ElmoMC SimplIQ Digital Servo Drives-Bell Command Reference - Manual (Page 229)

Specifying a very high oscillation frequency (CA[15] = -3 or -4) is not recommended,
because not enough position samples will be available for each sine cycle.
The setup program normally selects the parameters I and f at the “Establishing
Commutation” stage of auto-tuning.
4.3.1.2 Method Limitation
The algorithm presented here is quite robust, and should work for most motor systems,
including those with moderate backlash. It does, however, have the following limitations:
The encoder must have a resolution of at least 256 counts per pole pair. For example, if a
motor has three pole pairs, 256 lines (1000 counters/revolution) will suffice. An encoder
with 128 lines will not.
The system cannot be extremely unbalanced. It is essential that the motor does not
accelerate significantly when no current is applied.
The motor cannot be free to oscillate in both directions.
The motor static load should not change significantly. If the static load is subject to
considerable changes, tune the algorithm with the highest possible load. Namely, the
inertia of the load must be above 40% of its value from when the parameters were tuned,
and it cannot exceed 40% of its value from when the parameters were tuned. If the load
inertia is too high, the present torque level will not suffice for oscillating the motor shaft.
The algorithm will fail and the motor will not start.
The algorithm assumes that in the excitation frequency, the motor and the load behave
like inertia. This assumption fails in the following cases:
The excitation frequency is a resonant frequency of the system.
There is a large viscous (speed-dependent) friction and the excitation frequency is
so low that the phase of the transfer function between the torque and acceleration is
not in the range of [-30…30] degrees. If the transfer function phase is out of range,
the algorithm will fail and the motor will not start.
4.3.1.3 Protections
The method described here can work reliably in many practical situations, although it does
not match every application. If the parameters of the method are not tuned properly, or if
the method does not match the application, the motor starting process will fail.
After setting MO=1, the algorithm will attempt to rotate the motor back and forth and find
the commutation angle. If the results are not reliable, because the oscillation amplitude is
too small or because the load behavior is not inertial, MO will reset automatically to zero
and the motor will not start.
4.3.1.4 Maximum Number of Iterations for Auto-phasing
If the auto-phasing algorithm fails (the motion amplitude is less than CA[24]), it may
retry with the same frequency but with a doubled current.
SimplIQ for Steppers Application Note Commutation and Pole Identification
MAN-STECR (Ver. 1.1)
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