WO2023239304A1

WO2023239304A1 - A composite actuator

Info

Publication number: WO2023239304A1
Application number: PCT/SG2023/050406
Authority: WO
Inventors: Ajinkya Sarang BHAT; Chen Hua YEOW; Jonathan William AMBROSE
Original assignee: National University Of Singapore
Priority date: 2022-06-07
Filing date: 2023-06-07
Publication date: 2023-12-14

Abstract

The invention provides a composite actuator suitable for soft robotics that performs motions which include any one of bending, twisting, and extending, or a combination thereof. The composite actuator comprises a bladder, and a skin that covers the bladder. The skin has an overall Young's modulus that is larger than that of the bladder for acting as a deformation- controlling constraint so that motions are performed by the composite actuator during inflation or pressurisation of the bladder. The skin comprises one or more layers, with at least one layer being anisotropic in terms of having a minimum Young's modulus in a first direction and a maximum Young's modulus in a second direction that is orthogonal to the first direction, wherein the skin layer substantially envelops the bladder while being stretched along the first direction.

Description

RELATED APPLICATION

[001] The present invention claims priority to Singapore patent application no. 10202250086H filed on 7 June 2022, the disclosure of which is incorporated in its entirety.

FIELD OF INVENTION

[002] The invention relates to the field of soft robotics. More specifically, a composite actuator that has a composite structure that enables it to perform motions that include any one of a bending motion, a torsional motion, an extending motion, or a combination thereof.

BACKGROUND OF INVENTION

[003] Soft robotics involves the design and development of compliant robots, which provide advantages over rigid robots in terms of their power-to-weight ratio as well as wearability. Conventionally, soft robots, or fabric-based soft actuators, have been made in a homogeneous manner using materials, such as fabrics, thermoplastic polyurethane (TPU) or silicone rubber. However, the use of these materials in a homogeneous manner for fabricbased soft actuators presents challenges to the modularity, customisability, and reconfigurability of the soft robots since all materials have certain limitations in their structural integrity.

[004] Among disclosed technologies over the prior art that may relate to means to improve the modularity, customisability, and reconfigurability of fabric-based soft actuators include the disclosed work of Rafsanjani et al. (Kirigami skins make a simple soft actuator crawl, 2018). Here, bioinspired soft machines capable of crawling made of highly deformable materials were disclosed, whereby they have kirigami-inspired surfaces that transform them from flat sheets to textured surfaces that come with a significant change in their frictional properties.

[005] Yet another disclosed technology over the prior art that may relate to means to improve the modularity, customisability, and reconfigurability of fabric-based soft actuators includes the disclosed work of Nguyen et al. (Design and Computational Modeling of Fabric Soft Pneumatic Actuators for Wearable Assistive Devices, 2020). Here, soft pneumatic actuators (FSPAs) were disclosed that exploit the unique capabilities of different woven and knit textiles, allowing them to perform a torsional motion. The FSPAs were further disclosed to have zero initial stiffness, full collapsibility, high power-to-weight ratio, puncture resistance, and high stretchability.

[006] It is known that fabric-based soft actuators suffer from limitations. Fabric-based soft actuators lack the ability to increase their design complexity since they include TPU (Thermoplastic Polyurethane) in their composition, hence, they have a detrimental trade-off where a high pressure is required for them to provide a high output force. Meanwhile, soft actuators that have silicone-based designs tend to possess limited resistance to stress and strain force, and furthermore, they have a low output force

[007] Accordingly, it is desirable to provide a composite actuator suitable for soft robotics having a composite structure. In particular, the composite actuator comprises a bladder and a skin, wherein the skin covers the bladder. Preferably, the bladder acts as a fluid-tight enclosure whereby fluid is contained therein for its continuous inflation. Preferably, the skin that is external to the bladder acts as a deformation-controlling constraint that controls the motion of the actuator during the inflation of the bladder.

SUMMARY OF INVENTION

[008] An objective of the present invention is to provide a composite actuator suitable for use in soft robotics having a composite structure that enables it to perform motions that include any one of a bending motion, a twisting motion, an extending motion, or a combination thereof. Desirably, the composite actuator is a kind of fabric-based soft actuator, and it is to have an inner body in the form of a bladder covered with an outer covering that is in the form of a skin. Either one or both the bladder and the skin are configured to have variations to its stiffness for enabling the composite actuator to perform the aforementioned motions during inflation of the bladder. More specifically, the skin acts as a deformationcontrolling constraint that controls the motion of the actuator during the inflation of the bladder. The skin is to have one or more layers, wherein at least one of them has anisotropic properties. [009] Advantageously, the composite actuator having a skin with anisotropic properties enables the skin to have a targeted stiffness.

[0010] Advantageously as well, the composite actuator having a composite structure enables the use of more than one material in its construction.

[0011] Advantageously as well, the composite actuator having a composite structure enables a separation between the bladder and the skin that avoids the requirement of accommodating hermetic seals to provide an airtight enclosure like in the case of conventional fabric-based soft actuators. Thus, a complexity in motion is enabled in the composite actuator.

[0012] Advantageously as well, the composite actuator having a composite structure virtually allows any material to be used as a deformation-controlling constraint since they no longer need to consider or be limited by the need for hermetic seals much like in the case of conventional fabric-based soft actuators.

[0013] Advantageously as well, the composite actuator having a composite structure that enables a separation between bladder and skin enables a degree of modularity, customisability, and reconfigurability. Conventionally, fabric-based soft actuators are fabricated to perform a specific function and their behaviour cannot be modified significantly post-fabrication. The composite structure allows for modularity, customisability, and reconfigurability since the bladder and the skin are slidably movable with respect to each other for them to become separated from each other. This allows either one or both of the bladder and the skin to be materially configured to modify their behaviour. This also allows swapping of either one of the bladder or the skin based on the required motion.

[0014] Advantageously as well, the composite actuator having a composite structure exhibits compliance, meaning it can easily deform and conform to the environment or objects they interact with. This compliance allows for safe interactions with delicate or uneven surfaces without causing damage, and enables its use within wearable assistive devices.

[0015] Advantageously as well, the composite actuator having a composite structure, which may have a multi-material configuration, overcomes the limitations imposed by the use of a single material as in the case of conventional fabric-based soft actuators. Conventional fabric-based soft actuators are primarily comprised of thermoplastic polyurethane (TPU)- backed fabric for it to provide hermetic sealing. Whereas, with a composite structure, a wider range of fabrics besides TPU-backed fabric may be used, since the bladder assumes the role of a hermetic seal instead by being an airtight enclosure itself.

[0016] Advantageously as well, the composite actuator having a composite structure is able to achieve multiple motions due to its configurative versatility. It may achieve any complex motions that include any one of a bending motion, a torsional motion, an extending motion, or a combination thereof.

[0017] Advantageously as well, the composite actuator having a composite structure is able to perform complex motions as the properties of the bladder may be manipulated. In combination with the skin, complex motions are achieved.

[0018] Advantageously as well, the composite actuator having a composite structure is able to provide an output force that has a larger magnitude in comparison to conventional fabricbased soft actuators.

[0019] Advantageously as well, the composite actuator having a composite structure achieves a large deformation in comparison to conventional fabric-based soft actuators.

[0020] The present invention intends to provide a composite actuator comprising a bladder and a skin that covers the bladder. The skin has an overall Young’s modulus that is larger than the bladder for acting as a deformation-controlling constraint so that motions are performed by the composite actuator during inflation or pressurisation of the bladder.

[0021] Preferably, the skin is configured to have a constant Young’s modulus or a varying Young’s modulus, with the overall Young’s modulus of the skin being larger than the bladder.

[0022] Preferably, the bladder is configured to have a constant Young’s modulus or a varying Young’s modulus, with the overall Young’s modulus of the skin being larger than the bladder.

[0023] Preferably, the skin comprises one or more layers, with at least one layer being anisotropic in terms of having a minimum Young’s modulus in a first direction and a maximum Young’s modulus in a second direction that is orthogonal to the first direction, wherein it substantially envelops the bladder while being stretched along the first direction.

[0024] Preferably, wherein the layers of the skin comprise a first layer, which substantially envelops the bladder as a whole, a second layer that partially envelops a region of the first layer, and a third layer, which substantially envelops the second layer and the first layer as a whole. The first layer forms an overlapped region with its ends overlapped with each other as it envelopes the bladder, which shall be the region covered by the second layer, and the first layer bonds to the third layer with the second layer sandwiched therebetween.

[0025] Preferably, the layers of the skin comprise a first layer, which substantially envelops the bladder, with the first layer forming an overlapped region at a levelled surface of the bladder, it envelopes the bladder.

[0026] Preferably, the bladder is induced by the skin to perform a bending motion during inflation or pressurisation of the bladder.

[0027] Preferably, the layers of the skin comprise a first layer, which substantially envelops the bladder. The first layer is in the form of a strip that is orientated at an angle with respect to a central axis of the bladder for enveloping the bladder in a helical manner to form one or more overlapped regions.

[0028] Preferably, the layers of the skin further comprise a second layer, which substantially envelops portions of the first layer. The second layer is in the form of a strip that is orientated at an angle with respect to a central axis of the bladder for enveloping the overlapped regions of the first layer in a helical manner.

[0029] Preferably, the layers of the skin comprise a first layer, which substantially envelops the bladder as a whole, and a second layer, which substantially envelops portions of the first layer. The second layer is in the form of a strip that is orientated at an angle with respect to a central axis of the bladder and envelops portions of the first layer in a helical manner.

[0030] Preferably, the bladder is induced by the skin to perform a torsional motion during inflation or pressurisation of the bladder. [0031] Preferably, the bladder is comprised of multi-material for the bladder to be induced by the skin to perform both a bending motion and a torsional motion during inflation or pressurisation of the bladder.

[0032] Preferably, the layers of the skin comprise a first layer, which substantially envelops the bladder as a whole, and a second layer, which substantially envelops the first layer. The first layer forms a first overlapped region with its ends overlapped with each other as it envelopes the bladder that shall be the region covered by the second layer, and the second layer forms a second overlapped region with its ends overlapped with each other as it envelops the first layer.

[0033] Preferably, the first overlapped region and the second overlapped region are diametrically opposite to each other.

[0034] Preferably, the bladder is induced by the skin to perform an extending motion during inflation or pressurisation of the bladder.

[0035] Preferably, the skin is further formed with a first opening and a second opening at its ends.

[0036] Preferably, the composite actuator further comprises a pair of sealing means, with a first sealing means disposed about the first opening, and a second sealing means disposed about the second opening. The bladder is sealed within the skin by the first sealing means and the second sealing means.

[0037] Preferably, the bladder has a cross-section that is either in a shape of a circle or in a shape of a semi-circle or segmented circle.

[0038] Preferably, the bladder and the skin are in slidable movement with respect to each other when the bladder is deflated or depressurised.

[0039] Preferably, the layers of the skin are any one of fabric with an adhesive backing, fabric with a thermoplastic backing, or a combination thereof. [0040] One skilled in the art will readily appreciate that the invention is well adapted to carry out the objects and obtain the ends and advantages mentioned, as well as those inherent therein. The embodiments described herein are not intended as limitations on the scope of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

[0041] To facilitate an understanding of the present invention, there is illustrated in the accompanying drawings the preferred embodiments, from an inspection of which when considered in connection with the following description, the invention, its construction and operation and many of its advantages would be readily understood and appreciated.

[0042] FIGS. 1 to 3 are diagrams that illustrate the composite actuator in its first example embodiment. In particular, FIG. 1 illustrates a simplified exploded view of the first example embodiment, FIG. 2 illustrates a transverse cross-section of the first example embodiment, and FIG. 3 illustrates a longitudinal cross-section of the first example embodiment.

[0043] FIGS. 4 to 6 are diagrams that illustrate the composite actuator in its second example embodiment. In particular, FIG. 4 illustrates a simplified exploded view of the second example embodiment, FIG. 5 illustrates a transverse cross-section of the second example embodiment, and FIG. 6 illustrates a longitudinal cross-section of the second example embodiment.

[0044] FIGS. 7 to 9 are diagrams that illustrate further example embodiments of the composite actuator that are configured to perform a bending motion. In particular, FIG. 7 illustrates a transverse cross-section of the composite actuator in a third example embodiment, FIG. 8 illustrates a transverse cross-section of the composite actuator in a fourth example embodiment, and FIG. 9 illustrates an example method for producing a composite actuator that is configured to perform a bending motion, which is per the third example embodiment.

[0045] FIGS. 10 to 15 are diagrams that illustrate further example embodiments of the composite actuator that are configured to perform a torsional motion. In particular, FIG. 10 illustrates a longitudinal cross-section of the composite actuator in a fifth example embodiment, FIG. 11 illustrates a first example method for producing a composite actuator that is configured to perform a torsion motion, which is per the fifth example embodiment, FIG. 12 illustrates a longitudinal cross-section of the composite actuator in a sixth example embodiment, FIG. 13 illustrates a second example method for producing a composite actuator that is configured to perform a torsion motion, which is per the sixth example embodiment, FIG. 14 illustrates a longitudinal cross-section of the composite actuator in a seventh example embodiment, FIG. 15 illustrates a third example method for producing a composite actuator that is configured to perform a torsion motion, which is per the seventh example embodiment,

[0046] FIG. 16 illustrates an eighth example embodiment of the composite actuator that is configured to perform an extending motion, more specifically, its transverse cross-section.

[0047] FIGS. 17 to 19 are graphs that illustrate the results of one or more evaluations performed upon certain embodiments described above to validate their performance. In particular, FIG. 17 is a plot of blocked force (Nm) against pressure (kPa) that relates to embodiments of the composite actuator that performs a bending motion, FIG. 18 is a plot of tip angular displacement of the composite actuator (degrees) against pressure (kPa) that relates to embodiments of the composite actuator that performs a bending motion, and FIG. 19 is a plot of angular displacement of the composite actuator about its central axis (degrees) against pressure (kPa) that relates to embodiments of the composite actuator that performs a torsional motion.

DETAILED DESCRIPTION OF THE INVENTION

[0048] The present invention relates to a composite actuator for use in soft robotics that performs motions that include any one of a bending motion, a twisting motion, an extending motion, or a combination thereof. According to the concept of the invention, the actuator comprises an inflatable inner body, and an outer covering that covers the inner body. Either one or both the inner body and the outer covering are configured to have variations to its stiffness for enabling the composite actuator to perform the aforementioned motions during inflation of the inner body.

[0049] The invention will now be described in greater detail, by way of examples, with reference to the figures. For ease of reference, common reference numerals or series of numerals will be used throughout the figures when referring to the same or similar features common to the figures.

[0050] It is to be noted that from hereon, the inner body of the composite actuator may also be interchangeably referred to as a bladder, and the outer covering of the composite actuator may also be interchangeably referred to as a skin.

[0051] FIGS. 1 to 3 illustrate the composite actuator in its first example embodiment 1. In particular, FIG. 1 illustrates a simplified exploded view of the first example embodiment 1, FIG. 2 illustrates a transverse cross-section of the first example embodiment 1, while FIG. 3 illustrates a view of the longitudinal cross-section of the first example embodiment 1 along the lines A-A’.

[0052] As shown in FIG. 1, the first example embodiment 1 comprises a bladder 11 as its inner body, a skin 12 as its outer covering, a first sealing means 13a and a second sealing means 13b disposed at both ends of the first example embodiment for sealing the ends. The bladder 11 further comprises a tube 111 for delivering fluid to and fro the first example embodiment 1 for inflating (pressurising) or deflating (depressurising) the bladder 11, with the inflation or pressurisation of the bladder 11 inducing one or a combination of motions within the first example embodiment 1.

[0053] As shown in FIG. 2, in the first example embodiment 1, since the bladder 11 is substantially cylindrical, hence the cross-section of the bladder 11 has the shape of a circle or any other circular shape. Preferably, the skin 12 that envelops the bladder 11 conforms to the bladder 11, thus the skin 12 may correspondingly have a cross-section that has the shape of a circle or any other circular shape. [0054] As shown in FIG. 3, in the first example embodiment 1, the whole lateral surface of the bladder 11 is to be substantially enveloped with the skin 12. It is to be noted that the bladder 11 and the skin 12 are slidably movable with respect to each other when the bladder 11 is deflated. However, this slidable movement between the bladder 11 and the skin 12 may substantially decrease as the bladder 11 is inflated. When the bladder 11 is fully inflated, this slidable movement between the bladder 11 and the skin 12 may become absent.

[0055] FIGS. 4 to 6 illustrate the composite actuator in its second example embodiment 2. In particular, FIG. 4 illustrates a simplified exploded view of the second example embodiment 2, FIG. 5 illustrates a view of the transverse cross-section of the second example embodiment 2, while FIG. 6 illustrates a view of the longitudinal cross-section of the second example embodiment 2 along the lines B-B’.

[0056] As shown in FIG. 4, similar to the first example embodiment 1, the second example embodiment 2 comprises a bladder 21 as its inner body, a skin 22 as its outer covering, a first sealing means 23a and a second sealing means 23b disposed at both ends of second example embodiment 2 for sealing said ends. The bladder 21 further comprises a tube 211 for delivering fluid to and fro the second example embodiment 2 for inflating (pressurising) or deflating (depressurising) the bladder 21, with the inflation or pressurisation of the bladder 21 inducing one or a combination of motions within the second example embodiment 2.

[0057] As shown in FIG. 5, in the second example embodiment 2, since the bladder 21 is substantially semi-cylindrical, the cross-section of the bladder 21 has the shape of a semicircle or a segmented circle. With the skin 22 that covers the bladder 21 preferably conforming to the bladder 21, the skin 22 correspondingly has a cross-section that has the shape of a semi-circle or a segmented circle.

[0058] As shown in FIG. 6, in the second example embodiment 2, the whole lateral surface of the bladder 21 is to be substantially enveloped with the skin 22. It is to be noted that the bladder 21 and the skin 22 are slidably movable with respect to each other when the bladder 21 is deflated. However, this slidable movement between the bladder 11 and the skin 22 may substantially decrease as the bladder 21 is inflated. When the bladder 21 is fully inflated, this slidable movement between the bladder 21 and the skin 22 may become absent. [0059] Regarding the first example embodiment 1 and the second example embodiment 2, the bladder 11, 21 is preferably a fluid-tight enclosure that is elongate and inflatable under the provision of fluids such as gas or liquid through the tube 111, 211. The bladder 11, 21 is preferably stretchable and deformable, regardless of whether it is deflated or inflated. Likewise, the skin 12, 22 is an outer covering that is preferably stretchable and deformable.

[0060] Regarding the first example embodiment 1 and the second example embodiment 2, as the bladder 11, 21 is inflated, it may enlarge and may become in substantial contact with the skin 12, 22, which conforms thereto. For motions to be induced within the composite actuator during inflation of the bladder 11, 21, it is preferable that the bladder 11, 21 has an overall Young’s modulus that is smaller than that of the skin 12, 22 (Ebladde <E_ski_n , or that the skin 12, 22 has an overall Young’s modulus that is larger than the bladder 11, 21 E_ski_n> Ebiadder')- With this relationship, the skin 12, 22 acts as a deformation-controlling constraint that controls the motion of the composite actuator during the inflation of the bladder 11, 21, and motions may be induced within the composite actuator by the skin 12, 22 as the bladder 11, 21 is inflated. Upon the bladder 11, 21 becoming fully inflated, the motion performed by the composite actuator may end.

[0061] Regarding the first example embodiment 1 and the second example embodiment 2, the bladder 11, 21 may have a varying or non-constant Young’s modulus, but shall still have an overall Young’s modulus that is smaller than that of the skin 12, 22. The skin 12, 22 may also have a varying or non-constant Young’s modulus but shall still have an overall Young’s modulus that is larger than that of the bladder 11, 21.

[0062] Regarding the first example embodiment 1 and the second example embodiment 2, the bladder 11, 21 may be, by way of example, composed of silicone or any other material that is stretchable and deformable while capable of being inflated. The bladder 11, 21 may be entirely composed of homogeneous material, which may, by way of example, silicone. The bladder 11, 21 may also be composed of heterogeneous material, which may be, by way of example, a combination of silicones that include a first type of silicone and a second type of silicone, with the second type of silicone being stiffer than the first type of silicone. [0063] Regarding the first example embodiment 1 and the second example embodiment 2, the skin 12, 21 comprises one or more layers, among the layers, there is at least one layer that has anisotropic properties in terms of having a minimum Young’s modulus in a first direction and a maximum Young’s modulus in a second direction that is orthogonal to the first direction, wherein the layer is to substantially envelop the bladder 11, 21 while being stretched along the first direction. The layers may be in the form of a sheet that envelops bladder 11, 21 entirely or in the form of a tape that envelops portions of the bladder 11, 21. The fabrics may be composed of any one of a combination of fabrics that include spandex, nylon or cotton. Most preferably, the fabrics include an elastic material with an adhesive backing and/or fabric with a thermoplastic backing. Such fabrics may be found commercially as kinesiology tape and/or thermoplastic polyurethane (TPU)-backed fabrics. Other commercial fabrics that may be used as the skin 12, 22 may include cohesive tapes, medical bandages, surgical tapes, or any other known medical tapes or therapeutic tapes.

[0064] Regarding the first example embodiment 1 and the second example embodiment 2, the skin 12, 22 has a first opening and a second opening at its ends, which are to be correspondingly sealed with the first sealing means 13a, 23a and the second sealing means 13b, 23b. The first sealing means 13a, 23a and the second sealing means 13b, 23b may be part of the skin 12, 22. Preferably, the first sealing means 13a, 23a and the second sealing means 13b, 23b are hook and loop fasteners (i.e. VELCRO ®) that are to remain sealed throughout inflation of the bladder 11, 21 and movement of the composite actuator. Preferably, the first opening, sealed by the first sealing means 13a, 23a is an opening for the bladder 11, 21, whereas the second opening, sealed by the first sealing means 13a, 23a is an opening for the tube 111, 211. The bladder 11, 21 with its tube 111, 211 may be slid into the skin 12, 22 from the first opening, and the tube 111, 211 may then be pulled out from the skin 12, 22 from the second opening. After that, the first sealing means 13a, 23a and the second sealing means 13b, 23b may be sealed.

[0065] Regarding the first example embodiment 1 and the second example embodiment 2, since the bladder 11, 21 and skin 21, 22 are slidably movable with respect to each other, the composite actuator is effectively modular, customisable, and reconfigurable as the bladder 11, 21 and/or the skin 21, 22 may be readily removed from each other and further be swapped or replaced with a different bladder and/or the skin for another intended motion to be produced. This also provides a higher degree of flexibility in tweaking the performance of the composite actuator according its geometry and material.

[0066] From hereon, further embodiments of the composite actuator that shall be described may be a derivative embodiment of the first example embodiment 1 or the second example embodiment 2, and descriptions of the further embodiments are applicable to the first example embodiment 1 or the second example embodiment 2.

[0067] FIGS. 7 to 9 illustrate further example embodiments of the composite actuator that are configured to perform a bending motion. In particular, FIG. 7 illustrates a transverse cross-section of the composite actuator in a third example embodiment 3, FIG. 8 illustrates a transverse cross-section of the composite actuator in a fourth example embodiment 4, and FIG. 9 illustrates an example method for producing a composite actuator that is configured to perform a bending motion, which is per the third example embodiment 3.

[0068] FIG. 7 illustrates a longitudinal cross-section of the composite actuator in a third example embodiment 3. This third example embodiment 3 may be a derivative of the first example embodiment 1 described above. As shown, the third example embodiment 3 comprises a bladder 31 with a circular cross-section as its inner body, and a skin as its outer covering that comprises a first layer 321, a second layer 322, and a third layer 323. Preferably, the first layer 321 and the third layer 323 have anisotropic properties, and the second layer 322 is a strain limiter that provides supportive backing. Most preferably, the first layer 321 and the third layer 323 are kinesiology tape, and the second layer 322 is a thermoplastic polyurethane (TPU)-backed fabric.

[0069] In particular, the first layer 321 substantially envelops the bladder 31 as a whole, the second layer 322 partially covers a region of the first layer 321, and the third layer 323, envelops the second layer and the first layer as a whole. The first layer 321 forms an overlapped region with its ends overlapped with each other as it envelopes the bladder 31 that shall be the region covered by the second layer 322, and the first layer 321 bonds to the third layer 323 with the second layer 322 sandwiched therebetween.

[0070] FIG. 8 illustrates a longitudinal cross-section of the composite actuator in a fourth example embodiment 3. This fourth example embodiment 4 may be a derivative of the second example embodiment 2 described above. As shown, the fourth example embodiment 4 comprises a bladder 41 with a semi-circular cross-section as its inner body, and a skin as its outer covering that comprises a first layer 421. Preferably, the first layer 421 has anisotropic properties. Most preferably, the first layer 421 is kinesiology tape.

[0071] In particular, the first layer 421 envelops the bladder 41 to form an overlapped region upon the rectangular surface of the bladder 41. Whilst not shown, subsequent layers of the skin may envelop the first layer 421 in a manner similar to as described for the third example embodiment 3.

[0072] Regarding the third example embodiment 3 and the fourth example embodiment 4, it is to be noted that the formation of the overlapped region increases the Young’s modulus of the skin, particularly along a segment of overlapped region, hence, this overlapped portion allows for an increased bending along said region during inflation of the bladder 31, 41. As for the third example embodiment 3, the second layer 322 further contributes to limiting the strain across the overlapped region.

[0073] FIG. 9 illustrates an example method for producing a composite actuator that is configured to perform a bending motion, per the third example embodiment 3. The illustrated example method may comprise one or more steps.

[0074] In a first step, there is a step of preparing the bladder 31 or a tubular structure that is similar to the bladder, and layers of the skin that includes a first layer 321, a second layer 322, and a third layer 323. Each of the layers 321, 322, 323 may have an adhesive surface and a non-adhesive surface.

[0075] In a second step, the first layer 321 is made to substantially cover the lateral surface of the bladder 31 as a whole by substantially enveloping it. As the first layer 321 envelops the bladder 31, the adhesive surface of the first layer 321 faces away from the bladder 31, while the non-adhesive surface of the first layer 321 faces towards the bladder 31. Preferably, the first layer 321 is stretchable and deformable, and the first layer 321 is stretched to envelop the bladder 31 by being substantially wrapped around it. Preferably as well, the first layer 321 terminates with an overlap, i.e. the beginning and end of the first layer 321 overlap with each other, thereby forming an overlapped region that extends along a portion of the lateral surface of the composite actuator.

[0076] In a third step, the second layer 322 is overlaid onto the overlapped region that was formed by the first layer 321. Preferably, the second layer 322 only covers the extent of the aforementioned overlapped region and it acts as a backing to increase stiffness and limit the strain experienced across the aforementioned overlapped region.

[0077] In a fourth step, the third layer 323 is made to substantially envelop the lateral surface of the bladder 31 as a whole, which may now be incorporated with the first layer 321 and second layer 322, by being substantially wrapped around it. As the third layer 323 envelops the bladder, its adhesive surface faces towards the first layer 321 and second layer 322, while its non-adhesive surface faces away from the first layer 321 and second layer 322. Preferably as well, the third layer 323 terminates without an overlap.

[0078] It is to be noted as per the steps described in FIG. 9, the bladder 31 and the skin are in slidable movement with respect to each other when the bladder 31 is deflated, since the first layer 321 has its non-adhesive surfaces facing towards the bladder 31. This promotes modularity, customisability, and reconfigurability of the bladder 31 and the skin.

[0079] It is to be noted as per the steps described in FIG. 9, the first layer 321 and the third layer 323 have their adhesive surfaces in contact with each other. Hence, this increases the shearing resistance of the skin due to the bonding between the adhesive surfaces. Thus, the overall Young’s modulus of the skin is further increased.

[0080] This concludes the steps for constructing a composite actuator that is configured to perform a bending motion as shown in FIG. 9, which is as per the third example embodiment 3. These steps may also be understood to be applicable in constructing the fourth example embodiment 4.

[0081] FIGS. 10 to 15 illustrate further example embodiments of the composite actuator that are configured to perform a torsional motion. [0082] In particular, FIG. 10 illustrates a longitudinal cross-section of the composite actuator in a fifth example embodiment 5. Whereas, FIG. 11 illustrates a first example method for producing a composite actuator that is configured to perform a torsional motion, which is per the fifth example embodiment 5.

[0083] In particular, FIG. 12 illustrates a longitudinal cross-section of the composite actuator in a sixth example embodiment 6. Whereas, FIG. 13 illustrates a second example method for producing a composite actuator that is configured to perform a torsional motion, which is per the sixth example embodiment 6.

[0084] In particular, FIG. 14 illustrates a longitudinal cross-section of the composite actuator in a seventh example embodiment 7. Whereas, FIG. 15 illustrates a third example method for producing a composite actuator that is configured to perform a torsional motion, which is per the seventh example embodiment 7.

[0085] For the embodiments of the composite actuator as shown in FIGS. 10 to 15, the composite actuator is enabled to perform a torsional motion by the configuration of the skin. In particular, the skin may be configured to be of multiple layers. Furthermore, the skin may also be configured to have a varying or non-constant Young’s modulus by use of wrapping patterns, overlaps, overlap distributions, or folds within the layers of the skin, however, the skin shall still have an overall Young’s modulus that is larger than that of the bladder.

[0086] FIG. 10 illustrates a view of the longitudinal cross-section of the composite actuator in the fifth example embodiment 5. As shown in FIG. 11, the fifth example embodiment 5 comprises a bladder 51 as its inner body, and a skin as its outer covering that comprises a first layer 521 that envelops the bladder 51. Preferably, the first layer 521 has anisotropic properties. Most preferably, the first layer 521 is kinesiology tape.

[0087] In particular, the first layer 521 is in the form of a strip, which substantially envelops the bladder 51 while being orientated at an angle with respect to a central axis of the bladder (i.e. wrapping angle), for enveloping the bladder 51 in a helical manner to form one or more overlapped regions. Whilst the overlapped regions are not specifically drawn in FIG. 10, they are nevertheless present within the fifth example embodiment 5. [0088] FIG. 11 illustrates a first example method for producing a composite actuator that is configured to perform a torsional motion, per the fifth example embodiment 5. The illustrated example method may comprise one or more steps.

[0089] In a first step, there is a step of preparing the bladder 51 or a tubular structure that is similar to the bladder, and layers of the skin that includes a first layer 521 having anisotropic properties.

[0090] In a second step, the first layer 521 is to substantially envelop the lateral surface of the bladder 51 as a whole by being substantially wrapped around it while being orientated at an angle with respect to a central axis of the bladder, for enveloping the bladder in a helical manner.

[0091] In a third step, the first layer 521 is made to tighten around the bladder 51. With the first layer 521 enveloping the bladder 51 in such a way that it is stretched in the direction where it has a minimum Young’s modulus, its weaving patterns may now be orientated along the direction of wrapping. Due to the anisotropic nature of the first layer 521, there is a radial constraint around the wrap direction of the first layer 521. Moreover, during the wrapping of the first layer 521, one or more overlapped regions may be formed, and these overlapped regions may further act as torsional constraints. This concludes the steps for constructing a composite actuator that is configured to perform a torsional motion as shown in FIG. 11, which is as per the fifth example embodiment 5.

[0092] The fifth example embodiment 5 is capable of generating up to 540 degrees of rotation with respect to the central axis of the bladder 51 during inflation of the bladder 51. The deformations during the torsional motion are largely dependent on the material used for the skin and the presence of the overlapped regions on the skin. Larger deformations during a torsional motion by a composite actuator may be obtained by use of a skin with highly stretchable layers, or a skin having layers with smaller overlapped regions. Moreover, the behaviour of the torsional motion can also be tuned according to the wrapping angle.

[0093] FIG. 12 illustrates a view of the longitudinal cross-section of the composite actuator in the sixth example embodiment 6. As shown, the sixth example embodiment 6 comprises a bladder 61 as its inner body, and a skin as its outer covering that comprises a first layer 621 that envelops the bladder 61 in a helical manner, and a second layer 622 that envelopes the overlapped regions of the first layer 621 in a helical manner. Most preferably, the first layer 621 and the second layer 622 are kinesiology tapes.

[0094] In particular, the first layer 621 is in the form of a strip, which substantially envelops the bladder 61 while being orientated at a first angle with respect to a central axis of the bladder (i.e. first wrapping angle), for enveloping the bladder in a helical manner to form one or more overlapped regions. Whilst the overlapped regions are not specifically drawn in FIG. 12, they are nevertheless present within the sixth example embodiment 6.

[0095] In particular, the second layer 622 is also in the form of a strip, which substantially envelops the overlapped regions of the first layer 621 in a helical manner by being orientated at a second angle with respect to a central axis of the bladder (i.e. second wrapping angle). The second angle may be the same as the first angle. Moreover, the second layer 622 is distributed sparsely along the first layer 621.

[0096] As the sixth example embodiment 6 has a skin with one or more layers 621, 622 wrapped at different distributions and/or angles with respect to the bladder 61, it is robust to skin delamination since adhesive delamination that may occur at the overlapped regions of the first layer 621 are circumvented as these regions are bonded to the second layer 622.

[0097] FIG. 13 illustrates a second example method for producing a composite actuator that is configured to perform a torsional motion, per the sixth example embodiment 6. The illustrated example method may comprise one or more steps.

[0098] In a first step, there is a step of preparing the bladder 61 or a tubular structure that is similar to the bladder, and layers of the skin that includes a first layer 621 and a second layer 622, both having anisotropic properties.

[0099] In a second step, the first layer 621 is made to substantially envelop the lateral surface of the bladder 61 as a whole by being substantially wrapped around it at an angle in a helical manner and tighten around the bladder 61. With this, one or more overlapped regions are formed along the first layer 621. [00100] In a third step, the second layer 622 is made to envelop the overlapped regions of the first layer 621 by being substantially wrapped around these overlapped regions at an angle in a helical manner and tighten around said regions. This concludes the steps for constructing a composite actuator that is configured to perform a torsional motion as shown in FIG. 13, which is as per the sixth example embodiment 6.

[00101] FIG. 14 illustrates a view of the longitudinal cross-section of the composite actuator in the seventh example embodiment 7. As shown, the seventh example embodiment 7 comprises a bladder 71 as its inner body, and a skin as its outer covering that comprises first layer 721 that envelops the bladder 71, and a second layer 722 that wraps around the first layer 721 in a helical manner. Most preferably, the first layer 721 and the second layer 722 are kinesiology tapes. Alternatively, the first layer 721 is kinesiology tape, while the second layer 722 is a thermoplastic polyurethane (TPU)-backed fabric.

[00102] In particular, the first layer 721 substantially envelops the bladder 71 as a whole, while the second layer 722 substantially envelops portions of the first layer 721. The second layer 722 is in the form of a strip that is orientated at an angle with respect to a central axis of the bladder as it envelops portions of the first layer 721 in a helical manner.

[00103] FIG. 15 illustrates a third example method for producing a composite actuator that is configured to perform a torsional motion, per the seventh example embodiment 7. The illustrated example method may comprise one or more steps.

[00104] In a first step, there is a step of preparing the bladder 71 or a tubular structure that is similar to the bladder, and layers of the skin that includes a first layer 721 and a second layer 722, both having anisotropic properties.

[00105] In a second step, the first layer 721 is made to substantially envelop the lateral surface of the bladder 71 as a whole by being substantially wrapped around it entirely.

[00106] In a third step, the second layer 722 is made to substantially envelop the lateral surface of the bladder 71 as a whole, which may now be incorporated with the first layer 721, by being substantially wrapped at an angle in a helical manner around it. The second layer 722 may then be further bonded to the first layer 721 by use of heat-based sealing techniques. This concludes the steps for constructing a composite actuator that is configured to perform a torsional motion as shown in FIG. 15, which is as per the seventh example embodiment 7.

[00107] The sixth example embodiment 6 and the seventh example embodiment 7, having multiple layers, may withstand higher pressure forces and generate higher torque when compared to the fifth example embodiment 5.

[00108] FIG. 16 illustrates the composite actuator in its eighth example embodiment 8 that is configured to perform an extending motion (i.e. lengthening) during its inflation. More specifically, FIG. 16 illustrates the transverse cross-section of the eighth example embodiment 8.

[00109] As shown, the eighth example embodiment 8 comprises a bladder 81 as its inner body, and a skin as its outer covering that comprises a first layer 821 that envelops the bladder 81, and a second layer 822 that wraps around the first layer 821. Most preferably, the first layer 821 and the second layer 822 are kinesiology tapes.

[00110] In particular, the first layer 821 substantially envelops the bladder 81 as a whole, and the second layer 822 substantially envelops the first layer 821. The first layer 821 forms a first overlapped region with its ends overlapped with each other as it envelopes the bladder 81. This first overlapped region shall be enveloped by the second layer 822. The second layer 822 further forms a second overlapped region with its ends overlapped with each other as it envelops the first layer 821.

[00111] An example method for producing a composite actuator that is configured to perform an extending motion, per the eighth example embodiment 8, may comprise one or more steps.

[00112] In a first step, there is a step of preparing the bladder 81 or a tubular structure that is similar to the bladder, and layers of the skin that includes a first layer 821 and a second layer 822, both preferably having anisotropic properties.

[00113] In a second step, the first layer 821 is made to substantially envelop the lateral surface of the bladder 81 as a whole by being substantially wrapped around it entirely. The first layer 821 terminates with an overlap, i.e. the beginning and the end of the first layer 821 overlap with each other, thereby forming an overlapped region that extends along a portion of the lateral surface of the composite actuator.

[00114] In a third step, the second layer 822 is made to substantially envelop the lateral surface of the bladder 81 as a whole, which may now be incorporated with the first layer 821, by being substantially wrapped around it entirely. The second layer 822 terminates with an overlap, i.e. the beginning and the end of the second layer 822 overlap with each other, thereby forming an overlapped region that extends along a portion of the lateral surface of the composite actuator.

[00115] As shown in FIG. 16, the first overlapped region and the second overlapped region should be diametrically opposite to each other. This shall cancel out any bending motion induced by either overlapped regions, and thus the composite actuator shall perform an extending motion, preferably towards a single direction, during inflation of the bladder 81.

[00116] It is imperative that the above composite actuator as described may be configured to perform one or more motions for producing any one or a combination of a bending motion, torsional motion, or an extending motion. With the composite actuator comprising a bladder and a skin, either one or both the bladder or the skin may be configured to produce an intended combination of motions.

[00117] By way of example, the bladder may be configured to have varying or non-constant Young’s Modulus, i.e. have a main body made of silicone further having a comparatively stiffer silicone. Such a bladder provides a bending motion once inflated. Should such a bladder may then be wrapped with a skin similar to the as described in the fifth to seventh example embodiments 5, 6, 7, the resulting composite actuator may perform both bending and torsional motions, thereby resulting in a helical motion during inflation of the bladder, i.e. during inflation of the bladder, the composite actuator simultaneously bends and twists to follow a helical pathway.

[00118] FIGS. 17 to 19 are graphs that show the results of one or more evaluations performed upon certain embodiments described above to validate their performance. It is to be noted that parameters defined or determined in said evaluations are not meant or interpreted as limitations to the scope of the present invention.

[00119] FIG. 17 shows a graph that relates to the bending motion. More specifically, it is a plot of blocked force (N) against pressure (kPa), for the third example embodiment 3, which has a circular cross-section, and the fourth example embodiment 4, which has a semi-circular cross-section. As shown, the force output of the fourth example embodiment 4 is higher than the third example embodiment 3.

[00120] Further observation of FIG. 17 shows that the fourth example embodiment 4 generates about five times the amount of blocked force compared to the third example embodiment 3 when the fourth example embodiment 4 is inflated with the same pressure as the third example embodiment 3. The lower force output of the third example embodiment 3 is attributed to its circular cross-section losing energy due to a variety of factors, which includes the presence of the second layer 322 as a strain-limiting layer, or the bending or buckling of the bladder 31.

[00121] FIG. 18 shows a graph that relates to the bending motion. More specifically, it is a plot of tip angular displacement of the composite actuator (degrees) against pressure (kPa), for a composite actuator of a third example embodiment 3, which has a circular cross-section, and a composite embodiment of the fourth example embodiment 4, which has a semi-circular cross-section. As shown, the third example embodiment 3 can tolerate higher pressures and as a result has a higher maximum angular displacement, compared to the fourth example embodiment 4. Whereas, the fourth example embodiment 4 exhibits larger deformations at lower pressure.

[00122] FIG. 19 shows a graph that relates to the torsional motion. More specifically, it is a plot of angular displacement of the composite actuator about its central axis (degrees) against pressure (kPa), for a composite actuator of a fifth example embodiment 5, which has a singlelayer skin, and a composite embodiment of the sixth example embodiment 6, which has a double-layer skin. As shown, the fifth example embodiment 5 is able to undergo larger deformations, while the sixth example embodiment 6 is able to tolerate higher pressures. [00123] With the above description, the details pertaining to a composite actuator for use in soft robotics performs motions that include any one of bending, twisting, and extending, or a combination thereof, have been elucidated. The underlying principles of the present invention may be applied to the use of multiple materials to provide unique combinations of actuatable motions. The underlying principles of the present invention may be further extended to a new paradigm of complex multi-material-based actuators.

[00124] The composite actuators as described may be industrially applicable across a broad range of fields or industries, which includes soft manipulators within the manufacturing industry, locomotion robots within the search and rescue industry, assistive-rehabilitation devices within the rehabilitation industry, massaging devices within the healthcare industry, and haptic feedback devices within the gaming industry. More specifically, when applied within the assistive-rehabilitation devices, the composite actuator may provide wrist-and- hand assistance since its inherent compliance and its use of fabrics for its skin enables it to be easily mounted on a conventional compression sleeve wearable by a user.

[00125] The present disclosure includes the appended claims and the foregoing description. Although this invention has been described in its preferred form with a degree of particularity, it is understood that the present disclosure of the preferred form has been made only by way of example and that numerous changes in the details of construction and the combination and arrangements of parts may be resorted to without departing from the scope of the present invention.

Claims

CLAIMS:

1. A composite actuator comprising a bladder; and a skin that covers the bladder; wherein the skin has an overall Young’s modulus that is larger than that of the bladder for acting as a deformation-controlling constraint so that motions are performed by the composite actuator during inflation or pressurisation of the bladder.

2. The composite actuator according to claim 1, wherein: the skin is configured to have a constant Young’s modulus; or the skin is configured to have a varying Young’s modulus; wherein the overall Young’s modulus of the skin being larger than that of the bladder.

3. The composite actuator according to claim 1 or 2, wherein: the bladder is configured to have a constant Young’s modulus; or the bladder is configured to have a varying Young’s modulus; wherein the overall Young’s modulus of the skin being larger than that of the bladder.

4. The composite actuator according to any one of claims 1 to 3, wherein the skin comprises one or more layers, with at least one layer being anisotropic in terms of having a minimum Young’s modulus in a first direction and a maximum Young’s modulus in a second direction that is orthogonal to the first direction, wherein it substantially envelops the bladder while being stretched along the first direction.

5. The composite actuator according to claim 4, wherein the layers of the skin comprise: a first layer, which substantially envelops the bladder as a whole; a second layer that partially envelops a region of the first layer; and a third layer, which substantially envelops the second layer and the first layer as a whole; wherein: the first layer forms an overlapped region with its ends overlapped with each other as it envelopes the bladder that shall be the region covered by the second layer; and the first layer bonds to the third layer with the second layer sandwiched therebetween.

6. The composite actuator according to claim 4, wherein the layers of the skin comprise a first layer, which substantially envelops the bladder, with the first layer forming an overlapped region at a levelled surface of the bladder, it envelopes the bladder.

7. The composite actuator according to claim 5 or 6, wherein the bladder is induced by the skin to perform a bending motion during inflation or pressurisation of the bladder.

8. The composite actuator according to claim 4, wherein the layers of the skin comprise: a first layer, which substantially envelops the bladder; wherein the first layer is in the form of a strip that is orientated at an angle with respect to a central axis of the bladder for enveloping the bladder in a helical manner to form one or more overlapped regions.

9. The composite actuator according to claim 8, wherein the layers of the skin further comprise: a second layer, which substantially envelops portions of the first layer; wherein the second layer is in the form of a strip that is orientated at an angle with respect to a central axis of the bladder for enveloping the overlapped regions of the first layer in a helical manner.

10. The composite actuator according to claim 4, wherein the layers of the skin comprise: a first layer, which substantially envelops the bladder as a whole; and a second layer, which substantially envelops portions of the first layer; wherein the second layer is in the form of a strip that is orientated at an angle with respect to a central axis of the bladder and envelops portions of the first layer in a helical manner.

11. The composite actuator according to any one of claims 8 to 10, wherein the bladder is induced by the skin to perform a torsional motion during inflation or pressurisation of the bladder.

12. The composite actuator according to any of claims 8 to 10, wherein the bladder is comprised of multi-material for the bladder to be induced by the skin to perform both a bending motion and a torsional motion during inflation or pressurisation of the bladder.

13. The composite actuator according to claim 4, wherein the layers of the skin comprise: a first layer, which substantially envelops the bladder as a whole; and a second layer, which substantially envelops the first layer; wherein: the first layer forms a first overlapped region with its ends overlapped with each other as it envelopes the bladder; and the second layer forms a second overlapped region with its ends overlapped with each other as it envelops the first layer.

14. The composite actuator according to claim 12, wherein the first overlapped region and the second overlapped region are diametrically opposite to each other.

15. The composite actuator according to claim 13, wherein the bladder is induced by the skin to perform an extending motion during inflation or pressurisation of the bladder.

16. The composite actuator according to any of the preceding claims, wherein the skin is further formed with a first opening and a second opening at its ends.

17. The composite actuator according to claim 16, further comprising a pair of sealing means, with a first sealing means disposed about the first opening; and a second sealing means disposed about the second opening; wherein the bladder is sealed within the skin by the first sealing means and the second sealing means.

18. The composite actuator according to any of the preceding claims, wherein the bladder has a cross-section that is either circular or semi-circular.

19. The composite actuator according to any of the preceding claims, wherein the bladder and the skin are in slidable movement with respect to each other when the bladder is deflated or depressurised.

20. The composite actuator according to any of the preceding claims, wherein the layers of the skin are any one of: fabric with an adhesive backing; fabric with a thermoplastic backing; or a combination thereof.