4.3 Servomechanics (2) Flashcards
which direction do the magnetic field electrical field currents flow in the receiver when the transmitter and receiver are equally connected?
Opposite direction but of the same magnitude
in aligned synchros, what current can be regarded as negligible?
the magnetising current
when is torque moment present?
when magnetising fields are present, which allows current to flow
when a differential angle between transmitter rotor and receiver rotor
at what angle is the torque moment at its greatest?
90 degrees
at what angle is the torque moment at its least?
0/180
what must the design of a synchro take into consideration?
the effect of bearing friction and brush friction to keep it at a minimum
what must be low enough to allow low levels of current to flow?
resistance levels
what is the task of a differential transmitter?
to add or subtract angles
a differential transmitter is constructed with coils wired in a star shape on the rotor with a circular cross section. why is it constructed in this way?
so it doesn’t influence the magnetic field of the stator
in differential transmitters, if both shafts are rotated in the same direction, what is the action?
subtraction
in differential transmitters, if both shafts are rotated in the opposite direction, what is the action?
addition
in differential transmitters, the coupling and the translations are chose in such a way for what reason?
so that the maximum voltages between two stator terminals are of the same magnitude as the maximum voltages between two rotor terminals.
what is the role of a control synchro chain?
deliver voltage which depends on the differential angle between the transmitter rotor and receiver rotor
how is sufficient voltage produced from a small angle between the stator field and rotor coil axis?
because of its construction due to many windings
magnitude proportional to number of windings
why does a CT have a circular cross section?
to ensure magnetic field of the stator is not influenced
how many degrees are the coils in a resolvers stator and rotor displaced?
90 degrees
what can resolvers only exsist as?
control transmitters and receivers
why are servo systems used instead of torque synchro chain?
when larger rotational moments are required
in servo systems, what are CT and CX roles?
to deliver a voltage based on a measure of differential angle between CT and CX and passed to an amplifier to drive the servo motor
in servo systems, how is the motor made to rotate?
the phase of the excitation voltage will make the motor rotate left or right depending which phase it is till the point CT no longer generates a voltage
in servo systems, at small angles, what does the motor have?
the full power of the amplifier to allow for accurate start up when on load
(has hunting issue)
in servo systems, how is hunting prevented?
damping by means of reverse coupling
in rate generators, what should it provide?
a voltage which has a frequency that is equal to the excitation voltage
in rate generators, what is amplitude proportional to?
the rotational speed
in rate generators, what does the direction of rotation affect?
phase
in phase or out of phase
in rate generators, what is the construction?
2 coils displaced 90 degrees by each other with a squirrel cage rotor
in servo motors, what motors are used and why? (3)
two phase asynchronous motors
robust,
simply constructed
no parts subject to wear apart from bearings
in servo motors, what is needed from a motor in this system? why?
It to activate maximum moment at start up
Because it works against high mechanical loads
Has weak rotation moment-rotation speed behaviour
in servo motors, how is maximum moment at start up achieved?
By increasing rotor resistance
what is the efficiency of a servomotor? and what is the reason for this?
10-20%
due to high rotor resistance required for maximum moment at startup
how are synchro signals transformed into resolver signals?
scott connected transformers
in scott connected transformers, what should the voltages be?
voltages should be the same
maximum voltage between synchro terminals should be of the same magnitude as the maximum voltage between the resolver terminals
in scott connected transformers, where must tapping occur?
in the centre of the coil so the coupling factor K = 0.5
what can be done to synchros?
set in any position
as they have circular cross section and no external markings
what is a transformer?
helps with the conversion of electrical power
in transformers, what is their construction?
two electrical coils of wire, (primary and secondary)
wrapped around a soft iron core
in transformers, how are the primary and secondary windings connected?
magnetically linked through the common core to allow electrical power to be transfered
