of the present invention; Fig. 22 is a perspective view of a still further improved magnetic recording and retrieving head that can be accommodated in the magnetic head assembly of the present invention; Fig. 23 is a plan view of another improved magnetic recording and retrieving head that can be accommodated in the magnetic head assembly of the present invention; Fig. 24 is a cross-sectional view taken along the line XXIV-XXIV of Fig. 23; Fig. 25 is a cross-sectional view taken along the line XXV-XXV of Fig. 23; Fig. 26 is a cross-sectional view taken along the line XXVI-XXVI of Fig. 23; Fig. 27 is an exploded view of a flexible disk cartridge according to an embodiment of the present invention; Fig. 28 is an exploded view of a flexible disk cartridge according to another embodiment of the present invention; Fig. 29 is a cross-sectional view of a hub portion of the disk of Fig. 27 or 28, illustrating the mounting construction of the disk; and, Fig. 30 is a cross-sectional view of another hub portion of the disk of Fig. 27 or 28. DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring to Fig. 1 illustrating the construction of a typical example of a flexible magnetic recording disk with which a magnetic head assembly for a flexible magnetic disk drive unit of the present invention can be used, the flexible magnetic recording disk may be formed as, for example, a 3.5 inch double-sided perpendicular magnetic recording medium 10, and is provided with a flexible base film 11 made of polyester film 50 microns thick. The surface roughness (the average center line roughness Ra according to Japanese Industrial Standard B 0601) of the polyester film is 20 Å when measured by a roughness measuring instrument, i.e., an alpha step 200 of the Tencor Instrument Company of the U.S.A. On both sides of the flexible base-film 11, the medium 10 is provided with high magnetic permeable layers 12A and 12B formed by 0.5 microns thick Ni-Fe-Mo alloy layers having a magnetic coercive force of approximately 3 Oersteds, magnetic recording and retrieving layers 13A and 13B formed by 0.15 microns thick Co-Cr alloy layers having a perpendicular magnetic coercive force of approximately 600 Oersteds and a saturation magnetization of approximately 500 emu/cc, and protective layers 14A and 14B made of an 0.02 microns thick coating of tricobalt tetroxide (Co₃O₄). The formation of the respective layers is achieved by the opposed target type sputtering method disclosed in U.S. Patent No. 4,407,894. The double-sided perpendicular magnetic recording medium 10 is usually encased in a jacket and used as a flexible magnetic disk cartridge, as described later. Figures 2 through 5 show a magnetic head assembly for a flexible magnetic disk drive unit, which can be used with, for example, the flexible metallic thin-film type perpendicular magnetic recording medium 10 as shown in Fig. 1. The magnetic head assembly has a carriage 40 which is moved relative to the perpendicular magnetic recording medium 10 when driven by a drive source M, such as a conventional stepping motor, via a feed screw mechanism, in the same manner as the conventional carriage. The carriage 40 has an upper arm 41 and a lower arm 42 which laterally extends from a column 43. The upper arm 41 is fixedly attached to an upper end of the column 43 and is biased by a hinged leaf spring 44 toward the lower arm 42. A magnetic recording head portion 20 is held by the upper arm 41, preferably via a suitable resilient plate-like holder 45 (Fig. 3), and is provided with a head-penetration setting mechanism 21 utilizing a conventional micrometer and a magnetic recording and retrieving head 22 connected to the head-penetration setting mechanism 21. That is, the magnetic recording and retreiving head 22 is vertically moved toward and away from the upper face of the inserted flexible magnetic recording medium 10 by the head-penetration setting mechanism 21, to finely adjust the vertical position of the head 22. The magnetic recording head portion 20 is placed in elastic contact with the inserted flexible magnetic recording medium 10 by the hinged leaf spring 44 and the resilient characteristics of the flexible magnetic recording medium 10 per se. As best shown in Fig. 5, the magnetic recording and retrieving head 22 is constructed as a main-pole excitation type perpendicular magnetic recording and retrieving head, and is provided with a ferrite block 221 with an annular groove 223 at one end thereof for receiving therein an exciting coil 222, and a main magnetic pole 225 arranged in a head-slider 224 firmly connected to the end of the ferrite block 221. As shown in Fig. 4, the head 22 has a rectangular cross-sectional configuration 1.9 mm in width (W) and 1.3 mm in length (L) and a spherical contact end having a radius of curvature of approximately 10 mm. A pad unit 30 is held on the lower arm 42, and is provided with four button-type supporting pads 31A, 31B, 31C, and 31D, to support four positions of the flexible magnetic recording medium 10 from a side opposite to the side on which the magnetic recording and retrieving head 22 is arranged. The four supporting pads 31A, 31B, 31C, and 31D are fixedly seated on a support bed 32, and in the present embodiment, the four supporting pads 31A, 31B, 31C, and 31D are disposed at four corner points of a rectangle surrounding a contact position where contact between the main magnetic pole 225 of the head 22 and the flexible magnetic recording medium 10 takes place, as best shown in Fig. 4. Each of the supporting pads 31A, 31B, 31C, and 31D is formed by, for example, crystallized fluorine containing glass cylinder 3 mm in dia. and 1.5 mm in height, and has an end contact face generally in the shape of a spherical surface having a radius of curvature of 30 mm to prevent a concentration of an impact force on the end contact face while in contact with the flexible magnetic recording medium 10. Alternatively, from the point of view of preventing an impact force concentration, the end of each of the supporting pads 31A, 31B, 31C and 31D may be formed in a shape having two symmetrical oblique faces with a top narrow flat contact face, a semi-barrel shape with a small flat contact end face, or a truncated pyramid shape with a small square flat contact end face. At this stage, it should be understood that each of the supporting pads 31A through 31D can be referred to as a solid pad when compared with the conventional soft pads, for example, the animal skin pads. Preferably, the end contact face of each supporting head 31A, 31B, 31C or 31D is formed with slots or grooves 33 on both sides of the central contact area 34 (0.2 mm in width) with respect to the rotational direction (see the arrow in Figs. 3 and 4) of the flexible magnetic recording medium. The slots and grooves 33 are formed to trap dust and other foreign material during contact between the supporting pads 31A through 31D and the flexible magnetic recording medium. Each of the slots 33 is approximately 0.2 mm in width and approximately 0.5 mm in depth. The spacing between the centers of the supporting pads 31A and 31D or 31B and 31C in the direction of the circumferential direction of the medium 10 is set at 5 mm, and the spacing between the centers of the supporting pads 31A and 31B or 31D and 31C in the radial direction of the medium 10 is set at 9 mm. The present inventors have conducted experimental tests to evaluate the retrieving characteristics of the magnetic head assembly of the above-mentioned first embodiment. The assembly was built into a commercially available 3.5 inch floppy disk drive unit, and the above-mentioned perpendicular magnetic recording medium 10 encased in a commercially available 3.5 inch hard jacket was inserted into the assembly. Figure 6 illustrates the results of the measurements of the retrieving characteristics of the magnetic head assembly. That is, the curves in Fig. 6 are envelopes of the retrieving output signals obtained from the magnetic recording and retrieving head 22 set at a position 35 millimeters radially from the center of the rotation of the medium 10, under a later-described head penetration, during one complete revolution of the medium 10. From the illustration of the measured curves, it will be obvious that the modulation can be less than 10%, and that the carrier to noise ratio (C/N) at a carrier frequency was 54.5 dB. The measurement was conducted by the employment of an appropriate instrument, i.e., a spectro-analyzer TR-4171 manufactured and sold by Takeda Riken Co., Ltd. of Japan, under the measuring conditions of a 10 KH Z RBW (Resolution Band Width) and a 100 KH Z VBW (Video Band Width). When the head 22 was set a position 40 millimeters and 30 millimeters radially from the center of rotation of the 3.5 inch medium 10, the noise index (C/N) at a carrier frequency were 55 dB and 53.5 dB, respectively. The envelopes of the retrieving output signals were as stable as those shown in Fig. 6. On the other hand, Fig. 7 illustrates a result of a measurement of the magnetic retrieving characteristics in the case where the button-shaped main pole excitation type perpendicular magnetic head 22 was pressed against the medium 10 to carry out the magnetic retrieving without support by any supporting pad. That is, the case of Fig. 7 corresponds to the prior art supporting system of the magnetic head assembly. From the illustration of Fig. 7, it will be easily understood that, in the prior art supporting system the spacing between the head and the medium is not stable, and that the retrieving characteristics is not equalized in the circumferential direction of the medium 10. From a comparison between the results of Figs. 6 and 7, it will be readily understood that the corresponding magnetic head assembly extremely stable magnetic retrieving characteristics. Figure 8 illustrates the result of a measurement for evaluating the stability of the contact between the magnetic head assembly and the recording medium with respect to a change in the head-to-spindle penetration, i.e., the amount of pressure imposed by the head 22 against the face of the flexible magnetic recording medium 10 from a reference position where the medium 10 is set on the spinning spindle of the floppy disc drive unit. The ordinate of the graph of Fig. 8 indicates the carrier to noise ratio C/N (dB), and the abscissa indicates the change in the amount of head-to-spindle penetration. From the illustration of Fig. 8, it will be readily understood that the curve is almost flat over a wide range of the change in the head-to-spindle penetration (0 through 100 microns in the case of the present measurement). As a result, it is obvious that the contact between the head 22 and the medium 10 is stable regardless of any change in the head-to-spindle penetration. Therefore, a stable recording and retrieving can be guaranteed even if there is a change in the face characteristics of the medium 10, and thus the magnetic head assembly is always able to exhibit constant and stable recording and retrieving characteristics regardless of an exchange of one medium 10 for another. Further, with regard to the durability of the magnetic head assembly as well as the magnetic recording medium, it was confirmed by a test employing the head assembly of the above-mentioned type that the retrieving output level is substantially unchanged even after the flexible magnetic recording medium 10 was subjected to a specified number of turns, i.e., the 3 millions turns specified in the Japanese Industrial Standard as a reference index to indicate a typical level in practical use. Figures 9A and 9B illustrates another magnetic head assembly, which is provided with a magnetic recording and retrieving head unit having a pair of magnetic recording and retrieving heads, one for carrying out recording onto and retrieving from one of both sides of the flexible magnetic recording medium 10, and the other for carrying out recording onto and retrieving from the other of both sides of the flexible magnetic recording medium 10. The magnetic recording and retrieving head unit of the magnetic head assembly includes a pair of perpendicular magnetic recording and retrieving heads 22A and 22B, supporting pads 31E supporting the recording medium 10 from the underside, and supporting pads 31F supporting the recording medium 10 from the upper side. Each of the heads 22A and 22B may be of the same construction as the head 22 shown in Fig. 5, and each of the supporting pads 31E and 31F may be of the same construction as the supporting pads 31A through 31D. At this stage, it should be understood from the illustration of Fig. 9B that, in the disposition of the second embodiment, the heads 22A and the supporting pads 31E cooperate to provide a three-point support for the head 22B, and that the heads 22B and the supporting pads 31F cooperate to provide a three-point support for the head 22. That is, each of the magnetic recording and retrieving heads 22A and 22B is disposed so as to carry out a supporting function in addition to recording and retrieving functions. Thus, the magnetic head assembly can be made very compact. Figures 10A, 11 and 12 illustrates a magnetic head assembly according to an embodiment of the present invention, which has a first set of supporting pads for supporting a plurality of positions of a metallic thin-film type flexible magnetic recording medium and a second set of pads for restricting or suppressing an undulating motion of the medium during the rotation thereof. In the magnetic head assembly of the embodiment, the same or like elements and parts as in the magnetic head assembly of the first embodiment are designated by the same reference numerals. The magnetic head assembly has a head unit 20A and a pad unit 30 arranged on both sides of a metallic thin-film type flexible magnetic recording medium corresponding to the recording medium 10 of Fig. 1. The metallic thin-film type flexible magnetic magnetic recording medium 10, therefore, can be considered to be, for example, a 3.5 inch, 5 1/4 inch or 8.0 inch flexible perpendicular magnetic recording disk. The head unit 20A is provided with a bracket-like head seat 46 having a central recessed portion 46A and a leaf spring plate 45 on which a single magnetic recording and retrieving head 22 is held. The leaf spring plate 45 may be made of a phosphor bronze plate 100 microns thick, 3 mm in width, and 15 mm in length. The head unit 20A is also provided with a second set of suppressing pads 47 and 48 arranged to be spaced apart from one another and located on both sides of the head 22 in the direction of rotation (see the arrow in Fig. 10) of the recording medium 10. Further, the suppressing pads are located outward of the later-described first set of supporting pads 31A through 31D with respect to the head 22, as will be understood from the illustration of Figs. 10A and 12. The head seat 46 of the head unit 20A is attached to an upper arm 41 of a carriage 40, which corresponds to the carriage 40 in Figs. 2 through 4. A pad unit 30 attached to a lower arm 42 of the carriage 40 is provided with a support bed 32 on which four supporting pads 31A through 31D are mounted so as to support four positions surrounding a contact position at which contact between the head 22 and the flexible recording medium 10 takes place. Alternatively, as shown in Fig. 10B, the supporting pads 31A through 31D may be mounted on the support bed 32 via a leaf spring plate 45′. It should be understood that the head unit 20A and pad unit 30 are adjustably arranged in parallel with one another with an adjustable spacing therebetween. Thus, it is also possible to adjust the amount of penetration of the head 22 toward the face of the flexible recording medium 10 as well as the contact force of the suppressing pads 47 and 48, thereby adjusting the amount of undulation of the flexible recording medium 10. The magnetic recording and retrieving head 22 is preliminarily set so that a contact end of the head 22 is projected by 10 through 100 microns more than contact ends of the suppressing pads 47 and 48 toward the face of the flexible recording medium 10. The amount of the projection of the head 22 is determined by the impact force between the flexible recording medium 10 and the head 22 and the supporting pads 31A through 31D, and by the stability in the level of the recording and retrieving signals derived from the head 22. The head 22 accommodated in the assembly of the present embodiment is substantially the same as the head in Figs. 2 through 5. The first set of supporting pads 31A through 31D are the same as those in Figs. 2 through 4. The second set of suppressing pads 47 and 48 which may also be considered as solid pads, are made of a carbon material, e.g., manufactured by Tohoku Kyowa Carbon Co., Ltd. of Japan and sold by the same company under the trade name of "METAPHITE". Each of the suppressing pads 47 and 48 has a rectangular cross-sectional configuration 2.0 mm in width and 1.5 mm in length and a flat contact end chamferred on all edges thereof. The suppressing pads 47 and 48 is preferably held on the head seat 46 via an appropriate leaf spring (not shown) and is set so that the amount of projection of the contact end toward the face of the flexible medium 10 is less than that of the head 22 by, e.g., approximately 50 microns, as described before. The spacing between each of the suppressing pads 47 and 48 and the center of the head 22 is set at approximately several millimeters, e.g., 6 mm. The present inventors have conducted experimental tests to evaluate the durability characteristics of the magnetic head assembly of the above-mentioned third embodiment. The assembly was built into a commercially available 3.5 inch floppy disk drive unit, and the above-mentioned perpendicular magnetic recording medium 10 encased in a commercially available 3.5 inch hard jacket was inserted into the assembly. At this stage, the amount of maximum undulation of the flexible recording medium 10 was set at approximately 20 microns, as shown in Fig. 13, with the condition that the magnetic head 22 was not provided in the drive unit. The magnetic head 22 was then assembled into the drive unit, and the penetration of the head 22 was adjusted so that the retrieving output signal derived from the head 22 had an even enveloped signal curve. Further, after conducting a saturated recording at 70 KFRPI, the retrieving was repeatedly conducted to test the durability of the retrieving signal level. As a result, it was confirmed that the signal level was lowered by only 1 dB per 3 million rotations. Thus, it was confirmed that, due to the provision of the suppressing pads 47 and 48 according to the present embodiment, the magnetic head assembly exhibits an excellent durability. The durability test was further conducted with regard to a further magnetic head assembly according to the present invention, as shown in Figs. 14A and 14B, in which two supporting pads 31A and 31B and two suppressing pads 47 and 48 were accommodated without the magnetic head 22. The supporting pads 31A and 31B are spaced with a distance of 9 mm from the center of the pad 31A to that of the pad 31B in the radial direction of the flexible medium 10. The shape and material of the supporting pads 31A and 31B were the same as those of the pads 31A through 31D of the embodiment of Figs. 10 through 12. The suppressing pads 47 and 48 were also made of the same material as those of the embodiment of Figs. 10 through 12. Each of the suppressing pads 47 and 48 has the shape of a flat plate 4 mm in width, 4 mm in length, and 0.5 thick. All edges of each pad 47 or 48 were chamferred. Each of the two suppressing pads 47 and 48 was arranged on the head support 46 so as to be spaced 6 mm from a position where the magnetic head 22 should be held. Since the durability test and the test of the undulation characteristics were to be conducted, a magnetic head 22 was not accommodated in the magnetic head assembly. The magnetic head assembly of Figs. 14A and 14B was then assembled into a conventional 3.5 inch floppy disk drive unit, and the above-mentioned tests were conducted using the same flexible magnetic recording medium 10 as that used in the test of the embodiment of Figs. 10 through 12. The amount of undulation of the medium 10 was adjusted to a level shown in Fig. 15 (maximum undulation, 55 microns), and the flexible medium 10 was rotated at a speed of 600 r.p.m. for 13 million rotations. As a result, it was confirmed that the supporting and suppressing pads 31A, 31B, 47 and 48 and both faces of the medium 10 were not damaged in any way, for example, by scratching. On the other hand, when the medium 10 was inserted into a conventional commercially available 3.5 inch jacket, and was subjected to a similar durability test. The amount of undulation of the medium 10 in the jacket was as shown in Fig. 16. That is, due to the undulation suppression by the conventional soft liner, the maximum undulation of the medium 10 was 110 microns. As a result of the test, after 3 million rotations, many dirty marks appeared on the faces of the medium 10, and after 5 million rotations, a number of scratches appeared on the faces of the medium 10. Therefore, it was confirmed that the durability of the magnetic head assembly according to the present invention is superior to that of the conventional magnetic head, due to the arrangement of a plurality of supporting pads surrounding the contact position of the magnetic head with the flexible magnetic recording medium and the arrangement of a plurality of suppressing pads. From the foregoing description of the embodiments of the present invention, it will be understood that, in accordance with the present invention, the magnetic head assembly for a flexible magnetic disk drive unit adapted for practical use with a metallic thin-film type flexible magnetic recording medium, especially with a flexible perpendicular magnetic disk having a high recording density, can be realized. That is, the magnetic head assembly of the present invention is able to exhibit a long operational life and improved recording and retrieving characteristics, compared with the magnetic head assembly of the conventional flexible disk drive unit. Figures 17 through 20 illustrate a magnetic recording and retrieving head able to be incorporated into the magnetic head assembly according to the present invention. The magnetic recording and retrieving head of Figs. 17 through 20 is constructed as a head for carrying out recording onto and retrieving from the flexible magnetic recording medium or disk by the perpendicular magnetization system, as disclosed in U.S. Patent No. 4,251, 842 to Iwasaki et al. Referring to Figs. 17 through 20, the magnetic recording and retrieving head 122 is provided with a non-magnetic support 123 supporting a main magnetic pole 124 for recording and retrieving, and a main erasing pole 125. The support 123 is constituted by an approximately rectangular plate several millimeters in width and length and approximately less than 100 microns thick, made of crystallized glass, such as that manufactured and sold by Nippon Denki Glass Co., Ltd. of Japan under the name of "Neoceram" (Registered Trademark). Alternatively, the support 123 may be made of non-magnetic and abrasion-resistant material having slidable characteristics and a Vickers hardness of less than 1100, such as glass system ceramics, non-magnetic ferrite system ceramics, potassium titanate, calcium titanate or barium titanate. As best shown in Fig. 18, upper portions of the main poles 124 and 125, i.e., the portions located above later-described core sections 128b and 129b of auxiliary magnetic poles 128 and 129, are covered by protective films 126 and 127 several microns thick. The protective films 126 and 127 are formed by an aluminum oxide (Al₂O₃) film, respectively, attached to the faces of the main poles 124 and 125 by the RF sputtering method. The protective films 126 and 127 provide the main poles 124 and 125 with a chemical and mechanical durability. The main recording and retrieving pole 124 has a narrow pole portion 124a at an upper portion thereof and a wide magnetic path portion 124b connected to the lower end of the pole portion 124a. The width of the pole portion 124a of the main pole 124 corresponds approximately to that of the track of a magnetic recording and retrieving medium (not shown). The main erasing poles 125 have a pair of pole portions 125a arranged on both sides of the pole portion 124a of the main magnetic recording and retrieving pole 124, and a wide magnetic path portion 125b. The pair of pole portions 125a are spaced apart from one another at a distance corresponding approximately to the width of the above-mentioned track of the magnetic recording and retrieving medium. Both main poles 124 and 125 are formed of a soft magnetic thin-film such as permalloy film, sendust film or cobalt system amorphous alloy having a high magnetic permeability. The main poles 124 and 125 are formed of, for example, an amorphous magnetic film made of a Co-Nb-Zr alloy. The thick plate-like auxiliary magnetic poles 128 and 129 are arranged on both sides of the support 123. The auxiliary magnetic pole 128 has a body portion 128a and a central core portion 128b formed as a coil mount, and a magnetic path magnetically connected to the main magnetic recording and retrieving pole 124. The core portion 128b is bonded by a suitable adhesive to a central portion 124c (Fig. 19) of the main magnetic recording and retrieving pole 124. The auxiliary magnetic pole 129 has a body portion 129a and a central core portion 129b formed as a coil mount, and a magnetic path magnetically connected to the main erasing pole 125. The core portion 129b is bonded to a central portion 125c (Fig. 20) of the main magnetic erasing pole 125. The auxiliary magnetic poles 128 and 129 may be both made of a ferrite material. On upper faces 128c and 129c are fixedly mounted sliders 130 and 131, which are arranged so as to sandwich the support 123 in a direction corresponding to the sliding or direction of rotation of the flexible magnetic recording medium. The sliders 130 and 131 are centrally formed with recesses 132 and 133, respectively, as shown in Figs. 17 and 18. The width of each of the recesses 132 and 133 in the direction perpendicular to the sliding direction of the flexible magnetic recording medium is larger than those of the main poles 124 and 125 (see Fig. 17), and the depth of each of the recesses 132 and 133 in the direction corresponding to the sliding direction of the flexible magnetic recording medium is approximately more than 10 microns and less than 100 microns. As shown in Fig. 18, the two recesses 132 and 133 communicate with upper vacancies 134 and 135 formed between the support 123 and the body portions 128a and 129a. Therefore, these recesses 132 and 133 are able to receive and trap dust and abrasive powder produced between the head 122 and the flexible magnetic medium during the recording and retrieving operation of the head 122, and other foreign material. That is, due to the provision of the recesses 132 and 133, the top faces of the sliders 130 and 131 are always clean, resulting in an increase of the durability of the head 122 per se as well as the recording medium 0. Also, a stable recording and retrieving operation of the magnetic recording head 122 is ensured. The sliders 130 and 131 may be made of the same material as the slides of the conventional magnetic head. However, the sliders are preferably made of an abrasion-resistant material having a Vickers hardness of more than 1500, to ensure a sufficient durability while in use with a metallic thin-film type flexible magnetic recording medium. Therefore, alumina-titanium-carbide (Al₂O₃-TiC), SiC-ErO₂ , SiC, Si₃N₄ or Al₂O₃-ZrO₂ are preferably employed for the sliders 130 and 131. Between the sliders 130 and 131 and the upper faces 128c and 129c of the auxiliary magnetic poles 128 and 129 are interposed soft magnetic layers 136 and 137 made of permalloy film, which function as magnetic return paths, respectively. The provision of the soft magnetic layers 136 and 137 enhances the recording and retrieving sensitivity of the magnetic head 122. A magnetic recording and retrieving excitation coil 138 is wound around the core portion 128b, and a magnetic erasing excitation coil 139 is wound around the core portion 129b. The present inventors conducted a durability test of the above-described magnetic recording and retrieving head 122 using the flexible magnetic recording medium explained in Fig. 1, and confirmed that, after 6 million rotations, although the recesses 132 and 133 were contaminated, the upper faces of the support 123 and sliders 130 and 131 were not contaminated at the central areas thereof, i.e., only the ends of the upper faces of the support 123 and sliders 130 and 131 were slightly contaminated. In accordance with the magnetic recording and retrieving head 122 of the present invention, the following advantages are provided. (1) Due to the provision of the recesses before and after the main poles in the direction of rotation of the flexible magnetic recording medium, self-cleaning of the magnetic recording and retrieving head is always carried out during the recording and retrieving operation of the head, and thus the durability of the head and the magnetic recording medium are improved. (2) Since the support 123 is made of a non-magnetic material having a Vickers hardness of less than 1100, and since the slides 130 and 131 are made of a slidable and abrasion-resistant material having a Vickers hardness of more than 1500, the head has a long operation life and can be easily manufactured. (3) It is possible to reduce the dimensions of the top of the head, i.e., less than 1 mm in width and length, and to constantly maintain a stable contact between the head and the medium. (4) Since a magnetic path is formed around the main poles, the recording and retrieving sensitivity is excellent, without disturbance from the environment. (5) It is possible to construct a magnetic recording and retrieving head in which the magnetic recording and retrieving functions can be separated. (6) It is possible to construct a magnetic recording and retrieving head having an erasing head, which is indispensable for use with a flexible magnetic recording disk. Figure 21 illustrates another magnetic recording and retrieving head with recesses for trapping dust and foreign materials, constructed as a single pole type magnetic head for carrying out recording onto and retrieving from a flexible magnetic recording medium or disk, particularly a flexible metallic thin-film type perpendicular magnetic recording medium, by the perpendicular magnetization system. The magnetic head 322 of Fig. 21 has a main magnetic pole 324 held by symmetrically disposed supports 323a and 323b. The magnetic pole 324 is formed of a Co-Zr-Nb magnetic alloy film attached to an inner surface finished face of the support 323a by sputtering. The supports 323a and 323b are connected together by an adhesive, such as an epoxy resin, while sandwiching the main magnetic pole 324 therebetween. The supports 323a and 323b are made of, for example, glass system ceramics. The supports 323a and 323b may be made of non-magnetic ferrite, potassium titanate, calcium titanate or barium titanate. It is important that the non-magnetic material of the supports 323a and 323b has a Vickers hardness of less than 1100, so that difference of the hardness between the supports and the main magnetic pole 324 is kept as small as possible, and so that the supports can be easily manufactured. The supports 323a and 323b are formed with a recess 332 (only the recess of the support 323a is shown), respectively, on respective sides thereof opposite to the sides sandwiching the main magnetic pole 324. The recesses 332 are communicated with grooves 333 provided for an auxiliary magnetic pole 328, and are provided for trapping dust and other foreign materials during the magnetic recording and retrieving operations of the head 322. An arrow A indicates a direction in which a flexible magnetic recording medium (not shown) rotates or slides while in contact with the top face of the magnetic recording and retrieving head 322. The width of the recesses 332 in the direction perpendicular to the direction of rotation of the medium are determined to be larger than that of the main magnetic pole 324. An excitation coil 334 is seated on a main magnetic pole bed 327. Outer supports 325a and 325b are arranged outward of the above-mentioned supports 323a and 323b in the direction of rotation of the medium. These outer supports 325a and 325b are made of a non-magnetic abrasion-resistant material having a Vickers hardness of more than 1500, so that the durability of the head is increased. For example, alumina-titanium-carbide (Al₂O₃-TiC), SiC-ErO₂ , SiC, Si₃N₄ or Al₂O₃-ZrO₂ may be used for forming the outer supports 325a and 325b. The outer supports 325a and 325b are attached to the upper faces of the auxiliary magnetic pole 328, via a highly magnetic permeable film 326 formed of, e.g., conventional permalloy. The inwardly arranged supports 323a and 323b and the outer supports 325a and 325b are combined to form a combined rectangular plate-like support 2 mm in width, 2 mm in length, and approximately 100 microns thick, and positioning the main magnetic pole 324 onto the main magnetic pole bed 327. The uppermost face of the combined rectangular plate-like support is finished by polishing to a spherical surface having a radius of curvature of equal to or less than 200mm. In accordance with the above-described construction of the magnetic recording and retrieving head 322, the recesses 332 can trap dust and other foreign materials. Therefore, an accumulation of dust and foreign material between the head 322 and the flexible magnetic recording medium can be prevented. As a result, the durability of the head 322 per and the recording medium se can be improved, and erroneous recording and retrieving by the head 322 does not occur. Further, the provision of the highly magnetic permeable film 326 effectively increases the sectional area of the magnetic return path, thereby enhancing the sensitivity in recording and retrieving operations of the head 322 while decreasing the noise level. Figure 22 illustrates a further magnetic recording and retrieving head according to the present invention. The head 422 of Fig. 22 is different from that of Fig. 21 in that the area of the highly magnetic permeable film 326′ is greater than that of the highly magnetic permeable film 326. That is, supports 323a′ and 323b′ holding therebetween a main magnetic pole 324′ are formed as a plate smaller than the plate of the supports 323a and 323b of the head 322, and outer supports 325a′ and 325b′ are formed as a plate larger than the plate of the supports 325a and 325b of the head 322. The smaller supports 323a′ and 323b′ are fixed to the top of a main magnetic pole bed 327′, and the outer supports 325a′ and 325b′ are attached to the top of an auxiliary magnetic pole 328′, via the highly magnetic permeable film 326, thus forming a larger magnetic return path area than that of the highly magnetic permeable film 326 of the previously-described head 322. The large magnetic return path area of the film 326′ is effective for enhancing the sensitivity in the recording and retrieving operation of the head 422 and the resistance to disturbance from the environment of the head 422. Further, a recess 332′ is formed as a pocket-like groove enclosing small supports 323a′ and 323b′. The pocket-like groove 322′ is more effective for trapping dust and other foreign materials during the recording and retrieving operations of the head 422. An excitation coil 334′ is the same as the coil 334 of the head 322, and is seated on the bed 327′. Figures 23 through 26 illustrate a further embodiment of a magnetic recording and retrieving head that can be accommodated in the magnetic head assembly of the present invention. The magnetic recording and retrieving head 522 is constructed as a head for carrying out a perpendicular magnetization for a flexible metallic thin-film type magnetic recording medium, such as the medium 10 of Fig. 1. The magnetic recording and retrieving head 522 has a first magnetic pole portion 400 and a second magnetic pole portion 450. The first magnetic pole portion 400 includes a first auxiliary magnetic pole portion 401 having a main magnetic pole bed 402 surrounded by a recessed vacant portion 403, a main magnetic pole 404, a first excitation coil 410 wound around the main magnetic pole bed 402, and a slider 405 formed by an inner slider 405a supporting the main magnetic pole 404, and an outer slider 405b secured to an upper portion 406 of the auxiliary magnetic pole portion 401, via a highly magnetic permeable film 407. The highly magnetic permeable film 407 made of, e.g., permalloy, is arranged to form a magnetic return path as well as to prevent magnetic interference between the first magnetic pole portion 400 and the second magnetic pole portion 450. The formation of the recessed vacant portion 403 in the upper portion of the outer slider 405b also contributes to a prevention of the magnetic interference between the first and the second magnetic pole portions 400 and 450. The inner slider 405a is made of a non-magnetic and slidable material having a Vickers hardness of less than 1100, such as a glass system or non-magnetic ferrite system ceramics, potassium titanate, calcium titanate, barium titanate or crystallized glass. The inner slider 405a is formed by a pair of plates connected fixedly together. To one end face of the connected plates is attached a first main magnetic pole 404 made of Co-Zr-Nb alloy film by sputtering. On the other hand, the outer slider 405b is made of a non-magnetic and slidable material having a Vickers hardness of more than 1500, such as alumina-titaniumcarbide (Al₂O₃-TiC), SiC-ErO₂ , SiC, Si₃N₄ or Al₂O₃-ZrO₂. The inner and outer slider 405a and 405b of the slider has a recessed slit 408 connected to the recessed vacant portion 403 formed therebetween. The recessed slit 408 is extended so as to surround the inner slider 405b and is provided for trapping dust and other foreign materials during the recording and retrieving operations of the head 522. One end of the outer slider 405b is attached to a support base 411 interposed between the first and second magnetic pole portions 400 and 450. The support base 411 is made of a non-magnetic material of a suitable thickness, to magnetically isolate the first and second magnetic pole portions 400 and 450 from each other. The support base 411 is also provided as a support for a second main magnetic pole 415 of the second magnetic pole portion 450. Therefore, preferably the support base 411 is made of the same material as that of the inner slider 405a of the first magnetic pole portion 400. The second magnetic pole portion 450 includes the above-mentioned second magnetic pole 415 made of a Co-Zr-Nb alloy film having a pair of magnetic erasing poles 415a. The pair of magnetic erasing poles 415a are arranged so as to be spaced apart from one another, to thereby be able to magnetically erase both sides of a track of a flexible magnetic recording medium (not shown). The second magnetic pole portion 450 also includes a second auxiliary magnetic pole 413 having a connecting portion 413a connected to the second main magnetic pole 415, a second slider 414 formed by a second inner slider 414a secured to the face of the support base 411, and a second outer slider 414b connected to the upper face of the second auxiliary magnetic pole 413, via a high magnetic permeable film 417, and an excitation coil 420. The second inner slider 414a is made of the same material as the inner slider 405a of the first magnetic pole portion 400, i.e., a glass system ceramics. The second outer slider 414b is made of alumina-titanium-carbide (Al₂O₃-TiC). The uppermost face of the head 522 is finished by polishing to a rounded face having an appropriate radius of curvature, e.g., 30 millimeters. The slit 408 of the head 522 effectively catches dust and other foreign materials, thereby preventing an accumulation of such dust and other foreign materials between the head 522 and the flexible magnetic recording medium. As a result, the head 522 and the recording medium have a long operating life, respectively. Also, the provision of the highly magnetic permeable films 407 and 417 is effective for increasing the magnetic return path area. Therefore, a high sensitivity in the recording and retrieving can be ensured. The second magnetic pole 415 may be formed as a magnetic retrieving pole having a single pole 415a as shown in Fig. 26 instead of the pair of magnetic erasing poles 415a shown in Fig. 25. Figure 27 illustrates a flexible magnetic recording disk cartridge which can be used with the magnetic head assembly according to the present invention. The flexible magnetic recording disk cartridge 600 of Fig. 27 has a jacket 615 and a flexible magnetic disk 610 comprised of the same metallic thin-film type flexible magnetic medium as the medium 10 of Fig. 1. The jacket 615 (the hard jacket in the present embodiment) encasing the disk 610 therein is provided with an upper casing 620 and a lower casing 630. The upper casing 620 has four side walls 621 surrounding a rectangular base 622. The rectangular base 622 is formed with a central bore 623, a head window 624, and an indexing hole 625. The lower casing 630 has four side walls 631 surrounding a rectangular base 632. The rectangular base 632 is formed with a central bore 633, a head window 634, and an indexing hole 635. The central bore 623, the head window 624, and the indexing hole 625 of the upper casing 620 are brought into an alignment with the central bore 633, the head window 634, and the indexing hole 635 of the lower casing 630 when both casings 620 and 630 are mated together. The flexible magnetic disk 610 has a hub member 611 attached to the center of the disk 610 and an index hole 613 detected through the index holes 625 and 635 of the jacket 615. The hub member 611 has a spindle hole 612 in which a drive shaft (not shown) of a flexible magnetic disk drive unit is inserted when the cartridge 600 is set in the drive unit. The hub member 611 is rotatably mounted in the central bores 623 and 633 of the jacket 615 and is rotated together with the disk 610. The hub member 611 has a boss portion 611a used for driving the disk 610 and an annular flange portion 611b to which the flexible disk 610 is fixed, as shown in Fig. 29 or 30. When the flexible disk 610 is assembled in the jacket 615, the annular flange portion 611b of the hub member 611 is held between the upper and lower casings 620 and 630 of the jacket 615. Therefore, the flexible disk 610 is stable in both the direction of the axis of the rotation and in the radial direction; i.e., only a desired amount of play of the disk 610 in the above-mentioned directions is permitted. Thus, the flexible disk 610 is not subjected to any unfavourable force within the jacket 615. The upper and lower casings 620 and 630 are provided, on the inner faces of the rectangular bases 622 and 632, with cylindrical projections 640 (only the projections 640 on the face of the lower base 632 can be seen in Fig. 27) which are disposed along the outer peripheries of the flexible disc 610 and the hub member 611. These projections 640 are made of a non-magnetic and mechanically durable material similar to the material used for forming the afore-described slide of the magnetic recording and retrieving head, and act to prevent an unstable movement of the flexible disk 610 during the rotation of the disk. Where the disk 610 has a metallic thin-film recording layer, the cylindrical projections 640 should be made of a material having an abrasion-resistant property lower than that of the disk per se. However, the material should not cause condensation of an abrasion powder within the jacket 615. To satisfy these conditions, a fluorine contained crystallized glass is preferably used. The projections 640 also should be formed to have a round or spherical portion (a radius of curvature of 5 through 100 mm) in contact with the outer periphery of the flexible disk. The projections 640 of the upper casing 620 and those of the lower casing 630 are not required to be in alignment with one another. However, the projections 640 must prevent the flexible disk 610 from coming into contact with the inner faces of the bases 622 and 632. A fixing ring 614 (see Fig. 29 or 30) is provided for fixing the hub member 611 to the flexible disk 610. The fixing member 614 is preferably made of aluminum alloy or other easily machinable metallic material. An engineering plastic material also may be used for forming the fixing ring. In the case of the embodiment of Fig. 29, the fixing ring 614 is cemented to the outer cylindrical face of the boss portion 611a by an appropriate adhesive. The fixing ring 614 of the embodiment of Fig. 30 is threadedly engaged with the boss portion 611a of the hub member 611. Figure 28 illustrates another flexible disk cartridge that can be used with the magnetic head assembly of the present invention. The flexible disk cartridge 600′ is different from that of Fig. 27 in that a pair of plate-like pads 642 are provided on each inner face of the upper and lower casings 620 and 630, to restrict any undulation of the disk 610 during the spinning thereof within the jacket 615. The pair of plate-like pads 642 are disposed at positions adjacent to both sides of each head window 624 or 634 so that, when a portion of the disk 610 approaches and moves away from the head windows 624 and 634 during the rotation thereof, an undulation of that portion of the disk 610 is suppressed to a level of atmost less than 100 microns. As a result, contact between the disk 610 and the magnetic recording and retrieving head can be lightened. Thus, the mechanical durability of the magnetic head assembly as well as the disk per se can be enhanced, and a stable recording and retrieving can be realized. At this stage, the plate-like pads 642 are preferably made of carbon or glass carbon plate. Although, the embodiments of Figs. 27 and 28 are for a flexible disk cartridge encased in the hard jacket, the described constructions may be equally applied to a flexible disk cartridge encased in a soft jacket. From the foregoing description of the embodiment of the present invention, it will be understood that, according to the present invention, the magnetic head assembly for a flexible magnetic disk drive unit has a long operating life even when used with a metallic thin-film type flexible magnetic recording medium, especially a perpendicular magnetic recording medium. Further, the recording and retrieving characteristics of the magnetic head assembly are improved to a level at which it can be put to practical use.

Claims: A flexible magnetic disk drive unit provided with a magnetic head assembly for carrying out magnetic recording onto and retrieval from a rotating flexible magnetic disk (10) having a metallic thin-film type recording layer (13A) thereon and encased in a jacket (615), the magnetic head assembly comprising magnetic recording and retrieving head means having at least one magnetic recording and retrieving head (22) arranged on one side of the flexible magnetic disk so as to be in sliding contact with said metallic thin-film type recording layer of said flexible magnetic disk, and first pad means arranged to support said flexible magnetic disk from the side opposite said magnetic recording and retrieving head means, characterised in that said first pad means include a plurality of supporting pads (31A-31D) disposed respectively on opposed sides of a contact position at which contact between the magnetic recording and retrieving head and the rotating flexible magnetic disk takes place so that the disk is not sandwiched between the head and the pads, each of the supporting pads having a contact end face which is arranged in sliding contact with the flexible magnetic disk, and in that said magnetic head assembly further comprises second pad means arranged to restrict undulation of said flexible magnetic disk which occurs during rotation of said flexible magnetic disk, said second pad means including a plurality of suppressing pads (47, 48) arranged outward of said plurality of supporting pads of said first pad means with respect to said contact position at which contact between said magnetic recording and retrieving head and said rotating flexible magnetic disk takes place, each of said suppressing pads of said second pad means having an end face thereof in sliding contact with said flexible magnetic disk while said flexible magnetic disk is rotating. A flexible magnetic disk drive unit according to Claim 1, wherein said contact end face of each of said contact support pads of said first pad means has a spherical surface. A flexible magnetic disk drive unit according to Claim 1, wherein said contact end faces of said supporting pads of said first pad means and said end faces of said suppressing pads of said second pad means have respective Vickers hardnesses equal to or greater than 500. A flexible magnetic disk drive unit according to Claim 1, wherein said contact end faces of said supporting and suppressing pads of said first and second pad means are respectively formed with at least one recess (33) for trapping dust and other foreign materials therein. A flexible magnetic disk drive unit according to Claim 4, wherein said recess of each of said supporting and suppressing pads of said first and second pad means is formed so as to extend in a direction at approximately right angles to a sliding direction of said flexible magnetic disk in sliding contact with said supporting and suppressing pads. A flexible magnetic disk drive unit according to Claim 1, wherein said second pad means includes two groups of suppressing pads disposed at two separate groups of positions located on a line substantially tangent to a circle passing through said contact position at which contact between said magnetic recording and retrieving head and said rotating flexible magnetic disk takes place, said two separate groups of positions being located on one and the other sides of said contact positions with respect to a direction of rotation of said flexible magnetic disk. A flexible magnetic disk drive unit according to Claim 1, wherein said plurality of said supporting pads of said first pad means are disposed at a plurality of supporting positions on a circle or concentric circles with a center located at said contact positions at which contact between said magnetic disk takes place, said plurality of supporting positions being symmetrically distributed on both sides of a line substantially tangent to a circle having a center corresponding to a rotational center of said flexible magnetic disk and passing through said contact position. A flexible magnetic disk drive unit according to Claim 1, wherein said magnetic head assembly further comprises: carriage means (40) for commonly mounting thereon at least said magnetic recording and retrieving head means and said first pad means, said carriage means being movable relative to said magnetic flexible disk so that said magnetic recording and retrieving head means are positioned at a desired read/write position on said magnetic flexible disk. A flexible magnetic disk drive unit according to Claim 1, wherein said carriage means are arranged so as to further commonly mount said second pad means thereon. A flexible magnetic disk drive unit according to Claim 9, wherein said carriage means comprise a first mounting arm (41) extended above said one side of said magnetic flexible disk, and a second mounting arm (42) extended underneath said other side of said magnetic flexible disk, said first mounting arm being provided with a mounting bracket (46) holding thereon said second pad means (47, 48) and a spring element (45) attached to said mounting bracket and resiliently holding thereon said magnetic recording and retrieving head (22) with an end face thereof perpendicularly protruding toward said metallic thin-film type recording layer of said flexible magnetic disk beyond said contact end faces of said suppressing pads of said second pad means, and wherein said second mounting arm of said carriage means holds thereon said first pad means (31A-D). A flexible magnetic disk drive unit according to Claim 10, wherein said second mounting arm is provided with a spring element (45') on which said first pad means are resiliently held. A flexible magnetic disk drive unit according to Claim 10, wherein a difference in height of said end face of said magnetic recording and retrieving head and said contact end faces of said second pad means in the direction perpendicular to said flexible magnetic magnetic disk is maintained at between 5 to 100 µm. A flexible magnetic disk drive unit according to Claim 1, wherein said second pad means includes a pair of suppressing pads (47, 48) each being arranged outward of said plurality of supporting pads (31A-D) of said first pad means with respect to said contact position, said pair of suppressing pads being disposed so as to be spaced from one another in a direction corresponding to a sliding direction of said flexible magnetic disk. A flexible magnetic disk drive unit according to Claim 13, wherein each of said pair of said suppressing pads of said second pad means has a substantial length extending in a radial direction of said flexible magnetic disk. A flexible magnetic disk drive unit according to Claim 1, wherein said first and second pad means are made of an abrasion-resistant thermally conductive non-magnetic material. A flexible magnetic disk drive unit according to Claim 15, where in said first and second pad means are made of one of crystallized glass and alumina ceramics. A flexible magnetic disk drive unit according to Claim 1, wherein said magnetic recording and retrieving head means comprise: a first magnetic recording and retrieving head (22A) for carrying out magnetic recording onto and retrieving from a first metallic thin-film type recording layer disposed on one side of said flexible magnetic disk; and, a second magnetic recording and retrieving head (22B) for carrying out magnetic recording onto and retrieving from a second metallic thin-film type recording layer disposed on the other side of said flexible magnetic disk, said first and second magnetic recording and retrieving heads being arranged out of alignment with one another in a direction perpendicular to said flexible magnetic disk. A flexible magnetic disk drive unit according to Claim 17, wherein one of said first and second magnetic recording and retrieving heads is arranged so as to be a supporting pad when the other of said first and second magnetic recording and retrieving heads carries out the recording and retrieving. A flexible magnetic disk drive unit according to Claim 1, wherein said at least one magnetic recording and retrieving head of said magnetic recording and retrieving head means comprises: at least one main magnetic pole means (124) formed of a highly magnetic permeable material, said main magnetic pole means having a small pole portion (124a) adjacent to said contact position of said magnetic recording and retrieving head with said flexible magnetic disk; a non-magnetic support means (123) for supporting said main magnetic pole means; at least one auxiliary magnetic pole means (128) formed of a soft magnetic material and magnetically connected to said main magnetic pole at a position spaced from said small pole portion, said auxiliary magnetic pole means forming a magnetic return path arranged between said main magnetic pole means and said flexible magnetic disk; at least one excitation coil (138) for the recording and retrieving, said excitation coil being arranged on either one of said main and auxiliary magnetic pole means; slide means (130) made of a non-magnetic material, said slide means being attached to said auxiliary magnetic pole at a position at which it is in sliding contact with said flexible magnetic disk, said slide means being formed, at a position adjacent to said small pole portion, with a recess (132) for trapping dust and other foreign materials therein, said position of said recess being one of two positions located before and after said contact position in a direction at approximately right angles to a sliding direction of said flexible magnetic disk. A flexible magnetic disk drive unit according to Claim 19, wherein said recess formed in said slide means comprises a slot extended in said direction at approximately right angles to the sliding direction of said flexible magnetic disk. A flexible magnetic disk drive unit according to Claim 19, wherein said recess formed in said slide means comprises a pair of slots positioned on said two positions located before and after said contact position in a direction approximately at right angles to a sliding direction of said flexible magnetic disk, each of said slots being extended in said direction at approximately right angles to the sliding direction of said flexible magnetic disk. A flexible magnetic disk drive unit according to Claim 19, wherein said recess formed in said slide means is a groove extended so as to surround said main magnetic pole means. A flexible magnetic disk drive unit according to Claim 19, wherein said slide means are attached to said auxiliary magnetic pole means, via a highly magnetic permeable layer (136), for collecting magnetic return flux from said flexible magnetic disk. A flexible magnetic disk drive unit according to Claim 19, wherein said at least one magnetic recording and retrieving head of said magnetic recording and retrieving means comprises: a main magnetic read/write pole means (124) formed of a highly magnetic permeable material, said main magnetic read/write pole means having a small read/write pole portion (124a) adjacent to said contact position between said magnetic recording and retrieving head and said flexible magnetic disk; and, a main magnetic erase pole means (125) formed of a highly magnetic permeable material, said main magnetic erase pole means having a pair of small erasing pole portions (125a) arranged on both sides of said small read/write pole portion of said main magnetic read/write pole means, said main magnetic read/write and erase pole means being held by said non-magnetic support means (123) in such a manner that said magnetic read/write and erase pole means are spaced apart from one another in a sliding direction of said flexible magnetic disk. A flexible magnetic disk drive unit according to claim 19, wherein said non-magnetic pole means has a Vickers hardness of less than 1100, and wherein slide means (130) made of a non-magnetic material has a Vickers hardness of more than 1500.

Inventors: HONJYO KAZUHIKO, KADOKURA SADAO, KAMEI KAZUHIRO, HONJYO, KAZUHIKO, KADOKURA, SADAO, KAMEI, KAZUHIRO
Applicants: TEIJIN LTD, TEIJIN LIMITED
Application year: 1987
Main classification: G11B17
IPC codes: G11B23, G11B17, G11B5