example by a spur gear reduction set a worm gear and the likes with or without a ratcheting pawl or other suitable clutching arrangement the retainer 74 in this embodiment serves to constrain the leas screw 30 via restraining the gears of the connection 89 from translating along the rotational axis x as the lead screw 30 is rotated accordingly as the motor 12 is activated the shaft 22 outputs only rotary motion which causes the nut 58 to advance along the lead screw 30 thereby advancing the piston 64 and dispensing liquid drug from the container 66 in the illustrated embodiment shown by fig5 an encoder wheel 82 provided with markings or other features is mounted to the shaft 22 and read by an adjacent encoder 84 in this manner the encoder 84 tracks the revolutions of the shaft 22 and hence movement of nut 58 and provides the controller 16 with the revolution information such that the motor 12 is regulated to dispense only a desired amount of the drug from the container 66 in other pump drive embodiments the encoder wheel 82 or markings and encoder 84 may be placed on and provided adjacent respectively any other moving component of the infusion pump 28 which can provide an indication of the amount of liquid drug dispensed from the container 66 such as for example the motor body 24 the lead screw 30 a component of connection.