Pneumatic Artificial Muscles Research Articles

Design, analysis and experiment of robust adaptive repetitive angle tracking control for a one-DOF manipulator driven by pneumatic artificial muscles

There exist nonlinearities, uncertainties and time-varying characteristics in the system dynamics of manipulators driven by pneumatic artificial muscles (PAMs), which makes the accurate dynamic modeling and controller design challenging. In this paper, a robust adaptive repetitive control scheme is proposed to solve the periodic-trajectory tracking problem for a one-degree of freedom (one-DOF) manipulator driven by two PAMs. First, the system model of the one-DOF PAM-driven manipulator is analyzed and derived. Next, during output constraint design by using a barrier Lyapunov function, a sliding mode surface is reasonably constructed to compensate for the differential term of time-varying constraint parameter. Then, with the help of Lipchitz condition, signal replacement technique and reparameterization are implemented to deal with nonparametric uncertainties in the manipulator system for the subsequent uncertainty compensation by using difference learning method and robust feedback strategy. Moreover, the stability of closed-loop PAM-driven manipulator is proven theoretically by using Lyapunov synthesis. In the end, comparative experiments are provided on a self-built PAM testbed to demonstrated the effectiveness of the proposed robust adaptive repetitive control scheme.

Non-linear adaptive control inspired by neuromuscular systems

Current paradigms for neuromorphic computing focus on internal computing mechanisms, for instance using spiking-neuron models. In this study, we propose to exploit what is known about neuro-mechanical control, exploiting the mechanisms of neural ensembles and recruitment, combined with the use of second-order overdamped impulse responses corresponding to the mechanical twitches of muscle-fiber groups. Such systems may be used for controlling any analog process, by realizing three aspects: Timing, output quantity representation and wave-shape approximation. We present an electronic based model implementing a single motor unit for twitch generation. Such units can be used to construct random ensembles, separately for an agonist and antagonist ‘muscle’. Adaptivity is realized by assuming a multi-state memristive system for determining time constants in the circuit. Using SPICE-based simulations, several control tasks were implemented which involved timing, amplitude and wave shape: The inverted pendulum task, the ‘whack-a-mole’ task and a handwriting simulation. The proposed model can be used for both electric-to-electronic as well as electric-to-mechanical tasks. In particular, the ensemble-based approach and local adaptivity may be of use in future multi-fiber polymer or multi-actuator pneumatic artificial muscles, allowing for robust control under varying conditions and fatigue, as is the case in biological muscles.

A Novel Variable Stiffness Compound Extensor-Pneumatic Artificial Muscle (CE-PAM): Design and Mathematical Model

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.

DEVELOPMENT OF A PNEUMATIC, ARTIFICIAL-MUSCLE- BASED PRESS FOR PUNCHING THIN METAL SHEETS

The present study examines the nonlinear behavior of pneumatic, artificial muscles and investigates their availability for producing pressing forces over the experimentally determined tensile forces. It covers the design and manufacturing studies of a test setup and a pneumatic, artificial-muscle-based press to achieve this goal. The press design consists of a single pneumatic artificial muscle to provide the main pressing force and another two to bring the press back to the neutral position. The proposed approach is considered sufficient for thin sheet-metal punching molds and fills a gap in the spectrum of pressing technologies. A sufficient level of pressing force for thin sheet-metal punching is found to be achievable using a single 40-mm-diameter, pneumatic, artificial muscle. The results show that the press can produce (9.1, 23.1 and 36.9) kN pressing forces at (200, 400 and 600) kPa air pressures, respectively.

Design Optimization of a Miniaturized Pneumatic Artificial Muscle and Experimental Validation

Miniaturized pneumatic artificial muscles (MPAMs) are widely utilized in various applications due to their unique characteristics, such as a high power-to-weight ratio, flexibility, and compatibility with the human environment, as well as being compact enough to fit within small-scale mechanical systems. Maximizing the amount of force generated by these actuators while keeping their dimensions minimized can greatly affect their efficiency. In this study, a formal design optimization problem was formulated to identify optimal sizes of MPAMs while maximizing their blocked force as a novel approach to address the issue of low force outputs of these actuators. A force model for an MPAM including various correction terms was derived to better predict the response behavior of the actuator. The optimization results reveal that an MPAM with a bladder that has an outer diameter of 6 mm and a thickness of 0.7 mm, as well as a braid angle of 72 degrees, can produce up to almost 239 N of blocked force if the inlet pressure is increased to 600 kPa. An MPAM with optimal parameters was subsequently fabricated and experimentally tested to evaluate its quasi-static response behavior and to validate the theoretical optimization results. Experimental tests were conducted under a wide range of pressures (0–300 kPa) to evaluate the variation of the generated blocked force versus inlet pressure. The overall error between the simulation and the experimental blocked forces was found to be less than 10%. This study represents a significant contribution to the design optimization of MPAMs, and the resulting optimal design offers potential applications in various fields, from soft robots to medical devices.

Adaptive fuzzy sliding mode control of an actuator powered by two opposing pneumatic artificial muscles

Pneumatic artificial muscle (PAM) is a potential actuator in human–robot interaction systems, especially rehabilitation systems. However, PAM is a nonlinear actuator with uncertainty and a considerable delay in characteristics, making control challenging. This study presents a discrete-time sliding mode control approach combined with the adaptive fuzzy algorithm (AFSMC) to deal with the unknown disturbance of the PAM-based actuator. The developed fuzzy logic system has parameter vectors of the component rules that are automatically updated by an adaptive law. Consequently, the developed fuzzy logic system can reasonably approximate the system disturbance. When operating the PAM-based system in multi-scenario studies, experimental results confirm the efficiency of the proposed strategy.

Analysis of the Antagonistic Arrangement of Pneumatic Muscles Inspired by a Biological Model of the Human Arm

Technical solutions based on biological models are the subject of research by a wide range of experts and mainly concern their mechanical use. When designing a suitable actuator, they use the physical methods of biological representatives, of which a large group consists of actuators generally referred to as artificial muscles, while another group uses compressed air as an energy carrier. In order to perform the measurements described in this article, a test mechanism based on the opposing arrangement of a pair of pneumatic muscles was constructed. Measurements on the test mechanism were made at set constant pressures in the range of 0.4 MPa to 0.6 MPa, while at each pressure, measurements were made for the counterload range from 0 N to 107.87 N. The measured values were recorded using a microcontroller and subsequently processed into graphic outputs. As part of the measurements, a comparative measurement of the same opposite arrangement of a pair of linear double-acting pneumatic actuators with a single-sided piston rod was also performed. The experiment and measurements were carried out in order to determine the suitability of using pneumatic artificial muscles in the selected arrangement for the implementation of a mechanism imitating the human arm. The target parameters of the experiment were the reaction speed of the course of force when filling the muscle under load and the reaction of the mechanism to a change in the set pressure in the pneumatic system. The summary of the comparison of the measured results is the content of the discussion in this article.

Discrete-Time Backstepping Sliding Mode Control for a 2-DOF PAM-Based Exoskeleton

This study aims to propose a discrete-time backstepping sliding mode control technique (BSMC) for regulating a pneumatic artificial muscle (PAM)-based exoskeleton used in rehabilitating human lower extremities. The PAM system is challenging to control due to its high nonlinearity, parameter uncertainty, and significant delay resulting from using compressed air. A backstepping control method is a recursive approach that systematically designs control laws for nonlinear and complicated systems. This technique ensures stable and robust system control, even in uncertain circumstances. Furthermore, the backstepping controller can handle high-order systems and guarantee high-precision tracking of a desired trajectory. The incorporation of sliding mode control is aimed at enhancing the performance of the robot PAM system by reducing chattering and reaching time. The algorithm employs Lyapunov functions and sliding surfaces to design the control signal for operating the system. The study concludes with experimental scenarios demonstrating the effectiveness of the proposed approach.

Development and validation of a flexible fetoscope for fetoscopic laser coagulation.

Fetoscopic laser coagulation for twin-to-twin transfusion syndrome is challenging for anterior placenta due to the rigidity of current tools. The capacity to keep entry port forces minimal is critical for this procedure, as is optimal coagulation distance and orientation. This work introduces technological tools to this end. A novel fetoscope is presented with a rigid shaft and a flexible steerable segment at the distal end. The steerable segment can bend up to 90[Formula: see text] even when loaded with a laser fiber. An artificial pneumatic muscle makes such acute bending possible while allowing for a low-weight and disposable device. The flexible fetoscope was validated in a custom-made phantom model to measure visual range and coagulation efficacy. The flexible fetoscope shows promising results when compared to a clinical rigid curved fetoscope to reach anterior targets. The new fetoscope was then evaluated in vivo (pregnant ewe) where it successfully coagulated placental vasculature. The flexible fetoscope improved the ability to achieve optimal coagulation angle and distance on anteriorly located targets. The fetoscope also showed the potential to lead fetoscopic laser coagulation and other fetal surgical procedures toward safer and more effective interventions.

A length-adjustable vacuum-powered artificial muscle for wearable physiotherapy assistance in infants.

Soft pneumatic artificial muscles are increasingly popular in the field of soft robotics due to their light-weight, complex motions, and safe interfacing with humans. In this paper, we present a Vacuum-Powered Artificial Muscle (VPAM) with an adjustable operating length that offers adaptability throughout its use, particularly in settings with variable workspaces. To achieve the adjustable operating length, we designed the VPAM with a modular structure consisting of cells that can be clipped in a collapsed state and unclipped as desired. We then conducted a case study in infant physical therapy to demonstrate the capabilities of our actuator. We developed a dynamic model of the device and a model-informed open-loop control system, and validated their accuracy in a simulated patient setup. Our results showed that the VPAM maintains its performance as it grows. This is crucial in applications such as infant physical therapy where the device must adapt to the growth of the patient during a 6-month treatment regime without actuator replacement. The ability to adjust the length of the VPAM on demand offers a significant advantage over traditional fixed-length actuators, making it a promising solution for soft robotics. This actuator has potential for various applications that can leverage on demand expansion and shrinking, including exoskeletons, wearable devices, medical robots, and exploration robots.

A hybrid orthosis combining functional electrical stimulation and soft robotics for improved assistance of drop-foot

Drop-foot is characterised by an inability to lift the foot, and affects an estimated 3 million people worldwide. Current treatment methods include rigid splints, electromechanical systems, and functional electrical stimulation (FES). However, these all have limitations, with electromechanical systems being bulky and FES leading to muscle fatigue. This paper addresses the limitations with current treatments by developing a novel orthosis combining FES with a pneumatic artificial muscle (PAM). It is the first system to combine FES and soft robotics for application to the lower limb, as well as the first to employ a model of their interaction within the control scheme. The system embeds a hybrid controller based on model predictive control (MPC), which combines FES and PAM components to optimally balance gait cycle tracking, fatigue reduction and pressure demands. Model parameters are found using a clinically feasible model identification procedure. Experimental evaluation using the system with three healthy subjects demonstrated a reduction in fatigue compared with the case of only using FES, which is supported by numerical simulation results.

Development of an Earthworm-Type Electrical Wire Installation Assistance Robot Using Artificial Muscles

In this study, an earthworm-type electrical wire installation assistance robot is proposed using pneumatic artificial muscles. This paper contributes to describing the design and experiments regarding a robot that can safely and automatically install electrical wires in complex conduits within a limited installation deadline. In this study, we aim to develop a robot to assist in the installation of electrical wires in conduits. This study contributes to the development of a robot for electrical wire installation assistance and the results from field experiments. Based on previous studies, a robot to install wires in long and narrow conduits has not been developed. In this study, the applicability of the robot to electrical wire installation assistance is presented. The results showed that the robot can assist in the installation of electrical wires at average speeds of 9.6 mm/s in straight conduits and 8.4 mm/s in multi-conduits. The results show the potential that the proposed robot can significantly reduce the workload in wire installation. Furthermore, the model of the wire installation robot enables estimation of the duration of the wire installation. Therefore, in this study, insights into the development of an in-pipe wire installation assistance robot are provided.

Vision-Based Soft Mobile Robot Inspired by Silkworm Body and Movement Behavior

Designing an inexpensive, low-noise, safe for individual, mobile robot with an efficient vision system represents a challenge. This paper proposes a soft mobile robot inspired by the silkworm body structure and moving behavior. Two identical pneumatic artificial muscles (PAM) have been used to design the body of the robot by sewing the PAMs longitudinally. The proposed robot moves forward, left, and right in steps depending on the relative contraction ratio of the actuators. The connection between the two artificial muscles gives the steering performance at different air pressures of each PAM. A camera (eye) integrated into the proposed soft robot helps it to control its motion and direction. The silkworm soft robot detects a specific object and tracks it continuously. The proposed vision system is used to help with automatic tracking based on deep learning platforms with real-time live IR camera. The object detection platform, named, YOLOv3 is used effectively to solve the challenge of detecting high-speed tiny objects like Tennis balls. The model is trained with a dataset consisting of images of Tennis balls. The work is simulated with Google Colab and then tested in real-time on an embedded device mated with a fast GPU called Jetson Nano development kit. The presented object follower robot is cheap, fast-tracking, and friendly to the environment. The system reaches a 99% accuracy rate during training and testing. Validation results are obtained and recorded to prove the effectiveness of this novel silkworm soft robot. The research contribution is designing and implementing a soft mobile robot with an effective vision system.

Non-Leaner Control on the Pneumatic Artificial Muscles: A Comparative Study Between Adaptive Backstepping and Conventional Backstepping Algorithms

Non-Leaner Control on the Pneumatic Artificial Muscles: A Comparative Study Between Adaptive Backstepping and Conventional Backstepping Algorithms

Multifunctional Soft Stackable Robots by Netting-Rolling-Splicing Pneumatic Artificial Muscles.

Soft robots equipped with multifunctionalities have been increasingly needed for secure, adaptive, and autonomous functioning in unknown and unpredictable environments. Robotic stacking is a promising solution to increase the functional diversity of soft robots, which are required for safe human-machine interactions and adapting in unstructured environments. However, most existing multifunctional soft robots have a limited number of functions or have not fully shown the superiority of the robotic stacking method. In this study, we present a novel robotic stacking strategy, Netting-Rolling-Splicing (NRS) stacking, based on a dimensional raising method via 2D-to-3D rolling-and-splicing of netted stackable pneumatic artificial muscles to quickly and efficiently fabricate multifunctional soft robots based on the same, simple, and cost-effective elements. To demonstrate it, we developed a TriUnit robot that can crawl 0.46 ± 0.022 body length per second (BL/s) and climb 0.11 BL/s, and can carry a 3 kg payload while climbing. Also, the TriUnit can be used to achieve novel omnidirectional pipe climbing including rotating climbing, and conduct bionic swallowing-and-regurgitating, multi-degree-of-freedom manipulation based on their multimodal combinations. Apart from these, steady rolling, with a speed of 0.19 BL/s, can be achieved by using a pentagon unit. Furthermore, we applied the TriUnit pipe climbing robot in panoramic shooting and cargo transferring to demonstrate the robot's adaptability for different tasks. The NRS stacking-driven soft robot here has demonstrated the best overall performance among existing stackable soft robots, representing a new and effective way for building multifunctional and multimodal soft robots in a cost-effective and efficient way.

Control of Pneumatic Artificial Muscle Actuated Two Degrees-of-Freedom Robot Using PD-Based Pulse Width Modulation Strategy With Feed-Forward Outer Control Loop

AbstractThis work presents a novel approach for the design and control of a two degrees-of-freedom (DOF) robotic manipulator driven by one pneumatic artificial muscle (PAM) and one passive spring for each of its DOFs. The required air pressure is supplied to the PAMs using fast-switching on/off type pneumatic flow control valves. The proposed control architecture uses a proportional-derivative (PD) controller with a feed-forward term in the outer control loop to correct the position errors using an approximate model of the system dynamics and approximate PAM force-contraction characteristics. An inner pressure regulator loop tracks the reference pressure signals supplied by the outer loop using a pulse width modulation (PWM) scheme to control the pneumatic valves based on the approximated inflation–deflation characteristics for the given pneumatic flow circuit. The proposed controller is unique for PAM actuated robots that simultaneously consider three levels of complications, namely, coupled dynamics of multi-degrees-of-freedom system, non-linearities in the force-contraction characteristics of PAMs, and non-linearities involved in the use of on/off type pneumatic flow control valves. Experiments carried out using a laboratory prototype validate the effectiveness of the proposed control scheme.

Modeling and dynamic analysis of a robotic arm with pneumatic artificial muscle by transfer matrix method

Pneumatic artificial muscle (PAM) has attracted significant attention owing to its safe and compliant physical properties in industrial manipulators, along with advanced service technologies. Since PAM is prone to large deformation problems, actuation control, and dynamic identification is required to perceive considering precise and fast computation. This article presents a methodology for accurate dynamic modeling and analysis of a planar robotic arm in the presence of large deformations caused by the artificial muscle. This novel planar robotic arm with pneumatic actuation and spring loaded in an antagonistic form is designed and fabricated. This article deals with the displacement analysis of a new type of PAM-actuated mechanism for large deformation. The aim is to find an accurate mathematical model of this robotic arm with motion nonlinearity. Since vibration can be generated in the articulating operations according to the dynamic behavior of PAM, a transfer-matrix method is proposed to explore the effect of flexibility undergoing planar flexural deformation. An explanation of the procedure through presenting its general formulation is employed to experiment. The discrete method is analyzed beside the rich datasets generated for actuator identification in the preliminary experimental study. The transfer matrices are determined considering the flexibilities whereas results are verified using MSC.ADAMS©. Experimental validation and numerical modeling confirm that the presented modeling methods help to improve the performance of the pneumatic muscle drives in high-precision manipulators. This study leaves room for further development of this algorithmic framework with a more complicated mechanism with soft pneumatic network actuators for various designs.

Stiffness optimization based on muscle fatigue and muscle synergy for passive waist assistive exoskeleton

PurposeThis paper aims to optimize the stiffness coefficient of the elastic element for a passive waist assistive exoskeleton (WAE). There is a tradeoff between stiffness coefficient of elastic element of the exoskeleton and work efficiency of the wearer, because elastic element affects original bending motion of the wearer and the force requirement of erector spinae is compensated by the other muscles. However, there is no accepted conclusion on how to determine the proper stiffness coefficient, especially with respected to the effort of groups of muscles, not only erector spinae.Design/methodology/approachIn this study, a consumption indicator based on muscle fatigue of seven muscles is proposed and a Bayesian-based human-in-the-loop optimization approach is adopted to optimize the stiffness coefficient. Pneumatic artificial muscles are used to replace the mechanical elastic part to adjust the assistive force automatically. The proposed optimization method is verified by the way of load-lifting experiments with three different conditions: without exoskeleton, with fixed air pressure and with optimized air pressure. Six subjects participated in the experiment and each experiment is performed in different day.FindingsCompared with No-Exo condition and static assistance condition, the parameter-optimized waist exoskeleton averagely reduces muscle fatigue of the six subjects by 45.30 ± 29.14% and 30.94 ± 30.29%, respectively. The experimental results indicate that the proposed method is effective to reduce muscle fatigue during stoop lifting task.Originality/valueThis paper provides a novel cost function construction method based on muscle fatigue and muscle synergy for passive WAE stiffness optimization.

Relationship between the shape of the elliptical knee joint and jumping height in a leg-type robot driven by pneumatic artificial muscle

The McKibben pneumatic actuator (MPA) is a soft actuator used for performing various practical functions in robots. Particularly, many dynamic robots have been realized using MPAs. However, there is a trade-off between torque generated by MPA and the range of motion of the joint. In this study, we focus on the jumping motion of a leg-type robot and use an elliptical pulley whose moment arm changes depending on the robot’s posture. To confirm the effectiveness of the elliptical pulley, the relationship between the knee joint pulley (patella) shape and jumping height was analyzed by simulation, and the shape of the patella maximizing jumping height was determined. It was shown that an elongated elliptical patella shape is more effective for the jumping motion than a circular one. Furthermore, the effectiveness of the analytically determined patella shape was confirmed by experiments using an actual robot.

Implementation of Basic Reflex Functions on Musculoskeletal Robots Driven by Pneumatic Artificial Muscles

Musculoskeletal robots hold significant potential for the design of future robots. One of the challenges is the possibility of output delays from the muscles, which may prevent higher centers from compensating during sudden disturbances. The reflex system, widely observed in animals, is viewed as an efficient mechanism for overcoming this challenge. Specifically, the Ia and Ib reflex pathways, as the sensory pathways originating from muscle sensory receptors, are considered to contribute to the responsiveness and convergence of the feedback system with the dynamics of the musculoskeletal body. In this study, we propose a basic reflex system that can be implemented into a robot arm driven by pneumatic artificial muscles (PAMs) and investigate its effectiveness through two experiments: a sudden force shock and a position constraint. The results demonstrate that the reflex behavior is capable of reducing the impact of disturbances, with the Ia reflex pathways providing an immediate response to disturbances and the Ib reflex pathways curbing excessive output force.