Abstract:
Electro-magnetic actuators used to provide a displacement of an optical element such as a lens carrier comprise at least one ferromagnetic frame associated with a large air gap and at least one ferromagnetic member parallel to and separated from an elongated section of a frame by a small air gap. Actuation causes a magnetic circuit that appears in the at least one frame, the at least one member and small air gaps and by-passes or bridges the large air gap. In some embodiments, the resultant magnetic force moves the at least one member and leads to the displacement of an optical element attached thereto. In some embodiments, at least one frame and at least one member are arranged to provide a center hole and are dimensioned to enable insertion of a lens carrier in the hole. In some embodiments, the displacement is for auto-focus. In other embodiments, the displacement is for optical image stabilization.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application is related to and claims priority from U.S. Provisional Patent Application No. 61/900,442 having the same title and filed Nov. 6, 2013, which is incorporated herein by reference in its entirety. 
    
    
     FIELD 
     Embodiments disclosed herein relate in general to electromagnetic (EM) actuators having ferromagnetic members and conductive coils and more particularly to EM actuators used in miniature cameras. 
     BACKGROUND 
     In its basic form, an electronic camera, such as digital still camera or a camera embedded in a mobile (cell) phone or in a tablet computer includes two components: (1) a lens module comprising a set of one or more plastic or glass lens elements and used to create an optical image of the viewed scene, and (2) an image sensor (e.g. CMOS or CCD), which converts the optical image to the electronic domain, where the image can be processed and stored There are different types of electronic (or digital) cameras ranging by application (e.g., regular SLR, camera-phone, automotive, security and medical) and by functionality (e.g., with or without auto-focus). The simplest cameras are those in which the lens module is fixed in position with respect to the image sensor. These cameras are often called fixed-focus cameras, where the camera is focused to a pre-determined distance. Objects that fall within the depth of field of the camera can be captured sharply and those which fall beyond the depth of field will be blurred. In more advanced cameras, the position of the lens module (or at least one lens element in the lens module) can be changed by means of an actuator and the focus distance can be changed in accordance with the captured object or scene. In these cameras it is possible to capture objects from a very short distance (e.g., 10 cm) to infinity. Some advanced camera designs may include different groups of lenses that can move with respect to each other and hence change the effective focal length of the camera, which results in optical zoom capability. The trend in digital still cameras is to increase the zooming capabilities (e.g. to 5×, 10× or more) and, in cellphone cameras, to decrease the pixel size and increase the pixel count. These trends result in greater sensitivity to hand-shake or in a need for longer exposure time. This has created a need for optical image stabilization (OIS), which now appears in advanced cameras. In OIS-enabled cameras, the lens or camera module can change its lateral position or tilt angle in a fast manner to cancel the hand-shake during the image capture. 
     In compact (miniature) camera modules, the most ubiquitous form of an actuator is the Voice-Coil Motor (VCM), which includes a coil (wire turned on a cylinder), fixed (or “permanent” or “hard”) magnets and springs. When current is driven through the coil, an electro-magnetic (EM) force is applied and the lens module changes position. While the VCM is considered a mature technology, it is costly, large in size, uses rare-earth magnets, is slow in operation and consumes high power. Therefore, there is a need for, and it would be advantageous to have technical advances which overcome the shortcomings of VCM and related technologies. 
     SUMMARY 
     Embodiments disclosed herein teach EM actuators for miniature camera (as exemplarily in smart phones) auto-focus (AF) and OIS, as well as for any other functionality that can be obtained by tilting or moving a camera module or elements therewithin. The actuation force is magnetic, using ferromagnetic materials. Actuator structures disclosed herein include at least one ferromagnetic frame with frame arms and at least one ferromagnetic member, the arms and members having operating surfaces, the operating surfaces facing each other across air gaps. In some embodiments, the frame or frames are stationary, while the member or members are movable. Therefore, a relative movement occurs between the ferromagnetic frame(s) and ferromagnetic (member(s), where an optical element mechanically coupled to the member or members moves relative to the stationary frame(s). Note that while the description below follows focuses in general on embodiments in which the ferromagnetic frame(s) is/are stationary and the member(s) is/are moving, other embodiments may have the frame moving (and coupled to the optical element) while the member(s) are stationary. Yet other embodiments may have combinations of moving/stationary frame and member parts 
     Each actuator structure includes at least one large air gap in a magnetic circuit that includes all the frame parts. Each large air gap is either by-passed or bridged through smaller air gaps between arms and members by the magnetic field developing during operation. The actuator structures are designed to reduce the magnetic reluctance of the actuator and thereby provide a large EM force. Typically, the reluctance changes significantly with movement in a first (“force/actuation”) direction, while in a second (“indifferent”) direction, in-plane and orthogonal to the first direction, the reluctance is hardly changed or unchanged with movement. 
     In some embodiments there are provided electro-magnetic actuators used to move an optical element, comprising a ferromagnetic first frame that includes a core surrounded partially by a first conductive coil, a first arm and a second arm, each arm having an operative surface and an end surface, the first and second arms separated therebetween by a first large air gap, and a ferromagnetic first member having a respective operative surface and facing the first arm, the first member and the first arm disposed such that a first small air gap and an overlap are formed between their respective operative surfaces, wherein the first small air gap is smaller than the first large air gap, wherein the first member and the first frame undergo a relative movement therebetween when a magnetic force is generated by current in the coil, and wherein the movement is convertible into a displacement of the optical element from a first position to a second position. 
     In an embodiment, the frame may have a G-shape and the first member may have two operative surfaces and be nested between the two arms, each first member operative surface facing a respective operative surface of an arm across a respective small air gap. 
     In an embodiment, the actuator may further comprise a ferromagnetic second member rigidly coupled to the first member, the second member having a respective operative surface and facing the second arm, the second member and the second arm disposed such that a second small air gap and an overlap are formed between their respective operative surfaces, wherein the second small air gap is smaller than the first large air gap. 
     In an embodiment, the actuator may further comprise a ferromagnetic second frame that includes a second frame core surrounded partially by a second conductive coil, the second frame having first and second frame arms separated therebetween by a second large air gap, each second frame arm having at least one operative surface and an end surface, wherein the first member faces a first pair of arms formed by a first frame arm and a second frame arm, wherein the second member faces a second pair of arms formed by a first frame arm and a second frame arm, each of the first and second members and their respective facing first and second pairs of arms disposed such that a small air gap and an overlap are formed between their respective operative surfaces, wherein each small air gap is smaller than either the first or second air gaps, and wherein each member and its respective pair of arms undergo a relative movement therebetween when a magnetic force is generated by current in each of the first and second coils, the movement convertible into a displacement of the optical element from a first position to a second position. The first and second frames may be dimensioned to provide an internal open space that can accommodate the optical element, 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Non-limiting embodiments are herein described, by way of example only, with reference to the accompanying drawings, wherein: 
         FIG. 1A  shows an embodiment of an EM actuator disclosed herein in (a) an isometric view, (b) a cross section X 1 -X 2  in a relaxed state, and (c) a cross section X 1 -X 2  in an operative state; 
         FIG. 1B  shows another embodiment of an EM actuator disclosed herein in (a) an isometric view, (b) a cross section X 1 -X 2  in a relaxed state, and (c) a cross section X 1 -X 2  in an operative state; 
         FIG. 2  shows yet another embodiment of an EM actuator disclosed herein in (a) an isometric view, (b) a cross section X 1 -X 2  in a relaxed state, and (c) a cross section X 1 -X 2  in an operative state; 
         FIG. 3  shows yet another embodiment of an EM actuator disclosed herein in (a) an isometric view, (b) a cross section X 1 -X 2  in a relaxed state, and (c) a cross section X 1 -X 2  in an operative state; 
         FIG. 4  shows yet another embodiment of an EM actuator disclosed herein in (a) an isometric view, (b) a cross section X 1 -X 2  in a relaxed state, and (c) a cross section X 1 -X 2  in an operative state; 
         FIG. 5  shows yet another embodiment of an EM actuator disclosed herein in (a) an isometric view, (b) a cross section X 1 -X 2  in a first operative state, and (c) a cross section X 1 -X 2  in a second operative state; 
         FIG. 6  shows yet another embodiment of an EM actuator disclosed herein in (a) an isometric view, (b) a cross section X 1 -X 2  in a relaxed state, and (c) a cross section X 1 -X 2  in an operative state; 
         FIG. 7  shows an embodiment of an EM actuator disclosed herein and having tilted operative surfaces in (a) an isometric view, (b) a cross section X 1 -X 2  in a relaxed state, and (c) a cross section X 1 -X 2  in an operative state; 
         FIG. 8  shows another embodiment of an EM actuator disclosed herein and having tilted operative surfaces in (a) an isometric view, (b) a cross section X 1 -X 2  in a relaxed state, and (c) a cross section X 1 -X 2  in an operative state; 
         FIG. 9  shows yet another embodiment of an EM actuator disclosed herein and having tilted operative surfaces in (a) an isometric view, (b) a cross section X 1 -X 2  in a relaxed state, and (c) a cross section X 1 -X 2  in an operative state; 
         FIG. 10  shows an embodiment of an EM actuator for OIS disclosed herein in (a) an isometric view, (b) a cross section X 1 -X 2  in a relaxed state, and (c) a cross section X 1 -X 2  in an operative state; 
         FIG. 11  shows another embodiment of an EM actuator for OIS disclosed herein in (a) an isometric view, (b) a cross section X 1 -X 2  in a relaxed state, and (c) a cross section X 1 -X 2  in an operative state; 
         FIG. 12  shows schematically an embodiment of a camera module which includes an actuator assembly coupled to a lens carrier: (a) details showing two sets of springs coupled to the lens carrier, and (b) details showing a support structure for the actuator assembly and lens carrier. 
         FIG. 13  shows schematically another embodiment of a camera module which includes an actuator assembly coupled to a lens carrier and used for OIS: (a) details showing two sets of springs, and (b) details showing a support structure for the actuator assembly and lens carrier. 
     
    
    
     DETAILED DESCRIPTION 
       FIG. 1A  shows an embodiment of an EM actuator disclosed herein and numbered  100  in (a) an isometric view, (b) a cross section X 1 -X 2  in a relaxed state, and (c) a cross section X 1 -X 2  in an operative state. The X-Y-Z coordinate system shown in  FIG. 1A  holds for all other figures described below. Actuator  100  comprises two U-shaped ferromagnetic frames (henceforth referred to simply as “frames”), a first frame  102  and a second frame  104 . The two frames are arranged substantially in-plane (exemplarily the X-Z plane) in a “double-U” configuration. The structure of this actuator (as well as of the actuators of  FIGS. 2-10  below) has therefore a central open space (“hole”), marked here as  105 . The hole is designed to enable insertion of a lens carrier. Frames  102  and  104  are fixed (e.g. rigidly constrained to a support structure (see  1212  in  FIG. 12( b ) ). Each frame includes an elongated base member (core) (respectively  106  and  108 ) surrounded at least partially by a coil (respectively  110  and  112 ), and two arms (respectively  114   a  and  114   b  for member  102  and  116   a ,  116   b  for member  104 ). Opposite arms of the two frames (i.e.  114   a  and  116   a , and  114   b  and  116   b ) face each other across a large air gap (respectively, air gaps  118   a  and  118   b ). Actuator  100  further comprises two moving elongated ferromagnetic members (also referred to simply as “moving members”)  120   a  and  120   b  substantially parallel to the frame arms. In this and following embodiments, the moving members may be rigidly connected to each other (by a structure not shown) to move in unison relative to the frames. The lens carrier (see e.g. carrier  1204  in  FIG. 12 ) would be mechanically coupled to the moving members. Member  120   a  is parallel to arms  114   a  and  116   a  and is separated from them by a small air gap  122   a . Member  120   b  is parallel to arms  114   b  and  116   b  and is separated from them by another small air gap  122   b . Each of moving members  120   a  and  120   b  has an operative surface facing a respective operative surface of opposite fixed arms across the respective second air gap. Thus, member  120   a  has an operative surface  124   a  facing operative surfaces  126   a  and  128   a  of, respectively, arms  114   a  and  116   a . Member  120   b  has an operative surface  124   b  facing operative surfaces  126   b  and  128   b  of, respectively, arms  114   b  and  116   b.    
       FIG. 1B  shows another embodiment of an EM actuator disclosed herein and numbered  100 ′ in (a) an isometric view, (b) a cross section X 1 -X 2  in a relaxed state, and (c) a cross section X 1 -X 2  in an operative state. Actuator  100 ′ is similar to actuator  100  in that it may comprise the same elements, except that is includes a single moving elongated ferromagnetic member  120 ′ (instead of the two moving members  120   a  and  120   b ). Exemplarily, any unnumbered element in actuator  100 ′ may be considered as identical with a parallel element in actuator  100 . As in actuator  100 , member  120 ′ is substantially parallel to one set of the frame arms (e.g. as shown,  114   b ′ and  116   b ′). Such a single moving member configuration may have advantages in terms of less magnetic resistance, i.e. a larger output force relative to the same input power. 
     In all embodiments below, large air gaps are marked as having a width d 1  while small air gaps are marked as having a width d 2 . Exemplarily, the dimensions of an actuator  100  or  100 ′ may be about 10 mm×10 mm×2 mm. Exemplarily, the ferromagnetic arms and members may have a cross section of about 1×1 mm 2  Exemplarily, the large air gaps have the same width d 1 . In actuators such as actuators  100  or  100 ′ above and similar ones below, d 1  may be on the order of 0.5 mm. In other actuators below, d 1  may be between about 0.5 and a few mm. Exemplarily, the small air gaps have a same width d 2 . In all embodiments, d 2  is much smaller than d 1 . For example, d 2  may be one or two orders of magnitude smaller than d 1 . Exemplarily in some embodiments, d 2  may be about 30 μm. In other embodiments, d 2  may exemplarily be in the range 10-30 μm 
     In operation, when current passes through the coils, an EM field develops in a closed loop formed by the U-frame arms and the moving members. The field lines propagate through the small air gaps and not through the large air gaps, because of the difference in first and small gap sizes. In other words, during operation of the actuator of  FIG. 1  (as well as of those of  FIGS. 2, 3 and 6-10 ), the magnetic flux passes mainly through the small air gap(s) and by-passes the large air gap(s). The resulting magnetic force F moves the moving members in a direction Y indicated by arrows  130  parallel to the operating surfaces and perpendicular to the X-Z plane. F is approximately proportional to S(I×N) 2 /(B+d) where I is the current, N is the number of coil turns, B is a constant determined by the particular structure of the actuator and d is the gap width (d 2 ). To a first approximation, the EM force in this configuration depends essentially only on the current (i.e. is independent of position). The operative surfaces slide relative to each other with a displacement Δy occurring in the Y direction. Exemplarily, Δy may vary between 0 and 1000 μm. The displacement provides an overlap area SΔy, where S is the length of the overlap. The overlap area is minimal in the relaxed state,  FIG. 1 b   , and increases in an operative state to a maximal overlap,  FIG. 1 c   , which represents a “closed state”. Note that the movement direction is the same in all the embodiments of  FIGS. 1-9 . 
     Advantageously, the long overlap between the arms and the moving members and the small air gap between the operative surfaces of the arms and those of the moving members increase the actuator force/power ratio. This ratio can be further increased by an increase in the number of coil turns. As mentioned, the moving members are rigidly interconnected, so side forces (in the X-Z plane) perpendicular to the linear movement direction cancel out. Alternatively, each moving member may have two opposing operative surfaces so the side forces cancel out (as in  FIGS. 4 and 11 ). Note that in this and any of the following embodiments, operative surfaces facing each other may be straight (parallel to Y) or tilted across the air gap, or be non-flat (i.e. curved). Such features can control and/or shape the magnetic reluctance change during movement and result in an ability to shape the EM force behavior as a function of location of the moving member. 
       FIG. 2  shows another embodiment of an EM actuator disclosed herein and numbered  200  in (a) an isometric view, (b) a cross section X 1 -X 2  in a relaxed state, and (c) a cross section X 1 -X 2  in an operative state. Actuator  200  comprises two L-shaped frames  202  and  204  arranged substantially in the X-Z plane, and is termed accordingly a “double-L” configuration. The L-shaped frames are fixed (e.g. mechanically constrained to another structure, not shown). Each L-shaped frame includes a corner ferromagnetic member (respectively  206  and  208 ) surrounded at least partially by a coil (respectively  210  and  212 ). Each frame further includes two arms (respectively  214   a  and  214   b  for corner member  206  and  216   a  and  216   b  for corner member  208 ) fixedly joined to (or structurally integral with) the respective corner member. In actuator  200 , the two arms of each L-shaped frame are perpendicular to each other and form a 45° angle with the respective corner member. Note that other “approximate L-shape” geometries in which the arms are not perpendicular to each other and form an angle different than 45° with the corner member are possible. Free ends of arms  214   b  and  216   a  face each other across a large air gap  218   a . Free ends of arms  214   a  and  216   b  face each other across a large air gap  218   b . Note that large air gaps  218   a  and  218   b  are narrowest (with a width d 1 ) at internal corners formed between the ends of the arms of frames  202  and  204 . Actuator  200  further comprises two L-shaped ferromagnetic moving members  220   a  and  220   b . These members are “nested” either inside or outside frames  202  and  204 . In actuator  200 , the L-shaped members are nested inside the L-shaped frames such that arm  222   a  of member  220   a  and arm  224   b  of member  220   b  are parallel to arms  214   a  and  214   b  of frame  202 , and arms  222   b  of member  220   a  and  224   a  of member  220   b  are parallel to arms  216   a  and  216   b  of frame  204 . The parallel arms of the L-frames and the L-shaped members are separated by small air gaps. Thus, arms  214   a  and  222   a  are separated by a gap  226   a  (exemplarily with width d 2 ),  216   a  and  224   a  are separated by a gap  226   b  (exemplarily also with width d 2 ). Similarly,  214   b  and  224   b  are separated by a gap  228   a , and  216   b  and  222   b  are separated by a gap  228   b . L-shaped members  220   a  and  220   b  may be rigidly connected to each other to move in unison. Each of the arms has an operative surface facing a respective operative surface of an opposite arm across the respective second air gap. The operative surfaces may be smooth and planar, or smooth and structured, e.g. in a wavy form. 
     In an embodiment, the large air gaps have the same width d 1  and the small air gaps have a same width d 2  different from d 1 . d 1  is significantly larger (for example by an order of magnitude) than d 2 . The operation and movement of actuator  200  are similar to those of actuator  100 . In particular, during operation, most of the magnetic flux passes through the small air gaps and by-passes the large air gaps. 
       FIG. 3  in an isometric view shows yet another embodiment of an EM actuator disclosed herein and numbered  300  in (a) an isometric view, (b) a cross section X 1 -X 2  in a relaxed state and (c) a cross section X 1 -X 2  in an operative state. Actuator  300  is similar to actuator  200 , except that the L-shaped frames and members are replaced by semicircular-shaped frames and members. Therefore, aspects of design and operation that can be inferred from the description of actuator  200  above are not described in detail for actuator  300 . Actuator  300  comprises two fixed semicircular frames  302  and  304  arranged substantially in the same plane, each frame including a core section (respectively  306  and  308 ) surrounded at least partially by a coil (respectively  310  and  312 ) and two curved arm sections (respectively  314   a  and  314   b  for frame  302  and  316   a  and  316   b  for frame  304 ). Free ends of the curved arm sections face corresponding free ends of opposite curved arm sections across large air gaps (with width d 1 ). Actuator  300  further comprises two semicircular members  320   a  and  320   b , which may be positioned either inside or outside the frames. Members  320   a  and  320   b  may have the same curvatures as the curved arm sections, and are separated from them by small air gaps (with width d 2 ). The curved arm sections and the semicircular members have operative surfaces facing each other across the respective small air gaps. The large and small air gaps are dimensioned such that when current passes through the coils, the EM field exists in the curved arm sections and the semicircular members. The resulting EM force F moves the semicircular members in a direction Y parallel to the operating surfaces and perpendicular to the X-Z plane, providing a linear movement parallel to operative surfaces in the Y direction. 
     Note that the “semicircular” shape described is exemplary, and that other curved shapes such semi-elliptical, semi-oval, etc. may be used for both the frames and the ferromagnetic members, as long as the small air gaps formed therebetween ensure that the EM force formed when currents pass through the coils moves the ferromagnetic members in a direction parallel to the operative surfaces. 
       FIG. 4  shows in an isometric view yet another embodiment of an EM actuator disclosed herein and numbered  400  in (a) an isometric view, (b) a cross section X 1 -X 2  in a relaxed state and (c) a cross section X 1 -X 2  in an operative state. Similar to actuator  100 , actuator  400  comprises two U-shaped frames  402  and  404  arranged substantially in the same (X-Z) plane but shifted relative to each other to form a “double-U interlaced” configuration. Actuator  400  further comprises two elongated moving members  420   a  and  420   b . Frames  402  and  404  and moving members  420   a  and  420   b  are substantially similar to, respectively, frames  102  and  104  and members  120   a  and  120   b  in  FIG. 1 . However, because of an X-shift and a Z-shift of the frames, moving members  420   a  and  420   b  are now positioned between the arms of the U-frames. Thus, member  420   a  is positioned between and in parallel with arm  414   a  of frame  402  and arm  416   a  of frame  404 . Member  420   b  is positioned between and in parallel with arm  414   b  of frame  402  and arm  416   b  of frame  404 . Moving members  420   a  and  420   b  have each two operative surfaces ( 424   a  and  424   b  for member  420   a , and  426   a  and  426   b  for member  420   b ) facing across respective air gaps ( 430   a, b  for member  420   a  and  430   c, d  for member  420   b ) operative surfaces of the neighboring frame arms. A major advantage of this embodiment is that the overlap area between two frame arms and a moving member is doubled vs. that in embodiment  100 , so that side forces (in the X-Z plane) are inherently canceled out. 
     The operation and movement are similar to those of actuators  100 - 300 . Note however that the large air gap (d 1 ) in this case is between pairs of nearest frame arms. The actuation involves magnetic field bridging of the large direct gap through the arms of the two frames and the small air gaps (d 2 ). 
       FIG. 5  shows an embodiment of another EM actuator disclosed herein and numbered  500  in (a) an isometric view, (b) a cross section X 1 -X 2  in a relaxed state and (c) a cross section X 1 -X 2  in an operative state. Actuator  500  includes a fixed U-shaped frame  502  and a moving U-shaped frame  504 . Frame  502  includes an elongated base member  506  surrounded at least partially by a coil  508  and two arms  514   a  and  514   b  separated by a large “direct” gap (with a width d 1 ). Frame  504  includes an elongated base member  512  and two arms  516   a  and  516   b . Frame  504  is nested inside frame  502  such that operative surfaces of pairs of arms  514   a  and  516   a  and  514   b  and  516   b  face each other across small air gaps of width d 2 . Clearly, d 1  is much larger than d 2  (for example, by an order of magnitude). As in actuator  400 , the actuation involves magnetic field bridging of the large direct gap through the arms of the two frames and the small air gaps. 
       FIG. 6  shows in an isometric view yet another embodiment of an EM actuator disclosed herein and numbered  600  in (a) an isometric view, (b) a cross section X 1 -X 2  in a relaxed state, and (c) a cross section X 1 -X 2  in an operative state. Actuator  600  is similar to actuator  100 , except that its two fixed U-shaped frames  602  and  604  are not co-planar (in-plane). Instead, the two frames have respective arms  614   a ,  614   b  (for frame  602 ), and  616   a  and  616   b  (for frame  604 ) inclined at an angle θ (typically smaller than 5°) to the XZ plane. The same inclination exists for moving elongated ferromagnetic members  620   a  and  620   b , which move in the Y direction. The inclinations enable more flexibility in the increase in overlap of the operative surfaces as function of movement. As in previous embodiments, “d 1 ” marks large air gaps and “d 2 ” marks small air gaps. 
       FIG. 7  shows an embodiment of an EM actuator disclosed herein and numbered  700  in (a) an isometric view, (b) a cross section X 1 -X 2  in a first operative state, and (c) a cross section X 1 -X 2  in a second operative state. Actuator  700  is substantially similar to actuator  100 , except that arms  714   a ,  714   b ,  716   a  and  716   b  have tilted (to the Y-Z plane) operative surfaces (respectively  726   a ,  726   b ,  728   a  and  728   b ). Two moving elongated ferromagnetic members  720   a  and  720   b  have non-tilted (to the Y-Z plane) operative surfaces  724   a  and  724   b . The tilt angle φ is typically 1-2° and maximally ca. 5°. The small air gaps (d 2 ) formed between facing operative surfaces are thus non-uniform in the movement direction. A non-uniform gap is advantageous in that it allows better engineering of forces during movement (in the Y direction). 
       FIG. 8  shows an embodiment of an EM actuator disclosed herein and numbered  800  in (a) an isometric view, (b) a cross section X 1 -X 2  in a first operative state, and (c) a cross section X 1 -X 2  in a second operative state. Actuator  800  is substantially similar to actuator  100 , in that arms  814   a ,  814   b ,  816   a  and  816   b  have non-tilted operative surfaces (respectively  826   a ,  826   b ,  828   a  and  828   b ). However, two moving elongated ferromagnetic members  820   a  and  820   b  have tilted (to the Y-Z plane with angle φ) operative surfaces  824   a  and  824   b.    
       FIG. 9  shows an embodiment of an EM actuator disclosed herein and numbered  900  in (a) an isometric view, (b) a cross section X 1 -X 2  in a first operative state, and (c) a cross section X 1 -X 2  in a second operative state. Actuator  900  is substantially similar to actuator  100 , except that arms  914   a ,  914   b ,  916   a  and  916   b  and moving elongated ferromagnetic members  920   a  and  920   b  have tilted (to the Y-Z plane with angle φ) operative surfaces. Thus, arms  914   a ,  914   b ,  916   a  and  916   b  have tilted operative surfaces (respectively  926   a ,  926   b ,  928   a  and  928   b ), while members  920   a  and  920   b  have tilted operative surfaces  924   a  and  924   b.    
     While the designs of actuators  700 - 900  follow that of actuator  100 , tilted operative surfaces disclosed in these embodiments may equally be implemented in any of actuators  200  to  600 . Moreover, in designs where the operative surface of a moving member faces an operative surface of each of two arms, one of the arms may have a tilted operative surface while the other may have a non-tilted operative surface. 
     All actuator embodiments above may be used for linear movement (e.g. for focusing) of a lens. An actuator assembly embodiment disclosed in  FIG. 13  (comprising  4  actuators as in  FIG. 10  below) may be used for OIS. 
       FIG. 10  shows an embodiment of an EM actuator used for OIS disclosed herein and numbered  1000  in (a) an isometric view, (b) a cross section X 1 -X 2  in a relaxed state and (c) a cross section X 1 -X 2  in an operative state. Actuator  1000  comprises a first (e.g. fixed) frame  1002  and a second (e.g. moving) frame  1004 . Frame  1002  includes an elongated core  1006  surrounded at least partially by a coil  1008 , and two arms  1010   a  and  1010   b . Arms  1010   a  and  1010   b  face each other across a large air gap d 1 . Moving frame  1004  has a hollow rectangular shape, with two base members  1012   a  and  1012   b  and two arms  1014   a  and  1014   b . Arms  1014   a  and  1014   b  are nested inside frame  1002  in the X-Z plane. Pairs of arms  1014   a  and  1010   a  and  1014   b  and  1010   b  are substantially parallel and separated along a length dimension by a small air gap d 2 . Each arm has an operative surface bordering the small air gap. Thus, arm  1010   a  has an operative surface  1018   a , arm  1010   b  has an operative surface  1018   b , arm  1014   a  has an operative surface  1020   a , and arm  1014   b  has an operative surface  1020   b.    
     Since this actuator is used for OIS, it does not have to have a large hole that accommodates a lens carrier. Therefore, its width dimension (in the X direction) can be much smaller that in actuators  100 - 900 , for example 3-4 mm (instead of 10 mm). This provides a very compact actuator, decreasing the requirements for actuator height and space. 
     In operation, current passing through coil  1008  induces a magnetic field through the magnetic circuit. Large gap d 1  is bridged by moving frame  1004  and through the small air gaps. The symmetry of the structures ensures that side forces (in the X-Z plane) are inherently canceled out. The movement of frame  1004  is substantially in the Y direction. Movement in the Z direction is not blocked. The combined action of four such actuators, shown in  FIG. 13 , is used to provide OIS. 
       FIG. 11  shows in an isometric view yet another embodiment of an EM actuator used for OIS disclosed herein and numbered  1100  in (a) an isometric view, (b) a cross section X 1 -X 2  in a relaxed state, and (c) a cross section X 1 -X 2  in a operative state. Actuator  1100  comprises a fixed ferromagnetic element  1102  shaped like capital letter “G” and referred to hereinafter as a “G-frame”, and a moving elongated ferromagnetic member  1104 . G-frame  1102  includes three substantially parallel elongated sections  1106 ,  1108   a  and  1108   b . Section  1106  serves as core and it is surrounded at least partially by a coil  1110 . Advantageously, coil  1110  may have a large volume (large number of coil windings). Sections  1108   a  and  1108   b  are separated by a large air gap d 1 . Moving ferromagnetic member  704  is inserted between sections  1108   a  and  1108   b  and is separated from those sections by respective small air gaps d 2 . Sections  1108   a  and  1108   b  and member  1104  have operative surfaces facing each other across the small air gaps. The operation and movement is similar to that of actuator  1000 . Advantageously, the G-shape enables a long magnetic overlap between sections  1108   a  and  1108   b  and member  1104  and ensures that side forces (in the X-Z plane) are inherently canceled out. An exemplary width dimension of actuator  1100  is similar to that of actuator  1000 , i.e. 3-4 mm. 
       FIG. 12  shows schematically an embodiment of a camera module  1200  that includes an actuator assembly  1202  coupled to a lens carrier  1204 . Exemplarily, the dimensions of the camera module may be 10 mm×10 mm×6-7 mm. The actuator assembly includes two actuators  1206   a  and  1206   b , which can be any of the actuators  100 - 900  above. All such actuators have the internal hole that enables insertion and movement therewithin of the lens carrier holder and an associated mounted lens block (not shown).  FIG. 12( a )  shows details of the camera module and in particular a top set of springs  1208  and a bottom set of springs  1210 .  FIG. 12( b )  shows a support structure  1212  to which both sets of springs as well as the fixed frames of the actuator are rigidly coupled. Both sets of springs are rigidly coupled to the lens carrier  1204 . Since the lens carrier moves with the moving part of the actuator, the springs serve as a counter force to the magnetic force in the movement direction Y. The lens carrier (and the lens attached thereto) can thus be positioned in any number of positions by a balance of the two forces. 
       FIG. 13  shows a camera module  1300  used for OIS.  FIG. 13 ( a )  provides details showing an actuator assembly structure with four actuators and two sets of springs, and  FIG. 13( b )  provides details showing a support structure for the actuator assembly and lens carrier. Four actuators similar to actuators  1000 , labeled here  1300   a - d , are positioned in a rectangular structure, with the fixed frames rigidly attached to four sides of a base structure  1302 . The fixed frames of actuators  1300   a  and  1300   c  lie essentially in Y-X planes, while the fixed frames of actuators  1300   b  and  1300   d  lie essentially in Y-Z planes. The moving frames of actuators  1300   a  and  1300   c  can move along the Z-axis, while the moving frames of actuators  1300   b  and  1300   d  can move along the X-axis. The moving frames of all four actuators are mechanically coupled to a top flexible frame  1304 , which in turn can be coupled to and accommodate a lens carrier  1306 . Thus, a two-axis movement is made possible by the four actuators. The XZ movement of the lens can compensate for tilt movement of the complete camera. 
     While this disclosure has been described in terms of certain embodiments and generally associated methods, alterations and permutations of the embodiments and methods will be apparent to those skilled in the art. The disclosure is to be understood as not limited by the specific embodiments described herein, but only by the scope of the appended claims.