CAREER: Safe Autonomy for Soft Robots

Robots built from soft rubbery materials could work closely with humans in settings where rigid robots cannot, since unintentional contact would cause fewer injuries. However, the hope that soft robots are safer around humans neglects how multi-faceted the robot’s tasks may be, and how safety depends on much more than reducing accidental forces. For example, a soft robotic arm assisting in a medical procedure must meet constraints on both too much pressure as well as not enough pressure on a patient’s body, as well as timing and in sequencing of its actions.

This Faculty Early Career Development (CAREER) project supports research aimed at developing autonomous artificial intelligence systems that bring a soft robot into close contact with humans during verifiably-safe motion, no matter how safety is defined. The project’s novelty is the first application of safe-by-construction control to soft robots, as well as the focus on unique challenges therein such as controllable stiffening of the robot, lack of highly accurate mathematical models, and changes to the robot over time.

This project’s impacts are in the potential to make common medical procedures low-cost and widely accessible, while reducing biases arising from subjective clinician decisions about patient comfort and pain tolerance. To reduce these biases, the project is integrating research with education for a crowdsourced citizen science activity. The activity asks high school students to construct their own soft robot and define its safety limits for themselves, and compare their results with others so that we may ultimately answer: what makes a soft robot safe, and for whom?

This project reframes the control of soft robots as a specification satisfaction problem, rather than motion tracking, by seeking initial answers to three research questions: (RQ1) Does the embodied intelligence of soft materials assist a soft robot manipulator in meeting a safety constraint, or detract from its ability to do so, and under what conditions? (RQ2) What tradeoffs in control strategies can balance the inherent compliance of a soft manipulator, useful in unknown environments, with strictness in safety constraints, useful when an environment is well-defined? (RQ3) What synthesis techniques for safe autonomy could express successful task transitions of a soft robot arm during uncertain contact with a human? To do so, the project pursues corresponding innovations with three research objectives: (RO1) Develop safety-verified feedback systems for a soft robotic arm, meeting constraints on position, velocity, and force, via control barrier functions and optimization-based supervisory control. (RO2) Extend this framework for control of the soft robot’s stiffness, developing a new mediation/deconfliction system for verifying safety margins under multiple possibly-time-varying soft dynamics models. (RO3) Validate the use of temporal logic and automata for safe task transitions of a soft robot in hardware, during contact with a human tissue analog.

Together, this project sets a baseline for reconceptualizing the relationship between control and soft robots, with the possibility that harmonizing embodied intelligence with artificial intelligence may overcome fundamental limitations in human-robot contact.

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.