referring now to the drawings , and particularly to fig1 to 5 , one embodiment of the invention , in perhaps its most simplest form , is shown generally at numeral 10 . this embodiment 10 includes a lancet shown generally at numeral 12 having an elongated rigid , slender tubular shaft or shank 14 with a hypodermic needle - style piercing tip 16 disposed from its distal end as best seen in fig1 . connected at the other end of shank 14 is a cap 18 formed of molded plastic and generally of a cup - shaped configuration . this lancet 12 is structured such that shank 14 will slidably engage within protective support tube 22 over substantially the entire length of shank 14 . cap 18 is sized and structured so as to slidably engage over the outer surface over the corresponding end of protective tube 22 . the relative lengths between shank 14 and protective tube 22 are such that , when cap 18 is disposed a certain distance 26 from the corresponding end of protective tube 22 , piercing tip 16 is fully within the protective tube 22 as best seen in fig2 and 3 . however , when cap 18 is moved against the corresponding end of protective tube 22 as shown in fig4 the piercing tip 16 extends longitudinally outward from the other end of protective tube 22 to effect finger skin piercing . at least one bump or protrusion 24 is provided positioned so as to serve as a detent to inhibit cap 18 from being moved so as to contact the corresponding end of protective tube 22 except when the device 10 is to be used to pierce the skin of the finger . then , sufficient force may be exerted against cap 18 in the direction of the arrow shown in fig4 so as to overcome the slight interference posed by bumps 24 wherein cap 18 will override this obstruction so as to extend piercing tip 16 beyond the other end of protective tube 22 for use . a molded cover 20 is also provided which frictionally engages over the other end of molded plastic protective tube 22 . cover 20 is provided to be heat sealed over support tube 22 , as is cap 18 , so as to insure sterility of piercing tip 16 prior to use . cover 20 also is provided to be reinstalled as shown in fig5 after the device 10 is used so as to prevent blood from coming in contact with other persons and to help insure that no further contact is made with piercing tip 16 . note that , although shank 14 is here shown as a slender metal thin - wall tube into which piercing tip 16 is forcedly inserted , nonetheless the entire shank 14 and piercing tip 16 may be fabricated alternately of a single length of rigid wire . when fabricated in two parts , the shank 14 also provides an additional shoulder to further insure controlled piercing depth of piercing tip 16 . although the invention is described in its simplest form in fig1 to 5 , the entire device 10 may be incorporated into a reuseable carrying device such as in the shape of a typical mechanical ball point pen wherein cover 18 is structured to cooperatively interengage with the well - known ball point pen mechanism which is then used to forceably urge cap 18 in the direction of the arrow in fig4 so as to expose piercing tip 16 for use . additionally , well - known means for momentary inertia or spring biasing may be provided ( not shown ). although the distal end of support tube 22 is applied against the fingertip skin and is exposed to blood let as a result of the piercing action , because the entire device 10 is intended for only one time use and to be disposed of thereafter , there is no risk of cross contamination between patients . in addition to providing bumps 24 as previously described , cap 18 and cover 20 are also preferably heat sealed or spot welded as will be described and shown with respect to fig7 and 8 herebelow so as to ensure sterility from time of manufacture until time of actual use . referring now to fig6 an alternate embodiment of the lancet is shown generally at numeral 30 and includes a plastic molded cap 32 , again generally cup - shaped , which slideably engages over support tube 36 as previously described , this cap 32 is heat sealed to plastic support shaft 36 at assembly to help insure sterility . in this embodiment 30 , a solid surgical steel shank 34 is utilized rigidly connected into cap 32 as shown . the opposite end of shank 34 includes a formed hypodermic - type piercing tip positioned with respect to the distal end of support tube 36 as previously described . in this embodiment of lancet 30 , a compression return spring 42 is provided which automatically withdraws the piercing tip end ( not shown ) of shank 34 within the support tube 36 after use . bump 40 slideably engages within cavity 38 so as to limit the relative longitudinal travel between cap 32 and support tube 36 , and this controls the distance of extension of the piercing tip beyond the end of support tube 36 . referring lastly to fig7 and 8 , the lancet shown generally at 44 is provided to offer the limited one time use feature . in this embodiment 44 , again a solid shank 48 is utilized having a piercing tip 48 &# 39 ; at its distal end as shown in fig7 . the shank 48 is rigidly connected into cup - shaped plastic molded cap 46 as previously described . plastic support tube 50 serves to allow shank 48 to translate longitudinally therewithin . in this embodiment 44 , a spring steel formed washer 60 is provided to afford the automatic return feature in lieu of a conventional compression coil spring shown in fig6 . spring washer 60 compressively flattens as shown in phantom in fig7 into a thinner overall dimension than coil spring 42 in fig6 and is preferred . bump 56 translates longitudinally within cavity 58 so as to suitably limit the longitudinal travel of shank 48 and cap 46 relative to support tube 50 so as to both control the extending of piercing tip 48 &# 39 ; beyond the distal end of support tube 50 and to limit the distance of return of cap 46 away from the corresponding end of support tube 50 so that the entire assembly remains intact after use for disposal . in this embodiment 44 , a spot weld or heat seal is provided at 52 so as to insure sterility of the piercing tip 48 &# 39 ; prior to use in conjunction with a molded cover 20 at the opposite end of support tube 50 as previously described with respect to fig2 to 5 . however , the spot weld 52 also longitudinally secures cap 46 with respect to support shaft 50 so that inwardly biased tang 62 is pressed against the side of support shaft 50 on assembly . however , at use , cap 46 is displaced against the corresponding end of support shaft 50 , moving a distance equal to arrow a . spring washer 60 flattens to the orientation shown in phantom while piercing tip 48 is extended to accomplish its blood - letting purposes . thereafter , when axial force is released from cap 46 , it is allowed to travel in the opposite direction away from the corresponding end of support tube 50 a distance somewhat further than dimension a as controlled by the position of the end 58 &# 39 ; of cavity 58 as best seen in fig8 . when allowed to return this additional distance after use , inwardly biased tang 62 then moves in the direction of the arrow as shown in fig8 so as to impinge upon the corresponding end of support tube 50 and to remain there by its spring biasing configuration . this structural arrangement shown in fig8 is achieved after a one - time cycling of the device 44 . in this configuration , then the longitudinal positional relationship between support tube 50 and cap 46 / shank 48 / piercing tip / 48 &# 39 ; is fixed by the interaction of tang 62 against the corresponding end of support tube 50 and bump 56 against the end 58 &# 39 ; of cavity 58 . further relative axial movement between the components is impossible short of damaging the components . thus , inadvertent reuse of the device is virtually impossible . while the instant invention has been shown and described herein in what is conceived to be the most practical and preferred embodiment , it is recognized that departures may be made therefrom within the scope of the invention , which is therefore not to be limited to the details disclosed herein , but is to be accorded the full scope of the claims so as to embrace any and all equivalent apparatus and articles .
a disposable lancet for piercing a person &# 39 ; s finger skin sufficiently to let a small quantity of blood . the lancet includes a long , slender , rigid shank having a hypodermic needle - style piercing tip at one end and slidably mounted within a generally coextensive support tube over substantially its entire length . a cap is connected to the other end of the shank which , when in contact with one end of the support tube , is structured to allow the piercing tip to extend beyond the other end of the support tube a predetermined distance sufficient for piercing the skin . the shank has a stored position wherein the piercing tip is retracted fully within the support tube . single - use features are also disclosed .