Pneumatic Muscle Research Articles

Conceptual design and dimensional synthesis of a novel parallel mechanism for lower-limb rehabilitation

SUMMARYThis paper introduces a novel 2R1T parallel manipulator redundantly actuated by pneumatic muscles for lower-limb rehabilitation. First, the conceptual design of the proposed 3-DOF parallel mechanism is presented. Then, the inverse kinematics and the generalized Jacobian analysis are carried out. Based on the generalized Jacobian and the constraint characteristics of the mechanism, the force/motion transmissibility of the redundantly actuated parallel mechanism is investigatedviafour individual cases without actuation redundancy, leading to a suitable local transmission index for the evaluation of kinematic performance of the proposed mechanism. Finally, the design variables are optimized by maximizing the mean value of the local transmission index with the aid of genetic algorithm. The numerical result shows that the proposed parallel mechanism can achieve a good kinematic performance in its task workspace.

Pneumatic Muscle: Heat and Mass Transfer in the Cylindrical Membrane

A pneumatic muscle is a one-way reciprocating air motor. It is designed to create apullingforce. The pneumatic muscle return to its initial position is ensured by a reversible strain of its shell. The pneumatic muscle is based on the cylindrical membrane with a rigid bottom and a cover. The membrane cord is formed during the process of cross-spiral weaving from the super-hard synthetic fibers (for example, Kevlar). After the cord has been filled with an elastomer, a strong, deformable and elastic shell is formed. When an overpressure is provided to the internal cavity of the membrane, in a diamond-shaped cell that is formed as a result of weaving cord threads, the tangential diagonal is lengthened and the axial diagonal is shortened simultaneously. Using the pneumatic muscle cord structure of the MAS series produced by FESTO company as an example, we studied a strain of the diamond-shaped cell of the membrane and found the numerical relationships between the value of the pneumatic muscle contraction, the inner diameter of the membrane and the volume of its internal cavity of the pneumatic muscle, which allowed us to develop a mathematical model of an idealized cylindrical membrane in the dynamics of which the strain force of the elastomer that fills the diamond-shaped cell was not taken into account. The paper shows that the cylindrical membrane used in the pneumatic muscle should be considered as a thermodynamic system with full or partial heat and mass transfer. Also discusses the special aspects of using pneumatic muscles in engineering systems as applied to the type of a thermodynamic process. The study of the air movement features in throttling openings of control and management devices, as well as the changes in the state of compressed air during heat and mass transfer allowed us to estimate a length of the transient process in the pneumatic muscle that works as part of the pneumatic load positioning system. The results of the performed studies expand opportunities for predicting the pneumatic muscle dynamics at the design stage of the pneumatic control system, as well as during its operation.

Active Passive Nature of Assistive Wearable Gait Augment Suit for Enhanced Mobility

In this paper we discuss the active and passive nature of the assistive wearable gait augment suit (AWGAS). AWGAS is a soft, wearable, lightweight, and assists walking gait by reducing muscle activation during walking. It augments walking by reducing the muscle activation of the posterior and anterior muscles of the lower limb. The suit uses pneumatic gel muscles (PGM), foot sensors for gait detection, and pneumatic valves to control the air pressure. The assistive force is provided using the motion in loop feedforward control loop using foot sensors in shoes. PGMs are actuated with the help of pneumatic valves and portable air tanks. The elastic nature of the PGM allows AWGAS to assist walking in the absence of the air supply which makes AWGAS both active and passive walking assist suit. To evaluate the active and passive nature of the AWGAS, we experimented to measure surface EMG (sEMG) of the lower limb muscles. sEMG was recorded for unassisted walking, i.e., without the suit, passive assisted walking, i.e., wearing the suit with no air supply and active assisted walking, i.e., wearing the suit with air supply set at 60 kPa. The results shows reduction in the muscle activity for both passive and active assisted walking as compared to unassisted walking. The pilot trials of the AWGAS were conducted in collaboration with local farmers in the Hiroshima prefecture in Japan where feedback received is complementing the results obtained during the experiments.

A New Approach to Modeling and Controlling a Pneumatic Muscle Actuator-Driven Setup Using Back Propagation Neural Networks

Pneumatic muscle actuators (PMAs) own excellent compliance and a high power-to-weight ratio and have been widely used in bionic robots and rehabilitated robots. However, the high nonlinear characteristics of PMAs due to inherent construction and pneumatic driving principle bring great challenges in applications acquired accurately modeling and controlling. To tackle the tricky problem, a single PMA mass setup is constructed, and a back propagation neural network (BPNN) is employed to identify the dynamics of the setup. An offline model is built up using sampled data, and online modifications are performed to further improve the quality of the model. An adaptive controller based on BPNN is designed using gradient descent information of the built-up model. Experiments of identifying the PMA setup using BPNN and position tracking by adaptive BPNN controller are performed, and results demonstrate the good capacity in accurate controlling of the PMA setup.

Flatness-Based Control of a Two Degrees-of-Freedom Platform With Pneumatic Artificial Muscles

Pneumatic artificial muscles (PAMs) are an interesting type of actuators as they provide high power-to-weight and power-to-volume ratio. However, their efficient use requires very accurate control methods taking into account their complex and nonlinear dynamics. This paper considers a two degrees-of-freedom platform whose attitude is determined by three pneumatic muscles controlled by servovalves. An overactuation is present as three muscles are controlled for only two degrees-of-freedom. The contribution of this work is twofold. First, whereas most of the literature approaches the control of systems of similar nature with sliding mode control, we show that the platform can be controlled with the flatness-based approach. This method is a nonlinear open-loop controller. In addition, this approach is model-based, and it can be applied thanks to the accurate models of the muscles, the platform and the servovalves, experimentally developed. In addition to the flatness-based controller, which is mainly a feedforward control, a proportional-integral (PI) controller is added in order to overcome the modeling errors and to improve the control robustness. Second, we solve the overactuation of the platform by an adequate choice for the range of the efforts applied by the muscles. In this paper, we recall the basics of this control technique and then show how it is applied to the proposed experimental platform. At the end of the paper, the proposed approach is compared to the most commonly used control method, and its effectiveness is shown by means of experimental results.

Soft Wearable Augmented Walking Suit With Pneumatic Gel Muscles and Stance Phase Detection System to Assist Gait

The lower limbs of the human body are responsible for human locomotion and maintaining a good quality of life. However, there are many instances of muscle fatigue or injuries caused by stressful work environments, aging, and work that involves walking a long distance. Therefore, there is a need for an assistive suit for walking that can unload muscle efforts during walking and reduce the chances of lower-limb muscle fatigue. In this letter, we discuss the development of a lightweight and wearable augmented walking suit (AWS) using pneumatic gel muscle and its actuation control the using lower limb pose detection mechanism considering the human gait cycle. The objective of this assistive suit is to reduce the required muscle effort of the posterior and anterior muscles during the swing phase of the gait cycle, thereby making it easier to move forward. To evaluate the effects of the AWS, an experiment was conducted to record the surface EMG (sEMG) of eight primary lower limb muscles of seven subjects for two levels of assistive air pressure. The evaluation was done based on the sEMG signal envelope and the statistical difference in the average percentage of maximum voluntary contraction of the measured muscles. In our result, we found that all muscles showed a statistically significant reduction or no change in muscle activity while wearing the AWS as compared with when the AWS was not worn.

Improved RBF network torque control in flexible manipulator actuated by PMAs

SUMMARYA Pneumatic Muscle Actuator (PMA) is a new pneumatic component sharing similar characteristics with biological muscles, and the flexible manipulator actuated by PMAs can better reflect the flexibility of the mechanism. First and foremost, based on the study of the characteristics of human shoulder joints, the configuration design of the flexible manipulator is analyzed, and its kinematics and dynamics models are established. Furthermore, with regard to the nonlinearity, time-invariance and uncertainty of the control system, three aspects of improvement are proposed, which are based on the Radial Basis Function (RBF) network torque control algorithm. The Genetic Algorithm is used to optimize the initial values of RBF network parameters; RBF network parameters are adjusted dynamically by using the additional momentum method; the Levenberg--Marquardt (LM) algorithm, instead of the gradient descent method, is adopted to adjust Proportion Integration Differentiation (PID) parameters online in real time. At last, to test the effects that the improved algorithm exerts on the flexible manipulator control system, some physical platform experiments are carried out. It turns out that the control accuracy and robustness of the improved algorithm are well improved, and the mechanism can be controlled better to track the circular arc trajectory. It lays fundamental importance to the practical application for the working environment.

Trajectory Planning of an Intermittent Jumping Quadruped Robot with Variable Redundant and Underactuated Joints

The jumping robot has been a hot research field due to its prominent obstacle-climbing ability and excellent capacity in terrain adaptation and autonomous movement. However, huge impact between the robot and the ground when landing may cause structure damage, unbalanced movement, and even system crash. Therefore, trajectory planning of the jumping process has been a great challenge in robotic research, especially for the robot with varying underactuated and redundant joints. An intermittent jumping quadruped robot driven by pneumatic muscle actuators (PMAs) and owning variable redundant and underactuated joints designed in a previous study is taken as the study object. This paper divides the problem of trajectory planning into trajectory planning in the centroid space and joint space. Trajectory planning of different jumping phases in the centroid space adopts the scheme of minimizing the peak reaction force from the ground, then trajectory planning of the joint space is performed obeying the principle of minimizing consumed active torques. A jumping experiment is performed and validates the effectiveness of the proposed trajectory algorithm.

Pneumatic muscle actuated rotation modules for elbow rehabilitation equipment

The paper presents a theoretical study concerning the possibility of using a pneumatic actuation system for a piece of elbow rehabilitation equipment with two degrees of freedom. For this purpose the design and calculation of a rotation module for each movement performed by the equipment is necessary: flexion-extension and pronation-supination. Construction of the modules implies a force and torque analysis leading to the correct selection of the pneumatic muscles, able to perform the desired movements. The static analysis of the rotation module can be done in two different modalities. The first modality takes into account the influence of neuronal control quantities on the forces developed by the two pneumatic muscles, while the second one aims to determine forces based on the technical data and load pressures of the pneumatic muscles. The dynamic analysis of the rotation module starts from two equations of the dynamic model, where first taken into consideration are: J – the moment of inertia, ω – angular velocity, T – total moment in the joint and Tg – gravitational moment; then, for a simplified model, the term Tg is neglected. The exhaustive calculations carried out during the dynamic analysis yielded satisfying results. Further presented are variation graphs of pressure Δp and rotation angle θ versus time, respectively.

Structural and kinematic analysis of elbow rehabilitation equipment

The aim of this paper is to present the structural and kinematic analysis of a new constructive solution for the rehabilitation of patients suffering from posttraumatic elbow affections. The equipment with two degrees of freedom, one for flexion-extension movement and one for pronation-supination should be able to ensure the full recovery of the elbow joint. Each movement is achieved by means of a pair of pneumatic muscles. The structural analysis of the mechanism includes drawing the constructive, structural and block diagrams, identifying the exterior links (number of inputs and outputs), the mobility of the mechanism (the number of degrees of freedom), the analysis of the transmission of movements and forces and also the analysis of the hyperstaticity of the mechanism. The kinematic pairs composing the mechanisms are isostatic, i.e. with no potential links. The kinematic analysis involves equations that describe the kinematic behaviour of the rehabilitation equipment. Such behaviour can be described analytically or graphically. In the latter case, the equations will underlie the variation graphs of position, velocity and acceleration versus time plotted by means of SolidWorks software.

Ball and Beam Balancing Mechanism Actuated With Pneumatic Artificial Muscles

The paper presents the results of modeling and control of an original and unique ball-on-beam system with a pneumatic artificial muscle pair in an antagonistic configuration. This system represents a class of under-actuated, high-order nonlinear systems, which are characterized by an open-loop unstable equilibrium point. Since pneumatic muscles have elastic, nonlinear characteristics, they are more difficult to control. Considering that an additional nonlinearity is added to the system which makes it harder to stabilize. The nonlinear mathematical model has been derived based on the physical model of the ball-on-beam mechanism, the beam rotating by using an antagonistic muscle pair and the pneumatic muscle actuated by a proportional valve. Based on the nonlinear model, the linearized equations of motion have been derived and a control-oriented model has been developed, which is used in the state feedback controller design procedure. The proposed state feedback controller has been verified by means of computer simulations and experimentally on the laboratory setup. The simulation and experimental results have shown that the state feedback controller can stabilize the ball-on-beam system around an equilibrium position in the presence of external disturbances and to track a reference trajectory with a small tracking error.

공압근육을 이용한 상지근력 보조용 웨어러블 로봇의 설계 및 제어

This paper describes the design and control of a soft wearable robot capable of upper-limb muscle power assistance to prevent musculoskeletal injuries while lifting a patient repeatedly during a transfer process, in which a caregiver moves from a bed to a wheelchair. To minimize the weight of the wearable robot, pneumatic muscles were applied instead of typically used motors with reduction gears. The required specifications of the pneumatic artificial muscles were defined by mechanical analysis and manufactured specially for our robot. We also designed a soft wearing suit using fabric as the primary material and minimized the hard metal frames. This robot understands the intention of the user from the specific motions through the bracelet-type sensor named Myo that contains electromyography(EMG) sensors and accelerometers, without pressing a button. Finally, the performance of the wearable robot was experimentally verified through EMG measurements.

Linear positioner based on pneumatic muscle

The main goal of the work is to investigate the technical possibilities of creating a linear positioner on the basis of pneumatic muscle with acceptable characteristics for positioning. The experimental study of the power characteristics of the pneumatic muscle of the MAS 10-300 series of “FESTO” company is carried out. The physical essence of the cylindrical membrane operation is considered, on the basis of which the pneumatic muscle is constructed and a method for calculating the parameters of the positioning spring has been developed. It is shown that if the positional component is present in the load of pneumatic muscle then its rigidity (the dependence of the force on displacement) allows solving the task of positioning by controlling the pressure in the internal cavity of pneumatic muscle. If there is no positional component in the load or it is too small, then a positioning spring is needed to solve the positioning problem. Methods for determining the parameters of the positioning spring for positioners created on the basis of MAS pneumatic muscles of “FESTO” company are given. It has been established that the pneumatic muscle, which is used as a linear pneumatic motor, generates a pulling force which, with zero reduction of the pneumatic muscle, is 12 ... 14 times greater than the force developed on the return stroke by a pneumatic cylinder of equal working area of the piston and the specific force (force referred to the mass of the pneumatic motor) of pneumatic muscle is 100 times larger. This makes it possible to use pneumatic muscle as a loading device for brake, clamping and tensioning devices of transport systems and mobile units. To use the positioner in the tracking position control system, it must be provided with an analog feedback sensor. The static characteristic of the created physical layout of the positioner, obtained experimentally, has a quasilinear section in the range of the control pressure change of 2.5 ... 5 bar and agrees well with the calculation results. The nature of the transient process with respect to the input effect makes it possible to treat the positioner as an aperiodic link of the first order with a time constant T = 2 ... 5 s. As an example, the possibility of using a positioner in solving problems related to the need to stabilize a cargo platform in a horizontal position, in the case of a shift of the center of gravity of the cargo relative to the vertical axis of the platform, was investigated. The results of the work can be used and implemented in solving problems of linear and angular positioning of the load in flexible production systems, in executive devices of industrial robots, etc.

Adaptive Multi-Objective Optimization of Bionic Shoulder Joint Based on Particle Swarm Optimization

To get the movement mode and driving mechanism similar to human shoulder joint, a six degrees of freedom (DOF) serial-parallel bionic shoulder joint mechanism driven by pneumatic muscle actuators (PMAs) was designed. However, the structural parameters of the shoulder joint will affect various performances of the mechanism. To obtain the optimal structure parameters, the particle swarm optimization (PSO) was used. Besides, the mathematical expressions of indexes of rotation ranges, maximum bearing torque, discrete dexterity and muscle shrinkage of the bionic shoulder joint were established respectively to represent its many-sided characteristics. And the multi-objective optimization problem was transformed into a single-objective optimization problem by using the weighted-sum method. The normalization method and adaptive-weight method were used to determine each optimization index’s weight coefficient; then the particle swarm optimization was used to optimize the integrated objective function of the bionic shoulder joint and the optimal solution was obtained. Compared with the average optimization generations and the optimal target values of many experiments, using adaptive-weight method to adjust weights of integrated objective function is better than using normalization method, which validates superiority of the adaptive-weight method.

Pneumatic Muscle Actuated Wrist Rehabilitation Equipment Based on the Fin Ray Principle

Pneumatic Muscle Actuated Wrist Rehabilitation Equipment Based on the Fin Ray Principle

Frog-inspired jumping robot actuated by pneumatic muscle actuators

Jumping robots can be widely applied in archeology, interstellar probe, antiterrorism, and resource exploration. This article adopts the frog as the bionic object and briefly analyzes biological features and jumping movements in a complete jumping sequence of the frog. Then an equivalent six-bar mechanism model depicting frog jumping movement is built up, and the optimizing simulation of the six-bar mechanism model is performed. On the basis of the optimized results, the robot is designed and prototype is manufactured. An adaptive cascade controller is proposed to control the robot. Proportional–integral–derivative parameters of the controller are tuned online using radial basis function neural network to deal with nonlinearities of the robot. Jumping experiment demonstrates the jumping capacity of the robot and the ability of the proposed controller in tracking the desired trajectories.

Design, Kinematics and Controlling a Novel Soft Robot Arm with Parallel Motion

This article presents a novel design for a double bend pneumatic muscle actuator (DB-PMA) inspired by snake lateral undulation. The presented actuator has the ability to bend in opposite directions from its two halves. This behavior results in horizontal and vertical movements of the actuator distal ends. The kinematics for the proposed actuator are illustrated and experiments conducted to validate its unique features. Furthermore, a continuum robot arm with the ability to move in parallel (horizontal displacement) is designed with a single DB-PMA and a two-finger soft gripper. The performance of the soft robot arm presented is explained, then another design of the horizontal motion continuum robot arm is proposed, using two self-bending contraction actuators (SBCA) in series to overcome the payload effects on the upper half of the soft arm.

Model-based tracking control design, implementation of embedded digital controller and testing of a biomechatronic device for robotic rehabilitation

In this paper, the tracking control problem of a biomimetic exoskeleton powered by a pair of pneumatic artificial muscles is considered. The antagonistic configuration of the pair of pneumatic muscles, which is biologically inspired, enables safe and reliable actuation in applications of orthopaedic rehabilitation. However, during the inflation-deflation process, the pneumatic muscles introduce nonlinearity and hysteresis which deteriorate the control performance. A model of the antagonistic artificial muscles is adopted to develop a computed-torque control for feedforward compensation of the nonlinear dynamics of the actuated joint. A PID control action is used in combination with the feedforward compensation to achieve fast and accurate tracking control performance. The model, which possesses a reduced set of parameters as functions of the inflation/deflation phase, enables efficient nonlinear compensation. The experimental tests on the biomechatronic device, compared with other state-of-the-art approaches for controlling pneumatic artificial muscles, show better tracking performance in terms of convergence rate and robustness, justifying the convenience of using the proposed control methodology in the design of tracking controllers for exoskeletal biomechatronic devices.

Development of a Straight Fibers Pneumatic Muscle

This paper presents the development and implementation of a pneumatic muscle actuator based on an idea proposed by a research group at the University of Warsaw. The muscle comprises a silicone rubber tube with plugs at the ends. The tube wall contains high-rigidity wires arranged parallel to the tube axis. Circular rings are present on the exterior of the tube. When air is introduced into the tube, the actuator becomes bulky and contracts. In order to establish a prediction model of muscle behavior, a finite element model was developed, and in this model, the Mooney-Rivlin formulation was implemented with two coefficients for rubber simulation and truss elements for the wires. Several prototypes were developed, and a test bench for the experimental characterization of muscle performance was set up. The results of comparison between prototype behavior and model prediction are presented. The finite element model can be used to design the actuator with different dimensions; hence, it was used to conduct a simulated test campaign to develop a quick actuator sizing procedure. Using dimensional analysis, few project parameters were identified on which the performance of the actuator depends. Through a complete simulation campaign using the finite element model, an abacus was constructed. It allows sizing the actuator as required based on the desired performances according to an established procedure.

Modeling and vibration control of an active horizontal seat suspension with pneumatic muscles

In the following paper, the dynamic modeling of a horizontal seat suspension which uses pneumatic muscles for the purpose of active vibration control is discussed. An original control system structure is proposed in order to improve the vibro-isolation properties of a horizontal seat suspension system. The presented control system design is based on inverse models of the pneumatic muscles and the primary controller that calculates the desired active force. By using the configurable control algorithm developed in this paper, it is possible to achieve a significant reduction in vibrations transmitted into the human body with just a slight increasing of the suspension travel. The active seat shows improved performance over the passive system in the 1–10 Hz frequency range. The results presented in this paper are useful in selecting the horizontal vibration control system for improving the comfort of a drive.