Jaw movement mechanism and method for a surgical tool

1. A minimally invasive surgical tool having a stationary jaw and a movable jaw for grasping tissue by transverse movement of the moveable jaw relative to the stationary jaw at a distal end of a shaft assembly connected to a handle assembly, the handle assembly creating relative reciprocating movement transferred through a relatively stationary shaft member and a relatively movable shaft member of the shaft assembly to a jaw movement mechanism, the stationary jaw rigidly connected to the relatively stationary shaft member, each jaw has a straight working surface, the working surfaces of the jaws extend at an angular orientation with respect to one another at a fully open position, the working surfaces of the jaws extend at a parallel orientation with respect to one another at an intermediate position, the working surfaces of the jaws extend at a parallel orientation with respect to one another at a fully closed position, the jaw movement mechanism maintains the working surfaces of the jaws in the parallel orientation with respect to one another during transverse movement of the jaws between the intermediate position and the fully closed position, the jaw movement mechanism comprising:

a pivot link having a proximal end and a distal end, the proximal end of the pivot link pivotally connected to the relatively stationary shaft member by a pivot pin and the distal end of the pivot link pivotally connected to a proximal end of the movable jaw by a rear pin located within a rear slot defining a proximal lateral displacement for each change in longitudinal position of the relatively movable shaft member with respect to the relatively stationary shaft member, the rear slot being formed in the stationary shaft member; and

a front pin located within a front slot defining a distal lateral displacement for each longitudinal position of the relatively movable shaft member with respect to the relatively stationary shaft member,

wherein each of the rear slot and the front slot comprises a primary segment defining the respective lateral displacements moving the movable jaw between the intermediate position and the fully closed position, and

wherein the proximal lateral displacement defined for each longitudinal position in the primary segment of the rear slot is equal to the distal lateral displacement defined for each longitudinal position in the primary segment of the front slot.

2. A minimally invasive surgical tool as defined in claim 1 , wherein:

each of the rear slot and the front slot includes two angularly intersecting portions, a first of the angular intersecting portions being the primary segment and a second of the angular intersecting portions being a secondary segment creating and defining the lateral movement of its respective pin for each longitudinal position therein, the lateral movement of the pins in the secondary segment directly moving the movable jaw between the intermediate position and the fully open position.

3. A minimally invasive surgical tool as defined in claim 2 , wherein:

the primary section of the first slot extends generally parallel to the primary section of the second slot, the primary section of the first and second slots are non-parallel to the direction of relative reciprocating movement of the shaft members.

4. A minimally invasive surgical tool as defined in claim 3 , wherein:

one of the secondary segments of the first and second slots extends at an intersecting angle to the direction of relative reciprocating movement of the shaft members; and

the other one of the secondary segments of the first and second slots extends at an intersecting angle with respect to said one of the secondary segments of the first and second slots extending at an intersecting angle to the direction of relative reciprocating movement.

5. A minimally invasive surgical tool as defined in claim 2 , wherein:

the first and second pins move respectively in the first and second slots to positions which are farther separated from one another with movement of the jaw members from the intermediate position to the fully closed position.

6. A minimally invasive surgical tool as defined in claim 1 , wherein:

the relatively stationary shaft member comprises an interior rod having an open interior space within which the pivot link moves; and

the relatively movable shaft member comprises a sleeve housing having an interior which receives the interior rod and within which the pivot link pivots during movement of the jaws between the fully opened and the fully closed positions.

7. A minimally invasive surgical tool as defined in claim 6 , wherein:

the interior of the sleeve housing has a predetermined cross-sectional interior configuration;

the exterior of the interior rod has a predetermined cross-sectional exterior configuration; and

the predetermined cross-sectional configurations of the interior and exterior configurations of the sleeve housing and the interior rod permit relative longitudinal reciprocating movement of the sleeve housing and the rod and prevent relative rotational movement of the sleeve housing and the rod.

8. A minimally invasive surgical tool as defined in claim 1 , wherein:

the front slot is defined in the movable jaw and the rear pin is retained by the moveable jaw;

the front pin is retained by the relatively movable shaft;

the distance between the first and second pins increases as the jaws are moved from the fully opened position to the fully closed position; and

the distance between the first and second pins decreases as the jaws are moved from the fully closed position to the fully opened position.

9. A surgical tool as defined in claim 8 , wherein:

the first slot and the second pin are stationary relative to each other; and

the second slot and the first pin are stationary relative to each other.

10. A minimally invasive surgical tool defined in claim 1 , for fusing together tissue compressed between the jaws, wherein the jaws include elements for transferring energy to tissue compressed between the jaws.