GB2115971A

GB2115971A - A drive apparatus for an apertured recording medium

Info

Publication number: GB2115971A
Application number: GB08233743A
Authority: GB
Inventors: Klaus Manzke; Roland Brotzler; Joachim Hack
Original assignee: BASF SE
Current assignee: BASF SE
Priority date: 1981-11-28
Filing date: 1982-11-26
Publication date: 1983-09-14
Also published as: DE3147324A1; EP0080657A1; JPS5894176A; GB2115971B

Description

SPECIFICATION A drive apparatus for an apertured recording medium The present invention relates to a drive apparatus for an apertured recoring medium, especially a flexible disk record, such as a floppy disk, comprising a clamping part and a receiving part, one of these parts being driven, while the other part is rotatably mounted, so that, after the clamping and receiving parts have engaged, the driven part drives the undriven part, the recording medium being clamped, as the parts engage, between clamping surfaces on the clamping and receiving parts for rotation thereof, and engagement between the clamping and receiving parts being intensified by a magnetic force produced by a magnet system which is located coaxially with the central axis of the clamping and receiving parts. Disk drives using, as the recording medium, a flexible disk of thin sheet material are known, for example, from U.S. Patent Specifications Nos. 3,891,796 and 3,980,308. In these drives, the device for clamping the recording medium to be scanned is provided with a rigid cylindrical clamping member, or a rigid record support, carrying an annular magnet which is of large diameter, the outer diameter of this magnet substantially corresponding to the diameter of the clamped annular portion of the recording medium, and which exerts a pull on a soft-iron member when the clamping device is operative.Since the cylindrical clamping member and the record support are not resilient, there must be, in the clamped condition, an air gap between the permanent magnet and the soft-iron member to enable the annular clamping surfaces of the cylindrical clamping member, or of the record support, to bear against the flexible recording medium and thus clamp it in position. As a result of the existence of an air gap in the magnet system comprising the magnet and the soft-iron member, stray magnetic fields arise, which are undesirable in drives for magnetic disks. The abovementioned requirements also make it necessary to employ, in practice, large permanent magnets in order to achieve the requisite clamping force. It is also known, from U.S.Patent Specification No. 3,980,308, to use a centering member having a diameter which varies from smaller than to larger than the central hole in the recording medium, a flange being provided for supporting the recording medium, in this case a video disk. The respective designs of these conventional disk drives therefore differ significantly from that of the present apparatus. The object of the present invention is to provide a drive apparatus for apertured recording media, especially flexible disk records, which is of simple design and has a reliable clamping action. In addition, in the case of floppy disk drives the magnet system must be prevented from interfering with the recording and playback operations. The present invention can be used with advantage for any type of disk-shaped flexible recording medium having a central hole. According to the present invention there is provided a drive apparatus for an apertured recording medium, comprising relatively separable driving and driven clamping parts engageable to enable the driving clamping part to rotate, about an axis of rotation, said driven clamping part and an apertured recording medium releasably clamped between said engaged clamping parts, the said clamping parts being held in engagement at least partly by a magnetically generated clamping force, characterized in that the magnetically generated clamping force is produced between relatively separable first and second magnetic means on the driven and driving clamping parts, respectively,the first and second magnetic means both being disposed at least substantially within an imaginary cylinder coaxial with said axis of rotation and whose circumference is defined by the aperture of an apertured recording medium clamped between said clamping parts. As a result, after insertion of the recording medium, the requisite clamping force, exerted by the clamping part on the bearings of the drive spindle, can, surprisingly, be reduced to a very low value, virtually to zero pond. Moreover, in the case of the novel drive apparatus, the magnetic force which draws the clamping and receiving parts together is only approximately half the force which is conventionally. It is possible, according to the invention, to avoid the production of stray magnetic fields, and the unnecessary energy losses thereby, when the magnet system comprises one or more magnets and one or more flux-conducting members. In an advantageous embodiment, the magnet is a permanent magnet arranged inside a soft-iron hollow cylindrical member forming the return leg of a magnetic circuit, so that a powerful clamping action is achieved. In a further embodiment, the magnet comprises an electromagnet. In practical embodiment, the magnet and the flux-conducting member are arranged centrally on the clamping and receiving parts respectively, or vice versa. A particularly simple and effective design can be obtained when the permanent magnet is composed of a magnetic material having a high energy product, especially cobalt/samarium. As a result, the mass of the magnet and the size of the clamping and receiving parts can be reduced to a necessary minimum, without adversely affecting the functioning of the clamping device. In a particularly advantageous embodiment of the drive, a plain bearing is used for mounting the driven receiving part, instead of ball bearings. It is nevertheless possible to reduce the torque losses, as compared with drives with ball bearings, so that motors having a smaller power output can be employed as direct-drive elements for the driven part. In a further advantageous embodiment, the clamping surface on the receiving part is a hard annular surface, whereas the associated surface on the clamping part consists of a plurality of arcuate portions forming the lower faces of a corresponding number of springy members. As a result of this design, it is possible to obtain reliable centering of the clamping part, and hence also of the recording medium, before the parts of the magnet system come into engagement, the clamping force being exerted centrally and very uniformly on the edge of the central hole in the recording medium. Illustrative embodiments of drive apparatus according to the invention are described below with reference to the accompanying drawings, in which Figure 1A is a schematic cross-sectional view of the clamping device of a conventional drive apparatus for flexible recording media, Figure 1 is a schematic cross-sectional view of a first embodiment of the clamping device of a drive apparatus, according to the invention, with an actuating lever.Figure 2 is a schematic cross-sectional view of a clamping device similar to that shown in Figure 1, but with an actuating cover plate, Figure 3 is a scaled-up schematic cross-sectional view of the magnet system of Figures 1 and 2, also showing the magnetic flux paths, and Figure 4 is a schematic cross-sectional view of a second embodiment of the clamping device of a drive apparatus, according to the invention, having plain bearings for the receiving part. Figure 1A shows a portion of a known drive apparatus for flexible recording media, especially for Flexydisks (trademark of BASF Aktiengesellschaft, Ludwigshafen), the drive apparatus being of the kind shown in U.K. Patent Specification No. 1,596,703. In particularthe known apparatus is a so-called Diskette playback apparatus 20A having a casing 17A. The apparatus 20A is intended to playback a thin, flexible magnetic disk 4A, with a central opening and a stationary, rectangular envelope, and comprises the following components:- -A clamping and centering part 5A having a frustoconical portion and which is rotatably mounted and serves to clamp the thin magnetic disk 4A in position, - a hollow hub 6A, which can be caused to rotate by a drive motorthat drives pulley 29A via a belt, the housing 18A surrounding the hollow hub, which serves as the receiving part for the flexible magnetic disk 4A, being attached to the apparatus casing 17A, - an actuating lever 14A, which is connected to the clamping part 5A in such a manner that the latter can be moved toward, and away from, the hollow hub 6A,thus enabling the clamping part 5A and the hollow hub 6Ato engage and disengage. The actuating lever 14A can advantageously be operated directly via a flap in the apparatus casing 17A, this flap (not shown) being opened to insert or remove the envelope containing the disk. The operation of this lever is so timed that the flexible magnetic disk 4A is moved by the flap to its operating position before the part 5A and hub 6A engage, i.e. before the clamping operation starts. A guide shaft 15A ensures that the clamping part 5A moves perpendicularly to the flexible magnetic disk 4A. The hollow hub 6A is usually driven by means of a belt, not designated with a reference numeral in this drawing, which acts on the outer periphery of the pulley 29A. The hollow hub 6A is mounted for rotational movement in a double set of ball bearings 31A.The clamping part 5A is likewise rotatably mounted in ball bearings, in this case a single set of ball bearings 19A, in order to keep the drive torque which must be produced by the drive motor (not shown) within acceptable limits. The clamping force required to effectslip-free rotation of the flexible magnetic disk 4A, following the engagement of the clamping part 5A and the hollow hub 6A, is approximately 1 kilopond (kp) between the clamping part 5A and the apparatus casing 17A, and this force must be kept constant during rotation of the disk. However, only a portion of this force is in fact required for clamping the flexible magnetic disk 4A. The total force of approximately 1 kp is continuously exerted on the bearings 31A and 19A which consequently have to be ball bearings. Further details of the novel drive apparatus are disclosed in the following description in which, for the sake of clarity, the same reference numbers have been used as in Figure 1A, but without the A, to designate similar parts of the apparatus. Although the only recording medium that has hitherto been mentioned has been a thin flexible, magnetic disk 4A, any type of recording medium 4 having a central aperture can be employed which is suitable, in conjunction with the drive apparatus described below, for the recording and/or reproduction of signals, irrespective of the nature of these signals. Moreover, the recording medium 4 may comprise a plurality of circular portions which can be arranged above one another and possibly interconnected, or at least driven as a group when the medium is rotated. Figure 1 shows an embodiment of a clamping device of a drive apparatus 20 for recording media 4, the recording medium 4 being pressed, by means of the clamping and centering part 5, onto the hollow hub or receiving part 6, in the region of an annular surface 7, and being driven when the receiving part 6 rotates. The clamping part 5 is provided with springy portions 16, which are intended, by virtue if their shape and dimensions, to ensure both the centering of the clamping part 5 relative to the receiving part 6, and the non-damaging and reliable clamping of the recording medium 4. When the clamping part 5 and the receiving part 6 are in gripping engagement, as shown in Figures 1,2 and 4, a magnet system 8 is located coaxially with the central axis 21 of the parts 5 and 6. To be more precise, this magnet system 8 should be arranged at least substantially within the imaginary cylinder which is defined by the circumference of the central opening in the recording medium 4. Subject to the usual tolerances, the circumference of the central opening corresponds approximately to the circumference of the opening in the receiving part 5. The magnet system 8 consists essentially of a magnet 9 and a flux-conducting member 10 which are respectively attached to the parts 5 and 6.In the engaged position of the parts 5 and 6, the surfaces 12 are in contact with each other, if any roughness and/or waviness, present on the surface of the material as a result of the manufacturing process, is disregarded. Since there is no air gap between the surfaces 12, energy losses and stray magnetic fields are avoided. The magnetic 9 is preferably a permanent magnet, which is advantageously made from a magnetic material having a high energy product, such as cobalt/samarium. However, an electromagnetic can also be used. If a cobalt/samarium permanent magnet is used, which can be in the form of a cylinder having a diameter of 7 mm and a height of 3 mm, a material mass of one gram (1 g) is sufficient to provide the necessary pull and clamping force of only 500 pond between the parts 5 and 6. In this embodiment, the magnet 9 is surrounded by a soft-iron hollow cylindrical member 11 which forms the return leg of a magnetic circuit, and prevents the occurrence of lateral stray fields, only the pole surface facing flux-conducting member 10 remaining exposed. The member 10 is located inside the opening in the receiving part 6 and is expediently manufactured as an integral part thereof. In the engaged position, the end face of the soft-iron hollow cylindrical member 11 also abuts against the upper surface 12 of member 10. As a result, all the lines of magnetic flux leaving the magnet 9 are closed, thereby preventing the occurrence of stray fields and the partial erasure of a magnetic recording on the disk. The shape of two closed lines 13 of magnetic flux can be seen from Figure 3. It is expedient for the diameter of the upper surface of the member 10 to be larger than the external diameter of the soft-iron hollow cylindrical member 11. As the clamping part 5 moves downwards from its dash-dotted rest position, under the action of the actuating lever 14, to engage the recessed part 6, the first event to occur is the entry of the frusto-conical centring portion 22 of the clamping part 5 into the opening in the recessed part 6, after which the springy peripheral portions of the clamping part come to bear against the annular surface 7 of the hollow part 6, and least of all, in the illustrated embodiment, and not until the distance between the surfaces 12 is in the region of a few tenths of a millimeter do the surfaces strike each other due to the pull exerted by the magnet, and the final, clamped position of the recording medium is thus reached, and as mentioned above, 500 pond act as a continuous attracting force, holding the parts together. Hence, the maximum magnetic force can be utilized as a vertically-acting clamping force, and energy losses can be eliminated. The clamping force was determined experimentally, by measuring the torque at which slip occurs, that is to say, by determining the force required to cause the thin flexible magnetic disk 4 to start to slip. When carrying out this measurement, the magnetic head, which is not shown in the drawing, and the pressure pad of a floppy disk drive, which pad is located opposite the magnetic head, are positioned over the outermost track on the magnetic disk 4, and in contact with the disk, since, in this mode of operation, the drive motor has to produce the greatest torque. The force required to cause the disk 4 to slip is measured at the periphery of the pully 29, as it rotates, by means of a spring balance which is attached to the pulley.A force of approximately 500 pond was measured. This magnetic force is effective only between the surfaces 12, so that no axial forces are exerted on the bearings of the hollow part 6 and of the clamping part 5. It is consequently possible, as shown in the embodiments of Figures 1, 2 and 4, to dispense with the non-friction bearing (19A in Figure 1A) and, as illustrated in Figure 4, and to replace the ball bearings 31A and 31, shown in Figures 1A, 1 and 2, by plain bearings, which are unsuitable for dealing with axial forces but are more attractive on economic grounds. As a result of these two measures, it is possible to reduce the total drive torque required, so that, for example, the part 6 can be driven directly by means of a bolted-on low-power drive motor, not shown here, instead of by means of the pulley 29. To unclamp the magnetic disk, the actuating lever 14 is shifted to its rest position, advantageously by simply opening the flap, as in the case of the drive 20A, the force, for example a spring force, exerted on the clamping part 5 having to exceed the force of magnetic attraction. As a result, the clamping part 5 is lifted out of the hollow part 6, it being possible for its approximately central position relative to the hollow part to be maintained by means of a guide shaft 15. The use of such a guide shaft, though advantageous, is not essential. Following the raising of the clamping part 5, the disk-shaped recording medium 4 can be removed from the space between the clamping part 5 and the hollow part 6, and another disk can be inserted. Figure 2 shows a drive apparatus 30 with a clamping device for a recording medium 4, which apparatus is provided with a cover 23 instead of a lateral flap cooperating with an actuating lever 14 (cf. for example Figure 1). An opening 24 is provided in the cover 23, for a knob 25, which is directly attached to the clamping and centering part 5, When the apparatus is opened, the cover 23 is unlocked and caused to pivot, for example by spring force, into the dash-dotted position. Although the cover is pivotably mounted in this embodiment, it can of course be mounted for opening in any other suitable manner. At the same time, the knob 25 and the clamping part 5 are raised together with the cover, and the clamping part disengages from the hollow part 6. The recording medium 4 can then be removed.The knob 25 can also be detachably fastened to the clamping part 5, so that the magnetic system 8 is accessible for replacement for example. As a result, it is possible, for example, to employ recording media 4 having different masses and/or different dimensions on one and the same drive, without having to dispense with a reliable clamping force, if a magnet whose magnetic forec is matched to the particular recording medium is used. The parts 5 and 6 are brought into engagement in the same way as described with reference to Figure 1, by lowering the cover 23. The clamping device variant shown in Figure 4 includes a modified clamping part 26 with springy portions 27 which have a different shape than those described above. This design provides a larger contact area between the annular surface 7 of the hollow part 6 and the clamping surface of the clamping part 26. The use of ordinary commercial plain bearings 28, instead of expensive ball bearings, 31 and 31A, is regarded as particularly advantageous.

Claims

1. A drive apparatus for an apertured recording medium, especially a flexible disk record, comprising relatively separable driving and driven clamping parts engageable to enable the driving clamping part to rotate, about an axis of rotation, said driven clamping part and an apertured recording medium releasably clamped between said engaged clamping parts, the said clamping parts being held in engagement at least partly by a magnetically generated clamping force, characterized in that the magnetically generated clamping force is produced between relatively separable first and second magnetic means on the driven and driving clamping parts, respectively, the first and second magnetic means both being disposed at least substantially within an imaginary cylinder coaxial with said axis of rotation and whose circumference is defined by the aperture of an apertured recording medium clamped between said clamping parts.

2. A drive apparatus according to claim 1, in which the first magnetic means comprises at least one magnet and the second magnetic means comprises a ferromagnetic body forming a magnetic circuit with the said first magnetic means.

3. A drive apparatus according to claim 2, in which said at least one magnet comprises at least one permanent magnet.

4. A drive apparatus according to claim 2 or 3, in which the first magnetic means further comprises a soft-iron hollow cylindrical member enclosing the said at least one magnet, the said cylindrical member providing a return leg of said magnetic circuit.

5. A drive apparatus according to claim 3 or claim 4 when dependent upon . i̇m , in which said at least one permanent magnet is made from a material having a high energy product.

6. A drive apparatus according to claim 5, in which said at least one permanent magnet is made of cobalt/samarium.

7. A drive apparatus according to claim 2, in which said at least one magnetic comprises an electromagnet.

8. A drive apparatus according to any of the preceding claims, in which the said first and second magnetic means are located axially with respect to said axis of rotation on said driven and driving clamping parts, respectively.

9. A drive apparatus according to any of the preceding claims, in which one of said clamping parts has a hard annular clamping surface and the other of said clamping parts has a plurality of springy portions formed with co-operating clamping surfaces.

10. A drive apparatus according to any of the preceding claims, in which a plain bearing is provided for mounting the driven part.

11. A drive apparatus for an apertured recording medium, especially a flexible disk record, the drive apparatus being constructed and arranged substantially as herein described with reference to Figures 1, 2 and 3 or Figure 4 of the accompanying drawings.

12. Recording and/or playback apparatus having a drive apparatus according to any of the preceding claims. New claims filed on 18 March 1983 Superseded claims 1 and 2 New claims:- CLAIMS 1. A drive apparatus for a recording medium having a central aperture, especially a flexible disk record, comprising relatively separate driving and driven clamping parts engageable to enable the driving clamping part to rotate, about an axis of rotation, said driven clamping part and an apertured recording medium releasably clamped between said engaged clamping parts, the said clamping parts being held in engagement at least partly by a magnetically generated clamping force, characterised in that the magnetically generated clamping force is produced between relatively separable first and second magnetic means on the driven and driving clamping parts, respectively, the first and second magnetic means both being disposed mainly centrally within said aperture of the recording medium which is arranged coaxially with said axis of rotation and is clamped between said clamping parts. 2. A drive apparatus according to claim 1, in which the first magnetic means comprises at least one magnet, in which the second magnetic means comprises a ferromagnetic body forming a magnetic circuit with the said first magnetic means and in which the magnetic clamping force of said first and second magnetic means is approximately 500 pond.