SLIDING TENDONS FOR HIGH-STRAIN ELASTOMER ACTUATORS

A soft structure fiber reinforcement and actuation technology is provided. In an example embodiment, the tendon-driven, fiber-reinforced elastomer membrane comprises an elastomer matrix material and a fiber array embedded within the elastomer matrix material. The one or more tendons are not mechanically bonded to the elastomer matrix material, such that the one or more embedded tendons are able to move through the elastomer matrix material. One or more apparatuses may employ one or more such tendon-driven, fiber-reinforced elastomer membranes for use in a variety of applications.

BACKGROUND

Rigid structures are prone to critical failure when disturbances or perturbations result in high enough stress. For example, rigid robotic structures are prone to critical failure. In contrast, soft, flexible structures may be capable of bending and thus may accommodate such a disturbance and return to an operational state. As an additional example, traditional rigid robotic actuators do not drive motion of soft structures effectively, because they rely on transmitting large torques/forces through small contact points. Furthermore, it may be advantageous to change the shape and/or material properties of various structures, which may not be accomplished using traditional rigid structures. Thus, a need exists for soft structures with selectively controllable geometry and stiffness control.

BRIEF SUMMARY

According to various embodiments, a tendon-driven, fiber-reinforced elastomer membrane is described. The membrane comprises an elastomer matrix material; and a fiber array embedded within the elastomer matrix material, wherein: the fiber array comprises one or more tendons; and the one or more tendons are not mechanically bonded to the elastomer matrix material such that the one or more embedded tendons are able to move through the elastomer matrix material.

According to various embodiments, an inflatable apparatus is also described. The apparatus comprises: one or more tendon-driven, fiber-reinforced elastomer membranes, each of the one or more tendon-driven, fiber-reinforced elastomer membranes comprising: an elastomer matrix material; and a fiber array embedded within the elastomer matrix material, wherein: the fiber array comprises one or more tendons; and the one or more tendons are not mechanically bonded to the elastomer matrix material such that the one or more embedded tendons are able to move through the elastomer matrix material. The apparatus further comprises: a rigid plate, wherein the rigid plate comprises one or more fluid ports; a clamp ring; and one or more securing components, wherein the one or more securing components secures the clamp ring to the rigid plate.

DETAILED DESCRIPTION

The present invention will now be described more fully hereinafter with reference to the accompanying drawings, in which some, but not all embodiments of the invention are shown. Indeed, certain embodiments of the invention may be embodied by many different forms and should not be construed as limited to the embodiments set forth herein; rather, these embodiments are provided so that this disclosure will satisfy applicable legal requirements. Like numbers refer to like elements throughout.

FIG.1Ashows an example tendon-driven, fiber-reinforced elastomer membrane100. In some embodiments, the tendon-driven, fiber-reinforced elastomer membrane100comprises an elastomer matrix material130and a fiber array150(see alsoFIG.1B). In some embodiments, the fiber array150comprises one or more tendons110, visible in bothFIGS.1Aand D. In some embodiments, the fiber array150may also comprise one or more fixed fibers120.

In some embodiments, the elastomer matrix material130may be an elastic material that allows for large strains. For example, the elastomer matrix material may include a silicone material. In an example embodiment, the elastomer matrix material130may be constructed out of Ecoflex30elastomer from Smooth-On Inc. In some embodiments, the tensile strength of the elastomer matrix material is up to 200 pound-force per square inch (psi). In some embodiments, the 100% modulus of the elastomer material up to 10 psi. In some embodiments, the elongation at break of the elastomer material is up to 900 percent. Of course, additional or other elastomers may be used, as desirable for certain applications.

FIG.1Bshows an example a fiber array150comprising one or more tendons155(see alsoFIG.1C). In some embodiments, the fiber array150comprises one or more fixed fibers160(see alsoFIG.1D). In some embodiments, the one or more tendons155may be interwoven between others of the one or more tendons155and/or one or more fixed fibers160of the fiber array150. For example, one or more fixed fibers160may take the form of concentric rings of varying radii, for example, by knotting a first end and second end of a fixed fiber160together to form a knot160a. In some embodiments, the knot160aformed by the first end and second end of the fixed fiber160may be coated in an adhesive, such as cyanoacrylate glue, to prevent or mitigate slipping or untying of said knot160a. In some embodiments, the one or more fixed fibers160may form a continuous ring, such that the one or more fixed fibers160do not require knots160a. The one or more fixed fibers160may thus, in certain embodiments, be arranged throughout the fiber array150. In some embodiments, the one or more fixed fibers160may be equally distributed throughout tendon-driven, fiber-reinforced elastomer membrane; in other embodiments, distribution may be non-uniform, if desired.

Still further, one or more tendons155may be woven through and/or around the one or more fixed fibers160. In some embodiments, one end of the one or more tendons155may be anchored to a fixed fiber160, for example, by knotting the tendon155around the fixed fiber160to form a knot155a. In some embodiments, the tendon155may be knotted around the innermost fixed fiber160or otherwise. In some embodiments, interweaving the one or more tendons155may aid in constraining the one or more tendons such that the one or more tendons don't undesirably shift and/or move during actuation/de-actuation and/or inflation/deflation. In some embodiments, interweaving the one or more tendons155may also aid in preventing the one or more tendons from ripping through the elastomer matrix material130at high stress locations, such as at the internal edge of a clamp ring. In some embodiments, four tendons may be included in the fiber-reinforced elastomer membrane. Each of the fibers may be spaced substantially equidistant from one another.

In certain embodiments, the one or more tendons may also be of sufficient length, such that a first end and second end of a tendon extend past the edge of the tendon-driven, fiber-reinforced elastomer membrane100. As a result, the first end and second end may be grasped externally in at least one embodiment, such that an embedded portion of the length of a tendon may be embedded within the elastomer matrix material130, while a first external portion of the length and/or a second external portion of the length of the tendon may be external the elastomer matrix material130. For example,FIG.1Ashows the first external portion110aof a tendon110, the embedded portion110bof the tendon110, and the second external portion110cof the tendon110.

In some embodiments, the length of the first and/or second external portions of the length of the one or more tendons155may satisfy a length threshold such that the length of the first and second external portions of the length of the tendon are sufficient such that the length of the one or more tendons110are longer than the diameter of the tendon-driven, fiber-reinforced elastomer membrane100. The diameter of the tendon-driven, fiber-reinforced elastomer membrane may be any suitable size. In some embodiments, the diameter of the tendon-driven, fiber-reinforced elastomer membrane may range between approximately 100 millimeters to 125 millimeters. In some embodiments, the diameter of the tendon-driven, fiber-reinforced elastomer membrane is approximately 114 millimeters.

In some embodiments, the length of the one or more tendons110is sufficient such that the first external portion and/or second external portion of the tendons may be grasped or otherwise interacted with. For example, the length of the first and second external portions of the length may be configured such that both ends are easily accessed such that they may be manipulated. In some embodiments, a portion of the first and second external length portions of the one or more tendons may be wound. In some embodiments, a portion of the first and second external length portions of each of the one or more tendons may be wound in utilizing one or more pulleys310, as depicted later inFIG.3.

In some embodiments, the one or more tendons155may be comprised of a sufficiently smooth fiber.FIG.1Cdepicts a single tendon155. In some embodiments, the one or more tendons are monofilament fibers. In some embodiments, the static coefficient of friction between the one or more tendons155and the elastomer matrix material130is sufficiently low, such that the one or more embedded tendons155may slide through the elastomer matrix material130with low resistance. For example, in some embodiments, the static coefficient of friction between the one or more monofilament fibers and the elastomer matrix material160may be 0.3 or less. In some embodiments, the smoothness of the one or more tendons may prevent and/or limit the amount of the elastomer matrix material permeating the one or more associated pores of the one or more tendons155, such as during curing. In some embodiments, the surface roughness of the one or more monofilament fibers155may be below a predefined surface roughness value. Surface roughness may be measured in a variety of way including but not limited to arithmetical mean deviation, root mean squared, and/or variations thereof. For example, in some embodiments, the one or more monofilament fibers may have an arithmetic average roughness of 0.4 micrometers or less. As such, in some embodiments, the one or more tendons155do not mechanically bond to the elastomer matrix material130.

In some embodiments, the one or more tendons155may be cylindrical in shape. In some embodiments, the one or more tendons are comprised of one or more polymeric materials. In some embodiments, the one or more tendons may be comprised of nylon, polyvinylidene fluoride (PVDF), polyethylene. In some embodiments, the one or more tendons may be comprised of one or more fluoropolymers including fluorinated ethylene propylene (FEP), perfluoroalkoxy alkane (PFA), ethylene tetrafluoroethylene (ETFE), polyether ether ketone (PEEK). In some embodiments, each of the one or more tendons155are comprised of the same material. In some embodiments, the one or more tendons155are comprised of one or more different materials.

In some embodiments, the one or more fixed fibers160may be comprised of the same one or more materials as the one or more tendons155as described above. In some embodiments, the one or more fixed fibers160may be comprised of different, for example, one or more rough fibers. For example, the one or more fixed fibers160may be comprised of yarn, cotton thread, or the like.FIG.1Ddepicts a single fixed fiber160. In some embodiments, the static coefficient of friction between the one or more fixed fibers160and the elastomer matrix material130is larger than the coefficient of bonding between the one or more one or more tendons155and the elastomer matrix material130. In some embodiments, the static coefficient of friction between the elastomer matrix material130and the one or more fixed fibers is sufficiently large such that the one or more embedded tendons either do not slide through the elastomer matrix material130or slide with a high resistance. For example, in some embodiments, the one or more fixed fibers160may have a static coefficient of friction with the elastomer matrix material130greater than 0.3. In some embodiments, the smoothness of the one or more fixed fibers160may promote permeation of the elastomer matrix material130into the one or more associated pores of the one or more fixed fibers160, such as during curing. In some embodiments, the one or more fixed fibers160may have a larger arithmetic average roughness than that of the one or more monofilament fibers155. For example, in some embodiments, the one or more monofilament fibers may have an arithmetic average roughness of 10 micrometers or more. As such, the one or more fixed fibers160may mechanically bond to the elastomer matrix material130.

In some embodiments, the fiber array150may be initially arranged in a mold base, such as mold base190. In some embodiments, the one or more fixed fibers120are formed into concentric circles and are arranged throughout the mold base190. In some embodiments, the radii of the one or more fixed fibers may vary. In some embodiments, the radii of the one or more fixed fibers120may be the same. In some embodiments, the one or more fixed fibers120may be equally distributed throughout the mold base190such that the one or more fixed fibers are equally distributed throughout the tendon-driven, fiber-reinforced elastomer membrane100. In some embodiments, the one or more fixed fibers may be unequally distributed throughout the mold base190such that the one or more fixed fibers are unequally distributed throughout the tendon-driven, fiber-reinforced elastomer membrane100.

In some embodiments, the one or more tendons110pass through the center of the one or more concentric circles formed by the one or more fixed fibers120. In some embodiments, the one or more tendons110are bonded to the one or more fixed fibers120. In some embodiments, the one or more tendons110are bonded to the innermost fixed fiber of the one or more fixed fibers120. In some embodiments, the one or more tendons110are bonded to one or more fixed fibers at each point where the one or more tendons110intersect the one or more fixed fibers120.

In some embodiments, the mold base190may be indicative of the overall shape of the tendon-driven, fiber-reinforced elastomer membrane100. The shape of the tendon-driven, fiber-reinforced elastomer membrane100may be configurable. In some embodiments, the tendon-driven, fiber-reinforced elastomer membrane100may generally define a sheet plane such that the shape of the tendon-driven, fiber-reinforced elastomer membrane100is generally planar. In some embodiments, the tendon-driven, fiber-reinforced elastomer membrane100may be generally cylindrical or curved and the sheet plane may be locally defined as the plane tangent to the local curvature of the tendon-driven, fiber-reinforced elastomer membrane100. In some embodiments, the shape of the tendon-driven, fiber-reinforced elastomer membrane100may be generally conical. In some embodiments, the shape of the tendon-driven, fiber-reinforced elastomer membrane100may be generally spherical. The fiber array150may be arranged in a suitable configuration to match the desired shape of the tendon-driven, fiber-reinforced elastomer membrane100. However, as will be obvious to one of skill in the art, any geometric configuration of the tendon-driven, fiber-reinforced elastomer membrane100may be contemplated. Generally, the thickness of the tendon-driven, fiber-reinforced elastomer membrane100may be small. For example, the thickness of the tendon-driven, fiber-reinforced elastomer membrane100may be significantly smaller than the width and/or length of the tendon-driven, fiber-reinforced elastomer membrane100. In some embodiments, the tendon-driven, fiber-reinforced elastomer membrane may range between 2 millimeters to 10 millimeters in thickness. In some embodiments, the tendon-driven, fiber-reinforced elastomer membrane is approximately 5 millimeters thick.

Once the fiber array150is sufficiently configured, the elastomer matrix material130, which may be initially in liquid form, may be poured into the mold base190to a sufficient height. For example, the elastomer matrix material130may be poured such that it covers the highest point of the fiber array150by a threshold height. In some embodiments, the fiber array150may be embedded within the center of the elastomer matrix material130. In some embodiments, the elastomer matrix material130may be degassed before and/or after pouring into the mold base190. The elastomer matrix material130may be allowed to cure for one or more predetermined durations of time and at one or more predetermined temperatures. For example, the elastomer matrix material130may be allowed to cure at room temperature for 24 hours, 80° C. for 2 hours, and 100° C. for 1 hour. In some embodiments, the elastomer matrix material130may be allowed to cure at room temperature. After curing, the elastomer matrix material130may form a solid but elastic material with an embedded fiber array150and may thus form the tendon-driven, fiber-reinforced elastomer membrane100.

During the curing process, the elastomer matrix material130may not significantly chemically and/or mechanically bond to the one or more tendons155comprising the fiber array150. This may be due to the relatively small arithmetic average roughness of the one or more tendons. As such, the one or more tendons155, although embedded within the elastomer matrix material130, may have the freedom to glide or otherwise move within the elastomer matrix material130. In some embodiments, the elastomer matrix material130may chemically and/or mechanically bond to the one or more fixed fibers160comprising the fiber array150. As such, the one or more fixed fibers embedded within the elastomer matrix material130may provide fixed, non-adjustable support.

FIGS.2A-Cillustrate the tendon-driven, fiber-reinforced elastomer membrane as an inflatable apparatus. In some embodiments, the tendon-driven, fiber-reinforced elastomer membrane100may be secured to a flat, rigid plate215using a clamp ring210as depicted inFIG.2A. The clamp ring210may have a smaller diameter than the tendon-driven, fiber-reinforced elastomer membrane and as such, the tendon-driven, fiber-reinforced elastomer membrane may be fitted over the clamp ring210. In some embodiments, the clamp ring210may have a diameter between approximately 85 millimeters to 110 millimeters. In some embodiments, the clamp ring210has a diameter of approximately 94 millimeters.

In some embodiments, the tendon-driven, fiber-reinforced elastomer membrane205may include one or more clamp entry hole140(FIG.1A) for the clamp ring210to be attached to the rigid plate215. In some embodiments, the clamp ring210may secure the tendon-driven, fiber-reinforced elastomer membrane205using one or more screws that extend from the clamp ring210, through the tendon-driven, fiber-reinforced elastomer membrane205such as through one or more clamp entry holes140, and into the rigid plate215. One or more fluid ports within the rigid plate may allow fluid to enter the cavity between the rigid plate and the membrane, thus inflating the membrane with the fluid. The tendon-driven, fiber-reinforced elastomer membrane100may expand and inflate away from the rigid plate. In some embodiments, the one or more fluid ports may be fluidically connected to one or more fluid pumps.

FIG.2Aalso depicts the tendon-driven, fiber-reinforced elastomer membrane205in a deflated state200. For example, little to no fluid may occupy the cavity between the rigid plate215and the tendon-driven, fiber-reinforced elastomer membrane205, thus resulting in the deflated state200.

FIG.2Bshows the tendon-driven, fiber-reinforced elastomer membrane205in an inflated state220. For example, a volume of fluid may enter or otherwise occupy a partial or full volume of the cavity between the rigid plate215and the tendon-driven, fiber-reinforced elastomer membrane205. As the tendon-driven, fiber-reinforced elastomer membrane205inflates due to the presence of the fluid within the cavity between the space between the rigid plate215and the tendon-driven, fiber-reinforced elastomer membrane205, the one or more tendons comprising the fiber array are drawn into the elastomer matrix material and are pulled by one or more attachment points, e.g. one or more knots formed by a tendon around one or more fixed fibers. The one or more tendons may be pulled by the one or more attachment points onto the innermost fixed fiber and allow for the expansion to occur.

FIG.2Cshows the tendon-driven, fiber-reinforced elastomer membrane205in an actuated state. The tendon-driven, fiber-reinforced elastomer membrane205may enter an actuated state by applying tension to one or more tendons. Applying tension to the one or more tendons may add stress to the tendon-driven, fiber-reinforced elastomer membrane205. The asymmetric application of tension to the one or more tendons may cause a shift in the geometry of the tendon-driven, fiber-reinforced elastomer membrane205in the inflated state. For example, pulling a tendon end away from the center of the tendon-driven, fiber-reinforced elastomer membrane205may cause the tendon-driven, fiber-reinforced elastomer membrane205to bend in that direction. This may be due in part to the one or more attachment points between the one or more tendons and the one or more fixed fibers, which may experience a force in a direction of the applied tension. Additionally, applying tension to the one or more tendons may cause a change in the portion of the length of the embedded portion of the one or more tendons and the first and second external portions of the one or more tendons. For example, applying tension to a tendon may cause the length of the embedded portion of the tendon to decrease and the length of the first and second external portions of the tendon to increase. The resulting pressure experienced across the tendon-driven, fiber-reinforced elastomer membrane205may be based at least in part on the length of the one or more tendons, particularly the length of the embedded portion of the one or more tendons. As such, the tracking the length of each tendon and the pressure across the tendon-driven, fiber-reinforced elastomer membrane205may enable geometric control of the inflatable apparatus.

In some embodiments, the length of each tendon and/or the pressure across the tendon-driven, fiber-reinforced elastomer membrane may be controlled in part using a servomotor.FIG.3illustrates an example tendon-driven, fiber-reinforced elastomer membrane305with a servomotor315and one or more pulleys310. In some embodiments, each end of the one or more tendons may be attached to the servomotor315. In some embodiments, a portion of the first and second external length of the one or more tendons may be wound around one or more pulleys310. In some embodiments, the servomotor315may be a rotary actuator and/or linear actuator capable of controlling the angular and/or linear position of the first end and second end of the one or more tendons. For example, the servomotor315may be actuated such that the embedded length of the one or more tendons may be shortened. As another example, the servomotor315may be actuated such that the embedded length of the one or more tendons may be lengthened. In some embodiments, the servomotor315may provide a torque feedback indicative of the pressure experienced by the tendon-driven, fiber-reinforced elastomer membrane205. In some embodiments, the servomotor315may provide a length feedback indicative of current embedded length of the one or more tendons.

FIG.7further depict an exploded view of an example apparatus which uses a tendon-driven, fiber-reinforced elastomer membrane. In particular, the tendon-driven, fiber-reinforced elastomer membrane705may be positioned between a clamp ring710and a clamp body750. The tendon-driven, fiber-reinforced elastomer membrane705may be positioned over a plurality of attachment points upon the clamp body750and the clamp ring710may be further positioned over the tendon-driven, fiber-reinforced elastomer membrane. One or more securing screws may be used to tighten the clamp ring710to the clamp body750configured with one or more threaded holes. The clamp force exerted by the clamp ring710may be controlled by the tightness of the one or more screws. The clamp force may control the amount of fluid which can leak from the tendon-driven, fiber-reinforced elastomer membrane through the clamp. The clamp force may also determine the friction experienced by each tendon.

Each tendon (not shown) may be threaded between a tendon guide715and a ball bearing. They may further be wrapped around a pulley740. The pulley740may further be connected to a servomotor725, which may be used as a rotary actuator and/or linear actuator, as described above. Furthermore, the clamp body750may be configured with a pressure tap730and/or tube fitting735, thereby allowing pneumatic actuation of the tendon-driven, fiber reinforced elastomer membrane705. In some embodiments, the servomotor725may provide feedback (e.g., torque feedback, length feedback, etc.)

FIG.4Aillustrates an inflatable apparatus comprising a tendon-driven, fiber-reinforced elastomer membrane with a servomotor and one or more pulleys. In the inflated state410, the embedded length of the one or more tendons may be controlled such that the tension applied to the tendon-driven, fiber-reinforced elastomer membrane is minimal. For example, during the inflated state410, the tendon-driven, fiber-reinforced elastomer membrane may be able to fully expand.

FIGS.4B-Cillustrate an example actuated state420and430of the tendon-driven, fiber-reinforced elastomer membrane utilizing a servomotor and one or more pulleys. During the actuated state420, the embedded length of the tendon may be shortened on the right side, such that the tensions applied to the tendon-driven, fiber-reinforced elastomer membrane is asymmetric and greater on the right side. For example, this may occur in part due to one or more attachment points, e.g. one or more knots formed by a tendon around one or more fixed fibers, which may apply a force to the fixed fiber. Since the fixed fiber may be embedded in, and in some instances, chemically and/or mechanically bonded with the elastomer matrix material, the asymmetric application of tension to the right-most tendon results in a compressed tendon-driven, fiber-reinforced elastomer membrane with a right-leaning curvature. Similarly, during the actuated state430, the embedded length of the tendon may be shortened on the left side, such that the tension applied to the tendon-driven, fiber-reinforced elastomer membrane is asymmetric and greater on the left side. This results in a compressed tendon-driven, fiber-reinforced elastomer membrane with a left-leaning curvature.

Similarly,FIGS.8A-Fdepicts an example apparatus configured with a tendon-driven, fiber-reinforced elastomer membrane in various states of actuation. In particular,FIG.8Ashows the apparatus in the deflated state andFIG.8Bshows the apparatus in the inflated state without any tendon actuation.FIG.8Cshows the apparatus in an actuated state. Here, the apparatus is configured with four tendons and one tendon is actuated via applied tension. As such, the tendon-driven, fiber-reinforced elastomer membrane transforms from a substantially symmetrical inflated state to an asymmetric state with a curvature (e.g., bend) in the membrane.FIG.8Dalso shows the apparatus in an actuated state using two tendons. Here, a more pronounced curvature is depicted due to tension applied to two adjacent tendons. Alternatively, a two tendon actuation may apply tension to two tendons of opposite sides as shown inFIG.8E, resulting in a grabbing motion of the membrane. As shown inFIG.8F, the two tendon actuation with applied tension to tendons of opposite sides may be used to grasp objects in between the outer surface of the membrane. The grasping strength applied by the membrane may be controlled by the tension applied to the tendons. For example, greater applied tension to one or more of the two tendons may result in a stronger grasp by the membrane. In some embodiments, the grasping force may also be controlled by changing the inflation pressure.

FIG.9shows the membrane tip location (e.g., the top-most point of the membrane; depicted as1050inFIG.10) in an x-z coordinate plane as a function of tendon pull force applied to a single tendon (e.g.,FIG.8Cand depicted by the diamonds) and an equal tendon pull force applied to each of the four tendons (e.g., depicted by the stars). Each apparatus was inflated to approximately 16.9 kilopascal (kPa) and 16.4 kPa, respectively, and the force required to retract a tendon to its initial embedded length was measured. For the single tendon, a force of 32.6 Newtons (N) was required to retract the single tendon. For the equivalently applied tension to each tendon, a force of 22.0 N per tendon.

FIG.10depicts an inflated fiber-reinforced elastomer membrane without tendons in the inflated state. The corresponding coordinate system also shown inFIG.10was obtained using motion capture markers, which were outfitted on the fiber-reinforced elastomer membrane, thus yielding a view of the fiber-reinforced elastomer membrane as shown.FIG.11depicts a plot of the height of the inflatable apparatus with tendons (as shown with the ‘high clamp force’ and ‘low clamp force’ curves) and without tendons. The high clamp force apparatus with a tendon-driven, fiber-reinforced elastomer membrane was fitted such that the clamp force was sufficient to stop fluid (e.g., air) from leaking under the clamp while the low clamp force apparatus with a tendon-driven, fiber-reinforced elastomer membrane was fitted such that the clamp force allowed for fluid leaks. The height of the inflated membrane is measured using the motion captured marker1050, located at the center of the membrane. The stretch of the membrane along a tendon is measured by fitting a spline along the motion capture markers from the location of the clamp (e.g., at z=0 as shown by the coordinate system inFIG.10) to the highest marker (e.g.,1050). Table 1 further describes the values depicted inFIG.11.

Table 1 above summarizes measures ofFIG.10. In particular, a maximum pressure, height, and change in diameter are shown. Further, the length change for the membrane was measured as the stretch of the elastomer along the path of the tendons as indicated by a spline between motion capture markers. The maximum percentage stretch of the spline (MPSS) is measured along the spline between two consecutive motion capture markers. Friction generated between a tendon and the elastomer may reduce the extension of the elastomer, particularly when a high clamp force is applied as tendons slide under the clamp. As such, it may be beneficial to lubricate the tendons such that the friction between the tendon and the elastomer is reduced. The tendons may be lubricated using any sufficient lubricant.

The ability to dynamically actuate the tendon-driven, fiber-reinforced elastomer membrane by controlling the applied tension and therefore the embedded length of the one or more tendons may allow for different tendon-driven, fiber-reinforced elastomer membrane geometries. Such controllability of tendon-driven, fiber-reinforced elastomer membrane geometries may be useful in a number of applications. In some embodiments, the tendon-driven, fiber-reinforced elastomer membrane may be used in robot locomotion. For example, the tendon-driven, fiber-reinforced elastomer membrane may serve as an actuating leg capable of facilitating the movement of a robot in a desired direction. In some embodiments, the tendon-driven, fiber-reinforced elastomer membrane may be used as an inflatable arm capable of large bending motion. In some embodiments, the controllability of the geometry of the tendon-driven, fiber-reinforced elastomer membrane may be used as an adjustable mold. For example, the tendon-driven, fiber-reinforced elastomer membrane may be inflated and/or actuated to a desired shape and filled or surrounded with a hardening material such that it may then serve as a mold or mold negative.

In additional embodiments, the tendon-driven, fiber-reinforced elastomer membrane may be used in vehicles as controllable surfaces. For example, the tendon-driven, fiber-reinforced elastomer membrane may allow one or more configurations of various vehicle surfaces be used to achieve morphing wings, nose cones, and the like. In still further embodiments, the tendon-driven, fiber-reinforced elastomer membrane may be used as bladders with adjustable mass distribution. For example, the tendon-driven, fiber-reinforced elastomer membrane may be used in fuel tanks to alter the distribution of fuel and thus adjust vehicle dynamics. As another example, the tendon-driven, fiber-reinforced elastomer membrane may be used as a controllable and variable buoyancy system in submersibles.

FIGS.5A-Dillustrate an example of the tendon-driven, fiber-reinforced elastomer membrane as used for robot locomotion. As shown inFIG.5A, the robot500comprises a tendon-driven, fiber-reinforced elastomer membrane leg510a. In some embodiments, the robot500may also comprise a support strut505to support the robot during periods of rest and/or before and/or after locomotion. In some embodiments, the robot500may further comprise one or more additional tendon-driven, fiber-reinforced elastomer membrane legs (not shown). Although in this particular example embodiment, only one tendon-driven, fiber-reinforced elastomer membrane510aand support strut505are shown, any number of tendon-driven, fiber-reinforced elastomer membranes and support struts may be contemplated. The tendon-driven, fiber-reinforced elastomer membrane leg510ais in the deflated state initially. While the tendon-driven, fiber-reinforced elastomer membrane leg510ais in the deflated state, the support strut505is positioned substantially flat on the ground. The support strut505may provide support for the robot500while the tendon-driven, fiber-reinforced elastomer membrane leg510ais in the deflated state. Additionally, or alternatively, in some embodiments, one or more additional tendon-driven, fiber-reinforced elastomer membrane legs may be configured to inflate during periods of rest and/or before and/or after locomotion of the robot500such that the one or more additional tendon-driven, fiber-reinforced elastomer membrane legs provides support for the robot500.

FIG.5Bshows the tendon-driven, fiber-reinforced elastomer membrane leg510bin the actuated state. During inflation of the tendon-driven, fiber-reinforced elastomer membrane leg510b, the tendon-driven, fiber-reinforced elastomer membrane leg510bmay be actuated such that the tendon-driven, fiber-reinforced elastomer membrane510bbends to the left. As described above, the tendon-driven, fiber-reinforced elastomer membrane510cmay be actuated using any suitable method. In this example embodiment, the tendon-driven, fiber-reinforced elastomer membrane510bis actuated utilizing a servomotor and one or more pulleys as described inFIG.3andFIGS.4A-C. Additionally, the tendon-driven, fiber-reinforced elastomer membrane leg510bhas been inflated such that support strut505no longer provides support for the robot500. In some embodiments, the one or more additional tendon-driven, fiber-reinforced elastomer membrane legs may enter a deflated state or partially inflated state. The pressure exerted on the ground by the inflated tendon-driven, fiber-reinforced elastomer membrane leg510bmay due to the presence of internal fluid pressure within the cavity of the tendon-driven, fiber-reinforced elastomer membrane leg510b. As the internal fluid is added to the cavity, e.g., as tendon-driven, fiber-reinforced elastomer membrane leg510bis inflated, the internal fluid is constrained by the volume of the cavity and thus the internal fluid pressure increases. This results in the tendon-driven, fiber-reinforced elastomer membrane leg510bapplying a force on the ground and thus lifting the robot500.

FIG.5Cshows the tendon-driven, fiber-reinforced elastomer membrane510csuch that it is no longer actuated and now in an inflated state. The tendon-driven, fiber-reinforced elastomer membrane510cdoes not bend significantly in either direction. This may be accomplished by de-actuating the tendon-driven, fiber-reinforced elastomer membrane510csuch that no significant tension is applied to the tendon-driven, fiber-reinforced elastomer membrane510cin any direction.

FIG.5Dshows the tendon-driven, fiber-reinforced elastomer membrane510dactuated such that the tendon-driven, fiber-reinforced elastomer membrane510dbends to the right. Similarly as described with respect toFIG.5B, the tendon-driven, fiber-reinforced elastomer membrane510cis actuated utilizing a servomotor and one or more pulleys as described inFIG.3andFIGS.4A-C. More specifically, the tendon-driven, fiber-reinforced elastomer membrane leg510dmay be actuated such it rolls from the inflated position as depicted inFIG.5Cto the right bending position as depicted inFIG.5D. Ultimately, the tendon-driven, fiber-reinforced elastomer membrane leg510dis actuated such that it rolls from the left bending position depicted inFIG.5B, to the inflated position depicted inFIG.5C, to the right bending position depicted inFIG.5D. This may be accomplished by controlling the length of the one or more tendons comprising the tendon-driven, fiber-reinforced elastomer membrane510dand thus the tension experienced by the tendon-driven, fiber-reinforced elastomer membrane510d.

The tendon-driven, fiber-reinforced elastomer membrane leg510may return to a fully deflated or partially deflated state and the support strut505may once again provide support for the robot500, such as by inflating. Any portion of the process described above with reference toFIGS.5A-Dmay be repeated as many times as necessary. As such, the robot500may exhibit locomotion that may be similar to walking. Additionally, or alternatively, the tendon-driven, fiber-reinforced elastomer membrane leg510may be actuated in any desired direction such that the robot500may turn to the right or left and/or move backwards.

FIGS.12A-DandFIG.13depict the characterization of motion of an example robot which use one or more tendon-driven, fiber-reinforced elastomer membranes as legs.FIGS.12A-Ddepict various configurations of two apparatuses configured with tendon-driven, fiber-reinforced elastomer membranes. The two apparatuses may work in tandem to allow an example robot (e.g., as shown inFIGS.5A-DorFIGS.14A-D) to perform locomotion.FIG.13depicts the tip path for each tendon-driven, fiber-reinforced elastomer membrane as it moves from the example positions depicted inFIG.12AtoFIG.12B, fromFIG.12BtoFIG.12C, fromFIG.12CtoFIG.12D, and fromFIG.12DtoFIG.12A. This motion may be cyclical such that it repeats, and the example robot is able to continuously locomote.FIG.13further depicts the pressure applied to the tendon-driven, fiber-reinforced elastomer membrane by circulated fluid (e.g., air) during each example position.

FIGS.14A-Ddepict an example robot which uses tendon-driven, fiber-reinforced elastomer membrane legs as discussed above. Furthermore, the robot depicted inFIGS.14-D may further be configured with wheels, which may add support to the stability of the robot and additionally aid in facilitating movement during locomotion. As shown inFIG.14A-D, the robot may use the tendon-driven, fiber-reinforced elastomer membrane legs to travel on a flat surface (e.g., as depicted inFIG.14A), a ramp (e.g., a 20° ramp as depicted inFIG.14B), across a grate (e.g., as depicted inFIG.14C), and across a grate with an obstacle (e.g., a 25.4-millimeter obstacle as depicted inFIG.14D). The robot depicted inFIGS.14A-Dhad a total mass of 3.5 kilograms (kg) and the front tendon-driven, fiber-reinforced elastomer membrane leg carried a load of up to 1.4 kg while the rear tendon-driven, fiber-reinforced elastomer membrane leg carried a load of up to 2.3 kg. This load difference may be due to the proximity of the tendon-driven, fiber-reinforced elastomer membrane leg to the wheels. The robot may achieve average locomotion speeds of 12.4 millimeters per second (mm/s) and/or turning speeds of 2 degrees per second (°/s).

FIGS.6A-Cillustrate an example embodiment where the tendon-driven, fiber-reinforced elastomer membrane may function as an inflatable arm. The tendon-driven, fiber-reinforced elastomer membrane is depicted in the deflated state600inFIG.6A. The tendon-driven, fiber-reinforced elastomer membrane may comprise one or more fixed fibers615. The one or more fixed fibers615may be embedded midway through the thickness of the tendon-driven, fiber-reinforced elastomer membrane along its length. In some embodiments, the one or more fixed fibers615may be evenly spaced throughout the length of the tendon-driven, fiber-reinforced elastomer membrane. In some embodiments, the one or more fixed fibers615may limit the radial expansion of the tendon-driven, fiber-reinforced elastomer membrane.

In some embodiments, both ends of the tendon-driven, fiber-reinforced elastomer membrane are capped with one end configured with one or more fluid inlets. In some embodiments, the tendon-driven, fiber-reinforced elastomer membrane may comprise one or more tendons610. The one or more tendons may be embedded midway through the thickness of the tendon-driven, fiber-reinforced elastomer membrane with attachment points at the distal end600aand loose ends at the proximal end600bof the tendon-driven, fiber-reinforced elastomer membrane.

FIG.6Billustrates the tendon-driven, fiber-reinforced elastomer membrane during an inflated state620. To achieve the inflated state620, fluid may be pumped into the tendon-driven, fiber-reinforced elastomer membrane and causes the tendon-driven, fiber-reinforced elastomer membrane to expand along its longitudinal axis. In some embodiments, the inflated state620of the tendon-driven, fiber-reinforced elastomer membrane may exhibit significant elongation as compared to its deflated state. In some embodiments, longitudinal length of the tendon-driven, fiber-reinforced elastomer membrane may elongate by up to 900% of its deflated longitudinal length.

FIG.6Cillustrates the tendon-driven, fiber-reinforced elastomer membrane during an actuated state630. Similarly, as described above, the length of and the tension applied by the one or more tendons610may be controlled in any suitable manner. By actuating the tendon-driven, fiber-reinforced elastomer membrane, a bending motion may be achieved as depicted inFIG.6C. In some embodiments, the one or more tendons may have different attachment points such that a wide range of bending motions may be achieved. For example, one or more tendons may be knotted around one or more fixed fibers other than the fixed fiber located at the distal end600a.