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SENSING & PROCESSING
Humans, as you know, have five basic senses: taste; sight; hearing; touch and smell. The information from these sensors is processed by our brain which decides what to do with it. If something tastes good, for example, your brain might direct the relevant muscles in your body to pick up and eat a bit more of whatever it is that caught its fancy. Robots are just the same, they need to be able to detect what's around them and act on the information. But in the case of both human and robot, the way the information from the sensors is processed can have a dramatic effect on what happens next. There are two possiblities - an 'open loop system' or a 'closed loop system'.
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 What's an open loop system?
Imagine you went to the hairdressers for a haircut. Imagine too that while she was cutting your hair, the hairdresser spent the whole time daydreaming and looking out of the window, not even bothering to look at your head. The chances are, you'd end up with a terrible haircut because the hairdresser hadn't been looking at your head. She'd have been cutting your hair off at random. She used the scissors to cut your hair without also using her eyes to check where to cut.
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This is an example of an open loop system - the hairdresser isn't checking the effect of what she's doing - she keeps on cutting and cutting regardless of what your hair looks like. Because she's not looking at your head, her brain isn't receiving information about the state of your hair and where she should make the next scissor cut. The hairdresser's eyes are like visible light sensors - but because she's using her eyes to look out of the window and not at your head, her brain isn't receiving any information about the state of your hair. There's no feedback.
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What's a closed loop system?
Now imagine you go to a good hairdresser. While she works, she continually checks to make sure your hair's the right length. She uses her eyes to spot any bits that are too long and the information is fed back to her brain which processes the information and guides her hand to cut the long bits off.
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This is an example of a closed loop system. After cutting some hair, the hairdresser's eyes check again to make sure she's cut off the right bit and they also check whether she's cut off enough. There's continual feedback.
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So where do robots fit in?
If a robot is to be able to do a useful job it also needs sensors to know what's going on around it. But, like the good hairdresser, it also needs a feedback loop so its 'brain' (ie a computer processor) knows what it should be doing. Most robotic sensors detect waves from some part of the electromagnetic spectrum.
So what is the electromagnetic spectrum?
It's a collection of waves with similar properties. They all travel at the speed of light - 300,000 km per sec, they all travel through a vacuum and air and they are carried by changing electric and magnetic fields.
Are all the waves the same?
No, they're very different. They all have different wavelengths which determine how they behave. Long wave radio waves have the longest wavelength (about 3 km) and can carry radio signals. Gamma rays have the shortest wavelength (about a millionth of a millimetre) and are used for killing cancers.
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And what about Robot Constructor?
The sensors in Robot Constructor all have feedback loops. So, for example, if you give your robot a gamma detector, it will sense when there's a hazardous gamma source near the robot and make the robot avoid it. Other sensors available to your robot work in exactly the same way although if you give your robot a visible light detector, it will use it to 'see' where POWER supplies are located and guide your robot towards them.
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What types of receptors do humans have?
Eyes aren't the only sensors available to humans and animals. We also have other receptors which receive information about changes in the environment. These receptors are specialised cells capable of detecting changes in the area around the body. Cells on the retina at the back of the eye, detect light and the skin has receptors that can detect temperature and pressure. There are other receptors that can detect chemicals and electric current. Each type of receptor responds only to a particular type of stimulus. All receptors are connected to nerve cells, which carry the information from the receptor to the brain for processing. Like in the case of the good hairdresser mentioned earlier, the brain decides what to do with the information it receives from the receptor cells. It may for example send a signal along the nerves to some muscles to make them move - perhaps to turn the central heating on if you feel cold. This flow of information from receptor to the brain and brain to muscles is fast, but not fast enough to deal with emergency situations. |
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Like in the case of the good hairdresser mentioned above, the brain decides what to do with the information it receives from the receptor cells. It may for example send a signal along the nerves to some muscles to make them move - perhaps to turn the central heating on if you feel cold. This flow of information from receptor to the brain and brain to muscles is fast, but not fast enough to deal with emergency situations.
So what happens when we need to act really fast?
When you are in danger, for example if you burn your hand, you don't have the time to use your brain to think about how hot your hand is. What you need to do is get your hand away from the heat immediately.
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The thermoreceptors in your hand send lots of impulses very quickly along the nerves to the spinal cord. The impulses don't travel to the brain, wasting valuable time, but instead travel along the relay neurone in the spinal column and out through the motor neurone to the muscles in your arm. The muscles contract and your hand is pulled away from the heat source.
This sort of action is called a reflex, and the path along which the impulse travels to generate action or a response is called a reflex arc.
 Reflex actions ensure your survival and are always fast and automatic.
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SENSORS radio infra red light radiation
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