Zapi EPS-AC0 SWs&ENC User Manual page 19

4.5.1.2 Feedback Encoder
One big advantage of our eps-ac0 controller is that it can work with a cost-effective
very low-resolution encoder. Our competitors normally need a sensor bearing with
32 or higher pulses/rev; our eps-ac0 works also with a cheap encoder having 4
pulses/rev. That is more than enough for the angle measurement: in fact, with a total
reduction of 1:200 and a 4 pulses/revs resolution, we have 1600 events (encoder
transitions) within 180° of the steered angle. So the angle measurement is
determined with quanta of 180/1600=0.112 degrees. This is possible because our
patent system does not use the encoder for the AC motor control; it works
completely sensorless.
Following this statement, we have developed, together with a Zapi's partner AC-
motor-manufacturer, a 4 pulses/rev discrete encoder. It is an external device (not
integrated in the ball bearing) mounted in the backside of the motor (see Figure 4-5
below showing a 300 W AC Motor by "Best Motor" brand). The advantages of this
solution are both, money saving and effective time saving in case of encoder
replacement.
Figure 4-5
AEMZP0EA - EPS-AC0 SWs&ENC - User Manual Page - 19/95