Joint angle measurement by stretchable strain sensor

Abstract

Measurement of body motion is required in professional and amateur sports and in health-care services for the improvement and evaluation of human motion. This study proposes a method for measuring joint angles. The key device in this method is a stretchable strain sensor. The strain sensor stretches over 200% under strain with low elasticity and measures the amount of strain with high accuracy. The key advantages of the strain sensor are its thinness, light weight, and low elastic modulus. If the strain sensor is attached on human skin over a joint, it does not impede joint motion and can therefore measure the stretch of the skin. The proposed method estimates the joint angle from skin stretching based on simple mechanical models. In an experiment, the strain sensors were applied to knee and ankle joints. The average error between the estimated angles and reference joint angles measured by motion capture was within 5°.