Introduction to Marine Automation

Auto 1 – Marine Automation

● Ref: Marine Automation,

by Augusto U. Escolano

Ch 1 - General

● Development of Automatic Control

- Man's brute strength or animal's

- mechanical devices such as wheels or levers

- natural resources such as wind for powering sailing vessels, windmills and waterfalls for waterwheels

- steam engine. It provided power that could be harnessed at will.

Development of Automatic Control

● Early machines are manual in nature and the adjustments had to be reset frequently to maintain the desired output or performance.

● Newer equipment

- relieve people of monotonous activities so more time is devoted to other endeavors.

- complex controls that humans cannot duplicate.

Development of Automatic Control

● The invention of the diesel engine provided power to produce electricity

● The tracking apparatus of position was used in automatic steering of ships

● Application of negative feedback to an amplifier improved its frequency response and stability.

Electro-technical Control System

● Solenoid

- electromechanical device made up of coil which produces a magnetic field when electric current is passed through it. In some applications, the coil surrounds an iron plunger which becomes magnetized and moves in one direction upon application of current.

- produces a direct linear stroke, limited to a maximum distance of around 100mm


● Solenoid


● DC motor – when fitted with a tachometer and driven by a thyristor drive, can an excellent speed control but has high maintenance requirements for brushes and commutator.

● AC induction motor – maintenance free but a fixed speed device.

Both DC & AC motors are rotary and their outputs need to be converted to linear motion


● Electrical System Based on a Three-Phase Motor

Hydraulic Control System

● Ram – consists of a movable piston connected directly to the output shaft.

● If fluid is pumped into pipe A, the piston will move up and the shaft will extend; if into pipe B, the shaft will retract.

● Some method of retrieving fluid from the nonpressurized side of the piston must be incorporated.



- Precise control at low speeds- No over travel protection is required- the pump needs external power source- hydraulic fluids need to be very clean- leaks of fluid from the system are unsightly, slippery, and environmentally very undesirable

Pneumatic Control System

Pneumatic Control System

- operating pressure are lower than in a hydraulic system, so actuators are larger.

- return air is simply vented to the atmosphere.

Comparison

● Electro-technical

- small & adaptable with cheap flexible transmission line

- no moving parts, but generates heat

- stable, generally accurate

- low power consumption, direct application to computer but needs final control element transducers

Comparison

● Pneumatic

- no heat generation and safe in explosive atmosphere

- less susceptible to power supply fluctuation but have time lags

- direct application without transducer or too large final power actuators

Comparison

● Hydraulic

- instant responds as fluid is virtually incompressible

- readily provide any type of motion

- accurate position control

- high power amplification

A Simple Control Loop

● Measurement● Comparison● Judgment● Operates● confirms

Automatic Control● Has the ability to judge its own work and

performs its duty to the machine, such as measurement, comparison, and judgment.

● Example is the automatic control of liquid level in a boiler.

1. desired value 6. servo-motor

2. voltage 7. power source

3. differential xformer 8. float

4. adjuster 9. boiler

5. current 10. feed water

Automatic Control● Feedback control system or closed loop control

system● Detects quantities like temperature, pressure,

flow, voltage, current or the position of a machine in order to coincide them with the designated desired value, and compares and judges them with the desired value, and makes a machine perform correction action automatically according to the difference between the quantities.

Automatic Control● Uniformity of goods and attain mass production.● Economical and safe operation● Simplify facilities and ensure long life● Improved labor condition and safety● Reduce manual labor and related expenses

Automatic Operation

● Open loop control system● Automation (automatic operation /

automatization)● Automatic control

Block Diagram Symbols

Analog Device vs Digital Device

● Analog – the equation describing the operation of the device is analogous to that for the actual system

● Digital – extensively used in programming● Because of their ability to solve complicated

mathematical equations, they are incorporated as part of the control system to compute desired information

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Documents

Introduction to Marine Automation