Abstract:
A surgical stapling and severing instrument particularly suited to endoscopic procedures incorporates a handle that produces separate closing and firing motions to actuate an end effector. The handle produces multiple firing strokes to reduce the required amount of force required to fire (i.e., staple and sever) the end effector. A linked transmission reduces the required handle longitudinal length, yet achieves a rigid, strong configuration when straightened for firing. One or more electrically activated lockout mechanisms, such as electroactive polymer (EAP) actuators, are biased to prevent firing unless activated. One lockout is a spring-biased side pawl firing mechanism enabled by an EAP block actuator. Another is a firing trigger EAP lock. Yet another is a closure yoke EAP lock. Yet a further one is a manual retraction EAP lock that locks the firing mechanism. Thereby, various sensed or commanded inputs may be incorporated to prevent inadvertent firing.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
   This application claims the benefit of U.S. provisional application Ser. No. 60/591,694, entitled “SURGICAL INSTRUMENT INCORPORATING AN ELECTRICALLY ACTUATED ARTICULATION MECHANISM” to Shelton IV, filed 28 Jul. 2004. 

   FIELD OF THE INVENTION 
   The present invention relates in general to surgical stapler instruments that are capable of applying lines of staples to tissue while cutting the tissue between those staple lines and, more particularly, to improvements relating to stapler instruments and improvements in processes for forming various components of such stapler instruments that preclude inadvertent firing. 
   BACKGROUND OF THE INVENTION 
   Laparoscopic and endoscopic (“minimally invasive”) surgical instruments are often preferred over traditional open surgical devices since a smaller incision tends to reduce the post-operative recovery time and complications. Consequently, significant development has gone into a range of minimally invasive surgical instruments that are suitable for precise placement of a distal end effector at a desired surgical site through a cannula of a trocar. These distal end effectors engage the tissue in a number of ways to achieve a diagnostic or therapeutic effect (e.g., endocutter, grasper, cutter, staplers, clip applier, access device, drug/gene therapy delivery device, and energy device using ultrasound, RF, laser, etc.). 
   These devices often perform a mechanical surgical action upon tissue, such as grasping, anastomosis, cutting, stapling, etc. A reliable approach is to mechanically implement such a capability through the limited confines of the elongate shaft. Much development has gone into integrating one or more motions through the handle and shaft to realize successful instruments. 
   For instance, surgical staplers include an end effector that simultaneously makes a longitudinal incision in tissue and applies lines of staples on opposing sides of the incision. The end effector includes a pair of cooperating jaw members that, if the instrument is intended for endoscopic or laparoscopic applications, are capable of passing through a cannula passageway. One of the jaw members receives a staple cartridge having at least two laterally spaced rows of staples. The other jaw member defines an anvil having staple-forming pockets aligned with the rows of staples in the cartridge. The instrument includes a plurality of reciprocating wedges which, when driven distally, pass through openings in the staple cartridge and engage drivers supporting the staples to effect the firing of the staples toward the anvil. 
   Avoiding even extremely rare instances of equipment malfunction or human error is a highly desirable goal for minimally invasive instruments. To that end, many mechanical lockouts have been introduced. For instance, with regard to surgical staplers, it is known to mechanically lockout firing if a spent cartridge is present in the end effector or the end effector is not closed and clamped. 
   While such lockout mechanisms have certain advantages, it is desirable in some instances to provide an alternative or an additional lockout mechanism. Elaborate mechanical implementations often pose design challenges and introduce additional sources of failure or user complexity. 
   Consequently, a significant need exists for an improved surgical instrument that prevents inadvertent actuation. 
   BRIEF SUMMARY OF THE INVENTION 
   The invention overcomes the above-noted and other deficiencies of the prior art by providing a surgical stapling and severing instrument that advantageously incorporates an electrically actuated lockout mechanism in a handle that prevents actuation through an elongate shaft to an end effector. Insofar as an electrical actuator is biased toward locking out, a plurality of undesirable conditions for actuation may be avoided. 
   In one aspect of the invention, a surgical instrument that includes an end effector of opposing jaws is advantageously locked out by an electroactive polymer (EAP) actuator that is biased to lock a proximal actuator preventing closing of the jaws. Thereby, undesirable use of the instrument (e.g., insertion through a trocar, subsequent firing after closing) is avoided by this lockout. 
   In another aspect of the invention, a surgical instrument has a firing member that actuates an end effector that is a staple applying apparatus having a lower jaw and pivotally attached upper jaw. An electrically powered actuator locks to a proximal actuator that is coupled to the firing member to prevent firing in certain situations. 
   These and other objects and advantages of the present invention shall be made apparent from the accompanying drawings and the description thereof. 

   
     DESCRIPTION OF THE FIGURES 
     The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate embodiments of the invention, and, together with the general description of the invention given above, and the detailed description of the embodiments given below, serve to explain the principles of the present invention. 
       FIG. 1  is a left front perspective view of a surgical stapling and severing instrument incorporating an Electroactive Polymer (EAP) blocking, complete lockout mechanism in a handle portion. 
       FIG. 2  is a right aft perspective view of the handle portion of the surgical stapling and severing instrument of  FIG. 1  with a right half shell of a handle housing removed to expose closure and firing mechanisms. 
       FIG. 3  is a right aft perspective disassembled view of the handle portion and an elongate shaft of the surgical stapling and severing instrument of  FIG. 1 . 
       FIG. 4  is right side view of the surgical stapling and severing instrument of  FIG. 1  with a right half shell and distal portions of the implement portion removed to expose the closure and firing mechanisms in an initial state. 
       FIG. 5  is a right aft perspective view of the partially disassembled surgical stapling and severing instrument of  FIG. 4  with a closure mechanism closed and clamped and a side pawl firing mechanism completing a first stroke and with a manual retraction mechanism removed to expose a distal link of the linked rack that triggers automatic retraction of the firing mechanism. 
       FIG. 6  is a detail right aft disassembled perspective view of a linked rack firing mechanism of  FIG. 3  formed from a closure yoke assembly and the side pawl firing mechanism with an EAP lockout mechanism. 
       FIG. 7  is a right aft perspective view of the linked rack firing mechanism of  FIG. 6  depicted with a proximally retracted linked rack and a side pawl firing mechanism with the EAP lockout mechanism disengaged (electrically inactivated). 
       FIG. 8  is a right aft perspective view of the linked rack firing mechanism including a portion of the side pawl assembly of  FIG. 7  with the addition of a firing trigger and pawl block with a bumper spring shown in phantom. 
       FIG. 9  is a top view of the linked rack firing mechanism including a portion of the side pawl assembly of  FIG. 8  with the further addition of a kick-out block on the pawl block. 
       FIG. 10  is a top view of the linked rack firing mechanism of  FIG. 9  with the EAP lockout mechanism activated, shifting the linked rack to the right into engagement with the pawl block and kick-out block. 
       FIG. 11  is a right aft perspective view of the linked rack firing mechanism including the side pawl assembly, linked rack, closure yoke and rail, and firing trigger with the EAP lockout mechanism activated enabling firing. 
       FIG. 12  is a right aft perspective view of the linked rack firing mechanism of  FIG. 11  after a firing stroke with the EAP lockout mechanism inactivated, preventing advancement of the linked rack. 
       FIG. 13  is a right side view of a closure EAP lockout mechanism including an EAP actuator housed in a left side of a handle housing aligned to enter and lock a closure yoke, preventing closing and thus firing of an end effector of a surgical stapling and severing instrument. 
       FIG. 14  is a top view of the handle of  FIG. 13  with a right half shell of a handle housing removed and taken in horizontal cross section along lines  14 — 14  through a relaxed closure EAP actuator causing the closure EAP lockout mechanism to proximally lock the closure yoke, preventing closing and firing of the surgical stapling and severing instrument. 
       FIG. 15  is a top view of the handle of  FIG. 14  with the EAP actuator activated (laterally retracted) allowing distal movement of the closure yoke to close the anvil. 
       FIG. 16  is a disassembled perspective view of a manual retraction mechanism that provides firing position indication, manual release of the firing mechanism and manual retraction of the surgical stapling and severing instrument of  FIG. 1 . 
       FIG. 17  is a perspective view of the manual retraction mechanism of  FIG. 16 . 
       FIG. 18  is a left side view in elevation of a handle of the surgical stapling and severing instrument of  FIG. 1  partially disassembled to expose a detached retraction spring and the manual retraction mechanism. 
       FIG. 19  is a left side detail view of the handle of  FIG. 1  with a left half shell of the handle housing and components for closure and firing removed to expose the manual retraction mechanism, linked rack and anti-backup mechanism. 
       FIG. 20  is a left side detail view of the partially disassembled handle of  FIG. 19  with a manual retraction lever actuated proximally. 
       FIG. 21  is a left side detail view of the partially dissembled handle of  FIG. 20  with interaction with contacting surfaces between an anti-backup release lever and the manual retraction mechanism depicted in phantom. 
       FIG. 22  is a right side view of an alternative manual retraction mechanism for the surgical stapling and severing instrument of  FIG. 1  incorporating an EAP lockout mechanism depicted in a deactivated, locking condition. 
       FIG. 23  is a right side view of the alternative manual retraction mechanism of  FIG. 22  with the EAP lockout mechanism activated to an unlocked condition allowing firing and manual release. 
       FIG. 24  is a left side view of a portion of an alternative handle partially disassembled to expose a firing trigger EAP lockout mechanism in a deactivated, locked condition for the surgical stapling and severing instrument of  FIG. 1 . 
       FIG. 25  is a left side view of the EAP lockout mechanism of  FIG. 24  deactivated and unlocked allowing depression of the firing trigger. 
       FIG. 26  is an aft perspective view of the EAP lockout mechanism of  FIG. 24 . 
       FIG. 27  is a front perspective view of an upper portion of the alternative firing trigger of  FIG. 24 . 
       FIG. 28  is a left side of the upper portion of the alternative firing trigger of  FIG. 27 . 
   

   DETAILED DESCRIPTION OF THE INVENTION 
   In  FIG. 1 , a surgical stapling and severing instrument  10  includes multi-stroke firing of an end effector, which in the illustrative version is a staple applying apparatus  12 . An anvil  14  may be repeatably opened and closed about its pivotal attachment to an elongate (staple) channel  16 . The staple applying assembly  12  is proximally attached to elongate shaft  18 , forming an implement portion  22 . When the staple applying assembly  12  is closed, the implement portion  22  presents a small cross-sectional area suitable for insertion through a cannula of a trocar by manipulating handle  20 , which is attached to a proximal end of elongate shaft  18 . 
   The handle  20  has user controls mounted on its handle housing  154  user controls such as a rotation knob  30  that rotates the elongate shaft  18  and staple applying assembly  12  about a longitudinal axis of the shaft  18 . A closure trigger  26 , which pivots in front of a pistol grip  36  about a closure trigger pin  152  ( FIGS. 2–5 ) and is engaged laterally across the handle housing  154 , is depressed to close the staple applying assembly  12 . A multiple stroke firing trigger  34 , which pivots in front of the closure trigger  26 , causes the staple applying assembly  12  to simultaneously sever and staple tissue clamped therein. Since multiple firing strokes are employed to reduce the amount of force required per stroke by the surgeon&#39;s hand, right and left indicator gauge wheels  40 ,  41  (the former depicted in  FIG. 3 ) rotate presenting indicia of the firing progress. For instance, full firing travel may require three full firing strokes and thus the indicator wheels  40 ,  41  rotate up to one-third of a revolution each per stroke. A manual firing release lever  42  allows retraction before full firing travel if desired and allows assistance to retract in the presence of binding or a failure in the retraction bias. A closure release button  38  is outwardly presented when the closure trigger  26  is clamped and partial firing has not occurred that would prevent unclamping the closure trigger  26 . 
   With reference to  FIGS. 1–5 , the elongate shaft  18  has as its outer structure a longitudinally reciprocating closure tube  24  that pivots the anvil  14  ( FIG. 1 ) to effect closure in response to proximal depression of the closure trigger  26  of the handle  20 . With particular reference to  FIG. 3 , the elongate channel  18  is connected to the handle  20  by a frame  28  that is internal to the closure tube  24 . The frame  28  is rotatably engaged to the handle  20  so that twisting the rotation knob  30  causes rotation of the implement portion  22 . Each half shell of the rotation knob  30  includes an inward projection  31  that enters a respective longer side opening  70  in the closure tube  24  and projects further inward to engage the frame  28  to transfer the rotation of the rotation knob  30  to the implement portion  22 . The longitudinal length of the side opening  70  is sufficiently long to allow longitudinal closure motion of the closure tube  24  with the inward projection  31  remaining longitudinally at a fixed distance. 
   In  FIG. 3 , an upper portion  160  of the closure trigger  26  pushes forward a closure yoke  162  via a closure link  164 . The closure link  164  is pivotally attached at its distal end by a closure yoke pin  166  to the closure yoke  162  at attachment point  161  and is pivotally attached at its proximal end by a closure link pin  168 . The closure trigger  26  is urged to the open position by a closure trigger tension spring  246  that is connected proximally to the upper portion  160  of the closure trigger  26  and to the handle housing  154  formed by right and left half shells  156 ,  158 . The right and left half shells  156 ,  158  each include a closure yoke guide post  159  ( FIGS. 3 ,  4 ) that slides with a horizontally elongate rectangular aperture  169  formed in a left side of the closure yoke  162 , with the post  159  at a distal position in the aperture  169  as in  FIG. 4  when the closure yoke  162  is proximally positioned with anvil  14  open. 
   The upper portion  160  of the closure trigger  26  includes a proximal crest  170  with an aft notch  171 . The closure release button  38  and a pivoting locking arm  172  are connected by a central lateral pivot  173 . A compression spring  174  biases the closure release button  38  proximally (clockwise about the central lateral pivot  173  as viewed from the right), With the upper portion  160  back when the closure trigger  26  is released as depicted in  FIGS. 2 ,  4 , the pivoting locking arm  172  rides upon the proximal crest  170  drawing in the closure release button  38 . When the closure trigger  26  reaches its fully depressed position, it should be appreciated that the aft notch  171  is presented below the pivoting locking arm  172 , which drops into and locks against the aft notch  171  under the urging of the compression spring  174 . With the firing components retracted, manual depression of the closure release button  38  rotates the pivoting locking arm  172  upward unclamping the closure trigger  26 . 
   Once the closure trigger  26  is proximally clamped, a firing rod  32  is distally moved from the handle  20  in response to the multiple stroke firing trigger  34  being drawn to the pistol grip  36  with the amount of firing travel visible to the surgeon on right and left indicator gauge wheels  40 ,  41 . The firing trigger  34  pivots about a firing trigger pin  202  that laterally traverses and is engaged to the right and left half shells  156 ,  158 . 
   A linked transmission firing mechanism  150  is initially retracted, urged to remain in this position by the combination tension/compression spring  184  that is constrained within the pistol grip  36  of the handle  20 , with its nonmoving end  186  connected to a housing  154  and a moving end  188  connected to a downwardly flexed and proximal, retracted end  190  of a steel band  192 . 
   A distally-disposed end  194  of the steel band  192  is attached to an attachment feature  195  on a front link  196   a  of a plurality of links  196   a – 1196   d  that form a linked rack  200 . Linked rack  200  is flexible yet has distal links that form a straight rigid rack assembly that may transfer a significant firing force through the firing rod  32  in the implement portion  22 , yet readily retracts into the pistol grip  36  to minimize the longitudinal length of the handle  20 . It should be appreciated that the combination tension/compression spring  184  increases the amount of firing travel available while essentially reducing the minimum length by half over a single spring. 
   Anti-Backup Mechanism. 
   In  FIGS. 3–5 , an anti-backup mechanism  250  prevents the combination tension/compression spring  184  from retracting the linked rack  200  between firing strokes. A coupling tube  131  proximally distally connects to the firing rod  32  to communicate the firing motion. The guide posts  159  engage lateral recesses  133  on a proximal portion of coupling slide tube  131 . Links  196   a  and  196   b  enter a proximally open cavity in the coupling tube  131  when fired. The firing rod  32  extends proximally out of a proximal end of the frame  28  and through a through hole  408  of an anti-backup plate  266 . The through hole  408  is sized to slidingly receive the firing rod  32  when perpendicularly aligned but to bind when tipped. A lower tab attachment  271  extends proximally from a lower lip of the proximal end of the frame  28 , extending through an aperture  269  on a lower edge of the anti-backup plate  266 . This lower tab attachment  271  draws the lower portion of the anti-backup plate  266  proximate to the frame  28  so that the anti-backup plate  266  is perpendicular when the firing rod  32  is distally advanced and allowed to tip top aft into a binding state when the firing rod  32  attempts to retract. An anti-backup compression spring  264  is distally constrained by the proximal end of the frame  28  and proximally abutts a top portion of the anti-backup plate  266 , biasing the anti-backup plate  266  to a locking state. 
   Opposing the spring bias, an anti-backup cam tube  268  slidingly encompasses the coupling tube  131  and abuts the anti-backup plate  266 . A proximally projecting anti-backup yoke  256  attached to the anti-backup cam tube  268  extends overtop of the closure yoke  162 . 
   Linked Rack Triggered Automatic Retraction. 
   In  FIGS. 1–5 , a link triggered automatic retraction mechanism  289  is incorporated into the surgical stapling and severing instrument  10  to cause knife retraction at the end of full firing travel. To that end, the most proximal link  196   d  includes a tang  290  that projects upwardly when the most proximal link  196   d  is advanced into rack channel  291  formed in the closure yoke  162 . This tang  290  is aligned to activate a bottom proximal cam  292  on an anti-backup release lever  248 . Structures formed in the right and left half shells  156 ,  158  constrain movement of the anti-backup release lever  248 . A pin receptacle  296  and circular pin  293 , formed respectively inside right and left half shells  156 ,  158 , is received through a longitudinally elongate aperture  294  formed in the anti-backup release lever  248  distal to the bottom proximal cam  292 , thus allowing longitudinal translation as well as rotation about the circular pin  293  and pin receptacle  296 . In the right half shell  156 , a proximally open channel  295  includes a proximal horizontal portion that communicates with an upwardly and distally angled portion that receives a rightward aft pin  297  near the proximal end of the anti-backup release lever  248 , thus imparting an upward rotation as the anti-backup release lever  248  reaches the distal most portion of its translation. A blocking structure, formed in the right half shell  156  proximal to the anti-backup release lever  248 , prevents proximal movement thereof once assembled to maintain rightward aft pin  297  in the proximally open channel  295 . 
   A distal end  254  of the anti-backup release lever  248  thus is urged distally and downwardly, causing a rightward front pin  298  to drop into distally open step structure  299  formed in the right half shell  156 , which is urged into this engagement by a compression spring  300  hooked to a leftward hook  301  on the anti-backup release lever  248  between the rightward front pin  298  and the longitudinally elongate aperture  294 . The other end of the compression spring  300  is attached to a hook  302  mounted on the top surface of closure yoke  162 . The compression spring  300  thus pulls the distal end  254  of the anti-backup release lever  248  down and aft, which results in the rightward front pin  298  locking into the distally open step structure  299  when distally advanced. 
   Once tripped, the anti-backup release lever  248  remains forward holding the anti-backup plate  266  perpendicularly, thus allowing the linked rack  200  to be retracted. When the closure yoke  162  is subsequently retracted when unclamping the end effector  12 , an upwardly projecting reset tang  303  on the closure yoke  162  contacts a bottom distal cam  305  of the anti-backup release lever  248 , lifting the rightward front pin  298  out of the distally open step structure  299  so that the anti-backup compression spring  264  can proximally push the anti-backup cam tube  268  and the anti-backup release lever  248  to their retracted positions. 
   Side Pawl Firing Mechanism Incorporating EAP Lockout Mechanism. 
   The handle  20 , especially the linked rack firing mechanism  150 , is described in greater detail in the commonly-owned U.S. patent application Ser. No. 11/052,387, hereby incorporated by reference in its entirety, such as depictions of a side pawl assembly intermittently driving a linked rack. With particular reference to  FIG. 6 , however, a side pawl assembly  285  is modified to include an EAP lockout mechanism  199 . In particular, modifications to the linked rack firing mechanism  150 , specifically the closure yoke  162 , pawl slide (shuttle)  270 , and links  196   a–d , allow a bumper spring  201  to be distally gripped in a curved vertically open slot  203  in the pawl slide  270 , extending a proximal bowed portion along the left side of the pawl slide  270 . Each link  196   a–d  has a horizontal recess  205  along the bottom of its right side to present an uninterrupted contact surface to the bumper spring  201  to receive a leftward bias therefrom, moving the linked rack  200  out of engagement. An EAP block actuator  207  retained in a rightwardly open horizontal slot  209  in the closure yoke  162 , when activiated against the right side of the links  196   a–d , urges the linked rack  200  into close proximity to the pawl slide  270 , compressing the bumper spring  201 , thereby enabling firing. 
   It should be appreciated that a number of control circuitry features may thus be incorporated to prevent firing. For example, an enabling switch may be added to the handle  20 . As another example, sensors in the end effector  12  may be included, such as presence or absence of an unspent staple cartridge, and presence of an appropriate amount of tissue clamped into the end effector, presence or absence of ancillary compounds or therapeutic features (e.g., a cauterizing, sterilizing, etc.). Futher, control circuitry may comprise lumped analog components, a programmable logic array, a microcontroller, or other types of electronic circuits. 
   Electroactive Polymers. 
   Electroactive polymers (EAPs) are a set of conductive doped polymers that change shape when electrical voltage is applied. In essence, the conductive polymer is paired to some form of ionic fluid or gel and electrodes. Flow of the ions from the fluid/gel into or out of the conductive polymer is induced by the voltage potential applied and this flow induces the shape change of the polymer. The voltage potential ranges from 1V to 4 kV, depending on the polymer and ionic fluid used. Some of the EAPs contract when voltage is applied and some expand. The EAPs may be paired to mechanical means such as springs or flexible plates to change the effect that is caused when the voltage is applied. 
   There are two basic types and multiple configurations of each type. The two basic types are a fiber bundle and a laminate version. The fiber bundle consists of fibers around 30–50 microns. These fibers may be woven into a bundle much like textiles and are often called EAP yarn because of this. This type of EAP contracts when voltage is applied. The electrodes are usually a central wire core and a conductive outer sheath, which also serve to contain the ionic fluid that surrounds the fiber bundles. An example of a commercially available fiber EAP material is manufactured by Santa Fe Science and Technology, sold as PANION fiber and described in U.S. Pat. No. 6,667,825, which is hereby incorporated by reference in its entirety. 
   The other type is a laminate structure. It consists of a layer of EAP polymer, a layer of ionic gel and two flexible plates that are attached to either side of the laminate. When a voltage is applied, the square laminate plate expands in one direction and contracts in the perpendicular direction. An example of a commercially available laminate (plate) EAP material is available from Artificial Muscle Inc, a division of SRI Laboratories. Plate EAP material is also available from EAMEX of Japan and referred to as thin film EAP. 
   It should be noted that EAPs do not change volume when energized; they merely expand or contract in one direction while doing the opposite in the transverse direction. The laminate version may be used in its basic form by containing one side against a rigid structure and using the other much like a piston. It may also be adhered to either side of a flexible plate. When one side of the flexible plate EAP is energized it would expand, flexing the plate in the opposite direction. This allows the plate to be flexed either direction depending on which side is energized. 
   An EAP actuator usually consists of numerous layers or fibers bundled together to work in cooperation. The mechanical configuration of the EAP determines the EAP actuator and its capabilities for motion. The EAP may be formed into long stands and wrapped around a single central electrode. A flexible exterior outer sleeve will form the other electrode for the actuator as well as contain the ionic fluid necessary for the function of the device. In this configuration when the electrical field is applied to the electrodes, the strands of EAP shorten. This configuration of the EAP actuator is called a fiber EAP actuator. Likewise, the laminate configuration may be placed in numerous layers on either side of a flexible plate or merely in layers on itself to increase its capabilities. Typical fiber structures have an effective strain of 2–4% where the typical laminate version achieves 20–30%, utilizing much higher voltages. It should be appreciated, however, that these performance ranges are not determinative. 
   For instance, a laminate EAP composite may be formed from a positive plate electrode layer attached to an EAP layer, which in turn is attached to an ionic cell layer, which in turn is attached to a negative plate electrode layer. A plurality of laminate EAP composites may be affixed in a stack by adhesive layers therebetween to form an EAP plate actuator. It should be appreciated that opposing EAP actuators may be formed that can selectively bend in either direction. 
   A contracting EAP fiber actuator may include a longitudinal platinum cathode wire that passes through an insulative polymer proximal end cap, and then through an elongate cylindrical cavity formed within a plastic cylinder wall that is conductively doped to serve as a positive anode. A distal end of the platinum cathode wire is embedded into an insulative polymer distal end cap. A plurality of contracting polymer fibers are arranged parallel with and surrounding the cathode wire and have their ends embedded into respective end caps. The plastic cylinder wall is peripherally attached around respective end caps to enclose the cylindrical cavity to seal in ionic fluid or gel that fills the space between contracting polymer fibers and cathode wire. When a voltage is applied across the plastic cylinder wall (anode) and cathode wire, ionic fluid enters the contracting polymer fibers, causing their outer diameter to swell with a corresponding contraction in length, thereby drawing the end caps toward one another. 
   Firing and Automatic Retraction. 
   With particular reference to  FIGS. 2–5 , the firing trigger  34  pivots about a firing trigger pin  202  that is connected to the housing  154 . A firing actuator, depicted as an upper portion  204  of the firing trigger  34 , moves distally about the firing trigger pin  202  as the firing trigger  34  is depressed toward pistol grip  36 , stretching a proximally placed firing trigger tension spring  206  ( FIG. 3 ) proximally connected between the upper portion  204  of the firing trigger  34  and the housing  154 . The upper portion  204  of the firing trigger  34  engages the linked rack  200  during each firing trigger depression by a spring-biased side pawl mechanism  210  that also disengages when the firing trigger  34  is released. 
   In particular, a ramped right-side track  282  formed by a proximally and rightwardly facing beveled surface  284  in each of the links  196   a–   196   d  is engaged by a side pawl assembly  285 . In particular, the pawl slide (shuttle)  270  ( FIGS. 3 ,  6 ) has right and left lower guides  272  that slide respectively in a left track  274  ( FIGS. 3 ,  6 ) formed in the closure yoke  162  below the rack channel  291  and a right track  275  in a closure yoke rail  276  that parallels rack channel  291  and is attached to a rack channel cover  277  that closes a rightwardly open portion of the rack channel  291  in the closure yoke  162  that is distal to the travel of the pawl slide  270 . In  FIGS. 3 ,  6 , a compression spring  278  is attached between a hook  279  on a top proximal position on the closure yoke rail  276  and a hook  280  on a distal right side of the pawl slide  270 , which keeps the pawl slide  270  drawn proximally into contact with the upper portion  204  of the firing trigger  34 . The other depictions omit the compression spring  278  for clarity. 
   With particular reference to  FIG. 6 , a pawl block  318  sits on the pawl slide  270  pivoting about a vertical aft pin  320  that passes through a left proximal corner of pawl block  318  and pawl slide  270 . A kick-out block recess  322  is formed on a distal portion of a top surface of the block  318  to receive a kick-out block  324  pivotally pinned therein by a vertical pin  326  whose bottom tip extends into a pawl spring recess  328  on a top surface of the pawl slide  270 . A pawl spring  330  in the pawl spring recess  328  extends to the right of the vertical front pin  326 , urging the pawl block  318  to rotate counterclockwise when viewed from above into engagement with the ramped right-side track  282 . A small coil spring  332  in the kick-out block recess  322  urges the kick-out block  324  to rotate clockwise when viewed from above, its proximal end urged into contact with a contoured lip  334  formed in the closure yoke  162  above the rack channel  291 . 
   The stronger mechanical advantage of the pawl spring  330  over the small coil spring  332  means that the pawl block  318  tends toward engagement with the kick-out block  324  rotated clockwise. In  FIG. 5 , as the firing trigger  34  is fully depressed and begins to release, the kick-out block  324  encounters a ridge  336  in the contoured lip  334  as the pawl slide  270  retracts, forcing the kick-out block  324  to rotate clockwise when viewed from above and thereby kicking out the pawl block  318  from engagement with the linked rack  200 . The shape of the kick-out block recess  322  stops the clockwise rotation of the kick-out block  324  to a perpendicular orientation to the contoured lip  334  (FIG.  10 ), maintaining this disengagement during the full retraction and thereby eliminating a ratcheting noise. 
   With the exception of modifications described above to incorporate the afore-described EAP lockout mechanism  150 , the handle  20  is described in greater detail in two commonly-owned U.S. patent application Ser. Nos. 11/052,387 and 11/052,632, both filed on 7 Feb. 2005, the disclosures of both of which are hereby incorporated by reference in their entirety. 
   Operation of the EAP Firing Pawl Lockout Mechanism. 
   In  FIGS. 7–12 , the side pawl assembly  285  is depicted in operation performing locking out of firing. In particular, in  FIGS. 7–9 , the pawl slide  270  is laterally constrained by being longitudinally guided between the closure yoke  162  and the closure yoke rail  276 . The bumper spring  201  extends laterally to the left of the pawl slide  270  against the horizontal recess  205  of an adjacent link  196   a  of the linked rack  200 , urging the linked rack  200  to the left across the rack channel  291  formed in the closure yoke  162 . The EAP block actuator  207  is laterally contracted in a deactivated state, confined within the rightwardly open horizontal slot  209  in the closure yoke  162 . Thus, with the firing trigger  34  drawn from its relaxed position ( FIG. 8 ) to its depressed position ( FIG. 12 ), the top portion  204  of the firing trigger  34  advances the pawl slide  270  without the pawl block  318  engaging the proximally and rightwardly facing beveled surface  284  of the link  196   a . Thus, no force is imparted to the linked rack  200  that would have to be blocked downstream in the event of an undesirable firing condition. 
   Closure EAP Blocking Lockout. 
   In  FIGS. 13–15 , an alternate blocking lockout mechanism  600  may be incorporated into a surgical stapling and severing instrument  610  identical to that described above, but with the addition of an EAP actuator  612  contained within a recess  614  in a left half shell  658  of a handle housing  654  of a handle  620 . The left half shell  658  includes the closure yoke guide post  159  that slides with a horizontally elongate rectangular aperture  669  formed in a left side of the closure yoke  162 , with the guide post  159  at a distal position in the aperture  669  as in  FIG. 14  when the closure yoke  162  is proximally positioned with anvil  14  open. The guide post  159  projects inwardly to engage the coupling tube  131  whose proximally open cavity receives links  196   a ,  196   b  ( FIG. 15 ). In  FIG. 14 , the EAP actuator  612  is in its laterally extended, inactivated state engaged within the horizontally elongate rectangular aperture  669  aft of the guide post  659 . Thus, the closure yoke  162  is locked in its proximally retracted position. In  FIG. 15 , the EAP actuator  612  is activated, contracting to the left out of the rectangular aperture  669  in the closure yoke  162 , which has been distally advanced to close the anvil  14  (not shown in  FIGS. 13–15 ). 
   It should be appreciated that many laparoscopic or endoscopic surgical instruments include at least one movable member in the handle that may be modified to include an aperture or similar engaging feature to transversely receive an EAP locking mechanism. Thus, while a surgical stapling and severing instrument benefits from such a lockout, many other types of instruments would benefit. 
   Manual Retraction of Multiple-Stroke Firing Mechanism. 
   As also described in the afore-mentioned U.S. patent application Ser. Nos. 11/052,387 and 11/052,632, in  FIGS. 3 ,  5 , and  16 – 21 , the surgical stapling and severing instrument  10  includes a manual retraction mechanism  500  that provides firing position indication, manual release of the firing mechanism, and manual retraction. A gear mechanism  502  also functions to visually indicate progress of firing travel and to manually retract the knife. A front idler gear  220  engages a toothed upper, left surface  222  of the linked rack  200  ( FIGS. 3 ,  18 – 20 ). The front idler gear  220  also engages an aft idler gear  230  having a smaller right-side ratchet gear  231 . Both the front idler gear  220  and aft idler gear  230  are rotatably connected to the handle housing  154  respectively on front idler axle  232  and aft idler axle  234 . Each end of the aft axle  232  extend through the respective right and left housing half shells  156 ,  158  and are attached to the left and right indicator gauge wheels  40 ,  41 . Since the aft axle  234  is free spinning in the handle housing  154  and has a keyed engagement to the aft gear  230 , the indicator gauge wheels  40 ,  41  rotate with the aft gear  230 . The gear relationship between the linked rack  200 , idler gear  220  and aft gear  230  may be advantageously selected so that the toothed upper surface  222  has tooth dimensions that are suitably strong and the aft gear  230  makes no more than one revolution during the full firing travel of the linked transmission firing mechanism  150 . 
   The smaller right-side ratchet gear  231  of the aft idler gear  230  extends into a hub  506  of the manual retraction lever  42 , specifically aligned with a vertical longitudinally-aligned slot  508  ( FIG. 16 ) bisecting the hub  506 . A lateral through hole  510  of the hub  506  communicates with an upper recess  512 . A front portion  514  is shaped to receive a proximally directed locking pawl  516  that pivots about a rightward lateral pin  518  formed in a distal end of the upper recess  512 . An aft portion  520  is shaped to receive an L-shaped spring tab  522  that urges the locking pawl  516  downward into engagement with the right-side smaller ratchet gear  231 . A hold-up structure  524  ( FIG. 19 ) projects from the right half shell  156  into the upper recess  512  holding up the locking pawl  516  from engaging the smaller right-side ratchet gear  231  when the manual retraction lever  42  is down ( FIG. 19 ). A coil spring  525  ( FIG. 3 ) urges the manual retraction lever  42  down. 
   In use, as depicted in  FIGS. 18–19 , the combination tension/compression spring  184  may become disconnected with the linked rack distally positioned. In  FIGS. 20–21 , as the manual retraction lever  42  is raised, the locking pawl  516  rotates clockwise, no longer is held up by the hold-up structure  524  and engages the smaller right-side ratcheting gear  231 , rotating the aft idler gear  230  clockwise when viewed from the left. Thus, the forward idler gear  220  responds counterclockwise retracting the linked rack  200 . In addition, a rightward curved ridge  530  projects out from the hub  506 , sized to contact and distally move the anti-backup release lever  248  to release the anti-backup mechanism  250  as the manual retraction lever  42  is rotated until contacting a stop  531 . 
   EAP Firing Lockout Mechanism in Manual Retraction Mechanism. 
   In  FIGS. 22–23 , an EAP lockout mechanism  550  is advantageously incorporated into a modified hub  506 ′ of a manual retraction lever  24 ′. A distal side of an upper recess  514 ′ is shaped into a slot  513  to receive a held end  517  of an EAP locking member  519  and a proximal side of the upper recess  512 ′ is shaped into an actuator recess  527  to receive a locking plunger  521  that abuts a free end  523  of the EAP locking member  519 . An opposing compression spring  529  urges the locking plunger  521  distally out of the actuator recess  527 , as depicted in  FIG. 22  when the EAP locking member  519  is deactivated. The locking plunger  521  forces the L-shaped spring tab  522  and the locking pawl  516  downward into engagement with the right-side smaller ratchet gear  231 , preventing firing. Advantageously, the surgeon may manually retract the firing mechanism although further firing is locked out. In  FIG. 23 , the EAP locking member  519  is activated, expanding proximally, forcing the locking plunger  521  proximally into the actuator recess  527 , allowing the locking pawl  516  to ratchet up against the L-shaped spring tab  522  and thus allowing firing. 
   Firing Trigger EAP Locking Mechanism. 
   In  FIGS. 24–28 , an EAP locking mechanism  800  is advantageously incorporated into a handle  820  to lock an EAP locking actuator  822  against a locking ridge  802  formed in an upper end  804  of a firing trigger  834 . The EAP locking actuator  822  is constrained to move downwardly and slightly distally by an actuator guide  835  formed in a handle housing  854 . In  FIGS. 24–25 , the EAP actuator  822  is comprised of an EAP member  855  that has a fixed end  857  held in a top end of the actuator recess  835  with a moving end  859  held in an actuator piston  861 . A compression spring  863 , which encompasses the EAP member  855 , has an upper end  865  abutting the upper end of the actuator recess  835  and a lower end  869  abutting the actuator piston  861 . A hard tip  865  is attached to an exposed end of the actuator piston  861  to correspond to a recessed surface  867  adjacent to the locking ridge  802  of the firing trigger  834 . The EAP member  855  is normally expanded, as depicted in  FIGS. 24 ,  26 , with this hard tip  865  abutting the recessed surface  867  blocking forward rotation of the locking ridge  802  of the firing trigger  834 . In  FIG. 25 , the EAP member  855  is contracted, pulling up the actuator piston  861  and hard tip  865  and compressing the spring  863 , thus allowing depression of the firing trigger  834 . 
   It should be appreciated that a similar EAP locking mechanism may be incorporated into a closure trigger for surgical stapling and severing instruments that present two triggers instead of one that performs both functions. 
   While the present invention has been illustrated by description of several embodiments and while the illustrative embodiments have been described in considerable detail, it is not the intention of the applicant to restrict or in any way limit the scope of the appended claims to such detail. Additional advantages and modifications may readily appear to those skilled in the art. 
   It will be appreciated that the terms “proximal” and “distal” are used herein with reference to a clinician gripping a handle of an instrument. Thus, the end effector  12  is distal with respect to the more proximal handle  20 . Analogous terms such as “front” and “back” similarly correspond respectively to distal and proximal. It will be further appreciated that for convenience and clarity, spatial terms such as “vertical” and “horizontal” are used herein with respect to the drawings. However, surgical instruments are used in many orientations and positions, and these terms are not intended to be limiting and absolute. 
   The present invention is being discussed in terms of laparoscopic and endoscopic procedures and apparatus. However, use herein of terms such as “endoscopic” should not be construed to limit the present invention to a surgical stapling and severing instrument for use only in conjunction with a laparoscopic cannula (i.e., trocar). On the contrary, it is believed that the present invention may find use in any procedure where access is limited to a small incision, including but not limited to other laparoscopic procedures, as well as open procedures. 
   Applications consistent with the present invention may include a solid firing rack rather than a linked rack. 
   The linked rack  200  serves as a proximal engaging portion of a firing member that actuates the implement portion  22 . It should be appreciated that a frictional engagement may be used instead of a spring-biased side pawl assembly  285 , such as described in co-pending and commonly-owned U.S. patent application Ser. No. 10/673,662 to Jeffrey S. Swayze, et al., entitled “SURGICAL STAPLING INSTRUMENT HAVING MULTISTROKE FIRING INCORPORATING A TRACTION-BIASED RACHETING MECHANISM”, the disclosure of which is hereby incorporated by reference in its entirety. 
   In addition, the orientation of the side pawl assembly  285  to a linked rack  200  to its left is illustrative. It should be appreciated that a linked or solid rack may be oriented above, below, or to the right of a selectively engaging member coupled to a firing trigger (e.g., spring biased pawl, traction biased member). 
   In the above-described versions, a side pawl is spring biased into engagement with the rack  200  but held out of engagement during proximal movement when the firing trigger is released. A spring biases the pawl slide to avoid engagement unless overcome by the EAP lockout actuator. It should also be appreciated that applications consistent with the present invention may include an EAP lockout actuator that biases a pawl into engagement with a rack of a firing mechanism. Thus, a pawl may be biased out of engagement. A sensor coupled to a firing trigger enables an EAP lockout actuator, when the firing trigger is sensed, from being depressed and not released. The EAP lockout actuator is activated (optionally with other preconditions met) urging the pawl into engagement with the rack. 
   In the above-described versions, a rack and pawl engagement is advantageously described as providing a strong transfer of firing motion from a firing trigger to a firing bar. It should be appreciated that applications consistent with the present application may include a frictional engagement between a proximal portion of a firing member and a firing actuator such as a firing trigger. An EAP lockout actuator may prevent binding contact by effecting spacing or preventing a binding deflection (e.g., screen door damper lock). 
   While it is desirable in many applications for a lockout to default to a locked condition, even in an unpowered or failed condition, it should be appreciated that applications consistent with the present invention may include a lockout mechanism that is electrically actuated that defaults to an unlocked state, especially if power is required for the firing action that is being prevented by the locking mechanism to occur. As yet a further alternative, a bi-stable lock may remain in either a locked or an unlocked state until an electrically-powered actuator toggles the state of the locking mechanism. 
   As another example, the lockout mechanism may comprise an EAP actuator positioned on an opposite side of the pawl slide from the rack to push the pawl slide toward a rack. Further, this EAP actuator may be attached to the pawl slide or to a relatively stationary part of the handle adjacent to the pawl slide. 
   As yet another example, a bias of the lockout mechanism urging the proximal engaging portion of the firing member (e.g., rack) away from the engagement mechanism (e.g., pawl/pawl slide) may comprise a resilient strip of material affixed to an inner surface of the proximal engaging portion of the firing member and/or the engagement mechanism. 
   While an electroactive polymer has a number of benefits, in some applications consistent with the present invention, an electrically powered actuator may be substituted, such as a solenoid.