An improved method and apparatus for determining the speed and position values of a stepping motor for controlling or regulating the same. These values are derived from induced voltages within the bifilar windings of the stepping motor combined with voltages across and currents through the same bifilar...http://www.google.ca/patents/US4065708?utm_source=gb-gplus-sharePatent US4065708 - Method and apparatus for determining stepping motor parameters from induced voltages
