Patent ID: 7771392

Claim:
A drive system used to dispense a liquid drug from a drug container having a plunger, said drive system comprising: a lead screw having a rotational axis and operably connected to the plunger; a ratcheting mechanism having first and second ratchet wheels provided along the rotational axis, said first ratchet wheel is connected to the lead screw to move the lead screw; and a shape memory alloy wire operably connected to the second ratchet wheel and configured to drive incrementally the rotation of the second ratchet wheel via a contraction, which in turn drives the rotation of the first ratchet wheel about the rotational axis which moves the lead screw and advances the plunger to dispense the liquid drug from the drug container, and wherein the first and second ratchet wheels provide two opposing ratcheting surfaces with facing axially extended teeth which are spring biased axially for proper engagement via a torsion spring, wherein the torsion spring is also used to reset the shape memory alloy wire after the contraction driving incrementally the rotation of the second ratchet wheel.