Helical axis
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The helical axis of an object is a parameter for describing simultaneous rotation and translation components of that object. The axis is a directed line in space, along which a translation may occur, and about which rotation may occur. As an axis, this parameter cannot describe pure translation with no rotation component.
As this axis can vary over time, the term 'instantaneous helical axis' (IHA) is often used. This parameter is often used in biomechanics, when describing the motion of joints of the body. The IHA is also often called the instantaneous axis of rotation (IAR), instantaneous center of rotation (ICR), and sometimes called the screw axis or twist axis.
For any period of time, joint motion can be seen as the movement of a single point on one articulating surface with respect to the adjacent surface (usually distal with respect to proximal). The total translation and rotations along the path of motion can be defined as the time integrals of the instantaneous translation and rotation velocities at the IHA for a given reference time.[1]
In any single plane, the path formed by the locations of the moving helical axis is known as the 'centroid' and is used in the description of joint motion.
[edit] References
- ^ Woltring HJ, de Lange A, Kauer JMG, Huiskes R. 1987 Instantaneous helical axes estimation via natural, cross-validated splines. In: Bergmann G, Kölbel R, Rohlmann A (Editors). Biomechanics: Basic and Applied Research. Springer, pp 121-128.
