Abstract:
A medical cutting device is disclosed in which a pivoted element ( 50 ) is actuated by a trigger ( 34 ) and a cutting blade ( 30 ) is attached to the pivoted element ( 50 ) by a flexible connector and cam elements ( 46, 49 ) cause the blade ( 30 ) to move in an essentially parabolic path when making an incision on a patient.

Description:
FIELD 
       [0001]    This invention relates to medical instruments, and more particularly to a lancet used for making incisions in patients. 
       BACKGROUND 
       [0002]    Lancets are relatively small, hand-held medical cutting devices used for making incisions in patients such as, for example, in making incisions in the heels of infants to take blood samples. Hence, they are sometimes referred to as “heel sticks”. A number of prior art lancets have been proposed including for example U.S. Pat. Nos. 5,314,441; 5,951,582; 6,402,595 and 6,221,089 to list a few. However, all of the prior lancets have suffered from one or more problems such as, for example, producing non-ideally shaped incisions, causing more pain than desired, and being subject to variations in the incisions depending upon use by different medical personnel. In addition, they have been quite costly to produce, which is a serious problem since they are used only once and then disposed. 
         [0003]    The object of the present invention is to eliminate, or substantially reduce, these and other problems of prior art lancets. 
       SUMMARY 
       [0004]    A medical cutting device including a pivoted element, a trigger and a cutting blade flexibly connected to the pivoted element for producing cutting movement of the blade in a substantially parabolic path. 
     
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         [0005]      FIG. 1  is an elevational view of the bottom edge of the lancet; 
           [0006]      FIG. 2  is a top plan view of the lancet; 
           [0007]      FIG. 3   a  is a perspective view of a trigger button; 
           [0008]      FIG. 3   b  is an elevational view of the trigger button; 
           [0009]      FIG. 4  is a top plan view of the bottom inner wall of the casing before the cutting mechanism is installed; 
           [0010]      FIG. 5  is a top plan view, partly in cross-section, illustrating the cutting mechanism in a first pre-cutting position; 
           [0011]      FIG. 6  is a cross-sectional view taken along view line  6 - 6 ; 
           [0012]      FIG. 7  is a top plan view, partly in cross-section, illustrating the cutting mechanism in a second pre-cutting position; 
           [0013]      FIG. 8  is a top plan view, partly in cross-section, illustrating the cutting mechanism in a third pre-cutting position; 
           [0014]      FIG. 9  is a top plan view, partly in cross-section, illustrating the cutting mechanism in approximately the mid-point of the incision; 
           [0015]      FIG. 10  is a plan view, partly in cross-section, illustrating the cutting mechanism in the post-cutting position; 
           [0016]      FIG. 11  illustrates the off-center parabolic shape of the cutting path of the blade; 
           [0017]      FIG. 12  is an enlarged view of the cutting path shown in  FIG. 11 ; 
           [0018]      FIG. 13  is a top plan view of a second embodiment of the lance;  
           [0019]      FIG. 14  is a cross-sectional view taken along view line  14 - 14  of  FIG. 13 ; 
           [0020]      FIG. 15  is a top plan view of the second embodiment with the top cover removed; 
           [0021]      FIG. 16  is a top plan view of a third embodiment of the cutting mechanism in a first pre-cutting position; 
           [0022]      FIG. 17  is a cross-sectional view along view line  17 - 17  of  FIG. 16 ; 
           [0023]      FIG. 18  is a top plan view of the third embodiment showing the cutting mechanism in a second pre-cutting position; 
           [0024]      FIG. 19  is a top plan view of the third embodiment showing the cutting mechanism in a third pre-cutting position; 
           [0025]      FIG. 20  is a top plan view of the third embodiment showing the cutting mechanism in the cutting position; 
           [0026]      FIG. 21  is a top plan view of the third embodiment showing the cutting mechanism in the post-cutting position; 
           [0027]      FIG. 22  is a cross-sectional view taken along view line  22 - 22  of  FIG. 21 ; 
           [0028]      FIG. 23  is a top plan view of the fourth embodiment showing the cutting mechanism in a first pre-cutting position; 
           [0029]      FIG. 24  is a cross-sectional view along view line  24 - 24  of  FIG. 23 ; 
           [0030]      FIG. 25  is a top plan view of the fourth embodiment showing the cutting mechanism in a second pre-cutting position; 
           [0031]      FIG. 26  is a top plan view of the fourth embodiment showing the cutting mechanism in a third pre-cutting position; 
           [0032]      FIG. 27  is a top plan view of the fourth embodiment showing the cutting mechanism in the cutting position; 
           [0033]      FIG. 28  is a top plan view of the fourth embodiment showing the cutting mechanism in the post-cutting position; and 
       
    
    
     DETAILED DESCRIPTION 
       [0034]    Referring first to  FIGS. 1 and 2  which illustrate one preferred embodiment of the present invention, the mechanism of lancet  10  is housed within a clam shell casing comprising an upper casing half  14  and lower casing half  16  as viewed in  FIG. 1 . The casing halves are permanently secured together such as for example, by pins  18  in holes  20  in the periphery of the respective casing halves as shown in the fragmentary view in  FIG. 1 . Alternatively, they may be secured by adhesive or other known securing means. It will be understood that the casing is held vertically in the user&#39;s hand, between the thumb and middle finger, such that the top and bottom casing halves become the sides in use. In order to provide maximum gripping of the rather small lancet, the external surfaces of the casing halves are preferably provided with irregular, high friction projections such, for example, raised circular surfaces  22  and/or a raised waffle pattern  24 . Alternatively, it will be understood that other forms of high friction surfaces may be used. The casing  12  is further provided with a slot  26  in the circumferential edge walls  28 - 29  of the two casing halves for the purpose of allowing the tip of a cutting blade  30  to project out of the casing so as to make the incision on the patient. Preferably, the wall surfaces  28 - 29  adjacent to slot  26  are bevelled at  32  above and below the slot in order to provide an improved ergometric shape which conforms to the incision area of the patient such as, for example, the heel area of an infant. 
         [0035]    As further shown in  FIGS. 1 and 2 , one preferred embodiment of the lancet  10  includes a trigger button  34  including side walls  19  which slide downwardly in shallow grooves  21  on the outside surfaces of the casing halves. Trigger button  34  actuates the cutting mechanism, including blade  30  which is mounted in a holder  54 , as will be more fully explained hereafter. In this regard, it will be understood that the upper surface  33  of the trigger button is engaged by the user&#39;s index finger to push the button downwardly such that, preferably, the upper portion of the button is provided with a high friction surface such as, for example, a plurality of ridges and grooves  33  which may be molded into the button. Alternatively, of course, other forms of high friction surfaces may be used to prevent the user&#39;s index finger from slipping when depressing the trigger button. 
         [0036]    As most clearly shown in  FIGS. 3   a  and  3   b , in one preferred embodiment the trigger button includes a pair of legs  37  which slide downwardly along grooves  36  in the inner surface of the casing. The bottom portions of the button include two enlarged tip portions  38  which slide in grooves  39  in the outside of the casing. The top portion of groove  39  is closed such that the enlarged tip portions become trapped in groove  39 . Accordingly, once the button is inserted in the casing during manufacture of the lance, it is prevented from separating from the casing while being capable of vertical sliding movement. 
         [0037]    As further shown in  FIG. 2 , in order to prevent accidental depression of the trigger button, a positive safety lock  40  is provided. In the first embodiment as illustrated in  FIGS. 1-10 , the safety lock is in the form of a manually removable lock  40  having a handle portion  41  the lower end of which is pressed against circumferential edge walls  28 - 29  and the upper end against button  34 . The lock further includes one or more locking pins  42  which are received in one or more holes in button  34 . In this manner, trigger button  34  cannot be accidentally depressed, but rather, can only be depressed after the user has pulled lock  40  out of locking engagement with both the casing and the trigger button. 
         [0038]    Referring to  FIG. 4 , the lower casing half  16  is shown as it appears before the installation of the cutting mechanism. Lower casing half  16  includes a V-shaped cam  46  having a leading cam surface  47  and a trailing cam surface  48 . Cam  46  also includes a V-shaped slot  70 , and a second set of cam surfaces  49  and  73 . While the detailed cam action will be more fully explained hereafter, it will be understood from  FIG. 5 , for example, that cam surfaces  47  and  48  are engaged by a first cam follower pin  66  mounted on blade holder  54 , and cam surfaces  49  and  73  are engaged by a second cam follower pin  68  also mounted on blade holder  54 . While cam  46  may be manufactured as a separate element and secured to casing half  16 , it is preferred that the cam be molded on the inner surface  17  of casing half  16  as a one-piece, raised surface portion of casing half  16 . As such, cam  46  also serves as a thickened portion of the casing half  16  and includes a centrally located hole or journal  45 , as most clearly shown in  FIGS. 4-6 , for receiving a stub shaft  52  to be further described hereafter. Of course, while the cam portion and the journal portion are illustrated as being integral, it will be apparent that they may be molded or secured as two separate pieces. It is also to be understood that as shown in  FIG. 6 , upper casing half  14  includes an identical, mirror image cam with a journal  45 ′ such that, when the casing halves are assembled, stub shaft  52  is secured at both ends in the journals. 
         [0039]    The interior cutting mechanism will now be further described with reference to  FIGS. 5-10 . In one preferred embodiment, the cutting mechanism comprises the previously described blade  30  which is secured by known means in a blade holder  54 . Blade holder  54  is connected by a relatively thin C-shaped spring element  72  to a pivoted hub plate  50  which includes the previously described stub shaft  52  which is preferably molded as an integral, one-piece element. Thus, hub plate  50  pivots in the direction of arrow A as shaft  52  pivots in journal  45 . Hub plate  50  further includes an integral, one-piece trigger arm  56  having a smooth or rounded end  58  which is received between the spaced-apart legs  37  of trigger button  34 . Accordingly, depression of the button causes plate  50  to pivot in the direction of arrow A about journal  45 . Hub plate  50  further includes a second arm  60 , hereinafter referred to as a “trip arm”, and in the pre-cutting position illustrated in  FIG. 5 , the tip  61  of the arm bears against a protruding stop portion  62  of the casing. By reason of the cross-sectional area and composition of the one-piece plate  50 , such as molded plastic, trip arm  60  has a predetermined amount of flexibility. Thus, when trigger button  34  is depressed, tip  61  snaps over stop portion  62  and the entire one-piece hub plate  50 , including arms  56 ,  60  and blade holder  54 , pivots extremely rapidly in the direction of arrow A from the pre-cutting position shown in  FIG. 5  to the post-cutting position shown in  FIG. 10 . It will be understood that this entire motion from pre-cut to post-cut occurs virtually instantaneously; however, this motion will be described in the following distinct phases of motion. 
         [0040]    First, after the manual depression of button  34  to the position shown in  FIG. 7 , further downward motion of the button is stopped either because the bottom portion  35  of the button hits the top edge  23  of groove  21  in the casing, or in an alternative embodiment, the bottom of legs  37  hit the closed end of groove  36 . In either event, the movement of the button stops, and therefore, the further pivoted movements of hub plate  50  and blade  30  are due to momentum of the parts and are independent of the user&#39;s strength or dexterity. This is due to the substantial force built up in flexible finger  60  before it snaps over abutment  62 , which then imparts a very high arcuate velocity and momentum to the entire one-piece hub plate and the blade. 
         [0041]    As further shown in  FIG. 8 , hub plate  50  continues to pivot about shaft  52  while C-shaped tension spring  72  maintains cam follower  66  on blade holder  54  in engagement with leading cam edge  47 . Because of the V-shape of the cam, the blade is forced downwardly toward slot  26 , while cam follower  68  slides along cam surface  73 . This motion continues as the hub plate continues to pivot, thereby drawing arm  56  and end  58  downwardly between spaced legs  37  of button  34  as blade  30  approaches the right-hand edge of slot  26  as viewed in  FIG. 8 . 
         [0042]      FIG. 9  shows the incision at its point of deepest penetration into the patient. At this point, cam follower  66  is at the end of leading cam surface  47  and is about to move upwardly along trailing cam surface  48 . It will also be noted that cam follower  68  is also about to begin moving upwardly in engagement with cam surface  49  in slot  70  due to the tension of spring  72  pulling the blade holder upwardly. In addition, it should be noted that hub plate  50  is illustrated as having an additional arm  74 , and a projection  76  extending from blade holder  54  toward arm  74 . Thus, if desired in an alternative embodiment, the shape and angle of arm  74 , and the length of projection  76 , may be designed such that arm  74  may be made to engage projection  76  and thereby add a pushing force on the blade holder during the cutting phase. However, it has been found that such an additional force is not necessary, over and above the substantial momentum of the entire cutting mechanism as previously described, such that arm  74  and projection  76  may be entirely eliminated thereby adding to the cost reduction of the mechanism. 
         [0043]      FIG. 10  illustrates the final, post-cutting position in which the blade has completed the incision, and it has been retracted entirely into the interior of the casing such that it is not a hazard to any nearby personnel. This movement of the blade and holder is made possible by the provision of opening  71  at the upper end of cam  48  through which cam follower  68  passes outwardly from slot  70  under the action of spring  72  which flexes into its predetermined non-tensioned shape. 
         [0044]    As further illustrated in the dotted-line  FIG. 11 , dotted line B illustrates the cutting path of the tip of blade  30  as it performs the incision, and it will be noted that the cutting path of the blade is entirely a smooth curve with no jagged portions. It will be further noted that the initial portion X of the cutting path is at a relatively sharp, acute angle of less than 45 degrees with respect to slot  26  against which the patient&#39;s skin is in contact. This produces a clean and sharp initial incision which then becomes wider until it is subsequently withdrawn cleanly at portion Z, which is also at an acute angle but less acute than that of portion X. This precisely defined path, hereinafter referred to as an “off-center parabola”, in combination with the high speed motion and momentum of the blade produced by the stored energy of arm  60  before it snaps over abutment  62 , has been discovered to produce a substantially improved incision which produces the required amount of blood sample in a substantially less painful manner. Also, the speed and accuracy of the cutting is absolutely the same regardless of the dexterity or strength of the finger motion of the user. Thus, unlike the prior art which often produces a relatively jagged cut due to the jerking motion of driving springs, and or the uneven pressure by the finger of the user, the lancet of the present invention produces a clean, smooth and non-jagged incision of an ideal shape for obtaining blood samples with less pain inflicted on the patient, who usually is an infant. In addition, the fact that all of the moving parts and elements of the cutting mechanism comprise a single, one-piece element allows the entire mechanism to be mass produced by molding only the one-piece hub plate  50  at a substantially lower cost than previously possible. 
         [0045]    As further shown in  FIG. 12 , the cutting path of the tip of the blade, and hence the profile of the resulting incision, comprises a first path portion X which has a component of motion in the direction of the width W of the incision as the blade tip enters the skin and penetrates to depth D. Thereafter, the tip executes a smooth reversing curve at B, and then the blade is extracted along path Z which has a lesser component of motion along the width, and a larger component of motion along the direction of the depth of the cut which withdraws the blade with minimum width of cut. As a result of this precisely defined, and repeatable incision profile, both the depth and width of the cut is minimized and yet able to produce a completely sufficient blood sample. 
         [0046]    A second preferred embodiment of the present invention will now be described with reference to  FIGS. 13-15 . The cutting mechanism of this embodiment is the same as that previously described, and accordingly the same reference numerals are applied to  FIGS. 13-15  as in  FIGS. 1-12 . The difference of the second embodiment from the first embodiment pertains to the positive safety lock. In this embodiment, as shown most clearly in  FIGS. 13 and 15 , each of the upper and lower casing halves  14  and  16  are cut out with arcuate slots  80 , 80 ′ and  81 , 81 ′ to form two pivoted levers one on each side of the casing. Each of the two pivoted levers has a relatively large portion  86 , 86 ′ and a smaller portion  87 , 87 ′. Between the slots the casing is uncut so as to form connecting portions  82 , 82 ′ and  84 , 84 ′ which function as pivots allowing tilting movement of the large portions of the lever relative to the smaller portions. That is, when the user depresses portions  86 , 86 ′ into the lancet with his thumb and middle finger, the smaller portions  87 , 87 ′ are moved outwardly away from the casing. As shown most clearly in  FIG. 14 , locking pins  88 , 88 ′ are connected to and carried by the smaller pivoted lever portions  87 , 87 ′. When the levers are not depressed, the locking pins  88 - 88 ′ extend into the cutting mechanism and engage one of the arms on hub plate  50  such as, for example, between arms  56  and  60 . In this regard it will be understood that, in one preferred embodiment, arms  56  and  60  comprise a thinner portion  83  and a thicker edge portion  85  as shown in  FIGS. 14 and 15 . Thus, the locking pins engage the edges of the thicker portion  85  when lever portions  86 , 86 ′ are not depressed. This locking engagement prevents movement of arms  56  and  60  and thereby locks hub plate  50  in fixed, locked position. However, when the pivoted lever portions  86 , 86 ′ are depressed by the user, portions  87 , 87 ′ move outwardly of the casing and pull the locking pins out of engagement with arms  56 , 60  thereby releasing the hub plate for pivoted movement as previously described. In this manner, the second embodiment performs all of the functions and advantages previously described with respect to the first embodiment, and it will be apparent that other forms of pivoted locks may be used, such as for example, holes in any of the arms which may be engaged by pins, abutments or the like. 
         [0047]    A further embodiment will now be described with reference to  FIGS. 16-21 . Since the majority of the elements of this embodiment are the same as those previously described, the same numerals have been applied to those elements which are the same. 
         [0048]    As shown in each of  FIGS. 16-21 , the first difference of this embodiment is that trigger button  34  is formed as an integral, one-piece portion of hub plate  50 , preferably as a single molded part, and connected to the hub plate by an intermediate connecting portion  89  of plate  50 . 
         [0049]    A second difference from the embodiments previously described is the provision of a locking tab  90  which is also preferably an integral, one-piece portion of hub plate  50  As most clearly shown in  FIGS. 16 and 17 , locking tab  90  extends through a slot  94  formed between the casing halves. Thus, any accidental pushing down of the button is prevented by the bottom edge of the tab striking the casing at the bottom end  91  of the slot. However, tab  90  also includes a groove or other weakened portion  92  whereby the locking tab may be broken off by the user immediately prior to using the lancet to make an incision. Accordingly, when the user breaks off tab  90 , connecting portion  89  of the plate is free to move downwardly through slot  94  and thereby pivot hub plate  50  in the direction of arrow A. 
         [0050]    The third difference of this embodiment from those previously described is the provision of a post-cut lock as most clearly shown in  FIGS. 21 and 22  whereby the blade, which is retracted into the casing after making the incision, is positively locked in the post-cut position. In the preferred embodiment, this post-cut lock comprises a pair of projections  96 ,  96 ′ which are molded into or otherwise secured to the inner surfaces of each of the casing halves. Projections  96 ,  96 ′ are preferably provided with smooth and slightly angled upper surfaces which are engaged by the bottom surfaces of a pair of detents  98 ,  98 ′ carried by hub plate  50 . Thus, as shown most clearly in  FIG. 22 , when the hub plate has almost completed its full pivoted movement, and the blade has been retracted into a safe position in the casing as shown in  FIG. 21 , the last movement of the plate causes detents  98 ,  98 ′ to be forced downwardly between and below projections  96 ,  96 ′ which spread slightly due to the slight flexibility of the casing walls. Thus, the hub plate is prevented by projections  96 ,  96 ′ from moving in the opposite direction. Accordingly, the hub plate  50 , blade holder  54  and blade  30  are positively locked in a safe retracted position so as not to be able to injure any nearby personnel. 
         [0051]    The preferred mode of operation of this embodiment is as follows. First, the user breaks off locking tab  90  whereby hub plate  50  is free to be pivoted by the user pushing trigger button downwardly with the user&#39;s index finger. However, at this time finger  61  is in engagement with abutment  62 , and its length and degree of resilience is such that a certain degree of force is required to push the button downwardly. As the user increases this force by further pressure on the button, finally finger  61  snaps over abutment  62  whereby plate  50  is pivoted extremely rapidly in the direction of arrow A. Such high velocity of the hub plate creates sufficient momentum to carry the plate and blade completely through the cutting and post-cutting positions illustrated in  FIGS. 18-21  under the action of spring  72  and the cam surfaces on cam  46  as previously described in the prior embodiments. Therefore, in this mode, the entire force required is provided by momentum, and the user&#39;s finger merely follows the motion of the button rather than pushing the button to its final position. 
         [0052]    Alternatively, the lancet of this embodiment may be operated in a manual mode in which the user&#39;s finger continues to push the button throughout its path from the  FIG. 16  to  FIG. 21  positions, thereby assisting the force of a lesser amount of momentum such as may result from the use of a shorter and/or more flexible finger  61  which produces less velocity, and hence, less momentum. 
         [0053]    As another alternative mode, the lancet of this embodiment may operate in a mode in which the design of finger  61  is such as to create sufficient momentum to accomplish the required cutting phase without manual assistance, but additional manual force is applied to the button after the incision is completed. That is, the only additional manual force is to assist in the final phase to force detents  98  to pass through projections  96  to post-lock the blade in the casing. In another alternative embodiment, it will be noted that blade holder  54  is illustrated as including a projection  76  as in the first embodiment. Thus, the size and shape of projection  76  and that of portion  99  of hub  50  may be designed so that portion  99  strikes projection  76  and thereby assists the force of the momentum to make the incision. However, as in the first embodiment, projection  76  maybe eliminated and the lancet may be operated in either one of the above two describe modes. Thus, it is to be understood that the specific design of finger  61  may be used in each of the described embodiments to generate the specific amount of momentum which is desired for a particular configuration of that embodiment. 
         [0054]    Yet another embodiment will now be described with reference to  FIGS. 23-27 . Since the majority of the elements of this embodiment are the same as those in the previous embodiment, only the numerals relevant to the description below have been applied to the elements in  FIGS. 23-27 . The differences from the previous embodiment have been explained in detail below. 
         [0055]    As shown in each of  FIGS. 23-27 , the first difference of this embodiment is that the trigger button  34  is shaped ergonomically. The shape of the trigger button is such that it matches with the shape of the thumb of the user. This shape produces less strain on the user&#39;s finger. 
         [0056]    A second difference is that the profile  150  of the lower casing half  16  and the upper casing half  14  adjacent the trigger button  34  have been modified to reduce the travel distance of the trigger button. It is apparent from  FIGS. 23-27  that the portion  151  of the profile has been curved upwards to result in a shorter travel distance of the trigger arm. The upper casing half  14  and the lower casing half  16  together comprise the housing  160  as illustrated in  FIG. 24 . 
         [0057]    A third difference is the provision of a reinforcing structure  165 , such as a pin or a small projection in the housing and located adjacent the centre of the housing  160  to resist any inward deflection of one of the main walls of the upper casing half towards the lower casing half or one of the main walls of the lower casing half towards the upper casing half. The reinforcing structure  165  is preferably located on the cam  46 . In other words, the purpose of the pin is to maintain a gap between the upper and lower casing half and prevent them from pinching on the blade holder  54  when the cutting device is gripped by the user. When the blade holder is pinched, it is prevented from moving and the cutting device can no longer be used. 
         [0058]    A fourth difference is the provision of a ridge  170  on the blade holder  54  to provide a continuous flat surface, so that there will be no corners which can jam the movement of the blade holder hub if they are accidentally blocked from the sides of the cam  46  from moving. 
         [0059]    A fifth difference is that the leading cam surface  47  is longer when compared with the previous embodiment. By having a longer leading cam surface in the V-cam profile, there will be an increase in the length of the cut. 
         [0060]    The next difference is in the shape and arrangement of the abutment  62  in the lower casing half  16  of the housing  160  and the arm  60 . There is provided a first stop  175  on the tip of the abutment  62  and a corresponding catch  180  on the arm  60 . The arm is a resilient arm and the catch engages against the first stop  175  in the pre-cutting position. When the trigger button is pressed by the user, the pivoted hub plate  50  pivots which causes the deflection of the arm  60  to a deflected position for the catch to be released from the first stop. The position of the pivoted element  50  and the arm  60  after deflection is illustrated in  FIG. 25 . Once deflected, the pivoted element is free to pivot and moves quickly with the cutting blade moving through the cutting position. The presence of the catch and the first stop prevents any slight movement of the cutting blade, before the catch  180  is fully released from the first stop  175 . This prevents any pre-mature exposure of the cutting blade. In other words, pre-mature in this context is the cutting blade being exposed out of the slot  26  in the housing, even before the cutting blade moves through the cutting position at full speed. 
         [0061]    The last difference is the presence of a second stop  185  in the lower casing half  16  of the housing  160 . In the event of the blade holder being jammed and prevented from moving during the pivoting action of the pivoted element, stress builds up in the flexible spring element  72  and it suffers permanent deformation and becomes elongated due to over flexing. Subsequently if the blade holder becomes free to move, the elongated spring element  72  pushes the cutting blade  54  out of the slot  26  and the cutting blade dangles freely, posing a hazard to the user. The second stop  185  positioned adjacent the spring element prevents the spring element from over flexing in the event of stress build up in the spring element. 
         [0062]    It is to be understood that the foregoing description of several preferred embodiments is intended to be purely illustrative of the principles of the invention, rather than exhaustive thereof, and that changes and variations will be apparent to those skilled in the art, and that the present invention is not intended to be limited other than expressly set forth in the following claims.