Patent Publication Number: US-2022226038-A1

Title: Accurate jaw closure force in a catheter based instrument

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This is a continuation of U.S. patent application Ser. No. 12/786,589, filed on May 25, 2010. 
    
    
     FIELD 
     The present disclosure relates to an apparatus for remotely activating jaw members on an articulating surgical instrument. In particular, the apparatus includes a driving mechanism for appropriately transmitting force from a proximal end to a distal end of the instrument to properly clamp tissue between the jaw members. 
     BACKGROUND 
     Typically in a laparoscopic surgical procedure, a small incision or puncture is made in a patient&#39;s body. A cannula is then inserted into a body cavity through the incision, which provides a passageway for inserting various surgical devices such as scissors, dissectors, retractors, or similar instruments. To facilitate operability through the cannula, instruments adapted for laparoscopic surgery typically include a relatively narrow shaft supporting an end effector at its distal end and a handle at its proximal end. Arranging the shaft of such an instrument through the cannula allows a surgeon to manipulate the proximal handle from outside the body to cause the distal end effector to carry out a surgical procedure at a remote internal surgical site. 
     An articulating laparoscopic or endoscopic instrument may provide a surgeon with a range of operability suitable for a particular surgical procedure. The instrument may be configured such that the end effector may be aligned with an axis of the instrument to facilitate insertion through a cannula, and thereafter, the end effector may be caused to articulate, pivot or move off-axis as necessary to appropriately engage tissue. When the end effector of an articulating instrument comprises a pair of jaw members for grasping tissue, such as that of electrosurgical forceps, a force transmission mechanism such as a drive wire may be provided to open or close the jaw members. For example, the drive wire may extend through the shaft of the instrument from the handle to the jaw members such that the surgeon may create a dragging force in the drive wire which pulls the drive wire proximally for a predetermined distance. The dragging force in the drive wire leads to a pulling force acting upon the jaw members to move them close to one another for a distance determined by the traveling distance of the drive wire. As a result, proximal motion of the drive wire translates into rotational motion of the jaw members. As a result, the closure or clamping force generated in the jaw members is related to the pulling force acting upon the jaw members as well as the travelling distance of the drive wire. 
     Instruments such as electrosurgical forceps are commonly used in open and endoscopic surgical procedures to coagulate, cauterize and seal tissue. A detailed discussion of the use of an electrosurgical forceps may be found in U.S. Pat. No. 7,255,697 to Dycus et al. Such forceps typically includes a pair of jaw members that can be controlled by a surgeon to grasp a targeted tissue. The pair of jaw members generate a significant closure force between jaw members to coagulate, cauterize or seal small diameter blood vessels, vascular bundles or any two layers of tissue with the application of electrosurgical or RF energy. The two layers may be grasped and clamped together by the jaw members, and an appropriate amount of electrosurgical energy may be applied through the jaw members. The closure force typically generated by this type of procedure may present difficulties when using a typical drive wire to open and close the jaw members of an articulating instrument. 
     For example, a surgeon&#39;s efforts to close the jaw members may be frustrated due to articulation of the instrument. When the instrument is in its articulated configuration, the drive wire may contact the articulated shaft of the instrument thus resulting in friction that reduces the pulling force acting upon the jaw members. Additionally, the distance that the drive wire needs to travel to completely close the jaw members in an aligned configuration differs from that in an articulated configuration. 
     SUMMARY 
     The present disclosure describes an endoscopic surgical instrument including a housing, an end effector, an elongated shaft and a driving assembly. The end effector is operable from the housing to surgically manipulate tissue. The end effector includes two opposable jaw members which are movable from an open configuration for receiving tissue therebetween to a closed configuration for manipulating tissue. The elongated shaft extends between the housing and the end effector. The elongated shaft includes a proximal portion coupled to the housing, a distal portion coupled to the end effector and an articulation joint between the proximal portion and the distal portion. The proximal portion defines a longitudinal axis. The articulation joint is adapted to move the distal portion between an aligned configuration and an articulated configuration with respect to the longitudinal axis. The driving assembly comprises a first spring in connection with a drive wire. The driving assembly is configured to induce motion in the jaw members between the open configuration and the closed configuration. The driving assembly maintains a closure pressure in the range between about 3 kg/cm 2  and about 16 kg/cm 2  between the aligned configuration and the articulated configuration of the elongated shaft. 
     In one embodiment, the first spring defines a spring constant dimensioned to maintain a closure pressure in the range between about 3 kg/cm 2  and about 16 kg/cm 2  between the aligned configuration and the articulated configuration. 
     In another embodiment, the driving assembly includes a clutch assembly disposed between the drive wire and the end effector. The clutch assembly includes a clutch connected to the drive wire, and a second spring disposed between the clutch and the end effector. The clutch assembly imparts a consistent closure pressure between the aligned configuration and the articulated configuration. 
     The driving assembly may also include a tube circumferentially surrounding the drive wire. The tube defines a plurality of spaced protrusions on an inner wall thereof. The spaced protrusions are configured to maintain the drive wire in the center of the tube during translation thereof when the elongated shaft is disposed in the articulated configuration. The spaced protrusions on the inner wall of the tube include a friction coefficient substantially less than a friction coefficient of the elongated shaft. 
     In a certain embodiment, the driving assembly includes a rolling mechanism. The rolling mechanism includes a roller bearing feature connected to the first spring, a control wire connected to the distal end of the elongated shaft, a lever with a first end connected to the roller bearing feature and a second end connected to the control wire, and a second spring with a first end connected to the roller bearing feature and a second end connected to the drive wire. The rolling mechanism maintains a consistent closure force between the articulated and aligned configurations. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate embodiments of the present disclosure and, together with the detailed description of the embodiments given below, serve to explain the principles of the disclosure. 
         FIG. 1  is a perspective view of an articulating surgical instrument in accordance with an embodiment of the present disclosure; 
         FIG. 2  is an enlarged, perspective view of a distal articulating section of the instrument of  FIG. 1  in an articulated configuration; 
         FIG. 3  is a cross-section of the articulating surgical instrument of  FIG. 1  showing the internal working components thereof; 
         FIG. 4  is a perspective view of an end effector of one embodiment of the surgical instrument configured for bilateral movement; 
         FIG. 5  is a perspective view of an end effector of another embodiment of the surgical instrument configured for unilateral movement; 
         FIG. 6A  is cross-section of the articulating surgical instrument of  FIG. 1  showing the end effector in an open configuration; 
         FIG. 6B  is a cross-section of the articulating surgical instrument of  FIG. 1  showing the end effector in a closed configuration; 
         FIG. 7A  is an enlarged, perspective view of a prior art distal articulating section of the instrument of  FIG. 1  during proximal motion of a drive wire; 
         FIG. 7B  is a schematic illustration of an articulated path approximated by divided components of a linear path. 
         FIGS. 8A-B  are schematic illustrations of a spring in connection with the drive wire in accordance with one embodiment of the present disclosure; 
         FIG. 9A  is a schematic illustration of a clutch assembly in accordance with another embodiment of the present disclosure; 
         FIG. 9B  is a schematic illustration of a perspective view of another embodiment of the clutch assembly; 
         FIG. 9C  is a schematic illustration of a cross-section of the clutch assembly of  FIG. 9B ; 
         FIG. 10  is a schematic illustration of a tube circumferentially surrounding the drive wire in accordance with another embodiment of the present disclosure; 
         FIG. 11A  is a schematic illustration of a rolling mechanism in connection with the drive wire in an aligned configuration in accordance with another embodiment of the present disclosure; and 
         FIG. 11B  is a schematic illustration of the rolling mechanism of  FIG. 11A  in an articulated configuration. 
     
    
    
     DETAILED DESCRIPTION 
     Particular embodiments of the present disclosure will be described herein with reference to the accompanying drawings. As shown in the drawings and as described throughout the following description, and as is traditional when referring to relative positioning on an object, the term “proximal” or “trailing” refers to the end of the apparatus that is closer to the user and the term “distal” or “leading” refers to the end of the apparatus that is farther from the user. In the following description, well-known functions or constructions are not described in detail to avoid obscuring the present disclosure in unnecessary detail. 
     Referring initially to  FIG. 1 , an embodiment of an electrosurgical instrument is depicted generally as  10 . The instrument  10  includes a housing  12  remotely supporting an end effector  14  through an elongated shaft  16 . 
     Elongated shaft  16  includes a proximal portion  18  extending from the housing  12  and an articulating distal portion  20  supporting the end effector  14 . The proximal portion  18  defines a longitudinal axis A-A, and is sufficiently long to position the end effector  14  through a cannula (not shown). The articulating distal portion  20  defines one or more joints  22  between the proximal portion  18  of the elongated shaft  16  and the end effector  14  permitting the end effector  14  to articulate or pivot relative to the longitudinal axis A-A. The end effector  14  defines an end effector axis B-B, which may be aligned with the longitudinal axis A-A to facilitate insertion of the end effector  14  through the cannula (not shown), and thereafter moved to orient the end effector  14  relative to a surgical site within the body of a patient. When the end effector axis B-B is aligned with the longitudinal axis A-A of the proximal portion  18 , as illustrated in  FIG. 1 , the elongated shaft  16  is in an aligned configuration. By contrast, as illustrated in  FIG. 2 , when the end effector axis B-B is pivoted relative to the longitudinal axis A-A of the proximal portion  18  in the direction indicated by the arrow sign “R 1 ”, the elongated shaft  16  is in an articulated configuration. The elongated shaft  16  may be made of a rigid material. Alternatively, the elongated shaft  16  may be made of a flexible material, such as in a catheter-based instrument for endoluminal-type procedures. 
     With continued reference to  FIG. 1 , the end effector  14  includes a pair of opposing jaw members  30  and  32 . The jaw members  30 ,  32  are operable from the housing  12  to move between an open configuration to receive tissue, and a closed configuration to clamp the tissue and impart an appropriate closing pressure thereto. When the end effector  14  is in the open configuration, a distal portion of each of the jaw members  30 ,  32  is spaced from the distal portion of the other of the jaw members  30 ,  32 . When the end effector  14  is in the closed configuration, the distal portions of the jaw members  30 ,  32  are closer together. The end effector  14  is configured for bilateral movement wherein both jaw members  30  and  32  move relative to the end effector axis B-B between the open and closed configurations, as further discussed below with respect to  FIG. 4 . Unilateral motion is also contemplated wherein one of the jaw members  30 ,  32 , e.g., jaw member  32  remains stationary relative to the end effector axis B-B and the other of the jaw members  30 ,  32 , e.g., jaw member  30  is moveable relative to the end effector axis B-B, as discussed in detail below with respect to  FIG. 5 . 
     As best seen in  FIG. 1 , instrument  10  includes an electrical interface or plug  80  that connects the instrument  10  to a source of electrosurgical energy, e.g., a generator (not shown). An electrical cable  82  extends from the plug  80  to the housing  12  which securely connects the cable  82  to the instrument  10 . The electrical cable  82  is in electrical communication with at least one of the jaw members  30 ,  32  such that the electrosurgical energy supplied by the generator may be delivered to tissue clamped in the end effector  14 . 
     The housing  12  includes various actuators that are responsive to manipulation by an operator to induce these and other movements of the end effector  14 . For instance, actuation of the rotation assembly  40  rotates the elongated shaft  16  which, in turn, rotates the end effector  14  in the clockwise or counter-clockwise direction to manipulate and grasp tissue. The housing  12  further includes a handle assembly  50  and a driving assembly  60 , as shown in  FIG. 3 , which jointly impart movement of the opposing jaw members  30  and  32  relative to one another to grasp tissue therebetween. 
     With reference to  FIG. 3 , the handle assembly  50  can generally be characterized as a four-bar mechanical linkage composed of the following elements: movable handle  51 , a link  52 , a cam-like link  53  and a base link embodied by stationary handle  54  and a pair of pivot points  55  and  56 . The cam-like link  53  includes an upper cam piston  57 , a fixed pivot  58  and a handle pivot  59 . Although shown as a four-bar mechanical linkage, the present disclosure contemplates other linkages to effect relative motion of the jaw members  30  and  32  as is known in the art. Once actuated, movable handle  51  moves in a generally arcuate fashion towards stationary handle  54  which causes link  52  to rotate proximally about pivots  55  and  56  which, in turn, cause cam-like link  53  to rotate about pivots  58  and  59  in a generally proximal direction. Movement of the cam-like link  53  imparts movement to the driving assembly  60  as explained in more detail below. 
     The driving assembly  60  includes a coil spring  62  mounted atop a spring mount  64 . The spring mount  64  includes a circular flange  65  at the proximal end thereof, which is dimensioned to bias the proximal end of the coil spring  62  once the spring  62  is seated within the housing  12 . The distal end of the spring mount  64  has a compression tab  66  dimensioned to bias the distal end of the coil spring  62 . Once assembled, the spring  62  is poised for compression atop the spring mount  64  upon actuation of the handle assembly  50 . The driving assembly  60  further includes a compression sleeve  67  which is slidingly disposed within the spring mount  64 , and a drive wire  68  that extends through the elongated shaft  16  connecting between the end effector  14  and the housing  12 . The distal end of the compression sleeve  67  engages the proximal end of the drive wire  68  such that proximal movement of the compression sleeve  67  actuates the drive wire  68  in a proximal direction. Proximal movement of the drive wire  68  closes jaw members  30  and  32  about tissue, as explained further below with respect to  FIGS. 4 and 5 . 
     As best seen in  FIG. 3 , cam piston  57  is poised in abutting relationship with the compression tab  66  such that movement of the handle assembly  50  rotates cam piston  57  proximally against coil spring  62 . More particularly, movement of the cam piston  57  via movement of the handle assembly  50  moves the compression tab  66  proximally, which, in turn, compresses the coil spring  62 , and actuates the compression sleeve  67  to move proximally. Proximal motion of the compression sleeve  67  translates into proximal motion of the drive wire  68 , which, in turn, translates into rotational motion of the jaw members  30  and  32 . A more complete description of an instrument having a handle assembly and a driving assembly that impart proximal movement of a drive wire can be found in U.S. Pat. No. 7,083,618 to Couture et al. (hereinafter “Couture ‘618’ patent”). 
     In an example in which the end effector  14  is configured for bilateral movement, as illustrated in  FIG. 4 , the jaw members  30  and  32  are secured to the elongated shaft  16  through a pivot pin  71 . Each of the jaw members defines a cam slot (obstructed from view in  FIG. 4 ) having a common cam pin  72  disposed therethrough. The cam pin  72  is configured to ride along the cam slots and a longitudinal slot  73  defined on the elongated shaft  16 . Longitudinal reciprocation of the cam pin  72  through the cam slots and the longitudinal slot  73  rotates jaw members  30  and  32  about the pivot pin  71  between the open and closed configurations. The distal end of the drive wire  68  defines a pin slot (not shown) dimensioned to house the cam pin  72  such that longitudinal reciprocation of the drive wire  68  translates the cam pin  72  along the cam slots and the longitudinal slot  73 , which, in turn, rotates the jaw members  30  and  32  about the pivot pin  71 . More specifically, proximal motion of the drive wire  68  induces the jaw members  30  and  32  to a closed configuration, whereas distal motion of the drive wire  68  induces the jaw members  30  and  32  to an open configuration. A more complete description of an instrument having an end effector configured for bilateral movement can be found in the Couture &#39;618 patent. 
     In another example in which the end effector  14  is configured for unilateral movement, as illustrated in  FIG. 5 , the jaw member  32  is fixed relative to the shaft  16 , whereas the other jaw member  30  pivots about a pivot pin  74  to grasp tissue. The pivoting jaw member  30  includes a detent or protrusion  76  which extends from the jaw member  30  through a longitudinal slot  75  disposed within the drive sleeve  68 ′. The pivoting jaw member  30  is actuated by sliding the drive sleeve  68 ′ axially within the shaft  16  such that a distal end  77  of the longitudinal slot  75  abuts against the detent  76  on the pivoting jaw member  30 . Proximal motion of the drive sleeve  68 ′ closes the jaw members  30  and  32  about the tissue grasped therebetween, whereas distal motion of the drive sleeve  68 ′ opens the jaw members  30  and  32 . A more complete description of an instrument having an end effector configured for unilateral movement can be found in U.S. Pat. No. 7,156,846 to Dycus et al. 
     Based on the above configuration, movement of the movable handle  51  activates the four-bar linkage which, in turn, actuates the driving assembly  60 , and subsequently the jaw members  30  and  32 . More specifically, as the movable handle  51  is squeezed, the cam-like link  53 , through the mechanical advantage of the four-bar mechanical linkage, is rotated generally proximally about pivot points  58  and  59  such that the cam piston  57  biases compression tab  66  which compresses the spring  62  against the circular flange  65  of the spring mount  64 . Simultaneously, the drive wire  68  (or drive sleeve  68 ′) is pulled proximally by the compression sleeve  67  which, in turn, closes the jaw members  30  and  32  relative to one another, as explained above with respect to  FIGS. 4-5 . As illustrated in  FIG. 1 , motion of the movable handle  51  in the direction of arrows “T 0 ” induces motion in the jaw members  30  and  32  in the direction of arrow “T 1 ” from the open configuration to the closed configuration. On the other hand, separation of the movable handle  51  from the stationary handle  54  moves the jaw members  30 ,  32  from the closed configuration to the open configuration. 
     The handle assembly  50  enables the user to selectively compress the coil spring  62  for a specific distance Δy which, in turn, pushes the circular flange  65  proximally for a distance Δy, as illustrated in  FIGS. 6A-B . Proximal motion of the circular flange  65  results in proximal motion of the spring mount  64 , which, in turn, results in proximal motion of the compression sleeve  67 , and consequently results in proximal motion of the drive wire  68  (or drive sleeve  68 ′, referred to hereinafter for simplicity as drive wire  68 ) a distance ≢y. The proximal motion of the drive wire  68  translates into longitudinal motion of the cam pin  72  a distance Δy along the longitudinal slot  73  in the proximal direction, as illustrated in  FIGS. 6A-B . As shown in  FIGS. 6A-B , when the distance Δy corresponds to the length of the longitudinal slot  73 , the compression of the spring  62  causes the cam pin  72  to travel the entire length of the longitudinal slot  73 , thereby completely closing the jaw members. Further, the compression of the spring  62  imparts a specific load on the drive wire  68 . As illustrated in  FIG. 4 , the specific load on the drive wire  68  ultimately becomes a pulling force Fpulling acting upon the cam pin  72  to drive the pin  72  proximally. The specific load on the drive wire  68  is also converted to a closure force Fclosure exerted by the jaw members  30  and  32  about the jaw pivot  71  by way of cam pins  72 . Similarly, with respect to  FIG. 5 , the specific load on the drive sleeve  68 ′ becomes a pulling force Fpulling acting upon the detent  76  to cause it to move proximally. The load on the drive sleeve  68 ′ is also converted to a closure force Fclosure exerted by the jaw members  30  and  32  about the pivot pin  74  by way of the detent  76 . Thus, regardless of whether the end effector  14  is configured for bilateral or unilateral motion, proximal motion of the drive wire  68  of a distance Δy can translate into rotational motion of the opposing jaw members  30  and  32  from an open configuration to a closed configuration and simultaneously transmit a specific closure force to the opposing jaw members  30  and  32 . 
     To effectively clamp tissue between the jaw members  30  and  32 , a relatively high clamping force is typically generated to impart a closure pressure on the tissue in a desirable range of from about 3 kg/cm 2  to about 16 kg/cm 2 . The closure pressure is determined by two factors: (1) whether jaw members  30  and  32  are in a closed configuration and (2) the closure force exerted by the jaw members  30  and  32 . As explained above, both factors are determined by the proximal motion of the drive wire  68 , which is ultimately determined by the compression of the coil spring  62  through the handle assembly  50 . In the prior art, the closure pressure within the particularly desirable range can be readily achieved when the articulating instrument is in an aligned configuration, that is when the drive wire  68 , the articulating distal portion  20  of the elongated shaft  16  and the end effector  14  are aligned along the same axis, as depicted in  FIGS. 6A-B . 
     However, in the prior art, when the articulating instrument is in an articulated configuration as depicted in  FIG. 7A , compression of the coil spring  62  a distance Δy can no longer yield the desired closure pressure. Due to the articulation, linear motion of a distance Δy translates into curved motion of a newly defined distance Δy′ along the articulated path. As shown in  FIG. 7B , a linear displacement Δy can be broken down to an infinite number of linear segments y 1 , y 2 , y 3 , . . . yi . . . yn, such that Δy is defined by the following equation: 
       Δ y=y   1   +y   2   +y   3   +. . . +y   i   +. . .  30  y   n  
 
     Each linear segment yi comprises a divided component that represents a tangent to the articulated path. The articulated path can be approximated by its infinite number of tangent segments connecting each other. Therefore, the sum of all the divided components of the linear segments y 1 , y 2 , y 3 , . . . y i . . . y n  approximates the newly defined distance Δy′ along the articulated path. As shown in  FIG. 7B , each divided component forms an angle θ i  with respect to the linear axis, thus each linear displacement yi corresponds to a displacement of y i ×cos θ i  along the articulated path. Thus, the newly defined displacement Δy′ along the articulated path is defined by the following equation: 
       Δ y′=y   1 ·cos θ 1   +y   2 ·cos θ 2   +y   3 ·cos θ 3   +. . . +y   i ·cos θ i   +. . . +y   n ·cos θ n  
 
     Therefore, curved motion of Δy′ along the articulated path is much less than proximal motion of Δy along a linear path. As a result, in the prior art, proximal motion of the drive wire  68  for a distance of Δy ultimately translates into motion of the cam pin  72  for a distance of Δy′ along the longitudinal slot  73  as in a bilateral end effector as shown in  FIG. 4 , or translates into motion of the detent  76  for a distance of Δy′ along the longitudinal  75  as in a unilateral end effector as shown in  FIG. 5 . In both cases, jaw members  30  and  32  can no longer be completely closed or closed under the proper closing pressure. Rather, when the instrument  10  is in an articulated configuration, compression of the spring  62  would rotate the jaw members  30  and  32  to a position less than required to generate the proper closing pressure, resulting in a closure pressure significantly below the above-identified desirable range. 
     Further, in the prior art, when the instrument  10  is in an articulated configuration as depicted in  FIG. 7A , the drive wire  68  experiences friction F friction  as the drive wire  68  contacts surfaces within the articulating distal portion  20 , which reduces the load carried by the drive wire  68 . Ultimately, the closure force F closure  exerted by the jaw members  30  and  32  in an articulated configuration is substantially less than that in an aligned configuration. For the same reason, the closure pressure is significantly below the desirable range. 
     Still further, in the articulated configuration, when the jaw members  30  and  32  can hardly be closed, the surgeon may tend to apply an overly excessive amount of force on the handle  51 . However, any over-compression of the handle  51  may lead to an over-compression of the coil spring  62  which imparts an overload on the drive wire  68 , and which may result in an excessive rotation of the jaw members  30  and  32  relative to each other and an excessive increased closure force, eventually resulting in a closure pressure exceeding the desirable range. 
     The present disclosure provides solutions to compensate for the loss or increase of distance and closure force caused by the articulated path, thereby maintaining a consistent closure pressure within the desirable range between an aligned configuration and an articulated configuration. 
     In the first embodiment, as illustrated schematically in  FIGS. 8A-8B , the coil spring  62  has a spring constant such that the coil spring  62  can be stretched for a distance ΔL=L 2 -L 1  as the instrument  10  is articulated upon application of force through the movable handle  51 . The distance ΔL compensates for the loss of displacement due to articulation. In one example, the distance ΔL corresponds to the difference between Δy and Δy′. Based on this configuration, the drive wire  68  is induced to move proximally for an additional distance ΔL, thereby enabling the cam pin  72  of  FIG. 4  or the detent  76  of  FIG. 5  to travel across the full length of the longitudinal slot  73  of  FIG. 4  or the longitudinal slot  75  of  FIG. 5  in an articulated configuration, thereby allowing the jaw members  30  and  32  to reach a completely closed configuration under the appropriate pressure. The spring constant is also designed to provide an additional load on the drive wire  68 , during proximal motion of the drive wire  68 , thereby compensating the loss of load due to friction at the contact surfaces between the drive wire  68  and the articulating distal section  20  of the shaft  16 , when the instrument  10  is in an articulated configuration. Thus, a consistent closure pressure within the desirable range between about 3 kg/cm 2 and about 16 kg/cm 2 can be maintained from an aligned configuration to an articulated configuration. 
     In another embodiment, as illustrated schematically in  FIG. 9A , the driving assembly  60  includes a clutch assembly  83  disposed between the drive wire  68  and the jaw members  30  and  32 . The clutch assembly  83  includes a clutch  85  and a spring  88 . The clutch  85  may be either an analog clutch or a discrete clutch. The clutch  85  is securely attached to the end effector  14  through a rotational pivot  86 . When the drive wire  68  engages in proximal motion, any load on the drive wire  68  imparts a driving force Fdriving acting upon the clutch  85 . The clutch  85  slips about the rotational pivot  86  when the driving force Fdriving is beyond a certain predetermined value. During slippage of the clutch  85 , the driving force Fdriving converts to a driven force Fdriven acting upon the spring  88 , which distally connects to one of the plurality of clutch teeth  87 . The clutch  85  is configured to have a design ratio such that any driving force Fdriving beyond a certain predetermined value imparts a driven force Fdriven within a particular range considerably less than Fdriving. The driven force Fdriven within the particular range causes the spring  88  to stretch in the proximal direction for a predetermined distance, which, in turn, induces a constant closure force on the jaw members  30  and  32 . The predetermined distance corresponds to the length of the longitudinal slot  73  that the cam pin  72  needs to travel, as in a bilateral configuration illustrated in  FIG. 4 , or corresponds to the length of the longitudinal slot  75  that the detent  76  needs to travel as in a unilateral configuration illustrated in  FIG. 5 , in order to move jaw members  30  and  32  from an open configuration to a closed configuration. Thus, the clutch assembly  83  offloads any increase in force delivered by the drive wire  68  due to over-compression of the spring  62 , thereby ultimately creating a constant closure force on the jaw members  30  and  32 . Additionally, any excessive displacement by the drive wire  68  in the proximal direction due to over-compression is also reduced by the clutch assembly  83 , avoiding excessive rotation of the jaw members  30  and  32  relative to each other. As a result, the clutch assembly  83  ensures that the closure pressure upon the tissue clamped between the jaw members  30  and  32  is maintained within the desirable range 3 kg/cm 2 and about 16 kg/cm 2 all time. 
       FIGS. 9B-9C  together illustrate another embodiment of the clutch assembly  83 , where the clutch assembly  83  includes a torsion spring  84  and a friction plate  89  securely attached to a jaw member  30  or  32 . Unlike the clutch assembly  83  illustrated in  FIG. 9A  which has elements arranged in a linear fashion proximal to the jaw member  32 , the friction plate  89  and the torsion spring  84  are laterally placed within respect to the jaw member  32 , as clearly shown in the cross-section view of the clutch assembly  83  illustrated in  FIG. 9C . Thus, by taking advantage of the lateral space on the side of the jaw member  32  to store the clutch assembly  83 , this particular embodiment uses less physical space. Here, the torsion spring  84  is a spring that works by torsion or twisting, such that it stores mechanical energy when it is twisted. The amount of force or torque the torsion spring  84  exerts is proportional to the amount it is twisted. Similar to the clutch  85  discussed immediately above, the frictional plate  89  is designed to slip to overcome any increase in force delivered by the drive wire  68 , which, in turn, causes the spring  84  to twist or untwist for a predetermined distance, ultimately inducing a constant closure force on the jaw members  30  and  32 . In a preferred embodiment, the frictional plate  89  is designed to slip resulting in a closure pressure of 120 psi, which approximates to 8.437 kg/cm 2. 
       FIG. 10  shows another embodiment of the present disclosure for compensation for the increased or decreased forces on the drive wire during articulation. More particularly, the driving assembly  60  may include a tube  90  extending along the length of the elongated shaft  16 , circumferentially surrounding the drive wire  68 . The tube  90  serves as an intermediate layer between the elongated shaft  16  and the drive wire  68 . The tube  90  is made of a material that defines a friction coefficient substantially less than that of the elongated shaft  16 , resulting in an almost negligible friction between an inner surface of the tube  90  and the drive wire  68  when they are in motion. When the instrument  10  is in the articulated configuration, the tube  90  prevents direct contact between the drive wire  68  and the elongated shaft  16  that otherwise would occur in the prior art. Additionally, the tube  90  defines a plurality of spaced protrusions  91  on an inner wall thereof that protrude inwardly towards the drive wire  68 . The protrusions  91  reduce the contact area between the tube  90  and the drive wire  68  to a minimal degree, thus substantially reducing any contact friction that would be experienced by the drive wire  68  during translation. Further, when the instrument  10  is articulated, the protrusions  91  maintain the drive wire  68  in the center of the tube  90  during translation thereof. Due to the physical characteristics of the tube  90 , the loss of load on the drive wire  68  due to friction is significantly minimized. As such, the closure force Fclosure ultimately exerted by the jaw members  30  and  32  is maximized. The tube  90  feature may be implemented in conjunction with the spring feature as discussed in the first embodiment, such that they jointly compensate for the loss of displacement and the loss of load experienced by the jaw members due to articulation of the instrument. 
     Another embodiment of the present disclosure is shown in  FIGS. 11A-B , wherein the driving assembly  60  may further include a rolling mechanism  100  disposed between the spring  62  and the drive wire  68 . The rolling mechanism  100  includes a roller bearing feature  102 , a pivot link or lever  103 , a flexible control wire  104 , and a spring  105 . The roller bearing feature  102  has two structures  115  and  116  perpendicular with respect to each other. The horizontal structure  115  has a proximal end  107  connected to the spring  62  (not shown). The vertical structure  116  defines a top end  106  fixedly connected to the spring  105 . The pivot link  103  is securely connected to the housing  12  at a pivot point  109 . The pivot link  103  defines a top end  112  connected to the flexible control wire  104  and a bottom end  110  reciprocally engaged with the roller bearing feature  102 . Specifically, the pivot link  103  defines a longitudinal slot  111  which is configured to allow a slidable engagement with a cam pin  117  of the roller bearing feature  102 , such that the cam pin  117  may slide across the longitudinal slot  111 . Based on this configuration, rotation movement of the pivot link  103  may impart and/or inhibit proximal movement of the roller bearing feature  102 . The flexible control wire  104  connects between the top end  112  of the pivot link  103  and the distal end of the shaft  16 . 
     When the elongated shaft  16  is in an articulated configuration as shown in  FIG. 11B , compression of the spring  62  (not shown) translates into proximal motion of the roller bearing feature  102 , which, in turn, stretches the spring  105  proximally and simultaneously results in proximal motion of the drive wire  68 . The expansion of the spring  105  provides additional proximal displacement to the cam pin  72  shown  FIG. 4  or the detent  76  shown in  FIG. 5  that compensates for the loss of displacement due to articulation. Further, the force exerted by the spring  105  due to expansion provides an additional load on the drive wire  68  which compensates for the loss of load caused by friction at the contact surfaces between the drive wire  68  and the elongated shaft  16  in the articulated configuration. 
     When the elongated shaft  16  is articulated, the flexible control wire  104  is under tension exerting a force on the distal end  112  of the pivot link  103 , which, in turn, causes the pivot link  103  to pivot about the fixed pivot point  109  in a clockwise direction as illustrated in  FIG. 11B . Because the distance defined between the fixed pivot point  109  and the top end  112  is much less than the distance defined between the fixed pivot point  109  and the bottom end  110 , one small clockwise rotation at the top end  112  results in a relatively large proximal movement at the bottom end  110 . As the pivot link  103  rotates in the clockwise direction, the longitudinal slot  111  of the pivot link  103  induces proximal movement of the cam pin  117 , which, in turn, facilitates proximal movement of the roller bearing feature  102 . Due to the reciprocal relationship between the pivot link  103  and the roller bearing feature  102 , when the pivot link  103  cannot rotate any further, the cam pin  117  then reaches its proximal-most position, preventing further proximal movement of the roller bearing feature  102 . In short, the pivot link  103  through its engagement with the roller bearing feature  102 , facilitates proximal movement of the roller bearing feature  102 , however, it also prevents the roller bearing feature  102  from any further proximal movement once the roller bearing feature  102  moved proximally for a predefined distance. Thus, the pivot link  103  and the flexible control wire  104  together prevent the spring  105  from over stretching due to over-compression of the spring  102 . This configuration ensures that the closure pressure is always maintained within the desirable range between about 3 kg/cm 2 and 16 kg/cm 2 between the aligned configuration and the articulated configuration. Further, this particular embodiment allows a better spring design, and provides mechanisms to compensate for more frictional losses. 
     While several embodiments of the disclosure have been shown in the drawings and/or discussed herein, it is not intended that the disclosure be limited thereto, as it is intended that the disclosure be as broad in scope as the art will allow and that the specification be read likewise. Therefore, the above description should not be construed as limiting, but merely as exemplifications of particular embodiments. Those skilled in the art will envision other modifications within the scope and spirit of the claims appended hereto.