4.3 Servomechanics

Question 1

What is servo short for??

Answer 1

Servomechanism

Question 2

What is a servo?

Answer 2

An electromagnetic device that converts electricity into precise controlled motion using negative feedback

Question 3

Why are servos used?

Answer 3

Because they automatically correct the performance of a mechanism to ensure accuracy

Question 4

What is synchro short for?

Answer 4

Synchro-mechanism

Question 5

What is a synchro?

Answer 5

A type of rotary electrical transformer sensor used to measure the angle of a rotating machine

Question 6

What is an open-loop?

Answer 6

A control system in which human interface between input and output determines the system accuracy, response time, stability (using car brakes)

Question 7

What is an open-loop entirely reliant on?

Answer 7

The human operator for accuracy

Question 8

What is a closed-loop?

Answer 8

a system that automatically corrects itself to stay accurate (like a clothes iron staying at the correct temperature)

Question 9

In a closed-loop what is the job of the controller?

Answer 9

It’s responsible for comparing the input and output to calculate the ‘error’

Question 10

What is null voltage?

Answer 10

When there is no desired induced voltage however due to mechanical imperfections some voltage can appear

Question 11

What is meant by deadband?

Answer 11

An area of a signal range or band where no action occurs

Question 12

What is deadband sometimes called?

Answer 12

A neutral zone

Question 13

What is the purpose of deadband?

Answer 13

To prevent oscillation or repeated activation-deactivation cycles

Question 14

What is time lag?

Answer 14

Because a servo compares an input signal with a feedback response, there is always a time lag between input signal and movement of load

Question 15

How can time lag be decreased?

Answer 15

Increasing the gain of the servo amplifier

Question 16

What is feedback?

Answer 16

The system providing information about its load to the operator or its input

Question 17

What is the fundamental difference between an open-loop and a closed-loop?

Answer 17

Feedback

Question 18

What is hunting?

Answer 18

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

Question 19

What happens without the damping device that prevents hunting?

Answer 19

The receiver would constantly go past its desire target by smaller amounts each time until it finally came to rest

Question 20

What is follow-up?

Answer 20

The behaviour of a servomechanism upon detection of an error where it immediately returns to its desired position

Question 21

What are the two types of synchro systems?

Answer 21

Torque systems and control systems

Question 22

What does a torque system do?

Answer 22

It will provide mechanical output sufficient to align an indicating device, actuate a contact or move a light load without power amplification

Question 23

What does a control system do?

Answer 23

Provides a voltage for conversion to torque through an amplifier and servo motor

Question 24

What determines if a synchro is used as a transmitter or a receiver?

Answer 24

If its providing an input or an output

Question 25

What’s the difference between a synchros transmitter and a receiver?

Answer 25

They very similar apart from the receiver has low friction bearings to follow the movement of the transmitter and some form of damping

Question 26

What is a synchro?

Answer 26

An electromechanical transducer which is converted to a unique set of output voltages which is used to turn a second synchro to a matching position

Question 27

Simple synchros are used to turn?

Answer 27

Light loads (dials and pointer)

Question 28

If a synchro wanted to turn a heavier load what is required?

Answer 28

An amplifier or a motor

Question 29

What is an entire system that involves servos called?

Answer 29

Servomechanism

Question 30

What are torque synchros used for?

Answer 30

In systems that need to produce a turning force or torque necessary to move light loads

Question 31

What are control synchros used for?

Answer 31

To move heavy loads

Question 32

A synchro can be turned by a metal shaft to transmit motion from one point to another, why is this sometimes not the most efficient way?

Answer 32

Because the shaft is cumbersome, heavy, and difficult to route

Question 33

What i the problem in a synchro when you replace the turning shaft with a flexible cable (teleflex)?

Answer 33

Cannot drive heavy loads as the shaft twists and high friction

Question 34

What is the best way to link to synchros without using a shaft or a flexible shaft?

Answer 34

An electric motor with wires (typically 5 wires) which communicate and copy each others movements

Question 35

The five wires connecting the roque transmitter (TX) and the torque receiver (TR) are identified. What is S1?

Answer 35

X blue

Question 36

The five wires connecting the roque transmitter (TX) and the torque receiver (TR) are identified. What is S2?

Answer 36

Z Black

Question 37

The five wires connecting the roque transmitter (TX) and the torque receiver (TR) are identified. What is S3?

Answer 37

Y Yellow

Question 38

The five wires connecting the roque transmitter (TX) and the torque receiver (TR) are identified. What is R1?

Answer 38

H red and white line

Question 39

The five wires connecting the roque transmitter (TX) and the torque receiver (TR) are identified. What is R2?

Answer 39

C black and white line

Question 40

What are the advantages of synchros?

Answer 40

-long distance capabilities -easily routed -uses little electrical power -lightweight -cost effective

Question 41

What are the basic requirements of a closed-loop servo system?

Answer 41

-accept an order -evaluate the position of the input and output -evaluate the rate of change of any ‘error’ -carry out correcting orders

Question 42

In a synchro what angle intervals are the secondary windings placed at?

Answer 42

120˚

Question 43

In a synchro how does it know which position it is in?

Answer 43

Because the secondary coils are place 120˚ apart when an electronic signal is sent to the primary coil in the middle it will be able to tell from the magnetic field produced

Question 44

What is the normally AC supply to a torque system?

Answer 44

115V or 26V

Question 45

When is torque present in a torque transmitter and a torque receiver?

Answer 45

When current is flowing which generates magnetic fields

Question 46

What has a negative effect on precision inside a transmitter and a receiver?

Answer 46

Bearing and brush friction

Question 47

What does a differential transmitter do?

Answer 47

To add or subtract angles

Question 48

Why is a differential transmitter laid out in a star shape?

Answer 48

So it doesn’t influence the magnetic field of the stator

Question 49

How does a receiver of a control synchro work?

Answer 49

Instead of generating movement it delivers a voltage which can control other things

Question 50

What are the three types of control synchros?

Answer 50

-control transmitter (CX) -control transformer (CT) -control differential transmitter (CDX)

Question 51

What two signals does a current transformer compare?

Answer 51

Electrical signal applied to its stator and the mechanical signal applied to its rotor

Question 52

In a control transformer what is the rotor never connected to?

Answer 52

AC supply

Question 53

What is a resolver used for?

Answer 53

It’s a rotary electrical transformer use to measure degrees of rotation

Question 54

What type of device is a resolver considered?

Answer 54

Analogue but has digital counterparts

Question 55

What voltage flows through a resolver?

Answer 55

26V or 115V

Question 56

How many hertz go into a resolver?

Answer 56

400Hz

Question 57

What is a linear variable differential transformer?

Answer 57

An electromechanical transducer that can convert straight line motion into electrical signal

Question 58

What principle is used by which a linear variable differential transformer operates?

Answer 58

Electromagnetic induction

Question 59

How does a rotary variable differential transformer work?

Answer 59

It converts rotary motion of an object into electrical signal

Question 60

How do E and I bar transducers get their names?

Answer 60

Because there physical construction looks like an E and I

Question 61

Why re E and I bar transducers laminated?

Answer 61

To reduce eddy currents

Question 62

What are the two types of magnetic proximity switches?

Answer 62

-integrated type -separate type

Question 63

How does a integrated proximity switch work?

Answer 63

When an object enters a U-shaped structure which acts like a switch

Question 64

How does a separate type proximity switch work?

Answer 64

A switch unit is fixed into place and the magnet unit is mounted to a moving object to be detected (MLG proximity switch)

Question 65

What shapes do proximity switch mounts come in?

Answer 65

Cylindrical or rectangular

Question 66

How does a capacitive sensor work?

Answer 66

It uses an electrical field to detect solids or liquids without physical touch

Question 67

What are the four main parts of a capacitive sensor?

Answer 67

-sensor body -sensor face -Indicating light -cable

Question 68

Why are servo systems found in AC and not DC in modern day times?

Answer 68

Because DC servo systems require more servicing, unreliable, poor temperature stability, and weigh more