Pneumatic Muscle Actuators Research Articles

Anti-disturbance control of CPG bionic reflection in pneumatic muscle actuator

Anti-disturbance control of CPG bionic reflection in pneumatic muscle actuator

A bionic robotic ankle driven by the multiple pneumatic muscle actuators

The traditional pneumatic muscle robot joint has weak load capacity and low control precision. This paper proposes a bionic robotic ankle driven by multiple pneumatic muscle actuators. The structural design of the bionic robotic ankle and the drive mechanism that imitates human muscle recruitment are introduced. A dynamic model of the ankle and a static model of the pneumatic muscle actuator are established to analyze the driving characteristics. The multi-muscle recruiting strategy and load matching control method are optimized, and the output characteristics are simulated, including the robotic ankle driven by a single pneumatic muscle actuator, the robotic ankle driven by dual pneumatic muscle actuators, and the bionic ankle driven by multiple pneumatic muscle actuators. A prototype and testing platform are developed, and experimental research is carried out to validate the theoretical analysis and simulation. The results show that the bionic robotic ankle driven by multiple pneumatic muscle actuators can match varied loads, effectively reducing angle error and increasing output force.

Enhancing jumping performance of bionic leg with pneumatic muscle actuation based on neural network control

Enhancing jumping performance of bionic leg with pneumatic muscle actuation based on neural network control

A Current-Mode Analog Front-End for Capacitive Length Transducers in Pneumatic Muscle Actuators.

This paper reports on the design, implementation, and characterization of a current-mode analog-front-end circuit for capacitance-to-voltage conversion that can be used in connection with a large variety of sensors and actuators in industrial and rehabilitation medicine applications. The circuit is composed by: (i) an oscillator generating a square wave signal whose frequency and pulse width is a function of the value of input capacitance; (ii) a passive low-pass filter that extracts the DC average component of the square wave signal; (iii) a DC-DC amplifier with variable gain ranging from 1 to 1000. The circuit has been designed in the current-mode approach by employing the second-generation current conveyor circuit, and has been implemented by using commercial discrete components as the basic blocks. The circuit allows for gain and sensitivity tunability, offset compensation and regulation, and the capability to manage various ranges of variations of the input capacitance. For a circuit gain of 1000, the measured circuit sensitivity is equal to 167.34 mV/pF with a resolution in terms of capacitance of 5 fF. The implemented circuit has been employed to measure the variations of the capacitance of a McKibben pneumatic muscle associated with the variations of its length that linearly depend on the circuit output voltage. Under step-to-step conditions of movement of the pneumatic muscle, the overall system sensitivity is equal to 70 mV/mm with a standard deviation error of the muscle length variation of 0.008 mm.

Encrypted Simultaneous Control of Joint Angle and Stiffness of Antagonistic Pneumatic Artificial Muscle Actuator by Polynomial Approximation

Encrypted Simultaneous Control of Joint Angle and Stiffness of Antagonistic Pneumatic Artificial Muscle Actuator by Polynomial Approximation

A Systematic Review of Soft Actuators in Agriculture

Industrial machines and robots use actuators to facilitate repetitive tasks. Conventionally, stiff actuators are used to enable precise position control in a high-pace system. They are usually placed in human-free environments because of safety concerns as they do not comply in a collision. On the other hand, there has been a growing interest in human-robot interactions that require robots to be placed alongside humans. These applications need a soft actuator. An example of a soft actuator is a pneumatic muscle actuator (PMA) which produces a one-way motion and force as a result of the muscle’s contraction under air pressure. In this paper, the aim is to present a systematic review covering the main published solutions of soft actuators including PMA in agricultural applications. This paper provides a useful foundation on the soft actuators, their main applications in agriculture, their challenges and opportunities, as well as supporting new research works in the soft actuators' field.

Improving Exoskeleton Functionality: Design and Comparative Evaluation of Control Techniques for Pneumatic Artificial Muscle Actuators in Lower Limb Rehabilitation and Work Tasks

Improving Exoskeleton Functionality: Design and Comparative Evaluation of Control Techniques for Pneumatic Artificial Muscle Actuators in Lower Limb Rehabilitation and Work Tasks

Nonlinear response and fluctuating torque characteristics of the pneumatic muscle actuators at crankshaft application

The present study aims to investigate the availability of pneumatic muscle actuators (PMAs) for producing continuous rotational motion by simulating a crankshaft drive system actuated by artificial muscles. It examines the nonlinear behavior and fluctuating torque characteristic of the PMAs in the crankshaft drive system over the experimentally determined tensile forces. It also looks at the effects of the joint structure, the contraction rate, the timing of the pressurization, the use of a mechanical stopper, and the number of PMAs. It identifies and examines five design versions, including the variations of these parameters. It investigates the range of these parameters for an ideal configuration of the PMA-based crankshaft drive system. The results showed that 44.9 N·m average crankshaft torque fluctuating between 18 and 81.4 N·m is achievable using DMSP-20-300 PMAs at 600 kPa air pressure. Regarding continuous rotational motion, the crankshaft application differs from the PMA-based studies in the literature. The proposed approach fills a gap in the spectrum of activation technologies since it converts linear stroke into continuous and fluctuated rotational output through intermittent oscillating pulling motion generated by a single pneumatic artificial muscle.

Design of squeezing-tube-driven pump for soft pneumatic robotics based on spiral spring winding

Aiming at the demand for high-speed, easy-controllability, and integration of pneumatic soft robots and elastomer actuators, this study presents a squeezing-tube-driven pump (STDP) for soft pneumatic robotics based on spiral spring winding. This concept contains a customized spiral spring and a pneumatic tube with high-elasticity. The spiral spring is driven by an electric motor and coerced into winding deformation. Furthermore, the pneumatic tube is extruded by the spring and then the air in the tube is fast compressed to drive soft pneumatic grippers. The mechanical model and simulation are utilized to explain the operating principle of STDP. The air pressure and rotation angle of the spring under various rotation speeds are in a close linear correlation verified by the experimental results, which provides feasibility for easy controlling and rapid actuation. Finally, fast-gripping tests with an integrated gripper–pump system and a pneumatic muscle actuation test are presented to show the advantages of the proposed pump, respectively.

Position Control of a Cost-Effective Bellow Pneumatic Actuator Using an LQR Approach

Today, we are witnessing an increasing trend in the number of soft pneumatic actuator solutions in industrial environments, especially due to their human-safe interaction capabilities. An interesting solution in this frame is a vacuum pneumatic muscle actuator (PMA) with a bellow structure, which is characterized by a high contraction ratio and the ability to generate high forces considering its relatively small dimensions. Moreover, such a solution is generally very cost-effective since can be developed by using easily accessible, off-the-shelf components combined with additive manufacturing procedures. The presented research analyzes the precision positioning performances of a newly developed cost-effective bellow PMA in a closed-loop setting, by utilizing a Proportional-Integral-Derivative (PID) controller and a Linear Quadratic Regulator (LQR). In a first instance, the system identification was performed and a numerical model of the PMA was developed. It was experimentally shown that the actuator is characterized by nonlinear dynamical behavior. Based on the numerical model, a PID controller was developed as a benchmark. In the next phase, an LQR that involves a nonlinear pregain term was built. The point-to-point positioning experimental results showed that both controllers allow fast responses without overshoot within the whole working range. On the other hand, it was discovered that the LQR with the corresponding nonlinear pregain term allows an error of a few tens of micrometers to be achieved across the entire working range of the muscle. Additionally, two different experimental pneumatic solutions for indirect and direct vacuum control were analyzed with the aim of investigating the PMA response time and comparing their energy consumption. This research contributes to the future development of the pneumatically driven mechatronics systems used for precise position control.

Data-Driven Adaptive Iterative Learning Control of a Compliant Rehabilitation Robot for Repetitive Ankle Training

This letter investigates the repetitive range of motion (ROM) training control for a compliant ankle rehabilitation robot (CARR). The CARR utilizes four pneumatic muscle (PM) actuators to manipulate the ankle with three rational degree-of-freedoms (DoFs) and soft human-robot interaction, but the strong-nonlinearity of the PM actuator makes precise tracking difficult. To improve the training effectiveness, a data-driven adaptive iterative learning controller (DDAILC) is proposed based on compact form dynamic linearization (CFDL) with estimated pseudo-partial derivative (PPD). Instead of using a PM dynamic model, the estimated PPD is updated merely by online input-output (I/O) measures. Sufficient conditions are established to guarantee the convergence of tracking errors and the boundedness of control input. Experimental studies are conducted on ten human participants with two therapist-resembled trajectories. Compared with other data-driven methods, the proposed DDAILC demonstrates significant improvement on tracking performance.

Robust Iterative Learning Control for Pneumatic Muscle With Uncertainties and State Constraints

In this article, we propose a new iterative learning control (ILC) scheme for trajectory tracking of pneumatic muscle (PM) actuators with state constraints. A PM model is constructed in three-element form with both parametric and nonparametric uncertainties, while full state constraints are considered for enhancing operational safety. To ensure that system states are within the predefined bounds, the barrier Lyapunov function (BLF) is used in the analysis, which reaches infinity when some of its arguments approach limits. The proposed ILC incorporates the BLF with the composite energy function (CEF) approach and ensures the boundedness of CEF in the closed-loop, thus, assuring that those limits are not transgressed. Through rigorous analysis, we show that under the proposed ILC scheme, uniform convergences of PM state tracking errors are guaranteed. Simulation studies and experimental validations are conducted to illustrate the efficacy of the proposed scheme. Experimental results show that the proposed ILC satisfies the state constraint requirements and the tracking error is less than 2.5% of the desired trajectory.

Mechanical Structural Design and Actuation Technologies of Powered Knee Exoskeletons: A Review

Robot knee exoskeletons can not only help the rehabilitation training function of the elderly and disabled patients, but also enhance the performance of healthy people in normal walking and weigh-bearing walking by providing sufficient torques. In recent years, the exoskeletons of knee joints have been extensively explored. The review is to summarize the existing research results of mechanical structure design and actuation technologies, propose the future development trend, and promote the further development of the powered knee exoskeletons, related theories, and engineering applications. In this study, the mechanical structures of knee exoskeletons are first illustrated. Their mechanical structures are classified into two types: simple mechanical structures with one purely rotary DOF and biological geometry-based multi-DOF structures. Subsequently, the actuation design of wearable knee exoskeletons includes conventional driving actuators, pneumatic muscle actuators, variable stiffness actuators, and other actuators are compared and the driving compliance and the difficulty in the accurate control are analyzed. Furthermore, other crucial technologies such as motion intention recognition, control strategy and performance evaluation methods of most knee assistive devices are reviewed. Finally, the key technologies of structural design and actuation design in the research of knee exoskeletons are summarized and future research hotspots are proposed.

Design, Construction and Control of a Manipulator Driven by Pneumatic Artificial Muscles

This paper describes the design, construction and experimental testing of a single-joint manipulator arm actuated by pneumatic artificial muscles (PAMs) for the tasks of transporting and sorting work pieces. An antagonistic muscle pair is used in a rotational sense to produce a required torque on a pulley. The concept, operating principle and elementary properties of pneumatic muscle actuators are explained. Different conceptions of the system realizations are analyzed using the morphological-matrix conceptual design framework and top-rated solution was practically realized. A simplified, control-oriented mathematical model of the manipulator arm driven by PAMs and controlled with a proportional control valve is derived. The model is then used for a controller design process. Fluidic muscles have great potential for industrial applications and assembly automation to actuate new types of robots and manipulators. Their characteristics, such as compactness, high strength, high power-to-weight ratio, inherent safety and simplicity, are worthy features for advanced manipulation systems. The experiments were carried out on a practically realized manipulator actuated by a pair of muscle actuators set into an antagonistic configuration. The setup also includes an original solution for the subsystem to add work pieces in the working space of the manipulator.

Dynamic modeling of pneumatic braided muscle actuator based on Hill muscle model

This article presents a dynamic model of a pneumatic braided muscle (PBM) actuator which is inspired from skeletal muscle model. The behavior of the PBM actuator can be simulated as Hill muscle model and thus, it is modeled as an equivalent nonlinear spring dashpot system. Instead of empirical relations, the force-stretch relation of the actuator derived in our earlier work based on finite deformation theory is utilized. The nonlinear equation of motion is solved for both free and forced vibration cases numerically. The frequency analysis of the forced vibration is performed using the multiple scales method. Furthermore, the effect of various parameters like damping, material stiffness, and geometry on the nonlinear response of the actuator has been examined using time response, phase portrait, and frequency response at simple resonance condition. This study will assist researchers to determine safe system parameter range for diverse applications.

Output-based event-triggered tracking control for networked pneumatic muscle actuators system with packet disorders

Output-based event-triggered tracking control for networked pneumatic muscle actuators system with packet disorders

A Review on the Development of Pneumatic Artificial Muscle Actuators: Force Model and Application

Pneumatic artificial muscles (PAMs) are soft and flexible linear pneumatic actuators which produce human muscle like actuation. Due to these properties, the muscle actuators have an adaptable compliance for various robotic platforms as well as medical applications. While a variety of possible actuation schemes are present, there is still a need for the development of a soft actuator that is very light-weight, compact, and flexible with high power-to-weight ratio. To achieve this, the development of the PAM actuators has become an interesting topic for many researchers. In this review, the development of the different kinds of PAM available to date are presented along with manufacturing process and the operating principle. The various force models for artificial muscle presented in the literature are broadly reviewed with the constraints. Furthermore, the applications of PAM are included and classified based on the fields of biorobotics, medicine, and industry, along with advanced medical instrumentation. Finally, the needful improvements in terms of the dynamics of the muscle are discussed for the precise control of the PAMs as per the requirements for the applications. This review will be helpful for researchers working in the field of robotics and for designers to develop new type of artificial muscle depending on the applications.

Impedance Iterative Learning Backstepping Control for Output-Constrained Multisection Continuum Arms Based on PMA

Background: Pneumatic muscle actuator (PMA) actuated multisection continuum arms are widely applied in various fields with high flexibility and bionic properties. Nonetheless, their kinematic modeling and control strategy proves to be extremely challenging tasks. Methods: The relationship expression between the deformation parameters and the length of PMA with the geometric method is obtained under the assumption of piecewise constant curvature. Then, the kinematic model is established based on the improved D-H method. Considering the limitation of PMA telescopic length, an impedance iterative learning backstepping control strategy is investigated. For one thing, the impedance control is utilized to ensure that the ideal static balance force is maintained constant in the Cartesian space. For another, the iterative learning backstepping control is applied to guarantee that the desired trajectory of each PMA can be accurately tracked with the output-constrained requirement. Moreover, iterative learning control (ILC) is implemented to dynamically estimate the unknown model parameters and the precondition of zero initial error in ILC is released by the trajectory reconstruction. To further ensure the constraint requirement of the PMA tracking error, a log-type barrier Lyapunov function is employed in the backstepping control, whose convergence is demonstrated by the composite energy function. Results: The tracking error of PMA converges to 0.004 m and does not exceed the time-varying constraint function through cosimulation. Conclusion: From the cosimulation results, the superiority and validity of the proposed theory are verified.

A Comprehensive Comparison of Different Control Strategies to Adjust the Length of the Soft Contractor Pneumatic Muscle Actuator

According to the growing interest in the soft robotics research field, where various industrial and medical applications have been developed by employing soft robots. Our focus in this paper will be the Pneumatic Muscle Actuator (PMA), which is the heart of the soft robot. Achieving an accurate control method to adjust the actuator length to a predefined set point is a very difficult problem because of the hysteresis and nonlinearity behaviors of the PMA. So the construction and control of a 30 cm soft contractor pneumatic muscle actuator (SCPMA) were done here, and by using different strategies such as the PID controller, Bang-Bang controller, Neural network controller, and Fuzzy controller, to adjust the length of the (SCPMA) between 30 cm and 24 cm by utilizing the amount of air coming from the air compressor. All of these strategies will be theoretically implemented using the MATLAB/Simulink package. Also, the performance of these control systems will be compared with respect to the time-domain characteristics and the root mean square error (RMSE). As a result, the controller performance accuracy and robustness ranged from one controller to another, and we found that the fuzzy logic controller was one of the best strategies used here according to the simplicity of the implementation and the very accurate response obtained from this method.

Design, Development, and Control of a Novel Upper-Limb Power-Assist Exoskeleton System Driven by Pneumatic Muscle Actuators

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.