Time-Lag Generation Mechanical Valve for Enhancing Time Response of Back-Stretchable McKibben Muscles

McKibben artificial muscles are capable of con- tracting when pneumatic pressure is applied. However, they face difficulties in passively elongating from their natural length due to external forces when not pressurized. This limitation poses challenges in systems where artificial muscles interact, such as in antagonistic drive configurations. To address this issue, we have so far developed a novel type of McKibben artificial muscle called the back-stretchable McKibben muscle (BSM). The BSM consists of two primary sections: a contraction section and an elongation section. An inlet tube is inserted between these two sections to restrict airflow. This design enables the elongation section to activate prior to the contraction motion of the contraction section. While this sequential operation allows the BSM to be used in antagonistic drive systems, a new challenge emerged: the restricted airflow resulted in slower response times of the BSM. To address this issue, this paper proposes a mechanical valve called the “Time-lag generation mechanical valve (TLV),” which generates a time lag in air inflow to the sections without using an inlet tube. Experimental results demonstrate that incorporating the TLV into the BSM significantly enhances its time response: by approximately 300 times during contraction and approximately 230 times during pressure release. Furthermore, the integration of TLV- equipped BSMs enabled the successful implementation of object throwing in an antagonistic drive robotic arm, a feat previously unattainable with conventional BSMs.