Patent Publication Number: US-11650400-B2

Title: Rotational ball-guided voice coil motor

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application is a continuation application from U.S. patent application Ser. No. 16/154,093 filed Oct. 8, 2018 (now allowed), which was a continuation application from U.S. patent application Ser. No. 15/559,039 filed Sep. 16, 2017 (issued as U.S. Pat. No. 10,488,631), which was a 371 National Phase application from international application PCT/IB2017/052383 filed Apr. 25, 2017, and claims priority from U.S. Provisional Patent Applications No. 62/343,011 filed May 30, 2016 and 62/353,278 filed Jun. 22, 2016, both of which are incorporated herein by reference in their entirety. 
    
    
     FIELD 
     Embodiments disclosed herein relate in general to actuating mechanisms (“actuators”) and in particular to voice coil motor (VCM) actuators for digital cameras. 
     BACKGROUND 
     High-end digital camera modules, and specifically cellphone (e.g. smartphone) digital cameras include mechanisms that enable advanced optical function such as focus or optical image stabilization (OIS). Such mechanisms may actuate (e.g. displace, shift or tilt) an optical element (e.g. lens, image sensor, mirror) to create the desired optical function. A commonly used actuator is based on voice coil motor (VCM) technology. In VCM technology, a fixed (or permanent) magnet and a coil are used to create actuation force. The coil is positioned in the vicinity of the magnetic field of the fixed magnet. Upon driving current in the coil, a Lorentz force is created on the coil, an in return an equal counter-force is applied on the magnet. The magnet or the coil is rigidly attached to an optical element to construct an actuated assembly. The actuated assembly is then moved by the magnetic Lorenz force. Henceforth, the term VCM may be used to also refer to “VCM actuator”. 
     In addition to the magnetic force, a mechanical rail is used to set the course of motion for the optical element. The mechanical rail keeps the motion of the optical element in a desired path, as required by optical needs. A typical mechanical rail is known in the art as “spring-guided rail”, in which a spring or set of springs is used to set the motion direction. A VCM that includes a spring-guided rail is referred to as “spring-guided VCM”. For example, U.S. patent application 20110235196 discloses a lens element being shifted in a linear spring rail to create focus. For example, international patent application PCT/IB2016/052179 discloses the incorporation and use of a spring guided VCM in a folded camera structure (FCS). The disclosure teaches a lens element being shifted to create focus and OIS and a light folding element being shifted in a rotational manner to create OIS. 
     Another typical mechanical rail is known in the art a “ball-guided rail”, see e.g. U.S. Pat. No. 8,810,714. With a ball-guided rail, the optical element is bound to move in the desired direction by set of balls confined in a groove (also referred to as “slit”). A VCM that includes a ball-guided rail is referred to as a “ball-guided VCM”. A ball-guided VCM has several advantages over a spring-guided VCM. These include: (1) lower power consumption, because in a spring-guided VCM the magnetic force has to oppose a spring mechanical force, which does not exist in a ball-guided VCM, and (2) higher reliability in drops which may occur during the life-cycle of a camera that includes the VCM. 
     While the actuation method showed in U.S. Pat. No. 8,810,714 allows linear motion only, in some cases there is a need to create angular motion as well, for example to rotate (tilt) a light folding element (mirror or prism) in order to create OIS as described in PCT/IB2016/052179. Therefore there is a need for, and it would be advantageous to have, a rotational ball-guided VCM, i.e. a ball-guided VCM that can cause rotation (tilt) of an optical element. 
     SUMMARY 
     Aspects of embodiments disclosed herein relate to VCM actuators having curved ball-guided mechanisms, and to digital cameras, and in particular cameras with folded optics that incorporate VCMs. 
     In some exemplary embodiments there is provided an actuator for rotating or tilting an optical element, comprising a first VCM and a first curved ball-guided mechanism operative to create a rotation or tilt movement of the optical element around a first rotation axis upon actuation by the VCM. 
     In an embodiment, the first VCM includes a coil mechanically coupled to a static base and a fixed magnet mechanically coupled to a holder for holding the optical element, and the rotation or tilt movement is created by a current passing through the coil. 
     In an embodiment, an actuator further comprises a ferromagnetic yoke attached to the static base and used to pull the fixed magnet in order to prevent the first curved ball-guided mechanism from coming apart. 
     In an embodiment, the first ball-guided mechanism includes a pair of grooves having a plurality of balls located therebetween, wherein at least one of the grooves in the pair has a curvature defined by a radius that starts at a center of curvature which lies on the rotation axis. 
     In an embodiment, the optical element includes an optical path folding element (OPFE) that folds light from a first optical axis to a second optical axis. The OPFE may be exemplarily a prism or a mirror. 
     In an embodiment, the first rotation axis includes an axis perpendicular to both the first optical axis and the second optical axis. 
     In an embodiment, the first rotation axis includes an axis combining the second optical axis and an axis perpendicular to both the first optical axis and the second optical axis. 
     In an embodiment, the first curved ball-guided mechanism is positioned below the OPFE. 
     In an embodiment, the fixed magnet and the coil are positioned below the OPFE. 
     In an embodiment, the fixed magnet and the coil are positioned on a side of the OPFE in a plane parallel to a plane that includes both the first axis and the second optical axis. 
     In an embodiment, an actuator further comprises a position sensor for measuring an angle of the optical element relative to the static base. 
     In an embodiment, the position sensor is a Hall bar position sensor operative to measure the magnetic field of the fixed magnet. 
     In some embodiments, an actuator further comprises a second VCM and a second curved ball-guided mechanism operative to create a rotation or tilt movement of the optical element around a second rotation axis upon actuation by the second VCM, wherein the first rotation axis and the second rotation axis are not parallel. 
     In an embodiment, the first rotation axis and the second rotation axis are substantially orthogonal to each other. 
     In an embodiment, the first VCM includes a first coil mechanically coupled to a static base and a first fixed magnet mechanically coupled to a holder for holding the optical element, wherein the second VCM includes a second coil mechanically coupled to a static base and a second fixed magnet mechanically coupled to a holder for holding the optical element, and wherein the first rotation or tilt movement and the second rotation or tilt movement are created by a combination of currents passing through the first coil and the second coil. 
     In an embodiment, the first and second magnets are unified as a single magnet. 
     In an embodiment, an actuator further comprises a ferromagnetic yoke attached to the static base and used to pull the fixed magnet in order to prevent the first curved ball-guided mechanism and the second curved ball-guided mechanism from coming apart. 
     In an embodiment, the optical element includes an optical path folding element (OPFE) that folds light from a first optical axis to a second optical axis. 
     In an embodiment, the first rotation axis includes an axis perpendicular to both the first optical axis and the second optical axis, and the second rotation axis includes an axis parallel to either the first optical axis or the second optical axis 
     In an embodiment, an actuator further comprises a first position sensor and a second position sensor, wherein a combination of two position measurements allows determination of the position of the optical element holder relative to the static base with respect to both the first rotation axis and the second rotation axis. 
     In an embodiment, the center of curvature resides inside the optical element. 
     In an embodiment, the center of curvature resides outside the optical element. 
     In some exemplary embodiments, there are provides cameras comprising an actuator described above and below. 
     In some camera embodiments, the rotation or tilt movement is for allowing optical image stabilization. 
     In some camera embodiments, the rotation or tilt movement is for allowing extended field of view scanning. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Non-limiting examples of embodiments disclosed herein are described below with reference to figures attached hereto that are listed following this paragraph. The drawings and descriptions are meant to illuminate and clarify embodiments disclosed herein, and should not be considered limiting in any way. 
         FIG.  1 A  shows an embodiment of a rotational ball-guided VCM actuator disclosed herein in an isomeric view; 
         FIG.  1 B  shows the VCM actuator of  FIG.  1 A  in an exploded view; 
         FIG.  1 C  shows a bottom view of an actuated sub-assembly in the VCM actuator of  FIG.  1 A ; 
         FIG.  1 D  shows a cross section of the VCM actuator along a line A-A marked in  FIG.  1 A ; 
         FIG.  1 E  shows details of an electro-magnetic sub-assembly in the VCM actuator of  FIG.  1 A ; 
         FIG.  1 F  shows a cross section of the VCM actuator along a line B-B marked in  FIG.  1 A ; 
         FIG.  1 G  shows another embodiment of a rotational ball-guided VCM actuator disclosed herein in an isomeric view; 
         FIG.  1 H  shows the VCM actuator of  FIG.  1 G  in an exploded view; 
         FIG.  1 I  shows details of an actuated sub-assembly in the actuator of  FIG.  1 G ; 
         FIG.  1 J  shows a cross section of the VCM actuator along a line B-B marked in  FIG.  1 G ; 
         FIG.  1 K  shows schematically in a side view alternative embodiments of groove pairs; 
         FIG.  2    shows the actuator of  FIGS.  1 A- 1 F , coupled to a folded camera; 
         FIG.  3 A  shows yet another embodiment of a rotational ball-guided VCM actuator disclosed herein in an isomeric view; 
         FIG.  3 B  shows the VCM actuator of  FIG.  3 A  in an exploded view; 
         FIG.  3 C  shows details of a middle base of the VCM actuator of  FIGS.  3 A and  3 B ; 
         FIG.  3 D  shows details of an electro-magnetic sub-assembly in the VCM actuator of  FIGS.  3 A and  3 B ; 
         FIG.  4    shows the actuator of  FIGS.  3 A- 3 C , coupled to a folded camera; 
         FIG.  5 A  shows yet another embodiment of a rotational ball-guided VCM actuator disclosed herein in an isomeric view; 
         FIG.  5 B  shows the VCM actuator of  FIG.  2 A  in an exploded view from one side; 
         FIG.  5 C  shows the VCM actuator of  FIG.  2 A  in an exploded view from another side; 
         FIG.  5 D  shows a cross section of the VCM actuator along a line A-A marked in  FIG.  5 A ; 
         FIG.  5 E  shows details of an electro-magnetic sub-assembly in the VCM actuator of  FIG.  5 A ; 
         FIG.  6    shows the actuator of  FIGS.  5 A- 5 E , coupled to a folded camera. 
     
    
    
     DETAILED DESCRIPTION 
       FIGS.  1 A-F  show schematically various views and components of an exemplary embodiment of a rotational ball-guided VCM actuator disclosed herein and numbered  100 . For simplicity, the term “VCM actuator” or just “actuator” will replace the term “rotational ball-guided VCM actuator” in the description hereinbelow.  FIG.  1 A  shows actuator  100  in an isomeric view and  FIG.  1 B  shows actuator  100  in an exploded view. Actuator  100  allows tilting of an optical path folding element (OPFE)  150  around a single axis (exemplarily and as shown, axis X), as further described below. OPFE  150  folds light from a first optical axis (aligned with Z) to a second optical axis (aligned with Y). In  FIGS.  1 A,  1 B , OPFE  150  is exemplarily a prism. In other embodiments, the OPFE may be, for example, a mirror or a lens. Actuator  100  has exemplary length/width/height dimensions in the range of 5-15 mm, i.e. actuator  100  can be contained in a box with dimension of 5×5×5 mm 3  to 15×15×15 mm 3 . The description continues with reference to a coordinate system XYZ shown in  FIGS.  1 A and  1 B  as well as in a number of other figures. 
     In actuator  100 , OPFE  150  may be held in an optical element holder  102 , which can be made, for example, by a plastic mold that fits the shape of element OPFE  150 . A permanent (fixed) magnet  104  is fixedly attached (e.g. glued) to optical element holder  102  from below (negative Z direction in the  FIG.  1 A ). Hereinafter, the term “below” used with reference to an OPFE (e.g. prism) will refer to a side of the OPFE opposite to the side receiving light along the first optical axis. OPFE  150 , optical element holder  102  and magnet  104  form an “actuated sub-assembly”  106 . Actuated sub-assembly  106  is shown from a bottom view in  FIG.  1 C .  FIG.  1 D  shows a cross section of actuator  100  along a line A-A marked in  FIG.  1 A .  FIG.  1 E  shows details of an electro-magnetic (EM) sub-assembly of actuator  100 .  FIG.  1 F  shows a cross section of actuator  100  along a line B-B marked in  FIG.  1 A . Optical element holder  102  includes (i.e. is molded with) two parallel arc-shaped (or “curved”) grooves  102   a  and  102   b  ( FIG.  1 C ) positioned at two opposite sides of holder  102 , each arc-shaped groove having an angle α′&gt;α, where angle α is a required tilt stroke, as defined by optical needs. Angle α′ is shown in  FIG.  1 D . Arc-shaped grooves  102   a  and  102   b  have a center of curvature on a common rotation axis  108  ( FIG.  1 D ). 
     The distance of axis  108  from grooves  102   a  and  102   b  (radius of curvature) is typically 2-15 mm. As such axis  108  may pass through (be internal to) OPFE  150  or outside of (be external to) OPFE  150 , see also  FIG.  1 K . For optical image stabilization (OIS), α may exemplarily be in the range 0.25°&lt;α&lt;2°. To obtain an adjustable extended Tele field of view (FOV) in a dual-aperture zoom digital camera such as that described in co-owned U.S. Provisional patent application No. 62/272367, α may exemplarily be in the range 2°&lt;α&lt;12°. Typically, α′ is greater than α by about 0.5°. 
     Actuator  100  further includes a base  110 , typically made of plastic. Base  110  is also molded with two arc-shaped grooves  110   a  and  110   b  positioned at two opposite sides of base  110 , each arc-shaped groove ( 110   a  and  110   b ) having an angle α″&gt;α. Angle α″ is also shown in  FIG.  1 D . Typically, α″ is greater than α by about 0.5°. Arc-shaped grooves  110   a  and  110   b  also have a center of curvature on axis  108  ( FIG.  1 D ). Actuated sub-assembly  106  is positioned inside base  110  such that grooves  110   a  and  110   b  are parallel to and adjacent to grooves  102   a  and  102   b  respectively, and the centers of curvature for each couple of grooves are concentric respectively with axis  108 . 
     Since optical element holder  102  and base  110  are preferably plastic-molded (although they may also be made of aluminum or other metals) there is some tolerance allowed in part dimensions, typically up to a few tens of microns for each dimension. This tolerance may lead to misalignment of position between adjacent grooves  102   a - 110   a  and/or  102   b - 110   b.  In the embodiment shown and for better alignment, grooves  102   a,    110   a  and  110   b  have what is known in the art as a (non-limiting) ‘V’-groove cross-section shape to match the balls, while groove  102   b  has a cross-section which is wider and has a (non-limiting) ‘trapezoid’ cross-section. Grooves  102   a  and  110   a  are then aligned during assembly, while grooves  102   b  and  110   b  have some alignment freedom allowed by the trapezoid cross section. In other embodiments, all grooves ( 102   a,    102   b ,  110   a,  and  110   b ) may have a V-shape. 
     In actuator  100 , three balls  112   a,    114   a  and  116   a  are positioned in the space between grooves  102   a  and  110   a  and three balls  112   b,    114   b  and  116   b  are positioned in the space between grooves  102   b  and  110   b.  The number of balls (here 3) is exemplary. In other embodiments, a disclosed VCM actuator may have more or less of three balls (e.g. 2-7 balls) in the space between adjacent grooves. The balls are typically made of Alumina or another ceramic material, but may also be made of metal, plastic or other materials. The balls have a typical diameter in the range of 0.3-1 mm. Note that in actuator  100 , a distance L between grooves  102   a,b  and grooves  110   a,b  (and their respective sets of balls) is larger than a width W of OPFE  150 , such that the grooves and balls are “outside” of OPFE  150  with respect to the X axis. 
     In actuator  100 , grooves  102   a,    102   b,    110   a,    110   b  and balls  112   a,    112   b,    114   a,    114   b,    116   a  and  116   b  form a curved ball-guided mechanism  160  operative to impart a rotation or tilt movement to an optical element (e.g. OPFE  150 ) upon actuation by the VCM actuator (see  FIG.  1 K ) 
     In some embodiments, two different ball sizes may be used to provide smoother motion. The balls can be divided into a large diameter (LD) group and a small diameter (SD) group. The balls in each group have the same diameter. LD balls may have for example a 0.1-0.3 mm larger diameter than SD balls. A SD ball may be positioned between two LD balls to maintain the rolling ability of the mechanism. For example, in an embodiment, balls  112   a  and  116   a  may be LD balls and ball  114   a  may be a SD ball. 
     A metallic ferromagnetic yoke  118  is fixedly attached (e.g. glued) to base  110  from below (negative Z direction in the  FIG.  1 B ), such that it faces magnet  104 . The yoke  118  pulls magnet  104  (and thus pulls the actuated sub-assembly  106 ) by magnetic force and thus holds the curved ball-guided mechanism from coming apart. The magnetic force is in a direction marked in  FIGS.  1 A-C  as the negative Z direction. Balls  112   a,    114   a  and  116   a  and balls  112   b,    114   b  and  116   b  prevent actuated sub-assembly  106  from touching the base. Actuated sub-assembly  106  is thus confined along the Z-axis and does not move in positive or negative Z directions. Curved ball-guided mechanism  160  further confines the actuated sub-assembly along the X-axis, and thus the actuated sub-assembly can only move along the path defined by the parallel arc-shaped grooves  102   a,    102   b,    110   a  and  110   b.    
     Actuator  100  further includes an EM sub-assembly  120 ,  FIG.  1 E . Electro-magnetic sub-assembly  120  includes a coil  122 , a position sensor, for example a Hall bar element  124  and a printed circuit board (PCB)  126 . Coil  122  and Hall bar element  124  are preferably soldered (each on its own) to PCB  126 . Coil  122  has a stadium (oval) shape, and typically has a few tens of windings (e.g. but not limited to 50-250), and a typical resistance of 10-30 ohm. PCB  126  allows sending input and output currents to coil  122  and Hall bar element  124 . The currents carry both power and electronic signals needed for operation. PCB  126  is connected electronically to a camera (e.g. a camera as in  FIG.  2   ) which actuator  100  is part of, using wires (not shown). Electro-magnetic sub-assembly  120  is positioned between magnet  104  and yoke  118 . Driving a current in coil  122  creates a Lorentz force: a current in a clockwise direction will create force in the positive Y direction, while a current in counter clockwise direction will create a force in the negative Y direction. The full magnetic scheme (e.g. fixed magnet  104  pole direction) is known in the art and described for example in detail in co-owned patent PCT/IB2016/052179. 
     While magnetic force applied by the electro-magnetic sub-assembly is in the positive and negative Y directions, the rail formed by the balls and grooves cause confined actuated sub-assembly  104  to move along an arc parallel to grooves  102   a,    102   b,    110   a  and  110   b.  Hall bar element  124  can sense the intensity and direction of the magnetic field of magnet  104 . Upon actuation, the relative position of actuated sub-assembly  106  and Hall bar element  124  is changed. The intensity and direction of the magnetic field sensed by Hall bar element  124  change as well, and thus the position of actuated sub-assembly  106  can be determined. 
     A control circuit is used to control the position of the actuated sub-assembly and to set it to the position required by optical demands. The control circuit input is a signal from Hall bar element  124  and the output is the amount of current applied in coil  122 . The control circuit may be implemented in an integrated circuit (IC). In some cases the IC may be combined with Hall element  124 . In other cases, the IC may be a separate chip (not shown), which can be located outside of actuator  100  and of a camera including actuator  100  (e.g. see below embodiment  200 ). 
       FIGS.  1 G- 1 J  show schematically various views and components of another exemplary embodiment of a VCM actuator disclosed herein and numbered  100 ′.  FIG.  1 G  shows actuator  100  in an isomeric view,  FIG.  1 H  shows actuator  100  in an exploded view,  FIG.  11    shows details of an actuated sub-assembly  106 ′ in the actuator of  FIG.  1 G , and  FIG.  1 J  shows a cross section of the VCM actuator along a line B-B marked in  FIG.  1 G . Actuator  100 ′ is similar to actuator  100  in structure (and therefore similar elements/components are not numbered and/or described) and function except for a few differences: a) actuator  100 ′ includes three V-shaped grooves and one flat groove, i.e. exemplarily, in actuator  100 ′ optical element holder  102  is replaced by an optical element holder  102 ′ in which groove  102   b ′ is flat; b) in actuator  100 ′, a distance L′ between grooves  102   a,b  and grooves  110   a,b  (and their respective sets of balls) is equal to or smaller than a width W′ of OPFE  150 , such that the grooves and balls are “below” OPFE  150 . Thus, at least one dimension (width) and consequently the size of actuator  100 ′ is smaller than that of actuator  100 ; and c) actuator  100 ′ includes an added component, a shield  140 , which protect it from drops, hits, dust and stray light. The shape and dimensions of shield  140  are such as to minimally affect the size of the actuator. The shape and details shown are exemplary. Optionally, a shield such a shield  140  may also be provided for actuator  100 . Further and optionally actuator  100 ′ also includes an enclosure  142  (normally made of plastic) to protect the actuator against environmental and other factors. PCB  126 ′ has the same function as PCB  126  in actuator  100 . A curved ball-guided mechanism in actuator  100 ′ includes essentially the same components as in actuator  100 . 
     The shape of the grooves in a curved ball-guided mechanism disclosed in actuators  100  and  100 ′ is exemplary, and other shapes are possible, as indicated in  FIG.  1 K .  FIG.  1 K  shows in addition to shape embodiments “a” and “b” (axis  108  external or internal to OPFE  150 , with both grooves  102  and  110  of a pair curved “downwards”, i.e. with the center of curvature “above” the grove in the positive Z direction), a shape embodiment in “c” in which a groove  102  is curved downwards and a groove  110  is straight (linear), a shape embodiment in “d” in which both grooves  102  and  110  are curved upwards (center of curvature below the groove in the negative Z direction) and a shape embodiment in “e” in which grooves  102  are straight and grooves  110  are curved upwards. 
       FIG.  2    shows actuator  100  coupled to folded camera structure (FCS) or simply “folded camera”  200 . In folded camera  200 , an actuator such as  100  (or  100 ′) serves for example to rotate a light folding element, for example prism  150 . For simplicity, the description continues with reference to actuator  100 , with the understanding that it applies equally well to actuator  100 ′. Actuation by actuator  100  in folded camera  200  can be used, for example, to create optical image stabilization (OIS) as described in PCT/IB2016/052179 or to create an extended field of view, as described for example in PCT/IB2016/057366. A typical rotational stroke a in this case may be in the range of ±0.5 to ±2 degrees or ±2 to ±12 degrees of the original position of prism  150  respectively. Camera  200  further includes a lens element  202  and an image sensor  204 . 
     Folded camera  200  may further be coupled to or include actuation mechanisms to actuate lens element  204  for AF and\or OIS, for example described in PCT/IB2016/052179. The actuation mechanisms (and actuations) of lens  204  are independent of those of actuator  100  and are not shown in  FIG.  2   . The actuation mechanisms (and actuations) of lens  204  may be based on a VCM actuator with mechanical rails based on springs (as in PCT/IB2016/052179) or with mechanical rails based on a ball-guided mechanism. 
       FIGS.  3 A-D  shows schematically various views and components of another exemplary embodiment of a VCM actuator disclosed herein and numbered  300 .  FIG.  3 A  shows actuator  300  in an isomeric view and  FIG.  3 B  shows actuator  300  in an exploded view. As in actuator  100 , in actuator  300  an OPFE  350  is exemplarily a prism. OPFE  350  is held in an optical element holder  302 . A permanent magnet  304  is fixedly attached (e.g. glued) to optical element holder  302 . OPFE  350 , optical element holder  302  and magnet  304  form a “top actuated sub-assembly”  306 . Optical element holder  302  includes (e.g. is molded with) two parallel arc-shaped grooves  302   a  and  302   b  positioned at two opposite sides of holder  302 , each arc-shaped groove having an angle β′&gt;β, where angle β is a required rotational stroke, as defined by optical needs. Angles β′ and β″ are not shown, but its definition is similar to that of angles α′ and α″ in  FIG.  1 D . Exemplary values and ranges for β, β′ and β″ are similar to those for α, α′ and α″ above. Top actuated sub-assembly  306  and its parts are similar to actuated sub-assembly  106  in terms of materials, dimensions, etc. 
     Actuator  300  further includes a middle base  310 , typically made of plastic. Middle base  310  is also molded with two grooves  310   a  and  310   b.  Top-actuated sub-assembly  306  is positioned inside middle base  310  such that grooves  310   a  and  310   b  are parallel to grooves  302   a  and  302   b  respectively. In this embodiment, grooves  302   b,    310   a  and  310   b  have V-groove shape, while groove  302   a  has a trapezoid shape; the considerations for these shapes was given above in the description of actuator  100 . Three balls  312   a,    314   a  and  316   a  are positioned between grooves  302   a  and  310   a,  and, similarly, three balls  312   b,    314   b  and  316   b  are positioned between grooves  302   b  and  310   b.  In other embodiments, actuator  300  may have more or less than 3 balls in each groove, typically in the range of 2-7 balls. Considerations for size and materials of all balls are similar to those described in actuator  100 . Middle base  310  further includes two more arc-shaped grooves  310   c  and  310   d  on a single circle  320 , as seen in  FIG.  3 C . Top actuated sub-assembly  306 , balls  312   a - 314   a,    312   b - 314   b  and middle base  310  form a bottom actuated sub-assembly  334 . The diameter of circle  320  may exemplarily be in the range of 5-15 mm. Grooves  302   a,    302   b,    310   a ,  310   b  and balls  312   a,    312   b,    314   a,    314   b,    316   a  and  316   b  form a first curved ball-guided mechanism  360  of actuator  300 . 
     Actuator  300  further includes a bottom base  308 . Bottom base  308  is typically made of plastic, and is molded with two arc-shaped grooves  308   c  and  308   d.  Arc-shaped grooves  308   c  and  308   d  are on circle  320  with a center on an axis  321 , as can be seen in  FIG.  3 C . Bottom actuated sub-assembly  334  is positioned above bottom base  308  such that grooves  310   c  and  310   d  are parallel to grooves  308   c  and  308   d  respectively. In this embodiment, grooves  310   c,    308   c,    308   d  have V-groove shape, while groove  310   d  has a trapezoid shape; the considerations for these shapes were given above in the description of actuator  100 . Three balls  312   c,    314   c  and  316   c  are positioned between grooves  308   c  and  310   c,  and similarly three balls  312   d,    314   d  and  316   d  are positioned between grooves  308   d  and  310   d.  In other embodiments, actuator  300  may have more or less of 3 balls in each groove, typically in the range of 2-7. The considerations for size and materials of all balls are similar to those described in actuator  100 . Grooves  308   c,    308   d,    310   c ,  310   d  and balls  312   c,    312   d,    314   c,    314   d,    316   c  and  316   d  form a second curved ball-guided mechanism  362  of actuator  300 . 
     A metallic yoke  318  is fixedly attached (e.g. glued) to bottom base  308  from below, such that it faces magnet  304 . Metallic yoke  318  pulls magnet  304  (and thus pulls top actuated sub-assembly  306 ) by magnetic force and thus holds the two curved ball-guided mechanisms ( 360  and  362 ) from coming apart. The magnetic force is in direction marked in  FIG.  1    as the negative Z direction. Balls  312   a,    314   a  and  316   a  and  312   b,    314   b  and  316   b  prevent top actuated sub-assembly  306  from touching middle base  310 , and balls  312   c,    314   c  and  316   c  and  312   d,    314   d  and  316   d  prevent bottom actuated sub-assembly  334  from touching bottom base  308 . Top actuated sub-assembly  306  is thus confined along the Z-axis and does not move in positive or negative Z directions. First curved ball-guided mechanism  360  further confines top actuated sub-assembly  306  along the X-axis, and thus top actuated sub-assembly  306  can only move along the path defined by the parallel arcs  302   a,    302   b,    310   a  and  310   b.  Bottom actuated sub-assembly  334  is confined along the Z-axis and does not move in positive or negative Z directions. Second curved ball-guided mechanism  362  further confines bottom actuated sub-assembly  334  to move only in a rotational manner around circle  320  (rotation around the Z-axis). The typical magnitude/angle of this rotation (in degrees) is similar to that of a above. Magnet  304  acts on both curved ball-guiding mechanism. 
     Actuator  300  further includes an electro-magnetic sub-assembly  330 , shown in  FIG.  3 D . Electro-magnetic sub-assembly  330  includes two coils  322  and  324 , two Hall bar elements  326  and  328  and a printed circuit board (PCB)  329 . Coils  322 ,  324  and Hall bar elements  326 ,  328  are soldered (each one on its own) to PCB  329 . Coils  322 ,  324  have a stadium shape, typically with a few tens of windings (for example, in a non-limiting range of 50-250), with a typical resistance 10-30 ohm each. PCB  329  allows sending input and output currents to coils  322 ,  324  and to Hall bar elements  326 ,  328 , currents carrying both power and electronic signals needed for operation. PCB  329  is connected electronically to the external camera with wires not seen in  FIG.  3   . Electro-magnetic sub-assembly  330  is positioned between magnet  304  and yoke  318 . Upon driving current in coils  322 ,  324  a Lorentz force is created; a current in a clockwise direction will create force in the positive Y direction while a current in a counter clockwise direction will create a force in the negative Y direction. The full magnetic scheme (e.g. fixed magnet  304  pole direction) is similar to that in actuator  100 . As coil  322  ( 324 ) is not centered with circle  320 , the Lorentz force is also translated to clockwise (counter clockwise) torque around Z axis on bottom actuated sub-assembly  334 . 
     While the magnetic force applied by both of the coils  322  and  324  of electro-magnetic sub-assembly is in the positive and negative Y directions, top actuated sub-assembly  306  is confined by the first curved ball-guided mechanism to move along an arc parallel to grooves  302   a,    302   b ,  310   a  and  310   b  (i.e. rotate around the X axis). Similarly bottom actuated sub-assembly  334  is confined by the second curved ball-guided mechanism to move around circle  320  (i.e. rotate around the Z axis), and its motion is dominated by the net torque around Z axis applied by coils  322  and  324  around axis  321  (the difference between the torque around Z axis each of the coils applies). Hall bar elements  326 ,  328  can sense the intensity and direction of the magnetic field of magnet  304 . Upon actuation, the position of top actuated sub-assembly  306 , bottom actuated sub-assembly  334  and Hall bar elements  326 ,  328  is changed, and with it changes the intensity and direction of the magnetic field sensed. We mark with V HB-326  and V HB-328  the Hall output voltage of both sensors, which is proportional to the magnetic field sensed by each Hall sensor, as known in the art. Thus, the amount of rotation of top actuated sub-assembly  306  and bottom actuated sub-assembly  334  can be determined. In an example, the sum V HB-326 +V HB-328  is proportional to the amount of tilt around the first rotation axis and the difference V HB-326 −V HB-328  is proportional to the amount of tilt around the second rotation axis. A control circuit is used to control the position of the actuated sub-assembly and to set it to the position required by optical demands. The control circuit input includes signals of Hall bar elements  326 ,  328  and the output includes the amount of current applied in coils  322 ,  324 . The control circuit may be implemented in an integrated circuit (IC). In some cases, the IC may be combined with one of Hall elements  326 ,  328 . In other cases, the IC is a separate chip, which can be located outside of the camera (not shown). 
       FIG.  4    shows actuator  300  as part of a folded camera  400 . In folded camera  400 , actuator  300  serves for example to rotate an optical path folding element (OPFE) to create optical image stabilization in two directions, as described for example in U.S. provisional patent application 62/215,007. Folded camera  400  further includes a lens element  402  and an image sensor  404 . A typical actuation stroke in this case may be in the range of ±0.5 to ±2 degrees around the X axis and ±1 to ±3 degrees around the Z axis of the original position of the light-folding element (e.g. prism  450 ) for both rotation directions. Folded camera  400  may further include an actuation mechanism (not shown) for lens element  402  as known in the art (for example described in PCT/M2016/052179) for AF and/or OIS. The actuation mechanism of lens  402  is not dependent on the actuation done in actuator  300 . 
       FIGS.  5 A- 5 D  show schematically various views and components of another exemplary embodiment of a VCM actuator disclosed herein and numbered  500 .  FIG.  5 A  shows an isomeric view of an assembled actuator  500 , while  FIGS.  5 B,  5 C  show an exploded view of actuator  500  from two opposite directions along the X-axis.  FIG.  5 D  shows a cross section of actuator  500  along a line A-A marked in  FIG.  5 A . Actuator  500  allows the rotation of an OPFE  550  around a single axis (i.e. around the X-axis) as described below. In  FIGS.  5 A- 5 D , OPFE  550  is a prism while in other embodiments it may a mirror or another type of optical path bending element. 
     In actuator  500 , OPFE  550  is held in an OPFE holder  502 , which can be made, for example by plastic mold, fitting the shape of OPFE  550 . An actuation magnet  504  and a sensing magnet  506  are fixedly attached (e.g. glued) to optical element holder  502  from the side, in the same direction as an axis of rotation of OPFE  550  (the negative X direction in the figures). The assembly of OPFE  550 , optical element holder  502  and magnets  504 ,  506  is referred to as “actuated sub-assembly”  510 , shown from the side in  FIG.  5 D . Optical element holder  502  is molded with two arc-shaped grooves,  502   a  and  502   b.  Arcs  502   a  and  502   b  are concentric with each other, having a common center of rotation on an axis  508 . Arc-shaped grooves  502   a  and  502   b  have respective angles γ′ and γ″ fulfilling γ′&gt;γ and γ″&gt;γ, where angle γ is the required rotational stroke, as defined by optical needs. The center of rotation axis  508  and angles γ′, γ″ are seen in  FIG.  5 D . The typical values for γ, γ′ and γ″ are similar to those for α, α′ and α″. 
     Actuator  500  further includes a sidewall  514 . Sidewall  514  is a stationary part and is fixed rigidly to the actuator frame (not shown) and to the camera image sensor. Sidewall  514  is typically made of plastic. In some embodiments, sidewall  514  may be a part of the entire actuator&#39;s frame (known in the art as ‘base’). Sidewall  514  may be molded as a single piece of plastic which serves for the purposes described below, as well as other purposes needed for the camera which actuator  500  is part of (e.g. holding the lens or holding the image sensor). Sidewall  514  is also molded with two arc-shaped grooves  514   a  and  514   b.  Actuated sub-assembly  510  is positioned alongside sidewall  514  such that grooves  514   a  and  514   b  are parallel to grooves  502   a  and  502   b  respectively. In this embodiment grooves  502   b,    514   a  and  514   b  have V-groove shape, while groove  502   a  has a trapezoid shape; the considerations for these shapes was given above in the description of actuator  100 . 
     Three balls  512   a,    514   a  and  516   a  are positioned between grooves  502   a  and  514   a,  and, similarly, three balls  512   b,    514   b  and  516   b  are positioned between grooves  502   b  and  514   b.  In other embodiments, actuator  500  may have more or less than 3 balls in each groove, typically in the range of 2-7 balls. Consideration for size and materials of all balls is similar to the described in actuator  100 . The two pairs of grooves and their associated balls form a curved ball-guided mechanism  560  of actuator  500 . 
     A metallic ferromagnetic yoke  518  is fixedly attached (e.g. glued) to sidewall  514  from a side opposite to those of magnets  504 ,  506  such that it faces magnet  504 . Yoke  518  pulls magnet  504  (and thus pulls the actuated sub-assembly  510 ) by magnetic force and thus holds the curved ball-guided mechanism from coming apart. The magnetic force is in direction marked in  FIG.  5 A  as the negative X direction. Balls  512   a,    514   a  and  516   a  and  512   b,    514   b  and  516   b  prevent actuated sub-assembly  510  from touching sidewall  514 . Actuated sub-assembly  510  is thus confined along the X-axis and does not move in positive or negative X directions. Curved ball-guided mechanism  560  further confines the actuated sub-assembly  510  along other directions such that actuated sub-assembly can only move along the path defined by the parallel arcs  502   a,    502   b,    514   a  and  514   b    
     Actuator  500  further includes an electro-magnetic sub-assembly  530 , shown in  FIG.  5 E . Electro-magnetic sub-assembly  530  includes a coil  522 , a Hall bar element  524  and a PCB  526  Coil  522  and Hall bar element  524  are soldered (each one by its own) to the PCB. Coil  522  has a stadium shape, typically has few tens of winding (not limiting range of 50-250), with a typical resistance of 10-30 ohm. PCB  526  allows sending input and output currents to coil  522  and Hall bar element  524 , currents carrying both power and electronic signals needed for operation. PCB  526  is connected electronically to the external camera with wires (not shown). Electro-magnetic sub-assembly  530  is positioned between the magnets  504 ,  506  and yoke  518  such that there is an air-gap of typically about 100-200 μm between the magnets and the electro-magnetic sub-assembly (the Hall bar element, coil and magnets do not touch each other). Upon driving a current in coil  522  a Lorentz force is created: a current in a clockwise direction will create force in the positive Y direction while a current in counter clockwise direction will create a force in the negative Y direction. The full magnetic scheme (e.g. the fixed magnet  504  pole direction) is known in the art, and described for example in detail in co-owned patent PCT/IB2016/052179. 
     As for actuated sub-assemblies above, while the magnetic force applied by the electro-magnetic sub-assembly is in the positive and negative Y directions, the rail created by the balls and grooves create a confinement for actuated sub-assembly  510  to move along an arc parallel to grooves  502   a,    502   b,    514   a  and  110   b.  Hall bar element  524  can sense the intensity and direction of the magnetic field of sensing magnet  506 . Upon actuation, the relative position of actuated sub-assembly  510  and Hall bar element  524  is changed. The intensity and direction of the magnetic field senses by Hall bar element  524  changes as well and thus the position of actuated sub-assembly  510  can be determined. 
     A control circuit is used to control the position of the actuated sub-assembly and set to the position required by optical demands. The control circuit input is a signal from Hall bar element  524  and the output is the amount of current applied in coil  522 . The control circuit may be implemented in an IC. In some cases, the IC may be combined with Hall element  524 . In other cases, it is a separate chip, which can be located outside of the camera (not shown). 
     In some embodiments, the sensing magnet  506  can be removed and the Hall bar element  524  can be placed in the center of the coil so the actuation magnet  504  can be used for both actuation and sensing (as described for example above with reference to  FIG.  1 E ). 
     In some embodiments, sensing magnet  506  and actuation magnet  504  may be combined into one magnet with the suitable magnetization to allow the sensing and actuating functionality described above. 
       FIG.  6    shows actuator  500  as part of a folded camera  600 . In camera  600 , actuator  500  serves as an example of usage to rotate a light folding element, for example prism  550 . Actuation by actuator  500  in camera  600  can be used, for example, to create OIS as described in PCT/M2016/052179. Camera  600  further includes a lens element  602  and an image sensor  604 . A typical actuation stroke γ in this case should be in the range of ±0.5 to ±2 degrees of the original position of prism  550 . As described with reference to camera  200  above, camera  600  may further include actuation mechanisms to actuate lens element  602  for AF and/or OIS (not shown). 
     Any of the actuators disclosed above may be included in a folded camera which in turn may be included together with an upright (non-folded) camera in a dual-aperture camera with folded lens, for example as described in co-owned U.S. Pat. No. 9,392,188. 
     While this disclosure describes a limited number of embodiments, it will be appreciated that many variations, modifications and other applications of such embodiments may be made. In general, the disclosure is to be understood as not limited by the specific embodiments described herein, but only by the scope of the appended claims. 
     All references mentioned in this specification are herein incorporated in their entirety by reference into the specification, to the same extent as if each individual reference was specifically and individually indicated to be incorporated herein by reference. In addition, citation or identification of any reference in this application shall not be construed as an admission that such reference is available as prior art to the present application.