Soft actuators and wearable robotic systems offer safe, adaptable, and portable assistance for human users in industrial, medical, and daily living contexts. In the IRiS Lab, we design and build high power-to-weight ratio soft actuators and wearable devices that combine comfort with powerful assistance. Our work spans novel actuation mechanisms, such as Twisted String Actuators, to lightweight exosuits and ergonomically designed wearable interfaces.
By integrating advanced sensing, control, and human–robot interaction strategies, we aim to create wearable systems that enhance human capabilities while remaining unobtrusive and intuitive to use.
Twisting String Actuator (TSA) is powerful and compact linear actuator, in which a string or a set of strings connected to an electric motor act as a gear. When a load is attached to the string on the other end, the rotation imposed on the string by the motor will reduce the length of the string, thus causing the translational motion of the load due to the generated pulling force. Such actuators can be very light, cheap and quiet and provide a high (though nonlinear) transmission ratio, which makes them very attractive for use in various areas of engineering, such as robotics.
Associated Papers
Gaponov, I., Popov, D., & Ryu, J. H. (2013). Twisted string actuation systems: A study of the mathematical model and a comparison of twisted strings. IEEE/ASME Transactions on mechatronics, 19(4), 1331-1342. Link
Gaponov, I., Popov, D., & Ryu, J. (2014). Accurate dynamic modeling of twisted string actuators accounting for string compliance and friction. IEEE/ASME Trans. Mech., 19(4, 2014), 1331-1342. Link
Zhang, J., Sheng, J., O’Neill, C. T., Walsh, C. J., Wood, R. J., Ryu, J. H., … & Yip, M. C. (2019). Robotic artificial muscles: Current progress and future perspectives. IEEE transactions on robotics, 35(3), 761-781. Link
Nedelchev, S., Skvortsova, V., Guryev, B., Gaponov, I., & Ryu, J. H. (2021). On Energy-Preserving Motion in Twisted String Actuators. IEEE Robotics and Automation Letters, 6(4), 7406-7412. Link
To unlock the full potential of our soft actuators, we focus on advanced modeling and control. The effectiveness of actuators like the TSA is often challenged by inherent nonlinearities, including varying stiffness, friction, and hysteresis, which are not captured by simple models.
Our research overcomes these challenges by developing sophisticated dynamic models that accurately predict actuator behavior even during high-speed and high-force operation. These high-fidelity models enable the design of novel control algorithms. Our contributions include energy-preserving controllers for highly efficient periodic motion, adaptive tension controllers that compensate for material uncertainties, and pioneering strategies for the independent control of both position and stiffness in bidirectional systems. Our current research focuses on developing sensorless control strategies to eliminate the need for bulky sensors, enhancing the practicality of our systems. Ultimately, this work ensures our wearable systems can perform with the precision, efficiency, and robustness required for real-world interaction.
Associated Papers
Gaponov, I., Popov, D., & Ryu, J. H. (2013). Twisted string actuation systems: A study of the mathematical model and a comparison of twisted strings. IEEE/ASME Transactions on mechatronics, 19(4), 1331-1342. Link
Gaponov, I., Popov, D., & Ryu, J. (2014). Accurate dynamic modeling of twisted string actuators accounting for string compliance and friction. IEEE/ASME Trans. Mech., 19(4, 2014), 1331-1342. Link
Popov, D., Gaponov, I., & Ryu, J. H. (2014, September). Towards variable stiffness control of antagonistic twisted string actuators. In 2014 IEEE/RSJ International Conference on Intelligent Robots and Systems (pp. 2789-2794). IEEE. Link
Nedelchev, S., Skvortsova, V., Guryev, B., Gaponov, I., & Ryu, J. H. (2021). On Energy-Preserving Motion in Twisted String Actuators. IEEE Robotics and Automation Letters, 6(4), 7406-7412. Link
Baek, S., & Ryu, J. H. (2023). Tension control of twisted string actuators in variation of stiffness and original length of strings. IEEE/ASME Transactions on Mechatronics, 28(5), 2483-2494. Link
Wearables
Researchers: HyeonSeok Seong
TSA is a lightweight, high-force actuator with flexible routing that enables portable and comfortable wearable robots. We first developed an elbow exoskeleton for upper limb rehabilitation and a shoulder exosuit (Auxilio) that assists complex shoulder motions. We then expanded to lower limb support for daily and industrial tasks, developing exoskeletons for hip and knee assistance. We are now developing an active soft exosuit that maximizes the advantages of TSA and a quasi-passive exosuit that exploits intrinsic changes in the actuator’s mechanical properties to enable lightweight, energy-efficient operation. Across these systems, we target a high system-level power-to-weight ratio by optimizing actuator integration, transmission, and routing.
Associated Papers
Popov, D., Gaponov, I., & Ryu, J. H. (2013, April). A preliminary study on a twisted strings-based elbow exoskeleton. In 2013 World Haptics Conference (WHC) (pp. 479-484). IEEE. Link
Popov, D., Gaponov, I., & Ryu, J. H. (2013, November). Bidirectional elbow exoskeleton based on twisted-string actuators. In 2013 IEEE/RSJ International Conference on Intelligent Robots and Systems (pp. 5853-5858). IEEE. Link
Mehmood, U., Popov, D., Gaponov, I., & Ryu, J. H. (2015, July). Rotational twisted string actuator with linearized output: Mathematical model and experimental evaluation. In 2015 IEEE International Conference on Advanced Intelligent Mechatronics (AIM) (pp. 1072-1077). IEEE. Link
Popov, D., Gaponov, I., & Ryu, J. H. (2016). Portable exoskeleton glove with soft structure for hand assistance in activities of daily living. IEEE/ASME Transactions on Mechatronics, 22(2), 865-875. Link
Gaponov, I., Popov, D., Lee, S. J., & Ryu, J. H. (2017). Auxilio: A portable cable-driven exosuit for upper extremity assistance. International Journal of Control, Automation and Systems, 15(1), 73-84. Link
Seong, H. S., Kim, D. H., Gaponov, I., & Ryu, J. H. (2020, May). Development of a twisted string actuator-based exoskeleton for hip joint assistance in lifting tasks. In 2020 IEEE International Conference on Robotics and Automation (ICRA) (pp. 761-767). IEEE. Link
Sengupta, S., & Ryu, J. H. (2024, May). Design of a Knee-joint Exoskeleton to Reduce Misalignment in Both the Sagittal and Coronal Planes. In 2024 IEEE International Conference on Robotics and Automation (ICRA) (pp. 17472-17478). IEEE. Link
Our lab pioneers research on Twisted String Actuators (TSAs), enhancing their core mechanics and expanding their applications in robotics. We address fundamental limitations by developing solutions to overcome their uni-directional nature, including both passive return mechanisms and single-motor bidirectional actuation systems. We also create innovative methods to significantly improve their operational stroke and lifespan. Furthermore, our work on designs like variable radius pulleys not only enables this bidirectional control but also linearizes the actuator’s behavior, allowing for more intuitive and precise operation.
Building on these core improvements, we design advanced transmission systems, including both passive and active continuously variable transmissions. These innovations pave the way for exciting real-world applications. We have successfully developed compact robotic grippers, high-force haptic displays, and flexible actuators capable of operating through conduits for wearable and soft robotics. Our work continually pushes the boundaries of what is possible with this simple yet powerful actuation technology.
Equipment
Torque Sensores and Load cells.
FUTEK, TRS605-FSH02052
non-contact rotary torque sensor
maximum capacity: 1Nm
resolution: 0.01Nm
Dacell, UU3
push-pull loadcell
maximum capacity: 5Kgf, 10Kgf, 20Kgf, 50Kgf, 100Kgf
resolution: 0.2% of maximum capacity
ATI industry, mini45
F/T sensor
maximum capacity: Fx,Fy=580N, Fz=1160N, Tx, Ty, Tz= 20Nm