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Motor redundancy is a fundamental problem inherent to the inverse problem of motor planning in a muscle-activated endoskeleton such as that of a human and an anthropomorphic musculoskeletal robot. This paper proposes a biologically inspired control framework for multiple redundant muscles, based on the invariant structure in the group of agonist-antagonist coactivation. The theoretical framework explains...
Stroke rehabilitation requires intralimb coordination to achieve natural movement after recovery. Focusing on mechanical impedance by the coactivation of agonist muscles, we performed two experiments to assess the intralimb coordination of a post-stroke subject using two indices of the endpoint stiffness and muscle synergies. The results of the first experiment showed that the endpoint stiffness of...
This paper proposes a novel method for assessment of muscle imbalance based on muscle synergy hypothesis and equilibrium point (EP) hypothesis of motor control. We explain in detail the method for extracting muscle synergies under the concept of agonist-antagonist (AA) muscle pairs and for estimating EP trajectories and endpoint stiffness of human upper limbs in a horizontal plane using an electromyogram...
Based on the idea of synergy to explore the building blocks of movements, this study focused on the muscle space for reaching movements by human upper limbs on a horizontal plane to estimate the relationship among muscle synergies, equilibrium-point (EP) trajectories, and endpoint stiffness in two ways: (1) a novel estimation method that analyzes electromyographic signals under the concept of agonist-antagonist...
The tacit representation of muscle coordination has been a major topic of research on motor control since Bernstein's pioneering work. To unravel the mechanisms underlying voluntary movements, we investigated the electromyography signals of six muscles in a non-dominant upper limb during fast spiral movements on a horizontal plane. We considered muscle synergy to be a coordination index that we defined...
This paper describes a novel method for controlling a human-like musculoskeletal leg robot by implementing muscle coordination in human voluntary movement. To examine human motor control involving the ill-posed problem of redundant degrees-of-freedom (DOFs), we introduce the concept of the agonist-antagonist muscle pair ratio (A-A ratio) which represents the coordination of agonist-antagonist muscle...
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)....
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...
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...
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...
The need of solving the problem of multi-degrees-of-freedom in motor control is increasing as human-like robots become more popular these days. Muscle synergies hypothesis is a prominent suggestion for this problem. In this paper, we investigated the muscle synergies extracted from human subjects in a producing-force task to explore the mechanism of the human's skillful hand-movement at producing...
Recently, research into robots that coexist with people in many areas such as the service and medical industries is active. Such robots need to be both safe and flexible. To satisfy this demand, a pneumatic actuator is appropriate because it is lightweight and has natural compliance. Our research focuses on a joint angle control method for a five-fingered robot hand using low-pressure driven pneumatic...
We made a discovery that links with influential hypotheses that the central nervous system may produce movements by combining units of motor output. This paper introduces the key concept we call the “A-A ratio,” which is the EMG ratio of agonist-antagonist muscle pairs. The statistical analysis based on the A-A ratio specifies that (1) human lower limb movement during walking is explained as the superposition...
Recently, research into robots that coexist with people in areas such as the service and medical industries is active. Such robots need to be both safe and flexible. To satisfy this demand, a pneumatic actuator is appropriate because it has natural compliance and is lightweight. Our research focuses on a joint angle control method for a five-fingered robot hand using low-pressure driven pneumatic...
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