| In my opinion, I don't think inflatable robots are very practical.(except for niche applications) One of the most important things in robotics is reliability, the more work your robot does before breaking down or needing maintenance the more money it makes you. In industrial robot arms the gold standard for this is a Mean Time Between Failures of more than 100,000 hours. That's more than 10 years of continuous operation! I am skeptical that inflatable robots will be able to last this long. The fabric/elastomer combo is certainly not going to last through 10 years of continuous operation. Sure this part may be cheap, but you still need expensive valving and pneumatics to control said robot. Not to mention that maintenance costs money too. The payback period for robots is also shortening, The other problem that pneumatic robots suffer from is that air is compressible. This means that moving it around to drive pneumatics is gonna be inefficient and that pneumatic structures aren't that rigid. Higher rigidity means higher resonant frequency which means your robot can operate faster without wobbling around. The inefficiency might be compensated for because the robot is so light, but I have yet to see any hard numbers on this. This lack of rigidity is touted as a feature by the people who make inflatable robots. Because they are so light and aren't rigid they aren't going to hurt people if they fuck up. There are other ways to solve this problem that are currently used in the robotics industry. One of them is to put a spring on every link in the robot, which is what the Baxter robot does. Another is to make the robot as light as possible and limit speed which is what one of Kuka's human safe robots does[0]. Better control also fixes this problem, if you don't hit the human then you don't have any problem. But there might be niche applications. Maybe they will find use in the medical field where having anything rigid touch a human is unacceptable or where you need a weird shape to grab a human on a bed. Entertainment might be another, a while back a japanese company made giant inflatable robots for parades. [0] http://www.phriends.eu/URAI_08.pdf |
That's a very good paper. There are many advantages to using two opposed springs driven by actuators to simulate muscles. You get muscle-like properties. You get energy storage and recovery. (Humans recover about 70% of energy from muscle springiness when running. Cheetahs, 90%. BigDog, 0%.)
As that paper points out, there are several ways to do this. The cleanest is a double-ended pneumatic cylinder with proportional spool valves at each end able to connect to pressure or exhaust. That was tried on a legged robot at CWRU some years ago. There are schemes with linear springs, string, two motors, and linkages, which tend to be bulky and complex.[1][2] Those work, but are more of a research design than a production mechanism. Somebody will do a better design, probably with rotational springs and no strings.
I once considered a design with two motors, rotational springs, and a differential. One motor controls impedance, the other controls position. If you don't need to change impedance rapidly, which you usually don't, the impedance motor can be much smaller and geared down.
[1] http://mech.vub.ac.be/multibody/topics/maccepa.htm [2] http://www.inacomm2013.ammindia.org/Papers/106-inacomm2013_s...