US20110077678A1 - Coil Design for Improved Rotational Performance - Google Patents

Abstract

A coil for transmitting torque comprises a wire having a longitudinal axis and first and second longitudinal edges extending along the longitudinal axis, wherein the first longitudinal edge is formed with a first pattern and the second longitudinal edge is formed with a second pattern complementary to the first pattern, the first and second patterns being configured to interlock with one another when the wire is wound into a helical shape.

Description

PRIORITY CLAIM
• This application claims the priority to the U.S. Provisional Application Ser. No. 61/247,330, entitled “Coil Design for Improved Rotational Performance” filed Sep. 30, 2009. The specification of the above-identified application is incorporated herewith by reference.
BACKGROUND
• Devices with flexible shafts are often required to guide endoscopes to target sites within a body lumen or cavity. Such a guide shaft provides a semi-rigid structure through which an endoscope may be passed without causing damage thereto. Criteria for guide shafts may vary according to the procedure being performed but may include, among others, a combination of varying levels of kink resistance, crush resistance, flexibility, etc. Although these flexible shafts are often formed as coils, the ability of many of these coils to transmit rotational forces along their lengths is insufficient for certain applications.
SUMMARY OF THE INVENTION
• The present invention relates to a coil for transmitting torque comprising a wire having a longitudinal axis and first and second longitudinal edges extending along the longitudinal axis, wherein the first longitudinal edge is formed with a first pattern and the second longitudinal edge is formed with a second pattern complementary to the first pattern, the first and second patterns being configured to interlock with one another when the wire is wound into a helical shape.
BRIEF DESCRIPTION OF THE DRAWINGS
• FIG. 1 is a perspective view of a flexible conduit according to a first embodiment of the present invention;
• FIG. 2 is a perspective view of a flexible conduit according to a second embodiment of the present invention;
• FIG. 3 is a perspective view of a flexible conduit according to a third embodiment of the present invention;
• FIG. 4 is a perspective view of a flexible conduit according to a fourth embodiment of the present invention;
• FIG. 5 is a first perspective view of a forming die according to the present invention; and
• FIG. 6 is a second perspective view of the forming die ofFIG. 5.
DETAILED DESCRIPTION
• The present invention, which may be further understood with reference to the following description and the appended drawings, relates to shaft devices through which endoscopes and other medical devices are positioned in body lumens and cavities. For example, the present devices and methods may be used to guide endoscopes into and through body lumens such as the duodenum, esophagus, large intestine, gastrointestinal tract, etc. It is noted that, although the exemplary embodiments are described with respect to endoscopic procedures, the present invention is suitable for any of a number of alternate applications requiring a guide sheath transmitting rotational forces therealong. For example, the exemplary embodiment of the present invention may also be used to allow for or improve rotation in smaller medical devices including but not limited to hemostatis clips.
• Devices and methods according to the present invention employ a coiledguide sheath100 with a lumen passing therethrough for receiving therein an endoscope and/or other medical device. The coiledguide sheath100 according to the invention transmits rotation therealong so that a rotational force applied to a proximal end thereof causes a corresponding rotation of the distal end. For example, an exemplary coil sheath according to the invention is formed as a unibody structure relying on mechanical interaction between adjacent ones of the turns of the coil to transmit rotation therealong. It is noted that the use of the term distal herein refers to a direction extending away from a user of the device when the device is in an operative position while proximal refers to the toward the user. For example, the proximal portion of devices according to the invention remain external to the body when in an operative position while the distal end is inserted through a natural body lumen to a target site.
• Known coils embody a multitude of parameter combinations selected in an attempt to conform the performance of the coil to a procedure to be performed. Some of these parameters include whether the pitch of the coil is open or closed, whether the wire is round or flat, the dimensions of the wire and the coil, and an amount of preload on a closed pitch coil, as those skilled in the art will understand. Although manipulation of these parameters has enabled the achievement of many design criteria including, for example, desired coil rigidity or flexibility, it is desired to provide a coil having an improved ability to transmit rotation therealong.
• For example, one prior art coil includes adjacent turns of the coil welded together at a plurality of discrete location. Though this embodiment secures the turns together so as to increase rotational performance, the securing of these adjacent turns reduces the flexibility of the coil sheath. Furthermore, the welding process is expensive significantly increasing the cost of the device.
• An exemplary embodiment of the present invention is shown with respect toFIG. 1, which shows acoiled sheath100 forming a workingchannel110 extending therethrough from aproximal end101 to adistal end102. The coiledsheath101 is formed, for example, as a substantially helical coil comprised of a unibody wire substantially flat on radially inner and outer surfaces with a thickness of the wire transverse to a path of the coil (i.e., transverse to the path along which the wire is wound) varying to form a wave pattern. The wave pattern may be an inherent property of the design of the wire or ribbon before the wire is wound into a helix. Alternatively, the wave pattern may be imparted to the coil as a part of the winding or a subsequent process. Although the embodiments disclosed herein describe coils formed of wire, those skilled in the art will understand that this tend is applied herein to refer to traditional wires with circular cross-sections as well as to flat ribbons and other shapes of metal which may be would to form flexible conduits as described herein. Furthermore, thecoiled sheath100 may be formed of any material other than metal, including, but not limited to polymers and ceramics. In a preferred embodiment, the coiled sheath may be formed of a plastic when formed with a diameter exceeding 1 cm. In such an embodiment, a thermoplastic material may be extruded and interlocking features formed thereon via a continuous method such as knurling. The thermoplastic may then be formed into a coil around a mandrel (not shown).
• The wave pattern is selected relative to the diameter and pitch of the helix so that the troughs of the wave pattern of each turn of the coil mate with the peaks of the wave patterns of adjacent turns of the coil. Thus, adjacent turns of the coil are locked to one another and relative rotation therebetween is resisted. This allows thecoiled sheath100 to efficiently transmit to thedistal end102 thereof rotational forces applied to theproximal end101. More specifically, when a torsional force is applied to thecoiled sheath100 at theproximal end101, each of the turns of thecoiled sheath101 mechanically interact with adjacent turns of the coil to transmit the torsional force along the length of the coiledsheath100. In a preferred embodiment, the angular distance between each of the individual coils of thecoiled sheath100 is minimized (e.g., during the winding process) to increase the mechanical interaction between adjacent coils. In one embodiment, thecoiled sheath100 is constructed as a closed pitch coil with a preload representative of a compressive force holding the individual coils in close contact with one another. The preload applied in this embodiment is preferably selected to reduce an angular distance between the individual coils to the maximum extent which still retains the degree of flexibility required of the coiledsheath100 to enable the traversing of tortuous paths in the lumen into which it is to be inserted and to allow for controlled rotation of the coiledsheath100.
• It is noted that, in some instances, it may not be desirable to employ a closed pitch coil with a preload. Rotational movement may still be achieved in these instances after inducing an initial amount of deformation. This deformation may be achieved as a result of torsional input requiring the individuals coils of the coiledsheath100 to deform until mechanical interaction between each of the adjacent coils is achieved. Alternatively, thecoiled sheath100 may be deformed along a curved path, wherein the deformation may cause the individual coils to mechanically interact with another.
• The wave pattern of the wire or ribbon of the embodiment ofFIG. 1 may be varied in a number of different ways to achieve the desired balance between rotational (torsional) stiffness and longitudinal flexibility. For example, the wavelength of the wave pattern may be reduced so that a greater number of waves may be accommodated in each turn of the coil. The increased number of waves per unit length of wire increases the overall rigidity of the coiledsheath100 by increasing frictional forces between the individual turns of the coiledsheath100. The frictional force between each of the individual turns of the coil may also be increased by knurling the contacting surfaces of the turns or otherwise roughening the contacting surfaces of the turns. Those skilled in the art will understand that sanded and rough contacting surfaces increases the mechanical interaction between the turns of thecoiled sheath100.
• As would be understood by those skilled in the art, any of a wide variety of patterns of variations in the shape of the wire along its length may be employed to obtain the desired mechanical interaction between adjacent turns thereof while retaining a desired level of longitudinal flexibility. For example as shown inFIG. 2, thecoiled sheath200 of the present invention may form a first pattern on one side of the wire and a second pattern on the opposite side. A proximal side of the wire forming thecoiled sheath200 ofFIG. 2 extends along a wave pattern including a plurality of substantiallytrapezoidal projections210 separated from one another by a corresponding plurality of substantiallytrapezoidal troughs212. The distal side of the wire includes a plurality of substantiallystraight portions214 substantially parallel to the helical path of thecoiled sheath200 separated from one another by a plurality of substantiallyrectangular projections216. Therectangular projections216 are preferably separated from one another along the length of the wire by a distance substantially equal to a distance between the substantiallytrapezoidal troughs212 so that each of theprojections216 is received within acorresponding trough212 on an adjacent turn of thecoiled sheath200 while each of thetrapezoidal projections210 is received in a corresponding space between consecutive projections216 (i.e., along a corresponding straight portion214) of an adjacent turn of thecoiled sheath200. Those skilled in the art will recognize that the patterns on opposite sides of the wire may comprise any combination of complementary mating patterns on the abutting faces of adjacent turns of the coiledsheath200 to establish the mechanical interference required to provide the desired transmission of torque along the length of thesheath200. Furthermore, the heights and width of thetroughs212 andprojections216 may be selected to improve the performance of the coiledsheath200.
• It is noted that, although the exemplary embodiments are shown with substantially sharp edges, in practice the coiledsheaths100 and200 may comprise curved surfaces based on gear design principles for the interaction between coils. Employing such curves in this embodiment allows the effective transmission of torsional and rotational forces therealong the length of the coiledsheaths100 and200 while also allowing for self-alignment of the features during the winding process or while the coil is under load subsequent to the winding process. For example, the design may be selected to allow edges of adjacent turns of the ribbon or wire to interlock so that these adjacent turns of the coiledsheath100 and200 are pulled together as a toque is applied at one end.
• As shown inFIG. 3, acoiled sheath300 according to an alternate embodiment of the present invention is formed from a bound wire302 (or ribbon) with substantially smooth surfaces (i.e., without interlocking protrusions and indentations along the axis). Rather, progressive stamping or any other similar known technique may be used to form in the wire302 a plurality ofslots330 oriented so that, when thewire302 is bent into a helical coil, theslots330 extend substantially parallel to a longitudinal axis L of the coiledsheath300. In addition, a plurality oftabs340 project radially away from the longitudinal axis L are formed in alignment with theslots330 by, for example, bending radially outward portions of thewire302 stamped out of theslots330. Thewire302 is then bound into a helical coil with portions ofadjacent turns304 of the coil overlapping one another so that eachtab340 engages theslot330 of anadjacent turn304. As can be seen inFIG. 3, thewire302 is preferably bent into a helical shape with a slight angular cast along the thickness of thewire302 so that each turn of the coil is generally conical. This permits the narroweddistal end308 of afirst turn304 to fit within the enlargedproximal end306 of theadjacent turn304 so that thetab340 of thefirst turn304 can be received within theslot340 of theadjacent turn304. Those skilled in the art will understand that the direction of the cast may be reversed so that the distal ends of theturns304 are enlarged while the proximal ends306 are narrowed. In addition, those skilled in the art will understand that the extent of the projection of thetabs340 beyond the radiallyouter surface310 of eachturn304 is preferably selected so that, when thecoiled sheath300 is bent to the maximum extent permitted, the end of each of thetabs340 remains within thecorresponding slot330. The angle of the cast of thewire302 is preferably selected relative to the size of thetabs340 so that thetabs340 do not project beyond an outer profile of the enlarged ends306 of the turns of the coiledsheath300.
• Thetabs340 preventadjacent turns304 from rotating relative to one another, transmitting torque applied to one end of the coiledsheath300 to the other end thereof At the same time, the length of each of theslots330 along the longitudinal axis L is preferably selected to be greater than a length of thecorresponding tab340 along the longitudinal axis L by an amount required to impart a desired degree of longitudinal flexibility to the coiledsheath300. As would be understood by those skilled in the art, the width of each of the tabs340 (i.e., thickness in a direction substantially perpendicular to the longitudinal axis) is selected relative to the width of thecorresponding slot330 to permit thetabs340 to slide freely, or with a desired frictional resistance, therewithin. Thus, the length of theslot330 along which each of thetabs340 may slide dictates the permitted degree of bending of the coiled sheath300 (i.e., the minimum radius around which thesheath300 may be bent) along the longitudinal axis while the frictional engagement of thetabs340 within theslots330 dictates the force required to achieve the desired bending. Those skilled in the art will understand that this permitted degree of bending and/or the force required for bending may be constant along the length of the coiledsheath300 or may be varied therealong by varying the dimensions of thetabs340 and the correspondingslots330 to alter the distance along which thevarious tabs340 may slide as well as the resistance to this sliding.
• The embodiment ofFIG. 3 may also be modified in a number of ways without deviating from the scope of the invention. For example, one or both longitudinal surfaces of thewire302 may be knurled to roughen the surface and increase the frictional force between each of the turns of the coiledsheath300. In another embodiment, the flat surface of thewire302 may be rolled and/or stamped to form ribs or small dents and/or protrusions. Since thewire302 is wound in an overlapping manner, this increases the frictional force and mechanical interaction between theturns304. To this end,tabs340 may be constructed as folds (not shown) in the surface of thewire302. An external edge of each of the folds (not shown) protruding into aslot330 may act as a tab in this embodiment.
• As shown inFIG. 4, acoiled sheath300′ according to yet another embodiment of the invention is substantially similar to thecoil300 ofFIG. 3 except that thecoil300′ includestabs340′ bent radially inward toward the longitudinal axis L′. In this embodiment, each of thetabs340′ is formed near theenlarged end306 of theturn304 of the coil over aslot330′ of the reduceddiameter portion308′ of anadjacent turn304 received therewithin. With this arrangement, theouter surface310′ of the coiledsheath300′ remains substantially smooth minimizing the possibility of trauma and minimizing the required thickness of an outer sheath over thecoiled sheath300 and possibly eliminating the need for such an outer sheath altogether.
• Furthermore, it is noted that although the present embodiment is described usingrectangular tabs340,340′, any of a number of differently shaped indentations and projections may be employed without deviating from the scope of the present invention. For example, dimples, burrs, or other features may be used in place of discrete tabs. It is noted that the inherent concept of the present embodiment is the engagement of a protrusion with a slot formed on an adjacent turn of a wire to prevent relative rotation between adjacent turns of a coil.
• It is further noted that the present invention may be modified in a host of manners that may increase the friction force and mechanical interaction between each of the individual coils of the coiled sheath without deviating from the spirit and scope of the present invention.
• The embodiments ofFIGS. 1-4 have been described with respect to a single ribbon or wire wound into a helix. Those skilled in the art will understand that the single wire of the above-described embodiments may be replaced by 2 or more wires would together in a coil so long as the turns of the various wires mechanically interact with adjacent turns of wire in the manner described above to prevent relative rotation therebetween. For example, the distal side of a first longitudinal length of wire may interact mechanically with the proximal side of a longitudinal length of a second wire and vice versa along their lengths with each of the wires forming alternating ones of the turns of the coiled sheath. In another example, a first wire containing a plurality of tabs similar to those described above in regard toFIG. 3 may be wound within or around a second wire including a corresponding set of slots as described above. In yet another example, a single plastic ribbon or strip may be coiled into a helical shape. Such an embodiment may offer particular advantages when employed with direct drive endoscopic systems.
• FIGS. 5-6 depict a formingdie400 according to an exemplary embodiment of the present invention. The formingdie400 may be used to shape the wire of the coiledsheath100 or that of another ribbon or wire structure. Specifically, as described with respect to earlier embodiments, the wire or ribbon must be formed with features that interlock with one another when the wire or ribbon is coiled. The forming die comprises first and second formingwheels402,404 configured to engage one another. The first formingwheel402 comprises a pair oflateral wheels406,408 encasing amedial wheel410, thelateral wheels406,408 having a greater diameter than themedial wheel410. Themedial wheel410 has a smooth outer circumference and is connected to thelateral wheels406,408 byangled surfaces412. Specifically, theangled surfaces412 link the smaller diametermedial wheel410 with the increaseddiameter lateral wheels406,408. The second formingwheel404 also comprises a pair oflateral wheels414,416 connected by amedial wheel418. Themedial wheel418 has a greater diameter than thelateral wheels414,416, a diameter thereof being selected to permit apredetermined clearance420 between the first and second formingwheels402,404 when themedial wheel418 contacts themedial wheel410. Specifically, theclearance420 is configured to permit a wire such as thewire40 to be inserted therethrough with a substantial friction fit sufficient to cause a knurling or keying thereof as thewire40 is moved in the direction A as would be understood by those skilled in the art.
• The first and second formingwheels402,404 may be held together within a housing (not shown). The housing (not shown) may be configured to change a relationship of the first andsecond wheels402,404 relative to one another as needed (i.e., to change a size of theclearance420 depending on a thickness of thewire40 or a desired pressure to be applied thereto). In another embodiment of the present invention, the first and second formingwheels402,404 may be replaced by a single component permitting the insertion of a wire into a clearance area in substantially the same manner described above. In yet another embodiment, laterally separated sides of the wire may be formed by separate forming dies, which may be linked to one another via a gear system. Thus, as the wire is moved through the gear system, each side wall travels through a separate forming die to be shaped. In yet another embodiment, edges of the wire may be laser cut or the wire may undergo progressive stamping to affect a shape thereof, as those skilled in the art will understand. It is further noted that any combination and modification of the aforementioned embodiment may be employed to permit the keying of materials of different sizes and densities.
• Those skilled in the art will understand that the described exemplary embodiments of the present invention may be altered without departing from the spirit or scope of the invention. Thus, it is to be understood that these embodiments have been described in an exemplary manner and are not intended to limit the scope of the invention which is intended to cover all modifications and variations of this invention that come within the scope of the appended claims and their equivalents.

Claims (25)

1. A coil for transmitting torque, comprising:

a wire having a longitudinal axis and first and second longitudinal edges extending along the longitudinal axis, wherein the first longitudinal edge is formed with a first pattern and the second longitudinal edge is formed with a second pattern complementary to the first pattern, the first and second patterns being configured to interlock with one another when the wire is wound into a helical shape.

2. The coil according toclaim 1, wherein surface features on the first longitudinal edge of the wire are separated from corresponding features with which they are to mate on the second longitudinal edge by a distance along a path around which the coil is wound corresponding to a complete revolution of the coil about the longitudinal axis of the coil.

3. The coil according toclaim 2, wherein the first pattern is a first wave pattern and the second pattern is a second complementary wave pattern interlocking with the first wave pattern when the wire is wound into the coil.

4. The coil according toclaim 3, wherein the first wave pattern includes a plurality of first projections and first indentations, the first projections being sized to be received within corresponding second indentations in the second wave pattern and wherein the first indentations are sized to receive corresponding second projections of the second wave pattern.

5. The coil according toclaim 2, wherein the first pattern includes a plurality of trapezoidal protrusions and wherein the second pattern includes a pattern of complementarily sized substantially rectangular recesses.

6. The coil according toclaim 5, wherein the trapezoidal protrusions and substantially rectangular recesses comprise smoothed edges.

7. The coil according toclaim 2, wherein the wire is a flat strip, a width of the flat strip being substantially uniform along the length of the coil.

8. The coil according toclaim 1, wherein turns of the wound wire form a closed pitch coil.

9. The coil according toclaim 1, wherein the coil is wound with a preload greater than zero.

10. The coil according toclaim 2, wherein the first and second patterns are formed on the wire prior to winding the wire into the coil.

11. The coil according toclaim 9, wherein the first and second patterns are formed on the flat strip via one of progressive stamping and continuous knurling.

12. The coil according toclaim 1, wherein adjacent turns of the coil are wound in close proximity with one another to ensure mechanical interaction therebetween.

13. A coil for transmitting torque, comprising:

a wire having a longitudinal axis and first and second longitudinal planar surfaces extending along the longitudinal axis, wherein the first planar surface is formed with a first pattern and the second planar surface is formed with a second pattern complementary to the first pattern, the first and second patterns being configured to interlock with one another when the wire is wound into a helical shape.

14. The coil according toclaim 13, wherein surface features on the first planar surface of the wire are separated from corresponding features with which they are to mate on the second planar surface by a distance along a path around which the coil is wound corresponding to a complete revolution of the coil about the longitudinal axis of the coil.

15. The coil according toclaim 13, wherein first and second adjacent turns of the coil axially overlap over one another and wherein the first turn includes a projection slidably received in an aperture formed on the second turn to prevent rotation of the first and second turns relative to one another about a longitudinal axis of the elongated body.

16. The coil according toclaim 15, wherein portions of the turns overlapping adjacent turns include one of knurled and roughed edges to increase a mechanical interaction therebetween.

17. The coil according toclaim 14, wherein a first side of the flat strip includes a plurality of tabs and a second side of the flat strip includes a plurality of apertures spaced along the wire by a distance selected so that, when wound into a coil, each of the tabs is slidably received within a corresponding one of the apertures.

18. The coil according toclaim 17, wherein a difference between a length of the apertures and a length of the tabs is selected to achieve a desired minimum bending radius of the coil.

19. The coil according toclaim 17, wherein the wire is wound so that the tabs extend radially outward from a longitudinal axis of the elongated body and wherein the wire is wound into a coil including substantially conical individual turns with the tabs formed on reduced diameter portions of the turns received within enlarged diameter portions of adjacent turns so that each tab extends radially outward into a corresponding aperture.

20. The coil according toclaim 13, further comprising a second wound element interspersed with the first wound element within the coil.

21. The coil according toclaim 20, wherein adjacent surfaces of the first and second wound elements mechanically engage one another to prevent relative rotation between adjacent turns of the coil.

22. A medical device, comprising:

a coil configured to transmit torque comprising a wire having a longitudinal axis and first and second longitudinal edges extending along the longitudinal axis, wherein the first longitudinal edge is formed with a first pattern and the second longitudinal edge is formed with a second pattern complementary to the first pattern, the first and second patterns being configured to interlock with one another when the wire is wound into a helical shape, the coil comprising an elongated body defining an internal lumen configured to permit insertion of a medical instrument therethrough.

23. A medical device for forming a flat strip, comprising:

a first forming wheel comprising a first radially abutting portion; and

a second forming wheel comprising a first radial recess portion configured for engagement with the first radially abutting portion so that, when the first and second forming wheels are brought into an engaged configuration, a clearance is provided between, the clearance permitting insertion of the flat strip therethrough with a substantial friction fit to cause a desired forming thereof.

24. The medical device ofclaim 23, further comprising:

a housing configured to retain the first forming wheel and the second forming wheel in the engaged configuration relative to one another.

25. The medical device ofclaim 23, wherein the first and second forming wheels are selectively positionable to change a size of the clearance to accommodate a predetermined size of the flat strip.

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