Kenshiro Robot Uses Biomimicry To Copy Human Form

Tuesday, December 11, 2012

Kenshiro Robot
Researchers at the University of Tokyo are taking bio-inspired robots to new heights with Kenshiro, their new human-like musculoskeletal robot. Kenshiro’s underlying structures are the closest biomechanical creation to the human's form created.
Rolf Pfeifer and only a very few researchers have been able to mimic the human body down to muscles and bones in robotic form.

Now researchers at the University of Tokyo are taking bio-inspired robots to new heights with Kenshiro, their new human-like musculoskeletal robot revealed at the Humanoids conference this month.

They have added more muscles and more motors to their Kojiro robot from 2010, making Kenshiro’s underlying structure the closest to a human's form seen in robotics.

Kenshiro mimics the body of the average Japanese 12-year-old male, standing at 158 centimeters tall and weighing 50 kilograms. Kenshiro’s body mirrors almost all the major muscles in a human, with 160 pulley-like "muscles"—50 in the legs, 76 in the trunk, 12 in the shoulder, and 22 in the neck.

The robot has the most muscles of any other bio-inspired humanoid according to IEEE Spectrum.

The researchers found that getting a robot’s weight right is a tricky problem. Yuto Nakanishi, the head of the project, spoke about the weight problems of Kenzoh, Kenshiro's tendon-driven upper-body robot ancestor. Kenzoh was a hearty 45 kg, just for the upper body. Scaling up, they projected that a full-body Kenzoh could weigh as much as 100kg.

That was a lot of weight for a relatively small robot. So they decided to design a robot with the same weight ratios of a human. For example, a 55 kg boy would have about a 5 kg thigh and 2.5 kg calf. Kenshiro copies that ratio, with a 4 kg thigh and 2.76 kg calf.

Weight was one thing, but the researchers also tried to mimic the muscle torque and joint speeds. Kenshiro’s total power output is five times greater than the preceding Kojiro’s, allowing it to do things like the gymnastics-like leg lift.

Kenshiro can get almost the same amount of joint torque as a human, with joint angular speed not quite at human level, at 70-100 degrees per second. It’s a trade-off in weight and power: bigger and stronger motors are often heavier.

Like Kojiro, Kenshiro is actuated by a system of pulley-like muscles. This time, instead of single point-to-point muscles, they decided to make planar muscles -- flat and wide muscles that use only one motor and are much more stable.

The motors combined provide Kenshiro 64 degrees of freedom, with the exception of the hands: 13 in the neck, 13 in each arm, 7 in each leg, and 11 in the spine.  Impressive!

With the robot approaching lifelike motion, as seen in the video below, it is also conceivable that Nakanishi's work will also potentially lead to improved prosthetics and even bionic enhancements in the future.

Nakanishi is also focusing his energies on a robotics start-up called SCHAFT Inc. to participate in the DARPA Robotics Challenge. At Humanoids, he also gave us a sneak-peek as to how their submission (not Kenshiro) is shaping up. Here is a short bonus video:


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