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. In particular, the handle produces multiple firing strokes in order to reduce the required amount of force required to fire (i.e., staple and sever) the end effector. A firing member reciprocates within an elongate shaft to the end effector to transfer this firing motion. A retraction spring retracts the firing member after full firing. Between firing strokes as the firing trigger is released, an anti-backup mechanism activates an electrical actuator (e.g., elecroactive polymer actuator) that is physically grounded to the handle to bind the firing member preventing inadvertent retraction.

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 
   Endoscopic and laparoscopic surgical instruments are often preferred over traditional open surgical devices since a smaller incision tends to reduce the post-operative recovery time and complications. The use of laparoscopic and endoscopic surgical procedures has been relatively popular and has provided additional incentive to develop the procedures further. In laparoscopic procedures, surgery is performed in the interior of the abdomen through a small incision. Similarly, in endoscopic procedures, surgery is performed in any hollow viscus of the body through narrow endoscopic tubes inserted through small entrance wounds in the skin. 
   Laparoscopic and endoscopic procedures generally require that the surgical region be insufflated. Accordingly, any instrumentation inserted into the body must be sealed to ensure that gases do not enter or exit the body through the incision. Moreover, laparoscopic and endoscopic procedures often require the surgeon to act on organs, tissues and/or vessels far removed from the incision. Thus, instruments used in such procedures are typically long and narrow while being functionally controllable from a proximal end of the instrument. 
   Significant development has gone into a range of endoscopic 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.). 
   Known 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. 
   Generally, a single closing stroke followed by a single firing stroke is a convenient and efficient way to perform severing and stapling. However, in some instances, multiple firing strokes are desirable. For example, surgeons select a length of staple cartridge for the desired length of the cut from a range of jaw sizes. Longer staple cartridges require a longer firing stroke. Thus, to effect the firing, a hand-squeezed trigger is required to exert a larger force for these longer staple cartridges in order to sever more tissue and drive more staples as compared to a shorter staple cartridge. It would be desirable for the amount of force to be lower and comparable to shorter cartridges so as not to exceed the hand strength of some surgeons. In addition, some surgeons, not familiar with the larger staple cartridges, may become concerned that binding or other malfunction may occur when an unexpectedly higher force is required. 
   In co-pending and commonly-owned U.S. Pat. Appl. Publ. 2005/0067457 A1, Ser. No. 10/673,929, “SURGICAL STAPLING INSTRUMENT WITH MULTISTROKE FIRING INCORPORATING AN ANTI-BACKUP MECHANISM” to Shelton et al. filed on Sep. 29, 2003, the disclosure of which is hereby incorporated by reference in its entirety, an advantageous anti-backup mechanism mechanically disengages as a firing member distally moves during each firing stroke and then engages as the firing trigger is released between firing strokes, preventing inadvertent retraction. Upon full firing travel, a mechanical linkage is tripped that disengages the anti-backup mechanism, allowing a retraction spring to retract the firing member. Thereby, the advantages of multiple firing strokes were realized in combination with automatic retraction. 
   More recently, a similar anti-backup mechanism is described in two U.S. patent application Ser. Nos. 11/052,387 entitled “SURGICAL STAPLING INSTRUMENT INCORPORATING A MULTI-STROKE FIRING MECHANISM WITH RETURN SPRING ROTARY MANUAL RETRACTION SYSTEM” to Shelton et al., and U.S. patent application Ser. No. 11/052,632 entitled “SURGICAL STAPLING INSTRUMENT INCORPORATING A FIRING MECHANISM HAVING A LINKED RACK TRANSMISSION” to Swayze et al., both filed on 8 Feb. 2005, the disclosure of both being hereby incorporated by reference in its entirety. 
   While these mechanically controlled anti-backup mechanisms provide significant clinical utility, it is desirable to provide an alternate approach to preventing inadvertent retraction that allows for additional functionality. 
   Consequently, a significant need exists for an improved surgical stapling and severing instrument that performs multistroke firing for increased firing travel and/or reduced force to fire with a reliable and configurable prevention of inadvertent firing retraction between strokes. 
   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 a multiple firing stroke handle that actuates a long end effector without undue manual force required by the surgeon. A retraction bias on firing components assists in retracting a firing mechanism after full firing travel. Advantageously, an electrical actuator assists in preventing inadvertent retraction of firing components between firing strokes. 
   These and other objects and advantages of the present invention shall be made apparent from the accompanying drawings and the description thereof. 

   
     BRIEF 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 a multistroke firing mechanism with an electrically actuated anti-backup mechanism in a handle portion and a partially cut-away elongate shaft. 
       FIG. 2  is a right aft perspective disassembled view of the handle and an elongate shaft with an end effector omitted from the surgical stapling and severing instrument of  FIG. 1  with one version of the electrically actuated anti-backup mechanism including a hybrid electroactive polymer (EAP)-mechanically actuated anti-backup locking plate. 
       FIG. 3  is a right side view of an upper portion of the handle of  FIG. 2  with the right housing half shell and rotation knob removed. 
       FIG. 3A  is a right side detail view of an electrically and mechanically actuated anti-backup cam tube of  FIG. 3  with an actuated (unlocked) position shown in phantom. 
       FIG. 4  is left side view of another version of the electrically actuated anti-backup mechanism of  FIG. 1  with a spring biased locking plate and EAP-actuated anti-backup cam tube. 
       FIG. 5  is an aft perspective view of the EAP-actuated anti-backup cam tube of  FIG. 4 . 
       FIG. 6  is a perspective view of one EAP actuator of  FIGS. 4-5 . 
       FIG. 7  is a top left perspective view of a frame ground, left half shell of a handle housing and another version of the electrically actuated anti-backup mechanism of  FIG. 1  incorporating an EAP released binding coil. 
       FIG. 8  is a top left perspective detail view of the EAP actuator and proximal portion of the anti-backup binding coil of the  FIG. 7 . 
       FIG. 9  is a front view taken in cross section through the EAP released binding coil along lines  9 - 9  of the electrically actuated anti-backup mechanism of  FIG. 8 . 
       FIG. 10  is a left side view in elevation of electrically actuated anti-backup mechanism of  FIG. 7  with the frame ground removed to expose the EAP released binding coil. 
       FIG. 11  is a left side detail view in elevation of the electrically actuated anti-backup mechanism of  FIG. 7  with the frame ground and firing rod shown in phantom. 
       FIG. 12  is a top left perspective detail view of another version of the electrically actuated anti-backup mechanism of  FIG. 1  including an EAP split cylindrical binding sleeve. 
       FIG. 13  is a left side view in longitudinal cross section taken in elevation through an elongate shaft and the electrically actuated anti-backup mechanism along lines  13 - 13  of  FIG. 12 . 
       FIG. 14  is a front view taken in transverse cross section through the elongate shaft and EAP split cylindrical sleeve (expanded to lock) in a confining shell taken along lines  14 - 14  of  FIG. 12 . 
       FIG. 15  is a left side detail view taken in longitudinal cross section through the expand-to-lock EAP split cylindrical sleeve and firing rod of  FIG. 14  taken along lines  15 - 15 . 
       FIG. 16  is a front view taken in transverse cross section through the elongate shaft and an electrically actuated anti-backup mechanism of  FIG. 14  taken along lines  14 - 14  with an alternative EAP cylindrical sleeve (contract to lock). 
       FIG. 17  is a left side detail view taken in longitudinal cross section through the contract-to-lock EAP cylindrical sleeve and firing rod of  FIG. 16  taken along lines  17 - 17 . 
   

   DETAILED DESCRIPTION OF THE INVENTION 
   In  FIG. 1 , a surgical device suitable for endoscopic and laparoscopic use is depicted that advantageously combines a multiple firing stroke, automatic retraction of firing components, and an advantageously electrically actuated anti-backup mechanism consistent with the present invention to prevent inadvertent retraction between firing strokes. In  FIGS. 2-3 ,  3 A a version of the anti-backup mechanism of  FIG. 1  is depicted. In particular, an electrical-mechanical (hybrid) anti-backup mechanism modifies the wholly mechanical implementation described in more detail in the afore-mentioned U.S. patent application Ser. Nos. 11/052,387 and 11/052,632, both of which more fully explain closure and firing operations of the handle common to the illustrative versions herein. In  FIGS. 4-6 , a version of the electrically actuated anti-backup mechanism further omits the mechanical portions for the mechanical end of firing travel and manual release of an anti-backup mechanism, relying solely upon a spring-biased locking plate for preventing retraction opposed by an electroactive polymer (EAP) actuated anti-backup cam tube for release similar to that depicted in  FIGS. 2-3 ,  3 A. In  FIGS. 7-11 , a version of the electrically actuated anti-backup mechanism employs a coil closely wound to bind the firing mechanism that is loosened by an EAP actuator to release. In  FIGS. 12-15 , a version of the electrically actuated anti-backup mechanism employs an EAP split cylindrical sleeve that expands to lock, being forced inwardly into binding contact with the firing rod by an encompassing shell and contracts to unlock. In  FIGS. 16-17 , a version of the electrically actuated anti-backup mechanism employs an EAP cylindrical sleeve that contracts inwardly into binding contact with the firing rod and expands to unlock. 
   Turning to the Drawings wherein like numerals denote like components throughout the several views, 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 , which in turn is proximally attached to a handle.  20 . In particular, a frame ground  21  of the elongate shaft  16  is rotatably engaged to the handle  20  at its proximal end and attached to the staple channel  16  at its distal end. The shaft  18  and staple applying apparatus  12  together form an implement portion  22 . The staple applying assembly  12  is closed by distally advancing a closure tube  24  that encompasses the frame ground  21 . The closed staple applying assembly  22  of the implement portion  22  presents a small cross-sectional area suitable for insertion through a cannula of a trocar (not shown) by externally manipulating the handle  20 . With the implement portion  22  positioned, the staple applying assembly  12  is subsequently closed and clamped upon tissue. A firing member, depicted as a firing rod  25 , is distally advanced within the frame ground  21  to effect severing and stapling within the staple applying assembly  12 . 
   The handle  20  has user controls mounted on its handle housing  26  such as a rotation knob  27  that rotates the implement portion  22  about a longitudinal axis of the shaft  18 . A closure trigger  28 , which pivots in front of a pistol grip  30  about an attachment to the handle housing  27 , is depressed to close the staple applying assembly  12  by distally moving the closure tube  24 . A multiple stroke firing trigger  32 , which pivots in front of the closure trigger  28 , causes the staple applying assembly  12  to simultaneously sever and staple tissue clamped therein by distally advancing the firing rod  25 . 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 wheels  34 ,  36  (the latter depicted in  FIG. 2 ) rotate presenting indicia of the firing progress. For instance, full firing travel may require three full firing strokes and thus the indicator wheels  34 ,  36  rotate up to one-third of a revolution each per stroke. A manual retraction lever  38  allows retraction before full firing travel by manually disengaging a mechanical-electrical hybrid anti-backup mechanism  40  if desired and may further provide assistance to retract in the presence of binding or a failure in a retraction bias. A closure release button  41  is outwardly presented when the closure trigger  28  is clamped and partial firing has not occurred that would prevent unclamping the closure trigger  28 . 
   A retraction bias in the handle  20  retracts the firing rod  25  after firing. When the firing trigger is released for another stroke, the anti-backup mechanism  40  engages the firing rod  25  to prevent inadvertent retraction. Advantageously, an anti-backup electrical actuator  42  is positioned proximate to the firing rod  25  for selectively moving between a locking and an unlocking state. A control module  44  activates the anti-backup electrical actuator  42 . Electrical power may be provided by external power or as a depicted battery  46  connected to the control module  44  via a power button  48 , which illuminates when activated. The control module  44  monitors operation of the surgical severing and stapling instrument  10  to determine when to lock and unlock firing, such as illustrated by a firing release sensor  50 , depicted in phantom as a magnetic target  52  on an upper portion of the firing trigger  32  that moves relative to a Hall effect transducer  54  mounted inside of the handle housing  26 . It should be appreciated that other sensors may be employed to sense conditions that would warrant locking or releasing the firing rod  25 . 
   A version of the anti-backup mechanism  40  of  FIG. 1  is depicted in  FIGS. 2-3  that includes an anti-backup locking plate  56  with a through hole  66  ( FIG. 2 ) that tips a top  58  of the locking plate  56  forward to a transverse nonbinding (“unlocked”) position when the firing rod  25  distally advances and tips top  58  aft to an angled, binding (“locked”) position when the firing rod  25  attempts to retract, assisted by a resilient member  60  that encompasses the firing rod  25  and is positioned distal to the locking plate  56 . A lower tab attachment  62  ( FIG. 2 ) extends proximally from a lower lip  64  of the proximal end of the frame ground  21 , extending through an aperture (not shown) on a lower edge of the anti-backup locking plate  56 . This lower tab attachment  62  draws the lower portion of the anti-backup locking plate  56  proximate to the frame ground  21  so that the anti-backup locking plate  56  is perpendicular when the firing rod  25  is distally advanced and allowed to tip top  58  aft into a binding state when the firing rod  25  attempts to retract. 
   An anti-backup resilient biasing member  68  encompasses the firing rod  25  and is positioned distal to the locking plate  56 . Engagement between the biasing member  68  and locking plate  56  is limited to abutment between top edges of both to urge the locking plate  56  top back to lock. A distal side of the biasing member  68  abuts the frame ground  21 , permitting expansion thus only proximally. On the proximal side of the locking plate  56 , an anti-backup cam tube  70  encompasses the firing rod  25  and is constrained to move longitudinally. In particular, a proximally directed anti-backup cam yoke  72  is attached to a top proximal surface of the anti-backup cam tube  70  and is slidingly received into the handle housing  26 , constraining rotation motion and serving in this version as a mechanical release actuator. The anti-backup cam tube  70  itself may be distally advanced by the anti-backup cam yoke  72  but advantageously may also be advanced by a pair of electrical actuators, depicted as EAP cylindrical actuators  74 ,  76 . The anti-backup cam tube  70  and EAP cylindrical actuators  74 ,  76  are common to a version of the anti-backup mechanism  40  in  FIGS. 4-6  wherein a shortened cam yoke  72   a  serves only to guide the anti-backup cam tube  70  and is not coupled for mechanical actuation for release. With reference to  FIG. 3A , it is contemplated that passive and/or active biasing of the locking plate  56  may be incorporated by selecting one of several configurations. The anti-backup cam yoke  72  serves to communicate a mechanical release motion by either manual user input or automatic end of firing travel is provided. 
   The version of  FIG. 4  differs in that the resilient member  60  comprises an anti-backup compression spring  60   a  having a narrow distal coil  78  that grips and is distally constrained by a narrowed portion  80  of a firing rod  25   a . The anti-backup compression spring  60   a  also has a widened proximal coil  82  sized to contact the anti-backup locking plate  56 . Thus, the anti-backup compression spring  60   a  provides a full-time locking bias that is overcome by distal movement of the firing rod  25   a  or the anti-backup cam tube  72   a.    
   In  FIG. 3A , the EAP actuators  74 ,  76  have a relaxed, contracted shape which allows the proximal urging of the resilient member  60  against the anti-backup locking plate  56  to push the anti-backup cam tube  70  proximally to the handle housing  26 . When the EAP actuators  74 ,  76  are energized, the EAP actuators  74 ,  76  longitudinally expand as depicted in phantom, distally advancing the anti-backup cam tube  70 , also depicted in phantom. It is contemplated that the version of  FIG. 2-3 ,  3 A may be configured with the resilient member  60  formed from an EAP actuator having a relaxed, contracted state and an activated, expanded state (e.g., a cylindrical stacked EAP laminate with a through hole configured to longitudinally expanded when electrically stimulated). Thus, the locking bias may be selectively removed to reduce the force to fire. The firing trigger  32  requires less force to move the locking plate  56  against the resilient member  60 . Alternatively, the resilient member  60  may have a relaxed contracted state and an activated expanded state. Moreover, the resilient member  60  may be a combination compression spring longitudinally wrapped in EAP fiber actuators or be assisted and/or constrained by an EAP stacked laminate actuator. 
   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 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. 
   In  FIGS. 2-3 , the components of the handle  20  common to the afore-mentioned U.S. patent application Ser. Nos. 11/052,387 and 11/052,632 effect closure and firing and mechanical actuation of the anti-backup cam tube  72 . The frame ground  21  is rotatably engaged to the handle  20  so that twisting the rotation knob  27  causes rotation of the implement portion  22 . Each half shell of the rotation knob  27  includes an inward projection  90  ( FIG. 2 ) that enters a respective longer side opening  92  in the closure tube  24  and moves inward to engage the frame ground  21  that determines the rotated position of the implement portion  22 . The longitudinal length of the longer openings  92  is sufficiently long to allow longitudinal closure motion of the closure tube  24 . 
   The closure trigger  28  rotates about a closure trigger pin  93  that is laterally engaged within the handle housing  26 . An upper portion  94  of the closure trigger  28  above the closure trigger pin  95  pushes forward a closure yoke  96  via a closure link  98 . The closure link  98  is pivotally attached at its distal end by a closure yoke pin  100  to the closure yoke  96  and is pivotally attached at its proximal end by a closure link pin  102 . The closure trigger  28  is urged to the open position by a closure trigger tension spring  104  that is connected proximally to the upper portion  94  of the closure trigger  28  and to the handle housing  26 . 
   The upper portion  94  of the closure trigger  28  includes a proximal crest  106  with an aft notch  108 . The closure release button  41  and a pivoting locking arm  110  are connected by a central lateral pivot  112 . A compression spring  114  biases the closure release button  41  proximally (clockwise about the central lateral pivot  112  as viewed from the right), With the upper portion  94  back when the closure trigger  28  is released, the pivoting locking arm  110  rides upon the proximal crest  106  drawing in the closure release button  41 . When the closure trigger  28  reaches its fully depressed position, it should be appreciated that the aft notch  108  is presented below the pivoting locking arm  110 , which drops into and locks against the aft notch  108  under the urging of the compression spring  114 . With the firing components retracted, manual depression of the closure release button  41  rotates the pivoting locking arm  110  upward, unclamping the closure trigger  28 . 
   Once the closure trigger  28  is proximally clamped, the firing rod  25  is distally moved from the handle  20  in response to the multiple stroke firing trigger  32  being drawn to the pistol grip  30  with the amount of firing travel visible to the surgeon on the right and left indicator wheels  34 ,  36 . The firing trigger  32  pivots about a firing trigger pin  118  that laterally traverses and is engaged laterally across the handle housing  26 . 
   A linked transmission firing mechanism  120  is initially retracted, urged to remain in this position by a combination tension/compression spring  122  that is constrained within the pistol grip  30  of the handle  20 , with its nonmoving end  124  connected to the housing  26  and a moving end  126  connected to a downwardly flexed and proximal, retracted end  128  of a steel band  130 . 
   A distally-disposed end  132  of the steel band  130  is attached to an attachment feature  134  on a front link  136   a  of a plurality of links  136   a - 136   d  that form a linked rack  140 . A rack guide tube  141  has a proximally open internal cavity  142  shaped to receive the plurality of links  136   a - 136   d  when distally advanced and a smaller distal opening  143  shaped to allow the passage of the firing rod  25  that is attached to the distal most link  136   a . Left and right gripping features  144 ,  145  extend inwardly in opposition from the handle housing  26  through elongate slots  146 ,  147  respectively in the closure yoke  96  and a rack channel cover  148  to engage a respective proximal side recess  149  formed in the rack guide tube  141 . Thereby, a linked rack  140  is flexible yet has proximal links that form a straight rigid rack assembly that may transfer a significant firing force through the firing rod  25  in the implement portion  22 , yet readily retracts into the pistol grip  30  to minimize the longitudinal length of the handle  20 . It should be appreciated that the combination tension/compression spring  122  increases the amount of firing travel available while essentially reducing the minimum length by half over a single spring. 
   As mentioned, the anti-backup cam yoke  72  is moved to effect mechanical release of the anti-backup locking plate  56 . Automatic triggering is based upon the distal link  136   d  including a tang  150  that projects upwardly when the distal link  136   d  is advanced into a rack channel  152  formed in the closure yoke  96 . This tang  150  is aligned to activate a bottom proximal cam  154  on an anti-backup release lever  156 . Structures formed in the handle housing  26  constrain movement of the anti-backup release lever  156 . A pin receptacle  158  and circular pin  160 , formed respectively between right and left half shells of the handle housing  26 , is received through a longitudinally elongate aperture  162  formed in the anti-backup release lever  156  distal to the bottom proximal cam  154 , thus allowing longitudinal translation as well as rotation about the circular pin  160 . In the right half shell of the handle housing  26 , a proximally open channel  164  includes a proximal horizontal portion  166  that communicates with an upwardly and distally angled portion  168  that receives a rightward aft pin  170  near the proximal end of the anti-backup release lever  156 , thus imparting an upward rotation as the anti-backup release lever  156  reaches the distal most portion of its translation. A blocking structure  172 , formed in the right half shell of the handle housing  26  proximal to the anti-backup release lever  156 , prevents proximal movement thereof once assembled to maintain rightward aft pin  170  in the proximally open channel  164 . 
   A distal end  174  of the anti-backup release lever  156  thus is urged distally and downwardly, causing a rightward front pin  176  to drop into distally open step structure  178  formed in the right half shell of the handle housing  26 , which is urged into this engagement by a compression spring  180  hooked to a leftward hook  182  on the anti-backup release lever  156  between the rightward front pin  176  and the longitudinally elongate aperture  162 . The other end of the compression spring  180  is attached to a hook  184  formed in the right half shell of the handle housing  26  in a more proximal and lower position just above the closure yoke  96 . The compression spring  180  thus pulls the distal end  174  of the anti-backup release lever  156  down and aft, which results in the rightward front pin  176  locking into the distally open step structure  178  when distally advanced. 
   Once tripped, the anti-backup release lever  156  remains forward holding the anti-backup locking plate  56  perpendicularly, thus allowing the linked rack  140  to be retracted. When the closure yoke  96  is subsequently retracted when unclamping the end effector  12 , an upwardly projecting reset tang  186  on the closure yoke  96  contacts a bottom distal cam  188  of the anti-backup release lever  156 , lifting the rightward front pin  176  out of the distally open step structure  178  so that the anti-backup resilient member  60  can proximally push the anti-backup cam tube  70  and the anti-backup release lever  156  to their retracted positions. 
   The firing trigger  32  pivots about the firing trigger pin  118 , distally and proximally reciprocating an upper portion  190  of the firing trigger  32 , stretching a proximally placed firing trigger tension spring  192  proximally connected between the upper portion  190  of the firing trigger  32  and the housing  26 . The upper portion  190  of the firing trigger  32  engages the linked rack  140  during each firing trigger depression by a spring-biased side pawl mechanism  194  that also disengages when the firing trigger  32  is released. 
   In particular, a ramped right-side track  196  formed by a proximally and rightwardly facing beveled surface  198  in each of the links  136   a - 136   d  is engaged by a side pawl mechanism  194 . In particular, a pawl slide (shuttle)  200  has right and left lower guides  202  that slide respectively in a left track  204  formed in the closure yoke  96  below the rack channel  152  and a right track  206  formed in a closure yoke rail  208  that parallels rack channel  152  and is attached to the rack channel cover  148  that closes a rightwardly open portion of the rack channel  152  in the closure yoke  96  that is distal to the travel of the pawl slide  200 . In  FIGS. 3 ,  6 , a compression spring  212  is attached between a hook  214  on a top proximal position on the closure yoke rail  208  and a hook  216  on a distal right side of the pawl slide  200 , which keeps the pawl slide  200  drawn proximally into contact with the upper portion  190  of the firing trigger  32 . 
   A pawl block  218  sits on the pawl slide  200  pivoting about a vertical aft pin  220  that passes through a left proximal corner of pawl block  218  and pawl slide  200 . A kick-out block recess  222  is formed on a distal portion of a top surface of the block  218  to receive a kick-out block  224  pivotally pinned therein by a vertical pin  226  whose bottom tip extends into a pawl spring recess  228  on a top surface of the pawl slide  200 . A pawl spring  230  in the pawl spring recess  228  extends to the right of the vertical front pin  226 , urging the pawl block  218  to rotate counterclockwise when viewed from above into engagement with the ramped right-side track  196 . A small coil spring  232  in the kick-out block recess  222  urges the kick-out block  224  to rotate clockwise when viewed from above, its proximal end urged into contact with a contoured lip  234  formed in the closure yoke  96  above the rack channel  152 . 
   The stronger mechanical advantage of the pawl spring  230  over the small coil spring  232  means that the pawl block  218  tends toward engagement with the kick-out block  224  rotated clockwise. As the firing trigger  32  is fully depressed and begins to release, the kick-out block  224  encounters a ridge  236  in the contoured lip  234  as the pawl slide  200  retracts, forcing the kick-out block  224  to rotate clockwise when viewed from above and thereby kicking out the pawl block  218  from engagement with the linked rack  140 . The shape of the kick-out block recess  222  stops the clockwise rotation of the kick-out block  224  to a perpendicular orientation to the contoured lip  234 , maintaining this disengagement during the full retraction and thereby eliminating a ratcheting noise. 
   As mentioned, the surgical stapling and severing instrument  10  includes a manual retraction capability that provides firing position indication, manual release of the firing mechanism and manual retraction of the linked rack  140 . A front idler gear  240  engages a toothed upper, left surface  242  of the linked rack  140 . The front idler gear  240  also engages an aft idler gear  244  having a smaller right-side ratchet gear  246 . Both the front idler gear  240  and aft idler gear  244  are rotatably connected to the handle housing  26  respectively on front idler axle  248  and aft idler axle  250 . Each end of the aft idler axle  250  extends through the respective right and left housing half shells of the handle housing  26  and is attached to the left and right indicator wheels  34 ,  36 . Since the aft idler axle  250  is free spinning in the handle housing  26  and has a keyed engagement to the aft idler gear  244 , the indicator wheels  34 ,  36  rotate with the aft idler gear  244 . The gear relationship between the linked rack  140 , front idler gear  240  and aft idler gear  244  may be advantageously selected so that the toothed upper surface  242  has tooth dimensions that are suitably strong and so that the aft idler gear  244  makes no more than one revolution during the full firing travel of the linked rack  140 . 
   The smaller right-side ratchet gear  246  of the aft idler gear  244  extends into a hub  260  of the manual retraction lever  38 , specifically aligned with a vertical longitudinally-aligned slot  262  bisecting the hub  260 . A lateral through hole  264  of the hub  260  communicates with an upper recess  266 . A front portion of the upper recess  266  is shaped to receive a proximally directed locking pawl  268  that pivots about a rightward lateral pin  270  formed in a distal end of the upper recess  266 . An aft portion of the upper recess  266  is shaped to receive an L-shaped spring tab  272  that urges the locking pawl  268  downward into engagement with the right-side smaller ratchet gear  246 . A hold-up structure  274  projects from the right half shell of the handle housing  26  into the upper recess  266 , holding up the locking pawl  268  from engaging the smaller right-side ratchet gear  246  when the manual retraction lever  38  is down. A coil spring  276  urges the manual retraction lever  38  down. As the manual retraction lever  38  is raised, the locking pawl  268  rotates clockwise (when viewed from the right), and is no longer held up by the hold-up structure  274  and engages the smaller right-side ratcheting gear  246 , rotating the aft idler gear  244  counterclockwise when viewed from the right. Thus, the forward idler gear  240  responds clockwise, retracting the linked rack  140 . In addition, a rightward curved ridge  278  projects out from the hub  260 , sized to contact and distally move the anti-backup release lever  156  to mechanically release the anti-backup mechanism  40  as the manual retraction lever  38  is rotated. 
   In  FIGS. 7-11 , a version of the electrically actuated anti-backup mechanism  40  for a surgical stapling and severing instrument  310  includes a wound anti-backup spring  312  that closely encompasses a firing rod  314 . In particular, a distal end  316  of the wound anti-backup spring  312  extends longitudinally. With particular reference to  FIG. 8 , an upwardly open actuator recess  320  formed in a frame ground  322  includes a generally rectangular prism opening  324  with a distal vertical slot  326  that receives and prevents rotation of the distal end  316  of the wound anti-backup spring  312 . A leftward vertical slot  328  of the upwardly open actuator recess  320  is aligned to receive an upturned proximal end  328  of the wound anti-backup spring  312  when rotated top leftward by an EAP block actuator  330  positioned against a right proximal side of the upwardly open actuator recess  320 . In  FIG. 11 , the wound anti-backup spring  312  is coiled in a direction that tightens as the upturned proximal end  328  is rotated leftward. It should be appreciated that the energized state (e.g., laterally expanded, laterally contracted) of the EAP actuator  330  and the direction of tightening of the wound anti-backup spring  312  may be selected for biased locked or biased unlocked. 
   Alternatively, it should be appreciated that a wound spring (not shown) may be longitudinally shortened to a radially expanded, unlocked state and may be longitudinally extended to a radially contracted, locked state with an electrical actuator coupled across the length of the wound spring to effect this change. Alternatively, one end of the wound spring may be fixed relative to a frame ground and a free end of the wound spring may be moved by an electrical actuator relative to the frame ground to effect this change. 
   With particular reference to  FIG. 8 , a fixed collar  332  has a distal conducting circumferential ring  334  that is swiped by a contact  336  that serves as one electrode for the EAP block actuator  330  with an electrical ground path provided by the frame ground  322 . In  FIGS. 7-10 , a proximally projecting arm  338  is attached to a top proximal surface of the fixed collar  332  and is engaged to a handle housing  340  to prevent rotation or longitudinal movement of the fixed collar  332 . In  FIGS. 8-9 , a closure sleeve  342  has an elongate top aperture  344  sized to accommodate the extension of the contact  336  during closure translation. It should be appreciated that a rotation knob (not shown) overlies the elongate top aperture  344  of the closure sleeve  342  and the upwardly open actuator recess  320  in the frame ground  322 . 
   In  FIGS. 12-15 , a version of the electrically actuated anti-backup mechanism  40  for a surgical stapling and severing instrument  410  includes an EAP split cylindrical actuator  412  that closely encompasses a firing rod  414  and radially expands when energized. A rigid sleeve  416  encompasses the EAP split cylinder actuator  412  forcing expansion inwardly into binding contact with the firing rod  414 . With particular reference to  FIG. 12 , an upwardly open actuator recess  420  formed in a frame ground  422  includes a generally rectangular prism opening  424 . A fixed collar  432  has an outer distal conducting circumferential ring  434  that is swiped by a first contact  436  and an inner distal conducting circumferential ring  438  that is swiped by a second contact  440  that serves as electrodes (i.e., cathode, anode) for the EAP split cylindrical actuator  412 . A proximally projecting arm  442  is attached to a top proximal surface of the fixed collar  432  and is engaged to a handle housing  444  to prevent rotation or longitudinal movement of the fixed collar  432 . In  FIGS. 12-14 , a closure sleeve  446  has an elongate top aperture  448  sized to accommodate the extension of the contacts  436 ,  440  during closure translation. It should be appreciated that a rotation knob (not shown) overlies the elongate top aperture  448  of the closure sleeve  446  and the upwardly open actuator recess  420  in the frame ground  422 . 
   In  FIGS. 16-17 , a version of the electrically actuated anti-backup mechanism  40  for a surgical stapling and severing instrument  510  includes an EAP cylindrical actuator  412  that closely encompasses a firing rod  514 , having a relaxed, contracted state that forms a binding contact with the firing rod  514  and radially expands when energized out of binding contact. An upwardly open actuator recess  520  formed in a frame ground  522  includes a generally rectangular prism opening  524 . A fixed collar  532  has an outer distal conducting circumferential ring  534  that is swiped by a first contact  536  and an inner distal conducting circumferential ring  538  that is swiped by a second contact  540  that serves as electrodes (i.e., cathode, anode) for the EAP split cylindrical actuator  512 . A proximally projecting arm  542  is attached to a top proximal surface of the fixed collar  532  and is engaged to a handle housing (not shown) to prevent rotation or longitudinal movement of the fixed collar  532 . In  FIG. 16 , a closure sleeve  546  has an elongate top aperture  548  sized to accommodate the extension of the contacts  536 ,  540  during closure translation. It should be appreciated that a rotation knob (not shown) overlies the elongate top aperture  548  of the closure sleeve  546  and the upwardly open actuator recess  520  in the frame ground  522 . 
   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 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 an endoscopic tube (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 laparoscopic procedures, as well as open procedures. 
   Applications consistent with the present invention may include single firing stroke instruments as well as those with a solid firing rack rather than a linked rack. 
   As another example, a rocking boot type anti-backup lever may be positioned into binding contact. A manual rocking boot type anti-backup lever is disclosed in U.S. patent application Ser. No. 10/881,105, “SURGICAL STAPLING INSTRUMENT INCORPORATING A MULTISTROKE FIRING MECHANISM HAVING A ROTARY TRANSMISSION” to Whitacre et al., filed on 30 Jun. 2004, the disclosure of which is hereby incorporated by reference in its entirety.