Turntable assembly, method of manufacturing a turntable assembly, and disc player comprising a turntable assembly

Abstract: The invention relates to a turntable assembly for use in a disc player for rotating an optical or magneto-optical disc about an axis of rotation. The turntable assembly comprises a drive shaft (1), a turntable body (3) and a supporting ring (5) forming a supporting surface (P) for the disc. The turntable body is an injection-moulded product formed around the drive shaft by means of an injection moulding process and connected to the supporting ring while it is being moulded.

Description: Method of manufacturing a turntable assembly, turntable assembly obtainable by the method, and disc player comprising a turnable assembly. The invention, relates inter alia , to a method of manufacturing a turntable assembly for use in a disc player, in particular for rotating an optical or magneto-optical disc about an axis of rotation, in which method a drive shaft, a turntable body and a supporting ring are formed into an integral unit, as well as to a turtable assembly obtainable by such a method. Such a turntable assembly is known from US-A 4,679,185 and is commercially available and used in a disc player suitable for optically scanning an audio and/or a video disc, as is disclosed in for example said United States Patent Specification. The known turntable assembly comprises an aluminium turntable body, a steel drive shaft and a rubber supporting ring. The turntable body, which is manufactured on a lathe, has a central bore in which the drive shaft is fitted with a specific press-fit. The turntable body has a preformed surface to which the supporting ring is secured with a suitable type of adhesive. In order to ensure that the position of the supporting surface for the disc to be scanned, which surface is defined by the supporting ring, is correct within narrow tolerances the supporting ring is finished, for example by grinding, after it has been secured to the turntable body. A disadvantage of the known turntable assembly is the comparatively high manufacturing cost as a result of the rather laborious manufacturing method comprising a plurality of successive steps. These steps include the manufacture of the turntable body by means of a lathe, mounting and securing the drive shaft in the central bore of the turntable body, cementing the supporting ring to the turntable body and finishing the supporting ring. It is an object of the invention to provide a novel method enabling a turntable assembly to be manufactured in an efficient manner. To this end the method in accordance with the invention as defined in claim 1 is characterized in that the drive shaft and the supporting ring are placed in an open mould in such a way that the drive shaft extends perpendicularly to a reference face of said mould and the supporting ring extends parallel to said reference face, after which the mould is closed and the turntable body is formed around the drive shaft and is also connected to the supporting ring by injection-moulding. In the method in accordance with the invention the position of the drive shaft and the supporting ring relative to one another is dictated wholly by the mould. This has the advantage that during injection of the plastics into the mould the entire turntable assembly is formed, the supporting surface, formed by the supporting ring, and the drive shaft occupying exactly the desired concentric and perpendicular position relative to one another without any additional operations or treatments being required. The inventive method is very suitable to be mechanized, enabling cheap turntable assemblies of accurate dimensions to be manufactured in series production by means of one accurately manufactured mould. For specific uses it may be desirable to provide an additional strenghtened bond between the supporting ring and the turntable body. The invention then provides a solution in that the supporting ring, before it is placed into the mould, is provided with an adhesive layer on one side, after which the supporting ring is positioned in the mould in such a way that the turntable body is formed on said side provided with the adhesive layer. The adhesive is suitably a thermoplastic material which more or less fuses with the plastics in the process of injection moulding. The invention further relates to a turntable assembly obtainable by the method according to the invention. In this way a construction is obtained which is manufactured at least as accurately as but more simply and cheaply than the known turnable assembly. In the turnable assembly in accordance with the invention as defined in claim 7 the turnable body is an injection-moulded or diecast product which is formed around the drive shaft by an injection-moulding or diecasting method and which is secured to the supporting ring while being formed. Consequently, the turntable assembly in accordance with the invention comprises a turntable body which is formed in one manufacturing step, during which, in addition, the drive shaft and the supporting ring are connected to the turntable body in an accurately defined position relative to one another. In an embodiment of the turntable assembly in accordance with the invention the turntable body is made of a glass-reinforced plastics. Such a plastics, for example polycarbonate containing 30% of glass in the form of spheres, yields very favourable results. It is found that such a plastic enables the formation of tonsile and shrinkage stresses to be controlled effectively, thereby precluding deformations and/or cracking of the turntable body. It is to be noted that GB-A 2,063,548 describes a two-part turntable comprising an upper part and a lower part. The lower part is a moulded plastics part which can be coupled to a drive means and in which a metal bearing bush is secured. The upper part, which may also be made of a plastics, forms a supporting surface for a conventional audio disc and is detachably connected to the lower part by a snapped connection. The known turntable does not really resemble the turntable assembly in accordance with the invention both in respect of its construction and the attainable wobbling tolerance of the supporting surface. It is another object of the invention to provide a disc player which comprises a frame, an optical scanning unit and a turntable assembly in accordance with the invention, the assembly comprising a turntable body formed around a drive shaft and connected to a supporting ring by injection-moulding. The disc player in accordance with the invention as defined in claim 9 further comprises an electrical drive unit secured to the frame, for rotating the turntable assembly, the turntable assembly carrying means for centring the disc. The invention will now be described in more detail, by way of example, with reference to the accompanying drawings, in which Fig. 1 is a plan view of a turntable assembly in accordance with the invention, Fig. 2 is a sectional view taken on the line II-II in Fig. 1, Fig. 3 is a longitudinal sectional view of a centring member cooperating with turntable assembly shown in Fig. 1, Fig. 4 shows a part of a disc player partly in a cut-away perspective view and partly in exploded view, and Fig. 5 shows diagrammatically a mould for the manufacture of the turntable assembly in Fig. 1. The turntable assembly in accordance with the invention shown in Figs. 1 and 2 comprises a drive shaft 1, a turntable body 3 and a supporting ring 5. The drive shaft 1 is a metal, preferably steel, shaft, and the supporting ring is made of rubber, for example styrene or butadine rubber or chloroprene rubber. The turntable body 3 is an injection-moulded plastics product which is formed around the drive shaft 1 in a suitable mould. In order to improve the fixation of the turntable body 3 relative to the drive shaft 1 the latter is provided with a profile 1a. During manufacture of the turntable body 3 the supporting ring 5 is connected to said body. Generally, the supporting ring 5 will be provided with a thin layer of an adhesive at the side indicated by the numeral 7. The side 9 of the supporting ring 5, which extends parallel to the side 7, forms a supporting surface P for an optical or a magneto-optical disc to be scanned. The turntable assembly is rotatable about an axis of roation 11 which coincides with the central axis of the drive shaft 1 and which extends perpendicularly to said supporting surface P. The turntable assembly is constructed to cooperate with a centring member 13 (see Fig. 3). For this purpose the turntable body 3, which in the present example is made of polycarbonate reinforced with glass spheres, is formed with three openings 15, 16 and 17. The centring member 13 shown in Fig. 3, which is also made of a plastics, for example polycarbonate containing 20% of glass, comprising three fixing hooks, of which only one hook bearing the reference numeral 21 is visible in the drawings. In the assembled condition of the centring member 13 these three fixing hooks engage the openings 15, 16 and 17 respectively, a compression spring 23 being arranged between the central member 13 and a mounting surface 3a of the turntable body 3. The centring member 13 shown in Fig. 3 comprises two conical centring surfaces 25 and 27 for centring a Compact Disc and a Laser Vision disc respectively. In order to enable both centring facilities to be used the centring member 13 is axially movable to a limited extent relative to the turntable assembly in the assembled condition. The combination to be formed by the turntable assembly shown in Figs. 1 and 2 and the centring means shown in Fig. 3 is very suitable for use in an optical disc player. Fig. 4 shows an example of such a use. The disc player in accordance with the invention shown in Fig. 4 comprises a frame 31, to which an electric motor 33 having a motor shaft is secured. The motor shaft is constituted by the drive shaft 1 carrying the turntable body 3 with the supporting ring 5 secured thereto by injection moulding. For the purpose of centring an optical disc to be scanned the centring member 13 is centrally mounted on the turntable body 3. The electric motor 33 serves for rotating the turntable assembly about the axis of rotation 11 and also serves for supporting the turn table assembly. The disc player further comprises a slide 35 which is pivotable and translatable relative to the frame 31 and which carries an optical unit 37. The optical unit 37 comprises inter alia a laser, a collimator lens, a read diode, and an angular-position detector 39, and in addition it comprises a focus actuator 41 having an objective 43 with an optical axis 43a. The focus actuator may be of the type as described in European Patent Application 0,268,311. The pivotable slide 35 is supported directly in the frame 31 by slide-supporting means. The slide supporting means is constructed in such a way that the slide is capable of performing both a displacement in a radial direction and a pivotal movement about a pivotal axis 45 which is stationary relative to the frame 31. For this purpose the slide-supporting means comprises two supports 47 and 49. The support 47 comprises a shaft end portion which is adjustably secured to the frame 31 and which engages in a groove 51 formed in a longitudinal side of the slide 35. The support 49 comprises a rounded projection on the frame 31 and slidably supports a bearing surface 53 at the underside of the slide 35. The slide 35 is provided with a gear-rack construction 55 which cooperates with a pinion 57 of a slide drive unit 59. The slide drive unit serves for radially moving the objective 43 relative to the axis of rotation 11 of the turntable assembly, between a first position situated near the turntable assembly and a second position which is more remote therefrom. The present disc player further comprises an actuating element 61 which slidably engages an opening in the slide. One end of the actuating element 61 comprises a coupling portion 63 for cooperation with an eccentric mechanism 65 and an electrical drive unit 67. The angular-position detector 39 on the slide can be used for controlling the drive unit 67 to orient the optical axis 43a of the objective 43 perpendicularly to an optical disc placed on the supporting surface of the turntable assembly, i.e. to the side facing the objective. The method in accordance with the invention will now be described in more detail with reference to Fig. 5. By means of this method the turntable assembly described in the foregoing or a similar turntable assembly is manufactured in a multi-part mould. The mould mainly comprises two separable mould sections, i.e. a first mould section 71a and a second mould section 71b. The facing sides of the mould sections are formed with a plurality of moulding features which, in the closed condition of the mould, bound a cavity 73 whose contours correspond to those of the turntable body to be formed. The mould section 71b, which may be constructed as a stationary mould section, has a supporting surface 75 for supporting the rubber supporting ring 5. In the present example the supporting surface 75 coincides with a reference face 77 of the mould section 71b. At the location of the supporting ring 5 the mould section 71b has a circularly cylindrical centring rim 76 which changes to a conical moulding feature 78 in the cavity 73. The mould section 71b has an opening 79 whose central axis 79a is oriented perpendicularly to the reference face 77 for accurately positioningg the drive shaft 1. In the opening 79 a compression spring 80 is arranged. The first mould section 71a is movable relative to the mould section 71b along the axis 79a. In the position shown the mould is ready to form a turntable assembly in accordance with the invention. For this purpose a suitable plastics is injected into the mould cavity 73 via supply ducts not shown, the turntable body 3 being formed around the drive shaft 1 and being connected to the supporting ring 5 as the cavity is filled.

Claims: A method of manufacturing a turntable assembly for use in a disc player, in particular for rotating an optical or magneto-optical disc about an axis of rotation, in which method a drive shaft (1), a turntable body (3) and a supporting ring (5) are formed into an integral unit, characterized in that the drive shaft and the supporting ring are placed in an open mould (71a, 71b) in such a way that the drive shaft extends perpendicularly to a reference face (77) of said mould and the supporting ring extends parallel to said reference face, after which the mould is closed and the turntable body is formed around the drive shaft and is also connected to the supporting ring by injection-moulding. A method as claimed in Claim 1, characterized in that the supporting ring (5), before it is placed into the mould (71a, 71b), is provided with an adhesive layer on one side, after which the supporting ring is positioned in the mould in such a way that the turntable body (3) is formed on said side. A method as claimed in Claim 1 or 2, characterized in that the supporting ring (5) is centred around a circularly cylindrical centring rim (76) of the mould (71a, 71b). A method as claimed in Claims 1, 2 or 3, characterized in that the turntable (3) is made of a glass-reinforced plastics. A method as claimed in Claim 1, 2, 3 or 4, characterized in that a metal shaft is used as drive shaft (1). A method as claimed in Claims 1, 2, 3, 4 or 5, characterized in that a rubber ring is used as supporting ring (5). A turntable assembly for use in a disc player, in particular for rotating an optical or magneto-optical disc about an axis of rotation, the assembly comprising a drive shaft (1), a turnable body (3) secured to the drive shaft, and a supporting ring (5) secured to the turntable body and forming a supporting surface for the disc, characterized in that the turntable body is an injection-moulded or diecast product which is formed around the drive shaft by an injection moulding or diecasting method and which is secured to the supporting ring while being formed. A turnable assembly as claimed in Claim 7, characterized in that the turnable body is made of a glass-reinforced plastics. A disc record player comprising a turntable assembly as claimed in Claim 7 and comprising a frame (31), an optical scanning unit (37) and an electrical drive unit (33) secured to the frame, for rotating the turntable assembly, the turntable assembly carrying means (13) for centring a disc.

Inventors: HARTOG PIETER, HARTOG, PIETER
Applicants: PHILIPS NV, N.V. PHILIPS' GLOEILAMPENFABRIEKEN
Application year: 1989
Main classification: G11B17
IPC codes: B29C45, G11B17, G11B3, G11B19