ElmoMC SimplIQ Digital Servo Drives-Bell Command Reference - Manual (Page 227)

4.2.3 Initializing the High Resolution Position
Sensor Manually
The high resolution position counter can be set manually by the TW[63] command. The
use of TW[63] is here clarified by an example. Suppose that a motor has 3 pole pairs (i.e.,
12 steps) and an 8000 count/rev incremental encoder. We shall program CA[18]=8000,
CA[19]=3, and one electrical cycle of the motor will count approximately 8000/3=2667
encoder counts.
If we set TW[63]=1000, we assert that the present electrical position of the motor is
(1000/2667)
×360 ° which is approximately 135 ° .
Setting TW[63]=3667 is similar, since mod(3667,2667)=1000. In other words, the value we
set into the commutation counter reflects a full electrical cycle of 2667 counts, plus the
1000 counts that matter.
Note:
TW[N] commands are privileged; they work only after applying TP[6]=1.
4.3. Auto-phasing and Commutation Search
Auto-phasing is the process of initially estimating the rotor electrical angle, without any
Hall or absolute sensor.
SimplIQ supports the following methods for commutation initialization:
- Oscillation. This method is good when the motor may move a little on start.
- 2 nd harmonics. This method is good when the motor is braked before start.
Its success depends on the magnetic structure of the motor.
The parameter CA[17] selects the auto-phasing method to use.
4.3.1 Auto Phasing by Oscillation
When starting the motor, the rotor can be located anywhere. The torque of a brushless or
stepper motor is given by the equation:
si ) n(
T
T K I
θ = (1)
s r
θ θ θ = − (2)
where:
T is the motor torque.
K
T
is the motor constant.
I is the motor current.
θ is the electrical angle between the rotor and the field at the stator.
θs is the electrical angle of the stator field.
θr is the electrical angle of the rotor.
SimplIQ for Steppers Application Note Commutation and Pole Identification
MAN-STECR (Ver. 1.1)
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