Abstract:
A thumb wheel mechanism includes a thumb wheel with upper and lower surfaces, the lower surface including a bore with a ball connected to it, and an handle half with upper and lower surfaces, the upper surface including a divot, the thumb wheel lower surface being aligned with the handle half upper surface so that the ball rests in the divot of the handle half upper surface when the thumb wheel mechanism is in the neutral position, thereby minimizing the compression load on the thumb wheel mechanism.

Description:
FIELD OF THE INVENTION 
   This invention relates to a thumb wheel mechanism for a deflectable tip catheter. More particularly, this invention relates to a thumb wheel mechanism with a minimized compression force in a neutral position and a locking frictional force in an engaged position. 
   BACKGROUND OF THE INVENTION 
   A two dimensional/three dimensional steerable catheter can deflect four pull cables, generating curves in four different planes. Currently, this is accomplished by having a distal tip segment that can be deflected into four independent quadrants using separate pull cables attached to a distal tip. The four pull cables are controlled by two independent mechanisms. One of the mechanisms consists of a thumb wheel that, when rotated both in a clockwise and a counterclockwise direction from a neutral position, generates tension to two of the four independent cables. The second mechanism utilizes a slider control, which when slid forward and backward from a neutral position, generates tension to the remaining two independent cables. The construction and operation of the thumb wheel mechanism is further described in U.S. Pat. No. 5,611,777 to Bowden, Russel W., Falwell, Gary S. et al, issued Mar. 18, 1997 and U.S. Pat. No. 5,904,667 to Falwell, issued May 18, 1999, each of these patents is hereby incorporated by reference in its entirety. After the user actuates either of the handle mechanisms, it is desired that the degree of deflection be maintained until actively changed by the user. Therefore, each of the mechanisms must generate a frictional holding force which is larger than the unloading force of a fully actuated curve. 
   However, the frictional holding force has been found to significantly decrease after the materials which make up the mechanism are exposed to 65° C. during the sterilization cycle. The reason for this degradation in holding force is that residual stresses are introduced during the assembly of the handle. These stresses appear to be close to the yield strength of the materials used within the assembly at ambient temperatures. When the materials are exposed to an elevated temperature, they experience a decrease in modulus, causing the materials to yield within the assembly resulting in a decrease in holding force. 
   SUMMARY OF THE INVENTION 
   The thumb wheel mechanism is exposed to elevated temperatures when it is in neutral position during sterilization. By reducing the stress on the mechanism while in neutral position, this invention minimizes the amount of stress to the thumb wheel mechanism while it is exposed to an elevated temperature during sterilization. This is accomplished by applying a minimal compression load to the thumb wheel mechanism in neutral position. 

   
     DESCRIPTION OF THE DRAWINGS 
       FIG. 1   a  is a top view of a handle half of the thumb wheel mechanism according to an embodiment of the present invention; 
       FIG. 1   b  is a sectional side view of a divot in the handle half of  FIG. 1   a  along line  1   b - 1   b  according to an embodiment of the present invention; 
       FIG. 2  is a top view of the thumb wheel mechanism according to an embodiment of the present invention; 
       FIG. 3   a  is an exploded side sectional view of the thumb wheel mechanism of  FIG. 2  along line  3 - 3  according to an embodiment of the present invention; 
       FIG. 3   b  is a side section view of the thumb wheel mechanism of  FIG. 2  along line  3 - 3  with one of the balls nested into the base of the handle half according to an embodiment of the present invention; 
       FIG. 3   c  is a side section view of the thumb wheel mechanism of  FIG. 2  along line  3 - 3  with one of the balls located on the level surface outside one of the divots on the handle half according to an embodiment of the present invention; 
       FIG. 4   a  is a top view of a handle half of the thumb wheel mechanism including multiple divots of varying depths with divots having a maximum depth surrounding the divots corresponding to a neutral position of the thumb wheel according to an alternative embodiment of the present invention; 
       FIG. 4   b  is a sectional side view of a portion of the divots in the handle half of  FIG. 4   a  along line  4   b - 4   b  according to an alternative embodiment of the present invention; 
       FIG. 5   a  is a top view of a handle half of the thumb wheel mechanism including multiple divots of varying depths with divots having a minimum depth surrounding the divots corresponding to a neutral position of the thumb wheel according to an alternative embodiment of the present invention; 
       FIG. 5   b  is a sectional side view of a portion of the divots in the handle half of  FIG. 5   a  along line  5   b - 5   b  according to an alternative embodiment of the present invention; 
       FIG. 6   a  is a top view of a handle half of the thumb wheel mechanism including a divot ramp with a continuum of varying depths according to an alternative embodiment of the present invention; 
       FIG. 6   b  is a sectional side view of a portion of the divots in the handle half of  FIG. 6   a  along line  6   b - 6   b  according to an alternative embodiment of the present invention; 
       FIG. 7   a  is a top view of a handle half of the thumb wheel mechanism including a divot ramp with a continuum of varying depths connected to the divots according to an alternative embodiment of the present invention; and 
       FIG. 7   b  is a sectional side view of a portion of the divots in the handle half of  FIG. 7   a  along line  7   b - 7   b  according to an alternative embodiment of the present invention. 
   

   DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS 
   As shown in  FIGS. 1   a ,  1   b ,  3   a ,  3   b  and  3   c , one embodiment of the invention consists of thumb wheel mechanism  5  as follows: a handle half bolt circle  10  with three equally spaced full radius divots  12 . Three equally spaced counter bores  16  on a thumb wheel  20  (as shown in  FIG. 3   a ) to the handle half  10  are positioned on the thumb wheel  20 . Three stainless steel balls  18  are pressed into each of the three counter bores  16  in the thumb wheel  20 . The balls  18  can also be constructed from plastic, such as a polymer, nylon, Delrin® (manufactured by Hi-Tech Profiles, Inc., Pawcatuck, Conn.) and ABS® (manufactured by Hi-Tech Profiles, Inc., Pawcatuck, Conn.). The balls  18  either are nested into the base of the divots  12  or ride just outside the divots  12  on a level surface  15  of the handle half  10  along an arcuate path indicated as  13  in  FIG. 1   a . A friction disk  22  is inserted under the head of a shoulder screw  24 . The shoulder screw  24  and passes through the thumb wheel  20  acting as an axial and is screwed to the handle half  10 . Varying the depth of the shoulder screw  24  controls the compression rate of the friction disk  22 . When the thumb wheel mechanism  5  is assembled and placed in the neutral position, all three balls  18  are nested into the base of the divots  12 . In this position, the friction disk  22  is under minimal compression. This enables the thumb wheel mechanism  5  to be under minimal stresses in neutral position. Since all sterilization and aging is performed with the thumb wheel mechanism  5  in neutral position, this results in little to no change in holding force post sterilization and aging. As the thumb wheel  20  is rotated, the three balls  18  ride out of the divots  12  on surface  15  and thereby increase the compression forces on the friction disk  22 .  FIG. 1   b  is a sectional side view of a divot in the handle half of  FIG. 1   a  along line  1   b - 1   b  according to an embodiment of the present invention. 
   One advantage of the illustrated embodiment of the present invention is that the thumb wheel mechanism  5  can be rotated to hold a curve in the catheter which it controls without requiring a separate locking device. Also, the illustrated embodiment is able to maintain constant friction after it has been exposed to elevated temperatures and overcomes problems with material creep commonly associated with plastic components in a compression state under elevated temperatures. The balls  18  and divots  12  of the illustrated embodiment also provide tactile detents which indicate to the user that the thumb wheel mechanism  5  is in neutral position. Furthermore, the illustrated embodiment enables the thumb wheel mechanism  5  to maintain its set force after it has been through repeated temperature cycles. This provides an advantage if a catheter is subjected to repeated sterilization cycles required for re-processing or re-use. The illustrated embodiment also enables handle holding forces to be easily set in manufacturing. 
     FIG. 2  is a top view of the thumb wheel mechanism  5  according to an embodiment of the present invention, including a portion of the thumb wheel  20  protruding outside the handle of the catheter.  FIG. 3   a  is an exploded side sectional view of the thumb wheel mechanism  5  of  FIG. 2  along line  3 - 3  according to an embodiment of the present invention. The thumb wheel mechanism  5  is shown, including the thumb wheel  20  with a bore  16  and the handle half  10  with a divot  12 . Also shown is the shoulder screw  24 , the friction disk  22  located as assembled under the head of the shoulder screw  24  and threaded inserts  17  and set screw  19 . The inserts  17  and  19  secure the shoulder screw  24  as an axial through the thumb wheel  20  and attach the screw  24  to the handle half  10 . 
     FIG. 3   b  is a side section view of the thumb wheel mechanism of  FIG. 2  along line  3 - 3  with one of the balls  18  nested into the base of the handle half  10  according to an embodiment of the present invention. Also shown is the relationship between the shoulder screw  24 , the friction disk  22  and the threaded inserts  17  and set screw  19  as assembled. The positioning of the balls  18  nested into the divots  12  when the thumb wheel  20  is in neutral position results in a height h 1  of the friction disk  22 . Also in this embodiment, the thumb wheel  20  contacts the handle half  10 . In alternative embroilments, the thumb wheel  20  need not contact the handle half  10 , such as when the diameter of the balls  18  is greater than the combination of depths of the bores  16  and their corresponding divots  12 . 
     FIG. 3   c  is a side section view of the thumb wheel mechanism  5  of  FIG. 2  along line  3 - 3  with one of the balls  18  located on the level surface  15  outside of the divots  12  on the handle half  10  according to an embodiment of the present invention. The positioning of the balls  18  on the level surface  15  outside the divots  12  when the thumb wheel  20  is engaged results in an upward force on the friction disk  22 . Therefore, the friction disk  22  is compressed to a height h 2 , where h 2  is less than h 1 . An example of the dimensions of the  FIGS. 3   a ,  3   b  and  3   c  embodiment is as follows: the diameter of the balls  18  is 0.125 inches; the depth of the bores  16  is 0.01 inches; the depth of the divots  12  is 0.018 inches; the height h 1  of the friction disk  22  with the thumb wheel  20  in neutral position is 0.100 inches; the height h 2  of the friction disk  22  with the thumb wheel  20  engaged is 0.82 inches. 
     FIG. 4   a  is a top view of an alternative embodiment of the handle half  10  with additional divots  16 ,  18 ,  20 ,  21  and  23 . The additional divots  16 ,  18 ,  20 ,  21 , and  23  are located on the arcuate path  13  followed by the balls  18  between divots  12 . Divots  12  correspond to the placement of balls  18  in the neutral position of the thumb wheel  20 . It has been determined that the force on the thumb wheel  20  as the thumb wheel  20  is engaged to tension a cable into a curve is inversely proportional to the compression load on the friction disk  22  and the relationship is generally linear. Therefore, as the thumb wheel  20  is engaged to relocate the balls  18  out of the divots  12  to the surface  15  defined by the path  13 , there is a retention force at each point necessary to maintain the curvature of the cable. The transition from the depth of the divots  12  to the level surface  15  defined by the path  13  without further depressions (for example, as shown in  FIGS. 1   a  and  1   b ) can exceed the retention force required to maintain the curvature of the cable at points along path  13 . In this embodiment, the additional divots  16 ,  18 ,  20 ,  21  and  23  provide varying depths (for example, a maximum depth for divots  16  to a minimum depth for divots  23 ) which still provide the required retention force but also provide additional tactile indents to enable the user to optimize control of rotation of the thumb wheel  20  in relation to the curvature achieved. More particularly, the maximum depth is less than the depth of divots  12  which provide a neutral position of thumb wheel  20 . For example, the depth of divots  12  is 0.018 inches; the depth of divots  16  is 0.012 inches; the depth of divots  18  is 0.008 inches; the depth of divots  20  is 0.006 inches; the depth of divots  21  is 0.004 inches; and, the depth of divots  23  is 0.002 inches. In an alternative embodiment, the depth of each of divots  16 ,  18 ,  20 ,  21  and  23  can be equal and can provide a retention force for maintaining the curvature of the cable achieved by rotating the thumb wheel  20 . 
     FIG. 4   b  is a sectional side new of  FIG. 4   a  along line  4   b - 4   b  including a cross section of divots  12  and  14 . The variation in the depth of divots  12  and  14  is illustrated with the divots  12  depth being greater than the divots  14  depth. 
   A further alternative embodiment is shown in  FIG. 5   a  as a top view of a handle half  10  with additional divots  26 ,  28 ,  30 ,  32  and  34 . The additional divots serve the same purpose as the  FIG. 4   a  divots, however, in this embodiment, the divots vary from a minimal depth for divots  26  to a maximum depth for divots  34 . For example the depth of divots  12  is 0.018 inches; the depth of divots  26  is 0.002 inches; the depth of divots  28  is 0.005 inches; the depth of divots  30  0.008 inches; the depth of divots  32  is 0.012 inches; and, the depth of divots  34  is 0.016 inches. 
     FIG. 5   b  is a sectional side view of  FIG. 5   a  along line  5   b - 5   b  including a cross section of divots  12  and  26 . The variation in the depth of divots  12  and  26  is illustrated with the divot  12  depth being greater than the divot  26  depth. 
     FIG. 6   a  provides a further alternative embodiment based on a top view of handle half  10  with ramped divots  36 . The ramp divots  36  are located on the arcuate path  13  between each of the divots  12  along which the balls  18  move. There is a level surface  15  in between the divots  12  and the ramp divots  36 . The ramp divots  36  provide a varying depth from a minimum depth closest to divots  12  to a maximum depth at a point equidistant from two divots  12  along the arcuate path  13  (i.e., the location of divots  34  in  FIG. 5   a ) In an alternative embodiment, the ramp can be oriented with a maximum depth closest to the divots  12  and a minimum depth at a point equidistant from two divots  12 . The ramp  36  can also include an undulating shape, tooth patterns or any other shape where the maximum depth is less than the depth of divots  12 . 
     FIG. 6   b  is a sectional side view of  FIG. 6   a  along line  6   b - 6   b  including a cross section of divots  12  and ramp divots  36 . There is a level surface  15  in between divots  12  and  36  and the maximum depth of divot  36  is less than the depth of divot  12 . 
     FIG. 7   a  provides a further alternative embodiment based on a top view of handle half  10  with ramped divots  38 . In this embodiment the ramped divots abut divots  12  at the maximum depth of divots  38  then divots  38  incline to a minimum depth at a point equidistant from divots  12  along the arcuate path  13 . 
     FIG. 7   b  is a sectional side view of  FIG. 7   a  along line  7   b - 7   b  including a cross section of divots  12  and ramp divots  38 , showing the connection of divots  12  and ramp  38 . The maximum depth of divots  36  is less than the depth of divots  12 .