Pneumatic Muscle Research Articles

空気圧ゴム人工筋を利用した建設作業支援スーツのアシストゲイン設定に関する考察

空気圧ゴム人工筋を利用した建設作業支援スーツのアシストゲイン設定に関する考察

空気圧ゴム人工筋を使用した下肢用パワーアシストウェアの開発

空気圧ゴム人工筋を使用した下肢用パワーアシストウェアの開発

An artificial flexible robot arm based on pneumatic muscle actuators

The purpose of this paper is to develop a novel human-friendly artificial flexible robot arm using four parallel-connected pneumatic muscle actuators (PMAs). The PMA is a flexible silicone rubber actuator which has some behaviors nearest to the real biological muscle including translational and rotational motions. An inverse kinematic model for the motion control is also developed. Finally, from experiment results, it is proved that not only the axial contraction control of a single PMA but also the attitude control of the whole pneumatic flexible robot arm using PID controller are satisfactory.

Position/Stiffness Control of Antagonistic Bionic Joint Driven by Pneumatic Muscles Actuators

Position/Stiffness Control of Antagonistic Bionic Joint Driven by Pneumatic Muscles Actuators

Design Principles for Improved Fatigue Life of High-Strain Pneumatic Artificial Muscles

Abstract The fatigue life of pneumatic artificial muscles (PAMs) is a limitation to the development of reliability-intensive applications of soft robots in fields such as medical robotics, transportation, and industrial manufacturing. This article aims at improving the fatigue life of PAMs by (1) providing design principles for durable PAMs under high strains and (2) demonstrating these design principles by developing a representative optimal extensible pneumatic muscle (EPM) in the context of a soft surgical robot case study. Representative performance requirements are derived from an image-guided surgical robot taken as a case study. An experimental design study over relevant EPM geometries reveals three basic fatigue principles governing the failure of PAMs: fatigue limit, abrasion wear, and Hertz contact stress. Using these principles, a new extensible pneumatic muscle made of a silicone tube and a continuous orthotropic restraining sleeve is designed and characterized in terms of performance and fati...

Development of a body weight support system using pneumatic muscle actuators: Controlling and validation

This study introduces the development of a new body weight support system using pneumatic actuators for gait training. The main scope of this work is to provide a new design, validation, and assessment for active body weight support systems to reproduce a subject’s normal walking behavior. Based on the assessments and its evaluations, the novel body weight support system using pneumatic muscle actuators shows many advantageous characteristics, such as simplicity, low cost, maintenance of a constant unloading force, and ease of control of the supported force. The capability of the novel body weight support system to generate unloading forces that track the center of pressure, because it switches from left to right and vice versa as the subject walks, is especially interesting.

Adaptive tracking control of multi-link robots actuated by pneumatic muscles with additive disturbances

SUMMARYIn this paper, we study the problem of adaptive position tracking for a multi-link robot driven by two opposing pneumatic muscle groups with additive disturbances. In contrast to widely used sliding mode control methods, the proposed controller is continuous and able to prevent chattering. All physical parameters of the robot and the pneumatic muscles, including pneumatic muscle coefficients, link lengths and moments of inertia are unknown and can be time-varying and the unknown additive disturbances can be discontinuous. Under these conditions, we prove that closed-loop trajectories of all of the joint positions can track any C1 joint reference signal. The joint errors will be within a prescribed error bound in a finite time. The adaptive controller only uses the reference signal, not its derivative. The continuous adaptive gain is one-dimensional. Simulations including a two-link robot arm with friction and realistic muscle models are presented to demonstrate the robustness of the adaptive control under severe changes of the system parameters. In all simulations, the joint positions can track C1 trajectories and all errors are within the prescribed error bound in the same time frame, even though the muscle parameters are vastly different.

Accelerometer-based estimation and modal velocity feedback vibration control of a stress-ribbon bridge with pneumatic muscles

Lightweight footbridges are very elegant but also prone to vibration. By employing active vibration control, smart footbridges could accomplish not only the architectural concept but also the required serviceability and comfort. Inertial sensors such as accelerometers allow the estimation of nodal velocities and displacements. A Kalman filter together with a band-limited multiple Fourier linear combiner (BMFLC) is applied to enable a drift-free estimation of these signals for the quasi-periodic motion under pedestrian excitation without extra information from other kinds of auxiliary sensors. The modal velocities of the structure are determined by using a second Kalman filter with the known applied actuator forces as inputs and the estimated nodal displacement and velocities as measurements. The obtained multi-modal velocities are then used for feedback control. An ultra-lightweight stress-ribbon footbridge built in the Peter-Behrens- Halle at the Technische Universitat Berlin served as the research object. Using two inertial sensors in optimal points we can estimate the dominant modal characteristics of this bridge. Real-time implementation and evaluation results of the proposed estimator will be presented in comparison to signals derived from classical displacement encoders. The real-time estimated modal velocities were applied in a multi-modal velocity feedback vibration control scheme with lightweight pneumatic muscle actuators. Experimental results demonstrate the feasibility of using inertial sensors for active vibration control of lightweight footbridges.

Technical concept and evaluation of a novel shoulder simulator with adaptive muscle force generation and free motion

Abstract The human shoulder is one of the most complex joints of the human body, and due to the high range of motion and the complex soft tissue apparatus prone to injuries. Surgical therapies and joint replacements often lead to unsatisfactory results. To improve the understanding of the complex biomechanics of the shoulder, experimental investigations have to be conducted. For this purpose a new shoulder simulator with an innovative muscle force generation was developed. On the basis of a modular concept six artificial pneumatic muscles were integrated to represent the functionally most important muscles of the shoulder joint, whereby a free and controlled movement of the humerus can be conducted. For each muscle individual setpoints for muscle length control based on a user defined shoulder movement for any artificial or cadaver specimen are created by manual motion “Teach-In”. Additional to muscle forces and lengths, optical tracking and a joint force measurement is used to enable different biomechanical studies of the shoulder joint. This paper describes the technical setup as well as the control strategy and first results of its experimental functional validation.

Lower Limb Wearable Robots for Assistance and Rehabilitation: A State of the Art

Neurologic injuries, such as stroke, spinal cord injuries, and weaknesses of skeletal muscles with elderly people, may considerably limit the ability of this population to achieve the main daily living activities. Recently, there has been an increasing interest in the development of wearable devices, the so-called exoskeletons, to assist elderly as well as patients with limb pathologies, for movement assistance and rehabilitation. In this paper, we review and discuss the state of the art of the lower limb exoskeletons that are mainly used for physical movement assistance and rehabilitation. An overview of the commonly used actuation systems is presented. According to different case studies, a classification and comparison between different types of actuators is conducted, such as hydraulic actuators, electrical motors, series elastic actuators, and artificial pneumatic muscles. Additionally, the mainly used control strategies in lower limb exoskeletons are classified and reviewed, based on three types of human-robot interfaces: the signals collected from the human body, the interaction forces between the exoskeleton and the wearer, and the signals collected from exoskeletons. Furthermore, the performances of several typical lower limb exoskeletons are discussed, and some assessment methods and performance criteria are reviewed. Finally, a discussion of the major advances that have been made, some research directions, and future challenges are presented.

Effects of Bladder Geometry in Pneumatic Artificial Muscles

Designing optimal pneumatic muscles for a particular application requires an accurate model of the hyperelastic bladder and how it influences contraction force. Previous work does not fully explain the influence of bladder prestrain on actuator characteristics. We present here modeling and experimental data on the actuation properties of artificial muscles constructed with varying bladder prestrain and wall thickness. The tests determine quasi-static force–length relationships during extension and contraction, for muscles constructed with unstretched bladder lengths equal to 55%, 66%, and 97% of the stretched muscle length and two different wall thicknesses. Actuator force and maximum contraction length are found to depend strongly on both the prestrain and the thickness of the rubber, making existing models inadequate for choosing bladder geometry. A model is presented to better predict force–length characteristics from geometric parameters, using a novel thick-walled tube calculation to account for the nonlinear elastic properties of the bladder. It includes axial force generated by stretching the bladder lengthwise, and it also describes the hoop stress created by radial expansion of the muscle that partially counteracts the internal fluid pressure exerted outward on the mesh. This effective reduction in pressure affects both axial muscle force and mesh-on-bladder friction. The rubber bladder is modeled as a Mooney–Rivlin incompressible solid. The axial force generated by the mesh is found directly from contact forces rather than from potential energy. Modeling the bladder as a thin-walled tube gives a close match to experimental data on wall thickness, but a thick-walled bladder model is found to be necessary for explaining the effects of prestrain.

Study Concerning the Energy-to-Mass Ratio in Pneumatic Muscles

Study Concerning the Energy-to-Mass Ratio in Pneumatic Muscles

Cross-coupling integral adaptive robust posture control of a pneumatic parallel platform

A pneumatic parallel platform driven by an air cylinder and three circumambient pneumatic muscles was considered. Firstly, a mathematical model of the pneumatic servo system was developed for the MIMO nonlinear model-based controller designed. The pneumatic muscles were controlled by three proportional position valves, and the air cylinder was controlled by a proportional pressure valve. As the forward kinematics of this structure had no analytical solution, the control strategy should be designed in joint space. A cross-coupling integral adaptive robust controller (CCIARC) which combined cross-coupling control strategy and traditional adaptive robust control (ARC) theory was developed by back-stepping method to accomplish trajectory tracking control of the parallel platform. The cross-coupling part of the controller stabilized the length error in joint space as well as the synchronization error, and the adaptive robust control part attenuated the adverse effects of modelling error and disturbance. The force character of the pneumatic muscles was difficult to model precisely, so the on-line recursive least square estimation (RLSE) method was employed to modify the model compensation. The projector mapping method was used to condition the RLSE algorithm to bound the parameters estimated. An integral feedback part was added to the traditional robust function to reduce the negative influence of the slow time-varying characteristic of pneumatic muscles and enhance the ability of trajectory tracking. The stability of the controller designed was proved through Laypunov’s theory. Various contrast controllers were designed to testify the newly designed components of the CCIARC. Extensive experiments were conducted to illustrate the performance of the controller.

Thermally activated paraffin-filled McKibben muscles

McKibben artificial muscles are one of the most pragmatic contractile actuators, offering performances similar to skeletal muscles. The McKibben muscles operate by pumping pressurized fluid into a bladder constrained by a stiff braid so that tensile force generated is amplified in comparison to a conventional hydraulic ram. The need for heavy and bulky compressors/pumps makes pneumatic or hydraulic McKibben muscles unsuitable for microactuators, where a highly compact design is required. In an alternative approach, this article describes a new type of McKibben muscle using an expandable guest fill material, such as temperature-sensitive paraffin, to achieve a more compact and lightweight actuation system. Two different types of paraffin-filled McKibben muscles are introduced and compared. In the first system, the paraffin-filled McKibben muscle is simply immersed in a hot water bath and generates isometric forces up to 850 mN and a free contraction strain of 8.3% at 95°C. In the second system, paraffin is heated directly by embedded heating elements and exhibits the maximum isometric force of 2 N and 9% contraction strain. A quantitative model is also developed to predict the actuation performance of these temperature sensitive McKibben muscles as a function of temperature.

New wearable exoskeleton for gait rehabilitation assistance integrated with mobility system

Gait and mobility in patients with gait impairment are important in maintaining and improving their physical and psychological health and to return to society. Thus, the aims of the current study were to develop and evaluate a new wearable exoskeleton for gait rehabilitation assistance integrated with a mobility system (RehabWheel) for patients with gait impairment. A wearable exoskeleton was controlled by artificial pneumatic muscles to mimic joint movement; appropriate gait training was then undertaken. In total, 13 healthy males participated in evaluating RehabWheel by comparing joint angle kinematics and muscle activation patterns during walking over ground with RehabWheel and normal gaits. The joint angle kinematics of the hip and knee joints with RehabWheel were similar to those of normal gait despite differences in their magnitude. Additionally, muscle activations in the hip and knee joints were less during RehabWheel gait than normal gait and were associated with joint kinematics. These findings indicate that RehabWheel may have potential for incorporation into gait rehabilitative training assistance combined with a wheelchair platform for movement. This study is valuable for the initial identification of the practical feasibility of this new mobility system with both mobility and gait rehabilitation functions.

Design and Evaluation of the RUPERT Wearable Upper Extremity Exoskeleton Robot for Clinical and In-Home Therapies

A wearable, portable, low-cost, and easy-to-use upper extremity exoskeleton robot, RUPERT, is presented here for clinical and in-home therapies of patients who have survived a stroke. The robot system has five degrees-of-freedom and is driven by compliant and safe pneumatic muscles. Its primary function is to assist the movement of an affected arm in 3-D space and perform a daily training program in a virtual environment. Subjects are recruited for experiments of both clinical and in-home therapies. While using RUPERT, most subjects exhibited significant improvements in various functional measures. During their in-home therapy trials, subjects expressed enthusiasm regarding the modules and the use of our robotic system. The experimental results look promising and the proposed robotic system exhibits a good prospect for a future commercialized in-home therapy product.

Study Concerning the Hysteresis of Pneumatic Muscles

A known phenomenon during the contraction/expansion cycles of pneumatic muscles is the occurrence of hysteresis, caused by the elasticity of their component materials. The inherent hysteresis manifest in pneumatic muscles increases the non-linearity of the systems they are included in and consequently the complexity of the related control systems. The paper discusses a number of experimental results obtained for the hysteresis related behaviour of a small size Festo pneumatic muscle, where the specific hysteresis loops were highlighted via isotonic testing.

Impedance Control of an Intrinsically Compliant Parallel Ankle Rehabilitation Robot

Robot-aided physical therapy should encourage subject’s voluntary participation to achieve rapid motor function recovery. In order to enhance subject’s cooperation during training sessions, the robot should allow deviation in the prescribed path depending on the subject’s modified limb motions subsequent to the disability. In the present work, an interactive training paradigm based on the impedance control was developed for a lightweight intrinsically compliant parallel ankle rehabilitation robot. The parallel ankle robot is powered by pneumatic muscle actuators (PMAs). The proposed training paradigm allows the patients to modify the robot imposed motions according to their own level of disability. The parallel robot was operated in four training modes namely position control, zero-impedance control, nonzero-impedance control with high compliance, and nonzero-impedance control with low compliance to evaluate the performance of proposed control scheme. The impedance control scheme was evaluated on 10 neurologically intact subjects. The experimental results show that an increase in robotic compliance encouraged subjects to participate more actively in the training process. This work advances the current state of the art in the compliant actuation of parallel ankle rehabilitation robots in the context of interactive training.

Echo state network based predictive control with particle swarm optimization for pneumatic muscle actuator

To realize a high-accurate trajectory tracking control of the Pneumatic Muscle Actuator (PMA), a comprehensive single-layer neural network (SNN) and Echo State Neural Network (ESN) based predictive control with particle swarm optimization (PSO) is proposed, where PSO optimizes the weight coefficients of the SNN and the ESN state is updated by the online Recursive Least Square (RLS) algorithm for predictive control. Based on Lyapunov theory, the learning convergence theorem is established to guarantee the stability of the closed-loop system. The proposed control algorithm is employed for the trajectory tracking control of PMA. The interface between the xPC target and the virtual instrument was established to realize the real-time control and to make the control more accurate and stable. Both simulations and experiments were performed to verify the proposed methods. The experiments were conducted on the real PMA system, which was connected with the xPC target system. The results demonstrate the validity of PMA as well as the effectiveness of the novel control algorithm.

Analysis of possibilities for application of airless tires for motor-and-tractor vehicles and agricultural machinery

Ensuring of mobility and efficiency plays the key role in solution of problem of providing the stable, safe and efficient operation of mobile terrestrial motor-and-tractor vehicles, agricultural machinery, transport and technological complexes. At the present stage of development, for achievement of desired values of traction force and mobility, the application of airless tires becomes rational. This type of tires excludes the loss of mobility because of the loss of excessive internal gas pressure, and it is able to provide higher traction force in comparison with conventional pneumatic tires. As a result of analysis, it is found that the airless tires have characteristics similar to pneumatic ones, and they are fully capable to replace them. However, the airless tires cannot change stiffness properties during operation, in contrast to the pneumatic ones, in which the variation of value of excessive gas pressure inside the tire leads to stiffness change. Therefore, it is necessary to introduce in the design of airless tire an elastic element with characteristics that can vary during operation. Such elastic element could be represented by pneumatic muscles, electroactive polymer or special mechanical design of crosspieces-spokes. Introduction of elastic element with variable characteristics in the design of airless tire leads to the increasing of mobility and efficiency of tractors and agricultural machinery. It will make possible the automatic control of tires' parameters by means of electronic control units, without operator's assistance, thereby the human factor will be reduced to a minimum.