System for measuring the angle of rotation

A method for measuring the angle of rotation in order to determine the absolute angular position of the shaft of an electromotor, with a device for measuring the angle of rotation which is connected via an electric interface to a control unit, which device for measuring the angle of rotation transmits a sine-cosine signal pair dependent on the angle of rotation with a high number of periods per revolution via an analog process data channel of the interface to the control unit for the motor control and in which a signal reproducing a reference angular position with a high degree of accuracy is transferred via a digital parameter channel of the interface from the device for measuring the angle of rotation to the control unit and further information is transferred via said digital parameter channel in both directions between the device for measuring the angle of rotation and the control unit, the method comprising the steps of:

• initially determining an absolute angular position with a degree of accuracy sufficient for the starting commutation of the electromotor by using a sine-cosine signal pair with a number of periods per revolution corresponding at most to the number of pole pairs of the electromotor;
• determining a more accurate angular position using a sine-cosine signal pair with a high number of periods per revolution of the shaft of the electromotor;
• correcting the more absolute angular position using a synchronizing signal generated by using index marks which indicate an absolute angle of rotation of the shaft of the electromotor whose number corresponds to the number of periods of the sine-cosine signal pair for the initial determination of the absolute angular position.