Compact Flat Fabric Pneumatic Artificial Muscle (ffPAM) for Soft Wearable Robotic Devices

A pneumatic artificial muscle (PAM) has been widely adopted in a wide range of wearable applications, but the bulkiness and the slow response of the actuator have remained a challenge. In this work, we developed a flat fabric PAM (ffPAM), achieving high compactness, rapid response, and low hysteresis error. Our ffPAM exerts a maximum force of 118.0 N \pm 0.1 N at 172 kPa, an average maximum contraction ratio of 23.84% \pm 0.06%, and a maximum hysteresis error of 6.2%. Using the thin fabric as a base material, the actuator's total weight is 34.8 g. Based on dynamic response experiments, the ffPAM was verified to have a response time of 0.0318 s \pm 0.0012 s for contraction, and the bandwidth of more than 4 Hz, regarding the contraction length with respect to input pressure. Moreover, a maximum contraction length was maintained during 10 000 cycles. Additionally, we embedded a fabric-based soft contractile sensor for the measurement of the contraction. We validated that the capacitance of the embedded capacitive contractile sensor has a linear relationship with the contraction length at constant pressures. To emphasize the compactness of the ffPAM in practical wearable applications, the actuator was placed between the legs, and its compactness was compared with that of previous PAMs.