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Design and Development
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Japanese Team Designs Kenshiro Based on Human Musculoskeletal System
Despite having a frame that contains 160 pulley muscles, the robot only weighs 110 pounds
By Robotics Trends' News Sources - Filed Dec 19, 2012

More Design and Development stories
Robots have been doing our work for years now. As scientists make advancements in the field of robotics, they’ve been able to make these robots smarter and smaller, giving them even more jobs to do. Robots have even been made to break land speed records and run like speedy jungle cats.

Now, researchers at the University of Tokyo are showing off a robot that not only looks human, it’s also built like one.

Named Kenshiro, this robot features a skeletal system and a sort of muscular system built out of gears and pulleys. Kenshiro started as Kojiro who, in 2010, was built to closely resemble the musculoskeletal system of the human body. With these new additions, Kenshiro is said to mimic the body of the average 12-year old Japanese boy. At just over 5 feet tall and 110 pounds, Kenshiro’s body has nearly all of the human body’s major muscles represented in its robotic frame.

According to IEEE Spectrum, Kenshiro has 50 pulley muscles in its legs, 76 in its trunk, 12 in its shoulders and 22 in its neck. No other humanoid robot has this many “muscles” built into their frame.

According to Yuto Nakanishi, the head of the project, one of the trickier aspects to building Kenshiro was keeping the weight down.

In an earlier project, Nakanishi and team built a tendon-driven robot named Kenzoh. This robot’s upper body weighed in at just under 100 pounds. By the time the rest of Kenzoh would have been build, it would have weighed more than 220 pounds.

Nakanishi and team weren’t interested in building an obese robot, so they decided to pay close attention to the weight ratios of a typical human child.

To get the muscle action just right, the University of Tokyo team also paid close attention to muscle torque and joint speeds. With these factors nailed down, Kenshiro is now 5 times stronger than it was as Kojiro, enabling it to perform some gymnastic-style leg lifts. Kenshiro could be stronger, of course, but with bigger motors comes more weight, something which the team was not willing to sacrifice.

Nakanishi’s team also discovered that using pulley systems for muscles is a good analog for the real thing, combining the right amount of torque and fluidity.

It only takes one motor to drive these pulley muscles, thus keeping down on Kenshiro’s total weight and making it more stable.

These muscles also give the robot a full 64 degrees of freedom, with 13 degrees in the neck, 13 degrees in the arms, 7 degrees in the legs and 11 in the spine.

Kenhiro’s bone structure has also been built with an eye towards weight. The team chose aluminum bones not only to be lightweight, but to also add more rigidity to the entire structure.

Up next, Nakanishi plans to continue work on his entry into the DARPA Robotics Challenge. He plans to enter another humanoid robot into the competition, which will be used as a rescue robot to carry injured or wounded humans out of harm’s way.

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