Archive for September 2014

Selasa, 23 September 2014

Control Application is split into two parts: turtle graphics and the use of sensors to control or monitor applications.

I. Turtle Graphics

A ‘turtle’ is an on-screen object that follows command given to it by the user. As the turtle moves around the screen it drags a ‘pen’ that leaves a trail behind it.

The command language is called ‘LOGO’.

What is LOGO?

LOGO (also known as 'Turtle Graphics') was developed in 1967 as a way to teach

children basic computer programming.

In LOGO, a curser (called a turtle) can be controlled and moved around the screen by

inputting simple commands. As the curser moves around the screen it draws a line.

Here are some examples of LOGO commands being used to draw simple shapes. You will practice drawing each shape in an online

version of LOGO which can be accessed by clicking the link in the grey box found on the right of each example.

LOGO commands to draw it:

PENDOWN

FORWARD 60

RIGHT 90

FORWARD 60

RIGHT 90

FORWARD 30

RIGHT 90

FORWARD 30

LEFT 90

FORWARD 30

RIGHT 90

FORWARD 30

LOGO commands to draw it:

PENDOWN

FORWARD 40

RIGHT 90

FORWARD 20

PENUP

FORWARD 10

PENDOWN

FORWARD 20

RIGHT 90

FORWARD 40

RIGHT 90

FORWARD 20

PENUP

FORWARD 10

PENDOWN

FORWARD 20

(using REPEAT and ENDREPEAT)

Option 1:

PENDOWN

FORWARD 30

RIGHT 90

FORWARD 30

RIGHT 90

FORWARD 30

RIGHT 90

FORWARD 30

Option 2:

PENDOWN

REPEAT 4

FORWARD 30

RIGHT 90

ENDREPEAT

II. Application Using Sensors

Sensors could be used alongside computers to measure quantities (like temperature, light intensity etc) and then log changes in these quantities.

Sensors can also be used alongside computers to control different devices . The process

goes like this:

Input - Sensor detects data in the environment around it

Process - Data passed to a computer (microprocessor) inside the device which analyses it and decides what action to take. The computer sends instructions to the device telling it what to do.

Output - The device would carry out the instructions.

In both cases, sensors are used to send data to a computer where the data is processed – it is what happens next where the differences occur:

In monitoring, the computer simply reviews the data from the sensors

(by comparing it to data stored in memory) and updates its files and/or gives a warning signal if the values are outside given parameters. No changes to the process are made during monitoring.

In control applications, the computer again reviews the data from the sensors (by comparing it to data stored in memory). But if the values are outside the given parameters it takes action to try and get the values within acceptable ranges. It does this by sending signals to devices controlling the process (such as motors, valves, etc.).

Advantages of Using A Computer Control Devices

Cheaper

If a computer is monitoring and controlling applications, you don't need to employ people.

Higher Work Rate 

Computers can control applications all day, every day without getting tired or bored.

Safer Computers can work in conditions that would be too dangerous for people. Examples include chemical plants, radioactive sites and extremely cold areas (antarctic).

Accuracy Computers will respond to inputs from sensors accurately every time. E.g. a heater will be switched on as soon as the temperature falls below 10°C.

Speed Computers will respond to data received from sensors very quickly. E.g. as soon as an infrared sensor detects an intruder, the alarm will sound.

Radioactive sites can be too dangerous for people to work in.

Examples:

1. Burglar Alarms

Burglar alarms work in almost the same way as a security light system.

Input - Infrared sensor detects movement when the sensor is broken and this information is sent to the computer.

Process - Computer makes the decision to sound the alarm

Output - Alarm is activated

a modern alarm system with infra-red sensors

2. Central Heating

Modern central heating systems can be programmed to maintain a constant desirable

temperature.

Let's imagine our perfect room temperature was set at 25°C , we could use sensors and a

computer to:

- Maintain the optimum temperature of 25°C

- Turn heating off when it rises above 25°C

- Turn heating on when it falls below 25°C

Here is how it would work:

Input - Heat sensor detects the current temperature and sends this data to the computer built into the heating system

Process - Computer would check the sensor heat data against the temperature setting stored in it's memory. Computer decides if the heating needs to be turned on (or off)

Output - Heating is switched on or off.

3. Computer Controlled Greenhouse

Automatic greenhouses can provide the optimum conditions for growing plants by
using computer control.

Computers can be used to monitor conditions and control a range of applications

(devices) to keep the perfect conditions constant.

Sensors needed to collect data:

-Light sensor

-Moisture sensor

-Heat sensor

Control applications (devices) needed:

-Grow lights to make plants flourish

-Motor to turn sprinkler on if plants need water

-Heater to warm the greenhouse

-Motor to open window vent to cool greenhouse down if it gets too hot.

III. Robotics

Control Application & Robotics

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Minggu, 14 September 2014

A simulation is the creation of a model of a real system in order to study the behaviour of the system. The is computer generated and is based on mathematical representations.

The idea is to try and find out what mechanisms control how a system behaves and consequently predict the behaviour of the system in the future and also see if it is possible to influence this future behaviour.

Computer models have the advantage that they save money, can help find a solution more quickly and can be considerably safer (discussed further below). There are many examples of simulations, ranging from simple spreadsheet representations through to complex flight simulators. This section gives two examples: a model for showing a shop’s profit/loss and a traffic light simulation.

Why simulations are used?

They are less expensive than having to build the real thing (e.g. a bridge).
On many occasions it is safer to run a simulation – some real situations are hazardous (e.g. chemical processes).
With simulations, various scenarios can be tried out in advance.
It is nearly impossible to try out some tasks in real life because of the high risk involved or the remoteness (e.g. in outer space, under the sea, in nuclear reactors, crash testing cars, etc.).
It is often faster to do a simulation than the real thing. Some applications could take years before a result was known (e.g. climate change calculations, population growth, etc.).

Limitations:

They are only as good as the data used and the mathematical algorithms

representing the real-life situations.
They therefore have a limited use in some very complex applications (e.g. simulating a nuclear process).
They can be very expensive to set up and often require specialist software to be written.
They frequently require very fast processors/computer systems (which can be expensive) to do the necessary ‘number crunching’; many simulations are made up of

I. Tuck Shop Model

This example uses a spreadsheet to do the modelling. Spreadsheet models can be used to predict finance type outcomes based on mathematical values.

This prediction show us things like profit/loss, over budget/between budget, and help us answer 'What if ...?' type of questions, e.g. “What if we decrease the workforce by 15%? Will our profits increase or decrease?” .

This is made possible with the use of 'formulae' which recalculate results based on new data entered.

Running questions like this through the spreadsheet can help managers make 'informed decisions' and reduce the risk of overspending and reduced profits.

II. Driving Simulation

These mimics the skill required to control vehicles such as cars, trucks, trains,and buses.

Uses:

Use of vehicle controls (steering wheel, accelerator, gears, clutch etc)
Practice driving maneuvers (emergency stop, reversing, parking etc)
Learning how to handle large trucks safely
Driving in hazardous conditions (snow, heavy rain etc)

Trainee drivers can build up a high level of confidence using the driving simulation before they actually begin to drive for real. Advantage: any mistakes or crashes are just 'virtual' and vehicles are not damaged or any people hurt.

Some driving simulators are used to mimic the effects of high-speed car crashes on the driver and passengers.

This replaces the old method of using actual cars and crash-test dummies and is muchcheaper and easier to set up.

Data taken from the simulation allows engineers to design and build safer cars. This is known as 'Computer Aided Engineering' (CAE).

III. Bridge Simulation

A computer model of a bridge can be used to test the design.
Bridges have to be able to survive extreme weather conditions. It is obvious not practical to build a real bridge and then wait to see if it falls down in a storm. Instead, a computer model of the bridge is created and tested in virtual storms.

If the model breaks, it can be quickly and cheaply re-designed andre-tested. If it doesn’t break, the real bridge can be built, confident that it will survive real storms.

Bridges can also be tested to see if they can cope with heavy traffic. The virtual bridge can be loaded with a traffic jam of virtual trucks to check that it won’t collapse.
A similar system is used by building designers, especially for very large or tall buildings, such as skyscrapers.

VI. Traffic Light Simulation

In this simulation it is necessary to consider:

how and what data needs to be collected
how the simulation is carried out
how the system would work in real life.

The success (or failure) of a simulation model depends on how realistic it is, so the data needs to be collected by watching traffic for a long period of time at the Y-junction. This is best done by using induction loop sensors which count the number of vehicles at each junction.

Manual data collection is possible but is prone to errors and is difficult to do over an 18-hour period per day, for example. The following data is an indication of what would need to be collected:

the number of vehicles passing the junction in all directions
the time of day for the vehicle count
how many vehicles build up at the junction at different times of the day
how vehicle movements change at weekends, bank holidays, etc.
how long it takes a vehicle to clear the junction
how long it takes the slowest vehicle to pass through the junction
the movements made by vehicles (e.g. left turns, right turns, filtering, etc.)
additional environmental factors, such as whether there are pedestrian crossings nearby.

Carrying Out The Simulation

Data from the above list is entered into the computer and the simulation run. The results of the simulation are compared with actual traffic flow from a number of data sets. Once the designers are satisfied that it simulates the real situation accurately, then different scenarios can be tried out. For example:

vary the timing of the lights and see how the traffic flow is affected
build up the number of vehicles stopped at part of the junction and then change the timing of the lights to see how the traffic flow is affected
increase or decrease traffic flow in all directions
how emergency vehicles affect traffic flow at different times of the day.

Using the Simulation

This simulation can then be used to optimise the flow of traffic through the junction on an ongoing basis.

Sensors in the road gather data and count the number of vehicles at the junction.
This data is sent to a control box or to a computer. It may need to be convertedfirst into a form understood by the computer.
The gathered data is compared to data stored in the system. The stored data isbased on model/simulation predictions which were used to optimise the traffic flow.
The control box or computer ‘decides’ what action needs to be taken.
Signals are sent out to the traffic lights to change their timing if necessary.