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Actuators regulate motion in manufacturing and industrial automation by applying an excitation force or torque. Conventional actuators do have their advantages; however, they have multiple components (prone to wear and tear), are expensive during maintenance, bulky, and suffer from backlashes. Therefore, smart-material-based actuators have been increasingly proposed to overcome such shortcomings. Shape memory alloy (SMA) is generally considered for such applications due to its high power-to-weight ratio, noise-free, energy-efficient operation, and facilitating miniaturization. The current research exploits the advantages of the pennate musculature with the properties of SMA to develop a bipennate SMA-based rotary actuator. Pennate muscle fibers are aligned obliquely to the muscle line of action, enabling fiber force to be coupled to macro-level muscle force, resulting in increased force output. The study presents an ergonomic-design-integration-framework of an SMA-driven rotary actuator. The lightweight gearless actuator has drivability without backlash, compatible with a rhombus-based-compliant power transmission system. An analytical model of the bipennate SMA-based rotary actuator has been developed and experimentally validated. The new actuator delivers at least twice the actuation torque (2.1 N-m) compared to the SMA-based rotary actuators reported in the literature. The actuator also delivers a high associated angular displacement ranging from 60°-70°. The actuator design parameters have been optimized by implementing a constrained gradient descent algorithm such that the output torque, stroke, and efficiency of the actuator system can be tailored as per the requirement and application. The actuator has varied applications, from healthcare devices to next-generation space robots.
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