Pneumatic Artificial Muscles Research Articles

A High-Strength, Highly-Flexible Robotic Strap for Harnessing, Lifting, and Transferring Humans

Safely harnessing and lifting humans for transfer is a challenging unsolved problem for current robots because of the high forces and gentle interaction necessary to do so. Straps, however, are highly beneficial for manually performing this task primarily because of their simultaneously high tensile strength and high compliant bending flexibility. We propose the Robotic Strap, a novel concept and design for a new type of manipulator that can passively harness and lift humans safely as straps can, as well as actively articulate itself around the human into the desired harnessing configurations. The passive structure is characterized by the high tensile strength and bending flexibility of straps. The design consists of a hyper-articulated backbone with rolling-contact joints fastened by dual-pulley cord mechanisms, and soft thin McKibben artificial muscles embedded along its length that collectively actuate the joints. We present the concept, framework, realization, and implementation of the Robotic Strap design, as well as model and experimentally validate the key characteristics. The prototype has a tensile load capacity of 1314.0 N, a maximum joint bending resistance of <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$&lt;\! 0.1$</tex-math></inline-formula> Nm, and successfully demonstrated safe and effective harnessing and lifting of three human participants without any manual intervention.

Parametrically Excited Nonlinear Pneumatic Artificial Muscle Under Hard Excitation: A Theoretical and Experimental Investigation

In this work, a single degree of freedom system consisting of a mass and a Pneumatic Artificial Muscle subjected to time-varying pressure inside the muscle is considered. The system is subjected to hard excitation and the governing equation of motion is found to be that of a nonlinear forced and parametrically excited system under super- and sub-harmonic resonance conditions. The solution of the nonlinear governing equation of motion is obtained using the method of multiple scales. The time and frequency response, phase portraits, and basin of attraction are plotted to study the system response along with the stability and bifurcations. Further, the different muscle parameters are evaluated by performing experiments which are further used for numerically evaluating the system response using the theoretically obtained closed form equations. The responses obtained from the experiments are found to be in good agreement with those obtained from the method of multiple scales. With the help of examples, the procedure to obtain the safe operating range of different system parameters is illustrated.

Effect of Material Properties on Fiber-Shaped Pneumatic Actuators Performance

Thin fiber-shaped pneumatic artificial muscle (PAM) can generate contractile motions upon stimulation, and it is well known for its good compliance, high weight-to-power ratio, resemblance to animal muscle movements, and, most importantly, the capability to be integrated into fabrics and other textile forms for wearable devices. This fiber-shaped device, based on McKibben technology, consists of an elastomeric bladder that is wrapped around by a braided sleeve, which transfers radial expansion into longitudinal contraction due to the change in the sleeve’s braiding angle while being inflated. This paper investigates the effect of material properties on fiber-shaped PAM’s behavior, including the braiding yarn and bladder’s dimensional and mechanical properties. A range of samples with combinations of yarn and bladder parameters were developed and characterized. A robust fabrication process verified through several calibration and control experiments of PAM was applied, which ensured a more accurate characterization of the actuators. The results demonstrate that material properties, such as yarn stiffness, yarn diameter, bladder diameter, and bladder hardness, have significant effects on PAMs’ deformation strains and forces generated. The findings can serve as fundamental guidelines for the future design and development of fiber-shaped pneumatic actuators.

Fluidic Hardware Strategies for Powering Combined Negative‐ and Positive‐Pressure Artificial Muscles

The performance of pneumatic artificial muscles (PAMs) depends in large part on the fluidic hardware used to add and remove air from their volume. A complete fluidic system usually contains tubing, pneumatic regulators, pneumatic valves, and pneumatic pumps. However, for most PAMs, the performance of the actuator depends on how fast air can be taken into and out of the chamber as the presence of a single chamber entails relatively simple fluidic strategies. In the previous work, a type of PAM called hyperbaric vacuum artificial muscles (Hyper‐VAM) which utilizes a negative‐pressure inner chamber placed inside a positive‐pressure outer chamber has been introduced. Herein, advanced fluidic strategies for this actuator by making use of the pressure equilibrium between these two chambers as the building block for advanced fluidic strategies are investigated. It is shown that it is possible to operate the Hyper‐VAM in sub‐ and hyper‐atmospheric conditions during closed‐loop actuation and to use the atmosphere as a natural pump starting from a sub‐ or hyper‐atmospheric equilibrium. Herein, these strategies are demonstrated and compared to basic fluidic strategies and fluidic systems capable of implementing cyclic actuation are demonstrated using these strategies.

The Folded Pneumatic Artificial Muscle (foldPAM): Towards Programmability and Control via End Geometry

Soft pneumatic actuators have seen applications in many soft robotic systems, and their pressure-driven nature presents unique challenges and opportunities for controlling their motion. In this work, we present a new concept: designing and controlling pneumatic actuators via end geometry. We demonstrate a novel actuator class, named the folded Pneumatic Artificial Muscle (foldPAM), which features a thin-filmed air pouch that is symmetrically folded on each side. Varying the folded portion of the actuator changes the end constraints and, hence, the force-strain relationships. We investigated this change experimentally by measuring the force-strain relationship of individual foldPAM units with various lengths and amounts of folding. In addition to static-geometry units, an actuated foldPAM device was designed to produce continuous, on-demand adjustment of the end geometry, enabling closed-loop position control while maintaining constant pressure. Experiments with the device indicate that geometry control allows access to different areas on the force-strain plane and that closed-loop geometry control can achieve errors within 0.5% of the actuation range.

Development of Pneumatic Artificial Rubber Muscle Using Segmented Shape-Memory Polymer Sheets

We have developed a pneumatic artificial rubber muscle using two shape-memory polymer (SMP) sheets. We attached the SMP sheets to a linear pneumatic artificial rubber muscle. Utilizing the large difference in the elastic modulus below and above the glass transition temperature, the shape fixity and shape recovery of SMPs, the bending direction and the initial shape can be changed. In this study, in order to increase the bending motion range, we developed a segmented SMP sheet with embedded electrical heating wires, and evaluated its mechanical properties using bending and tensile tests. Moreover, we attached such sheets to an artificial muscle and evaluated the bending motion. Bending tests showed that segmenting the SMP sheets greatly reduced their bending stiffness. In tensile tests at temperatures below the glass transition temperature, it was found that the artificial muscle with the attached sheet withstood high elongating loads without failure. Attachment of such segmented SMP sheets to an artificial muscle resulted in an increased bending angle. Through isotonic and isometric tests, we showed that the prototype actuator could bend in two directions.

Development of a Bimanual Wearable Force Feedback Device with Pneumatic Artificial Muscles, MR Fluid Brakes, and Sensibility Evaluation Based on Pushing Motion

In a virtual reality (VR) space, wearing a head-mounted display can help with the visualization of objects; however, users cannot experience realistic tactile sensations. Recently, several force feedback devices have been developed, including wearable devices that use straight-fiber-type pneumatic muscles and magnetorheological fluids. This allows the devices to render elastic, frictional, and viscous forces during spatially unrestricted movement. Nevertheless, a problem remains in that previous devices could handle many bilateral upper limb movement tasks. Therefore, this study aims to develop a device that can handle movements that interact with both arms. Based on experiments concerning the pushing motion in a VR space, the influence of the pseudo force sense was determined to not be small. In addition, we confirmed that the force sensation presented by this system was more realistic when the robot was operated with both arms than when operated with the right arm.

An Adaptive Sliding Mode Controller for a PAM-based Actuator

The Pneumatic Artificial Muscle (PAM) is a promising actuator for developing the human-robot interaction system. However, modeling and controlling PAM-based actuators are a significant difficulty due to the inherent uncertainty and hysteresis of PAM. Besides, the control approach of a PAM-based system also deals with unknown disturbances that always exist in any system. This study developed a sliding mode controller that employs an adaptive law to deal with issues and improve control performance. Furthermore, the stability of the proposed controller is proven based on the Lyapunov stability criterion. Finally, through a series of tests, the effectiveness of the proposed control approach is verified.

Advances in artificial muscles: A brief literature and patent review.

Background: Artificial muscles are an active research area now. Methods: A bibliometric analysis was performed to evaluate the development of artificial muscles based on research papers and patents. A detailed overview of artificial muscles' scientific and technological innovation was presented from aspects of productive countries/regions, institutions, journals, researchers, highly cited papers, and emerging topics. Results: 1,743 papers and 1,925 patents were identified after retrieval in Science Citation Index-Expanded (SCI-E) and Derwent Innovations Index (DII). The results show that China, the United States, and Japan are leading in the scientific and technological innovation of artificial muscles. The University of Wollongong has the most publications and Spinks is the most productive author in artificial muscle research. Smart Materials and Structures is the journal most productive in this field. Materials science, mechanical and automation, and robotics are the three fields related to artificial muscles most. Types of artificial muscles like pneumatic artificial muscles (PAMs) and dielectric elastomer actuator (DEA) are maturing. Shape memory alloy (SMA), carbon nanotubes (CNTs), graphene, and other novel materials have shown promising applications in this field. Conclusion: Along with the development of new materials and processes, researchers are paying more attention to the performance improvement and cost reduction of artificial muscles.

Pneumatic Artificial Muscles (PAMs) Identification for Actuating a Wrist-Joint Rehabilitation Robot

Pneumatic Artificial Muscles (PAMs) Identification for Actuating a Wrist-Joint Rehabilitation Robot

Characterization and Joint Control Study of Pneumatic Artificial Muscles

Physical dynamic characteristics and control studies were conducted for pneumatic artificial muscle (PAM), the core component of the drive of lower limb rehabilitation robots. Firstly, a static model and a dynamic model of the pneumatic artificial muscle were established. Then a test bench was designed to perform dynamic characteristic test simulations and experiments. After that, the pneumatic artificial muscle test bench was designed to simulate and test its dynamic characteristics. Finally, a typical PID (Proportional Integral Derivative) controller was built to perform control simulations and step control experiments for the pneumatic artificial muscle. Experiments show that the PID can achieve stable and accurate tracking of the signal and meet the application requirements of PAM.

Design, Construction and Control of a Manipulator Driven by Pneumatic Artificial Muscles

This paper describes the design, construction and experimental testing of a single-joint manipulator arm actuated by pneumatic artificial muscles (PAMs) for the tasks of transporting and sorting work pieces. An antagonistic muscle pair is used in a rotational sense to produce a required torque on a pulley. The concept, operating principle and elementary properties of pneumatic muscle actuators are explained. Different conceptions of the system realizations are analyzed using the morphological-matrix conceptual design framework and top-rated solution was practically realized. A simplified, control-oriented mathematical model of the manipulator arm driven by PAMs and controlled with a proportional control valve is derived. The model is then used for a controller design process. Fluidic muscles have great potential for industrial applications and assembly automation to actuate new types of robots and manipulators. Their characteristics, such as compactness, high strength, high power-to-weight ratio, inherent safety and simplicity, are worthy features for advanced manipulation systems. The experiments were carried out on a practically realized manipulator actuated by a pair of muscle actuators set into an antagonistic configuration. The setup also includes an original solution for the subsystem to add work pieces in the working space of the manipulator.

Robotized Knee-Ankle-Foot Orthosis-Assisted Gait Training on Genu Recurvatum during Gait in Patients with Chronic Stroke: A Feasibility Study and Case Report.

Genu recurvatum (knee hyperextension) is a common problem after stroke. It is important to promote the coordination between knee and ankle movements during gait; however, no study has investigated how multi-joint assistance affects genu recurvatum. We are developing a gait training technique that uses robotized knee-ankle-foot orthosis (KAFO) to assists the knee and ankle joints simultaneously. This report aimed to investigate the safety of robotized KAFO-assisted gait training (Experiment 1) and a clinical trial to treat genu recurvatum in a patient with stroke (Experiment 2). Six healthy participants and eight patients with chronic stroke participated in Experiment 1. They received robotized KAFO-assisted gait training for one or 10 sessions. One patient with chronic stroke participated in Experiment 2 to investigate the effect of robotized KAFO-assisted gait training on genu recurvatum. The patient received the training for 30 min/day for nine days. The robot consisted of KAFO and an attached actuator of four pneumatic artificial muscles. The assistance parameters were adjusted by therapists to prevent genu recurvatum during gait. In Experiment 2, we evaluated the knee joint angle during overground gait, Fugl-Meyer Assessment of lower extremity (FMA-LE), modified Ashworth scale (MAS), Gait Assessment and Intervention Tool (G.A.I.T.), 10-m gait speed test, and 6-min walk test (6MWT) before and after the intervention without the robot. All participants completed the training in both experiments safely. In Experiment 2, genu recurvatum, FMA-LE, MAS, G.A.I.T., and 6MWT improved after robotized KAFO-assisted gait training. The results indicated that the multi-joint assistance robot may be effective for genu recurvatum after stroke.

Active textile: woven-cloth-like mechanisms consist of thin McKibben actuators

ABSTRACT Pneumatic artificial muscles have some advantages. Especially, the flexibility of artificial muscles contributes to compose novel mechanisms. Authors succeeded in manufacturing novel soft mechanisms that are composed of only woven artificial muscles and strings. We called this mechanism active textile. The structure is uniformed with woven artificial muscles; nevertheless, the forms and movements of mechanisms are diverse. We aim to establish a design method for these active textiles. We reported that deformations of active textiles are changed by woven structures. In addition to that, wefts' characteristics such as cross-sectional shape, bending stiffness and elasticity determine the characteristic of a textile. Deformations of active textiles are caused by the contraction and the expansion of thin McKibben muscles. In this paper, authors focus on the contraction and curvature deformation of the active textile due to the drive of the artificial muscles.We fabricated active textiles with different wefts and different weave structures.Contraction and bending deformations of active textiles in the warp and weft directions are assumed geometrically. In addition, we verified the validity by experiments.

Posture Estimation by Clustering Pressure Information and Control Implementation for Pneumatically Driven Gait-Assistive Robot

Pneumatic artificial muscles (PAMs) are light and soft, and are expected to be applied to gait assistance robots with multiple actuators on the human body. The PAMs can be used as not only actuators, but also sensors to detect the gait phase by using their deformable bodies whose internal pressure changes in response to the wearer’s gait. However, conventional methods to detect the gait phase by PAMs have targeted single point detection in a gait phase and used for only ON/OFF control of the PAM actuators. In this study, we proposed an algorithm to estimate the postural state of the wearer, especially the state of both hip joints, from the internal pressure information of the PAMs with a small amount of calculation by using clustering method, and succeeded in controlling the PAMs’ pressure continuously based on this algorithm. The effectiveness of the proposed control method was verified through gait-assistive experiments using a treadmill. We measured the electromyogram of the adductor longus muscle under 3 subjects and a one-sided significant difference test was performed. As a result, we confirmed significant differences at the 1% significance level for 2 subjects and at the 10% significance level for the remaining subject, allowing us to evaluate the effectiveness of the proposed PAM control strategy.

Development and Evaluation of body weight reducing walker driven by pneumatic artificial muscle

Development and Evaluation of body weight reducing walker driven by pneumatic artificial muscle

Manufacturing and Design of Inflatable Kirigami Actuators

Kirigami structures are human-made structures that enable the fabrication of stretchable structures from materials with limited stretching properties through the geometrical re-orientation of their features. But these structures are generally complex in shape with many edges which makes their precise fabrication difficult without the use of engineering manufacturing tools. Building a pneumatic artificial muscle making use of kirigami concepts would be useful as the structure could make use of the re-orientation of its features rather than just relying on the stretching or expansion of the structure, but the structure must remain airtight despite its complex shape which would result in air channels needing to be sealed along each edge of this structure. This letter introduces a simple three-step manufacturing method capable of manufacturing inflatable kirigami actuators with networks of air channels with a wide range of shapes. Three novel inflatable kirigami actuators designs are presented making use of this manufacturing process: parallel kirigami actuators, out-of-plane kirigami actuators and spiral kirigami actuators. These actuators are capable of contraction ratios far exceeding those of previous inflatable pneumatic artificial muscles and can be readily implemented as active electronic muscles. This manufacturing method for inflatable kirigami actuators opens the door to a wide range of new inflatable actuator designs and could lead to further optimized designs for wearable uses.

Two-link Manipulator Driven by a Pair of Antagonistic Rubber Artificial Muscle

Pneumatic rubber artificial muscles have been extensively researched as a driving device capable of soft movements that are compatible with humans, and are expected to be applied to human friendly robots. However, it is difficult in principle to achieve high-precision positioning and high-rigidity position retention due to low stiffness and delayed response as a result of air compressibility. Normally, a 2-link manipulator requires 4 (2 pairs) artificial muscles, but here, by attaching two MR brakes to each axis and switching the drive shaft, a manipulator that controls a 2-link manipulator with 2 (1 pair) artificial muscles, is proposed.

Error Tracking-Based Neuro-Adaptive Learning Control for Pneumatic Artificial Muscle Systems With Output Constraint

Error Tracking-Based Neuro-Adaptive Learning Control for Pneumatic Artificial Muscle Systems With Output Constraint

Increase of Deformation of 2-DOF Weaved Tube Plane Surface Soft Actuator with Extensional Pneumatic Artificial Muscles

Increase of Deformation of 2-DOF Weaved Tube Plane Surface Soft Actuator with Extensional Pneumatic Artificial Muscles