Pneumatic Artificial Muscle With Large Stroke Based on a Contraction Ratio Amplification Mechanism and Self-Contained Sensing

Abstract

This study proposes a novel artificial muscle based on a pouch-type actuator with a contraction ratio amplification mechanism (CRAM). The CRAM places the final length of the pouch-type actuator into a secondary direction, while the main direction is used only for contraction purpose. Thus, the contraction ratio is substantially increased. The interaction process model between the pouch-type actuator and the mechanism is developed through the principle of virtual work, allowing us to select the adequate parameters so that the contraction ratio of the pouch-type actuator improves up to 48.3%. This improvement is 1.372 times that of the original pouch-type actuator. The output characterization is tested to verify the virtual work model of the process. Moreover, a capacitance-based displacement sensor with low root-mean-square error is built and placed in the actuator. The sensor does not increase the complexity of the system and has high repeatability and linearity. The overall functionality of the sensor is verified through sinusoidal and square-wave tracking experiments employing closed-loop control. Finally, a preliminary upper-limb-assisting test verifies that the actuator can reduce 17.48% of the muscle effort. In sum, this artificial muscle with good performance provides a design reference and alternative for wearable applications.