Patent Publication Number: US-7590505-B2

Title: Manufacturable micropositioning system employing sensor target

Description:
RELATED APPLICATIONS 
   This patent application claims priority under 35 U.S.C. 119(e) of the U.S. Provisional Pat. App. No. 60/836,616, filed Aug. 8, 2006, entitled MINIATURIZED ZOOM MODULE WITH ROTATIONAL PIEZO ACTUATOR WITH ANTI-LOCK FEATURE, EVEN FORCE DISTRIBUTION, SHOCK DAMAGE PREVENTION AND A NOVEL POSITION SENSING METHODS”, which is hereby incorporated by reference. 
   In addition, this patent application is a continuation-in-part of U.S. patent application Ser. No. 11/514,811, filed on Sep. 1, 2006 and entitled “AUTO-FOCUS AND ZOOM MODULE, now U.S. Pat. No. 7,531,773 which claims priority under 35 U.S.C. 119(e) of the U.S. Provisional Pat. App. No. 60/715,533, filed Sep. 8, 2005, entitled “3× ZOOM MINI MODULE”, both of which are also hereby incorporated by reference. 

   FIELD OF THE INVENTION 
   The invention relates to controlled positioning and position sensing of functional elements, including optical elements, within a small form factor component. More particularly, this invention is directed toward an auto-focus and zoom module. 
   BACKGROUND 
   Recently, there have been numerous developments in digital camera technology that rely on positioning of micro-scale elements. One such development is the further miniaturization of optical and mechanical parts to the millimeter and sub millimeter dimensions. The reduction in size of the moving parts of cameras has allowed the implementation of modern digital camera and optical technology into a broader range of devices, which are continually being designed and constructed into smaller and smaller form factors. Though moving parts shrink, they still must be accurately positioned for optical and mechanically precise tasks. Further, the components responsible for precisely positioning such components also must become smaller. 
   A wide variety of strategies for small-scale positioning of optical and other functional elements are known. However, there is no available solution for accurate, small-scale positioning within a small form-factor and economically manufacturable device. 
   SUMMARY OF THE DISCLOSURE 
   Embodiments of the present invention relate to systems for and methods of position sensing that use a sensing target with a pattern or repeating feature thereupon. Further, embodiments relate to positioning of functional elements using such position sensing systems. In particular, some embodiments relate to positioning of optical elements. 
   In some embodiments of the present invention, a position sensing system uses a sensing target which have a pattern of features with an average critical dimension. The position sensing system includes an encoding module and a processing module. The encoding module has an active encoding region through which the sensing target is configured to move. Further, the encoding module is configured to generate a signal based on a portion of the sensing target within the active encoding region. The active encoding region has a dimension greater than the average critical dimension of the pattern of features. The processing module is configured to convert the signal generated into position data based on an input range condition and an initial position condition. 
   In certain embodiments of the present invention, a micropositioning module comprises a functional group, a drive shaft, an actuator, a sensing target, and a position sensing system. The functional group is coupled to the drive shaft. The actuator is configured for translating the drive shaft to move the functional group. The sensing target is configured to represent movement of the functional group at a first resolution, preferably during movement of the functional group by the drive shaft. The position sensing system is configured with the sensing target to perform several steps. First, to detect movement of the functional group at the first resolution as raw movement data. Then, to process the raw movement data into corrected movement data having a second resolution. Finally, to translate the corrected movement data into position data representing the position of the first functional group. The second resolution is greater than the first resolution. 
   In some other embodiments, a micropositioning module includes a functional group, an actuator, a sensing target, and a position sensing system. The functional group is coupled to a lead screw so that rotation of the lead screw results in translation of the functional group along an axis parallel to the lead screw. The actuator is configured for rotating the lead screw. The sensing target is configured to represent rotation of the lead screw at a first resolution. The position sensing system is configured with the sensing target to detect rotation of the lead screw at the first resolution as raw rotation data. The position sensing system processes the raw rotation data into corrected rotation data having a second resolution, wherein the second resolution is greater than the first resolution. The position sensing system converts the corrected rotation data into position data representing a position of the functional group. 
   Some embodiments relate to a method of detecting a position of a functional group coupled to a sensing target configured to represent movement of the functional group at a first resolution. The method comprises steps of using the sensing target to detect movement of the functional group at the first resolution, encoding raw movement data representing the detected movement, processing the raw movement data into corrected movement data having a second resolution, wherein the second resolution is greater than the first resolution, and converting the corrected movement data into position data representing the position of the functional group. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The novel features of the invention are set forth in the appended claims. However, for purpose of explanation, several embodiments of the invention are set forth in the following figures. 
       FIG. 1  is an isometric view of an auto-focus and zoom module in accordance with some embodiments of the invention. 
       FIG. 2  is an isometric view of an auto-focus and zoom module in accordance with some embodiments of the invention. 
       FIG. 3  is an isometric view of internal parts of an auto-focus and zoom module in an end stop position in accordance with some embodiments of the invention. 
       FIG. 4  is an alternative isometric view of internal parts of an auto-focus and zoom module in end stop position accordance with some embodiments of the invention. 
       FIG. 5A  is an isometric view of internal parts of an auto-focus and zoom module in a mid position in accordance with some embodiments of the invention. 
       FIG. 5B  is a plan view of internal spring elements of an auto-focus and zoom module in a mid position in accordance with some embodiments of the invention. 
       FIG. 6A  is an alternative plan view of internal spring elements of an auto-focus and zoom module in a mid position in accordance with some embodiments of the invention. 
       FIG. 6B  is an isometric view of internal spring elements of an auto-focus and zoom module in a mid position in accordance with some embodiments of the invention. 
       FIG. 7A  is a plan view of internal spring elements of an auto-focus and zoom module in tele position in accordance with some embodiments of the invention. 
       FIG. 7B  is an isometric view of internal spring elements of an auto-focus and zoom module in tele position in accordance with some embodiments of the invention. 
       FIG. 8A  illustrates an auto-focus and zoom module in an end stop position in accordance with some embodiments of the invention. 
       FIG. 8B  illustrates an auto-focus and zoom module in a mid position in accordance with some embodiments of the invention. 
       FIG. 8C  illustrates an auto-focus and zoom module in a tele position in accordance with some embodiments of the invention. 
       FIG. 9  is a plan view along the optical axis of an auto-focus and zoom module in accordance with some embodiments of the invention. 
       FIG. 10A  is a plan view of a prior art actuator assembly utilized in some embodiments of the invention. 
       FIG. 10B  is an isometric view of a prior art actuator assembly utilized in some embodiments of the invention. 
       FIG. 10C  is an isometric view of a prior art actuator assembly utilized in some embodiments of the invention. 
       FIG. 11A  is a schematic representation of a position sensor in accordance with some embodiments of the invention. 
       FIG. 11B  is a schematic representation of beam spreading that occurs during sensing in accordance with some embodiments of the invention. 
       FIG. 11C  is a schematic representation of beam spreading that occurs during sensing in accordance with some embodiments of the invention. 
       FIG. 12A  is a schematic illustration of a direct imaging solution for position sensing in schematic representation of beam spreading that occurs during position sensing in accordance with some embodiments of the invention. 
       FIG. 12B  is a schematic illustration of a lens-based imaging solution for position sensing in accordance with some embodiments of the invention. 
       FIG. 12C  is a schematic illustration of a pinhole-based imaging solution for position sensing in accordance with some embodiments of the invention. 
       FIG. 13A  is an exploded isometric view of an assembly for position sensing in accordance with some embodiments of the invention. 
       FIG. 13B  is an exploded isometric view of an assembly for position sensing in accordance with some embodiments of the invention. 
       FIG. 14A  is a detailed view of a position-sensing portion of an optical module in accordance with some embodiments of the invention. 
       FIG. 14B  is a detailed view of a position-sensing portion of an optical module in accordance with some embodiments of the invention. 
       FIG. 15  is a detailed schematic of an active area of interface between a sensing target and a sensor consistent with some embodiments of the invention. 
       FIG. 16  is a schematic representation of a signal produced from a sensing target consistent with some embodiments of the invention. 
       FIG. 17  is a flowchart illustrating a method of sensing a position consistent with some embodiments of the present invention. 
   

   DETAILED DESCRIPTION 
   In the following description, numerous details and alternatives are set forth for purpose of explanation. However, one of ordinary skill in the art will realize that the invention can be practiced without the use of these specific details. In other instances, well-known structures and devices are shown in block diagram form in order not to obscure the description of the invention with unnecessary detail. 
     FIGS. 1 to 10C  in particular deal with an auto-focus and zoom module employing a positioning system consistent with the present invention. These figures and the accompanying discussion, as well as related discussion in the position sensing section, relate to embodiments of the invention implemented in an optics context, but should not be taken as limiting the invention. The full scope of the invention is best appreciated by reading the appended claims. 
     FIGS. 1 and 2  illustrate an auto-focus and zoom module  1000  in accordance with some embodiments of the invention. The module  1000  is shown with the exterior electro magnetic interference (EMI) shield removed. 
   As shown, the module is built over an image sensor board  10 . The module  1000  comprises a stiffener  1  disposed on a first side of the image sensor board  10 , and a main structure  20  disposed opposite the stiffener  1 . Preferably, the stiffener  1  and the main body  20  are coupled with one another and with the image sensor board  10 . 
   The main structure  20  comprises a base guide portion  22 . The base guide portion  22  includes features configured to retain the guide pins  601  and  602 . The end guide plate  2  is disposed opposite the base guide portion  22 . The holes  2   a  and  2   b  interface with and retain the guide pins  601  and  602 , respectively. The base guide portion  22  further includes a void region (not shown) configured to permit passage of radiation, e.g. visible light, through the lens structure of the module (discussed below) to the image sensor (discussed below) of the image sensor board  10 . In addition, the base guide portion  22  includes a pass-thru  25  configured to permit the image sensor board extension  11  to pass therethrough. 
   Disposed between the base guide portion  22  and the end guide plate  2  are the main body  20  and other components of the module  1000 . The main body  20  further includes the upper structure  24 , and the lower structure  26 . Both the lower  26  and upper  24  structures include specialized features configured to mate with or allow pass-through of working components of the module  1000 . Thus, the main body  20  provides both a structure framework and functional support to the workings of the module  1000 . 
   For example, the lower structure  26  includes the pivot boss  32 , configured to act as a fulcrum for the low-variation preload lever assembly (discussed below). In addition, the lower structure  26  includes the pass through  27 , configured to permit movement of the lever assembly through a desired range. Similarly, the upper portion  24  includes a pass through configured to permit coupling between a main PCB and the sensor  901  discussed below. 
   A variety of components of the module  1000  are coupled to the main body  20 . Some of these components are immobilized relative to the main body  20 . In addition to the guide pins  601  and  602 , the actuator housings  1020  and  1030  are coupled to the main body  20  in an immobile position. Thus, the actuator housings  1020  and  1030  are in a fixed position relative to the guide pins  601  and  602 . 
     FIGS. 3 and 4  show the internal components of the module  1000 . The main body  20  (shown in  FIGS. 1 and 2 ) is not shown. As shown in these figures, the module  1000  includes a front optics group  400 , a rear optics group  500 , and an image sensor  14 . The front optics group  400  and rear optics group  500  each typically comprise one or more optical elements such as a lens group. One of ordinary skill will recognize both complex and simple lens arrangements for the optics groups  400  and  500 . 
   Optionally attached to the main body  20  and the end guide plate  2  is a prism  40 , (shown in  FIG. 2 ). The module  1000  preferably further includes a casing and a cover mechanism, as well as an EMI shield as mentioned above. The cover mechanism preferably prevents light leakage and dust contamination from affecting the internal components of the module, particularly the lens groups  400  and  500  and the image sensor  14 . In some embodiments, a single external housing functions as both an EMI shield and a cover mechanism. An infrared (IR) filter and/or a low pass filter is optionally attached to the image sensor board  10 . 
     FIGS. 3 and 4  illustrate further details of the module  1000 . As mentioned above, the actuator housings  1020  and  1030  are coupled to the main body  20 . This coupling, along with the coupling between the main body  20 , the end guide plate  2 , and the guide pins  601  and  602  positions and secures the components relative to one another, and to the target region  12  of the image sensor  14 , providing a chassis for an auto-focus and zoom module capable of providing an image with a magnification and zoom to the target region  12 . 
   Image Sensor 
   As shown in the figures, the image sensor  14  is substantially planar. The image sensor  14  can be of any type conventionally known in the art such as a CMOS image sensor or alternatively a CCD image sensor. The plane of the image sensor is preferably perpendicular to the axes of the guide pins  601  and  701 . Typically, the module  1000  is configured to provide an image to the image sensor  14  along an image vector parallel to these axes. 
   Guide Pins 
     FIGS. 3 and 4  illustrates a guide pin arrangement for an auto-focus and zoom module in accordance with the present invention. Some embodiments include a pair of guide pins, while other embodiments employ a different number of guide pins. Regardless of their number, the guide pins  601  and  602  are typically mounted along a linear axis of the module  1000  to permit the rear barrel  530  and the front barrel  430  to move relative to the image sensor  14 . In the module  1000 , the primary guide pin  601  and the secondary guide pin  602  are aligned so that their axes are substantially parallel to each other. Further, the lead screw assemblies  200  and  300  are also aligned so that their axes are substantially parallel to each other, and to the guide pins  601  and  602 . 
   Typically, the guide pins  601  and  602  are coupled to the main body  20  and the end guide plate  2  as outlined above. Preferably, the guide pins are coupled on opposite sides of the image vector of the image sensor  14 . However, one skilled in the art will recognize that other configurations are possible. The lead screws  200  and  300  are typically disposed along an edge of the image sensor  14  and parallel to its optical axis. 
   In some embodiments, the range of motion provided to the rear barrel  530  and parallel to the guide pins  601  and  602  is approximately 7 millimeters. In some embodiments, the range of motion provided to the front barrel  430  and parallel to the guide pins  601  and  602  is approximately 2 millimeters. Due to this range of motion, however, the guide pins  601  and  602  of some embodiments often affect the form factor of the module  1000 . Hence, some embodiments further include means for modifying and/or concealing the form factor of the module  1000 . 
   Prism Feature 
   Certain embodiments additionally include a prism feature, e.g.  40  of  FIG. 2 . This feature allows the auto-focus and zoom module to be disposed and/or mounted in a variety of orientations. For instance, the dimension available to a particular implementation along the initial direction of an image vector is often limited such that the module is preferably disposed lengthwise in the vertical plane of an enclosure. This orientation allows the range of motion of the front and rear barrels along the guide pins, as described above, to be implemented in a device having a small width and/or depth form factor. For example, in a mobile phone implementation where a user will want to aim a camera at a desired image using the display as a viewfinder, the image vector is advantageously perpendicular to the display for usability purposes. However, the dimension of the device perpendicular to the display is often the thinnest dimension of a mobile phone. 
   Referring to  FIGS. 2 and 3 , the prism feature  40  of some embodiments is mounted adjacent to the front barrel  430 . The prism  40  redirects the light from an image at an angle with respect to the front barrel  430 . As described above, the front barrel  430  typically houses a front lens group. The front lens group contains one or more front optical elements. Hence the prism  100  allows the module  1000  to be disposed in a variety of orientations within a device that is typically held at an angle with respect to the subject being viewed and/or photographed. Though a prism is preferably used, it will be apparent that other optical elements such as a mirror can be used to redirect the light from the object to the image sensor  14 . 
   Lens System 
   As shown in  FIGS. 3 ,  4  and  5 A, the rear optics group  500  and front optics group  400  have preferred constructions. The rear optics group  500  further includes the rear barrel  530 , the rear guide sleeve  510 , and the rear guide slot  520 . The rear barrel  530  typically houses one or more lenses or other optical elements. As illustrated, the rear barrel  530  houses the rear lens  540 . The rear barrel  530  is preferably a substantially cylindrical body with a central axis. The rear lens  540  is configured to direct light along the central axis of the rear barrel  530 . The rear guide sleeve  510  is an elongated, substantially cylindrical body coupled to the rear barrel  530  so that the central axis of the rear barrel  530  and an axis of the rear guide sleeve  510  are substantially parallel. The rear guide slot  520  is a slotted feature configured to interface with a cylinder. 
   The front optics group  400  further includes the front barrel  430 , the front guide sleeve  410 , and the front guide slot  420 . The front barrel typically houses the front lens group  440 . The front barrel  430  is a substantially cylindrical body with a central axis. The front lens group  440  is configured to direct light along the central axis of the front barrel  430 . The front guide sleeve  410  ( FIG. 6B ) is an elongated, substantially cylindrical body coupled to the front barrel  430  so that the central axis of the front barrel  430  and an axis of the front guide sleeve  410  are substantially parallel. The front guide slot  420  is a slotted feature configured to interface with a cylinder. 
   Lens-Guide Pin Interface 
   Referring now to  FIG. 6B , the front optics group  400  includes the front guide sleeve  410 , which couples with the primary guide pin  601 . As illustrated, the front guide sleeve  410  is substantially elongated relative to the front barrel  430 . Further, the front guide sleeve  410  is rigidly coupled to the front barrel  430 . This configuration prevents the front optics group  400  from rotating around an axis perpendicular to the axis of the primary guide pin  601 , but permits rotation around the axis of the primary guide pin  601 . The rear optics group  500  includes the rear guide sleeve  510 , which also couples with the primary guide pin  601 . As illustrated, the rear guide sleeve  510  is substantially elongated relative to the rear barrel  530 . Further, the rear guide sleeve  510  is preferably rigidly coupled to the rear barrel  530 . This configuration prevents the rear optics group  500  from rotating around an axis perpendicular to the primary guide pin  601 , but permits rotation around the axis of the guide pin. 
   Referring now to  FIG. 4 , the front optics group  400  also includes the front guide slot  420 , configured to couple with the secondary guide pin  602 . The coupling between the guide slot  420  and the secondary guide pin  602  prevents the front optics group  400  from rotating around the axis of the primary guide pin  601 . The coupling between the front optics group  400  and guide pins  601  and  602  permits the front optics group  400  to translate along an axis substantially parallel to the two guide pins. 
   The rear optics group  500  also includes the rear guide slot  520 , configured to couple with the secondary guide pin  602 . The coupling between the guide slot  520  and the secondary guide pin  602  prevents the rear optics group  500  from rotating around the axis of the primary guide pin  601 . The coupling between the rear optics group  500  and guide pins  601  and  602  permits the rear optics group  500  to translate along an axis substantially parallel to the two guide pins. 
   Actuator Modules 
   Preferably, the actuators used within embodiments of the present invention are vibrational actuators. Most preferably, these vibrational actuators are of the type that oscillates in a standing wave pattern to drive a threaded shaft placed therein to rotate, thus rotating the threaded shaft. Embodiments of the present invention include certain preferred standing wave patterns for driving the vibrational actuators. However, a variety of standing wave patterns are contemplated. 
   The present invention contemplates a variety of actuator constructions. These include vibrational actuators as disclosed in U.S. Pat. No. 5,966,248 issued Oct. 12, 1999 and U.S. Pat. No. 6,940,209 issued Sep. 6, 2005. These also include actuators as shown for example in  FIGS. 10A to 10C . The actuator  700 ′ comprises a flexible body surrounded by a plurality of piezoelectric strips,  701 ,  702 , and  704 . A fourth strip, not shown, is disposed opposite the strip  701 . The strips are arranged symmetrically around a flexible body that has a plurality of thread-interface features disposed therein. The thread interface features are configured to mate with the threads of the lead screw  360 ′. During operation, the piezoelectric strips drive an oscillating motion within the flexible body. Actuators of this type typically require an operating preload. Preferably, this preload is applied to the lead screw via techniques disclosed elsewhere in this document. 
   In order to effectively drive a threaded shaft by using the preferred vibrational actuators, some embodiments of the present invention include specialized actuator housings, designed to constrain the actuator to only the degree necessary and also to provide shock protection for the actuator. In addition, the actuator housings permit close positioning of actuator relative to the guide pin and optics group. Typically, each actuator within the embodiment is combined with an actuator housing to form an actuator module. 
   Some embodiments of the present invention include actuator modules such as those illustrated in  FIGS. 10A to 10C . A typical actuator module, as illustrated, includes an actuator  700 ′, an actuator housing  1030 ′, and a flexible coupling  710 . 
   The flexible coupling  710  constrains a portion of the actuator  700 ′ to a substantially fixed position relative to the actuator housing  1030 ′. This permits the actuator to drive a lead screw to translate relative to the actuator housing  1030 ′. For example, the contact pads  710  prevent the actuator  700 ′ from rotating relative to the housing. 
   However, by constraining only a portion of the actuator  700 ′, the embodiment permits relatively free vibration of the actuator  700 ′ to impart movement to a lead screw, e.g.  360 ′. Further, because the flexible coupling  710  preferably constrains the actuator  700 ′ at a node point of the preferred standing wave pattern of the actuator  700 ′, the effect of the constraint on the efficiency of the actuator is reduced. Preferably, the fixed location is chosen to be a node point of a variety of standing wave patterns, thus permitting efficient operation of the actuator under a variety of conditions. 
   As illustrated, the actuator housing  1030 ′ includes openings  1034  and  1036  to admit the lead screw  360 ′. In addition, the housing includes openings  1032  and  1038  configured to admit electrical connections to a main PCB board (not shown). In addition, the actuator housing  1030 ′ is specialized to prevent shock damage to the actuator  700 ′. The actuator housing  1030 ′ is preferably a five-sided chamber that forms a parallelepiped therein. This parallelepiped, called the actuator retention region, is larger in volume than the actuator  700 ′. Further, the actuator retention region is larger along every dimension than the corresponding dimension of the actuator  700 ′. In addition, when the actuator  700 ′ is constrained within the actuator retention region by the flexible coupling  710 , preferably a surface of the actuator  700 ′ is parallel with the surface of the parallelepiped that does not include a portion of the actuator housing. Further, the ends of the actuator  700 ′ are preferably approximately equidistant from the openings  1034  and  1036 , respectively. Thus, the actuator  700 ′ is suspended within the retention region with a buffer distance between it and each adjacent surface of the actuator housing  1030 ′. 
   Further, the size of the parallelepiped actuator retention region and the actuator  700 ′ are matched to one another, and to the type of flexible coupling  710  used to retain the actuator. Preferably, the buffer distance between the actuator  700 ′ and the inner surfaces of the housing  1030 ′ adjacent to the openings  1034  and  1036  are chosen relative to the maximum displacement permitted prior to failure by the flexible coupling  710 . Thus, during a mechanical shock, such as received from dropping a cell phone, the actuator  700 ′ will encounter an inner surface of the housing  1030 ′ prior to stretching the flexible coupling  710  to failure. In addition, similar stretching along axes perpendicular to the lead screw  360 ′ is prevented by the coupling between the lead screw  360 ′ and the actuator  700 ′. 
   The actuator housings  1030  and  1020  permit close positioning of actuators  700  and  500  relative to the primary guide pin  601 . As shown in  FIG. 9 , this close positioning is permitted because the open end of the actuator housings  1020  and  1030  allow the actuators  500  and  700  to be disposed at a surface of the actuator module. Thus, the actuators  500  and  700  are placed proximate to the primary guide pin  601 , leaving clearance for the guide sleeves  410  and  510 . 
   Close positioning increases precision by minimizing torque effects as the actuators  200  and  300  drive the optics modules  400  and  500 , respectively. The center of mass of the optics modules  400  and  500  lies between the guide pins  601  and  602 . The lead screw coupling surfaces  480  and lie off center. Thus, driving the optics modules  400  and  500  by the coupling surfaces  480  and  570  tends to introduce a torque. The guide pins, including the primary guide pin  601 , counteract the torque effect. However, configuring the modules so that the actuators  500  and  700 , and the coupling surfaces, are nearly aligned with the guide pin  601  reduces the amount of torque on the guide pins. 
   Lead Screw Assemblies 
   Referring now to  FIGS. 10A to 10C , the exemplary lead screw assembly  300 ′ is shown coupled with the actuator housing  1030 ′. The lead screw assembly  300 ′ is structured around the lead screw  360 ′. The assembly includes cam  320 ′ and the referencing cap  340 . The lead screw  360 ′ comprises a threaded region  5 , a first end, and a second end. The first end of the lead screw  360 ′ and the referencing cap  340  are integrally formed. 
   Lead Screw-Optics Group Interface 
   Referring now to  FIG. 8A , the front optics group  400  and rear optics group  500 , respectively, couple with the lead screws through the lead screw coupling surfaces  480  and  570  respectively. Both primary guide sleeves  410  and  510  couple with the primary guide pin  601 . 
   In the preferred configuration, movement of a lead screw transmits force through its counterpart lead screw coupling surface. Since the coupling surfaces are each a rigidly coupled component of an optics group, translation of a coupling surface results in translation of its counterpart optics group. However, a simple rigid connection between a coupling surface and a lead screw can accomplish this function. The illustrated configuration provides additional benefits by isolating the optics group from non-translational movements of the lead screw. Preferably, a reference cap coupled to the first end of a lead screw contacts the coupling surface, for example, see the reference cap  340  of  FIG. 10C . 
   The small contact area between the reference cap and the coupling surface serves to minimize friction, permitting movement of the coupling surface relative to the reference cap and the lead screw in the axes orthogonal to the axis of the lead screw. This configuration isolates most mechanical vibration or disturbance of the lead screw from the optics group. Further, the isolation means that only the translational degree of freedom of the lead screw need be controlled to achieve a required precision for positioning of the optics group. Though non-translational movement of the lead screw is not present in the preferred embodiment, these features permit embodiments of the present invention to deal with this type of wobble when present. 
   To maintain coupling between a coupling surface and lead screw, some embodiments of the present invention rely on preload springs otherwise required for accurate operation of the actuators. 
   Preload Springs 
   In addition to the features mentioned above, the actuators used within embodiments of the present invention typically utilize a low-variation preload force. This preload is provided by a spring with a low force constant. In small displacement implementations this method typically works well. 
   Some embodiments of the present invention rely on spring forces which act on the optics groups to provide preload to the lead screws used to drive the groups. Thus, to an extent, the required displacement of the optics group determines the type of spring force transmission mechanism required. 
   For example, in some embodiments of the present invention the front optics group  400  is used for focusing and zoom operations and need only be displaced a millimeter or two. Because the preferred range of motion of the front optics group  400  is less than two millimeters, choosing a low force constant spring for the spring and coupling it to directly exert spring forces on the optics group results in a relatively low variation preload. 
   As illustrated in  FIG. 8B , the front lead screw coupling surface  480  is adjacent to the first end of the lead screw  260 . To couple the surface with the lead screw and provide preload, the preload spring urges the surface against the lead screw. Because of the small movements involved in focusing, directly providing the spring force is permissible in this case. Thus, the front preload spring  180  is coupled to the front optics group  400  via the preload interface feature  470  ( FIG. 6B ) and configured to directly exert force on the optics group  400 . 
   In another example, the rear optics group  500  is used for zoom operations and need be displaced several millimeters or more. Because the preferred range of motion of the front optics group  500  is more than four millimeters, choosing a low force constant spring for the spring and coupling it to directly exert spring forces on the optics group results to high a variation in preload. 
   As illustrated in  FIGS. 6A and 6B , the rear lead screw coupling surface  570  is adjacent to the lead screw  360 . To couple the surface with the lead screw and provide preload, thus preload spring urges the surface against the lead screw. However, direct provision of the preload is undesirable in this case. 
   Thus, the preload spring  110  is configured on the opposite end of a preload lever  100 . The zoom preload lever  100  includes a pivot hole  140  configured to mate with the pivot boss  32  of the main body  20 . In addition, the preload lever  100  includes a preload spring hook  130  and a preload force transfer point  120 . 
   The pivot hole  140  is skewed toward the preload spring hook  130  so that movement at the hook end of the preload lever  100  is amplified at the force transfer point end. By the same mechanism, large movements at the force transfer point  120  end of the zoom lever  100  translate into relatively smaller movements at the spring hook  130  end. This reduces variations in the preload force over the relatively larger travel distance of the zoom lens system. Preferably, the location of the pivot hole  140  is chosen to decrease the travel from the force transfer end to the spring hook end, in this example by a factor of five. Other embodiments employ a different factor. 
   The spring hook  130  is coupled with the preload spring  110 , and the force transfer point  120  is coupled with one face of the rear lead screw coupling surface  570 . The coupling surface  570  is also adjacent to the lead screw  360 . To couple the surface with the lead screw and provide preload, the preload spring must urge the surface against the lead screw. Indirectly providing the spring force from the rear preload spring  110  through the lever  100  means that travel of the rear optics group  500  translates indirectly into extension of the preload spring  110 . The specific proportionality of group travel to spring extension depends on the positioning of the lever pivot relative to the force transfer point and spring hook. As described above, the preferred ratio is one-fifth. 
   In either case, indirect or direct preload spring force application, the opposite end of the preload spring is preferably coupled to the main body  20 . 
   Sensing Target 
   Some embodiments of the present invention include sensing targets to provide feedback on positioning. In some embodiments, a sensing target is disposed on a lead screw. In some embodiments, a sensing target is disposed on an optics group. Both linear and rotational targets can be used with the present invention. 
   A lead screw assembly in accordance with some embodiments of the present invention includes a sensing target. Some lead screw assemblies, such as the assembly  300 ′ of  FIG. 10A to 10C , do not include a sensing target. However, the lead screw assembly  200 , shown for example in  FIG. 8C , includes the sensing target  290  positioned adjacent to the cam  220 . In the illustrated embodiment, the target  290  is a rotational target. The use of a rotational target is preferred in contexts that require very fine positioning. 
   Typically, a sensing target adapted for coupling to a lead screw includes a feature that interfaces with a registering feature of lead screw. In some embodiments the sensing target interfaces with the threads of a lead screw. The position sensing target  290  is configured to engage with the position sensor  902 . 
   In some embodiments, a sensing target is included as part of an optics group. For example, in  FIGS. 8A to 8C , the sensing target  590  is configured as part of the rear optics group  500 . Here, the target  590  is constructed as an integral part of the optics group  500 . However, in some embodiments, a sensing target is modular, or merely coupled with an optics group. 
   In addition, the sensing target  590  is a linearly moving sensing target. Linearly moving targets are acceptable in relatively low precision positioning applications. Further, linearly moving targets are preferred in applications where the target moves over a relatively large range. Here, the linearly moving target is employed in the rear optics group  500  because the group is used for zoom purposes. 
   In  FIG. 8A  the module is in an end stop position. In some embodiments, the position sensors  901  and  902  are disengaged from the sensing targets  590  and  290 , respectively, during end stop. In this position, also illustrated in  FIGS. 3 and 4 , the lead screw positions are registered at a mechanical hard stop via means discussed elsewhere in this document. Thus, because in these embodiments the lead screw positions correlate with the optical group positions, the registering of the lead screws defines the position of the optical groups as well. 
   In  FIGS. 8B and 8C , the modules are in mid position and tele position, respectively. Preferably, the sensing targets  590  and  290  are engaged with the position sensors  901  and  902 , respectively, while in mid and tele position. Preferably, the position sensors and sensing targets are engaged throughout all zoom positioning. 
   Mechanical Hard Stop Latch 
   Preferably, embodiments of the present invention include features configured to permit referencing of the optics group via a mechanical hard stop. 
   Referring now to  FIGS. 3 and 4 , these embodiments include the hard stop latch spring  310  and the hard stop latch spring  410 . The hard stop latch spring  310  is mounted to the main body  20  on the spring boss  21 . As shown in  FIGS. 3 and 4 , the hard stop latch spring  310  comprises a substantially rigid body and an active spring  312 . The rigid body includes the lens group interface surface  314 , the pivot hole  318 , and the latch  316 . The lens group interface surface  314  and the latch  316  are each arranged on separate arms positioned approximately 90 degrees apart around the pivot hole  318 , and extending outward therefrom. The latch  316  arm is substantially longer than the group interface surface  314  arm. At rest the active spring  312  is aligned with the latch  316  arm. 
   The pivot hole  318  is mated with the spring boss  21  and configured to pivot around the boss  21 . The group interface surface  314  is configured to mate with the spring driver  580  of the rear lens group  500 . At rest, the latch  316  is disposed out of line with the actuator housing  1030 , e.g.  FIG. 5A . The hard stop latch spring  310  pivots around the hole  318  when the spring driver  580  urges the group interface surface  314  toward the image sensor, flexing the active spring  312 . When pivoted, the latch  316  moves into place to interface with the cam feature  322  of the cam  320 . This provides a mechanical hard stop for the lead screw  360 . 
   The hard stop latch spring  210  is mounted to the actuator housing  1020  on the spring boss  1028 , as shown in  FIG. 5B . The hard stop latch spring  210  comprises a substantially rigid body and an active spring  212 . The rigid body includes the lens group interface surface  214 , the pivot hole  218 , and the latch  216 , e.g.  FIG. 4 . The lens group interface surface  214  and the latch  216  are each arranged on separate arms positioned approximately 90 degrees apart around the pivot hole  218 , and extending outward therefrom. The latch  216  arm is substantially longer than the group interface surface  214  arm. At rest the active spring  212  is aligned with the latch  216  arm. 
   The pivot hole  218  is mated with the spring boss  1028  and configured to pivot around the boss  1028 . The group interface surface  214  is configured to mate with the spring driver  480  of the front lens group  400 . At rest, the latch  216  is disposed out of line with the actuator housing  1020 , e.g.  FIG. 5A . The hard stop latch spring  210  pivots around the boss  1028  when the spring driver  480  urges the group interface surface  214  toward the image sensor, flexing the active spring  212 . When pivoted, the latch  316  moves into place to interface with the cam feature  222  of the cam  220 . This provides a mechanical hard stop for the lead screw  260 , e.g. as shown in  FIG. 8A . 
   Position Sensing 
   Embodiments of the present invention include position-sensing elements configured to provide feedback to an actuator control system. These elements permit the module to accurately position functional groups, e.g. optics, by using non-linear actuator motors. 
   Preferred embodiments of the present invention employ a sensing target that moves in concert with a functional group of the module, and a sensor configured to detect and encode data representing movement of the sensing target. For example, some embodiments use reflection encoding of a mobile sensing target that comprises regions of differing reflectance. An exemplary position sensing system comprises the position sensors  1030  and the position sensing targets  250  and  350  of the module  1000  of  FIG. 1 . 
   Reflection Encoding 
   In the exemplary reflection encoding system, a sensor includes an element that emits radiation and an element that detects radiation. A target includes dark and light bands, for example. The dark bands tend to absorb a greater proportion of the emitted radiation than do the light bands. The radiation reflected by the bands is detected by the sensor. As the target moves relative to the sensor, the absorption and reflectance of the sensing target portion aligned with the sensor varies. The sensor encodes this variation. A variety of encoding algorithms and processes are consistent with the present invention. For example, a sensor could simply detect each transition between a dark and light band. 
   System Resolution 
   The resolution of a reflection encoding system is determined by several factors. The distance between the emitter/detector and the target, the beam spread of the radiation used, and the native target resolution all play a role in determining a resolution of a system. These three factors do not act separately, rather they interact, and each must be tuned relative to the others. 
   Native target resolution is essentially a function of feature size. The smaller the critical dimension—the dimension parallel to sensor movement—of a target&#39;s features, the greater its native target resolution. For example the target  590  of  FIGS. 8A and 8B  uses stripe pairs as features. The sensing system is configured to move stripes along their narrow dimension across a field of view of the sensor. Thus a critical dimension of a stripe pair in the illustrated configuration is its width along the narrow dimension. 
   However, a position sensing system does not guarantee high resolution simply by using a high native target resolution. A suitable combination of low beam spread radiation and tight emitter-target tolerances is required to achieve a maximal resolution permitted by a given feature size. The beam spread and tolerance specifications are complementary: a decrease in beam spread combined with an appropriate increase in tolerance can maintain a given resolution, and vice versa. 
   For a given feature size, there is a maximum radiation beam spread above which the features are not resolvable via reflection encoding.  FIG. 11B  illustrates the maximum beam spread for a series of light sources (white squares on left hand side) emitting light towards a series of absorptive and reflective bands (right hand side). The detail shown in  FIG. 11C  illustrates a 20-micron wide light source paired with a target having similarly-sized features. In this example, the maximum tolerable spread is 10 microns; other systems allow other spreads. 
   Under set diffusion conditions, the maximum tolerable spread and desired resolution determine a maximum spacing between a radiation source and the target. This spacing, distance d in  FIG. 11C , is proportional to the required resolution, and inversely proportional to the tangent of an angle representing the diffusion of the radiation. For example, given a typical LED diffusion angle of 30 degrees, to achieve 10 micron resolution the distance d should be less than 56.7 microns. Thus, to achieve the native target resolution, a suitable combination of beam spread radiation and spacing should be employed. 
   Native Target Resolution 
   Some embodiments of the present invention employ position sensing systems with beam spread and tolerance optimized to operate at native target resolution. In reflection encoding, a variety of methods, strategies, and devices are available to achieve this goal. 
     FIG. 12A  illustrates a direct imaging approach where a radiation emitter (white rectangle), e.g. an LED, produces radiation which is supplied to the target without additional processing. A portion of the radiation reflecting from the target is detected by a detector (hatched rectangle). In this type of approach, the emitter must produce radiation with a sufficiently low beam spread to resolve the target features. 
   Tolerances 
   One method of achieving native target resolution is closely spacing the emitter/detector and the scanning target. However, tightening tolerances increases the precision required in manufacturing both the target, and the device as a whole. For example, the cross-sectional roundness of a cylindrical target becomes increasingly important as the spacing decreases. For these and other reasons, embodiments of the present invention preferably space the emitter/detector and scanning target at distances achievable within tolerances typical of mass-manufacturing. 
   Active Area—Emitter/Detector Modification 
   Several combinations of features and methods can be employed to lessen the spacing requirements tolerances or decrease problems caused by diffusion of the radiation. In reflection encoding, a portion of the sensing target is excited by radiation and a detector receives a signal from the sensing target. The signal received represents the characteristics of an active area of the sensing target. Preferably, the active area is sized and located to match critical feature dimensions of the sensing target. For example,  FIG. 15  illustrates the active area of a sensing target. 
   The size and location of the active area are determined by characteristics of both the emitter and the detector. In some cases, the radiation is conditioned to limit the portion of the sensing target excited by radiation. In some cases, the field of view of the detector is cropped. 
   Some techniques involve radiation processing measures that permit the use of higher resolution targets at manufacturable spacings than would be possible using more diffusive radiation.  FIG. 12B  illustrates a system in which a lens is used to collimate radiation from a detector. Collimating the radiation permits target-sensor spacing to increase relative to direct imaging while maintaining ability to resolve a set feature size. The maximum spacing and resolvable feature sizes are determined by the spreading of the radiation following collimation. 
   Some techniques involve elements configured to limit the field of view of a sensor to a portion of its native field of view.  FIG. 12C  illustrates a system in which a pinhole is used to prevent ‘bleed over’ from an adjacent region from preventing detection of a transition. In this case, reflected radiation must pass through the centered pinhole placed near to the target surface before reaching the detector. This system can require higher intensity emitters, as relatively little radiation is available through the pinhole. 
   Though certain embodiments of the present invention do employ active area cropping strategies, such as radiation conditioning, the additional devices or features needed to carry out these strategies increases the cost and complexity of the manufactured module. Preferably, embodiments of the present invention employ other means to achieve desired resolutions. 
   Beyond Native Target Resolution 
   At certain thresholds, achieving high system resolution though use of high native target resolution begins to necessitate radiation conditioning or tight spacing. As outlined above, these elements increase the complexity of a module and the precision required in manufacturing. Therefore, for resolutions above these thresholds, embodiments of the present invention preferably employ a lower native target resolution combined with at least one of a variety of strategies for achieving system resolution greater than native target resolution. 
   Active Area—Target Modification 
   The methods of defining an active area referred to above relate to conditioning radiation from an emitter, selecting a detector with an appropriate field of view, or modifying the field of view using an external device. However, alternative methods relate to configuring the sensing target to limit the portion thereof excited by radiation at any one time, and thus cropping the active area. 
   For example, the cross-sectional view of  FIG. 11A  illustrates a configuration in which the feature size is paired with arc of a cylindrical sensing target to limit the field of view of a detector. The field of view of the emitter/detector  3030  subtends a region of the target  3350  that includes a maximum of two transitions. 
   Preferably, the sensing target and detector are configured such that a single feature dominates the field of view. For example, as illustrated in  FIG. 15 , an active area is sized to match the width of a stripe pair. Typically, the feature size of the target is chosen based on the field of view. However, the required resolution can also be a factor in determining feature size. 
   Data Processing 
   Preferably, embodiments of the present invention process data from a sensor to achieve resolutions higher than native target resolution. A variety of processing techniques, methods and elements are employed within various embodiments of the invention, including threshold-based signal conversion and interpolation. 
   Preferably, embodiments of the present invention encode a portion of the sensing target within the active area into an voltage. The voltage varies depending on the character of the portion of the sensing target within the active area at time of encoding. 
   Embodiments of the present invention preferably match the dimensions of the active area to the critical dimensions of the sensing target features in order to produce a smoothly varying signal.  FIG. 15  illustrates a preferred relationship between the active area and sensing target feature dimensions. The active area is sufficiently large along the direction of the critical dimensions so that it will not sequentially encounter regions with the same light/dark characteristics. In the illustrated embodiment, along the critical dimension the active area is larger than one feature&#39;s width and smaller than twice that width. This type of configuration substantially prevents ‘flat’ spots from occurring within the analog signal produced. 
   Over time, as the sensing target moves through the active area, the system forms a signal representing the portions of the sensing region that have passed through the area. As shown in  FIG. 16 , a sensing target, part A, and a varying signal, part B, are correlated along a time axis t. The strength of the signal in part B at a given point in time is determined by the characteristics, e.g. the proportion of light and dark stripe, within the active region at that time. As illustrated, the minima of the signal in part B correspond in time to the central axes of the dark stripes. Similarly, the maxima of the signal in part B correspond in time to the central axes of the light stripes. 
   In some embodiments the signal is a continuous encoding of the voltage, in other embodiments the signal is a series of discrete samples taken at a particular frequency. In either case, the signal preferably contains multiple samples related to each feature of the sensing target as it moves across the sensor&#39;s field of view. 
   The encoding process produces a variable signal representing the movement of the sensing target. The minima and maxima of the signal represent movement of the sensing target at its native target resolution. Preferably, this variable signal is an analog voltage. In some embodiments, interpolation is used to construct higher resolution data between the minima and maxima of the variable signal. Preferably the interpolation error occurs only within a given period of the native target resolution and is reset with each minimum or maximum of the signal. This limits the error introduced by interpolation to a substantially fixed percentage of the native resolution. 
   A processing system receives a variable signal from the sensor and produces corrected movement data at a resolution higher than native target resolution. For example, in some embodiments, the analog voltage signal is supplied to an analog to digital converter (ADC). The analog signal, which was produced at a sampling rate that results in multiple samples per feature, contains sufficient information to support ADC production of digital signal with a resolution greater than native target resolution. In some embodiments, an ADC process using multiple thresholds is used to encode an analog signal to a higher-resolution digital signal. 
   The corrected movement data is then translated into position data which represents the position of a functional group coupled to the sensing target. For example, in some embodiments digital data from the ADC is supplied to a controller where it is analyzed and translated into position data. 
   One method in accordance with the present invention is illustrated in  FIG. 17 . The method seeks to detect a position of a functional group coupled to a sensing target configured to represent movement of the functional group a first resolution. It comprises a step  5010 , of using the sensing target to detect movement of the functional group at the first resolution. The method further comprises a step  5020 , of encoding raw movement data representing the detected movement. In another step  5030 , the method comprises processing the raw movement data into corrected movement data having a second resolution, wherein the second resolution is greater than the first resolution. Further, the method includes a step  5040 , of translating the corrected movement data into position data representing the position of the functional group. 
   Preferably, embodiments include additional calibration of processing circuitry. In the preferred embodiment, an initial calibration is accomplished automatically during power on. For example, in an ADC-based system, self-calibration during power-on preferably determines the input range needed for data. Embodiments that use self-calibration do not require initial calibration during manufacturing or storage of fixed calibration parameters over their lifetime. In addition, the calibration preferably defines the initial position for each functional group. In some embodiments, these initial positions are determined by a hard reference stop discussed elsewhere in greater detail. In some embodiments, the positions are determined via information embedded into the sensing target. In some embodiments, position is referenced by the absence of interaction between the sensor and sensing target. 
   Specifically, referring to  FIG. 14A , as the rear barrel  530 , sensing target  590  and guide sleeve  510  move along the guide pin  601 , the sensing target  590  and the sensor  901  eventually become disengaged. At this point the signal read by the sensor  901  changes, permitting the system to reference the location of the sensing target  590 , the rear barrel  530 , or the rear lens (not shown). In addition, during the same movement, the spring driver  580  contacts the lens group interface surface  314  of the hard stop latch spring  310 , eventually reaching a mechanical hard stop, which can also be used as a reference as described above. 
   Referring now to  FIG. 14B , a similar process can be employed for the front lens position sensor. The front sensing target  290  and the sensor  902  eventually become disengaged during movement of the front lead screw  260 . At this point the signal read by the sensor  902  changes, permitting the system to reference the location of the front sensing target  290 , or the front lens (not shown). In addition, during the same movement, the cam feature  222  of the cam  220  contacts the lens group interface surface  216  of the hard stop latch spring  210 , eventually reaching a mechanical hard stop, which can also be used as a reference as described above. 
   However, some embodiments also include continuous calibration during sensing to handle signals with noisy time-variance. A variety of configurations produce signals with slight instabilities over time. For example,  FIG. 16 , part C illustrates a signal with an average magnitude that ‘wobbles’. A variety of design and manufacturing decisions may result in such signals, for example off center mounting of a cylindrical sensing target. In some embodiments a calibration constant correlated to instabilities is used to counteract them and dynamically correct the processing output. For example, the average magnitude over a trailing time or frequency period. 
   In some embodiments, non-volatile memory elements are included in the control or processing circuitry and used to provide additional manufacturing and calibration data. Preferably, this additional data is used to adjust for component variation and manufacturing tolerances. 
   Some embodiments that employ interpolation use additional hardware and/or firmware (e.g. a clock for timing and for analysis). If the actuator is very non-linear, interpolation can introduce positioning error. Preferably, embodiments of the present invention use ADC techniques. 
   Configurations 
   Embodiments of the present invention include position sensing systems that employ a variety of different configurations of sensors and sensing targets. Some embodiments include cylindrical sensing targets, closed surfaces configured to rotate along with a lead screw or other rotational drive mechanism. Since the functional group is coupled with the lead screw, which has known thread pitch, lead screw rotation is proportional to translation of the functional group along the lead screw axis. In addition, some embodiments include linear sensing targets coupled to a functional group and configured to move therewith. The sensing systems discussed in the examples below are illustrated with cylindrical sensing targets; however, the methods, strategies and equipment described are also contemplated for use with linear targets within some embodiments of the present invention. 
   For example, a system employing a rotational sensing target is illustrated in  FIG. 11A . As shown by the cross sectional view, a position sensing system includes the cylindrical target  3350  positioned a distance d from the emitter/detector  3030 . The field of view of the emitter/detector  3030  subtends a region of the target  3350  that includes a maximum of two transitions. In some embodiments the emitter/detector is a photoreflector. 
   In another example, illustrated in  FIG. 13B , an emitter/detector  4030  comprises a sensor  4034 , and an emitter  4032 . The emitter/detector further includes a mask structure  4030 ′ includes the emitter window  4032 ′ and the two sensor windows  4034 ′ and  4034 ″. In some embodiments the emitter is an LED. 
   The dark bands of the sensing target  4350  absorb radiation emitted from the emitter, while the light bands of the sensing target reflect radiation emitted from the emitter. The sensors detect transitions in absorption and reflectance as the bands move relative to the sensor windows. Preferably, the sensor  4034  separately detects transitions in both sensor windows  4032 ′ and  4034 ″. In some embodiments the emitter/detector  4030  is a photoreflector. 
   In yet another example, illustrated in  FIG. 13A , an two-detector module is employed. The emitter/detector  3030  comprises a first sensor  3034 A, a second sensor  3034 B, and an emitter  3032 . The mask structure  3030 ′ includes the emitter window  3032 ′ and the four sensor windows  3034 A′,  3034 A″,  3034 B′, and  3034 B″. In some embodiments, the emitter/detector  3030  is a photoreflector. In some embodiments the emitter is an LED. 
   Radiation from the emitter  3032  is substantially absorbed by dark bands and substantially reflected by the light bands of the sensing target  3350 . The sensors  3034 A and  3034 B detect transitions in absorption and reflectance as the bands move relative to the sensor windows. Both the first sensor  3034 A and the second sensor  3034 B detect transitions. 
   In some embodiments, a detector encodes a given transition at different points in time. In addition, in some embodiments, a detector includes means for encoding a transition in two data forms that differ by a constant, such as a phase. In some embodiments, e.g.  FIG. 13A , two separate sensors encode transitions out of phase of one another. In other embodiments, a single sensor views transitions at two different points in space, e.g. the two windows  3034 ′ and  3034 ″ of  FIG. 13B . Preferably, in these embodiments a control system combines the out-of-phase data, permitting it to detect a direction of movement as well as its magnitude. 
   In a cylindrical sensing target within the above configurations, each feature preferably covers 60 degrees of the circumference. Thus, in one embodiment, a cylindrical target having a 12 mm circumference includes six 2 mm stripes in an alternating reflective/absorptive pattern. In addition, processing steps as outlined above are preferably employed to increase resolution above that offered natively by this type of target. 
   A position sensing system provides position data for a lens group over its range of motion. In some embodiments of the present invention, a position sensing system tracks the relative position of an optics group to within 70 microns over a range of 10 mm. 
   Operation 
   Preferred systems employ the position sensor data to control an actuator. In some embodiments, the data is used to predict the movement per cycle of the actuator. In some embodiments, the data is used to predict the movement per unit time that the actuator is engaged and powered on. In some embodiments, the data are used on a real-time basis with a correction cycle for increased accuracy. Preferably, the particular implementation used is determined in accordance with the particular actuator used. 
   Some embodiments of the present invention use the position data during zoom and auto-focus operation to accurately position and track optics groups. Preferably, during zoom operation, multiple lens groups are moved and tracked. The actuator control circuitry preferably accurately interprets position data to accomplish tracking and movement. In some embodiments, the control circuitry uses tracking interpretation data that is stored in a table. In some embodiments, the control circuitry uses tracking interpretation data that is stored as a mathematical function. Sometimes, this data is defined in a calibration cycle. Preferably, this calibration cycle takes place during manufacturing. 
   In addition, the actuator control circuitry preferably accomplishes zoom operations within a specified time frame. Preferably, in embodiments that relate to video optics, the zoom operations are accomplished in a manner that does not disturb video recording. In some embodiments, the zoom range and frame rate are used to determine an optimal step size. For example, the total zoom range is divided by the number of frames within the desired seek time to yield the step size. Thus, each step can occur within a frame. Preferably, when zoom operations occur, the steps are synchronized with the frame rate. In addition, the movement of multiple groups during zoom operations is preferably interleaved. Thus, as each group is moved, the remaining groups are stationary. Interleaving reduces driver and instantaneous power requirements. 
   In addition, during auto focus operation, typically a single group is moved. Preferably, a group is moved through a focus range in small increments. Preferably, an accurate position sensor and actuator control circuit is employed to permit s positioning in increments below 20 micrometers. In addition, though a variety of circuitry and hardware can be used to implement the auto-focus algorithm, preferred implementations permit reliable return of the group to the position that shows best focus. 
   As described above, the optical elements of some embodiments are divided into two groups, one group housed in a front barrel, the other group housed in a rear barrel. Typically, the precise motion of these optics groups group within confined spaces is achieved by using the mechanism(s) described above. 
   The form factor of the auto-focus and zoom module of some embodiments is approximately 9×14×22 mm without a prism or approximately 9×14×30 mm including a prism. 
   Embodiments of the present invention permit micro-scale positioning using non-linear motors within easily manufacturable devices. These embodiments include strategies to achieve system resolution above the native resolution of a sensing target, to deal with instabilities in movement data, and to provide repeatable referencing solutions for both initial and continuous calibration schemes. 
   A wide variety of mass manufactured devices require robust and precise positioning of functional elements. These include medical devices, optical devices, and micromechanical devices. With the present invention, such mass manufactured devices can use non-linear motors where linear motors were previously required. 
   While the invention has been described with reference to numerous specific details, one of ordinary skill in the art will recognize that the invention can be embodied in other specific forms without departing from the spirit of the invention. Thus, one of ordinary skill in the art will understand that the invention is not to be limited by the foregoing illustrative details, but rather is to be defined by the appended claims.