Automatic lancet

A lancet device which comprises:

• a housing;
• a movable arm pivoted in the housing for rotation about a pivot therein through a limited angle;
• a holder at one end of the arm remote from the pivot, the holder being adapted to receive a replaceable mounted lancet needle and to hold the latter by its mounting pointing in the tangential direction;
• spring means acting on the arm to bias it angularly for rotation about its pivot from a retracted position towards an operative position in which the point of a mounted lancet needle carried in the holder will be exposed projecting forwardly for a pricking operation;
• and
• releasable latch means for holding the arm in the said retracted position against the force of the said spring means;
• said latch means including a manually-operable trigger for releasing said latch means, whereby on release of said latch means the arm will be urged forwardly by said spring means to rotate into its operative position to perform a pricking operation;
• said spring means having a characteristic such that the resultant biasing torque which it exerts on the arm reduces progressively in magnitude as the arm rotates from its retracted position towards its operative position until the arm reaches a neutral position shortly before its operative position, the resultant biasing torque reaching zero in said neutral position of the arm and thereafter reversing in angular direction to increase progressively as the arm is carried by inertia towards its operative position against the reversed biasing torque, whereby the said spring means will tend to retract the arm from its operative position towards and into its neutral position so that the tip of the needle is automatically withdrawn after a pricking operation.