Actuators and Controlling Devices

Actuators and controlling devices are the unsung heroes of automated control systems. In simple terms, they represent the muscles and brains of automated systems.

Actuators convert commands to actions; that is, they perform the physical work of a control system.

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Robotics Task 9

Create a page called Robotics Task 8 and answer the following questions:

  1. What is a controlling device in a control system? Give an example.

  2. What is the difference between a closed-loop system and an open-loop system?

  3. Describe the functions performed by actuators in automated control systems.

  4. Compare and contrast how the models of open-loop and closed-loop systems function.

  5. There are people who say they would rather have a robot help them take a bath than rely on help from another person. Discuss whether

    or not you believe the sick and elderly would prefer a robot carer as opposed to a human.

  6. Robots are not substitutes for humans. Do you agree, however, that before long we will consider it commonplace for people to have emotional bonds with robots? Discuss your answer.

Note: This task is due on Week 8

Electric Motors

A push movement may be used to connect the starter motor of a system, such as a car starter motor. A pull movement may be used to open a valve, such as in an automatic watering system.

Electric motors provide smooth, continuous rotational motion in a clockwise and anti-clockwise direction. Motors are the most commonly used type of actuators in a control system. They can produce a wide range of movements using gears and levers.

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Relays are also called switches. They consist of a solenoid connected to a mechanical switch. Relays are often used with a small electric current to turn on a large electric current. For example, a 5 volt signal from a computer could be used to turn on a 240 volt power supply to an electric motor. Relays often serve as a safety mechanism for systems using large currents.


Controlling Devices

The controlling devices in automated control systems are responsible for coordinating a range of processes. The controller usually consists of a microcomputer and a memory unit.

Microprocessors - Often the controller of an automatic control system is the microprocessor of a computer. Like other systems, the microprocessor is set up to accept data from input devices, process it and send data to output devices. In a controlled system, the microprocessor receives its input from sensors and, once processed, sends the appropriate signals to the actuators.

Use of feedback to the controller

There are several methods of classifying automated control systems. An open-loop control system does not use feedback. The system has some form of input, process and output, but the input does not rely on the system itself. An example of an open-loop system is an oven, where the cook chooses the oven temperature and settings to initiate the cooking cycle. While the food is being cooked, there is no check made on the state of food.


A solenoid consists of a magnetized iron rod surrounded by a tightly bound coil of wire. When an electric current passes through the wire, a strong magnetic force is produced which is strong enough to move the rod. When the current is switched on, the force moves the rod in one direction. When the current is switched off, the rod moves in the opposite direction.


Stepping Motors

Stepping motors provide precise movement to a specified location. The rotational movement may be controlled to an accurate number of degrees. Stepping motors are useful in automated systems when very precise movements are required.

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Pumps can be hydraulic (oil) or pneumatic (air). The forces created by a pump make the pistons move, causing a mechanical action. Pumps are often used in robotic arms and can achieve very rapid and precise movements.



Open-loop and closed-loop system

In the manufacturing industry, open loop automation usually involves devices which pick up and place objects.

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A closed-loop system uses feedback. The input of the system depends in some way on the output of the system. An example is a temperature control system, or thermostat, used to control an air- conditioning unit in a building.

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