Development of real-time muscle stiffness sensor based on resonance frequency for physical human robot interactions

This paper presents a new type of muscle contraction sensor for motion intention detection algorithm in physical human robot interaction (pHRI). The resonance frequency shift by muscle contraction was measured by piezoelectric material. The developed sensor can measure muscle activations accurately over clothes and this is an advantage over the conventional surface Electromyography (sEMG). Performances of the sensor are evaluated through isometric wrist flexion motion tests based on maximal voluntary contraction (MVC) in two aspects: accuracy and speed. While the flexor carpi radialis (FCR) contraction tests up to 40% MVC, sensor outputs are compared with force sensor outputs. The result shows that we can measure muscle contraction by the developed sensor with high correlation and fast response, which is desirable for many physical human robot interactions including exoskeleton devices.