Abstract:
An overforce mechanism comprising a driving assembly, a driven assembly, and a variably engageable coupling, shunts or dampens a motion of a control cylinder for a hydraulic device when that motion exceeds a predefined, unsafe threshold. The overforce mechanism avoids or reduces damage either to the device itself, to ancillary devices and/or to the patient. In an aspect, the variably engageable coupling may include a biasing mechanism and a coupling member, wherein the biasing mechanism automatically resets or releases upon reaching a force or tension threshold. Further, the overforce driven assembly may include an overforce rod that allows the force or motion to be channeled away from the source. The variably engageable coupling may comprise a dowel and spring mechanism that automatically resets with tension.

Description:
[0001]    This application claims priority to U.S. Provisional Patent Appl. No. 61/298,784 filed on Jan. 27, 2010. This application is also related to Applicant&#39;s co-pending PCT Appl. No. PCT/US2011/022086 titled “HYDRAULIC DEVICE INCLUDING A SPOOL VALVE” filed on Jan. 21, 2011 and PCT Appl. No. PCT/US10/46619 titled “ARTICULATED SURGICAL TOOL” filed on Aug. 25, 2010. The entirety of each of the proceeding applications is hereby incorporated by reference herein. 
     
    
     BACKGROUND 
       [0002]    1. Field of the Invention 
         [0003]    Aspects of the present invention relate to mechanical devices and overforce mechanisms used in mechanical devices. 
         [0004]    2. Background of the Related Art 
         [0005]    Laparoscopic surgical tools, as well as tools for other surgical procedures, are known. However, current laparoscopic surgical instruments typically have considerable limitations, including those relating to their capability to access portions of the body obstructed by organs or other impediments, difficulty in sterilizing such instruments, and limitations with structural configurations that are awkward and difficult to use. While such existing laparoscopic surgical instruments can perform invasive surgical procedures, the instruments are awkward to manipulate and perform complicated movements that are often necessary in surgery. In particular, such instruments can be difficult to manipulate around corners, obstacles and to use in obstructed or otherwise difficult to reach environments. 
         [0006]    Moreover, existing laparoscopic surgical instruments typically use cables and hydraulic lines to manipulate the surgical tip of the instruments. Such tools can be expensive and difficult to clean and sterilize. Since the cleaning procedure must be performed after each use, any expense incurred can substantially add to the cost of use of the device. Alternatively, if disposable tools are used, this can add to the cost of the overall system. Further, disposable tools may be made from less robust materials than those meant for multiple uses, leading to increased potential of problems due to equipment malfunction and/or fracture. 
         [0007]    Moreover, laparoscopic surgical instruments using cables and hydraulic lines to remotely manipulate the surgical tip of the instruments can be vulnerable to accidental misuse or user overcompensation, which sometimes may be due to a lack of direct tactile feedback. In particular, problems can arise when a user moves a control for a laparoscopic surgical device in such a way that can cause damage to the device itself, to ancillary devices and/or to the patient. 
         [0008]    Thus, there is a need in the art for a hand-actuated, articulating surgical instrument that provides the user with an increased degree of freedom of motion but that also prevents damage to the device, to ancillary devices and/or to the patient. 
       SUMMARY 
       [0009]    While discussion of the aspects of the present invention that follows uses surgery for an illustrative purpose, it should be appreciated that aspects of the present invention are not limited to surgery and may be used in a variety of other environments. For example, aspects of the present invention may be used in manufacturing, construction, assembly lines, handling and disposing of hazardous materials, underwater manipulations, handling high temperature materials, or any other environment where a user may be remote from the item being manipulated or may experience fatigue when operating a mechanical device. 
         [0010]    In one aspect of the present invention, an overforce mechanism shunts or dampens the motion of a control cylinder for a hydraulic device when that motion exceeds a predefined, unsafe threshold. As such, the described overforce mechanism avoids or reduces damage to the device itself, to ancillary devices and/or to the patient. In an aspect, the overforce mechanism includes a ball and spring mechanism that automatically releases upon reaching a force or tension threshold. Further, the overforce mechanism may further include an overforce rod that allows the force or motion to be channeled away from the source. 
         [0011]    In another aspect of the present invention, an overforce mechanism shunts or dampens the motion of a control cylinder for a hydraulic device when that motion exceeds a predefined, unsafe threshold. The overforce mechanism includes a dowel and spring mechanism as well as an overforce rod that allows the motion to be channeled away from the source. 
         [0012]    In yet another aspect of the present invention, multiple overforce mechanisms are used for multiple components on the same device. The overforce mechanisms may, for example, be used on different mechanical controls or on controls for different aspects of mechanical operations of the device. The multiple overforce mechanisms may be identical, or they may vary substantially, depending on the particular application. 
         [0013]    Aspects of the present invention may incorporate methods, features, and operations as shown and described in U.S. Pat. No. 6,607,475 to Doyle, et al., the entirety of which is incorporated herein by reference. However, it should be noted that aspects of the present invention are not limited in application to devices shown in U.S. Pat. No. 6,607,475 or in related patents and applications. In some aspects, the present invention provides an apparatus for controlling the micro-movements and macro-movements of hydraulically actuated devices, including an articulated surgical tool. In these aspects, the present invention may enhance the control and manipulation of the device. 
         [0014]    Aspects of the present invention provide benefits and advantages that include the ability to prevent unwanted force and resulting damage to actuated systems. Thus, actuated systems can be made more robust and precision instrumentation can be used in environments that would otherwise compromise relatively delicate equipment. 
         [0015]    Additional advantages and novel features relating to aspects of the present invention will be set forth in part in the description that follows, and in part will become more apparent to those skilled in the art upon examination of the following or upon learning by practice of aspects of the invention. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0016]    Aspects of the present invention will become fully understood from the detailed description given herein below and the accompanying drawings, which are given by way of illustration and example only and thus not limited with respect to aspects of the present invention, wherein: 
           [0017]      FIG. 1A  is a diagram of an exemplary system for use in accordance with aspects of the present invention; 
           [0018]      FIG. 1B  is a diagram of a variation of the slave portion of a device that may be used in alternative to the slave portion of the device shown in  FIG. 1A ; 
           [0019]      FIG. 2A  is a detailed drawing of one aspect of an exemplary control unit that may be used in conjunction with aspects of the present invention; 
           [0020]      FIG. 2B  is a detailed drawing of another aspect of an exemplary control unit that may be used in conjunction with aspects of the present invention; 
           [0021]      FIG. 3  is a partial cutaway view of an exemplary overforce mechanism; 
           [0022]      FIG. 4  is a diagram of an exemplary overforce mechanism in engaged mode in accordance with aspects of the present invention; 
           [0023]      FIGS. 5A and 5B  show the exemplary overforce mechanism of  FIG. 4  in a cut-away view, in engaged and disengaged operations respectively, in accordance with aspects of the present invention; 
           [0024]      FIG. 6  is a close-up of a partially transparent view of the relationship between the balls of the exemplary overforce mechanism and the depression in the overforce rod  306 , shown in  FIGS. 5A and 5B , without the overforce slide, in accordance with aspects of the present invention; 
           [0025]      FIG. 7  is a schematic, partially transparent side view of the exemplary overforce mechanism of  FIG. 4  in engaged mode, in accordance with aspects of the present invention; 
           [0026]      FIG. 8  is a schematic of another exemplary overforce mechanism of  FIG. 4  in engaged mode, in accordance with aspects of the present invention. 
       
    
    
     DETAILED DESCRIPTION 
       [0027]    Aspects of the present invention will now be described more fully hereinafter with reference to the accompanying drawings, in which variations and aspects of the present invention are shown. Aspects of the present invention may, however, be realized in many different forms and should not be construed as limited to the variations set forth herein; rather, the variations are provided so that this disclosure will be thorough and complete in the illustrative implementations, and will fully convey the scope thereof to those skilled in the art. 
         [0028]    Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which aspects of the present invention belong. The methods and examples provided herein are illustrative only and not intended to be limiting. 
         [0029]      FIG. 1A  is a diagram of an exemplary system of an overforce mechanism of aspects of the present invention that may be utilized in performing surgery on a patient P. Device  1  is described in more detail in U.S. Pat. No. 6,607,475, the entirety of which is incorporated herein by reference. Device  1  may include any number of suitable hydraulically driven mechanical devices to assist in the performance of surgery, maintenance and/or other mechanical operations. Although  FIG. 1A  shows a surgical device  1 , it is to be understood that variations of aspects of the present invention can be used in conjunction with any suitable device with mechanical actuating features. Some of the hydraulically driven mechanical devices, such as the one shown in  FIG. 1A , may contain control portions with a single control cylinder  5  or control portions with multiple control cylinders  7 . The control portions with single or multiple control cylinders may serve to allow a user, such a surgeon, to actuate mechanical operations in another portion of the device. For example, the control portions with a single or multiple control cylinders may actuate and move various tools  2  for performing of surgery. 
         [0030]    Generally speaking, the control portions (e.g., control portions with a single or multiple control cylinders) are part of the “control portion” of the device  1  and the various tools  2  are part of the “slave portion” of the device  1 .  FIG. 1B  is a diagram of a variation of the slave portion of the device that may be used in alternative to the slave portion of the device shown in  FIG. 1A . As shown in  FIG. 1B , the slave portion  9  of the device includes various tools  2  that may be utilized for performing surgery and/or other mechanical operations. The connections between the control and slave portions may be primarily hydraulic, for example, to allow transmission of mechanical forces between the two portions. However, other connections (e.g., electrical, hydraulic, electromagnetic, cable, optical, etc.) may also be present in order to transmit various types of information, forces or motion between the control and slave portions of the device. 
         [0031]      FIG. 2A  is a detailed drawing of one variation of an exemplary control unit that may be used in conjunction with aspects of the present invention.  FIG. 2A  shows several exemplary features of control portion  10 , including a handle  11  and a thumb loop  12  for interacting with the user. Generally, the user may grasp the handle  11 , place his thumb inside the thumb loop  12  and squeeze. This and/or similar motions generally affect a mechanical response in the control cylinder  100 , also shown in  FIG. 2A , which transmits the mechanical response to another portion of the device referred to as a “slave portion” (not shown). The overforce mechanism would, for example, be a portion attached to or in the vicinity of the control cylinder, as shown in  FIG. 2A . In addition to the control cylinder  100 , certain variations of the device may include “spool valves” that may be, for example, positioned as shown in  FIG. 2A . One purpose of the spool valve, among others, is to control fluid communication between the control cylinder  100  and the slave portion of the device. The control portion  10  in  FIG. 2A  is purely exemplary of one of the types of control portions that may be used in conjunction with aspects of the present invention. Aspects of the present invention may be used in conjunction with a variety of other devices, including different control portions. 
         [0032]      FIG. 2B  is a detailed drawing of another variation of an exemplary control unit that may be used in conjunction with aspects of the present invention.  FIG. 2B  shows several exemplary features of control portion  200 , including a handle  211  and a trigger loop  212  for interacting with the user. The control portion  200  differs from the exemplary control portion  10  shown in  FIG. 2A  mainly in that it allows more degrees of freedom in the motions that may be transmitted from the user to the slave portion of the device. Each degree of freedom corresponds to its own control cylinder  100 , as shown in  FIG. 2B . As shown in  FIGS. 2A and 2B , the overforce mechanism may be part of a control cylinder. Each may be implemented on several portions of the device simultaneously. Generally, the user may grasp the handle  211 , place the user&#39;s fingers inside the trigger loop  212 , squeeze the trigger loop  212  and move the handle  211  in various directions. This and/or similar motions generally affect a mechanical response in the control cylinders  100 , which transmit the mechanical response to the slave portion of the device (not shown). The responses may be mediated by the overforce mechanism, in accordance with aspects of the instant invention.  FIG. 2B  also shows exemplary spool valves  150  connected to control cylinders  100 . As shown in  FIG. 2B , the spool valves  150  are generally connected to each of the control cylinders  100 . In  FIG. 2B , the fluid connections between the exemplary spool valves  150  and the slave portion of the device, inlets  150   a , are explicitly shown. Generally, a hydraulic line may be connected to one end of inlets  150   a , the other end of which may be connected to a corresponding control cylinder (not shown) on the control or slave portion of the device. In this and other exemplary configurations, each degree of freedom generally has one control cylinder in the control portion and one control cylinder in the respectfully associated slave portion. Control portion  200  in  FIG. 2B  is purely exemplary of one of the types of control portions that may be used in conjunction with aspects of the present invention. Aspects of the present invention may be used in conjunction with a variety of other devices, including different control portions. 
         [0033]      FIGS. 3 to 7  illustrate an exemplary overforce mechanism  300  that may be used in accordance with aspects of the present invention. The overforce mechanism includes a driving assembly, a driven assembly, and a variably engageable coupling, which are described in detail below. The driving assembly is the portion of the overforce member operatively coupled with the control portion  5 . Referring to  FIG. 3 , which shows a partial cutaway view of the overforce mechanism includes a cradle  301  for receiving a rod  306  and a cylinder  302 , The overforce mechanism further comprises an overforce slide mechanism  303 , including biasing mechanisms  304  ( FIGS. 4 to 5B ), such as springs, and coupling members  305  ( FIGS. 4 to 6 ), such as ball bearings, among other things, serves to mechanically couple and de-couple the overforce rod  306  to the overforce slide  303 . As shown in  FIG. 3 , the cylinder  302  rests within the cradle  301 . A shaft  306   a  is slideably provided within the cylinder  302 . As seen in  FIG. 3 , one end of the shaft  306   a  extends from the cylinder  302  and mates with the rod  306 , while the other end of the rod  306   a  is coupled with a piston  306   c . Therefore, because of the mating of the rod  306  with the shaft  306   a , movement of the rod  306  produces sliding of the shaft  306   a  and piston  306   c  axially within the cylinder  302 . The cylinder  302  further comprises hydraulic fluid  20  which is displaced as the piston  306   a  moves within the cylinder  302 . 
         [0034]    As will be described in more detail below, the conditions in which the rod  306  and the overforce slide  303  are coupled and de-coupled to one another will be referred to as the “engaged operation” of the apparatus below.  FIGS. 5A and 5B  show the exemplary overforce mechanism  300  of  FIGS. 3 and 4  in a cross-sectional view, in engaged and disengaged operations respectively. 
         [0035]    As also shown in  FIG. 5A , hydraulic fluid  20  may be disposed in the cylinder  302 . The hydraulics of the exemplary overforce mechanism  300  shown in  FIGS. 4 ,  5 A and  5 B may be substantially similar as described in more detail in U.S. Pat. No. 6,607,475. In particular,  FIG. 5A  shows the hydraulic fluid  20  contained in the cylinder  302 . Hydraulic fluid  20  can exit the cylinder  102  through an inlet, which may create hydraulic pressure at a point in the distal end of the device. Additional hydraulic fluid  20 , displaced from a slave cylinder, may enter in to the back of the piston  306   c  through another inlet, thereby keeping the volume of the hydraulic fluid  20  in the system constant. It is within the scope of aspects of the present invention that alternative hydraulic arrangements may be utilized. For example, hydraulic fluid  20  may be located differently with respect to the inner cylinder  302  or contained in ancillary vessels (not shown). There may be additional hydraulic lines and connections not shown in the Figures, and additional components may be added or removed without altering the nature of aspects of the invention. 
         [0036]      FIGS. 4 ,  5 A and  5 B show one exemplary implementation of the overforce mechanism  300 . As shown in  FIGS. 4 ,  5 A and  5 B, the variably engageable coupling may include the overforce slide  303  and various mechanical components to couple the overforce slide to the overforce rod  306 , which is attached to the shaft  306   a  of the cylinder  302 . For example, the overforce mechanism  300  may include, as shown in  FIGS. 4 ,  5 A and  5 B, a set of ball bearings  305  that ride in a track  301   a , or guiding portion, in the cradle  301 , and the biasing mechanism ( 304 ). The driven assembly includes the portion of the overforce mechanism that is driven by the driving assembly, such as the rod  306  and the shaft  306   a.    
         [0037]    The ball bearings  305  may make contact with the other portions of the device via holes  303   a  in the overforce slide  303 . In addition, there may be a channel or depression  306   b  in the overforce rod  306  sized to accommodate at least a portion of the ball bearings  305 .  FIG. 6  is a close-up partially transparent view of the relationship between the ball bearings  305  of the exemplary overforce mechanism  300  and the depression  306   b  in the overforce rod  306 , without the overforce slide  303  being visible.  FIG. 7  is a schematic, partially transparent side view of the exemplary overforce mechanism of  FIGS. 3 and 4  in engaged mode in accordance with aspects of the present invention. As shown in  FIGS. 6 and 7 , the ball bearings  305  may be held in the depression  306   b  via the springs  304 . When the ball bearings  305  are retained in place via the biasing features  304  through the retention features  303   a  in the overforce slide  303 , the coupling members  305 , such as ball bearings, may mechanically couple the overforce slide  303  and the overforce rod  306 . In other words, when the ball bearings  305  are fixed in the depression  306   b  by the springs  304 , the overforce slide  303 , the overforce rod  306 , and the piston  306   c  may move as a single unit. Thus the force applied to the overforce slide  303  is releasably connected to the overforce rod  306 , which is attached to the shaft  306   a , and thereby causes motion of the piston  306   b  in order to pump hydraulic fluid  20  to and from slave cylinders. This is merely one exemplary implementation and that other implementations in accordance with aspects of the present invention are also possible. For example, alternatively, the ball bearings  305  may be fixed in the reverse sense, such that there are openings in the overforce rod  306  and a depression in the overforce slide  303 . In this case, the spring  304  may be fixed onto or inside the overforce rod  306  instead of, or in addition to, on the overforce slide  303 , as shown in  FIGS. 4 ,  5 A and  5 B. If the overforce mechanism is fixed in the reverse sense, its operation may be substantially the reverse of that described in the following paragraphs. 
         [0038]    In engagement operation, as shown in  FIGS. 4 and 5A , when the ball bearings  305  are positioned such that they are inside the depression  306   b  of the overforce rod  306 , as shown in  FIGS. 5A ,  6  and  7 , they may transmit motion of the slide  303  to the overforce rod  306  and the piston  306   c . In other words, the coupling provided by the ball bearings  305  may allow the overforce rod  306 , the piston  306   b  and the overforce slide  303  move as a single unit. When the user imparts a force greater than a threshold set by a spring force of the spring  304 , the force imparted to the ball bearings  305  by the overforce rod  306  may press outwardly on the springs  304  to such an extent that the balls overcome the force of the springs  304 , resulting in the breaking of the coupling provided by the ball bearings  305 . In this situation, referred to as “disengaged operation,” the mechanical coupling of the overforce rod  306  and the slide  303  may be broken. As such, the spring  304  may be selected to have a desired spring force corresponding to a force threshold that disengages the coupling provided by the ball bearings  305 , thereby activating the disengaged operation and halting a transfer of force or motion to the slave portions and/or end effectors or tools of the device. 
         [0039]    Engaged operation is defined as when force imparted by the user to the exemplary overforce mechanism  300  is insufficient to overcome the force of the spring  304 . Generally, in engaged operation, most or all of the mechanical motion performed by the user may be transmitted by the user through the system to the target or operating theater. In this situation, the ball bearings  305  may remain fixed with respect to the overforce slide  303  in the position shown in  FIG. 4 . In other words, the overforce rod  306  and the slide  303  may move as one unit. Alternatively, ordinary conditions may be defined such that the overforce slide  303  and the overforce rod  306  allow some motion relative to one another. 
         [0040]    In engaged operation, upon squeezing the thumb loop, for example, the overforce mechanism  300  may be actuated through a series of levers and gears, as described in more detail in U.S. Pat. No. 6,607,475, from the retracted position to the extended position. In engaged operation, the ball bearings  305  may be centrally located within the depression  306   b  of the overforce rod  306 , as shown in  FIG. 5A , and may remain fixed with respect to the depression  306   b . In this manner, among others, the control portions  5  may use the exemplary overforce mechanism  300  to channel the mechanical force from the user to the application. Generally speaking, devices actuated by the exemplary overforce mechanism  300  are referred to as the “slave” portion of the device. These devices may include mechanical grippers, lever arms, pivoting devices, translating devices, swiveling devices, cutting tools, grasping tools and any other suitable devices. The mechanical force can be used in any number of suitable ways by the slave portion of the devices. For example, control portions  5  can be used to conduct surgical procedures, move objects or to mechanically provide force for any suitable number of applications. As shown in  FIG. 1A , control portions  5  may be coupled to various surgical apparatus (e.g., clamps, shears, needles, etc.) for performing a surgical operation. 
         [0041]    However, when the thumb loop is actuated too quickly or too severely by the user, the overforce mechanism  300  may actuate portions of the slave portion of the device in such a manner as to cause damage either to the device itself or elsewhere (as described above). In this case, the exemplary overforce mechanism  300  may enter disengaged operation such that the overforce slide  303  is decoupled from the overforce rod  306  in the manner described below.  FIG. 5B  shows the exemplary overforce mechanism of  FIG. 5B  in disengaged operation. 
         [0042]    Disengaged operation may be initiated when the impulse (i.e., applied force over a unit time) from the user in the control portion of the device is large enough to dislodge the ball bearings  305  from the depression  306   b  in the overforce rod  306 . As shown in  FIG. 5B , in disengaged operation, the ball bearings  305  may become dislodged from the depression  306   b  when, among other things, there is too much force applied, such that the ball bearings  305  move with respect to the depression  306   b . When the ball bearings  305  move with respect to the depression  306   b , they may be forced outwardly with respect to the overforce rod  306  by the contours of the depression  306   b . The outward motion of the ball bearings  305  may be generally along direction D shown in  FIG. 4  and may cause the ball bearings  305  to press on the spring  304  with a force that may be so large as to overcome a spring force. Once the spring force is overcome, the ball bearings  305  may slide free of the depression  306   b  of the overforce rod  306 . This action may de-couple the overforce slide  303  from the overforce rod  306  and the rest of the exemplary overforce mechanism  300  such that user motion is no longer transmitted. If user motion is not transmitted in disengaged operation, the motion may not be transmitted hydraulically to other portions of the device, including the slave portion of the device. In this situation, the overforce slide  303  may slide freely with respect to the overforce rod  306  in response to the user input. In this way, the motion of the user is not transmitted by the device and the slave portions of the device (not shown) do not react to the user input. 
         [0043]      FIG. 8  shows another exemplary implementation of an overforce mechanism, in accordance with aspects of the present invention. As shown in  FIG. 8 , the overforce slide  403  of the overforce mechanism  400  may be substantially similar to the overforce slide  303  of the exemplary overforce mechanism  300 . However, the mechanical components for coupling the overforce slide  403  to the shaft  401  and the cylinder  402  may be different. For example, the overforce mechanism  400  may include, as shown in  FIG. 8 , a spring  404  that holds a dowel  405  in contact with the overforce rod  406 . 
         [0044]    The dowel  405  may make contact with the other portions of the device via a dowel-accommodation opening  403   a  in the overforce slide  403 . The dowel  405  may be held, via the spring  404 , in contact with the overforce rod  406 , as shown in  FIG. 8 , similarly to the way the ball bearings  305  are sandwiched between spring  304  and overforce rod  306  shown in  FIG. 5A . In addition, there may be a depression  406   b  in the overforce rod  406  that accommodates at least a portion of dowel  405 . The depression  406   b  may be, for example, substantially similar to the depression  306   b  in the overforce rod  306  shown in  FIG. 6 . 
         [0045]    As best shown in  FIG. 8 , the dowel  405  may be pressed or fixed into the depression  406   b  by a spring force supplied via the spring  404 . When the dowel  405  is pressed into place by spring  404  through the dowel-accommodation opening  403   a  in the overforce slide  403 , the dowel  405  may mechanically couple the overforce slide  403  and the overforce rod  406 . In other words, when the dowel  405  is fixed in the depression  406   b  by spring  404 , the overforce slide  403  and the overforce rod  406  may move as a single unit. This is merely one exemplary implementation and that other implementations in accordance with aspects of the present invention are also possible. For example, the dowel  405  may be, alternatively, fixed in the reverse sense such that there are openings in the in the overforce rod  406  and a depression in the overforce slide  403 . In this case, the spring  304  may be fixed onto or inside the overforce rod  406  instead of, or in addition to, on the overforce slide  403 , as shown in  FIG. 8 . If the overforce mechanism is fixed in the reverse sense, its operation may be substantially the reverse of that described in the following paragraphs. 
         [0046]    In engagement operation, as shown in  FIG. 8 , when the dowel  405  is positioned such that it is inside the depression  406   b  of the overforce rod  406 , it may transmit motion of the overforce rod  406  to the shaft  406   a . In other words, because of the coupling provided by the dowel  405 , the overforce rod  406  and the overforce slide  403  may move as a single unit. When the user imparts a force greater than a threshold set by the spring  304 , the force imparted to the dowel  405  by the overforce rod  406  may press outwardly on the spring  404  to such an extent that the dowel  305  may overcome a force of the spring  404 . In this situation, referred to as “disengaged operation,” the mechanical coupling of the overforce rod  406  and the overforce slide  403  may be broken. 
         [0047]    Engaged operation is defined as when a force imparted by the user to the exemplary overforce mechanism  400  is insufficient to overcome the force of the spring  304 . Generally, in engaged operation, most or all of the mechanical motion performed by the user may be transmitted by the user through the system to the target or operating theater. In this situation, the dowel  405  may remain fixed with respect to the overforce slide  403  in the position shown in  FIG. 8 . In other words, the overforce slide  403  and overforce rod  406  (and thus the shaft  406   a ) may move as one unit. 
         [0048]    In engaged operation, upon squeezing the thumb loop, for example, the overforce mechanism  400  may be actuated through a series of levers and gears, as described in more detail in U.S. Pat. No. 6,607,475, from the retracted position to the extended position. In engaged operation, the dowel  405  may be centrally located within the depression  406   b  of the overforce rod  406  and remains fixed with respect to the depression  406   b . In this manner, among others, control portions  5  use the exemplary overforce mechanism  400  to channel the mechanical force from the user to the application. Generally speaking, devices actuated by the exemplary overforce mechanism  400  are referred to as the “slave” portion of the device. These devices may include mechanical grippers, lever arms, pivoting devices, translating devices, swiveling devices, cutting tools, grasping tools and any other suitable devices. The mechanical force may be used in any number of suitable ways by the slave portion of the devices. For example, the control portions  5  may be used to conduct surgical procedures, move objects or to mechanically provide force for any suitable number of applications. As shown in  FIG. 1A , the control portions  5  may be coupled to various surgical apparatus (e.g., clamps, shears, needles, etc.) for performing a surgical operation. 
         [0049]    However, when the thumb loop is actuated too quickly or too severely by the user, a danger may arise in that the overforce mechanism  400  may actuate portions of the slave portion of the device in such a way as to cause damage either to the device itself or elsewhere (as described above). In this case, the overforce mechanism  400  may enter a disengaged operation, such that the overforce slide  403  mechanism decouples the inner and outer cylinders  402  and  401  in the manner described below. Although not shown, disengagement operation for the exemplary overforce mechanism  400  may be substantially similar to disengagement operation of the exemplary overforce mechanism  300  shown in  FIG. 5B . 
         [0050]    Disengaged operation may be initiated when the impulse (i.e., applied force over a unit time) from the user in the control portion of the device is large enough to dislodge the dowel  405  from the depression  406   b  in the overforce rod  406 . In disengaged operation, the dowel  405  may become dislodged from the depression  406   b  when, for example, there too much force applied to the overforce rod  406  such that the dowel  405  moves with respect to the depression  406   b . When the dowel  405  moves with respect to the depression  406   b , it may be forced outwardly with respect to the overforce rod  406  by the contours of the depression  406   b . The outward motion of the dowel  405  may generally be along direction D shown in  FIG. 8  and may cause the dowel  405  to press a the spring or other restoring force member (not shown) with a force is so large as to overcome, for example, a spring force. If the spring force is overcome, the dowel  405  may slide free of the depression  406   b  of the overforce rod  406  and through the dowel-accommodation opening  403   a  of the overforce slide  403 . This motion of the dowel may de-couple the overforce slide  403  from the overforce rod  406  and the rest of the exemplary overforce mechanism  400  such that user motion is no longer transmitted. In this situation, the overforce slide  403  may slide freely in response to the user input, while the cylinder shaft  401  and the overforce rod  406  may remain fixed. In this way, the motion of the user may not be transmitted by the device, and the slave portions of the device (not shown) do not react to the user input. 
         [0051]    Although aspects of the invention have been described with reference to various aspects of the present invention and examples with respect to a surgical instrument, it is within the scope and spirit of the invention to incorporate use with any suitable mechanical device. Further, while the invention has been described with reference to a surgeon, the invention may be used by another user, depending on circumstances in which the invention is used. Additionally, while the invention has been described using hydraulic mechanisms, it is within the scope of the invention that non-hydraulic mechanisms may be implemented, such as cable-pulley or push-pull cable devices. Thus, it should be understood that numerous and various modifications may be made without departing from the spirit of the invention.