Kenshiro: Strong robot with 160 muscles.

The tendon-controlled humanoid robot created by the University of Tokyo has more than 160 artificial muscles and is the result of many years of experience. Around 100 brushless dc motors from maxon ensures the 1.58 m tall robot has humanlike movements.

The University of Tokyo has developed a tendon-controlled humanoid robot that is capable of very realistic humanlike movements. He is called Kenshiro – a well-known name in Japan, thanks to a hero in a famous 1980s manga comic series. During the development of the robot, the Japanese scientists used the human anatomy as orientation to create an artificial human that looks as natural as possible. “We wanted to understand the movements and appearance of humans and replicate it as closely as possible in Kenshiro,” explains Prof. Kei Okada. With a height of 1.58 m and weight of 50 kg, the robot corresponds to the dimensions of a 12-year old Japanese boy.

To imitate the human anatomy, the scientists equipped Kenshiro with the most important human muscles: 50 in the legs, 76 in the torso, 12 in the shoulder and 22 in the neck. Thus the robot has the largest number of muscles ever installed in a humanoid robot. In comparison: with around 640 muscles, humans have a very complex anatomy. Kenshiro's 160 individual tendon-controlled “muscles” make many humanlike movement patterns possible, but the robot does not come close to copying all human movements, as the biological movement patterns of a human being is extremely complex. Kenshiro can move his arms, legs and torso. He still has to learn how to walk properly. But how does a robot learn humanlike movements? It's simple: demonstrate a movement, he will then imitate it. A simple learning method, implemented by means of open-source intelligent software and a mechanical interface. But learning how to walk requires more.
Kenshiro's “bones” are made of aluminum and, as is the case in the human body, are movably connected to each other.,The 50 kg weight presented the biggest challenges to the scientists, led by Professor Masayuki Inaba. A replica with the size of an adult would weigh approx. 100 kg. This means a higher load, higher energy requirements and slower movements.

93 motors for 160 muscles
The researchers from the Jouhou System Kougaku Laboratory (JSK) of the University of Tokyo decided on a drive system from maxon. Kenshiro's 160 muscles are contracted by 93 maxon EC brushless DC motors. For the contraction of special muscles, for example the abdominal muscle and thoracic muscles, only a single motor provides the necessary drive. Here the brushless EC 16 and EC 22 motors of maxon are used. The electronically commutated servo motors stand out with excellent torque characteristics, high dynamics, an extremely wide speed range, and their very long service life. Strong BLDC motors are required for the muscle contractions, therefore 60 W to 100 W maxon motors are used. Another important criteria for the motor selection was the temperature the motor as it is not possible to install a cooling system in the robot. According to Prof. Kei Okada, it was therefore very important that the motors develop very little heat.

JSK has been building different robots since 1980 – first various service robots and industrial robots and today also humanlike robots like Kenshiro. Just like with his predecessors Kenta, Kotaro, Kojiro and Kenzoh, the aim is to have Kenshiro copy the human body as closely as possible. But this also means he needs a humanlike appearance. Therefore the Japanese scientists are currently working on a skin for the robot. In the near future, Kenshiro should be able to interact with his environment even more actively. The next goal is to improve Kenshiro's gait, so that he can walk longer and with more stability.

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