WO2007015193A1

WO2007015193A1 - Compact asymmetric 3d-actuator and an optical pick-up unit comprising such an actuator

Info

Publication number: WO2007015193A1
Application number: PCT/IB2006/052558
Authority: WO
Inventors: Peter M. S. M. Heijmans; Michael A. H. Van Der Aa; Johannes A. Van Rooij; Jeroen A. L. J. Raaymakers
Original assignee: Koninklijke Philips Electronics N.V.
Priority date: 2005-08-04
Filing date: 2006-07-26
Publication date: 2007-02-08
Also published as: TW200725599A

Abstract

Actuator (1) for use in an optical pick-up unit comprising a moveable lens holder (2), holding a lens (5), and a retaining structure (4), the actuator (1) comprising a coil system (6) and a magnet system (7), configured to interact with each other during use to move the lens holder (2) with respect to the retaining structure (4), wherein a first part of the coil system (6) is arranged opposite a first side (7a) of the magnet system (7) and a second part of the coil system is arranged opposite a second side (7b) of the magnet system (7), said second side (7b) being faced away from said first side (7a); and optical pick-up unit, preferably for a notebook, comprising such an actuator (1).

Description

Compact asymmetric 3D-actuator and an optical pick-up unit comprising such an actuator

The invention relates to an actuator for use in an optical pick-up unit comprising a moveable lens holder, holding a lens, and a retaining structure, the actuator comprising a coil system and a magnet system, configured to interact with each other during use to move the lens holder with respect to the retaining structure. Such an actuator is known from WO 03/102929, which is incorporated herein by reference. WO '929 discloses a symmetrical actuator, wherein tracking and focusing coils extend substantially in two parallel planes at two sides of the lens holder and the lens is arranged between the coil systems. Advantage of this kind of actuator is its high dynamics and efficiency. Due to its configuration, the light path in a symmetrical actuator can have access problems.

In a notebook optical pick-up unit, the form factor limits the access of the laser light to the objective lens. In general to have good access, an asymmetrical actuator layout is chosen in a notebook optical pick-up unit. Compared with a symmetrical actuator, the asymmetrical actuator has a better light path access. Asymmetrical actuators are for instance known from US/2003/0012090. The asymmetrical actuator comprises a magnet circuit for cooperation with the focussing, tracking and tilting coils, wherein the focussing, tracking and tilting coils are placed within a magnetic gap of the magnet circuit. In the actuator, one magnet is provided wherein the coils are arranged at one side of the magnet. Disadvantage of this actuator is the low-grade of dynamics and efficiency, and the less compact size. Furthermore this actuator comprises different coils for tracking, focussing and tilting of the objective lens. Due to technical developments the actuators become smaller and lighter to fit in smaller optical disk drives. Especially for slim and/or ultra slim notebook applications (CD/DVD/Blu-ray Disc (BD)) an as small as possible actuator is desired. Therefore, a limited amount of separate coils is advantageous for the compactness of the actuator. It also contributes to a low cost manufacturing of the actuator. Furthermore, developments in

CD/DVD/Blu-ray disc drives cause the read/write speed to increase as well as the density of information on a disk to increase. Consequently, a high level of accuracy is needed even though the acceleration of the lens holder is high as well. It is therefore an object of the invention to provide an actuator of the above- described type, wherein the above-described disadvantages of the known actuators are overcome, while maintaining the advantages thereof. More particular, it is an object of the invention to improve the dynamical performance of the actuator and at the same time provide an actuator with a good access of the laser light path, wherein the actuator is as small as possible and cheap to manufacture.

To that end, an actuator according to the invention is characterized by the features of claim 1.

In order to achieve this object, the actuator in accordance with the invention is characterized in that a first part of the coil system is arranged opposite a first side of the magnet system and a second part of the coil system is arranged opposite a second side of the magnet system, said second side being faced away from said first side. Such an actuator combines the advantages of a symmetrical and an asymmetrical actuator. The actuator according to the invention is compact and has a high efficiency and good dynamics properties. Herein, for example, said efficiency can be defined as the amount of acceleration [m/s²] that can be achieved to the objective lens with a certain amount of input power to the actuator coils. Also, for example, said dynamics can be defined by the displacement of the objective lens (unit "meter") due to an applied AC-voltage (unit "volt") to the coils. The dynamics of the actuator (or frequency response of the actuator) can be given by the parameter [displacement / Volt] as function of the frequency.

According to a further elaboration of the invention both the magnet system and coil system can be arranged substantially asymmetrical with respect to said lens, which can provide a good light path towards the optical disc. For example, during use, light can come in from a right hand side of the actuator and can be deflected with a 45 degrees mirror through a centre of the objective lens.

In further advantageous elaboration of the invention both the magnet system and coil system are arranged substantially in an area, which extends on one side of said lens, when viewed in a focussing direction of that lens. Furthermore, due to the separate magnet that is not fixed to the lens holder, the lens holder is very light and can move fast. According to a further elaboration of the invention, said magnet system consists of a single multi pole magnet, for example a magnet which is magnetised in at least three polarities, for example in four polarities. The use of such a single magnet contributes to a simple actuator design, which is advantageous for the manufacturing costs. Another contribution to the simple actuator design is that in further elaboration of the invention said magnet system substantially extends along a single plane, particularly a plane that is substantially parallel to both a focussing direction and tracking direction of said lens.

In further elaboration of the invention, the coil system is provided on two opposite planes surrounding an aperture in the lens holder, the opposite planes preferably being provided at a distance from the objective lens, perpendicular to a central axis of the actuator extending through the lens, wherein the aperture is arranged for receiving the magnet.

In this way, a force generation point and a point of movement (=objective lens) can become relatively small, which can lead to good dynamics properties. According to a further elaboration of the invention said first coils system part and second coil system part are mirror symmetrical with respect to a mirror plane, said mirror plane particularly extending through said magnet system.

According to a further elaboration of the invention the coil system comprises tracking and focusing coils. For example, the first coil system part at the first plane of the aperture can be mirror symmetrical to the second coil system part at the opposite plane with respect to a longitudinal axis of the aperture. These coils of the two parts of the coil system cooperate with the magnet at the same time and therefore are simultaneously drivable by the magnetic field on both sides of the magnet. Consequently, the actuator makes the best use of the existing magnet field. An additional advantage is that symmetrical configuration allows for better accuracy and on average the current through each coil system will be less than with a non symmetrical configuration, which leads to less power dissipation.

According to a further elaboration of the invention, each coil system part comprises one tracking coil in the centre of the coil system and a left focusing coil and a right focusing coil on both sides next to the tracking coil. This leads to an even distribution of weight of the coils on the lens holder and enables the lens holder to move easily. Other coil configurations are also possible.

In further elaboration of the invention, the focusing coils of each coil system part are arranged in pairs being usable as tilting means or tilting coils. For example, no additional tilting means have to be provided to the actuator according to the invention. Consequently, the total mass of coils available on the actuator is less than with separate tilting coils provided. This allows the actuator being small and having less weight to displace. Also, the actuator has a simple design and therefore the manufacturing costs are low.

According to a further elaboration of the invention, supplying unequal currents to the individual focusing coils causes these coils to tilt the lens holder with the lens during use. By supplying unequal currents to the individual focusing coils, unequal electromagnetic forces are generated, which cause tilting of the lens holder. This provides a simple way of tilting the lens holder, so that the objective lens can be positioned very accurately, which enables the read and write quality to be high. According to a further elaboration of the invention, the focusing coils and tracking coil of each coil system part are arranged in one plane. Because of the in one plane arranged and flat shaped coils, the magnet used in the actuator to drive the movable lens holder to bring the lens in position, can be small. The magnetic field of such a small magnet will suffice. Consequently, a small magnet volume helps to keep the actuator dimensions small and to minimize the manufacturing costs. Furthermore, due to the coils extending in one plane, the design of the lens holder can be relatively simple.

In further elaboration of the invention, the coils are manufactured by fine pattern coil technology. This enables miniaturization and high sensitivity of the actuator. Minimization of the total mass of the lens holder increases the efficiency. The invention also relates to an optical pick-up unit, preferably for a notebook, comprising the actuator according to the invention. Furthermore the invention relates to a notebook comprising the optical pick-up unit according to the invention.

The invention will be further elucidated by means of an exemplary embodiment with reference to the accompanying drawing in which:

Fig. 1 shows a top view of the asymmetrical actuator;

Fig. 2 shows a perspective view of the asymmetrical actuator;

Fig. 3 shows an example of the multi-pole magnet; and Fig. 4 shows a schematically perspective view of the magnet and coils.

In the present application, equal or similar parts have equal or similar reference signs. Figure 1 shows a top view of the layout of the asymmetrical actuator 1 according to an embodiment of the invention. The actuator 1 comprises a movable lens holder 2 that is suspended by suspension wires 3 to a retaining structure 4. The movable lens holder 2 holds an objective lens 5. A coil system 6 is coupled or fixed to the lens holder 2. The coil system 6 is provided with focusing coils 8 and tracking coils 9 for respectively focusing of the lens holder 2 and tracking of the lens holder 2 so that the objective lens 5 is positioned for irradiating light to a precise position on the disk surface. The disk can for instance be a DVD, a CD or a Blu-ray disc. The suspension wires 3 are the electrical connection to the coils. The actuator 1 further comprises a magnet system 7 that is coupled or fixed to the retaining structure (not shown) of the actuator 1. The coil system 6 and the magnet system 7 are configured to interact with each other during use to move the lens holder with respect to the retaining structure 4. A first part of the coil system 6 is arranged opposite a first side 7a of the magnet system 7 and a second remaining part of the coil system 6 is arranged opposite a second side 7b of the magnet system 7, said second side 7b being faced away from said first side 7a. Furthermore, the magnet system 7 and the coil system 6 are arranged substantially asymmetrically from the objective lens 5. For example, both the magnet system 7 and the coil system 6 are arranged substantially in an area, which extends on one side of said lens 5, when viewed in a focussing direction F of that lens 5. The magnet system 7 substantially extends along a single plane, particularly a plane which is substantially parallel to both a focussing direction F and tracking direction Tr of said lens 5. The two parts of the coil system 6 are arranged substantially parallel to respective opposite sides of the magnet system 7. The distance d between the coil system 6 and the lens 5 is relatively small, preferably maximal 2 mm. In figure 2, a perspective view of the actuator 1 according to an embodiment of the invention is shown. The movable lens holder 2 with the objective lens 5 is also provided with an aperture 10. The coil system 6 is provided on two opposite planes 11, 11' surrounding said aperture 10. The opposite planes 11, 11' are provided at a distance d from the objective lens 5 and are perpendicular to a central axis C of the actuator 1 extending through the objective lens 5 and the aperture is arranged for receiving the magnet system (not shown). The first coil system part 6' and second coil system part 6" are mirror symmetrical with respect to a mirror plane, said mirror plane particularly extending through said magnet system (not shown). The first coil system part 6' at the first plane 11 of the aperture 10 is mirror symmetrical to the second coil system part 6" at the opposite plane 11' with respect to a longitudinal axis L of the aperture 10. Each coil system part 6', 6" comprises one tracking coil 9 in the centre of the coil system 6 and a left focusing coil 8 and a right focusing coil 8 on both sides next to the tracking coil 9. It is also clear from the figure that the coils of one part of the coil system are arranged in one plane. The coils are not arranged behind each other or do have a different thickness. Preferably, the coils are manufactured by fine pattern technology. The relatively flat shape of the coils demands only a small magnet 7 for driving the lens holder 2. In another embodiment the coils can also be wound coils.

Figure 3 shows an example of the magnet 7. The magnet 7 is a single multi pole magnet, for example a magnet which is magnetized in at least three polarities, for example four polarities. The magnet can also be assembled from separate single pole magnets. This magnet 7 is magnetized in four regions N', N", S', S" vertically symmetrical with regard to axis A, wherein adjacent regions have opposite magnetization. Also one part of the coils system 6, comprising one tracking coil 9 and two focusing coils 8, 8', is shown in figure 3. The focusing coils 8, 8' each face an upper N', S' and an adjacent lower region S", N" of the magnet 7 and the tracking coil 9 faces a left N' and an adjacent right region S' of the magnet 7. Each coil faces two regions of opposite magnetization of the magnet 7. This configuration enables the coils to be easily moved causing the lens to move.

Fig. 4 shows a schematically perspective view of the magnet 7 and the coils. If current flows through the coils and electromagnetic force caused by interaction with the magnet is generated, the objective lens (not shown) is driven. To drive the lens in a focusing direction indicated by arrow F, an electromagnet force Ff is generated in all four focusing coils 8 and has the same direction. The focusing coils 8 of each coil system part 6', 6" are arranged in pairs being usable as tilting means or tilting coils. By supplying unequal currents to the individual coils, these coils cause the lens holder with the lens to tilt during use. The unequal currents cause unequal electromagnetic forces in the focusing coils 8. If the electromagnetic forces in one pair of focusing coils 8 is larger than in the other pair, that side of the lens holder makes a larger move than the other side of the lens holder, causing the lens holder to tilt in a tilting direction Ti.

To move the lens holder in a tracking direction Tr, a current is supplied to the tracking coils. Depending on the flowing direction of the current, an electromagnetic force is generated and enables the lens holder to move in tracking direction TrI of Tr2.

Although an illustrative embodiment of the present invention has been described in greater detail with reference to the accompanying drawing, it is to be understood that the invention is not limited to the embodiment. Various changes or modifications may be effected by one skilled in the art without departing from the scope or the spirit of the invention as defined in the claims.

For instance, modifications with respect to the configuration of coils at each part of the coil system and depending configuration of the magnetized regions of the multi pole magnetized magnet fall within the scope of the invention.

Claims

CLAIMS:

1. Actuator (1) for use in an optical pick-up unit comprising a moveable lens holder (2), holding a lens (5), and a retaining structure (4), the actuator (1) comprising a coil system (6) and a magnet system (7), configured to interact with each other during use to move the lens holder (2) with respect to the retaining structure (4), wherein a first part of the coil system (6) is arranged opposite a first side (7a) of the magnet system (7) and a second part of the coil system (6) is arranged opposite a second side (7b) of the magnet system (7), said second side (7b) being faced away from said first side (7a).

2. Actuator (1) according to claim 1, wherein both the magnet system (7) and coil system (6) are arranged substantially asymmetrical with respect to said lens (5).

3. Actuator (1) according to claim 1 or 2, wherein both the magnet system (7) and coil system (6) are arranged substantially in an area which extends on one side of said lens (5), when viewed in a focussing direction (F) of that lens (5).

4. Actuator (1) according to any of the preceding claims, wherein said magnet system (7) consists of a single multi pole magnet (7), for example a magnet which is magnetised in at least three polarities, for example in four polarities.

5. Actuator (1) according to any of the preceding claims, wherein said magnet system (7) substantially extends along a single plane, particularly a plane which is substantially parallel to both a focussing direction (F) and tracking direction (Tr) of said lens (5).

6. Actuator (1) according to any of the preceding claims, wherein both said parts of the coil system (6) are arranged substantially parallel to respective opposite sides (7a, 7b) of said magnet system (7).

7. Actuator (1) according to any of the preceding claims, wherein said coil system (6) is coupled or fixed to said lens holder (2), wherein said magnet system (7) is coupled or fixed to said retaining structure (4).

8. Actuator (1) according to any of the preceding claims, wherein the coil system

(6) is provided on two opposite planes surrounding an aperture (10) in the lens holder (2), the opposite planes preferably provided at a distance (d) from the lens (5), perpendicular to a central axis (C) of the actuator (1) extending through the lens (5), wherein the aperture (10) is arranged for receiving the magnet system (7).

9. Actuator (1) according to claim 8, wherein the first coil system part (6¹) at the first plane (11) of the aperture (10) of the lens holder (2) is mirror symmetrical to the second coil system part (6") at the opposite plane (H') with respect to a longitudinal axis (L) of said aperture (10).

10. Actuator (1) according to any of the preceding claims, wherein said first coil system part (6¹) and second coil system part (6") are mirror symmetrical with respect to a mirror plane, said mirror plane particularly extending through said magnet system (7).

11. Actuator (1 ) according to any of the preceding claims, wherein the coil system comprises tracking (9) and focusing (8) coils.

12. Actuator (1) according to claim 11, wherein each coil system part comprises one tracking coil (9) in the centre of the coil system (6) and a left focusing coil (8) and a right focusing coil (8) on both sides next to said tracking coil (9).

13. Actuator (1) according to claim 11 or 12, wherein the focusing coils (8) of each coil system part (6¹, 6") are arranged in pairs being usable as tilting means or tilting coils.

14. Actuator (1) according any of claims 11-13, wherein supplying unequal currents to the individual focusing coils (8) causes these coils to tilt the lens holder (2) with the lens (5) during use.

15. Actuator (1) according to any of claims 11-14, wherein the focusing coils (9) and tracking coils (8) of each part of the coil system (6) are arranged in one plane.

16. Actuator (1) according to any of claims 11- 15, wherein said focusing coils (8) each face an upper (N, S') and an adjacent lower region (S", N") of the magnet system (7) and said tracking coils (9) each face a left (N) and an adjacent right region (S') of the magnet system (7).

17. Actuator (1) according to any of the preceding claims, wherein the magnet system (7) has four regions (N, N", S', S"), wherein adjacent regions have opposite magnetization.

18. Actuator (1) according to any of the preceding claims, wherein said coils are manufactured by fine pattern coil technology.

19. Actuator (1) according to any of claims 1-17, wherein said coils are wound coils.

20. Actuator (1) according to any of the preceding claims, wherein the distance (d) between said coil system (6) and said lens (5) is relatively small, preferably maximal 2 mm.

21. Optical pick-up unit comprising the actuator (1) according to any one of claims 1-20.

22. Notebook provided with the optical pick-up unit according to claim 21.