Relationship between Upper Limb Load and Inspection Accuracy during Tactile Inspection

Abstract

The appearance inspection process depends partly on manual work in which there are issues concerning detection accuracy and inspection efficiency. Tactile inspection, which is part of the appearance inspection, involves touching a target object with the palm of the hand to detect poor appearance, such as the distortion of product shape and unevenness of product surface. Such tactile inspection, involves repetitive motion and maintaining an awkward work posture for long periods of time, which may cause upper-limb disorders. Therefore, guidelines to reduce upper-limb load are required. However, few studies have evaluated that upper-limb load is related to tactile inspection quantitatively. This study targeted tactile inspection performed by workers. We focused on the factors affecting inspection accuracy to clarify the relationship between upper-limb load and inspection accuracy during tactile inspection. Ten healthy subjects participated in the experiment. Participants were asked to inspect an object with convex points at different heights. Evaluation involved two factors : one was the type-II error rate, which is the index of failure oversight, and the other was control force applied vertically to the object. The results showed that control force decreased when the wrist joint load increased, and inspection accuracy decreased with it. Furthermore, using the results of a previous study, an inspection condition considering both inspection accuracy and upper-limb load was derived. As a result, it was revealed that it is possible to reduce upper-limb load and improve inspection accuracy when the worker conducts inspections at chest height in front of the shoulder.