Novel Design of a Pneumatic Longitudinal Actuator for Both Extending and Contracting Motions

Various types of extendable and contractible soft actuators have been developed by utilizing their strength, lightweight, and flexibility. Most soft actuators focus on either the extending or contracting motion. In this study, we aim to achieve both motions in a single actuator. We propose a novel lightweight soft extendible actuator driven solely by air. Driven in low pressure, this actuator exhibits a high contraction rate and extends without the aid of any external force, such as gravity, and contracts under tension loads. The actuator weighed 191 g and realized a maximum length of 980 mm at extension and contraction rates of 870%. We experimentally evaluated the performance of the actuator with respect to the operating parameters and internal pressure during the extending motion and with respect to the exhaust air volume and contraction rate during the contracting motion under the application of a contraction force. The results indicate that the actuation principle can effectively prevent buckling. Additionally, an efficient contracting motion can be achieved as the contraction force relies on the exhaust volume and length.