Relating to skin prickers

A skin pricker has a body (1) with a spring-loaded lancet holder (4) with a forward facing socket (20) to receive the rear end of a lancet. The socket (20) is radially expandable/compressible and the spring-loading is a coil spring (5) part of which embraces the socket and tends to close it up. This allows lancets of slightly varying diameters to be firmly held. The pricker is primed by pressing a lancet into the socket (20), which urges the holder (4) back to be releasably held by a trigger mechanism (3, 9).

This invention relates to skin prickers. 
A small blood sample is required for analysis or testing in many medical 
situations. Often, it is left to the patient to draw his own sample and 
carry out his own test on home use equipment, and many lancet devices have 
been devised to make the procedure simple, safe and as painless as 
possible. Commonly, there is a firing mechanism which can be used many 
times, but at each use it has to be loaded with a fresh lancet, which is 
thrown away once the sample has been taken. There are obvious dangers in 
reusing a lancet. 
To be throwaway items, the lancets have to be cheap. The usual form is a 
needle encased in a generally cylindrical plastics body, leaving just the 
tip exposed when an integrally moulded tear-off cap is removed. Such 
lancets, although they may conform to this general pattern, are not 
uniformly sized, and there can even be differences in a batch from the 
same manufacturer. 
A common way of holding the lancet in the firing device is to press its 
rear end into a socket at the forward end of a spring loaded holder which 
is released by a trigger mechanism. The press fit should hold the lancet 
secure during use, but due to the variations in size mentioned above, this 
is not always the case. Sometimes the lancets are loose, and sometimes 
they are too large to be pressed into the sockets, at least not without 
damage or permanent distension. 
It is the aim of this invention to provide a simple skin pricker which can 
accommodate to variations in lancet size. 
According to the present invention there is provided a skin pricker having 
a body containing a spring loaded lancet carrier releasable from a 
rearward position to cause the lancet tip to project momentarily from the 
leading end of the body, wherein the lancet carrier has a forwardly open 
socket into which the rear end of a lancet is plugged, and wherein the 
spring loading is a coil spring part of which embraces the socket normally 
to constrict it to a minimum diameter but which allows the socket to 
expand to receive the rear end of a lancet with a diameter greater than 
said minimum. 
Thus, a lancet can be pressed into the socket and it will expand as 
necessary to accommodate it, the spring ensuring that it retains a firm 
grip. The mouth of the socket may be flared to ease entry and generate the 
initial expansion. 
In one preferred form the socket has a longitudinal split from mouth to 
base, and at the base on either side of this split the socket wall is cut 
away circumferentially so that there are two wings which can spread to 
widen the split. There may be more than one such split around the 
circumference of the socket. 
The lancet carrier preferably has a portion extending rearwardly of the 
socket with a detent for retention by a release mechanism when the carrier 
is moved to its rearward position. This release mechanism may include two 
rearwardly projecting figures internal of the body and flanking said 
portion to co-operate with opposed detents, and a pressure element at the 
rear of the body to co-operate with the fingers and, when pressed, to 
spread them to disengage the detents. 
The lancet carrier will generally be of moulded plastics, in which case 
said portion may have forwardly and outwardly projecting fingers which 
form spring elements that co-operate with an abutment internal of the body 
to cushion the end of the forward stroke of the lancet carrier and promote 
the return of the lancet tip within the body. The rear end of the coil 
spring conveniently acts against the forward side of said abutment.

The main components of the skin pricker are a generally box section body 1, 
a cap 2 which fits the forward end of the body, a pressure member 3 which 
fits the rear end of the body, a lancet holder 4 within the body, and a 
spring 5. 
The body 1 is of box section from its leading end to a bulkhead 6 having a 
central aperture 7. To the rear of that two opposed faces extend in 
parallel wings 8 while the other two faces stop short at the bulkhead 6. 
On either side of the aperture 7 two fingers 9 extend rearwardly parallel 
to and inside the wings 8, and on the inside these fingers have teeth 10 
near their rear ends and teeth 11 adjacent their roots. Beyond the teeth 
10, the inside surfaces 12 of the fingers flare outwardly. Forward of the 
bulkhead 6, two opposed inside faces of the body 1 have longitudinal ribs 
forming guide channels 13. 
The cap 2 is externally ribbed at 14 for grip and has an aperture 15 at its 
leading end through which the tip of a lancet will be projected. It is a 
close fit over an external rebate at the leading end of the body 1, and 
internally two opposite sides of the cap 2 have ribs 16 which snap into 
grooves in that rebate. The cap is therefore secure enough for use, but 
can be pulled off and pressed on when exchanging lancets. 
The pressure member 3 is generally U-shaped and its side limbs 17 
substantially fill the spaces between the edges of the wings 8, which are 
stepped positively to retain the pressure member 3 to the body, but 
allowing it limited longitudinal movement. Internally, the base of the 
member 3 has a cup 18 which can freely receive the rear end of the lancet 
holder 4 and whose rim co-operates with the flared surfaces 12 of the 
fingers 9. At opposite sides, the cup is extended by two forwardly 
projecting fingers 19. 
The lancet holder 4, which can be seen separately, with its spring, in 
FIGS. 5 and 6 is approximately of wine glass shape. At the forward end, 
the "bowl" is a generally cylindrical socket 20 provided externally at 
about its mid-length with a circumferential rib 21 having diametrically 
opposed projecting lugs 22. These guide the holder 4 by engaging in the 
channels 13. The socket has a longitudinal split 23 from mouth to base, 
and adjacent the base 24 the walls are circumferentially cut away at 25 in 
both directions, forming wings on either side of the split 23. The mouth 
of the socket is internally flared as shown at 26 in FIG. 6. 
The stem 27 terminates at the rear end in two opposed lateral teeth 29 
alternating around the stem with two opposed fingers 30 extending 
forwardly and outwardly. The holder 4 is of plastics material and the 
fingers are thin enough to have resilience and act as springs. 
The main coil spring 5 encircles the stem 28 and the rear portion of the 
socket 20, to bear against the rib 21. But it does more than just bear 
against this rib; its final turn squeezes the socket normally to keep the 
split 23 closed up. This assembly is then entered into the body 1 from the 
forward end, and the fingers 30 close up to the stem 28 to allow the rear 
end to squeeze through the aperture 7. The fingers 30 then spread out 
again and the spring 5 is left bearing against the forward side of the 
bulkhead 6. The teeth 29 can snap past the teeth 11 and 10 to the position 
of FIG. 3, where the device is primed. This final motion may be achieved 
when plugging the rear end of a lancet into the socket 19, which spreads 
as necessary to receive the lancet. The lancet will be of the usual 
generally cylindrical form, with a plastics body encasing a steel needle. 
Initial entry is eased by the flare 26, while the coil spring 5 ensures 
that the grip is firm. The fingers 19, by co-operating with the fingers 
30, keep the lancet holder from tilting in the plane of FIG. 4, while any 
tendency to tilt at right angles to this is prevented by the fingers 9. 
For firing the device, the pressure member 3 is urged forwards, and the cup 
18 spreads the fingers 9 by acting on the surfaces 12. The teeth 10 then 
release the teeth 29 and the lancet holder 4 shoots forward briefly to 
project the needle tip. The ends of the fingers 30 hit the bulkhead 6 and 
spread. A definite limit on the forward movement is imposed by the teeth 
29 meeting the teeth 11, which will not have been parted to any 
significant degree by the pressure member 3. The fingers 30 then recover 
to pull the holder 4 back to retract the needle tip inwards from the 
aperture 15. The cap 2 can then be removed and the lancet unplugged simply 
by pulling it away from the socket 20. The device is then ready to receive 
a fresh lancet.