Abstract:
Systems and methods for articulating an elongate articulatable body which is adapted to be delivered within a body cavity. Particularly, systems and methods for enhancing an articulating force on the elongate body without increasing an actuation force applied by an actuator.

Description:
INCORPORATION BY REFERENCE 
       [0001]    All publications and patent applications mentioned in this specification are incorporated herein, in their entirety, by reference to the same extent as if each individual publication or patent application was specifically and individually indicated to be incorporated by reference. 
       BACKGROUND OF THE INVENTION 
       [0002]    The forms of robots vary widely, but all robots share the features of a mechanical, movable structure under some form of control. The mechanical structure or kinematic chain (analogous to the human skeleton) of a robot is formed from several links (analogous to human bones), actuators (analogous to human muscle) and joints permitting one or more degrees of freedom of motion of the links. A continuum or multi-segment robot is a continuously curving device, like an elephant trunk for example. An example of a continuum or multi-segment robot is a snake-like endoscopic device, like that under investigation by NeoGuide Systems, Inc., and described in U.S. Pat. Nos. 6,468,203; 6,610,007; 6,800,056; 6,974,411; 6,984,203; 6,837,846; and 6,858,005. Another example of a snake-like robotic device is shown and described in U.S. Patent Publication US2005/0059960 to Simaan, et al. 
         [0003]    Snake-like robots transfer forces from an actuator to particular sections or segments of the snake-like robot to effect articulation of that section or segment. The amount of articulating force that is ultimately applied to the section or segment can be less than the actuation force applied by an actuator in the robotic system. This can be due to, for example, frictional losses between system components. In robotic systems with many moveable parts that may be in very close proximity to one another, those losses can be magnified. Thus, a system is needed that can enhance the amount of force applied to articulate a segment or section of a robotic system (i.e., an articulating force) without increasing the amount of force applied by an actuator in the system (i.e., an actuation force). 
       SUMMARY OF THE INVENTION 
       [0004]    The present invention relates generally to systems and methods for articulating an elongate articulatable body which is adapted to be delivered within a body cavity. Particularly, the invention relates to systems and methods for enhancing an articulating force on the elongate body without increasing an actuation force that is applied by an actuator. 
         [0005]    One aspect of the invention is a system for modifying (e.g., enhancing) an articulating force on an articulatable elongate body deliverable within a body cavity. The system includes an elongate body comprising at least one articulatable segment, wherein the at least one articulatable segment comprises a plurality of links and at least one force modifying element. The system also includes a coil pipe within the elongate body which has a proximal end terminated outside of the elongate body and a distal end terminated at a proximal portion of the segment. The system also includes a tendon disposed at least partially within the coil pipe, the tendon having a proximal end and a distal end, where the proximal end is coupled to an actuator outside of the elongate body, the distal end is coupled to a link proximal to the force modifying element, and the tendon interacts with the force modifying element. 
         [0006]    In some embodiments the force modifying element is disposed at a distal portion of the segment and the distal end of the tendon is coupled to a proximal portion of the segment. 
         [0007]    In some embodiments the coil pipe and the distal end of the tendon are coupled to the same link. 
         [0008]    In some embodiments the at least one segment comprises a plurality of force modifying elements, and wherein the system comprises a plurality of tendons each coupled at their proximal ends to the actuator. The plurality of tendons can be at least three tendons and the plurality of force modifying elements can be at least three force modifying elements. In some embodiments two of the at least three force modifying elements are coupled to a first link, and at least the third force enhancing element is coupled to a second link adjacent the first link. 
         [0009]    The force modifying element can comprise a curved surface and the tendon and force modifying element can slidingly interact. The curved surface can be a fixed curve surface such that the tendon loops around and slides over the curved surface when actuated, or alternatively the curved surface can be adapted to move, such as, for example and without limitation, a pulley. 
         [0010]    In some embodiments, the plurality of links are adapted such that when an actuation force is applied to the segment at least one link does not become locked in position relative to an adjacent link. In these embodiments the segment can therefore continue to articulate, or bend, as additional actuation, or tensioning, forces are applied to the segment. Although articulation of the segment may cause a link to come into contact with an adjacent link or to be temporarily fixed in place relative to an adjacent link, the links are adapted to be able to continue to move relative to one another (i.e., the segment can continue to be articulated) as additional tensioning forces are applied to articulate the segment. 
         [0011]    One aspect of the invention is a method of modifying an articulating force on an elongate body deliverable within a body cavity. The method includes inserting an elongate articulatable instrument into a body cavity, extending a tendon along the length of the elongate articulatable instrument, wherein the elongate articulatable instrument comprises a force modifying element in a distal region of the elongate articulatable instrument, and wherein the tendon interacts with the force enhancing element. The method also includes articulating the elongate articulatable instrument by applying a tensioning force on the tendon with an actuator coupled to the proximal end of the tendon, thereby generating an articulation force in the distal region of the elongate articulatable instrument that is larger than the tensioning force. In one embodiment of this method, the elongate articulatable instrument comprises multiple segments, and at least one of the segments has the force modifying element that engages with the tendon. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0012]    The novel features of the invention are set forth with particularity in the claims that follow. A better understanding of the features and advantages of the present invention will be obtained by reference to the detailed description below that sets forth illustrative embodiments, in which the principles of the invention are utilized, and the accompanying drawings. 
           [0013]    In the drawings: 
           [0014]      FIG. 1  illustrates an exemplary system in accordance with an embodiment of the present invention. 
           [0015]      FIG. 2  illustrates an exemplary articulatable segment including a plurality of links. 
           [0016]      FIGS. 3A-3C  illustrate a schematic diagram of an articulatable segment in accordance with the present invention. 
           [0017]      FIGS. 4A-4E  illustrate embodiments of vertebrae-type control rings in accordance with embodiments of the present invention. 
           [0018]      FIG. 4F  illustrates an exemplary articulatable segment in accordance with the present invention. 
           [0019]      FIG. 5  illustrates a schematic of an exemplary system showing relative positions of actuators, coil pipes, tendons, and an articulatable segment. 
           [0020]      FIGS. 6A-6B  illustrate front and side views on an exemplary force modifying element. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0021]      FIG. 1  illustrates an exemplary system into which the present invention can be incorporated. Endoscope  10  has elongate body  12  with steerable distal portion  14 , automatically controlled proximal portion  16 , and flexible and passively manipulated proximal portion  18 . The skilled artisan will appreciate that automatically controlled proximal portion  16  may also be flexible and passively manipulated, although it is preferred to provide automatically controlled proximal portion  16 . The skilled artisan will also appreciate that elongate body  12  can have only steerable distal portion  14  and automatically controlled portion  16 . Fiber optic imaging bundle  20  (or other imaging system) and illumination fiber(s)  22  may extend through elongate body  12  to steerable distal portion  14 , or video camera  24  (e.g., CCD or CMOS camera) may be positioned at the distal end of steerable distal portion  14 . Generally, a user views live or delayed video feed from video camera  24  via a video cable (e.g., wire or optical fiber, not shown) or through wireless transmission of the video signal. Endoscope  10  will typically also include one or more access lumens, working channels, light channels, air and water channels, vacuum channels, and a host of other well known complements useful for both medical and industrial endoscopy. These channels and other amenities are shown generically as  26 , because such channels and amenities are well known in the art. 
         [0022]    Preferably, system  10  comprises a plurality of articulatable segments  28  (which includes steerable distal portion  14 ), which are controlled via computer and/or electronic controller  30 . Such an exemplary automatically controlled endoscope is described in further detail in commonly assigned U.S. patent application Ser. Nos. 10/229,577 (now U.S. Pat. No. 6,858,005) and 11/750,988, both previously incorporated herein by reference. Preferably, the distal end of a tendon (more thoroughly described below) is mechanically connected to each articulatable segment  28 , while the proximal end of the tendon is mechanically connected to an actuator which is used to articulate segments  28  and/or steerable distal portion  14 . This is more fully described below and in U.S. patent application Ser. Nos. 10/229,577 (now U.S. Pat. No. 6,858,005) and 11/750,988, both incorporated by reference herein. 
         [0023]    The actuators driving the tendons may include a variety of different types of mechanisms capable of applying a force to a tendon, e.g., electromechanical motors, pneumatic and hydraulic cylinders, pneumatic and hydraulic motors, solenoids, shape memory alloy wires, electronic rotary actuators or other devices or methods as known in the art. If shape memory alloy wires are used, they are preferably configured into several wire bundles attached at a proximal end of each of the tendons within the controller. Segment articulation may be accomplished by applying energy, e.g., electrical current, electrical voltage, heat, etc., to each of the bundles to actuate a linear motion in the wire bundles which in turn actuate the tendon movement. The linear translation of the actuators within the controller may be configured to move over a relatively short distance to accomplish effective articulation depending upon the desired degree of segment movement and articulation. In addition, the skilled artisan will also appreciate that knobs attached to rack and pinion gearing can be used to actuate the tendons attached to steerable distal portion  14 . Axial motion transducer  32  (also called a depth referencing device or datum) may be provided for measuring the axial motion, i.e., the depth change, of elongate body  12  as it is advanced and withdrawn. As elongate body  12  of endoscope  10  slides through axial motion transducer  32 , it indicates the axial position of the elongate body  12  with respect to a fixed point of reference. Axial motion transducer  32  is more fully described in U.S. patent application Ser. No. 10/229,577, which is incorporated herein by reference. 
         [0024]    In the embodiment depicted in  FIG. 1 , handle  34  is connected to illumination source  36  by illumination cable  38  that is connected to or continuous with illumination fibers  22 . Handle  34  is connected to electronic controller  30  by way of controller cable  40 . Steering controller  42  (e.g., a joy stick) is connected to electronic controller  30  by way of second cable  44  or directly to handle  34 . Electronic controller  30  controls the movement of the segmented automatically controlled proximal portion  16 , which is described more thoroughly below and in U.S. patent application Ser. No. 11/750,988, previously incorporated herein by reference. 
         [0025]      FIG. 2  illustrates a portion of an exemplary articulatable segment  28  preferably constructed from a plurality of links  46 . It will be appreciated that a segment may be comprised of a single link or a plurality of links. Five links  46  are shown for the sake of clarity, although the skilled artisan will recognize that any number of links may be used, the ultimate number being primarily defined by the purpose for which the articulatable segment  28  or steerable distal portion  14  will be used. Each link  46  connects one joint  47  to an adjacent joint  47 . Each link  46 , in this embodiment, can move (at the joints) with one degree of freedom relative to an adjacent link. 
         [0026]    Referring now to  FIG. 3A-C , simplified schematic diagrams of segments  28  according to the invention are provided for discussion purposes and to explain a preferred system and method for articulating segments  28 . The skilled artisan will recognize that the system and method for articulation is the same for both steerable distal portion  14  and segments  28  of automatically controlled proximal portion  16 . Therefore, the system and method for articulation will be described referring only to segments  28 , with the recognition that the description also applies equally to steerable distal portion  14 . It is noted that details relating to links  46 , joints  47  and the interconnections of the links have been eliminated from this figure for the sake of clarity. 
         [0027]      FIG. 3A  shows a three-dimensional view of segment  28  in its substantially straight configuration. The most distal link  46 A and most proximal link  46 B are depicted as circles. Cables extend down the length of elongate body  12  (not shown in  FIG. 3A-C ) and comprise coil pipes  48  and tendons  50 . The proximal end of the tendon  50  is coupled to an actuator (not shown) and the distal end is coupled to the most proximal link  46 B. Coil pipes  48  house tendons  50  (i.e. a Bowden-type cable) along the length of elongate body  12  (not shown in  FIG. 3A-C ) and coil pipes  48  are fixed at (or near) the proximal end of segment  28 . Tendons  50  extend out of coil pipes  48  at or near the proximal end of segment  28  along the length of segment  28 , interact with force modifying elements located at or near the distal end of segment  28  (not shown but described below), and the distal ends of tendons are mechanically attached to segment  28  at a point proximal to the distal end of segment  28 , and preferably at or near the proximal end of segment  28 . 
         [0028]    In  FIGS. 3A-C , four tendons  50  are depicted to articulate segment  28 , but more or fewer may be used. The coil pipe/tendon combination, or Bowden cables, can be used to apply force to articulate segments  28  and can be actuated remotely to deliver forces as desired to articulate segments  28 . In this manner, actuation of one or more tendons  50  causes segment  28  to articulate. In the embodiment depicted, links  46  have joints  47  offset by 90 degrees (see  FIGS. 2 and 4 ). Thus, an articulatable segment is able to move in many directions, limited only by the number and position of joints. As will be appreciated by the skilled artisan, tendons  50  can be made from a variety of materials, which is primarily dictated by the purpose for which the system will be used. Without limitation, tendons  50  can be made from stainless steel, titanium, nitinol, ultra high molecular weight polyethylene, the latter of which is preferred, or any other suitable material known to the skilled artisan. 
         [0029]    Four tendons can reliably articulate segment  28  in many directions. The distal ends of tendons  50  are shown attached to the most proximal link near the periphery spaced equally apart. They are shown positioned at 12, 3, 6, and 9 o&#39;clock. If more or fewer are used, the tendons can remain equally spaced around the periphery of the segment. For example, if three tendons are used, they can be positioned at the 12, 4, and 8 o&#39;clock positions. Alternatively, if only two are used, they can be positioned at the 12 and 6 o&#39;clock positions. 
         [0030]      FIGS. 3B-C  show segment  28  articulated by independently pulling or slacking at least one of the four tendons  50 . For example, referring to  FIG. 3B , pulling on tendon  50  at the 12 o&#39;clock position and easing tension on tendon  50  at the 6 o&#39;clock position causes steerable distal portion  28  to articulate in the positive y-direction with respect to the z-y-x reference frame  52 . It is noted that the most distal z-y-x coordinate frame  52   distal  rotates with respect to the z-y-x reference frame  52  and that  13  is the degree of overall articulation of segment  28 . In this situation β is only along the positive y-axis, up, because only tendon  50  at the 12 o&#39;clock position was pulled while easing tension or giving slack to tendon  50  at 6 o&#39;clock. The tendons  50  at 3 and 9 o&#39;clock were left substantially static in this example, and, thus, had approximately no or little affect on articulation of segment  28 . The reverse situation (not depicted), pulling on tendon  50  at the 6 o&#39;clock position and slacking or easing the tension on tendon  50  at the 12 o&#39;clock position results in articulation of segment  28  in the negative y-direction, or down. Referring to  FIG. 3C  the same logic applies to articulate segment  28  in the positive x-direction (right) or a negative x-direction (left, not shown). Segment  28  can be articulated in any direction by applying varying tensions to the tendons off axis, e.g., applying tension to the tendons at 12 o&#39;clock and 3 o&#39;clock results in an articulation up and to the left. 
         [0031]    Referring now to  FIG. 4 , links  46  may be control rings to provide the structure needed to construct segments  28 .  FIG. 4A  shows a first variation of a vertebra-type control ring  54 .  FIG. 4B  shows an end view of a single vertebra-type control ring  54  of this first variation. In this embodiment the vertebra-type control ring  54  defines a central aperture  56  that collectively form an internal lumen of the segment, which internal lumen is used to house the various access lumens, working channels, light channels, air and water channels, vacuum channels, and any other known complements useful for both medical and industrial endoscopy. Vertebrae-type control rings  54  have two pairs of joints or hinges  58 A and  58 B; the first pair  58 A projecting perpendicularly from a first face of the vertebra and a second pair  58 B, located 90 degrees around the circumference from the first pair, projecting perpendicularly away from the face of the vertebra on a second face of the vertebra opposite to the first face. Hinges  58 A and  58 B are tab-shaped, however other shapes may also be used. 
         [0032]    Referring briefly to  FIG. 5 , tension applied to a tendon  50  by actuator  60  is isolated to a particular segment  28  by use of coil pipes  48  which house tendons  50 , as previously described. While not shown in  FIG. 5  for sake of clarity, it is understood that the tendons extend from coil pipes  48  to the distal end of the segment  28  (at which point the tendons engage a force modifying element, described in more detail below), then extend proximally to a location proximal to the distal end where they are attached. Referring to  FIG. 4B , control ring  54  is shown with four holes  61  through the edge of control ring  54  that may act as, e.g., attachment sites for tendon  50 , as a throughway for tendon  50  in other vertebrae-type control rings  54  (links) of that particular segment  28 , and/or attachment sites for coil pipes  48  when vertebra-type control ring  54  is the most proximal link in segment  28 . The skilled artisan will appreciate that the number of tendons  50  used to articulate each segment  28  determines the number of holes  61  provided for passage of tendons  50 . When hole  61  is used as an attachment site for a coil pipe and the distal end of the tendon  50  is also attached to control ring  54  (after engaging with force modifying element), the distal end of tendon  50  can simply be attached to the most proximal link with almost any type of attachment mechanism, e.g., adhesive, tying, or there may be an additional hole or rod close to hole  61  to which the tendon can be tied. 
         [0033]    The outer edge of vertebra-type control ring  54  in the variation depicted in  FIGS. 4A-B  may be scalloped to provide bypass spaces  62  for tendons  50  and coil pipes  48  that control more distal segments  28  that bypass vertebra-type control ring  54  and the present segment  28 . These coil pipe bypass spaces  62 , in this variation of the vertebrae-type control ring  54 , preferably conform to the outer diameter of coil pipes  48 . The number of coil pipe bypass spaces  62  vary depending on the number of tendons, and, therefore, the number of coil pipes needed to articulate all the segments  28  and steerable distal portion  14 . It will be appreciated that not all vertebrae-type control rings  54  of a particular segment  28  need to have coil pipe bypass spaces  62 . As described further below, intermediate vertebra-type control rings  54 ′ ( FIG. 4C ) between segments need not have coil pipe bypass spaces  62 , rather the coil pipes can simply pass through the lumen formed by central aperture  56 ′. In this alternative, the lumen formed by central aperture  56 ′ house the various access lumens, working channels, light channels, air and water channels, vacuum channels, as described above, as well as coil pipe/tendon combinations that do not control that particular segment. 
         [0034]      FIGS. 4D-E  show an exemplary control ring  64  in sectional and perspective proximal views (i.e., looking in the distal direction) and a segment can comprise one or more of these links. 
         [0035]    Control ring  64  comprises body  66 , which is hingedly coupled to inner cross bar member  57  at joints  59 . Joints  59  are the same joints at which a second link (although not shown) adjacent and proximal to link  64  is hingedly coupled to link  64 . Inner cross bar member  57  is therefore hingedly coupled to two links at joints  59 , and can be thought of as being axially disposed “between” the two links. Cross bar member  57  can also be fixed relative to one or both of the adjacent links. The exemplary inner cross bar member  57  comprises force modifying elements  104  which each interact with a tendon  50  (not shown in  FIG. 4D and 4E ) to increase the amount of force applied to the articulatable segment when an actuation/tensioning force is applied to the tendon (e.g., through an actuator). 
         [0036]      FIG. 4F  shows a side view of an articulatable segment  28 , which includes the link shown in  FIG. 4D and 4E . Inner cross bar members  57  are shown hingedly coupled to and “between” links D 1  and D 2 , P 3  and P 2 , and P 2  and P 1 . Coil pipes  48  are shown attached to holes  63  (shown in  FIG. 4D and 4E ) of the inner cross bar member  57  disposed between links P 2  and P 3 . Tendons  50  exit the coil pipes and extend distally from the inner cross bar member  57  and pass through peripheral holes in intermediate control ring  110 . Intermediate control ring  110  helps maintain the position of the tendons towards the periphery and away from the inner lumens of the segment. The tendons then extend further distally until they engage force modifying elements  104 , which are shown coupled to the inner bar cross member  57  that is disposed between links D 1  and D 2 . It should be understood that the force modifying elements  104  that are coupled to the most distal inner cross bar member shown, while not disposed at the literal distal end of the segment, are considered to be at the “distal end” and/or “near the distal end” as these phrases may be used herein. Tendons  50  engage force modifying elements  104  and extend proximally from the force modifying elements  104  as the distal ends of tendon  50  are attached to tendon attachment points  112 . 
         [0037]    In one embodiment the tendon attachment point comprises a hole and tendons  50  are tied-off in the hole; in other more preferred embodiments the attachment point is a bar to which the tendon is tied or otherwise attached. The tendons can, however, be attached to tendon attachment points  112  by any attachment mechanism that will suit the purpose, such as an adhesive. 
         [0038]    Holes  67  in the cross-bar are generally used to guide tendons axially along the segment, while holes  63  are generally used as the attachment locations for the coil pipes. Holes  63  are shown (In  FIG. 4D and 4E ) to have a slightly smaller diameter than holes  67 , although the size differentiation could be reversed or the sizes could be the same. 
         [0039]    While not shown, it is understood that the segment  28  shown in  FIG. 4F  comprises a third and fourth coil pipe, which are offset by 90 degrees from the two coil pipes shown. These two additional coil pipes are attached to the holes  63  (not shown) of the inner cross bar member  57  between links P 1  and P 2 . In the figure, one of the additional coil pipes is essentially “behind” joint  47  that hingedly couples P 1  and P 2  together, while the fourth coil pipe is offset 180 degrees from that coil pipe. It is, therefore, understood that two of the coil pipes (which are shown) are attached to the inner cross bar member between the second and third most proximal links (P 2  and P 3 ), while two of the coil pipes (those not shown) are attached to an inner cross bar member between the most proximal and second most proximal links (P 1  and P 2 ). 
         [0040]    Similarly, the four force modifying elements (two of which are shown and two of which are not) assume similar relative positions. The tendons which extend from the coil pipes which are attached to the P 2 /P 3  cross bar member engage and interact with the force modifying elements coupled to the cross bar member between the most distal and second most distal links (D 1  and D 2 ). The third and fourth tendons (not shown) which extend from the coil pipe which is attached to the P 1 /P 2  inner bar cross member engage and interact with the force modifying elements (not shown) which are coupled to the cross bar member between the second and third most distal links (D 2  and D 3 ). 
         [0041]    Therefore, in the embodiment shown in  FIG. 4F , all four of the coil pipes do not attach to the same link, nor are all four force modifying elements coupled to the same link. The second pair (not shown) is located across from each other and at 90 degrees to the two coil pipes which are shown. 
         [0042]    The position of the force modifying elements relative to the joints that hinge the links together can cause the segment to more efficiently articulate. As the tendon  50  shown to the left in  FIG. 4F  is actuated, the segment can more efficiently be articulated because as forces are applied along the path of the tendon (in response to the actuation force), the segment articulates more efficiently at joint  47 , as D 2  bends towards the left of the page relative to D 3 , because the force modifying element enhances the force applied across the segment. Joint  47  that connects D 2  and D 3  is offset 90 degrees from the force modifying element. 
         [0043]    The skilled artisan will appreciate that all the coil pipe-tendon-force modifying combinations may be located on a single cross-bar or on a single link, rather than adjacent links or adjacent cross-bars, as in the depicted embodiment. Additionally, the skilled artisan will recognize that use of four combinations is a preferred embodiment, and that more or fewer may be used to achieve the desired purpose. 
         [0044]    It is understood that the cross-bar members of the segment can be considered to be a part of either of the two links to which it is hingedly coupled, or a separate element altogether. For example, when referring to force modifying element  104  disposed on cross bar member  57 , it may be understood that either of the adjacent links comprises the force modifying element. 
         [0045]    In preferred embodiments the distal end of the tendon is attached to the link to which the coil tube that houses that tendon is terminated. For example, as shown in  FIG. 4F , tendons  50  are shown extending from the cross bar member  57  of the P 2 /P 3  links, and tendons  50  are attached to tendon attachment points  112  of the same cross bar member  57 . This will likely create the greatest amount of articulating force along the segment when the tendon is actuated. It should be appreciated, however, that the distal end of the tendon need not attach to the same link or the location to which the coil tube which houses that tendon is terminated. After engaging the force modifying element, the tendon can be coupled to any of the links proximal to the force modifying element, and preferably to the link of the coil tube termination. However, it should be noted that attachment of the tendon to links distal of the link where the coil tube terminates may change or alter the amount or distribution of force along the segment and concomitantly reduce the effectiveness of the force modifying element. The coil pipe does not need to be attached to the most proximal link (or the second most proximal link) in the segment. While the forces and distribution of forces generated along the segment may be altered along a segment by such an arrangement, it is not intended to be a limitation. 
         [0046]    Similarly, the force modifying element(s) does not need to be coupled to either of the two most distal links. The advantage arises from attaching the distal end of tendon  50  to a location proximal to the force modifying element. 
         [0047]    In the embodiment in  FIG. 4F , the two most proximal links P 1  and P 2  of segment  28  serve as the two most distal links for a segment disposed proximally and adjacently to the segment shown in  FIG. 4F  (not shown). Force modifying elements  104  coupled to the cross bar member  57  of the P 2 /P 3  link will engage and interact with tendons (not shown) that are used to articulate the adjacent proximal segment. The force modifying elements are coupled to the tendon attachment points in the preferred embodiment, although this is not intended as a limitation. The force modifying element engages and interacts with a tendon used to articulate a given segment, but the tendon attachment point coupled to that force modifying element is coupled to the distal end of a different tendon used to articulate an adjacent distal segment. Similarly, links D 1  and D 2  shown in  FIG. 4F  can serve as the two most proximal links of an adjacent distal segment (unless, of course, segment  28  in  FIG. 4F  is the distal most steering segment  14 ). 
         [0048]    Again, while cross bar members  57  have been described as hingedly coupled to the links, they can be rigidly attached thereto, or they, or their components, can be integral with either one or both of the links. For example, the tendon attachment point and/or the force modifying element can be integral with a body  66  of link  64 . 
         [0049]    The force modifying elements  104  as shown in  FIGS. 4D-4F  are shown comprising curved surfaces with which the tendons  50  engage and interact. As shown, the tendons pass over the force modifying element, engaging with their curved surfaces.  FIGS. 6A and 6B  show a more detailed front and side views of the force modifying elements  104  shown in  FIGS. 4D-4F , which include curved surface  120  and pin  122  (as shown, the force modifying element is also coupled to and integral with tendon attachment point  112  described above).  FIG. 6B  also shows a second tendon  50  attached to tendon attachment point  112  which would be used to articulate the adjacent distal segment. 
         [0050]    Tendon  50  as shown engages and can slidingly interact with force modifying element  104  such that when the tendon is actuated (such as with a proximally-directed tensioning force) tendon  50  slides over curved surface  120  (in the direction as indicated by the arrows in  FIG. 5B ) as the segment articulates as described herein. In this embodiment the curved surface does not rotate, and the frictional forces between the sliding tendon and the curved surface  120  are minimized as much as possible. This will ensure that the largest articulating force possible is applied to the segment (to articulate the segment), as well as to minimize wear on the tendon. In this preferred embodiment, the tendon comprises polyethylene, which should smoothly slide over curved surface  120 . It will be appreciated that curved surface  120  and pin  122  can have the configuration of a pulley, but it is not intended to be limited to a pulley arrangement. 
         [0051]    The force modifying element shown comprises curved surface  120 . Curved surface  120  assumes a “saddle-like” configuration, with raised edges  124  which can reduce friction between the tendon and the force modifying element body  126 . When the force modifying element comprises a fixed surface which does not rotate, the surface need not be limited to a curved, cylindrically-shaped surface as described. It can assume a variety of configurations which allow the tendon to engage and interact with the force modifying element. In addition, surface  120  of the force modifying element can be integral with the link body. For example, the force modifying element can simply comprise two holes in a link with a smooth surface therebetween, wherein the holes allow for the tendon to pass through and over the curved surface. 
         [0052]    In an alternative embodiment, the force modifying element may be a curved pulley surface that rotates about a pin or axel. The tendon will apply a force to the curved surface and also to the pin  122  when the tendon is actuated. When working with a system with small components, the size and materials of the force modifying element can be important to prevent deformation of the materials when relatively large forces are applied to them. For example, the axel diameter “AD”, relative to the pulley diameter “PD”, as well as the materials for each, are important in order to prevent catastrophic degradation of either the pulley or the axel as a result of the loads placed on each. 
         [0053]    In a preferred embodiment, PD is 0.15 inches and AD is 0.04 inches, and the pin is comprised of a stainless type of alloy (preferably 416 family) and the working surface is comprised of a polymer such as polyetheretherketone (PEEK). 
         [0054]    While the force modifying element has been described comprising a fixed smooth surface that slidingly interacts with a tendon, the force modifying element can be a variety of structures that create an increased amount of force applied to the articulatable segment to cause the segment to bend relative to one another. For example, the force modifying element can comprise a pulley, an axially moveable pulley, a plurality of such pulleys, a fixed ferrule, or other similar devices. 
         [0055]    Referring again to  FIG. 5 , coil pipes  48  are fixed at their proximal and distal ends between actuator  60  and the proximal end of segment  28 . When tendons  50  are placed under tension by actuation, the force is transferred across the length of segment  28 ; coil pipes  48  provide the opposite force at the proximal end of the segment being articulated in order to cause the articulation. This force is, primarily, a compression force or axial loading transferred along the length of the coil pipe. The force modifying element provides a mechanical advantage which results in a larger articulating force than would have existed but for the force modifying element. Theoretically, if 1 unit of force is imparted to the tendon by the actuator, 2 units of articulating force will be delivered. There will be some frictional losses, and therefore the ratio will not likely be as high as 2:1. The articulating force will, however, be larger than without the force modifying element. And even though the system is adapted to generate a theoretical 2:1 ratio force reduction, the system could obviously be adapted to have theoretical ratios different than 2:1, depending on the number and type of force modifying elements in each of the segments. For example, a plurality of pulleys could be used to generate a 4:1 mechanical advantage. 
         [0056]    In some embodiments, the plurality of links are adapted such that when an actuation or tensioning force is applied to the segment the links do not become locked in position relative to an adjacent link (i.e., such that the links can not move relative to one another). In these embodiments the segment can therefore continue to articulate, or bend, as additional actuation, or tensioning, forces are applied to the segment. Although articulation of the segment may cause a link to come into contact with an adjacent link or to be temporarily fixed in place relative to an adjacent link, the links are adapted to be able to continue to move relative to one another (i.e., the segment can continue to be articulated) as additional tensioning forces are applied to articulate the segment. For example,  FIG. 5  shows some of the links in segment  28  in contact with an adjacent link. Each link is not, however, in a locked position relative to an adjacent link. A link may continue to move relative to an adjacent link if a tensioning force is applied to the segment by one of the other tendons. Therefore, as additional tensioning forces are applied to the segment, the segment can continue to articulate. 
         [0057]    A preferred embodiment of the present invention utilizes one actuator per tendon, and utilizes four tendons per segment, as described above. Details relating to actuator  60  and connecting actuator  60  to tendons  50  are described in U.S. patent application Ser. No. 10/988,212, incorporated herein by reference. 
         [0058]    While the system has been described as an endoscope, it should be understood that the invention can be used in a wide variety of surgical tools and instruments used in a wide variety of treatments and procedures. Such devices may be used for a variety of different diagnostic and interventional procedures, including colonoscopy, bronchoscopy, thoracoscopy, laparoscopy, video endoscopy, and natural orifice transluminal (gastric) endoscopic surgery, etc. 
         [0059]    The foregoing description, for purposes of explanation, used some specific nomenclature to provide a thorough understanding of the invention. Nevertheless, the foregoing descriptions of the preferred embodiments of the present invention are presented for purposes of illustration and description and are not intended to be exhaustive or to limit the invention to the precise forms disclosed; obvious modification and variation are possible in view of the above teachings.