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The purpose of this study is to propose a method to evaluate operations involving forearm torsion, such as screw driving and knob turning, for digital human models. The rotational ranges of an object gripped with a hand and the working postures of the upper limb were measured at various positions of the object. The results demonstrated that the rotational ranges of the object varied depending on the working posture. The degree of coincidence was defined among direction vectors for each segment in the link model consisting of the upper limb and the rotated object. A method was proposed to estimate the rotational ranges of the object from the degree of coincidence. Based on this method, software has been developed in order to evaluate operations involving forearm torsion.

The purpose of this study is to construct a 3D skeletal model consisting of ulna and radius of human forearm in order to develop a digital human model with real forearm structure and simulate the 3D movements of pronation and supination of the forearm. To analyze in-vivo 3D kinematics of the forearm rotation, helical CT-data were acquired from three male subjects in four rotational positions of the right forearm, i.e. maximal pronation, 45° pronation, neutral, and maximal supination. This procedure was repeated in each case of extension and flexion of the arm. Based on the CT-data a 3D graphical model of the forearm consisting of the ulna and radius was constructed to simulate the torsional movements of the forearm.

The purpose of this study is to formulate the degree of postural instability in working based on the data acquisition of center of pressure (COP) and surface electromyography (EMG). In the previous studies [1]-[4], the limits to which we could move the COP such as the functional stability limits and the balance limits were obtained. In this study experiments were carried out for ten male subjects to measure the COP displacements and EMG signals of leg muscles when the subjects leaned as far as possible while taking every four brief pauses in four directions. As a result, it was found that the muscle load increased exponentially with the COP displacement. Therefore we considered that postural instability also increased exponentially with the COP displacement. Finally we formulated the degree of postural instability. By installing the formulation into a digital human model Jack (Siemens), proactive evaluation of working postural stability could be conducted.