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1. WO2006095306 - DISK DRIVE UNIT HAVING A SLEDGE MECHANISM

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[ EN ]

Disk drive unit having a sledge mechanism

FIELD OF THE INVENTION
The invention relates to a disk drive unit for a disk to be used in a device for reading and/or writing data on the disk, which disk drive unit is provided with a sledge mechanism.

BACKGROUND OF THE INVENTION
Most pickup units for DVD players which are currently available make use of a so-called Zamac (a Zinc alloy) material for the sledge of the pickup unit. The reason for this material choice is the fact that Zamac material is relatively cheap and has a good heat conduction property, which is needed especially for high-speed DVD writing and high ambient temperature requirements. However, Zamac has a low wear resistant and hence using Zamac material for the whole sledge is not preferred. The sledge could easily wear off when sliding along the guide. Consequently, additional bearing components need to be installed to the sledge as a wear protection. Copper alloy bushes are commonly used as the bearings due to the high wear resistant properties of this material. Using copper alloy bushes as the bearings is however costly, not only due to the relatively high material cost, but also due to the additional mounting and trimming operations on the bushes.
US 2003/0133397 Al discloses an optical disk drive unit in which a follower engages around a lead screw and is in engagement with the lead screw to transmit the rotation of the drive shaft into a translation of the sledge. The follower is connected to the sledge by means of screws.

SUMMARY OF THE INVENTION
It is an object of the invention to provide an improved optical pick up unit, particularly the sledge mechanism thereof, in order to reduce manufacturing costs.
In order to accomplish that objective, the optical pick up unit according to the invention is characterised by the features of claim 1.
In the pick up unit according to the invention, the follower and sledge can be made of a material suited for its particular purpose. The sledge can be made of a cheap material having good heat conducting properties, whereas the follower can be made of a material having good sliding properties, such as a polymer material, in particular a thermoplastic material, preferably an acetal plastic. Such material does not require separate bushes, which saves material and assembly costs. Preferably, the sledge and follower are connected to each other by a screwless connection, which saves further material and assembly cost. Virtually the follower and the bushes are integrated into one part.
In a preferred embodiment, the sledge and follower are connected to each other through an interlocking connection. This obviates the need of a screw and allows an interconnection without separate faster elements. For example, the sledge has at least two holes, the axis of which extends parallel to the guide, and the follower has two integrated connecting bushes fitting into the holes so as to interlock the follower and the sledge in directions perpendicular to the guide.
Such connection can be made with very tight tolerances, so that a high accuracy can be obtained.
Preferably, the bushes of the follower can be fitted into the holes of the sledge by a relative translation of the sledge in the direction of the bushes, the interlock between the follower and the sledge being active in the operative position of the sledge and follower.
This feature enables a very easy assembly of the sledge and the follower, especially if also the follower and sledge being provided with a co-operating hook and shoulder, interlocking the sledge and follower in their operative position. In that case, the interlock will automatically be activated if the sledge and the follower are connected by the relative translational movement.
In a favourable embodiment, the follower engages around the guide by means of guide bushes, the axis of the connecting bushes of the follower being aligned with the axis of the guide bushes, the connecting bushes also engaging around the guide, but having an inner diameter that is slightly larger than that of the guide bushes. In this embodiment, the guide bushes and connecting bushes are integrated into a unit whereby the sledge also engages around the guide. However, because the inner diameter of the connecting bushes is slightly larger than that of the guide bushes, any deformation of the connecting bushes due to the engagement with the sledge will not have an affect on the guiding properties or on the accuracy of the engagement of the guide and the follower.
In the embodiment wherein the drive shaft is a screw shaft, the follower may comprise at least one tooth engaging with the screw shaft, said tooth preferably engaging only a part of the circumference of the screw shaft.

In this embodiment, the follower can be made quite simple. The at least one tooth will be kept in engagement with the screw shaft by a spring member or by the stiffness of the follower, if the follower is urged against the screw shaft in its operative position.
The invention also includes a device for reading and/or writing data on the disk, such as an optical player, comprising the disk drive unit according to the invention.
These and other aspects and advantages of the invention will be apparent from the following description with reference to the drawings.

BRIEF DESCRIPTION OF THE DRAWINGS
Fig. 1 is a very schematic drawing of an optical player including a disk drive unit according to the invention.
Fig. 2 is a perspective view of a part of the disk drive unit according to the invention.
Fig. 3 A, 3B is a perspective bottom view of the follower of the disk drive unit of Fig. 2 in two different embodiments.
Fig. 4 is a plan view of a part of the sledge and follower, illustrating the assembly thereof.
Fig. 5 is a perspective view of detail V in Fig. 3B, but turned 180°.
Fig. 6 is a very schematic sectional view according to the line VI-VI in Fig. 5.
Fig. 7 A, 7B is a perspective view of a part of the sledge and follower in assembled condition, in the two different embodiments.
Fig. 8 A, 8B is a side view of a part of the sledge and follower and drive shaft, in the two different embodiments.

DESCRIPTION OF PRESENTLY PREFERRED EMBODIMENTS
Fig. 1 diagrammatically shows an optical player in accordance with the invention, which comprises a turntable 1, which can be rotated about an axis of rotation 3 and driven by an electric motor 5, which is secured on a frame 7. An optically scannable information carrier or disk 9, such as a CD, DVD or Blue ray disk, can be placed on the turntable 1, which disk is provided with a disk-shaped substrate 11 on which an information layer 13 having a spiral-shaped information track is present. The information layer 13 is covered with a transparent protective layer 14.
The optical player further comprises an optical pickup unit 15 in accordance with the invention for optically scanning the information track present on the information layer 13 of the disk 9. The optical pickup unit 15 can be displaced with respect to the axis of rotation 3 mainly in two opposite radial directions Y and Y' by means of a sledge mechanism 17 of the optical player. For this purpose, the optical pickup unit 15 is secured to a sledge 19 of the sledge mechanism 17, and the sledge mechanism 17 is further provided with a straight guide 21 provided on the frame 7 and extending parallel to the Y direction, over which guide 21 the sledge 19 is displaceably guided, and with an electric motor 23 by means of which the sledge 19 can be displaced over the guide 21. In operation, an electrical control unit of the optical player, which is not shown in Fig. 1, controls the motors 5 and 23 so as to cause the disk 9 to rotate about the axis of rotation 3 and, simultaneously, the optical pickup unit 15 to be displaced parallel to the Y-direction, in such a manner that the spiral- shaped information track present on the information layer 13 of the disk 9 is scanned by the optical pickup unit 15. During scanning, the information present on the information track can be read by the optical pickup unit 15, or information can be written on the information track by the optical pickup unit 15.
The disk 9 is read by detection of light reflected in the disk 9. For example, a light beam is reflected in the direction of the disk 9 by means of a mirror, which is part of the optical pickup unit 15. If the optical pickup unit 15 is also suited for writing information on the disk, the light beam will have a different power level and/or wavelength during writing, but must also be focussed onto a point in the disk 9, as is the case when the disk 9 is being read. Light reflected by the mirror is focussed onto the disk 9 by means of an objective lens 25, situated in a lens holder 27 (see Fig. 2). The lens holder 27 can make small movements with respect to the sledge 19 by means of an actuator which is not further described here.
With reference to Fig. 2, the guide 21 comprises two guide shafts 29, 31 extending parallel at a distance from each other. The guide shafts 29 and 31 are smooth and straight shafts having a circular cross section and being precisely manufactured and positioned on the frame 7. The sledge 19 of the sledge mechanism 17 is positioned between the guide shafts 29 and 31. The sledge 19 is guided with respected to the guide shaft 29 by means of a slider 33.
At the position of the other guide shaft 31, the sledge 19 is provided with a separate part, i.e. a follower 35. This follower 35 is connected to the sledge 19 in a manner to be described and is in engagement with a drive shaft 37 which is driven by the electric motor 23 in order to rotate about its longitudinal axis. The follower 35 and shaft 37 are provided with a transmission, here consisting of a lead screw transmission, i.e. the drive shaft 37 is constructed as a screw shaft, whereas the follower 35 with at least one tooth (here two teeth 38, see Fig. 3 A5B and 4) which is in engagement with the screw thread of the drive shaft 37. By means of this transmission, a rotation of the drive shaft 37 is transmitted into a translation of the sledge 19 along the guide shafts 29 and 31. The drive shaft 37 extends parallel to the guide shafts 29 and 31 and along side the guide shaft 31 on the opposite side of the sledge 19.
According to the invention, the sledge 19 is guided by the guide shaft 31 through the follower 35 as the follower 35 is in engagement with the guide shaft 31, while the sledge 19 is connected to and supported by the follower 35.
Figs. 3-8 show the sledge and follower arrangement in more detail. Fig. 3 shows that the follower 35 has two aligned guide bushes 39. The diameter of the guide bushes 39 is such that they precisely fit with the guide shaft 31, such that the follower 35 is precisely and smoothly guided by the guide shaft 31.
Each guide bush 39 has an integrated connecting bush 41 which is aligned with the guide bush 39 and is formed adjacent thereto. Both connecting bushes 41 are on the same side of their respective guide bush 39. The outer diameter of the connecting bush 41 is larger than the inner diameter of the guide bush 39 and fits with a sliding fit tolerance or with an interference fit in a respective hole 43 in the sledge 19. This interlocking connection prevents relative movements between the follower and sledge in directions perpendicular to the guide shaft 31.
Fig. 6 shows a section of the guide and connecting bushes 39 and 41 with the guide shaft 31 extending there through. It is shown that the connecting bush 41 fits into a hole 43 of the sledge 19. It also shows that the inner diameter of the connecting bush 41 is slightly larger than that of the guide bush 39. In this way, the connecting bush 41 engages around the guide shaft 31, but any deformations resulting from the assembly of the connecting bush 41 in the hole 43 of the sledge 19 (in case of an interference fit) does not affect the engagement of the follower 35 with the guide shaft 31. This different inner diameters of the guide bush 39 and connecting bush 41 is also illustrated in Fig. 5.
As is illustrated in Fig. 4, the follower 35 and sledge 19 can be connected to each other by a relative translational movement of the sledge 19 and follower 35 parallel to the central axis of the guide and connecting bushes 39, 41 (see arrow A). The connecting bush 41 of the follower can be fitted into the holes 43 in the sledge so as to connect the follower 35 and sledge 19 and lock them together in a precise manner in directions perpendicularly to the guide shaft 31. To also lock the sledge 19 and follower 35 in a direction parallel to the guide shaft 31, there is provided an interlock between the sledge 19 and the follower 35, here in a form of a hook 45 which is adapted to engage behind a shoulder of the sledge 19, here in the form of an edge 47 of the sledge 19 directed away from the guide in connecting bushes 39 and 41.
Due to these engagement of the follower and sledge through connecting bush 41 and the hook 45, there is obtained a very stable and precise connection, such that the stack up tolerances between the guide shaft 31 and the optical lens 25 is very small. Furthermore, there is no need for additional components, such as a fastener, to connect the follower 35 and sledge 19. The follower 35 can be made of a material which is very well suited to perform a guiding function in combination with the guide shaft 31. Preferably, the follower 45 is made of a polymer material, particularly a thermoplastic material such as acetal plastic, in particular polyoxymethylene (POM). POM has low friction and high wear-resistance properties and therefore there is no need for additional components, such as bearing bushes, to obtain a proper guidance. This reduces assembly and material costs. The sledge can be made of a material which is suited for its purpose (for example, Zamac which is cheap and has good thermal properties), and the same can be said for the follower 35.
Figs. 3 A5B, 7A,B and 8A,B show two different embodiments of the follower 35 which differ in the way of holding the follower 35 in engagement with the drive shaft 37. In the embodiment of Figs. 3 A, 7A and 8A there is provided a spring member 49, here a coiled compression spring, causing a pretension force on the teeth 38 thereby keeping them in engagement with the screw thread of the drive shaft 37. The follower 35 is allowed able to pivot with respect to the sledge 19 due to the sliding fit engagement of the connecting bushes 41 within the holes 43. The follower 35 is then in fact allowed to pivot slightly about the guide shaft 31.
In the embodiment of Figs. 3B, 7B and 8B, the elasticity of the follower 45 itself keeps the teeth 38 of the follower 35 in engagement with the screw thread of the drive shaft 37 as the connection between the follower 35 and the sledge 19 is such that the end of the follower 35 where the teeth are formed, is urged against the drive shaft 37. In this case, the follower is prevented from pivoting about the connecting bushes 41. In the embodiment shown, this is done by fitting the connecting bushes 41 in the holes 43 with an interference or other tight fit. In case of an interference fit, the outer diameter of the connecting bush 41 is slightly larger than that of the hole 43. Pressing the connecting bushes 41 into the holes 43 will result in a slight deformation of the connecting bushes 41. In this respect, the stepped configuration of the inner diameters of the connecting and guide bushes 39 and 41, as shown in Figs. 5 and 6, is very useful to improve accuracy and smooth running. This embodiment also further reduces the number of parts.
The teeth 38 have a simple straight shape and are formed on the lower side of a substantially flat part of the follower 35. Due to the pretension on the follower, there is no need for the follower/teeth to engage around the drive shaft 37.
The invention is not restricted to the above-described embodiment as shown in the drawing, which can be varied in several ways without departing from the scope of the invention. For example, the interlocking arrangement between the follower and sledge may be designed differently. The sledge and follower may be brought into engagement with each other in a different direction. The interlock in a direction parallel to the guide may be activated by a rotational instead of a translational movement, for example. The drive shaft 37 and the guide shaft 31 may be combined into a single shaft.
In the presently preferred embodiments, the disk is an optical disk. However, it should be understood that the invention can also be used for all kinds of other disks e.g. ferro-electric, magnetic, magneto-optic, near- field, active charge storage disks or other disks using combinations of these techniques or other reading and/or writing techniques. In these cases the lens and laser will be replaced by another reading/writing member which may require cooling.
In general it is noted that, in this application, the expression "comprising" does not exclude other elements, and "a" or "an" does not exclude a plurality. A single processor or unit may fulfil the functions of several elements in the appended claims. Reference signs in the claims shall not be construed as limiting the scope thereof.