Artificial muscle drive units with load-bearing supports for improved performance

An artificial muscle drive unit includes a base and an artificial muscle disposed on the base. The artificial muscle includes an expandable reservoir and a fluid. The fluid is movable within said expandable reservoir to switch the artificial muscle between a non-actuated state in which a dimension of the artificial muscle in a movement direction is a minimum value, and an actuated state, in which the dimension of the artificial muscle is a maximum value. The artificial muscle drive unit also includes a load-bearing support disposed on the base, the load-bearing support comprising a dimension in the movement direction that is greater than or equal to the minimum value.

TECHNICAL FIELD

The present specification generally relates to artificial muscle drive units with load-bearing supports for improved performance.

BACKGROUND

Current robotic technologies rely on rigid components, such as servomotors to perform tasks, often in a structured environment. This rigidity presents limitations in many robotic applications, caused, at least in part, by the weight-to-power ratio of servomotors and other rigid robotics devices. The field of soft robotics improves on these limitations by using artificial muscles and other soft actuators. Artificial muscles attempt to mimic the versatility, performance, and reliability of a biological muscle. Some artificial muscles rely on fluid-based actuators. For example, certain artificial muscles may introduce fluid into and out of a volume to expand or contract the artificial muscles to perform mechanical work on a load. The presence of a load may hinder operation of such fluid-based artificial muscles if the artificial muscles encounter the load in an unexpanded state.

Accordingly, a need exists for artificial muscle drive units that are structured to avoid the presence of loads hindering operation of the artificial muscles.

SUMMARY

In one embodiment, an artificial muscle drive unit includes a base and an artificial muscle disposed on the base. The artificial muscle includes an expandable reservoir and a fluid. The fluid is movable within said expandable reservoir to switch the artificial muscle between a non-actuated state in which a dimension of the artificial muscle in a movement direction is a minimum value, and an actuated state, in which the dimension of the artificial muscle is a maximum value. The artificial muscle drive unit also includes a load-bearing support disposed on the base, the load-bearing support comprising a dimension in the movement direction that is greater than or equal to the minimum value.

In another embodiment, an artificial muscle device includes one or more actuation platforms interleaved with one or more mounting platforms to form one or more actuation cavities between one or more platform pairs, each platform pair comprising an individual mounting platform and an individual actuation platform. One or more artificial muscles is disposed in each of the one or more actuation cavities. Each of the one or more artificial muscles includes expandable reservoir and a fluid. The fluid is movable within said expandable reservoir to switch the one or more artificial muscles between a non-actuated state in which a dimension of the artificial muscle in a movement direction is a minimum value, and an actuated state, in which the dimension is a maximum value in the movement direction. A load-bearing support is disposed in at least one of the one or more actuation cavities, the load-bearing support includes a dimension in the movement direction that is greater than or equal to the minimum value.

In another embodiment, an artificial muscle device includes one or more actuation platforms interleaved with one or more mounting platforms to form one or more actuation cavities between one or more platform pairs. Each platform includes an individual mounting platform and an individual actuation platform. The artificial muscle device also includes one or more artificial muscles disposed in each of the one or more actuation cavities. The one or more artificial muscles each include an expandable reservoir and a fluid. The fluid is movable within the expandable reservoir to actuate the one or more artificial muscles between a non-actuated state in which a dimension of the artificial muscle in a movement direction is a minimum value, and an actuated state, in which the dimension is a maximum value in the movement direction. The artificial muscle device also includes a load-bearing support disposed in at least one of the one or more actuation cavities, the load-bearing support comprising a dimension in the movement direction that is greater than or equal to the minimum value.

In yet another embodiment, a method of actuating an artificial muscle drive unit, the method includes positioning the artificial muscle drive unit relative to a load source such that the load source imparts a force on a load-bearing support of the artificial muscle drive unit. The load-bearing support is positioned relative to an artificial muscle of the artificial muscle drive unit such that the force is not directly imparted on an expandable reservoir of the artificial muscle when the artificial muscle is in a non-actuated state. The method also includes manipulating a fluid disposed within the expandable reservoir of the artificial muscle such that at least a portion of the expandable reservoir expands in a movement direction prior to encountering the force imparted on the load-bearing support and continues to expand in the movement direction upon encountering the force imparted by the load-bearing support, thereby imparting an artificial muscle force on the load source.

DETAILED DESCRIPTION

Embodiments described herein are directed to artificial muscle drive units including a base and an artificial muscle disposed on the base. The artificial muscle may be controllably deformable to impart a force on an external object (e.g., a load source) in a movement direction. The artificial muscle may include an expandable reservoir and a fluid, and the fluid may be movable within the expandable reservoir such that the artificial muscle can be switched from a non-actuated state, in which a distance between an external surface of the expandable reservoir and the base in the movement direction is a minimum value, to an actuated state, in which the distance between the external surface of the expandable reservoir and the base in the movement direction is a maximum value (assuming no load is encounter by the artificial muscle preventing expansion of the expandable reservoir). The artificial muscle drive units described herein further include a load-bearing support disposed on the base. The load-bearing support includes a dimension in the movement direction that is greater than or equal to the minimum value, and is positioned relative to the artificial muscle such that, when a load is applied to the artificial muscle drive unit, no force is imparted on the expandable reservoir when the artificial muscle is in the non-actuated state.

In embodiments, the artificial muscle may be in a partially activated state (e.g., in which the distance between the external surface of the expandable reservoir and the base in the movement direction is an intermediate value between the minimum value and the maximum value) when the expandable reservoir encounters a load. The avoidance of loads on the expandable reservoir when the artificial muscle is in the non-actuated state may facilitate a desired movement pattern of the fluid disposed therein to effectuate a transition from the non-actuated state towards the actuated state. That is, if the expandable reservoir were to encounter external forces in the non-actuated state, the distribution of the fluid therein may be effected, thereby inhibiting movement of the fluid in a pattern that maximizes expansion of the expandable reservoir in the movement direction. Avoidance of such disruptions on non-actuated artificial muscles may result in improved force and displacement outputs, resulting in performance improvements in the incorporating device.

Referring now toFIGS. 1A, 1B, and 1C, an artificial muscle drive unit10is schematically depicted. The artificial muscle drive unit10includes a base12and an artificial muscle14disposed on the base12.FIG. 1Adepicts the artificial muscle drive unit10with the artificial muscle14in a non-actuated state.FIG. 1Bdepicts the artificial muscle drive unit10with the artificial muscle14in a partially actuated state.FIG. 1Cdepicts the artificial muscle drive unit10in an actuated state. The artificial muscle14includes an expandable reservoir16and a fluid18disposed in the expandable reservoir16. The expandable reservoir16and fluid18may include variety of different forms depending on the implementation. For example, in embodiments, the artificial muscle14is in fluid communication with an external fluid source (e.g. a pump, not depicted) and the external fluid source may be controlled to adjust a volume of fluid contained within the expandable reservoir16. In such embodiments, at least a portion of the expandable reservoir16may be constructed of a flexible material such that the expandable reservoir expands or contracts along a movement direction22in response to fluctuations in the amount of the fluid18disposed in the expandable reservoir16.

In embodiments, the artificial muscle14includes a closed-fluid system, in which the volume of the fluid18disposed in the expandable reservoir16is fixed, but the distribution of the fluid18is manipulated to alter the shape of the expandable reservoir16. In some such closed-fluid system embodiments, the expandable reservoir16comprises an entirety of a volume containing the fluid18(e.g., the expandable reservoir comprises an entire vessel holding the fluid18). In some such closed-fluid system embodiments, the expandable reservoir16comprises a portion of a volume containing the fluid18(e.g., only a portion of the vessel holding the fluid18—corresponding to the expandable reservoir—may move in the movement direction22). For example, in embodiments, the expandable reservoir16comprises an electrode portion and an expandable portion, and an electrical potential between electrodes of the electrode portion may be adjusted to alter a spacing between the electrodes and manipulate a distribution of the fluid18to expand the expandable portion in the movement direction22. In embodiments, the artificial muscle14comprises a hydraulically amplified self-healing electrostatic (HASEL) actuators described in the paper titled “Hydraulically amplified self-healing electrostatic actuators with muscle-like performance” by E. Acome, S. K. Mitchell, T. G. Morrissey, M. B. Emmett, C. Benjamin, M. King, M. Radakovitz, and C. Keplinger (Science 5 Jan. 2018: Vol. 359, Issue 6371, pp. 61-65). In embodiments, the artificial muscle14comprises the artificial muscles100,100′ described herein. It should be understood that the artificial muscle drive unit10may include any type of fluid-based artificial muscle and that the example artificial muscles described herein should not be interpreted to limit the applicability of the present disclosure to any particular type of artificial muscle.

Moreover, it should be understood that the artificial muscle drive unit10depicted inFIGS. 1A, 1B, and 1Cincludes only a single artificial muscle for purposes of discussion. In embodiments, artificial muscle drive unit10include a plurality of artificial muscles including any number (e.g., tens, hundreds, thousands, hundreds of thousands, etc.) of artificial muscles. Such a plurality of artificial muscles may be combined with one another in any structural arrangement. For example, in embodiments, the artificial muscle14depicted inFIGS. 1A, 1B, and 1Ccomprises a plurality of the artificial muscles100described herein that are arranged in an in any of the artificial muscle stacks201,301,301′ (FIGS. 6A-8) described herein or the layered actuation structure500(FIGS. 9A-11) described herein. While the example structures of such groupings of artificial muscles are described in detail herein, it should be understood that other artificial structures and arrangements are contemplated and within the scope of the present disclosure.

In embodiments, the volume and/or distribution of the fluid18within the expandable reservoir16is actively controlled to manipulate the shape of the expandable reservoir16such that the artificial muscle14generates a desired movement pattern and force. In the embodiment depicted inFIGS. 1A, 1B, and 1C, for example, the distribution of the fluid18is manipulated to alter a dimension32of the artificial muscle14in the movement direction22(e.g., so as to apply a force to an object26in contact with the artificial muscle drive unit10in the movement direction22). The exact location within the artificial muscle14at which the dimension32is measured may vary depending on the implementation, depending on the design of the artificial muscle14and the force that the artificial muscle14is designed to impart on the object26in contact with the artificial muscle drive unit10. In the depicted embodiment, for example, the dimension32is measured as a linear distance between different points on an external surface20of the artificial muscle14(e.g., the external surface20of the expandable reservoir16) along a central axis34extending parallel to the movement direction22. In embodiments, the central axis34may represent a position of maximum dimensional change between the non-actuated state depicted inFIG. 1Aand the actuated state depicted inFIG. 1Bdue to the configuration of the artificial muscle14. Other embodiments are envisioned where the dimension32is measured off the central axis34and/or in directions other than the movement direction22.

As depicted inFIG. 1A, when the artificial muscle drive unit10is in a non-actuated state, the dimension32is a minimum value Dminin the movement direction22. For example, in the non-actuated state, the fluid18may be distributed to the largest lateral extent in a plane perpendicular to the movement direction (e.g., the X-Y plane depicted inFIG. 1A). Such a wide fluid distribution may lead to the dimension32possessing the minimum value Dmin. In the depicted embodiment, the artificial muscle14is disposed directly on the base12, such that the dimension32measures a maximum distance in the movement direction22between a surface of the base12and the external surface20of the expandable reservoir16. As depicted inFIG. 1C, when in the actuated state, the dimension32is a maximum value Dmaxin the movement direction22. For example, the distribution of the fluid18may be altered (e.g., via providing a potential difference between electrodes to cause contraction of regions of the expandable reservoir16, causing movement of the fluid18and expansion of an expanding region in the movement direction22) such that the dimension32possesses the maximum value Dmax. The actuated state depicted inFIG. 1Cmay represent a maximum designed expansion of the expandable reservoir16in the movement direction22(e.g., based on material properties of the expandable reservoir16, based on a minimum separation distance and lateral extent of electrodes). As depicted inFIG. 1B, when the artificial muscle drive unit10is between the non-actuated state depicted inFIG. 1Aand the actuated state depicted inFIG. 1C, the dimension32is an intermediate value Dintthat is greater than Dminand less than Dmax. In embodiments, the partially activated state depicted inFIG. 1Brepresents a transient state of the artificial muscle14where the fluid is moving to place the artificial muscle14in the actuated or non-actuated states. In embodiments, the partially activated state depicted inFIG. 1Brepresents a static state of the artificial muscle14(e.g., the dimension32may be fixed at the intermediate value Dintfor a predetermined time period).

In embodiments, the artificial muscle drive unit10is structured such that the expandable reservoir16(or at least a portion of the expandable reservoir16that moves to transition the artificial muscle14between the actuated and non-actuated states described herein) does not encounter external forces when in the non-actuated state. It has been found that external forces may alter a shape of the expandable reservoir16or disrupt movement thereof so as to impede re-distribution of the fluid18(e.g., in response to additional fluid being pumped into the expandable reservoir16, in response to the shape of the artificial muscle14being manipulated with an external stimulates such as a voltage) in the transition of the artificial muscle14to the actuated state. Such impediments caused by external forces may result in the artificial muscle14having a reduced force output or displacement.

In view of the foregoing, the artificial muscle drive unit10may include one or more load-bearing supports that are positioned so as to prevent the application of external force to the expandable reservoir16. The structure and arrangement of the one or more load-bearing supports may vary depending on the structure of the artificial muscle drive unit10, the form of the artificial muscle14, and the particular force that the artificial muscle14is designed to apply to external objects. For example, referring toFIG. 1A, the artificial muscle drive unit10includes an actuation platform28that is moved relative to the base12via the artificial muscle14.FIG. 1Adepicts the actuation platform28in a resting orientation. In embodiments, the actuation platform28extends perpendicular to the movement direction22in the resting orientation to protect the artificial muscle14when the object26is placed thereon.

In embodiments, the object26may be in contact with the actuation platform28such that, when the artificial muscle14applies a force to the actuation platform28(e.g., to move the actuation platform28in the movement direction22), the artificial muscle drive unit10applies a force to the object26via the actuation platform28. To prevent the object26from placing a load on the artificial muscle14, the artificial muscle drive unit10includes load-bearing supports24and30disposed between the base12and the actuation platform28. In embodiments, the load-bearing supports24and30are fixedly attached to the base12and the actuation platform28moves relative to the load-bearing supports24and30in response to actuation of the artificial muscle14. In embodiments, the load-bearing supports24and30are fixedly attached to the actuation platform28such that the load-bearing support24and30move in conjunction with the actuation platform28in response to actuation of the artificial muscle14.

Referring still toFIG. 1A, the load-bearing supports24and30include a dimension (e.g., height) in the movement direction22that is greater than or equal to the minimum value Dminof the dimension32of the artificial muscle14when in the non-actuated state. In embodiments, the actuation platform28rests on the load-bearing supports24and30such that the actuation platform28and the artificial muscle14are separated by an offset distance36in the movement direction22when the artificial muscle14is in the non-actuated state. Such separation of the artificial muscle14and the actuation platform28by the offset distance36beneficially prevents the object26from placing a load on the artificial muscle14in the non-actuated state, avoiding disruptions in re-distribution of the fluid18and allowing the artificial muscle14to transition from the non-actuated state towards the actuated state in an unimpeded manner. The extent of the offset distance36in the movement direction22may vary depending on the implementation. For example, in embodiments, the load-bearing supports24and30are designed to minimize the offset distance36(e.g., such that the offset distance36is a small, non-zero value that is less than or equal to a difference between Dminand Dmax). In such embodiments, it may be beneficial if the load-bearing supports24and30are constructed of a relatively rigid material (e.g., a metallic material, an alloy, a composite, a plastic) so that the offset distance36may be maintained within a suitable tolerance.

In embodiments, the offset distance36is greater than or equal to Dminto ensure adequate clearance in order to initiate fluid motion within the expandable reservoir16to transition the artificial muscle14from the non-actuated state. For example, as depicted inFIG. 1B, the expandable reservoir16initially contacts the actuation platform28when the artificial muscle14is in the partially activated state between the non-actuated and actuated states depicted inFIG. 1AandFIG. 1C, respectively. The offset distance36(seeFIG. 1A) beneficially enables the fluid18to re-distribute within the expandable reservoir16such that the expandable reservoir16partially expands in the movement direction22to contact the actuation platform28. As depicted inFIG. 1C, once the artificial muscle14is placed in the fully actuated state, the actuation platform28is displaced by the stroking distance Dsin the movement direction22. As will be appreciated, the magnitude of the stroking distance Dsmay vary depending on the design of the artificial muscle14and the magnitude of load placed thereon (e.g., due to the mass of the object26and/or the actuation platform28). It has been found that, despite the offset distance36created by the load-bearing supports24and30, the artificial muscle14can achieve a greater stroking distance Dswith the load-bearing supports24and30than without the load-bearing supports24and30. That is, if the object26imparts a force on the artificial muscle14in the non-actuated state, the magnitude of the stroking distance Ds, and the force imparted on the object26is diminished. The load-bearing supports24and30thus improve the performance of the artificial muscle14, holding other factors (e.g., the magnitude of the load imparted by the object26) constant.

It should be appreciated that the number and positioning of the load-bearing supports in the artificial muscle drive unit10may vary depending on the implementation. For example, in embodiments, one or more of the load-bearing supports24and30may extend through the artificial muscle14. For example, in embodiments, the expandable reservoir16may have an opening extending therethrough (e.g., to define a substantially-ring shaped reservoir with an opening extending through its center) and one or more of the load-bearing supports24and30may extend through the opening. Such implementation may be beneficial in that the load-bearing supports are disposed very close to the moving portions of the expandable reservoir16thereby allowing for tighter tolerance in the dimensions of the load-bearing supports24and30. Embodiments are also envisioned where one or more of the load-bearing supports24and30are incorporated into the artificial muscle14. For example, in embodiments, one or more of the load-bearing supports24and30may be disposed in the expandable reservoir16, and the expandable reservoir16may expand in the movement direction greater than the height of the one or more load-bearing supports24and30.

The artificial muscle drive unit10may include any number of load bearing supports (e.g., 1, 2, 3, 4, 5, 6, 7, 8, etc.) depending on the implementation. For example, in embodiments, the artificial muscle drive unit10only includes a single load-bearing support (e.g., one of the load-bearing supports24and30may be omitted). Additionally, the load-bearing supports24and30may take a variety of different shapes. For example, in embodiments, the load-bearing supports24and30are integrating into a single component that extends around an entirety of the circumference of the artificial muscle14. In embodiments, the load-bearing supports24and30are shaped differently from one another.

In the embodiment depicted inFIGS. 1A, 1B, and 1C, the load-bearing supports24and30are designed to provide structural support via the actuation platform28, which extends substantially perpendicular to the movement direction22(e.g., in the X-direction depicted inFIGS. 1A, 1B, and 1C). In embodiments, the actuation platform28may be omitted and the load-bearing supports24and30may directly prevent the expandable reservoir16from encountering external forces. In embodiments, the actuation platform28and the load-bearing supports24and30are integrated into a single component (e.g., such that the artificial muscle14moves the load-bearing supports24and30and the actuation platform28in combination). In embodiments, the load-bearing supports24and30and the base12are integrated into a single component.

Moreover, the directionality of the support provided by the load-bearing supports24and30may extend in directions other than that depicted inFIGS. 1A, 1B, and 1C. For example, in embodiments, the load-bearing supports24and30may include different heights such that the actuation platform28extends at an angle to the base12rather than parallel thereto as depicted. In embodiments, the load-bearing supports24and30form a load-bearing support surface that extends perpendicular to a particular movement direction22of the artificial muscle14. In embodiments, the load-bearing supports24and30perform the function described herein with respect to a plurality of the artificial muscles14(or a plurality of groupings of artificial muscles) simultaneously.

In embodiments, the load-bearing supports24and30are removable from the artificial muscle drive unit10. Such a configuration may beneficially facilitate replacement of the load-bearing supports24and30to adjust the operating parameters of the artificial muscle drive unit10. For example, the load-bearing supports24and30may be removed and replaced with load-bearing supports having different heights depending on the circumstances (e.g., the mass of the object26). The actuation structures described herein may include a plurality of the artificial muscle drive units10in a plurality of different arrangements to achieve a desired actuation chain of the artificial muscles14. For example, as described herein with respect toFIGS. 9A and 9B, a plurality of the artificial muscle drive units10may be stacked on one another in the movement direction22such that the displacements generated by the plurality of artificial muscle drive units are combined.

Referring now toFIGS. 2, 3, 4A, and 4B, an example artificial muscle100that may be used as the artificial muscle14of the artificial muscle drive unit10described herein with respect toFIGS. 1A, 1B, and 1Cis schematically depicted. The artificial muscle100may also be displaced in an artificial muscle stack (e.g., such as the artificial muscle stacks201,301,301′ described herein withFIGS. 6A-8) and in a layered actuation structure (e.g., the layered actuation structure500described herein with respect toFIGS. 9A-13).

The artificial muscle100comprises a housing110, an electrode pair104, including a first electrode106and a second electrode108(seeFIG. 4A), fixed to opposite surfaces of the housing110, a first electrical insulator layer111fixed to the first electrode106, and a second electrical insulator layer112fixed to the second electrode108. In some embodiments, the housing110is a one-piece monolithic layer including a pair of opposite inner surfaces, such as a first inner surface114and a second inner surface116, and a pair of opposite outer surfaces, such as a first outer surface118and a second outer surface120. In some embodiments, the first inner surface114and the second inner surface116of the housing110are heat-sealable. In other embodiments, the housing110may be a pair of individually fabricated film layers, such as a first film layer122and a second film layer124. Thus, the first film layer122includes the first inner surface114and the first outer surface118, and the second film layer124includes the second inner surface116and the second outer surface120.

While the embodiments described herein primarily refer to the housing110as comprising the first film layer122and the second film layer124, as opposed to the one-piece housing, it should be understood that either arrangement is contemplated. In some embodiments, the first film layer122and the second film layer124generally include the same structure and composition. For example, in some embodiments, the first film layer122and the second film layer124each comprises biaxially oriented polypropylene.

The first electrode106and the second electrode108are each positioned between the first film layer122and the second film layer124. In some embodiments, the first electrode106and the second electrode108are each aluminum-coated polyester such as, for example, Mylar®. In addition, one of the first electrode106and the second electrode108is a negatively charged electrode and the other of the first electrode106and the second electrode108is a positively charged electrode. For purposes discussed herein, either electrode106,108may be positively charged so long as the other electrode106,108of the artificial muscle100is negatively charged.

The first electrode106has a film-facing surface126and an opposite inner surface128. The first electrode106is positioned against the first film layer122, specifically, the first inner surface114of the first film layer122. In addition, the first electrode106includes a first terminal130extending from the first electrode106past an edge of the first film layer122such that the first terminal130can be connected to a power supply to actuate the first electrode106. Specifically, the terminal is coupled, either directly or in series, to a power supply and a controller of an actuation system400, as shown inFIG. 8. Similarly, the second electrode108has a film-facing surface148and an opposite inner surface150. The second electrode108is positioned against the second film layer124, specifically, the second inner surface116of the second film layer124. The second electrode108includes a second terminal152extending from the second electrode108past an edge of the second film layer124such that the second terminal152can be connected to a power supply and a controller of the actuation system400to actuate the second electrode108.

The first electrode106includes two or more tab portions132and two or more bridge portions140. Each bridge portion140is positioned between adjacent tab portions132, interconnecting these adjacent tab portions132. Each tab portion132has a first end134extending radially from a center axis C of the first electrode106to an opposite second end136of the tab portion132, where the second end136defines a portion of an outer perimeter138of the first electrode106. Each bridge portion140has a first end142extending radially from the center axis C of the first electrode106to an opposite second end144of the bridge portion140defining another portion of the outer perimeter138of the first electrode106. Each tab portion132has a tab length L1and each bridge portion140has a bridge length L2extending in a radial direction from the center axis C of the first electrode106. The tab length L1is a distance from the first end134to the second end136of the tab portion132and the bridge length L2is a distance from the first end142to the second end144of the bridge portion140. The tab length L1of each tab portion132is longer than the bridge length L2of each bridge portion140. In some embodiments, the bridge length L2is 20% to 50% of the tab length L1, such as 30% to 40% of the tab length L1.

In some embodiments, the two or more tab portions132are arranged in one or more pairs of tab portions132. Each pair of tab portions132includes two tab portions132arranged diametrically opposed to one another. In some embodiments, the first electrode106may include only two tab portions132positioned on opposite sides or ends of the first electrode106. In some embodiments, as shown inFIGS. 2 and 3, the first electrode106includes four tab portions132and four bridge portions140interconnecting adjacent tab portions132. In this embodiment, the four tab portion132are arranged as two pairs of tab portions132diametrically opposed to one another. Furthermore, as shown, the first terminal130extends from the second end136of one of the tab portions132and is integrally formed therewith.

Like the first electrode106, the second electrode108includes at least a pair of tab portions154and two or more bridge portions162. Each bridge portion162is positioned between adjacent tab portions154, interconnecting these adjacent tab portions154. Each tab portion154has a first end156extending radially from a center axis C of the second electrode108to an opposite second end158of the tab portion154, where the second end158defines a portion of an outer perimeter160of the second electrode108. Due to the first electrode106and the second electrode108being coaxial with one another, the center axis C of the first electrode106and the second electrode108are the same. Each bridge portion162has a first end164extending radially from the center axis C of the second electrode to an opposite second end166of the bridge portion162defining another portion of the outer perimeter160of the second electrode108. Each tab portion154has a tab length L3and each bridge portion162has a bridge length L4extending in a radial direction from the center axis C of the second electrode108. The tab length L3is a distance from the first end156to the second end158of the tab portion154and the bridge length L4is a distance from the first end164to the second end166of the bridge portion162. The tab length L3is longer than the bridge length L4of each bridge portion162. In some embodiments, the bridge length L4is 20% to 50% of the tab length L3, such as 30% to 40% of the tab length L3.

In some embodiments, the two or more tab portions154are arranged in one or more pairs of tab portions154. Each pair of tab portions154includes two tab portions154arranged diametrically opposed to one another. In some embodiments, the second electrode108may include only two tab portions154positioned on opposite sides or ends of the first electrode106. In some embodiments, as shown inFIGS. 2 and 3, the second electrode108includes four tab portions154and four bridge portions162interconnecting adjacent tab portions154. In this embodiment, the four tab portions154are arranged as two pairs of tab portions154diametrically opposed to one another. Furthermore, as shown, the second terminal152extends from the second end158of one of the tab portions154and is integrally formed therewith.

Referring nowFIGS. 2-5B, at least one of the first electrode106and the second electrode108has a central opening formed therein between the first end134of the tab portions132and the first end142of the bridge portions140. InFIGS. 4A and 4B, the first electrode106has a central opening146. However, it should be understood that the first electrode106does not need to include the central opening146when a central opening is provided within the second electrode108, as shown inFIGS. 5A and 5B. Alternatively, the second electrode108does not need to include the central opening when the central opening146is provided within the first electrode106. Referring still toFIGS. 2-5B, the first electrical insulator layer111and the second electrical insulator layer112have a geometry generally corresponding to the first electrode106and the second electrode108, respectively. Thus, the first electrical insulator layer111and the second electrical insulator layer112each have tab portions170,172and bridge portions174,176corresponding to like portions on the first electrode106and the second electrode108. Further, the first electrical insulator layer111and the second electrical insulator layer112each have an outer perimeter178,180corresponding to the outer perimeter138of the first electrode106and the outer perimeter160of the second electrode108, respectively, when positioned thereon.

It should be appreciated that, in some embodiments, the first electrical insulator layer111and the second electrical insulator layer112generally include the same structure and composition. As such, in some embodiments, the first electrical insulator layer111and the second electrical insulator layer112each include an adhesive surface182,184and an opposite non-sealable surface186,188, respectively. Thus, in some embodiments, the first electrical insulator layer111and the second electrical insulator layer112are each a polymer tape adhered to the inner surface128of the first electrode106and the inner surface150of the second electrode108, respectively.

Referring now toFIGS. 3-5B, the artificial muscle100is shown in its assembled form with the first terminal130of the first electrode106and the second terminal152of the second electrode108extending past an outer perimeter of the housing110, i.e., the first film layer122and the second film layer124. As shown inFIG. 3, the second electrode108is stacked on top of the first electrode106and, therefore, the first electrode106, the first film layer122, and the second film layer124are not shown. In its assembled form, the first electrode106, the second electrode108, the first electrical insulator layer111, and the second electrical insulator layer112are sandwiched between the first film layer122and the second film layer124. The first film layer122is partially sealed to the second film layer124at an area surrounding the outer perimeter138of the first electrode106and the outer perimeter160of the second electrode108. In some embodiments, the first film layer122is heat-sealed to the second film layer124. Specifically, in some embodiments, the first film layer122is sealed to the second film layer124to define a sealed portion190surrounding the first electrode106and the second electrode108. The first film layer122and the second film layer124may be sealed in any suitable manner, such as using an adhesive, heat sealing, or the like.

The first electrode106, the second electrode108, the first electrical insulator layer111, and the second electrical insulator layer112provide a barrier that prevents the first film layer122from sealing to the second film layer124forming an unsealed portion192. The unsealed portion192of the housing110includes the electrode region194, in which the electrode pair104is provided, and the expandable fluid region196, which is surrounded by the electrode region194. The expandable fluid region196of the artificial muscle100corresponds to the expandable reservoir16of the artificial muscle14ofFIGS. 1A-1C. The central openings146,168of the first electrode106and the second electrode108form the expandable fluid region196and are arranged to be axially stacked on one another. Although not shown, the housing110may be cut to conform to the geometry of the electrode pair104and reduce the size of the artificial muscle100, namely, the size of the sealed portion190.

A dielectric fluid198is provided within the unsealed portion192and flows freely between the first electrode106and the second electrode108. A “dielectric” fluid as used herein is a medium or material that transmits electrical force without conduction and as such has low electrical conductivity. Some non-limiting example dielectric fluids include perfluoroalkanes, transformer oils, and deionized water. It should be appreciated that the dielectric fluid198may be injected into the unsealed portion192of the artificial muscle100using a needle or other suitable injection device.

Referring now toFIGS. 4A and 4B, the artificial muscle100is actuatable between a non-actuated state and an actuated state. In the non-actuated state, as shown inFIG. 4A, the first electrode106and the second electrode108are partially spaced apart from one another proximate the central openings146,168thereof and the first end134,156of the tab portions132,154. The second end136,158of the tab portions132,154remain in position relative to one another due to the housing110being sealed at the outer perimeter138of the first electrode106and the outer perimeter160of the second electrode108. In the actuated state, as shown inFIG. 4B, the first electrode106and the second electrode108are brought into contact with and oriented parallel to one another to force the dielectric fluid198into the expandable fluid region196. This causes the dielectric fluid198to flow through the central openings146,168of the first electrode106and the second electrode108and inflate the expandable fluid region196.

Referring now toFIG. 4A, the artificial muscle100is shown in the non-actuated state. The electrode pair104is provided within the electrode region194of the unsealed portion192of the housing110. The central opening146of the first electrode106and the central opening168of the second electrode108are coaxially aligned within the expandable fluid region196. In the non-actuated state, the first electrode106and the second electrode108are partially spaced apart from and non-parallel to one another. Due to the first film layer122being sealed to the second film layer124around the electrode pair104, the second end136,158of the tab portions132,154are brought into contact with one another. Thus, dielectric fluid198is provided between the first electrode106and the second electrode108, thereby separating the first end134,156of the tab portions132,154proximate the expandable fluid region196. Stated another way, a distance between the first end134of the tab portion132of the first electrode106and the first end156of the tab portion154of the second electrode108is greater than a distance between the second end136of the tab portion132of the first electrode106and the second end158of the tab portion154of the second electrode108. This results in the electrode pair104zippering toward the expandable fluid region196when actuated. In some embodiments, the first electrode106and the second electrode108may be flexible. Thus, as shown inFIG. 4A, the first electrode106and the second electrode108are convex such that the second ends136,158of the tab portions132,154thereof may remain close to one another, but spaced apart from one another proximate the central openings146,168. In the non-actuated state, the expandable fluid region196has a first height H1.

When actuated, as shown inFIG. 4B, the first electrode106and the second electrode108zipper toward one another from the second ends144,158of the tab portions132,154thereof, thereby pushing the dielectric fluid198into the expandable fluid region196. As shown, when in the actuated state, the first electrode106and the second electrode108are parallel to one another. In the actuated state, the dielectric fluid198flows into the expandable fluid region196to inflate the expandable fluid region196. As such, the first film layer122and the second film layer124expand in opposite directions. In the actuated state, the expandable fluid region196has a second height H2, which is greater than the first height H1of the expandable fluid region196when in the non-actuated state. Although not shown, it should be noted that the electrode pair104may be partially actuated to a position between the non-actuated state and the actuated state. This would allow for partial inflation of the expandable fluid region196and adjustments when necessary.

In order to move the first electrode106and the second electrode108toward one another, a voltage is applied by a power supply (such as power supply48ofFIG. 13). In some embodiments, a voltage of up to 10 kV may be provided from the power supply to induce an electric field through the dielectric fluid198. The resulting attraction between the first electrode106and the second electrode108pushes the dielectric fluid198into the expandable fluid region196. Pressure from the dielectric fluid198within the expandable fluid region196causes the first film layer122and the first electrical insulator layer111to deform in a first axial direction along the center axis C of the first electrode106and causes the second film layer124and the second electrical insulator layer112to deform in an opposite second axial direction along the center axis C of the second electrode108. Once the voltage being supplied to the first electrode106and the second electrode108is discontinued, the first electrode106and the second electrode108return to their initial, non-parallel position in the non-actuated state. In operation, voltage may be applied to one or multiple artificial muscles100of the artificial muscle stacks201,301,301′ ofFIGS. 6A-8and the layered actuation structure500(FIGS. 9A-11) to collectively and/or selectively actuate the artificial muscles100of the artificial muscle stacks201,301,301′ and the layered actuation structure500.

It should be appreciated that the present embodiments of the artificial muscle100disclosed herein, specifically, the tab portions132,154with the interconnecting bridge portions174,176, provide a number of improvements over actuators that do not include the tab portions132,154, such as hydraulically amplified self-healing electrostatic (HASEL) actuators described in the paper titled “Hydraulically amplified self-healing electrostatic actuators with muscle-like performance” by E. Acome, S. K. Mitchell, T. G. Morrissey, M. B. Emmett, C. Benjamin, M. King, M. Radakovitz, and C. Keplinger (Science 5 Jan. 2018: Vol. 359, Issue 6371, pp. 61-65). Embodiments of the artificial muscle100including two pairs of tab portions132,154on each of the first electrode106and the second electrode108, respectively, reduces the overall mass and thickness of the artificial muscle100, reduces the amount of voltage required during actuation, and decreases the total volume of the artificial muscle101without reducing the amount of resulting force after actuation as compared to known HASEL actuators including donut-shaped electrodes having a uniform, radially-extending width. More particularly, the tab portions132,154of the artificial muscle100provide zipping fronts that result in increased actuation power by providing localized and uniform hydraulic actuation of the artificial muscle100compared to HASEL actuators including donut-shaped electrodes. Specifically, one pair of tab portions132,154provides twice the amount of actuator power per unit volume as compared to donut-shaped HASEL actuators, while two pairs of tab portions132,154provide four times the amount of actuator power per unit volume. The bridge portions174,176interconnecting the tab portions132,154also limit buckling of the tab portions132,154by maintaining the distance between adjacent tab portions132,154during actuation. Because the bridge portions174,176are integrally formed with the tab portions132,154, the bridge portions174,176also prevent leakage between the tab portions132,154by eliminating attachment locations that provide an increased risk of rupturing.

In operation, when the artificial muscle100is actuated by providing a voltage and applying the voltage to the electrode pair104of the artificial muscle100, expansion of the expandable fluid region196produces a force of 3 Newton-millimeters (N·mm) per cubic centimeter (cm3) of actuator volume or greater, such as 4 N·mm per cm3or greater, 5 N·mm per cm3or greater, 6 N·mm per cm3or greater, 7 N·mm per cm3or greater, 8 N·mm per cm3or greater, or the like. Providing the voltage may comprise generating the voltage, for example, in an embodiment in which the power supply48(FIGS. 9A-13) is a battery, converting the voltage, for example, in an embodiment in which the power supply48(FIGS. 9A-13) is a power adaptor, or any other known or yet to be developed technique for readying a voltage for application. In one example, when the artificial muscle100is actuated by a voltage of 9.5 kilovolts (kV), the artificial muscle100provides a resulting force of 5 N. In another example, when the artificial muscle100is actuated by a voltage of 10 kV the artificial muscle100provides 440% strain under a 500 gram load.

Moreover, the size of the first electrode106and the second electrode108is proportional to the amount of displacement of the dielectric fluid198. Therefore, when greater displacement within the expandable fluid region196is desired, the size of the electrode pair104is increased relative to the size of the expandable fluid region196. It should be appreciated that the size of the expandable fluid region196is defined by the central openings146,168in the first electrode106and the second electrode108. Thus, the degree of displacement within the expandable fluid region196may alternatively, or in addition, be controlled by increasing or reducing the size of the central openings146,168.

As shown inFIGS. 5A and 5B, another embodiment of an artificial muscle100′ is illustrated. The artificial muscle100′ is substantially similar to the artificial muscle100. As such, like structure is indicated with like reference numerals. However, as shown, the first electrode106does not include a central opening. Thus, only the second electrode108includes the central opening168formed therein. As shown inFIG. 5A, the artificial muscle100′ is in the non-actuated state with the first electrode106being planar and the second electrode108being convex relative to the first electrode106. In the non-actuated state, the expandable fluid region196has a first height H3. In the actuated state, as shown inFIG. 5B, the expandable fluid region196has a second height H4, which is greater than the first height H3. It should be appreciated that by providing the central opening168only in the second electrode108as opposed to both the first electrode106and the second electrode108, the total deformation may be formed on one side of the artificial muscle100′. In addition, because the total deformation is formed on only one side of the artificial muscle100′, the second height H4of the expandable fluid region196of the artificial muscle100′ extends further from a longitudinal axis perpendicular to the central axis C of the artificial muscle100′ than the second height H2of the expandable fluid region196of the artificial muscle100when all other dimensions, orientations, and volume of dielectric fluid are the same.

Referring now toFIGS. 6A-8, artificial muscle stacks201,301,301′ are depicted. InFIGS. 6A-8, each artificial muscle stack201,301,301′ comprises a plurality of artificial muscle layers210,310and each of the plurality of artificial muscle layers210,310comprise one of more artificial muscles100. In some embodiments, the plurality of artificial muscle layers may alternatively or additionally comprise the artificial muscles100′ ofFIGS. 5A and 5B). In operation, artificial muscle stacks201,301,301′ generate more actuation force than a single artificial muscle100.FIGS. 6A-8depict a few different stack arrangements that may be used to generate increased actuation force.

The artificial muscle stack201ofFIGS. 6A-6Ccomprises a plurality of artificial muscle layers210disposed in coaxial alignment, such that expandable fluid regions196of each individual artificial muscle100of an individual artificial muscle layer210is in coaxial alignment with an individual artificial muscle100of each of the other individual artificial muscle layers210. As shown in the side view ofFIGS. 6B and 6C, the artificial muscle stack201comprises three artificial muscle layers210A-210C. It should be understood that any number of artificial muscle layers210is contemplated.FIG. 6Bdepicts the artificial muscle stack201in an unactuated state andFIG. 6Cdepicts the artificial muscle stack201in an actuated state. In each layer of the artificial muscle stack201, individual artificial muscles100do not overlap. Further, artificial muscles100in adjacent artificial muscle layers210may be adhered or sewn together to help stabilize their positioning. Thus, while the artificial muscle stack201ofFIGS. 6A-6Bmay generate a collective actuation force, the coaxial alignment of the individual artificial muscles100of each artificial muscle layer210creates a large footprint. To reduce the footprint of the arrangement of artificial muscles, the artificial muscle stack301depicted inFIGS. 7A-7Emay be implemented.

The artificial muscle stack301ofFIGS. 7A-7E, comprises a plurality of artificial muscle layers310arranged in an alternatingly offset arrangement. The artificial muscle stack301comprises four artificial muscle layers310, a first artificial muscle layer310A, a second artificial muscle layer310B, a third artificial muscle layer310C, and a fourth artificial muscle layer310D.FIG. 7Ais a top view of the artificial muscle stack301andFIGS. 7B-7Eare side views of the artificial muscle stack301.FIGS. 7B and 7Cshow a side view of the artificial muscle stack301along line6B-6B in an unactuated state (FIG. 7B) and in an actuated state (FIG. 7C).FIGS. 7Dand7E show a side view of the artificial muscle stack301along line6D-6D in an unactuated state (FIG. 7D) and in an actuated state (FIG. 7E). Line6B-6B is orthogonal to line7D-7D and thusFIGS. 7B and 7Cshow a different side of the artificial muscle stack301thanFIGS. 7D and 7Eand the side shown byFIGS. 7B and 7Cis orthogonal to the side shown byFIGS. 7D and 7E.

Each artificial muscle layer310comprises one or more artificial muscles100, for example, a plurality of artificial muscles100. For example, inFIG. 7A, a first artificial muscle100A is illustrative of the artificial muscles100of the artificial muscle stack301. It should be understood that embodiments are contemplated in which some of the artificial muscle layers310of the artificial muscle stack301comprises a single artificial muscle100. Further, artificial muscles100in adjacent artificial muscle layers310may be adhered or sewn together to help stabilize their positioning. In the alternating offset arrangement of the artificial muscle stack301depicted inFIGS. 7A-7E, the plurality of artificial muscle layers310are arranged such that each expandable fluid region196of the housing110of the one or more artificial muscles100of each artificial muscle layer310overlaps at least one tab portion132,154of one or more artificial muscles100of an adjacent artificial muscle layer310. In other words, each expandable fluid region196of the housing110of the one or more artificial muscles100of each artificial muscle layer310overlaps the electrode region194of the housing110of one or more artificial muscles100of an adjacent artificial muscle layer310. In some embodiments, an individual tab portion132,154of one artificial muscle100may overlap the expandable fluid region196of an artificial muscle100in an adjacent artificial muscle layer310such that the second end136,158of the individual tab portion132,154terminates at or near the center axis C of the expandable fluid region196of the artificial muscle100in the adjacent muscle layer310. Thus, some of the expandable fluid regions196may be overlapped by two tab portions132,154, each from a different artificial muscle100, on one or both sides of the expandable fluid region196. The tab portions154of the second electrode108of the electrode pair104are shown inFIG. 7Abut it should be understood that the electrode pair104also includes the first electrode106with tab portions132.

To illustrate the alternatingly offset arrangement of the artificial muscle stack301inFIGS. 7A-7E, relative line thickness of the artificial muscles100of each artificial muscle layer310is used to illustrate a relative spatial positioning of the respective artificial muscle layers310. For example, inFIG. 7A, the first artificial muscle layer310A is the top layer, so the artificial muscles100of the first artificial muscle layer310A are depicted with the widest line thickness of the plurality of artificial muscle layers310. Similarly, inFIG. 7A, the fourth artificial muscle layer310D is the bottom layer, so the artificial muscles100of the fourth artificial muscle layer310D are depicted with the narrowest line thickness of the plurality artificial muscle layers310.

In the alternatingly offset arrangement of the artificial muscle stack301, adjacent artificial muscle layers310of the artificial muscle stack301are offset from one another along one or more tab axes, such as a first tab axis338or a second tab axis340. Each tab axis extends from a center axis C of the expandable fluid region196of an individual artificial muscle100of the plurality of artificial muscle layers310to an end (i.e., the second end136,158) of at least one of the tab portions132,154of the individual artificial muscle100of the plurality of artificial muscle layers310. As the embodiments of the artificial muscles100of the artificial muscle stack301depicted inFIGS. 7A-7Eeach comprise four tab portions132,154arranged in diametrically opposed pairs, the first tab axis338is orthogonal the second tab axis340. While the artificial muscles100of the artificial muscle stack301comprise four tab portions132,154(i.e., each electrode of the electrode pair104of each artificial muscles100comprises four tab portions132,154), it should be understood that embodiments are contemplated with artificial muscles100comprising more or less than four tab portions132,154. These embodiments may comprise more than two tab axis, such as in an embodiment with three tab portions per electrode, five tab portions per electrode, or six tab portions per electrode, or just a single tab axis, such as embodiments comprising a single pair of diametrically opposed tab portions. Moreover, it should be understood that embodiments are contemplated in which other artificial muscle designs are arranged in an alternatingly offset arrangement, for example, triangular or rectangular artificial muscles.

Referring still toFIGS. 7A-7E, embodiments of the artificial muscle stack301comprising at least three artificial muscle layers310include at least one inner artificial muscle layer, which is an artificial muscle layer310adjacent two other artificial muscle layers310. In these embodiments, each inner artificial muscle layer is offset a first adjacent artificial muscle layer along a first tab axis338and offset a second adjacent artificial muscle layer along a second tab axis340. This multi-axis offset is depicted in the side views ofFIGS. 7B-7Eby a lateral shift, which shows offset along one tab axis, and by a relative line thickness, which shows offset along the other tab axis. InFIGS. 7B and 7C, offsets between artificial muscle layers310along the second tab axis340are shown by a lateral shift and offsets between adjacent artificial muscle layers310along the first tab axis338are shown by a relative line thickness. In particular, a wider line thickness inFIGS. 7B and 7Cdenotes artificial muscle layers310shifted along the first tab axis338into the foreground (i.e., out of the page) and a narrower line thickness inFIGS. 7B and 7Cdenotes artificial muscle layers310shifted along the first tab axis338into the background (i.e., into the page). InFIGS. 7D and 7E, offsets between artificial muscle layers310along the first tab axis338are shown by a lateral shift and offsets between adjacent artificial muscle layers310along the second tab axis340are shown by a relative line thickness. In particular, a wider line thickness inFIGS. 7D and 7Edenotes artificial muscle layers310shifted along the second tab axis340into the foreground (i.e., out of the page) and a narrower line thickness inFIGS. 6D and 6Edenotes artificial muscle layers310shifted along the second tab axis340into the background (i.e., into the page).

InFIGS. 7A-7E, the second artificial muscle layer310B and the third artificial muscle layer310C are inner artificial muscle layers. The second artificial muscle layer310B is offset from the first artificial muscle layer310A along the first tab axis338and offset from the third artificial muscle layer310C along the second tab axis340. The third artificial muscle layer310C is offset from the second artificial muscle layer310B along the second tab axis340and offset from the fourth artificial muscle layer310D along the first tab axis338. In artificial muscle stacks301with increased numbers of artificial muscle layers310, this pattern may repeat allowing for a closely packed stacked arrangement of artificial muscle layers.

Referring still toFIGS. 7A-7E, the overlap between the tab portions132,154and expandable fluid regions196in adjacent artificial muscle layers310in the alternatingly offset arrangement of the artificial muscle stack301allows an increased number artificial muscles100to be disposed within a particular footprint when compared to the artificial muscle stack201ofFIGS. 5A-5C. Indeed, the artificial muscle stack301maximizes the number of artificial muscles100that may be disposed in a particular footprint, in both a lateral direction (i.e., along the first and second tab axes338,340) and in a depth direction, maximizing the collective actuation force per unit volume of the artificial muscle stack301. When each artificial muscle100actuates, the tab portions132,154of the electrode pair104close together (e.g., flatten) and the expandable fluid region expands196. Because the tab portions132,154flatten, expandable fluid regions196of artificial muscles100may be positioned above and/or below tab portions of adjacent artificial muscle layers310. This allows an increased number of artificial muscles to be positioned together in a condensed block (i.e., the artificial muscle stack301) and operate cooperatively. Indeed, the artificial muscle stack301is designed such that the artificial muscles100of each artificial muscle layer310are able to express their collective force in an additive manner. In contrast, the coaxial alignment of the artificial muscle stack201ofFIG. 6Alimits the additive force generated by each artificial muscle layer210because the expandable fluid regions196of each artificial muscle layer210overlap.

Referring now toFIG. 8, the artificial muscle stack301′ is depicted. The artificial muscle stack301′ comprises the artificial muscle stack301ofFIGS. 7A-7Ewith the addition of perimeter artificial muscles315. The perimeter artificial muscles315comprise the same structure as the artificial muscles100but have fewer tab portions132,154than the artificial muscles100of the artificial muscle stack301′, as shown by first perimeter artificial muscles315A. As shown inFIG. 8, the artificial muscles100of the artificial muscle stack301′ comprise four tab portions132,154and the perimeter artificial muscles315comprise either two or three tab portions132,154. In particular, the perimeter artificial muscles315may comprise edge perimeter artificial muscles316and corner perimeter artificial muscles318. The edge perimeter artificial muscles316extend along a single side of the artificial muscle stack301and the corner perimeter artificial muscles318are disposed at a corner of the artificial muscle stack301such that one tab portion of the corner perimeter artificial muscles318extends along one side of the artificial muscle stack301and another tab of the corner perimeter artificial muscle318extend along another side of the artificial muscle stack301.

As shown inFIGS. 7A-7E, the alternating offset arrangement of the plurality of artificial muscle layers310of the artificial muscle stack301creates a symmetry imbalance along the edges of the artificial muscle stack301. That is, due to the alternating offset arrangement, the artificial muscle layers310may laterally terminate at different locations, leaving edge gaps in the artificial muscle stack301. As shown inFIG. 8, the perimeter artificial muscles315may be used to fill these edge gaps such that each artificial muscle layer310of the artificial muscle stack301′ are laterally coterminous. In some embodiments, each artificial muscle layer310may comprise perimeter artificial muscles315, for example, a combination of edge perimeter artificial muscles316and corner perimeter artificial muscle318to both balance the symmetric along the edges of the artificial muscles stack301and add additional actuation force to the artificial muscle stack301without increasing the overall footprint.

Referring now toFIGS. 9A and 9B, the layered actuation structure500is schematically depicted.FIG. 9Aschematically depicts the layered actuation structure500in a non-actuated state.FIG. 9Bschematically depicts the layered actuation structure500in an actuated state. The layered actuation structure500includes one or more actuation platforms502interleaved with one or more mounting platforms506to form one or more platform pairs510. Each platform pair510includes a mounting platform506and actuation platform502forming an actuation cavity512therebetween. The one or more actuation platforms502each comprise a cavity-facing surface504. Similarly, the one or more mounting platforms506each comprise a cavity-facing surface508. In each platform pair510, the cavity-facing surface504of the individual actuation platform502faces the cavity-facing surface508of the individual mounting platform506. In some embodiments, the actuation platforms502and the mounting platforms506each comprise a thickness of from ¼ inch to 1/32 inch, for example, ¼ inch, ⅛ inch, 1/10 inch, 1/12 inch, 1/16 inch, 1/20 inch, 1/24 inch, 1/28 inch, 1/32 inch, or any range having any two of these values as endpoints.

Referring still toFIGS. 9A and 9B, each of the platform pairs510is spaced from at least one adjacent one of the platform pairs510by at least a cavity displacement distance530to provide clearance for the one or more actuation platforms502to move relative to the one or more mounting platforms506in a movement direction (e.g., the Y-direction depicted inFIGS. 9A and 9B). Moreover, one or more artificial muscles100are disposed in each of the actuation cavities512such that actuation of the one or more artificial muscles100, that is, expansion of the expandable fluid region196applies pressure to the one or more actuation platforms502, generating translational motion of the one or more actuation platforms502. While the artificial muscles100are depicted inFIGS. 9A and 9B, it should be understood that the layered actuation structure500may include any embodiment of an artificial muscle described herein. In some embodiments, a single artificial muscle100is disposed in some or all of the actuation cavities512. In other embodiments, a plurality of artificial muscles100are disposed in some or all of the actuation cavities512. Moreover, when a plurality of artificial muscles100are disposed in an actuation cavity, the plurality of artificial muscles100are disposed in an artificial muscle stack301comprising a plurality of artificial muscles layers arranged in an alternating offset arrangement, as described above with respect toFIGS. 7A-8.

Referring toFIGS. 9A and 9B, the actuation structure500includes one or more load-bearing supports560. In the depicted embodiment, the actuation structure500includes a plurality of load-bearing supports560, with one or more of the plurality of load-bearing supports560being disposed in one of the actuation cavities512. In embodiments, the plurality of load-bearing supports560define a minimum separation distance between each pair of cavity-facing surfaces504and508defining each of the actuation cavities512. The minimum separation distance may extend in a movement direction in which the plurality of artificial muscles100are designed to expand and move an actuation surface540. In embodiments, the actuation surface540may encounter loads from external sources (e.g., an object may be placed on the actuation surface540). The load-bearing supports560beneficially prevent the actuation platforms502from compressing the artificial muscles100of the actuation structure500when the artificial muscles100are in the non-actuated state.

In embodiments, the height of one of the load-bearing supports560(e.g., in the Y-direction depicted inFIGS. 9A and 9B) is determined based on a height of the artificial muscle structure disposed in the actuation cavity512of the load-bearing support560. In embodiments, the heights of the plurality of load-bearing supports560are at least as great as the heights as the artificial muscle structures disposed in the actuation cavities512containing the plurality of load-bearing supports (e.g., a combined height when the plurality of artificial muscles100are stacked in the movement direction). In embodiments where the actuation cavities512include differing numbers and arrangements of the artificial muscles100described therein, for example, the heights of the plurality of load-bearing supports560may vary throughout the actuation structure500. To illustrate, if a first one of the actuation cavities512includes a single one of the artificial muscles100, the height of the load-bearing support560disposed therein may be less than that disposed in another one of the actuation cavities512having the artificial muscle stack301′ disposed therein. Embodiments are also envisioned where the plurality of load-bearing supports560comprise the same structure (e.g., height) irrespective of the structure of artificial muscles disposed in each of the actuation cavities.

Referring toFIG. 9A, when the plurality of artificial muscles100are in the non-actuated state described herein, the plurality of load-bearing supports560maintain a clearance between the cavity-facing surfaces504and508and the external surfaces of the plurality of artificial muscles100. As described herein, such clearance facilitates movement of fluid within each of the plurality of artificial muscles100to facilitate a transition from the non-actuated state to a partially activated state and then to an actuated state. In embodiments, such clearance facilitates the plurality of artificial muscles100having greater expansion capacities when the actuation structure500encounters an external load (e.g., if an object is placed on the actuation surface540) over embodiments not including the plurality of load-bearing supports560.

Referring toFIG. 9B, when the plurality of artificial muscles100are in the actuated state described herein, external surfaces of the plurality of artificial muscles100contact the cavity-facing surfaces504and508and apply a force thereto in the movement direction. In embodiments, the plurality of mounting platforms506are fixed (e.g., via a support arm524being coupled to a base) and the plurality of actuation platforms502are movable in the movement direction (e.g., via coupling to an actuation arm522that is movable relative to the base), such that the force from the plurality of artificial muscles100lifts each actuation platform502above each of the plurality of load-bearing supports560by the cavity displacement distance530in the movement direction.

Referring still toFIGS. 9A and 9B, in embodiments, the plurality of load-bearing supports560are disposed within each of the actuation cavities512(e.g., between the support arm524and the actuation arm522). In embodiments, the plurality of load-bearing supports560are disposed outside of the plurality of artificial muscles100(e.g., the plurality of load-bearing supports560do not overlap the plurality of artificial muscles100in the movement directions). In embodiments, the plurality of load-bearing supports560are disposed in a peripheral region of each of the actuation cavities512, and the plurality of artificial muscles100are disposed in a central region of each of the actuation cavities512.

In embodiments, the plurality of load-bearing supports560are disposed outside of the actuation cavities512. For example, as described herein with respect toFIG. 11, in embodiments, the mounting platforms506and actuation platforms502may include extension tabs (such as extension tabs570depicted inFIG. 11) that extend peripherally outward from the actuation cavities512in a direction perpendicular to the movement direction (e.g., in the X-direction depicted inFIG. 9B), and the plurality of load-bearing supports560may extend between the extension tabs. Such implementations may facilitate compactness of the actuation structure500by limiting the lateral extent of main bodies of the actuation platforms502and mounting platforms506to the sizes of the artificial muscle arrangements disposed therein. Embodiments are also envisioned where the plurality of load-bearing supports560extend through the arrangement of artificial muscles100disposed in one or more the actuation cavities512or the plurality of load-bearing supports560are integrated into the structure of the plurality of artificial muscles100.

Referring still toFIGS. 9A and 9B, the one or more actuation platforms502and the one or more mounting platforms506each comprise one or more bumps550extending into the one or more actuation cavities512. In particular, the bumps550extend outward from the cavity-facing surface504of the actuation platforms502and the cavity-facing surface508of the mounting platforms506. The one or more bumps550are sized and positioned to overlap with the electrode region194of at least one of the one or more artificial muscles100arranged in the actuation cavities512. In operation, when the expandable fluid regions196of the artificial muscles100expand and press against the cavity-facing surfaces504,508of the actuation platform502and the mounting platform506, the contracted electrode regions194press against the bump550. In some embodiments, the bumps550are arranged to correspond with the alternating offset arrangement of the artificial muscle stack301. That is, the one or more bumps550are positioned such that an individual bump550aligns with at least one tab portion132which is positioned in the electrode region194of at least one artificial muscle100. In some embodiments the plurality of load-bearing supports560may also maintain a clearance between the one or more bumps550and the external surface of the plurality of artificial muscles100.

Referring toFIGS. 9A-11, in embodiments, the layered actuation structure500further includes one or more platform linking arms520that connect the platform pairs510to one another. The platform linking arms520retain the lateral positioning of platform pairs510(i.e., positioning in the X and Z directions), retain the spacing between the mounting platforms506of adjacent platform pairs510in the movement direction (i.e., in the Y direction) and allow for translational motion of the actuation platforms502of each platform pair510in the movement direction. As shown inFIGS. 10-11, in embodiments, the one or more platform linking arms520include a plurality of platform linking arms520that include at least one actuation arm522coupled to the one or more actuation platforms502and at least one support arm524coupled to the one or more mounting platforms506. In particular, the actuation arm522is rigidly coupled to each actuation platform502and translatably coupled to each mounting platform506and the support arm524is rigidly coupled to each mounting platform506and translatably coupled to each actuation platform502. This translatable connection may be a slideable connection. For example, as depicted inFIG. 10, the platform linking arms520may comprise a plurality of notches525to which provide a location for connectors526, such as screws, to connect the platform linking arms520to the actuation platforms502and the mounting platforms506and also allow motion of the actuation platforms502during operation of the layered actuation structure500while retaining a connection between the platform linking arms520and the platform pairs510. In some embodiments, the actuation platforms502and the mounting platforms506may comprise screw block sections, which are thicker than the remaining portion of each platform502,506and provide a connection location for the connectors526.

As depicted inFIGS. 10 and 11, in some embodiments, the layered actuation structure500comprises multiple support arms524and multiple actuation arms522. For example, the layered actuation structure500may comprise a first support arm524A, a second support arm524B, a first actuation arm522A, and a second actuation arm522B. The first and second support arms524A,524B are each coupled to the one or more mounting platforms506and the first and second actuation arms522A,522B are each coupled to the one or more actuation platforms502. The first support arm524A and the second support arm524B are coupled to the one or more mounting platforms506at opposite locations along an edge507of the one or more mounting platforms506. The first actuation arm522A and the second actuation arm522B are coupled to the one or more actuation platforms502at opposite locations along an edge503of the one or more actuation platforms502. Furthermore, the first and second support arms524A,524B are positioned relative the first and second actuation arms522A,522B such that an axis extending between the first support arm524A and the second support arm524B is orthogonal an axis extending between the first actuation arm520A and the second actuation arm520B.

Referring still toFIGS. 9A-11, the layered actuation structure500further comprises an actuation surface540configured to apply the cavity force (e.g., an individual cavity force or multi-cavity force) generated by the translational motion of the one or more actuation platforms502. In some embodiments, the actuation surface540is a surface of an actuation block542, which may be coupled to at least one actuation arm522, as shown inFIGS. 9A and 9B, or coupled to an actuation platform502(e.g., the upward-most or endmost actuation platform502), as shown inFIG. 10. In other embodiments, the actuation surface540may be a surface of an actuation platform502itself, as shown inFIG. 11.

In operation, when the one or more artificial muscles100apply pressure to the cavity-facing surfaces504of the one or more actuation platforms502, the actuation platforms502translate relative to the mounting platforms506in the movement direction. That is, actuation the one or more artificial muscles100disposed in at least one of the actuation cavities512generates a translation motion of the one or more actuation platforms502along a cavity displacement distance530. While the cavity displacement distance may be increased by increasing the number of layers of artificial muscles100in embodiments in which artificial muscle stacks are disposed in the actuation cavities512, the cavity displacement distance530is not increased by increasing the number of platform pairs510. However, the translation motion of an individual actuation platform502generates and individual cavity force, which is an additive force.

That is, when layered actuation structure500comprises a plurality of actuation cavities512, such as in the embodiments depicted inFIGS. 9A and 9B, each individual actuation platform generates the individual cavity force such that the layered actuation structure generates a multi-cavity force. The multi-cavity force is an additive force of each of the individual cavity forces. In some embodiments, the multi-cavity force is 10 Newtons (N) or greater, such as 15 N or greater, 20 N or greater, 25 N or greater, 30 N or greater, 35 N or greater, 40 N or greater, 45 N or greater, 50 N or greater, 55 N or greater, 60 N or greater, 65 N or greater, 70 N or greater, 75 N or greater, 80 N or greater, 85 N or greater, 90 N or greater, 95 N or greater, 100 N or greater, 105 N or greater, 110 N or greater, 115 N or greater, 120 N or greater, or any range having any two of these values as endpoints. Indeed, embodiments are contemplated in which a layered actuation structure500comprising a 5 cm×5 cm lateral footprint is capable of generating a multi-cavity force of 80 N.

In the embodiment depicted inFIG. 10, the plurality of load-bearing supports560are disposed inward of one or more platform linking arms520within each one of the actuation cavities512. In the depicted embodiment, each one of the actuation cavities512comprises 8 load-bearing supports560disposed therein (e.g., one on either side of the one or more platform linking arms520to provide robust, symmetrical support). It should be understood that alternative embodiments with differing number of load-bearing supports per actuation cavity are contemplated and within the scope of the present disclosure. For example, in embodiments, each actuation cavity512includes a single load-bearing support560disposed therein, and the load-bearing support560may include a frame-shaped member extending around the entire periphery of each actuation cavity512. Embodiments are also envisioned where the plurality of actuation cavities512include different numbers of load-bearing supports560with different shapes and sizes.

In the embodiment depicted inFIG. 11, the plurality of load-bearing supports560are disposed outward of the actuation arms522and support arms524. The plurality of mounting platforms506and the plurality of actuation platforms502each include a plurality of extension tabs570extending laterally outward from main bodies thereof such that each of the actuation cavities512has one or more sets of extension tabs570associated therewith. The plurality of load-bearing supports560may be disposed locally between the plurality of extension tabs570associated with the mounting platforms506and actuation platforms502of each actuation cavity512. Such a structure beneficially facilitates the load-bearing supports560being laterally offset from the main bodies of the mounting platforms506and the actuation platforms502. More artificial muscles may be placed within each actuation cavity512as a result of the extension tabs570, beneficially increasing the density of force per overall unit weight of the actuation structure500.

Referring now toFIG. 12, a plot1200of force versus displacement for one of the plurality of artificial muscles100described herein. The plot1200depicts a magnitude of force provided by one of the artificial muscles100versus displacement in a case where a load-bearing support is used and a case where a load-bearing support is not used. In the case without the load-bearing support, the artificial muscle100encountered a force from an external force when in the non-actuated state described herein. As shown, the load-bearing support provides a greater force per unit displacement of the artificial muscle100(for certain displacements, the magnitude of force is greater than 30% improved). This example demonstrates the efficacy of the load-bearing supports described herein in improving actuation performance.

Referring now toFIG. 13, an actuation system400may be provided for operating each individual artificial muscle100of the layered actuation structure500or the artificial muscle14of the artificial muscle drive unit10described herein with respect toFIGS. 1A, 1B, and 1C. The actuation system400may comprise a controller50, an operating device46, a power supply48, a display device42, network interface hardware44, and a communication path41communicatively coupled these components.

The controller50comprises a processor52and a non-transitory electronic memory54to which various components are communicatively coupled. In some embodiments, the processor52and the non-transitory electronic memory54and/or the other components are included within a single device. In other embodiments, the processor52and the non-transitory electronic memory54and/or the other components may be distributed among multiple devices that are communicatively coupled. The controller50includes non-transitory electronic memory54that stores a set of machine-readable instructions. The processor52executes the machine-readable instructions stored in the non-transitory electronic memory54. The non-transitory electronic memory54may comprise RAM, ROM, flash memories, hard drives, or any device capable of storing machine-readable instructions such that the machine-readable instructions can be accessed by the processor52. Accordingly, the actuation system400described herein may be implemented in any conventional computer programming language, as pre-programmed hardware elements, or as a combination of hardware and software components. The non-transitory electronic memory54may be implemented as one memory module or a plurality of memory modules.

In some embodiments, the non-transitory electronic memory54includes instructions for executing the functions of the actuation system400. The instructions may include instructions for operating the layered actuation structure500, for example, instructions for actuating the one or more artificial muscles100, individually or collectively, and actuating the artificial muscle layers210,310, individually or collectively.

The processor52may be any device capable of executing machine-readable instructions. For example, the processor52may be an integrated circuit, a microchip, a computer, or any other computing device. The non-transitory electronic memory54and the processor52are coupled to the communication path41that provides signal interconnectivity between various components and/or modules of the actuation system400. Accordingly, the communication path41may communicatively couple any number of processors with one another, and allow the modules coupled to the communication path41to operate in a distributed computing environment. Specifically, each of the modules may operate as a node that may send and/or receive data. As used herein, the term “communicatively coupled” means that coupled components are capable of exchanging data signals with one another such as, for example, electrical signals via conductive medium, electromagnetic signals via air, optical signals via optical waveguides, and the like.

As schematically depicted inFIG. 13, the communication path41communicatively couples the processor52and the non-transitory electronic memory54of the controller50with a plurality of other components of the actuation system400. For example, the actuation system400depicted inFIG. 11includes the processor52and the non-transitory electronic memory54communicatively coupled with the operating device46and the power supply48.

The operating device46allows for a user to control operation of the artificial muscles100of the layered actuation structure500. In some embodiments, the operating device46may be a switch, toggle, button, or any combination of controls to provide user operation. The operating device46is coupled to the communication path41such that the communication path41communicatively couples the operating device46to other modules of the actuation system400. The operating device46may provide a user interface for receiving user instructions as to a specific operating configuration of the layered actuation structure500.

The power supply48(e.g., battery) provides power to the one or more artificial muscles100of the layered actuation structure500. In some embodiments, the power supply48is a rechargeable direct current power source. It is to be understood that the power supply48may be a single power supply or battery for providing power to the one or more artificial muscles100of the layered actuation structure500. A power adapter (not shown) may be provided and electrically coupled via a wiring harness or the like for providing power to the one or more artificial muscles100of the layered actuation structure500via the power supply48. Indeed, the power supply48is a device that can receive power at one level (e.g., one voltage, power level, or current) and output power at a second level (e.g., a second voltage, power level, or current).

In some embodiments, the actuation system400also includes a display device42. The display device42is coupled to the communication path41such that the communication path41communicatively couples the display device42to other modules of the actuation system400. The display device42may be a touchscreen that, in addition to providing optical information, detects the presence and location of a tactile input upon a surface of or adjacent to the display device42. Accordingly, the display device42may include the operating device46and receive mechanical input directly upon the optical output provided by the display device42.

In some embodiments, the actuation system400includes network interface hardware44for communicatively coupling the actuation system400to a portable device70via a network60. The portable device70may include, without limitation, a smartphone, a tablet, a personal media player, or any other electric device that includes wireless communication functionality. It is to be appreciated that, when provided, the portable device70may serve to provide user commands to the controller50, instead of the operating device46. As such, a user may be able to control or set a program for controlling the artificial muscles100of the layered actuation structure500utilizing the controls of the operating device46. Thus, the artificial muscles100of the layered actuation structure500may be controlled remotely via the portable device70wirelessly communicating with the controller50via the network60.

It should now be understood that embodiments described herein are directed to a layered actuation structure having one or more actuation platforms interleaved with one or more mounting platforms forming platform pairs. Artificial muscles are disposed in an actuation cavity of each platform pair and are expandable on demand to selectively raise the actuation platforms. The translational motion of each of the one or more actuation platforms generates an additive force that may be increased by adding additional platform pairs to the layered actuation structure. Each additional platform pair of the layered actuation structure increases the achievable maximum force without increasing the total displacement that occurs during actuation. Thus, the layered actuation structure is useful in small footprint applications, particular small lateral footprint applications.