Abstract:
A skin pricker has a barrel ( 1,11 ) in which a hammer ( 2,29 ) released by a trigger mechanism ( 32,34 ) can be shot forwards by a compressed spring ( 3,38 ) to impact on a lancet ( 24 ) and momentarily project its tip. The rear end of the spring acts against a barrier ( 4,39 ) adjustable axially of the barrel, so that the spring can be more or less compressed before release, causing the hammer to act with greater or lesser force on the lancet. The barrier ( 4,39 ) may have projections ( 6,8,42 ) that engage in skew slots ( 7,9,43 ) in the barrel, so that rotation of the barrier axially adjusts it. A sleeve ( 44 ) over the rear part of the barrel instrumental in priming the device may co-operate with the projections and be rotatable to set the desired spring force.

Description:
BACKGROUND OF THE INVENTION 
   This invention relates to medical skin piercing devices. 
   DESCRIPTION OF THE RELATED ART 
   Many skin prickers have a spring-operated mechanism that projects the tip of a lancet from a leading end of a barrel. The device is held against the user&#39;s skin and “fired”. 
   Usually the springs have a set rate and the force with which the lancet is urged forwards is always the same for the particular device in question. But that is not ideal. 
   For example some skins can be very tough, while others, particularly of infants, can be very soft and easily pierced. Therefore it is desirable to have available devices which can cope with such variations. 
   SUMMARY OF THE INVENTION 
   According to the present invention, there is provided a medical skin piercing device comprising a barrel, means for carrying a lancet in the forward part of the barrel to allow the tip of the lancet to advance from a retracted to a projection position, a hammer arranged when released from a rearward position to act on the rear of the lancet to cause such advance, a barrier to the rear of the hammer and adjustable axially within the barrel by cam action as a result of rotation, a spring acting between the barrier and the hammer, and a trigger mechanism for holding the hammer in, and releasing it from, said rearward position with the spring compressed to a degree determined by the axial adjustment of the barrier. 
   Conveniently, the barrel has slots skew to the axis of the barrel in which projections on the barrier engage. The slots may have short portions non-skew to said axis to locate the projections in set positions. These projections may be on resilient formations integral with the barrier, allowing the projections to be moved radially inwards for insertion of the barrier into the barrel, the projections springing outwardly when they register with the slots. 
   Preferably, the rear portion of the barrel is encased by a captive sleeve spring urged forwardly, the sleeve having a lost motion connection through the rear end of the barrel and through the barrier to the hammer, whereby pulling back the sleeve retracts the hammer to said rearward position, and release of the sleeve allows the sleeve to revert to its forward position disconnected from the hammer. 
   The sleeve when pulled back may reveal the slots for adjustment of the projections in the slots, but preferably it will co-operate with at least one said projection and be rotatable to adjust the barrier. 
   A nose section of the barrel will conveniently be removable to expose the lancet carrying means and allow lancets to be removed and replaced. These lancet carrying means may be a generally tubular member with limited axial movement, into which a lancet fits from the forward end and spring urged rearwardly normally to maintain a lancet tip retracted. 
   To avoid handling a lancet after use, an ejector rod can extend lengthwise of the barrel through the barrier and the hammer and be movable forwards to eject a lancet from the carrying means when the nose section is removed. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     For a better understanding of the invention some embodiments will now be described, by way of example, with reference to the accompanying drawings, in which: 
       FIG. 1  is a diagrammatic side view, partly in section and partly in ghost, of a device for adjusting the penetration force of a medical needle or lancet, set to a maximum, 
       FIG. 2  is a cross-section on the line II-II of  FIG. 1 , 
       FIG. 3  is a side view similar to  FIG. 1  but with the device set to a minimum, 
       FIG. 4  is a cross-section on the line IV-IV of  FIG. 3 , 
       FIG. 5  is a development of a curved slot in the barrel of the device. 
       FIG. 6  is a side view of a skin pricker, 
       FIG. 7  is a longitudinal section of the skin pricker, on the line VII-VII of  FIG. 6 , 
       FIG. 8  is a perspective view of a spring force adjuster forming part of the pricker of  FIG. 6 , and 
       FIG. 9  is a longitudinal section of the rear portion of the pricker of  FIG. 6 , the sectional plane being at right angles to that of  FIG. 7 . 
   

   DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
   The device of  FIG. 1  has a barrel  1  with a hammer  2  loosely plugging its forward end and urged forwards by a spring  3 . There is a trigger mechanism (not shown) which holds the hammer  2  in the cocked position shown. The spring  3  reacts against an axially adjustable barrier  4  towards the rear end and when the trigger is operated it shoots the released hammer  2  forwards. 
   The barrier  4  is of thick, disc-like form with a protuberance  5  on its forward side around which the spring locates. The cylindrical surface of the disc, of a radius slightly less than the inner radius of the barrel, has two diametrically opposed projections, one being a cam  6  which projects into a part-helical slot  7  in the barrel and the other being a small stud  8  which co-operates with a part-helical slot  9  complementary to the slot  7 . 
   The slots  7  and  9  are not smooth sided over their whole lengths. At their ends and at their mid-points they divert into flats  10  normal rather than skew to the axis of the barrel. This enables the cam  6  and stud  8  to locate stably at three set positions, the extreme ones being shown in  FIGS. 1 to 4  and the intermediate one in  FIG. 5 . It would be possible to have more than one intermediate position. 
   The barrel  1  is of moulded plastics, giving some elasticity and resilience. This enables the barrier  4  to be pressed into place through the rear end of the barrel. 
   It may be convenient to push it in aslant, with the cam  6  leading, and skew to correspond to the angle of the slot  7 . 
   Then the cam  6  can be worked up, with the adjacent portion of the barrier  4 , into the slot  7 , followed by the portion adjacent the stud  8  being pushed until the stud registers with the slot  9 . The barrier is then manipulated until it is co-axial with the barrel  1 . It will be kept substantially square on to the axis by the spring  3 , by the cam  6  in the slot  7  and the stud  8  in the slot  9 , and by the cooperation of its cylindrical end surface with the inner surface of the barrel (which will have reverted to its proper shape following any distortion suffered as a result of inserting the barrier). 
   The cam  6  is accessible, and the user can shift it along the slot  7  to cause the barrier  4  to increase or decrease the compression of the spring  3 . When the barrier is forwards, as in  FIG. 1 , there is maximum initial compression, and the hammer  2  is propelled forwards with maximum force. Correspondingly, when the barrier is rearwards, as in  FIG. 3 , the hammer is propelled forwards with lesser force. 
   A practical example is shown in  FIGS. 6 to 9  in which a skin pricker has a cylindrical barrel  11  with a reduced forward end portion  12  over which fits a connecting collar  13 , screwing to the barrel at shoulder  14 . A nose piece  15  attaches to the collar  13 , being fitted over a reduced forward end portion  16  before being trapped by a non-return formation. But although captive, it can still be rotated, using grip  17 , to adjust its axial position within limits. 
   An internal ring  18  determines this, and thereby controls the amount by which a lancet tip will project through aperture  19 . 
   The barrel portion  12  receives and guides a tubular lancet holder  20  whose rear out-turned rim  21  is initially held back from the shoulder  14  by a light spring  22 . At about its mid-length the holder has shallow internal projections  23  which retain a lancet  24  snapped in from the front end, and more pronounced external barbs  25  which snap into slots  26  in the portion  12  from the rear, allowing limited axial travel of the holder  20 . Initially, the tip of the lancet  24  is retracted within the nose piece  15 . 
   An ejector rod  27  extends co-axially through the barrel and beyond to the rear, and when the collar  13 , with the nose piece  15 , is removed it can be pressed by rear end knob  28  to snap the lancet forwardly out of the holder  20 . 
   A hammer  29  has a generally cylindrical hollow body through which the rod  27  freely passes, and with a cylindrical spigot at its forward end around which snaps a rubber ring  30 . When released, this will hit the rim  21  to drive the holder  20  and thus the lancet forwards. This ring device serves as a damper and the rubber ensures virtually silent operation. A narrow U-shaped slot in the cylindrical wall of the hammer forms a flexible finger  31  which, at its free forward end, has an outwardly projecting stud  32  engaged in a slot  33  in the barrel. This is part of a trigger mechanism, whose other part is an oval button  34  mounted over this region of the barrel and with an inner projection  35  that co-operates with the stud  32 . Pressure on the button flexes the finger  31  in to release the stud  32  from the slot  33  and allows the hammer to shoot forwards. 
   The finger  31  can almost immediately recover its original attitude with the stud  32  entering another slot  36 . 
   At its rear end, the hammer  29  has a short cylindrical extension  37  which locates the forward end of a helical drive spring  38 , whose rear end reacts against a force adjuster  39 . 
   The force adjuster is best seen in  FIG. 8 . It has a cylindrical plastics body  40 , through which the rod  27  will freely pass, and on the outside of that two diametrically opposed integral loops  41  of arcuate form, each subtending an angle of about 90°. The outer surfaces of the loops are of a radius corresponding to the interior of the barrel  11  but the loops are thin enough to be deformed radially inwards, to allow outwardly projecting studs  42  at the centres of those outer surfaces to be depressed sufficiently to enable the adjuster to be entered into the rear of the barrel. When the studs reach opposed inclined slots  43  in the barrel the loops  41  spring outwards, and the studs are captive. 
   A sleeve  44  sheaths the rear end of the barrel  11  and provides at its rear end a guide slot  45  for the knob  28  of the rod  27 . 
   The sleeve  44  is made from two substantially semicylindrical halves, one half  46  having at its leading end a recess  47  matching in shape the rear part of a low wall  48  proud of the barrel  11  and closely surrounding the trigger button  34 . The sleeve  44  is urged forwardly by a helical spring  49  around the barrel, acting between a rear end flange  50  on the barrel and an annular rib  51  internal of the sleeve. Normally, the spring  49  causes the sleeve  44  to be located with the wall  48  nesting in the recess  47 . 
   The ejector rod  27  is reduced to semi-circular cross-section over much of its length and along this portion lies a complementarily shaped, shorter, loading rod  52  with a certain freedom of axial movement relative to the rod  27 . 
   This has a rear end head  53  which is trapped by internal webs  54  of the sleeve  44  and it passes through the force adjuster  39  into the hammer  29 , where barbs or spring fingers engage the rear wall of the hammer. Initially, both the hammer  29  and the sleeve  44  are in their forward positions. But once the lancet has been loaded, the sleeve  44  is pulled back, and the loading rod  52 , drawn by its head  53 , pulls back the hammer  29 , the stud  32  being temporarily pressed inwards by the bridge between the slots  33  and  36 . 
   Then the hammer is trapped in its rearward ready-to-fire position and the sleeve  44  can be allowed to spring forwards, taking the rod  52  with it and freeing the hammer  29  for forward movement. 
   When the sleeve  44  is in its rearward position, it can be rotated to operate the force adjuster  39 , being turned one way to move the adjuster forwards and increase the initial spring force, and the other way to move the adjuster rearwardly and reduce that initial force. At least one of the studs  42  will be proud of the barrel  11  and can be positively engaged by a formation within the forward end of the sleeve, behind inturned rib  51 . The amount of force adjustment can be gauged by the amount of rotation. Once the sleeve is released to spring forwards, it is guided into its original alignment by the recess  47  meeting the wall  48 . 
   The sleeve  44  could be arranged to expose at least one of the studs  42 , so that the user could directly manipulate the force adjuster. But that might prove awkward in practice. 
   In these figures the slots in the barrel are shown without flats, but their angle is such that the studs will remain where positioned by friction. But flats could be provided if desired.