Development of a Surface Muscle Pressure Monitoring System for Wearable Robotic Devices

Monitoring of muscle activities of human limbs is essential for designing controllers of wearable robotic devices such as prosthetics, orthotics and exoskeletons. Human-robot interaction (HRI) is generally studied to control these devices and ascertain comfort levels of the wearer. Cognitive-HRI (cHRI) and physical-HRI (pHRI) are the two main types of HRI methods identified in literature. Surface electromyography (sEMG) signals of skeletal muscles are commonly used in cHRI methods to identify the motion intentions. However, sEMG signals are sensitive to the environmental conditions such as electric and magnetic disturbances. Alternatively, changes to muscle stiffness and volume are measured in pHRI methods. Accordingly, this paper presents a novel sensory system to detect motions of upper or lower limbs by monitoring surface-muscle pressure (SMP). It is comprised of specially designed 'pressurized-air-pouches' made of silicone. Experiments were carried out with the developed SMP monitoring system to detect muscles activities during biceps curls. The results were compared against sEMG signals to evaluate the validity of the proposed method. The analysis indicated a strong correlation between the signals measured and verifies the potential of using SMP as an effective muscle activity sensing method.