Jaw closure mechanism for a surgical clip applier

[0001] The present application claims the benefit of and priority to U.S. Provisional Application Ser. No. 61/577,130, filed on Dec. 19, 2011, the entire contents of which are incorporated herein by reference.

[0002] 1. Technical Field

[0003] The present disclosure relates to surgical instruments. More particularly, the present disclosure relates to a jaw closure mechanism for use in a surgical clip applier.

[0004] 2. Description of Related Art

[0005] Surgical staplers and clip appliers are known in the art and are used for a number of distinct and useful surgical procedures. In the case of a laparoscopic surgical procedure, access to the interior of an abdomen is achieved through narrow tubes or cannulas inserted through a small entrance incision in the skin. Minimally invasive procedures performed elsewhere in the body are often generally referred to as endoscopic procedures. Typically, a tube or cannula device is extended into the patient's body through the entrance incision to provide an access port. The port allows the surgeon to insert a number of different surgical instruments therethrough using a trocar and for performing surgical procedures far removed from the incision.

[0006] During a majority of these procedures, the surgeon must often terminate the flow of blood or another fluid through one or more vessels. The surgeon will often apply a surgical clip to a blood vessel or another duct to prevent the flow of body fluids therethrough during the procedure. An endoscopic clip applier is known in the art for applying a single clip or a series of clips during a surgical procedure. Such clips are typically fabricated from a biocompatible material and are usually compressed over a vessel. Once applied to the vessel, the compressed clip terminates the flow of fluid therethrough. Open surgical clip appliers operate in a similar fashion.

[0007] Endoscopic clip appliers that are able to apply multiple clips in endoscopic or laparoscopic procedures during a single entry into the body cavity are described in commonly-assigned U.S. Pat. Nos. 5,084,057 and 5,100,420 to Green et al., which are both incorporated by reference in their entirety. Another multiple endoscopic clip applier is disclosed in commonly-assigned U.S. Pat. No. 5,607,436 by Pratt et al., the contents of which is also hereby incorporated by reference herein in its entirety. These devices are typically, though not necessarily, used during a single surgical procedure. U.S. patent application Ser. No. 08/515,341 now U.S. Pat. No. 5,695,502 to Pier et al., the disclosure of which is hereby incorporated by reference herein, discloses a resterilizable surgical clip applier. The clip applier advances and forms multiple clips during a single insertion into the body cavity. This resterilizable clip applier is configured to receive and cooperate with an interchangeable clip magazine so as to advance and form multiple clips during a single entry into a body cavity.

[0008] One significant design goal in the manufacture of clip appliers is to provide a clip applier that maximizes the jaw closure force imparted to the jaws to help ensure complete and proper formation of the clip onto the body tissue or vessel while also minimizing the drive force applied by the user to actuate the jaws so as to permit relatively easy actuation of the jaws and to inhibit fatigue during the course of a surgical procedure. In particular, it would be desirable to provide a clip applier having a jaw closure mechanism configured to maximize the ratio of jaw closure force to drive force.

[0009] In accordance with the present disclosure, a jaw closure mechanism for use in a surgical clip applier having first and second jaws movable relative to one another between a spaced-apart position and an approximated position to form a surgical clip about tissue is provided. The jaw closure mechanism includes first and second eccentric wheels and a cable disposed about the first and second eccentric wheels. The first and second eccentric are wheels rotatably coupled to the respective first and second jaws. Each of the first and second eccentric wheels includes a center and a pivot point that is offset relative to the center. A cable is disposed about each of the first and second eccentric wheels. More specifically, the cable is engaged to the first eccentric wheel at a first engagement point and to the second eccentric wheel at a second engagement point such that, upon application of a drive force to the cable, the first and second eccentric wheels are rotated and displaced relative to the respective first and second jaws from a first position to a second position to urge the first and second jaws from the spaced-apart position to the approximated position.

[0010] In the first position, the center, the pivot point, and/or the engagement point of each of the first and second eccentric wheels may be axially aligned with one another. Additionally or alternatively, in the second position the center, the pivot point, and the engagement point of each of the first and second eccentric wheels may be angled with respect to one another.

[0011] In embodiments, the jaw closure mechanism further includes a drive bar coupled to the cable and configured to apply the drive force to the cable. More specifically, the drive bar may be selectively translatable between a more distal position and a more proximal position to apply the drive force to the cable.

[0012] In embodiments, upon translation of the drive bar from the more distal position to the more proximal position, the cable applies an oblique force to each of the first and second eccentric wheels. Further, the oblique force applied to each of the first and second eccentric wheels may urge the first and second eccentric wheels to displace and rotate relative to the respective first and second jaws, thereby applying a jaw closure force to the first and second jaws to move the first and second jaws from the spaced-apart position to the approximated position.

[0013] In embodiments, the jaw closure force is a product of the drive force and a force transformation multiplier. The force transformation multiplier is inversely proportional to an angle defined between a direction of the oblique force and a direction of the jaw closure force.

[0014] In embodiments, the rotation and displacement of the first and second eccentric wheels minimizes the angle defined between the direction of the oblique force and the direction of the jaw closure force as the first and second eccentric wheels are transitioned from the first position to the second position, thereby maximizing the force transformation multiplier.

[0015] In embodiments, the jaw closure mechanism is releasably engagable with the first and second jaws.

[0016] A surgical clip applier is also provided in accordance with the present disclosure. The surgical clip applier includes a jaw assembly and a jaw closure mechanism. The jaw assembly includes first and second jaws movable between a spaced-apart position and an approximated position to apply a surgical clip to tissue. The jaw closure mechanism includes first and second eccentric wheels rotatably coupled to the respective first and second jaws and a cable disposed about each of the first and second eccentric wheels. The cable is engaged to the first eccentric wheel at a first engagement point and to the second eccentric wheel at a second engagement point such that, upon application of a longitudinal drive force to the cable, the cable applies an oblique force to each of the first and second eccentric wheels to rotate and displace the first and second eccentric wheels, thereby applying a transverse jaw closure force to the first and second jaws to urge the first and second jaws from the spaced-apart position to the approximated position.

[0017] In embodiments, the surgical clip applier further includes a drive assembly having a drive bar that is coupled to the cable. The drive bar is selectively translatable between a more distal position and a more proximal position to apply the longitudinal drive force to the cable.

[0018] In embodiments, the surgical clip applier further includes a trigger assembly that is operably coupled to the drive assembly. The trigger assembly is selectively actuatable to translate the drive bar between the more distal position and the more proximal position.

[0019] In embodiments, the transverse jaw closure force is a product of the longitudinal drive force and a force transformation multiplier. The force transformation multiplier being inversely proportional to an angle defined between a direction of the oblique force and a direction of the transverse jaw closure force. In such embodiments, the rotation and displacement of the first and second eccentric wheels may be configured to minimize the angle defined between the direction of the oblique force and the direction of the transverse jaw closure force as the first and second jaws are urged from the spaced-apart position to the approximated position, thereby maximizing the force transformation multiplier.

[0020] In embodiments, the jaw closure mechanism is releasably engagable with jaw assembly.

[0021] A method of transforming a longitudinal drive force into a transverse jaw closure force in a surgical clip applier having first and second jaws movable relative to one another between a spaced-apart position and an approximated position to form a surgical clip about tissue is also provided in accordance with the present disclosure. The method includes applying a longitudinal drive force, transforming the longitudinal drive force into a transverse jaw closure force, applying the transverse jaw closure force to the first and second jaws to move the first and second jaws relative to one another between the spaced-apart position and the approximated position to form the surgical clip about tissue, and minimizing an angle defined between a direction of the oblique force and a direction of the transverse jaw closure force while the transverse jaw closure force is being applied to the first and second jaws to thereby maximize a ratio of jaw closure force to longitudinal drive force.

[0031] Embodiments of a jaw closure mechanism for a surgical clip applier in accordance with the present disclosure will now be described in detail with reference to the drawing figures wherein like reference numerals identify similar or identical structural elements. As shown in the drawings and described throughout the following description, as is traditional when referring to relative positioning on a surgical instrument, the term “proximal” refers to the end which is closer to the user and the term “distal” refers to the end which is further away from the user.

[0032] Referring briefly to FIG. 1, an endoscopic surgical clip applier is shown generally identified by reference numeral 100. Surgical clip applier 100 generally includes a handle assembly 102 and an endoscopic portion including a shaft assembly 104 extending distally from handle assembly 102 and having a jaw assembly 120 disposed at a distal end thereof. Handle assembly 102 further includes a rotating assembly 110 rotatable in either direction to effect corresponding rotation of jaw assembly 120, and a trigger assembly 108 that is selectively squeezable to actuate jaw assembly 120 to form a surgical clip “C” (FIGS. 4A-4B) about tissue. A stack of surgical clips is typically loaded and/or retained within shaft assembly 104 in a manner so as to slide therewithin and/or therealong, ultimately such that a plurality of surgical clips “C” (FIGS. 4A-4B) may be sequentially provided to jaw assembly 120 for formation about tissue. A complete description of the inner-workings and operation of surgical clip applier 100 can be found in commonly-assigned U.S. patent application Ser. No. 12/055,446 to Whitfield et. al. (U.S. Patent Application Publication No. 2008/0243145), filed on Mar. 26, 2008, the entire contents of which are hereby incorporated by reference herein.

[0033] Referring briefly to FIG. 2, an open surgical clip applier is shown generally identified by reference numeral 200. Surgical clip applier 200 generally includes a handle assembly 202 including a housing 204 and a shaft assembly 208 extending distally from housing 204 and including a jaw assembly 220 disposed at a distal end thereof. Housing 204 further includes a pair of handles 206 pivotally coupled thereto and extending outwardly from housing 204. Handles 206 are selectively squeezable to actuate jaw assembly 220 to form a surgical clip “C” (FIGS. 4A-4B) about tissue. A stack of surgical clips is typically loaded and/or retained within shaft assembly 208 in a manner so as to slide therewithin and/or therealong, ultimately such that a plurality of surgical clips “C” (FIGS. 4A-4B) may be sequentially provided to jaw assembly 220 for formation about tissue. A complete description of the inner-workings and operation of surgical clip applier 200 can be found in commonly-assigned U.S. patent application Ser. No. 12/540,475 to Zergiebel (U.S. Patent Application Publication No. 2010/0049216), filed on Aug. 13, 2009, the entire contents of which are hereby incorporated by reference herein.

[0034] Turning now to FIG. 3, jaw assembly 120 of surgical clip applier 100 (FIG. 1) is shown, although jaw assembly 120 may alternatively be configured for use with surgical clip applier 200 (FIG. 2), or any other suitable surgical clip applier. However, for purposes of simplicity and consistency, jaw assembly 120 will be described in conjunction with surgical clip applier 100 only.

[0035] Referring to FIG. 3, in conjunction with FIG. 1, jaw assembly 120 is mounted in the distal end of shaft assembly 104 such that jaws 120a, 120b are longitudinally stationary relative thereto. Jaws 120a and 120b of jaw assembly 120 each define a recess 122a, 122b on an inwardly facing surface thereof that is configured to guide passage of a surgical clip “C” (FIGS. 4A-4B) therethrough. Once the surgical clip “C” (FIGS. 4A-4B) is positioned between jaws 120a, 120b, trigger assembly 108 may be actuated to approximate jaws 120a, 120b relative to one another to form the surgical clip “C” (FIGS. 4A-4B) about tissue. More specifically, a jaw closure mechanism 150 is coupled to each of jaws 120a, 120b of jaw assembly 120 and to drive bar 140 (FIGS. 4A-4B) such that, upon actuation of trigger assembly 108 to translate drive bar 140 (FIGS. 4A-4B) proximally, jaws 120a, 120b are moved from a first, spaced-apart position (FIG. 4A) to a second, approximated position (FIG. 4B) to form the surgical clip “C” (FIGS. 4A-4B) disposed therebetween about tissue. Further, jaws 120a, 120b may be biased towards the first, spaced-apart position (FIG. 4A) such that jaws 120a, 120b are returned to the first, spaced-apart position (FIG. 4A) upon release of trigger assembly 108. Jaw closure mechanism 150 is described in greater detail below with reference to FIGS. 4A-5B.

[0036] Turning now to FIGS. 4A-4B and 5A-5B, jaw closure mechanism 150 is described. Jaw closure mechanism 150 generally includes a pair of discs, or wheels 152, 154 each of which is rotatably mounted on one of the jaws 120a, 120b, respectively, and a belt, or cable 156 looped about both of the wheels 152, 154. More specifically, each jaw 120a, 120b includes a pivot post 123a, 123b extending upwardly therefrom that is received within an aperture 153, 155 defined through wheels 152, 154, respectively, to rotatably couple wheels 152, 154 to jaws 120a, 120b, respectively. However, although pivot posts 123a, 123b are shown extending upwardly from respective jaws 120a, 120b, it is envisioned that pivot posts 123a, 123b may be positioned to extend downwardly from jaws 120a, 120b, may extend through a cavity defined within jaws 120a, 120b, or may otherwise be positioned to rotatably support wheels 152, 154 thereon.

[0037] Continuing with reference to FIGS. 4A-4B and 5A-5B, apertures 153, 155, defined through wheels 152, 154, respectively, are eccentrically positioned relative to wheels 152, 154. That is, apertures 153, 155 are not defined through the center “X” of wheels 152, 154 but, rather, are offset from the center “X” of wheels 152, 152, respectively, a distance “d₁.” Such a feature, as will be described below, increases the ratio of jaw closure force (e.g., the force acting normal to jaws 120a, 120b to urge jaws 120a, 120b from the first, spaced-apart position (FIGS. 4A and 5A) to the second, approximated position (FIGS. 4B and 5B)) to drive force (e.g., the force acting on drive bar 140 to translate drive bar 140 proximally).

[0038] As mentioned above, cable 156 is looped about both of the wheels 152, 154. More specifically, cable 156 is looped about wheels 152, 154 and is fixedly engaged to the outer periphery of each wheel 152, 154 at engagement points “E₁,” “E₂,” respectively. Cable 156 may be engaged to wheels 152, 154 in any suitable fashion, e.g., pinching, welding, pin-aperture engagement, etc. Further, cable 156 may be formed from a rigid, semi-rigid, or flexible material. Cable 156 may also be disposed about wheels 152, 154 in a tensioned state such that cable 156 biases jaws 120a, 120b towards the spaced-apart position.

[0039] As best shown in FIGS. 4A and 4B, cable 156 includes a distal segment 157 and a proximal segment 158, while the remainder of cable 156 is circumferentially disposed about a portion of either of wheels 152, 124. Distal segment 157 of cable 156 extends between wheels 152, 154 and, more particularly, between engagement points “E₁,” “E₂” of wheels 152, 154, respectively, towards the distal end of jaw closure mechanism 150. As can be appreciated, since cable 156 is fixed at engagement points “E₁” and “E₂,” the distance between engagement points “E₁” and “E₂” along cable 156 is a fixed distance “d₂.” Proximal segment 158 of cable 156, on the other hand, extends between wheels 152, 154 towards the proximal end of jaw closure mechanism 150.

[0040] Drive bar 140 is engaged to proximal segment 158 of cable 156 in any suitable fashion, e.g., pinching, welding, pin-aperture engagement, etc., and extends proximally therefrom, ultimately coupling to a drive mechanism (not shown) disposed within handle assembly 102 (FIG. 1) that, upon actuation of trigger assembly 108 (FIG. 1), cooperate to translate drive bar 140 proximally relative to jaw assembly 120 to move jaws 120a, 120b between the first, spaced-apart position (FIGS. 4A and 5A) and the second, approximated position (FIGS. 4B and 5B). More particularly, as will be described in greater detail below, proximal translation of drive bar 140 pulls proximal segment 158 of cable 156 proximally such that wheels 152, 154 are rotated about pivot posts 123a, 123b, respectively, and, ultimately such that jaws 120a, 120b are brought into approximation with one another.

[0041] Referring again to FIGS. 4A-4B and 5A-5B, the use and operation of jaw closure mechanism 150, including a more detailed description of the working components thereof, is described. Initially, as shown in FIGS. 4A and 5A, jaws 120a, 120b are disposed in the first, spaced-apart position. With jaws 120a, 120b in the first, spaced-apart position, drive bar 140 is in a more distal position and, accordingly, cable 156 is disposed in an at-rest position defining a generally oval-shaped configuration wherein distal and proximal segments 157, 158, respectively, of cable 156 are substantially parallel to one another in generally transverse orientation relative to jaws 120a, 120b. Further, in the initial position, engagement points “E₁” and “E₂” are distally spaced from and axially aligned with the center “X” of respective wheels 152, 154. Apertures 153, 155, through which posts 123a, 123b of jaws 120a, 120b, respectively, extend, are proximally spaced from and axially aligned with the center “X” of respective wheels 152, 154 as well as with the respective attachment point “E₁,” “E₂” thereof.

[0042] Continuing with reference to FIGS. 4A and 5A, in this initial position, jaws 120a, 120b are spaced-apart a maximum distance “G,” which is dependent at least on the length of cable 156, the distance “d₂” between engagement points “E₁” and “E₂,” and the diameters of wheels 152, 154. Accordingly, cable 156 and wheels 152, 154 may be configured and/or dimensioned to define a specific maximum distance “G” therebetween, which may ultimately depend on the type, size, and/or shape of the surgical clip “C” to be applied to tissue, or on other factors. To this end, jaw closure mechanism 150 may be releasably engagable with jaw assembly 120, e.g., wheels 152, 154 may be coupled to posts 123a, 123b, respectively, such that an appropriately configured jaw closure mechanism 150 may be selected and engaged to jaw assembly 120 depending on the particular type, size, and/or shape of the surgical clip “C” to be applied, or on other factors.

[0043] Referring again to FIGS. 4A-4B and 5A-5B, upon actuation, e.g., upon actuation of trigger assembly 108 (FIG. 1), or prior thereto, e.g., upon release of trigger assembly 108 (FIG. 1) after a previous actuation, a surgical clip “C” is loaded into, or advanced between, jaws 120a, 120b. Next, with the surgical clip “C” disposed between jaws 120a, 120b, jaws 120a, 120b may be approximated relative to one another to form the surgical clip “C” about tissue (not shown). In order to approximate jaws 120a, 120b, the drive assembly (not shown) is activated, e.g., via actuation of trigger assembly 108 (FIG. 1), to translate, or pull, drive bar 140 proximally relative to jaw assembly 120. As drive bar 140 is pulled proximally, cable 156 and, in particular, proximal segment 158 of cable 156, is likewise pulled proximally due to the engagement between drive bar 140 and proximal segment 158 of cable 156.

[0044] As drive bar 140 is pulled proximally to similarly pull proximal segment 158 of cable 156 proximally, wheels 152, 154 are rotated about posts 123a, 123b of jaws 120a, 120b, respectively, in the direction of arrows “R” due to the engagement of cable 156 to wheels 152, 154 at respective engagement points “E₁” and “E₂.” Rotation of wheels 152, 154 in the direction of arrows “R” not only rotates wheels 152, 154 relative to jaws 120a, 120b, but also displaces wheels 152, 154 relative to jaws 120a, 120b. More specifically, due to the eccentric positioning of apertures 153, 155 (i.e., the pivot points of wheels 152, 154) relative to the centers “X” of respective wheels 152, 154, rotation of wheels 152, 154 about posts 123a, 123b displaces wheels 152, 154 such that the centers “X” of wheels 152, 154, are moved in a generally outward and proximal direction relative to jaws 120a, 120b. As a result of this eccentric rotation of wheels 152, 154 and corresponding displacement of wheels 152, 154, jaws 120a, 120b are urged toward one another, i.e., toward the approximated position, to maintain the fixed distance “d₂” along cable 156 between engagement points “E₁” and “E₂.”

[0045] With reference to FIGS. 4B and 5B, as drive bar 140 is pulled further proximally, wheels 152, 154 are rotated further in the direction of arrows “R” and are displaced further proximally and outwardly, such that jaws 120a, 120b are ultimately moved to the approximated position to form the surgical clip “C” disposed therebetween about tissue. In the approximated position, jaws 120a, 120b define a minimum gap distance “g” therebetween. The minimum gap distance “g” is dependent at least on the length of cable 156, the distance “d₂” between engagement points “E₁” and “E₂,” the diameters of wheels 152, 154, and the distance “d₁” between the centers “X” of wheels 152, 154 and the pivot points, i.e., apertures 153, 155, respectively, thereof. Accordingly, a suitably configured jaw closure mechanism 150 may be selected to achieve a desired minimum gap distance “g” between jaws 120a, 120b in the approximated position. Further, in the approximated position, engagement points “E₁” and “E₂” may be longitudinally aligned with and transversely spaced from the center “X” of respective wheels 152, 154. Apertures 153, 155, through which posts 123a, 123b of jaws 120a, 120b, respectively, extend, may be longitudinally aligned with and transversely spaced from the center “X” of respective wheels 152, 154 and with engagement points “E₁” and “E₂.”

[0046] Referring again to FIGS. 4A-4B and 5A-5B, once the surgical clip “C” has been formed about tissue, jaws 120a, 120b may be returned to the spaced-apart position, e.g., via release of trigger assembly 109 (FIG. 1). More specifically, in order to return jaws 120a, 120b back to the spaced-apart position, drive bar 140 is translated distally such that cable 156 is likewise translated distally (or is returned under bias) to permit wheels 152, 154 to rotate (in a direction opposite of arrows “R”) and move back to the initial position shown in FIGS. 4A and 5A. As wheels 152, 154 are rotated and moved back to the initial position, jaws 120a, 120b are permitted to return under bias back to the spaced-apart position shown in FIGS. 4A and 5A. Thereafter, jaw assembly 120 may be removed from the surgical site or repositioned adjacent additional tissue structure(s) for applying one or more surgical clips “C” thereto.

[0047] Turning now to FIGS. 5A-5B and 6, in conjunction with FIGS. 4A-4B, the improved mechanical advantage of the presently disclosed jaw closure mechanism 150, as compared to a prior art jaw assembly 320, is described. With respect to the presently disclosed jaw closure mechanism 150, as shown schematically in FIGS. 5A-5B, proximal translation of drive bar 140 exerts a proximal drive force “F_D” on cable 156 which, in turn, exerts a generally inward and proximal, i.e., an oblique force “F_G,” on the portions of proximal segment 158 of cable 156 that extend between each of wheels 152, 154 and drive bar 140. As a result of the oblique forces “F_G” exerted on cable 156, wheels 152, 154 are rotated and displaced, thereby exerting a jaw closure force “F_G” on jaws 120a, 120b (i.e., a force normal to the opposed surfaces of jaws 120a, 120b) to urge jaws 120a, 120b towards the approximated position.

[0048] As can be appreciated, force vectors “F_D” and “F_C” are normal to one another, i.e., force vector “F_D” is applied in a longitudinal direction and force vector “F_C” is applied in a transverse direction, while force vectors “F_C” and “F_G” define an angle “α₁” therebetween. Thus, the relationship between the drive force “F_D” and the jaw closure force “F_C” for jaw closure mechanism 150 can be represented as:

[0049] $\begin{array}{cc}{F}_C=F_D*\frac{\left(1+\cos {\alpha }_1\right)}{2\sin {\alpha }_1}& \mathrm{EQ}1:\end{array}$

[0050] Equation 1 (EQ 1), above, can be simplified by rewriting the relationship between the drive force “F_D” and the jaw closure force “F_C” in terms of a force transformation multiplier “T₁” as either:
F_C=F_D*T₁  EQ2:
or, in the alternative, as:

[0051] $\begin{array}{cc}{F}_D=\frac{F_C}{T_1}& \mathrm{EQ}3:\end{array}$
where “T₁,” the force transformation multiplier, is:

[0052] $\begin{array}{cc}{T}_1=\frac{\left(1+\cos {\alpha }_1\right)}{2\sin {\alpha }_1}& \mathrm{EQ}4:\end{array}$

[0053] Thus, the force transformation multiplier “T₁” is dependent on the angle “α₁” between force vectors “F_C” and “F_G.” As can be appreciated, it is desirable to maximize the force transformation multiplier “T₁” such that a greater jaw closure force “F_C” can be achieved relative to the drive force “F_D” applied, or, put another way, such that a relatively reduced drive force “F_D” can be applied to achieve the desired jaw closure force “F_C.”

[0054] The following table, Table 1, indicates an approximation of the force transformation multiplier “T₁” for jaw closure mechanism 150 at various different angles “α₁”:

[0055]

	TABLE 1
	“α1” (degrees)	5	10	15	20
	“T1”	11.45	5.71	3.79	2.83

[0056] Further, according to Equation 4 (EQ 4), above, and the exemplary Table 1, above, minimizing the angle “α₁” maximizes the force transformation multiplier “T₁.” The presently disclosed jaw closure mechanism 150 takes advantage of this relationship in that jaw closure mechanism 150 minimizes the angle “α₁” between force vectors “F_C” and “F_G.” More specifically, due to the eccentric feature of wheels 152, 154, wheels 152, 154 are rotated and displaced relative to jaws 120a, 120b upon application of drive force “F_D” to cable 156 such that the angle “α₁” is minimized as wheels 152, 154 are rotated. Thus, the eccentric features of wheels 152, 154 maximize the force transformation multiplier “T₁” and, accordingly, allow for greater jaw closure force “F_C” for a given drive force “F_D” (see Equation 2 (EQ 2), above) or, in the alternative, allow for the application of a reduced drive force “F_D” to achieve a desired jaw closure force “F_C” (see Equation 3 (EQ 3), above).

[0057] Turning now to FIG. 6, a prior art jaw assembly 320 is shown generally including first and second jaws 320a, 320b and a cam sleeve 340 that is translatable about and relative to jaws 320a, 320b to move jaws 320a, 320b between a spaced-apart position (as shown) and an approximated position (shown in phantom). In this configuration, the drive force “F_D′” is applied in a longitudinal and distal direction and the jaw closure force “F_C′” is applied in a transverse direction. Further, a drive force of ½ “F_D′” is applied to each of the jaws 320a, 320b and the angle “α₂” is the angle between the force vector “F_C′” and the plane normal to the outer surface of each of jaws 320a, 320b at the respective point of contact between cam sleeve 340 and jaws 320a, 320b. As such, the drive force “F_D′” and the jaw closure force “F_C′” for jaw assembly 320 an be represented as:
F_C′=F_D′*T₂  EQ5:
or, in the alternative, as:

[0058] $\begin{array}{cc}{F}_{D^{\prime }}=\frac{F_{C^{\prime }}}{T_2}& \mathrm{EQ}6:\end{array}$
where “T₂” the force transformation multiplier, is:

[0059] $\begin{array}{cc}{T}_2=\frac{1}{2\tan {\alpha }_2}& \mathrm{EQ}7:\end{array}$

[0060] Comparing Equations 2 and 3 (EQ 2, EQ 3), above, with Equations 5 and 6 (EQ 5, EQ6), above, it is shown that jaw closure mechanism 150 (FIGS. 4A-5B) provides approximately double the jaw closure force for a given drive force or, in the alternative, requires only half the drive force to achieve a given jaw closure force, as compared to prior art jaw assembly 320 (FIG. 6).

[0061] The following table, Table 2, indicates an approximation of the force transformation multiplier “T₂” for jaw assembly 320 at various different angles “α₂”:

[0062]

	TABLE 2
	“α2” (degrees)	5	10	15	20
	“T2”	5.71	2.83	1.86	1.37

[0063] Again, as shown via comparison of Tables 1 and 2, above, the ratio of transformation multipliers “T₁” and “T₂” is approximately 2 over the range of angles.

[0064] It should be understood that the foregoing description is only illustrative of the present disclosure. Various alternatives and modifications can be devised by those skilled in the art without departing from the disclosure. Accordingly, the present disclosure is intended to embrace all such alternatives, modifications and variances. The embodiments described with reference to the attached drawing figures are presented only to demonstrate certain examples of the disclosure. Other elements, steps, methods and techniques that are insubstantially different from those described above and/or in the appended claims are also intended to be within the scope of the disclosure.