project specification

Musculoskeletal Lower-Limb Robot

A musculoskeletal robot using a bundle of thin McKibben muscles which enables a multifilament muscle that has characteristics similar to those of human muscles. Actuators of conventional musculoskeletal robots are heavy, not densely attached and have poor back-drivability. Multifilament muscles are light and can be densely attached and therefor we can attach them to the musculoskeletal robot as skeletal muscle and achieve a redundant system that is equivalent to a human drive mechanism. The multifilament muscle has a tendon at each end and is connected to the skeleton. One end has a tendon made of Dyneema (high-density polyethylene) fibers and an air-supply port that is made of heat-shrink plastic. The other end has a tendon only.

Specifications

Actuator Silicone Tube
1.3 mm outer diameter
0.9 mm inner diameter
Outer diameter of the thin McKibben muscle1.8 mm
Maximum contraction force per thin muscle11 N
Maximum contraction ratio24 %
Air pressure0.35 MPa
Outer-sleeve yarnTetoron mono-filament
0.12 mm

Overview

Contrary to other types of actuators, multi-filament muscles are lighter and can be densely attached. Therefore, they can be attached to a robot's skeleton in a similar way as muscle in a human body and achieve a redundant system that is equivalent to a human drive mechanism.
The prototype robot is a redundant system, in which 20 multi-filament muscles work independently. It demonstrates nearly the same range of motion as a human lower limb by using the same muscle arrangement and bone structure.

The McKibben muscle specifically developed for this robot is thin, deformable and light enough to be used inside a body with limited space; it generates a comparable contracting force and ratio as human muscles, and also its elasticity and compliance are similar. Furthermore, the thin McKibben muscles can be bundled to form various shaped multi-filament muscles, (e.g. a muscle that has two ends on one side, such as a biceps muscle).


Multi-filament muscles

The project also established a method for fabricating multi-filament muscles: They have a tendon at each end and are connected to the skeleton. One end has a tendon made of Dyneema (high-density polyethylene) fibers and an air-supply port that is made of heat-shrink plastic. The other end only has a tendon.
The multi-filament muscle works as a contracting linear actuator.


The lower-limb musculoskeletal robot

The robot itself has 8 multifilament muscles that affect knee motions on the thigh and 12 muscles that affect ankle motions on the lower leg, where the shape and size of the muscles are almost equivalent to those of a human.
The multifilament muscles are attached to the robot's skeleton considering the fixed ends and the directions of the tendons. The sheath of a tendon, made of a soft tube, makes the tendon move smoothly.

The muscles are provided with air pressure through a regulator and solenoid valves. The air pressure is controlled by a single regulator and the muscles on our musculo-skeletal robot are operated by ON/OFF control solnoid valves.

References

Describes the background of the project, and goes into the McKibben muscles. Describes the design of the multifilament muscle and its structure. Goes into the design of the lower limbs and the design of the knee motions.

Shunichi Kurumaya, Koichi Suzumori, Hiroyuki Nabae, et al - ROBOMECH Journal 2016.

Wevolver 2022