Abstract:
A incremental rotational displacement mechanism is provided. The mechanism includes a circular detent housing having a plurality of detents arranged along the circumference of the detent housing. A detent ring is positioned coplanar to and within the circumference of the detent housing. At least a portion of the at least one detent arm engages at least a portion of the detent housing. A handle may engage the detent ring, so that a force applied to the handle causes the detent ring to rotate with respect to the circular detent housing. The mechanism is suitable for a variety of applications, including endoscopic instruments.

Description:
BACKGROUND 
     This invention generally relates to endoscopic instruments. More particularly, the present invention provides a ratcheting mechanism to rotationally adjust an endoscopic instrument. 
     Laparoscopic, endoscopic, and other minimally invasive surgical techniques enable surgeons to perform fairly complicated procedures through relatively small entry points in the body. The term “laparoscopic” refers to surgical procedures performed on the interior of the abdomen, while the term “endoscopic” refers more generally to procedures performed in any portion of the body. Endoscopic surgery involves the use of an endoscope, which is an instrument permitting the visual inspection and magnification of a body cavity. The endoscope is inserted into a body cavity through a cannula extending through a hole in the soft tissue protecting the body cavity. The hole is made with a trocar, which includes a cutting instrument slidably and removably disposed within a trocar cannula. After forming the hole, the cutting instrument can be withdrawn from the trocar cannula. A surgeon can then perform diagnostic and/or therapeutic procedures at the surgical site with the aid of specialized medical instruments adapted to fit through the trocar cannula. Additional trocar cannulas may provide openings into the desired body cavity. 
     Some known advantages of minimally invasive surgical techniques include reduced trauma to the patient, reduced likelihood of infection at the surgical site, and lower overall medical costs. Accordingly, minimally invasive surgical techniques are being applied to an increasingly wider array of medical procedures. 
     FIG. 1 depicts a typical example of an endoscopic instrument  100 . The instrument  100  may include a handle  110 , a knob  120 , and a tubular member  130 . The handle  110  may be one of a variety of conventional configurations, such as a grip handle shown in FIG. 1. A portion of the handle  110  fits within a proximal end of the knob  120 , providing an axis about which the knob  120  can be rotated. A distal end of the knob  120  may engage the proximal end of the tubular member  130 , such that any rotation of the knob  120  may cause the tubular member  130  to rotate as well. The distal end of the tubular member  130  may include one of a variety of instruments or so-called end effectors. For example, the distal end may be equipped with jaws, cutting blades, or some other instrument, depending on the desired use of the endoscopic instrument. 
     It is often useful for a practitioner of endoscopic surgery to rotationally manipulate the distal end of the tubular member  130  while firmly grasping the handle  110  in a comfortable manner, thus allowing the distal end of the tubular member to rotate relative to the handle. Additionally, it is often useful to incrementally rotate the distal end of the tubular member  130  by some predetermined angular displacement so that the practitioner may visualize the rotation relative to the handle  110 . 
     FIG. 2 depicts a cross section of a knob  120  having a conventional ball and spring detent mechanism. Within the knob  120  is a cylindrical drum  205  having a plurality of detents  210 . Typically, a channel  215  may extend partially through the knob  120 , the channel  215  being oriented radially with respect to the cylindrical drum  205 . The ball and spring mechanism is positioned within the channel  215 . As the name implies, a compression spring  220  is used to hold a ball  225  in contact with the cylindrical drum  205 . To prevent the ball and spring mechanism from falling out of the knob  120 , a set screw  230  may be used to seal the channel  215 . The set screw  230  may also be used to adjust the amount of compression force that is applied to the spring  220 . The ball, spring, and set screw may be separate components or may be integrated into a single component, as is known to the art. The portion of the handle that fits within the knob may engage the cylindrical drum  205 , or the cylindrical drum  205  may be an integral part of the handle. 
     As the knob  120  is rotated with respect to the handle, the ball  225  travels around the circumference of the cylindrical drum  205 . When the ball  225  is aligned opposite to one of the detents  210 , the spring  220  pushes the ball  225  into the detent  210 . If additional rotational force is applied to the knob  120 , then the ball  225  is removed from the detent  210 . The amount of force needed to remove the ball  225  from the detent  210  depends on a number of factors, including the shape and depth of the detent  210 , the shape and size of the ball  225 , and the amount of compression force applied by the spring  220  and/or set screw  230 . The spring  220  is conventionally made of metal to provide sufficient compressive force. The movement of the ball  225  into and out of the detents  210  provides tactile feedback to the user. 
     While the ball and spring detent mechanism design approach is functional, it requires several components and assembly processes to assure instrument reliability. Even so, these devices often fail over time as the metal components corrode causing the mechanism to jam. 
     Accordingly, there is a need to provide an incremental rotational displacement mechanism for use with endoscopic instruments that is resistant to corrosion failure and that may be easily assembled. 
     SUMMARY 
     In accordance with the present invention, there is an endoscopic instrument having a circular detent housing coupled to a first end of a knob. The circular detent housing has a plurality of detents arranged along the perimeter of the detent housing. A tubular member fixedly engages a second end of the knob. A detent ring is positioned coplanar to and within the perimeter of the detent housing. The detent ring has at least one detent arm and at least a portion of the at least one detent arm engages at least a portion of the detent housing. A handle is coupled to the detent ring. 
     In accordance with another aspect of the invention, there is an incremental rotational displacement mechanism. The mechanism includes a circular detent housing, a detent ring, and a handle. The detent housing has a plurality of detents arranged along the circumference of the detent housing. The detent ring has at least one detent arm and is positioned coplanar to and within the circumference of the detent housing, such that at least a portion of the at least one detent arm engages at least a portion of the detent housing. The handle engaging the detent ring such that a force applied to the handle causes the detent ring to rotate with respect to the circular detent housing. 
     In accordance with yet another aspect of the invention, the circular detent housing is formed within the first end of the knob. 
     In accordance with still another aspect of the invention, the detent ring has at least two arms. The two arms may have the same length or have different lengths. 
     In accordance with another aspect of the invention, the plurality of detents are arranged at either regular or irregular intervals along the perimeter of the detent housing. 
     It should be emphasized that the term “comprises” or “comprising,” when used in this specification, is taken to specify the presence of stated features, integers, steps, or components, but does not preclude the presence or addition of one or more other features, integers, steps, components, or groups thereof 
    
    
     BRIEF DESCRIPTION OF DRAWINGS 
     The objects and advantages of the invention will be understood by reading the following detailed description in conjunction with the drawings in which: 
     FIG. 1 is a plan view of an endoscopic instrument; 
     FIG. 2 is a partial cross-section of the knob of an endoscopic instrument having a conventional ball and spring detent mechanism; 
     FIG. 3 is an exploded view of the knob of an endoscopic instrument showing an exemplary embodiment of a detent mechanism in accordance the invention; 
     FIG. 4 is a plan view of the proximal end of the knob; 
     FIGS. 5 a  and  5   b  are a plan views of two embodiments of the detent ring; 
     FIGS. 6 a ,  6   b , and  6   c  are sequence drawings of a knob rotation; and 
     FIG. 7 is a plan view of another embodiment of the detent ring. 
    
    
     DETAILED DESCRIPTION 
     The present invention improves upon the state of the art by providing a more reliable incremental rotational displacement mechanism for use with endoscopic instruments. Furthermore, the mechanism may be implemented using fewer components. 
     FIG. 3 is an exploded view of a knob  300  of an endoscopic instrument showing an exemplary embodiment of an incremental rotational displacement mechanism in accordance with the invention. It will be appreciated that the knob  300  shown in FIG. 3 replaces the knob  120  shown in FIG.  1 . Thus, from the perspective of the user, each of the knobs  300 ,  120  performs an equivalent function. 
     A cylindrical cavity  305  is formed in a proximal end of the knob  300 . Arranged around the circumference of the cavity  305  are a plurality of scalloped detents  310 . A detent ring  315  may be disposed at least partially within the cavity  305  and in the same plane as the cavity  305 . A knob plug  320  may be disposed at least partially within the cavity  305  and positioned proximally to the detent ring  315 . The knob plug  320  provides a mechanical seal for the cavity  305  and retains the detent ring  315  in place. As discussed below, the shaft portion of the handle  110  mates with a center hole of the detent ring  315 , thereby rotationally fixing the detent ring to the shaft portion  110  of the handle. 
     FIG. 4 shows a plan view of the knob  300  showing the cylindrical cavity  305  and the plurality of scalloped detents  310 . The knob  300  may be formed from a variety of materials, such as polymers and metals, using conventional techniques. For example, the knob may be formed by injection molding an acetal resin, such as Delrin®  150  available from E.I. du Pont de Nemours and Company. If the knob  300  is injection molded, then the knob  300 , the cylindrical cavity  305 , and the plurality of scalloped detents  310  maybe formed from a single process step. 
     As can be appreciated, the number of detents  310  and the distance between each of the detents  310  may determine the angular resolution of the incremental rotational displacement mechanism. In one embodiment, twelve detents  310  are equally spaced around the perimeter of the cavity  305 , resulting in a granularity of about 30 degrees of angular resolution. The number of detents may be increased or decreased to provide a greater or lesser amount of angular resolution. In addition, detents may be absent from portions of the perimeter of the cavity, creating “dead zones”. 
     FIG. 5 a  shows a plan view of the detent ring  315 . The detent ring may include a main body  510  and at least one arm  520 . One end of the arm  520  may be connected to the main body  510  and the other end of the arm may terminate in a tab  530 . In another embodiment, shown in FIG. 5 b , the arm  520  may extend from one end of the main body  510  to another end of the main body  510 , with the tab  530  located along the length of the arm. In either case, the tab  530  may be shaped to engage the scalloped detents. The tab  530  and at least one arm  520  are arranged such that the tab  530  moves in and out of the detents  310  as the detent ring  315  is rotated within the cavity  305 . As the tab  530  moves in and out of the detents  310 , the user experiences some tactile feedback, similar to that felt with the conventional ball and spring mechanism shown in FIG.  2 . 
     As mentioned above, an opening  540  may extend through the center of the main body  510 . The opening  540  may have at least one flat portion. The shaft of the handle may be “keyed” to the shape of the opening  540 , so that when the shaft is inserted into the opening, the shaft and the detent ring may be rotationally fixed. 
     The material used to make the detent ring  315  should be compatible with that material used to make the knob  300 . Factors used to determine compatibility may include chemical interaction. In addition, the material should be chosen to minimize any burring or wear of either the detent ring  315  or the detents  310  after repeated used. The detent ring  315  may be formed using similar materials and techniques used to form the knob  300 . For example, the detent ring  315  may be formed by injection molding an acetal resin, such as the previously described Delrin®  150 . 
     The amount of force needed to rotate the knob  300  can be varied by changing the characteristics of the detent ring  315 . For example, the thickness of at least one arm  540  can be increased or decreased to provide a greater or lesser amount of resistance to movement with respect to the main body  510 . In addition, the composition of the material used to make the detent ring  315  can be changed. For example, other polymers could be mixed with or substituted for the acetal resin used to make the detent ring  315 . In addition, metal or alloys could be used to form all or part of the detent ring  315 . Examples of other suitable materials include stainless steel or nickel titanium alloys, such as nitinol. 
     FIG. 6 a  shows the detent ring  315  positioned within the cylindrical cavity  305  of the knob  300 . The shaft of the handle  110  and the knob plug  320  are not shown. In FIG. 6 a , the tabs  530  fully engage the detents  310 . As shown in FIG. 6 b , the knob  300  maybe rotated counter-clockwise with respect to the detent ring  315 , as indicated by the arrow  601 . As the knob  300  is rotated, a portion of the detents  310  assert a radial force against the tab  530  portions of the arms  520 , pushing the arms  520  toward the main body  510  portion of the detent ring  315 . This is indicated by the arrows  602 ,  603  in FIG. 6 b . The knob  300  may continue to be rotated counter-clockwise until the tabs  530  fully engage another pair of detents  310 , as shown in FIG. 6 c . As can be appreciated, while FIGS. 6 a ,  6   b , and  6   c  show the knob  300  being rotated counter-clockwise, the knob  300  may also be rotated clockwise. Due to the symmetrical shape of the tab  530 , the detent ring  315  interacts with the detents  310  in the same manner regardless of which direction the knob  300  is rotated. 
     As noted above, the number of detents  310  and the distance between each of the detents  310  may determine the angular resolution of the incremental rotational displacement mechanism. The angular resolution of the incremental rotational displacement mechanism may also be determined by the length of the arms of the detent ring. For example, FIG. 7 depicts an embodiment of the detent ring  315  having arms of unequal lengths. A first arm may have length L 1  and a second arm may have length L 2 , where L 2  is greater than L 1 . As can be appreciated, one tab  530  may be engaged in a detent while the other tab is situated somewhere between two adjacent detents and is thus disengaged. As the knob  300  is rotated, the engaged tab may become disengaged from its detent and the previously disengaged tab may become engaged in another detent. Thus, the effective angular rotation of the incremental rotational displacement mechanism may be somewhere between the angular distance between two adjacent detents. 
     The invention has now been described with respect to several embodiments. In light of this disclosure, those skilled in the art will likely make alternate embodiments of this invention. These and other alternate embodiments are intended to fall within the scope of the claims which follow.