Blood lancet device
The present invention is concerned with blood letting devices and more particularly with finger pricking devices using disposable blades for repeated samplings of capillary blood for home use with minimal pain and injury to the patient. 
     In the treatment of diabetes with insulin, it is generally agreed that the serious complications of the disease are prevented or delayed by careful control of the blood sugar level. Effective control of the blood sugar level often requires monitoring or measuring the concentration of blood sugar by repeated samplings. There are simple blood sugar measuring devices for patient use that simply involve placing a small portion of blood on a thin membrane strip and comparing color developed to a standard chart. There are such problems with obtaining the small samples of blood that fewer than one-fifth of the diabetics routinely monitor their blood sugar. The result is that most diabetics fail to maintain their blood sugar levels within the range that will be most effective. 
     The biggest drawback to routinely drawing small blood samples is the pain inflicted by the currently available lancets or finger-sticking devices. The most favored site of sampling is the rich capillary bed of the skin of the finger tip which readily yields a drop of blood from a small cut. The finger tip is also rich in pain receptors, and the pain is increased when the incision is too deep, or is too close to a recent incision, or is not deep enough requiring an additional incision. Furthermore the pain may be increased if the cutting blade penetrates slowly or is withdrawn slowly. Furthermore, the user may be forced to make a larger incision than is necessary in order to get a drop of blood to form for transfer to the measuring strip. 
     SUMMARY OF THE INVENTION 
     It is, accordingly, an object of the invention to provide a blood letting device employing a replaceable and disposable blade with a stabbing or blade advancing and retracting means that carefully controls the depth of penetration and automatically advances and retracts the blade in a minimum of time for reduced pain. 
     It is a further object to provide the device as described that carefully locates the site of incision and ensures that subsequent incisions will be made at other locations on the finger tip. 
     It is yet another object of the invention to provide the device as described with a volumetric blood collecting means so that the user will be assured that the volume of blood necessary for the measurement has been collected in a form most convenient for measurement. 
     The blood lancet device of the invention comprises a finger positioning ring that fits on the fingertip with a locating arm that extends over the fingernail. An assembly carrier is rotatably attached to the end of the ring with a spring loaded detent with four click-stops so that the assembly carrier can be positioned to four different orientations. The locating arm on the finger positioning ring enables the user to position the device to the same location on the finger, and by rotating the assembly carrier to the next orientation, the incision is automatically made at a new site, thereby reducing discomfort. A lancet assembly fits within the assembly carrier. The lancet assembly has a blade holder for conveniently removing and installing disposable skin incising blades. The blade holder has a blade advancing and retracting mechanism that is powered by a cocked spring. When a pushbutton is depressed, the mechanism advances the blade holder and blade a fixed distance and promptly retracts it in a very fast motion provided by a rotary to translatory mechanism. The lancet assembly moves axially within the assembly carrier, and a skin surface sensor at the end of the assembly positions the assembly a fixed distance above the skin surface so that the blade will penetrate a controlled depth through the skin regardless of the curvature of the finger tip or the click-stop position. The skin surface sensor may be adjustable to change the depth of penetration of the blade. 
     These and other objects, advantages and features of the invention will become more fully apparent when the following detailed description of the preferred embodiment of the invention is read in conjunction with the accompanying drawings. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a side elevation of the device in place on a fingertip with portions broken away to show internal structure. 
     FIG. 2 is a cross sectional view taken through plane 2--2 of FIG. 1. 
     FIG. 3 is a longitudinal section through the device. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Referring now first to FIG. 1, an index position for reproducibly positioning the lancet device 6 on the finger 1 is the point 5 where the lateral edge 3 of the fingernail meets the cuticle 4. A transparent finger-positioning ring 7 has a locating arm 9 with markings 10 for reproducibly positioning the device 6 relative to finger 1 by always setting a mark 10 at the point 5. An assembly carrier 11 is rotatably attached to finger-positioning ring 7 with a spring loaded detent 12 providing four click stops much like the aperture settings on a camera so that assembly carrier 11 may be rotated to any one of four positions relative to the finger 1, as indicated by blades 36 shown in phantom in FIG. 2. 
     Within the assembly carrier 11 is the lancet assembly 13 that is axially slidable within the assembly carrier. A soft compression spring 14 gently urges the bottom 16 of lancet assembly 13 against the skin surface. A skin surface sensor 15 mounted on end 16 of the lancet assembly holds the lancet assembly and the blade a fixed distance above the skin surface. The sensor 15 is very close to the point of the lancet blade 17 so that the distance of the point above the skin surface is automatically set regardless of the curvature of the finger tip or the click-stop setting. 
     A pushbutton 19 on the side of the assembly carrier 11 fires the spring loaded blade 17 which rapidly moves downward below the bottom edge 16 of lancet assembly 13 a fixed distance and then retracts. The motion is very fast through a powerful spring to reduce pain. 
     FIGS. 2 and 3 show further details of construction. The skin surface sensor 15 may be a small socket head screw that may be adjusted to increase or decrease the effective depth of penetration of the blade 17 in its motion. The blade 17 has two holes in its shank portion that engages two pins 20 fixed to blade holder 21. A pair of permanent magnets 22 mounted on blade holder 21 hold the blade 17 in place after it is slipped onto the two pins so that installing a fresh blade is very easy. A push pin 23 mounted on holder 21 opposite to pins 20 is pushed in to force a used blade away from the magnets 22 and off holding pins 20 to discard a used blade without touching it. A spring catch 24 limits the downward motion of lancet assembly 13 within the assembly carrier 11. To change blades, the catch 24 is pressed with the device 6 held vertically and the assembly will move out far enough to expose the blade carrier to permit changing the blade. After a new blade is installed, the assembly 13 may be retracted into carrier 11 by inverting it and striking the end against a hard surface. The blade advancing and retracting mechanism includes a rotary wheel 25 connected to a spiral spring 26 that is always partially wound. The wheel 25 rotates on axle 27 affixed to the lancet assembly 13, a connecting rod 29 connects the outer edge of wheel 25 to the blade carrier 21, which is restricted to axial movement by rollers 30. A winding handle 31 on the opposite side of wheel 25 (shown in phantom in FIG. 3) is turned through 180 degrees to increase spring tension and springy catch 32 holds the wheel in this cocked position until pushbutton 19 is pressed to release it. Rotation is stopped at stop 35 after 180 degrees of rotation. Note that axial movement of lancet assembly 13 within assembly carrier 11 doesn&#39;t affect the pushbutton operation. 
     A glass capillary tube 33 with an exact inside diameter and length is snapped into spring fingers 34 mounted on the side of assembly carrier 11. It is available in this convenient location for aspirating by capillarity the exact volume of blood necessary to fill it. The capillary dimensions are selected to provide the exact volume of blood required for the measurement. This ensures optimum test conditions and avoids trying to get more blood than is necessary. 
     The above disclosed invention has a number of particular features which should preferably be employed in combination although each is useful separately without departure from the scope of the invention. While I have shown and described the preferred embodiments of my invention, it will be understood that the invention may be embodied otherwise than as herein specifically illustrated or described, and that certain changes in the form and arrangement of parts and the specific manner of practicing the invention may be made within the underlying idea or principles of the invention within the scope of the appended claims.