Abstract: An electromechanical actuator includes a brushless motor driving an output shaft through a torque-amplifying geartrain. An integrated motor commutation sensor includes an annular, two-pole magnet rotating with the motor and two ratiometric Hall-effect sensors at right angles around the magnet. The sensor signals are utilized by a processor to compute motor angle over 360 degrees rotation. An integrated output position sensor includes a second annular magnet rotating with the output shaft, and a second pair of Hall-effect sensors providing signals to the processor for computation of output shaft absolute position. The commutation magnet angle is predicted from the output shaft position, and compared to the motor's sensed rotational angle. The difference is used to correct the output shaft sensed angle with improved accuracy proportional to the gear ratio. The processor also provides logic signals to control motor winding current and provide closed-loop control of actuator position.

Abstract: A contactless rotary shaft position sensor provides for precision computation of shaft angle for a wide range of input shaft rotational angles. The sensor includes two annular two-pole magnets which are connected by a precision, motion-transmitting gear train. An optional second gear train between one of the magnets and the input shaft can provide additional angular rotation scaling to accurately measure either fractional or a large number of multiple turns of the input shaft. The gear ratios are selected such that one of the magnets does not rotate more than one revolution. Pairs of ratiometric Hall-effect or magnetoresistive sensors provide differential voltage signals which are used for sensing angular position of each magnet over a full 360 degrees of rotation. The single-turn magnet provides an absolute, coarse indication of input shaft rotation with a typical accuracy of 2%. The gear ratio between the magnets produces several turns of the second magnet for each turn of the single-turn magnet.