Experimental investigation of hybrid shape memory alloy pneumatic actuators

摘要

Pneumatic actuators are a lightweight, compliant means of exerting force and are especially promising for systems thatinteract with the human body. These actuators typically consist of an elastomeric bladder and a surrounding sleeve. Thesleeve is created using traditional textile manufacturing processes (e.g., wrapping, braiding, and knitting) where the fiberswithin the textile sleeves are inextensible components that limit the local expansion of the bladder. By varying the fiberangles and applied pressure, different kinematic motions (extension, contraction, bending, and twisting) are achieved.Anti-symmetric fiber angles within the textile sleeve architecture result in axial and radial motion. In this experimentalinvestigation, shape memory alloy (SMA) wires are integrated into two types of passive sleeves (wrapped and knitted) toincrease the range of motion of the actuator. Applying pressure to the system pre-strains the martensitic SMA throughradial expansion of the actuator. When heated above the austenite finish temperature, the shape memory effect enablescontraction of the SMA wire. This fiber contraction causes reorientation of the textile architecture, resulting in additionalmotion. The effect of the control variables, air pressure and electrical current, on axial displacements and rotations areexperimentally characterized using discrete marker tracking. This study explores two basic textile sleeve architectures forhybrid SMA-pneumatic actuators and sets the foundation for increased kinematic tailorability through the design ofcomplex multi-functional actuating textile sleeves.