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RE: ICR, joint moments, and stability

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  • RE: ICR, joint moments, and stability

    I have been quite interested in the recent BIOMCH-L postings about
    joint kinematics and kinetics, in particular about the planar ICR
    (instant center of rotation) and the spatial ISA (instant screw axis)
    - also denoted as the spatial IHA (instant helical axis). I have two
    points which I would like to discuss in this regard.

    1) We have developed linear least-squares methods to compute both
    two- and three-dimensional INSTANTANEOUS angular velocity and
    angular acceleration - and consequently the ICR/ISA and the AAA
    (angular acceleration axis) - from positon, velocity, and
    acceleration of multiple point landmarks on a rigid body. If using
    video/photo methods, the velocity and acceleration of the landmarks
    may be determined by smoothing and differentiating landmark
    position trajectories. These methods have been combined to also
    determine the instantaneous central point of the screw axode ruled
    surface (the point on the ISA with minimum acceleration about
    which the ISA instantaneously changes direction with time) denoted
    as the spatial ICR by Herman Woltring in recent BIOMCH-L postings.

    Mathematical development of these methods has been presented and
    published through ASME. Application of these methods to
    biomechanics will be presented in July at the Int. Symp. on 3D
    Analysis of Human Movement in Montreal.

    2) Although Herman Woltring and I may be the only two people in the
    world interested, these methods may be easily extended to
    determine two- and three-dimensional angular jerk from third
    derivatives of landmark position trajectories.

    H.J Sommer, Professor of Mechanical Engineering
    The Pennsylvania State University
    University Park, PA 16802 USA
    phone (814)865-9214 FAX (814)863-4848
    bitnet hjs@psuecl internet