Patent ID: 7058537

Claim:
A method for ascertaining an rpm of a drive mechanism ( 1 ) comprising an electric motor, in which a position transducer ( 2 , 3 , 4 ) is provided which is disposed in a fixed angular position relative to a rotation of the drive mechanism, in which the position transducer ( 2 , 3 , 4 ) outputs a position signal when the drive mechanism is in a fixed angular position, and in which the position signal is carried to a control unit ( 5 ), the control unit ( 5 ), from the chronological spacing of the position signals, calculates an rpm of the drive mechanism ( 1 ) using an internal timer ( 33 ); within a time frame that is defined by a position signal a new position signal is expected by the control unit ( 5 ); the time since last the position signal is measured by the control unit ( 5 ) using a time counter ( 6 ); if the position signal continues to be absent, an rpm of the drive mechanism ( 1 ) is ascertained by the control unit ( 5 ) on the basis of the counter state of the time counter ( 6 ).