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Abstract

The present invention concerns a drug delivery device with an electric brushless DC or stepper motor. A novel approach to motor control uses the micro-stepping technique in combination with over-revving the commutation of the stepper motor and reversing the rotor for a small number of microsteps with each delivery cycle. This approach has the effect of keeping the elasticity of the drive train behind the plunger in a relaxed state after completing a delivery cycle, providing better control of the movement of the rotor. Loss of steps can be avoided for a wide range of friction or speed situations, increasing the accuracy of drug delivery and making tracking of the rotor position and detecting loss of steps a much better parameter to detect blockage or occlusion. The increased controllability allows to substantially increase the motor speed for delivery, resulting in an optimum of energy efficiency while still ensuring reliable operation.

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First Claim