Patent ID: 8377004

Claim:
A method for dispensing a liquid drug from a drug container having a piston, said method comprising: providing a lead screw having a rotational axis and operably connected to the piston; providing a ratchet wheel along the rotational axis and operably connected to the lead screw to move the lead screw; providing a piezoelectric motor having a shaft, a nut engaging the shaft, and piezoelectric elements configured to produce reciprocating linear motion of the shaft relative to the nut adjacent the rotational axis, wherein the shaft of the piezoelectric motor is situated parallel to the rotational axis and is connected to a slider; providing a pawl operably connected to the shaft and engaging the ratchet wheel such that the reciprocating linear motion of the shaft is converted into unidirectional rotary motion of the ratcheted wheel about the rotational axis which moves the lead screw, wherein moving the lead screw advances the piston dispensing the liquid drug from the drug container; and providing a cam rotatably mounted about the rotational axis, the cam having a slot having at least a portion thereof provided at an angle to the rotational axis, the slider having a portion slidably mounted in the slot of the cam, and wherein the pawl has an end fixed to the cam.