Patent ID: 8725440

Claim:
An apparatus ( 1 ) for processing an armature current signal (I a ) of a DC motor ( 4 ), the apparatus comprising: a measuring device ( 3 ) adapted to detect an armature current signal (I a ) and a motor voltage signal (U m ) of the DC motor; a first function module ( 10 ) adapted to determine a back-emf signal (S f ) of the DC motor ( 4 ); and a controllable frequency filter ( 2 ) comprising a control input ( 9 ), a signal input ( 5 ), and a signal output ( 15 ), wherein: a control signal (S′ f ) based on the back-emf signal (S f ) is passed to the control input ( 9 ); a filter input signal (I f ), which is derived from the armature current signal (I a ) and the motor voltage signal(U m )is passed to the signal input ( 5 );and an output signal (I r ), which is generated using a current ripple contained in the filter input signal (I f ) is adapted to be tapped off at the signal output ( 15 ).