Antagonistic Pneumatic Artificial Muscles Research Articles

Dynamics and Computed-Muscle-Force Control of a Planar Muscle-Driven Snake Robot

This paper presents the dynamic formulation of an artificial-muscle-driven and computed-muscle–force control for the planar locomotion of a snake robot. The snake robot uses a series of antagonistic pneumatic artificial muscles, assembled at the joints, to generate the locomotion. Kinematics of the artificial-muscle-driven robot in the joint and Cartesian spaces was derived with respect to the muscles’ motion. The Lagrangian mechanics was employed for the formulation of the dynamic model of the robot and deriving the equations of motion. A model-based computed-muscle-force control was designed to track the desired paths/trajectories in Cartesian space. The feedback linearization method based on a change of coordinate was utilized to determine an equivalent linear (input-to-state) system. Then, a full state feedback control law was designed, which satisfies the stability and tracking problems. The performance of the dynamic model and the controller were successfully demonstrated in simulation studies for tracking a circle-shape path and a square-shape path with a constant linear velocity while generating the lateral undulation gait. The results indicate a low magnitude of tracking errors where the controlled muscle force are bounded to the actual pneumatic artificial muscle’s limitations.

Detailed Dynamic Model of Antagonistic PAM System and Its Experimental Validation: Sensorless Angle and Torque Control With UKF

This article proposes a detailed nonlinear mathematical model of an antagonistic pneumatic artificial muscle (PAM) actuator system for estimating the joint angle and torque using an unscented Kalman filter (UKF). The proposed model is described in a hybrid state-space representation. It includes the contraction force of the PAM, joint dynamics, fluid dynamics of compressed air, mass flows of a valve, and friction models. A part of the friction models is modified to obtain a novel form of the Coulomb friction depending on the inner pressure of the PAM. For model validation, offline and online UKF estimations and sensorless tracking control of the joint angle and torque are conducted to evaluate the estimation accuracy and tracking control performance. The estimation error is less than 7.91 %, and the steady-state tracking control performance is more than 94.75 %. These results confirm that the proposed model is detailed and could be used as the state estimator of an antagonistic PAM system.

Cyber-secure pneumatic actuator system equipped with encrypted controller and attack detectors

A cyber-secure and flexible actuator is essential for cyber-physical-human systems. The use of wireless communication in such systems improves their usability but adds cybersecurity risks. This study proposes a cyber-secure flexible antagonistic pneumatic artificial muscle (PAM) actuator system. The proposed PAM actuator system has an encrypted proportional-integral controller and a real-time detector for cyberattacks. The controller is concealed in the encrypted control fashion using a homomorphic encryption scheme with security parameter 64 bit, and the control signal is computed over a cipher space. The detector has a threshold to detect significant changes in control inputs caused by cyberattacks such as signal injection and parameter falsification. The experimental results demonstrate that the proposed PAM actuator system achieves the desired control performance and improves the reliability of control operations under cyberattacks. The main contribution of this study is the first implementation of an encrypted controller for a pneumatic actuator to develop a secure PAM actuator with real-time detection of cyberattacks. The results of this study contribute to the future development of safe remote systems that interact with humans in the medical and industrial fields.

Sensorless angle and stiffness control of antagonistic PAM actuator using reference set

This paper proposes a simultaneous control method for the angle and stiffness of the joint in an antagonistic pneumatic artificial muscle (PAM) actuator system using only pressure measurements in the absence of an external force, and clarifies the allowable references for the PAM actuator system. To achieve a sensorless control, the proposed method estimates the joint angle and contraction forces using an unscented Kalman filter that employs a detailed model of the actuator system. Unlike the previous control methods, the proposed method does not require any encoder and force sensor to achieve angle and stiffness control of the PAM actuator system. Experimental validations using three control scenarios confirm that the proposed method can control the joint angle and stiffness simultaneously and independently. Moreover, it is shown that a reference admissible set can be used as an indicator to establish the reference values by demonstrating that the reference set covers the experimentally obtained trajectories of the angle and stiffness.

An extended state observer-based full-order sliding mode control for robotic joint actuated by antagonistic pneumatic artificial muscles

Pneumatic artificial muscles (PAMs) are expected to play an important role in endowing the advanced robot with the compliant manipulation, which is very important for a robot to coexist and cooperate with humans. However, the strong nonlinear characteristics of PAMs hinder its wide application in robots, and therefore, advanced control algorithms are urgently needed for making the best use of the advantages and bypassing the disadvantages of PAMs. In this article, we propose a full-order sliding mode control extended state observer (fSMC-ESO) algorithm that combines the ESO and the fSMC for a robotic joint actuated by a pair of antagonistic PAMs. The fSMC is employed to eliminate the chattering and to guarantee the finite-time convergence, and the ESO is adopted to observe both the total disturbance and the states of the robot system, so that we can inhibit the disturbance and compensate the nonlinearity efficiently. Both simulations and physical experiments are conducted to validate the proposed method. We suggest that the proposed method can be applied to the robotic systems actuated by PAMs and remarkably improve the performance of the robot system.

Analysis and control of a parallel lower limb based on pneumatic artificial muscles

Most robots that are actuated by antagonistic pneumatic artificial muscles are controlled by various control algorithms that cannot adequately imitate the actual muscle distribution of human limbs. Other robots in which the distribution of pneumatic artificial muscle is similar to that of human limbs can only analyze the position of the robot using perceptual data instead of rational knowledge. In order to better imitate the movement of a human limb, the article proposes a humanoid lower limb in the form of a parallel mechanism where muscle is unevenly distributed. Next, the kinematic and dynamic movements of bionic hip joint are analyzed, where the joint movement is controlled by an observer-based fuzzy adaptive control algorithm as a whole rather than each individual pneumatic artificial muscle and parameters that are optimized by a neural network. Finally, experimental results are provided to confirm the effectiveness of the proposed method. We also document the role of muscle in trajectory tracking for the piriformis and musculi obturator internus in isobaric processes.

Level-Ground Walking for 3D Quasi-Passive Walker with Flat Feet - Lateral-plane Input using McKibben-Type Artificial Muscle -

Currently, many bipedal robots have been proposed to realize the high energy efficiency walking. The passive dynamic walking does not require control input. Generally, a foot of passive dynamic walking robot is an arc foot. In this paper, it is intended to establish a control method and control mechanism to achieve energy efficient and stable gate. Therefore, we developed 3D quasi-passive walker with flat feet driven by an antagonistic pneumatic artificial muscle. An antagonistic mechanism is constituted by a pair of McKibben muscle. And an antagonistic pneumatic system is used as joint actuators of linkage mechanisms which control the torque, joint stiffness and position simultaneously. Finally, this report shows that the 3D quasi-passive walking in the level ground can realize by the swinging (simple) input of the frontal direction, and the stride of the robot is proportional to lateral-plane input.

Mechanism and bias considerations for design of a bi-directional pneumatic artificial muscle actuator

Pneumatic artificial muscles (PAMs), or McKibben actuators, have received considerable attention for robotic manipulators and in aerospace applications due to their similarity to natural muscles. Like natural muscles, PAMs are a purely contractile actuator, so that, in order to produce bi-directional or rotational motion, they must be arranged in an agonist/antagonist pair, which inherently limits the deflection of the system due to the high parasitic stiffness of the antagonistic PAM. This study presents two methods for increasing the performance of an antagonistic PAM system by decreasing the passive parasitic torque, rather than increasing the active torque. The first involves selection of the kinematic mechanism geometry, and the second involves the introduction of bias into the system, both in terms of PAM contraction and passive (antagonistic) PAM pressure. It was found with the proper selection of design parameters, including mechanism geometry, PAM geometry, and bias conditions, that an ideal actuator configuration can be chosen that maximizes deflection for a given arbitrary loading. When comparing a baseline design to an improved design for a simplified case, a nearly 50% increase in maximum deflection was predicted simply by optimizing mechanism geometry and bias contraction. These results were experimentally verified with quasi-static testing that showed a 300% increase in actuator deflection over the baseline design.

Dynamics of a pneumatic artificial muscle actuation system driving a trailing edge flap

This study presents a time domain dynamic model of an antagonistic pneumatic artificial muscle (PAM) driven trailing edge flap (TEF) system for next generation active helicopter rotors. Active rotor concepts are currently being widely researched in the rotorcraft community as a means to provide a significant leap forward in performance through primary aircraft control, vibration mitigation and noise reduction. Recent work has shown PAMs to be a promising candidate for active rotor actuation due to their combination of high force, large stroke, light weight, and suitable bandwidth. When arranged into biologically inspired agonist/antagonist muscle pairs they can produce bidirectional torques for effectively driving a TEF. However, there are no analytical dynamic models in the literature that can accurately capture the behavior of such systems across the broad range of frequencies required for this demanding application. This work combines mechanical, pneumatic, and aerodynamic component models into a global flap system model developed for the Bell 407 rotor system. This model can accurately predict pressure, force, and flap angle response to pneumatic control valve inputs over a range of operating frequencies from 7 to 35 Hz (1/rev to 5/rev for the Bell 407) and operating pressures from 30 to 90 psi.

Extraction and implementation of muscle synergies in neuro-mechanical control of upper limb movement

This work faces the redundancy problem, a central concern in robotics, in a particular force-producing task by using muscle synergies to simplify the control. We extracted muscle synergies from human electromyograph signals and interpreted the physical meaning of the identified muscle synergies. Based on the human analysis results, we hypothesized a novel control framework that can explain the mechanism of the human motor control. The framework was tested in controlling a pneumatic-driven robotic arm to perform a reaching task. This control method, which uses only two synergies as manipulated variables for driving antagonistic pneumatic artificial muscles to generate desired movements, would be useful to deal with the redundancy problem; thus, suggesting a simple but efficient control for human-like robots to work safely and compliantly with humans.

1A1-A06 空気圧人工筋を拮抗配置した回転関節における仮想粘弾性係数同定(ワイヤ駆動系の機構と制御)

1A1-A06 空気圧人工筋を拮抗配置した回転関節における仮想粘弾性係数同定(ワイヤ駆動系の機構と制御)

3D quasi-passive walking of bipedal robot with flat feet: quasi-passive walker driven by antagonistic pneumatic artificial muscle

In this paper, we develop the three-dimensional quasi-passive walker with flat feet which is driven by antagonistic pneumatic artificial muscle. An antagonistic pneumatic system is used as joint actuators of linkage mechanisms which control the torque, joint stiffness and position simultaneously. We examine the structure of an ankle, the control method of an antagonistic pneumatic system and gait analysis using centre of pressure (COP) and rollover shape (ROS). As a result, a three-dimensional quasi-passive walking is realisable by means of adjusting the stiffness of an ankle joint. The average gaits were obtained with the travel distance 1,350 mm, the stride of a step: 210 mm, and the number of steps: six steps. It was demonstrated that the quasi-passive walking is stabilised when both the robotic motions in a lateral plane and in a sagittal plane are synchronised. The COP behaviour of robot gait was almost the same trend of human COP. It was demonstrated that rollover shapes of the sagittal and lateral plane could be adjusted by the internal pressure of the antagonistic pneumatic mechanism.

Research on Movement Stability of Robotic Arm Driven by Antagonistic Pneumatic Artificial Muscle with Mechanical Properties

This paper presents a method how to implement stable rotation of an 1D robotic arm driven by antagonistic pneumatic artificial muscles (PAM) based on SIMULINK platform. Through simulation analysis, the optimal values of the torque from tensile difference of PAM, damping coefficient and rotational inertia were determined to ensure that the robotic arm can smoothly turn from starting point to target one inside an limited interval of time. The results of the study provide a useful reference for the rational design of mechanical characteristics and structure features of the dynamic system. And they also provide more ideal system parameters for successive control of the system.

307 扁平足を有した2足歩行ロボットの3D準受動歩行:-拮抗駆動型空気圧人工筋を装備した準受動歩行機の足首特性-(ロボティクス・メカトロニクスII)

307 扁平足を有した2足歩行ロボットの3D準受動歩行:-拮抗駆動型空気圧人工筋を装備した準受動歩行機の足首特性-(ロボティクス・メカトロニクスII)