4.3 Servomechanics

Question 1

what are synchros and resolvers mainly used for?

Answer 1

in electromechanical servo systems for position waves on specific functional angles

Question 2

what are the advantages of synchros and resolvers?

Answer 2

cheap and most reliable method of measurement of functional angles

Question 3

what are servo systems loosely divided into?

Answer 3

open and closed loop systems

Question 4

what is an open loop system?

Answer 4

input position converted to electrical signals and demand signal amplified to motor to position load.

Question 5

in an open loop system, what is not accurately controlled?

Answer 5

the final position of the system

Question 6

what is a closed loop system?

Answer 6

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

Question 7

what is the signal sent back to the comparator called?

Answer 7

feedback

Question 8

in construction, what are synchros similar to?

Answer 8

AC current generators

Question 9

how are synchros constructed? (3)

Answer 9

laminated stator core
three coils staggered by 120 degrees
wired in star shaped config

Question 10

what is the accuracy range of CX and CT?

Answer 10

between +/- 4 and +/- 10 arc minutes

Question 11

what is the accuracy range of TX and TR?

Answer 11

60 arc minutes

Question 12

what accuracy range could be achieved by a synchro?

Answer 12

+/- 2 arc minutes

Question 13

what are pancake synchros?

Answer 13

used in gyroscope frames and manufactured to customer specs
accuracy level of 20 arc seconds and 3 arc seconds

Question 14

what is null voltage?

Answer 14

when voltage is induced into a rotor at the minimum coupling position due to imperfections/winding errors/distortions

Question 15

what is deadband?

Answer 15

area of a signal range or band where no action occurs

Question 16

what is the purpose of deadband?

Answer 16

prevent oscillation or repeated activation/deactivation cycles

Question 17

what is hunting?

Answer 17

refers to overshoot and undershoot that occurs as the receiving device tries to match the transmitter

Question 18

how are the primary and secondary coils of synchros and resolvers usually represented?

Answer 18

primary = rotor
secondary = stator windings

Question 19

what does the induced voltage in a stator coil depend on?

Answer 19

the coupling factor between the rotor coil and the stator coil and the angle between the two coil axes

Question 20

the excitation voltage forms a sine curve, what angle is the maximum voltage for a stator coil occur?

Answer 20

angle = 0

as this is when the axes of both coils line up

Question 21

in a torque synchro chain, how are the connections made?

Answer 21

in such a way that the terminal of each transmitter is connected to the corresponding receiver terminal

Question 22

in a torque synchro chain, what happens if both rotors are excited simultaneously?

Answer 22

the receiver motor moves into position of the transmitter rotor

Question 23

how is the rotation moment necessary to put the rotor in the receiver position created?

Answer 23

by the interaction between the magnetic fields of the stator and the rotor.

Question 24

what is the amplitude of the magnetic field proportional to?

Answer 24

to the cosine of the angle between the rotor coil and the stator.

Question 25

what happens when the rotor of the receiver are activated and excited with the same voltage?

Answer 25

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