Abstract:
A camera module includes an image sensor having a first threaded portion. A lens assembly includes an electro-active polymer (EAP) structure having a frusto-conical shape with an opening formed in the tip. A lens is secured to a lens holder that is attached to the EAP structure surrounding the opening. A first electrode is attached to a rear face of the EAP structure and extends along a side. A second electrode is attached to the rear face of the EAP structure along the tip. A base frame is attached to the base of the EAP structure. The base frame includes a second threaded portion that engages the first threaded portion, joining the lens assembly to the image sensor assembly and allowing the lens assembly to be rotated relative to the image sensor to adjust the distance between the lens assembly and the image sensor to establish a default focal distance.

Description:
BACKGROUND 
     1. Field 
     Embodiments of the invention relate to the field of digital camera modules; and more specifically, to structures for setting the initial focus position during factory assembly. 
     2. Background 
     Many portable electronic devices, such as mobile cellular telephones, include a digital camera. The lenses for such cameras must be compact to fit within the case of the portable electronic device. At the same time there is a desire to provide an increasingly high quality camera function in these devices. To provide a higher quality image, some cameras found in portable electronic devices provide an autofocus feature and/or an adjustable iris to control exposure. 
     An image sensor, lens, and actuators for the lens are typically assembled into a camera module. The lens may be mounted in a actuator that moves the lens along its optical axis to change the distance between the lens and the image sensor. This changes the focal distance of the camera and allows a sharper image to be obtained for subjects over a greater range of distances from the camera. One such lens moving mechanism for moving a lens is a voice coil motor. Voice coil motors are relatively complex assemblies with a number of parts. Voice coil motors also consume a significant amount of power. The addition of an adjustable iris further increases mechanical complexity and power consumption in the camera module. 
     It would be desirable to provide a camera module that provides a focus actuator and adjustable iris with a structure that reduces mechanical complexity and power consumption. 
     SUMMARY 
     An embodiment of the invention described here is an artificial muscle or EAP actuator that also provides a variable aperture, for use with moveable camera imaging optics. An electrode arrangement is formed in an EAP structure that may achieve both camera optics displacement (actuation) and variable aperture functions. 
     The above summary does not include an exhaustive list of all aspects of the present invention. It is contemplated that the invention includes all systems and methods that can be practiced from all suitable combinations of the various aspects summarized above, as well as those disclosed in the Detailed Description below and particularly pointed out in the claims filed with the application. Such combinations have particular advantages not specifically recited in the above summary. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Embodiments of the invention will now be described with reference to the drawings summarized below. The embodiments of the invention are illustrated by way of example and not by way of limitation in the figures of the accompanying drawings in which like references indicate similar elements. It should be noted that references to “an” or “one” embodiment of the invention in this disclosure are not necessarily to the same embodiment, and they mean at least one. 
         FIG. 1  is a pictorial view of a camera module that embodies the invention. 
         FIG. 2  is an exploded view of the camera module of  FIG. 1 , showing the sub-assemblies of the module. 
         FIG. 3  is a cross-section view of the camera module taken along section line  3 - 3  in  FIG. 1 . 
         FIG. 4  is an exploded pictorial view of an exemplary artificial muscle actuator structure. 
         FIG. 5  is a bottom view of the exemplary artificial muscle actuator structure looking from the image sensor toward the lens. 
         FIG. 6  is a plan view of the top side of a signal terminal ring. 
         FIG. 7  is a plan view of the bottom side of the signal terminal ring shown bonded to the artificial muscle actuator. 
         FIG. 8  is a further exploded view of the camera module of  FIG. 2 , showing component parts of the sub-assemblies. 
         FIG. 9  is a plan view of the top side of the assembly focus ring. 
         FIG. 10  is a plan view of the bottom side of the assembly focus ring. 
         FIG. 11  is a plan view of the top side of the base assembly. 
         FIG. 12  is a side view of the assembly focus ring on the threaded portion of the base assembly. 
     
    
    
     DETAILED DESCRIPTION 
     Several embodiments of the invention with reference to the appended drawings are now explained. Whenever the shapes, relative positions, and other aspects of the parts described in the embodiments are not clearly defined, the scope of the invention is not limited only to the parts shown, which are meant merely for the purpose of illustration. Also, while numerous details are set forth, it is understood that some embodiments of the invention may be practiced without these details. In other instances, well-known circuits, structures, and techniques have not been shown in detail so as not to obscure the understanding of this description. 
     In the following description, reference is made to the accompanying drawings, which illustrate several embodiments of the present invention. It is understood that other embodiments may be utilized, and mechanical compositional, structural, electrical, and operational changes may be made without departing from the spirit and scope of the present disclosure. The following detailed description is not to be taken in a limiting sense, and the scope of the embodiments of the present invention is defined only by the claims of the issued patent. 
     The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention. Spatially relative terms, such as “beneath”, “below”, “lower”, “above”, “upper”, and the like may be used herein for ease of description to describe one element&#39;s or feature&#39;s relationship to another element(s) or feature(s) as illustrated in the figures. It will be understood that the spatially relative terms are intended to encompass different orientations of the device in use or operation in addition to the orientation depicted in the figures. For example, if the device in the figures is turned over, elements described as “below” or “beneath” other elements or features would then be oriented “above” the other elements or features. Thus, the exemplary term “below” can encompass both an orientation of above and below. The device may be otherwise oriented (e.g., rotated 90 degrees or at other orientations) and the spatially relative descriptors used herein interpreted accordingly. 
     As used herein, the singular forms “a”, “an”, and “the” are intended to include the plural forms as well, unless the context indicates otherwise. It will be further understood that the terms “comprises” and/or “comprising” specify the presence of stated features, steps, operations, elements, and/or components, but do not preclude the presence or addition of one or more other features, steps, operations, elements, components, and/or groups thereof. 
       FIG. 1  is a pictorial view of a camera module  100  that embodies the invention.  FIG. 2  is an exploded view of the camera module  100 , showing the sub-assemblies of the module. A base assembly  220  supports an optical assembly  210  that is covered by a shield  200 . The base assembly  220  provides a threaded portion  222  to mate with a corresponding threaded portion of an assembly focus ring  212  of the optical assembly  210 . The threaded connection between the base assembly  220  and the optical assembly  210  allows the optical assembly to be focused on an image sensor in the base assembly during the manufacturing process as will be further described below. 
       FIG. 3  is a cross-section view of the camera module  100 , taken along section line  3 - 3  in  FIG. 1 . The base assembly  220  may include a substrate  316  (e.g., a printed circuit carrier such as a flex circuit) that supports an image sensor  318  and a cover glass  314 , which may be an infrared cut filter that reduces the amount of infrared light that reaches the image sensor. A base frame  312  may be assembled to the substrate  316  to provide the aforementioned threaded portion  222  and electrical tracks as will be further described below. The base frame  312  may include an opening that allows light from a scene to reach the active pixel area of the image sensor  318 . The base frame  312  may be made of an electric insulator material such as plastic. If the base frame  312  is made of a sufficiently clear light transparent material, then the physical opening shown in  FIG. 3  may not be needed. 
     The optical assembly  210  includes a lens assembly  306  that provides the imaging optics for the camera module  100 . The lens assembly  306  is supported by springs  308  that are supported in turn by the assembly focus ring  212 . The lens assembly  306  is held against the springs  308  by the artificial muscle actuator  300  that provides lens displacement for focusing as well as the variable aperture. The artificial muscle actuator  300  may be part of an autofocus lens subsystem, for example. The artificial muscle is an electroactive polymer (EAP) that exhibits a change in size or shape when stimulated by an electric field. A common terminal ring  302  and a signal terminal ring  304  provide electrical connections to the artificial muscle actuator  300  as will be further described below. 
       FIG. 4  is an exploded pictorial view of an exemplary artificial muscle actuator  300  structure.  FIG. 5  is a bottom view of the exemplary artificial muscle actuator  300  structure looking from the image sensor  318  toward the lens  306 . In this case, the muscle structure is generally frusto-conical, and as seen in  FIG. 2 , its larger lower base is attached to the assembly focus ring  212  (e.g., via a clamping mechanism). The smaller upper base of the frusto-conical structure (or frustum) has a central, generally circular opening  324  that serves as a variable aperture. 
     The artificial muscle may have a structure of one or more layers of silicon based polymers that react to a differential of potential between two electrodes that cover the polymer layers. This potential differential creates a sufficient electric field that activates the conductive particles of the polymer material, and creates a significant amount of force through the material to provide elongation. As a result, the structure may strain along its length proportionally to the square of the voltage input. 
     The strain in the artificial muscle actuator  300  is used here for at least two different purposes. An electrode arrangement is formed on the artificial muscle structure (EAP structure) that may achieve both camera lens displacement actuation and variable aperture functions. 
     For lens focus actuation, the artificial muscle can move a lens or other optics forward and backward (or up and down) along the imaging axis of the lens. This may yield significant cost reduction versus a voice coil actuator (VCM). The artificial muscle actuator may support large optics with improved system integration due to its generally frusto-conical shape. Power consumption may be minimal. 
     As a variable aperture element, the actuator may be able to change an aperture diameter of the optics in smaller f-number increments, and it can support relatively large aperture diameters thereby yielding fast optics and better low light performance. To combine lens focus actuation and variable aperture features, a “focus actuation electrode” of the muscle is separated (electrically isolated) from an “aperture electrode” that is used to provide the variable aperture. 
     An electroactive polymer (EAP)  402  is between positive and negative electrodes that create an electrical potential across the EAP. The muscle  402  is activated (deforms) when a sufficient electric field is created through and across the artificial muscle structure, due to sufficient voltage being applied to the opposing or complementary electrodes (formed on opposite faces of the muscle). These so-called positive and negative electrodes may be screen-printed onto the rear and front surfaces, respectively, of the EAP material, in such a way that the positive and negative electrodes substantially overlap each other to increase the electric field strength that is created between them. In one embodiment, to enable displacement of optics, the driver circuit may need to deliver around 500V to 1000V potential to the electrode, through its respective terminal, relative to ground. In one embodiment, the negative electrode of the actuator is also connected to ground. 
     In this example, the forward surface  404 , which is adjacent the shield  200 , is the common, negative electrode. The shield  200  is connected to ground to provide some immunity from electromagnetic interference. As best seen in bottom view of  FIG. 5 , the positive focus actuation electrode has two segments  406 ,  408 , each segment covering a little less than one half of the entire side surface area of the rear side of the EAP frustum  402  closest to the image sensor  318 . A “gap”  510  is formed between the two segments that may extend from one edge of the base, up to the tip and then down to an opposite edge of the base, as shown in the bottom view of  FIG. 5 . 
     The positive aperture electrode  410 , which in this case has a single segment, lies in the gap  510 . In this example, the positive aperture electrode  410  has two arms that extend down from the tip of the frustum on opposite sides, to opposing edges of the base of the frustum. As also seen in  FIG. 5 , the positive aperture electrode  410  covers essentially the entire surface area of the tip (with the central opening therein that serves as the variable aperture). Note however that the particular arrangement of the electrodes shown in  FIGS. 4 and 5  is just one example of how the positive electrode (actuation and aperture portions) can be formed on the inner or rear face of a frusto-conical muscle. Other electrode patterns are possible. 
     A focusing force F 1  may be produced by the actuator  300  in its non-energized state, where F 1  may be substantially along the imaging axis in a so-called rearward direction that moves the lens assembly  306  toward the image sensor  318 . An opposing force F 2  is produced by the spring  308  that urges the lens assembly  306  away from the image sensor  318 . When the actuator  300  deforms in response to a potential difference between the common, negative electrode  404  and the positive focus actuation electrode  406 ,  408 , the focusing force F 1  is reduced allowing the opposing force F 2  produced by the spring  308  to move the lens assembly  306  away from the image sensor  318 . The forces act upon the lens assembly  306 , in which the lenses may be rigidly fixed, to move the lens assembly forward and backward as necessary for focusing an image on the image sensor  318 . 
     A variable aperture function may be produced by the actuator  300  deforming in response to a potential difference between the common, negative electrode  404  and the positive aperture electrode  410 . As the annular portion at the tip of the EAP frustrum deforms in response to an increasing potential difference delta P  as distributed to the aperture electrodes, the circular opening  324  decreases in diameter, providing a higher f-number for the variable aperture. 
       FIG. 3  depicts an example of the infinity lens position that can be obtained from the actuator when not energized. In this case, the artificial muscle is under pre-tension (material elasticity in the side surface of the frustum in the longitudinal direction or along a length direction of the frustum), when it is not active. In this state, this pre-tension is compressing the spring mechanism (spring loading). Now, when the potential difference delta P  as distributed to the actuator electrodes has been increased sufficiently, the pre-tension of the muscle releases, thereby allowing the lens barrel to be pushed up away from the image sensor under the spring loading. The shield  200  may provide a hard stop that defines the maximum actuator stroke possible. 
     The infinity lens position obtained from the actuator when not energized is typically set when the camera module is assembled. This may be accomplished by rotating the assembly focus ring  212  at the lower end of the artificial muscle actuator  300  to adjust the distance between the optical assembly  210  and the image sensor  318  by the screw action between the threaded portion of the assembly focus ring  212  with the corresponding threaded portion  222  of the base  312 . 
     The near end of the artificial muscle actuator  300  may be fixed against the assembly focus ring  212  by capturing the near end between the common terminal ring  302  and the signal terminal ring  304 . The terminal rings are, in turn, attached to the assembly focus ring  212 . The assembly focus ring  212  is coupled to the base  312  by engaging the threaded portion of the assembly focus ring  212  with the corresponding threaded portion  222  of the base. 
       FIG. 6  is a plan view of the top side of the signal terminal ring  304 , which may be bonded to the artificial muscle actuator  300  by a conductive adhesive such as epoxy or tape. The signal terminal ring body  600  may be made of a non-conductive material such as a glass fiber and epoxy composite. The signal terminal ring body  600  may include features such as tabs  602  to facilitate orienting and holding the signal terminal ring during assembly. 
     A number of conductive pads are provided on the top side of the signal terminal ring  304  to provide electrical connections to the positive focus electrodes on the lower surface of the artificial muscle actuator  300 . The exemplary signal terminal ring  304  provides two upper conductive pads  604  to be coupled to the two segments  406 ,  408  of the positive focus actuation electrode. The exemplary signal terminal ring  304  also provides two upper conductive pads  606  to be coupled to the two ends  310  of the positive aperture electrode  410 . 
       FIG. 7  is a plan view of the bottom side of the signal terminal ring  304  shown bonded to the artificial muscle actuator  300 . A number of conductive pads are provided on the bottom side of the signal terminal ring  304  to provide electrical connections from the positive focus electrodes on the lower surface of the artificial muscle actuator  300  to the exemplary signal terminal ring  304 . The terminal ring provides four lower conductive pads  704  to be coupled to the two segments  406 ,  408  of the positive focus actuation electrode. The exemplary signal terminal ring  304  also provides two lower conductive pads  706  to be coupled to the two ends of the positive aperture electrode  410 . The upper and lower conductive pads are electrically coupled, such as by vias  710 , that provide an electrical path across the signal terminal ring body  600 . 
     The signal terminal ring  304  is mechanically and electrically coupled to the assembly focus ring  212 . 
     It will be seen in the exemplary signal terminal ring  304  that the lower conductive pads on the bottom side of the signal terminal ring are smaller and more widely separated than the corresponding upper conductive pads on the top side of the signal terminal ring. This may facilitate making electrical connections to the assembly focus ring  212 . 
     The lower conductive pads are arranged to cooperate with conductive pads on the base  312  so that at least one lower conductive pad is aligned with a corresponding base conductive pad for each of the positive electrodes regardless of the angular position of the signal terminal ring  304 . 
       FIG. 8  is a further exploded view of the camera module  100 , showing component parts of the sub-assemblies. The base assembly  220  may include the substrate  316  (e.g., a printed circuit carrier such as a flex circuit) that supports the image sensor  318  and the cover glass  314 , which may be an infrared cut filter that reduces the amount of infrared light that reaches the image sensor. The base frame  312  may be assembled to the substrate  316  to provide the threaded portion  222  and electrical tracks as will be further described below. The base frame  312  may include an opening or be made of a sufficiently clear light transparent material to allow light from a scene to reach the active pixel area of the image sensor  318 . 
     The optical assembly  210  includes the lens assembly  306  that provides the imaging optics for the camera module  100 . The lens assembly  306  is supported by springs  308  that are supported in turn by the assembly focus ring  212 . The lens assembly  306  is held against the springs  308  by an artificial muscle actuator  300  that provides lens displacement for focusing as well as a variable aperture. The artificial muscle actuator  300  may be part of an autofocus lens subsystem, for example. The artificial muscle is an electroactive polymer (EAP) that exhibits a change in size or shape when stimulated by an electric field. A common terminal ring  302  and a signal terminal ring  304  provide electrical connections to the artificial muscle actuator  300 . 
     The camera module  100  is assembled by assembling the component parts into the sub-assemblies of the base assembly  220 , the optical assembly  210 , and the shield  200 , which may be a single component. The optical assembly  210  is first coupled to the base assembly  220 . The optical assembly  210  is coupled to the base assembly  220  by the threaded connection between the assembly focus ring  212  and the threaded portion  222  of the base assembly. The threaded connection allows the lens assembly  306  to be focused on the image sensor  318  during the assembly process to provide a reference focal position for the autofocus system. The shield  200  is then coupled to the base assembly  220  to enclose the optical assembly  210  and form the camera module  100 . 
     It is also necessary to electrically couple the optical assembly  210  to the base assembly  220  to provide the electrical signals that actuate the artificial muscle actuator  300 . At least two terminals  820 ,  822  are formed on the base frame  312 , to bring a differential of potential up to the electrodes  406 ,  408 ,  410  of the artificial muscle actuator  300 . One terminal  820  may be connected to the focus actuation electrode  406 ,  408 . Another terminal  822  may be connected to the aperture electrode  410 . The two terminals  820 ,  822  may be driven by separately controllable driver circuits. Each terminal may be electrically connected to a driver circuit (not shown) through conductive traces or routes (not shown) in the substrate  316 , which produces sufficient voltage needed for the desired deformation of the artificial muscle actuator  300 . 
       FIG. 9  is a plan view of the top side of the assembly focus ring  212 . The top side of the assembly focus ring is immediately adjacent the bottom side of the signal terminal ring  304  as seen in  FIG. 7 . The signal terminal ring  600  may be mechanically aligned to the assembly focus ring  212  by engaging features on the signal terminal ring, such as tabs  602 , with mating features on the assembly focus ring, such as notches  902 . This may hold the signal terminal ring  304  in the proper orientation on the assembly focus ring  212  during assembly. The conductive pads  704 ,  706  on the signal terminal ring  304  face corresponding conductive pads  904 ,  906  on the assembly focus ring  212 . The corresponding conductive pads are mechanically and electrically coupled such as by soldering or by a conductive adhesive such as epoxy or tape. 
     There are at least two conductive pads  904 ,  906  on the assembly focus ring  212 , at least one of which is coupled to the focus actuation electrode  406 ,  408  and at least one other of which is coupled to the aperture electrode  410 . If there are two or more conductive pads on the assembly focus ring  212  that are coupled to the same electrode on the artificial muscle actuator  300 , the conductive pads on the assembly focus ring may be electrically coupled by an electrical path  905  on the assembly focus ring. 
       FIG. 10  is a plan view of the bottom side of the assembly focus ring  212 . The bottom side of the assembly focus ring is immediately adjacent the base assembly  220 . The conductive pads  904 ,  906  on the assembly focus ring  212  extend onto the bottom side of the assembly focus ring. The conductive pads  904 ,  906  may be on a beveled outside surface of the bottom side of the assembly focus ring as best seen in  FIG. 3 . The conductive pads  904 ,  906  on the bottom side of the assembly focus ring  212  are arranged to cover a majority of the circumference of the assembly focus ring. The conductive pads  904 ,  906  on the bottom side of the assembly focus ring  212  are further arranged such that each of the at least two conductive pads  904 ,  906  on the assembly focus ring  212  covers more than 90 degrees of total arc on the circumference of the assembly focus ring. 
       FIG. 11  is a plan view of the top side of the base assembly  220 . The top side of the base assembly is immediately adjacent the bottom side of the assembly focus ring  212  as seen in  FIG. 10 . The optical assembly  210  is mechanically coupled to the base assembly  220  by the threaded engagement of the assembly focus ring  212  on the threaded portion  222  of the base assembly. The optical assembly  210  is rotated relative to the base assembly  220  to adjust the initial focus of the camera module  100  during the assembly process. 
     At least two terminals  820 ,  822  are formed on the base frame  312 , to bring a differential of potential up to the electrodes  406 ,  408 ,  410  of the artificial muscle actuator  300 . As seen in  FIG. 11 , the terminals  820 ,  822  are distributed on the base frame  312  such that each of the two terminals is provided at multiple points around the circumference. For example, in the embodiment illustrated, each of the two terminals is provided at six places around the circumference of the threaded portion  222  of the base assembly  312 . The terminals may be advantageously arranged to lie in the four corner regions of a generally square base frame  312 . 
     The arrangement of the conductive pads  904 ,  906  on the bottom side of the assembly focus ring  212  and the arrangement of the terminals  820 ,  822  on the base frame  312  are such that at least one of the conductive pads on the bottom side of the assembly focus ring will be adjacent at least one corresponding terminal on the base frame regardless of the relative orientation of the optical assembly  210  to the base assembly  220 . When the optical assembly  210  is correctly focused, at least one of the conductive pads on the bottom side of the assembly focus ring is mechanically and electrically coupled to an adjacent corresponding terminal on the base frame  312  for each of the two terminals on the base frame. 
       FIG. 12  is a side view of the  212  on the threaded portion  222  of the base assembly. The corresponding conductive pads and terminals are mechanically and electrically coupled  1104  such as by soldering or by an electrically conductive adhesive such as silver conductive epoxy. This coupling provides both an electrical path for the electrical signals that actuate the artificial muscle actuator  300  and a mechanical fixing of the assembly focus of the optical assembly  210  on the image sensor  318  in the base assembly  220 . It will be appreciated that beveling at least one of the corresponding conductive pads and terminals provides a V-shaped region, which may be advantageous for the coupling of the pads and terminals. 
     Assembly of the camera module  100  is completed by placing the shield assembly  200  over the optical assembly  210 . The shield assembly is mechanically and electrically coupled to the shield to terminals  224  on the base assembly  220 . The shield and terminals are mechanically and electrically coupled such as by soldering or by a conductive adhesive such as epoxy or tape. This coupling provides both an electrical path for the common electrical signal that actuates the artificial muscle actuator  300  and a mechanical fixing of the shield  200  to the base assembly  220 . The shielding structure  200  may be electrically grounded through the substrate  316 . The shielding structure  200  may provide shielding against electromagnetic interference. 
     For purposes of explanation, specific embodiments were described to provide a thorough understanding of the present invention. These should not be construed as limiting the scope of the invention but merely as illustrating different examples and aspects of the invention. It should be appreciated that the scope of the invention includes other embodiments not discussed in detail above. Various other modifications, changes, and variations which will be apparent to those skilled in the art may be made in the arrangement, operation, and details of the systems and methods of the present invention disclosed herein without departing from the spirit and scope of the invention as defined in the appended claims. Therefore, the scope of the invention should be determined by the claims and their legal equivalents. Such equivalents include both currently known equivalents as well as equivalents developed in the future, i.e. any elements developed that perform the same function, regardless of structure. Furthermore, no element, component, or method step is intended to be dedicated to the public regardless of whether the element, component, or method step is explicitly recited in the claims. 
     While certain exemplary embodiments have been described and shown in the accompanying drawings, it is to be understood that such embodiments are merely illustrative of and not restrictive on the broad invention, and that this invention is not limited to the specific constructions and arrangements shown and described, since various other modifications may occur to those of ordinary skill in the art. The description is thus to be regarded as illustrative instead of limiting.