Patent ID: 8222843

Claim:
A method for determining the angle of rotation of a rotor of a mechanically commutated direct current (DC) servo motor, which is arranged in the shunt arm of a bridge circuit and whose armature current is preset by an electromechanically actuated switching device having at least one switching contact, comprising: analyzing the current ripple present in the armature current and attributable to the mechanical commutation by a control and analysis unit, initiating a switching operation of at least one of the switching contacts to start, brake, or reverse operation of the motor, wherein the switching operation of the at least one switching contact causes a switching contact vibration time interval during which the armature current is disturbed, sending a switching contact voltage feedback signal to the control and analysis unit via a feedback circuit from each of the at least one switching contact of the switching device, and determining by the control and analysis unit a start time and an end time of the switching contact vibration time interval caused by the switching operation of the at least one switching contact using the at least one switching contact voltage feedback signal, counting the current ripple for a duration leading up to and stopping at the determined start point of the switching contact vibration time interval, and again for a duration starting at the determined end point of the switching contact vibration time interval, but not for the duration during the switching contact vibration time interval, and estimating the current ripple during the switching contact vibration time interval, based at least on the determined start point and end point of the switching contact vibration time interval.