Patent Application
20220401235
The present disclosure relates to microcapacitor arrays in general, and, more particularly, to a double-helix weave architecture for wiring of microcapacitor arrays in artificial muscles.
Traditional robotic actuation is done via electric motors or pneumatics/hydraulics. Electromagnetic step motors offer precision, use a convenient form of power, and have some capability for miniaturization, making them the usual choice for small robots and prosthetics. However, these motors are actually electromagnetic (EM) motors, which require a strong magnetic field generated either by strong permanent magnets or solenoids running large currents. Conventional EM motors often choose the latter path and require significant power to operate, while generating excess heat.
Pneumatic systems provide more force in large systems, e.g., construction vehicles, industrial assembly lines, the US Army's Mule walking robot, etc., but they require compressors, an spring leaks, and output less force when scaled down for use in compact systems. Furthermore, complex fluid motions are difficult to achieve by pneumatics because pressure is typically either on or off, producing jerky choppy motion that may be acceptable in an industrial robot but impractical in exoskeletons, prosthetics, etc.
Due to these limitations, a wide range of applications requiring actuation, such as exoskeletal locomotion, walking robots, biomimetic underwater propulsion, prosthetics, medical servo-assists, and small-scale biomimetic robots, look to different actuation systems as a potential solution, including artificial muscles. Artificial muscles can be organized in several large groups: piezoelectrics, pneumatic artificial muscles (PAM), thermal actuators, and electroactive polymers (EAP).
Embodiments described herein related to a double-helix weave architecture for an artificial muscle. In some cases, the artificial muscle includes a number of microfluidic channels that are arranged into artificial muscles fibers, where each artificial muscle fiber includes two independent mutually-unconnected microfluidic channels that are entwined in a double helix weave and maintained at opposite electrical polarity.
The patent or application file contains at least one drawing executed in color. Copies of this patent or patent application publication with color drawing(s) will be provided by the Office upon request and payment of the necessary fee.
For a more complete understanding of the present disclosure, reference is now made to the following descriptions taken in conjunction with the accompanying drawings, in which:
The following description is provided to enable any person skilled in the art to use the invention and sets forth the best mode contemplated by the inventor for carrying out the invention. Various modifications, however, will remain readily apparent to those skilled in the art since the principles of the present invention are defined herein specifically to provide microcapacitor arrays for artificial muscles.
Related patent applications described artificial muscles based on a combination of microfluidics, electrostatic actuation, liquid electrodes, and 3D-printing. Briefly, arrays of microcapacitor stacks defined microfluidically and connected in parallel can produce a longitudinal contractive force density that scales as the square of applied voltage and the inverse square of the distance between the microcapacitor plates. COMSOL simulations predict up to 33 MPa force density at current extreme limits of manufacture and materials. While these muscles boast high promise and utility, a major problem remains to be solved, i.e. how to connect and organize the microcapacitor arrays fluidically and electrically in a scalable fashion that also allows reliable loading of the liquid/gel electrodes. Embodiments herein describe an innovative solution for the needed large-scale microfluidic architecture.
The basic problem of wiring the microcapacitor arrays stems from microfluidic, mechanical, electrical, and scaling restrictions, with the added challenge that all such must be satisfied simultaneously for the architecture to be functional and practicable.
From a mechanical perspective, the microcapacitors should be arranged in columns, so that their individual microscopic contractions add up to a macroscopic elongation along the longitudinal direction of the device, to produce the required length of motion during actuation. Furthermore, the individual columns of stacked microcapacitors must be arranged in parallel to the longitudinal direction and arrayed laterally in the remaining two orthogonal dimensions. This ensures that the columns contract in parallel and the generated forces add constructively to output a cumulative force to the macroscale world.
As a third requirement, the bulk polymer between adjacent columns should be as monolithic and mechanically strong as possible, since it would serve as a tendon equivalent. In biological muscles, the individual fibers are grouped in bundles while their sheathing is made of connective tissue that becomes the tendons by which the muscle attaches to the bones. As the biological muscle fibers contract, they pull on the tendons, which transfer the generated force to the outside world. Similarly, the microcapacitor stacks convey their contraction to the surrounding polymer material, which acts as tendon and transfers a portion of the generated force to the outer macroscale world. The tendon would be strongest if there are as few disruptions as possible in the lateral directions. So, any channel serving as wiring inside the structure should be ideally precluded from running perpendicular to the tendons as it would weaken them structurally. The periodicity in the design should reflect that as well.
From electrical perspective, each microcapacitor is a set of two plates of opposite polarity, so each plate should be connected to an outside electrode of the respective polarity. Because the microcapacitors are stacked in columns, this means the polarity should alternate along each column, from plate to adjacent plate. The simplest design to achieve this is two combs kept at opposite polarity and facing each other with their prongs interdigitated. This would work electrically but produces a fluidic problem: The prongs are dead-end channels which would be difficult to fill with conducting fluid.
If the matrix of the polymer is permeable to air (e.g. silicone), this can be done by dead-end priming, but 3D printing is done in resin, which in general would have very low permeability to air. With dead-end priming not an option, it is necessary to have a through-channel to ensure proper air evacuation as the conducting fluid fills the channel. Moreover, fluidic resistance would not be constant along all prongs, which can produce shunts and resulting filling problems. To avoid that, each comb can be replaced with a binary-tree architecture, but that significantly increases the complexity as well as the vascularity in the lateral direction, thereby weakening the tendons and contradicting a major mechanical requirement.
To ensure proper evacuation and avoid tendon weakening, the wiring should be done in the longitudinal direction with longitudinal periodicity and no dead ends. This means each plate 103A, 103B should be accessed by its connecting input and output channels ideally at opposite corners as shown in
The unit device 100 is then arrayed longitudinally to produce the structure of a single muscle fiber 106 as shown in
Mechanical considerations dictate a limit to the aspect ratio between plate width and plate thickness. Excessive aspect ratio can lead to plate collapse and improper filling. That would degrade electrical performance since it would decrease the electrode area and capacitance, leading to diminished charge and force at the same voltage. Furthermore, force transfer to the tendon ought to be more efficient with smaller plates 103A-D. As a result, the optimal design should be a bundle of a large number of thin parallel fibers arrayed laterally. Also, such fibers should be wired together in a scalable fashion. The solution is again microfluidic and based on a binary tree.
The structure in shown in
There are tradeoffs in the two bundling techniques. On the upside, the first method should have most of the cross-tendon vascularity limited to parallel planes, which leaves the tendon likely stronger overall. On the downside, the first method has far fewer vertical connections, which runs a higher risk of single-point failures disabling large subsections of the overall array. Conversely, the second method 110 distributes the cross-tendon vascularity in both lateral directions, likely weakening the tendon to a greater extent, but the more distributed vascularity would be more resistant to single-point failures.
Because the output force density would scale as the inverse square of the plate separation within each microcapacitor, it would pay to make that separation as small as possible while still avoiding dielectric breakdown. Hence, in practice the plates would be arranged far denser than depicted in
Artificial muscles based on microfluidics, arrayed micro-capacitors, electrostatic forces, and 3D printing offer a great promise for a wide range of applications. Making those a reality requires a complex wiring scheme that should simultaneously satisfy a list of mechanical, microfluidic, electrical, and scaling requirements. Herein we have presented such a solution—an innovative practicable scalable double-helix weave architecture that satisfies all requirements. Hence, the embodiments herein are a major development towards practical implementation of artificial muscles.
Embodiments of the invention may include a system of microfluidic channels, where the channels are arranged into artificial muscles fibers. Each muscle fiber can include two independent mutually-unconnected microfluidic channels entwining in a double helix weave and kept at opposite electrical polarity as shown in
In some embodiments, each helix in each fiber can be a single channel that includes a series of parallel microcapacitor plates connected with connecting channels, where each rectangular (or square) plate is connected to its two neighbors in the same helix by corresponding opposite corners, e.g. from the bottom left corner through the plate to the top right corner of the same plate, to the top right corner of the next plate through that plate to its bottom left corner, etc. The arrangement of the channels ensures easy loading with liquid or gel conductor, avoidance of fluidic shunts, bubbles, and other defects.
In some embodiments, one helix uses the bottom left and top right corners of its plates for inter-plate connections within the same helix, while the other helix uses the top left and bottom right corners of its plates for the same purpose.
In some embodiments, the artificial muscle fibers are arranged in parallel with the longitudinal direction of the overall muscle, in a two-dimensional array where the fibers are arrayed in a horizontal plane and connected with one another in pairs by the same polarity, then the pairs are connected in pairs by the same polarity, etc., in a binary tree arrangement, where the number of fibers is N where N is a power of base 2, thereby producing only two inputs and two outputs to the whole array, regardless of the number of fibers in the two-dimensional array. The arrangement of the two-dimensional array is constructed to avoid dead ends, bubbles, and defects in the fluidic loading of the channels with liquid or gel conductor. Further, a goal the two-dimensional array is to ensure the same fluidic resistance along any specific pathway from input to output, ensuring symmetric vascularity, to ease loading and prevent shunts.
In some embodiments, two-dimensional arrays as described above can be arranged into an M number of planes of fiber arrays constructed that are arrayed vertically as stacks of fiber arrays, where the stacks are connected in adjacent pair by same polarity, then the pairs are connected in pairs, etc., following a binary tree architecture, where M is a power of 2, thereby producing a three-dimensional array of artificial muscle fibers, called a muscle fiber bundle. There are only two inputs and two outputs to the whole muscle fiber bundle regardless of the actual values of the parameters M and N. In some cases, M is equal to N and both are a power of 2. This arrangement of arraying maximizes the mechanical strength of the surrounding bulk material acting as tendons of the artificial muscle, by minimizing lateral vascularity, i.e. the channels running in directions lateral to the longitudinal axis of the muscle fiber bundle.
In some embodiments, the basic unit of a fiber bundle is four adjacent fibers arranged in parallel to the longitudinal axis of the muscle and bundle while also arranged in a 2×2 formation when viewed cross-sectionally, i.e. two fibers side-by-side horizontally on top and two fibers side-by-side horizontally on the bottom, wherein the matching polarities of the top pair are connected in pairs, just as the matching polarities of the bottom pair are also connected in pairs, and finally the matching polarities of the two pairs are also correspondingly connected in pairs, thereby producing a configuration wherein the 2×2 fiber bundle has only two inputs and two outputs regardless of the length of the bundle.
The fiber bundle described above can itself be arrayed first in the horizontal then in the vertical direction by iterative doubling, e.g. one unit bundle doubles to two horizontal unit bundles, connected in pairs by matching polarity, then the pair is doubled vertically to produce a 2×2 array of bundles, also connected in pairs by polarity, followed by horizontal doubling, etc., thereby alternating the direction of the doubling with each doubling, to produce a fractal architecture of arbitrary size and matching pair-wise connectivity. This bundle arraying maximizes the resilience of the structure to defects, at the expense of additional lateral wiring, i.e. increased lateral vascularity, that may decrease the strength of the tendon compared to the stacks of two-dimensional arrays described above.
In some cases, the fiber bundles may be of variable size of power of base 2, as lateral direction is alternated, to adjust and optimize the strength of the tendon versus the resilience of the structure to defects. There may be P number of fibers, where P is a power of 2, that are arrayed in one lateral direction, e.g. horizontal, then fractally connected accordingly in the same plane. This structure of P fibers can then be arrayed Q times along the orthogonal lateral direction, e.g. vertical, wherein Q is a power of 2, to adjust and optimize the strength of tendon versus defects resilience, e.g. with values of (P,Q) of (2,2), (4,4), (8,8), (16,16), (2,4), (2,8), (2,16), (4,8), (4,16), (8,16), etc. The resulting bundle can itself be arrayed by the same multiplicities in alternating lateral dimensions, to allow for array growth to arbitrary size.
This description provides exemplary embodiments of the present invention. The scope of the present invention is not limited by these exemplary embodiments. Numerous variations, whether explicitly provided for by the specification or implied by the specification or not, may be implemented by one of skill in the art in view of this disclosure.
It is to be understood that the above-described arrangements are only illustrative of the application of the principles of the present invention, and it is not intended to be exhaustive or limit the invention to the precise form disclosed. Numerous modifications and alternative arrangements may be devised by those skilled in the art in light of the above teachings without departing from the spirit and scope of the present invention.
This patent application is a non-provisional of and claims the benefit of U.S. Provisional application 63/213,178, filed Jun. 21, 2021, which is hereby incorporated by reference in its entirety.
| Number | Date | Country | |
|---|---|---|---|
| 63213178 | Jun 2021 | US |
