Systems and Control

Systems and Control
1. Product design and Evaluation
  1. Approaching a Design
    1. The first stage of design of a new product involves studying other products with similar or desirable features, through identification, analysis and evaluation. I don't think we need to know this, but meh
      1. This process helps the designer in a number of ways:
      2. It avoids copying other designers' work (this is called plagiarism (really? I would never have guessed!)).
      3. It identifies features or aspects of existing products which could be improved - such as by reducing the cost, adding extra features, making it easier or more comfortable to use or making it look more attractive to certain groups.
      4. It can identify technologies or ideas which could be transferred or applied to a new function or area.
  2. Evaluating a design
    1. What makes a design successful? How do you judge a design? There are a wide range of methods and strategies for analysing and evaluating designs. The two methods that follow are easy-to-remember acronyms:
      1. F.A.C.E. value
      2. Function - What does it do and how does it work?
      3. Aesthetics - Is it attractive, why and what makes it so?
      4. Construction - What is it made from, how and why?
      5. Economics - How much does it cost and is this good value for money?
      6. C.A.F.E.Q.U.E. (Yeah, WTF?)
      7. Cost - How much does it cost and is it good value for money?
      8. Aesthetics - Is it attractive, why and what makes it so?
      9. Function - What does it do and how does it work?
      10. Ergonomics - How easy or comfortable is it to use?
      11. Quality - How well is it built, what materials are used?
      12. User - Who is it for and is it appropriate?
      13. Environment - What effect do the product's manufacture, use and disposal have?
    2. A product's unique characteristics and features are called the product specification. You need to be able to identify these and compare them with the specification of other similar products. This will help you to evaluate how successful a product's design has been.
  3. Quality Control (QC)
    1. Quality control or QC is a way of controlling a manufacturing system. It is accomplished by a series of checks and inspections throughout the design and making of the product to ensure it is being made to specification and to the required standard. The results of the quality control checks are then fedback into the system to rectify any shortcomings. Quality control is also sometimes known as quality assurance or QA.
      1. As a systems and control designer you need to be able to devise and apply test procedures to check the quality of your work, as well as identify critical stages of the manufacture for quality checks.
2. ICT
  1. Information and communication technology (ICT) is an essential tool in designing and manufacturing products.
  2. There are three key areas of ICT in the designing and making process: modelling and simulation, computer-aided design, and computer-aided manufacture.
  3. Modelling and simulation
    1. Electronic circuits can be modelled in real life using a prototyping board - also known as a breadboard. However, this can be time consuming and uses real components, which can be damaged. Computerised simulation software can be used to test circuits without the need to physically build them. In addition, the computer simulation can be saved and edited.
    2. Simulation software can also be used to simulate control programmes for programmable interface controllers (PICs). Typically, flowchart symbols can be placed or dragged on-screen. The action will be simulated to ensure that they operate as intended.
    3. Advantages and disadvantages of using modelling and simulation
      1. Advantages
      2. Doesn't require any physical components, so money isn't wasted on expensive parts
      3. Speeds up production process.
      4. You can save and edit ideas, which makes it easier and cheaper to modify your design as you go along.
      5. You can choose pre-drawn circuits or system blocks, which speeds up the process even further.
      6. Disadvantages
      7. The software itself can be expensive so initial costs are high. There are free software packages though.
      8. Staff need to be trained how to use the software, which also adds to costs.
      9. Requires a PC. (Alan is sorted there then)
      10. It doesn't always accurately simulate 'real world' circuits or ideas, so may not be as effective as a prototyping board.
  4. Computer-aided design (CAD)
    1. When a circuit has been finalised, a printed circuit board is usually designed and manufactured. Specialist software can be used to plan where the tracks, pads, strain holes and mounting holes will be on the PCB.
    2. CAD software can also be used to design the structure or housing of control systems. Software can also be used for writing the program used in microcontrollers. It is written in programme-editing software before being downloaded onto the chip.
    3. Advantages and disadvantages of using CAD
      1. Advantages
      2. Can be more accurate than hand-drawn designs - it reduces human error.
      3. You can save and edit ideas, which makes it easier and cheaper to modify your design as you go along.
      4. You can modify existing ideas, which saves time.
      5. Disadvantages
      6. The software itself can be expensive so initial costs are high. There are free software packages though.
      7. Staff need to be trained how to use the software, which also adds to costs.
      8. Requires a PC.
  5. Computer-aided manufacture (CAM)
    1. When a PCB layout has been designed using CAD, the board can be produced or manufactured using CAM.
      1. Two examples of CAM are:-
      2. A design machined by a computer numeric control (CNC) miller, which removes all the unwanted copper from the board.
      3. A design layout printed on to acetate and transferred to a copper-clad board using the photo transfer method. The unwanted copper is removed using acid. We use this method =)
    2. Advantages and disadvantages of using CAM
      1. Advantages
      2. In large-scale production, the results are consistent (always the same).
      3. Enables very high accuracy levels in large-scale production.
      4. Usually speeds up production of low-volume products.
      5. Disadvantages
      6. The software itself is expensive so initial costs are high.
      7. Can be slower than traditional methods for one-off or low-volume production.
      8. Staff need to be trained how to use the software and machinery, which adds to costs.
3. Societal and moral factors, health and safety
  1. Every design is influenced by outside factors such as consumer demand, the state of the market, client expectations, and consumer laws.
  2. Product lifecycle, consumers and clients
    1. Designers need to consider a product's maintenance and disposal requirements - the whole product life-cycle - not just the design and making phase. And products and innovations may have effects beyond just the individual who buys and uses them - they can impact on society at large or the environment.
    2. Health and safety is a key factor in all areas of industry. You need to know what implications it has for both designers and manufacturers
    3. Product lifecycle
      1. Products don't disappear once they're sold - they last for a shorter or longer time, and will need to be maintained and disposed of safely at the end of their life. The designer needs to think about the expected length of life of a product, and about maintenance issues such as ease of replacement of batteries or the level of skill required to replace worn-out components - because all these things influence the design process.
    4. Consumers
      1. The people or organisations who purchase and use a product are called end-users or consumers. Without consumers who want a product and are prepared to buy it, there's not much point in designing or making it. So consumer demand - what consumers want or need in a product - is a key influence on product design. Moreover, consumers want to have a wide choice of products, so they can find one that suits their individual requirements.
      2. Consumers have a lot of power. They have organisations to represent their interests - eg, The Consumers' Association and specialist organisations such as the Electricity Consumers' Council. They also have rights, enshrined in law, which give them a means of hitting back if necessary against those who have sold them wrongly-described or faulty goods. Enough said!
    5. The client
      1. Designers usually work for someone who pays them to solve a design problem. This is the client - and it is usually the client (an individual or a company) who gives the designer a design brief, and turns his or her ideas into products for consumers in the market place. Since the client is paying, their wishes are also a key influence on product design.
  3. Moral and legal issues
    1. Moral Issues
      1. Recycling and reusing. Recyclable materials such as aluminium cans and paper can be processed and used to produce new products. Products which are made using recycled materials are usually clearly marked. Reusable products are those which can be reused without the need for processing - for example, refillable milk bottles, scrap vehicle parts, or chips taken from an old circuit and reused in a new one.
      2. Most designers will feel that they have a responsibility to make products that do not have too damaging an impact on the environment. This might mean that they seek to use:
      3. 'Green' technology uses materials, components and systems which limit the damage to the world's environment caused by pollution from industry, transport, etc.
      4. Renewable energy is energy that is replaceable or cannot be used up. Replaceable energy sources such as biomass can be used alongside the Earth's natural renewable sources such as solar, wind, hydroelectric and tidal energy.
      5. Renewable materials are ones which we actively replace at least as fast as we use them up - eg paper from managed forests.
      6. Seeking to minimise negative effects on the environment in this way is called a sustainable approach, because it does not damage the livelihood of future generations. Remember that sustainable development? You can't escape it, not even in DT
      7. A designer may also want to think about the impact his or her products might have on people's religious or cultural susceptibilities. Certain images and slogans have the power to deeply shock or offend people, which will probably not encourage them to buy the product! A picture of Muhammed on a product, is not a good idea =)
    2. Legal constraints
      1. There may also be legal constraints on the designer, as well as purely moral ones. For example the The Data Protection Act protects the consumer by limiting the access that other individuals or organisations have to private information about them, as well as the ways in which this information can be used. Companies are required to work to guidelines on how information is processed, recorded and stored. Limitations are also placed on the length of time data should be kept and how it is shared.
  4. Risk assessment, health and safety
    1. Great. This
      1. Health and safety is a key factor in all areas of industry. Manufacturers are expected to ensure that both employees and customers are safe. They must put procedures in place to ensure safe working practices and that products will meet the safety standards in each country where they are sold.
      2. Manufacturers are required to identify and assess all potential risks in the manufacturing environment. This is called risk assessment. It affects product manufacturing, choice and use of components, tools, equipment and work. Once a risk or hazard has been identified, safe working practices are implemented.
      3. Where a risk cannot be reasonably avoided by safety procedures and safe working practices, control systems are used to increase safety. For example, when working with machine tools, the working area where mechanisms are exposed must be protected by a moveable guard. Many machine tools have a microswitch attached to the guard which isolates the power when the guard is up (exposing the mechanism).
4. Focus Technologies (Whatever those are =))
  1. Electronics
    1. Materials
      1. Electronics components are made up of three types of materials: conductors, insulators and semi-conductors. Components can be either separate devices linked together in a circuit, or integrated circuits incorporating large numbers of semi-conductor components etched onto a chip of silicon inside tiny a plastic case.
      2. Modern electronic systems are controlled by microprocessors and microcontrolers - computer-like components which are programmable and can therefore be used in different ways in different products.
      3. Electronic components work together in circuits, and these can be represented in circuit diagrams using standard symbols for the components. You need to know some common input and output components, and be familiar with two common types of integrated circuit - the 555 timer and Op-Amp circuit.
      4. There are three types of materials used in electronic components:
      5. Electrical conductors are materials that allow electricity to flow through them easily.
      6. Electrical insulators are materials that prevent electrical flow. In the diagram to the right, the insulating material (plastic) surrounds the conducting material (copper wires).
      7. Semi-conducting materials exhibit both conducting and insulating properties. The way in which the material is connected to a power supply determines whether it will conduct an electrical current or prevent it from flowing.
      8. The most common semi-conducting material is silicon. Silicon needs to have very small amounts of other elements such as boron and phosphorous added to it in order to become a semi-conductor. This is called doping. Doped silicon is used to make components such as:
      9. Transistors
      10. Diodes
      11. Integrated circuits
      12. The simplest kind of semiconductor device is a diode. In a diode the electrical current can be made to flow in one direction only (see diagram below). If the diode is reversed the flow of current is stopped. This behaviour is due to the semi-conducting property of the doped silicon.
      13. Another semi-conducting material is germanium, but this material is used less widely than silicon.
      14. The ease with which electricity flows through a material is called its resistivity. The value of resistivity is measured in ohms. The higher a material's resistivity, the more difficult it will be for electricity to flow through it:
      15. Insulators have very high resistivity values.
      16. Conductors have low resistivity values.
    2. Components
      1. Electronic components can be divided into two groups, Discrete electronic components and Integrated circuits (ICs).
      2. Discrete electronic components
      3. These are separate components that you can combine together to make a circuit on a breadboard, printed circuit board or veroboard (discrete means separate). Examples are resistors, transistors, capacitors, relays and light emitting diodes or LEDs.
      4. These components are called discrete because you can select them individually and combine them to make up the circuit you require. Discrete components can also be used as external components of an integrated circuit system. For example a 555 astable integrated circuit requires two discrete resistors and a discrete capacitor to make it work.
      5. Integrated circuits (ICs)
      6. These are miniature circuits incorporating large numbers of components, all etched on to a piece of silicon or chip. These chips are encapsulated inside a protective plastic package, and nowadays are manufactured in vast numbers. The circuits inside the package are arranged in different configurations for particular purposes, for building circuits in schools the DIL package is used, it is big enough to handle. To save space on commercial products surface mount chips are used.
      7. When using ICs you need to know which pins need to be connected, the function of each pin and how the IC is connected to the power supply. A circuit diagram that includes one or more ICs should show the pin numbers and how the pins are connected to the rest of the circuit.
    3. Programmable components
      1. Many electronic devices on the market are now designed using components that can be programmed to function in different ways. The advantage is that the same key component used in one product can also be used in something completely different. This reduces costs, as expensive customised integrated circuits do not need to be designed and manufactured for every new product.
      2. A microprocessor is a multi-function programmable device. Microprocessors enable computers to work, and they can also be used to control many types of electronic system.
      3. An alternative type of programmable component is the microcontroller or PIC. Microcontrollers are essentially single-purpose microprocessors, and they enable designers to use the same device to control a wide range of situations, while being cheaper than a computer control system. The rate at which the PIC works is controlled by an internal clock.
      4. The advantage of the microprocessor is that one device can control everything. The disadvantage comes if the microprocessor malfunctions: all the systems could be affected and the replacement cost is high. With microcontrollers, on the other hand, if one is damaged it can be easily replaced and when one fails the others continue to function.
    4. Electronic circuits
      1. In electronic systems, many components work together in circuits.
      2. Rather than drawing the components as they look in real life, symbols are used to produce circuit diagrams or schematics, showing the components and connections between them. These symbols are recognised universally around the world and avoid confusion between components which look similar.
      3. Inputs and outputs in electronic circuits
      4. The input is what sets an electrical circuit in action. Any of the following components can be used as inputs:
      5. a switch (eg push-switch, microswitch)
      6. a key pad
      7. a Light Dependent Resistor (LDR)
      8. a thermistor
      9. a photodiode
      10. a phototransistor
      11. an opto-isolator
      12. a proximity switch or reed switch.
      13. The output is what results from an electrical circuit. Any of the following components may be used as outputs:
      14. an LED
      15. a lamp
      16. a buzzer
      17. a piezo
      18. a motor or stepper motor
      19. a solenoid
      20. a relay
      21. a seven-segment display.
      22. Logic gates
      23. Logic gates are a family of digital devices which compare two or more inputs and give a specific output. Each logic gate (NOT, AND, NAND, OR, NOR etc) acts in a different way, and will always act so. The action of any logic gate is shown by a Truth Table, eg the AND gate will only give a high output, when all the inputs are high.
    5. ICs
      1. The 555 timer
      2. The 555 timer IC, shown in the diagram , has many functions. Two of them are: monostable and astable circuits.
      3. Monostable mode
      4. A 555 monostable timer is usually, unless a circuit turns it on by applying a voltage to pin 2. When the voltage at pin 2 goes above a level the 555's output will go high, but only for one pulse, after which the 555 will return to the low stable state. So this type of circuit is used where a single, timed output is required, either as an on-for-a-period or as a timed delay.
      5. Astable mode
      6. In an astable timer the output is not stable in either the on or the off state, but instead is pulsed on and off continuously. The frequency (number of pulses per second) is determined by the RC network connected to the 555 timer. When connected to an LED an astable timer gives a continuously flashing light. When set to a very high frequency and connected to a loudspeaker it will generate a tone.
      7. Op Amp
      8. The operational amplifier or Op-Amp amplifies the difference between the two inputs to produce a voltage gain as high as 100,000 times the difference. The output voltage cannot be any greater than the power-supply voltages. It cannot output a voltage more than two volts above or below its power connections. If the power supply is + 12 and -12 volts the maximum values at the output are likely to be +10 and -10 volts. An estimate of 85% of the supply may also be used. The diagram shows the pin set-up of an Op-Amp.
  2. Mechanisms
    1. A mechanism is simply a device which takes an input motion and force, and outputs a different motion and force. The point of a mechanism is to make the job easier to do. The mechanisms most commonly used in mechanical systems are levers, linkages, cams, gears, and and pulleys.
    2. Levers:
      1. You need to know how to calculate the mechanical advantage obtained by using levers, the velocity ratio in levers and pulley systems, and gear ratio and output speed when using gears.
      2. A lever is the simplest kind of mechanism. There are three different types of lever. Common examples of each type are the crowbar, the wheelbarrow and the pair of tweezers.
      3. All levers are one of three types, usually called classes. The class of a lever depends on the relative position of the load, effort and fulcrum:
      4. The load is the object you are trying to move.
      5. The effort is the force applied to move the load.
      6. The fulcrum (or pivot) is the point where the load is pivoted
      7. Class 1 levers
      8. A class 1 lever has the load and the effort on opposite sides of the fulcrum, like a seesaw. Examples of a class-one lever are a pair of pliers and a crowbar.
      9. Class 2 levers
      10. A class 2 lever has the load and the effort on the same side of the fulcrum, with the load nearer the fulcrum. Examples of a class-two lever are a pair of nutcrackers or a wheelbarrow.
      11. Class 3 levers
      12. A class 3 lever does not have the mechanical advantage of class-one levers and class-two levers, so examples are less common. The effort and the load are both on the same side of the fulcrum, but the effort is closer to the fulcrum than the load, so more force is put in the effort than is applied to the load. These levers are good for grabbing something small, fiddly or dirty, or picking up something that could be squashed or broken if too much pressure is applied. The common example of class 3 levers is a pair of barbeque tongs or a pair of tweezers.
      13. Mechanical advantage and velocity ratio
      14. Mechanical Advantage
      15. Class 1 and class 2 levers both provide mechanical advantage. This means that they allow you to move a large output load with a small effort. Load and effort are forces and are measured in Newtons (N). Mechanical advantage is calculated as follows:
      16. Mechanical advantage = load ÷ effort
      17. Velocity Ratio
      18. The mechanical advantage gained with class-one levers and class-two levers makes it seem like you are getting something for nothing: moving a large load with a small effort. The catch is that to make the effort smaller, you have to move a greater distance. In the first diagram the trade-off is that you need to push the lever down further to move the load up a smaller distance. This trade-off is calculated by the velocity ratio:
      19. Velocity ratio = distance moved by effort ÷ distance moved by load
    3. Linkages
      1. Linkages are mechanisms which allow force or motion to be directed where it is needed. Linkages can be used to change:
      2. The direction of motion
      3. The type of motion
      4. The size of a force
      5. A linkage consists of a system of rods or other rigid materials connected by joints or pivots. The ability of each rod to move will be limited by moving and fixed pivots. The input at one end of the mechanical linkages will be different from the output, in place, speed, direction and other ways.
      6. Reverse-motion linkage
      7. A reverse-motion linkage changes the direction of motion. In the diagram , note how the linkage looks a little like a "Z". See how the central rod moves around a central fixed pivot. By pulling (or pushing) the linkage in one direction, it creates an exact opposite motion in the other direction. If the fixed pivot was not central, it would create a larger or smaller motion in the opposite direction.
      8. Parallel-motion linkage
      9. A parallel-motion linkage creates an identical parallel motion. In the diagram below, how the linkage looks a little like an "n". This time, it is the two side rods that move around two central fixed pivots, while the top of the "n" moves freely. By pulling (or pushing) the linkage in one direction, it creates an identical parallel motion at the other end of the linkage.
      10. Bell-crank linkage
      11. A bell-crank linkage changes the direction of movement through 90°. A bell-crank linkage tends to look a little like an "L" or, as shown in the diagram, a mirror image of an "L". By pulling (or pushing) the linkage in one direction, it creates a similar motion at the other end of the linkage. For example, a bell-crank linkage could be used to turn a vertical movement into horizontal movement, as in a bicycle braking system.
      12. Treadle linkage
      13. A treadle linkage shows how linkages can be used to change one type of motion into another. In this case, the rotary motion of the cam moves a parallel-motion linkage. The parallel-motion linkage controls the identical side-to-side, or oscillating motion, of two windscreen wipers.
    4. Cams
      1. A cam is a shaped piece of metal or plastic fixed to a rotating shaft. A cam mechanism has three parts: cam, slide and follower.
      2. The cam shaft rotates continually, turning the cam. The follower is a rod that rests on the edge of the turning cam. The follower is free to move up and down, but is prevented from moving from side to side by a slide or guide, so the follower can only do three things:
      3. Rise (move up)
      4. Fall (move down) or
      5. Dwell (remain stationary)
      6. The follower's pattern of movement depends on the profile or outside edge of the cam that it follows. If the cam is perfectly round and the fixed shaft is in the centre of the cam, the follower will dwell. But if the cam is a different shape, and/or the shaft is not central, the follower will rise or fall. How often and how quickly the follower moves is determined by the shape of the cam and the position of the shaft.
      7. Cams come in many different shapes - for example pear-shaped, triangular or square.
      8. The cam may have a chunk or chunks removed, so that the follower falls into a gap and is then is pushed out again.
      9. Whatever the shape of the cam, positioning the shaft off-centre will alter the behaviour of the follower.
      10. Pear-shaped cam
      11. The pear shape of this cam means that for half the cycle, the follower will dwell. Then, as the pointed part of the cam approaches, the follower is pushed up (rises), then, as the point passes, falls and dwells - and the cycle starts again.
      12. Eccentric cam
      13. The eccentric cam is perfectly circular, but the rotating shaft is off-centre, which affects how it turns. This type of cam produces a smooth, symmetrical rise and fall motion in the follower, which never pauses to dwell.
      14. Drop cam
      15. With a drop cam the shaft is central in a perfectly round cam, which has a chunk removed. The follower will dwell for most of the cycle, until it suddenly falls into the removed section, then rises again as the cam regains its circular shape.
    5. Gears
      1. Gears consist of toothed wheels fixed to shafts. The teeth interlock with each other, and as the first shaft (the driver shaft) rotates, the motion is transmitted to the second or driven shaft. The motion output at the driven shaft will be different from the motion input at the driver shaft - in place, speed, direction and other ways.
      2. A number of gears connected together are called a gear train. The input (eg a motor) is connected to the driver gear. The output, (eg the wheel of a buggy) is connected to the driven gear.
      3. Spur gears
      4. The toothed gears, the most common. Drawn as two circles, of varying sizes to show where the teeth would be
      5. Gear ratio and output speed
      6. Where there are two gears of different sizes, the smaller gear will rotate faster than the larger gear. The difference between these two speeds is called the velocity ratio, or the gear ratio, and can be calculated using the number of teeth. The formula is:
      7. Gear ratio = number or teeth on driven gear ÷ number of teeth on the driver gear
      8. If you know the gear ratio, and the speed input at the driver gear, you can calculate the speed output at the driven gear using the formula:
      9. Output speed = input speed ÷ gear ratio
    6. Pulley systems
      1. Pulleys are used to change the speed, direction of rotation, or turning force or torque.
      2. A pulley system consists of two pulley wheels each on a shaft, connected by a belt. This transmits rotary motion and force from the input, or driver shaft, to the output, or driven shaft.
      3. If the pulley wheels are different sizes, the smaller one will spin faster than the larger one. The difference in speed is called the velocity ratio. This is calculated using the formula:
      4. Velocity ratio = diameter of the driven pulley ÷ diameter of the driver pulley
      5. If you know the velocity ratio and the input speed of a pulley system, you can calculate the output speed using the formula:
      6. Output speed = input speed ÷ velocity ratio
      7. Torque
      8. The velocity ratio of a pulley system also determines the amount of turning force or torque transmitted from the driver pulley to the driven pulley. The formula is:
      9. output torque = input torque × velocity ratio.
      10. Pulley drive belts
      11. Drive belts are usually made of synthetic fibres such as neoprene and polyurethane, with a V-shaped cross section. It is possible to reverse the direction of the driven pulley by twisting the belt as it crosses from input to output. Pulley belts have the advantage over chains that they do not need lubrication (though unlike a chain, a belt can slip).
    7. Types of motion
      1. There are four basic types of motion in mechanical systems:
      2. Rotary motion is turning round in a circle, such as a wheel turning.
      3. Linear motion is moving in a straight line, such as on a paper trimmer.
      4. Reciprocating motion is moving backwards and forwards in a straight line, as in cutting with a saw.
      5. Oscillating motion is swinging from side to side, like a pendulum in a clock.
    8. Mechanical systems and sub-systems
      1. Small systems can be combined to make more complex systems. A cam which is turned by an electric motor can operate a micro switch which could be used to turn a light on or off. Two mechanical systems can be connected together to give complex movements.
5. Production Techniques
  1. The competitive nature of the manufacturing industry means that companies are constantly looking for ways to increase the efficiency and productivity of their systems.
  2. Three of the most important ways companies can achieve this are by using standard components, modular systems, and different production methods.
  3. Standard components
    1. It is common practice in modern manufacturing for the production of the components that make up a product to be outsourced to other companies.
    2. For example, modern headlights for cars are usually built as a whole unit, rather than an individual lens and reflector. The light shown in the picture below could easily be built in France and shipped to the UK to be assembled into a vehicle.
    3. The advantage with using standard components is that it speeds up manufacturing and reduces manufacturing and maintenance costs, as the same units can be purchased and used all around the world.
  4. Modular systems
    1. As the electronics used in products have become more complex, many manufacturers have adopted a modular approach to control systems. Modular systems have the following advantages:
      1. they allow inputs, processes and output to be combined permanently or temporarily, and
      2. they make replacements and upgrades easier, because only the broken / outdated part needs a replacement / upgrade. For example, you can replace (or upgrade) the hard drive or disk drive of a computer, without having to replace the whole computer.
  5. Production methods
    1. You should remember this! It's easy!
      1. There are three main production methods used in manufacturing: one-off, batch and mass production.
      2. One-off production:
      3. Sometimes known as job or custom production, this is where a single item is required - for example a suspension bridge or a custom-made engine for a racing car. The unit cost is high for this method, as the production system needs to be changed for each different unit.
      4. Batch production:
      5. This occurs where quantities of an item are sold regularly - for example a local baker producing many batches of specialist loaves each day for sale in local shops. Batch production will involve producing and storing the components which will make up the end product, eg the batch production of PCBs.
      6. Mass production:
      7. Products that sell in high volume, nationally or internationally, are manufactured on production or assembly lines. The initial set-up cost (or capital investment) of mass production is high, due to the specialist equipment used - but the cost is spread across a very large number of products, so the unit cost is low. When a mass-production line runs continuously round the clock, it is called continuous flow.
6. Working with systems
  1. Elements of a system
    1. Input
      1. What makes it do it?
    2. Process
      1. How does it do it?
    3. Output
      1. What does it do?
  2. Programmed Systems
    1. Systems need to be controlled, to ensure that the system's output continues to be the one we want. Digital control systems use a sequence of instructions called a programme. There are two main ways of writing programmes:
      1. graphically, using flowcharts
      2. using computer programming languages, such as BASIC, C, C++
  3. Flowcharts
    1. This can either be a system flowchart (industry) or a control flowchart (electronics). They use the same symbols
      1. Start and end
      2. These are known as terminators. Not the 'I'll be back' kind
      3. Decision
      4. The magical yes/no question. The no usually links back to itself
      5. Input
      6. This is self explanatory. The symbol is also used for output
  4. Control Systems in industry
    1. Just in time (JIT)
      1. Just-in-time manufacturing systems rely on efficient control systems to ensure that the inputs, processes and output are perfectly synchronised to avoid delays.
    2. Control systems in manufacture:
    3. provide a high level of accuracy.
    4. automate quality control checks.
    5. monitor safety and performance.
    6. automate tedious repetitive tasks.
    7. are quick and can operate continuously.
Resistant Materials (Core for us doing SandC)
1. Materials
  1. The material types used in D&T Resistant Materials are woods, metals, plastics, ceramics and composites. Each of these has its own characteristic working properties such as strength, malleability, conductivity, toughness and durability.
  2. Types of materials
    1. You need to be familiar with the different properties of ferrous and non-ferrous metals; softwood and hardwood timbers; and thermoplastics and thermoset plastics.
    2. When working with resistant materials you need to be able to choose the best material for a job. Wood, metal and plastics are the most common materials used, followed by composites and ceramics.
    3. Plastics
      1. Thermoplastics
      2. Can be heated and shaped many times
      3. Thermosetting Plastics
      4. Will only set once. Useful for things like light bulb switches
    4. Composite materials
      1. Composite materials are formed by combining and bonding two or more materials - a reinforcing material and a bonding agent such as glue. MDF and GRP are examples of composite materials. NB alloys are not composite materials.
    5. Metals
      1. Metals can be either ferrous or non-ferrous. Ferrous metals contain iron while non-ferrous metals do not.
      2. Both ferrous and non-ferrous metals are divided into pure metals and alloys. A pure metal is an element - eg iron, copper, gold - unalloyed (not mixed) with another substance. An alloy is a mixture of two or more elements (eg, iron and carbon) to make another metal with particular properties (eg steel).
    6. Ceramics
      1. Ceramics are made from clay, sand and feldspar. These materials are ground to a fine powder, mixed together and fired at high temperatures (700 - 2000°C) in the production process.
    7. Timbers
      1. Timbers are divided into hardwood timbers and softwood timbers. Hardwood timbers get their name because of their cellular structure when seen under a microscope - not because they are hard to cut.Softwoods do not have this same hard cellular structure.
    8. Working properties
      1. Different materials exhibit different working properties. Listed below are the key properties which determine how materials behave. You need to know what each of these terms mean.
      2. Conductivity
      3. The ability of a material to conduct heat or electrical energy.
      4. Strength
      5. The ability of a material to withstand a force without breaking or bending.
      6. Elasticity
      7. The ability of a material to bend and then to return to its orginal shape and size.
      8. Plasticity
      9. The ability of a material to permanently change in shape.
      10. Malleability
      11. The ability of a material to permanently deform in all directions without cracking.
      12. Other terms you should know
      13. Ductility is the ability of a material to deform, usually by stretching along its length.
      14. Hardness is the ability of a material to resist wear, scratching and indentation.
      15. Toughness is the ability of a material to withstand blows or sudden shocks without breaking.
      16. Durability is the ability of a material to withstand wear, especially as a result of weathering.
      17. Fusibility is the ability of a material to change into a liquid or molten state when heated to its melting point.
2. Joints
  1. Joints between materials can be either temporary or permanent, and may be formed with adhesives, with frame joints, brazed or welded joints, or with fastening components such as nails, screws, bolts, and rivets.
  2. Types of joint
    1. Joints in wood can be with screws, nails, glues and knock-down components, or with frame joints - eg butt joints, halving joints, mortice-and-tenon, dovetail, and box joints.
    2. Joints in metal can be made with brazing, soldering, welding or rivets. Joints in plastics can be made with plastic adhesive, rivets, bolts or machine screws.
    3. Most products are made from more than one piece of material, so when the product is assembled or fabricated the pieces need to be joined. Joints can be either permanent or temporary, and there are many different types.
    4. Permanent and temporary joints
      1. Permanent joints are intended to stay put. They may make use of adhesives, nails, rivets, or one of the heat processes of brazing, soldering or welding. Assembly jigs are often used to hold components in place while they are being joined. For example, the parts of a steel roof frame can be put into the jig and then welded together.
      2. Temporary fixings usually involve components with a screw thread, such as screws, nuts and bolts.
    5. Adhesives
      1. There are many types of adhesives to suit different materials. When you are choosing the right one for your product you will have to take into consideration the type of material, the strength of the bond required and the environment the product will work in - for example if you are gluing timber for outdoor use, you would not use polyvinyl acetate (PVA), because it is water soluble.
      2. Double-sided tape will join almost anything to anything. It is widely used in industry, for example, many parts of aircraft are held together with double-sided tape!