What are the materials and methods used to build ROMAC artificial air-muscles?

Question

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:

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.

Answer 1

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:

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.

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.