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So, I was reading about pneumatic artificial muscles, and to my surprise I found that there is a lot of types of air-muscles.

One that called my attention was ROMAC artificial muscle:

enter image description here

In this article it is said:

"The flexible walls of the ROMAC are not designed to work as elastometers. Rather, the geometry of the individual pyramid elements allows for greater contraction. Additionally, the wire restraining cables and pyramid elements are combined into a "single surface" actuator designed to eliminate sliding friction during contraction, reducing wear on the soft parts and extending service life."

In this other article (page 7) is said:

"The bladder is made of a sheath, that is characterized by its high tensile stiffness, its flexibility and its fluid-tightness (e.g. impregnated para-aramid fiber fabric). The netting or harness is comprised of nonstretchable flexible tension links which are joined at nodes so as to form four-sided diamond shaped apertures in the network, as shown in Figure 14. The harness expands radially and contracts axially, thereby changing the base of each protruding lobe. As a result of this mechanism the enclosed volume changes. The total surface of this actuator is constant regardless of contraction-elongation due to the tensile stiffness of the membrane material. "

But unlike other articles detailing how the muscle is built, I couldn't find anything useful about ROMAC muscles. Only illustrations explaining how it works and just the above image showing how it works.

As it is said in the first article it is a patent "GUY IMMEGA AND MIRKO KUKOLJ", but I couldn't find the patent, neither the types of material used (besides the metal cable) to achieve such shapes in the muscle.

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  • $\begingroup$ This is an interesting bit of research, however you don't appear to have a question. Could you edit this to have a question. Please make sure it's a practical, answerable questions based on actual problems that you face Please take a look at How to Ask & tour for more information on how stack exchange works. $\endgroup$
    – Tully
    May 26 at 17:48
  • $\begingroup$ @Tully I edited it, it is ok now? $\endgroup$
    – Fulano
    May 26 at 18:05
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    $\begingroup$ Thanks for making the question a little bit more concrete. The problem is that we want things that can be answered by members of this community and will be useful to others who have the same question. It is very unlikely that anyone will know the answer to your question about a patent filing from 30 years ago off hand. The only way to find a real answer to this is to do historical research and find an original source and present it. $\endgroup$
    – Tully
    May 26 at 18:12
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    $\begingroup$ Then you can reflect on it a bit more. Will someone else benefit from knowing the answer to your question? Will someone else search for this result such that it's worth me or someone else spending time to help you and the aggregate future users who will find value in this question. Or is this question likely to just sit here and be an open question that our experts can't answer and thus will dilute the helpful body of questions with answers on the site? We want the site to be concrete question with real answers to be able to help both the original poster and the many more people who visit. $\endgroup$
    – Tully
    May 26 at 18:17
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    $\begingroup$ Doesn't it say impregnated para-aramid fiber fabric in the quote you posted? Are you looking for something else? $\endgroup$
    – Chuck
    May 26 at 19:01

1 Answer 1

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I found the patent on google patents.

  • The method of fabrication:

Each base side of a protrusion is attached to a base side of an adjacent protrusion by a flexible seam or continuous fold, and each protrusion foldable about a plane dividing the protrusion into two parts from an axially-extended condition in which the base sides are substantially parallel to an axially-contracted condition in which the protrusion encloses a volume larger than that enclosed in the axially-extended condition.

A pair of axially-aligned end terminations is formed at each end of the enclosure with one of the end terminations being hollow. A pair of end connectors are each coupled to respective end terminations with one of the end connectors having an axial bore which provides fluid communication between an interior of the hollow enclosure and a source of pressurized fluid.

A provision of a plurality of protrusions articulating about their base seams and sides allows the use of substantially non-elastic material for the membrane of the hollow enclosure or bladder, thereby avoiding failure problems associated with elastomeric material.

Moreover, the hollow enclosure may be made from flat sheet material which is strong enough to withstand standard pneumatic line pressures. Alternatively, the hollow enclosure may be a single-curved hollow membrane.

Moreover, the output force exerted and work done by such an actuator is relatively large due to the large change in volume and a large percentage contraction achievable by the enclosure. The percentage contraction is large due to the ability of the enclosures to articulate without excessive radial bulging.

Furthermore, if the hollow enclosure is made from flat sheet material, the volume enclosed by the actuator in the axially-extended state becomes significantly minimized, thus increasing actuator efficiency.

Each base side of a protrusion is attached to a base side of an adjacent protrusion by a flexible seam or continuous fold, and each protrusion foldable about a plane dividing the protrusion into two parts from an axially-extended condition in which the base sides are substantially parallel to an axially-contracted condition in which the protrusion encloses a volume larger than that enclosed in the axially-extended condition.

A pair of axially-aligned end terminations is formed at each end of the enclosure with one of the end terminations being hollow. A pair of end connectors are each coupled to respective end terminations with one of the end connectors having an axial bore which provides fluid communication between an interior of the hollow enclosure and a source of pressurized fluid.

A provision of a plurality of protrusions articulating about their base seams and sides allows the use of substantially non-elastic material for the membrane of the hollow enclosure or bladder, thereby avoiding failure problems associated with elastomeric material.

Moreover, the hollow enclosure may be made from flat sheet material which is strong enough to withstand standard pneumatic line pressures. Alternatively, the hollow enclosure may be a single-curved hollow membrane.

Moreover, the output force exerted and work done by such an actuator is relatively large due to the large change in volume and a large percentage contraction achievable by the enclosure. The percentage contraction is large due to the ability of the enclosures to articulate without excessive radial bulging.

Furthermore, if the hollow enclosure is made from flat sheet material, the volume enclosed by the actuator in the axially-extended state becomes significantly minimized, thus increasing actuator efficiency.

Images of certain parts:

enter image description here

FIG. 9 is a perspective view of a four-sided pyramidal protrusion forming one of several which comprise a hollow enclosure.

FIG. 10 is a perspective view of a truncated pyramidal polyhedron which is adapted to form one of the plurality of polyhedrons of the hollow enclosure.

enter image description here

FIG. 11 is a perspective view of the forces on an element of fabric of the hollow enclosure.

FIG. 12 is a schematic force diagram showing the fabric-cable interaction.

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