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Braiding Thin McKibben Muscles to Enhance Their Contracting Abilities
Abstract
This paper presents a novel concept of braiding thin McKibben muscles to improve their contracting ability compared to original muscles. Whereas a single original muscle and the conventional bundled muscle had a contracting ratio of 28%, braiding the muscles realized a contracting ratio of37%. We designed, fabricated, and tested several prototypes with different braiding parameters, and demonstrated their effects both theoretically and experimentally. The results were promising and we believe that thin braided McKibben muscles will facilitate the development of novel musculoskeletal robots and be useful in various applications requiring soft robotic abilities.
... TMMs filaments can be bundled together to multiply the contracting force (Figure 1). Such TMMs have been demonstrated in a wide variety of wearable devices for human support and assistance and have been successfully knitted into textiles (Koizumi et al., 2018;Abe et al., 2019). ...
... The TMM (Thin McKibben Muscles) used in this study are a modified version of the devices developed by the authors in previous works (Kurumaya et al., 2017;Koizumi et al., 2018;Suzumori et al., 2018;Abe et al., 2019). To enable operation of the TMMs using Stretchable Pumps instead of industrial pressure source required lowering the TMM actuation pressure from 100 to 200 kPa to 10-20 kPa, resulting in LPTMMs (Low Pressure Thin McKibben Muscles). ...
... After the first contraction, the actuator always follows the same cycle, showing very high repeatability (maximum standard deviation of 0.0312 N among five trials). The reasons for the lower force values at the first contraction are related to the sliding between the inner chamber and outer sleeve of the LPTMMs and related friction each time the soft muscles are fully depressurized and pressurized again (Kurumaya et al., 2017;Koizumi et al., 2018;Abe et al., 2019). Figure 7 shows the force vs. pressure results for the LPTMMs. ...
Soft wearable robots could provide support for lower and upper limbs, increase weight lifting ability, decrease energy required for walking and running, and even provide haptic feedback. However, to date most of wearable robots are based on electromagnetic motors or fluidic actuators, the former being rigid and bulky, the latter requiring external pumps or compressors, greatly limiting integration and portability. Here we describe a new class of electrically-driven soft fluidic muscles combining thin, fiber-like McKibben actuators with fully Stretchable Pumps. These pumps rely on ElectroHydroDynamics, a solid-state pumping mechanism that directly accelerates liquid molecules by means of an electric field. Requiring no moving parts, these pumps are silent and can be bent and stretched while operating. Each electrically-driven fluidic muscle consists of one Stretchable Pump and one thin McKibben actuator, resulting in a slender soft device weighing 2 g. We characterized the response of these devices, obtaining a blocked force of 0.84 N and a maximum stroke of 4 mm. Future work will focus on decreasing the response time and increasing the energy efficiency. Modular and straightforward to integrate in textiles, these electrically-driven fluidic muscles will enable soft smart clothing with multi-functional capabilities for human assistance and augmentation.
... The term 'soft' in this context most often refers to non-metal materials with low hardness from which the soft actuator or robot body is fabricated. This follows the definition given in [14] By weaving the fibres around the soft tube, rapid production of this type is possible [42]. As in [43] a fibre-reinforced soft actuator can also be made with 3D printing. ...
... Currently, some small-diameter actuators with 1.3 mm outside diameter and arbitrary lengths are produced by the Tokyo Institute of Technology. Their model, design, and fabrication have been presented in [42]. As artificial muscles have similarities with biological muscles [116,117], the actuators are used extensively to develop bio-inspired robots [17, 118,119]. ...
Soft robotics has emerged as a new branch of robotics gaining huge research interest in recent decades. Owning intrinsic advantages such as compliance and safety, soft robots are closely associated with the medical requirements of medical robots. This review is written to overview advances in the medical applications of soft robots, either for readers primarily familiar with traditional medical systems, or for researchers planning to develop soft robots for medical applications. Recent publications related to soft medical robots were reviewed to represent the state’, ’of’, ’the’, ’art advances in this field. The review tends to compress the scope to trunk’, ’shaped soft robots and appraise the status of soft robots and their distance from clinical use. Several papers related to the construction and capabilities of soft robots were referenced. Roughly 190 related articles published in the current period from 2018 to the publication date (representing almost 90% of the references to the theme totally identified) were reviewed. Structure of soft robots, advances in technology, and the aptitudes in medical applications were discussed. The trunk’, ’like soft robots conspicuously are proposed for applications including robot assisted surgery where a probe is inserted into the human body. Such robots are also present in other medical robots as actuators. The literature shows that different methods are used to fabricate soft robots and employ them in different robotics tasks including positioning, grasping, and force exertion. Noticeably, such studies were done in robotics laboratories, dealing with robotics engineering problems. This review suggests that the technology is actively developing, but further focus on specific medical applications is required to fill the gap between soft robotics and its clinical use.
... The outer diameter of the developed thin artificial muscle is only 1.8 mm, making it more compliant than conventional McKibben artificial muscles. Therefore, it is possible to consider it to be composed of fibers and accumulate them in the form of strings and cloths to realize accumulated structures with softness as well as high contractility and force [4][5][6][7][8]. They are not only applied to power-assist and rehabilitation devices, but also to musculoskeletal mechanisms that mimic the redundant drive mechanism of the human body and robot arms with multiple degrees of freedom for contraction, bending, and twisting movements [9][10][11][12][13]. ...
... This can be observed from the figure in which hysteresis occurs. The generation of hysteresis in the driving characteristics of the accumulated structure of thin artificial muscles is a general phenomenon and has been reported [6,25]. There are two main reasons for this: the effect of the original hysteresis of the thin artificial muscles and the generation of friction force between the thin artificial muscles. ...
A thin McKibben artificial muscle is a pneumatic actuator with an outer diameter of only 1.8 mm. We fabricated a string-shaped actuator called an “active string actuator,” which achieves a high contractile displacement by accumulating thin McKibben artificial muscles. To control the displacement, the length of the active string actuator should be estimated. However, this is difficult because bulky and rigid sensors are unsuitable for the sensor element of the active string actuator. Therefore, in this study, we propose a new sensing method for estimating the length of an active string actuator. The proposed sensing system is simple and comprises only three components: a step-index multimode optical fiber, a light emitter, and a light receiver. A step-index multimode optical fiber was combined with the active string actuator, and the length was estimated from the change in the amount of light propagating in the optical fiber when the active string actuator was driven. Fundamental experiments were conducted in this study, and the results demonstrated that the optical fiber sensor value changed with the actuator length. This suggests that it is possible to estimate the displacement of an active string actuator using an optical fiber sensor.
... In addition, they stay flexible when pressurized, allowing them to bend while contracting [14]. These features make them exceptionally suitable for use in wearable soft robotic devices, as they enable alignment very close to the body, distribution of actuation across the body surface and organization into larger structures, such as bundles [14], braids [15], weaves [16] and active textiles [17], [18]. Their application to upper-limb soft exosuits was previously shown by Abe et. ...
... Their pressure dependent stiffness properties are determined in isobaric quasistatic experiments on a tensile test setup consisting of a COMS PM80B-50X linear precision stage, Nidec-Shimpo FGP-50 digital force gauge, ANEST IWATA SLP-07EED air compressor and a CKD RP1000-8-07 precision regulator. This setup is identical to the one used in [15], [16] and [18]. Aside from measurements within the normal operating range, additional measurements for 0 and 0.5 MPa are conducted to determine the stiffness beyond the fully extended state. ...
In this paper we demonstrate a pneumatic bending actuator for upper-limb assistive wearable robots which uses thin McKibben muscles in combination with a flexure strip. The actuator features both active soft actuation and passive gravity support, and in terms of force transmission bridges the gap between the classic rigid type actuators and the emerging soft actuator technologies. Its flexure strip leverages the high-force low-displacement properties of McKibben muscles towards a large rotational range of motion and reduces localized forces at the attachments. We explain the synthesis method by which these actuators can be obtained and optimized for high specific moment output. Physical specimens of three optimized actuator designs are built and tested on a dedicated experimental setup, verifying the computational models. Furthermore, a proof-of-concept upper-limb assistive wearable robot is presented to illustrate a practical application of this actuator and its potential for close-to-body alignment. We found that based on our currently available components actuators can be built which, given a width of 80 mm, are able to produce a moment exceeding 4 Nm at an arm elevation of 90 deg.
... When an AM is pressurized and depressurized, the strain energy stored in the rubber tube restores the AM assembly back to its original resting length, similar to a mechanical spring being loaded and unloaded. Empirical data showing this nonlinear spring-like behavior has been reported by a number of researchers [3,[12][13][14][15]. Most approaches to model this nonlinear stiffness have been empirical. ...
... Comparing the theoretical approach to the empirical method in [12] shows that the theoretical approach is able to match high order curve fit methods in predictive performance without the need of experimental data beforehand. The model is able to predict the nonlinear pressure displacement that has been reported by several researchers [3,[12][13][14][15]. The model promises to be useful for various analyses, including mechanical system design, parameter optimization, control stability analysis, and model-based control. ...
The high force-to-weight ratios of braided fluidic artificial muscles are ideal for human scale and mobile robot applications. Prior modeling efforts focus on the theoretical static characteristics or empirical dynamic models of these actuators when pressurized. This paper develops a comprehensive high fidelity theoretical dynamic model based on first principles for braided pneumatic artificial muscles and presents experimental validation. A novel theoretical model for the nonlinear stiffness is derived to describe the pressure-displacement behavior. The stiffness model, together with friction, damping, and inertia models, forms an equation of motion for braided pneumatic artificial muscles. The equation of motion is coupled with first-order servopneumatic pressure dynamics, resulting in a third-order system model. System model simulations are compared to experimental results of prototypes with nine different geometries. On average , the system model is able to predict the quasi-static displacement within 7% and the dynamic response within 11%. The theoretical model is also benchmarked against a high fidelity curve fit method, with the empirical method showing a 2% improvement in only quasi-static scenarios. The model promises to be useful for mechanical system and model-based control designs.
... They also developed three mathematical models [61]. Koizumi et al. achieved a contraction rate of up to 37% by braiding the McKibben muscles together in the actuator, but this model achieved a lower contraction force [62]. ...
Pneumatic artificial muscles (PAMs) have been exploited in robots utilized in various fields, including industry and medicine, due to their numerous advantages, such as their light weight; smooth, fast responses; and ability to generate significant force when fully extended. The actuator's stiffness is important in these applications, and extensor PAMs (EPAMs) have a lower stiffness when compared to contractor PAMs (CPAMs). Because of this, this research presents the compound extensor PAM (CE-PAM), which is a novel actuator that has higher stiffness and can alter its stiffness at a fixed length or maintain a fixed stiffness at a variable length. This makes it useful in applications such as surgery robots and wearable robots. The CE-PAM is created by inserting the CPAM into the EPAM. Then, a mathematical model is developed to calculate the output force using several mathematical equations that relate the force, actuator size, and applied pressure to each other. The force is also calculated experimentally, and when comparing the mathematical with the experimental results, the error percentage appears greater than 20%. So the mathematical model is enhanced by calculating the wasted energy consumed by the actuator before the start of the bladder's expansion, at which the force is zero because the pressure is consumed only for bladder expansion to touch the sleeve. The effect of the bladder's thickness is calculated to further enhance the model by calculating the volume of air entering the muscle rather than the total muscle volume. To illustrate the effect of thickness on the actuator, experiments are conducted on CPAMs made of the same bladder material but with different thicknesses. A balloon is used in the manufacture of the bladder. Because it is a lightweight, thin material with a low thickness, it requires very low pressure to expand.
... 2,3 Their most basic shape is that of a stretchable tube made of rubber or polymer, which contracts through the lateral expansion of its volume. [4][5][6] Various variations on this concept have been proposed, including ones functioning through the unfolding of pleats or origami patterns, [7][8][9] or replacing the thick matrix with thin films. [10][11][12][13] Vacuum-based alternative designs have been proposed using either polymers or thin films with rigid or semirigid skeletons. ...
To make robots more human-like and safer to use around humans, artificial muscles exhibiting compliance have gained significant attention from researchers. However, despite having excellent performance, pneumatic artificial muscles (PAMs) have failed to gain significant traction in commercial mobile applications due to their requirement to be tethered to a pneumatic source. This study presents a thermo-PAM called Thermo-PAM that relies on heating of a volume of air to produce a deformation. This allows for pneumatic actuation using only an electrical power source and thus enables pumpless pneumatic actuation. The actuator uses a high ratio between the heating volume and the deformable volume to produce a high actuation force throughout its entire motion and can produce either contractile or extension motions. The controllability of the actuator was demonstrated as well as its ability to handle heavy payloads. Moreover, it is possible to rely on either positive or negative pressure actuation modes where the positive pressure actuation mode actuates when heated and the negative pressure actuation mode relaxes when heated. The ability to use Thermo-PAMs for different modes of actuation with different operation methods makes the proposed actuator highly versatile and demonstrates its potential for advanced pumpless robotic applications.
... Some researchers have improved McKibben muscles to obtain a higher contraction ratio. Koizumi et al. [13,14] improved the contraction ratio of thin McKibben muscles up to 0.37 by braiding once and 0.41 by braiding twice. Daniel et al. [15] improved the contraction ratio of thin McKibben muscles up to 0.5 by introducing bending deformations. ...
In this study, a novel pouch-type pneumatic artificial muscle for wearable applications with a high contraction ratio was proposed. It utilizes a rotary plate-belt mechanism to transfer the expansion of the folded pouch into the contraction of the belt. Modular design of the actuation unit enhances the adaptivity to multiple application scenarios. Based on the principle of virtual work, a force-contraction model considering energy loss was established and verified experimentally. Test results indicate that the actuation unit can attain a contraction force of 35.3 N and contraction ratio of 49.27%. Moreover, self-contained displacement and force sensing were designed, calibrated, and validated for this actuator. The good displacement tracking and force monitoring performance in the primary feedback control test proved the effectiveness of the self-sensing methods. Finally, surface electromyography (sEMG) of biceps brachii with actuator revealed that muscle activation could be reduced by 30.72% and 41.27% without and with 3kg load, respectively.
... One study by Abe et al. (2018Abe et al. ( , 2019 wove the soft actuators in an "18 weave" braid to increase the contraction ratio compared to the singular soft actuator [6,7]. Another study by Koizumi et al. (2018Koizumi et al. ( , 2019) also used weaving technique to increase the contraction ratio. This study uses an 8-strand braid to increase the detour in which the actuator has to travel by [8,9]. ...
Nutrition education is an integral part of a series of disease prevention and control, including covid-
19. This mini-review aims to investigate the role of nutritional status on the severity of covid-19
symptoms. Balanced nutritional intake is the essential capital to maintain metabolic balance, maintain
nutritional status, and increase endurance. This is very useful to prevent or at least suppress the symp-
toms of covid-19. Excessive and unhealthy food intake (high in sugar and high in fat) can cause
metabolic disorders, increase body weight resulting in obesity, and increase the risk of degenerative
diseases such as diabetes mellitus and hypertension. This will increase inflammation in the body,
which can reduce immunity. Several studies have suggested that nutritional status is related to the
severity of Covid-19 symptoms. Most of the patients with confirmed Covid-19 with poor nutritional
status had more severe respiratory complaints. So, nutrition education is needed to prevent the covid-
19 infections.
... However, these actuators rely on changes in volume through either inflation or deflation to produce mechanical work, which means that their mechanical characteristics depend on how they deform. One of the first soft pneumatic actuators to be developed was the McKibben actuator, which consists of a tubular structure that expands radially and contracts longitudinally when pressurized [10], [11], [12]. This actuator relies on the use of a bladder and a braided mesh for its structure and can withstand high pressures while producing high blocked forces, but its maximum contraction ratio is generally below 0.3. ...
The performance of soft robots depends in large part on the actuation performance of the soft actuators used to drive them, and those making use of fluidic actuation have gained the most traction in the form of pneumatic artificial muscles (PAMs). These PAMs make use of the change in volume of a structure through pressurization of their volume to produce mechanical work. However, their performance depends in large part on how this volume deforms throughout the motion. Pouch motors have been proposed as a lightweight yet powerful soft actuator, but their sealed ends limit their performance. This article proposed the addition of gussets onto pouch motors to form gusseted pouch motors for improved performance. This allows for the actuator to produce a larger contraction ratio than without gussets and allows for the force to increase as the length of the actuator increases. This article explains the manufacturing of the actuator, proposes a numerical model that predicts well the performance of the actuator, shows experimental results for different actuator dimensions, and provides a comparison with regular pouch motors. It then demonstrates stiffness control using antagonistic pouch motors and implements the actuator into a simple robotic arm with angular position control.
... It has been applied to the prosthesis hand for children, the wearable support device and the soft robot because of its lightweight and high flexibility [1][2][3]. In addition, basic research aimed at improving the convenience of thin artificial muscle has been actively conducted [4,5]. ...
We have fabricated a string-shaped actuator called “Active string” that has high contractile displacement/force by accumulating thin pneumatic artificial muscles using the string production process. However, displacement control of the active string is challenging because general bulky and rigid displacement sensors are not suitable for the sensor element of the active string. Therefore, in this report, a flexible optical fiber sensor is combined with the active string to enable sensing of its displacement. As the active string contracts, the radius of curvature of the optical fiber decreases, and light intensity propagating in the optical fiber decreases due to bending loss. The experimental results showed that the optical fiber sensor value changed with corresponding to the displacement of the active string. It shows the possibility that it is possible to make a displacement estimation of the displacement of the active string using an optical fiber sensor.
... (Polygerinos et al., 2017;Ilievski et al., 2011) Consequently, the applied fluid causes asymmetric extension of fluidic networks and strain-limiting appendages, and the whole soft body produces pre-programmed motion such as bending, (Ilievski et al., 2011;Mosadegh et al., 2014;Tang et al., 2020;Yap et al., 2016) twisting, (Connolly et al., 2015) and contraction. (Yang et al., 2017;Koizumi et al., 2018) Researches to date have mainly focused on architecting fluidic networks and have achieved rapid actuation, (Mosadegh et al., 2014) high aspect ratio design, (Becker et al., 2020) and high force generation. (Tang et al., 2020;Yap et al., 2016) However, the current design method compels soft robots to be shaped as a long elastomeric beam or a cylinder because their form factors are subordinated to inextensible strain-limiting appendages, which may limit their spatial efficiency, and make it inconvenient for soft fluidic robots to be used with other mechanical elements due to physical interferences. ...
Soft fluidic actuators produce continuous and life-like motions that are intrinsically safe, but current designs are not yet mature enough to enable large deployment with high force and low-cost fabrication methods. Here, soft fluidic actuators with two superimposed origami architectures are reported. Driven by a fluid input, the presented dual-origami soft actuators produce quasi-sequential deployment and bending motion that is guided by unsymmetric unfolding of low-stretchable origami components. The dominance between the deployment and bending can be shifted by varying the unfolding behavior, enabling pre-programming of the motion. The proposed origami-inspired soft actuators are directly fabricated by low-cost fused deposition modeling 3D-printing, and subjected to a heat treatment post-processing to enhance the fluid sealing performance. Finally, soft gripper applications are presented and they successfully demonstrate gripping tasks that each requires strength, delicacy, precision and dexterity. The dual-origami approach offers a design guidance for soft robots to embody grow-and-retract motion with a small initial form factor, promising for applications in next-generation soft robotic systems.
... (Polygerinos et al., 2017;Ilievski et al., 2011) Consequently, the applied fluid causes asymmetric extension of fluidic networks and strain-limiting appendages, and the whole soft body produces pre-programmed motion such as bending, (Ilievski et al., 2011;Mosadegh et al., 2014;Tang et al., 2020;Yap et al., 2016) twisting, (Connolly et al., 2015) and contraction. (Yang et al., 2017;Koizumi et al., 2018) Researches to date have mainly focused on architecting fluidic networks and have achieved rapid actuation, (Mosadegh et al., 2014) high aspect ratio design, (Becker et al., 2020) and high force generation. (Tang et al., 2020;Yap et al., 2016) However, the current design method compels soft robots to be shaped as a long elastomeric beam or a cylinder because their form factors are subordinated to inextensible strain-limiting appendages, which may limit their spatial efficiency, and make it inconvenient for soft fluidic robots to be used with other mechanical elements due to physical interferences. ...
Soft fluidic actuators produce continuous and life-like motions that are intrinsically safe, but current designs are not yet mature enough to enable large deployment with high force and low-cost fabrication methods. Here, soft fluidic actuators with two superimposed origami architectures are reported. Driven by a fluid input, the presented dual-origami soft actuators produce quasi-sequential deployment and bending motion that is guided by unsymmetric unfolding of low-stretchable origami components. The dominance between the deployment and bending can be shifted by varying the unfolding behavior, enabling pre-programming of the motion. The proposed origami-inspired soft actuators are directly fabricated by low-cost fused deposition modeling 3D-printing, and subjected to a heat treatment post-processing to enhance the fluid sealing performance. Finally, soft gripper applications are presented and they successfully demonstrate gripping tasks that each requires strength, delicacy, precision and dexterity. The dual-origami approach offers a design guidance for soft robots to embody grow-and-retract motion with a small initial form factor, promising for applications in next-generation soft robotic systems.
... Recently, novel soft actuators have been developed (Koizumi et al., 2018;Li et al., 2017;Marchese et al., 2015;Robertson and Paik, 2017). They have soft materials and are driven by fluid; our approach could be applied to model identification for wearable robots with soft actuators. ...
Recent breakthroughs in wearable robots, such as exoskeleton robots with soft actuators and soft exosuits, have enabled the use of safe and comfortable movement assistance. However, modeling and identification methods for soft actuators used in wearable robots have yet to be sufficiently explored. In this study, we propose a novel approach for obtaining accurate soft actuator models through the design of physical user–robot interactions for wearable robots, in which the user applies external forces to the robot. To obtain an accurate soft actuator model from the limited amount of data acquired through an interaction, we leverage an active learning framework based on Gaussian process regression. We conducted experiments using a two-degree-of-freedom upper-limb exoskeleton robot with four pneumatic artificial muscles (PAMs). Experimental results showed that physical interactions between the exoskeleton robot and the user were successfully designed to allow PAM models to be identified. Furthermore, we found that data acquired through an interaction could result in more accurate soft actuator models for the exoskeleton robots than data acquired without a physical interaction between the exoskeleton robot and the user.
... Thin McKibben muscle is a versatile actuator which enable bending even under pressurised state and it is lightweight with a contraction ratio of approximately 25%, which is comparable to human muscles. Moreover, it has a contraction force several times larger than that of human muscles, and this can be further increased by bundling the muscles and employing a multifilament structure [12,13]. ...
In recent years, soft actuator has been extensively developed in robotic research. This type of robot is expected to work with human with its flexible and adaptable advantage. The actuator material is soft, light, safe and high compliant. Due to these factors, soft McKibben is of interest as an actuator for this research for bending application. This paper introduces a variant bending analysis of a soft body manipulated using soft McKibben actuators. A series of 1.80 mm width with the length of 120.0 mm McKibben actuator is used to control the bending motion. The design consists of four McKibben actuators arranged in parallel and compacted in a soft body. The bending behavior was evaluated using an experimental test with a variety of pneumatic input pressure and length section on the actuator. The experiment showed that the bending angle was influenced by the segmentation length of the actuator, where the segmentation length and increased input pressure also allow more bending on the actuator. The actuator with lot of section gave more bending response compared to the actuator with lesser section. With the performance exhibited from this study, McKibben actuator can be applied in a wider use for continuum manipulator.
... PAMs can be divided into positive and negative pressure types according to the driving pressure of air. The most classic representative of a positive pressure-type PAM is the McKibben muscle, which has been widely used [12][13] and improved [14][15]. Due to the characteristics of simple structure, rapid response, high output force and low commercial cost, McKibben muscles have been widely used in various situations. Much work has been performed in the investigation and improvement of McKibben muscles. ...
... Variants may extend, twist or bend and their particular actuation direction determines the response space layout. Standard McKibben actuators are studied because they produce higher forces than extending variants [15] and remain popular in soft arms and grippers [13,16]. McKibben actuators are composed of a cylindrical elastomeric enclosure (e.g., silicone, rubber, polyurethane) that is wrapped by a braided set of fibers with a helix angle below 54.7 • , as measured from the helix axis [3]. ...
Soft robots join body and actuation, forming their structure from the same elements that induce motion. Soft actuators are commonly modeled or characterized as primary movers, but their second role as support structure introduces strain-pressure combinations outside of normal actuation. This manuscript examines a more complete set of possible strain-pressure combinations for McKibben actuators, including passive extension, passive compression, pressurized extension and compression of a pressurized actuator beyond the maximum actuation strain. Each region is investigated experimentally, and empirical force-displacement-pressure relationships are identified. Particular focus is placed on ensuring empirical relationships are consistent at boundaries between an actuator's strain-pressure regions. The presented methodology is applied to seven McKibben actuator designs, which span variations in wall thickness, enclosure material and actuator diameter. Empirical results demonstrate a trade-off between maximum contraction strain and force required to passively extend. The results also show that stiffer elastomers require an extreme increase in pressure to contract without a compensatory increase in maximum achieved force. Empirical force-displacement-pressure models were developed for each variant across all the studied strain-pressure regions, enabling future design variation studies for soft robots that use actuators as structures.
... Other works used linear or polynomial models for the AM stiffness [11,12]. The advent of using hydraulics has highlighted the nonlinear behavior of the pressuredisplacement free contraction curve for AMs and has made the need for theoretical stiffness models using Newton's second law more apparent [2,[13][14][15][16]. Slightam proposed coupling linear pressure vessel theory and the theory of large deformations to derive an accurate stiffness model for mechanical system simulation and model-based con-troller designs [17]. ...
Fluidic braided artificial muscles have been studied for close to seventy years. Their high power-to-weight ratio and force-to-weight ratio make them a desirable actuation technology for compact and lightweight mobile manipulation. Use of hydraulics with fluidic artificial muscles has helped realize high actuation forces with new potential applications. To achieve large actuation forces produced from high internal pressure, artificial muscles operate near the limitations of their mechanical strength. Design improvements and future applications in mechanical systems will benefit from detailed theoretical analysis of the fluidic artificial muscle mechanics. This paper presents the theoretical modeling of a hydraulic artificial muscle, analysis of its mechanics , and experimental results that validate the model. A prototype is analyzed that operates at 14 MPa and can generate up to 6.3 kN of force and a displacement of 21.5 mm. This model promises to be useful for mechanical system design and model-based control.
In this study, we propose a fabric muscle based on the Zigzag Shape Memory Alloy (ZSMA) actuator. Soft wearable robots have been gaining attention due to their flexibility and the ability to provide significant power support to the user without hindering their movement and mobility. There has been an increasing focus on the research and development of fabric muscles, which are crucial components of these robots. This article introduces a high-performance fabric muscle utilizing zigzag-shaped shape memory alloy (SMA), ZSMA, a new form of SMA actuator. Through modeling and experimentation of the ZSMA actuator, we identified an optimized actuator design and detailed the fabric muscle fabrication process. The proposed fabric actuator, weighing only 7.5 g, demonstrated the impressive capability to lift a weight of 2 kg with a contraction displacement of 40%. This significant achievement paves the way for future research possibilities in soft wearable robotics.
This paper aims to solve the trajectory tracking task of the pneumatic musculoskeletal robot within a model-based reinforcement learning framework. Considering the limited sensors and short lifespan of self-made pneumatic artificial muscles, physics priors are encoded into Gaussian process regression to implement a semi-parametric model for micro-data system identification and the identified model is combined with cross-entropy method (CEM)-based model predictive control to plan for the optimal action online. To further compensate for the model imperfection and improve the control performance, a hybrid feedforward and feedback controller-like strategy is proposed to guide the search space of the original CEM solver. The effectiveness of our approach is verified on a real musculoskeletal manipulator with two degrees of freedom and the results show that only 50 s of interacting with the environment is enough for the robot to learn writing alphabet letters from scratch.
McKibben artificial muscles are used in many musculoskeletal robots because they have characteristics similar to those of natural skeletal muscles in terms of the contraction ratio and force generated. However, they differ from natural skeletal muscles in that they cannot perform passive elongation movements (referred to as “back-stretching” in this study), in which the muscle is stretched by an external force from its natural length while deactivated. Therefore, when using McKibben artificial muscles for antagonist muscle drives, it is necessary to use artificial muscles that are longer than the linear distance between the origin and insertion point of the muscle (causing them to sag while deactivated). However, when acting as an agonist muscle, such an artificial muscle does not fully utilize its contractile capacity and reduces the range of motion of the joint. This is different from natural skeletal muscles, which are placed along the bone without sagging under the skin. In this study, we proposed a back-stretchable McKibben muscle that contracts like a conventional McKibben artificial muscle when air pressure is applied and back-stretches like a natural skeletal muscle with no applied pressure. In addition, we developed a design method based on a mechanical model. In comparative experiments on a robotic arm, we achieved a 1.22-fold increase in the antagonist muscle driving range compared with conventional McKibben artificial muscles without causing the muscles to sag significantly.
The rapid development in the field of artificial intelligence has increased the demand for neuromorphic computing hardware and its information‐processing capability. A spintronics device is a promising candidate for neuromorphic computing hardware and can be used in extreme environments due to its high resistance to radiation. Improving the information‐processing capability of neuromorphic computing is an important challenge for implementation. Herein, a novel neuromorphic computing framework using spintronics devices is proposed. This framework is called coupled spintronics reservoir (CSR) computing and exploits the high‐dimensional dynamics of coupled spin‐torque oscillators as a computational resource. The relationships among various bifurcations of the CSR and its information‐processing capabilities through numerical experiments are analyzed and it is found that certain configurations of the CSR boost the information‐processing capability of the spintronics reservoir toward or even beyond the standard level of machine learning networks. The effectiveness of our approach is demonstrated through conventional machine learning benchmarks and edge computing in real physical experiments using pneumatic artificial muscle‐based wearables, which assist human operations in various environments. This study significantly advances the availability of neuromorphic computing for practical uses. A novel neuromorphic computing framework that couples a number of nanoscale spintronic oscillators is proposed. The framework is demonstrated to boost the computational power of the spintronics neuromorphic computing toward or even beyond the standard level of machine learning networks. The effectiveness of this framework is shown through edge computing in real physical experiments using pneumatic artificial muscle‐based wearables.
Existing pneumatic artificial muscles generally rely on the use of either positive or negative pressure for actuation with each having their own advantages and disadvantages. Herein, a hyperbaric vacuum‐based artificial muscle (Hyper‐VAM) making use of both positive and negative pressures almost interchangeably is described. This is done by placing a vacuum‐based actuator inside a hyperbaric chamber which enables both the large deformations possible using negative pressure, and large forces through the action of high pressure differential, exceeding those possible using only negative pressure. This actuator can lift heavy payloads (up to 80 kg) for its entire contraction range, with large deformations (89.1% contraction of the active length) and high power (maximum power of 101.3 W), while using relatively low pressures, which can be supplied by a portable pneumatic pump. By exchanging air between the two chambers in closed‐loop pneumatic actuation, this actuator can also be driven using a single pump without exchanging air with the environment and its position can be controlled using a single pneumatic regulator. Herein, a hyperbaric vacuum‐based artificial muscle (Hyper‐VAM) making use of both positive and negative pressures almost interchangeably is described. This actuator can lift heavy payloads for its entire contraction range (up to 80 kg), with large deformations (89.1% contraction ratio), and high power (101.3 W), while using relatively low pressures which can be supplied by a portable pneumatic pump.
This study presents the usage of Braided Actuators with Nested Structures to improve the stroke characteristics of the McKibben actuators. Thin McKibben actuators can contract 23% of their original length when pressurized. Usage of braiding and nested structures to improve contraction ratio has proven successful. In this study, we use a combined telescopic Nested Structure and Braided Actuators to increase the contraction ratio of the actuators. The Nested Braided Actuator (NBA) performance was compared to Single Actuator (SA), Braided Actuator (BA), and Nested Actuator (NA). The results at 350 kPa indicate that, NBA had the highest contraction ratio of 45.5%, followed by NA (39.38%), BA (29.57%), and SA (23.41%). At 350 kPa, the contraction force per actuator NBA was 36.29 N, NA exerted 41.33 N, BA exerted 30.41 N and SA exerted 43.8 N. The actuator's performance showed that it was capable of high stroke with only a 20–30% loss in contraction force compared to the SA.
The primary role of a robot exploring an unknown space is to investigate the state and the spatial shape of the environment. We have designed a soft robot that aims to move forward in an unknown space as it recognizes and adapts to the spatial shape of the environment. We previously reported that soft tensegrity and recurrent neural network can be used to realize tensegrity structure shape recognition. In this study, a tensegrity robot was designed to actively generate propulsive force as it presses its body against a wall in its surrounding environment. This robot design includes a novel artificial muscle arrangement called “4/3 muscle winding,” which induces large deformation in the tensegrity structure. The application of this new artificial muscle arrangement allows two types of large deformations to be induced in the tensegrity structure, which results in displacements of 20% to 40% in the axial and radial directions. We have demonstrated that the robot, which was created by connecting the tensegrity structures, is lightweight and possesses passive shape adaptability in a three-dimensional environment. This tensegrity robot could enter an unknown space, such as a cave, and recognize the spatial shape of the surrounding environment by recognizing the tensegrity structure shape.
Soft robotics aims at creating systems with improved performance of movement and adaptability in unknown, challenging, environments and with higher level of safety during interactions with humans. This Roadmap on Soft Robotics covers selected aspects for the design of soft robots significantly linked to the area of multifunctional materials, as these are considered a fundamental component in the design of soft robots for an improvement of their peculiar abilities, such as morphing, adaptivity and growth. The roadmap includes different approaches for components and systems design, bioinspired materials, methodologies for building soft robots, strategies for the implementation and control of their functionalities and behaviour, and examples of soft-bodied systems showing abilities across different environments. For each covered topic, the author(s) describe the current status and research directions, current and future challenges, and perspective advances in science and technology to meet the challenges.
Soft fluidic actuators produce continuous and life-like motions that are intrinsically safe, but current designs are not yet mature enough to enable large deployment with high force and low-cost fabrication methods. Herein, soft fluidic actuators with two superimposed origami architectures are reported. Driven by a fluid input, the presented dual-origami soft actuators produce quasisequential deployment and bending motion that is guided by unsymmetric unfolding of low-stretchable origami components. The dominance between the deployment and bending can be shifted by varying the unfolding behavior, enabling preprogramming of the motion. The proposed origami-inspired soft actuators are directly fabricated by low-cost fused deposition modeling 3D printing and subjected to heat treatment postprocessing to enhance the fluid sealing performance. Finally, soft gripper applications are presented and they successfully demonstrate gripping tasks where each requires strength, delicacy, precision, and dexterity. The dual-origami approach offers a design guidance for soft robots to embody grow-and-retract motion with a small initial form factor, promising for applications in next-generation soft robotic systems. An interactive preprint version of the article can be found here: https://www.authorea.com/doi/full/10.22541/au.163698906.68661340.
McKibben artificial muscles, comprised of an expandable bladder wrapped in a double-helix-braided sheath, have the ability to generate forces without restricting motion to occur exclusively along the direction of actuation. This makes them attractive for a variety of applications including soft, wearable, and biomimetic robots. Despite their advantages, the theoretical maximum contraction ratio of McKibben muscles is only 36.3\%, which restricts the range of motion of the systems they actuate. This work introduces a novel ‘chain-link actuator’ that exploits the bending stiffness of McKibben muscles to achieve contraction ratios of more than 50\%. A static model that captures the relationship between pressure, displacement, and force is presented and validated on several real chain-link actuator systems.
Pneumatic muscle actuators (PMA) are a class of soft actuators known for their high power to weight ratio and inherent compliance. The pneumatic muscle's inherent properties make them very favorable for assistive applications (e.g., medical exoskeletons). This study presents a novel end-fitting design that makes the developed pneumatic muscle actuator lightweight, cost-effective, and modular, thus simplifying the process of assembly and maintenance. The pneumatic muscle actuator assembled using the novel end fittings achieves a shorter overall length without compromising its contraction percentage. The pneumatic muscle actuator has been assembled using a commercial bladder and a braided sleeve alongside a pair of 3D printed novel end-fittings. The paper also details the developed actuator's characterization for force and deflection parameters at various operating pressures. A total of four muscle actuators of varying diameters with constant actuation length (100 mm) were developed and tested to showcase the effect of size on the muscle actuator's behavior. The study presented here also involved comparing three mathematical models developed for pneumatic muscles in order to find a model which closely resembles the developed muscle actuator. Finally, the developed pneumatic muscle actuator's behavior is compared with a commercially available muscle to determine the efficacy of the developed muscle's design. The tests showed that the muscle using a bladder of smaller volume but higher tensile modulus had a higher accuracy and stable performance. As the muscle is intended for medical applications, it was also put through an endurance test with realistic loading and pressure conditions, which revealed very promising results.
Soft robots join body and actuation, forming their structure from the same elements that induce motion. Soft actuators are commonly modeled or characterized as primary movers, but their second role as support structure introduces strain-pressure combinations outside of normal actuation. This manuscript examines a more complete set of possible strain-pressure combinations for McKibben actuators, including passive, or unpressurized, deformation, pressurized extension and compression of a pressurized actuator beyond the maximum actuation strain. Each region is investigated experimentally, and empirical force-displacement-pressure relationships are identified. Particular focus is placed on ensuring empirical relationships are consistent at boundaries between an actuator's strain-pressure regions. The presented methodology is applied to seven McKibben actuator designs, which span variations in wall thickness, enclosure material and actuator diameter. Empirical results demonstrate a trade-off between maximum contraction strain and force required to passively extend. The results also show that stiffer elastomers require an extreme increase in pressure to contract without a compensatory increase in maximum achieved force. Empirical force-displacement-pressure models were developed for each variant across all the studied strain-pressure regions, enabling future design variation studies for soft robots that use actuators as structures.
Textiles have emerged as a promising class of materials for developing wearable robots that move and feel like everyday clothing. Textiles represent a favorable material platform for wearable robots due to their flexibility, low weight, breathability, and soft hand‐feel. Textiles also offer a unique level of programmability because of their inherent hierarchical nature, enabling researchers to modify and tune properties at several interdependent material scales. With these advantages and capabilities in mind, roboticists have begun to use textiles, not simply as substrates, but as functional components that program actuation and sensing. In parallel, materials scientists are developing new materials that respond to thermal, electrical, and hygroscopic stimuli by leveraging textile structures for function. Although textiles are one of humankind's oldest technologies, materials scientists and roboticists are just beginning to tap into their potential. This review provides a textile‐centric survey of the current state of the art in wearable robotic garments and highlights metrics that will guide materials development. Recent advances in textile materials for robotic components (i.e., as sensors, actuators, and integration components) are described with a focus on how these materials and technologies set the stage for wearable robots programmed at the material level.
In this study, a pneumatically contracting active cloth has been developed; its application is proposed for a safe sitting-posture recovery system for wheelchair users to avoid fall-related accidents. The active cloth consists of thin artificial muscles knitted via a flat string machine. The safe wheelchair system is configured with an active cloth and seating pressure sensor. The seating pressure sensor, located on the seating surface of the wheelchair, estimates the inclination of the upper body of the user; when this reaches an angle that is dangerous for falling from the wheelchair, the active cloth contracts to correct the posture of the upper body. In this paper, we clarify the fabrication process and fundamental characteristics of the active cloth and indicate its potential as a mechanical element for welfare apparatuses by demonstrating a safe wheelchair system.
ABSTRACT: The use of mobile phones especially smartphones with their sophisticated applications including social media is no more a sign of one’s standard of life resembling his/her wealth or richness, but an indispensable part of most people’s lives. It is not an exaggeration to mention that if a person who uses a smartphone forgets to carry it with him/her for a day, that person would feel paralyzed and inactive the whole day. Many individuals have now learnt to live without people around them, but not the smartphone. While it brings several advantages to the human being, its influence on children is mostly undesired in many aspects, especially with regard to morality and health. Child psychologists, pediatricians and educationists have expressed their concerns over this intruder device in children’s naturally innocent lives. Thus the aim of this paper is to discuss the negative impacts of the use of mobile platforms among youngsters. The study was conducted using published material including books, reports and research papers. Findings show that timely action needs to be taken before it becomes too late. The recommendations of experts include parental control over the use mobile platforms and social media.
This study presents a novel idea of rebraiding thin McKibben muscles to overcome their limitation of contraction. The thin McKibben muscles, presented in the authors' previous work, have the flexibility that allows them to be braided. According to the experimental results of our previous research, the original single muscles have a contracting ratio of 28%, and the corresponding value for the muscles braided once is 37%. In this research, we achieved 41% contraction of thin McKibben muscles by braiding twice. The contraction ratio increases if the muscles are braided more. They will then overcome their limitation of contraction. In this report, several prototypes of muscles with different braiding times are designed, fabricated, modeled, and tested. As a result, the increase in the contraction ratio was confirmed from both a theoretical and an experimental point of view; the results were promising. We believe that recurrent-braided thin McKibben muscles will considerably help improve and develop various soft robotic applications in cases where a high contraction ratio is required.
We propose a novel active weave named ‘18 Weave’ using a thin McKibben muscle and report on the application to a prototype soft power support suit for the upper limb. The active weave utilizes the flexibility of the thin McKibben muscle, which is used for warps and wefts. From the proposed structure, we confirmed that a 19.4% additional displacement is achieved compared to a single artificial muscle. The flexible and lightweight assistance suit can be realized with the active weave that has advantages of flexibility and shape adaptability. We confirmed the compliance and fatigue alleviation effect of the suit. Measurements of the myopotentials confirmed significant decreases in the activities of the anterior deltoid, posterior deltoid, biceps brachii, and triceps brachii muscles in their iEMGs.
This paper presents a redundant musculoskeletal robot using thin McKibben muscles that is based on human anatomy. The purpose of this robot is to achieve motions and characteristics that are very similar to a human body. We use a thin McKibben muscle, which is compliant and flexible, as the actuator of a musculoskeletal robot. Using a bundle of thin McKibben muscles, we develop a multifilament muscle that has characteristics similar to those of human muscles. In contrast, the actuators of conventional musculoskeletal robots are very heavy, not densely attached and have poor backdrivability. Because multifilament muscles are light and can be densely attached, we can attach them to the musculoskeletal robot as skeletal muscle and achieve a redundant system that is equivalent to a human drive mechanism. In this paper, we report a method for fabricating multifilament muscles that imitate various muscles, the development of a lower-limb muscle mechanism for the redundant musculoskeletal robot with thin McKibben muscles and experimental results showing that the proposed musculoskeletal robot achieves humanlike motions that have not yet been reported for other robots.
Pneumatic artificial muscles (PAMs) are well known for their excellent actuator characteristics, including high specific work, specific power, and power density. Recent research has focused on miniaturizing this pneumatic actuator technology in order to develop PAMs for use in small-scale mechanical systems, such as those found in robotic or aerospace applications. The first step in implementing these miniature PAMs was to design and characterize the actuator. To that end, this study presents the manufacturing process, experimental characterization, and analytical modeling of PAMs with millimeter-scale diameters. A fabrication method was developed to consistently produce low-cost, high performance, miniature PAMs using commercially available materials. The quasi-static behavior of these PAMs was determined through experimentation on a single actuator with an active length of 39.16 mm (1.54 in) and a diameter of 4.13 mm (0.1625 in). Testing revealed the PAM's full evolution of force with displacement for operating pressures ranging from 207 to 552 kPa (30–80 psi in 10 psi increments), as well as the blocked force and free contraction at each pressure. Three key nonlinear phenomena were observed: nonlinear PAM stiffness, hysteresis of the force versus displacement response for a given pressure, and a pressure deadband. To address the analysis of the nonlinear response of these miniature PAMs, a nonlinear stress versus strain model, a hysteresis model, and a pressure bias are introduced into a previously developed force balance analysis. Parameters of these nonlinear model refinements are identified from the measured force versus displacement data. This improved nonlinear force balance model is shown to capture the full actuation behavior of the miniature PAMs at each operating pressure and reconstruct miniature PAM response with much more accuracy than previously possible.
This article is intended as an introduction to and an overview of Pneumatic Artificial Muscles (PAMs). These are pneumatic actuators made mainly of a flexible and inflatable membrane. First, their concept and way of operation are explained. Next, the properties of these actuators are given, the most important of which are the compliant behavior and extremely low weight. A classification and review is following this section. Typical applications are dealt with in the last but one section and, finally, some concluding remarks are made.
This article is intended as an introduction to and an overview of Pneumatic Artificial Muscles (PAMs). These are pneumatic actuators made mainly of a flexible and inflatable membrane. First, their concept and way of operation are explained. Next, the properties of these actuators are given, the most important of which are the compliant behavior and extremely low weight. A classification and review is following this section. Typical applications are dealt with in the last but one section and, finally, some concluding remarks are made.
This letter introduces a lightweight hexapod robot, Giacometti robot, made with long and narrow legs following the Alberto Giacometti's sculpture conception. The goal is achieved by, firstly, using multiple links with thin and soft McKibben actuators, and secondly, choosing a leg design which is narrow in comparison to its body's length and height, unlike conventional robot design. By such design characteristic, the leg will exhibit elastic deformations due to the low stiffness property of the thin link structure. Then, we model the leg structure and conduct the deflection analysis to confirm the capability of the leg to perform walking motion. The high force to weight ratio characteristics of the actuator provided the ability to drive the system, as shown by a static model and further validated experimentally. To compensate for the high elastic structural flexibility of the legs, we introduced two walking gaits namely customized wave gait and Giacometti gait. The robot could walk successfully with both gaits at maximum speed of 0.005 m/s and 0.05 m/s, respectively. It is envisaged that the lightweight Giacometti robot design can be very useful in legged robotic exploration.
This letter presents an Index finger of Human-Like robotics hand which intends to closely replicate the human hand not only in term of bone, ligaments and tendon shape and size but also the muscles of the human hand by using McKibben type muscles. The muscles of the index finger consist of three intrinsic and 3 extrinsic muscles fabricated by using thin multifilament McKibben muscles with diameters 1.3 mm and 4.0 mm, respectively. We present the fabrication method of index finger and model it based on Landsmeer Model I, II and III. We compared it for extension and flexion motion to validate the properties of our developed finger. We also conducted radial and ulnar deviation experiment and compared it with the human range of motion. Finally, we demonstrated the capabilities of the finger using visual tracker software to compare sweeps of their robot hand with a cadaver hand motion for normal and finger deformity condition. Having McKibben muscles as the actuator that mimics the human muscle, one can better understand the human finger functioning and this model may be used for training purposes and also for modeling of human finger disorders.
Current McKibben muscles are usually 10 to 40 mm in diameter, which makes them very stiff during contraction and difficult to deform rendering them unsuitable for dense mounting with shape adaptability in small spaces. In this research, to solve these problems, our group has developed the thinnest McKibben muscle reported until now. Bundling the muscles results in a multifilament muscle of the desired shape and flexibility. This paper reports the design of the thin McKibben muscle and the multifilament muscle and their static characteristics. In addition, we propose two theoretical models of multifilament muscles and derive their theoretical characteristics. The static characteristics of multifilament muscles with various design parameters have been evaluated through experiments and modeling. As a result, the greater contraction ratio of the multifilament muscles compared to that of the single muscle was demonstrated both theoretically and experimentally.
We propose the nonlinear model of the rubber actuator which includes the variation of compliance with the volume change. It is clear that the model is adequate to express dynamics of an artificial muscle.
The aim of this article is to present a survey on applications of Pneumatic Artificial Muscles (PAMs). PAMs are highly non-linear pneumatic actuators where their elongation is proportional to the interval pressure. During the last decade, there has been a significant increase in the industrial and scientific utilization of PAMs due to their advantages such as high strength and small weight, while various types of PAMs with different technical characteristics have been appeared in the relative scientific literature. This article will summarize the key enabling applications in PAMs that are focusing in the following areas: a) Biorobotic, b) Medical, c) Industrial, and d) Aerospace applications.
Reports on the design of a biorobotic actuator. Biological
requirements are developed from published reports in the muscle
physiology literature whose parameters are extracted and applied in the
form of the Hill muscle model. Data from several vertebrate species
(rat, frog, cat, and human) are used to evaluate the performance of a
McKibben pneumatic actuator. The experimental results show the
force-length properties of the actuator are muscle-like, but the
force-velocity properties are not. The design of a hydraulic damper with
fixed orifices, placed in parallel with the McKibben actuator, is
proposed to improve the force-velocity performance. Simulation results
of this practical design indicate a significant improvement
McKibben artificial muscles : Pneumatic actuators with biomechanical intelligence
- G K Klute
- J M Czemiecki
- B Hannaford