title: Point of optimal kinematic error: improvement of the instantaneous helical pivot method for locating centers of rotation.
abstract: This paper proposes a variation of the instantaneous helical pivot technique for locating centers of rotation. The point of optimal kinematic error (POKE), which minimizes the velocity at the center of rotation, may be obtained by just adding a weighting factor equal to the square of angular velocity in Woltring׳s equation of the pivot of instantaneous helical axes (PIHA). Calculations are simplified with respect to the original method, since it is not necessary to make explicit calculations of the helical axis, and the effect of accidental errors is reduced. The improved performance of this method was validated by simulations based on a functional calibration task for the gleno-humeral joint center. Noisy data caused a systematic dislocation of the calculated center of rotation towards the center of the arm marker cluster. This error in PIHA could even exceed the effect of soft tissue artifacts associated to small and medium deformations, but it was successfully reduced by the POKE estimation.
authors.affiliation: Instituto de Biomecánica de Valencia, Universitat Politècnica de València, Edificio 9C, Camino de Vera s/n, E-46022 Valencia, Spain; Grupo de Tecnología Sanitaria del IBV, CIBER de Bioingeniería, Biomateriales y Nanomedicina (CIBER-BBN), Valencia, Spain. Electronic address: helios.derosario@ibv.upv.es.
authors.forename: Helios
authors.initials: H
authors.lastname: De Rosario
authors.affiliation: Departamento de Física Aplicada, Universitat Politècnica de València, Spain; Grupo de Tecnología Sanitaria del IBV, CIBER de Bioingeniería, Biomateriales y Nanomedicina (CIBER-BBN), Valencia, Spain.
authors.forename: Alvaro
authors.initials: A
authors.lastname: Page
authors.affiliation: Departamento de Ingeniería Mecánica y de Materiales, Universitat Politècnica de València, Spain.
authors.forename: Vicente
authors.initials: V
authors.lastname: Mata
mesh_terms: D016477:Artifacts; D001696:Biomechanical Phenomena; D002138:Calibration; D006801:Humans; D008954:Models, Biological; D012399:Rotation; D012785:Shoulder Joint / Q000502:physiology*
keywords: Center of rotation; Functional calibration; Instantaneous helical axis; Optimization