Micro-actuator unit and micro-actuator

Abstract

A micro-actuator unit, a micro-actuator, and a method of manufacturing thereof. The micro- actuator unit comprises an insulating member having a first surface and a second surface opposing the first surface, the first and second surface defining a centre axis, the insulating member defining a plurality of openings; a first electrode coupled to the first surface, the first electrode having a plurality of conductive apertures, the conductive apertures and the openings forming a plurality of fluid conduits, each fluid conduit defining a respective flow direction parallel to the centre axis; and a second electrode coupled to the second surface of the insulating member, the second electrode having a plurality of conductive projections, each conductive projection protruding towards a corresponding one of the fluid conduits along the respective flow direction, the conductive projections are disposed with a first rotational symmetry about the centre axis.

Description

MICRO-ACTUATOR UNIT AND MICRO-ACTUATORCROSS-REFERENCE TO RELATED APPLICATION

[0001] This application claims the benefit of priority to the Singapore application no. 10202302018T filed July 17, 2023, the contents of which are hereby incorporated by reference in their entirety for all purposes.TECHNICAL FIELD

[0002] This application relates to liquid-based actuation without moving parts and more particularly to a micro-actuator, a micro-actuator unit, and a method of manufacturing a microactuator unit.BACKGROUND

[0003] In the field of micro-actuation, fluidic elastomer actuators (FEA), also known as soft pneumatic actuators, are highly promising due to their effective coupling of a high bending force with a large bending angle. Typically, a compressed gas cylinder or compression pump is employed as an external pressure source for fluidic elastomer actuators. However, such external pressure sources have the drawback of large volumes, heavy weights, and are often constructed as stiff and rigid structures. In an attempt to overcome these drawbacks, some implementations propose using fluidic elastomer actuators which are filled with low boiling point solvent and the solvent is heated to create pressure through in-built flexible heater. However, the long heating and cooling phases of such fluidic elastomer actuators limit the application due to slow response time.SUMMARY

[0004] According to an aspect, disclosed herein is a micro-actuator unit. The micro-actuator unit comprises an insulating member having a first surface and a second surface opposing the first surface, the first surface and the second surface defining a centre axis, the insulating member defining a plurality of openings; a first electrode coupled to the first surface, the first electrode having a plurality of conductive apertures, the plurality of conductive apertures and the plurality of openings forming a plurality of fluid conduits, each of the plurality of fluid conduits defining a respective flow direction parallel to the centre axis; and a second electrode coupled to the second surface of the insulating member, the second electrode having a plurality of conductive projections, each of the plurality of conductive projections protruding towards a corresponding one of the plurality of fluid conduits along the respective flow direction, wherein the plurality of conductive projections are disposed with a first rotational symmetry about the centre axis.

[0005] According to another aspect, disclosed herein is a micro-actuator. The micro-actuator comprises: a housing defining a chamber extending along an actuator axis; and a first plurality of the micro-actuator unit as described above, the first plurality of the micro-actuator unit being disposed in the chamber, the first plurality of the micro-actuator unit being spaced apart from one another along the actuator axis to define a plurality of first sub-chambers in the housing, wherein the respective flow directions of the first plurality of the micro-actuator unit are aligned in a first common direction parallel to the actuator axis.

[0006] According to yet another aspect, disclosed herein is a gripper system. The gripper system comprises: a reservoir, the reservoir containing a dielectric liquid; a gripper, the gripper being configured to be pneumatically actuated by the dielectric liquid; the micro-actuator as described above, wherein the micro-actuator is in fluid communication between the gripper and the reservoir; and a circuit, the circuit being configured to apply a potential difference acrossthe first electrode and the second electrode, wherein, responsive to the potential difference applied across the first electrode and the second electrode, the micro-actuator electrohydrodynamically pushes the dielectric liquid towards the gripper at a liquid pressure.

[0007] In addition, according to another aspect, disclosed herein is a method of manufacturing a micro-actuator unit. The method comprises: providing an insulating member having a first surface and a second surface opposing the first surface, the first surface and the second surface defining a centre axis, the insulating member defining a plurality of openings; coupling a first electrode to the first surface, the first electrode having a plurality of conductive apertures, the plurality of conductive apertures and the plurality of openings forming a plurality of fluid conduits, each of the plurality of fluid conduits defining a respective flow direction parallel to the centre axis; and coupling a second electrode to the second surface of the insulating member, the second electrode having a plurality of conductive projections, each of the plurality of conductive projections protruding towards a corresponding one of the plurality of fluid conduits along the respective flow direction, wherein the plurality of conductive projections are disposed with a first rotational symmetry about the centre axis.BRIEF DESCRIPTION OF THE DRAWINGS

[0008] Various embodiments of the present disclosure are described below with reference to the following drawings:

[0009] FIG. 1 is a schematic diagram illustrating electrohydrodynamic (EHD) principles of a dielectric liquid.

[0010] FIG. 2 illustrates a gripper system and a micro-actuator according to embodiments of the present disclosure.

[0011] FIG. 3 is a perspective view of a micro-actuator according to embodiments of the present disclosure.

[0012] FIG. 4 illustrates another gripper system according to embodiments of the present disclosure.

[0013] FIG. 5 is a perspective view of a micro-actuator unit according to various embodiments.

[0014] FIGs. 6A and 6B show exploded views of the micro-actuator unit of FIG. 5 from different perspectives.

[0015] FIG. 7A shows a perspective sectional view of the micro-actuator unit of FIG. 5.

[0016] FIG. 7B shows a side view of FIG. 7A.

[0017] FIG. 8A shows a sectional view of a micro-actuator unit during operation according to various embodiments.

[0018] FIG. 8B shows a sectional view of another micro-actuator unit during operation according to various embodiments.

[0019] FIGs. 9A to 9F schematically show the various configurations of conductive apertures and conductive projections according to various exemplary micro-actuator units.

[0020] FIGs. 10A to 10C schematically show the various configurations of conductive apertures and flow apertures according to various exemplary micro-actuator units.

[0021] FIGs. 11 A to 1 IF show the various components of the micro -actuator unit at different fabrication stages, FIGs. 11A and 1 IB show the needle electrode and the hole electrode printed using soft PU polymer, FIGs. 11C and 11D show the needle electrode and the hole electrode coated with a thin layer of copper, FIG. HE shows the 3D printed concentrator or insulating member, and FIG. 1 IF shows the micro-actuator unit which includes two electrodes and a concentrator.

[0022] FIG. 12 shows a plot of the output pressure of a single micro-actuator unit with and without a concentrator.

[0023] FIGs. 13A to 13C show the plots of the output pressure of micro-actuators with different number of serially connected micro-actuator units. The micro -actuator in FIG. 13A, 13B, and 13C have two, four, and eight serially connected micro-actuator units, respectively.

[0024] FIG. 14 is a photo of an exemplary gripper system with a micro-actuator, FEA- based three finger gripper, liquid reservoir, and pressure converter.

[0025] FIGs. 1 A to 15C are photos of the exemplary gripper system gripping an orange with a weight of digrams. FIG. 15A shows the bending angle test for a single finger. FIG. 15B shows the plots of the bending angle and bending force of the single finger of FIG. 15A. FIG. 15C shows the process of the gripper system lifting and lowering the orange.

[0026] FIG. 16 is a schematic diagram illustrating a method of manufacturing a microactuator unit according to various embodiments of the present di closure.DETAILED DESCRIPTION

[0027] The following detailed description is made with reference to the accompanying drawings, showing details and embodiments of the present disclosure for the purposes of illustration. Features that are described in the context of an embodiment may correspondingly be applicable to the same or similar features in the other embodiments, even if not explicitly described in these other embodiments. Additions and / or combinations and / or alternatives as described for a feature in the context of an embodiment may correspondingly be applicable to the same or similar feature in the other embodiments.

[0028] In the context of various embodiments, the articles “a”, “an” and “the” as used with regard to a feature or element include a reference to one or more of the features or elements.

[0029] In the context of various embodiments, the term “about” or “approximately” as applied to a numeric value encompasses the exact value and a reasonable variance as generally understood in the relevant technical field, e.g., within 10% of the specified value.

[0030] As used herein, the term “and / or” includes any and all combinations of one or more of the associated listed items.

[0031] For the sake of brevity, the term “micro-actuator” or “micro-actuator unit” may include an implementation or device for providing, facilitating and / or enabling a movement or an actuation. In the context of fluidic elastomer actuators, the “actuator” or “micro-actuator” may be a pressure source, which enables actuation to an end-effector or actuating device. As used herein, the term “micro-actuator” may be used to refer to any one or more of the terms “actuator”, “actuation device”, “actuating mechanism”, “pressure source”, etc., as will be understood from the context. In some examples, the “micro-actuator” may be a pressure pump or micro-fluidic pump.

[0032] The term “insulating member”, “insulating material”, “insulation”, “insulator” may generally refer to a structure or material in which electric current does not flow freely therethrough or between a first point and a second point disposed on the structure or material. The term “electrode” may include a non-conductivc structure coated with a conductive surface layer. The term “electrode” may also include a non-conductive structure partially coated with a conductive surface layer. The term “electrode” may also include a fully conductive structure formed from a conductive material. The term “electrode” may also include a partially conductive structure formed from a combination of conductive material and insulating material.

[0033] Soft gripper systems are suitable for various controlled / low contact force applications, such as human-machine interfaces, agriculture 4.0, smart prosthetics, special industrial manufacturing, bionic robots, etc. Typically, soft gripper systems may be used for grasping objects with complex shapes and / or fragile objects with high dexterity and high degrees of freedom without compromising or damaging the objects. While there exist various types of soft gripper systems (such as contact-driven, tendon-driven, dielectric elastomer actuators, ionic polymer-metal composites, and photothermal actuators), fluidic elastomeractuator (FEA) systems or fluid elastomer-based gripper systems are considered promising due to high bending output force and large output bending angle.

[0034] FIG. 1 illustrates a working principle of electrohydrodynamics (EHD). FIG. 1 schematically shows the electrohydrodynamics effect whereby molecules of a dielectric liquid accept electron(s) at the negative electrode to form anions (x-1). Thereafter, the anions (x1) formed at the negative electrode are accelerated by an electric field formed across the pair of positive and negative electrode, to move from the negative electrode towards the positive electrode to create a fluid movement and fluid pressure. However, due to the low output pressure and lack of consistent performance, electrohydrodynamics-based actuators are not implemented conventionally.

[0035] The present disclosure proposes a micro-actuator, a micro-actuator unit and a method for manufacturing a micro-actuator unit. According to an aspect, the proposed micro-actuator may be configured as an actuation source or a pressure source for fluidic elastomer-based soft grippers. According to various embodiments, the proposed micro-actuator may overcome the various drawbacks and challenges of conventional actuators or pressure sources, such as large volumes, heavy weights, rigid, slow responses, etc. According to various embodiments, the micro-actuator may be based on electrohydrodynamic (EHD) principles which involve the interaction between a dielectric liquid, electric field and fluid flow. According to various implementations, the EHD interaction between electric field and fluid flow may contribute to effective electrically-induced mixing, pumping, and improved heat transfer.

[0036] Unlike typically pressure sources which are bulky and rigid, the proposed microactuator and gripper system may be made from flexible / soft and light materials. In addition, the proposed micro-actuator may provide a high pressure in a compact and low volume / weight configuration, enabling portability without reducing pressure output. Beneficially, the proposed micro-actuator may have a low weight and size, for example below 15 grams. In addition, theproposed micro-actuator may provide a high liquid pressure or output pressure to the soft gripper. In an exemplary implementation, the proposed micro-actuator was able to output a liquid pressure of 45 kPa. Due to the lack of moving parts in the proposed micro-actuator, wear and tear of the micro-actuator during operation is kept at a minimum advantageously prolonging operational duration. In addition, the proposed micro-actuator produces low to inaudible noise, which makes the micro-actuator suitable for various medical applications such as a micro-pump suitable for medical wards. Incorporating the proposed micro-actuator with a gripper provides a gripper system with good gripping performance. In an exemplary implementation, the gripper demonstrated a tight grip on an object with a weight of 500 grams.

[0037] According to various embodiments, the proposed micro-actuator and gripper system exhibits high output pressure and consistency in performance, overcoming the conventional performance limitation of electrohydrodynamics-based actuators.

[0038] FIG. 2 illustrates a soft gripper system 50 according to various embodiments. The gripper system 50 may be a fluidic elastomer-based gripper system configured to grip or hold complex objects and / or fragile objects. The gripper system 50 may include a reservoir 60 for containing or holding a dielectric liquid, and an end-effector or an actuator end, such as a gripper 70. In addition, a micro-actuator 100 may be provided disposed between and in fluid communication with the reservoir 60 and the gripper 70.

[0039] In various embodiments, the gripper 70 may be formed from an elastic material and may be actuatable by a liquid, such as a dielectric liquid, to perform a gripping / clamping action. In other embodiments, the end-effector may perform other forms of movement, such as linear translation, rotation, etc. without being limiting. In order to actuate the gripper 70, the microactuator 100 may be a pressure pump for moving the dielectric liquid in the reservoir 60 towards or away from the gripper 70. In some embodiments, the micro-actuator 100 may be a pressure source for the gripper 70. For instance, the micro-actuator 100 may form a liquid pressure inthe dielectric liquid along a first common direction 61 to move or pump the dielectric liquid from the reservoir 60 towards the gripper 70, to actuate the gripper 70. Conversely, the microactuator 100 may also form a liquid pressure in the dielectric liquid along a second common direction 62 to move or pump the dielectric liquid from the gripper 70 towards the reservoir 60, to release the gripper 70. Therefore, the first common direction 61 may be opposite to the second common direction 62. In other words, a dielectric liquid flow in the first common direction 61 is opposite to a dielectric liquid flow in the second common direction 62.

[0040] The dielectric liquid may include one or a mixture of multiple liquid materials which form ions (such as positively charged ions and / or negatively charged ions) responsive to exposure to an electric field. In an example, the dielectric liquid may be Linalyl acetate.

[0041] In various embodiments, the gripper system 50 may further include a circuit 80 in signal communication with the micro-actuator 100. In some embodiments, responsive to receiving a voltage or potential difference from the circuit 80, the micro -actuator 100 may provide a liquid pressure to the dielectric liquid based on clcctrohydrodynamics. In other words, the micro-actuator 100 may electrohydrodynamically move the dielectric liquid along a direction. In some embodiments, responsive to a voltage applied by the circuit 80, the microactuator 100 may electrohydrodynamically push the dielectric liquid from the reservoir 60 towards the gripper 70. Further, in some embodiments, the circuit 80 may also be configured to apply another voltage or another potential difference to the micro-actuator 100 to electrohydrodynamically push the dielectric liquid in a reverse direction, from the gripper 70 towards the reservoir 60.

[0042] In various embodiments, the fluid reservoir 60, the micro-actuator 100, and the gripper 70 may form a closed fluid path. The dielectric liquid may be contained or held within the closed fluid path and may be prohibited from exiting the gripper system 50. The closed fluidpath advantageously provides a closed system in which the dielectric liquid may be reused during operation of the gripper system 50.

[0043] In some embodiments, the gripper 70 may be a pneumatically-actuated gripper 70. The gripper system 50 may further include a pressure converter 72 in fluid communication between the gripper 70 and the micro-actuator 100. The pressure converter 72 may be configured to convert a liquid pressure of the dielectric liquid into a pneumatic pressure acting on the pneumatic-actuated gripper 70. Therefore, the fluid reservoir 60, the micro-actuator 100, and pressure converter 72 may form a closed fluid path. The dielectric liquid is contained or held within the closed fluid path.

[0044] Referring to FIGs. 2 and 3, in various embodiments, the micro-actuator 100 may include a housing 1 10. The housing 1 10 may define a chamber 1 12 formed therein. The housing 110 may further include a first port 114 and a second port 116 both in fluid communication with the chamber 112. The chamber 112 may extend along an actuator axis 118. The actuator axis 118 may be parallel to the first common direction 61 and the second common direction 62. In some embodiments, the first port 114 may be in fluid conununication with the reservoir 60, and the second port 1 16 may be in fluid communication with the gripper 70.

[0045] The micro-actuator 100 may include multiple micro-actuator units 200 disposed in the chamber 112. The multiple micro-actuator units 200 may be disposed in series along the actuator axis 118. The micro-actuator units 200 may each act as a micro-pump to provide a pressure differential across each micro-actuator unit 200. The number of micro-actuator units 200 may be linearly or near-linearly correlated with the liquid pressure provided by the microactuator 100. For instance, a higher number of micro-actuator units 200 may result in a higher liquid pressure in the dielectric liquid output from the micro-actuator 100.

[0046] In various embodiments, the micro-actuator 100 may include a first plurality of the micro-actuator units 201 disposed in the chamber 112 spaced apart from one another along theactuator axis 118. The first plurality of micro-actuator units 201 may each define a common flow direction. Each common flow direction of the first plurality of micro-actuator units 201 may be aligned in a first common direction 61. In various embodiments, each of the first plurality of micro-actuator units 201 may provide a pressure differential along the first common direction 61 between each of the first sub-chambers 113. The first plurality of micro-actuator units 201 may define a plurality of first sub-chambers 1 13 in the housing 1 10. In various embodiments, each adjacent pair of first sub-chambers 113 may be in fluid communication with each other via a respective one of the first plurality of micro-actuator units 201. Hence, each of the first plurality of micro-actuator units 201 may provide a fluid path and a pressure differential between each adjacent pair of first sub-chambers 113.

[0047] Similarly, the micro-actuator 100 may further include a second plurality of the microactuator units 202 disposed in the chamber 112 spaced apart from one another along the actuator axis 118. The second plurality of micro-actuator units 202 may each define a common flow direction. Each common flow direction of the second plurality of micro-actuator units 202 may be aligned in the second common direction 62. In various embodiments, each of the second plurality of the micro-actuator units 202 may provide a pressure differential along the second common direction 62 between each of the second sub-chambers 115. The second plurality of the micro-actuator units 202 may define a plurality of second sub-chambers 115 in the housing 110. In various embodiments, each adjacent pair of second sub-chambers 115 may be in fluid communication with each other via a respective one of the second plurality of micro-actuator units 202. Hence, each of the second plurality of micro-actuator units 202 may provide a fluid path and a pressure differential between each adjacent pair of second sub-chambers 115.

[0048] Therefore, in various embodiments, responsive to a first voltage applied to each of the first plurality of micro-actuator units 201, a pressure differential is formed along the first common direction 61 to push the dielectric liquid from the fluid reservoir 60 to wards the gripper70 via the second port 116, to actuate the gripper 70. Similarly, responsive to a second voltage applied to each of the second plurality of micro-actuator units 202, a pressure differential is formed along the second common direction 62 to push the dielectric liquid from the gripper 70 back towards the fluid reservoir 60 via the first port 114, to release the gripper 70.

[0049] In some embodiments, the number of micro-actuator units 200 in the first plurality of the micro-actuator units 201 is equal to the number of micro-actuator units 200 in the second plurality of the micro-actuator units 202. This beneficially allows similar liquid pressure in both of the first common direction 61 and the second common direction 62.

[0050] In other embodiments, the number of micro -actuator units 200 in the first plurality of the micro-actuator units 201 is different from the number of micro -actuator units 200 in the second plurality of the micro-actuator units 202. This enables higher pressure output from the micro-actuator 100 biased towards one of the first common direction 61 and the second common direction 62. Referring to FIG. 2, in an example, five micro-actuator units 200 may be disposed in the chamber 112, with an unequal number of micro-actuator units 201 / 202. In another example as shown in FIG. 3, eight micro-actuator units 200 may be disposed in the chamber 1 12, with an equal number of micro-actuator units 201 / 202.

[0051] Referring now to FIG. 4, according to various embodiments, the gripper system 50 may include a first micro-actuator 100a and a second micro-actuator 100b. The first microactuator 100a and the second micro-actuator 100b may be in a parallel fluid communication with the reservoir 60 and the gripper 70. Therefore, it may be appreciated that each of the first micro-actuator 100a and the second micro-actuator 100b are independently in fluid communication with the reservoir 60 and the gripper 70. In some embodiments, the first microactuator 100a and the second micro-actuator 100b are in a parallel fluid communication.

[0052] The first micro-actuator 100a may include a first housing 110a defining a first chamber 112a. The first micro-actuator 100a may include a first plurality of the micro-actuatorunits 201 disposed in the chamber 112a spaced apart from one another. The first plurality of micro-actuator units 201 may each define a respective flow direction. Each flow direction of the first plurality of micro-actuator units 201 may be aligned in the first common direction 61. The second micro-actuator 100b may include a second housing 110b defining a second chamber 112b. The second micro-actuator 100b may include a second plurality of the micro-actuator units 202 disposed in the chamber 1 12b spaced apart from one another. The second plurality of micro-actuator units 202 may each define a respective flow direction. Each flow direction of the second plurality of micro-actuator units 202 may be aligned in the second common direction 62. In some embodiments, the first housing 110a and the second housing 110b may be integrally formed as a single housing 110 which defines two chambers 112a / l 12b.

[0053] The gripper system 50 may further include a valve, such as a three-way valve 64, in fluid communication with the chambers 112a / 112b. The three-way valve 64 may be controllable by the circuit 80. The three-way valve 64 allows a selectable fluid communication between the gripper 70 and each of the first micro-actuator 100a and second micro-actuator 100b. In some embodiments, only one of the first micro-actuator 100a and the second microactuator 100b may be in fluid communication with the gripper 70 at any one time instant.

[0054] It may be appreciated that the control of the three-way valve 64 may coincide with the moving or pumping of the dielectric liquid from the reservoi r 60 towards the gripper 70, or conversely, the moving or pumping of the dielectric liquid from the gripper 70 towards the reservoir 60. Further, the three-way valve 64 may also form a closed liquid loop between the reservoir 60, the first micro-actuator 100a and the second micro-actuator 100b for purpose of circulating the dielectric liquid in the gripper system 50 or during cleaning of the gripper system 50.

[0055] FIGs. 5 to 8B illustrate various embodiments of a micro-actuator unit 200. The micro-actuator unit 200 may include an insulating member 210; a first electrode 220 coupledto the insulating member 210; and a second electrode 230 coupled to the insulating member 210. The insulating member 210 may define a first surface 210a and a second surface 210b opposing the first surface 210a. The first surface 210a and the second surface 210b may define a centre axis 205. The first electrode 220 may be coupled to the first surface 210a of the insulating member 210. The second electrode 230 may be coupled to the second surface 210b of the insulating member 210.

[0056] The insulating member may define a plurality of openings 212. Each of the plurality of openings 212 may include an insulating inner wall 214. In other words, the inner wall of the openings 212 may be formed from an insulating material. The first electrode 220 may include a plurality of conductive apertures 222. The conductive apertures 222 may include conductive inner walls 224. In some implementations, the conductive apertures 222 may be formed as an inner wall coated with conductive material. In other implementations, the conductive apertures 222 may be formed as apertures in a bulk conductive material.

[0057] In some embodiments, the plurality of conductive apertures 222 may correspond or be aligned with the plurality of openings 212. In other words, each of the conductive apertures 222 may correspond to and be aligned with a respective one of the openings 212. There may be equal number of conductive apertures 222 and openings 212. In some embodiments, a positional relationship (such as the relative distances) between the multiple conductive apertures 222 corresponds to a positional relationship (such as the relative distances) between the multiple openings 212.

[0058] In some embodiments, the second electrode 230 may be formed with a plurality of conductive projections 232. In some implementations, the conductive projections 232 may be formed as projections coated with a conductive material. In other implementations, the projections 232 may be formed as projections in a bulk conductive material.

[0059] Similar to the positional relationships between the conductive apertures 222 and the openings 212, the plurality of conductive apertures 222 may correspond or be aligned with the plurality of conductive projections 232. In other words, each of the conductive apertures 222 may correspond to and be aligned with a respective one of the conductive projections 232. There may be equal number of conductive apertures 222 and conductive projections 232. In some embodiments, a positional relationship between the multiple conductive apertures 222 corresponds to a positional relationship between the multiple conductive projections 232.

[0060] In various embodiments, the conductive projections 232 are similarly shaped. In various embodiments, each of the conductive projections 232 may be shaped in a frustoconical form. In other embodiments, the conductive projections 232 may be shaped in a conical form. In yet other embodiments, the conductive projections 232 may be shaped in a cylindrical form. It may be appreciated that the shape / form of the conductive projections listed above are non- exhaustive.

[0061] Referring to FIGs. 6A and 6B, in various embodiments, the plurality of conductive projections 232 may be disposed with a first rotational symmetry about the centre axis 205. It may be appreciated that the plurality of openings 212 and the plurality of conductive apertures 222 may also be disposed in a similar configuration, i.e. in rotational symmetry about the centre axis 205.

[0062] In some embodiments, the first electrode 220 may include a first conductive surface 220a abutting the first surface 210a of the insulating member 210. Similarly, the second electrode 230 may include a second conductive surface 230a abutting the second surface 210b of the insulating member 210. In some embodiments, each of the insulating member 210, the first electrode 220, and the second electrode 230 may be a plate member or a generally planar member.[0063 J The insulating member 210 may define two alignment slots 219. In addition, the first electrode 220 may include a first aligning portion 228, and the second electrode 230 may include a second aligning portion 238. Each of the first aligning portion 228 and the second aligning portion 238 may be received in a corresponding alignment slot 219 to align the first electrode 220 and the second electrode 230 with the insulating member 210. Using the complementing alignment slots 219 and aligning portions 228 / 238, alignment of the multiple openings 212, conductive apertures 222 and conductive projections 232 may be achieved concurrently.

[0064] In various embodiments, each of the first aligning portion 228 and the second aligning portion 238 may be electrically conductive. The first aligning portion 228 may be in electric connection with the conductive apertures 222. The second aligning portion 238 may be in electric connection with the conductive projections 232. Therefore, the first aligning portion 228 and the second aligning portion 238 may act as electrical connection portions / points with the circuit 80.

[0065] In various embodiments, the first electrode 220 and the second electrode 230 may each include an insulating core / base coated with a conductive material, such as a coated copper layer. In an example, a thickness of the coated copper layer may be around 40 micrometres.

[0066] Referring to FIGs. 7A and 7B, in some embodiments, the first electrode 220 may be in abutment with the first surface 210a to form a fluid seal, such that each of the plurality of conductive apertures 222 and respective ones of the plurality of openings 212 collectively form a plurality of fluid conduits 204. In other words, one conductive aperture 222 and one opening 212 collectively form a respective fluid conduit 204.

[0067] In some embodiments, each of the plurality of fluid conduits 204 defines a respective flow direction 207. Each of the flow directions 207 may be parallel to the centre axis 205. In some embodiments, each opening 212 may be concentrically aligned or substantially alignedwith high concentricity with the respective conductive aperture 222 along the flow direction. Further, each of the plurality of conductive projections 232 may protrude towards a corresponding one of the plurality of fluid conduits 204 along the respective flow direction 207. In other words, each of the conductive projections 232 may be disposed aligned with a respective conductive aperture 222 along a respective flow direction 207. In some embodiments, each conductive projection 232 may be concentrically aligned or substantially aligned with high concentricity with the respective conductive aperture 222.

[0068] In various embodiments, each of the conductive projections 232 may comprise a tip 233. Each of the tips 233 may be aligned with a centre of a corresponding conductive aperture 222 along the respective flow direction 207. Referring to FIGs. 8A and 8B, in some embodiments, each of the tips 233 may form an electrode gap (G) with the corresponding conductive aperture 222 along the respective flow direction 207. According to an implementation, the electrode gap (G) is in a range from 0.5 millimetres (mm) to 1.0mm; the tip 233 has a diameter in a range from 0.3mm to 0.5mm; the corresponding conductive aperture 222 has a diameter in a range from 0.8mm to 1 ,2mm, and the corresponding opening 212 around 0.93mm.

[0069] In various embodiments, the second electrode 230 may further define a plurality of flow apertures 234. The flow apertures 234 may be formed neighbouring or adjacent to the conductive projections 232. The second electrode 230 may be in abutment with the second surface 210b to form a fluid seal, such that each of the flow apertures 234 may form a part of one corresponding fluid conduit 204. In some embodiments, each fluid conduit 204 may comprise one or more flow apertures 234 defined by the second electrode 230. Therefore, each fluid conduit 204 may be defined by one opening 212, one conductive aperture 222, and one or more flow apertures 234.

[0070] In some embodiments, each conductive projection 232 may be disposed adjacent to a set of multiple flow apertures 234. The set of multiple flow apertures 234 may be disposed with a second rotational symmetry about the conductive projection 232. In some embodiments, the set of multiple flow apertures 234 may be disposed rotationally symmetrical about the respective flow direction 207. Hence, in some embodiments, each fluid conduit 204 may comprise a set of multiple flow apertures 234 in fluid communication with one opening 212 and one conductive aperture 222. The one opening 212 and the one conductive aperture 222 may be in axial alignment along the respective flow direction 207.

[0071] The fluid conduits 204 allow fluid communication between a first side 200a of the micro-actuator unit 200 to a second side 200b of the micro-actuator unit 200. The first side 200a may correspond to one sub-chamber 1 13a, and the second side 200b may correspond to another sub-chamber 113b of the micro-actuator 100. The fluid conduits 204 form parallel flow paths enabling the dielectric liquid to flow from one sub-chamber 113a (the first side 200a) to another sub-chamber 113b (the second side 200b).

[0072] Referring to FIGs. 8A and 8B, in various embodiments, each fluid conduit 204 comprises a conductive inner wall portion (which corresponds to the conductive inner walls 224) and an insulating inner wall portion (which corresponds to the insulating inner wall 214). The conductive inner wall portion may be disposed adjacent to the insulating inner wall portion. The insulating inner wall portion provides an electrode gap (G) such that the electrical field lines (as shown in FIG. 8B) may be extended substantially along the flow direction 207 to provide a flow vector substantially along the flow direction 207.

[0073] Each of the plurality of openings 212 may define a varying diameter along the flow direction 207. For example, as shown in FIG. 8B, the plurality of openings 212 may include a narrowing step acting as a concentrator of liquid flow, to increase or concentrate the flow ofdielectric liquid through the fluid conduit 204. In other examples, the plurality of openings 212 may be gradually or linearly narrowed along the How direction 207.

[0074] FIGs. 8A and 8B illustrate an operation of a micro-actuator unit 200 according to various embodiments. Referring again to FIG. 2, the circuit 80 may be in signal communication or electrical connection with each of the micro -actuator units 200. The circuit 80 may be configured to apply a potential difference or voltage across the first electrode 220 and the second electrode 230 of each micro-actuator unit 200.

[0075] In an implementation illustrated in FIGs. 8A and 8B, the first electrode 220 may be positively charged and the second electrode 230 may be negatively charged. In some embodiments, for other dielectric liquids in which positive ions may be formed, the first electrode 220 may instead be negatively charged and the second electrode 230 may be positively charged.

[0076] During operation, responsive to a voltage applied across the first electrode 220 and the second electrode 230, a potential difference is formed between each conductive projection 232 and the corresponding conductive aperture 222. The potential difference between each pair of conductive projection 232 and conductive aperture 222 electrohydrodynamically pushes the dielectric liquid adjacent to the respective conductive projection 232 along the respective flow direction 207 through the corresponding fluid conduit 204. As an example, dielectric liquid adjacent to the tip 233 of the conductive projection 232 may be pushed through the fluid conduit to exit the conductive aperture 222.

[0077] Referring to FIG. 7B, in various embodiments, with the provision of the flow apertures 234 on the second electrode 230, dielectric liquid from the first side 200a of the microactuator unit 200, may be electrohydrodynamically pushed through the fluid conduits 204 towards the second side 200b of the micro-actuator unit 200 via a liquid movement 66.Therefore, a liquid pressure is formed by the micro-actuator unit 200 responsive to the potential difference.

[0078] With multiple micro-actuator units 200 arranged in series as shown in FIG. 2, responsive to a potential different applied to each of the first plurality of micro-actuator units 201, the dielectric liquid may be pushed from a sub-chamber into an adjacent sub-chamber along the first common direction 61 . This enables pressure to build up over the multiple microactuator units 200 arranged in series between the first port 114 of the housing to the second port 116 of the housing, flowing the dielectric liquid from the reservoir 60 towards the gripper 70.

[0079] Similarly, responsive to a potential different applied to each of the second plurality of micro-actuator units 202, the dielectric liquid may be pushed from a sub-chamber into an adjacent sub-chamber along the second common direction 62. This enables pressure to build up over the multiple micro-actuator units 200 arranged in series between the second port 116 of the housing to the first port 114 of the housing, flowing the dielectric liquid from the gripper 70 towards the reservoir 60.

[0080] In various embodiments, in prevention of forming a penetrating current between the first electrode and the second electrode, the potential difference is limited at a maximum voltage. This is in contradiction to common understanding, in which a higher potential difference is related to a higher output liquid pressure. In an exemplary setup, the dielectric liquid used may be linalyl acetate, the maximum voltage may be 15 kV, the potential difference applied may be in a range of 10 to 14 kV, and the operating temperature of the dielectric liquid may be in a range of -85 to 194 degree Celsius.

[0081] In various embodiments, the first rotational symmetry of the conductive projections 232 (and conductive apertures 222) about the centre axis 205 may aid in the uniformity of electric field formed by the conductive projections 232 and the conductive apertures 222. This beneficially improves the flow of the dielectric liquid through each of the fluid conduits 204.FIGs. 9A to 9F illustrate various non-exhaustive examples of corresponding pairs of conductive projections 232 and the conductive apertures 222 which are rotationally symmetrical about the centre axis 205.

[0082] According to various embodiments, the second rotational symmetry of multiple flow apertures 234 about the corresponding conductive projection 232, may aid in the flow symmetry of dielectric liquid from the sub-chamber into the micro-actuator unit 200. FIGs. 10A to 10C illustrate various non-exhaustive examples of the set of multiple flow apertures 234 rotationally symmetrical about the conductive projections 232.

[0083] Exemplary Implementation

[0084] The following section discloses various aspects of an exemplary 3D printable soft micro-actuator or micro-pump with multiple (for example, eight) serially connected microactuator units. The exemplary micro-actuator is in fluid communication with a 3D printed soft gripper to form a working gripper system. A soft polyurethane -based ink was used for 3D printing each component of the micro-actuator. All components of the micro-actuator arc 3D printed by a digital light processing (DLP) 3D printer with the polyurethane-based ink. The micro-actuator units exhibit good output pressure (maximum 6 kPa) and repeatability between various samples are good, owing to the effective control and optimization of geometry parameters. Eight units are serially connected and sealed together to form a powerful microactuator that achieves high output pressure (approx, maximum 45 kPa) as well as consistent performance across different micro-actuator samples. During an experiment, a three-finger FEA gripper with this micro-actuator was able to grip object of 500 grams.

[0085] 1.0 Fabrication

[0086] 1.1 Fabrication of the micro-actuator unit

[0087] a. The three components of the micro-actuator unit are the insulating member or concentrator (thickness: 1.7mm); the first electrode or hole electrode (diameter: 1mm); and thesecond electrode or needle electrode (diameter: 0.2mm). Autodesk Fusion 360 was used to create the 3D model of the individual parts. The 3D model was then cut into slices using the slicing program HALOT BOX, with the slicing thickness set to 30 pm. Thereafter, the sliced 3D model was input into the 3D printer. To ensure strong adhesion between the work plate and the printed product, the first layer's exposing time was set to 17 seconds, and the subsequent layer's exposing time was set to 5seconds.

[0088] b. A thin layer of copper (or any metal with good electrical conductivity) was coated on the surface of the needle electrode and hole electrode, with the needle electrode and hole electrode adhered to the thermal evaporator plate. The copper layer on the respective electrodes is around 2.5 m thick to ensure good conductivity.

[0089] c. The needle electrode and hole electrode were arranged on opposing sides of the concentrator through the opening or positioning hole. UV glue was applied to the gaps between the electrodes and the concentrator and followed by five seconds of UV curing to ensure the stability of the structure.

[0090] 1.2 Fabrication the micro-actuator

[0091] a. The shell of the micro- actuator, which was printed with the same material of the micro-actuator units, was designed with two parts: the bottom and the top part. The printing parameters of the shell were the same as for the pump units.

[0092] b. To ensure that the liquid flowed in the same direction, the pump units were installed into the bottom shell aligned in a single common direction. Following that, the top shell was glued together with the bottom shell. Following the steps, the shell was wrapped around the pump units, allowing only a portion of the electrodes to penetrate on the left and right side of the micro-actuator. A copper wire was connected the electrodes' penetrated parts on the same side. Finally, UV glue was used to seal the gaps between the shell and the penetrated electrodes.

[0093] 1.3 The arrangement of gripper system

[0094] a. The micro-actuator was connected to two 3D-printed transparent chambers. One chamber was connected to an inlet of the micro-actuator and used as a liquid reservoir, while the other chamber was connected with an outlet and used as a pressure converter which transfers the liquid pressure to ah' pressure. The converter's exit was next joined to a three-finger FEA gripper. Finally, 20 grams of dielectric liquid (in this implementation, linalyl acetate) was injected into the micro-actuator via the reservoir.

[0095] b. The needle electrodes were connected to the negative electrode, and the hole electrodes were connected to the positive electrode of a circuit, such as a high-voltage DC power source.

[0096] 2.0 Characterization of micro-actuator

[0097] FIGs. 11A to 1 IF illustrate the sample that after 3D printing, copper coating, and assembly with the insulating member or concentrator. As shown in FIGs. 11A and 11B, the needle electrode and the hole electrode printed by the DLP 3D printer each include sharp edges indicating high printing accuracy and resolution. FIGs. 11C and 11D illustrate the 3D printed electrodes coated with a thin layer of copper. Prior to coating with the layer of copper, the respective electrodes retain good flexibility as the copper layer is only 2.5pm thick. FIG. 11E shows the printed concentrator that limits the liquid flow and serves as a framework for the needle electrode and hole electrode.

[0098] FIG. 12 A shows the output pressure of a single micro-actuator unit with the concentrator (square data points) and without the concentrator (round data points). As shown in FIG. 12 it is evident that the insulating member or concentrator increases the output pressure by about 30% at 10 kV of potential difference. For a single micro-actuator unit with concentrator, the maximum output pressure is approximately 5 kPa.

[0099] 3.0 Characterizations of micro-actuator with different number of micro-actuator units serially connected

[0100] As shown in FIGs. 13A to 13C, various numbers of micro-actuator units were connected in series, and the output pressure was measured. Referring to FIG. 13A, two microactuator units are serially connected and tested to demonstrate the concept that improved output pressure can be achieved by serially connecting micro-actuator units. FIG. 13A includes a photograph of a micro-pump with two micro-actuator units and the output pressure results under various voltage applications. The maximum output pressure of 12 kPa was achieved, which was two times higher than the maximum output pressure of 5kPA of a single micro-actuator unit. This indicated that with increasing number of serially connected micro -actuator units, an output pressure from the micro-actuator may be increased.

[0101] Further, as shown in FIGs. 13B and 13C, micro-actuator with respective four and eight micro -actuator units serially connected were fabricated and tested, the maximum output pressure of the micro-actuator with four serially connected micro-actuator units serially was 25 kPa, while the output pressure increased to 45 kPa for the micro-actuator with eight serially connected micro-actuator units. Accordingly, the maximum output pressure may be linearly related or substantially linearly related to the number of micro-actuator units.

[0102] 4.0 Characterizations of micro-actuator actuated gripper system

[0103] As shown in FIG. 14, a micro-actuator with eight micro-actuator units serially connected was used to provide a fluid pressure to a FEA-based gripper. As a first step, the micro-actuator was used to transfer the dielectric liquid from the liquid reservoir to the pressure converter. Thereafter, the dielectric liquid was deposited in or held by the pressure converter, moving the air out of the pressure converter via a top outlet. As the dielectric liquid has a higher density than air, this process allows the liquid pressure to be transformed to air pressure at the pressure converter. The FEA-based gripper connected to the exit of the pressure converter wasactuated by the air pressure from the pressure converter. FIG. 15A shows the bending angle and force of a single gripper finger. FIG. 15B shows the bending angle and bending force of the gripper finger. It may be seen that the gripper finger has a bending angle larger than 170 degrees, with a bending force of 0.9 N which is sufficient to grip many related heavy objects. FIG. 15C demonstrates the gripper powered by a micro-actuator with eight serially connected microactuator, successfully lifting and lowering an orange (digrams in weight).

[0104] According to another aspect of the present disclosure, FIG. 16 shows a method 700 of manufacturing a micro-actuator unit according to various embodiments. The method 700 comprises: in 710, providing an insulating member having a first surface and a second surface opposing the first surface, the first surface and the second surface defining a centre axis, the insulating member defining a plurality of openings; in 720, coupling a first electrode to the first surface, the first electrode having a plurality of conductive apertures, the plurality of conductive apertures and the plurality of openings forming a plurality of fluid conduits, each of the plurality of fluid conduits defining a respective flow direction parallel to the centre axis; and in 730, coupling a second electrode to the second surface of the insulating member, the second electrode having a plurality of conductive projections, each of the plurality of conductive projections protruding towards a corresponding one of the plurality of fluid conduits along the respective flow direction, wherein the plurality of conductive projections are disposed with a first rotational symmetry about the centre axis.

[0105] In various embodiments, the method further comprises: additively forming the insulating member with an insulating material. In various embodiments, the method further comprises: additively forming a first substate; and coating the first substrate with a first metallic coat to form the first electrode. In various embodiments, the method further comprises: additively forming a second substate; and coating the second substrate with a second metallic coat to form the second electrode. In various embodiments, the method further comprises:forming a first recess in the first surface of the insulating member to receive the first electrode; and forming a second recess in the second surface of the insulating member to receive the second electrode. In various embodiments, the method further comprises: press fitting the first electrode with the first recess; and press fitting the second electrode with the second recess.

[0106] All examples described herein, whether of methods, materials, or products, are presented for the purpose of illustration and to aid understanding and are not intended to be limiting or exhaustive. Modifications may be made by one of ordinary skill in the art without departing from the scope of the invention as claimed.

Claims

CLAIMS1. A micro-actuator unit, comprising: an insulating member having a first surface and a second surface opposing the first surface, the first surface and the second surface defining a centre axis, the insulating member defining a plurality of openings; a first electrode coupled to the first surface, the first electrode having a plurality of conductive apertures, the plurality of conductive apertures and the plurality of openings forming a plurality of fluid conduits, each of the plurality of fluid conduits defining a respective flow direction parallel to the centre axis; and a second electrode coupled to the second surface of the insulating member, the second electrode having a plurality of conductive projections, each of the plurality of conductive projections protruding towards a corresponding one of the plurality of fluid conduits along the respective flow direction, wherein the plurality of conductive projections are disposed with a first rotational symmetry about the centre axis.

2. The micro-actuator unit as recited in claim 1, wherein each of the plurality of fluid conduits comprises a plurality of flow apertures defined by the second electrode.

3. The micro-actuator unit as recited in claim 2, wherein multiples of the plurality of flow apertures are disposed with a second rotational symmetry about each of the plurality of conductive projections.

4. The micro-actuator unit as recited in any one of claims 1 to 3, wherein each of the plurality of fluid conduits comprises a first plurality of flow apertures in fluid communication with one of the plurality of openings and one of the plurality of conductive apertures, the one of the plurality of openings and the one of the plurality of conductive apertures being in axial alignment along the respective flow direction.

5. The micro-actuator unit as recited in any one of claims 1 to 4, wherein each of the plurality of conductive projections comprises a tip, the tip being aligned with a centre of a corresponding one of the plurality of conductive apertures along the respective flow direction.

6. The micro-actuator unit as recited in claim 5, wherein each of the tip forms an electrode gap with the corresponding one of the plurality of conductive apertures along the respective flow direction.

7. The micro-actuator unit as recited in claim 6, wherein the electrode gap is in a range from 0.5mm to 1.0mm, and wherein the tip has a diameter in a range from 0.3mm to 0.5mm, and wherein the corresponding one of the plurality of conductive apertures has a diameter in a range from 0.8mm to 1.2mm.

8. The micro-actuator unit as recited in any one of claims 1 to 7, wherein the first electrode further comprises a first conductive surface abutting the first surface of the insulating member, and the second electrode further comprises a second conductive surface abutting the second surface of the insulating member.

9. The micro-actuator unit as recited in any one of claims 1 to 8, wherein each of the plurality of fluid conduits comprises a conductive inner wall portion and an insulating inner wall portion, the conductive inner wall portion disposed adjacent to the insulating inner wall portion.

10. The micro-actuator unit as recited in any one of claims 1 to 9, wherein each of the plurality of openings defines a varying diameter along the flow direction.

11. The micro-actuator unit as recited in any one of claims 1 to 10, the insulating member defining two alignment slots, wherein the first electrode further comprises a first aligning portion, and wherein the second electrode further comprises a second aligning portion, each of the first aligning portion and the second aligning portion being received in a corresponding one of the two alignment slots.

12. The micro-actuator unit as recited in claim 11, wherein the first aligning portion and the second aligning portion are electrically conductive.

13. The micro-actuator unit as recited in any one of claims 1 to 12, wherein each of the first electrode, the second electrode, and the insulating member is a plate member.

14. The micro-actuator unit as recited in any one of claims 1 to 13, wherein responsive to a potential difference applied between the first electrode and the second electrode, a dielectric liquid adjacent to the plurality of conductive projections is electrohydrodynamically pushed along the respective flow direction through the corresponding one of the plurality of fluid conduits.

15. The micro-actuator unit as recited in claim 14, wherein the potential difference is limited at a maximum voltage, wherein an applied potential difference above the maximum voltage forms a penetrating current between the first electrode and the second electrode.

16. The micro-actuator unit as recited in any one of claims 14 to 15, wherein the potential difference is in a range of 10 to 14 kV, and the maximum voltage is 15 kV.

17. A micro-actuator comprising: a housing defining a chamber extending along an actuator axis; and a first plurality of the micro-actuator unit as recited in any one of claims 1 to 15, the first plurality of the micro -actuator unit being disposed in the chamber, the first plurality of the micro-actuator unit being spaced apart from one another along the actuator axis to define a plurality of first sub-chambers in the housing, wherein the respective flow directions of the first plurality of the micro-actuator unit are aligned in a first common direction parallel to the actuator axis.

18. The micro-actuator as recited in claim 17, further comprising: a second plurality of the micro-actuator unit as recited in any one of claims 1 to 15, the second plurality of the micro-actuator unit being disposed in the chamber, the second plurality of the micro-actuator unit being spaced apart from one another along the actuator axis to define a plurality of second sub-chambers in the housing, wherein the respective flow directions of the second plurality of the micro-actuator unit are aligned in a second common direction parallel to the actuator axis, the second common direction being opposite to the first common direction.

19. A gripper system comprising: a reservoir, the reservoir containing a dielectric liquid; a gripper, the gripper being configured to be pneumatically actuated by the dielectric liquid; the micro-actuator as recited in any one of claims 17 to 18, wherein the microactuator is in fluid communication between the gripper and the reservoir; and a circuit, the circuit being configured to apply a potential difference across the first electrode and the second electrode, wherein, responsive to the potential difference applied across the first electrode and the second electrode, the micro-actuator electrohydrodynamically pushes the dielectric liquid towards the gripper at a liquid pressure.

20. The gripper system as recited in claim 19, further comprising a pressure converter in fluid communication between the gripper and the micro-actuator, wherein the pressure converter is configured to convert the liquid pressure to a pneumatic pressure acting on the pneumatic-actuated gripper.

21. A method of manufacturing a micro-actuator unit, the method comprising: providing an insulating member having a first surface and a second surface opposing the first surface, the first surface and the second surface defining a centre axis, the insulating member defining a plurality of openings; coupling a first electrode to the first surface, the first electrode having a plurality of conductive apertures, the plurality of conductive apertures and the plurality ofopenings forming a plurality of fluid conduits, each of the plurality of fluid conduits defining a respective flow direction parallel to the centre axis; and coupling a second electrode to the second surface of the insulating member, the second electrode having a plurality of conductive projections, each of the plurality of conductive projections protruding towards a corresponding one of the plurality of fluid conduits along the respective flow direction, wherein the plurality of conductive projections are disposed with a first rotational symmetry about the centre axis. , The method as recited in claim 21, further comprising: additively forming the insulating member with an insulating material. , The method as recited in any one of claims 21 to 22, further comprising: additively forming a first substatc; and coating the first substrate with a first metallic coat to form the first electrode. , The method as recited in any one of claims 21 to 23, further comprising: additively forming a second substate; and coating the second substrate with a second metallic coat to form the second electrode. , The method as recited in any one of claims 21 to 24, further comprising forming a first recess in the first surface of the insulating member to receive the first electrode; and forming a second recess in the second surface of the insulating member to receive the second electrode.

26. The method as recited in claim 25, further comprising press fitting the first electrode with the first recess; and press fitting the second electrode with the second recess.

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