119 - 23/May/97
5.4 Speed and Position Sensing
The DBM multiaxes drive is equipped with an interface for resolver-type shaft sensors.
These sensors are preferred for the reason of inherent absolute position sensing, much
wider operating temperature range than the optical devices, and a robustness intrinsic to the
resolver mechanical mounting (that is, the one of an electric machine). Resolvers have a pair
of detection windings on the stator side, name "SINE" and "COSINE" winding, spatially
displaced by 90 degrees. Excitation of the resolver is performed by a 10kHz, 7Vrms
sinusoidal signal, supplied to the resolver from the DBM module. By means of a rotational
transformer, fitted within the resolver, the excitation is being fed to the excitation winding
installed inside the rotor of the resolver. Through a transformer action, 10kHz electromotive
forces will be induced in the detection winding.
The amplitude (and phase) of these electromotive forces depend upon the shaft position.
Namely, when the shaft is in such a position that the rotor excitation winding of the resolver
is aligned with the "SINE" detection winding, the induced electromotive force in the "SINE"
winding will be on its maximum, and will be in phase with the excitation signal. At the same
time, the voltage detected at the terminals of the "COSINE" winding will be close to zero (i.e.,
will be zero if we disregard the noise). Moreover, assuming that the "SINE" winding spatial
axes is in opposite direction with respect to the excitation winding, the situation will be alike,
but the "SINE" winding voltage will be in counter-phase with respect to the excitation signal.
In the end, the ratio of the "SINE" and the "COSINE" signals taken at the instant of positive
peak of the excitation sinusoid will uniquely determine the shaft position.
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