Abstract:
The present invention relates, generally, to the reduction or elimination of permanent and catastrophic herniations in Bowden cables or coil pipes in articulating devices or snake-like robots. More particularly, the present invention relates managing the coil pipes in a spiral pattern along the articulating device or snake-like robot to reduce or eliminate the necessity of the Bowden cables or coil pipes to slide along the length of the articulating device or snake-like robot. Reduction or elimination of the necessity for the Bowden cables or coil pipes to slide reduces or eliminates catastrophic herniations in articulating devices or snake-like robots undergoing one or more articulations.

Description:
[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. 
       FIELD OF THE INVENTION 
       [0002]    The present invention relates, generally, to management of Bowden-type cables in articulating instruments or snake-like robots. More particularly, the present invention relates to managing Bowden-type cables to reduce or eliminate catastrophic permanent lateral plastic deformation (also referred to herein as kinking or herniation) of these cables in articulating instruments or snake-like robots. 
       BACKGROUND OF THE INVENTION 
       [0003]    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. 
         [0004]    Snake-like robots often use Bowden cables to transfer forces from an actuator to particular sections or segments of the snake-like robot to effect articulation of that section or segment. Multiple, simultaneous articulations of the snake-like robot require the Bowden cables to go through multiple tortuous paths. One challenge faced by the practitioner is that Bowden cables can herniate under overloading conditions and axial loads placed upon them as a result of articulation. Various embodiments of the present invention address this issue. 
       SUMMARY OF THE INVENTION 
       [0005]    An embodiment of the present invention is a system for managing the transmission of force to articulate an elongate device or snake-like robot. The system, of this embodiment, has an elongate body comprising a plurality of articulatable segments. The system includes a plurality of coil pipes, where each coil pipe is fixed at its proximal end relative to an actuator, at its distal end relative to a proximal portion of one of the plurality of articulatable segments, and where the coil pipes extend along each segment in a spiral pattern. A plurality of tensioning members is provided, where the tensioning members are housed in the plurality of coil pipes. The proximal end of each tensioning member is coupled to the actuator, and the distal end extends out the distal end of the coil pipe and is coupled to the articulatable segment to which the distal end of the coil pipe is fixed. The coil pipe/tensioning member combination works like a Bowden cable. The tensioning of one or more of the tensioning members causes articulation of the articulatable segment. In an alternative embodiment of the present invention, the articulatable segments are constructed from at least two links and preferably at least four links jointed together. Preferably, the links are control rings, such as and without limitation vertebrae, and the joints are hinges between the vertebrae. In an alternative embodiment the spiral pattern comprises an approximate integral number of approximately full turns along each of the plurality of articulatable segments, and preferably approximately one full turn. 
         [0006]    In an alternative system for managing the transmission of force in an articulating device, the system comprises an elongate body have a plurality of articulatable segments. Bowden cables are coupled at a proximal end to an actuator and at a distal end to a proximal portion of one of the articulatable segments. Actuation of one or more of the Bowden cables causes the articulation of one or more of the segments to which the Bowden cables are coupled. The Bowden cables extend along each segment in a spiral pattern. 
         [0007]    In another embodiment coil pipes are constructed from approximately round wire, D-shaped wire or are centerless ground. A D-shaped coil pipe that is less susceptible to herniation or axial overloading, in accordance with an embodiment of the present invention, can comprise D-shaped wire coiled, around a mandrel, for example, into a pipe shape. The wire used to make this embodiment of coil pipe has a cross-section having two approximately parallel approximately flat sides, a convex side and a concave side approximately parallel to said convex side. Preferably, the concave side of the wire of a first coil approximately nests with the convex side of the wire in a second adjacent coil, and the approximately parallel flat sides form an interior and an exterior of the coil pipe. The convex and concave sides can have an approximately curved shape, such as and without limitation a portion of a circle. Alternatively, the convex and concave sides can have an angular shape, such as and without limitation a V-shape. Alternatively, the wire can have a square or rectangular cross-section. A coil pipe can also comprise approximately circular cross-section wire coiled, around a mandrel for example, into a pipe shape. In a further embodiment of the present invention the pipe shape is ground or otherwise has material removed to form approximately parallel exterior flat sides, thereby forming a centerless ground coil pipe. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0008]    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. 
           [0009]    In the drawings: 
           [0010]      FIG. 1  depicts an endoscope in accordance with an embodiment of the present invention; 
           [0011]      FIG. 2  depicts an embodiment of a steerable distal portion or a controllable segment of an endoscope in accordance with the present invention; 
           [0012]      FIG. 3  depicts a schematic diagram of either a steerable distal portion or a controllable segment of an endoscope in accordance with the present invention; 
           [0013]      FIG. 4  depicts embodiments of vertebrae-type control rings in accordance with an embodiment of the present invention; 
           [0014]      FIG. 5  depicts a schematic of how to arrange coil pipes and tendons relative to actuators and an articulatable segment or tip; 
           [0015]      FIG. 6  provides a graphic for explaining static radial frictional forces between tendons and coil pipes in an embodiment of the present invention where the coil pipes are not spiraled; 
           [0016]      FIG. 7  depicts a schematic of advancing an endoscope in a colon in accordance with an embodiment of the present invention; 
           [0017]      FIG. 8  depicts a schematic of an undesirable bell-shape bend of a coil tube; 
           [0018]      FIG. 9  depicts an embodiment of a coil pipe made with circular cross-section wire and a herniation of the coil pipe; 
           [0019]      FIG. 10  depicts a centerless ground coil pipe in accordance with an embodiment of the present invention; 
           [0020]      FIG. 11  depicts a coil pipe made with “D-shaped” wire in accordance with an embodiment of the present invention, and various embodiments of how to make “D-shaped” wire; 
           [0021]      FIG. 12  depicts an illustration of coil pipe spiraled along a segment in accordance with an embodiment of the present invention; 
           [0022]      FIG. 13  provides a graphic for explaining static radial frictional forces between tendons and coil pipes in an embodiment of the present invention where the coil pipes are spiraled; 
           [0023]      FIG. 14  provides a schematic for describing one alternative for spiraling of coil pipes along a segment in accordance with an embodiment of the present invention; and 
           [0024]      FIG. 15  depicts an alternative embodiment of a steerable distal portion or a controllable segment. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0025]      FIG. 1  depicts endoscope  10 , a colonoscope in particular, in accordance with an embodiment of the present invention. 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  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 , as known by the skilled artisan. As the skilled artisan appreciates, 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. Typically, as will be appreciated by the skilled artisan, endoscope  10  will 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 and appreciated by the skilled artisan. 
         [0026]    Preferably, automatically controlled proximal portion  16  comprises a plurality of segments  28 , which are controlled via computer and/or electronic controller  30 . Such an 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 a each segment  28  or steerable distal portion  14 , with the proximal end of the tendon mechanically connected to actuators to articulate segments  28  or steerable distal portion  14 , which 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 previously incorporated herein by reference. 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 . An 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, previously incorporated herein by reference. 
         [0027]    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. 
         [0028]    Referring to  FIG. 2 , steerable distal portion  14  and segments  28  of automatically controlled proximal portion  16  are preferably constructed from a plurality of links  46 . Five links  46  are shown in this example 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 segments  28  or steerable distal portion  14  will be used. Each link  46  connects one joint (e.g.,  47 ) to an adjacent joint (e.g.,  47 ). Each link  46 , in this embodiment, can move with two degrees of freedom relative to an adjacent link. 
         [0029]    Referring now to  FIG. 3A-C  a schematic diagram of either steerable distal portion  14  or segments  28  is provided for discussion purposes and to explain a preferred system and method for articulating steerable distal portion  14  or 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. 
         [0030]      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. Bowden cables extend down the length of elongate body  12  (not shown in  FIGS. 3A-C ) and comprise coil pipes  48  and tendons  50 . The proximal end of the Bowden-type cable is coupled to an actuator (not shown) and the distal end is coupled to the segment for which it controls articulation. Coil pipes  48  house tendons  50  (i.e. a Bowden-type cable) along the length of elongate body  12  (not shown in  FIGS. 3A-C ) and coil pipes  48  are fixed at the proximal end of segment  28 . Tendons  50  extend out of coil pipes  48  at the proximal end of segment  28  along the length of segment  28 , and are mechanically attached to the distal portion of segment  28 . It will be appreciated that the distal end of tendons  50  need only be attached to the segment being articulated by that tendon  50  at a location required to transfer the actuated force to that segment to effect articulation; the distal portion of the segment is provided by way of explanation and example, and not by way of limitation. In the variation depicted in  FIG. 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  alternating by 90 degrees (see  FIGS. 2 and 4 ). Thus, an assembly of multiple links  46  is able to move in many directions, limited only by the number of actuated 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 endoscope 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. 
         [0031]    In the variation depicted in  FIG. 3A-C , four tendons  50  are used to articulate segment  28 , although more or fewer tendons could be used, as will be appreciated by the skilled artisan. Four tendons can reliably articulate segment  28  in many directions. Tendons  50  are attached at the most distal link  46 A, for the purposes of this discussion but not by way of limitation, close to the edge spaced equally apart at 12, 3, 6, and 9 O&#39;clock. 
         [0032]      FIG. 3B-C  show segment  28  articulated by independently pulling or slacking each 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 P is the degree of overall articulation of segment  28 . In this situation P 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. 
         [0033]    Referring now to  FIG. 4 , links  46  may be control rings to provide the structure needed to construct steerable distal portion  14  and segments  28 .  FIG. 4A  shows a first variation of a vertebra-type control ring  54  that forms segments  28  or steerable distal portion  14 .  FIG. 4B  shows an end view of a single vertebra-type control ring  54  of this first variation. In this embodiment each vertebra-type control ring  54  define a central aperture  56  that collectively form an internal lumen of the device, which internal lumen is used to house the various 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. 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. 
         [0034]    Referring briefly to  FIG. 5 , tension applied to tendon  50  by actuator  60  is isolated to a particular segment  28  by use of coil pipe  48  housing tendon  50 , as previously described. Referring back again to  FIG. 4A , vertebra-type control ring  54  is shown with four holes  60  through the edge of vertebra-type 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  or tip  14  determines the number of holes  60  provided for passage of tendons  50 . 
         [0035]    The outer edge of vertebra-type control ring  54  in the variation depicted in  FIG. 4A-B  may be scalloped to provide bypass spaces  62  for tendons  50  and coil pipes  48  that control more distal segments  28  or tip  14 , and 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. 
         [0036]      FIG. 4D-E  show another variation of vertebra-type control ring  64  in sectional and perspective views. In  FIG. 4D-E , tendons  50  and coil pipes  48  that bypass a segment may be contained within body  66  ( FIG. 4D ) of vertebra-type control ring  64  in an alternative coil pipe bypassing space or quadrant  68 , rather than the scallops  62  along the outer edge of vertebra-type control ring  54  as previously described. Quadrants  68  are the preferred way to handle coil pipes  48  that must by-pass a segment. Vertebra-type control ring  64  of  FIG. 4D-4E  show four coil pipe bypassing spaces/quadrants  68 , but more or fewer may be used. It will be appreciated that cross bar  57  can pivot at hinge points  59  in one embodiment or may fixed relative to body  66 . Other aspects of this variation of vertebra-type control ring are similar to that described above and are, accordingly, called out with the same reference number. It is noted that tie-off rods  104  can be used to tie off the distal ends of tendons  50  in this embodiment. 
         [0037]    The skilled artisan will appreciate that coil pipes  48  by-passing a vertebrae via quadrants  68  will define an approximately cylindrical coil pipe containment space roughly defined by the outer diameter of vertebrae-type control ring  64 . This space is loosely defined by the grouped coil pipes as they pass through and between the vertebrae. As described more thoroughly below, it is possible and preferred to have intermediate vertebra-type control rings without coil pipe bypassing spaces, as shown in vertebra-type control ring  54 ′ ( FIG. 4C ) or  65  ( FIG. 4F ). In either construction, central aperture  56  or  56 ′ of the control rings collectively forms a lumen (not shown) through which channels and cables necessary or desired for the endoscope function pass, as well as coil pipes and tendons by-passing that particular segment. Preferably, more proximal segments will have larger diameter vertebrae in order to provide larger quadrants  68  or central aperture  56  or  56 ′ to accommodate a larger number of coil pipes  48  that must reach the more distal segments  28  and tip  14 . The more distal segments  28  and steerable distal portion  14  can be constructed with vertebrae-type control rings  64  or  65  having a smaller diameter, thereby making the distal portions of elongate body  12  have a smaller diameter. While this is preferred, the skilled artisan will recognize that any diameter vertebrae may be used limited only by the need to accommodate the coil pipes and tendons necessary to articulate segments  28  and steerable distal portion  14  of the endoscope. 
         [0038]    Referring again to  FIG. 5 , coil pipes  48  are fixed at their distal and proximal ends between actuators  60  and the proximal end of segment  28  under control by those actuators.  FIG. 5  shows only one segment  28  (which, as discussed, could also be steerable distal portion  14 ), and, for clarity, the other parts of a complete endoscope have been omitted from  FIG. 5 . When tendons  50  are placed under tension, 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 where it is fixed between the actuator and the proximal end of the segment being articulated. A preferred embodiment of the present invention utilizes one actuator per tendon, and utilizes four tendons per segment, as described above, although only one actuator  60  is depicted for clarity. Details relating to actuator  60  and connecting actuator  60  to tendons  50  are described in U.S. patent application Ser. No. 10/988,212, previously incorporated by reference. 
         [0039]    The skilled artisan will appreciate that articulation of multiple segments  28  along the length of elongate body  12  will require that many coil pipes  50  extend down the length of elongate body  12  and through coil pipe by-passing spaces, with the number decreasing by four coil pipes (in this example) at the proximal end of each segment. Thus, a  17  segmented elongate body (16 segments  28  and 1 tip  14 ) requires 68 coil pipes going into the proximal end of elongate body  12 , which decreases by four coil pipes for each distally adjacent segment  28  (assuming one uses four tendon/coil pipes combinations per segment as in the present example). It also requires the actuation or tensioning of  68  tendons, with four tendons terminating at the distal end of each segment. This requires 68 actuators in this preferred embodiment, one actuator per tendon  50 . 
         [0040]    The skilled artisan will also appreciate that there is not a one to one correspondence between the force applied by actuators  60  at the proximal end of tendons  50  and the force realized at the distal end of tendons  50  to articulate segment  28 . When elongate body  12  is in its substantially straight configuration, friction between tendons  50  and coil pipes  48  results in frictional losses along the length of the coil pipe while applying tension to articulate a segment or the tip. Articulation of segments  28  and steerable distal portion  14  results in further losses and inefficiencies for many reasons. For example, and without limitation, when elongate body  12  articulates (for example at the Sigmoid colon during a colonoscopy procedure), coil pipes  48  must move longitudinally along elongate body  12  to either “gain” or “lose” length depending whether coil pipes  48  are on the inner or outer portion of the bend created by the articulation. As described above, an embodiment of the present invention provides quadrants  68  or coil pipe by-passing spaces  62  that permit the passage of coil pipes  48  along elongate body  12  until they reach the proximal portion of the segment they control. The “gain” or “loss” of coil pipe length requires coil pipes  48  to slide up and down elongate body  12  and within quadrants  68  or coil pipe by-passing spaces  62  creating further frictional losses by virtue of friction between the coil pipes and/or between the coil pipes and the vertebra. There is also the additional friction created between a coil pipe and a tendon by virtue of the bend. 
         [0041]    Frictional losses caused by the coil pipe/tendon bending (by virtue of a segment bending) reduce the working force available to articulate segments. The frictional loss is dependent on the material coefficient of friction and the accumulated bend (total tortuosity) of the coil pipe/tendon as elongate body  12  moves through a tortuous path. Total tortuosity is the amount of accumulated bend along the length of a coil pipe, which is closely approximated by the amount of accumulated bend along the length of that portion of elongate body  12  through which the coil pipe travels. For example an S-bend through the Sigmoid colon would contribute approximately 2×90° or 180° to the total tortuosity. As a segment bends coil pipes/tendons within that segment will also bend. The tendon tension applies a normal load towards the center of curvature of the coil pipe, as depicted in  FIG. 6  that graphically depicts a coil pipe going through a  180  bend around a column. 
         [0042]    Referring to  FIG. 6 , the static friction for coil pipes extending down the length of elongate body  12  can be represented by the following balanced equations, where θ is the total tortuosity. Delta_F is constant with a given load L on either tendon. Note there are at least three sources of friction: (1) friction between the tendons and the coil pipe; (2) friction between the coil pipes and the ring structures; and (3) friction between the individual coil pipes. 
         [0000]    
       
         
           
             
               
                 
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             L 
           
         
       
     
         [0043]    Having found Delta_F, the general normal cable loading is F N =Delta_F*θ=L*θ. The static radial friction is, therefore, F r (θ)=F N *μ=Delta_F*θ*μ=L*θ*μ (μ is coefficient of friction). Note that this equation has been solved for an ideal, hypothetical situation where the coil pipe is bent around a hypothetical column and static equal load is place at either end of the tendon going through the coil pipe. The same analysis applies for the static friction between a coil pipe and ring structures of a segment, where L is the given external load on the coil pipe. The solution is the same, but will have different loads (L) and different coefficients of friction (μ). This is a reasonable model to assess the static frictional loads for a coil pipe going through a segment comprised of vertebra-type ring structures having a total tortuosity of θ. Therefore, the static friction force for 180 degrees of accumulated tortuosity (two ninety degree bends or an S-bend, for example) is F r (π)=π*L*μ. The calculation for brake free forces and dynamic resistance loads is more complicated but can also be solved with an exponentially decaying resistance load. 
         [0044]    Additionally, but related, elongate body  12  may enter more than one tortuous bend simultaneously. Referring to  FIG. 7A-B , this occurs when, for example and without limitation, performing a colonoscopy with an embodiment of the present invention elongate body  12  must move through a highly tortuous path. Electronic controller  30 , in a preferred embodiment, controls the articulation of each segment  28  to take the shape of adjacent segments or tip as elongate body  12  is advanced through a tortuous path, such as the colon. Referring to  FIG. 7A , a user articulates steerable distal portion  14  to select a desired path, through the Sigmoid colon S for example (an approximate S-bend or 180 degrees of total tortuosity), and then advances the endoscope through the anus A. Electronic controller  30  knows the shape of segments  28  and steerable distal portion  14  prior to the advancement of elongate body  12  into the colon, as described more thoroughly in U.S. patent application Ser. No. 11/019,963, previously incorporated herein by reference. Electronic controller  30  causes adjacent segments to adopt the shape of the segment or steerable distal portion immediately preceding it. Therefore, upon advancing elongate body  12  through the colon C, electronic motion controller  30  will maintain the approximate tortuous S-shape of the Sigmoid colon S in elongate body  12  by automatically controlling segments  28  to adopt the approximate shape of the immediately preceding segment. This follow-the-leader technique is further described in U.S. patent application Ser. No. 11/019,963, previously incorporated herein by reference. As described above, coil pipes  48  need to slide along elongate body  12  to accommodate the “gain” or “loss” of coil pipe length resulting from the articulation of elongate body  12 . Recall from the equation above that the frictional force is proportional to both total tortuosity and the material coefficient of friction. There are two coefficients of friction of interest, one for the tendon against the internal lumen of the coil pipe, and the other for the coil pipe against the vertebra-type ring structures. 
         [0045]    Referring to  FIG. 7B , when steerable distal portion  14  of elongate body  12  enters into a second tortuous bend, at the splenic flexure F 1  of the colon for example, coil pipes  48  need to accommodate the “gain” or “loss” of coil pipe length for both the new bend in the splenic flexure F 1  and for the first S-bend at the Sigmoid colon S. As the user advances elongate body  12  into the transverse colon T electronic controller  30  continues to maintain the bends at the splenic flexure F 1  and the Sigmoid colon S. However, coil pipes  48  need to slide the entire length of elongate body  12  (as described above), including through the first tortuous proximal bend in the Sigmoid colon S, and the second tortuous more distal bend in the splenic flexure F 1  to accommodate for the “loss” and “gain” of coil pipe length. 
         [0046]    It was found that coil pipes  48  did not have the ability to slide along the length of elongate body  12  when in such a tortuous state. Without wishing to be bound by any particular theory, the inventors believe that the frictional forces between the coil pipes and the vertebra-type ring structures bind the coil pipes and they are unable to slide along the length of elongate body  12 . Referring to  FIG. 8 , catastrophically the coil pipe exits the coil pipe containment boundary (discussed previously) in a severe bell-curve type shape  70 , or adopts severe bends (not shown) within the coil pipe containment boundary. This bell-curve bend  70  and/or other severe bends in coil pipes  48  dramatically increases friction between coil pipes  48  and tendons  50 , and also stiffens the segments requiring greater forces to achieve the desired articulation than would otherwise be required without the bell-curve or other severe bends in the coil pipes. As the segments having bell-shape curve  70  and/or other severe bends in coil pipe  48  straighten, the excess coil pipe length is no longer required to accommodate the bend in that particular segment of elongate body  12 . Therefore, coil pipe  48  moves back into the coil pipe containment area and/or the other severe bends begin to straighten as the bend in segment  28  begins to straighten, but in doing so coil pipe  48  frequently herniates. The skilled artisan will appreciate that herniation of the coil pipe can be caused by a variety of mechanisms. Moreover, the skilled artisan will appreciate that bell-curve shape  70  or other severe bends can occur anywhere along the length of elongate body  12 , and the location of such bends is not limited to the bending segments. A herniation, as will be described more fully below, is a permanent or plastic lateral deformation of the coil pipe. The primary cause of a herniation is believed by the inventors (without wishing to be bound by any particular theory) to be the result of the coil pipes binding (i.e. inability to slide or significantly reduced ability to slide) along the length of elongate body  12 . 
         [0047]    Referring to  FIG. 9 , coil pipes  48  are typically made of circular cross-section high tensile strength wire  72  wound in a tight coil to form a hollow pipe-like structure. The larger the tensile strength the more difficult it will be to make the material plastically deform. In a preferred embodiment high tensile  302 ,  303  or  304  VT SST was specified with a tensile strength greater than about 40,000 PSI. In a herniated coil pipe  48 H ( FIG. 9B ) at least one of the coils  74  is permanently, laterally displaced, thereby significantly decreasing the effective diameter through which tendon  50  may pass. This results in a concomitant catastrophic increase in the frictional losses caused by friction between the coil pipe and the tendon passing therethrough. This lateral displacement also significantly reduces column strength of the coil pipe, thereby significantly reducing the ability to articulate a segment. In addition to significantly reducing the amount of force delivered by tendon  50  to articulate the segment or tip, the additional friction will prematurely wear out tendon  50 . 
         [0048]    Without wishing to be bound by any particular theory, the inventors believe that the coil pipes rubbing on the vertebrae (or other ring structure) as the coil pipes re-enter the coil pipe containment area or otherwise straighten cause lateral forces on the coil pipes, which cause the coil pipes to resist axial movement or bind leading them to herniate. The inventors further hypothesize, again without wishing to be bound by any particular theory, that the ridges  76  ( FIG. 9A ) of the coiled wire  72  bump along the vertebrae or ring structure as the coil pipes re-enter the coil pipe containment area or otherwise straighten creating additional forces on the coil pipe structure. This is further exacerbated, again without being bound by any particular theory, by the bell-shaped curve or other severe bends separating the coils similar to the bending of a spring, thereby making the ridges more pronounced. 
         [0049]      FIG. 10  depicts an embodiment of centerless ground coil pipe  78  in accordance with an embodiment of the present invention. As described above coil pipes  48  slide along the length of elongate body  12  as segments  28  articulate along a tortuous path. Adding lubricity between coil pipes  48  is, therefore, desired. However, using a lubricant, such as oil or other substance, is not highly desired because, at a minimum, the lubricant wears out making more frequent service of the endoscope necessary. Centerless ground coil pipe  78  is essentially the same as coil pipe  48  described above, but approximately half the diameter of coil wire  72  (shown in shadow) on either side of centerless ground coil pipe  78  is ground away or removed to create the centerless ground coil pipe  78 . The opposing flat sides  80  provide increased lubricity between coil pipes as they slide up and down elongate body  12 , and also provide increased lubricity as “excess” coil pipe length slides back into the coil pipe containment area or otherwise straightens. The skilled artisan will appreciate that any appropriate lubricant may also be used in combination with the centerless ground coil pipes, although this is not preferred. The inventors found that this solution did not sufficiently resolve the binding and ultimate herniation of the coil pipes. The inventors hypothesize that the design is sound, but the less preferred outcome of the solution resulted from the difficulty in reliably manufacturing centerless ground coil pipes with substantially opposing substantially flat sides. 
         [0050]    In accordance with an alternative embodiment of the present invention  FIG. 11A  depicts D-shaped coil pipe  82  made from D-shaped wire  84 . In this embodiment convex portion  90  of D-shaped wire approximately nests in concave portion  92  of D-shaped wire ( FIG. 11A ). D-shaped wire  84  can be manufactured in a number of ways as will be appreciated by the skilled artisan. In one embodiment, referring to  FIG. 11B , round wire  72  is rolled by first roller  91  or “Turkshead die” into an approximate oval shape  93  and the wire is rotated approximately 90 degrees and fed into second roller  94  or “Turkshead die.” Second roller  94  creates the concave shape  92  and convex shape  90  at opposite ends of the parallel substantially flat sides  86  created by first roller  91 . Alternatively, D-shaped wire can be formed by extrusion or by pulling a fully annealed or soft wire through one or more dies as shown in  FIG. 11C . First, wire  72  is pulled through die  92  to obtain an approximately oval shaped wire  96 . Oval shaped wire  96  is then pulled through die  98  to provide the concave shape  92  and convex shape  90  at opposite ends of the parallel substantially flat sides  86 . The wire is then hardened to hold a set shape as in a coil pipe. The skilled artisan will appreciate that dies  95  and  98  can be a single die and that orientation of the die or rotation of the wire is a matter of manufacturing choice. This would also be true with the orientation of first and second rollers discussed above. 
         [0051]    Manufacture of D-shaped coil pipe  82  with D-shaped wire is similar to the manufacture of coil pipe made with circular wire. Referring to  FIG. 11D , the main difference is that D-shaped wire  84  needs to be oriented with one of the flat sides  86  against mandrel  88 . Preferably, the convex portion  90  of the “D” approximately nests into the concave portion  92  of the “D” as the D-shaped wire is wound onto the mandrel to form the coil pipe. 
         [0052]    Nesting convex portion  90  into concave portion  92  provides for a higher surface area contact between wires of each coil than a coil pipe manufactured with circular cross section wire, particularly when the coil pipe is under compressive stresses. Additionally, the sides of convex portion  90  and concave portion  92  provide resistance against herniation upon application of lateral forces. Like the centerless ground coil pipe  78 , D-shaped coil pipe  82  also provides increased lubricity by virtue of substantially flat portions  86  of D-shaped coil pipe  82 . D-shaped coil pipe  82  worked better than centerless ground coil pipe  78  in preventing herniations, and is therefore more preferred over centerless ground coil pipe  78 . Additionally, the manufacturability of D-shaped coil pipe  82  is more consistent than that of the centerless ground coil pipe  78 , which adds to the preference of D-shaped coil pipe  82 . Furthermore, orienting coil pipe  48  to grind off or flatten the sides to achieve centerless ground coil pipe  78  can prove challenging, as discussed above. The skilled artisan will appreciate that shapes of wire other than D-shaped may be used in accordance with the present invention. For example the concave and convex portion of D-shaped coil pipe  82  may have any geometrical shape that can nest together. These may include, without limitation, V-shaped coil pipe  94  ( FIG. 11E ). Furthermore, an alternative embodiment, though not preferred, could be square or rectangular cross-section wire oriented to have flat sides against each other, as shown in  FIG. 11F , which also will provide resistance against herniation upon application of lateral forces. Additionally, a benefit of using Bowden-type cables made from coil pipes is that they are flexible even when under compressive load. D-shaped coil pipes also remain very flexible under high compressive loads. 
         [0053]      FIG. 12  depicts a preferred alternative embodiment for managing the coil pipes that reduces or eliminates the herniation problem by reducing or eliminating the need for the coil pipes to slide along the entire length of elongate body  12 . As described above, coil pipe  48  must slide up or down the entire length of elongate body  12  to accommodate a bend in a segment. Referring to  FIG. 12 , spiraling coil pipes  48  along elongate body  12  and segments  28  significantly reduces and effectively eliminates the herniation problems identified above. Without wishing to be bound by any particular theory, the inventors hypothesize that the spiraled coil pipe localizes the movement or slacking of the coil pipes to an area at or close to the segment undergoing articulation. Therefore, again without wishing to be bound by any particular theory, when a segment articulates the spiraled coil pipe moves within or near a segment locally, thereby reducing or eliminating the need for the coil pipe to slide up or down the entire length of the elongate body. An analogy, again without wishing to be bound by any particular theory, would be a rope or cable made of spiraled strands bending over a pulley; the gain and loss of length of the individual strands in the rope takes place locally at the point of the bend around the pulley, because the strands alternate from the outside to the inside of the bend; the inside strand section gives what the outside strand needs. 
         [0054]    The inventors observed that the spiraled coil pipes did not exit the coil pipe containment area in bell shaped curves or exhibit other extreme bends as described above, and they observed little to no herniation of the coil pipes. Spiraling the coil pipes will reduce or prevent herniation with D-Shaped, centerless ground or circular wire coil pipes as well. However, circular wire coil pipes are preferred for ease of manufacturing reasons. 
         [0055]    The main benefit with using a spiraled structure identified by the inventors is reduced friction between a coil pipe and vertebra-type ring structures by virtue of the elimination or reduction of sliding of the coil pipes along the elongate body. There is a relatively smaller increase of frictional forces resulting from the increase of overall length of coil pipe through which a tendon must pass, and an increase of overall tortuosity as a result of spiraling the coil pipes along elongate body  12 . 
         [0056]    The static friction from a spiral loading differs from that of radial loading described above. Tendon tension, as described for radial loading, applies a normal load toward the center of curvature and results in static radial friction of F r (n)=μ*L*μ for 180 degrees of total tortuosity. Static radial loading for a spiraled coil pipe can be solved and calculated in the same fashion. It is noted that because, as hypothesized by the inventors, spiraling localizes coil pipe movement to a segment undergoing a bend friction for coil pipes sliding against vertebra-type ring structures is reduced or eliminated. Referring to  FIG. 13 , cable load L is assumed to be the same at both ends of the spiral. Balanced equations follow, where γ is the spiral angle and θ is, again, total tortuosity, which as noted is increased by virtue of the spiral: 
         [0000]    
       
         
           
             
               
                 
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         [0057]    Having found Delta_F the general normal cable loading is F N =Delta_F*θ*sin(γ)=L*θ*sin(γ). The static radial friction is, therefore, F r (θ)=F N *μ=Delta_F*θ*sin(γ)*μ=μ*L*θ*sin(γ). Note that this equation has been solved for an ideal, hypothetical situation where the coil pipe is spiraled around a hypothetical column 180° and static equal load is place at either end of the tendon going through the coil pipe. This is a reasonable model to assess the static frictional loads for a coil pipe spiraling through a segment comprised of vertebra-type ring structures. It must be recalled, however, that total tortuosity is now increased as a result of the spiraling. 
         [0058]    Total tortuosity is the sum of all angles of bends in a coil pipe from its proximal end assuming the coil pipes are not spiraled along the elongate body. However, as will be appreciated, the spiral angle γ adds to the total tortuosity, but under larger (high degree of) bends of a segment the amount of tortuosity added by for small spiral angles (γ) is approximately the same as that of a non-spiraled embodiment undergoing the same multiple bends, so long as the spiraling is not excessive. Excessive spiraling with large spiral angle γ or wrapping the coil pipe too many times around a segment has a deleterious affect for several reasons. One reason is that the increased number of wraps dramatically increases the length of the coil pipe, thereby increasing the friction between the coil pipe and the tendon. More importantly, the overall tortuosity θ increases to an unacceptable level with the increased number of wraps (which proportionally increases the static friction) and spiral angle, i.e., friction added (F r ≈*L*θ*sin(γ)) increases directly with spiral angle. The inventors reasoned that too much spiraling would result in the detriment of increased friction by virtue of the increase of total tortuosity (θ) out weighing the benefit of reducing or eliminating binding. Numerically the inventors determined that a single 360 degree spiral, or approximately one wrap along each segment is the preferred amount of spiraling. It was determined empirically and numerically that approximately one 360 degree spiral wrap per segment of approximately 10 cm along the elongate body reduced or eliminated the need for the coil pipe to slide between segments to accommodate a bend, thereby reducing or eliminating herniation, and that this benefit far outweighed any increase of friction resulting from the amount of tortuosity added by the spiraled coil pipes. It was also determined numerically that an integral number of spiral wraps was preferred to ensure localization of coil pipe movement during the bending of a segment. The skilled artisan will appreciate the amount of spiraling or wraps used will depend on the system and the purpose for which the system will be used. It will also be appreciated that the spiral angle (γ) need not be constant along the length of a segment. 
         [0059]    Referring back to  FIG. 4D-F , in an embodiment of the present invention, quadrants  68  of vertebrae type control ring  64  are used to maintain coil pipes  48  spiraled along elongate body  12 . In this embodiment more than one vertebra-type control ring  64  in a segment has quadrants  68 , and the coil pipes are passed through the quadrants to established the preferred approximately one spiral wrap per segment. In another preferred embodiment, referring briefly to  FIG. 15A , distal (not shown) and proximal vertebrae-type control rings  64  of each segment have quadrants  68 , and intermediate vertebrae-type control rings  65  do not have quadrants  68 . In this preferred embodiment the quadrants are approximately longitudinally aligned, and coil pipes are passed through the aligned quadrants after spiraling within the intermediate control rings  65  to achieve the preferred approximately one spiral wrap. It will be appreciated that the number of coil pipes passing through the quadrants will be equally divided between the quadrants, although other configurations can be used. The skilled artisan will appreciate that many different configurations and mechanisms may be used to maintain the spiral along the length of elongate body  12 . 
         [0060]    Referring to  FIG. 14 , coil pipes  48  are routed through quadrants  68  (not shown) in proximal vertebra-type control ring  64  in segment  28 , through vertebra-type control rings  65  without quadrants in that segment, through quadrants  68  (not shown) in distal vertebra-type control ring  64  in that segment. The working channel, fiber optics cable, suction channel, video cable and the like (not shown) are routed through central opening  56  of vertebra-type control rings  64  and through the lumen (along with the coil pipes) created by intermediate vertebra-type control rings  65  without quadrants. The vertebrae  64  with the quadrants are then rotated relative to each other to achieve the amount of desired spiraling of the coil pipes, the rotation being depicted graphically in  FIG. 14B . Hinging of the vertebrae will maintain the spiral, as will be appreciated by the skilled artisan. As noted, approximately a full spiral wrap of  2   a  per segment is preferred, but the skilled artisan will appreciate that the number of wraps will depend on the purpose for which the device will be used. As will also be appreciated, only four coil pipes are depicted with the other details of the segments and endoscope being omitted from  FIG. 14  for purposes of clarity. It is noted that the skilled artisan will appreciate many different configurations of vertebra-type control rings with and without quadrants can be used to achieve the desired spiraling. 
         [0061]    As noted, at least one vertebra control ring  64  with quadrants  68  is used per segment and preferably two to maintain the preferred spiral structure of the coil pipes by-passing that segment, and that the remaining vertebra-type control rings of that segment do not have quadrants. As discussed above, central opening  56  of vertebra-type control ring  64  provides a location for passing working channels, optical cables and the like through vertebra-type control ring  64  and quadrants  68  provide a separate by-pass space for coil pipes not controlling articulation of that particular segment, and for maintaining the spiral structure of the coil pipes. The remaining control rings  65  of a segment have no by-pass space. Rather, the coil pipes, the working channel, air line, water line, suction line, optical cables and the like all pass through the central lumen created by central opening  56 ′ ( FIG. 4F ) of vertebra-type control rings  65  by aligning vertebra-type control rings  65 , and are not separated by quadrants  68  as in vertebra-type control rings  64 . 
         [0062]    Referring again to  FIG. 15 , tendons  50  controlling a particular segment are kept separate from the spiraled coil pipes, the working channel, air line, water line etc. by intermediate ring structures  100  attached at the hinge between control rings  65  not having quadrants  68 . These intermediate ring structures  100  ( FIG. 15B ) are situated between vertebra control rings  65 . Four holes  102  are shown in ring structure  100  through which tendons  50  controlling articulation of that segment run. More holes may be used per tendon depending on how force is applied to the segment via the tendon(s), and the total number of holes depends on the number of tendons  50  used to control the segment, tour in this example. In the proximal vertebra-type control ring  64  having quadrants  68 , holes  60  are where coil pipes controlling that segment terminate and are fixed. As described above, tendon  50  extends out of the coil pipe and along the segment through holes  100  and then terminate at the distal end of the segment at tie off rods  104  of the distal vertebra-type control ring  64 . The skilled artisan will recognize that tendon  50  controlling a particular segment need only terminate somewhere within that segment such that force can be effectively transferred to and along that segment to effect articulation. 
         [0063]    This preferred embodiment has the advantage of, at least, (1) spiraling the coil pipes along the length of the elongate body, as described above, and (2) providing relatively unconstrained space in vertebra-type control rings  65  without quadrants  68  intermediate to vertebra-type control rings  64  having quadrants  68 , such that coil pipes can move locally and relatively unconstrained to accommodate articulation of that particular segment. The inventors believe, again without wishing to be bound by any particular theory, that this permits the coil pipes to move locally and accommodate the bend in a segment without having to slide the entire length of the elongate body, thereby not binding the coil pipes and the concomitant reduction or elimination of herniations in the coil pipes. 
         [0064]    The skilled artisan will appreciate there are many different ring structures and many different ways to achieve the desired spiral structure of coil pipes. For example, and without limitation, the coil pipes could be spirally arranged in scalloped by-pass spaces  62  in the outer edge of vertebra-type control ring  60  ( FIG. 4A-B ), although this is less desirable because it moves the coil pipes further away from the desired longitudinal centerline of elongate body  12 , and these spaces have more friction than when the coil pipes are passed through quadrants  68  or the center  65  of vertebrae. Additionally, the skilled artisan will appreciate that quadrants  68  can exist in more than one vertebra-type control ring  64  within a segment, and that more or fewer than four quadrants can be used. The skilled artisan will appreciate how to orient quadrants on one vertebra relative those on an other vertebra(e) having quadrants within a segment and along the elongate body to achieve the desired spiral arrangement of coil pipes. 
         [0065]    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.