WO2000031732A1

WO2000031732A1 - Apparatus for testing data-carrying discs

Info

Publication number: WO2000031732A1
Application number: PCT/GB1999/003894
Authority: WO
Inventors: James H. Steynor; Michael A. Cliffe
Original assignee: Aerosonic Ltd.
Priority date: 1998-11-23
Filing date: 1999-11-23
Publication date: 2000-06-02
Also published as: GB9825633D0

Abstract

The invention relates to apparatus for use in testing a data-carrying disc, such as a master digital disc from which production digital versatile discs (DVDs) or compact discs (CDs) are physically copied. The apparatus includes a holder (1) having a generally planar support surface (2) for supporting a master disc (12), and a manifold arrangement including a network or matrix of intercommunicating annular channels (2c) opening into the support surface (2) and, communicating via a valve (3b, 3c) with a port (4b) releasably connectable to a source of low pressure. In use, when a master disc (12) is positioned on the support surface (2) and the channels (2c) are evacuated via the valve (3b, 3c) and port (4b), and subsequently the valve is closed by manually tightening a screw (4a) and the low pressure source is disconnected, the master disc is held located against the support surface by the residual vacuum in the channels. Thus, the assembly comprising the holder and vacuum-clamped master disc, after the low pressure source has been disconnected, may be handles, and transferred to a player where the master disc recording is played back and its quality investigated.

Description

APPARATUS FOR TESTING DATA-CARRYING DISCS

The present invention relates to data-carrying discs, and in particular to digital discs, such as digital versatile discs (DVDs) and compact discs (CDs).

Data-carrying discs, their manufacture and testing, are disclosed, in US- A-5,579,113, 4,868,805 and 5,350,923, EP-A-495,281 , 255,088 204,378 and 94,273, DE-A-2,527,084 and 2,642,342, and AT-A-401 ,832.

More particularly, the invention relates to the testing of the quality of the recorded data on master discs (known as "stampers") from which the final or production DVDs or CDs are physically copied, for example using molding or coating techniques. A master disc or stamper is usually a relatively thin (e.g. of the order of

0.3 mm thick) nickel disc, with the readable recorded digital data in relief on one face of the disc. The disc is relatively flexible, and the recorded data is delicate and is liable to be damaged if contacted, making the disc relatively difficult to handle and test. Currently, in order to test play a master disc to ascertain the quality of its recorded data, the disc is mechanically clamped, around its central locating aperture, between a circular holder and a glass disc arrangement. The glass disc extends over the recorded face of the master disc, with a clearance or air gap therebetween intended to ensure that the recorded data will not come into contact with the glass disc, and suffer consequential damage, if the master disc should flex between its clamped inner and outer peripheries. The master disc/glass disc/holder assembly is loaded as a unit, glass disc down, onto the turntable of an appropriate disc player and played back to ascertain the quality of the recorded data. During playback, the assembly is rotated relative to an optical reading head which reads the recorded data on the face of the master disc, upwardly through the glass disc. The glass disc is intended to simulate the optical characteristics, i.e. refractive index, of the transparent substrate or layer which extends over the recorded face of the production disc, i.e. the CD or DVD, produced from the master disc, with the intention that the readout/ playback from the master disc will represent, as closely as possible, the readout/playback from the resultant production disc.

However, in practice, such a disc/holder assembly suffers from the disadvantage that flexure of the master disc may take place during playback, and a relatively large clearance or air gap is required between the recorded face of the master disc and adjacent surface of the glass disc. On the other hand, no equivalent flexing occurs in a production disc during playback, and there is no air gap between the transparent substrate and the recorded face of the production disc. Furthermore, due to the presence of the air gap, the distance between the recorded face of the master disc and the front surface of the associated glass disc is greater than the corresponding distance between the recorded rear face, and the front surface, of the transparent substrate of the production disc. Since the front surfaces of the glass disc and substrate rest on the turntable of the player during playback and therefore determine the position of the associated recorded faces relative to the focal point of the optical system of the player which reads the discs, the positions of the recorded faces relative to the objective lens of the pick-up head are not the same for the master disc and production disc. Due to these various factors, the recording played back from the master disc is not necessaπly an accurate indication of the recording played back from the resultant production disc.

Instead of mechanically clamping the master disc around its central locating aperture, it has alternatively been proposed to magnetically clamp the master disc to the holder around the periphery of the holder. However, this also gives rise to the problems described above.

It has also been proposed to magnetically clamp the master disc to the holder by magnetic clamp elements distributed across the surface of the holder which supports the disc behind the region carrying the recorded data. However, this arrangement of magnetic clamp elements, as well as the peripheral arrangement descπbed in the preceding paragraph, can give rise to the problem that the magnetic fields generated by the elements interfere with the galvanometer - controlled optical system used to read the disc.

It is an object of the present invention to provide an improved apparatus or equipment for testing digital discs such as master discs used in the manufacture of DVDs or CDs. According to the present invention, there is provided apparatus for use in testing a data-carrying disc, such as a master digital disc, which apparatus includes a holder having a generally planar support surface for supporting a data-carrying disc, and a manifold arrangement opening through said support surface, the manifold arrangement communicating via valve means with a port releasably connectable to a source of low pressure, whereby, in use, when a data-carrying disc is positioned on said support surface and the manifold arrangement is evacuated via the valve means and port, and subsequently the valve means is closed and the low pressure source is disconnected, the data- carrying disc is held located against said support surface by the residual vacuum in the manifold arrangement.

Thus, the assembly comprising the holder and vacuum-clamped disc, for example master disc, after the low pressure source has been disconnected, may be handled, and transferred to a player where the master disc recording is played back and its quality investigated. The residual vacuum in the manifold arrangement holds the master disc firmly against the planar support surface, significantly reducing or effectively eliminating the tendency for the master disc to flex. As a result, the glass or equivalent disc, if provided, may be positioned over the recorded face of the master disc with a reduced clearance or air gap without risk of the recorded data on the disc contacting, and being damaged by, the glass disc.

The manifold arrangement may include a network or matrix of intercommunicating channels opening into the planar support surface of the holder, and connected to the evacuation port via the valve means, the planar support surface being defined by extensive lands between the channels. In one embodiment, the support surface of the holder is circular, and is provided with an axial opening. The matrix of channels occupies an annular zone of the support surface bounded by concentric, radially inner and outer annular channels in the support surface. The inner and outer channels contain associated sealing rings which, in operation, sealingly cooperate with the rear face of the master disc to prevent leakage of the residual vacuum to atmosphere.

The glass or equivalent transparent disc, if provided, is not required to clamp the master disc. It will, however, have a central boss or hub bonded thereto which fits into the central locating aperture in the master disc and over a central spigot on the player turntable to positively and accurately locate and center the disc during playback.

In one embodiment, the glass disc is releasably attached to the holder, with the master disc sandwiched therebetween, by a system of magnets. For example, the holder, and preferably a central boss or hub formed integrally with the holder, is provided with an array of circumferentially spaced magnets, with adjacent magnets being of opposite polarity. The central boss or hub of the glass disc is provided with a corresponding array of circumferentially spaced magnets of alternate polarity. Thus, when the holder and glass disc are assembled with the hub of the glass disc passing through the central opening in the master disc, and located in a bore in the holder hub, the glass disc will be magnetically attracted and retained against the holder when holder and glass disc magnets of opposite polarity are aligned, while the hub of the glass disc will center both the master disc and the holder. However, the glass disc may be simply separated from the holder by magnetic repulsion when required, for example after testing when it is desired to remove the master disc, by manually rotating the glass disc and holder relative to each other to bring magnets of like polarity into or towards mutual alignment.

In order that the invention may be more readily understood, one embodiment thereof will now be described with reference to the accompanying drawings, in which:- Fig. 1 is a front elevation of a master disc holder embodying the invention; Fig. 2 is an axial section on the line X-X of the holder shown in Fig. 1 ; Fig. 3 is a rear elevation of the holder boss or hub shown in Fig. 1 (and also showing the section line X-X);

Fig. 3A is a fragmentary section on the line Y-Y in Fig. 3; Fig. 4 is an axial section of the holder, valve and hub cap assembly;

Fig. 5 is a further rear elevation of the holder hub; Fig. 6 is a rear elevation of the holder hub cap shown in Fig. 4; Figs. 7 and 8 are, respectively, an axial section and a front elevation of a glass disc arrangement for use with the holder of Figs. 1 to 6; Figs. 9 and 10 are, respectively, an axial section and a front elevation of a fixture for use with the holder and glass disc arrangement shown in Figs. 1 to 8; and

Fig. 11 is an exploded axial section illustrating the assembly of the various components. Referring to Figs. 1 to 6, the backplate or holder 1 comprises a generally circular plate or disc having a generally flat front face 2 for receiving and supporting a master disc or stamper (not shown) from which DVDs are to be molded or stamped. The holder has a rearwardly extending central boss or hub 3 provided with a stepped axial bore 3g., intended to receive and locate the hub 8 of the glass disc arrangement 6 shown in Figs. 7 and 8. The front face 2 is formed with uninterrupted, annular, radially inner and outer channels

2a, 2b, each of which contains a resilient O-ring seal 2 .. Between the inner and outer channels, an annular network or matrix of interconnected narrow annular channels 2c and radial channels 2d is formed in the front support surface as clearly shown in Fig. 1 , with flat expansive lands 2e therebetween.

A single inclined passage 2f extends from the channel matrix 2c, 2d, through the hub 3, to a rearwardly opening stepped cylindrical cavity 3a in the hub 3 which, as shown in Fig. 4, contains a valve seat 3b comprising a resilient O- ring seal, with which a valve element comprising a ball 3c is releasably sealingly cooperable. The cylindrical cavity 3a communicates, via a circumferentially extending channel 3d shown in Figs. 3 and 5, with a further rearwardly opening cylindrical cavity 3e in the hub. Diametrically opposed "dummy" cavities and an interconnecting channel, indicated generally at 3f, are provided in the hub to counterbalance the cavities 3a, 3e and channel 3d, with a view to minimizing unbalance and resultant vibration when the holder is rotated (e.g. at up to 4000 r.p.m.) during playback.

A cap 4 as shown in Figs. 4 and 6 is attached to the rear face of the hub 3. The cap is provided with a threaded bore containing a manually adjustable threaded member such as a grub screw 4a in alignment with the cavity 3a containing the ball valve 3c, and with a stepped cylindrical evacuation port 4b communicating with the further cavity 3e and containing a resilient O-ring seal 4c. For convenience and clarity, the latter port, cavity and seal are shown displaced to the bottom of Fig. 4, although it is to be understood that they are, in fact, located at the position of the upper cavity 3e as viewed in Figs. 3 and 5. The cap may also be provided with an axial aperture 4d intended to receive a fixing screw to secure the holder to the hub of the glass disc arrangement described later.

The holder 1 is formed with one or more cut-outs or reliefs, for example four equi-spaced cut-outs 5 around its periphery, as shown in Fig. 1 , the purpose of which will be described later. The holder and cap are formed from aluminum alloy or other lightweight rigid material, so as to minimise inertia and other loads imposed on the turntable of the disc player when the disc/holder assembly is rotated during playback.

When a master disc or stamper is positioned and axially aligned with its rear (unrecorded) face on the front surface 2 of the holder, its inner and outer peripheries will overly the O-ring seals 2ρ. in the inner and outer channels 2a. When the grub screw 4a is partially unscrewed to open the valve 3b, 3c, and a vacuum pump or other vacuum or low pressure source is connected to the channel matrix by an appropriate tube press-fitted into the port 4b in the hub cap 4 and resiliently and sealingly engaging the O-ring seal 4c, the channel matrix 2b, 2c will be evacuated via the channel 3f and the passage 2f. The rear face of the flexible master disc will be drawn and held firmly against the planar lands 2e on the front surface of the holder. The width/area of the lands 2e is significantly greater than the width/area of the matrix channels 2c, 2d, and the degree of vacuum applied to the matrix channels, is such that the flexible master disc will be positively held on the lands in a flat condition, without flexing or deformation to any significant degree.

When the matrix channels have been evacuated, the grub screw 4a is tightened, forcing the ball valve 3c tightly against its seat 3b and sealing off the evacuation port 4b from the passage 2f leading to the matrix channels. The vacuum pump is then disconnected from the holder by pulling its connecting tube out of the port. The dimensions/total volume of the manifold formed by the matrix channels 2b, 2c and passageway 2f are such that the manifold acts as a vacuum reservoir or plenum to maintain a sufficient residual vacuum in the matrix channels to ensure that the master disc is held in place for a significant period of time, for example two hours or more, sufficient to enable the master disc/holder assembly to be loaded into a player and played back for test purposes, without the need to replenish the vacuum. The O-ring seals 2g located in the inner an outer channels 2a, 2b in the front surface of the holder, which, under vacuum, seal against the rear (unrecorded) face of the master disc, in combination with the closed ball valve, serve to prevent or minimise leakage of the vacuum to atmosphere.

The holder 1 is used in combination with a glass disc arrangement 6 as shown in Figs. 7 and 8. The arrangement comprises a glass disc 7 having a stepped hub 8, for example of aluminum alloy, mounted on, for example bonded to, its rear surface. The hub is configured to locate in the bore 3g in the holder hub 3, and includes a tapered root portion 8a terminating in a radially extending spacer flange 8b. The hub 8 is also provided with pockets containing a circumferential array of magnets 8c of alternate polarity, on a pitch circle diameter, and of a number and spacing, corresponding to an array of alternate polarity magnets 3h (see Figs. 4 and 5) located in opposing pockets in the holder hub 3. The outer periphery of the glass disc 7 is enclosed in an annular, radially inwardly opening, generally U-section spacer ring 9 provided with one or more pairs of diametrically opposed cut-outs or reliefs 9a. The side wall 9b of the spacer ring on the rear surface of the glass disc, in use, cooperates with the outer periphery of the front face of a master disc, to accurately predetermine, in that region, the stand-off or separation between the rear surface of the glass disc and the front face of the master disc. The stand-off or separation in the region of the inner periphery of the master disc is determined by the thickness of the spacer flange 8b. Figs. 9 and 10 illustrate a fixture or jig 10 which may be used to assemble the holder, glass disc arrangement and a master digital disc to be tested. The fixture comprises a circular plate having a surface 1 1 which, in use, is oriented to face upwardly (see Fig. 1 1 ). This upper surface is provided with an annular recess 1 1 a defining radially inner and outer annular lands 1 1 b and 1 1 c respectively. The outer land 1 1 c is provided with a pair of diametrically opposed locating pegs l id, and the inner land 11 b is provided with an axial locating peg 1 1 e.

In use, and with reference to Fig. 1 1 , firstly, the glass disc arrangement 6 is placed front face-down on the upper surface of the fixture 10, with the spacer ring 9 resting on the outer land 1 1 c and with two of its diametrically opposed reliefs 9a located by the pegs 1 1 d.. The axial peg 1 1 e is located in the bore in the hub 8, and the front face of the glass disc covered by the hub rests on the inner land 1 1 b. The annular zone of the front surface of the glass disc through which, during testing, the recorded digital data on the master disc is read, overlies the annular recess 1 1 a, so that it is not scratched or otherwise damaged by contact with the fixture.

A master disc or stamper 12 is then lowered front (recorded) face down onto the rear of the glass disc arrangement, guided by the inclined root portion 8a of the hub which cooperates with the central aperture in the master disc. The master disc rests on the spacer flange 8b of the hub and side wall 9b of the spacer ring to space the recorded digital data on the front face of the master disc from the glass disc. The hub accurately centers the master disc.

The backplate or holder 1 is then lowered front surface down onto the rear face of the master disc, engaging the holder hub 3 over the hub 8, centering the hub 3 and holder 1 , and opposite polarity magnets 3h and 8c are brought into alignment to magnetically clamp the holder and glass disc arrangement together. The vacuum pump tube is then pressed into the evacuation port 4b in the holder hub cap 4 and the channel matrix 2c, 2d evacuated, the valve 3b, 3c closed, and the vacuum pump tube removed, as described earlier. The master disc/glass disc/holder assembly is then removed from the fixture 10, and transferred to a turntable of a disc player, where it is mounted, glass disc-down, on the player turntable, with the hub 8 of the glass disc located over a central spigot of the turntable to center the assembly. The assembly is rotated and the recorded digital data is read from the master disc upwardly through the glass disc. The read-out data is then played back, and tested/processed as required to determine its quality, etc.

Following completion of the test procedure, the grub screw 4a is loosened to release the ball valve 3c and allow the residual vacuum in the channel matrix to leak away. The glass disc arrangement is turned relative to the holder to bring like polarity magnets 3h and 8c into alignment, causing or facilitating separation of the glass disc arrangement and holder by magnetic repulsion. Turning and separation may be facilitated if necessary by using the cut-outs or reliefs 5 and/or 9a as finger holds. The master disc is then removed from the holder, assisted by using the cut-outs or reliefs 5 in the holder which underlie and give access to the outer periphery of the master disc. The master disc is then used to produce multiple copies, e.g. CDs or DVDs, provided that the recorded data on the master disc passed the necessary tests.

Since the master disc is vacuum-clamped to the holder surface by the residual depression in the channel matrix during handling of the assembly and execution of the text procedures, flexing of the master disc is effectively eliminated. This improves the consistency and reliability of the test procedures, since the master disc is maintained flat during read-out. In addition, the separation between the front face of the master disc and the adjacent rear face of the glass disc may be significantly reduced, for example from about 0.5 mm to about 0.2 mm for a 0.3 mm thick, 120 mm diameter, nickel master disc, without risk of the recorded data on the front face being damaged or degraded by coming into contact with the glass disc. This reduction in separation results in the reading of the data via the optical system of the read-out head of the player to match more closely the read-out from a resultant production CD or DVD.

Since the master disc is held in place by a residual vacuum, without the use of mechanical clamping mechanisms, and the vacuum source is disconnected after initial evacuation, the weight of the assembly may be reduced to a minimum, correspondingly reducing the loads on the player turntable.

It will be understood that various modifications may be made without departing from the scope of the present invention.

For example, the holder, glass or other transparent disc arrangement, and/or fixture may be made in different sizes to accommodate DVD, CD or other digital master discs of different sizes.

The configuration, number, size, and/or distribution of the channels or equivalent in the matrix may be changed. The bail valve arrangement may be replaced by other types of valves, which may be self-sealing or automatic, instead of manually actuated. The valve may, for example, be combined with the releasable coupling or port for connection to the vacuum source.

The magnetic attachment/release arrangement may be positioned in other regions of the hubs of the holder and glass disc arrangement. For example, the holder magnets may be mounted in pockets in the hub cap 4, and the glass disc magnets may be located in the rear face of the hub thereof. Additionally or alternatively, magnets may be associated with the outer, periphery or rim of the holder, and the rim, or spacer ring 9 of the glass disc. Although six holder magnets are shown in Fig. 5, fewer or more pairs of holder and glass disc magnets may be employed. Additionally or alternatively, the holder and glass disc arrangement may be connected together by a screw extending through the axial aperture 4d in the holder hub cap 4. The holder, with or without the glass or other transparent disc arrangement, may be used to accommodate other types of data-carrying flexible discs which are to be tested. The discs may be master discs, intermediate discs used in the manufacture of the final or production discs (e.g. DVDs or CDs) from master discs, or the final or production discs themselves, which may be tested. The holder possesses the advantage that it can be used to test discs, for example production discs, which are warped.since it serves to hold them flat during testing. The holders may also be used to accommodate discs which carry readable data on both faces, for example discs known as half-discs, which carry data on one face and which are bonded together to form double-sided discs, such as DVDs known as DVD-9s.

Claims

1. Apparatus for use in testing a data-carrying disc, which includes a holder having a generally planar support surface for supporting a data-carrying disc, and a manifold arrangement opening through said support surface, the manifold arrangement communicating via valve means with a port releasably connectable to a source of low pressure, whereby, in use, when a data- carrying disc is positioned on said support surface and the manifold arrangement is evacuated via the valve means and port, and subsequently the valve means is closed and the low pressure source is disconnected, the data- carrying disc is held located against said support surface by the residual vacuum in the manifold arrangement.

2. Apparatus as claimed in claim 1 , wherein the manifold arrangement includes a network or matrix of intercommunicating channels opening into the planar support surface of the holder, and connected to the evacuation port via the valve means, the planar support surface being defined by extensive lands between the channels.

3. Apparatus as claimed in claim 2, wherein the support surface of the holder is circular, and is provided with an axial opening and wherein the matrix of channels occupies an annular zone of the support surface bounded by concentric, radially inner and outer annular channels in the support surface, the inner and outer channels containing associated sealing rings which, in operation, sealingly cooperate with the rear face of the data-carrying disc to prevent leakage of the residual vacuum to atmosphere.

4. Apparatus as claimed in claim 3, including a disc of glass or equivalent transparent material which, in use of the apparatus, is releasably attached to the holder overlying the recorded face of the data-carrying disc without clamping the data-carrying disc, the transparent disc having a central boss or hub bonded thereto which fits into a central locating aperture in the data- carrying disc and over a central spigot on a player turntable to positively and accurately locate and center the data-carrying disc during playback.

5. Apparatus as claimed in claim 4, wherein the transparent disc is releasably attached to the holder, with the data-carrying disc interposed therebetween, by a system of magnets.

6. Apparatus as claimed in claim 5, wherein the holder includes a central boss or hub provided with an array of circumferentially spaced magnets, with adjacent magnets being of opposite polarity, and the central boss or hub of the transparent disc is provided with a corresponding array of circumferentially spaced magnets of alternate polarity, whereby, when the holder and transparent disc are assembled with the hub of the transparent disc passing through the central aperture in the data-carrying disc, and located in a bore in the holder hub, the transparent disc will be magnetically attracted and retained against the holder when holder and disc magnets of opposite polarity are aligned, while the hub of the transparent disc will center both the data-carrying disc and the holder, and whereby the transparent disc is separable from the holder by magnetic repulsion when required by rotating the transparent disc and holder relative to each other to bring magnets of like polarity into or towards mutual alignment.