Applications: Load Sway Example

Applications: Load Sway Example

Cranes load and unload containers to/from ships

- Load always sways- Swaying load may hit other

containers- Swaying load cannot be released

Applications: Load Sway Example

Cranes load and unload containers to/from ships

- Load always sways- Swaying load may hit other

containers- Swaying load cannot be released

Applications: Load Sway Example

Ineffective solutions:

1. Position the crane over the target and wait for sway to subside

2. Move container slow, so no sway occurs

3. Use additional links (cables) to fix the load in place and prevent sway

Applications: Load Sway Example

Most cranes are still controlled by human operators that have skills to quickly compensate the swaying of the load!

Why the problem was not solved by the classical control theory?

Applications: Load Sway Example

PID control:

- The problem is non-linear (for example, sway minimization is important only close to the target)

- Many unknown variables

Applications: Load Sway Example

Model-based control:

- Fifth-degree differential equation that describes the system

- Works in theory, does not work in practice(too many simplifications and unknown variables)

Applications: Load Sway ExampleHeuristic strategy:• Start with medium power. • If you get started and you are still far away from

target, adjust the motor power so that the container gets a little behind the crane head.

• If you are closer to the target, reduce 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 the sway is zero, stop the motor.

Applications: Load Sway Example

Fuzzy controller

Applications: Load Sway Example

Membership functions for angle

Applications: Load Sway Example

Membership functions for distance

Applications: Load Sway Example

Membership functions for power

Applications: Load Sway Example

• if distance is positiveLarge then power is positiveLarge

• if distance is positiveLarge and (angle is negativeLarge or angle is positiveLarge) then power is positiveMedium

• if distance is positiveMedium then power is positiveMedium

• if distance is positiveMedium and (angle is negativeLarge or angle is positiveLarge) then power is positiveSmall

• if distance is positiveSmall then power is positiveSmall

• if distance is zero and angle is zero then power is zero

Rules to move the crane

Applications: Load Sway Example

• if (distance is zero or distance is positiveSmall or distance is negativeSmall) and angle is negative then power is positiveSmall

• if (distance is zero or distance is positiveSmall or distance is negativeSmall) and angle is positive then power is negativeSmall

Rules to prevent sway

Applications: Load Sway Example