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Pneumatically-driven Quadruped Robot PIGORASS

IROS 2011 takes place later this month in San Francisco (25th ~ 30th), and as usual there’s so many interesting projects being presented that attendees won’t be able to see them all. We’ve looked at the schedule and will highlight some of them, beginning with this robot developed at the Graduate School of Information Science & Technology, The University of Tokyo, Japan.

PIGORASS is a pneumatically-driven quadruped robot developed by Yasunori Yamada, Satoshi Nishikawa, Kazuya Shida and Yasuo Kuniyoshi at the ISI Lab (Intelligent Systems and Informatics Lab), the same lab that brought us the jumping robot Mowgli and the running Athlete Robot.  Its skeleton (made of ABS resin and carbon-fiber-reinforced plastic), 10 artificial pneumatic muscles, and 10 passive spring muscles weigh only 4kg (8.8 lbs).  Its total body length is only 35cm (13″) long.  The artificial muscles are driven by an external air compressor, and pressure sensors and potentiometers replicate how real muscles sense their length and tension.

What’s interesting about PIGORASS is that its movements are not programmed in advance (as you would with robots using conventional motors), but emerges from the structure of its body and fluctuating signals from each muscle’s neural oscillator using what is called a spinobulbar model.  The neurons that individually control each muscle can fire in pairs (alternating between front and hind legs) to perform a kind of gallop, or fired all at once to produce a jumping motion.

In this diagram, pneumatic muscles are red while passive springs are blue.

Galloping is a term used pretty loosely, since the flight phase (in which all legs are off the ground) is only about 0.1 second.  And, due to the emergent nature of these motions they can be unpredictable and sometimes cause the robot to simply twitch in place or trip and fall over (as you’ll see in the following video).  Frankly, it’s pretty amazing that it manages to produce meaningful movements at all, since they stem from the dynamic interactions between the physical body and simple instructions from the muscle neurons.

“In the jumping experiment… the extension of the hip joint makes the tension of the rectus femoris strong, and as a result, the knee joint is extended. In this way, we showed a part of function of mechanism that generates motions. We aim [to clarify] the role that the musculoskeletal system plays through further analyses.”

Video:

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Video, as well as photos from “Dynamic Motions by a Quadruped Musculoskeletal Robot with Angle-Dependent Moment Arms” are owned & copyright by Satoshi Nishikawa, Yasunori Yamada, Kazuya Shida and Yasuo Kuniyoshi, Graduate School of Information Science & Technology, The University of Tokyo.

[source: Yasunori Yamada’s homepage]