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Temperature control

Feedback can be used to control temperature. Watch Professor Richard Mitchell explain more in this video.
In this video, we consider feedback for temperature control of homes, humans, and even the Earth. And this will lead on to considering Daisyworld, which is an example of artificial life, which is how it fits in with robotics.
So going back to the dear old steersman, he controls his boat, steering to the left if the boat goes to the right, steering to the right if the boat goes to the left. Two opposite control actions. And if you’re riding a horse, you similarly steer your horses by pulling one way or the other using your reins. So such dual action is called rein control. Rein control exists with temperature. If we take an air conditioning system, which is controlling the temperature of your room, it blows hot air if it’s too cold, or cold air if it’s too hot. In human beings, body temperature is also controlled. If you were too hot, you sweat. The action is to cool.
If you’re too cold, you shiver, which warms you up. Of course, if you’re still too cold, you turn up your air conditioning system. But this idea of temperature control even relates to our planet. James Lovelock, who was formally a visiting professor of cybernetics here at Reading, developed the Gaia Theory, which suggests that life on Earth and the planet work together, using feedback to try to control key aspects, such as temperature. He argued that life influences the environment. Biologists argue that life adapts to the environment. To address their concerns, Lovelock, with his colleague Andrew Watson, developed a model of an imaginary planet whose only life were two species of daisies.
It’s therefore called Daisyworld, which, like Earth, orbits a sun whose output is increasing over time and, hence, heating the planet.
Daisyworld. It’s a planet which has grey soil. And there are Daisy seeds in its soil. And there are two species of daisies– black ones and white ones. And daisies don’t grow if it’s too cold or it’s too hot. But grow best at 22 degrees and that’s similar to what happens here. So how does daisies temperature vary as its sun heats up? Things to remember. Black objects absorb heat, and so heat a local area. White objects reflect heat away, and so cool it. So you can get rein control on Daisyworld. How does it work? Well initially the sun is too cold. Therefore the planet is too cold. There’s no life.
But when it’s just warm enough, black daisies grow which heat the planet. Which means there more likely for black daisies to grow. So more black daisies grow. So very rapidly the temperature rises till it reaches the optimum. Now if the temperature rises further from there, then it’s got too hot if you’ve got black daisies, but white daisies can come into their own, and act to cool the planet. If they cool too much, then black daisies will grow to warm it. So you got rein control. Black daisies and white daisies heating and cooling. And as the sun heats up more and more, you need to do less heating with black daisies. So you have fewer black daisies and more white daisies.
And, eventually, the whole planet is covered in white daisies. No cooling is possible. And the planet dies. But for a long period, temperature is controlled. Let’s look at a simulation of this. So here is a simulation. It’s of Daisyworld. And it shows the proportion of black daisies and white daisies over time. The red here shows what the temperature would be if there was just the sun increasing. The blue is the actual temperature. And as you can see, it’s not perfectly flat, but it’s pretty flat. And that’s been achieved because once things start to get warm enough, you have black daisies. And then the back daisy population decays away, and the white daisy population grows.
And as you’re proceeding, you have fewer black, more white, and so forth. Overall the temperature is quite close. And if I animate it, we see what happens.
And the diagram over there represents Daisyworld. And you see the amounts of black and white. So temperature control has worked quite nicely. If you have more species of data, it’s not just black or white ones, but have grey in the middle. So we’ve got four. Then you end up with something like that. You notice that the graph is much flatter. So Daisyworld has, with further shades of grey, managed to control its temperature. I can animate that as well.
So here we’ve got a web page, which you can investigate what happens if you’ve got different numbers of species of daisies, even just black ones or white ones.
So the Daisyworld simulation, it works quite well. And what we see is that it’s actually better if you don’t have just black and white daisies, but you have the different shades of grey. Which, if you like, is an argument for biodiversity. Now of course, Daisyworld is an imaginary planet, but it does have relevance to Earth. Because polar ice caps can grow or shrink, acting like white daisies. So as the polar caps grow, you have more cooling, for instance. Large forest areas are dark, as is the sea. They act like black daisies, in the sense of absorbing heat. And clouds can form over tropical rainforests or over the seas. And from the top, clouds are white.
So they act as white daisies. So the amount of cloud, which it turns out, is affected by life on the planet, can determine how black or white the planet looks. And therefore, can influence the temperature. Why is this robotics? Well, rein control obviously applies to robots. But also it applies to temperature control, the steersman, and so forth. The key point, though, is that control is demonstrated using Daisyworld. Which is here populated by artificial life. In this case software artificial life, because it was a simulation I wrote. But mobile robots are also examples of artificial life. ERICs are artificial life made in hardware. The robot simulations are artifical life in software.
So a study of robots is also applicable to thinking about Gaia Theory and Earth and Daisyworld. Feel free to investigate the web page.

We have seen that feedback control is used by the steersman to ensure his boat stays on course and that it can be used to ensure that our robot moves at the desired speed.

It is straightforward to realise that the concept applies everywhere. If you are driving your car, you keep on the road in the correct lane by looking where you are going (just like the steersman) and turning the steering wheel as appropriate.

Similarly, you drive at the correct speed by monitoring the speedometer. If, for instance, you are in a 30mph speed limit, and you notice that the speedometer indicates you are travelling at 40mph, you slow down (particularly if there is a speed camera!)

It should be noted that it is important that what you measure is correct – if your speedometer is faulty, and says you are travelling at 30mph when you are in fact going at 40mph, you will drive too fast.

In addition, feedback can be used to control temperature. In the video Richard discusses so-called Rein control (which the steersman uses) and how it applies to control of the temperature of a house or room, the human body – and even Earth itself – as proposed by James Lovelock in his Gaia Theory. To demonstrate his ideas, Lovelock and his colleague Andrew Watson, modelled an imaginary planet, Daisyworld, which features artificial life (in this case daisies). In the video Richard shows the web page he created to simulate Daisyworld. The video concludes by relating this to robotics.

If you’re interested in the Temperature Control demo mentioned in this video – you can try the Daisyworld Web Page yourself.

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