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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. [ABSTRACT FROM AUTHOR]

The McKibben muscle types are pneumatic actuators known to be intrinsically safe for their high power-to-weight ratio. For these reasons, they are suitable for robotic, biomechanical, and medical applications. In these application fields and, above all, in collaborative robotics, where safety must be ensured for human–robot interactions, the values of pressure, force, and length are necessary and must be continuously monitored and controlled. Force and pressure transducers are commercially available to be integrated into a McKibben muscle type. On the contrary, no commercial-length transducers can be adopted. This work presents a novel McKibben muscle prototype with an embedded capacitive-length transducer. The latter is a cylindrical capacitor made of a telescopic system composed of two tubes: one of its ends is connected to the muscle. A change in the length of the muscle causes a proportional change in the transducer capacitance. The paper reports in detail on the working principle of McKibben's muscle, its fabrication, characterization, and validation of four prototype capacitive transducers. The results achieved from the experimental activities demonstrate that it is possible to control the variations of the muscle length relative to its elongation and compression for values less than 1 mm. This is the consequence of the ability to measure the transducer capacitance with a typical statistical relative indetermination better than 0.25%, which is a figure of merit for the reliability and mechanical and electrical stability of the proposed McKibben muscle prototype. Moreover, it has been demonstrated that the transducer capacitance as a function of the muscle length is linear, with maximum deviations from linearity equal to 2.44% and 5.22% during the muscle elongation and compression, respectively. [ABSTRACT FROM AUTHOR]

The exoskeleton plays an essential role in the field of physical rehabilitation. Several actuators are used for the exoskeleton application, but the pneumatic muscle actuator has proved to be the best due to its high power to weight ratio, compliance, and safe operation. The objective of this paper involves the fabrication and experimental characterization of a pneumatic muscle actuator to actuate an exoskeleton for the elbow joint. This paper presents the development and testing of twelve pneumatic muscles of varying materials and sizes, to find the best combination to suit the intended application. The characterization process involved several tests, which related force, deflection, and pressure at various loading conditions. A modular test rig was developed to conduct all the tests with minor adjustments to the test setup. The study also involved designing and developing an elbow exoskeleton to test the pneumatic muscle in the real-world scenario. The exoskeleton is designed with a novel hinge to compensate for the antagonistic nature of the pneumatic muscle actuator. The tests showed the muscles with higher tensile modules bladders having a lower hysteresis and better load handling capability, but these suffered from lower contraction and force characteristics. The styrene-based muscle with a 12mm bladder (S12LB) showed the best force and deflection characteristics at various pressures and loading conditions. The styrene bladder has a modulus closer to the skeletal muscle, therefore demonstrating higher compliance and making it a preferred choice for the exoskeleton application

Pneumatic muscle actuator (PMA) similar to biological muscle is a new type of pneumatic actuator. The flexible manipulator based on PMAs was constructed to simulate the actual movement of the human upper arm. Considering the model errors and external disturbances, the fuzzing sliding mode control based on the saturation function was proposed. Compared with other fuzzy control methods, fuzzy control and saturation function are used to adjust the robust terms to improve the tracking accuracy and reduce the high-frequency chattering. [ABSTRACT FROM AUTHOR]

Dynamic characteristics and control of thin McKibben muscle (TMM) have not yet been fully investigated, especially on the translational antagonistic pair system. Therefore, the objective of this study is to propose a Switching Model Predictive Control (SMPC) based on a Piecewise Affine (PWA) system model to control a translational antagonistic-pair TMM servo actuator. A novel configuration enables the servo actuator to achieve a position control of 40 mm within a small footprint. The result shows that the feedback system gives minimal steady-state errors when tracking staircase and setpoint references ranging from 0 to 3.5 cm. The controller also produces better transient and steady-state responses than our previously developed Gain-scheduled Proportional–Integral–Derivative (GSPID) controller. The evidence from this study suggests that a predictive control for a TMM servo actuator is feasible. [ABSTRACT FROM AUTHOR]

An innovative wearable upper-limb power-assist exoskeleton system (UPES) was designed for laborers to improve work efficiency and reduce the risk of musculoskeletal disorders. This novel wearable UPES consists of four joints, each comprising a single actuated pneumatic muscle actuator (PMA) and a torsion spring module driven via a steel cable. Unlike most single-joint applications, where dual-PMAs are driven by antagonism, this design aims to combine a torsion spring module with a single-PMA via a steel cable for a 1-degree of freedom (1-DOF) joint controlled by a proportional-pressure regulator. The proposed four driving degrees of freedom wearable UPES is suitable for power assistance in work and characterizes a simple structure, safety, and compliance with the motion of an upper limb. However, due to the hysteresis, time-varying characteristics of the PMA, and non-linear movement between joint flexion and extension, the model parameters are difficult to identify accurately, resulting in unmeasurable uncertainties and disturbances of the wearable UPES. To address this issue, we propose an improved proxy-based sliding mode controller integrated with a linear extended state observer (IPSMC-LESO) to achieve accurate power-assisted control for the upper limb and ensure safe interaction between the UPES and the wearer. This control method can slow the underdamped dynamic recovery motion to tend the target trajectory without overshoots from large tracking errors that result in actuator saturation, and without deteriorating the power assist effect during regular operation. The experimental results show that IPSMC-LESO can effectively control a 4-DOF wearable UPES, observe the unknown states and total disturbance online of the system, and adapt to the external environment and load changes to improve system control performance. The results prove that the joint torsion spring module combining the single-PMA can reduce the number of PMAs and proportional-pressure regulators by half and obtain a control response similar to that of the dual-PMA structure. [ABSTRACT FROM AUTHOR]

The human-centered robotic systems demand safe and robust controllers in many applications. This paper proposes an adaptive proxy-based sliding mode control approach for a class of typical second-order nonlinear systems. A new PID-type virtual coupling is designed between a virtual proxy and the physical object. Considering the unknown bound of lumped disturbances, an adaptation law is applied to online adjust the gain of a sign function which ensures the proxy to track the reference accurately. By using the Lyapunov theorem, the closed-loop system stability is proved. Both simulations and experiments are conducted to verify the proposed method based on a real-world pneumatic muscle actuator control platform. The results show that the proposed adaptive proxy-based sliding mode control approach presents better tracking accuracy, safety, and robustness than the conventional PID control and sliding mode control. [ABSTRACT FROM AUTHOR]

Pneumatic muscle actuators (PMAs) are frequently used in a wide variety of biorobotic applications, such as robotic orthoses and wearable exoskeletons, due to their high power/weight ratio and significant compliance. However, the asymmetric hysteresis nonlinearity reduces their fidelity and cause difficulties in the accurate control procedure. In this paper, Bouc–Wen hysteresis model is modified to describe the asymmetric force/length hysteresis of the PMA. The effect of muscle length on hysteretic restoring force is considered in this modified model and experimental results show that the proposed model has a better performance to characterize the asymmetric hysteresis loop of pneumatic muscles. The nonlinear pressure/force model of these actuators also is modeled precisely and its performance is experimentally verified for different muscle lengths. [ABSTRACT FROM AUTHOR]

This paper presents a novel force sensorless reflecting controller for a haptic-enabled device driven by a bilateral pneumatic artificial muscle system, which proposed configuration for the first time the bilateral haptic teleoperation. For details, an adaptive force observer scheme considered to be an alternative to direct force measurement is proposed to estimate the interaction force with an unknown environment for the force reflecting control design. Meanwhile, the separately fast finite time nonsingular terminal sliding mode control schemes are developed based on the force estimation in both subsystems to achieve good tracking performance and fast response. Thus, the great transparency performance with both force feedback and position tracking can be achieved simultaneously by using our proposed method. The finite-time stability of the total controlled system is demonstrated by the Lyapunov approach. Moreover, the comparative experiments are carried out on the developed testbench to validate the effectiveness and advantages of our proposed control design in the different working conditions.

Abstract A bionic flexible manipulator driven by pneumatic muscle actuator (PMA) can better reflect the flexibility of the mechanism. Current research on PMA mainly focuses on the modeling and control strategy of the pneumatic manipulator system. Compared with traditional electro-hydraulic actuators, the structure of PMA is simple but possesses strong nonlinearity and flexibility, which leads to the difficulty in improving the control accuracy. In this paper, the configuration design of a bionic flexible manipulator is performed by human physiological map, the kinematic model of the mechanism is established, and the dynamics is analyzed by Lagrange method. A fuzzy torque control algorithm is designed based on the computed torque method, where the fuzzy control theory is applied. The hardware experimental system is established. Through the co-simulation contrast test on MATLAB and ADAMS, it is found that the fuzzy torque control algorithm has better tracking performance and higher tracking accuracy than the computed torque method, and is applied to the entity control test. The experimental results show that the fuzzy torque algorithm can better control the trajectory tracking movement of the bionic flexible manipulator. This research proposes a fuzzy torque control algorithm which can compensate the error more effectively, and possesses the preferred trajectory tracking performance.

The McKibben muscle types are pneumatic actuators known to be intrinsically safe for their high power-to-weight ratio. For these reasons, they are suitable for robotic, biomechanical, and medical applications. In these application fields and, above all, in collaborative robotics, where safety must be ensured for human–robot interactions, the values of pressure, force, and length are necessary and must be continuously monitored and controlled. Force and pressure transducers are commercially available to be integrated into a McKibben muscle type. On the contrary, no commercial-length transducers can be adopted. This work presents a novel McKibben muscle prototype with an embedded capacitive-length transducer. The latter is a cylindrical capacitor made of a telescopic system composed of two tubes: one of its ends is connected to the muscle. A change in the length of the muscle causes a proportional change in the transducer capacitance. The paper reports in detail on the working principle of McKibben’s muscle, its fabrication, characterization, and validation of four prototype capacitive transducers. The results achieved from the experimental activities demonstrate that it is possible to control the variations of the muscle length relative to its elongation and compression for values less than 1 mm. This is the consequence of the ability to measure the transducer capacitance with a typical statistical relative indetermination better than 0.25%, which is a figure of merit for the reliability and mechanical and electrical stability of the proposed McKibben muscle prototype. Moreover, it has been demonstrated that the transducer capacitance as a function of the muscle length is linear, with maximum deviations from linearity equal to 2.44% and 5.22% during the muscle elongation and compression, respectively.

An innovative wearable upper-limb power-assist exoskeleton system (UPES) was designed for laborers to improve work efficiency and reduce the risk of musculoskeletal disorders. This novel wearable UPES consists of four joints, each comprising a single actuated pneumatic muscle actuator (PMA) and a torsion spring module driven via a steel cable. Unlike most single-joint applications, where dual-PMAs are driven by antagonism, this design aims to combine a torsion spring module with a single-PMA via a steel cable for a 1-degree of freedom (1-DOF) joint controlled by a proportional-pressure regulator. The proposed four driving degrees of freedom wearable UPES is suitable for power assistance in work and characterizes a simple structure, safety, and compliance with the motion of an upper limb. However, due to the hysteresis, time-varying characteristics of the PMA, and non-linear movement between joint flexion and extension, the model parameters are difficult to identify accurately, resulting in unmeasurable uncertainties and disturbances of the wearable UPES. To address this issue, we propose an improved proxy-based sliding mode controller integrated with a linear extended state observer (IPSMC-LESO) to achieve accurate power-assisted control for the upper limb and ensure safe interaction between the UPES and the wearer. This control method can slow the underdamped dynamic recovery motion to tend the target trajectory without overshoots from large tracking errors that result in actuator saturation, and without deteriorating the power assist effect during regular operation. The experimental results show that IPSMC-LESO can effectively control a 4-DOF wearable UPES, observe the unknown states and total disturbance online of the system, and adapt to the external environment and load changes to improve system control performance. The results prove that the joint torsion spring module combining the single-PMA can reduce the number of PMAs and proportional-pressure regulators by half and obtain a control response similar to that of the dual-PMA structure.

Dynamic characteristics and control of thin McKibben muscle (TMM) have not yet been fully investigated, especially on the translational antagonistic pair system. Therefore, the objective of this study is to propose a Switching Model Predictive Control (SMPC) based on a Piecewise Affine (PWA) system model to control a translational antagonistic-pair TMM servo actuator. A novel configuration enables the servo actuator to achieve a position control of 40 mm within a small footprint. The result shows that the feedback system gives minimal steady-state errors when tracking staircase and setpoint references ranging from 0 to 3.5 cm. The controller also produces better transient and steady-state responses than our previously developed Gain-scheduled Proportional–Integral–Derivative (GSPID) controller. The evidence from this study suggests that a predictive control for a TMM servo actuator is feasible.

In pneumatic muscle actuators (PMAs)-driven robotic applications, there might exist unpredictable shocks which lead to the sudden change of desired trajectories and large tracking errors. This is dangerous for physical systems. In this article, we propose a novel adaptive proxy-based robust controller (APRC) for PMAs, which is effective in realizing a damped response and regulating the behaviors of the PMA via a virtual proxy. Moreover, the integration of the APRC and the nonlinear disturbance observer further handles the system uncertainties/disturbances and improves the system robustness. According to the Lyapunov theorem, the tracking states of the closed-loop PMA control system are proven to be globally uniformly ultimately bounded through two motion phases. Extensive experiments are conducted to verify the superior performance of our approach, in multiple tracking scenarios. [ABSTRACT FROM AUTHOR]

Summary: This paper presents a lower-limb exoskeleton that is actuated by pneumatic muscle actuators (PMAs). This exoskeleton system is composed of the mechanical structures, a treadmill, and a weight support system. With the cooperative work of the three parts, the system aims to assist either the elderly for muscle strengthening by conducting walking activities or the stroke patients during a rehabilitation training program. A mechanism is developed to separate the PMAs from the wearer's legs to reduce the subject's physical exertion. Furthermore, considering the difficulty in the modeling of proposed PMAs-driven exoskeleton, a safe and model-free control strategy called proxy-based sliding mode control (PSMC) is used to ensure proper control of the exoskeleton. However, the favorable performances are strongly dependent on the appropriate control parameters, which may be difficult to obtain with blind tuning. Therefore, we propose a global parameters optimization algorithm called switch-mode firefly algorithm (SMFA) to automatically calculate the pre-defined object function and attain the most applicable parameters. Experimental studies are conducted, and the results show the effectiveness of the proposed method. [ABSTRACT FROM AUTHOR]

This paper presents the trajectory tracking control of a multi-section continuum and compliant manipulator with large workspace. Fluidic muscles are utilized as actuators in this manipulator and inertial sensors used to measure its shape in configuration space. The robot's large workspace signifies the effects of the inertial, gravitational, and applied external forces on the trajectory tracking control of the robot end-effector. In this study, a model-based sliding-surface controller is proposed by deriving a simplified Pseudo-Rigid Body (PRB) dynamic model, which utilizes modified constant curvature assumptions to describe the couplings between the robot sections and actuators. Simplification steps are proposed for a PRB dynamic model by eliminating negligible dynamic effects to achieve a computationally efficient implementation with real-time control performance. The unmodeled dynamics and the error of model simplifications are considered as system uncertainties and an integral sliding surface with a variable sliding gain is proposed to overcome these uncertain dynamics. The sliding gain considers changes in the upper bounds of uncertainties. The closed-loop system stability in trajectory tracking is mathematically proved based on the Lyapunov stability theorem. Experiments throughout the manipulator's large workspace in challenging configurations including sudden release of unknown loads at the robot tip also highlight the potential of our contributed controller. [ABSTRACT FROM AUTHOR]

This paper presents a tracking control method for pneumatic muscle actuators (PMAs). Considering that the PMA platform only feedbacks position, and the velocity and disturbances cannot be observed directly, we use the extended-state-observer (ESO) for simultaneously estimating the system states and disturbances by using measurable variables. Integrated with the ESO, a super twisting controller (STC) is design based on estimated states to realize the high-precision tracking. According to the Lyapunov theorem, the stability of the closed-loop system is ensured. Simulation and experimental studies are conducted, and the results show the convergence of the ESO and the effectiveness of the proposed method.

The pneumatic muscle actuator (PMA) has many advantages, such as good flexibility, high power / weight ratio, but its nonlinearity makes it difficult to build a static mathematical model with high precision. A new method is proposed to establish the model of PMA. The concept of hybrid elastic modulus which is related to the static characteristic of PMA is put forward, and the energy conservation law is used to achieve the expression of the hybrid elastic modulus, which can be fitted out based on experimental data, and the model of PMA can be derived from this expression. At the same time, a 3 - DOF parallel mechanism(a new bionic shoulder joint)driven by five PMAs is designed. This bionic shoulder joint adopts the structure of two antagonistic PMAs actualizing a rotation control and three PMAs controlling another two rotations to get better rotation characteristics. The kinematic and dynamic characteristics of the mechanism are analyzed and a new static model of PMA is used to control it. Experimental results demonstrate the effectiveness of this new static model. [ABSTRACT FROM AUTHOR]

SUMMARY: A 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. [ABSTRACT FROM AUTHOR]

Implementation of a prototype of a 4-degree of freedom (4-DOF) upper-limb exoskeleton robot for rehabilitation was described in this paper. The proposed exoskeleton robot has three DOFs at the shoulder joint and one DOF at the elbow joint. The upper-limb exoskeleton robot is driven by pneumatic muscle actuators (PMA) via steel cables. To implement the passive rehabilitation control, the rehabilitation trajectories expressed in the Fourier series were first planned by the curve fitting. The fuzzy sliding mode controller (FSMC) was then applied to the upper-limb exoskeleton robot for rehabilitation control. Several rehabilitation scenarios were carried out to validate the designed PMA-actuated exoskeleton robot.

A lesser known type of pneumatic actuators is pneumatic muscle actuator (PMA) although the first investigations related to PMAs are mentioned by a Russian researcher Garasiev in 1930s. Recently, the most often applied PMA is the Fluidic Muscle manufactured by Festo Company. Generally, PMAs differ from standard cylindrical pneumatic actuators as they have no inner moved parts and there is no sliding on the surfaces. Another difference is that the force develepod by a standard cylindrical pneumatic actuator depends only on the applied pressure and piston surface but the force produced by a PMA depends on the displacement as well. This paper focuses on PMA, especially Fluidic Muscle and a human-like hand actuated by PMAs designed in Solid Edge by academic students is presented. [ABSTRACT FROM AUTHOR]

Pneumatic muscle actuators have the highest power/weight ratio of any actuator and therefore it has a broad application prospect in soft robotics. This paper presents a two degree of freedom (2-DOF) pneumatic muscle actuator that consists of four pneumatic artificial muscles (PAMs) and two rotation joins. However, this pneumatic muscle actuator has highly nonlinear and hysteretic properties (among muscle force, muscle displacement and pressure in the muscle), which lead to difficulty in accurate position control. Pneumatic muscle actuator usually necessitate the use various nonlinear techniques for control in order to improve their performance. The paper contains selection of computational intelligence methods designed for application in pneumatic muscle actuator. There are described and compared MLP neural network and RBF neural network. [ABSTRACT FROM AUTHOR]

Soft robotics, often taking inspirations from biomimetics, is an exciting novel research field and has great capability to work with creatures. A new type of bio-soft robot inspired by elephant trunk and octopus was proposed, which has a promising application in robotic agricultural harvesting. The two modularized structures, basal segment and caudal segment, were elaborated in detail. They both have three side chambers and one central chamber, which are reinforced by springs for better stretch performance in axial direction without radial expansion. All the chambers can act as drivers when inflated with compressed air. More importantly, the central chamber was designed for regulating the stiffness of the robot module as needed in application. The primary static model for axial elongation was established for the fundamental analysis of the bio-soft robot module's features, such as iso-force, isobaric and isometric characteristics. Simulation and experimental results showed that the motion of the proposed bio-soft module has approximate linearity in iso-force and isobaric conditions, and strict linearity in isometric condition. [ABSTRACT FROM AUTHOR]

Electrics, hydraulics and pneumatics can be the main motion power of industrial robots. Pneumatic cylinders, pneumatic motors, pneumatic stepper motors and pneumatic bellows are widely used in industrial environment due to their power/weight ratio, power/volume ratio, strength, compactness, simplicity, reliability and cost. Disadvantages of pneumatic actuators can be summarized as follows: difficult to control accurately, air compressibility, compliance and noisiness. Relatively new type of the pneumatic actuators is the pneumatic artificial muscle (PAM) or pneumatic muscle actuator (PMA). Fluidic Muscle made by Festo Company is one of the most investigated commercially available PMA. Pneumatic muscle actuators can be used in industrial environment as well as in prosthesis or rehabilitation devices. In this paper a humanoid arm actuated by Fluidic Muscle is developed and presented. [ABSTRACT FROM AUTHOR]

The control of the standard pneumatic muscle actuators is provided by increasing the air pressure in the one artificial muscle, while reducing the pressure in the second (antagonist) artificial muscle. The paper contains information about the control and basic properties of the rotary actuator based on pneumatic artificial muscles. It presents equations for the values of the actuator arm displacement depending on an input pressure; it shows the static characteristics of the actuator and the utilization of the muscle contraction. Pneumatic artificial muscles are connected in an antagonistic system through an oval centrally symmetric pulley. Due to the fact that with increasing rotating of actuator arm the torque decrease from the both artificial muscles; the stiffness of the actuator also decreasing in both directions. The proposed method of the present control in this paper has resulted in a small increase of torque of the rotary muscle actuator and thus adequate and symmetric stiffness of actuator. [ABSTRACT FROM AUTHOR]

This paper presents a nonlinear adaptive backstepping algorithm for position control of an anthropomorphic robotic hand. The contraction force of the pneumatic artificial muscle (PAM) actuators has been modeled based on an empirical approach and the overall finger is represented as a nonlinear second order system, taking into account the system uncertainty caused by hysteresis phenomenon in PAM actuators. Adaptive backstepping controller has been developed by formulating the estimator of the system uncertainty. A cascade control system is developed by combining a conventional PID control, as an inner loop controller, with the adaptive backstepping position control as the outer loop of the controller. Finally, a simulation test is conducted to evaluate the performance of the proposed controller. [ABSTRACT FROM AUTHOR]