Patent Description:
Fluidic artificial muscles are utilized in aerospace, robotic and minimally invasive surgery applications for their relatively large stroke and high actuation force at low weight. Traditionally, fluidic artificial muscles have been designed with an inflatable bladder operably coupled to end fittings at opposite ends of the bladder. The bladder expands when inflated causing the muscle to radially expand and axially contract. Such fluidic artificial muscles are referred to as contractile. Different types of fluidic artificial muscles have been developed over time. These can be classified based on their operation (pneumatic or hydraulic, both types are referred to herein as fluidic), on the type of bladder used (stretching membrane or rearranging membrane) and on the presence or absence of a sleeve enveloping the bladder (braided sleeve, netted sleeve or reinforcement embedded in the bladder membrane). One common type of fluidic artificial muscle is referred to as McKibben muscle and comprises a stretching membrane-type bladder enveloped with a braided sleeve. Both the bladder and the sleeve are connected to the end fittings. A comprehensive overview of contractile fluidic artificial muscles can be found in <NPL>.

These fluidic artificial muscles are contractile devices and consequently can generate motion in one direction only. To generate bidirectional motion, two actuators need to be coupled in a so-called antagonistic setup, where they are connected in opposition to a load.

<CIT> discloses an actuation system including a first pneumatic muscle connected in series to a second pneumatic muscle and a valve connected to the pneumatic muscles to control a pressure in the pneumatic muscles. The system also includes a positioning mechanism to control a movement of a component to be actuated by the actuation system and a controller connected to the pneumatic muscles, the valve, and the positioning mechanism, the controller to control actuation of the component by controlling the pressure in the pneumatic muscles. The first pneumatic muscle can be in a contracted state when the second pneumatic muscle is in an extended state, and the first pneumatic muscle can transition to an extended state when the second pneumatic muscle transitions to a contracted state. The controller can be configured to control the valve to control the pressure in the first pneumatic muscle and a pressure in the second pneumatic muscle. To actuate the component in a first direction, the controller performs operations including controlling the valve to apply an increasing pressure in the first pneumatic muscle and controlling the valve to apply a decreasing pressure in the second pneumatic muscle while applying the increasing pressure in the first pneumatic muscle. To actuate the component in a second direction opposite the first direction, the controller performs operations including controlling the valve to apply a decreasing pressure in the first pneumatic muscle and controlling the valve to apply a increasing pressure in the second pneumatic muscle while applying the decreasing pressure in the first pneumatic muscle. The first and the second pneumatic muscles are hence both contractile and arranged in an antagonistic setup. Even though such an antagonistic setup allows to actuate a motion in two opposite directions, the positioning control is still difficult to realize. Indeed, while pressure must be increased in one of the two pneumatic muscles, pressure must be decreased in the other pneumatic muscle to allow advancement and the equilibrium position of the driven component is determined by the ratio of the gauge pressures in both pneumatic muscles. Hence, a separate control of the gauge pressures in the two pneumatic muscles is required.

On the other hand, extensile fluidic artificial muscles are known from <NPL>. An extensile fluidic artificial muscle can be formed based on McKibben muscles, one common variety of fluidic artificial muscles. McKibben muscles typically consist of a braided mesh of inextensible fibers enclosing an elastic bladder which is held in place by attachment points at both ends. The bladder expands when pressurized causing the muscle to either contract or extend, depending on the angle of the braid that is used in the muscle's construction. It was reported that, when measured parallel to the longitudinal axis of the McKibben muscle, a muscle with braid angle below <NUM>° will contract, while a muscle with a higher braid angle will extend when pressurized. Extensile fluidic artificial muscles produce a larger stroke compared to contractile fluidic artificial muscles, but much lower forces.

There is a need in the art to provide bidirectional fluidic artificial muscle actuators allowing both a high stroke and a high applied force. There is a need to provide such actuators where the radial expansion of the muscle is limited. There is a need to provide bidirectional fluidic artificial muscle actuators allowing improved bidirectional positioning control. There is a need to provide bidirectional fluidic artificial muscle actuators having simpler construction and/or allowing a simpler motion control.

According to a first aspect of the present disclosure, there is therefore provided a fluidic artificial muscle actuator as set out in the appended claims. A fluidic artificial muscle actuator comprises at least one inflatable bladder defining a first inflatable segment and a second inflatable segment. The first inflatable segment is coupled to a first member and to a second member arranged at opposite ends of the first inflatable segment. The second inflatable segment is coupled to a third member and to a fourth member arranged at opposite ends of the second inflatable segment. An effector provides an output of the actuator, the effector being operably coupled to the first inflatable segment and to the second inflatable segment. The first member and the second member define a first longitudinal direction, which can be straight (linear) or curved. The third member and the fourth member define a second longitudinal direction, which can be straight (linear) or curved. In some examples, one inflatable bladder can extend continuously along the first and the second inflatable segments. In other examples, the first and the second inflatable segments are defined by a first and a second inflatable bladder, respectively. The first inflatable segment is configured to contract in the first longitudinal direction with increase in fluid pressure in the first inflatable segment and the second inflatable segment is configured to extend in the second longitudinal direction with increase in fluid pressure in the second inflatable segment.

The fluidic artificial muscle actuator as set forth in the present disclosure hence combines a contractile and an extensile artificial muscle, such that both apply force on the load in a same direction, resulting in a higher force to be transmitted and/or larger stroke compared to prior art fluidic artificial muscles. Furthermore, to operate fluidic artificial muscle actuators of the present disclosure, pressure is increased or decreased in both the first and second inflatable segments, which greatly simplifies the fluid supply system, resulting in lower cost and smaller footprint. Fluidic pneumatic actuators as set forth in the present disclosure advantageously enable miniaturization, which is key for utilizing these actuators in endoscopes with limited cross sectional area.

Advantageously, the first and the second inflatable segments are in fluid communication with one another. A fluid supply system is configured to inflate/pressurize the at least one inflatable bladder in one of the first and second inflatable segments, and fluid is supplied from the one of the first and the second inflatable segments to the other one for inflating/pressurizing. By so doing, a single fluid supply system can be utilized, further simplifying construction and reducing cost and dimensions, enabling further miniaturization.

According to a second aspect of the present disclosure, there is provided a device, such as a minimally invasive surgical device, e.g. a catheter or endoscope, or a robot, comprising the fluidic artificial muscle actuator as described herein. Multiple fluidic artificial muscle actuators of the present disclosure can be integrated to the device for actuating robotic motion.

Aspects of the present disclosure will now be described in more detail with reference to the appended drawings, wherein same reference numerals illustrate same features and wherein:.

Referring to <FIG>, an artificial muscle actuator <NUM> according to the present disclosure comprises a first inflatable bladder <NUM> and a second inflatable bladder <NUM>. Either one, or both the first bladder <NUM> and the second bladder <NUM> can be formed of: a membrane which expands upon increasing pressure in the bladder, a membrane having faces that rearrange upon increasing pressure in the bladder, a combination of both, or any other inflatable bladder suitable for use in fluidic artificial muscles. First inflatable bladder <NUM> is attached or at least operably coupled to end fittings <NUM> and <NUM> arranged at opposite ends of the first bladder <NUM>. First inflatable bladder can be, though does not need to be, of elongate shape with longitudinal axis <NUM> defined by the end fittings <NUM>, <NUM>. Second inflatable bladder <NUM> is attached or at least operably coupled to end fittings <NUM> and <NUM> arranged at opposite ends of the second bladder <NUM>. Second inflatable bladder can be, though does not need to be, of elongate shape with longitudinal axis <NUM> defined by the end fittings <NUM> and <NUM>. Longitudinal axes <NUM> and <NUM> can be parallel and possibly collinear, even though this is not strictly required. Longitudinal axes <NUM> and <NUM> can e.g. be curved. In the example of <FIG>, the longitudinal axes <NUM> and <NUM> are collinear and the first and second inflatable bladders <NUM>, <NUM> are arranged side by side at opposite ends of effector <NUM>.

End fittings <NUM> and <NUM> are advantageously fixedly positioned relative to each other, e.g. they can be fixed to a support <NUM>, such as a casing. The end fittings <NUM> and <NUM> are fixed to each other and both can be fixed to the effector <NUM> at opposite sides thereof. End fittings <NUM>, <NUM> hence act as one integral member to move the effector <NUM>. Effector <NUM> in this case is configured for linear motion along longitudinal axis <NUM>/<NUM>. The effector <NUM> advantageously comprises coupling means <NUM> for transmitting force and/or motion to a load, which can be any structure that needs to be actuated.

The setup as in <FIG> resembles an antagonistic setup of two contractile fluidic artificial muscles. However, one important aspect of the present disclosure is that, while the first inflatable bladder <NUM> is configured for functioning as a contractile fluidic artificial muscle, the second inflatable bladder <NUM> is configured for functioning as an extensile fluidic artificial muscle. Therefore, while in a conventional antagonistic setup an increase in pressure in one bladder must correspond to a decrease in pressure in the other bladder in order to move the effector in either direction, in the present actuator <NUM>, the effector can be actuated by either increasing or decreasing the pressure in both the first bladder <NUM> and the second bladder <NUM>.

Compared to an antagonistic setup of two contractile fluidic artificial muscles, in which one muscle actuates the load while the other one acts as a brake to stop the load, the contractile and extensile muscles of the fluidic artificial muscle actuator of the present disclosure can both apply force on the load in a same direction, resulting in a higher force to be transmitted and/or larger stroke.

Any means allowing the first inflatable bladder <NUM> to be configured as contractile, i.e. the bladder <NUM> is configured to decrease the distance between fittings <NUM> and <NUM> upon increase in pressure in the bladder <NUM>, can be provided. By way of example, the first bladder is enveloped in a braided sleeve <NUM> attached to the fittings <NUM> and <NUM>. The braided sleeve <NUM> can allow a radial expansion of the first bladder <NUM> along with an axial contraction of the bladder <NUM> when the pressure in the bladder <NUM> is increased. This setup is known as a McKibben contractile artificial muscle. It is however not required that the bladder <NUM> itself be directly attached to the fittings <NUM> and <NUM>, since the braided sleeve <NUM> can provide for force engagement with fittings <NUM> and <NUM>. Any other type of contractile fluidic artificial muscle can be used in the alternative. The first bladder <NUM> and the second bladder <NUM> are advantageously configured for functioning under pressure higher than atmospheric pressure.

Any means allowing the second inflatable bladder <NUM> to be configured as extensile, i.e. the bladder <NUM> is configured to increase the distance between fittings <NUM> and <NUM> upon increase in pressure in the bladder <NUM>, can be provided. By way of example, the second bladder <NUM> is enveloped in a braided sleeve <NUM> attached to fittings <NUM> and <NUM>. The braided sleeve <NUM> can allow a radial contraction of the second bladder <NUM> along with an axial extension of the bladder <NUM> when the pressure in the bladder <NUM> is increased. In other examples, the second bladder <NUM> is formed by a plurality of bellows attached to one another along the longitudinal axis <NUM> and fluidly communicating with one another. The bellows each have a middle segment and connecting segments at either side of the middle segment along the longitudinal axis. Connecting segments of consecutive bellows are attached to one another. The middle segment has larger cross-sectional area than the cross-sectional area of the connecting segments. When pressure inside the plurality of bellows is increased, the connecting segments radially expand, resulting in an axial extension of the second bladder.

Referring to <FIG>, for a braided sleeve <NUM> to be contractile, it was reported that the angle θ0c of the threads of the braid, measured relative to the longitudinal axis <NUM>, must be smaller than about <NUM>°, particularly smaller than about <NUM>°, in particular smaller than <NUM>°, in a rest position (i.e. not inflated state of the bladder and no force applied to the braid), e.g. zero differential pressure P in the bladder with respect to atmospheric pressure (<FIG>). When the bladder is inflated and the differential pressure P inside the bladder increases, the braided sleeve <NUM> will extend radially and contract axially (<FIG>). In this case the threads of the braid rearrange to an angle θ larger than θ0c.

Referring to <FIG>, for a braided sleeve <NUM> to be extensile, it was reported that the angle θ0e of the threads of the braid, measured relative to the longitudinal axis <NUM>, must be larger than about <NUM>°, particularly larger than about <NUM>°, in particular larger than <NUM>°, in a rest position (i.e. not inflated state of the bladder and no force applied to the braid), e.g. zero differential pressure P in the bladder with respect to atmospheric pressure (<FIG>). When the bladder is inflated and the differential pressure P inside the bladder increases, the braided sleeve <NUM> will contract radially and extend axially (<FIG>). In this case the threads of the braid rearrange to an angle θ smaller than θ0e.

The braid angle θ0c for contractile braid <NUM> and the braid angle θ0e for extensile braid <NUM> can be selected independently of one another, allowing for greater freedom in designing a fluidic artificial muscle actuator having desired characteristics.

Alternative muscle configurations for the first and/or the second bladder can be, without limitation: a sleeved bladder muscle, a pleated pneumatic artificial muscle, a netted fluidic artificial muscle, a Yarlott artificial muscle, a ROMAC (Robotic Muscle Actuator), a Kukolj artificial muscle, a Morin artificial muscle, a Baldwin artificial muscle, a Paynter knitted artificial muscle, a Paynter hyperboloid artificial muscle, a bellows artificial muscle, an underpressure artificial muscle.

Referring again to <FIG>, the actuator <NUM> can comprise a control unit <NUM> and a fluid supply system <NUM> for inflating the first bladder <NUM> and the second bladder <NUM>. The fluid supply system <NUM> comprises a source of pressurized fluid, such as a fluid pump <NUM>. Alternatively, a reservoir of pressurized fluid can be provided (not shown). The fluid supply system can comprise a valve <NUM> fluidly connected to the source of pressurized fluid (fluid pump <NUM>). The valve <NUM> allows to control pressure in the first and/or the second bladder. The first bladder <NUM> comprises a first fluid port <NUM> and the second bladder comprises a second fluid port <NUM>. Valve <NUM> is in fluid communication with the first fluid port <NUM> through a fluid supply duct <NUM>. Alternatively, or in addition, fluid supply duct <NUM> can fluidly connect valve <NUM> to the second fluid supply port <NUM>.

In the context of the present disclosure the term fluid can refer to a gas, such as air, CO<NUM>, nitrogen, helium or any other suitable gas, or to a liquid, such as water, saline solutions, contrast agent or any other suitable liquid. Hence, in the context of the present disclosure, a fluidic artificial muscle actuator can refer to a pneumatic artificial muscle actuator or a hydraulic artificial muscle actuator.

The first and second bladders <NUM> and <NUM> can have substantially identical unpressurized diameters. Alternatively, the (unpressurized) diameter of the second, extensile bladder <NUM> can be larger than an (unpressurized) diameter of the first, contractile bladder <NUM>. This avoids that the diameter of the second bladder <NUM> shrinks under pressurization to a too small value which can lead to stability problems. Additionally or alternatively the second bladder <NUM> can be made with a smaller wall thickness compared to the wall thickness of the first bladder <NUM>, e.g. such that the unpressurized internal diameter of the second bladder is larger than the internal diameter of the first bladder. Alternatively, the first bladder <NUM> and the second bladder <NUM> can be made with a same wall thickness.

Advantageously, the actuator <NUM> comprises a single fluid supply system <NUM> configured to supply fluid to both the first bladder <NUM> and to the second bladder <NUM> through the first and the second fluid ports <NUM>, <NUM> respectively. Advantageously, a fluid communication channel <NUM> is provided between the first bladder <NUM> and the second bladder <NUM>. In the embodiment of <FIG>, the fluid supply system <NUM> is configured to inflate the first bladder <NUM> through the first fluid supply port <NUM>. The second bladder <NUM> is inflated by supplying fluid from the first bladder <NUM> through fluid communication channel <NUM> to the second fluid supply port <NUM>. Advantageously, in a steady state, the first and the second bladders have equal pressure. Advantageously, both the first and the second bladders are configured for being utilized with positive gauge pressure.

Referring to <FIG> showing an enlarged detail of the effector <NUM>, the first bladder <NUM> comprises a third fluid supply port <NUM>. The fluid communication channel <NUM> extends from the third fluid supply port <NUM> to the second fluid supply port <NUM>. Particularly, the second and the third fluid supply ports <NUM>, <NUM> are provided at respective opposite ends of the effector <NUM> and the fluid communication channel <NUM> can comprise a bore through the effector <NUM>, between the second and the third fluid supply ports <NUM>, <NUM> respectively.

A single fluid supply system allows to simplify construction of the actuator and rendering it less bulky, since less tubing and cabling is required. Actuators according to the present disclosure therefore allow improved miniaturization compared to prior art fluidic artificial muscle actuators.

The fluid communication channel <NUM> can comprise an orifice <NUM> such as a diaphragm or nozzle providing a constriction of the fluid communication channel, which allows to control a pressure equalization between a pressure in the first bladder <NUM> and a pressure in the second bladder <NUM>. This allows to obtain desired dynamics of the actuator <NUM>.

It is alternatively possible to provide individual fluid supply systems (not shown) for separately inflating the first and the second bladders. It will be convenient to note that the fluid communication channel <NUM> and optionally the orifice <NUM> can be provided even when individual fluid supply systems are provided. This may allow obtaining a faster dynamics of the actuator.

A linear motion guide (not shown) can further be connected to the support <NUM> and a respective slide connected to the effector <NUM> so as to constrain translation of effector <NUM> and/or avoid problems of buckling of the artificial muscles.

Referring to <FIG>, fluidic artificial muscle actuator <NUM> differs from the artificial muscle actuator <NUM> in that it comprises a tubular member <NUM> acting as a support instead of, or in addition to, support (casing) <NUM> of artificial muscle actuator <NUM> as shown in <FIG>. The contractile first bladder <NUM> is attached to end fitting <NUM> at one end and to effector <NUM> at the opposite end. The extensile second bladder <NUM> is attached to end fitting <NUM> at one end and to effector <NUM> at the opposite end. The effector <NUM> can comprise a fitting <NUM> for attachment of the first bladder <NUM> and/or the first braided sleeve <NUM> at one end, and a fitting <NUM> for attachment of the second bladder <NUM> and/or the second braided sleeve <NUM> at an opposite end (<FIG>). The fittings <NUM> and <NUM> are fixed to each other and to the effector <NUM>. The first and second bladders can be identical to the ones described in relation to <FIG>.

End fittings <NUM> and <NUM> are arranged on the outer periphery of a tubular member <NUM> and are advantageously fixedly attached thereto. Effector <NUM> is slidable along tubular member <NUM>. Effector <NUM> can e.g. comprise a through bore <NUM> and the tubular member <NUM> extends through the through bore <NUM>. As a result, the tubular member <NUM> extends centrally through the first and second bladders <NUM>, <NUM> (<FIG>).

The through bore <NUM> can be made somewhat larger than the outer diameter of tubular member <NUM>. By so doing, the fluid communication channel <NUM> between the first and second bladders can be easily provided. Alternatively, fluid communication channel <NUM> can be provided as a separate bore from through bore <NUM>. Tubular member <NUM> can have a circular cross section. It can be advantageous to utilize (outer and/or inner) cross sections different from circular, e.g. polygonal, for tubular member <NUM>, which may prevent rotation of the effector <NUM> about the longitudinal axis <NUM>.

One advantage of the artificial muscle actuator <NUM> is that, since the end fittings <NUM> and <NUM> are fixedly mounted to tubular member <NUM>, sealing of the first and second inflatable bladders <NUM>, <NUM> is made easy. Even if the first and second bladders would be provided with individual fluid supply systems, a possible leakage of fluid between the bladders via the sliding surface of effector <NUM> over the tubular member can be tolerated. Furthermore, this setup is particularly suitable for being utilized with a single fluid supply system, e.g. with a single fluid supply duct <NUM> as shown in <FIG> and <FIG>, for supplying both first and second bladders with fluid.

It is alternatively possible to utilize the tubular member <NUM> for transmitting forces generated by the actuator <NUM>. In this case, the effector <NUM> is rigidly fixed to tubular member <NUM>, while the end fittings <NUM> and <NUM> are slidable with respect to the tubular member <NUM>. By way of example, end fittings <NUM> and <NUM> can be fixed to a surrounding support structure <NUM> as shown in <FIG> for end fittings <NUM> and <NUM>.

Tubular member <NUM> defines a lumen <NUM> which is fluidly isolated from the fluid chambers formed by the first bladder <NUM> and the second bladder <NUM>. Lumen <NUM> can advantageously be used as a working channel, e.g. for passing instruments through the artificial muscle actuator <NUM>, and hence allows further miniaturization. This is particularly useful for minimally invasive surgical devices. Referring to <FIG>, the artificial muscle actuator <NUM> can be used as an actuator for driving a deflection system of a shaft <NUM> of a device, which may be a catheter or endoscope. The shaft can comprise a lumen communicating with the lumen <NUM> of tubular member <NUM>. By supplying fluid to the artificial muscle actuator <NUM>, the effector <NUM> is moved, and the motion transmitted to the deflection system of shaft <NUM> via coupling means <NUM> to change the state of the shaft <NUM> from non-deflected (<FIG>) to deflected (<FIG>).

It can be beneficial to make the (unpressurized) diameter of the second, extensile bladder <NUM> larger than an (unpressurized) diameter of the first, contractile bladder <NUM>. This prevents interaction between the second bladder and the tubular member as the second bladder shrinks radially during pressurization. Alternatively, or in addition, a same effect can be achieved by making the second bladder <NUM> with a smaller wall thickness compared to the wall thickness of the first bladder <NUM>, e.g. such that the unpressurized internal diameter of the second bladder is larger than the internal diameter of the first bladder. Alternatively or in addition, the second, extensile bladder can be made from a lubricious material to reduce possible friction between the inner side of the second bladder and the tubular member. Still alternatively, a lubricant may be provided on the outer surface of the tubular member and/or the inner surface of the second bladder. than the contractile bladder.

Alternatively, referring to <FIG>, the artificial muscle actuator can be embedded in a lumen <NUM> of the shaft <NUM>, possibly in proximity of a bending segment <NUM> of the shaft <NUM>. Bending segment <NUM> is made to have a flexible geometry and extends between a distal end <NUM> and a proximal end <NUM> which may be rigid. The shaft <NUM> comprises a bracket <NUM> operably coupled to bending segment <NUM>. By way of example, bracket <NUM> comprises a base in force transmitting engagement with the distal end <NUM> (or alternatively with proximal end <NUM>) and a free end <NUM>, to which the effector of the artificial muscle actuator (not shown in <FIG>) can be attached. The artificial muscle actuator, such as actuator <NUM> (<FIG>), is embedded in lumen <NUM> such that end fitting <NUM> is fixed to the distal end <NUM> and end fitting <NUM> is fixed to the proximal end <NUM> (or vice versa). Effector <NUM> is coupled to the free end <NUM> of the bracket <NUM>. In this configuration, under pressurization, the first bladder <NUM> would contract and the second bladder <NUM> would expand, causing the effector <NUM> to move bracket <NUM> towards distal end <NUM> and to bend the segment <NUM> in accordance with its geometry.

The lumen <NUM> can be configured to allow radial expansion of the contractile bladder, such as by providing cut out sections in correspondence of the first bladder, the second bladder, or both. Such a configuration allows to leverage expandability of the artificial muscle actuator especially in surgical applications, i.e. the actuator when unpressurized could be small enough to fit into lumen <NUM> and/or through shaft introduction portals or anatomical chokepoints, then when navigated to the (surgical) target space and pressurized, the actuator can expand beyond the original footprint. This allows use of a larger diameter muscle actuator providing increased force while maintaining low cross-sectional area while the device is being brought to target anatomy.

In the above configuration, it is alternatively possible to accommodate the artificial muscle actuator <NUM> (<FIG>) into lumen <NUM>. The tubular member <NUM> of artificial muscle actuator <NUM> can be flexible, allowing to accommodate the artificial muscle actuator <NUM> in the lumen <NUM> of the shaft <NUM> at a position corresponding to the bending segment <NUM>, while providing a through-channel between the proximal end <NUM> and the distal end <NUM>.

In some examples, the braided sleeves <NUM>, <NUM> enveloping the first and/or second bladders can be coated in a protective covering made of silicone or other appropriate material. This can prevent damage of the braided sleeve during movement and/or prevent the braided sleeve from damaging or interacting with the environment (e.g. body tissues) in such case.

Multiple muscle actuators <NUM>, <NUM> can be arranged in series in the shaft <NUM>, in a same section or in different sections of the shaft, allowing to actuate motion of the (section of the) shaft along multiple degrees of freedom, e.g. bending about two orthogonal axes of rotation.

Referring to <FIG>, another example of an artificial fluidic muscle actuator <NUM> according to the present disclosure comprises a single inflatable bladder <NUM>, instead of two bladders <NUM>, <NUM> as described previously. A first longitudinal portion <NUM> of bladder <NUM> is enveloped by a contractile braided sleeve <NUM> and a second longitudinal portion <NUM> of bladder <NUM> is enveloped by an extensile braided sleeve <NUM>. The first and second longitudinal portions <NUM> and <NUM> are juxtaposed and can span the entire length of bladder <NUM>. The contractile braided sleeve <NUM> is attached to end fittings <NUM> and <NUM>, and extensile braided sleeve is attached to end fittings <NUM> and <NUM>, with the end fittings <NUM> and <NUM> fixed to each other and to the effector <NUM>.

Effector <NUM> can comprise a through bore <NUM> with bladder <NUM> continuously extending through the through bore <NUM>. Possibly ring-like end fittings <NUM> and <NUM> are fixed at opposite ends of the effector <NUM>. In such a configuration, under pressurization, the contractile and extensile braided sleeves <NUM>, <NUM> respectively will impart differing deformation to the bladder <NUM> along the first and second longitudinal segments <NUM>, <NUM> respectively. Contractile braided sleeve <NUM> forces bladder <NUM> to expand radially while contracting longitudinally in segment <NUM>. Extensile braided sleeve forces bladder <NUM> to extend longitudinally while contracting radially in segment <NUM>. By so doing, a same motion and/or force can be actuated to the coupling means <NUM>.

It may be advantageous for the effector <NUM> to constrain a radial size of the bladder <NUM>. By way of example, the diameter of through bore <NUM> can be smaller than the natural (unpressurized) outer diameter of bladder <NUM>. This can be useful to prevent effector <NUM> from moving with respect to bladder <NUM> during actuation. Alternatively, the effector <NUM> can be fixedly attached to bladder <NUM>. By way of example, bladder <NUM> can be made with a pre-molded part designed to correspond to effector <NUM>, further coupling the two elements.

It will be convenient to note that the above actuator configurations with two bladders/bladder segments, i.e. one contractile and another extensile, can be extended with additional inflatable bladders or bladder segments arranged in series. This allows for achieving higher force outputs of the actuator while reducing or at least limiting the (expanded) dimensions of the bladders.

Fluidic artificial muscle actuators according to the present disclosure can alternatively be utilized to actuate rotational motion, instead of linear motion. Referring to <FIG>, the first bladder <NUM> and the second bladder <NUM> are arranged with parallel but offset longitudinal axes <NUM>, <NUM> respectively. The effector <NUM> comprises a fitting <NUM> attached or operably coupled to the first bladder <NUM> and a fitting <NUM> attached or operably coupled to the second bladder <NUM>. Fittings <NUM> and <NUM> are operably coupled to a lever arm <NUM> configured to pivot about a pivot axis <NUM> that can be perpendicular to a plane defined by the longitudinal axes <NUM> and <NUM>. Supplying the first and the second bladder with pressurized fluid causes the lever arm to pivot about axis <NUM> in direction of the arrow indicated in the figure.

In this configuration, it is possible to provide a fluid communication channel <NUM> fluidly connecting the first and the second bladder <NUM>, <NUM>. Fluid communication channel can further be fluidly connected to fluid supply duct <NUM> and a (single) source of pressurized fluid <NUM> configured to supply both bladders with fluid under pressure.

It will be convenient to note that other configurations of the first and second bladder are possible, e.g. where the longitudinal axes <NUM> and <NUM> are not parallel.

A setup was built according to the diagram of <FIG>. This configuration enables rapid testing of the approximate force and displacement generated by the proposed actuator while simplifying construction. The end fittings and effector were 3D printed on a Prusa SL1 machine (Prague, Czechia) using an ABS resin. The bladder material used in both first and second bladder is a <NUM> OD <NUM> wall thickness silicone tubing (Dow Corning, Michigan, USA). The bladders were both provided with a polyimide braided sleeve with <NUM>° braid angle (Bossert Kast, Germany). The contractile bladder chamber is <NUM> in length while the length of the extensile bladder chamber is <NUM>. An additional <NUM> length of braid was compressed onto the extensile bladder chamber tubing during construction to approximate a braid angle of <NUM>°. Components were bonded together and pneumatically sealed using Loctite <NUM><NUM>-part epoxy (Henkel, Germany). The assembled muscle is <NUM> in diameter at the expandable portion and <NUM> in diameter at the attachment to the fittings, with an overall length of <NUM>.

The artificial muscle was clamped in place in a custom jig to evaluate force generation and stroke length. Force was measured via a <NUM> load cell (Tedea-Huntleigh model <NUM>) attached to the effector, while displacement of the effector was measured by a laser sensor (model OADM 12I6460/S35A, Baumer, Switzerland). Air pressure supplied to the bladders was controlled by a proportional pressure regulator (model VEAA, Festo, Germany) and measured via a pressure transducer (PA-21Y, Keller, Germany). A National Instruments (Texas, USA) cDAQ-<NUM> system with modules NI9205 (Analog voltage input), NI9237 (Analog bridge input), NI9263 (Analog voltage output), and NI9203 (Analog current input) was used along with LabVIEW software (National Instruments, Texas, USA) to record sensor measurements and produce a variable output signal to control the proportional pressure regulator.

Experiments were performed in order to characterize the actuator's response to a range of pneumatic inputs similar to those required for use in a robotically controlled surgical device. In order to measure force generated by the muscle the travelling attachment point was rigidly connected to the load cell. The results of this test are visible in Fig.12B, showing the actuator hysteresis in response to a <NUM> sinusoidal pressure input and <FIG>, showing the time-domain response of the system to a <NUM> sinusoidal pressure input. This configuration was also used to characterize the response bandwidth of the actuator to a sinusoidal pressure inputs at a range of frequencies, as shown in <FIG>.

In order to measure the stroke of the actuator the load cell was disconnected, allowing the effector to move freely. These results are shown in <FIG>, showing the actuator hysteresis in response to a <NUM> sinusoidal pressure input and <FIG>, showing the actuator's response to various step changes in pressure level. Tests were performed over a pressure range of <NUM> to <NUM> bar, covering typical operating ranges of McKibben muscles and the full range of the proportional pressure regulator used in the experimental setup. Force and pressure tests reported in <FIG> and Figs. 12A-D were each repeated over three cycles.

The results shown demonstrate the operability of a prototype fluidic muscle actuation system according to the present disclosure. This configuration produced a maximum force of <NUM> N and displacement stroke of <NUM>. As seen in <FIG>, the actuator is capable of moving <NUM> in <NUM> seconds, which is a speed of <NUM>/sec. These values are higher than or within the range of typical actuator requirements for robotic surgical devices (<NUM>-<NUM> Newtons force, <NUM>-<NUM>/sec speed, and <NUM> - <NUM> displacement).

Claim 1:
Fluidic artificial muscle actuator (<NUM>, <NUM>, <NUM>), comprising:
at least one inflatable bladder defining a first inflatable segment (<NUM>, <NUM>) and a second inflatable segment (<NUM>, <NUM>),
the first inflatable segment (<NUM>, <NUM>) coupled to a first member (<NUM>, <NUM>) and to a second member (<NUM>, <NUM>, <NUM>) arranged at opposite ends of the first inflatable segment, the first member and the second member defining a first longitudinal direction (<NUM>),
the second inflatable segment (<NUM>, <NUM>) coupled to a third member (<NUM>, <NUM>, <NUM>) and to a fourth member (<NUM>, <NUM>) arranged at opposite ends of the second inflatable segment, the third member and the fourth member defining a second longitudinal direction (<NUM>), and
an effector (<NUM>, <NUM>, <NUM>, <NUM>) operably coupled to the first inflatable segment and to the second inflatable segment for providing an actuator output,
wherein the first inflatable segment (<NUM>, <NUM>) is configured to contract in the first longitudinal direction with increase in fluid pressure in the first inflatable segment,
characterised in that the second inflatable segment (<NUM>) is configured to extend in the second longitudinal direction with increase in fluid pressure in the second inflatable segment.