4.3 Servomechanics Flashcards
what are synchros and resolvers mainly used for?
in electromechanical servo systems for position waves on specific functional angles
what are the advantages of synchros and resolvers?
cheap and most reliable method of measurement of functional angles
what are servo systems loosely divided into?
open and closed loop systems
what is an open loop system?
input position converted to electrical signals and demand signal amplified to motor to position load.
in an open loop system, what is not accurately controlled?
the final position of the system
what is a closed loop system?
initially the same as an open loop, but the load position is sensed and sent back to the summing amplifier/comparator which calculates the difference between input signal and actual position and adjusts the load until it reaches the demand signal
what is the signal sent back to the comparator called?
feedback
in construction, what are synchros similar to?
AC current generators
how are synchros constructed? (3)
laminated stator core
three coils staggered by 120 degrees
wired in star shaped config
what is the accuracy range of CX and CT?
between +/- 4 and +/- 10 arc minutes
what is the accuracy range of TX and TR?
60 arc minutes
what accuracy range could be achieved by a synchro?
+/- 2 arc minutes
what are pancake synchros?
used in gyroscope frames and manufactured to customer specs
accuracy level of 20 arc seconds and 3 arc seconds
what is null voltage?
when voltage is induced into a rotor at the minimum coupling position due to imperfections/winding errors/distortions
what is deadband?
area of a signal range or band where no action occurs
what is the purpose of deadband?
prevent oscillation or repeated activation/deactivation cycles
what is hunting?
refers to overshoot and undershoot that occurs as the receiving device tries to match the transmitter
how are the primary and secondary coils of synchros and resolvers usually represented?
primary = rotor
secondary = stator windings
what does the induced voltage in a stator coil depend on?
the coupling factor between the rotor coil and the stator coil and the angle between the two coil axes
the excitation voltage forms a sine curve, what angle is the maximum voltage for a stator coil occur?
angle = 0
as this is when the axes of both coils line up
in a torque synchro chain, how are the connections made?
in such a way that the terminal of each transmitter is connected to the corresponding receiver terminal
in a torque synchro chain, what happens if both rotors are excited simultaneously?
the receiver motor moves into position of the transmitter rotor
how is the rotation moment necessary to put the rotor in the receiver position created?
by the interaction between the magnetic fields of the stator and the rotor.
what is the amplitude of the magnetic field proportional to?
to the cosine of the angle between the rotor coil and the stator.
what happens when the rotor of the receiver are activated and excited with the same voltage?
it adjust itself so that the magnetic field lines of both rotor and stator are aligned parallel to each other and in the same direction
