ElmoMC SimplIQ Digital Servo Drives-Bell Command Reference - Manual (Page 228)

The angle θs is known because the drive controls it directly. The angle θr is unknown.
If θs is rotated — that is, θs –2πf * t, where f is a frequency and t is the time — the result is
the following sinusoidal torque:
T = K
T
* I * sin(2 πf * t - θr) (3)
For that torque, the motor shaft will move according to:
P(t) = A(f) * K
T
* I * sin (2 πf * t - θr – φ(f)),
where:
P(t) is the motor shaft position.
A(f)e
j φ(f) is the transfer function of the motor and its load at the frequency f.
By applying a torque of (3) and measuring the position, both A(f) and
r
θ can be
identified.
4.3.1.1 Selecting Parameters
The parameters I and f can be selected from the following range:
Parameter Description
I The torque is selected by the parameter CA[26], which defines I as a
percentage of the continuous current rating CL[1]. For example, if
CA[26] = 50, then I = 0.5 CL[1].
f CA[15] controls the frequency of the sinusoidal motor torque. The basic
frequency (with CA[15] = 0) is such that a cycle is completed in 128 * TS
microseconds. For a
SimplIQ drive with TT[1]=40, this will be a cycle of
5120 microseconds, which is about 200 Hz.
The frequency is 2
CA[15] * basic frequency of CA[15] in the range [-4…4].
For example, with CA[15] = 2, the frequency is about 80 Hz, whereas
with CA[15] = -2, the frequency is about 1280 Hz.
The selection rules for parameters I and f are as follows:
The torque I must be as large as possible so as to reduce the relative effect of disturbance
torques (such as cogging and friction) on the resulting waveform. Normally, I is taken as
about 50% of the continuous motor current.
The frequency f must be selected so that the amplitude of the position sine is at least 1
electrical degree, and at least 6 to 8 bits. The motor position can be analyzed accurately
enough when the position sine amplitude is 4 encoder bits or more. A slightly higher
amplitude is set to prevent minor load changes from disturbing the analysis. Larger
position amplitudes will work, but the shaft oscillation at the motor starting process will
be unnecessarily large.
The frequency f must be such that in that frequency, the load behaves inertially. This
means that in that frequency, the phase angle φ(f) is in the range of [-140…-220] degrees,
and that the amplitude function A(f) does not have the high gradient of near resonance
regions. The algorithm will not function near a resonant frequency, or in a low
frequency in which a large viscous friction is present.
SimplIQ for Steppers Application Note Commutation and Pole Identification
MAN-STECR (Ver. 1.1)
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