A robot that runs and swims like a salamander | Auke Ijspeert

814,541 views ・ 2016-02-18

TED


Please double-click on the English subtitles below to play the video.

00:12
This is Pleurobot.
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Pleurobot is a robot that we designed to closely mimic a salamander species
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called Pleurodeles waltl.
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Pleurobot can walk, as you can see here,
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and as you'll see later, it can also swim.
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So you might ask, why did we design this robot?
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And in fact, this robot has been designed as a scientific tool for neuroscience.
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Indeed, we designed it together with neurobiologists
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to understand how animals move,
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and especially how the spinal cord controls locomotion.
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But the more I work in biorobotics,
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the more I'm really impressed by animal locomotion.
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If you think of a dolphin swimming or a cat running or jumping around,
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or even us as humans,
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when you go jogging or play tennis,
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we do amazing things.
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And in fact, our nervous system solves a very, very complex control problem.
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It has to coordinate more or less 200 muscles perfectly,
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because if the coordination is bad, we fall over or we do bad locomotion.
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And my goal is to understand how this works.
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There are four main components behind animal locomotion.
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The first component is just the body,
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and in fact we should never underestimate
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to what extent the biomechanics already simplify locomotion in animals.
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Then you have the spinal cord,
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and in the spinal cord you find reflexes,
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multiple reflexes that create a sensorimotor coordination loop
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between neural activity in the spinal cord and mechanical activity.
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A third component are central pattern generators.
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These are very interesting circuits in the spinal cord of vertebrate animals
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that can generate, by themselves,
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very coordinated rhythmic patterns of activity
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while receiving only very simple input signals.
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And these input signals
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coming from descending modulation from higher parts of the brain,
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like the motor cortex, the cerebellum, the basal ganglia,
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will all modulate activity of the spinal cord
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while we do locomotion.
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But what's interesting is to what extent just a low-level component,
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the spinal cord, together with the body,
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already solve a big part of the locomotion problem.
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You probably know it by the fact that you can cut the head off a chicken,
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it can still run for a while,
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showing that just the lower part, spinal cord and body,
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already solve a big part of locomotion.
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Now, understanding how this works is very complex,
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because first of all,
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recording activity in the spinal cord is very difficult.
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It's much easier to implant electrodes in the motor cortex
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than in the spinal cord, because it's protected by the vertebrae.
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Especially in humans, very hard to do.
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A second difficulty is that locomotion is really due to a very complex
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and very dynamic interaction between these four components.
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So it's very hard to find out what's the role of each over time.
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This is where biorobots like Pleurobot and mathematical models
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can really help.
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So what's biorobotics?
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Biorobotics is a very active field of research in robotics
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where people want to take inspiration from animals
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to make robots to go outdoors,
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like service robots or search and rescue robots
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or field robots.
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And the big goal here is to take inspiration from animals
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to make robots that can handle complex terrain --
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stairs, mountains, forests,
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places where robots still have difficulties
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and where animals can do a much better job.
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The robot can be a wonderful scientific tool as well.
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There are some very nice projects where robots are used,
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like a scientific tool for neuroscience, for biomechanics or for hydrodynamics.
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And this is exactly the purpose of Pleurobot.
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So what we do in my lab is to collaborate with neurobiologists
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like Jean-Marie Cabelguen, a neurobiologist in Bordeaux in France,
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and we want to make spinal cord models and validate them on robots.
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And here we want to start simple.
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So it's good to start with simple animals
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like lampreys, which are very primitive fish,
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and then gradually go toward more complex locomotion,
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like in salamanders,
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but also in cats and in humans,
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in mammals.
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And here, a robot becomes an interesting tool
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to validate our models.
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And in fact, for me, Pleurobot is a kind of dream becoming true.
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Like, more or less 20 years ago I was already working on a computer
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making simulations of lamprey and salamander locomotion
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during my PhD.
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But I always knew that my simulations were just approximations.
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Like, simulating the physics in water or with mud or with complex ground,
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it's very hard to simulate that properly on a computer.
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Why not have a real robot and real physics?
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So among all these animals, one of my favorites is the salamander.
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You might ask why, and it's because as an amphibian,
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it's a really key animal from an evolutionary point of view.
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It makes a wonderful link between swimming,
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as you find it in eels or fish,
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and quadruped locomotion, as you see in mammals, in cats and humans.
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And in fact, the modern salamander
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is very close to the first terrestrial vertebrate,
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so it's almost a living fossil,
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which gives us access to our ancestor,
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the ancestor to all terrestrial tetrapods.
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So the salamander swims
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by doing what's called an anguilliform swimming gait,
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so they propagate a nice traveling wave of muscle activity from head to tail.
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And if you place the salamander on the ground,
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it switches to what's called a walking trot gait.
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In this case, you have nice periodic activation of the limbs
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which are very nicely coordinated
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with this standing wave undulation of the body,
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and that's exactly the gait that you are seeing here on Pleurobot.
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Now, one thing which is very surprising and fascinating in fact
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is the fact that all this can be generated just by the spinal cord and the body.
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So if you take a decerebrated salamander --
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it's not so nice but you remove the head --
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and if you electrically stimulate the spinal cord,
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at low level of stimulation this will induce a walking-like gait.
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If you stimulate a bit more, the gait accelerates.
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And at some point, there's a threshold,
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and automatically, the animal switches to swimming.
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This is amazing.
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Just changing the global drive,
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as if you are pressing the gas pedal
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of descending modulation to your spinal cord,
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makes a complete switch between two very different gaits.
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And in fact, the same has been observed in cats.
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If you stimulate the spinal cord of a cat,
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you can switch between walk, trot and gallop.
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Or in birds, you can make a bird switch between walking,
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at a low level of stimulation,
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and flapping its wings at high-level stimulation.
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And this really shows that the spinal cord
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is a very sophisticated locomotion controller.
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So we studied salamander locomotion in more detail,
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and we had in fact access to a very nice X-ray video machine
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from Professor Martin Fischer in Jena University in Germany.
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And thanks to that, you really have an amazing machine
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to record all the bone motion in great detail.
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That's what we did.
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So we basically figured out which bones are important for us
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and collected their motion in 3D.
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And what we did is collect a whole database of motions,
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both on ground and in water,
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to really collect a whole database of motor behaviors
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that a real animal can do.
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And then our job as roboticists was to replicate that in our robot.
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So we did a whole optimization process to find out the right structure,
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where to place the motors, how to connect them together,
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to be able to replay these motions as well as possible.
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And this is how Pleurobot came to life.
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So let's look at how close it is to the real animal.
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So what you see here is almost a direct comparison
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between the walking of the real animal and the Pleurobot.
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You can see that we have almost a one-to-one exact replay
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of the walking gait.
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If you go backwards and slowly, you see it even better.
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But even better, we can do swimming.
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So for that we have a dry suit that we put all over the robot --
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(Laughter)
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and then we can go in water and start replaying the swimming gaits.
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And here, we were very happy, because this is difficult to do.
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The physics of interaction are complex.
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Our robot is much bigger than a small animal,
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so we had to do what's called dynamic scaling of the frequencies
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to make sure we had the same interaction physics.
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But you see at the end, we have a very close match,
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and we were very, very happy with this.
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So let's go to the spinal cord.
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So here what we did with Jean-Marie Cabelguen
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is model the spinal cord circuits.
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And what's interesting is that the salamander
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has kept a very primitive circuit,
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which is very similar to the one we find in the lamprey,
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this primitive eel-like fish,
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and it looks like during evolution,
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new neural oscillators have been added to control the limbs,
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to do the leg locomotion.
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And we know where these neural oscillators are
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but what we did was to make a mathematical model
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to see how they should be coupled
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to allow this transition between the two very different gaits.
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And we tested that on board of a robot.
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And this is how it looks.
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So what you see here is a previous version of Pleurobot
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that's completely controlled by our spinal cord model
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programmed on board of the robot.
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And the only thing we do
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is send to the robot through a remote control
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the two descending signals it normally should receive
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from the upper part of the brain.
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And what's interesting is, by playing with these signals,
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we can completely control speed, heading and type of gait.
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For instance,
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when we stimulate at a low level, we have the walking gait,
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and at some point, if we stimulate a lot,
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very rapidly it switches to the swimming gait.
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And finally, we can also do turning very nicely
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by just stimulating more one side of the spinal cord than the other.
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And I think it's really beautiful
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how nature has distributed control
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to really give a lot of responsibility to the spinal cord
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so that the upper part of the brain doesn't need to worry about every muscle.
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It just has to worry about this high-level modulation,
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and it's really the job of the spinal cord to coordinate all the muscles.
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So now let's go to cat locomotion and the importance of biomechanics.
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So this is another project
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where we studied cat biomechanics,
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and we wanted to see how much the morphology helps locomotion.
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And we found three important criteria in the properties,
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basically, of the limbs.
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The first one is that a cat limb
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more or less looks like a pantograph-like structure.
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So a pantograph is a mechanical structure
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which keeps the upper segment and the lower segments always parallel.
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So a simple geometrical system that kind of coordinates a bit
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the internal movement of the segments.
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A second property of cat limbs is that they are very lightweight.
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Most of the muscles are in the trunk,
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which is a good idea, because then the limbs have low inertia
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and can be moved very rapidly.
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The last final important property is this very elastic behavior of the cat limb,
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so to handle impacts and forces.
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And this is how we designed Cheetah-Cub.
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So let's invite Cheetah-Cub onstage.
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So this is Peter Eckert, who does his PhD on this robot,
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and as you see, it's a cute little robot.
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It looks a bit like a toy,
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but it was really used as a scientific tool
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to investigate these properties of the legs of the cat.
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So you see, it's very compliant, very lightweight,
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and also very elastic,
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so you can easily press it down and it will not break.
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It will just jump, in fact.
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And this very elastic property is also very important.
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And you also see a bit these properties
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of these three segments of the leg as pantograph.
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Now, what's interesting is that this quite dynamic gait
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is obtained purely in open loop,
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meaning no sensors, no complex feedback loops.
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And that's interesting, because it means
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that just the mechanics already stabilized this quite rapid gait,
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and that really good mechanics already basically simplify locomotion.
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To the extent that we can even disturb a bit locomotion,
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as you will see in the next video,
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where we can for instance do some exercise where we have the robot go down a step,
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and the robot will not fall over,
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which was a surprise for us.
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This is a small perturbation.
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I was expecting the robot to immediately fall over,
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because there are no sensors, no fast feedback loop.
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But no, just the mechanics stabilized the gait,
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and the robot doesn't fall over.
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Obviously, if you make the step bigger, and if you have obstacles,
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you need the full control loops and reflexes and everything.
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But what's important here is that just for small perturbation,
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the mechanics are right.
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And I think this is a very important message
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from biomechanics and robotics to neuroscience,
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saying don't underestimate to what extent the body already helps locomotion.
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Now, how does this relate to human locomotion?
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Clearly, human locomotion is more complex than cat and salamander locomotion,
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but at the same time, the nervous system of humans is very similar
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to that of other vertebrates.
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And especially the spinal cord
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is also the key controller for locomotion in humans.
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That's why, if there's a lesion of the spinal cord,
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this has dramatic effects.
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The person can become paraplegic or tetraplegic.
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This is because the brain loses this communication
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with the spinal cord.
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Especially, it loses this descending modulation
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to initiate and modulate locomotion.
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So a big goal of neuroprosthetics
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is to be able to reactivate that communication
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using electrical or chemical stimulations.
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And there are several teams in the world that do exactly that,
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especially at EPFL.
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My colleagues GrΓ©goire Courtine and Silvestro Micera,
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with whom I collaborate.
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But to do this properly, it's very important to understand
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how the spinal cord works,
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how it interacts with the body,
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and how the brain communicates with the spinal cord.
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This is where the robots and models that I've presented today
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will hopefully play a key role
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towards these very important goals.
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Thank you.
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(Applause)
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Bruno Giussani: Auke, I've seen in your lab other robots
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that do things like swim in pollution
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and measure the pollution while they swim.
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But for this one,
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you mentioned in your talk, like a side project,
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search and rescue,
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and it does have a camera on its nose.
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Auke Ijspeert: Absolutely. So the robot --
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We have some spin-off projects
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where we would like to use the robots to do search and rescue inspection,
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so this robot is now seeing you.
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And the big dream is to, if you have a difficult situation
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like a collapsed building or a building that is flooded,
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and this is very dangerous for a rescue team or even rescue dogs,
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why not send in a robot that can crawl around, swim, walk,
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with a camera onboard to do inspection and identify survivors
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and possibly create a communication link with the survivor.
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BG: Of course, assuming the survivors don't get scared by the shape of this.
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AI: Yeah, we should probably change the appearance quite a bit,
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because here I guess a survivor might die of a heart attack
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just of being worried that this would feed on you.
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But by changing the appearance and it making it more robust,
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I'm sure we can make a good tool out of it.
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BG: Thank you very much. Thank you and your team.
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