Discrete Variable Stiffness Actuators with Fast Stiffness Switch for Safe Human-Robot Interaction

Human-robot co-working is at the human-technology frontier of the future of work, one of NSF’s “10 Big Ideas.” Co-robots allow the full use of human intelligence and robot precision and strength to improve the combined performance as a team in various scenarios including manufacturing, logistics, military, medical care, home companion and others. A fundamental challenge for the development of co-robots is balancing high performance and ensuring human safety.

With respect to rigidity, achieving high performance (high accuracy and payload) often relies on high stiffness co-robots, while safe interactions with humans often requires low stiffness. This work conducts fundamental research on compliant robot stiffness by researching a new concept of discrete variable stiffness actuators and developing a systematic design methodology with high-performance control algorithms, validated by experimental tests.

Based on this, a new generation of robot manipulators with switchable compliance for safe human-robot co-working is envisioned in the near future. Moreover, the developed compliant actuators will benefit the robotics industry with adaptable compliant dynamics enabled by variable stiffness on walking robots, exoskeletons, entertainment, medical and education robotics with human robot physical interactions and needs of intrinsic safety.

The developed technology will enhance the US’s high-tech capability and benefit its economy. The integrated research and education work will encourage and inspire young students to join engineering majors through STEM workshops and hands-on activities. The early engagement and curriculum introduction to K-12 underrepresented students will contribute to preparing the future workforce with robotics skills, knowledge, and interests for advanced manufacturing in the “Industry 4.0” era.

The project discrete variable stiffness actuators (DVSAs) contribute to the fundamental robotics research on developing compliant actuators that are central to synergistic human-robot collaboration. The new actuator concept avoids issues with existing variable stiffness actuators (VSAs) relying on continuous stiffness change mechanisms and brings a discrete design methodology for fast stiffness level selection, low power consumption, zero back driving force in stiffness change, and compact designs.

The project will deliver (1) a design criterion in determining representative discrete stiffness levels by covering both human and robot safety, (2) a design synthesis method in developing discrete variable stiffness mechanisms for DVSAs, (3) detailed discrete stiffness change dynamics modelling considering the mechanical engagement process, (4) optimal control algorithms for DVSA operation stability and human-robot safe interaction, (5) experimental and simulation data verifying the design and control methods, and (6) open software and hardware platforms including a modular DVSA actuator and a 3-DOF compliant arm.

This project is supported by the cross-directorate Foundational Research in Robotics program, jointly managed and funded by the Directorates for Engineering (ENG) and Computer and Information Science and Engineering (CISE).

This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.