Abstract:
A lancing device has a spring-loaded lancet holder slidably mounted within a housing for carrying a disposable lancet and needle. A slider mounted in a slot in the housing is moved back for cocking the device and, after the lancet is fired, is moved forward to eject the used lancet. A releasable connector reversibly immobilizes the holder while the lancet is being ejected. The releasable connector permits a shortened ejection stroke, which, in turn, permits a shorter slot in the housing.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     This invention relates to a lancing device to pierce the skin to obtain a blood sample; more particularly, a lancing device that has a shortened stroke for ejecting the lancet after lancing. 
     2. Background of the Related Art 
     Lancing devices are an unfortunate fact of life for the millions of people with diabetes who must test their blood glucose levels up to five or more times each day. They typically use the devices to draw a drop of blood from a finger, apply the blood to a disposable strip, and measure the blood glucose concentration in a meter. Obvious goals of such lancing devices are to provide an adequate sample of blood with minimal pain, inconvenience, and cost to the user. 
     U.S. Pat. No. 4,503,856, issued on Mar. 12, 1985 to Cornell et al., discloses a lancet device that has a tubular housing, a slidable lancet holder in the housing and a compressible spring that provides the force to move the holder linearly to a skin piercing position, after which it goes back to a neutral position. 
     U.S. Pat. No. 4,527,561, issued on Jul. 9, 1985 to Burns, discloses a lancet assembly that includes a second spring for retracting the lancet holder after the lancet has penetrated the user&#39;s skin (see also U.S. Pat. Nos. 4,535,769 and 4,553,541). 
     U.S. Pat. No. 4,895,147, issued on Jan. 23, 1990 to Bodicky et al., discloses a lancet device that includes a penetration depth selector and a mechanism for creating a vacuum after the skin has been pierced to assist in drawing blood from the puncture site. 
     U.S. Pat. No. 4,976,724, issued on Dec. 11, 1990 to Nieto et al., discloses a lancet device that includes a mechanism that permits the user to eject a used lancet without touching it. 
     U.S. Pat. No. 5,318,584, issued on Jun. 7, 1994 to Lange et al., discloses a lancet device that includes a rotary/sliding transmission system that permits a puncture to be made with less pain. 
     SUMMARY OF THE INVENTION 
     The present invention provides a lancing device for withdrawing a blood sample. It comprises a generally elongate housing having a cap with a through hole at a forward end and a closure at a back end, opposite the forward end, and containing 
     (a) a lancet holder, slidably mounted within the housing, 
     (b) a first spring for urging the holder forward, having a first end that bears on the housing and a second end that bears on the holder, 
     (c) a slider, slidably mounted in a wall of the housing, comprising 
     (i) a projection outside the wall and 
     (ii) a pushing means, reversibly engageable with the holder, to push the holder back into a cocked position and to push a lancet forward from the device, 
     (d) a second spring for urging the holder back, having a first end that bears on the holder and a second end that bears on the slider, 
     (e) a button, movable between a first position in which the holder is restrained when the device is cocked and a second position in which the restraint is removed, permitting the first spring to thrust the holder forward, and 
     (f) a releasable connector mounted within the housing for immobilizing the holder when the slider is moved forward to eject the lancet from the device. 
     Several advantages result from the releasable connector of the present lancing device. First, it permits the cocking and ejecting mechanisms not to be directly linked, permitting a shortened stroke. A shorter stroke facilitates one-handed operation of the device. In addition, a shorter stroke permits a shorter slot for the slider travel. By using a shorter slot, it is possible to provide the slot with a covering to prevent infiltration of debris, without the covering interfering with the actuator during ejection of the lancet. 
     Another advantage of the releasable connector is that it creates interference between the slider and the housing during lancet ejection, which provides friction feedback to let the user know that the device is in the ejection mode. The interference also eliminates the need for a return spring to provide tension for the slider. If there were no interference, the slider would be (undesirably) free to move around. 
     Still another advantage of the releasable connector is to prevent the slider from moving forward unintentionally when the cap is removed. Instead, the slider is forced forward against a stop on the connector by the second (retraction) spring. The connector thereby permits the cap to be removed and refastened without interference from the slider. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a perspective view of a device of this invention with half the housing removed. 
     FIG. 2 is a cross section of the device of FIG. 1 in its rest position. 
     FIG. 3 is a cross section of the device of FIG. 1 as it is being cocked. 
     FIG. 4 is a cross section of the device of FIG. 1 in the over-cocked position. 
     FIG. 5 is a cross section of the device of FIG. 1 when it is cocked. 
     FIG. 6 is a cross section of the device of FIG. 1 as it is being fired. 
     FIG. 7 is a cross section that depicts lancet ejection from a device of this invention. 
     FIGS. 7A-7F are enlarged views of a part of FIG. 7, showing various alternative embodiments of a releasable connector. 
     FIG. 8 is a cross section of a device of this invention after lancet ejection. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     The present invention provides a lancing device that incorporates a releasable connector for simpler construction and more convenient operation. 
     FIG. 1 depicts a lancing device  10  of this invention, with one side of the housing removed to permit a view of the interior. The front end of the device has cap  12 , with through hole  14 . Cap  12  is removably joined, for example by a screw thread, to the housing  16 , which is conveniently of two parts. One half  16 A is shown, while the other half has been removed. At the back end of the device opposite cap  12 , housing  16  is joined to knob  18 . Knob  18  has cantilever fingers  18 A that provide a mechanical stop, whose position can be varied by a thread, such as a helical thread, that attaches the knob to the housing. The mechanical stop is preferably provided by undercuts on the inside of the cantilever fingers. 
     A lancet holder  20  holds and guides a disposable lancet throughout the operation of the device. A drive spring  22  stores the energy needed for driving the lancet forward. Drive spring  22  is contained within holder  20  and bears on post  23  of the housing. A second, “retraction” spring  24 , also contained in holder  20 , provides a mechanism for removing the lancet needle from the skin after the skin has been punctured. The spring constant of retraction spring  24  is substantially less than that of drive spring  22 ; thus, drive spring  22  is substantially “stronger.” Slider  26  is slidably mounted on housing  16  and has a projection  26 A outside the housing that is manually movable—back to cock the device and forward to eject the lancet. When the device is being cocked, slider  26  engages holder  20 . Button  30  is mounted through the housing, with tab  30 A projecting inside the housing. After the device is cocked, pushing button  30  releases the restraint on lancet holder  20  to permit spring  22  to thrust the holder forward. Reference to element  30  as a “button” is not to suggest that the actuator element pictured is the only one contemplated. As used in this specification and the appended claims, “button” is to be understood as applying broadly to any actuator, of the type well known in the art, that can release the restraint on the lancet holder. 
     The operation of the lancing device can be understood with the help of a series of Figs. that show the configuration of the elements of the device in sequence during device operation. 
     FIG. 2 shows a cross section of the device at rest, with the internal part  26 B of slider  26  resting against top  28 A of releasable connector  28 . Drive spring  22  and retraction spring  24  are in balance, bearing on one another. Both springs are compressed, drive spring  22  much less than return spring  24 , because its spring constant is much larger. Lancet  40  and needle  42  are seen inside cap  12 . 
     FIG. 3 shows a cross section of the device in an intermediate position as it is in the process of being cocked, by slider  26  being moved back (to the right in FIG.  3 ). The force exerted by the backward motion of pushing element  26 C of slider  26  causes retraction spring  24  to be compressed more than in FIG.  2 . Because of its much larger spring constant, drive spring  22  remains relatively uncompressed. 
     FIG. 4 depicts the lancing device when it is in the “over-cocked” position; i.e., slider  26  has been moved to the far rearward position of its travel. Cantilever extension  44  of lancet holder  20  has moved slightly beyond (to the right of) housing stop  46 . Drive spring  22  is compressed and retraction spring  24  remains compressed to about the same degree as in FIG.  3 . 
     FIG. 5 depicts the lancing device when it is cocked and at rest. Drive spring  22  is forcing extension  44  of lancet holder  20  against housing stop  46 . Slider  26  has returned to its initial (FIG. 2) position. Retraction spring  24  is less compressed than in FIGS. 3 and 4. If button  30  is now pushed, tab  30 A pushes extension  44  free of (under) stop  46  and enables lancet holder  20  to be thrust forward (to the left) in response to the force exerted by compressed drive spring  22 . 
     That sequence leads to the instantaneous situation depicted in FIG. 6, in which lancet  40  has reached its extreme left position, with needle  42  protruding through cap opening  14 . Lancet holder  20  has been stopped in its forward (leftward) motion by protuberances on cantilever fingers  18 A, which are internal elements of knob  18 . As was discussed earlier, the cantilever fingers deflect slightly, whereby they absorb some vibration and reduce noise to reduce pain to the user. Slider  26  is still at its initial position. Drive spring  22  has been thrown forward with holder  20  and is uncompressed. Retraction spring  24  is compressed, whereby it will exert a force rearward (to the right) on holder  20 , with the result that lancet  40  and needle  42  will be retracted and the configuration of the elements will return to that shown in FIG.  2 . 
     Following a piercing operation, the used lancet must be removed from the device. FIG. 7 is a section in partial cutaway that depicts the lancet ejection when the releasable connector  28  is a cantilever latch. Cap  12  must first be removed. As slider  26  is moved forward, it pushes down the top  28 A of latch  28 , forcing teeth  50  on latch  28  to mesh with corresponding teeth  52  on holder  20 , preventing the holder from moving forward, as the pushing element  26 C of slider  26  pushes the used lancet  40  out of the device. By locking the holder in place during the process, a desirably shorter slider stroke serves to accomplish the ejection. In addition, friction between the slider and top  28 A provides desirable tactile feedback to a user during the ejection step. 
     FIG. 7A focuses on the construction of the cantilever latch  28  and its teeth  50  that engage corresponding teeth  52  on holder  20 . As shown, both sets of teeth are asymmetrical, which is preferred for the following reason. Although the device is preferably cocked by moving slider  26  back, as discussed above in connection with FIGS. 3,  4 , and  5 , it can also be cocked by pushing a fresh lancet  40  into the device after a used lancet has been ejected. In that case, the cantilever latch and holder may still have their teeth engaged, as shown in FIG.  7 A. But the asymmetric teeth will permit the holder to move back (to the right) to reach, sequentially, the positions shown in FIGS. 3,  4 , and  5 . 
     FIG. 8 shows the elements of the device when slider  26  has been pushed forward to the end of its travel, causing pushing element  26 C of slider  26  to drive the lancet (not shown) from the device. 
     Although FIGS. 7 and 7A depict a preferred releasable connector  28 , in which a cantilever latch has a cantilever arm for releasable contact with holder  20  and teeth  50  on the latch to engage teeth  52  on the holder, other embodiments of the releasable connector are also contemplated in this invention. These are depicted in a series of figs. that show focused views of the parts of the alternative releasable connectors that correspond to the parts of the cantilever latch shown in FIG.  7 A. 
     FIG. 7B depicts a connector in which the arm  128  has a pivot  128 A rather than being cantilevered. 
     FIG. 7C depicts a connector in which arm  228  is spring-loaded, supported by leaf springs  228 A and  228 B. Clearly other types of springs, such as coil springs, could be used. FIG. 7C illustrates the fact that the term “arm” is not to be interpreted as necessarily referring to an elongated element; rather, it simply identifies the element that carries the engaging mechanism. 
     FIG. 7D depicts a connector in which arm  328  is rotatably mounted on axis  328 A, spring-loaded with a torsion spring  328 B. 
     FIG. 7E depicts an embodiment in which holder  20  has a reversibly deformable surface that is deformed by connector  428  to immobilize the holder. 
     FIG. 7F depicts an embodiment in which cantilever connector  528  has a rough surface  550  that engages a rough surface  552  on the holder to immobilize the holder. 
     It will be understood by those skilled in the art that the foregoing description and figures are illustrative of practicing the present invention, but are in no way limiting. Variations of the detail presented herein may be made without departing from the scope and spirit of the present invention.