DISC CLAMPING DEVICE

Abstract: A disc clamping device comprises a disc base (1) on which to set a disc (4) and which has a spindle (2) for rotating the disc, and a disc holding member (7) movable in the axial direc­ tion of the spindle. The disc holding member comprises a portion for pressing a disc with centering hub (5) and a por­ tion to be engaged with the center hold of a disc with no centering hub.

Description: Background of the Invention The present invention relates to a disc clamping device for engaging an information recording disc such as an optical disc or an optical magnetic disc coaxially with a turntable. One conventional disc clamping device is shown in Fig. 3. Here, a turntable 1 has a spindle 2, and a magnet 3 is embedded in the turntable. An information recording disc 4, includes a ferromagnetic centering hub 5 with a center hole 6. The turntable 1, integrally fixed to the spindle 2 is designed to rotate the information recording disc 4. The centering hub 5 is fixed on the disc 4 by bonding. The center hole 6 of the centering hub 5 has a diameter that fits on the spindle 2 with a specified clearance. The sequence of fixing the information recording disc 4 on the above conventional disc clamping device is as follows. The spindle 2 is inserted into the center hole 6 of the centering hub 5 for centering the disc 4. Then, the magnet 3 attracts the ferromagnetic centering hub 5 thereby fixing the disc 4 on the turntable 1. The above conventional device has the following problems. The spindle 2 is required to have such an accurate diameter as fits in the centre hole 6 of the centering hub 5 with the specified clearance. However, the centering hub hole can differ in diameter from disc to disc. Some discs may have too small a centering hub hole for the spindle to fit in, and some may have too large a centering hub hole to properly centre the discs, resulting in the centre displacement so that the recording/reading head cannot trace the tracks. The disc clamping device has another problem for an information recording disc that has no centre hole because of a manufacturing process-related reason. Supposing the spindle is inserted in the centering hub hole of such a disc, if the axial length of the spindle effective for engagement with the centering hub is greater than the thickness of the centering hub, the spindle end comes to the disc face, preventing the disc from being fixed in the device. Japanese patent application serial no. JP-A-60 7642, published 16th January 1985, discloses a second type of disc clamping device. This device is intended to accommodate a disc of the type which has a centre hole but does not include a ferromagnetic centering hub. In order to allow for variation in the diameter of the centre hole, the disc is engaged by a member which has a frusto-conical outer surface. However, this device is unsuitable for clamping a disc of the type shown in Figure 3, i.e. having a centering hub 5. Summary of the Invention It is an aim of the present invention to alleviate at least some of the aforementioned problems. In accordance with the present invention, there is provided a disc clamping device capable of clamping a disc of a first or second kind, said disk of the second kind having a smaller diameter of its center hole than the disk of said first kind, the device comprising: a rotatably mounted disc base (1) for supporting a disc; a spindle (2) extending from the centre of said disc base and fixed thereto; a disc holding member (7) spaced above said spindle (2); pressing means (9) arranged to press said disc holding member (7) toward said disc base (1) to clamp a disc therebetween; said disc holding member (7) comprising a first portion having a circumferentially-tapered outer surface for engagement of the center hole of a disc of the first kind, a second portion for pressing engagement of the hub of a disc of the second kind, and a centre hole (8) for receiving said spindle (2) when a disc of the first kind is clamped; characterized by said disc base (1) including magnetic means (3) positioned around said spindle (2) for magnetic interaction with the hub of a disc according to the second kind having a ferromagnetic centering hub. Brief Description of the Drawings The present invention will become more fully understood from the detailed description given hereinbelow and the accompanying drawings which are given by way of illustration only, and thus are not limitative of the present invention and wherein: Figs. 1 and 2 are side sectional views of an embodiment of a disc clamping device of the present invention; and Fig. 3 is a side sectional view of the conventional disc clamping device. Detailed Description of the Invention Fig. 1 is a side sectional view of an embodiment of the invention. The same reference numbers are allotted to parts identical with those of Fig. 3. Referring to Fig. 1, a turntable 1, has a spindle 2. A magnet 3 is embedded in the turntable 1. An information recording disc 4, has a centering hub 5 made of ferromagnetic substance bonded on the information recording disc 4, with a center hole 6. The center hole 6 has a diameter permitting the spindle 2 to be inserted and fixed therein. A disc holding member 7 includes a portion tapering downwardly and a center hole 8. The center hole 8 has a diameter which permits the spindle 2 to be inserted and fixed in the center hole 8. A compression spring 9 is provided for pressing the disc holding member downwardly. The operation of the disc clamping device of the present invention is described in the following. The disc holding member 7 is lifted upwardly by a mechanism in the disc recorder/reader (not shown). The information recording disc 4 is inserted in the space between the disc holding member 7 and the turntable 1. The disc 4 is then set with the center hole 6 approximately over the spindle 2 by an initial positioning mechanism. The disc 4 lowers or the turntable 1 rises so that the spindle 2 is inserted into the center hole 6, thus centering the disc 4. Due to the attracting force between the ferromagnetic centering hub 5 and the magnet 3 embedded in the turntable 1, the disc 4 is securely fixed on the turntable 1. The disc is clamped in the above operation when it has a centering hub. Some discs have no center hole for the purpose of simplifying the manufacturing process. To accommodate such discs, the spindle is designed so the spindle end inserted into the centering hub 5 does not come in contact with the disc 4. More specifically, the length effective for engagement of the spindle does not exceed the thickness of the centering hub 5, or alternatively the spindle may be axially slidable. Fig. 2 explains the operation of the disc clamping device for an information recording disc with no centering hub. The disc 4 is placed around the center hole of the turntable 1 by the initial positioning mechanism. The disc holding member 7 is lowered in the axial direction, centering the disc 4. The disc holding member 7 is further lowered until the center hole 8 of the disc holding member 7 comes into engagement with the spindle 2, thereby centering the disc 4 accurately. Since the disc holding member 7 holds the disc 4 by the tapered circumferential wall of the conical section, it can hold a disc with various center hole diameters. The disc holding member 7 is pressed against the disc 4 due to the elasticity of the compression spring 9 provided in the upper part of the disc holding member 7. To increase the clamping force, the disc holding member 7 may be made of ferromagnetic material so that the magnet 3 in the turntable 1 and the disc holding member 7 attract each other. As described above, the disc clamping device of the present invention comprises the disc base on which to set a disc and which has the spindle for rotating the disc, and the disc holding member which is movable in the axial direction of the spindle and which comprises the portion for pressing a disc with centering hub and the portion for engagement with the center hole of a disc with no centering hub. Accordingly, the disc clamping device of the present invention provides a substantial advantage that it can clamp a disc securely regardless of difference in the construction. Since the device is capable of clamping a disc with no center hole, it helps solve various problems in the disc manufacturing process; the disc with no center hole provides such merits as reduction in material processing cost, ease in forming recording layer and ease in transportation and handling.

Claims: A disc clamping device capable of clamping a disc of a first or second kind, said disk of the second kind having a smaller diameter of its center hole than the disk of said first kind, the device comprising: a rotatably mounted disc base (1) for supporting a disc; a spindle (2) extending from the centre of said disc base and fixed thereto; a disc holding member (7) spaced above said spindle (2); pressing means (9) arranged to press said disc holding member (7) toward said disc base (1) to clamp a disc therebetween; said disc holding member (7) comprising a first portion having a circumferentially-tapered outer surface for engagement of the center hole of a disc of the first kind, a second portion for pressing engagement of the hub of a disc of the second kind, and a centre hole (8) for receiving said spindle (2) when a disc of the first kind is clamped; characterized by said disc base (1) including magnetic means (3) positioned around said spindle (2) for magnetic interaction with the hub of a disc according to the second kind having a ferromagnetic centering hub. A disc clamping device according to claim 1, wherein the spindle (2) is arranged such that in operation it stops short of the plane in which the lower face of the disc lies when pressed on the disc base (1). A device according to claim 2, wherein the spindle (2) is axially slidable with respect to said disc base (1). A device according to claim 2, wherein the length of the spindle (2), for engagement of the centre hole (6) formed in the centering hub (5) of a disc does not exceed the thickness of the centre hub (5). A device according to any one of the preceding claims, wherein the disc holding member (7) is made of ferromagnetic material.

Inventors: JUNICHI, WASHO, KENJI, OHTA, MASAHIRO, HORII, SHIGEO, TERASHIMA, TAKAO, HYUGA, TOSHIHISA, DEGUCHI DAIYA-HAITSU GAKUENMAE C-722
Applicants: SHARP KABUSHIKI KAISHA
Application year: 1987
Main classification: G11B17
IPC codes: G11B17