Chapter 4 - Principles of Operation
4.2.6 Synchro Reference
The ac reference signal for the synchro(s) is generated in the 3860 by tapping
off the switched ac input power. This reference signal is distributed to the
synchros in the pedestal and to the Synchro/Resolver Assembly to facilitate
data conversion.
4.2.7 Analog Rate Loop Assembly (Optional)
The 3860 ACU Analog Rate Loop Assembly operation is considered on two
circuit levels in this section: the Loop Compensation circuit and the
Differential Tach/Torque Bias circuit.
4.2.7.1 Loop Compensation
The Loop Compensation circuit receives analog input commands from the
ACU Servo Assembly and tach feedback signals from the pedestal through
differential amplifiers. The signals are compared resulting in a dc Rate Error
signal. This signal is then compensated to generate an error signal
proportional to the difference in command and tachometer voltage. This
error signal is used as input command to the servo amplifier. In the case of
dual drive axis, the error signal for each drive is combined with the
differential tach loop signal and torque bias voltage to produce the dc input
command used by each servo amplifier to drive its respective motor.
4.2.7.2 Differential Tach/torque Bias (dual Drive System)
A tachometer is rigidly attached to the shaft of each motor. Each tachometer
produces a voltage proportional to the instantaneous velocity of the shaft.
These voltages are amplified to generate synchronizing signals. One of the
tachometer signals is applied directly to one amplifier, The second
tachometer signal is inverted by a second amplifier being applied to a
summing amplifier. Thus, the output of the summing amplifier is
proportional to the difference been the two tachometer signals. If the two
tachometers are rotating at the same speed, the two signals are equal and the
output of the summing amplifier is zero. Under this condition, the
synchronizing signals are also zero. If for any reason the tachometers are
instantaneously rotating at different speeds, the output of the summing
amplifier will not be zero since it is proportional to the difference between
the two tachometer voltages. The output of the summing amplifier is
coupled to the respective DC error signal. The phasing of these signals is
such that the motor producing the higher velocity is driven toward a lower
velocity, and the motor producing the lower velocity is driver toward a
higher velocity. A balance adjustment is provided to compensate for the
difference in tachometer voltage gradients. A gain adjustment is provided to
adjust the gain of the synchronizing loop.
Bias voltages from potentiometers provide means for introducing a bias
torque in the pedestal dual drive train to minimize backlash.
3862 Autotrack Controller
4-13
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