The design and mathematical modelling of novel extensor bending pneumatic artificial muscles (EBPAMs) for soft exoskeletons

This article presents the development of a power augmentation and rehabilitation exoskeleton based on a novel actuator. The proposed soft actuators are extensor bending pneumatic artificial muscles. This type of soft actuator is derived from extending McKibben artificial muscles by reinforcing one side to prevent extension. This research has experimentally assessed the performance of this new actuator and an output force mathematical model for it has been developed. This new mathematical model based on the geometrical parameters of the extensor bending pneumatic artificial muscle determines the output force as a function of the input pressure. This model is examined experimentally for different actuator sizes. After promising initial experimental results, further model enhancements were made to improve the model of the proposed actuator. To demonstrate the new bending actuators a power augmentation and rehabilitation soft glove has been developed. This soft hand exoskeleton is able to fit any adult hand size without the need for any mechanical system changes or calibration. EMG signals from the human hand have been monitored to prove the performance of this new design of soft exoskeleton. This power augmentation and rehabilitation wearable robot has been shown to reduce the amount of muscles effort needed to perform a number of simple grasps

Grip force measurement of soft- Actuated finger exoskeleton

Over recent years, the reseach in the field of soft actuation has been extensively increased for achieving more complex motion path with smooth, high flexible movement and high generated force at minimum operating pressure. This paper presents the study on gripping force capability of soft actuators applied on glove-type finger exoskeleton, developed in motivation to assist individuals having weak finger gripping ability in their rehabilitation exercise towards hand function restoration. The exoskeleton utilizes five cylindrical shaped pneumatic bending actuators developed in the lab, which use fiber reinforcement as a cause of bending motion that drive finger’s flexion movement. Four right-handed healthy volunteers simulated paralysis participated in the study. At 200kPa safe operating pressure, the soft exoskeleton worn by the subjects demonstrates the ability to provide adequate grip force. The grip force generated from exoskeleton worn on passive right hand is 4.66 ± 0.2 N and 3.61± 0.2 N from passive left hand, both higher than the minimum grip forces measured to hold the Hand Dynamometer of 240 g. It shows good potential to be used as a finger rehabilitation assist device

Novel soft bending actuator based power augmentation hand exoskeleton controlled by human intention

This article presents the development of a soft material power augmentation wearable robot using novel bending soft artificial muscles. This soft exoskeleton was developed as a human hand power augmentation system for healthy or partially hand disabled individuals. The proposed prototype serves healthy manual workers by decreasing the muscular effort needed for grasping objects. Furthermore, it is a power augmentation wearable robot for partially hand disabled or post-stroke patients, supporting and augmenting the fingers’ grasping force with minimum muscular effort in most everyday activities. This wearable robot can fit any adult hand size without the need for any mechanical system changes or calibration. Novel bending soft actuators are developed to actuate this power augmentation device. The performance of these actuators has been experimentally assessed. A geometrical kinematic analysis and mathematical output force model have been developed for the novel actuators. The performance of this mathematical model has been proven experimentally with promising results. The control system of this exoskeleton is created by hybridization between cascaded position and force closed loop intelligent controllers. The cascaded position controller is designed for the bending actuators to follow the fingers in their bending movements. The force controller is developed to control the grasping force augmentation. The operation of the control system with the exoskeleton has been experimentally validated. EMG signals were monitored during the experiments to determine that the proposed exoskeleton system decreased the muscular efforts of the wearer

State-of-the-Art of Hand Exoskeleton Systems

This paper deals with the analysis of the state-of-the-art of robotic hand exoskeletons (updated at May 2011), which is intended as the first step of a designing activity. A large number of hand exoskeletons (both products and prototypes) that feature some common characteristics and many special peculiarities are reported in the literature. Indeed, in spite of very similar functionalities, different hand exoskeletons can be extremely different for the characteristics of their mechanism architectures, control systems and working principles. The aim of this paper is to provide the reader with a complete and schematic picture of the state-of-the-art of hand exoskeletons. The focus is placed on the description of the main aspects that are involved in the exoskeleton design such as the system kinematics, the actuator systems, the transmission parts and the control schemes. Additionally, the critical issues provided by the literature analysis are discussed in order to enlighten the differences and the common features of different practical solutions. This paper may help to understand both the reasons why certain solutions are proposed for the different applications and the advantages and drawbacks of the different designs proposed in the literature. The motivation of this study is the need to design a new hand exoskeleton for rehabilitation purposes

A procedure for the fatigue life prediction of straight fibers pneumatic muscles

Different from the McKibben pneumatic muscle actuator, the straight fibers one is made of an elastomeric tube closed at the two ends by two heads that ensure a mechanical and pneumatic seal. High stiffness threads are placed longitudinally into the wall of the tube while external rings are placed at some sections of it to limit the radial expansion of the tube. The inner pressure in the tube causes shortening of the actuator. The working mode of the muscle actuator requires a series of critical repeated contractions and extensions that cause it to rupture. The fatigue life duration of a pneumatic muscle is often lower than traditional pneumatic actuators. The paper presents a procedure for the fatigue life prediction of a straight-fibers muscle based on experimental tests directly carried out with the muscles instead of with specimens of the silicone rubber material which the muscle is made of. The proposed procedure was experimentally validated. Although the procedure is based on fatigue life duration data for silicone rubber, it can be extended to all straight-fibers muscles once the fatigue life duration data of any material considered for the muscles is known

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

Pneumatic Artificial Muscles (PAMs) are the most promising type of pneumatic-based actuators. Recently, they have been widely used in medical and rehabilitation robotic systems due to their flexibility, reliability, and high load-to-weight ratio. The aim of this work is to introduce an accurate mathematical model for describing the performance of the pneumatic artificial muscles under different applied pressures and loads by examining different previously proposed models. Being motivated by the muscles’ usage in a wearable robotic device for wrist rehabilitation where the required muscle force is not so large, it is interesting to consider the model that best expresses the muscle behavior over a lower range of the muscle force. An experimental system for measuring the muscle contraction at different applied pressures and loads is set up. Then, an algorithm for the parameters identification of the examined models based on the least squared error approach is developed using MATLAB Software

The Research on Soft Pneumatic Actuators in Italy: Design Solutions and Applications

Interest in soft actuators has increased enormously in the last 10 years. Thanks to their compliance and flexibility, they are suitable to be employed to actuate devices that must safely interact with humans or delicate objects or to actuate bio-inspired robots able to move in hostile environments. This paper reviews the research on soft pneumatic actuators conducted in Italy, focusing on mechanical design, analytical modeling, and possible application. A classification based on the geometry is proposed, since a wide set of architectures and manufacturing solutions are available. This aspect is confirmed by the extent of scenarios in which researchers take advantage of such systems’ improved flexibility and functionality. Several applications regarding bio-robotics, bioengineering, wearable devices, and more are presented and discussed

Design Criteria of Soft Exogloves for Hand Rehabilitation- Assistance Tasks

This paper establishes design criteria for soft exogloves (SEG) to be used as rehabilitation or assistance devices. This research consists in identifying, selecting, and grouping SEG features based on the analysis of 91 systems that have been proposed during the last decade. Thus, function, mobility, and usability criteria are defined and explicitly discussed to highlight SEG design guidelines. Additionally, this study provides a detailed description of each system that was analysed including application, functional task, palm design, actuation type, assistance mode, degrees of freedom (DOF), target fingers, motions, material, weight, force, pressure (only for fluids), control strategy, and assessment. Such characteristics have been reported according to specific design methodologies and operating principles. Technological trends are contemplated in this contribution with emphasis on SEG design opportunity areas. In this review, suggestions, limitations, and implications are also discussed in order to enhance future SEG developments aimed at stroke survivors or people with hand disabilities

A new fiber braided soft bending actuator for singer exoskeleton

This thesis presents a design, development and analysis of a novel bending-type pneumatic soft actuator as a drive source for a finger exoskeleton. Soft actuators are gaining momentum in robotic applications due to their simple structure, high compliance, high power-to-weight ratio and low production cost. Smaller and lighter soft actuator that can provide higher power transmission at lower operating air pressure will benefit finger actuation mechanism compared to motorized cable and pulley-driven finger rehabilitation devices. In this study, a soft actuator with new bending method is proposed. It is based on fibre reinforcement of two fibre braided angles of contraction and extension characteristics combined in a single-chamber cylindrical actuator. Another four design parameters identified that affect the bending motion and the actuating force were the air chamber diameter, position of fibre layer reinforcement, fibre reinforcement coverage angle, and silicone rubber materials. Geometrical and material parameters were varied in Finite Element Method (FEM) simulation for design optimization and some parameters were tested experimentally to validate the FEM models. The effects of fibre angles (contraction and extension) on the bending motion and force were analyzed. The optimized actuator can generate bending motion up to 131° bending angle and the end tip of the actuator can make contact with the other base tip at only 240 kPa given input pressure. Both displacement simulation and experimental testing results matched closely. Maximum bending force of 5.42 N was generated at 350 kPa. A wearable finger soft exoskeleton prototype with five optimized bending actuators was tested to drive finger flexion motion of eight healthy subjects with simulated paralysis conditions. The finger soft exoskeleton demonstrated the ability to provide gripping force of 3.61 ± 0.22 N, gained at 200 kPa given air pressure. The device can successfully provide assistance to weak fingers in gripping at least 240 g object. It shows potential in helping people with weakened finger muscle to be more independent in their finger rehabilitation exercise