Abstract:
Systems and method are described for counterbalancing the force required to deform a flexure joint. The system includes an elastically deformable flexure joint, a control joint, and an energy balance system. The control joint is mechanically linked to the flexure joint such that movement of the control joint causes a corresponding deformation of the flexure joint. The energy balance system provides a spring force to aid movement of the control joint and to overcome an elastic force required to deform the flexure joint.

Description:
RELATED APPLICATIONS 
       [0001]    This application claims the benefit of U.S. Provisional Patent Application No. 61/877,391, filed Sep. 13, 2013, the entire contents of which are incorporated herein by reference. 
     
    
     BACKGROUND 
       [0002]    The present invention relates to flexure mechanism such as, for example, a flexure joint of a surgical tool. Because a flexure joint bends by elastic deformation of a structure, force is required to maintain the position of a flexure joint and to prevent it from returning to its original, non-deformed shape. 
       SUMMARY 
       [0003]    Joints that involve elastic deformation of a structure in order to operation (e.g., “flexure joints”) can be used in various applications including, for example, robotic and manually actuated surgical arms, manipulators, flexible scopes, and catheters. The elastic deformation of the structure causes that joints/structure to act like a compressed spring. This spring energy is typically felt by either the user or servo motor as a constant force pushing back against the controls and trying to return the joint/structure to its unbent state. Because of the constant force needed to actuate and hold the continuum joint in a deformed position, flexure joints alone are not practical for use with manual tool. 
         [0004]    In one embodiment, the invention provides a mechanical energy balance of a flexure joint. This balance mechanism balances the joint&#39;s potential energy such that the user/servo motor no longer needs to resist a constant restoring force. In some embodiments, the flexure joint includes a continuum joint integrated into a dexterous laparoscopic manipulator such as, for example, an elbow joint in a surgical tool. In some embodiments, the energy balance mechanism includes a joint, a control handle, and a spring mechanism. The joint is a flexure joint that elastically stores energy when deformed. The control handle moves above the joint and controls the movement of the joint. The force required to move the control handle is mechanically linked to the joint. The spring mechanism is attached to the control handle and provides energy balance. 
         [0005]    In another embodiment, the invention provides a tool including an elastically deformable flexure joint, a control joint, and an energy balance system. The control joint is mechanically linked to the flexure joint such that movement of the control joint causes a corresponding deformation of the flexure joint. The energy balance system provides a spring force to aid movement of the control joint and to overcome an elastic force required to deform the flexure joint. 
         [0006]    In yet another embodiment, the invention provides a surgical tool that includes a hollow shaft and an end effector coupled to the distal end of the hollow shaft by an elastically deformable flexure joint. A joint control arm is coupled to the proximal end of the hollow shaft by a control joint. The control joint is mechanically coupled to the flexure joint such that movement of the control joint causes a corresponding deformation of the flexure joint. An energy balance system provides a spring force that aids movement of the control joint and overcomes an elastic force required to deform the flexure joint. 
         [0007]    Other aspects of the invention will become apparent by consideration of the detailed description and accompanying drawings. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0008]      FIG. 1  is a perspective view of a manually actuated surgical tool including a flexure joint. 
           [0009]      FIG. 2  is a cross-sectional view of the flexure joint of the surgical tool of  FIG. 1 . 
           [0010]      FIG. 3  is a detailed view of the flexure joint of the surgical tool of  FIG. 1  in a deformed state. 
           [0011]      FIG. 4  is a perspective view of a manually actuated surgical tool including an energy balance mechanism. 
           [0012]      FIG. 5  is a graph of forces required to deform the flexure joint of the surgical tool of  FIG. 1  and the flexure joint of the surgical tool of  FIG. 4 . 
           [0013]      FIG. 6  is a perspective view of a surgical tool including an energy balance mechanism that includes a single spring. 
           [0014]      FIG. 7  is a perspective view of a surgical tool including an energy balance mechanism with the spring(s) removed to show the details of the gimbal structures. 
           [0015]      FIG. 8  is a detailed view of the control joint of the surgical tool of  FIG. 7 . 
           [0016]      FIG. 9  is a perspective view of a surgical tool including a cam/pulley energy balance mechanism. 
           [0017]      FIG. 10  is a perspective view of a surgical tool including a sliding link energy balance mechanism. 
       
    
    
     DETAILED DESCRIPTION 
       [0018]    Before any embodiments of the invention are explained in detail, it is to be understood that the invention is not limited in its application to the details of construction and the arrangement of components set forth in the following description or illustrated in the following drawings. The invention is capable of other embodiments and of being practiced or of being carried out in various ways. 
         [0019]      FIG. 1  illustrates a manually operated laparoscopic manipulator. The surgical tool  100  includes a hollow shaft  101  with a gripper tool  103  positioned at the distal end. An end effector control handle  105  is used to control the orientation and operation of the gripper tool  103 . The control handle  105  can be tilted in two degrees of freedom to control the angle of the gripper  103  (i.e., a “wrist joint”) and the handles of the control handle  105  can be squeezed together to open and close the gripper  103 . 
         [0020]    In addition to a mechanical wrist joint incorporated into the gripper structure  103  itself, the tool  100  includes a flexure joint  107  positioned between the gripper  103  and the hollow shaft  101 . The flexure joint  107  as described in further detail below includes a deformable portion of a continuum shaft. The bend and shape of the flexure joint  107  is controlled by moving the flex joint control handle  109 . In particular, the joint control handle  109  is bent relative to the shaft  101  at control joint  111 . Due to the structure of the continuum shaft, the flexure joint  107  bends in response to a bend at the control joint  111  such that the base of the gripper  103  remains substantially parallel with the flex joint control handle  109 . The control joint  111  allows the flex joint control handle  109  to move with two degrees of freedom. Therefore, the flexure joint  107  is also capable of moving with two degrees of freedom. 
         [0021]      FIG. 2  further illustrates the details of the continuum shaft that makes up the flexure joint  107  from  FIG. 1 . The continuum shaft includes a plurality of discs  201  arranged along the length of the continuum shaft. The continuum shaft runs from the control handle  109  through the hollow shaft  101  and extends to the base of the gripper  103 . Each disc is fixedly joined to the other discs by a backbone that connects to the center of each disc  201  at  203 . A plurality of flexible tubes also extend through each disc at points  205 . However, these secondary tubes are only affixed to the end discs of the continuum shaft. Therefore, they can be pushed and pulled through holes  205  to control the shape of the continuum shaft. Each disc also includes one or more access ports (not pictured) that allow control devices to extend from the end effector control handle  105  to the gripper  103  and to control the operation of the gripper  103 . 
         [0022]    When the control joint  111  is bent in a first direction, it pushes the secondary tubes on the right side of the continuum shaft and pulls the secondary tubes on the left side fo the continuum shaft. Because the hollow shaft  101  (of  FIG. 1 ) holds the continuum shaft straight, the movement of the control joint  111  and the corresponding pushing and pulling of the secondary tubes causes the flexure joint to bend to the left as shown in Fig 
         [0023]    In this example, each secondary tube is a hollow structure formed of a nitonol material. Each secondary tube has a 1.8 mm outer diameter and a 1.4 mm inner diameter. Movement of the control joint  111  causes a circular bend arc at the flexure joint  107  and the secondary tubes exhibit negligible stretching. The disc  201  has a diameter of 6 mm and the length of the flexure joint is 15 mm along the centerline. The difference between bends along the blue axis (in  FIG. 2 ) and the red axis is less than 0.01% and the flexure joint experiences almost linear stiffness in bending (˜1% increase from 0 degrees to 45 degrees). The effective torsional spring rate is 0/632 Nm/rad. 
         [0024]      FIG. 4  illustrates an example of a manually actuated surgical tool  400  that is similar to the tool  100  illustrated in  FIG. 1 . The surgical tool  400  includes a flex joint control handle  401 , a hollow shaft  403 , and a flexure joint  405  positioned at the distal end of the hollow shaft  403 . The flex joint control handle  401  of the surgical tool  400  is only able to move about a single axis and, therefore, one moves with one degree of freedom. Therefore, the flexure joint  405  is also limited to movement with one degree of freedom. The surgical tool  400  also includes a spring  407  coupled to the flex joint control arm  401  and the hollow shaft  403 . As discussed above, deformation of the flexure joint  405  and holding the flexure joint  405  in a deformed position requires constant force on the flex joint control arm  401 . However, the spring  407  counteracts the elasticity of the joint and reduces (or eliminates) the force required to move the joint and hold the joint in a deformed position. 
         [0025]      FIG. 5  illustrates the force required to move the flexure joint as a function of the total displacement of the flexure joint. The graph illustrates the difference between the force required to move the uncompensated flexure joint of  FIG. 1  compared to the compensated flexure joint of  FIG. 4 . As shown in  FIG. 5 , the required force increases linearly in the uncompensated system. However, the force required to move the joint in the compensated system remains at (or, in some cases, below) zero. 
         [0026]      FIG. 6  illustrates another example of a surgical tool  600  with a compensated flexure joint that provides for movement with two degrees of freedom. The surgical tool  600  includes a hollow shaft  601  with a gripper  603  at the distal end and an end effector control handle  605  at the opposite end. A flexure joint  607  is provided between the gripper  603  and the hollow shaft  601 . A flex joint control arm  609  is coupled to the hollow shaft  601  by a control joint  611 . The energy balance compensation is provided by a spring  613  mounted over the control joint  611  such that the control joint  611  operates inside the spring  613 . The ends of the spring  613  are attached to gimbals  615 ,  617  mounted on either end of the control joint  611 . The gimbals  615 ,  617  are linearly fixed to the end of the hollow shaft  601  and the flex joint control arm  609 . However, the gimbals  615 ,  617  are configured to pivot such that the pull of the spring  613  keeps the gimbals  615 ,  617  substantially parallel with each other to prevent bending of the spring as the control joint  611  is actuated. 
         [0027]    The spring  613  applies its force along the centerline of the hollow shaft  601  and the flex joint control arm  609 . As with the one degree of freedom example of  FIG. 4 , the spring  613  provides force compensation as the control joint  611  is bent to overcome the elasticity of the flexure joint  607 . 
         [0028]      FIG. 7  illustrates another example of a compensated surgical tool  700  with the springs removed to further illustrate the detail of the gimbals and the control joint. The surgical tool  700  includes a hollow shaft  701  with a gripper  702  at the distal end and an end effector control handle  705  at the proximal end. A flexure joint  707  is provided between the hollow shaft  701  and the gripper  703  while a flex joint control arm  709  is coupled to the hollow shaft  701  by a control joint  711 . A pair of gimbals  715 ,  717  are provided on either side of the control joint  711 . 
         [0029]    Although the example of  FIG. 6  (discussed above) utilizes a single spring wrapped around the control joint  611 , it is possible to implement an energy balance mechanism with different spring arrangement. For example, the surgical tool  700  is designed to utilize three springs  813  that couple the first gimbal  715  to the second gimbal  717  on either end of the control joint  711 . Although the springs  813  are omitted from the drawing of  FIG. 7 ,  FIG. 8  provides a more detailed view of the control joint and gimbal arrangement including the three springs  813 . 
         [0030]    As shown in  FIG. 8 , the first gimbal  715  and the second gimbal  717  are each formed of a three piece structure. An inner ring  821  is fixedly attached to the flex joint control arm  709 . A middle ring  823  is coupled to the inner ring  821  at two points to allow the middle ring  823  to pivot relative to the inner ring  821  on a first pivot axis. Similarly, an outer ring  825  is coupled to the middle ring  823  at two points to allow the outer ring  825  to pivot relative to the middle ring  823  on a second pivot axis. The points of connection between the middle ring  823  and the outer ring  825  are positioned such that the second pivot axis is perpendicular to the first pivot axis (i.e., the pivot axis between the middle ring  823  and the inner ring  821 ). The outer ring  825  also includes a series of three spring anchor points  827  positioned at regular intervals around the circumference of the ring. 
         [0031]    Although not specifically labeled in  FIG. 8 , the first gimbal  715  in this example includes the same three-piece ring structure and a series of three corresponding spring anchor points as the second gimbal  717 . Each spring  813  couples one anchor point  827  of the second gimbal  717  to a corresponding anchor point of the first gimbal  715 . As a result, the springs provide a force that keeps the outer ring of the first gimbal  715  substantially parallel to the outer ring  825  of the second gimbal  717  regardless of the bend angle of the control joint  711 . The three balance springs  813  in this arrangement kinematically act as a single spring to provide force compensation to counter act the elastic force of the deformed flexure joint  707 . As described above, this force provides a counterbalance to the force required to deform the control joint (more specifically, to counterbalance the force required to deform the secondary tubes of the continuum shaft). 
         [0032]    As discussed in detail above, the secondary tubes of the continuum shaft are relatively resistant to bending. However, when bending does occur, excessive force can cause the secondary tubes to break. Therefore, the control joint mechanisms of the surgical tool  700  provides a third gimbal structure that maintains a degree of separation between the first gimbal  715  and the second gimbal  717  and prevents the spring force (from springs  813 ) from causing the secondary tubes of the continuum shaft to break. The third gimbal in this example of  FIG. 8  is positioned at the center of the control joint  711 . A first pair of spacers  831  is fixedly connected to the stationary inner ring  821  of the second gimbal  717 . The other end of each spacer is pivotally coupled to a central joint gimbal ring  833 . This arrangement allows the central joint gimbal ring to pivot relative to the flex joint control arm  709 . Similarly, a second pair of spacers  835  is fixedly coupled to the inner ring of the first gimbal  715  and pivotally coupled to central joint gimbal ring  833 . The second pair of spacers  835  is positioned such that the pivot axis between the hollow shaft  701  and the central joint gimbal ring  833  is substantially perpendicular to the pivot axis between the flex joint control arm  709  and the central joint gimbal ring  833 . 
         [0033]      FIG. 9  illustrates yet another example of a surgical tool  900  with a counterbalance joint to compensate for the force required to deform the continuum shaft at the control joint. The surgical tool  900  includes a hollow shaft  901  and gripper end effector  903  with a flexure joint  907  between them. Like the other examples described above, a flexure joint control arm  909  is moveable relative to the hollow shaft  901  at a control joint and, thereby, causes a corresponding movement of the flexure joint  907 . However, the flexure joint control arm  909  is only pivotable upon a single axis (i.e., left-to-right and right-to-left in  FIG. 9 ). 
         [0034]    A cam wheel  911  is positioned at the control joint. It is fixedly coupled to the control arm  909  and, therefore, pivots with the control arm  909  relative to the hollow shaft  901 . A cable  913  wraps around the outer surface of the cam  911  with each end coupled to a spring  915 ,  917 . The opposite end of each spring  915 ,  917  is coupled to an anchor point  919  which is fixedly coupled to the hollow shaft  901 . The cam wheel  911  is shaped and positioned such that one surface  921  has a larger radius than the others. This enlarged radius surface  921  is positioned such that it is facing away from the end effector  903  when the control arm  909  is at a centered position. As a result, the spring force provided by the springs  915 ,  917  is the greatest when the control arm  909  is centered and the cam profile works to move the handle away from centered. As the control arm  909  is pivoted, the cam wheel  911  rotates and the effective pulley diameters are changed. Thus, the two springs  915 ,  917  are balanced when the control arm  909  is centered. When the control arm  909  is deflected, one cam increases in diameter and thus pulls harder on the lever as compared to the other cam. The cam wheel  911  is sized and the springs  915 ,  917  are selected such that the increase in cam diameter overcomes the decrease in spring force as the spring stretch is decreased. 
         [0035]      FIG. 10  illustrates still another example of a surgical tool  1000  with a counterbalance joint to compensate for the force required to deform the continuum shaft at the control joint. The surgical tool  1000  includes a hollow shaft  1001 , a gripper end effector (not shown), and a flexure joint (not shown) between the hollow shaft  1001  and the end effector. A flexure joint control arm  1009  is pivotally coupled to the hollows shaft  1001  at a control joint  1011 . A coupling link  1021  is pivotally connected to the hollow shaft  1001  at one end and coupled to a slider  1023  at the other. The slider  1023  allows the end of the coupling link  1021  to move up and down the length of the control arm  1009  as the control arm  1009  is pivoted relative to the hollow shaft  1001 . A spring  1025  is coupled between the coupling link  1021  and another point on the hollow shaft  1011 . 
         [0036]    In this example, the spring  1025  is coupled to the hollow shaft  1001  at a point that is further from the control joint  1011  than the point of coupling between the coupling link  1021  and the hollow shaft  1001 . Therefore, the length of the spring  1025  decreases as the control joint  1011  is further deflected. As a result, the force provided by the spring  1025  pulls the control arm  1009  away from center and counter balances the force required to deform the secondary tubes of the continuum shaft. 
         [0037]    Thus, the invention provides, among other things, an energy balance mechanism for a flexure joint that counteract the elastic force caused by deformation of the flexure joint. Various features and advantages of the invention are set forth in the following claims.