GB2352078A - Focusing/tracking limit bumpers for an optical pickup - Google Patents

Abstract

An optical pickup device includes noise damping resilient bumpers at the mechanical focussing and/or tracking limits 29,30,36,37 of a focus/tracking actuator 1 for moving an objective lens 2. The mechanical limits may form part of a rigid support means eg frame 4 having the resilient bumpers 40,41 disposed between the support and the actuator, or be included on the actuator eg as end stops about the objective lens. The actuator can be supported in a cradle 4, the cradle being attached to the support by two pairs suspension wires 16,17 and 18,19 to neutrally bias the actuator. The bumpers can be domed in construction. Use of the bumpers aims to suppress or eliminate rattling of the actuator caused by external vibrations eg in an optical disc player in a moving vehicle.

Description

2352078 Optical Media Pickup Anti-rattle The present invention relates to

a means f or suppressing externally induced rattle of an optical media pickup for 5 reading from and/or writing to an optical storage medium.

Optical media, such as optical discs, card or tape, are usually read and/or written to by an optical pickup containing an objective lens mounted in a voice coil actuator which performs focus and optionally tracking on the optical media. The objective lens is normally mounted in a carriage on a suspension, f or example at the ends of flexible or hinged arms, with a biasing means that biases the lens to a neutral position of ten at the centre of a f ocussing range of about 1 mm. The f ocus motor is usually a voice coil actuator, which moves between limits such as end stops that protect the f ocus actuator or lens f rom potential mechanical damage.

During normal operation in focussing on optical media, the end stops should never be reached, as a f ocus servo will keep the pickup focussed on the optical media. When the optical pickup is not being used, it may be moved of f to one side of the optical media, so that the lens is no longer in position to read/write to/from the media.

The inventors have noted a problem with Compact Disc (CD) optical pickups in motor vehicles. Engine, road and wind noise reduction and rattle elimination is always desirable to provide for a quieter ride. In a very quiet car, rattles were noted in a CD player when the car was driven on a bumpy surf ace. The source of the noise was traced to the CD pickup hitting the f ocus end stops when the pickup was in a parked position, owing to vertical vehicle movement and vibrations.

GB198-1517 01 July 1999 It is an object of the present invention to provide an optical media pickup with improved rattle characteristics.

Accordingly, the invention provides an optical pickup for reading from and/or writing to an optical storage medium, the optical pickup comprising one or more sources of light, an objective lens, a focus and/or tracking actuator f or moving the lens to f ocus and/or track the light on the optical medium and mechanical limits to limit the focus and/or tracking movement of the lens; characterised in that the mechanical limits include a resilient structure to dampen noise from the actuator hitting the limits.

The mechanical limits are those portions of the structure of the pickup, whether of a moving actuator or of a stationary structure, that define the limits to movement of the actuator.

Because the resilient structure dampens noise from the actuator hitting the stops, rattling of the actuator is suppressed or eliminated.

The mechanical limits may be defined by the construction of the optical pickup, for example being provided by end stops about the lens and separated by a spacing along an axial focus direction of the lens, or along a tracking direction transverse to the axial position.

The light may be any suitable visible or invisible light source, for example, near infra-red laser light or LED light.

The term optical media includes optical disc, tape and card media. These include read-only media such as compact GB198-1517 01 July 1999 discs, and read/write/erase media such as those using magneto-optic materials.

In a preferred embodiment of the invention, the optical pickup is moved to a park position away f rom the optical medium when not being used with such an optical medium.

The optical pickup may be used in an optical media system in a vehicle, such as a motor car, which will be subject to vibrations from the road when moving.

The invention will now be further described, by way of example, with reference to the accompanying drawings, in which:

Figure 1 is a schematic view of a focusand tracking actuator of an optical pickup as seen from inside the pickup along the optical axis ot an objective lens; Figure 2 is a cross-section through the actuator of Figure 1, taken along line II-II; Figure 3 is a cross-section through the actuator of Figure 1, taken along line III-III; and Figure 4 is a schematic view of an optical pickup comprising the focus and tracking actuator being used with an optical disc.

Figures 1, 2 and 3 show a f ocus and tracking voice coil actuator I of conventional design f or an optical pickup.

The actuator has an objective lens 2 with a numerical G81 96-1517 01 July 1999 aperture of 0.6 held in a surrounding cradle 4. The cradle 4 supports pairs of coils 6, 8. One pair of coils 6 has a common axis 10 transverse to an optical axis 12 of the lens, and serves as a tracking actuator. The other pair of 5 coils 8 has a common axis coincident with the optical axis 12 and serves as a focus actuator.

When electrical current is passed through a pair of coils 6,8, this generates a magnetic field which then interacts with a permanent magnetic field produced by a pair of permanent magnets 14 on opposite sides of the optical axis 12, in order to drive the cradle and objective lens along either the tracking axis 10 or the focus axis 12.

The cradle is supported by four straight suspension wires 16,17,18,19, which are arranged in pairs 16,17 and 18,19. As shown in Figure 2, one pair 16,17 is generally above the coils 6,8 and the other pair 18,19 is generally below the coils 6,8. The wires all terminate at one end away from the cradle at corresponding electrical terminals 20 on a terminal block 22, and at the other end to corresponding terminals 24 to which ends of the coils 6,8 are wired. Therefore, current to drive the focus and tracking actuator 1 is supplied to the coils through the suspension wires 16-19.

Tension in the wires 16-19 when these are moved away from a neutral position creates biasing forces, which will tend to return the cradle 4 to a neutral position.

The terminal block supports a frame 26 that extends fully around the cradle 4 in a plane transverse to the optical axis 12 of the lens 2.

The frame 26 in turn supports a pair of end stops 29,30 GB198-1517 01 July 1999 shown most clearly in Figure 2, one of which 29 is on a member 28 that extends frame-like about the optical axis 12 above the cradle, and the other of which 30 includes a pair of ledges 31,32 that are inwardly directed towards 5 the lens 2 in a plane generally below the cradle 4.

When the focus actuator is driven fully inwards, a top surface 34 of the cradle 4 contacts the upper stop 29, and when the focus actuator is driven fully outwards, a bottom surface 35 of the cradle 4 contacts the lower stop 30.

The frame 26 also supports a pair of end stops 36,37 that define the limits of movement in the tracking direction.

The focus and tracking stops 29,30,36,37 act to protect the focus and tracking actuator 1, and particularly the suspension wires 16-19, from mechanical damage which would occur at an extreme movement of the cradle 4 relative to the terminal block 22. 20 In order to suppress the sound of the cradle hitting the end stops 29,30, 36,37, the end stops are formed in a twopiece resilient structure, consisting of a rigid support with resilient bumpers 40,41 disposed between the rigid support and the actuator so that the movement of the actuator is limited by contact between the actuator and the bumpers.

In the case of the focus movement end stops 29,30, the rigid supports are provided at one limit of travel by the f rame 28, and at the other limit of travel by the pair of ledges 31,32. These then have domed elastomeric bumpers 40, which are held in place by an adhesive layer (not shown).

GB198-1517 01 July 1999 In the case of the tracking movement end stops 36,37, there is a rigid support in the form of projections 42,43 on frame 26 that extends fully around the cradle 4. The projections are inwardly directed on opposite sides of the frame 26. These projections 42,43 each have one domed elastomeric bumper 41, which is held in place by an adhesive layer (not shown).

It has been discovered that in a motor car CD player, that vibrations from the road are strongest in the focus direction when the player is oriented so that the a compact disc is held horizontally. Therefore, in this application, it may only be necessary for bumpers to be provided on the focus end stops 29,30. In other applications, it may be the case that bumpers need only be provided in the tracking direction.

However, it will usually be the case that bumpers are needed at least on the focus end stops 29,30, because the focus actuator is less stiff than the tracking actuator.

This difference in stiffness is due to the fact that the required frequency response of the tracking actuator is less than that required from the focus actuator.

Figure 4 shows a schematic view of an optical pickup 50 comprising the focus and tracking actuator 1. The optical pickup 50 includes a laser diode 52, which generates a infra-red light 53 that is focussed 54 onto an information carrying layer 55 of an optical disc 56. The internal optical construction of the optical pickup 50, and its connection to electronics such as a laser driver, and focus and tracking servos, is conventional, and so will not be described here.

Although the resilient structure has been described above GB198-1517 01 July 1999 as being provided on a structure surrounding the moving actuator, the resilient structure could also be provided on the moving actuator. It is, however, generally preferred to minimise the weight of the moving actuator in order to increase its frequency response. Therefore the resilient structure is preferably provided elsewhere than on the moving actuator.

The invention therefore provides a way in which rattling of a focus and/or tracking actuator may be suppressed or eliminated in the presence of external vibrations of an optical pickup. This is particularly useful in an automotive application, where in-vehicle rattles can be annoying to a driver or passengers.

GB198-1517 01 July 1999 8

Claims (5)

Claims

1. An optical pickup f or reading from and/or writing to an optical storage medium, the optical pickup comprising one or more sources of light, an objective lens, a focus and/or tracking actuator for moving the lens to focus and/or track the light on the optical medium and mechanical limits to limit the focus and/or tracking movement of the lens; characterised in that the mechanical limits- include a resilient structure to dampen noise from the actuator hitting the limits.

2. An optical pickup as claimed in Claim 1, in which the mechanical limits include a rigid support with resilient bumpers disposed between the rigid support and the actuator so that the movement of the actuator is limited by contact between the actuator and the bumpers.

3. An optical pickup as claimed in Claim 2, in which the bumpers are domed.

4. An optical pickup as claimed in any preceding claim, in which the resilient structure is provided elsewhere than on the moving actuator

5. An optical pickup substantially as herein described, with. reference to or as shown in the accompanying drawings.

GB198-1517 01 July 1999