Design and Stiffness Analysis of a Bio-inspired Soft Actuator with Bi-direction Tunable Stiffness Property

Jianfeng Lin, Ruikang Xiao, Zhao Guo

The ability to modulate the stiffness of soft actuators plays a vital role in improving the efficiency of interacting with the environment. However, for the unidirectional stiffness modulation mechanism, high lateral stiffness and a wide range of bending stiffness cannot be guaranteed at the same time. Therefore, we draw inspiration from the anatomical structure of the finger, proposing a soft actuator with bi-direction tunable stiffness property (BTSA). BTSA is composed of air-tendon hybrid actuation (ATA) and bone-like structure (BLS). The bending stiffness can be tuned by ATA from 0.2 N/mm to 0.7 N/mm, about a magnification of 3.5 times. The lateral stiffness with BLS is enhanced up to 4.2 times compared to the one without BLS. Meanwhile the lateral stiffness can be tuned decoupling within a certain range of stiffness (e.g. from 0.35 N/mm to 0.46 when the bending angle is 45 deg). The BLS is designed according to a simplified stiffness analysis model. And a lost-wax based fabrication method is proposed to ensure the airtightness. The experiments about fingertip force, bending stiffness, and lateral stiffness are conducted to verify the property.

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