Patent Publication Number: US-10765434-B2

Title: Biased-track revolver loading surgical clip applier

Description:
BACKGROUND 
     Minimally invasive surgical (MIS) instruments are often preferred over traditional open surgical devices due to reduced post-operative recovery time and minimal scarring. Endoscopic surgery is one type of MIS procedure in which an elongate flexible shaft is introduced into the body of a patient through a natural orifice. Laparoscopic surgery is another type of MIS procedure in which one or more small incisions are formed in the abdomen of a patient and a trocar is inserted through the incision to form a pathway that provides access to the abdominal cavity. Through the trocar (i.e., a trocar cannula), a variety of instruments and surgical tools can be introduced into the abdominal cavity to engage and/or treat tissue in a number of ways to achieve a diagnostic or therapeutic effect. 
     One surgical instrument commonly used with a trocar is a surgical clip applier, which can be used to ligate blood vessels, ducts, shunts, or portions of body tissue during surgery. Traditional surgical clip appliers have a handle and an elongate shaft extending from the handle. A pair of movable opposed jaws is positioned at the end of the elongate shaft for holding and forming a surgical clip or “ligation clip” therebetween. In operation, a user (e.g., a surgeon or clinician) positions the jaws around the vessel or duct and squeezes a trigger on the handle to close the jaws and thereby collapse the surgical clip over the vessel. 
     More recently, however, robotic systems have been developed to assist in MIS procedures. Instead of directly engaging a surgical instrument, users are now able to manipulate and engage surgical instruments via an electronic interface communicatively coupled to a robotic manipulator. With the advances of robotic surgery, a user need not even be in the operating room with the patient during the surgery. 
     Robotic surgical systems are also now capable of utilizing robotically controlled clip appliers. Such clip appliers include features for robotically feeding and forming surgical clips. Advances and improvements to the methods and devices for applying surgical clips to vessels, ducts, shunts, etc. is continuously in demand to make the process more efficient and safe. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The following figures are included to illustrate certain aspects of the present disclosure, and should not be viewed as exclusive embodiments. The subject matter disclosed is capable of considerable modifications, alterations, combinations, and equivalents in form and function, without departing from the scope of this disclosure. 
         FIG. 1  is a block diagram of an example robotic surgical system that may incorporate some or all of the principles of the present disclosure. 
         FIG. 2  is an isometric top view of an example surgical tool that may incorporate some or all of the principles of the present disclosure. 
         FIG. 3  is an isometric bottom view of the surgical tool of  FIG. 2 . 
         FIG. 4  is an exploded view of the elongate shaft and the end effector of the surgical tool of  FIGS. 2 and 3 . 
         FIG. 5  is an exposed isometric view of the surgical tool of  FIG. 2 . 
         FIG. 6  is a side view of an example surgical tool that may incorporate some or all of the principles of the present disclosure. 
         FIG. 7  illustrates potential degrees of freedom in which the wrist of  FIG. 1  may be able to articulate (pivot). 
         FIG. 8  is an enlarged isometric view of the distal end of the surgical tool of  FIG. 6 . 
         FIG. 9  is a bottom view of the drive housing of the surgical tool of  FIG. 6 . 
         FIG. 10  is an isometric exposed view of the interior of the drive housing of the surgical tool of  FIG. 6 . 
         FIG. 11  is an exposed, partial cross-sectional side view of an example end effector. 
         FIG. 12  is an enlarged isometric view of the revolver of the end effector of  FIG. 11 . 
         FIG. 13  is an isometric exposed view of the interior of the drive housing of the surgical tool of  FIG. 11 . 
         FIGS. 14A-14E  are progressive exposed, partial isometric views of the end effector of  FIG. 11  during example operation. 
         FIG. 15  is an enlarged isometric view of another example end effector. 
         FIG. 16  is an exposed, partial cross-sectional side view of the revolver of the end effector of  FIG. 15 . 
         FIGS. 17A-17B  are progressive exposed, partial isometric views of the end effector of  FIG. 15  during an example reloading operation. 
     
    
    
     DETAILED DESCRIPTION 
     The present disclosure is related to surgical systems and, more particularly, to surgical clip appliers with rotating clip cartridges and feeder bars that selectively feed surgical clips between opposed jaw members. 
     Embodiments discussed herein describe improvements to clip applier end effectors. Some end effector embodiments described herein include a body having a clip revolver that is rotatably coupled within the body near its distal end and containing one or more surgical clips. An indexer may be slidingly coupled within the body to engage the revolver and cause rotation thereof, and a feeder bar may be arranged within the body and extend through the revolver and the indexer to feed surgical clips distally. The body may include a rotation region that defines a plurality of rails, and a biasing member may be arranged within the rotation region such that the revolver is constrained between the biasing member and the rails. A first cam surface may be arranged at a distal end of the indexer and a second cam surface that corresponds with the first cam surface may be arranged at a proximal end of the revolver. In example operation, the indexer is actuated in a distal direction until the first cam surface thereof engages the second cam surface of the revolver, which pushes the revolver in a distal direction until it clears the rails within the rotation region after which the biasing member causes the revolver to rotate into position where one of the surgical clips is in alignment with the feeder bar. 
     Other end effector embodiments disclosed herein describe an elongate body, a revolver that holds a plurality of surgical clips, a pusher that articulates within the revolver to selectively engage each surgical clip, and a torsion member that is arranged around the revolver and secured at one end to the elongate body. The revolver may include a plurality of grooves that each align with one of the surgical clips, and the pusher may be configured to travel (traverse) within such grooves thereby constraining rotation of the revolver. The torsion member may exert a force on the revolver and thus urge rotation of the revolver. Rotation of the revolver via the torsion member may be generally inhibited when the pusher is positioned in a distal region of the grooves. However, as the pusher travels proximally, the grooves may each open into a channel that leads and connects to another of the grooves such that stored mechanical energy in the torsion member may be released to cause revolver rotation. Thus, as the pusher travels proximate to the channels, the torsion member may rotate the revolver such that the pusher travels into the channel, and then into another of the grooves to thereby index the revolver. 
     In contrast to conventional clip appliers, the revolver that holds the surgical clips may be arranged at a location distal to an articulable wrist joint, which helps mitigate obstructions that would otherwise impede the surgical clips having to traverse the wrist. Moreover, the presently described revolver embodiments may be configured to store surgical clips arrayed in a nested helically arrayed arrangement, which facilitates storage of a larger number of clips resulting in the tools needing to be reloaded or replaced less often during operation. 
       FIG. 1  is a block diagram of an example robotic surgical system  100  that may incorporate some or all of the principles of the present disclosure. As illustrated, the system  100  can include at least one master controller  102   a  and at least one arm cart  104 . The arm cart  104  may be mechanically and/or electrically coupled to a robotic manipulator and, more particularly, to one or more robotic arms  106  or “tool drivers”. Each robotic arm  106  may include and otherwise provide a location for mounting one or more surgical tools or instruments  108  for performing various surgical tasks on a patient  110 . Operation of the robotic arms  106  and instruments  108  may be directed by a clinician  112   a  (e.g., a surgeon) from the master controller  102   a.    
     In some embodiments, a second master controller  102   b  (shown in dashed lines) operated by a second clinician  112   b  may also direct operation of the robotic arms  106  and instruments  108  in conjunction with the first clinician  112   a . In such embodiments, for example, each clinician  102   a,b  may control different robotic arms  106  or, in some cases, complete control of the robotic arms  106  may be passed between the clinicians  102   a,b . In some embodiments, additional arm carts (not shown) having additional robotic arms (not shown) may be utilized during surgery on a patient  110 , and these additional robotic arms may be controlled by one or more of the master controllers  102   a,b.    
     The arm cart  104  and the master controllers  102   a,b  may be in communication with one another via a communications link  114 , which may be any type of wired or wireless telecommunications means configured to carry a variety of communication signals (e.g., electrical, optical, infrared, etc.) according to any communications protocol. 
     The master controllers  102   a,b  generally include one or more physical controllers that can be grasped by the clinicians  112   a,b  and manipulated in space while the surgeon views the procedure via a stereo display. The physical controllers generally comprise manual input devices movable in multiple degrees of freedom, and which often include an actuatable handle for actuating the surgical instrument(s)  108 , for example, for opening and closing opposing jaws, applying an electrical potential (current) to an electrode, or the like. The master controllers  102   a,b  can also include an optional feedback meter viewable by the clinicians  112   a,b  via a display to provide a visual indication of various surgical instrument metrics, such as the amount of force being applied to the surgical instrument (i.e., a cutting instrument or dynamic clamping member). 
     Example implementations of robotic surgical systems, such as the system  100 , are disclosed in U.S. Pat. No. 7,524,320, the contents of which are incorporated herein by reference. The various particularities of such devices will not be described in detail herein beyond that which may be necessary to understand the various embodiments and forms of the various embodiments of robotic surgery apparatus, systems, and methods disclosed herein. 
       FIG. 2  is an isometric top view of an example surgical tool  200  that may incorporate some or all of the principles of the present disclosure. The surgical tool  200  may be the same as or similar to the surgical instrument(s)  108  of  FIG. 1  and, therefore, may be used in conjunction with the robotic surgical system  100  of  FIG. 1 . Accordingly, the surgical tool  200  may be designed to be releasably coupled to a robotic arm  106  ( FIG. 1 ) of a robotic manipulator of the robotic surgical system  100 . Full detail and operational description of the surgical tool  200  is provided in U.S. Patent Pub. 2016/0287252, entitled “Clip Applier Adapted for Use with a Surgical Robot,” the contents of which are hereby incorporated by reference in their entirety. 
     While the surgical tool  200  is described herein with reference to a robotic surgical system, it is noted that the principles of the present disclosure are equally applicable to non-robotic surgical tools or, more specifically, manually operated surgical tools. Accordingly, the discussion provided herein relating to robotic surgical systems merely encompasses one example application of the presently disclosed inventive concepts. 
     As illustrated, the surgical tool  200  can include an elongate shaft  202 , an end effector  204  coupled to the distal end of the shaft  202 , and a drive housing  206  coupled to the proximal end of the shaft  202 . The terms “proximal” and “distal” are defined herein relative to a robotic surgical system having an interface configured to mechanically and electrically couple the surgical tool  200  (e.g., the drive housing  206 ) to a robotic manipulator. The term “proximal” refers to the position of an element closer to the robotic manipulator and the term “distal” refers to the position of an element closer to the end effector  204  and thus further away from the robotic manipulator. Moreover, the use of directional terms such as above, below, upper, lower, upward, downward, left, right, and the like are used in relation to the illustrative embodiments as they are depicted in the figures, the upward or upper direction being toward the top of the corresponding figure and the downward or lower direction being toward the bottom of the corresponding figure. 
     In applications where the surgical tool  200  is used in conjunction with a robotic surgical system (e.g., system  100  of  FIG. 1 ), the drive housing  206  can include a tool mounting portion  208  designed with features that releasably couple the surgical tool  200  to a robotic arm (e.g., the robotic arms  106  or “tool drivers” of  FIG. 1 ) of a robotic manipulator. The tool mounting portion  208  may releasably attach (couple) the drive housing  206  to a tool driver in a variety of ways, such as by clamping thereto, clipping thereto, or slidably mating therewith. In some embodiments, the tool mounting portion  208  may include an array of electrical connecting pins, which may be coupled to an electrical connection on the mounting surface of the tool driver. While the tool mounting portion  208  is described herein with reference to mechanical, electrical, and magnetic coupling elements, it should be understood that a wide variety of telemetry modalities might be used, including infrared, inductive coupling, or the like. 
       FIG. 3  is an isometric bottom view of the surgical tool  200 . The surgical tool  200  further includes an interface  302  that mechanically and electrically couples the tool mounting portion  208  to a robotic manipulator. In various embodiments, the tool mounting portion  208  includes a tool mounting plate  304  that operably supports a plurality of drive inputs, shown as a first drive input  306   a , a second drive input  306   b , and a third drive input  306   c . While only three drive inputs  306   a - c  are shown in  FIG. 3 , more or less than three may be employed, without departing from the scope of the disclosure. 
     In the illustrated embodiment, each drive input  306   a - c  comprises a rotatable disc configured to align with and couple to a corresponding input actuator (not shown) of a given tool driver. Moreover, each drive input  306   a - c  provides or defines one or more surface features  308  configured to align with mating surface features provided on the corresponding input actuator. The surface features  308  can include, for example, various protrusions and/or indentations that facilitate a mating engagement. 
       FIG. 4  is an exploded view of one example of the elongate shaft  202  and the end effector  204  of the surgical tool  200  of  FIGS. 2 and 3 , according to one or more embodiments. As illustrated, the shaft  202  includes an outer tube  402  that houses the various components of the shaft  202 , which can include a jaw retaining assembly  404 . The jaw retaining assembly  404  includes a jaw retainer shaft  406  with a clip track  408  and a push rod channel  410  formed thereon. The end effector  204  includes opposing jaws  412  that are configured to mate to a distal end of the clip track  408 . 
     The shaft  202  also includes a clip advancing assembly, which, in one example embodiment, can include a feeder shoe  414  adapted to be slidably disposed within the clip track  408 . The feeder shoe  414  is designed to advance a series of clips  416  positioned within the clip track  408 , and a feedbar  418  is adapted to drive the feeder shoe  414  through the clip track  408 . An advancer assembly  420  is adapted to mate to a distal end of the feedbar  418  for advancing a distal-most clip into the jaws  412 . 
     The shaft  202  furthers include a clip forming or camming assembly operable to collapse the jaws  412  and thereby crimp (crush) a surgical clip  416  positioned between (interposing) the jaws  412 . The camming assembly includes a cam  422  that slidably mates to the jaws  412 , and a push rod  424  that moves the cam  422  relative to the jaws  412  to collapse the jaws  412 . A tissue stop  426  can mate to a distal end of the clip track  408  to help position the jaws  412  relative to a surgical site. 
     The jaw retainer shaft  406  is extendable within and couples to the outer tube  402  at a proximal end  428   a , and its distal end  428   b  is adapted to mate with the jaws  412 . The push rod channel  410  formed on the jaw retainer shaft  406  may be configured to slidably receive the push rod  424 , which is used to advance the cam  422  over the jaws  412 . The clip track  408  extends distally beyond the distal end  428   b  of the jaw retainer shaft  406  to allow a distal end of the clip track  408  to be substantially aligned with the jaws  412 . 
     The clip track  408  can include several openings  430  formed therein for receiving an upper or “superior” tang  432   a  formed on the feeder shoe  414  adapted to be disposed within the clip track  408 . The clip track  408  can also include a stop tang  434  formed thereon that is effective to be engaged by a corresponding stop tang formed on the feeder shoe  414  to prevent movement of the feeder shoe  414  beyond a distal-most position. To facilitate proximal-movement of the feeder shoe  414  within the clip track  408 , the feeder shoe  414  can also include a lower or “inferior” tang  432   b  formed on the underside thereof for allowing the feeder shoe  414  to be engaged by the feedbar  418  as the feedbar  418  is moved distally. In use, each time the feedbar  418  is moved distally, a detent formed in the feedbar  418  engages the inferior tang  432   b  and moves the feeder shoe  414  distally a predetermined distance within the clip track  408 . The feedbar  418  can then be moved proximally to return to its initial position, and the angle of the inferior tang  432   b  allows the inferior tang  432   b  to slide into the next detent formed in the feedbar  418 . 
     The jaws  412  include first and second opposed jaw members that are movable (collapsible) relative to one another and are configured to receive a surgical clip from the series of clips  416  therebetween. The jaw members can each include a groove formed on opposed inner surfaces thereof for receiving the legs of a surgical clip  416  in alignment with the jaw members. In the illustrated embodiment, the jaw members are biased to an open position and a force is required to urge the jaw members toward one another to crimp the interposing clip  416 . The jaw members can also each include a cam track formed thereon for allowing the cam  422  to slidably engage and move the jaw members toward one another. A proximal end  436   a  of the cam  422  is matable with a distal end  438   a  of the push rod  424 , and a distal end  436   b  of the cam  422  is adapted to engage and actuate the jaws  412 . The proximal end  438   b  of the push rod  424  is matable with a closure link assembly associated with the drive housing  206  for moving the push rod  424  and the cam  422  relative to the jaws  412 . 
     The distal end  436   b  of the cam  422  includes a camming channel or tapering recess formed therein for slidably receiving corresponding cam tracks provided by the jaw members. In operation, the cam  422  is advanced from a proximal position, in which the jaw members are spaced apart from one another, to a distal position, where the jaw members are collapsed to a closed position. As the cam  422  is advanced over the jaw members, the tapering recess at the distal end  436   b  serves to push the jaw members toward one another, thereby crimping a surgical clip  416  disposed therebetween. 
       FIG. 5  is an exposed isometric view of the surgical tool  200  of  FIG. 2 , according to one or more embodiments. The shroud or covering of the drive housing  206  has been removed to reveal the internal component parts. As illustrated, the surgical tool  200  may include a first drive gear  502   a , a second drive gear  502   b , and a third drive gear  502   c . The first drive gear  502   a  may be operatively coupled to (or extend from) the first drive input  306   a  ( FIG. 3 ) such that actuation of the first drive input  306   a  correspondingly rotates the first drive gear  502   a . Similarly, the second and third drive gears  502   b,c  may be operatively coupled to (or extend from) the second and third drive inputs  306   b,c  ( FIG. 3 ), respectively, such that actuation of the second and third drive inputs  306   b,c  correspondingly rotates the second and third drive gears  502   b,c , respectively. 
     The first drive gear  502   a  may be configured to intermesh with a first driven gear  504   a , which is operatively coupled to the shaft  202 . In the illustrated embodiment, the driven gear  504   a  comprises a helical gear. In operation, rotation of the first drive gear  502   a  about a first axis correspondingly rotates the first driven gear  504   a  about a second axis orthogonal to the first axis to control rotation of the shaft  202  in clockwise and counter-clockwise directions based on the rotational direction of the first drive gear  502   a.    
     The second drive gear  502   b  may be configured to intermesh with a second driven gear  504   b  (partially visible in  FIG. 5 ), and the third drive gear  502   c  may be configured to intermesh with a third driven gear  504   c . In the illustrated embodiment, the second and third drive and driven gears  502   b,c ,  504   b,c  comprise corresponding rack and pinion interfaces, where the driven gears  504   b,c  comprise the rack and the drive gears  502   b,c  comprise the pinion. Independent rotation of the second and third drive gears  502   b,c  will cause the second and third driven gears  504   b,c , respectively, to translate linearly relative to (independent of) one another. 
     In at least one embodiment, actuation (rotation) of the third drive gear  502   c  will result in a surgical clip  416  ( FIG. 4 ) being fed into the jaws  412 . More particularly, the third driven gear  504   c  may be operatively coupled to the feedbar  418  ( FIG. 4 ) and, upon rotation of the third drive gear  502   c  in a first angular direction, the third driven gear  504   c  will advance distally and correspondingly advance the feedbar  418  a sufficient distance to fully advance a surgical clip into the jaws  412 . Rotation of the third drive gear  502   c  may be precisely controlled by an electrical and software interface to deliver the exact linear travel to the third driven gear  504   c  necessary to feed a clip  416  into the jaws  412 . 
     Upon delivery of a clip into the jaws  412 , or after a predetermined amount of rotation of the third drive gear  502   c , rotation of the third drive gear  502   c  is reversed in a second angular direction to move the third driven gear  504   c  linearly in a proximal direction, which correspondingly moves the feedbar  418  proximally. This process may be repeated several times to accommodate a predetermined number of clips residing in the shaft  202 . 
     Actuation of the second drive gear  502   b  causes the jaws  412  to close or collapse to crimp a surgical clip. More particularly, the second driven gear  504   b  may be coupled to the proximal end  438   b  ( FIG. 4 ) of the push rod  424  ( FIG. 4 ) and, upon actuation of the second drive gear  502   b  in a first angular direction, the second driven gear  504   b  will be advanced linearly in a distal direction and correspondingly drive the push rod  424  distally, which drives the cam  422  over the jaws  412  to collapse the jaw members and crimp a surgical clip positioned in the jaws  412 . Once a surgical clip is successfully deployed, rotation of the second drive gear  502   b  is reversed in the opposite angular direction to move the second driven gear  504   b  in a proximal direction, which correspondingly moves the push rod  424  and the cam  422  proximally and permits the jaws  412  to open once again. 
     The processes of delivering a surgical clip into the jaws  412  and collapsing the jaws  412  to crimp the surgical clip are not limited to the actuation mechanisms and structures described herein. In alternative embodiments, for example, the second and third driven gears  504   b,c  may instead comprise capstan pulleys configured to route and translate drive cables within the shaft  202 . In such embodiments, the drive cables may be operatively coupled to one or more lead screws or other types of rotating members positioned within the shaft  202  near the distal end and capable of advancing the feedbar  418  to deliver a surgical clip into the jaws  412  and advancing the cam  422  to collapse the jaws  412  and crimp the surgical clip. 
       FIG. 6  is an isometric top view of another example surgical tool  600  that may incorporate some or all of the principles of the present disclosure. Similar to the surgical tool  200  of  FIG. 2 , the surgical tool  600  may be used in conjunction with the robotic surgical system  100  of  FIG. 1 . As illustrated, the surgical tool  600  includes an elongate shaft  602 , an end effector  604  positioned at the distal end of the shaft  602 , an articulating joint  606  (alternately referred to as a “articulable wrist joint”) that couples the end effector  604  to the distal end of the shaft  602 , and a drive housing  608  coupled to the proximal end of the shaft  602 . In some embodiments, the shaft  602 , and hence the end effector  604  coupled thereto, is configured to rotate about a longitudinal axis A 1 . 
     In the illustrated embodiment, the end effector  604  comprises a clip applier that includes opposing jaw members  610 ,  612  configured to collapse toward one another to crimp a surgical clip. The articulating joint  606  facilitates pivoting movement of the end effector  604  relative to the shaft  602  to position the end effector  604  at desired orientations and locations relative to a surgical site. The housing  608  includes (contains) various actuation mechanisms designed to control articulation at the articulating joint  606  and operation of the end effector  604 . 
       FIG. 7  illustrates the potential degrees of freedom in which the articulating joint  606  may be able to articulate (pivot). The degrees of freedom of the articulating joint  606  are represented by three translational variables (i.e., surge, heave, and sway), and by three rotational variables (i.e., Euler angles or roll, pitch, and yaw). The translational and rotational variables describe the position and orientation of a component of a surgical system (e.g., the end effector  604 ) with respect to a given reference Cartesian frame. As depicted in  FIG. 7 , “surge” refers to forward and backward translational movement, “heave” refers to translational movement up and down, and “sway” refers to translational movement left and right. With regard to the rotational terms, “roll” refers to tilting side to side, “pitch” refers to tilting forward and backward, and “yaw” refers to turning left and right. 
     The pivoting motion can include pitch movement about a first axis of the articulating joint  606  (e.g., X-axis), yaw movement about a second axis of the articulating joint  606  (e.g., Y-axis), and combinations thereof to allow for 360° rotational movement of the end effector  604  about the articulating joint  606 . In other applications, the pivoting motion can be limited to movement in a single plane, e.g., only pitch movement about the first axis of the articulating joint  606  or only yaw movement about the second axis of the articulating joint  606 , such that the end effector  604  moves only in a single plane. 
     Referring again to  FIG. 6 , the surgical tool  600  includes a plurality of drive cables (generally obscured in  FIG. 6 ) that form part of a cable driven motion system configured to facilitate operation and articulation (movement) of the end effector  604  relative to the shaft  602 . For example, selectively moving the drive cables can actuate the end effector  604  and thereby collapse the jaw members  610 ,  612  toward each other. Moreover, moving the drive cables can also move the end effector  604  between an unarticulated position and an articulated position. The end effector  604  is depicted in  FIG. 6  in the unarticulated position where a longitudinal axis A 2  of the end effector  604  is substantially aligned with the longitudinal axis A 1  of the shaft  602 , such that the end effector  604  is at a substantially zero angle relative to the shaft  602 . In the articulated position, the longitudinal axes A 1 , A 2  would be angularly offset from each other such that the end effector  604  is at a non-zero angle relative to the shaft  602 . 
       FIG. 8  is an enlarged isometric view of the distal end of the surgical tool  600  of  FIG. 6 . More specifically,  FIG. 8  depicts an enlarged and partially exploded view of the end effector  604  and the articulating joint  606 . The articulating joint  606  operatively couples the end effector  604  to the shaft  602 . To accomplish this, the articulating joint  606  includes a distal clevis  802   a , a proximal clevis  802   b , and a spacer  803  interposing the distal and proximal clevises  802   a,b . The end effector  604  is coupled to the distal clevis  802   a  and the distal clevis  802   a  is rotatably mounted to the spacer  803  at a first axle  804   a . The spacer  803  is rotatably mounted to the proximal clevis  802   b  at a second axle  804   b  and the proximal clevis  802   b  is coupled to a distal end  806  of the shaft  602 . 
     The articulating joint  606  provides a first pivot axis P 1  that extends through the first axle  804   a  and a second pivot axis P 2  that extends through the second axle  804   b . The first pivot axis P 1  is substantially perpendicular (orthogonal) to the longitudinal axis A 2  of the end effector  604 , and the second pivot axis P 2  is substantially perpendicular (orthogonal) to both the longitudinal axis A 2  and the first pivot axis P 1 . Movement about the first pivot axis P 1  provides “yaw” articulation of the end effector  604 , and movement about the second pivot axis P 2  provides “pitch” articulation of the end effector  604 . 
     A plurality of drive cables  808  extend longitudinally within the shaft  602  and pass through the wrist  106  to be operatively coupled to the end effector  604 . The drive cables  808  form part of the cable driven motion system briefly described above, and may be referred to and otherwise characterized as cables, bands, lines, cords, wires, ropes, strings, twisted strings, elongate members, etc. The drive cables  808  can be made from a variety of materials including, but not limited to, metal (e.g., tungsten, stainless steel, etc.) or a polymer. 
     The drive cables  808  extend proximally from the end effector  604  to the drive housing  608  ( FIG. 6 ) where they are operatively coupled to various actuation mechanisms or devices housed (contained) therein to facilitate longitudinal movement (translation) of the drive cables  808 . Selective actuation of the drive cables  808  causes the end effector  604  to articulate (pivot) relative to the shaft  602 . Moving a given drive cable  808  constitutes applying tension (i.e., pull force) to the given drive cable  808  in a proximal direction, which causes the given drive cable  808  to translate and thereby cause the end effector  604  to move (articulate) relative to the shaft  602 . 
     One or more actuation cables  810 , shown as first actuation cables  810   a  and second actuation cables  810   b , may also extend longitudinally within the shaft  602  and pass through the wrist  106  to be operatively coupled to the end effector  604 . The actuation cables  810   a,b  may be similar to the drive cables  808  and also form part of the cable driven motion system. Selectively actuating the actuation cables  810   a,b  causes the end effector  604  to actuate, such as collapsing the first and second jaw members  610 ,  612  to crimp a surgical clip (not shown). 
     More specifically, the actuation cables  810   a,b  may be operatively coupled to a cam  812  that is slidably engageable with the jaw members  610 ,  612 . One or more pulleys  814  may be used to receive and redirect the first actuation cables  810   a  for engagement with the cam  812 . Longitudinal movement of the first actuation cables  810   a  correspondingly moves the cam  812  distally relative to the jaw members  610 ,  612 . The distal end of the cam  812  includes a tapering recess or camming channel  816  formed therein for slidably receiving corresponding cam tracks  818  provided by the jaw members  610 ,  612 . As the cam  812  is advanced distally, the camming channel  816  pushes (collapses) the jaw members  610 ,  612  toward one another, thereby crimping a surgical clip (not shown) disposed therebetween. Actuation of the second actuation cables  810   b  (one shown) pulls the cam  812  proximally, thereby allowing the jaw members  610 ,  612  to open again to receive another surgical clip. 
     Although not expressly depicted in  FIG. 8 , an assembly including, for example, a feedbar, a feeder shoe, and a clip track may be included at or near the end effector  604  to facilitate feeding surgical clips into the jaw members  610 ,  612 . In some embodiments, the feedbar (or a connecting member) may be flexible and extend through the articulating joint  606 . 
       FIG. 9  is a bottom view of the drive housing  608 , according to one or more embodiments. As illustrated, the drive housing  608  may include a tool mounting interface  902  used to operatively couple the drive housing  608  to a tool driver of a robotic manipulator. The tool mounting interface  902  may mechanically, magnetically, and/or electrically couple the drive housing  608  to a tool driver. 
     As illustrated, the interface  902  includes and supports a plurality of drive inputs, shown as drive inputs  906   a ,  906   b ,  906   c ,  906   d ,  906   e , and  906   f . Each drive input  906   a - f  may comprise a rotatable disc configured to align with and couple to a corresponding input actuator (not shown) of a tool driver. Moreover, each drive input  906   a - f  provides or defines one or more surface features  908  configured to align with mating features provided on the corresponding input actuator. The surface features  908  can include, for example, various protrusions and/or indentations that facilitate a mating engagement. 
     In some embodiments, actuation of the first drive input  906   a  may control rotation of the elongate shaft  602  about its longitudinal axis A 1 . Depending on the rotational actuation of the first drive input  906   a , the elongate shaft  602  may be rotated clockwise or counter-clockwise. In some embodiments, selective actuation of the second and third drive inputs  906   b,c  may cause movement (axial translation) of the actuation cables  810   a,b  ( FIG. 8 ), which causes the cam  812  ( FIG. 8 ) to move and crimp a surgical clip, as generally described above. In some embodiments, actuation of the fourth drive input  906   d  feeds a surgical clip into the jaw members  610 ,  612  ( FIG. 8 ). In some embodiments, actuation of the fifth and sixth drive inputs  906   e,f  causes movement (axial translation) of the drive cables  808  ( FIG. 8 ), which results in articulation of the end effector  604 . Each of the drive inputs  906   a - f  may be actuated based on user inputs communicated to a tool driver coupled to the interface  902 , and the user inputs may be received via a computer system incorporated into the robotic surgical system. 
       FIG. 10  is an isometric exposed view of the interior of the drive housing  608 , according to one or more embodiments. Several component parts that may otherwise be contained within the drive housing  608  are not shown in  FIG. 10  to enable discussion of the depicted component parts. 
     As illustrated, the drive housing  608  contains a first capstan  1002   a , which is operatively coupled to or extends from the first drive input  906   a  ( FIG. 9 ) such that actuation of the first drive input  906   a  results in rotation of the first capstan  1002   a . A helical drive gear  1004  is coupled to or forms part of the first capstan  1002   a  and is configured to mesh and interact with a driven gear  1006  operatively coupled to the shaft  602  such that rotation of the driven gear  1006  correspondingly rotates the shaft  602 . Accordingly, rotation of the helical drive gear  1004  (via actuation of the first drive input  906   a  of  FIG. 9 ) will drive the driven gear  1006  and thereby control rotation of the elongate shaft  602  about the longitudinal axis A 1 . 
     The drive housing  608  also includes second and third capstans  1002   b  and  1002   c  operatively coupled to or extending from the second and third drive inputs  906   b,c  ( FIG. 9 ), respectively, such that actuation of the second and third drive inputs  906   b,c  results in rotation of the second and third capstans  1002   b,c . The second and third capstans  1002   b,c  comprise capstan pulleys operatively coupled to the actuation cables  810   a,b  ( FIG. 8 ) such that rotation of a given capstan  1002   b,c  actuates (longitudinally moves) a corresponding one of the actuation cables  810   a,b . Accordingly, selective rotation of the second and third capstans  1002   b,c  via actuation of the second and third drive inputs  906   b,c , respectively, will cause movement (axial translation) of the actuation cables  810   a,b , which causes the cam  812  ( FIG. 8 ) to move and crimp a surgical clip. 
     The drive housing  608  further includes a fourth capstan  1002   d , which is operatively coupled to or extends from the fourth drive input  906   d  ( FIG. 9 ) such that actuation of the fourth drive input  906   d  results in rotation of the fourth capstan  1002   d . A spur gear  1008  is coupled to or forms part of the fourth capstan  1002   d  and is configured to mesh and interact with a rack gear (not shown) also contained within the drive housing  608 . The rack gear may be operatively coupled to a feedbar (or another connecting member) which facilitates operation of a feeder shoe and associated clip track to feed surgical clips into the jaw members  610 ,  612  ( FIGS. 6 and 8 ). Accordingly, rotation of the spur gear  1008  (via actuation of the fourth drive input  906   d ) will control the feedbar and thereby control loading of surgical clips into the jaw members  610 ,  612  as desired. 
     The drive housing  608  further contains or houses fifth and sixth capstans  1002   e  and  1002   f  operatively coupled to or extending from the fifth and sixth drive inputs  906   e,f  ( FIG. 9 ), respectively, such that actuation of the fifth and sixth drive inputs  906   e,f  results in rotation of the fifth and sixth capstans  1002   e,f . The fifth and sixth capstans  1002   e,f  comprise capstan pulleys operatively coupled to the drive cables  808  ( FIG. 8 ) such that rotation of a given capstan  1002   e,f  actuates (longitudinally moves) a corresponding one of the actuation cables  808 . Accordingly, selective rotation of the fifth and sixth capstans  1002   e,f  via actuation of the fifth and sixth drive inputs  906   e,f , respectively, will cause movement (axial translation) of the drive cables  808  and thereby articulate (pivot) the end effector  604  relative to the shaft  602 . 
     The surgical tools  200 ,  600  described herein above may incorporate and facilitate the principles of the present disclosure in improving feeding and/or forming of surgical clips in robotic or non-robotic clip appliers. Moreover, it is contemplated herein to combine some or all of the features of the surgical tools  200 ,  600  to facilitate operation of the embodiments described below. Accordingly, example surgical tools that may incorporate the principles of the present disclosure may include geared actuators, capstan pulley and cable actuators, or any combination thereof, without departing from the scope of the disclosure. 
       FIG. 11  is an enlarged isometric cross-sectional view of an example end effector  1102 , according to one or more embodiments of the present disclosure. The end effector  1102  may be similar in some respects to the end effectors  204  and  604  of  FIGS. 2 and 6 , respectively. Similar to the end effectors  204 ,  604 , for example, the end effector  1102  may be incorporated into either or both of the surgical tools  200 ,  600  described herein above. In addition, the end effector  1102  may comprise a clip applier having opposed jaw members  1104  and  1106  configured to collapse toward one another to crimp a surgical clip  1108  (four shown in a stacked arrangement). As described herein, the end effector  1102  may incorporate various component parts and actuatable mechanisms or features that facilitate the feeding of the surgical clip(s)  1108  into the opposed jaw members  1104 , 1106  and collapsing the opposed jaw members  1104 , 1106  to crimp the surgical clip(s)  1108  when desired. Moreover, the corresponding inner surfaces of each of the opposed jaw members  1104 , 1106  may define or otherwise provide a groove  1104 ′, 1106 ′ that together define a path, slot, or track that the surgical clips  1108  may travel as they are pushed or fed into interposition between the opposed jaw members  1104 , 1106 , as hereinafter described. 
     As illustrated, the end effector  1102  extends along a longitudinal axis A 3  and includes an elongate body  1110  having a proximal end  1112   a  and a distal end  1112   b . The jaw members  1104 , 1106  extend out of or otherwise past the distal end  1112   b . In addition, the end effector  1102  includes a revolver  1114 , a biasing member  1116 , an indexer  1118 , and a clip advancer  1120  (referred to hereinafter as an “advancer”) that are each arranged within the body  1110 . The indexer  1118  and the pusher  1120  may be longitudinally actuatable (movable) to cause the revolver  1114  to index (rotate) and thereby selectively discharge a surgical clip  1108  housed within the revolver  1114 . To accomplish this, the indexer  1118  and the pusher  1120  may be operatively coupled to a drive input of a drive housing, such as one of the drive housings  206 ,  608  of  FIGS. 2 and 6 , respectively. In such embodiments, for example, the indexer  1118  and the pusher  1120  may be operatively coupled to the second and third drive and driven gears  502   b,c ,  504   b,c  of  FIG. 5  or one or more of the rotatable capstans  1002   b - f  of  FIG. 10 . 
     The surgical clips  1108  may be housed within the revolver  1114 , and the indexer  1118  may be actuatable to longitudinally translate to engage and index the revolver  1114 . Indexing the revolver  1114  selectively facilitates sequential axial alignment of each surgical clip  1108  with the opposed jaw members  1104 , 1106 , as hereinafter described. Thereafter, the pusher  1120  may be actuatable to discharge and deploy the aligned surgical clip  1108  from the revolver  1114  and into interposition between the opposed jaw members  1104 , 1106  where it can be crimped. 
     As illustrated, the body  1110  is generally cylindrical and hollow. Consequently, the body  1110  defines a bore  1113  that extends the length of the end effector  1102 , from the proximal end  1112   a  to the distal end  1112   b . As described below, the bore  1113  may comprise various regions or compartments that house or otherwise accommodate the revolver  1114 , the indexer  1118 , and the pusher  1120 . The body  1110  defines an annular flange  1122  at the distal end  1112   b  and an interior surface  1115  of the bore  1113  extends proximally therefrom. In some embodiments, the proximal end  1112   a  may be operatively coupled to an elongate shaft of a surgical tool, such as the shaft  202  of the surgical tool  200  of  FIG. 2 . In other embodiments, however, the proximal end  1112   a  may be operatively coupled to an articulable wrist joint, such as the wrist  606  of the surgical tool  600  of  FIG. 6 . 
     The revolver  1114  includes a proximal end  1124   a  and a distal end  1124   b . The revolver  1114  may be hollow to accommodate the surgical clips  1108  at or near the distal end  1124   b . Each surgical clip  1108  includes a crown  1108 ′ (alternately referred to as an “apex”) and a pair of legs  1108 ″ extending longitudinally from the crown  1108 ′. As illustrated, the surgical clips  1108  are stored within the clip revolver  1114  in a nested helical array. As used herein in conjunction with the stacking arrangement of the surgical clips  1108 , the phrase “nested helical array” refers to the surgical clips  1108  being arranged (stacked) with the crown of the more proximal surgical clips  1108  stacked upon (or in close proximity to) the crown of the more distal surgical clips, and the legs of the more proximal surgical clips  1108  extending past the crown of the more distal surgical clips  1108 , and where the legs of all the surgical clips  1108  extend substantially parallel to the longitudinal axis A 3 . Moreover, “nested helical array” also refers to the surgical clips  1108  being stacked such that they are angularly offset from each other. More specifically, the surgical clips  1108  are stacked such that each successive surgical clip  1108  resides in a different radial plane relative to the longitudinal axis A 3 . Accordingly, the surgical clips  1108  are arranged within the clip revolver  1114  with the legs  1108 ″ leading towards the jaw members  1104 , 1106  and the crown  1108 ′ extending proximally therefrom. As a result, the surgical clips  1108  are fed legs  1108 ″ first into the jaw members  1104 , 1106 . 
     The revolver  1114  provides a plurality of cams  1126  defined at the proximal end  1124   a . Each cam  1126  defines a corresponding camming surface  1126 ′ engageable with the indexer  1118  to effect rotation of the revolver  1114 , as described below. The revolver  1114  also provides or otherwise defines a plurality of guides  1128  arranged on an outer radial surface thereof. The guides  1128  are outwardly protruding features that are positioned between the proximal and distal ends  1124   a , 1124   b , distal of the cams  1126 , and may be equidistantly spaced about the outer radial surface of the revolver  1114 . Each guide  1128  may define a camming surface  1128 ′ and, in some embodiments, each guide  1128  may axially align with a corresponding one of the cams  1126  such that the camming surfaces  1126 ′, 1128 ′ have corresponding orientations. The revolver  1114  is further described below with reference to  FIG. 12 . 
     As mentioned above, the bore  1113  of the body  1110  includes one or more discrete internal regions or compartments that are formed into the body  1110 . In the illustrated embodiment, the bore  1113  defines or provides a revolver compartment  1130  and an indexer compartment  1140  that each extend along the longitudinal axis A 3 . Here, the revolver compartment  1130  is proximate to the distal end  1112   b  and exhibits an increased diameter section of the bore  1113  that extends proximally from the annular flange  1122 . The indexer compartment  1140  is located proximal to the revolver compartment  1130 . The revolver  1114  and the indexer  1118  are disposed within the body  1110  and are each arranged to slide or translate along the longitudinal axis A 3  at least partially into the revolver compartment  1130  and the indexer compartment  1140 . The revolver  1114  is also arranged to rotate about the longitudinal axis A 3 . Rotating the revolver  1114  may be configured to sequentially align each surgical clip  1108  with the opposed jaw members  1104 , 1106 . 
     The revolver compartment  1130  includes a proximal region  1132   a  and a distal region  1132   b , where the distal region  1132   b  extends proximally from an interior lip  1134  of the annular flange  1122  and terminates at the indexer compartment  1140 . The indexer compartment  1140  includes a proximal region  1142   a  and a distal region  1142   b , where the distal region  1142   b  extends proximally from the revolver compartment  1130 . In the illustrated embodiment, the indexer compartment  1140  has a smaller diameter than the revolver compartment  1130 , thereby defining a distally facing annular face  1142   b ′ that marks the intersection of the revolver compartment  1130  and the indexer compartment  1140 . 
     The revolver compartment  1130  includes a plurality of camming grooves  1136  defined in the body  1110  and sized to slidably receive the guides  1128 . In the illustrated embodiment, the camming grooves  1136  are axially aligned with and otherwise extend parallel to the longitudinal axis A 3 , but they may alternatively have different orientations in other embodiments. Similar to the guides  1128 , the camming grooves  1136  may be equidistantly spaced about the inner surface of the body  1110 . Moreover, the number of guides  1128  and camming grooves  1136  may be generally the same, but could be different in alternative embodiments. 
     The revolver  1114  and the indexer  1118  may translate relative to the revolver compartment  1130  and the indexer compartment  1140  without being caught, impeded, or obstructed by the distally facing annular face  1142   b ′ or any other protruding corners or edges formed at the intersection of the camming grooves  1136  and the indexer compartment  1140 . Each camming groove  1136  may also define a camming surface  1136 ′ at a distal end thereof that is engageable with a corresponding one of the camming surfaces  1128 ′ of the guides  1128 . Accordingly, the camming surfaces  1136 ′ of the camming grooves  1136  and the camming surfaces  1128 ′ may be substantially alignable when the revolver  1114  rotates (indexes) and may exhibit corresponding and complementary geometries. In addition, the camming surfaces  1136 ′, 1128 ′ may also be cooperatively angled or oriented to help properly orient the guides  1128  within the camming grooves  1136 . 
     Each camming groove  1136  may be configured to receive a corresponding one of the guides  1128  and thereby direct the revolver  1114  along a path defined by the geometry of the corresponding camming grooves  1136 . More specifically, the camming grooves  1136  extend longitudinally and guide the revolver  1114  along a linear path when the guides  1128  are fully received therein. Thus, as the revolver  1114  translates proximally into the proximal region  1132   a  of the revolver compartment  1130 , the guides  1128  are received within the camming grooves  1136  so that the revolver  1114  travels linearly without rotation. As the revolver  1114  travels distally during operation, the guides  1128  will eventually exit the camming grooves  1136  to allow the revolver  1114  to rotate (index). 
     The indexer compartment  1140  is configured to receive the indexer  1118 , at least when the end effector  1102  is unactuated, such that the indexer  1118  may slide therein. In addition, the indexer compartment  1140  may partially receive the revolver  1114  during operation. Here, the cams  1126  of the revolver  1114  may extend into the distal region  1142   b  of the indexer compartment  1140 , for example, when the end effector  1102  is unactuated. 
     The indexer  1118  may be configured to travel (reciprocate) within the indexer compartment  1140 . To help guide and orient the indexer  1118  as it translates within the indexer compartment  1140 , the body  1110  may define one or more indexer guides  1144  (one shown). In the illustrated embodiment, the indexer guides  1144  are channels, recesses, or tracks that are formed into the inner surface of the indexer compartment  1140  and extend longitudinally. The indexer guides  1144  may be configured to slidably receive one or more corresponding indexer rails  1148  (two shown) provided on the outer radial surface of the indexer  1118  and thereby orient the indexer  1118  as it travels between the proximal region  1142   a  and the distal region  1142   b.    
     While the illustrated embodiment includes a pair of indexer rails  1148 , it will be appreciated that more or less may be utilized, depending on the number of indexer guides  1144 . Also, while the indexer rails  1148  are illustrated as being oriented with the longitudinal axis A 3  and extending from a proximal end  1146   a  to a distal end  1146   b  of the indexer  1118 , the indexer rails  1148  may alternatively exhibit different geometries. For example, one or both of the indexer rails  1148  may be replaced with one or more pins or protrusions that are receivable within the indexer guides  1144 . In even other embodiments, the indexer rails  1148  may be provided as recesses (grooves) configured to receive corresponding indexer guides  1144  in the form of protrusions. 
     The indexer guides  1144  may direct the indexer  1118  along various predetermined paths. Here, the indexer guides  1144  are linear (extend longitudinally) and thus inhibit rotation of the indexer  1118  about the longitudinal axis A 3 . In other embodiments, however, the indexer guides  1144  may be non-linear and extend helically around the inner surface. 
     As mentioned, the indexer  1118  may be operatively coupled to a drive input of a drive housing (e.g., one of the drive housings  206 ,  608  of  FIGS. 2 and 6 , respectively). The proximal end  1146   a  of the indexer  1118  may be operatively connected to one or more members extending through the elongate shaft  202 ,  602  ( FIGS. 2 and 6 , respectively) such that it may be actuated. For example, the proximal end  1146   a  may be attached to a thrust shaft that extends through the length of the elongate shaft  202 ,  602  and may extend from one of the drive inputs included in the drive housing. However, the indexer  1118  may be differently reciprocated without departing from the present disclosure. Upon actuation, the indexer  1118  may be moved distally within the bore  1113  of the body  1110  and thereby engage and cause the revolver  1114  to index (rotate). 
     The indexer  1118  causes the revolver  1114  to index by engaging the cams  1126  of the revolver  1114 . In the illustrated embodiment, the indexer  1118  includes a plurality of cams  1150  disposed on the distal end  1146   b  of the indexer  1118 , and each cam  1150  defines a camming surface  1150 ′ configured to engage a corresponding one of the camming surfaces  1126 ′ of the revolver  1114 . The camming surfaces  1126 ′, 1150 ′ may have corresponding geometries and orientations. Upon actuation of the end effector  1102 , the indexer  1118  may translate distally to engage the revolver  1114  by engaging the cams  1150  of the indexer  1118  against the cams  1126  of the revolver  1114 . 
     Similar to the indexer  1118 , the pusher  1120  may be operatively coupled to a drive input of a drive housing (e.g., one of the drive housings  206 ,  608  of  FIGS. 2 and 6 , respectively) such that, upon actuation, it is caused to move (e.g., reciprocate) within the bore  1113  to deploy a surgical clip  1108  from the revolver  1114  and into the opposed jaw members  1104 , 1106 . The revolver  1114  may be configured to index such that a distal-most surgical clip  1108  becomes axially aligned with the pusher  1120  and is simultaneously placed in alignment with the opposed jaw members  1104 , 1106 . In the illustrated embodiment, the pusher  1120  may be configured to enter and translate distally through the indexer  1118  and the revolver  1114  to locate and apply an axial load on an aligned surgical clip  1108 . 
     In the illustrated embodiment, the pusher  1120  includes a pusher shaft  1170  having a proximal end  1172   a  and a distal end  1172   b . In some embodiments, the proximal end  1172   a  may extend to a drive housing where it may be operatively coupled to a drive input configured to actuate (longitudinally drive) the pusher  1120 . In some embodiments, the pusher  1120  may be bifurcated at the distal end  1172   b  and thereby provide a pair of opposed pushing elements  1174 , 1176  that extend distally from the distal end  1172   b . The pushing elements  1174 , 1176  may be generally aligned with the opposed jaw members  1104 , 1106 , respectively. 
     The biasing member  1116  imparts a force on the revolver  1114  that helps facilitate repeated indexing of the revolver  1114  as it is alternatingly engaged and disengaged by the indexer  1118 . In the illustrated embodiment, the biasing member  1116  is a spring  1160 ; however, it will be appreciated that the biasing member  1116  may instead comprise different materials or devices capable of providing a biasing force, without departing from the present disclosure. Here, the spring  1160  is provided in the distal region  1132   b  of the revolver compartment  1130 , and arranged around the distal end  1124   b  of the revolver  1114 . The spring  1160  extends between the annular flange  1122  and the guides  1128  and thus provides a passive biasing load on the revolver  1114  in the proximal direction. 
     The spring  1160  acts on the revolver  1114  to help facilitate rotation and indexing of the revolver  1114 . More specifically, the spring  1160  biases the revolver  1114  proximally where its guides  1128  are fully engaged in the camming grooves  1136 . When the indexer  1118  is distally translated, it engages and advances the revolver  1114  distally. The spring  1160  applies a counteracting force that maintains engagement of the camming surfaces  1126 ′, 1150 ′ of the revolver  1114  and indexer  1118 , respectively. As the revolver  1114  advances distally, engagement between the camming grooves  1136  and the guides inhibit rotation of the revolver  1114 . However, once the guides  1128  exit the camming grooves  1136 , the revolver  1114  is able to rotate (index) as the corresponding camming surfaces  1126 ′, 1150 ′ slidably interact. The inclination (angle) of the camming surfaces  1126 ′, 1150 ′ causes the revolver  1114  to simultaneously translate in a proximal direction such that the guides  1128  become angularly aligned with angularly adjacent camming grooves  1136 . Once the revolver  1114  is properly indexed, a penultimate surgical clip  1108  becomes aligned with the opposed jaws  1104 , 1106  for deployment by the pusher  1120 . As will be appreciated, this indexing action is similar in some respects to the operation of a click-action ballpoint pen. 
       FIG. 12  is an enlarged isometric view of the revolver  1114 , according to one or more embodiments. The revolver  1114  is hollow and includes an inner bore  1200  extending from the proximal end  1124   a  to the distal end  1124   b  thereof. As illustrated, the inner bore  1200  defines a clip chamber  1202  designed to hold/store the surgical clips  1108 . The clip chamber  1202  also orients the surgical clips  1108  to be deployed legs  1108 ″ first by the pusher  1120  ( FIG. 11 ). Here, the clip chamber  1202  extends into the inner bore  1200  from the distal end  1124   b . As will be appreciated, the distance that the clip chamber  1202  extends into the inner bore  1200  may depend on the length of the surgical clips  1108  and the number of surgical clips  1108  capable of being nested therein. 
     The clip chamber  1202  includes a plurality of clip slots  1204  defined into the inner surface of the inner bore  1200 . Each clip slot  1204  may be configured to receive one leg of a given surgical clip  1108  and may be angularly opposite an opposing clip slot  1204  configured to receive the second leg of the given surgical clip  1108 . Consequently, a pair of angularly opposite clips slots  1204  may be configured to receive and seat a single surgical clip  1108 . In the illustrated embodiment, the clip chamber  1202  includes eight clip slots  1204  equidistantly spaced about the inner bore  1200  and therefore capable of receiving a corresponding four surgical clips  1108  stacked in a helical array. It will be appreciated, however, that more or less than four surgical clips  1108  may be accommodated within the revolver  1114  without departing from the present disclosure. The angular spacing and orientation of the clip slots  1204  helps the surgical clips  1108  to be arranged in a nested helical array, as illustrated. 
     As illustrated, the helically arrayed surgical clips  1108  are stacked (nested) one on top of the other from the proximal end  1124   a  towards the distal end  1124   b . Here, the surgical clips  1108  include a proximal-most clip  1208   a , a distal-most clip  1208   d , and two intermediate clips  1208   b , 1208   c . The surgical clips  1208   a - d  are arranged within the clips slots  1204  such that each surgical clip  1208   a - d  resides in a different radial plane relative to the longitudinal axis A 3  of the end effector  1102  ( FIG. 1 ) and, therefore, the surgical clips are angularly offset from each other. In operation, the revolver  1114  may be rotated to align the distal-most clip  1208   d  with the opposed jaw members  1104 , 1106  for deployment. Following deployment of the distal-most clip  1208   d , the end effector  1102  ( FIG. 11 ) may be actuated again to rotate the revolver  1114  and thereby align the penultimate clip  1208   c  for deployment. This process may be repeated until the revolver  1114  is rotated to align the proximal-most clip  1208   a  with the jaw members  1104 , 1106  for deployment. 
       FIG. 12  also includes depicts the distal end  1129  of the guides  1128 . As indicated above, the spring  1160  ( FIG. 11 ) may be configured to engage the distal end  1129  of each guide  1128 . In at least one embodiment, the distal end  1129  of each guide  1128  may be contoured and otherwise configured to receive the spring  1160  in a secure manner that inhibits slipping. However, in other embodiments, the distal ends  1129  may include different surface finishes or none at all. 
       FIG. 13  is an isometric exposed view of the interior of an example embodiment of the drive housing  608 , according to one or more embodiments. Various internal components of the drive housing  608  have been removed to view devices capable of actuating the indexer  1118  and the pusher  1120 . In the illustrated embodiment, a linear actuator  1300  may be utilized to actuate the indexer  1118 , which causes the revolver  1114  ( FIGS. 11 and 12 ) to index (rotate). 
     As illustrated, the linear actuator  1300  may include a thrust shaft  1302  that includes a proximal end  1304   a  and a distal end  1304   b . Here, the thrust shaft  1302  extends through the elongate shaft  602 , with the proximal end  1304   a  extending into the drive housing  608  and the distal end  1304   b  being attached to the proximal end  1146   a  of the indexer  1118 . While the indexer  1118  is described herein as being operatively coupled to the thrust shaft  1302 , it is contemplated herein that the indexer  1118  may alternatively form an integral part or extension of the thrust shaft  1302 , without departing from the scope of the disclosure. 
     The linear actuator  1300  may also include a rack gear  1306  attached to the proximal end  1304  of the thrust shaft  1302  and configured to mesh and interact with the spur gear  1008  operatively coupled to the fourth capstan  1002   d . Accordingly, rotation of the spur gear  1008  (via actuation of the fourth drive input  906   d  of  FIG. 9 ) will control the thrust shaft  1302  and thereby control indexing of the revolver  1114  ( FIGS. 11 and 12 ). It will be appreciated, however, that the thrust shaft  1302  may be differently configured, for example to be actuated by any of the other capstans and corresponding drive inputs and/or with a different gearing assembly, without departing from the present disclosure. 
     The pusher  1120  may be actuated separately from the indexer  1118 , or timed to deploy a surgical clip  1108  ( FIGS. 11 and 12 ) after the revolver  1114  ( FIGS. 11 and 12 ) has indexed the surgical clip  1108  into alignment with the opposed jaw members  1104 , 1106  ( FIG. 11 ) as desired. In the illustrated embodiment, the thrust shaft  1302  is hollow and the pusher  1120  extends through the thrust shaft  1302 , with the proximal end  1172   a  of the pusher shaft  1170  extending into the drive housing  608  and the distal end  1172   b  of the pusher shaft  1170  extending distally therefrom to a location proximate to the indexer  1118 . In addition, a first link member  1310  is coupled to or forms part of the third capstan  1002   c  such that they rotate in unison. The first link member  1310  is coupled to a second link member  1312  that is configured to rotate relative to the first link member  1310 . The second link member  1312  is coupled to the proximal end  1172   a  of the pusher shaft  1170  such that it may also rotate relative to the pusher shaft  1170 , and thus interconnects the first link member  1310  and the proximal end  1172   a  of the pusher shaft  1170 . Accordingly, rotation of the third capstan  1002   c  (via actuation of the third drive input  906   c ) will control linear movement of the pusher  1120  within the shaft  602  and thereby control loading of surgical clips  1108  into the opposed jaw members  1104 , 1106  as desired. It will be appreciated, however, that that the pusher  1120  may be differently configured, for example, to be actuated by any of the other capstans and corresponding drive inputs and/or with a gear arrangement in lieu of the linkage assembly, without departing from the present disclosure. 
       FIGS. 14A-14E  are progressive isometric views of the end effector  1102  during example operation, according to one or more embodiments.  FIG. 14A  illustrates the end effector  1102  prior to actuation where the indexer  1118  and the pusher  1120  are retracted within the bore  1113  towards the proximal end  1112   a  of the body  1110 . In this position, the revolver  1114  is fully seated within the camming grooves  1136  of the body  1110  and the spring  1160  biases the revolver  1114  proximally to enable the guides  1128  to be received within the camming grooves  1136 . In the embodiment illustrated in  FIG. 14A , it is assumed that the distal-most clip  1208   d  of the surgical clips  1108  is rotationally aligned with the opposed jaw members  1104 , 1106  ( FIG. 14D ) when the revolver  1114  is constrained in the camming grooves  1136 , such that the pusher  1120  may deploy the distal-most clip  1108   d  before the revolver has indexed, as hereinafter described. However, in other embodiments, the distal-most clip  1208   d  is not rotationally aligned with the opposed jaw members  1104 , 1106  when the revolver  1112  is fully seated, but requires that the end effector  1102  be actuated to index the revolver  1114  to align the distal-most clip  1208   d  with the jaw members  1104 , 1106 , before actuating the pusher  1120  to deploy the distal-most clip  1208   d.    
     In  FIG. 14B , the end effector  1102  is actuated to cause distal translation of the indexer  1118  to properly orient the distal-most surgical clip  1108  for deployment into the opposed jaw members  1104 , 1106  ( FIG. 14D ). Upon actuation, the indexer  1118  slides distally such that the cams  1150  make contact with the cams  1126  of the revolver  1114 , which correspondingly drives the revolver  1114  distally and the guides  1128  of the revolver  1114  slide distally within the camming grooves  1136 . Rotation of the revolver  1114  is inhibited when the guides  1128  are within the camming grooves  1136 . In embodiments where the surgical clips  1108  align with the opposed jaws  1104 , 1106  when the revolver  1114  is constrained in the camming grooves  1136 , the pusher  1120  may deploy the distal-most clip  1108   d  before the revolver  1114  is indexed. However, in embodiments where the distal-most clip  1208   d  is not rotationally aligned with the opposed jaws  1104 , 1106  when the revolver  1114  is constrained in the camming grooves  1136 , the pusher  11120  deploys the distal-most surgical clip  1208   d  after the revolver  1114  is rotated. 
     In  FIG. 14C , the revolver  1114  rotates to index the distal-most clip  1208   d  ( FIG. 14D ) into alignment with the opposed jaw members  1104 , 1106  ( FIG. 14D ) as the indexer  1118  continues to distally drive the revolver  1114 . More specifically, the revolver  1114  may be able to rotate once the guides  1128  exit the camming grooves  1136  and the camming surface  1126 ′ ( FIG. 14A ) of each cam  1126  is able to slidably engage the corresponding camming surfaces  1150 ′ ( FIG. 14A ) of the cams  1150 , which facilitates (urges) rotation of the revolver  1114 . The revolver  1114  continues to rotate until the cams  1126  bottom out in the cams  1150 . In embodiments where the distal-most clip  1208   d  is not rotationally aligned with the opposed jaw members  1104 , 1106  ( FIG. 14D ) when the revolver  1112  is seated within the camming grooves  1136 , the distal-most clip  1208   d  will be in alignment with the opposed jaw members  1104 , 1106  and the pusher  1120  once the revolver  1114  finishes rotating. In other embodiments where the distal-most clip  1208   d  is rotationally aligned with the opposed jaw members  1104 , 1106  ( FIG. 14D ) when the revolver  1112  is seated within the camming grooves  1136 , the next distal-most surgical clip  1108  (e.g., the intermediate clip  1208   c ) will be in alignment the opposed jaw members  1104 , 1106  and the pusher  1120  once the revolver  1114  finishes rotating. 
     Once the distal-most clip  1208   d  is aligned with the opposed jaw members  1104 , 1106  ( FIG. 14D ), the pusher  1120  may be actuated to deploy the distal-most clip  1208   d.    
     In  FIG. 14D , the pusher  1120  is actuated distally and the pushing elements  1174 , 1176  are correspondingly moved to engage the aligned distal-most surgical clip  1208   d  at the crown  1108 ′ thereof. The crown  1108 ′ may include a pair of arms  1474 , 1476  configured to receive the corresponding pushing elements  1174 , 1176 . Here, the arms  1474 , 1476  of the crown  1108 ′ are angled and the pushing elements  1174 , 1176  have contact surfaces  1174 ′, 1176 ′ that are correspondingly angled and contoured to make complete contact therewith. It will be appreciated, however, that the crown  1108 ′ may have various geometries and, therefore, that the contact surfaces  1174 ′, 1176 ′ of the pusher  1120  may be contoured with various corresponding geometries. In addition, the contact surfaces  1174 ′, 1176 ′ may include various features to inhibit slipping of the pushing elements  1174 , 1176  when engaging the crown  1108 ′. For example, the contact surfaces  1174 ′, 1176 ′ may include barbs, ridges, and/or an elastomeric element that may increase friction when engaged with the surgical clips  1108 . 
     Once the distal-most clip  1208   d  is deployed and positioned between the opposed jaw members  1104 , 1106 , both the revolver  1114  and the indexer  1118  may be retracted proximally into the bore  1113  of the body  1110 . 
     In  FIG. 14E , the indexer  1118  is shown being retracted proximally into the bore  1113 , which allows the spring  1160  to push the revolver  1114  proximally, and thereby causing the revolver  1114  to follow the indexer  1118  as it (i.e., the indexer  1118 ) translates proximally into the body  1110 . Moreover, the guides  1128  of the revolver  1114  enter angularly adjacent camming grooves  1136  as the spring  1160  pushes the revolver  1114  proximally into the bore  1113 . During this process, the camming surfaces  1128 ′ of the guides  1128  slide upon the corresponding camming surfaces  1136 ′ of the camming grooves  1136  to rotate the revolver  1114  so that the guides  1128  properly align with the angularly adjacent camming grooves  1136 , and permits further axial translation of the revolver  1114 . 
     Once the revolver  1114  rotates, the spring  1160  continues to proximally push the revolver  1114  until the revolver  1114  is seated within the body  1110  such that the guides  1128  are fully engaged in the appropriate camming grooves  1136 . Seating the revolver  1114  in this position simultaneously places the penultimate clip  1208   c  into alignment with the opposed jaw members  1104 , 1106  ( FIG. 14D ) for deployment therein via subsequent actuation of the indexer  1118 . In other embodiments, however, subsequent actuation of the indexer  1118  may be needed to rotate the penultimate clip  1208   c  into alignment with the opposed jaw members  1104 , 1106  ( FIG. 14D ) prior to deployment via the pusher  1120 . Also in the illustrated embodiment, the guides  1128  of the revolver  1114  are already rotated into alignment with the camming grooves  1136  of the body  1110  such that the spring  1160  may fully seat the guides  1128  into the camming grooves  1136  of the body  1110  without any obstruction and camming action between the guides  1128  and the camming grooves  1136 . In other embodiments, however, additional camming action between the camming surfaces  1128 ′ of the guides  1128  and the corresponding camming surfaces  1136 ′ of the camming grooves  1136  facilitates fully seating the guides  1128  within the camming grooves  1136 . 
       FIG. 15  is an enlarged isometric view of another example end effector  1502 , according to one or more embodiments of the present disclosure. The end effector  1502  may be similar in some respects to the end effector  1102  of  FIG. 11 , and thus may be incorporated into either or both of the surgical tools  200 ,  600  described herein above. Moreover, the end effector  1502  may comprise a clip applier having opposed jaw members  1504  and  1506  configured to collapse toward one another to crimp a surgical clip  1508  (four shown). As described herein, the end effector  1502  may incorporate various component parts and actuatable mechanisms or features that facilitate the feeding of the surgical clip  1508  into the opposed jaw members  1504 , 1506  and collapsing the opposed jaw members  1504 , 1506  to crimp the surgical clip  1508  when desired. 
     The end effector  1502  extends along a longitudinal axis A 4  and includes an elongate body  1510 , a revolver  1512 , a torsion member  1514 , and a pusher  1516 . The pusher  1516  may be longitudinally actuatable (movable) to index (rotate) the revolver  1512  and thereby selectively deploy the surgical clips  1508  housed within the revolver  1512 . To accomplish this, the pusher  1516  may be operatively coupled to a drive input of a drive housing, such as one of the drive housings  206 ,  608  of  FIGS. 2 and 6 , respectively. In such embodiments, pusher  1516  may be operatively coupled to the second or third drive and driven gears  502   b,c ,  504   b,c  of  FIG. 5  or one of the rotatable capstans  1002   b - f  of  FIG. 10 . The opposed jaw members  1504 , 1506  may each define a groove  1504 ′, 1506 ′ that together define a path, slot, or track that the surgical clips  1508  travel as the pusher  1516  feeds them into interposition between the opposed jaw members  1504 , 1506  from the revolver  1512 . 
     The body  1510  is generally cylindrical and includes a proximal end  1518   a  and a distal end  1518   b . Moreover, the body  1510  defines a bore  1520  that extends between the proximal and distal ends  1518   a , 1518   b  and is sized to receive the revolver  1512  and the torsion member  1514  therein. The revolver  1512  may be adapted for rotation within the body  1510  and about the longitudinal axis A 4 , as described below. 
     The torsion member  1514  may comprise a torsion spring that includes a first end  1522   a  and a second end  1522   b , and may be configured to build/store mechanical energy when the first and second ends  1522   a , 1522   b  are twisted relative to each other. However, the torsion member  1514  may comprise other structures or materials in lieu of, or in addition to, the torsion spring, without departing from the present disclosure. As illustrated, the body  1510  defines an aperture  1524  through which the first end  1522   a  of the torsion member  1514  extends to enable the revolver  1512  to be “spring loaded” when installed within the bore  1520 , as hereinafter described. 
     The pusher  1516  may be configured to longitudinally translate at least partially through the body  1510  and the revolver  1512  to selectively deploy the surgical clips  1508  into the opposed jaw members  1504 , 1506  as desired. Similar to the pusher  1120  of  FIG. 11 , the pusher  1516  is fork shaped and includes a pair of opposed pushing elements  1526   a , 1526   b  that extend distally. The pushing elements  1526   a , 1526   b  may be aligned with the opposed jaw members  1504 , 1506 , respectively, and therefore may be capable of engaging and distally moving the surgical clips  1508  into interposition therebetween. 
     The pusher  1516  may be actuated to distally drive one of the surgical clips  1508  into the opposed jaw members  1504 , 1506 . In some embodiments, the pusher  1516  is operatively coupled to one or more of the capstans  1002   b - f  within the drive housing  608  ( FIGS. 6 and 13 ). For example, the pusher  1516  may include a shaft that extends proximally through the elongate shaft  602  and is coupled to one or more of the capstans  1002  within the drive housing  608  via a linkage assembly or rack and pinion interface. In one embodiment, the shaft of the pusher  1516  extends into the drive housing  608  and is coupled to the rack gear  1306  that is configured to mesh and interact with the spur gear  1008  operatively coupled to the fourth capstan  1002   d  ( FIGS. 6 and 13 ). In another embodiment, the shaft of the pusher  1516  extends into the drive housing  608  and is operatively coupled to the third capstan  1002   c  via the first link member  1310  and the second link member  1312  ( FIGS. 6 and 13 ). However, the pusher  1516  may be differently reciprocated without departing from the present disclosure. 
     The pusher  1516  further includes one or more features that may help guide the pusher  1516  within the revolver  1512 . In the illustrated embodiment, the pusher  1516  includes a pair of opposed studs  1528   a  and  1528   b  (obscured from view) that extend laterally from the opposed pushing elements  1526   a , 1526   b , respectively. It will be appreciated that more or less than the pair of studs  1528   a , 1528   b  may be utilized, without departing from the present disclosure. Moreover, it will be appreciated that the pair of studs  1528   a , 1528   b  (or any of them) may include different geometries and/or be differently arranged on the pusher  1516  without departing from the present disclosure. 
       FIG. 16  is an enlarged isometric cross-sectional view of the revolver  1512 , according to one or more embodiments of the present disclosure. As illustrated, the revolver  1512  comprises a revolver body  1530  that has an open proximal end  1532   a , an open distal end  1532   b , and a bore  1534  extending therebetween. The revolver body  1530  may be cylindrically shaped and sized to be received within the body  1510  ( FIG. 15 ). In other embodiments, however, the revolver body  1530  may include other geometries, without departing from the present disclosure. In some embodiments, the revolver  1512  is disposed within the body  1510  with the open distal end  1532   b  extending past the distal end  1518   b  ( FIG. 15 ) of the body  1510  and arranged proximate to the opposed jaw member  1504 , 1506 . In other embodiments, however, the open distal end  1532   b  may be arranged within the body  1510  and otherwise proximal to the distal end  1518   b  of the body  1510 . 
     The revolver  1512  includes a detent or spline  1536  configured to receive and abut the second end  1522   b  ( FIG. 15 ) of the torsion member  1514  ( FIG. 15 ) such that the torsion member  1514  is able to retain tension when its first and second ends  1522   a , 1522   b  are twisted. Accordingly, the torsion member  1514  imparts a constant torsion load on the revolver  1512  when twisted out of an equilibrium position, thereby urging the revolver  1512  to rotate about the longitudinal axis A 4 . 
     In the illustrated embodiment, the spline  1536  is provided or otherwise defined on the revolver  1114  and arranged to abut the second end  1522   b  of the torsion member  1514 . Here, the spline  1536  extends radially from the revolver body  1530  and includes a front face  1538   a  and rear face  1538   b . In addition, the spline  1536  defines a recess  1540  that allows the torsion member  1514  to extend around the spline  1536  such that the second end  1522   b  thereof may abut the rear face  1538   b . Thus, the torsion member  1514  may retain tension when impinged between the aperture  1524  ( FIG. 15 ) of the body  1510  ( FIG. 15 ) and the spline  1536  of the revolver  1512 . Moreover, the spline  1536  extends substantially parallel to the longitudinal axis A 4 . 
     The revolver  1512  includes a plurality of discrete regions arranged within the bore  1534 . As illustrated, a clip region  1550  is formed within the bore  1534  and configured to receive one or more of the surgical clips  1508 . In operation, the surgical clips  1508  are stacked within the clip region  1550  in a nested helical array. The clip region  1550  defines a plurality of clip slots  1552  defined into the inner surface of the bore  1534 . Each clip slot  1552  may be configured to receive one leg of a given surgical clip  1508  and may be angularly opposite an opposing clip slot  1504  configured to receive the second leg of the given surgical clip  1508 . Consequently, a pair of angularly opposite clips slots  1552  may be configured to receive and seat a single surgical clip  1508 . In the illustrated embodiment, the clip region  1550  includes eight clip slots  1552  equidistantly spaced about the bore  1534  and thereby capable of receiving a corresponding four surgical clips  1508  stacked in a helical array. It will be appreciated, however, that more or less than four surgical clips  1508  may be housed within the revolver  1512  without departing from the present disclosure. The angular spacing and orientation of the clip slots  1552  helps the surgical clips  1508  to be arranged in a nested helical array, as illustrated. 
     In the illustrated example, the surgical clips  1508  include a proximal-most clip  1508   a , a pair of intermediate clips  1508   b , 1508   c , and a distal-most surgical clip  1508   d . To load the revolver  1512 , the proximal-most clip  1508   a  is first inserted into a first pair of clip slots  1552 . The first intermediate clip  1508   b  is then inserted into a second pair of clip slots  1552  angularly offset from the first pair of clip slots  1552 , the second intermediate clip  1508   c  is inserted into a third pair of clip slots  1552  angularly offset from the second pair of clip slots  1552 , and the distal-most surgical clip  1508   d  is inserted into a fourth pair of clip slots  1552  angularly offset from the third pair of clip slots  1552 . Thus, the clip slots  1552  orient the surgical clips  1508   a - 1508   d  in a helical array when stacked/stored within the clip region  1550 . It will be appreciated, however, that the clip region  1550  may be differently configured with more or less clip slots  1552  to house any number of the surgical clips  1508  in various orientations without departing from the present disclosure. 
     The revolver  1512  also includes a biasing region  1560  configured to guide the pusher  1516  ( FIG. 15 ). The biasing region  1560  extends into the bore  1534  at the open proximal end  1532   a  and terminates at or near the clip region  1550 . As hereinafter described, the pusher  1516  may be configured to engage the biasing region  1560  and help index the revolver  1512  as it traverses the biasing region  1560 . 
     As illustrated, the biasing region  1560  includes a plurality of biasing grooves  1562  (referred to hereinafter as a “plurality of grooves”) configured to receive and guide the pusher  1516  ( FIG. 15 ) as it reciprocates distally and proximally within the bore  1534 . Each angularly opposite pair of the grooves  1562  may be axially aligned with a corresponding angularly opposite pair of the clip slots  1552  of the clip region  1550 . The studs  1528   a , 1528   b  ( FIG. 15 ) of the pusher  1516  may be configured to selectively and sequentially traverse within each pair of the grooves  1562  so that the pushing elements  1526   a , 1526   b  are aligned to drive each surgical clip  1508  into the opposed jaw members  1504 , 1506 . The illustrated embodiment includes four pairs of grooves  1562  that each correspond with one of the four pairs of clip slots  1552 . In other embodiments, however, more or less than four pairs of grooves  1562  (and corresponding pairs of clip slots  1552 ) may be utilized. 
     Each of the pairs of grooves  1562  includes a proximal portion  1564   a , a distal portion  1564   b , and a connecting channel  1566  that interconnects the proximal and distal portions  1564   a , 1564   b  of each groove  1562  and thereby provides a pathway that connects each groove  1562  to an angularly adjacent (neighboring) groove  1562 . The proximal portion  1564   a , the distal portion  1564   b , and the connecting channel  1566  are each arranged to slidably receive the studs  1528   a , 1528   b  ( FIG. 15 ) of the pusher  1516 , which in turn rotates the revolver  1512  within the body  1510  as the pusher  1516  traverses the groove  1562 . Thus, the connecting channel  1566  connect angularly adjacent pairs of grooves  1562  and facilitate rotation of the revolver  1512  when the studs  1528   a , 1528   b  travel into the angularly adjacent pair of grooves  1562 . 
     In the illustrated embodiment, the pairs of grooves  1562  include a first pair of grooves  1562   a , a second pair of grooves  1562   b , a third pair of grooves  1562   c , and a fourth pair of grooves  1562   d . Here, a first of the connecting channels  1566  connects the first pair of grooves  1562   a  to its neighboring second and fourth pairs of grooves  1562   b , 1562   d ; a second of the connecting channels  1566  connects the second pair of grooves  1562   b  to its neighboring first and third pairs of grooves  1562   a , 1562   c ; a third of the connecting channels  1566  connects the third pair of grooves  1562   c  to its neighboring second and fourth pairs of grooves  1562   b , 1562   d ; and a fourth of the connecting channels  1566  connects the fourth pair of grooves  1562   d  to its neighboring third and first pairs of grooves  1562   c , 1562   a.    
     The revolver  1512  is constantly biased to rotate in an attempt to relieve the torsional load (spring force) built up in the torsion member  1514 . As the pusher  1516  advances distally, the studs  1528   a , 1528   b  are able to bypass (traverse) the connecting channels  1566  in the distal direction and, therefore, remain in the same pair of grooves  1562  to thereby engage the distal-most surgical clip  1508   d  and discharge it from the revolver  1512 . However, upon retracting the pusher  1516  in the proximal direction, the torsional load provided by the torsion member  1514  forces the studs  1528   a , 1528   b  to enter and follow the connecting channels  1566 , which allows the revolver  1512  to rotate and place the studs  1528   a , 1528   b  in the angularly adjacent pair of grooves  1562 . Allowing the revolver  1512  to rotate where the studs  1528   a , 1528   b  are positioned in the angularly adjacent pair of grooves  1562  simultaneously aligns the penultimate surgical clip  1508  with the pusher  1516 . This process is repeated to discharge the penultimate surgical clip  1508  from the revolver  1512 . 
       FIGS. 17A-17B  are isometric views of the end effector  1502  showing example operation, according to one or more embodiments of the present disclosure. In  FIG. 17A , the pusher  1516  is shown being moved in a distal direction  1702  to engage and drive the distal-most surgical clip  1508   d  from its respective clip slot  1552  ( FIG. 16 ) within the revolver  1512  and into the grooves  1504 ′, 1506 ′ defined in the opposed jaw members  1504 , 1506 . While not fully illustrated, the studs  1528   a , 1528   b  of the pusher  1516  are engaged within the distal portion  1564   b  ( FIG. 16 ) of the groove  1562  ( FIG. 16 ) that are aligned with the grooves  1504 ′, 1506 ′ (e.g., the third pair of grooves  1562   c  of  FIG. 16 ). 
       FIG. 17B  illustrates the pusher  1516  as it moves in a proximal direction  1704  relative to the revolver  1512 . Moving the pusher  1516  in the proximal direction  1704  allows the revolver  1512  to index or rotate in a counter-clockwise direction  1706 . More specifically, the torsion member  1514  is installed in the end effector  1502  and twisted to build up a torsional load that continuously biases the revolver  1512  in the counter-clockwise direction  1706 . Rotation of the revolver  1512  is constrained when the studs  1528   a , 1528   b  of the pusher  1516  are engaged within the distal portion  1564   b  of the groove  1562  (e.g., the third pair of grooves  1562   c  ( FIG. 16 )). Once the pusher  1516  moves in the proximal direction  1704  a sufficient distance such the studs  1528   a , 1528   b  ( FIG. 17A ) are no longer engaged within the distal portion  1564   b  thereof, rotation of the revolver  1512  is no longer inhibited and the torsion member  1514  rotates the revolver  1512  in the counter-clockwise direction  1706  such that the studs  1528   a , 1528   b  enter the connecting channels  1566 . The connecting channels  1566  direct the studs  1528   a , 1528   b  in a downward path  1708  so that they enter the proximal portion  1564   a  of the angularly adjacent pair of grooves  1562  (e.g., the second pair of grooves  1562   b  ( FIG. 16 )), which simultaneously aligns the penultimate surgical clip  1508  with the pusher  1516 . The pusher  1516  may then advance distally in the angularly adjacent pair of grooves  1562 , with the studs  1528   a , 1528   b  bypassing (traversing) the connecting channels  1566  and remaining in the same pair of grooves  1562 , to engage the penultimate surgical clip  1508  and discharge it from the revolver  1512 . This process may be repeated to discharge the next penultimate surgical clip  1508  from the revolver  1512 . 
     Embodiments disclosed herein include: 
     A. An end effector for a surgical clip applier that includes an elongate body, a clip revolver rotatably positioned within the elongate body and providing an inner bore that defines a plurality of clip slots angularly spaced from each other about an inner surface of the inner bore, wherein a plurality of surgical clips are receivable within the plurality of clip slots in a nested helical array, a clip advancer longitudinally movable within the elongate body and selectively engageable with each surgical clip based on rotation of the clip revolver, and first and second jaw members extending past a distal end of the elongate body and aligned to receive axially-aligned surgical clips from the clip revolver as the clip advancer advances distally, wherein the clip revolver is rotatable to sequentially align each surgical clip with the first and second jaw members. 
     B. A method of operating an end effector of a surgical clip applier that includes positioning the end effector adjacent a patient for operation, the end effector including an elongate body, a clip revolver rotatably positioned within the elongate body and providing an inner bore that defines a plurality of clip slots angularly spaced from each other about an inner surface of the inner bore, a plurality of surgical clips arranged within the plurality of clip slots in a nested helical array, a clip advancer longitudinally movable within the elongate body, and first and second jaw members extending past a distal end of the elongate body. The method further including distally advancing the clip advancer to engage a distal-most surgical clip of the plurality of surgical clips, distally advancing the distal-most surgical clip out of the clip revolver and into interposition between the first and second jaw members with the clip advancer, and collapsing the first and second jaw members to crimp the distal-most surgical clip. 
     C. A surgical clip applier that includes a drive housing, an elongate shaft that extends from the drive housing, and an end effector arranged at a distal end of the elongate shaft, the end effector including an elongate body, a clip revolver rotatably positioned within the elongate body and providing an inner bore that defines a plurality of clip slots angularly spaced from each other about an inner surface of the inner bore, wherein a plurality of surgical clips are receivable within the plurality of clip slots in a nested helical array, a clip advancer longitudinally movable within the elongate body and selectively engageable with each surgical clip based on rotation of the clip revolver, and first and second jaw members extending past a distal end of the elongate body and aligned to receive axially-aligned surgical clips from the clip revolver as the clip advancer advances distally, wherein the clip revolver is rotatable to sequentially align each surgical clip with the first and second jaw members. 
     Each of embodiments A, B, and C may have one or more of the following additional elements in any combination: Element 1: further comprising an indexer longitudinally movable within the elongate body and engageable with the clip revolver to rotate the clip revolver. Element 2: wherein the indexer includes one or more rails that are received within one or more corresponding guides provided in an inner surface of the elongate body. Element 3: wherein a camming surface of the indexer is engageable with a corresponding camming surface of the clip revolver to rotate the clip revolver. Element 4: further comprising a plurality of axially-extending camming grooves provided on an inner radial surface of the body, and a plurality of guides extending radially from an outer surface of the clip revolver and receivable within the plurality of camming grooves. Element 5: further comprising a biasing member arranged within the body to bias the plurality of guides into the plurality of camming grooves. Element 6: further comprising a torsion member operatively coupled to the elongate body and the clip revolver and imparting a torsional load on the clip revolver that urges the clip revolver to rotate relative to the elongate body, a plurality of axially-extending grooves defined on the inner bore of the clip revolver, one or more studs extending laterally from the clip advancer and receivable within the plurality of axially-extending grooves to prevent the clip revolver from rotating, and a channel groove that interconnects angularly adjacent axially-extending grooves of the plurality of axially-extending grooves. Element 7: wherein the one or more studs bypass the channel groove as the clip advancer advances distally within a given axially-extending groove of the plurality of axially-extending grooves, wherein the one or more studs are received within the channel groove as the clip advancer retracts proximally within the given axially-extending groove, and wherein the torsional load rotates the clip revolver and forces the one or more studs to enter and follow an angularly adjacent axially-extending groove of the plurality of axially-extending grooves. Element 8: wherein the plurality of clip slots forms pairs of angularly opposite clip slots, and each pair of angularly opposite clip slots receives a corresponding one of the plurality of surgical clips, and wherein the plurality of surgical clips are receivable within the pairs of clip slots such that each surgical clip resides in a different radial plane relative to a longitudinal axis of the end effector. Element 9: wherein the plurality of surgical clips are angularly offset from each other within the pairs of clips slots, and wherein the revolver is rotatable to sequentially align the pairs of clips slots with the first and second jaw members. Element 10: wherein the plurality of surgical clips are receivable within the plurality of clip slots such that a crown of more proximal surgical clips are stacked upon a crown of more distal surgical clips, and legs of the more proximal surgical clips extend past the crown of the more distal surgical clips. 
     Element 11: further comprising rotating the clip revolver from a first position to a second position where a penultimate surgical clip of the plurality of surgical clips aligns with the first and second jaw members. Element 12: wherein a plurality of guides extend radially from an outer surface of the clip revolver and a plurality of axially-extending camming grooves are provided in an inner radial surface of the elongate body, the method further comprising maintaining the clip revolver in the first position by biasing the plurality of guides into the plurality of axially-extending camming grooves, and distally advancing the clip revolver such that the plurality of guides exit the plurality of camming grooves and thereby allow the clip revolver to rotate from the first position to the second position. Element 13: wherein the end effector further includes a torsion member operatively coupled to the elongate body and the clip revolver, a plurality of axially-extending grooves defined on the inner bore of the clip revolver, and a channel groove that interconnects angularly adjacent axially-extending grooves of the plurality of axially-extending grooves, the method further comprising imparting a torsional load on the clip revolver with the torsion member and thereby urging the clip revolver to rotate away from the first position, and maintaining the clip revolver in the first position with one or more studs extending laterally from the clip advancer and received within the plurality of axially-extending grooves. Element 14: further comprising when the revolver is in the first position, bypassing the channel groove with the one or more studs as the clip advancer advances distally within a given axially-extending groove of the plurality of axially-extending grooves, receiving the one or more studs within the channel groove as the clip advancer retracts proximally within the given axially-extending groove, rotating the clip revolver to the second position with the torsional load once the one or more studs enter the channel groove, and receiving the one or more studs within an angularly adjacent axially-extending groove of the plurality of axially-extending grooves. Element 15: further comprising distally advancing the penultimate surgical clip out of the clip revolver and into interposition between the first and second jaw members, and collapsing the first and second jaw members to crimp the penultimate surgical clip. 
     Element 16: further comprising an articulable wrist joint interposing the end effector and the elongate shaft. Element 17: wherein the plurality of clip slots forms pairs of angularly opposite clip slots, and each pair of angularly opposite clip slots receives a corresponding one of the plurality of surgical clips, and wherein the plurality of surgical clips are receivable within the pairs of clip slots such that each surgical clip resides in a different radial plane relative to a longitudinal axis of the end effector. 
     By way of non-limiting example, exemplary combinations applicable to A, B, and C include: Element 1 with Element 2; Element 1 with Element 3; Element 3 with Element 4; Element 4 with Element 5; Element 6 with Element 7; Element 8 with Element 9; Element 8 with Element 10; Element 11 with Element 12; Element 11 with Element 13; and Element 14 with Element 15. 
     Therefore, the disclosed systems and methods are well adapted to attain the ends and advantages mentioned as well as those that are inherent therein. The particular embodiments disclosed above are illustrative only, as the teachings of the present disclosure may be modified and practiced in different but equivalent manners apparent to those skilled in the art having the benefit of the teachings herein. Furthermore, no limitations are intended to the details of construction or design herein shown, other than as described in the claims below. It is therefore evident that the particular illustrative embodiments disclosed above may be altered, combined, or modified and all such variations are considered within the scope of the present disclosure. The systems and methods illustratively disclosed herein may suitably be practiced in the absence of any element that is not specifically disclosed herein and/or any optional element disclosed herein. While compositions and methods are described in terms of “comprising,” “containing,” or “including” various components or steps, the compositions and methods can also “consist essentially of” or “consist of” the various components and steps. All numbers and ranges disclosed above may vary by some amount. Whenever a numerical range with a lower limit and an upper limit is disclosed, any number and any included range falling within the range is specifically disclosed. In particular, every range of values (of the form, “from about a to about b,” or, equivalently, “from approximately a to b,” or, equivalently, “from approximately a-b”) disclosed herein is to be understood to set forth every number and range encompassed within the broader range of values. Also, the terms in the claims have their plain, ordinary meaning unless otherwise explicitly and clearly defined by the patentee. Moreover, the indefinite articles “a” or “an,” as used in the claims, are defined herein to mean one or more than one of the elements that it introduces. If there is any conflict in the usages of a word or term in this specification and one or more patent or other documents that may be incorporated herein by reference, the definitions that are consistent with this specification should be adopted. 
     As used herein, the phrase “at least one of” preceding a series of items, with the terms “and” or “or” to separate any of the items, modifies the list as a whole, rather than each member of the list (i.e., each item). The phrase “at least one of” allows a meaning that includes at least one of any one of the items, and/or at least one of any combination of the items, and/or at least one of each of the items. By way of example, the phrases “at least one of A, B, and C” or “at least one of A, B, or C” each refer to only A, only B, or only C; any combination of A, B, and C; and/or at least one of each of A, B, and C.