WO2003096334A1

WO2003096334A1 - System comprising a registration carrier and a drive device for this

Info

Publication number: WO2003096334A1
Application number: PCT/IB2003/001540
Authority: WO
Inventors: Michiel A. H. Van Der Aa; Waltherus C. J. Bierhoff; Johannes M. M. Hensing
Original assignee: Koninklijke Philips Electronics N.V.
Priority date: 2002-05-08
Filing date: 2003-04-17
Publication date: 2003-11-20
Also published as: AU2003222617A1

Abstract

An electromagnetic device (10) comprising a stator part (12) and a rotor part (14) which is rotatable with respect to the stator part. The stator part comprises a drive coil unit (21) and the rotor part, which is provided with a support surface (24) for supporting an information disc (100), comprises a permanent-magnet unit (26) for magnetic cooperation with the drive coil unit so as to rotate the rotor part and for magnetic cooperation with a magnetic element (106) of the information disc so as to clamp the information disc against the support surface.

Description

System comprising a registration carrier and a drive device for this

The invention relates to a system comprising a disc-shaped registration carrier, also denoted information carrier, and an electromagnetic drive device for rotating the registration carrier.

US-A 4,823,337 discloses such a system. The known system comprises an optical disc and an optical playback unit for writing and/or reading the optical disc. The optical disc is provided with a central opening. The optical playback unit is provided with a turntable and an electric motor unit for driving the turntable into rotation. The turntable has a support surface for the optical disc. Opposite the turntable there is a clamping device for clamping the optical disc against the support surface of the turntable. The clamping device comprises a holder which is displaceable between an operational position and an idle position and which has a disc presser that is movably supported in the holder. In the operational position, the disc presser presses the optical disc against the support surface of the turntable. Permanent magnets present in the holder exert on the disc presser a magnetic force that is directed towards the turntable during this so as to realize the required clamping of the optical disc against the support surface of the turntable.

Although such a disc clamping device is in itself capable of providing a satisfactory clamping force, the device is less suitable for miniaturization. A reason for this is that disc scanning devices of small dimensions give rise to magnetic interference between the magnetic fields of the plate clamping device and the electric plate drive device, which jeopardizes a correct functioning of both the clamping device and the drive device.

It is an object of the invention to provide the system described in the opening paragraph with means such that both the required clamping of the registration carrier and the required rotation of the registration carrier can be realized under operational conditions also in the case of progressing miniaturization.

This object is achieved by means of the system according to the invention, which comprises a disc-shaped registration carrier with a central axis and an electromagnetic drive device for rotating the registration carrier about the central axis, wherein the registration carrier is provided with a registration area extending around and transversely to the central axis and is provided with a magnetic element, preferably in the form of an annular body surrounding the central axis, and wherein the drive device is provided with a stator part and a rotor part which is rotatable about an axis of rotation with respect to the stator part and which comprises a support surface for the registration carrier oriented transversely to the axis of rotation, and wherein the drive device comprises a drive coil unit and furthermore a permanent-magnet unit for generating a rotation of the rotor part in magnetic cooperation with the drive coil unit and for clamping the registration carrier against the support surface of the rotor part in magnetic cooperation with the magnetic element. A drive device is thus used in the system according to the invention of which the permanent-magnet part has a dual function, i.e. on the one hand cooperating with the drive coil unit for driving the rotor part into rotation, and on the other hand cooperating with the magnetic element of the registration carrier present on the support surface so as to clamp this registration carrier against the support surface of the rotor part. The magnetic element need merely be made from a soft- magnetic material, such as soft iron. A magnetic force is generated by the cooperation with the permanent-magnet unit, which comprises one or several permanent magnets, thus causing and indeed safeguarding the required clamping of the registration carrier.

If so desired, the permanent-magnet unit may have a battlement shape at its side facing the support surface, such that a number of projecting pole portions are present, directed towards the support surface. In this manner the distance between the permanent- magnet unit of the drive device and the magnetic element of the registration carrier can be attuned to the magnetic clamping force desired to be acting on the registration carrier, without this leading to concessions as regards the drive function of the permanent-magnet unit. It will be obvious from the above that the use of the electromagnetic drive device renders a separate clamping magnet for clamping the registration disc unnecessary, so that the magnetic interference occurring in miniaturization of the known magnetic clamping devices cannot arise in a miniaturized version of the system according to the invention. The system according to the invention is accordingly highly suitable for systems with small to very small dimensions, such as systems for use in personal digit assistants (PDAs), portable MP3 players, and mobile telephones. In a practical embodiment, the stator part of the drive device comprises the drive coil unit composed of one or several drive coils, and the rotor part of the drive device comprises the permanent-magnet unit. To achieve an accurate centering of the registration carrier with respect to the axis of rotation of the drive unit, it is preferable to construct the magnetic element as a hub, in particular a centering hub, said magnetic element being usually annular in shape for reasons of symmetry and being arranged around the central axis of the registration carrier. It is also preferable in this respect to provide the rotor part of the drive device with a rotatable rotor shaft with a centerline coinciding with the axis of rotation, while the hub can be centered on the rotor shaft. In a further practical embodiment, the permanent-magnet unit of the drive device is of an at least partial circular-cylindrical shape, said unit extending at least partly around the axis of rotation.

Embodiments of the system according to the invention are defined in the dependent claims 2 to 7. The invention further relates to a registration carrier, in particular a registration carrier suitable and designed for use in the system according to the invention. The registration carrier may be an optical, magnetic, or magneto-optical writable and/or readable registration carrier based on known principles. The registration carrier according to the invention, which is rotatable about its central axis when used in the system according to the invention, is provided with a disc-shaped registration area extending around and transversely to the central axis and is furthermore provided with a magnetic element that preferably surrounds the central axis. Said element may be a soft-magnetic, in particular ferromagnetic, annular element. In a practical embodiment, the registration area is present on a substrate, whereas the magnetic element extends at least partly into the substrate or is recessed therein. The magnetic element does not give the registration carrier an additional thickness thanks to this arrangement of the magnetic element. In an alternative embodiment, the substrate itself forms the magnetic element.

Embodiments of the registration carrier according to the invention are defined in claims 9 to 11.

The invention further relates to an electromagnetic drive device, in particular a drive device for driving a disc-shaped registration carrier into rotation and specially suited to and designed for the system according to the invention. This relates in particular to very small drive devices which are suitable, for example, for efficiently clamping and rotating registration carriers provided with a magnetic element with a diameter of the order of 25 to 30 mm. The drive device according to the invention has a stator part and a rotor part which is rotatable with respect to the former about an axis of rotation and which has a support surface oriented transversely to the axis of rotation and designed to support a registration carrier provided with a magnetic element, which stator part is provided with a drive coil unit, while said rotor part is provided with a permanent-magnet unit for generating a rotation of the rotor part in magnetic cooperation with the drive coil unit and for clamping the registration carrier against the support surface in magnetic cooperation with the registration carrier. The permanent-magnet unit has permanent-magnet parts of, for example, NdFeB.

The drive device according to the invention is based on the recognition that the magnetic field required for magnetic clamping may be supplied by the permanent-magnet parts of the drive device that are present anyway for the rotation, so that a separate clamping magnet can be dispensed with, while at the same time magnetic interference with such a magnet is avoided. The permanent-magnet unit used may be manufactured by a technology which is known per se. Thus the permanent-magnet unit may be constructed, for example, as a pressed magnetic body. The drive device is preferably constructed as a radial field motor, but it may alternatively be an axial field motor. Depending on the application, the number of pole pairs may vary, as may the number of drive coils cooperating therewith. Embodiments of the drive device according to the invention are defined in the dependent claims 13 to 16.

The invention also relates to a scanning device for scanning a disc-shaped registration carrier, in particular a registration carrier provided with a magnetic element. The scanning device according to the invention is provided with the drive device according to the invention and is in addition provided with a writing and/or reading unit for writing and/or reading a registration carrier which is clamped against the support surface of the rotor part of the drive device. The writing and/or reading unit may be an optical unit, but a magnetic sensor unit is equally possible.

It is noted with reference to the claims that the embodiments defined therein may occur in all possible combinations.

The invention will now be explained in more detail by way of example with reference to the drawing, in which Fig. 1 is a plan view of a diagrammatically depicted embodiment of the drive device according to the invention,

Fig. 2 is a cross-section taken on the line II-II of the embodiment of Fig. 1, Fig. 3 is a plan view of a diagrammatically depicted embodiment of the system according to the invention, in which the embodiment of Fig. 1 is used, Fig. 4 is a cross-section taken on the line IN-IN of the embodiment of Fig. 3, and

Fig. 5 is a perspective view of the permanent-magnet unit for the drive device of Fig. 1.

The following description relates to all Figs. 1 to 4. The drive device according to the invention is referenced 10 and the registration carrier according to the invention 100. The system according to the invention comprises the drive device 10 and the registration carrier 100. The drive device 10 has a stator part 12 and a rotor part 14 that can rotate with respect to the stator part 12 about an axis of rotation 16. The stator part 12 has a frame 18 provided with a magnetic yoke 19 of a soft-magnetic material and a number of drive coils 20 arranged in a circle which together form a drive coil unit 21, said drive coils 20 being coiled in a manner known per se. The rotor part 14 is provided with a raised rim 22 serving as a support surface 24 for the registration carrier 100 and has a rotor shaft 25 and a permanent-magnet unit 26 comprising a number of permanent magnets. The permanent- magnet unit 26 is circular-cylindrical in shape and extends around the axis of rotation 16, the magnets being radially magnetized. The hard-magnetic material of the permanent-magnet unit 26 is ΝdFeB. A radial bearing 28 and a thrust bearing 30 provide the support of the rotor part 14 in the stator part 12, while a member provided with a hook 34 or hooks 34 ensures the axial retention of the rotor part 14. In this example, the permanent-magnet unit 26 is provided with local elevations at its side facing the support surface 24, resulting in projecting pole portions 32 directed towards the support surface with poles 32A located close to the support surface 24. These pole portions 32 are radially magnetized, as are the other permanent- magnet parts of the unit 26. If so desired, the pole parts may be polarized in a different manner, in particular axially. In this example the permanent-magnet unit is a pressed product. The registration carrier 100 is provided with a central opening 101 having a central axis 102 and with a substrate 103 on which a registration layer forming a disc-shaped registration area 104 is present at one of the two main surfaces and in which an annular magnetic element 106 is provided at that side which is designed for being clamped against the support surface 24 of the drive device 10. The magnetic element 106 is manufactured -from a ferromagnetic material. It is noted in this context that the use of a magnetic element of a hard-magnetic material is not preferred, but is definitely an option. It is attractive for reasons of centering to design the magnetic element 106 as a centering hub 106 A, which hub 106A will then preferably be centered around the rotor shaft 25.

In the system formed by the drive device 10 and the registration carrier 100, said registration carrier 100 is pulled against the raised rim 22 of the drive device 10 in the operational position by means of a magnetic force resulting from the magnetic cooperation between the permanent-magnet unit 26 and the magnetic element 106. Further clamping devices are not necessary. The system as a result is of a simple construction, comprises only a limited number of components, and does not require an intricate or involved manufacturing method. Most of all, the system according to the invention is reliable and efficient. A combination of the drive device 0 with a writing and/or reading unit, which unit may be constructed in principle in a manner which is known per se, yields a scanning device which is particularly attractive because of the achievable small dimensions. Fig. 4 diagrammatically shows the writing and reading unit, which is referenced 200. The registration carrier 100 rotates during writing or reading, while the writing and/or reading unit is displaced over the registration carrier 100 in radial or substantially radial direction with respect to the axis of rotation 16. The unit 200 is for this purpose supported on a slide or a swiveling arm. Electronic operations on the information to be written or read take place in an electronic unit of the scanning device which is known per se and which is connected to the unit 200. A scanning device provided with the drive device 10 is highly suitable for use in portable equipment of pocket size, such as PDAs. The invention for this reason also relates to such an application. The scanning device according to the invention may be an optical, magnetic, or magneto-optical scanning device.

It is noted that the invention is not limited to the embodiments shown. Thus it is not absolutely necessary to use projecting pole portions. Furthermore, the number of magnets in the permanent-magnet unit and the number of coils in the drive coil unit are not essential to the invention. It is further noted that the term "registration carrier" also covers other usual designations such as information carrier, information disc, and data storage plate. Information may be and/or have been stored in such information media in the form of circular tracks, or quasi-circular tracks, or spiraling tracks.

Claims

CLAIMS:

1. A system comprising a disc-shaped registration carrier with a central axis and an electromagnetic drive device for rotating the registration carrier about the central axis, which registration carrier is provided with a registration area extending around and transversely to the central axis and is provided with a magnetic element, and which drive device is provided with a stator part and a rotor part which is rotatable about an axis of rotation with respect to the stator part and which comprises a support surface for the registration carrier oriented transversely to the axis of rotation, wherein the drive device comprises a drive coil unit and furthermore a permanent-magnet unit for generating a rotation of the rotor part in magnetic cooperation with the drive coil unit and for clamping the registration carrier against the support surface of the rotor part in magnetic cooperation with the magnetic element.

2. A system as claimed in claim 1, wherein the stator part comprises the drive coil unit and the rotor part comprises the permanent-magnet unit.

3. A system as claimed in claim 1 or 2, wherein the magnetic element is an annular body of a soft-magnetic material arranged around the central axis.

4. A system as claimed in claim 1, 2, or 3, wherein the magnetic element is constructed as a hub for centering the registration carrier with respect to the rotor part.

5. A system as claimed in claim 4, wherein the rotor part is provided with a rotor shaft whose centerline coincides with the axis of rotation, and on which the hub is fastened or can be fastened.

6. A system as claimed in claim 1 or 2, wherein the permanent-magnet unit is at least partly circular-cylindrical in shape and extends around the axis of rotation.

7. A system as claimed in claim 6, wherein the permanent-magnet unit is battlement-shaped at its side facing the support surface, as seen in circumferential direction of the permanent-magnet unit.

8. A registration carrier designed in particular for use in the system as claimed in any one of the preceding claims, in which application the registration carrier can be rotated about its central axis and is provided with a disc-shaped registration area extending around and transversely to the central axis, and is further provided with a magnetic element.

9. A registration carrier as claimed in claim 8, wherein the magnetic element is formed from a soft-magnetic material.

10. A registration carrier as claimed in claim 8 or 9, wherein the registration area is present on a substrate, and the magnetic element is present at least partly in the substrate.

11. A registration carrier as claimed in claim 8, 9, or 10, wherein the registration carrier is provided with a central opening, and wherein the magnetic element is annular in shape and extends into the central opening so as to have a centering rim therein.

12. An electromagnetic drive device, in particular suitable for use in the system as claimed in any one of the claims 1 to 7, which drive device has a stator part and a rotor part which is rotatable with respect to the stator part about an axis of rotation and which has a support surface oriented transversely to the axis of rotation and designed to support a registration carrier provided with a magnetic element, which stator part is provided with a drive coil unit, while said rotor part is provided with a permanent-magnet unit for generating a rotation of the rotor part in magnetic cooperation with the drive coil unit and for clamping the registration carrier against the support surface in magnetic cooperation with the registration carrier.

13. A drive device as claimed in claim 12, wherein the permanent-magnet unit has a circular-cylindrical shape and extends around the axis of rotation.

14. A drive device as claimed in claim 13, wherein the permanent-magnet unit is provided with projecting pole portions directed towards the support surface at its side facing said support surface.

15. A drive device as claimed in claim 12, wherein the permanent-magnet unit comprises radially magnetized magnets.

16. A drive device as claimed in claim 14 or 15, wherein the projecting pole portions directed towards the support surface are axially magnetized.

17. A scanning device for scanning a disc-shaped registration carrier, provided with the drive device as claimed in any one of the claims 12 to 16, and further provided with a writing and/or reading unit for writing and/or reading of a registration carrier clamped against the support surface of the rotor part of the drive device.

18. A scanning device as claimed in claim 17, wherein the writing and/or reading unit is an optical unit.

19. A portable appliance of pocket size, provided with the scanning device as claimed in claim 17 or 18.