TECHNICAL FIELD

The present invention relates to an actuator for a camera module. In particular, the invention presents a linear actuator for a camera module, which may be suitable for a mobile device, like a smartphone. The linear actuator makes use of one or more shape- memory alloy (SMA) wires, which are operable to move a piston to drive a driven element of the camera module. The invention also presents a camera module that includes the actuator, and a method for operating the actuator to drive the driven element.

BACKGROUND Camera modules, e.g. installed in smartphones, are key differentiators within the mobile industry. As performance levels are steadily increasing, new features are needed. For instance, by introducing tunable lenses (e.g. deformable lenses) or movable lenses (typically non-deformable), new camera modules are able to perform focusing, image stabilization, or other operations, more efficiently. However, these camera modules need a suitable electromechanical actuator, in order to deform or move the lenses.

The most popular technology for realizing an actuator for moving a lens barrel perpendicular to an image sensor, is a voice coil motor (VCM) actuator. Another popular technology is a piezo-electric motor actuator. In addition, electrostatic, electromagnetic or magnetostrictive actuators, stepper motor actuators, and electroactive polymer actuators are known.

However, all of these actuators typically generate a too small force, in particular when they are to be used for deforming or moving lenses in a camera module. For example, shape changing materials of a tunable lens (such as liquids and polymers) require considerable physical deformation and thus larger forces. Further, movable lenses are often rather heavy and thus require larger forces for being moved. Disadvantageously, as an example, a VCM actuator is barely able to generate 50 mN of operating forces within a reasonable space and with a reasonable power consumption. This force is not sufficient for the above-mentioned application scenarios.

SUMMARY

In view of the above-mentioned challenges and disadvantages, embodiments of the invention aim to provide an improved actuator for a camera module. An objective is in particular to provide an actuator, which is capable of generating a higher force. Further, the actuator should enable high speed operations and accurate positioning. At the same time, the power consumption of the actuator should be low. Further, the actuator should be compact, and should have reasonable production costs.

The objective is achieved by the embodiments of the invention as described in the enclosed independent claims. Advantageous implementations of the embodiments of the invention are further defined in the dependent claims.

A first aspect of the invention provides a linear actuator for a camera module, the actuator comprising: a piston connectable or connected to a driven element of the camera module, one or more lever arms connected to the piston, and one or more SMA wires, each SMA wire coupled to one of the lever arms, wherein the one or more SMA wires are operable to change their lengths and thereby move the one or more lever arms so as to produce a linear movement of the piston.

The linear movement of the piston may be substantially linear. That is, it may deviate but little from a perfectly linear (i.e. perfectly straight) movement. The linear movement may be considered substantially linear if it deviates by not more than a maximum angular deviation (which is a certain small angle) from a straight line over a whole possible range of motion of the piston. For example, the maximum angular deviation may be less than 10°, or less than 5°, or even less than 2°.

The SMA wire based linear actuator of the first aspect is an improved actuator for a camera modules. In particular, the actuator is able to generate a higher force more efficiently than a conventional actuator. The actuator of the first aspect also achieves a better electromechanical packaging density, i.e. it can be built more compactly than a conventional actuator. Further, by operating the one or more SMA wires independently or simultaneously, the linear movement of the piston can be controlled very accurately, such that it can be used for performing a focusing operation in the camera module. Moreover, the actuator of the first aspect allows fast operation, i.e. a fast movement of the piston, particularly back-and-forth along an axis. This makes the linear actuator beneficial for zooming operations in the camera module. In addition, the power consumption of the actuator is low, and thus also the power consumption of the camera module is limited.

The one or more SMA wires may be connected to the members inside the actuator or camera module by coupling and suspension mechanisms, particularly to the lever arms or fixed structures. These mechanisms can meet the assembly, operation and reliability requirements set by typical mobile handsets. Thus, the linear actuator of the first aspect is suitable for a camera module to be installed in a mobile device, like a smartphone.

The actuator of the first aspect further may have a high electromagnetic immunity, which is beneficial when it is combined - e.g. in a multi-camera system - with other actuators. The electromagnetic immunity particularly helps avoiding interference between adjacent magnetic fields produced by other actuators.

In an implementation form of the first aspect, the length changes of the SMA wires are converted by the movement of the lever arm into the linear movement of the piston.

Due to the lever arms, a high force can be generated, and a large stroke of the piston can be achieved by a comparably small length change of the one or more SMA wires.

In an implementation form of the first aspect, the actuator further comprises one or more sensors configured to measure a linear position of the piston.

Each sensor may be configured to measure the linear position. The one or more sensors allow a precise movement and positioning of the actuator (piston), in order to accurately drive the driven element. This enables, for instance, a fast and accurate focusing operation in a camera module. The one or more sensors may, in particular, be one or more Hall sensors. One or more of such sensors may also be provided on the driven element.

In an implementation form of the first aspect, the one or more lever arms hold the piston.

Thus, the lever arms do not only serve for driving the piston (i.e. for imparting a momentum to the piston), but also for supporting the piston, in particular when driving the piston and also when the piston is stationary. The one or more lever arms may thus also act as a bearing, support, or mount, which keeps the piston at a desired/intended place at any time. For example, the piston may be mounted to the one or more of the lever arms via one or more joints, e.g. one or more pivots.

In an implementation form of the first aspect, the actuator further comprises a sliding bearing or ball bearing for guiding the piston.

The piston can thus be guided more accurately than by the lever arms alone. A sliding bearing is beneficial in terms of cost, while a ball bearing has less friction and backlash.

In an implementation form of the first aspect, each lever arm comprises a first section and a second section, which together form a bend of the lever arm and meet at a pivot point of the lever arm, the lever arm is connected with its second section to the piston, the SMA wire that is coupled to the lever arm is coupled to the first section of the lever arm, and the length change of the SMA wire causes the lever arm to pivot about the pivot point.

The one or more lever arms may accordingly be non-straight. In this way, a high force and large stroke can be generated for the movement of the piston. In other embodiments, however, the one or more lever arms can also be straight, which allows for a simpler and more compact design.

In an implementation form of the first aspect, the second section is longer than the first section. The actuator can thus generate a force particularly efficiently, i.e. a length change of the one or more SMA wires generates a large force of the moving piston.

In an implementation form of the first aspect, each SMA wire is connected with one of its ends to a fixed structure and with its other end to the lever arm, or each SMA wire is connected with both of its ends to a fixed structure and has an intermediate portion connected to an attachment portion of the lever arm.

Each lever arm may be coupled to one or more SMA wires to cause its movement. A SMA wire may be looped around the attachment portion to couple to the lever arm, while its ends are fixed to the fixed structure. Alternatively, two SMA wires may be used for the same effect.

In an implementation form of the first aspect, the actuator further comprises a first lever arm and a second lever arm, which are connected to different locations on the piston, wherein the one or more SMA wires include a first SMA wire coupled to the first lever arm and a second SMA wire coupled to the second lever arm, wherein a length change of the first SMA wire and/or of the second SMA wire causes the linear movement of the piston.

By operating the first SMA wire and the second SMA wire, independently and/or simultaneously, the piston can be moved very accurately, and also rapidly along an axis. Thereby, the piston may be moved into opposite directions along the axis.

In an implementation form of the first aspect, the first SMA wire and the second SMA wire together form a V-shape or X-shape.

In an implementation form of the first aspect, the actuator is further configured to actuate each SMA wire independently, or simultaneously with at least one other SMA wire, wherein each actuation changes the length of the respective wire.

In this way, the movement of the piston can be controlled very precisely. A second aspect of the invention provides a camera module, comprising: a driven element, and a linear actuator according to the first aspect or any of its implementation forms, wherein the piston of the linear actuator is connected to the driven element.

The camera module benefits from all the advantages described above for the linear actuator of the first aspect. In particular, the driven element of the camera module can be driven with a higher force than with a conventional actuator. Further, it can be driven very accurately and fast. This makes the camera module very suitable for a driven element comprising one or more tunable or movable lenses, for instance, usable in a mobile device camera.

In an implementation form of the second aspect, the driven element comprises an optical element.

The driven element may also comprise one or more sensors, in particular Hall sensors, to measure the position of the piston.

In an implementation form of the second aspect, the optical element comprises one or more of a lens, a prism, or a mirror.

In an implementation form of the second aspect, the optical element comprises a lens, wherein the lens is configured to be deformed by the linear movement of the piston, or the lens is rigid and configured to be moved by a movement of the piston.

The rigid lens may be non-deformable. The deformable lens may be a tunable lens, wherein deformation of the optical material of the lens may change its refractive index.

In an implementation form of the second aspect, the camera module further comprises an image sensor, wherein the linear actuator is configured to perform a focusing operation by moving the piston of the actuator.

A focusing operation is an operation that comprises (or aims at) focusing an image on the image sensor. The image may be a still image or a frame of a video. A third aspect of the invention provides a method for driving a driven element of a camera module, the method comprising: operating one or more SMA wires to change their lengths, wherein each SMA wire is coupled to one of one or more lever arms, the one or more lever arms are connected to a piston, and the piston is connectable or connected to the driven element, and wherein the one or more SMA wires are operated to change their lengths and thereby move the one or more lever arms so as to produce a linear movement of the piston.

The method may be carried out by operating the actuator of the first aspect or its implementation forms. The method may also be carried out by operating the actuator of the camera module of the second aspect or its implementation forms. The method achieves the same advantages as described above.

In summary, the aspects and implementation forms (embodiments) describe an electromechanical actuation arrangement (i.e. the linear actuator) for use in an optical system (specifically the camera module). The camera module may be designed for a mobile device camera, and may include a (e.g. deformation-based) tunable lens or a (heavy-weight and/or rigid) non-deformable lens.

The embodiments of the invention combine a piston with one or more lever arms, wherein more lever arms may be arranged as a parallelogram. The piston may have some sort of self-measuring capability, e.g. realized by using the above-mentioned one or more Hall sensors. Furthermore, the piston may have a coupling with a tunable lens or rigid lens of the camera module. An optical surface of the tunable lens may be deformed by linearly or quasi-linearly moving the piston. Alternatively, the position of the rigid lens may be changed by moving the piston. The piston movements can be carried out in two opposite directions. The one or more SMA wires may each be suspended on one of the lever arms, in order to move the one or more lever arms when operated, and thereby to linearly or quasi-linearly move the piston.

It has to be noted that all devices, elements, units and means described in the present application could be implemented in the software or hardware elements or any kind of combination thereof. All steps which are performed by the various entities described in the present application as well as the functionalities described to be performed by the various entities are intended to mean that the respective entity is adapted to or configured to perform the respective steps and functionalities. Even if, in the following description of specific embodiments, a specific functionality or step to be performed by external entities is not reflected in the description of a specific detailed element of that entity which performs that specific step or functionality, it should be clear for a skilled person that these methods and functionalities can be implemented in respective software or hardware elements, or any kind of combination thereof.

BRIEF DESCRIPTION OF DRAWINGS

The above described aspects and implementation forms of the invention will be explained in the following description of specific embodiments in relation to the enclosed drawings, in which:

FIG. 1 shows a linear actuator according to an embodiment of the invention.

FIG. 2 shows camera modules according to embodiments of the invention.

FIG. 3 shows an example of a deformable lens, which can be used in a camera module according to an embodiment of the invention.

FIG. 4 shows lever arms and a piston of a linear actuator according to an embodiment of the invention.

FIG. 5 shows a linear actuator according to an embodiment of the invention in an initial position. FIG. 6 shows a linear actuator according to an embodiment of the invention in a first operating position. FIG. 7 shows a linear actuator according to an embodiment of the invention in a second operating position.

FIG. 8 shows a linear actuator according to an embodiment of the invention.

FIG. 9 shows bearings for guiding a piston of a linear actuator according to embodiments of the invention.

DETAILED DESCRIPTION OF EMBODIMENTS

FIG. 1 shows a linear actuator 100 according to an embodiment of the invention. The linear actuator 100 is suitable for a camera module 200 (see FIG. 2), e.g. a camera module of a mobile device like a smartphone, tablet, laptop or the like. In particular, the linear actuator 100 is configured to move a driven element 110 of the camera module 200.

The linear actuator 100 comprises a piston 101, one or more lever arms 102, and one or more SMA wires. The piston 101 is connectable or connected to the driven element 110 of the camera module 200. The one or more lever arms 102 are connected to the piston 101. The one or more lever arms 102 may thereby hold and/or guide the piston 101. If there is more than one lever arm 102, the multiple lever arms 102 may be respectively connected to the piston 101 at different locations. The one or more SMA wires 103 are each coupled to one of the lever arms 102. Thereby, more than one SMA wire 103 may be coupled to a single lever arm 102. Each of the one or more SMA wires 103 may be connected with an end or with an intermediate portion to an attachment portion of one lever arm 102. The other end or both ends, respectively, of each of the one or more SMA wires 103 may be fixedly held, e.g. attached to some fixed structure or portion of the actuator 100 or camera module 200.

The one or more SMA wires 103 are operable to change their lengths 104, i.e. each SMA wire 103 can be operated to change its length 104, e.g. by a driving current. Thereby, each of the SMA wires 103 may be operated/actuated independently or simultaneously from/with at least one other SMA wire 103, in order to cause the length change of that SMA wire 103. The length change(s) of the one or more SMA wire 103 may all be of the same or different amount. The length changes(s) of the one or more SMA wires 101 moves the one or more lever arms 102, so as to produce a linear or quasi-linear movement 105 of the piston 101. The linear or quasi-linear movement of the piston 101 may be directed along an axis. The piston 101 may be movable in opposite directions along that axis, i.e. forwards or backwards, depending on whether a length 104 of the one or more SMA wires 103 is increased or decreased.

It is known that SMAs are characterized by a structural transition between two phases, namely the so-called Martensite phase which is stable at a lower temperature, and the so- called Austenite phase, which is stable at a higher temperature. A SMA is characterized by four temperatures, Mf, Ms, As, Af. Mf is the temperature below which the SMA is completely in the Martensite phase, i.e. it has a martensitic structure, while Af is the temperature above which the SMA is fully in the Austenite phase, i.e. it has an austenitic structure. Wires made of a SMA, also known as SMA wires, can be trained to change their shape when temperature changes from below Mf to above Af, and vice-versa. Processing and training of SMA wires are widely known procedures in the field, as exemplified by the paper "Shape Memory Alloy Shape Training Tutorial" dating back to the Fall 2004 training section "ME559 - Smart Materials and Structures".

It is also known that wires made of a SMA start to shorten at a temperature equal to or higher than the Austenite start temperature As and reach their final length when heated at a temperature equal or above the Austenite final temperature Af.

Compared to a conventional actuator, with which only a light portion of an optical stack can be moved, or only a very small tunable lens can be deformed, in order to perform an autofocus and/or zoom operation of a camera module - for compared to a VCM actuator - the linear actuator 100 according to embodiments of the invention can move can move a heavier weight (e.g. of a larger rigid lens), or can deform a stiffer membrane (e.g. arranged on a fluid capacity of a larger tunable lens). This is because the actuator 100 is based on the one or more lever arms 102 and the one or more SMA wires 103.

FIG. 2 illustrates in this respect in (a) and (b) different camera modules 200 according to embodiments of the invention, which both use the linear actuator 100 according to an embodiment of the invention, e.g. as shown in FIG. 1. The camera modules 200 comprise the driven element 110 and the linear actuator 100. The piston 101 of the actuator 100 is connected to the driven element 110. The driven element 110 typically comprises one or more optical elements, like a lens, prism and/or mirror. In FIG. 2(a) the driven element 110 specifically comprises a tunable lens 201 (e.g. deformable lens), and in FIG. 2(b) the driven element 110 specifically comprises a movable lens 201. The tunable lens 201 may be configured to be deformed by the linear movement 105 of the piston 101, while the movable lens 202 may be configured to be moved by the linear movement 105 of the piston 101. The movement of the piston 101 can thus be used to realize an auto focus and/or zoom operation in the camera module 200, e.g. to focus an image on an image sensor included in the camera module 200.

FIG. 3 shows an example of a deformable tunable lens 201. A movement of the guided piston 101 (not shown in Figure 3) of the actuator 100 may act on a rigid element 300 on a tunable lens membrane of a first cavity. Thereby, a fluid pressure may be generated, which modifies the optical membrane of a second cavity on the optical axis. Thus, the movement of the piston 101 may be used for adjusting light refraction of the tunable lens 201.

FIG. 4 shows partly an actuator 100 according to an embodiment of the invention, which builds on the actuator 100 of FIG. 1. In particular, FIG. 4 shows that an implementation of the actuator 100 can comprise two lever arms 102 and the piston 101. The piston 101 may be a guided piston, e.g. it may be guided by the two lever arms 102. The two lever arms 102 may each be attached with one end at a fixed structure 400, e.g. at a housing of the actuator 100 or the camera module 200, and with the other end to the piston 102, in particular at different locations of the piston 101. Thereby, each of the lever arms 102 may be attached via a first joint 401 to the piston 101 and via a second joint 402 to the fixed structure 400, wherein the joints 401, 402 may be pivots. Accordingly, the two lever arms 102 may together form a flexure, in particular an x-type flexure, which is connected to the piston 101. Notably, a single-type flexure can also be realized with only one lever arm 102, as e.g. shown in FIG. 1. The flexure (and thus the one or more lever arms 102) may be made of plastic or metal, and may be simple to assemble and very robust. FIG. 5 shows an implementation of a linear actuator 100 according to an embodiment of the invention, which builds on the linear actuator 100 shown in FIG. 1 and FIG. 3, respectively. In particular, the linear actuator 100 of FIG. 5 combines the arrangement of the two lever arms 102 and the piston 101 (shown in FIG. 3) with at least two SMA wires 103, i.e. with at least a first SMA wire 103 and a second SMA wire 103. The two SMA wires 103 form a V-shape. Both SMA wires 103 are coupled to one of the lever arms 102. Each SMA wire 103 is shown to be connected with one of its ends to the fixed structure 400, e.g. housing, and with its other end to the lever arm 102. In particular, the SMA wires 103 are thereby connected to different locations of the fixed structure 400, but are connected to the same attachment portion of the lever arm 102. Thus, the V-shape is formed.

As the preferred way to actuate the SMA wire is by heating via Joule effect, if more than one SMA wire are used then:

• If the SMA wires 103 are concurrently actuated, they do not need to be electrically insulated (cooperative configuration).

• If the SMA wires 103 need to be separately actuated or need to be in a different actuation state (i.e. temperature), the SMA wires 103 need to be electrically insulated among themselves (antagonistic configuration).

The lever arm 102 may have a total length 502 (“L2”), and the attachment portion may be arranged on the lever arm 102 at a determined distance 501 (“LI”) from the joint 402, which couples the lever arm 102 to the fixed structure 400. A length change of the first SMA wire 103 and/or of the second SMA wire 103 causes a movement of lever arm 102, and also causes the linear movement 105 of the piston 101.

FIG. 6, FIG. 7 and FIG. 8, respectively, show another implementation of a linear actuator 100 according to an embodiment of the invention, which builds on the linear actuator 100 shown in FIG. 1. In particular, the linear actuator 100 of FIG. 6-8 comprises two lever arms 102, i.e. a fist lever arm 102 and a second lever arm 102, which are connected at different locations to the piston 101, via joints 401. The other end of each of the lever arms 102 is connected via a joint 402 to the fixed structure 400, e.g. housing. Each of the lever arms 102 comprises a first section 601 and a second section 602. These sections 601 and 602 meet in and form a bend of the lever arm 102, and meet at a pivot point of the lever arm 102, which is defined by the corresponding joint 402. Each of the lever arms 102 is connected with the second section 602 to the piston 101.

Further, the actuator 100 comprises at least two SMA wires 103, i.e. at least a first SMA wire 103 and second SMA wire 103, wherein each of the SMA wires 103 is connected to one of the lever arms 102 and to the fixed structure 400, respectively. In particular, each SMA wire 103 is shown to be connected with both of its ends to the fixed structure 400 and with an intermediate portion to an attachment portion of the lever arm 102. Of course, two separate SMA wires 103 could be used per lever arm 102 instead of one looped SMA wire 103, and in this case each of these two SMA wires 103 would be connected with one of its ends to the fixed structure 400 and with the other one of its end to the lever arm 102. The first SMA wire 103 and the second SMA wire 103 together form an X-shape.

Each of the SMA wires 103 is coupled to the first section 601 of the lever arm 102, which it is associated with. A length change of one or more of the SMA wires 103 causes the lever arms 102 to pivot about the respective pivot points 402, and thus causes the movement 105 of the piston 101.

In the embodiments of the linear actuator 100, in the power off status the piston 101 may be in a middle (initial) position. This is shown for the previously described implementation of the actuator 100 in FIG. 6. FIG. 7 shows the piston 101 in a first operation position, i.e. the piston 101 has been moved linearly from the initial position of FIG. 6 into one direction. FIG. 8 shows the piston 101 in a second operation position, i.e. the piston has been moved linearly from the initial position of FIG. 6 into a direction opposite to that in FIG. 7.

FIG. 5 is a good example of SMA wires 103 in an antagonistic configuration, i.e. the two SMA wires 103 work in opposition against each other, whereas FIGs. 6-8 show two SMA wires 103 in cooperative configuration. In a camera module 200 including a tunable/deformable lens 201 as shown in FIG. 3, if the piston 101 is in the initial position, this may mean that the membrane of the tunable lens 201 is not loaded by any force of the actuator 100. Notably, there may be a hard stop to limit the movement 105 of the piston 101. If the piston 101 is then linearly moved to deform the membrane of the tunable lens 201, a counterforce may be provided by the membrane, which acts on the piston 101 and all movable parts of the actuator 100. A force generated by operating the one or more SMA wires 103 may work against the force of the membrane of the deformable lens 201, supported by the lever effect of the one or more lever arms 102.

In the embodiments of the linear actuator 100, each of the one or more SMA wires 103 may be able to contract, by applying a current, by 1% - 4% of its original wire length 104. Each of the one or more SMA wires 103 may further be attached to the fixed structure 400, e.g. an actuator base of housing, by using a crimp connection. The actuator 100 may specifically be designed to push and pull the piston 101 for performing the linear movement 105.

In an embodiment of the camera module 200, while an autofocus function is active, an image signal processor (ISP) may drive the linear actuator 100 into a position determined to allow taking the best image (i.e. the position that is believed to be the best for obtaining a sharp image). When driving a current through the one or more SMA wires 103, the piston 101 may move parallel to a base structure (e.g. the fixed structure 400) of the actuator 100, and towards the driven element 110. Thereby, a maximum full stroke of the piston 101 of the actuator 100 may be limited by a hard stop, which helps protecting the actuator 100 against damages, for instance, while a drop test performed in device testing.

Dynamic stroke requirements for focusing and zooming operations in high-magnification optical zoom camera modules, especially including tunable/deformable lenses, are 3-8 times higher than conventional requirements for a fixed focal length camera module. Further, the required forces are 3-10 times higher than for conventional focusing optics. Therefore, the behavior of one or more SMA wires 103 (i.e. high force and high stroke) offers the best package and force specification, and is beneficial to drive larger deformable or movable lenses 201, 202. In addition, sensing the position of the piston 101 through resistance allows omitting additional position sensors, in order to realize a smaller package, as nowadays requested for smartphones.

FIG. 9 shows bearings suitable for guiding a piston 101 of a linear actuator 100 according to an embodiment of the invention. Technically, such a linear guidance (i.e. a guidance of the linear piston movement 105), can be realized by a sliding bearing 901 (shown in FIG. 9(a)) or a ball bearing 902 (shown in FIG. 9(b)). The sliding bearing 901 is beneficial in terms of cost, but may add some friction and/or backlash. The ball bearing 902 overcomes these drawbacks, but may add more complexity to the assembly. Systemically there is no difference on how the actuator stroke, i.e. the linear movement 105 of the piston 100, is guided. There is just a generic difference in using a linear guidance, like a bearing 901, 902, or a parallel linkage, like realized by a flexure, or even both.

In summary, the embodiments of the invention provide some key benefits, which are listed below:

• The linear actuator 100 has an optimized electro-mechanical design that utilizes SMA wire technology for driving the driven element 110 - e.g. comprising the deformable lens 201 or rigid lens 202 or other optical element. This allows producing precise focusing and/or fast zoom operations in the camera module 200.

• The combination of the one or more lever arms 102 and the piston 101 (possibly moved in a guidance) leads to higher possible forces, while maintaining precision. In particular, the actuator 100 is able to generate forces as high as a few hundreds of rhN. Such forces are suitable for generating deformations of a larger tunable lens 201 or for generating a quick movement of a heavy weight rigid lens 202.

• The linear actuator 100 operates accurately and with good sensitivity, wherein it may be supported by using the at least one Hall sensor measuring the movement 105 of the piston 101. This is especially useful for performing a focusing operations in the camera module 200.

• The linear actuator 100 has electromagnetic immunity against adjacent magnetic fields, which may be produced by camera modules using VCM actuators. This may occur if the linear actuator 100 is used in a multi-camera module assembly. • The linear actuator 100 does not generate audible noise, but operates silently. This is beneficial, as two of the actuators 100 (for example, for focusing and zooming, respectively) may be operated simultaneously in a camera module 200. The present invention has been described in conjunction with various embodiments as examples as well as implementations. However, other variations can be understood and effected by those persons skilled in the art and practicing the claimed invention, from the studies of the drawings, this disclosure and the independent claims. In the claims as well as in the description the word“comprising” does not exclude other elements or steps and the indefinite article“a” or“an” does not exclude a plurality. A single element or other unit may fulfill the functions of several entities or items recited in the claims. The mere fact that certain measures are recited in the mutual different dependent claims does not indicate that a combination of these measures cannot be used in an advantageous implementation.

Also the embodiments of the present invention are not limited to any specific SMA material or SMA wire diameter, even though preferred is the use of Ni-Ti based alloys such as Nitinol, with or without additional elements chosen among Hf, Nb, Pt, Cu. Suitable diameters for the SMA wire actuator element are comprised between 75 and 25 pm, in particular between 75 and 50 pm, but not limited to this. Since the SMA wires 103 are real objects, their cross sections might not be perfectly circular, so the term "diameter" is to be intended as the diameter of the circle enclosing the real cross section.