Patent ID: 7800321

Claim:
A method for the detection of the rotational position of the rotor of a DC motor with commutator by evaluating the time development of a rotor current signal of the DC motor, said signal comprising a periodic waviness around an average value and comprising current ripples generated by commutation which are superimposed to said waviness, wherein the rotor current signal of a current ripple detector unit ( 30 ) is supplied for detecting the current ripples of the rotor current signal, the rotor current signal is further supplied to a waviness detector unit ( 34 ) for detecting a half or full wave of the rotor current signal, for each detected current ripple, a current ripple pulse is output by the current ripple detector unit ( 30 ), for each period of the waviness, a waviness pulse is output by the waviness detector unit ( 34 ), and the output signals of both of said detector units ( 30 , 34 ) are supplied to a logic OR unit ( 38 ) for generating a logic signal, within a period of the rotor current signal, a pulse is output by at least one of said detector units ( 30 , 34 ) whereby said logic signal comprises a logic pulse for each period of the rotor current signal.