Article

Redundancy Resolution of the Human Arm and an Upper Limb Exoskeleton

Department of Electrical Engineering, University of California Santa Cruz, Santa Cruz, CA 95064, USA.
IEEE transactions on bio-medical engineering (Impact Factor: 2.23). 04/2012; 59(6):1770-9. DOI: 10.1109/TBME.2012.2194489
Source: PubMed

ABSTRACT The human arm has 7 degrees of freedom (DOF) while only 6 DOF are required to position the wrist and orient the palm. Thus, the inverse kinematics of an human arm has a nonunique solution. Resolving this redundancy becomes critical as the human interacts with a wearable robot and the inverse kinematics solution of these two coupled systems must be identical to guarantee an seamless integration. The redundancy of the arm can be formulated by defining the swivel angle, the rotation angle of the plane defined by the upper and lower arm around a virtual axis that connects the shoulder and wrist joints. Analyzing reaching tasks recorded with a motion capture system indicates that the swivel angle is selected such that when the elbow joint is flexed, the palm points to the head. Based on these experimental results, a new criterion is formed to resolve the human arm redundancy. This criterion was implemented into the control algorithm of an upper limb 7-DOF wearable robot. Experimental results indicate that by using the proposed redundancy resolution criterion, the error between the predicted and the actual swivel angle adopted by the motor control system is less then 5°.

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    • "With respect to degrees of freedom in human upper limb motion, it has one additional degree of freedom to execute motion in task space. Therefore, human hand is a better example for redundant manipulator [8]. Redundancy in robotic manipulator leads to interesting results: higher dexterity in workspace, avoids obstacle in operational space, minimizing singularities, improves dexterous workspace and minimizing joint torques [4]. "
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    ABSTRACT: Exoskeleton manipulators are used for different applications in robotic field. Human motion is highly complicated and flexible; therefore obtain human like motion from exoskeleton manipulator becomes a challenge to researches in this field. This paper presents an improvement of dexterity measure as a result of adding redundancy to upper limb exoskeleton manipulator. Proposed manipulator has four degree of freedom. This takes the effect of DOF at human elbow and wrist of the upper limb. Dexterity of the manipulator is measured using manipulability index and minimum singular value. All measures are based on Jacobian of the manipulator. This four DOF manipulator is then modified by adding two more degrees of freedom to make total of six. Therefore with respect to task defined in operational space; modified exoskeleton manipulator operates as redundant. Manipulability index and minimum singular value are again determined for six degree of freedom modified exoskeleton manipulator. The effect of redundancy in order to improve the manipulation in upper limb exoskeleton robot is investigated in this study.
    IEEE International Conference on Industrial and Information Systems, Kandy, Sri Lanka; 12/2013
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    • "It is clear that human upper limb processes an additional degree of freedom than required. Therefore, human hand is a better example for redundant manipulator [8]. Redundancy of a manipulator leads to interesting results: higher dexterity in workspace, avoids obstacle in operational space, minimizing singularities, improves dexterous workspace and minimizing joint torques [4]. "
    [Show abstract] [Hide abstract]
    ABSTRACT: Exoskeleton manipulators are used for different applications in robotic field. Human motion is highly complicated and flexible; therefore obtain human like motion from exoskeleton manipulator becomes a challenge to researches in this field. This paper presents an improvement of dexterity measure as a result of adding redundancy to upper limb exoskeleton manipulator. Proposed manipulator has four degree of freedom. This takes the effect of DOF at human elbow and wrist of the upper limb. Dexterity of the manipulator is measured using manipulability index and minimum singular value. All measures are based on Jacobian of the manipulator. This four DOF manipulator is then modified by adding two more degrees of freedom to make total of six. Therefore with respect to task defined in operational space; modified exoskeleton manipulator operates as redundant. Manipulability index and minimum singular value are again determined for six degree of freedom modified exoskeleton manipulator. The effect of redundancy in order to improve the manipulation in upper limb exoskeleton robot is investigated in this study.
    2013 IEEE 8th International Conference on Industrial and Information Systems (ICIIS); 12/2013
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    • "Similar methods have been used to optimize the inverse kinematics of redundant manipulators [5] [6] [7] [8] [9] [10], and have been used to avoid obstacles, joint limits, velocity limits, and minimize jerk. Recent studies have also proposed various methods for optimizing the pose of the upper arm, analyzing the arm as a 7 degree of freedom system and optimizing the swivel and angle to resolve the redundancy [11] [12]. Zacharias et al. have optimized the pose of a robot with two 7 degree of freedom arms based on a series of ergonomic conditions [13]. "
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    ABSTRACT: This paper reviews the variations in human upper body motion of subjects completing activities of daily living. This study was completed to serve as a reference to evaluate the quality of simulated of human motion. In this paper we define the variation in motion as the variation in subjects' parameters (link lengths), joint angles, and hand positions, for a given task. All of these variations are related by forward kinematic equations. Motion data from eight healthy right hand dominant adults performing three activities of daily living (brushing hair, drinking from a cup, and opening a door) were collected using an eight camera Vicon motion analysis system. Subject parameters were calculated using relative positions of functional joint center locations between segments. Joint angles were calculated by Euler angle rotations between body segments. Hand position was defined as the origin of the hand frame relative to the pelvis frame. The variance of recorded human motion was analyzed based on the standard deviations of subject parameters, joint angles, and hand positions. Variances in joint angles were found to be similar in magnitude to root mean squared error of kinematics based motion simulation. To evaluate the relative variance, the forward kinematic solutions of the trials were found after removing subject parameter variance and reducing joint angle variance. The variance in the forward kinematic solution was then compared to the recorded hand position variance. Reductions in subject parameter and joint angle variance produced a proportionally much smaller reduction in the calculated hand position variance. Using the average instead of individual subject parameters had only a small impact on hand position variance. Modifying joint angles to reduce variance had a greater impact on the calculated hand position variance than using average subject parameters, but was still a relatively small change. Future work will focus on using these results to create formalized procedures for quantifying the human likeness of artificial human motions, to serve as a basis for performance comparison between different methods.
    Conference proceedings: ... Annual International Conference of the IEEE Engineering in Medicine and Biology Society. IEEE Engineering in Medicine and Biology Society. Conference 07/2013; 2013:6937-6940. DOI:10.1109/EMBC.2013.6611153
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