8
CARLO
TROMBETTI
400 cycles/sec) but shifted by 90 0 in advance on the time of the former. This
phase difference is obtained by means of the condensers shown in fig. 3 {dephasing
circuit). ?
Thus a rotating magnetic field is created (with a 400 c/s frequency), of varia
ble intensity, from nought to a maximum, according to the voltage in the control
winding. Hence the speed of the rotor varies proportionately to the intensity of the
rotating field and, consequently, proportionally to the voltage of the error signal.
The rotation of the said motor is transmitted, by means of a mechanical redu
ction system (fig. 5) both to the members operating movement X (or Y) of the
drawing table, and to the synchro-receiver, in the sense that they bring back the
sincro-ricevitore
motore bifase
Alla trasmissioneXfoYj
de/ tavolo
Fig. 5 - Mechanical coupling of the twophase motor with
synchro and table
Collegamento meccanico del motore bifase col sincro e col tavolo
axis of the latter rotor coil to the coincidence, i. e. perpendicular to the direction
of the transmitted field.
Once this position is arrived at, the voltage error is annulled ; correspondingly
also the voltage in the control winding of the biphase motor is annulled and there
fore the motor stops.
Under these conditions the system has reached the new coincidence position.
2. Moto-tachymeter and tachymetric reaction.
The design of the above described servo may be definitely improved in its
dynamic behaviour by means of a system allowing the quick damping of the servo
transients without oscillations around the steady-state position.
This may only be obtained by introducing the so-called tachymetric reaction.
To attain this end we must set up a tachymeter, of the type described hereafter,
coaxial to the small biphase motor. The whole equipment, called a motor-tachymeter
(fig. 6) thus consists of two separate parts : the motor and the tachymeter.
The motor part is the same as the one we have already described, i. e. it con
sists of the small biphase motor.
