WO2012155276A1

WO2012155276A1 - Positioning device

Info

Publication number: WO2012155276A1
Application number: PCT/CH2011/000119
Authority: WO
Inventors: Manuel Aschwanden
Original assignee: Optotune Ag
Priority date: 2011-05-19
Filing date: 2011-05-19
Publication date: 2012-11-22

Abstract

An embodiment of an electroactive positioning device (1) comprises an elastic polymer film (3) having a first and a second surface (31, 32). A first and a third compliant electrode (41, 51) are connected to the first surface (31) and a (segmented) second compliant electrode (42) is connected to the second surface (32). A (segmented) inclined or curved fourth, rigid electrode (52) and an insulation layer (54) are arranged above and/ or below the polymer film (3). Upon application of a voltage to the electrodes (41, 42, 51, 52), an element (2) that is connected to the polymer film (3) (such as an optical lens) can be moved with five degrees of freedom.

Description

Positioning device

Technical Field

The present invention relates to a position- ing device for a movable element, in particular an opti- cal element, and to methods for operating, using, and fabricating such a device.

Introduction and Background Art

A positioning device is used to move (i.e., displace and/ or tilt) an element in different directions and/ or around different tilt axes. While many different multi-axes positioning devices for optical elements have existed for many years (e.g., relying on mechanical actuation via fine pitch threads or piezo actuation) , a lot of these devices are unsuitable for applications that require compact components, e.g., in miniaturized optical systems. Therefore, compact positioning devices have gained an increasing attention, e.g., for use as autofo- cus actuators or vibration compensation actuators in compact camera modules, e.g., in cellphones, PDAs, webcaras, or tablet computers.

For use, e.g., in a cell phone, the positioning device and the movable (optical) element is preferably compact, low-cost, as easy to manufacture as possible, and highly functional. Highly functional in this respect means that the optical element can be moved with a plurality of degrees of freedom.

US 2008/0204909 Al discloses an electrode- sandwiched polymer actuator suitable for compact optical systems. However, this actuator has the disadvantage that the optical element can only be moved in one axial direction (and tilted to some degree) . Thus, efficient vibration compensation is not possible with such a device.

Disclosure of the Invention Hence, it is a general objective of the present invention to provide an improved positioning device that can displace and/ or tilt a movable element with more degrees of freedom. It is a further objective of the invention to provide methods for operating, using, and fabricating such a device.

These objectives are achieved by the device and methods of the independent claims.

Accordingly, a highly functional positioning device (i.e., with a plurality of degrees of freedom) is provided that is capable of moving and/ or tilting an element, in particular an optical element (such as a lens, a lens barrel, or an image sensor) . The positioning device comprises a polymer film that is interconnected to the element that is to be displaced and/ or tilted by the positioning device. An electroactive polymer actuator is used to displace the element in a lateral direction x, y that is perpendicular to an axial direction z: For. this purpose, a first surface of the polymer film on a first side is interconnected to a first electrode and a second surface of the polymer film (opposing the first surface) is interconnected to a second electrode. Upon application or change of a voltage difference between the first electrode and the second electrode, the electrodes either attract or repel each other and thus lead to a lateral displacement (due to Maxwell stress in the polymer film) of the polymer film and thus of the movable element itself. The movable element is thus displaced from a first position to a second position. Advantageously, voltage biasing is possible, i.e., a nonzero voltage difference can be applied between the first electrode and the second electrode to hold the movable element in its first position. Then, upon changing the voltage difference, the element can be displaced in two opposing (i.e., antiparal- lel) lateral directions depending on the sign of the voltage-difference change. Furthermore, the positioning device comprises at least one electrostatic actuator to tilt the movable element and/ or displace the movable element in an axial direction z. The electrostatic actuator comprises a third electrode interconnected to the first surface of the polymer film and a fourth electrode which is interconnected to a rigid support. An insulation layer is arranged between the third electrode and the fourth electrode, i.e., the third electrode is insulated with respect to the fourth electrode. At least in the case that no voltage difference (i.e., a zero voltage difference) is applied between the third electrode and the fourth electrode, at least a part of the fourth electrode is arranged non- parallel to the third electrode. E.g., the polymer film can be arranged planar in the x-y-plane and at least a part of the fourth electrode is arranged at an angle (i.e., with an inclination) to this plane. As an example, the inner part of the fourth electrode (i.e., the part that is closer to an optical axis z' of the movable element) is arranged at an inclination angle with respect to the lateral directions x, y. In other words, generally speaking, at least when no voltage difference is applied between the third and the fourth electrode, the axial distance (along z) between the third electrode and the fourth electrode is a non-constant function of a lateral position (along x and/ or y, i.e.,. a lateral or radial distance from the optical axis z' ) . Now, when a nonzero voltage difference is applied or changed between the third electrode on the first surface of the polymer film and the fourth electrode on the support, the third electrode is gradually pulled towards the fourth electrode (or gradually repelled from it) , similar to the parts in a zipper. For this reason, the electrostatic actuator is sometimes called "zipper actuator". Thus, the polymer film and the connected element can be displaced along the axial direction z from a third position to a fourth posi- tion. If, e.g., the fourth electrode and/ or the applied voltage difference (s) is/ are not rotationally symmetric around the optical axis z' , a tilting motion results for the element. The tilt axes φ, Θ are parallel to lines in the lateral plane x-y, i.e., the plane that is perpendicular to the axial direction z. In other words, the optical axis z' of the element in its fourth position is tilted around a tilt axis φ, Θ with respect to its third position. Advantageously, voltage biasing is possible for the electrostatic actuator as well (as described above) , i.e., a nonzero voltage is already applied between the third and the fourth electrode when the element is in its third position. Then, upon changing this voltage difference, the element is, e.g., displaced along +z or -z, depending on the sign of the change of the voltage difference.

In a preferred embodiment, the first, second, and third electrode are compliant electrodes, i.e., the electrodes are able to reversibly and elastically follow deformations of at least 5%, in particular of at least 20% of the polymer film without being damaged and/ or constraining the deformations. Furthermore, the compliant electrodes remain conductive under strain.

In another advantageous embodiment, the first electrode of the electroactive polymer actuator and the third electrode of the electrostatic actuator are a common (or, in other words, the same) electrode. Thus, the step of manufacturing one electrode is saved during the manufacturing process and per-unit costs are reduced. Furthermore, a common reference potential (e.g., ground GND) can be applied to the electroactive polymer actuator and the electrostatic actuator, thus simplifying operation of the positioning device.

In another preferred embodiment, the displacements that result from the electroactive polymer actuator and the electrostatic actuator are combinable. In other words, the element is then displaced and/ or tilted from its first position to its fourth position. The fourth position differs from the first position in lateral (along x, y) coordinates and/ or in axial coordinates (along z) and/ or the optical axis z' of the element in the fourth position is tilted with respect to the optical axis z' of the element in the first position. The control of the displacement/ tilting is achieved by a control unit that applies suitable voltage differences between the first and the second electrode of the electroactive polymer actuator and between the third and the fourth electrode of the electrostatic actuator. In principle, the order of these voltage applications to the electroactive polymer actuator and the electrostatic actuator is not crucial. However, depending on the actual device, it is possible that an actuation of the electroactive polymer actuator (leading to a lateral displacement along x, y) prior to an actuation of the electrostatic actuator (leading to an axial displacement and/ or tilting) is advantageous because in such an order the polymer film is less pre-stretched by the electrostatic actuation and thus the electroactive polymer actuating is more efficient: Due to the larger active areas of the first and second electrodes in the case of an unactuated electrostatic actuator, a larger lateral displacement can be achieved because a higher percentage of the area of the first and second electrodes of the electroactive polymer actuator is still free to move.

In another preferred embodiment, two electrostatic actuators are arranged on opposing sides of the polymer film. Thus, a larger movement along the axial direction z and/ or a larger tilting is possible. Furthermore, a bidirectional actuation along +z and -z is enabled without voltage-biasing the electrodes of the electrostatic actuator. In another advantageous embodiment, the positioning device comprises a rotator device in addition to the describe electroactive polymer actuator and the electrostatic actuator. Thus, a rotation motion, e.g., around a rotation axis parallel to the axial direction z (or the optical axis z' ) is enabled and an additional degree of freedom is added for moving the movable element. This is advantageous, e.g., if the movable element is not rota- tionally symmetric around the optical axis z' .

Preferably, the polymer film is freely suspended in a holding frame, advantageously in a pre- stretched manner. Thus, a better lateral actuation and a facilitated mounting of the positioning device can be achieved.

In another preferred embodiment the second electrode of the electroactive polymer actuator is divided into isolated segments. These segments are arranged at different angular positions (advantageously perpendicular to each other, e.g., in the x-direction and in the y-direction) around the axial direction z, e.g., similar to a pizza-slice- or piece-of-cake-configuration . Thus, when the different segments are activated individually (i.e., an individual voltage difference is applied between the respective segment and the first electrode), an independent displacement in two (advantageously perpendicular) directions is enabled. Thus, the element can be displaced laterally with two degrees of freedom.

In another preferred embodiment the fourth electrode of the electrostatic actuator (i.e., the electrode on the rigid support) comprises first segments and second segments, e.g., at different angular positions around the axial direction z. Each of the second segments is arranged between two of the first segments. Furthermore, the resistivity of the ^'first segments is smaller than the resistivity of the second segments. Now, a voltage difference is applied between the third electrode and a first segment of the fourth electrode and a different voltage difference is applied between the third electrode and another (e.g., neighboring) first segment of the fourth electrode. This leads to the buildup of a voltage gradient across the second segment that connects the respective first segments. Depending on the locally varying voltage difference between said second segment of the fourth electrode and the third electrode, the Coulomb attraction force between the fourth electrode and the third electrode varies with location. This results in a smoother and stepless actuation (e.g., tilting) compared to a gradient-free implementation. There, the. displacement of the polymer film would be partly absorbed by the polymer film due to steep voltage steps at the segment-edges. For moving the element with three degrees of freedom (i.e., along the axial direction z and around two tilting axes φ, θ) , the minimum number of these first and second segments is three each.

In_. another preferred embodiment the movable element comprises, e.g., a lens barrel which could itself comprise a plurality of lenses (e.g., forming an objective for a camera device) . Due to the larger dimensions (in particular along the axial direction z) of such a lens barrel compared to a typical single lens, two elec- troactive polymer actuators (specifically, the polymer films of the electroactive polymer actuators) and/ or electrostatic actuators can be interconnected to two opposing sides of the movable element (or, e.g., the lens barrel itself) . Thus, a more stable actuation becomes possible. An alternative approach for stabilization would be a spring element that is interconnected to the movable element on a side opposing the positioning device.

In an advantageous embodiment, a separation ring can be used to improve decoupling between the electroactive polymer actuator (s) and the electrostatic actuator (s) . A separation ring can also be arranged on the edges of. the movable element in the polymer film. Thus, a facilitated manufacturing is possible as the movable element can be inserted after the positioning device has been completely manufactured.

Furthermore, methods for operating, using, and fabricating a positioning device are provided.

A method for operating a positioning device comprises the application or change of a voltage difference between the first and the second electrodes of the electroactive polymer actuator. This displaces the movable element from its first position to its second position, wherein the first position at least laterally differs from the second position. The method further comprises the application or change of a voltage difference between the third and the fourth electrodes of the electrostatic actuator. This tilts and/ or displaces the movable element from its third to its fourth position, wherein the third position differs axially from the fourth position and/ or wherein the moveable element is tilted in the fourth position compared to the third position .

As it is discussed above, the application or change of the voltage difference between the first and the second electrodes of the electroactive polymer actuator prior to the application or change of the voltage difference between the third and the fourth electrodes of the electrostatic actuator can advantageously lead to a larger lateral displacement because of the larger active area of the first and second electrodes that is still free to move in the case of an unactuated electrostatic actuator .

The positioning device can be used for positioning of an element comprising or consisting of a spherical lens, a Fresnel lens, a cylindrical lens, an aspherical lens, a mirror, a grating, a lens assembly, a lens barrel (11), a GRIN lens, a square, a triangle, a line, a pyramid, - a hologram, a diffuser, a needle, an im^¬ age sensor, and a mechanical element. Advantageously, the positioning accuracy and/ or repeatability is better than 20μπι for said displacement and/ or 5mrad for said titling .

By integrating the■ positioning device into a camera module and by moving a lens or lens system with respect to the image sensor of the camera module by means of the positioning device, efficient vibration compensation counteracting camera-shake and/ or auto-focusing can be achieved. Thus, longer exposure times are achieved and image guality can be enhanced.

During fabrication of the positioning device, the first, second, and third electrodes are interconnected to the polymer film. The fourth electrode is interconnected to the rigid support and the insulation layer is interconnected to the fourth electrode. The movable element is interconnected to the polymer film. The polymer film is mechanically interconnected to the rigid support, advantageously after the first, second, and third electrodes have been interconnected to the polymer film and after the fourth electrode and the insulation layer have been interconnected to the rigid support .

Advantageously, the polymer film can be pre- strained (i.e., prestretched) during manufacturing, thus the tensional strain tries to keep the polymer film straight and lateral movements of the element are amplified .

Brief Description of the Drawings

The invention will be better understood and objectives other than those set forth above will become apparent when consideration is given to the following detailed description of the invention. This description makes reference to the annexed drawings, wherein: Fig. 1 shows a side view of a first embodiment of the positioning device with the element in a first position,

Fig. 2 shows a side view of the first embodiment of the positioning device with the element in a second position,

Fig. 3 shows a side view of the first embodiment of the positioning device with the element displaced along the axial direction z,

Fig. 4 shows a side view of the first embodiment of the positioning device with the element in a fourth position,

Fig. 5 shows a side view of the first embodiment of the positioning device with the optical axis z' of the element tilted,

Fig. 6 shows a top view of the second electrode of the electroactive polymer actuator of the first embodiment of the positioning device, wherein the second electrode comprises four segments,

Fig. 7 shows an xy projection of a top view of the fourth electrode of the electrostatic actuator of the first embodiment of the positioning device, wherein the fourth electrode comprises four first segments and four second segments,

Figs. 8-9 show side views of a second and a third embodiment of the positioning device with different shapes of the rigid support of the electrostatic actuator,

Fig. 10 shows a side view of a fourth embodiment of the positioning device with one electroactive polymer actuator and two electrostatic actuators,

Fig. 11 shows a side view of a fifth embodiment of the positioning device with a slimmer second electrode of the electroactive polymer actuator,

Fig. 12 shows a top view of the fifth embodiment of the positioning device, Fig. 13 shows a side view of a sixth embodiment of the positioning device comprising separation rings and decoupled first/ third electrodes,

Fig. 14 shows a side view of a seventh embodiment of the positioning device comprising a rotator device and a holding frame,

Fig. 15 shows a side view of an eighth embodiment of the positioning device comprising a lens barrel, two electroactive polymer actuators, and two electrostatic actuators,

Fig. 16 shows a side view of a ninth embodiment of the positioning device comprising a lens barrel, two electroactive polymer actuators, and one electrostatic actuator,

Fig.. 17 shows a side view of a tenth embodiment of the positioning device comprising a lens barrel, one electroactive polymer actuator, one electrostatic actuator, and one spring element,

Fig. 18 shows a side view of an eleventh embodiment of the positioning device wherein the movable element comprises an image sensor,

Fig. 19 shows a top view of the second electrode of the electroactive polymer actuator of a twelfth embodiment of the positioning device, wherein the second electrode comprises two segments,

Fig. 20 shows an xy projection of a top view of the fourth electrode of the electrostatic actuator of a thirteenth embodiment of the positioning device, wherein the fourth electrode comprises three first segments and three second segments.

Modes for Carrying Out the Invention

An embodiment of an electroactive positioning device comprises an elastic polymer film having a first and a second surface. A first and a third compliant elec- trode are connected to the first surface and a (segmented) second compliant electrode is connected to the second surface. A (segmented) inclined or curved fourth, rigid electrode and an insulation layer are arranged above and/ or below the polymer film. Upon application of a voltage to the electrodes, an element that is connected to the polymer film (such as an optical lens) can be moved with five degrees of freedom.

Description of the Figures:

First, twelfth, and thirteenth embodiment Figs. 1-5 show, a first embodiment of the positioning device according to the invention in different actuation states in side views (in the y-z-plane with the x-vector pointing into the y-z-plane, thus forming a dex- tral coordinate system) . The positioning device 1 comprises an electroactive polymer actuator 4 for displacing the movable element 2 (here: an optical lens) at least in a lateral direction along x, y, or any combination of x and y coordinates. The electroactive polymer actuator 4 comprises a polymer film 3 (e.g., an elastomer membrane) that is partly sandwiched between a first compliant electrode 41 on the polymer film's first surface 31 and a second compliant electrode 42a, 42c on the polymer film's second surface 32. The compliant electrodes may, e.g., be formed through metal ion implantation. This produces a compliant electrode with high adhesion and low roughness. Another possibility to create compliant (i.e., able to reversibly and elastically follow deformations of the polymer film without being damaged) electrodes comprises the dispersing of conducting particles (such as carbon black) in a polymer matrix and applying this via inkjet printing, pad printing, screen printing, or spray deposition. See below for alternative manufacturing techniques. By applying (or changing) a voltage difference U between the first and the second compliant electrodes 41 and 42a, 42c, the electrodes either attract or repel each .other which leads to a squeezing or an extension of the polymer film in axial direction (i.e., along the z-axis) . Due to Maxwell-stress in the material, the polymer film 3 and the interconnected element 2 is thus displaced in a lateral direction, thus allowing, e.g., for vibration stabilization in a camera device. This lateral displacement along +y is illustrated in Fig. 2. Here, a voltage U≠0 is applied between the electrode 41 and the left electrode segment 42c, but not between the electrode 41 and the right electrode segment 42a. For improved results, the polymer film can be pre-stretched laterally.

To enable axial displacement and/ or tilting of the element 2, e.g., for autofocus actuation and/ or improved vibration reduction actuation in a camera, an additional electrostatic actuator 5 comprising a third compliant electrode 51 on the first surface 31 of the polymer film 3 and a fourth electrode 52 (that can be segmented into segments 52a-h) interconnected to a rigid support 53 is provided. These electrodes are electrically isolated from each other by an insulation layer 54 that is arranged between the electrodes. At least a part of the fourth electrode 52 is arranged in a non-parallel fashion to the third electrode when the electrostatic actuator 5 is unactuated. Here, the axial distance between the central part of the fourth electrode 52 and the third electrode 51 decreases linearly with radial distance from the optical axis z' of the lens 2 in its center position. The angle between the rigid electrode 52 and the compliant electrode 51 of the electrostatic actuator 5 is designed to reach a good balance between actuator force and displacement. It should ideally be below 10 degrees. The stiffness of the third compliant electrode 51 can be varied with its material and manufacturing parameters as well as with the parameters of the polymer film 3 itself (such as material type, thickness, and amount of pre- strain) .· Increasing stiffness increases actuator force but reduces polymer film deformation and it should be op^¬ timized depending on the device geometry. In this first embodiment, the first electrode 41 of the electroactive polymer actuator 4 and the third electrode 51 of the electrostatic actuator are a common electrode, thus al^¬ lowing for an easy application of a common electrical reference potential, e.g., ground GND. The common electrode is furthermore rotationally symmetric around z' in its center position, in particular the common electrode is not divided into segments.

Fig. 3 shows an actuation state of the electrostatic actuator 5, i.e., the element 2 is displaced along +z as a^' nonzero voltage is applied to (all segments of the) fourth electrode 52.

In Fig. 4 a displacement of the element 2 in both a lateral direction +y and an axial direction +z is shown. For this, a first nonzero voltage difference is applied between the common electrode 41/51 and the second electrode segment 42c of the electroactive polymer actuator 4. This leads to the lateral displacement of the element 2 along +y. A second voltage difference is applied between the common electrode 41/51 and (all segments of) the electrode 52 of the electrostatic actuator 5. This leads to the axial displacement along +z. As discussed above, an order of application of voltages/ voltage differences is not crucial for operation. An actuation of the electroactive polymer actuator 4 prior to the electrostatic actuator 5 can be advantageous due to larger area of the compliant electrodes 42 and 41 that is able to move freely at the time of the lateral displacement.

Fig. 5 shows a tilting movement of the element 2 around a tilt axis φ which is in this case anti- parallel to the x-direction, i.e., pointing out from the y-z-plane. The tilting movement is achieved by applying a nonzero voltage difference between the common electrode 41/51 and only some segments (here: the highly conductive segments 52b and 52c) of the fourth electrode 52 of the electrostatic actuator 5 (see below) . Thus, due to a non rotationally symmetric Coulomb attraction, the optical axis z '. of the element 2 can be rotated around φ. A similar rotation around a second tilt axis Θ is^■ possible by applying a nonzero voltage between the common electrode 41/51 and the highly conductive segments 52c and 52d of the fourth electrode 52 of the electrostatic actuator 5.

Fig. 6 shows a top view of the second electrode 42 of the electroactive polymer actuator 4 of the. first embodiment of the positioning device 1. The second electrode 42 is divided into four electrically isolated segments 42a, 42b, 42c, 42d that are arranged at different angular positions around the optical axis z' of the element 2 in its equilibrium (i.e., unactuated) position. Here, the first segment 42a is located around a 3 o'clock position, the second segment 42b is located around a 12 o'clock position, the third segment 42c is located around a 9 o'clock position and the fourth segment 42d is located around a 6 o'clock position. With this arrangement and independent actuation of the individual segments (i.e., individual voltages can be applied between the common electrode 41/51 and the segments 42a-d) , a displacement of the element 2 in two different directions (that are advantageously perpendicular to each other, i.e., here, the x and the y direction) is possible.

In principle, two electrode segments 42a and 42b (with an angular extension of, e.g., 80 degrees each and a 10 degrees gap) as shown ^' in Fig. 19 (eleventh embodiment) are sufficient to enable a bilateral displacement along .the x and the y directions, when the segments are voltage-biased, i.e., a nonzero voltage is applied between the common electrode 41/51 and the segments 42a-b to bring the element 2 in its center position. Now, e.g., if the voltage on segment 42a is reduced, the element 2 is displaced along +y, if this voltage is increased, the element 2 is displaced along -y. The same applies for the x-direction for the segment 42b.

Fig. 7 shows an x-y projection of a top view of the fourth electrode 52 of the electrostatic actuator 5 of the first embodiment of the positioning device' 1, wherein the fourth electrode 52 comprises four first segments 52a, 52b, 52c, 52d and four second segments 52e, 52f, 52g, 52h. Each of the second segments 52e-h is arranged between two of the first segments 52a-d and vice versa. Furthermore, the resistivity of the first segments 52a-d is smaller than the resistivity of the second segments 52e-h. Typical sheet resistance values are lOOOhm/square for the first segments 52a-d and lOOkOhm/square for the second segments 52e-h.

When a voltage difference is applied between the common electrode 41/51 and a first segment 52a-d of the fourth electrode 52 and a different voltage difference is applied between the common electrode 41/51 and another (e.g., neighboring) first segment 52a-d of the fourth electrode 52, this leads to the buildup of a voltage gradient across the second segment 52e-h that connects the respective first segments 52a-d. Depending on the locally varying voltage difference between the second segment 52e-h of the fourth electrode 52 and the third electrode 51, the Coulomb attraction force between the fourth electrode and the third electrode 51 varies with (angular) location. This results in a smoother and more stepless actuation (e.g., for tilting the element 2) compared to a gradient-free implementation. A gradient-free implementation of the fourth electrode 52 (similar to the one shown in Fig. 6 for the second electrode 42) is, however, possible as well.

For moving the element with three degrees of freedom (i.e., along the axial direction z and around two tilting axes φ, Θ in the x-y-plane) , the minimum number of first and second segments 52a-h is three each (e.g., with an angular extension of 10 degrees for each first segment and 110 degrees for each second segment) as it is shown in Fig. 20 in the twelfth embodiment. This has the advantage that the system is fully defined and all tilting movements are enabled.

The first electrode 41 and/ or the third electrode 51 are typically realized continuously, i.e., segment-free. In other words, this/ these electrode (s) is/ are rotationally symmetric about the optical axis z' of the element 2 in its center position.

Second and third embodiment

Figs. 8 and 9 show a side view of a second and third embodiment of the positioning device 1 with different shapes of the rigid support 53, the third electrode 51, and the insulation layer 54 of the electrostatic actuator 5. As it is discussed above, the angle between the rigid electrode 52 and the compliant common electrode 41/51 is designed to reach a good balance between actuator force and displacement. This angle between the polymer film 3 (and thus the common electrode 41/51) and the fourth electrode 52 changes when zipping progresses. By tuning the shape of the fourth electrode 52, this change can be compensated for. Thus, by tuning the shape of the fourth electrode, an, e.g., linear dependency between applied voltage difference and displacement is possible which simplifies operation of the positioning device.

Fourth embodiment

Fig. 10 shows a side view of a fourth embodiment of the positioning device 1 with one electroactive polymer actuator 4 and two electrostatic actuators 5, 5' . The fourth embodiment is very similar to the first embodiment of the positioning device 1 with the exception that a second electrostatic actuator 5' is arranged on the second side (with the second surface 32) of the polymer film 3. The working principle of the second electrostatic actuator 5' is the same as for the first electrostatic actuator 5 which is arranged on the first side (with the first surface 31) of the polymer film 3. This embodiment has the advantage of an amplified focus range (i.e., displacement range along the z-direction) due to the utilization of two electrostatic actuators 5, 5' . Furthermore, an axial displacement of the element 2 along the +z and the -z direction is possible without voltage- biasing an electrostatic actuator. Thus, the passive state focus, i.e., the axial position of the element 2 without voltages applied to the electrostatic actuators 5, 5', can be in an intermediate focus state.

Fifth embodiment

Fig. 11 shows a side view of a fifth embodiment of the positioning device 1 with a slimmer (i.e., less extended in the lateral direction and in particular not extending to the outer edge of the polymer film 3) second electrode 42 of the electroactive polymer actuator 4. The operation principle of the fifth embodiment of the positioning device 1 is very similar to the first embodiment, with the exception that the second electrode 42 of the electroactive polymer actuator 4 does not laterally overlap an outer part of the fourth electrode 52 of the electrostatic actuator 5. Thus, the decoupling of the electroactive polymer actuator 4 and the electrostatic actuator 5 is improved and the order of voltage- applications to the electroactive polymer actuator 4 and the electrostatic actuator 5 (when the element 2 is to be moved from its first position to its fourth position) is even less critical than discussed with respect to the first embodiment. The radial gap (i.e., the non- overlapping distance in radial direction) between elec- trodes 42 and 52 should be 200μπι or more to enable a good decoupling .

Fig. 12 shows a top view (i.e., an x-y projection) of the fifth embodiment of the positioning device 1. It is clearly visible that the segments 42a-d of the,_: second electrode 42 (cross-hatched) o the electroactive polymer actuator 4 do not extend to the outer edge of the polymer film 3. Slim electrode ridges 42e-h extend to the outer edge of the polymer film 3 for connecting the electrode segments 42a-d to the control unit 6 for application of voltage difference. Thus, the outer part (outward from approximately 90% of the diameter) of the fourth electrode 52 (dotted circle shows its outer edge) of the electrostatic actuator 5 is not laterally overlapped by the second electrode 42 of the electroactive polymer actuator 4. This leads to a better decoupling of the actuators .

Sixth embodiment

Fig. 13 shows a side view of a sixth embodiment of the positioning device 1 comprising separation rings 8a, 8b and decoupled first/ third electrodes 41, 51. In the sixth embodiment of the positioning device 1 a separation ring 8a is arranged at the edge of the movable element 2 in . the polymer film 1. Thus, the whole positioning device 1 can be manufactured without mounting the movable element 2 which can be done later in a final mounting stage. Thus, the manufacturing process is simplified. Alternatively, the positioning device 1 can be fully manufactured and tested and shipped to a customer who can mount his own movable element 2 in the separation ring 8a. A second separation ring 8b with a larger diameter than the first separation ring 8a is arranged in the polymer film 3 laterally between the electroactive polymer actuator 4 and the electrostatic actuator 5. In this embodiment of the positioning device 1, the first elec- trode 41 and the third electrode 51 are not a common electrode as in the embodiments discussed above. This leads to an even better decoupling of both actuators, as both actuators are now mechanically decoupled.

Seventh embodiment

Fig. 14 shows a side view of a seventh embodiment of the positioning device 1 comprising a rotator device 9 and a holding frame 10. The seventh embodiment is very similar to the first embodiment but additionally comprises a rotator device 9 for rotating the electrostatic polymer actuator 4 and the electrostatic actuator 5 and the element 2 around an axial direction, i.e., a direction which is parallel to the axial direction z. In particular, the rotator device 9 can comprise a piezo ring motor, which relies on a slow shearing of axial piezo legs (rotation phase) and a quick return of the legs (slipping phase) . Details on the operation of piezo ring motors can, e.g., be found under pcbmotor.com. Thus, an additional degree of freedom is added for moving the movable element 2. This is advantageous, e.g., if the movable element is not rotationally symmetric around its optical axis z' . In this embodiment, the polymer film 3 of the electroactive polymer actuator 4 is freely suspended in a holding frame 10, advantageously the polymer film 3 is prestretched in a lateral direction prior to mounting (i.e., by clamping, gluing, welding etc.) it to the holding frame 10. This helps to keep the polymer film straight and increases lateral displacability of the movable element 2.

Eighth, ninth, and tenth embodiment Fig. 15 shows a side view of an eighth embodiment of the positioning device 1 wherein the movable element 2 comprises a lens barrel 11, two electroactive polymer actuators 4, 4' and two electrostatic actuators 5, 5' . The lens barrel 11 can, e.g., comprise a plurality of_. lenses (e.g., for correction of optical aberrations) and can be used as objective for a camera module. Since the axial extension of the. lens barrel (i.e., the dimension in the z-direction) is larger than that of a typical single lens, it is advantageous to interconnect the lens barrel 11 to two electroactive polymer actuators 4, 4' and two electrostatic actuators 5, 5' on two opposing sides. This increases the mechanical stability of the lens barrel and improves actuation ranges. Furthermore, the lens barrel is less likely to be unintentionally tilted, thus improving image quality if used in a camera.

The second electrostatic actuator 5' can also be omitted as in the ninth embodiment as shown in Fig. 16. This makes the positioning device 1 more compact and cheaper compared to the eighth embodiment, but at the cost of a slightly reduced z-actuation-range .

In a tenth embodiment as shown in Fig. 17, the second electroactive polymer actuator 4' is replaced by a metal spring element 12. This has the advantage that the positioning device 1 can be produced even cheaper without sacrificing much stability, but at the cost of a slightly reduced x-^y-actuation range.

Eleventh embodiment

Fig. 18 shows a side view of an eleventh embodiment of the positioning device 1 wherein the movable element 2 comprises an image sensor 13. In this embodiment, the positioning device 1 is used in a camera. Here, not a lens or a lens barrel 11 is moved for vibration reduction and or focusing, but the image sensor 13. The lens barrel 11 is held in place by a modified holding frame 10. In principle, it is not crucial if the lens barrel 11 or the image sensor 13 are moved, as for efficient vibration reduction and/ or focusing, only the rel- ative movement of the two elements with respect to each other is relevant.

Definitions :

The term "axial" (along the z direction) is generally used to designate a direction perpendicular to the surface of the polymer film in its relaxed state, which corresponds to a direction parallel to the untilted optical axis z' of the (optical) element as shown in some of the figures. The term "lateral" (along the x and/ or y direction) is used to designate a direction perpendicular to the axial direction z, i.e., a direction parallel to the relaxed polymer film. The term "radial" is used synonymously to "lateral".

Notes :

To reduce the adhesion between the insulation layer 54 and the polymer film 3 and or the third electrode 51, which may introduce hysteresis, the polymer film 3 and/ or the insulation layer 54 may be coated with a self-assembled monolayer (SAM) . The SAM molecules consists of a head group adhering to the substrate (e.g. a silane or a phosphonic acid) and a tail group having adhesion reducing properties (such as perfluorinated alkyle chains) . Another means to reduce adhesion is nanostruc- turing of the insulation layer 54 and/ or the polymer film 3 and/ or the third electrode 51. To diminish the effects of any introduced roughness while keeping actuation voltage low, high-k isolators with comparatively high layer thickness can be used.

The insulation layer 54 can be composed of or comprise ceramics such as AI2O3, Si=2, T1O2, HfC>2, SrTiC>3; polymers such as Parylene, Polystyrene, Poly Vi- nylidene diFluoride (PVDF) ; commercial dielectric resins such as SU-8, BCB, epoxy-based resins; and/ or nanocompo- sites such as high-k nanoparticles (e.g., barium titan- ate) dispersed in a polymer matrix.

Deposition of the insulation layer can comprise the steps of chemical vapor deposition (CVD) , atomic deposition (ALD) , evaporation, sputtering, spin- _* coating, and/ or spray-coating.

The higher-resistivity electrode segments 52e-h of the fourth electrode 52 may be produced with a conductive polymer such as PEDOT, or a nanocomposite with a polymer matrix and conductive nanoparticles (such as carbon black) .

The polymer film 3 is preferably connected to a holding frame 10 and/ or prestretched . As an example, an edge region of polymer film 3 can be clamped between a top and a bottom part of the holding frame 10. As known to the skilled person, the term "prestretching" (or pre- straining) can be understood as suspending the polymer film in the holding frame 10 in such a manner that it is under tensional strain, i.e., a tensional force tries to keep the polymer film straight. The polymer film 3 can be freely suspended in the holding frame 10, i.e., it is only supported by the holding frame 10 with no further stationary, rigid elements being in contact with its surfaces 31, 32 (with the exception of the movable element 2) .

The first, second, and third electrodes 41, 42, 51 should be compliant, i.e., they should be able to reversibly and elastically follow deformations of at least 5%, in particular of at least 20% of the polymer film 3 without being damaged and/ or constraining the deformations. Advantageously, the electrodes are therefore manufactured from one of the following materials: - Carbon nanotubes (see "Self-clearable carbon nanotube electrodes for improved performance of dielectric elastomer actuators", Proc. SPIE, Vol. 6927, 69270P (2008))

- Carbon black (see "Low voltage, highly tunable diffraction grating based on dielectric elastomer actuators", Proc. SPIE, Vol. 6524, 65241N (2007))

- Carbon grease / conducting greases

- Metal ions (Au, Cu, Cr,...) (see "Mechanical properties of electroactive polymer microactuators with ion-implanted electrodes", Proc. SPIE, Vol. 6524, 652410 (2007))

- Liquid metals (e.g. Galinstan)

- Metallic powders, in particular metallic nanoparticles (gold, silver, copper)

- Conducting polymers (intrinsically conducting or composites)

The electrodes may be deposited by means of any of the following techniques:

- Spraying

- Ion-implantation (see "Mechanical properties of electroactive polymer microactuators with ion- implanted electrodes", Proc. SPIE, Vol. 6524,. 652410 (2007))

- PVD, CVD

- Evaporation

- Sputtering

- Photolithography

- Printing, in particular contact printing, inkjet printing, laser printing, pad printing and screen printing .

- Field-guided self-assembly (see e.g. "Local surface charges direct the deposition of carbon nanotubes and fullerenes into nanoscale patterns", L. Seemann, A. Stemmer, and N. Naujoks, Nano Letters 7,· 10, 3007-3012, 2007)

- Brushing

- Electrode plating

Movable elements can consist of or comprise, e.g.,

- spherical lenses (convex and concave) ,

- Fresnel lenses,

- cylindrical lenses,

- aspherical lenses (convex and concave) ,

- mirrors,

- gratings,

- lens assemblies,

- GRIN lenses,

- squares, triangles, lines or pyramids,

- holograms .

- diffusers

- needles

- or any other mechanical element

Any micro (e.g. micro lens array, diffraction grating, hologram) or nano (e.g. antireflection coating) structure can be integrated into the movable element 2 and the compliant electrode containing polymer film. When an anti-reflective layer is to be applied to at least one surface of the element 2, it is advantageously formed by fine structures having a size smaller than the wavelength of the transmitted light. Typically, this size should be smaller than 5 μηι for infrared applications, smaller than 1 μπι for near-infrared applications, and smaller than 200 nm for applications using visible light.

Any of the following methods can e.g. be applied for forming and structuring the element 2: ·- Casting, in particular injection molding/ mold processing

- Nano-imprinting, e.g. by hot embossing nanometer-sized structures

- Etching (e.g. chemical or plasma)

- Sputtering ■

- Hot embossing

- Soft lithography (i.e. casting a polymer onto a pre-shaped substrate)

- Chemical self-assembly (see e.g. "Surface tension-powered self-assembly of microstructures - the state-of-the-art", R.R.A. Syms, E. M. Yeatman, V. . Bright, G.M. Whitesides, Journal of Microelectromechani- cal Systems 12(4), 2003, pp. 387 - 417)

- Electro-magnetic field guided pattern forming (see e.g. "Electro-magnetic field guided pattern forming", L. Seemann, A. Stemmer, and N. Naujoks, Nano Lett., 7 (10), 3007 - 3012, 2007. 10.1021/nl0713373.

The material for the element 2 can e.g. comprise or consist of:

- PMMA or PC

- Glass

- Plastic

- Polymer

- Metals

- Crystalline, in particular single crystal material .

The material for the polymer film 3 can e.g. comprise or consist of:

- Gels (Optical Gel OG-1001 by Liteway) ,

- Elastomers (TPE, LCE, Silicones e.g. PDMS Sylgard 186, Acrylics, Urethanes)

- Thermoplast (ABS, PA, PC, PMMA, PET, PE, PP, PS, PVC,...)

- Duroplast The geometries of the electrodes can be round, square, segmented, or any other appropriate form.

While there are shown and described presently preferred embodiments of the invention, it is to be distinctly understood that the invention is not limited to these embodiments but may be otherwise variously embodied and practiced within the scope of the following claims.

Claims

1. Positioning device (1) for an element (2), in particular for an optical element (2), comprising a polymer film (3) interconnected to said element (2) , an electroactive polymer actuator (4) for displacing said element (2) at least in a lateral direction¹' (x, y) and an electrostatic actuator (5) for tilting said element (2) around at least one tilt axis (φ, Θ) and/ or for displacing said element (2) in an axial direction (z),

wherein said lateral direction (x, y) is perpendicular to said axial direction (z),

wherein said polymer film (3) comprises a first surface (31) on a first side and a second surface (32) on a second side of said polymer film (3) ,

wherein said electroactive polymer actuator (4) comprises a first electrode (41) interconnected to said first surface (31) and a second electrode (42) interconnected to said second surface (32) of said polymer film (3),

wherein said element (2) is displaceable from a first position to a second position by an application or change of a voltage difference between said first and said second electrode (41, 42) ,

wherein said first position differs from said second position at least in said lateral direction (x, y⁾ ,

wherein said electrostatic actuator (5) comprises a third electrode (51) interconnected to said first surface (31) of said polymer film (3), a fourth electrode (52) interconnected to a rigid support (53), and an insulation layer (54) arranged between said third electrode (51) and said fourth electrode (52) and wherein at least upon application of a zero voltage difference between said third electrode and said fourth electrode at least a part of said fourth electrode (52) is arranged non-parallel to said third electrode (51), wherein said element (2) is tiltable and/ or displaceable from a third position to a fourth position by an application or change of said voltage difference between said third and said fourth electrodes (51, 52), wherein said third position differs from said fourth position in said axial direction (z) and/ or wherein said element (2) is tilted in said fourth position with respect to said third position.

2. The positioning device (1) of claim 1 wherein said first and second electrodes (41, 42) of said electroactive po^'lymer actuator (4) and said third electrode (51) of said electrostatic actuator (5) are compliant electrodes.

3. The positioning device (1) of any of the preceding claims wherein said first electrode (41) of said electroactive polymer actuator (4; 4') and said third electrode (51) of said electrostatic actuator (5; 5') are embodied as a common electrode.

4. The positioning device (1) of any of the preceding claims further comprising a control unit (6) wherein said control unit (6) is adapted to apply and/ or change said voltage differences of said electroactive polymer actuator (4; 4') and said electrostatic actuator (5; 5') such that said displacement of said element (2) in said lateral direction (x, y) and/ or said displacement of said element (2) in said axial direction (z) and/ or said tilting of said element (2) are combinable.

5. The positioning device (1) of any of the preceding claims wherein a second electrostatic actuator (5') is arranged on said second side of said polymer film (3) opposite said electrostatic actuator (5) on said first side of said polymer film (3) .

6. The positioning device (1) of any of the preceding claims further comprising a rotator device (9), in particular a piezo ring motor (9), wherein said rota- tor device (9) is interconnected to said support (53) and/ or a holding frame (10) .

7. The positioning device (1) of any of the preceding claims wherein said polymer film (3) is freely suspended in a holding frame (10) .

8. The positioning device (1) of claim 7 wherein said polymer film (3) is attachable to said holding frame (10) in a prestretched manner.

9. The positioning device (1) of any of the preceding claims wherein said electroactive polymer actuator (4; 4') and/ or said electrostatic actuator (5; 5') is/ are voltage bias-able when the element (2) is in its first or third position.

10. The positioning device (1) of any of the preceding claims wherein the element (2) comprises at least one of the group of a lens, a grating, a mirror, a lens barrel (11), a lens assembly, a diffuser, and an image sensor.

11. The positioning device (1) of any of the preceding claims wherein said second electrode (42) of said electroactive polymer actuator (4; 4') comprises at least a first and a second segment (42a, 42b, 42c, 42d) , wherein said segments (42a, 42b, 42c, 42d) are electrically isolated with respect to each other, wherein said segments (42a, 42b, 42c, 42d) are arranged at different angular positions around said axial direction (z), and wherein individual voltage differences are applicable between said first electrode (41) and each of said segments (42a, 42b, 42c, 42d) .

12. The positioning device (1) of claim 11 wherein a number of said segments (42a, 42b, 42c, 42d) is two and wherein said first and said second segment (42a, 42b) are arranged such that said element (2) is independently displaceable in two lateral directions (x, y) , wherein said lateral directions (x, y) are perpendicular to each other and to said axial direction (z).

13. The positioning device (1) of any of the preceding claims wherein said fourth electrode (.52) of said electrostatic actuator (5; 5' ) comprises at least two first segments (52a, 52b, 52c, 52d) with a first resistivity and at least one second segment (52e, 52f, 52g, 52h) with a second resistivity,^ wherein said first resistivity is smaller than said second resistivity, and wherein each of said second segments (52e, 52f, 52g, 52h) is arranged between and electrically connected to two of said first segments (52a, 52b, 52c, 52d) .

14. The positioning device of claim 13, wherein a number of said first segments and said second segments (52a, 52b, 52c, 52e, 52f, 52g) is three each.

15. The positioning device (1) of any of the preceding claims further comprising a second electroac- tive polymer actuator (4') with a second polymer film (3' ) and/ or a second electrostatic actuator (5' ) and/ or a spring element (12) interconnected to a second side of ^'said element (2) opposing a first side of said element

(2) , wherein said polymer film (3) of said first electro- active polymer actuator (4) is interconnected to said first side of said element (2) .

16. The positioning device (1) of any of the preceding claims further comprising at least one separation ring ( 8 ) .

17. A method for operating a positioning device (1) of any of the claims 1 to 16 comprising:

applying or changing said voltage difference between said first and said second electrodes (41, 42) of said electroactive polymer actuator (4) to displace said element (2) from said first position to said second position, wherein said first position differs from said second position at least in said lateral direction (x, y) , applying or changing said voltage difference between said third and said fourth electrodes (51, 52) of said electrostatic actuator (5) to tilt and/ or displace said element (2) from said third to said fourth position, wherein said third position differs from said fourth position in said axial direction (z) and/ or wherein said element is tilted in said fourth position with respect to said third position.

18. The method of claim 17 wherein said applying or changing of said voltage difference between said first and said second electrodes (41, 42) of said electroactive polymer actuator (4) occurs prior to said applying or changing of said voltage difference between said third and said fourth electrodes (51, 52) of said electrostatic actuator (5).

19. A method for positioning an element (2) consisting of or comprising at least one of the group of a spherical lens, a Fresnel lens, a cylindrical lens, an aspherical lens, a mirror, a grating, a lens assembly, a lens barrel (11), a GRIN lens, a square, a triangle, a line, a pyramid, a hologram, a diffuser, a needle, an image sensor, and a mechanical element by means of a positioning device (1) of any of the claims 1 to 16.

20. The method of claim 19 wherein a displacement resolution is better than 20 m and/ or a tilt resolution is better than 5mrad.

21. The method of any of the claims 19 or 20 wherein said positioning device (1) is used for a vibration compensation and/ or an auto-focusing in a camera module .

22. A method for fabricating a positioning device (1) of any of the claims 1 to 16 comprising the steps of

interconnecting the first, second, and third electrodes (41, 42, 51) to the polymer film (3) ,

interconnecting the fourth electrode (52) to the rigid support (53) and interconnect- ing the insulation layer (54) to the fourth electrode (53) ,

interconnecting the element (2) to the polymer film (3).

interconnecting the polymer film (3) to the rigid support (53).

23. The method of claim 22 further comprising the step of prestraining the polymer film (3) .