Patent ID: 7301300

Claim:
A method for operating stepper motors, comprising a first operational mode for a normal motor operation in which an alternating current (I L ) is impressed into at least one of the coils (L) of the stepper motor, and a second operational mode for detecting a reference position of the stepper motor from an increase of the load caused by driving the stepper motor against a mechanical stop, by comparing the level of a measuring current (I S,EMK ) flowing in the coil (L), with at least one lower threshold value, wherein the level of the measuring current (I S,EMK ) is determined substantially by the phase of a voltage (U EMK ) which is counter induced by a rotor of the motor in the coil (L), wherein the reference position is set and defined, respectively, when the measuring current (I S,EMK ) becomes smaller than the lower threshold value, and wherein the second operational mode for the coil (L) is activated during a time window (Z) of the first operational mode either by short-circuiting the coil (L) when the alternating current (I L ) impressed into the coil (L) approaches a zero crossing, or by reversing the polarity of the alternating current (I L ) impressed into the coil.