RADIAL DAMPING MECHANISM FOR TURNTABLE IN CD PLAYER

Abstract: The invention relates to a turntable for a CD player, more specifically a reference player. A damping mechanism is mounted between the rotary shaft and the turntable to prevent radial vibrations in the shaft from being transmitted to the turntable. The turntable is fitted such that, by means of a plurality of ball bearings and a plurality of spring-loaded elements, a certain amount of radial freedom of movement relative to the shaft is ensured.

Description: Radial damping mechanism for turntable in CD player The invention relates to a turntable to be used in a CD player or recorder, comprising a bearing-mounted shaft to which a tray is attached for supporting a CD. More specifically, the invention relates to a turntable for so- called reference players. Reference players are used for testing Compact Disks (CDs) which have been pressed in a die. The testing is aimed at evaluating the quality of the die, as the pressing causes it to be subject to wear. Reference players are particularly used to determine the radial displacement of the track of the pressed CD relative to a nominal track, the so-called radial noise. This noise, expressed in a distance value, shall be limited to several to a dozen nanometres. The radial noise can be measured by scanning the track in the usual way with the aid of a light beam connected to a scanning arm. The radial noise level of the track can be measured on the basis of the positional error of the scanning arm. The frequency spectrum of the radial noise is in the order of 500 to 10,000 Hz in single speed mode. A problem encountered with reference players is that the bearing of the shaft incorporated in the turntable adds a certain amount of additional noise which is indistinguishable from the radial noise produced by the CD, which is due to the fact that the frequency spectrum overlaps the frequency spectrum of the radial noise produced by the CD. A well-known solution to this problem is seen in the application of a liquid-filled bearing, which introduces much less noise in comparison with the radial noise produced by the CD. This has the drawback that liquid-filled bearings are expensive compared with ball bearings. The turntable according to the invention is designed to provide a far cheaper solution enabling the continued use of a ball bearing. It is thereto characterized in that the fastening means between the bearing-mounted shaft and the tray comprises a damping mechanism for damping radial vibrations of the shaft relative to the tray. An advantageous, simple and comparatively low-cost embodiment is characterized in that the damping mechanism comprises a first bearing surface mounted at least substantially perpendicularly to the rotary shaft and a second bearing surface mounted at least substantially parallel to the first bearing surface and connected to the object, a plurality of roller elements which contact with the bearing surfaces and a plurality of spring-loaded elements fitted between the tray and the rotary shaft. The damping mechanism according to the invention will now be described with reference to the following figures of which Fig. 1A represents a cross-section of the damping mechanism according to the invention; Fig. IB represents a top view of a segment of Fig. 1A. The figure shows a cross-section of a turntable 1, connected to a rotary shaft 2 which is supported in a ball bearing 3 and is actuated by drive motor 4. Turntable 1 is provided with an at least substantially cylindrical projection 5 concentric with the shaft 2. A CD (not shown) having a centre hole can be clamped on the turntable 1 by moving the hole over a clamping mechanism 6. The clamping mechanism 6 comprises a substantially cylindrical body of rotation, known in the art, which fits the cylindrical projection 5 and is on the periphery provided with a plurality of spring lugs 7 which lock into the hole, thus being able to clamp the CD in position. The CD is additionally held in position by a cap 8, which is placed on top of the CD and is magnetically clamped to the projection 5 in the centre of the turntable 1. The rotation of shaft 2 will set up radial vibrations, indicated by double arrow 9, in ball bearing 3, the vibrations being transmitted to the shaft 2. The damping mechanism is designed to shield the turntable 1 from the effects of these radial vibrations occurring in the shaft 2. To that end, a first bearing surface 10 is connected substantially perpendicularly to the shaft 2 and a second bearing surface 11 is connected to the turntable 1. The bearing surfaces in the example of the embodiment form a circular band around the shaft 2. The second bearing surface 11 and the first bearing surface 10 are separated by a plurality of preferably three, identical ball bearings or other spherical elements 12, disposed substantially equidistantly in a circle around the shaft 2, of which one is shown in the figure. The ball bearings in this case make contact with the bearing surfaces 10 and 11, which are preferably made from metal carbide. The ball bearings are separated by means of a cage construction (not shown) . At the same time, the bearing surfaces 10 and 11 are pulled together by means of a plurality of, preferably six, helical springs 13, likewise disposed in a circle around the shaft 2, of which one is shown in the figure. The springs 13 are preferably fitted on either side of a ball bearing. This construction gives the second bearing surface 11 a certain amount of radial freedom of movement relative to the rotating shaft 2. Besides, the turntable 1 has a certain amount of rotational freedom of movement relative to the shaft 2. In axial direction, the connection is rigid because the springs 13 press the bearing surfaces against the ball bearings 12. The principle of operation of the damping mechanism is as follows. If a radial vibration is set up in the shaft 2, the turntable 1 will, as a result of its mass inertia, ensure that practically no radial vibration is transmitted to the CD, the cap 8 and the additional components connected to the turntable, because in radial direction it is fitted to the shaft 2 by means of springs. The ball bearings 12 ensure a friction-free relative translation of the bearing surfaces. The damping will be greater as the mass inertia of the turntable in combination with the CD it carries is greater. Besides, in actual practice a certain measure of viscous and/or coulomb friction will always occur, or more generally a force which opposes a motion of the turntable and which is preferably greater as the speed of radial motion of the turntable relative to the shaft is greater. The viscous damping with reference to the mass of the turntable and the total spring constant of the fitted springs is preferably selected such that the turntable is damped beyond a critical value so that no oscillations occur. The bandwidth of the overall system of springs and turntable and the masses connected thereto shall preferably not exceed 100 Hz. This gives a sufficient separation of the frequency band from the radial noise on the track of the CD. A suitable viscous damping can for instance be obtained by the correct choice of material for bearing surfaces 10 and 11. The springs are preferably fitted parallel to the shaft 2. In this position, the transmitted radial forces are at least in the rest position theoretically equal to zero. Only a minor deviation of the turntable from the rest position will cause the springs to extend slightly, so that the turntable is pulled back to the rest position. Thus, under application of an otherwise stiff spring, a weak recoil strength is obtained. A high spring stiffness is of course required to press the bearing surfaces against the ball bearings, a low spring stiffness, on the other hand, conduces to an improved vibration damping. This is accomplished by fitting the springs parallel to the shaft 2. In addition to the embodiment set out above, an embodiment is conceivable in which the second bearing surface 11 is located under the first bearing surface 10 so that in the operating position, the turntable is suspended from the springs.

Claims: Claims : 1. Turntable to be used in a CD player or recorder, comprising a bearing-mounted shaft to which a tray is attached for supporting a CD, characterized in that the fastening means between the bearing-mounted shaft and the plate comprises a damping mechanism for damping radial vibrations of the shaft relative to the tray. 2. Turntable as claimed in claim 1, characterized in that the damping mechanism comprises a first bearing surface mounted at least substantially perpendicularly to the rotary shaft and a second bearing surface mounted at least substantially parallel to the first bearing surface and connected to the object, a plurality of roller elements which contact with the bearing surfaces and a plurality of spring-loaded elements fitted between the tray and the rotary shaft. 3. Damping mechanisme for damping radial vibrations of a rotary shaft relative to an object capable of rotation about the rotary shaft, for instance a turntable, characterized by a first bearing surface mounted at least substantially perpendicularly to the rotary shaft and a second bearing surface mounted at least substantially parallel to the first bearing surface, a plurality of roller elements which contact with the bearing surfaces and a plurality of spring-loaded elements fitted between the object and the rotary shaft. 4. Damping mechanism as claimed in claim 3, characterized in that the roller elements comprise spherical elements. 5. Damping mechanism as claimed in claim 3, characterized in that the spring-loaded elements comprise helical springs. 6. Damping mechanism as claimed in claim 3, characterized in that the spring-loaded elements are fitted substantially parallel to the rotary shaft. 7. Damping mechanism as claimed in claim 3, characterized in that the spring-loaded elements are disposed at least substantially equidistantly in a circle concentric with the shaft. 8. Damping mechanism as claimed in claim 3, characterized in that there is furthermore provided a cage in which the roller elements are fitted such that they can move at least substantially equidistantly and at least substantially on a circle concentrical with the rotary shaft.

Inventors: BOUWMEESTER FRED, HERMANS NICOLAAS JOZEF MARIE, VERBURG CORNELIS, BOUWMEESTER, FRED, HERMANS, NICOLAAS, JOZEF, MARIE, VERBURG, CORNELIS
Applicants: BOUWMEESTER FRED, HERMANS NICOLAAS JOZEF MARIE, HOLLANDSE SIGNAALAPPARATEN BV, VERBURG CORNELIS, BOUWMEESTER, FRED, HERMANS, NICOLAAS, JOZEF, MARIE, HOLLANDSE SIGNAALAPPARATEN B.V., VERBURG, CORNELIS
Application year: 1997
Main classification: G11B19
IPC codes: F16C19, F16F7, F16F15, G11B19, G11B33