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Evaluation of physical workload during work behavior for work environment design from biomechanical perspective: a case study in initial orientation selection of work object for manual handling tasks

Abstract To improve workability, designing the work environment by considering physical workload can be effective. This paper proposes a new quantitative evaluation method of physical workload during work behavior, which uses quaternion and joint torque ratio. As an indicator of physical workload, the proposed method calculated a dimensionless value based on joint rotation angle, joint rotation axis angle, and joint torque ratio. Joint rotation angle and joint rotation axis angle are angle changes in the joint and its rotational axis from those in the previous sampling, respectively. These angles were calculated using quaternions. Joint torque ratio was calculated using a three-dimensional rigid link model that simulates the human body. The applicability of the proposed method was examined in several conditions of manual handling tasks set by varying the initial pose of the work object. In the experiments, posture and electromyogram (EMG) of the upper limb were measured. The results showed that the proposed method can evaluate workability of initial orientation of work objects on biomechanical perspective, whereas EMG could not.