Implementation

The primary advantage of the McKibben compared to all other actuators presented is their raw force output (relative to size and ease of construction). The use of air pressure allows the actuator to generate larger forces than those reliant on thermal expansion, electric fields, or the spring-like properties of a twisted string. High force output lends well to applications that involve lifting loads, such as exoskeletons, and the high power density also allows them to be downscaled for precision surgical robotics.

When the McKibben actuators (black tubes) contract, the leg will straighten.

The same design, fitted around a human leg. Note the electrodes, used to sense muscle movement and control the actuators accordingly.

Exoskeletons

By far the most common application of McKibben actuators, various research groups have demonstrated these actuators as flexible joints in exoskeletons. One design (left) has been shown by a Taiwanese research group lead by Y. P. Sun.

This type of implementation can be simple but effective. Two frames, each designed to fit around a human limb, are connected by a hinge joint. The McKibben actuator extends across the two frames, and bends the hinge joint such that the exoskeletons move alongside a natural human joint.

A common use for exoskeletons is amplifying human strength and endurance (think: Iron Man). However, exoskeletons can also have a therapeutic application, potentially restoring movement to paralyzed individuals, or assisting movement in those suffering from muscular atrophy.

Surgical Robotics

Surgical robotics deals with robots for use in surgeries, allowing for precise control of scalpels, catheters, etc. for surgical operations. The advantages of a robot for surgery are numerous -- they can be remotely controlled and, unlike human surgeons, do not have shaky hands. Many surgical robot designs have been demonstrated, such as Intuitive Surgical's da Vinci machine, Auris Health's Monarch, and Stryker Medical's Mako.

While no commercial surgical robot makes use of McKibben actuators, there is potential for this to emerge in the future. McKibben actuators that operate using hydraulics (liquid pressure) can be controlled precisely, and move in multiple degrees of freedom.

One proposed design by researchers at KU Leuven's Robot-Assisted Surgery group (right) features an intricate arrangement of small-scale McKibben actuators, which can create bending, twisting, shortening, or extension of the whip-like arm.

Model and images of the RAS group's steerable limb. Water is used to drive the McKibben actuators.

References

Sun, Yun-Ping et al. “Design of a Bionic-Inspired Exoskeleton Robot for Lower Limb Assist.” Journal of Vibroengineering 18.8 (2016): 5452–5461. Crossref. Web.
"Steerable Instruments." Departement Werktuigkunde – Departement Werktuigkunde (WTK), 6 Jan. 2018 www.mech.kuleuven.be/en/pma/research/ras/researchtopics/steer.html.

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