Hang T. T. Pham

Novel equilibrium-point control of agonist-antagonist system with pneumatic artificial muscles

This paper presents an electromyographic-based human-machine interface for the agonist-antagonist system with two pairs of pneumatic artificial muscles (PAMs) that replicates the human elbow-joint system. We introduce the novel concepts of agonist-antagonist muscle-pair ratio (A-A ratio) and agonist-antagonist muscle-pair activity (A-A activity) to link the human muscle system to the PAM system, and we propose a linear control method translating the equilibrium point of human muscle system into that of PAM system. The human-robot experiment demonstrates the validity of the proposed method.

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. Graphical Abstract

A simple control design for human-robot coordination based on the knowledge of dynamical role division

This paper discusses skillful role divisions of coordinated motion between two agents in a crank-rotation task. The roles for coordination, called “dynamical role division,” emerge from dynamic interaction between the agents, through which each agent comes to play a specialized role without conscious understanding. This paper also proposes a novel approach to apply this latent skill in coordinated motions to human-robot coordination, and showing the following advantages of this method: 1) controls of each agents actions are simplified; 2) task performances are improved in a simple manner.

A study on dynamical role division in a crank-rotation task from the viewpoint of kinetics and muscle activity analysis

This paper focuses on dynamical role divisions of cooperation interaction between two human subjects in a typical cooperation task, the crank-rotation task. The dynamical role division in which each subject plays a specialized role without conscious understanding is a key issue that brings the efficiency to the performance of the crank-cooperation work. By investigating kinetics and muscle activities, we found out interesting results about the correlation between the muscle activities and the hand motion, thus, suggesting a method to design control of robots which involve in the crank-cooperation task and presumably in other cooperative interaction with humans.

Novel equilibrium-point control of agonist-antagonist system with pneumatic artificial muscles: II. Application to EMG-based human-machine interface for an elbow-joint system

This paper presents a novel method for controlling a single-joint robot arm driven by two pneumatic artificial muscles (PAMs). We introduce the concepts of the agonist-antagonist muscle-pairs ratio (A-A ratio) and the agonist-antagonist muscle-pairs activity (A-A activity), and demonstrate that our concepts enable separate linear control of the equilibrium joint angle and joint stiffness. We also discuss our approach in comparison with the equilibrium-point (EP) hypothesis.

A preliminary experiment for transferring human motion to a musculoskeletal robot - Decomposition of human running based on muscular coordination

The study of decomposition of body movement into motor primitives is evolving in neuroscience. Meanwhile, in robotics, the motor control of human-like musculoskeletal robots is difficult due to redundant degrees of freedom (DOF) of the robot body. The application of the concept of decomposing into units of motor function to robotics is anticipated to render the control of the robot low-dimensional. We try to achieve fewer-DOF control of a human-like musculoskeletal robot by using our knowledge of the units of motor function based on muscular coordination. In this paper, we introduce “the agonist-antagonist muscle pairs (A-A) ratio” and “A-A activity.” These parameters are defined by using electromyographic (EMG) data for describing the coordination between the agonist and antagonist muscles. Human running is decomposed into two units of motor function using Principal Component Analysis (PCA) for these parameters. We propose a new method of modular control of a musculoskeletal leg robot using the extracted patterns of muscle coordination, and we thus find kinematic meanings of the patterns of muscle coordination.

Dynamical role division between two subjects in a crank-rotation task

This paper discusses skillful role divisions of coordinated motion between two subjects in a crank-rotation task. The roles for coordination, called “specialization”, emerge from only haptic interaction between the subjects, through which each subject comes to play a specialized role without conscious understanding. The purpose of this paper is, therefore, to deepen the understanding of “specialization”, which may be useful for improving coordination methods between humans and/or machines.

Muscle synergy analysis of human adaptation to a variable-stiffness exoskeleton: Human walk with a knee exoskeleton with pneumatic artificial muscles

This paper presents a variable-stiffness knee exoskeleton to enhance human walking. The developed exoskeleton is an agonist-antagonist system with pneumatic artificial muscles (PAMs), and its equilibrium-joint angle and joint stiffness are separately controlled using on our concepts of the agonist-antagonist muscle-pair ratio (A-A ratio) and agonist-antagonist muscle-pair activity (A-A activity). We focus on human adaptation to the variable-stiffness assistance of the exoskeleton, and explore the stiffness control strategy of the device to reduce the subjects excess muscle activity. Muscle synergy analysis of A-A activity indicates that our stiffness-control approach based on EMG analysis leads to successful performance of the human musculoskeletal system with exoskeleton assistance.