Patent ID: 7785293

Claim:
A drive mechanism for delivery of infusion medium comprising: an inlet for receiving infusion medium; an outlet for discharging infusion medium; a piston channel through which infusion medium is communicated between the inlet and the outlet; a piston located within the piston channel to define a fluid flow path between the inlet and outlet, the piston being moveable axially within the piston channel between a retracted position and a forward position to drive infusion medium toward the outlet, the piston comprising a magnetically permeable material, an armature located on one side of the piston channel and moveable between a retracted position and a forward position; a coil located in a position relative to the armature to generate an electromagnetic field upon energization sufficient to cause the armature and piston to move from their retracted positions to their forward positions; and a magnet arranged relative to at least one of the armature and the piston to impart a force on the piston sufficient to move the piston from the forward position to the retracted position upon deenergization of the coil; wherein the armature is arranged between the magnet and the piston and includes a first section free of magnetically permeable material through which magnetic flux from the magnet passes to the piston in a path that is free of magnetically permeable material from the magnet to the piston.