the entire disclosure of u . s . patent application ser . no . 11 / 082 , 495 , entitled surgical instrument incorporating an electrically actuated articulation mechanism , filed on mar . 17 , 2005 , now u . s . pat . no . 7 , 506 , 790 , is incorporated herein by reference . the entire disclosure of u . s . pat . no . 6 , 667 , 825 , entitled stable conjugated polymer electrochromic devices incorporating ionic liquids , issued on jan . 3 , 2002 , is incorporated herein by reference . the entire disclosure of u . s . patent application ser . no . 11 / 061 , 908 , entitled surgical instrument incorporating a fluid transfer controlled articulation mechanism , filed on feb . 18 , 2005 , now u . s . pat . no . 7 , 559 , 450 , is incorporated herein by reference . in fig1 - 3 , a surgical stapling instrument 10 has at its distal end an end effector , depicted as a staple applying assembly 12 , spaced apart from a handle 14 ( fig2 ) by an elongate shaft 16 . the staple applying assembly 12 includes a staple channel 18 for receiving a replaceable staple cartridge 20 . pivotally attached to the staple channel 18 is an anvil 22 that clamps tissue to the staple cartridge 20 and serves to deform staples 23 ( fig3 ) driven up from staple holes 24 in the staple cartridge 20 against staple forming recesses 26 ( fig6 ) in an anvil undersurface 28 into a closed shape . when the staple applying assembly 12 is closed , its cross sectional area , as well as the elongate shaft 16 are suitable for insertion through a small surgical opening , such as through a cannula of a trocar ( not shown ). with particular reference to fig1 , correct placement and orientation of the staple applying assembly 12 is facilitated by controls on the handle 14 . in particular , a rotation knob 30 causes rotation of the shaft 16 about its longitudinal axis , and hence rotation of the staple applying assembly 12 . additional positioning is enabled at an articulation joint 32 in the shaft 16 that pivots the staple applying assembly 12 in an arc from the longitudinal axis of the shaft 16 , thereby allowing placement behind an organ or allowing other instruments such as an endoscope ( not shown ) to be oriented behind the staple applying assembly 12 . this articulation is advantageously effected by an articulation control switch 34 on the handle 14 that transmits an electrical signal to the articulation joint 32 to an electroactive polymer ( eap ) actuator 36 , powered by an eap controller and power supply 38 contained within the handle 14 . once positioned with tissue in the staple applying assembly 12 , a surgeon closes the anvil 22 by drawing a closure trigger 40 proximally toward a pistol grip 42 . once clamped thus , the surgeon may grasp a more distally presented firing trigger 44 , drawing it back to effect firing of the staple applying assembly 12 , which in some applications is achieved in one single firing stroke and in other applications by multiple firing strokes . firing accomplishes simultaneously stapling of at least two rows of staples while severing the tissue therebetween . retraction of the firing components may be automatically initiated upon full travel . alternatively , a retraction lever 46 may be drawn aft to effect retraction . with the firing components retracted , the staple applying assembly 12 may be unclamped and opened by the surgeon slightly drawing the closure trigger 40 aft toward the pistol grip 42 and depressing a closure release button 48 and then releasing the closure trigger 40 , thereby releasing the two stapled ends of severed tissue from the staple applying assembly 12 . while an articulation joint 32 is depicted in fig1 , for clarity and as an alternative application , the surgical stapling instrument 10 of fig2 - 14 omit an articulation joint 32 . it should be appreciated , however , that aspects of the present invention have particular advantages for articulation as described below with regard to fig1 - 18 . in fig1 - 3 , the staple applying assembly 12 accomplishes the functions of clamping onto tissue , driving staples and severing tissue by two distinct motions transferred longitudinally down the shaft 16 over a shaft frame 70 . this shaft frame 70 is proximally attached to the handle 14 and coupled for rotation with the rotation knob 30 . an illustrative multi - stroke handle 14 for the surgical stapling and severing instrument 10 of fig1 is described in greater detail in the co - owned u . s . patent application ser . no . 10 / 674 , 026 , entitled surgical stapling instrument incorporating a multistroke firing position indicator and retraction mechanism , now u . s . pat . no . 7 , 364 , 061 , the disclosure of which is hereby incorporated by reference in its entirety , with additional features and variation as described herein . while a multi - stroke handle 14 advantageously supports applications with high firing forces over a long distance , applications consistent with the present invention may incorporate a single firing stroke , such as described in commonly owned u . s . patent application ser . no . 10 / 441 , 632 , entitled surgical stapling instrument having separate distinct closing and firing systems , now u . s . pat . no . 7 , 000 , 818 , the disclosure of which is hereby incorporated by reference in its entirety . with particular reference to fig3 , the distal end of the shaft frame 70 is attached to the staple channel 18 . the anvil 22 has a proximal pivoting end 72 that is pivotally received within a proximal end 74 of the staple channel 18 , just distal to its engagement to the shaft frame 70 . the pivoting end 72 of the anvil 22 includes a closure feature 76 proximate but distal to its pivotal attachment with the staple channel 18 . thus , a closure tube 78 , whose distal end includes a horseshoe aperture 80 that engages this closure feature 76 , selectively imparts an opening motion to the anvil 22 during proximal longitudinal motion and a closing motion to the anvil 22 during distal longitudinal motion of the closure tube 78 sliding over the shaft frame 70 in response to the closure trigger 40 . the shaft frame 70 encompasses and guides a firing motion from the handle 14 through a longitudinally reciprocating , two - piece knife and firing bar 90 . in particular , the shaft frame 70 includes a longitudinal firing bar slot 92 that receives a proximal portion of the two - piece knife and firing bar 90 , specifically a laminate tapered firing bar 94 . it should be appreciated that the laminated tapered firing bar 94 may be substituted with a solid firing bar or of other materials in applications not intended to pass through an articulation joint , such as depicted in fig2 - 14 . an e - beam 102 is the distal portion of the two - piece knife and firing bar 90 , which facilitates separate closure and firing as well as spacing of the anvil 22 from the elongate staple channel 18 during firing . with particular reference to fig3 - 4 , in addition to any attachment treatment such as brazing or an adhesive , the knife and firing bar 90 are formed of a female vertical attachment aperture 104 proximally formed in the e - beam 102 that receives a corresponding male attachment member 106 distally presented by the laminated tapered firing bar 94 , allowing each portion to be formed of a selected material and process suitable for their disparate functions ( e . g ., strength , flexibility , friction ). the e - beam 102 may be advantageously formed of a material having suitable material properties for forming a pair of top pins 110 , a pair of middle pins 112 and a bottom pin or foot 114 , as well as being able to acquire a sharp cutting edge 116 . in addition , integrally formed and proximally projecting top guide 118 and middle guide 120 bracketing each vertical end of the cutting edge 116 further define a tissue staging area 122 assisting in guiding tissue to the sharp cutting edge 116 prior to being severed . the middle guide 120 also serves to engage and fire the staple applying apparatus 12 by abutting a stepped central member 124 of a wedge sled 126 ( fig5 ) that effects staple formation by the staple applying assembly 12 , as described in greater detail below . forming these features ( e . g ., top pins 110 , middle pins 112 , and bottom foot 114 ) integrally with the e - beam 102 facilitates manufacturing at tighter tolerances relative to one another as compared to being assembled from a plurality of parts , ensuring desired operation during firing and / or effective interaction with various lockout features of the staple applying assembly 12 . in fig6 - 7 , the surgical stapling instrument 10 is shown open , with the e - beam 102 fully retracted . during assembly , the lower foot 114 of the e - beam 102 is dropped through a widened hole 130 in the staple channel 18 and the e - beam 102 is then advanced such that the e - beam 102 slides distally along a lower track 132 formed in the staple channel 18 . in particular , the lower track 132 includes a narrow slot 133 that opens up as a widened slot 134 on an undersurface of the staple channel 18 to form an inverted t - shape in lateral cross section , as depicted particularly in fig7 and 8 , which communicates with the widened hole 130 . once assembled , the components proximally coupled to the laminate tapered firing bar 94 do not allow the lower foot 114 to proximally travel again to the widened hole 130 to permit disengagement . in fig9 , the laminate tapered firing bar 94 facilitates insertion of the staple applying assembly 12 through a trocar . in particular , a more distal , downward projection 136 raises the e - beam 102 when fully retracted . this is accomplished by placement of the downward projection 136 at a point where it cams upwardly on a proximal edge of the widened hole 130 in the staple channel 18 . in fig1 , the laminate tapered firing bar 94 also enhances operation of certain lockout features that may be incorporated into the staple channel 18 by including a more proximal upward projection 138 that is urged downwardly by the shaft frame 70 during an initial portion of the firing travel . in particular , a lateral bar 140 is defined between a pair of square apertures 142 in the shaft frame 70 ( fig3 ). a clip spring 144 that encompasses the lateral bar 140 downwardly urges a portion of the laminate tapered firing bar 94 projecting distally out of the longitudinal firing bar slot 92 , which ensures certain advantageous lockout features are engaged when appropriate . this urging is more pronounced or confined solely to that portion of the firing travel when the upward projection 138 contacts the clip spring 144 . in fig6 - 7 , the e - beam 102 is retracted with the top pins 110 thereof residing within an anvil pocket 150 near the pivoting proximal end of the anvil 22 . a downwardly open vertical anvil slot 152 ( fig2 ) laterally widens in the anvil 22 into an anvil internal track 154 that captures the top pins 110 of the e - beam 102 as they distally advance during firing , as depicted in fig9 - 10 , affirmatively spacing the anvil 22 from the staple channel 18 . thus , with the e - beam 102 retracted , the surgeon is able to repeatably open and close the staple applying assembly 12 until satisfied with the placement and orientation of tissue captured therein for stapling and severing , yet the e - beam 102 assists in proper positioning of tissue even for a staple applying assembly 12 of reduced diameter and correspondingly reduced rigidity . in fig2 - 3 , 5 - 6 , 8 - 14 , the staple applying assembly 12 is shown with the replaceable staple cartridge 20 that includes the wedge sled 126 . longitudinally aligned and parallel plurality of downwardly open wedge slots 202 ( fig8 ) receive respective wedges 204 integral to the wedge sled 126 . in fig8 - 10 , the wedge sled 126 thus cams upwardly a plurality of staple drivers 206 that are vertically slidable within staple driver recesses 208 . in this illustrative version , each staple driver 206 includes two vertical prongs , each translating upwardly into a respective staple hole 210 to upwardly force out and deform a staple 23 resting thereupon against a staple forming surface 214 ( fig1 ) of the anvil 22 . a central firing recess 216 ( fig3 ) defined within the staple cartridge 20 proximate to the staple channel 18 allows the passage of the bottom , horizontal portion 218 ( fig5 ) of the wedge sled 126 as well as the middle pins 112 of the e - beam 102 . specifically , a staple cartridge tray 220 ( fig3 ) attaches to and underlies a polymer staple cartridge body 222 that has the staple driver recesses 208 , staple holes 210 , and central firing recess 216 formed therein . as staples 23 are thus formed to either side , the sharp cutting edge 116 enters a vertical through slot 230 passing through the longitudinal axis of the staple cartridge 20 , excepting only a most distal end thereof . firing the staple applying assembly 12 begins as depicted in fig1 with the two - piece knife and firing bar 90 proximally drawn until the downward projection 136 cams the middle guide 120 on the e - beam 102 upward and aft , allowing a new staple cartridge 20 to be inserted into the staple channel 18 when the anvil 22 is open as depicted in fig2 . in fig1 , the two - piece knife and firing bar 90 has been distally advanced a small distance , allowing the downward projection 136 to drop into the widened hole 130 of the lower track 132 under the urging of the clip spring 144 against the upward projection 138 of the laminate tapered firing bar 94 . the middle guide 120 prevents further downward rotation by resting upon the stepped central member 124 of the wedge sled 126 , thus maintaining the middle pin 112 of the e - beam within the central firing recess 216 . in fig1 , the two - piece knife and firing bar 90 has been distally fired , advancing the wedge sled 126 to cause formation of staples 23 while severing tissue 242 clamped between the anvil 22 and staple cartridge 20 with the sharp cutting edge 116 . thereafter , in fig1 , the two - piece knife and firing bar 90 is retracted , leaving the wedge sled 126 distally positioned . in fig1 , the middle pin 112 is allowed to translate down into a lockout recess 240 formed in the staple channel 18 ( also see fig7 ). thus , the operator would receive a tactile indication as the middle pin 112 encounters the distal edge of the lockout recess 240 when the wedge sled 126 ( not shown in fig1 ) is not proximally positioned ( i . e ., missing staple cartridge 20 or spent staple cartridge 20 ). in fig1 , an articulation joint 32 is depicted that advantageously benefits from the flexible strength of the two - piece knife and firing bar 90 . in fig1 - 18 , the articulation joint 32 is depicted as a flex neck joint 300 formed by vertebral column body 302 having laterally symmetric pairs of arcing recesses 304 that allow articulation in an articulation plane . it is generally known to simultaneously compress and expand respective lateral sides 306 , 308 by selective movement of control rods ( not shown ) that longitudinally pass through the respective lateral sides 306 , 308 . depicted , however , are eap plate actuators 310 , 312 , each capable of powered deflection to one or both lateral directions . a central passage 320 ( fig1 ) defined longitudinally through the vertebral column body 302 receives a pair of support plates 322 , 324 that prevent buckling and binding of the laminate tapered firing bar 94 . in the illustrative version , each support plate 322 , 324 has a proximal fixed end 326 ( fig1 ) and a sliding end 328 to accommodate changes in radial distance during articulation . having a firing bar 94 of a thinner thickness is thus supported . 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 . for example , while there are a number of advantages to having a wedge sled integral to a staple cartridge , in some applications consistent with aspects of the present invention , the wedge sled may be integral instead to an e - beam . for instance , an entire end effector may be replaceable rather than just the staple cartridge .
a surgical severing and stapling instrument , suitable for laparoscopic and endoscopic clinical procedures , clamps tissue within an end effector of an elongate channel pivotally opposed by an anvil . an e - beam firing bar moves distally through the clamped end effector to sever tissue and to drive staples on each side of the cut . the e - beam firing bar affirmatively spaces the anvil from the elongate channel to assure properly formed closed staples , especially when an amount of tissue is clamped that is inadequate to space the end effector . in particular , an upper pin of the firing bar longitudinally moves through an anvil slot and a channel slot is captured between a lower cap and a middle pin of the firing bar to assure a minimum spacing . forming the e - beam from a thickened distal portion and a thinned proximal strip enhances manufacturability and facilitates use in such articulating surgical instruments .