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Abstract: Soft materials and compliant actuation concepts have generated new design and control approaches in areas from robotics to wearable devices. Despite the potential of soft robotic systems, most designs currently use hard pumps, valves, and electromagnetic actuators. In this work, we take a step towards fully soft robots by developing a new compliant electromagnetic actuator architecture using gallium indium liquid metal conductors, as well as compliant permanent magnetic and compliant iron composites. Properties of the new materials are first characterized and then co-fabricated to create an exemplary biologically inspired soft actuator with pulsing or grasping motions, similar to Xenia corals. As current is applied to the liquid metal coil, the compliant permanent magnetic tips on passive silicone arms are attracted or repelled. The dynamics of the robotic actuator are characterized using stochastic system identification techniques and then operated at the resonant frequency of 7 Hz to generate high-stroke (>6 mm) motions.
The soft electromagnetic actuator concept is shown using compliant magnets, liquid metal coils, and compliant iron core. The robot replicates the motion of Xenia coral, which is shown in the middle figure. As the electromagnet attracts and repels the magnets, a pulsing motion is created, which resembles the motion of the Xenia coral.
N. Kohls, I. Abdeally, B. P. Ruddy and Y. C. Mazumdar, “Design of a Xenia Coral Robot using a High-stroke Compliant Linear Electromagnetic Actuator,” ASME Letters in Dynamic Systems and Controls, vol.1(3), 031011, 2021 [https://doi.org/10.1115/1.4050041]
Media Coverage: Robotics Tomorrow, Robotics and Automation News, and Georgia Tech College of Engineering
Abstract: Electromagnetic actuators provide fast speed, large forces, high strokes, and wide bandwidths. Most designs, however, are constructed from rigid components, making these benefits inaccessible for many soft robotics applications. In this work, we develop a new soft electromagnetic linear actuator using liquid gallium–indium for the conductor and neodymium–iron–boron and polymer composites for the permanent magnet. When combined in a solenoid configuration, high strokes can be generated using entirely soft components. To emulate the pulsing motion of Xenia coral arms, we develop an additional soft flexure system that converts the linear translation to rotary motion. The design and fabrication of the electromagnetic actuator and compliant flexure are first described. Models for the magnetic forces and the joint kinematics are then developed and compared with the experimental results. Finally, the robot dynamics are analyzed using stochastic system identification techniques. Results show that the compliant actuator is able to achieve an 18 mm stroke, allowing the soft arms to bend up to 120 deg. This further enables the tips of the arms to traverse an arc length of 42 mm. Bandwidths up to 30 Hz were also observed. While this article focuses on emulating a biological system, this highly deformable actuator design can also be utilized for fully soft grasping or wearables applications
This design improves the stroke length of the previous actuator by utilizing compliant hinges and an internal magnet. The larger stroke length allows the soft arms to fully open and close to mimic the motion of the Xenia coral.
N. Kohls, B. Dias, Y. Mensah, B. P. Ruddy, and Y. C. Mazumdar, “Compliant Electromagnetic Actuator Architecture for Soft Robotics,” Proceedings of the 2020 IEEE International Conference on Robotics and Automation (ICRA), pp. 9042-9049, 2020 [https://doi.org/10.1109/ICRA40945.2020.9197442]
Media Coverage: IEEE Spectrum Video Friday
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