ElmoMC SimplIQ Digital Servo Drives-Bell Command Reference - Manual (Page 223)

Command Description
WS[20] Stator field angle, in 1024 counts/revolution units.
Stator field angle (degrees) = WS[20] x (360/1024).
WS[21] Commutation counter. WS[21] counts the main high-resolution
position sensor, modulo CA[18].
For analog encoders, WS[21] counts the position with maximum interpolation,
regardless of the user selected interpolation factor CA[31]
The process of initializing the commutation counter WS[21] is called commutation
finding, or pole identification.
Commutation finding is made when the motor is first set to ON. The process of
commutation finding may involve extra motions, according to the method you select –
refer to the next sections of this chapter. The PN[6] parameter determines if commutation
search is made every motor ON or just the first time.
4.2. Commutation Sensors
Vector commutation requires rotor position sensors. Commutation sensors are divided
into two main groups:
Direct field sensors that sense the magnetic field of the motor
Shaft position sensors
Commutation with position sensor is always made with the main sensor, even if
the auxiliary sensor is the position feedback (UM=4).
4.2.1 Hall Sensors
The Hall sensors report the rotor electrical position directly. However, digital Hall
sensors provide only rough information with six counts per electrical cycle.
SimplIQ can use Hall sensors as the only information for commutation. Many applications
achieve smoother commutation by using digital Hall sensors for initial pole identification
and for backup; most of the time the commutation is made by a higher-resolution
position sensor.
The following table describes the most common digital Hall sensor arrangement.
Hall A
Hall B
Hall C Electrical Rotor
Position (Degrees) Transformation angle
for best torque
(Degrees)
0 0 0 Illegal
1 0 0 330 – 30 90
1 1 0 30 – 90 150
SimplIQ for Steppers Application Note Commutation and Pole Identification
MAN-STECR (Ver. 1.1)
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