engineering

Pneumatic artificial muscles

Pneumatic artificial muscles is a engineering topic covered in the lgStudy science library. This page brings together a partial reference excerpt, illustrations, worked examples, real-world applications and a short study plan, so you can understand Pneumatic artificial muscles rather than just read about it. In short: Pneumatic artificial muscles (PAMs) are contractile or extensional devices operated by pressurized air filling a pneumatic bladder. In an approximation of human muscles, pneumatic artificial muscles are usually grouped in pairs: one agonist and one antagonist.

Key takeaways

Pneumatic artificial muscles belongs to engineering; place it in that map before memorising details.
Learn the definition first, then one example that makes the definition concrete.
Connect Pneumatic artificial muscles to a quantity you can measure, compute or draw — that is where exam questions come from.
Reproduce the core statement of Pneumatic artificial muscles from memory before moving on to harder problems.

Reference excerpt

Pneumatic artificial muscles (PAMs) are contractile or extensional devices operated by pressurized air filling a pneumatic bladder. In an approximation of human muscles, pneumatic artificial muscles are usually grouped in pairs: one agonist and one antagonist. PAMs were first developed (under the name of McKibben Artificial Muscles) for use in artificial limbs. Joseph Laws McKibben, a physicist at the Los Alamos National Laboratory and motivated by his daughter Karan's paralysed hands due to polio, invented the PAM in 1957. The Bridgestone rubber company (Japan) commercialized the idea in the 1980s under the name of Rubbertuators. The actuation function of PAMs are dependent on the braid angle of the relaxed actuator state. PAMs which utilize a weave with a braid angle smaller than the critical locking angle (54.7°) will contract when pressurized, while PAMs utilizing a braid angle greater than the critical locking angle will extend when pressurized. The retraction strength of the PAM is limited by the sum total strength of individual fibers in the woven shell. The exertion distance is limited by the tightness of the weave; a very loose weave allows greater bulging, which further twists individual fibers in the weave. One example of a complex configuration of air muscles is the Shadow Dexterous Hand developed by the Shadow Robot Company, which also sells a range of muscles for integration into other projects/systems.

Advantages PAMs are very lightweight because their main element is a thin membrane. This allows them to be directly connected to the structure they power, which is an advantage when considering the replacement of a defective muscle. If a defective muscle has to be substituted, its location will always be known and its substitution becomes easier. This is an important characteristic, since the membrane is connected to rigid endpoints, which introduces tension concentrations and therefore possible membrane ruptures. Another advantage of PAMs is their inherent compliant behavior: when a force is exerted on the PAM, it "gives in", without increasing the force in the actuation. This is an important feature when the PAM is used as an actuator in a robot that interacts with a human, or when delicate operations have to be carried out. In PAMs the force is not only dependent on pressure but also on their state of inflation. This is one of the major advantages; the mathematical model that supports the PAMs functionality is a non-linear system, which makes them much easier than conventional pneumatic cylinder actuators to control precisely. The relationship between force and extension in PAMs mirrors what is seen in the length-tension relationship in biological muscle systems. The compressibility of the gas is also an advantage since it adds compliance. As with other pneumatic systems PAM actuators usually need electric valves and a compressed air generator. The loose-weave nature of the outer fiber shell also enables PAMs to be flexible and to mimic biological systems. If the surface fibers are very badly damaged and become unevenly distributed leaving a gap, the internal bladder may inflate through the gap and rupture. As with all pneumatic systems it is important that they are not operated when damaged.

Hydraulic operation Although the technology is primarily pneumatically (gas) operated, there is nothing that prevents the technology from also being hydraulically (liquid) operated. Using an incompressible fluid increases system rigidity and reduces compliant behavior. In 2017, such a device was presented by Bridgestone and the Tokyo Institute of Technology, with a claimed strength-to-weight ratio five to ten times higher than for conventional electric motors and hydraulic cylinders.

See also Artificial muscle Electroactive polymer Exoskeleton Exosuit Soft robotics

Notes

External links

Pneumatic Artificial Muscles: actuators for robotics and automation Bas Overvelde's ballooning muscles Pneumatic artificial muscles Biped robot powered by pneumatic artificial muscles Soft Robot Manipulators with McKibben muscles Air Muscles from Images Company Air Muscles from Shadow Robots

Worked examples

Example 1 — a first encounter with Pneumatic artificial muscles

Start with the simplest possible case. Write down what Pneumatic artificial muscles claims or describes in one sentence, then invent the smallest concrete situation in which that sentence is true. In engineering, the smallest case is usually a single object, a single equation or a single measurement. Check that every symbol or term in your sentence has a meaning in that case.

Example 2 — changing one variable

Take the situation from Example 1 and change exactly one quantity: double it, halve it, or set it to zero. Predict what should happen to Pneumatic artificial muscles before you calculate. Comparing your prediction with the result is the fastest way to find out whether you understand the idea or only the words.

Example 3 — an exam-style question

Typical questions about Pneumatic artificial muscles ask you to (a) state it precisely, (b) apply it to given data, and (c) explain a limitation. Practise writing all three answers in under five minutes; the third part is what separates a full-mark answer from an average one.

Applications of Pneumatic artificial muscles

In research: Pneumatic artificial muscles appears in engineering research whenever the underlying quantities have to be modelled precisely. Papers usually cite it as a starting assumption and then explore where it breaks down.
In technology and industry: Engineering practice reuses Pneumatic artificial muscles in design rules, simulations and safety margins. Knowing the idea lets you read a specification sheet and understand why the numbers look the way they do.
In the classroom: Pneumatic artificial muscles is common in secondary-school and first-year university syllabi. It links to neighbouring topics Pneumatic actuators, Robotics hardware, so understanding it makes those chapters shorter.
In everyday life: Look for Pneumatic artificial muscles outside the textbook — in sport, cooking, traffic, electronics or the sky above you. An example you found yourself is remembered far longer than one you were given.

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How to study Pneumatic artificial muscles in 20 minutes

Read the reference excerpt below once, without taking notes.
Close the page and write down what Pneumatic artificial muscles means in your own words.
Compare your version with the excerpt and mark what you missed.
Work through the three examples above with pen and paper.
Explain Pneumatic artificial muscles out loud to somebody else — or to Teacher Smith in the lgStudy chat.

Frequently asked questions

What is Pneumatic artificial muscles in simple terms?

Why does Pneumatic artificial muscles matter?

Because it connects several engineering ideas at once: it gives you a definition you can apply, a quantity you can calculate, and a way to check whether a result is plausible.

How should I study Pneumatic artificial muscles?

Read the excerpt, restate it from memory, then work through the examples and applications listed on this page. The five-step study plan above takes about twenty minutes.

What does this page cover?

It gives you a compact reference excerpt plus original lgStudy explanations, examples, applications and study material on Pneumatic artificial muscles.