Research

Research Themes 


Technical Keywords 

Design, modeling, control systems, robotics, machine learning 

Artificial muscles 

Artificial muscles are compliant materials or structures that can generate shape changes under external stimuli. They are advantageous over rigid actuators like electric motors in many aspects due to their inherent compliance. We are broadly interested in developing high-performance artificial muscles and obtaining generalizable, elegant, and precise modeling and control for artificial muscles. We are currently focusing on three emerging artificial muscles: 


In addition, we open-sourced a graphical user interface (GUI) for designing TSAs using inverse modeling. 

Open-source GUI for designing TSAs


Existing studies often use ad hoc procedures to select the strings and motors of TSA components. We developed a systematic design framework for TSAs based on the desired performance properties by inverting the TSA models. A graphical user interface (GUI) was created to easily download and use the algorithm.

GUI on GitHub: https://github.com/UNR-Smart-Robotics-Lab/TSA-Design-Algorithm-GUI

Additional instructions: https://unr-smart-robotics-lab.github.io/TSA-Design-Algorithm-GUI/ 

Recent Publications

[1] D. Bombara, R. Konda, Z. Kibria, and J. Zhang, "Inverse modeling for component selection oftwisted string actuators," IEEE/ASME Transactions on Mechatronics, vol. 28. no. 2, pp. 1047-1058, 2023 

[2] R. Konda*, D. Bombara*, and J. Zhang, "Overtwisting and coiling highly enhances straingeneration of twisted string actuators," Soft Robotics, 2023

[3] D. Bombara, S. Fowzer and J. Zhang, "Compliant, large-strain, and self-sensing twistedstring actuators," Soft Robotics, vol.9, no. 1, pp. 72-88, 2022 

[4] R. Konda and J. Zhang, "Hysteresis with lonely stroke in artificial muscles: Characterization,modeling, and inverse compensation," Mechanical Systems and Signal Processing, vol. 164, p.108240, 2022 

[5] D. Bombara, R. Konda, and J. Zhang, "Experimental characterization and modeling of theself-sensing property in compliant twisted string actuators," IEEE Robotics and Automation Letters (chosen for presentation at the 2021 IEEE International Conference on Soft Robotics),vol. 6, no. 2, pp. 974-981, 2021 [Best Paper Award] 

[6] T. Tsabedze and J. Zhang, "Design, characterization, modeling, and comparison of helicallywrapped super-coiled polymer artificial muscles," Sensors and Actuators: A. Physical, vol. 331,p. 113018, 2021 

[7] J. Zhang, "Modeling of a bending supercoiled polymer (SCP) artificial muscle," IEEE Robotics and Automation Letters (chosen for presentation at the 2020 IEEE InternationalConference on Soft Robotics), vol. 5, no. 3, pp. 3822-3829, 2020 

Soft Robotics 


Soft robots are ideal to operate in unstructured and human environments due to their softrobot materials and compliant actuators. We are especially interested in developing andemploying agile soft robots to complete unconventional tasks, where it is impossible to realizeif only rigid robots are used. We are currently focusing on developing three types of softrobots using TSAs:


Recent Publications

[1] R. Konda*, D. Bombara*, S. Swanbeck*, and J. Zhang, "Anthropomorphic twisted stringactuated soft robotic gripper with tendon-based stiffening," IEEE Transactions onRobotics, vol. 39, no. 2, pp. 1178-1195, 2023 (*equal contribution) 

[2] D. Bombara*, R. Konda*, E. Chow, and J. Zhang, "Physics-based kinematic modeling of atwisted string actuator-driven soft robotic manipulator, Proceedings of the 2022 AmericanControl Conference, Atlanta, Georgia, USA, pp. 4365-4370, 2022 (*equal contribution) 

[3] D. Bombara*, R. Coulter*, R. Konda* and J. Zhang, "A twisted string actuator-driven softrobotic manipulator," Proceedings of the 2021 Modeling, Estimation, and ControlConference, Austin, Texas, USA, pp. 141-146, 2021 (*equal contribution) 

Wearable Robotics 


Wearable robots can enhance the quality of life in numerous scenarios, such as assisting ineveryday tasks and rehabilitation purposes. We are particularly interested in developingeffective and comfortable wearable devices by employing artificial muscle technologies. Weare currently working on two types of wearable robots using TSAs:

Recent Publications:

[1] T. Tsabedze, J. Trinh, A. Alomran, J. Clayton, and J. Zhang, "Design and characterization ofAWARD: An active wearable assistive and resistive device," Proceedings of the 2022 IEEE/ASMEInternational Conference on Advanced Intelligent Mechatronics (AIM), Sapporo, Hokkaido,Japan, pp. 844-849, 2022 

[2] T. Tsabedze, E. Hartman, and J. Zhang, "A compact, compliant, and biomimetic roboticassistive glove driven by twisted string actuators," International Journal of IntelligentRobotics and Applications, vol. 5, no. 3, pp. 381-394, 2021 [site] 

[3] T. Tsabedze, E. Hartman, C. Brennan, and J. Zhang, "A compliant robotic wrist orthosisdriven by twisted string actuators," Proceedings of the 2021 IEEE International Symposiumon Medical Robotics (ISMR), Atlanta, Georgia, USA, 2021