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Uni Course > Control Precis 2 > Flashcards

Control Precis 2 Flashcards

1
Q

A SERVO is defined as ?

A

Servo:

Error actuated
Power amplified
Feedback/control system

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2
Q

What are the Characteristics of a Tacho Generator?

A
  • No mechanical input, no electrical output
  • Linear
  • Polarity dependant on direction of rotation
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3
Q

SERVO equation?

A

Ve = Vi - Vo

Ve = feedback

Vi = Volts in

Vo = Volts out

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4
Q

TACHO Generator formula?

A

Vo = (V/RPM) x o/p RPM

Vo = Volts out

V = Volts

RPM = Reps per min

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5
Q

Name 2 features of a Closed Loops control (Servo)

A
  • Error actuated (tachogenerator)

- Power amplifying control system (Op Amp)

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6
Q

What is meant by a RATE SERVO?

A

We are able to vary the RATE OF SPEED

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7
Q

What is the role of the Tachogenerator in a rate servo?

A

Turning mechanical energy into electrical (V) to be used as feedback

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8
Q

What will happen to the rate of movement on a DC RATE SERVO if…

Large I/P voltage = ?

Small I/P voltage = ?

A

Large I/P voltage = Fast rate of movement (speed)

Small I/P voltage = Slow rate of movement (speed)

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9
Q

What term is used to alter the speed of a RATE SERVO ?

A

SPEED-GRADING

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10
Q

What is SPEED-GRADING ?

A

Technique used to ALTER THE SPEED of the system by keeping the INPUT VOLTAGE the same.

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11
Q

Name two ways in which speed grading can be achieved?

A

Altering:

  • Gain of the amplifier
  • Amount of tachogenerator feedback
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12
Q

What are the effects of varying the GAIN on SPEED-GRADING?

A

0.8V/1000rpm

Gain (amplifier) x1 = 0.8V

Vo = Vi - Ve
Vo = 40 - 0.8
Vo = 39.2V = 3920rpm

Gain (amplifier) x10 = 0.08V

Vo = Vi - Ve
Vo = 40 - 0.08
Vo = 39.92V = 3992rpm

Increasing the amplifiers gain x10 will increase the SPEED-GRADING
But has a small speed increase for a large gain increase

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13
Q

What are the effects of varying the % FEEDBACK on the TACHOGENERATOR on SPEED-GRADING?

A

0.01V/1000rpm

Vo = Vi - Ve
Vo = 30 - 0.01
Vo = 29.9V = 2990rpm

Set Tachogenerator to 50% F/B
0.01V/2
(New) 0.005V/1000rpm

TG FORMULA: Vo = (V/rpm)
Vo = (29.9/0.005) =5980rpm

Halving the Tacho feedback doubles the motor speed (SPEED-GRADING)
Small change for a big increase

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14
Q

What is meant by a DC POSITIONAL SERVO?

A

By aligning an O/P SHAFT with an I/P SHAFT, the position being determined by a input voltage

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15
Q

Describe the function of the following diagram?

P3-21

A

The A and B coils are winded in opposition to rectify the error Voltage coming in (achieve equilibrium)

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16
Q

How can we overcome a POSITIONAL SERVO from over shooting or going into a PENDULUM ?

A

By the use of DAMPING

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17
Q

Why do we require DAMPING?

A
  • Overcome inertia

- Reach a steady state as fast as possible

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18
Q

What do we need to add to the system achieve DAMPING?

A

FRICTION has to be added to the system to achieve DAMPING

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19
Q

Name 3 types of FRICTION?

A
  • Static friction (Stiction)
  • Coulomb friction
  • Viscous (fluid) friction
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20
Q

What is STATIC FRICTION (STICTION)

Use or draw a diagram to explain

P3-25 (figure.1)

A

All the friction is upon START, once overcome it drops down to nothing

P3-25 (figure.1)

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21
Q

What is COULOMB FRICTION

Use or draw a diagram to explain

P3-25 (figure.2)

A

Equipment friction(rubbing) like a bearing.

Lubricated bearing = Less friction
Un-lubricated bearing = more friction

But both their individual friction amounts will stay the same throughout

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22
Q

Show the effects of COULOMB FRICTION on a positional servo by use of a diagram?

A

Step input - coulomb friction - deadzone

P3-26 (Figure. 3)

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23
Q

What is VISCOUS (FLUID) FRICTION

Use or draw a diagram to explain

P3-27 (figure.4)

A

Like running in water:

Faster speed = Higher friction(drag)
Slower speed = Less friction(drag)

Friction is proportionate to the speed

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24
Q

What is a typical response to a STEP INPUT?

A

Step input
Coulomb friction
Deadzone

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25
Q

Draw and describe the following types of STEP INPUT RESPONSES?

Undamped
Under damped
Critically damped
Over damped
Ideal
A

Undamped - Oscillate indefinitely

Under damped - Has two or more overshoots

Critically damped - No overshoot(2nd fastest)

Over damped - Very slow

Ideal - One overshoot (Fastest)

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26
Q

What is a typical response to RAMP INPUT (constant velocity input)?

A

Ramp input
Viscous friction
Velocity lag

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27
Q

Draw a diagram and describe VELOCITY LAG?

P3-28 (Figure.7)

A
  • Ramp input (constant velocity input)
  • Viscous friction (present)
  • Velocity lag (caused)
28
Q

What type of DYNAMIC BRAKING do we use and how is it used?

A

REGENERATIVE BRAKING:

Generates a current which is fed to the DC batteries to act as a heavy load to the armature and helps bring it to a stop.

29
Q

Why do we want to use a system that uses ERROR RATE CONTROL ?

A

To overcome VELOCITY LAG

30
Q

ERROR RATE CONTROL

Advantages ?

Disadvantages?

A

Advantages:

  • No increase in Velocity lag
  • Acceleration boost over NVFB
  • Cheaper than a Tachogenerator

Disadvantages:

  • Not suitable for low speed control
  • Adjustment not easy
  • complicated in AC servos
31
Q

What does the INTEGRATOR NETWORK DO?

A

Sums up the error over time.

32
Q

What does a Three Term Controller (PID) do?

A

Produces an overall improvement in:

  • Immediate response (system GAIN)
  • Long term errors
  • Short term errors
33
Q

Draw a THREE TERM CONTROLLER (PID)

P3-51 (Figure. 7)

A

P3-51 (Figure. 7)

34
Q

What does the (P) in PID controller do?

A

Proportional control:

  • Responds immediately to changes
  • Insensitive to errors
  • Improves the ACCURACY and SPEED of RESPONSE (Gain)
35
Q

What does the (I) in PID controller do?

A

INTEGRAL control:

  • Responds to LONG TERM ERRORS
  • Minimises / Eliminates steady state errors
36
Q

What does the (D) in PID controller do?

A

DERIVATIVE control:

  • Responds to SHORT TERM ERRORS
  • Increases SPEED of response
  • Controls overall system DAMPING (remember D for DAMPING)
37
Q

What is a SYNCRO SYSTEM?

A

a General term used to names devices that uses a VRT(variable ratio transformer)

38
Q

What are the Principles of a VRT(Variable Ratio Transformer)?

A

That of VARYING FLUX LINKAGE between two coils

  • One fixed (with AC power)
  • Other free to rotate (output voltage taken from its coils)
39
Q

If a VRT rotates what are the PHASE relationship of the Voltage?

0 degrees

90 degrees

180 degrees

A

0 degrees. - Voltages are IN-PHASE

90 degrees. - ELECTRICAL ZERO

180 degrees. - PHASE INVERSION

40
Q

What are the Disadvantages of a VRT?

A

Disadvantages:

  • Voltage can only represent TWO ANGULAR positions
  • Can only read +/- 90 degrees
41
Q

Name two SYNCRO used in servo systems?

A

CX (controller transmitter)

CT (control transformer)

42
Q

What are a CX-CT link used for ?

A

They are used to provide continuous error detection over 360 degrees

(Instead of 90 like the VRT)

43
Q

Draw a AC POSITIONAL SERVO

P4-11 (Figure. 8)

A

P4-11 (Figure. 8)

  • CX input 30 degrees / CT output 0 degrees
  • CX has a AC input voltage / CT has a induced EMF created by the system(error voltage)
  • ERROR voltage IN PHASE - Motor turn CW
  • ERROR voltage ANTI-PHASE - Motor turn CCW
  • Motor will STOP if the induced EMF coils fall to ZERO
44
Q

Explain how the 2 PHASE A.C servo motor works?

P4-16

A

P4-16

  • Stator carries two COILS at right angles (90 degrees)
  • Coil A is more CAPACITIVE (so will LEAD) - Carries the A.C voltage
  • Coil B is more INDUCTIVE (LAG behind) - Carries ERROR signal from the amp
  • Result being a COMBINED FLUX VECTOR POSITION
45
Q

Explain the AC TACHO( induction generator) diagram?

P4-17 (Figure. 11)

A

P4-17 (Figure. 11)

  • Input windings(AC ref Voltage) are 90 degrees to the output windings
  • When the IRON CORE rotates, EDDY CURRENTS are induced which DISTORTS the ref field
  • Causing a VOLTAGE to appear at the output PROPORTIONAL to SPEED
  • Output will be IN-PHASE for CW / ANTI-PHASE for CCW
46
Q

What are the requirements for a A.C TACHO (induced) GENERATOR?

A
  • ZERO in for ZERO out
  • Voltage PROPORTIONAL to SPEED /
  • IN PHASE (+) = CW
  • ANTI-PHASE (-) = CCW
47
Q

Wiring Faults (CX-CT link)?

ROTOR:

CX rotor O/C
CT rotor O/C
R1 and R2 reversed on CX-CT
S/C across  R1 and R2 on CX
S/C across  R1 and R2 on CT
A

CX rotor O/C - Nothing is going to happen

CT rotor O/C - Nothing is going to happen (maybe a dither)

R1 and R2 reversed on CX-CT - 180 degree out

S/C across R1 and R2 on CX - Nothing is going to happen (blown fuse)

S/C across R1 and R2 on CT - Nothing is going to happen (no response)

48
Q

Wiring Faults (CX-CT link)?

STATOR:

O/C stator coil S1
O/C stator coil S2
O/C stator coil S3

A

O/C stator coil S1 - STOP in line with S1

O/C stator coil S2 - STOP in line with S2

O/C stator coil S3 - STOP in line with S3

49
Q

Wiring Faults (CX-CT link)?

STATOR:

S/C stator coil S1 and S2
S/C stator coil S2 and S3
S/C stator coil S3 and S1

A

S/C stator coil S1 and S2 - 90 degrees S3 (one not effected)

S/C stator coil S2 and S3 - 90 degrees S1 (one not effected)

S/C stator coil S3 and S1 - 90 degrees S2 (one not effected)

50
Q

Wiring Faults (CX-CT link)?

STATOR:

CROSS Connection of any TWO (2) coils

CROSS Connection of all THREE (3) coils - shifted by 1
CROSS Connection of all THREE (3) coils - shifted by 2

A

CROSS Connection of any 2 coils

  • Direction of the load will go ANTI-CLOCKWISE to the input

CROSS Connection of all 3 coils (S1/s2 - S2/s3 - S3/s1)

  • Stators SHIFTED by 1
  • Turn CW
  • 120 degrees out from I/P

CROSS Connection of all 3 coils (S1/s3 - S2/s1 - S3/s2)

  • Stators SHIFTED by 1
  • Turn CCW
  • 240 degrees out from I/P
51
Q

Advantages of

A.C and D.C positional servos?

A

A.C Positional Servo

  • Synchros provide 360 degree continuous error detection

D.C Positional Servo

  • D.C motors have a higher POWER/WEIGHT ratio and A.C motors
52
Q

Draw a combined A.C and D.C system that uses PSD?

Explain how it operates

P4-26 (Figure. 18)

A

P4-26 (Figure. 18)

  • AC ref voltage is comes from the CX (input shaft)
  • A.C Ve (Voltage error) comes from the CT (output shaft)
  • Both fed into a PSD (PHASE SHIFT DEMODULATOR)
  • A smoothing circuit smooths the D.C voltage which is fed to the D.C motor
53
Q

What are the requirements for a PSD(PHASE SHIFT DEMODULATOR)?

A
  • ZERO in for ZERO out
  • AC in for DC out
  • AC proportional to DC
  • AC phase error =

IN PHASE / pos + DC output. (CW)
ANTI PHASE / neg - DC output. (CCW)

54
Q

Explain how the DIODE PSD works?

P4-30

A

P4-30

During a CLOCKWISE rotation of the shaft

  • AC supply Positive HALF cycle
  • AC error signal IN PHASE with supply
  • Diodes will conduct and allow POS + current through
  • Driving the DC motor CW

During a ANTI-CLOCKWISE rotation of the shaft

  • AC supply
  • AC error ANTI-PHASE with the supply
  • Drive the DC motor CCW
55
Q

What are RESOLVERS used for?

A

May be used to resolve right angled triangles in a system

56
Q

Draw a RESOLVER diagram showing CW and CCW motion of:

Vin=5sinwt

Diagram P4-33 (Figure. 2)

A

Diagram P4-33 (Figure. 2)

57
Q

Draw a SPACE or FREE gyro and name a few properties?

P4-43 (Figure. 1)

A

P4-43 (Figure. 1)

  • 2 degrees of freedom (2 axis)
  • Spatial rigidity (stays rigid in whatever position you leave it)
  • Direction finding (used in aviation)
58
Q

Draw a RATE gyro and name a few properties?

P4-44 (Figure. 2)

A

P4-44 (Figure. 2)

  • 1 degree of freedom
  • Uses the Application of precession (with the sprigs)
  • Angular velocity (works out speed of change in movement)
  • SPERRY’s rule to work out rotation of PRECESSION
59
Q

What does the RATE gyro measure?

A

Angular velocity

Used to keep a tank turret locked onto a target no matter the movement of the tank

60
Q

What happens to the Application of PRECESSION when a force is applied to INNER or OUTER GIMBAL them?

A

Precession is when:

Force applied to INNER gimbal = OUTER gimbal moves

Force applied to OUTER gimbal = INNER gimbal moves

61
Q

What is SPATIAL RIGIDITY?

A

The ability for a spinning GYRO to maintain its position in space

62
Q

Describe how SPERRY’s RULE acts when applying a force to a GYRO?

A

Remember:

Force applied to INNER gimbal = OUTER gimbal moves

  • Apply a force on inner gimbal
  • Follow direction of spin 90 degrees (ie. left)
  • Outer gimbal will move

Force applied to OUTER gimbal = INNER gimbal moves

  • Apply force to the outer gimbal
  • Follow the direction of spin 90 degrees
  • Inner gimbal will go the opposite direction of the applied force
63
Q

How does a NORTH SEEKING GYRO avoid drifting off its Axis?

A

By the use of some gravity control using a PENDULUM

64
Q

Explain the operation of a RING LASER GYRO?

A
  • 3 Optical Laser beams travel in opposition to each other around an optical cavity.
  • As the GYRO moves the optical paths become longer or shorter
  • Thus for a given rotation, one FREQ will fall and the other will rise
  • The difference is called the BEAT FREQUENCY, which changes the FRINGE pattern and gives a digital O/P
65
Q

What does the 3 OPTICAL paths measure in the Ring Laser Gyro?

A

3 Optical Paths:

Role
Pitch
Yaw

66
Q

How can a LOCK-IN occur?

A

Output has to be LINEAR

(but is not linear at low frequencies)

Causing a LOCK-IN

67
Q

How do we overcome a LOCK-IN on a RLG (ring laser gyro)?

A

By using MECHANICAL DITHER:

2 x greater than the LOCK-IN rate

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