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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
Draw and describe the following types of STEP INPUT RESPONSES? ``` Undamped Under damped Critically damped Over damped Ideal ```
Undamped - Oscillate indefinitely Under damped - Has two or more overshoots Critically damped - No overshoot(2nd fastest) Over damped - Very slow Ideal - One overshoot (Fastest)
26
What is a typical response to RAMP INPUT (constant velocity input)?
Ramp input Viscous friction Velocity lag
27
Draw a diagram and describe VELOCITY LAG? P3-28 (Figure.7)
- Ramp input (constant velocity input) - Viscous friction (present) - Velocity lag (caused)
28
What type of DYNAMIC BRAKING do we use and how is it used?
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
Why do we want to use a system that uses ERROR RATE CONTROL ?
To overcome VELOCITY LAG
30
ERROR RATE CONTROL Advantages ? Disadvantages?
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
What does the INTEGRATOR NETWORK DO?
Sums up the error over time.
32
What does a Three Term Controller (PID) do?
Produces an overall improvement in: - Immediate response (system GAIN) - Long term errors - Short term errors
33
Draw a THREE TERM CONTROLLER (PID) P3-51 (Figure. 7)
P3-51 (Figure. 7)
34
What does the (P) in PID controller do?
Proportional control: - Responds immediately to changes - Insensitive to errors - Improves the ACCURACY and SPEED of RESPONSE (Gain)
35
What does the (I) in PID controller do?
INTEGRAL control: - Responds to LONG TERM ERRORS - Minimises / Eliminates steady state errors
36
What does the (D) in PID controller do?
DERIVATIVE control: - Responds to SHORT TERM ERRORS - Increases SPEED of response - Controls overall system DAMPING (remember D for DAMPING)
37
What is a SYNCRO SYSTEM?
a General term used to names devices that uses a VRT(variable ratio transformer)
38
What are the Principles of a VRT(Variable Ratio Transformer)?
That of VARYING FLUX LINKAGE between two coils - One fixed (with AC power) - Other free to rotate (output voltage taken from its coils)
39
If a VRT rotates what are the PHASE relationship of the Voltage? 0 degrees 90 degrees 180 degrees
0 degrees. - Voltages are IN-PHASE 90 degrees. - ELECTRICAL ZERO 180 degrees. - PHASE INVERSION
40
What are the Disadvantages of a VRT?
Disadvantages: - Voltage can only represent TWO ANGULAR positions - Can only read +/- 90 degrees
41
Name two SYNCRO used in servo systems?
CX (controller transmitter) CT (control transformer)
42
What are a CX-CT link used for ?
They are used to provide continuous error detection over 360 degrees (Instead of 90 like the VRT)
43
Draw a AC POSITIONAL SERVO P4-11 (Figure. 8)
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
Explain how the 2 PHASE A.C servo motor works? P4-16
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
Explain the AC TACHO( induction generator) diagram? P4-17 (Figure. 11)
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
What are the requirements for a A.C TACHO (induced) GENERATOR?
- ZERO in for ZERO out - Voltage PROPORTIONAL to SPEED / - IN PHASE (+) = CW - ANTI-PHASE (-) = CCW
47
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 ```
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
Wiring Faults (CX-CT link)? STATOR: O/C stator coil S1 O/C stator coil S2 O/C stator coil S3
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
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
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
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
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
Advantages of A.C and D.C positional servos?
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
Draw a combined A.C and D.C system that uses PSD? Explain how it operates P4-26 (Figure. 18)
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
What are the requirements for a PSD(PHASE SHIFT DEMODULATOR)?
- 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
Explain how the DIODE PSD works? P4-30
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
What are RESOLVERS used for?
May be used to resolve right angled triangles in a system
56
Draw a RESOLVER diagram showing CW and CCW motion of: Vin=5sinwt Diagram P4-33 (Figure. 2)
Diagram P4-33 (Figure. 2)
57
Draw a SPACE or FREE gyro and name a few properties? P4-43 (Figure. 1)
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
Draw a RATE gyro and name a few properties? P4-44 (Figure. 2)
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
What does the RATE gyro measure?
Angular velocity Used to keep a tank turret locked onto a target no matter the movement of the tank
60
What happens to the Application of PRECESSION when a force is applied to INNER or OUTER GIMBAL them?
Precession is when: Force applied to INNER gimbal = OUTER gimbal moves Force applied to OUTER gimbal = INNER gimbal moves
61
What is SPATIAL RIGIDITY?
The ability for a spinning GYRO to maintain its position in space
62
Describe how SPERRY’s RULE acts when applying a force to a GYRO?
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
How does a NORTH SEEKING GYRO avoid drifting off its Axis?
By the use of some gravity control using a PENDULUM
64
Explain the operation of a RING LASER GYRO?
- 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
What does the 3 OPTICAL paths measure in the Ring Laser Gyro?
3 Optical Paths: Role Pitch Yaw
66
How can a LOCK-IN occur?
Output has to be LINEAR (but is not linear at low frequencies) Causing a LOCK-IN
67
How do we overcome a LOCK-IN on a RLG (ring laser gyro)?
By using MECHANICAL DITHER: 2 x greater than the LOCK-IN rate

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