Pneumatic Muscle Research Articles

An Adaptive Finite-Time Force-Sensorless Tracking Control Scheme for Pneumatic Muscle Actuators by an Optimal Force Estimation

The prime challenges of the force control generated by pneumatic muscle actuators (PMAs) have arisen from their highly nonlinear properties, which are perturbed by dynamic uncertainties and external disturbances. To achieve fast response, high accuracy, and robust force tracking performance without using a force sensor, this letter proposes an adaptive finite-time force-sensorless control scheme for a single-joint manipulator configured by a pair of antagonistic PMAs. First, a newly time-varying adaptive optimal force estimation scheme is proposed to obtain the environmental contact force using only position information, such that improvements of transient response and estimated accuracy are assisted by the cost function of the predefined estimation error. Next, the principal control method relied on core elements of a finite-time integral fast terminal sliding mode control procedure is developed. Additionally, a force-based time delay estimation technique is deployed to estimate the lumped uncertainties. Meanwhile, the new adaptive gain law assists in compensating for the remained error of the estimator. The stability and finite-time convergence features of the whole system are demonstrated through Lyapunov theory. Finally, a series of trials are conducted on an actual paradigm with an adjustable environment configuration. The reliability and superiority of our approach are confirmed by comparing the experimental results with other approaches.

A Composite Flexible Sensor for Direct Ventricular Assist Device.

A direct ventricular assist device is one of the effective means to treat patients with heart failure; the key point of the problem is the flexible sensor that can measure the drive pressure and shape variable of the heart auxiliary device. This study was based on the high-voltage electric field guidance process and the porous foaming process, and designed an implantable resistance/capacitive composite flexible sensor that can effectively detect the pressure and deformation signal caused by fine surface contact and pneumatic muscle expansion. Experiments showed the performance of composite sensors with special structure design was greatly improved compared with the control group—the strain measurement sensitivity was 22, pressure measurement sensitivity was up to 0.19 Kpa−1. Stable strain measurements were made up to 35 times and pressure measurements over 100 times. In addition, we solved the interference problem of resistance/capacitance flexible sensors through an optimized common substrate process. Finally, we tested a pneumatic muscle direct ventricular assist device with a composite flexible sensor on a model heart; the experiment showed that this resistance/capacitive composite flexible sensor can effectively detect surface contact with pneumatic muscle and the displacement signals.

Gas Flow Measurement Method with Temperature Compensation for a Quasi-Isothermal Cavity

Pneumatic transmission is a technology that uses compressed air as a power source to drive and control various mechanical equipment to realize the mechanization and automation of production processes. With the development of industrial mechanization and automation, pneumatic technology, represented by pneumatic muscle, is increasingly becoming more widely used in various fields. The current standards for research are more complex for the measurement of flow without a flowmeter, some of them do not consider the influence of temperature change on flow measurement, and some of them are simplified as adiabatic or isothermal models, which are inaccurate measurement methods in actual practical application. This paper describes a method to determine flow rate by measuring the pressure change in the process of gas tank inflation. This study used the method of temperature compensation to eliminate the influence of temperature in the isothermal formula. The measurement structure was simple and the calculation was accurate, which has a certain practical significance. Based on this method, charging experiments were carried out with a gas tank that had a volume of 3 L or 5 L with or without copper wire filling, and the experimental results were used in the processed research. The temperature compensation parameters were identified with or without an isothermal environment and in different sizes of tanks. This method identified the different parameters of the 5 L tank and 3 L tank. Finally, the flow compensation was completed for the gas tank filled with copper wire. After verification, the results of the quasi-isothermal calculation formula and temperature compensation formula were close to those measured by a high-precision flow sensor in the experiment. The method introduced in this study is a novel flow calculation method that is simple in structure and accurate in calculation compared with the conventional isothermal calculation method; furthermore, it can be used in real world situations without the need for a high-precision flow sensor.

Modeling-Based EMG Signal (MBES) Classifier for Robotic Remote-Control Purposes

The fast-growing human–robot collaboration predicts that a human operator could command a robot without mechanical interface if effective communication channels are established. In noisy, vibrating and light sensitive environments, some sensors for detecting the human intention could find critical issues to be adopted. On the contrary, biological signals, as electromyographic (EMG) signals, seem to be more effective. In order to command a laboratory collaborative robot powered by McKibben pneumatic muscles, promising actuators for human–robot collaboration due to their inherent compliance and safety features have been researched, a novel modeling-based electromyographic signal (MBES) classifier has been developed. It is based on one EMG sensor, a Myotrac one, an Arduino Uno and a proper code, developed in the Matlab environment, that performs the EMG signal recognition. The classifier can recognize the EMG signals generated by three hand-finger movements, regardless of the amplitude and time duration of the signal and the muscular effort, relying on three mathematical models: exponential, fractional and Gaussian. These mathematical models have been selected so that they are the best fitting with the EMG signal curves. Each of them can be assigned a consent signal for performing the wanted pick-and-place task by the robot. An experimental activity was carried out to test and achieve the best performance of the classifier. The validated classifier was applied for controlling three pressure levels of a McKibben-type pneumatic muscle. Encouraging results suggest that the developed classifier can be a valid command interface for robotic purposes.

Designing of Capio-active, Lower Extremity and Brain Energized Full Body Exoskeleton with IoT Edge for Assisting Paralyzed Patients

Exoskeleton can be defined as "wearable, external mechanical structure" whose objective is to reinforce or restore the physical performance of the person. The exoskeletons are placed on the user’s body and can be classified into two categories: • Passive: This kind of exoskeleton does not use any type of electrical power source. On the other hand, these are constituted with mechanisms as springs, dampers or high-pressure springs. It can be used for weight re-distribution or energy capture to support the users with the posture or motion. • Active: unlike passive exoskeletons, active exoskeletons do use some type of actuator which in- creases human power. This actuator can be an electric motor, pneumatic muscles or hydraulic power.

Design and Hierarchical Force-Position Control of Redundant Pneumatic Muscles-Cable-Driven Ankle Rehabilitation Robot

Ankle dysfunction is common in the public following injuries, especially for stroke patients. Most of the current robotic ankle rehabilitation devices are driven by rigid actuators and have problems such as limited degrees of freedom, lack of safety and compliance, and poor flexibility. In this letter, we design a new type of compliant ankle rehabilitation robot redundantly driven by pneumatic muscles (PMs) and cables to provide full range of motion and torque ability for the human ankle with enhanced safety and adaptability, attributing to the PM's high power/mass ratio, good flexibility and lightweight advantages. The ankle joint can be compliantly driven by the robot with full three degrees of freedom to perform the dorsiflexion/plantarflexion, inversion/ eversion, and adduction/abduction training. In order to keep all PMs and cables in tension which is essential to ensure the robot's controllability and patient's safety, Karush-Kuhn-Tucker (KKT) theorem and analytic-iterative algorithm are utilized to realize a hierarchical force-position control (HFPC) scheme with optimal force distribution for the redundant compliant robot. Experiment results demonstrate that all PMs are kept in tension during the control while the position tracking accuracy of the robot is acceptable, which ensures controllability and stability throughout the compliant robot-assisted rehabilitation training.

Static characteristics of the new artificial pneumatic muscle

The pneumatic artificial muscles are used as driving elements of mobile, anthropomorphic, bionic and humanoid robots as well as rehabilitation and physiotherapeutic manipulators. The PAMs are also increasingly used for the automation of industrial processes. The article presents test stands and methods used to determine the static, isobaric, isotonic and isometric characteristics of the new pneumatic artificial muscles. The muscles have been designed and developed at the Kielce University of Technology. Comparative tests of technical parameters of the designed muscle with the muscles available on the market have been performed.

Control of a gripper finger actuated by a pneumatic muscle: new schemes based on a model-free approach

In this paper, model-free based control strategies are applied to a finger of a gripper activated by Mckibben pneumatic muscles. In order to emulate the grasping phase of an object using a simple finger, a ”hybrid” type model-free based control strategy is proposed to manage the effort control phase, and the object release phase. The strategy is divided into a phase of approach to the object with a speed control, then a phase of contact with the object for which a control of the effort is applied to maintain a controlled pressure on the object, and finally, a release phase for which the withdrawal of the object is controlled in position. An experimental setup is introduced to experiment with the control strategies on a single phalanx finger.

Analysis on the Characteristics with Biological Variable Stiffness of the Bionic-body Driven by Pneumatic Muscle Fibers

Analysis on the Characteristics with Biological Variable Stiffness of the Bionic-body Driven by Pneumatic Muscle Fibers

Effect of velocity and acceleration in joint angle estimation for an EMG-Based upper-limb exoskeleton control

Most studies on estimating user's joint angles to control upper-limb exoskeleton have focused on using surface electromyogram (sEMG) signals. However, the variations in limb velocity and acceleration can affect the sEMG data and decrease the angle estimation performance in the practical use of the exoskeleton. This paper demonstrated that the variations in elbow angular velocity (EAV) and elbow angular acceleration (EAA) associated with normal use led to a large effect on the elbow joint angle estimation. To minimize this effect, we proposed two methods: (1) collecting sEMG data of multiple EAVs and EAAs as training data and (2) measuring the values of EAV and EAA with a gyroscope. A self-developed upper-limb exoskeleton with pneumatic muscles was used in the online control phase to verify our methods' effectiveness. The predicted elbow angle from the sEMG-angle models which were trained in the offline estimation phase was transferred to control signal of the pneumatic muscles to actuate the exoskeleton to move to the same angle. In the offline estimation phase, the average root mean square error (RMSE) between predicted elbow angle and actual elbow angle was reduced from 22.54° to 10.01° (using method one) and to 6.45° (using method two), respectively; in the online control phase, method two achieved a best control performance (average RMSE = 6.87°). The results showed that using multi-sensor fusion (sEMG sensors and gyroscope) achieved a better estimation performance than using only sEMG sensor, which was helpful to eliminate the velocity and acceleration effect in real-time joint angle estimation for upper-limb exoskeleton control.

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.

Sensing Model FBG-Based Used for Position and Orientation Detection of Soft Manipulator

To make the end of the soft manipulator reach accurately the designated position, its position and orientation must be measured in real time, which is the basis for motion control and gait planning. In the paper, the sensing network based on the bidirectional helical fiber Bragg grating (FBG) can decouple the coupled strains including tension, bending, and torsion in real time, which removes the restriction of constant axial length in the conventional models. The mapping relationship between the strains and nonlinearity of the soft material determines the deformable parameters. Then, we propose an adaptive following detection (AFD) model to detect the spatial shape and pose by re-coupling the deformable parameters. The model is general enough for any sensor proving the corresponding parameters to sense kinds of soft manipulators (actuated by cable and pneumatic muscle, etc.). We conduct extensive experiments to verify the AFD model. The position and orientation errors of the end are less than 0.23mm and 0.0055rad respectively. The results show that it has the potential to realize the closed-loop control as the feedback signal and provides new ideas for other detection and control models.

Modelling, simulation and implementation of a hybrid model reference adaptive controller applied to a manipulator driven by pneumatic artificial muscles

AbstractThe present research aims to model, simulate and implement a new hybrid control approach based on a combination of proportional integral derivative (PID) Controller and Model Reference Adaptive Controller (MRAC), in which Lyapunov’s theory is used to ensure asymptotic stability to control a two degrees of freedom (DoF) manipulator driven by McKibben’s artificial pneumatic muscles. The MRAC controller works as a nonlinearity compensator and PID controller works during the transient period, as the MRAC performs poorly in this regime. This new approach is entitled Hybrid Model Reference Adaptive Controller (H-MRAC) and it has an unprecedented topological structure based on three terms. The feedforward term acts in disturbances rejection, the derivative term in oscillations damping and the feedback term acts in error convergence to zero. In this article, a control system dedicated to pneumatic manipulators was developed. As a result, proof of asymptotic convergence was performed for the proposed topological approach, which was validated on a two DoF manipulator. The proposed mechanism satisfactorily met the ISO/TS 15066 standard, and the position tracking obtained a global error of 37.69% and 51.01% smaller than found in the literature examples, entitled MRAC and A-PID, respectively, for simulations and 37.46% and 30.25% for experiments.

Studies regarding the Use of Pneumatic Muscles in Precise Positioning Systems

The paper presents the methods and results of an experimental study that highlights the behavior of a pneumatic actuator under different pressures and with different loads applied. One important challenge that occurs in the application of pneumatic muscles is the phenomenon of hysteresis, which causes a nonlinear relationship between the input–output values. The aim of this study is to identify the occurrence of hysteresis in the operation of a small pneumatic muscle in different conditions. Thus, different loads are attached to the free end of a pneumatic muscle and different successive pressures are applied in order to examine the hysteresis of the contraction ratio when the muscle is inflated and then deflated. The obtained equations that describe the relationship between the input pressure and the axial contraction are significant for reaching a high-performance position control. In this regard, the article proposes a solution to increase positioning accuracy based on pressure control using a proportional pressure regulator and a programmable logic controller.

Research on frog-inspired swimming robot driven by pneumatic muscles

AbstractThis article designs a frog-inspired swimming robot based on pneumatic muscles. The musculoskeletal characteristics of the frog are refined and used as the basis for the design of the robot joint structure and movement mode. The posture adjustment module, joint water seal, and power system are designed to meet the robot’s motion requirements, and the structure optimization design of the robot is completed by combining simulation analysis. The body length of the robot is about 710 mm, and the overall mass is 10 kg. Combining the structural characteristics of the robot, the control system is built to realize the frog-like motion. The robot’s propulsion speed is about 0.6 m/s, the propulsion distance reaches 2.4 m, the turning angle is 30°, and the turning radius is 0.6 m. The prototype experiment verifies the rationality of the frog-inspired swimming robot structure design and the reliability of the control system and water seal.

Design and Control of 6-DOF Robotic Manipulator Driven by Pneumatic Muscles and Motor

Design and Control of 6-DOF Robotic Manipulator Driven by Pneumatic Muscles and Motor

Design, Fabrication, and Performance Analysis of a Vertically Suspended Soft Manipulator

Soft continuum manipulators are comprised of flexible materials in a serpentine shape. Such manipulators can be controlled mechanically through tendons or pneumatic muscles. Continuum manipulators utilizing tendons are traditionally formed in a thick cross section, which presents limitations in achieving a high bending range as well as difficulties for storage and transportation. This study introduces a continuum manipulator comprised of two thin plastic bands and driven by a tendon to provide a bending action. The manipulator’s thin body form enables it to be rolled up for storage and transportation. Experimental results on different section lengths show the possibility of achieving a horizontal displacement of up to 34% of the bending-segment’s length, and a full closed-loop curvature for most segments. However, the results also indicated an elongation of the tip paths owing to gravity. These results, in addition to the manipulator’s flexibility and light weight features, confirm its suitability for applications in space and underwater environments.

Determination of the Function of the Course of the Static Property of PAMs as Actuators in Industrial Robotics

Current efforts are focused on assembling new constructions while applying non-conventional actuators, for example, artificial pneumatic muscles, in engineering manufacturing processes. The reason is to eliminate stiffness and inflexibility of equipment structures that make sharing the working space of the technological equipment complicated. This article presents the results of experimental measurements of pressures in artificial muscles and rotations of the actuator with artificial muscles at various loads, using a testing device of an antagonistic actuator. The measurement results were used to create the function of the course of the static property of the antagonistic actuator with artificial muscles of the Festo type and to determine a mathematical model of the actuator dynamics, while applying the method of least squares.

Observer-based finite-time control for trajectory tracking of lower extremity exoskeleton

In this article, an advanced observer-based finite-time trajectory tracking controller is investigated for lower extremity exoskeleton without available joint angular velocities to improve the movement ability of dependent persons, which is robust against uncertain dynamics, human active joint torque and external disturbances. First, the Lagrange principle is applied to analyze the dynamic properties of lower extremity exoskeleton driven by artificial pneumatic muscles, and its swing phase model is established. After that, a novel finite-time extended state observer is proposed to observe the lumped disturbances and unavailable angular velocities of the lower limb exoskeleton simultaneously. Furthermore, a finite-time sliding mode controller of exoskeleton is designed based on the extended state observer, and the finite-time convergence of tracking error is rigorously demonstrated based on the Lyapunov theory. Finally, the control system simulation is established and experimental tests are conducted with a voluntary subject during flexion of wearer’s knee and hip joints, the obtained results demonstrate fast and high-precision tracking performance of the proposed approach.

Upper extremity prosthesis 3D bio-pneumatic self-adjusting clamping to non-homogeneous surfaces under the principle of communicating vessel

There are several models that emulate the mechanical behavior of biological tissues. Its automation, new materials and manufacturing techniques will enable its use in the near future. This research is based on the use of compressed air in pneumatic muscles that actuate the phalanges. The research is important because it proposes a system that adapts to the needs and economic accessibility or people with limited resources. The problem to solve is that it meets certain standards such as: stable grip and pressure and that it adapts to irregularly shaped objects with more natural movements. The principle of communicating vessels and the force exerted by a fluid on the walls of the container that is used. Consequently, the fluid exerts pressure in all directions. The prosthesis with the design of the Flexy Hand 2 is manufactured by inserting pneumatic muscles to each of the fingers connecting them by means of nylon ropes that are attached to the homemade pneumatic muscles connected to a common manifold, regulating the pressure by means of a valve and a degree of freedom. As a result of the above, it can be concluded that the prototype worked favorably.