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Case Study. Container Crane Control <using FuzzyTech>. Objectives of Ports. For delivery of goods through containers transported by cargo ships. Example is PTP in Johore, Wesport in Klang and of course Singapore. Crane Productivity.

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case study

Case Study

Container Crane Control

<using FuzzyTech>

objectives of ports
Objectives of Ports
  • For delivery of goods through containers transported by cargo ships.
  • Example is PTP in Johore, Wesport in Klang and of course Singapore.
crane productivity
Crane Productivity
  • Crane productivity is measured by how fast the Port Authority can move the cranes.
  • Singapore = 25 moves/hour
  • Jakarta = 17 moves/hour
  • Malaysia Westport=22 moves/hour
container crane control
Container Crane Control
  • Loading and unloading of containers are done in harbors in every country around the world.
  • For transportation of manufactured goods, food, etc.
  • Container cranes are used for such purpose.
operations and problems
Operations and Problems
  • When a container is picked up and the crane head starts to move, the container begins to sway.
  • Swaying of the container is not a problem during transportation but a swaying container cannot be released.
container crane control8
Container Crane Control
  • Two ways to solve this problem:
    • To position the crane head exactly over the target position, and then just wait until the sway dampens to an acceptable level.
    • To pick up the container and just move slowly that no sway ever occurs.
    • Both ways would be alright on a non-windy day but it takes too much time.
    • An alternative is to build container cranes where additional cables fix the position of the container during operation- but this would be too expensive.
slide9
For these reasons, most container cranes use continuous speed control of the crane motor- a human operator then control the speed of the motor.
  • The operator has to simultaneously compensate for the sway and make sure the target position is reached in time.
  • This is not an easy and would need very skilled operators.<You can try to manually control the crane through simulation>
several control modes
Several Control Modes
  • Many engineers have tried to automate this control task of controlling the crane by using:
      • Conventional PID Control
      • Model-based control
      • Fuzzy logic control
  • Problems with PID
      • This is a nonlinear problem.
      • Minimizing the “swaying of the container” is important when the container is closed to the target where PID is insufficient due to high nonlinearity.
  • Problems with Model-based control
      • Usually math-models tend to be an assumption (reduced-order model) and the crane motor behavior is far less linear than assumed in the model.
      • The crane head only moves with friction.
      • Disturbances such as wind cannot be modelled easily.
a linguistic control strategy
A Linguistic Control Strategy
  • A skilled operator is capable to control the crane.
  • He does not even need to use differential equations or a cable-length sensor which many control techniques would require.
  • So how does he do it?
slide12

Human-operated Crane System

  • Once he has picked the container, he starts the crane with medium power to see how the container sways.
  • Depending on the reaction, he adjusts motor power to get the container a little behind the crane head.
  • In this position, maximum speed can be reached with minimum sway.
  • Getting closer to the target position, the operator reduces motor power or might even apply negative brake.
  • With that the container gets a little ahead of the crane head until the container reaches the target position.
  • Then motor power is increased so that the crane head is over the target position and sway is zero.
analysis of operator s actions
Analysis of Operator’s actions
  • Start with medium power.
  • If you get started and still far away from the target, adjust the motor power so the container gets a little behind the crane head.
  • If you are closer to the target, reduce motor speed so the container gets a little ahead of the crane head.
  • When the container is very close to the target position, power up the motor.
  • When the container is over the target and sway is zero, stop the motor.
see if you can write the rules to control this container crane system
See if you can write the rules to control this container crane system
  • First identify the antecedent variables
  • Next the consequent variable
  • Then write the rules according to the analysis of the operators action in the previous page.
  • 6 rules can be written- Try?
the control strategy
The Control Strategy
  • IF Distance = far AND Angle = zero THEN power = pos_medium

2. IF Distance = far AND Angle = neg_small THEN power = pos_big

  • IF Distance = far AND Angle = neg_big THEN power = pos_medium
  • IF Distance = medium AND Angle = neg_small THEN power = neg_medium
  • IF Distance = close AND Angle = pos_small THEN power = pos_medium
  • IF Distance = zero AND Angle = zero THEN power = zero
fuzzy controller design
Fuzzy Controller Design
  • From what you have studied thus far, let’s design our Fuzzy Controller to solve this problem.
  • What next?
conventional fuzzy control
Conventional Fuzzy Control

Antecedents

Fuzzification

Consequent

Inference

Defuzzfication

antecedents
Antecedents

Partition or break your antecedents into several fuzzy sets that can reflect the system

slide19

too far

neg_big

far

pos_big

zero

neg_small

medium

close

zero

pos_

small

  • For each antecedent, identify the range for the universe of discourse.
  • Distance  Metres or Yards
  • Angle  From -90o to +90o
  • Break up each antecedent 5 fuzzy sets each and provide the appropriate label that reflect the variables

Distance

Angle

slide20

Distance

Angle

Next design appropriate membership functions for each fuzzy set and set them on the universe of each antecedent

Typical design would be as follows:

similarly for the consequent

neg_high

pos_high

neg_medium

zero

pos_

medium

Similarly for the consequent
  • Identify the motor power range
  • Break up into 5 fuzzy sets

Power

next develop the rules use matrix form how many rules maximum
Next develop the rulesuse matrix formHow many rules maximum?

Distance

close

med

zero

far

Too far

NB

NS

Angle

ZE

PS

PB

inference procedure
Inference procedure?
  • Max-min or (min/max as described in FuzzyTech)
  • Max-dot
  • Etc.
defuzzification
Defuzzification
  • Centroid
  • Mean of max