Patent ID: 8480633

Claim:
A pump drive used to dispense a liquid drug from a container having a plunger piston, said pump drive comprising: a lead screw having a rotational axis and being operably connected to the plunger piston, wherein rotation of the lead screw about the rotational axis advances the piston plunger in a dispensing direction which dispenses the liquid drug from the container; a wheel; a unidirectional clutch provided about the rotational axis and supporting centrally the wheel, the unidirectional clutch having an inner race connected centrally to the lead screw, wherein the unidirectional clutch is configured to rotate both the inner race and lead screw about the rotational axis in unison with rotation of the wheel in only a first rotational direction, and to let the wheel rotate relative to the inner race without rotating the lead screw about the rotational axis in a second rotational direction opposite to the first rotational direction; a spring to rotate the wheel in the second rotational direction; and a plurality of shape memory alloy wires to provide the motor force when excited to rotate the wheel in at least the first rotational direction; wherein the spring is connected directly to the wheel and the plurality of shape memory alloy wires are also connected directly to the wheel.