Dr. Kaveh Akbari Hamed, an assistant professor in mechanical engineering at San Diego State University (SDSU), has been awarded an NSF National Robotics Initiative grant of $612,213.00 for his project, “Decentralized Feedback Control Design for Cooperative Robotic Walking with Application to Powered Prosthetic Legs”. This project is in collaboration with Dr. Robert D. Gregg, an assistant professor of mechanical engineering at the University of Texas at Dallas (UT Dallas).
The past few years have seen an accelerated effort to design rehabilitation and emergency response robots and to develop robots with human and animal traits. Legged locomotion is extremely important in this advancement. Legged robots can climb stairs, step over gaps in terrain, and are more effective in uneven environments than wheels. The study of legged locomotion has been motivated by the desire to allow people with disabilities to walk (i.e., co-walkers) and to assist or replace humans in hazardous environments (i.e., co-workers). Legged co-robots that can perform at this level do not yet exist, and part of what is holding back their development and deployment is adequate feedback control theory. While the technology involved in robot construction is advancing rapidly, there is a fundamental gap in knowledge in feedback control theory for stabilizing the dynamical models of these increasingly sophisticated legged robots.
State-of-the-art control approaches for legged machines make use of centralized feedback control algorithms, in which multiple links and joints of the robot communicate their sensor measurements to a central controller. This controller interprets the data from all joints and relays decisions back to all actuators. By contrast, decentralized control problems define lower-dimensional subsystems (e.g., each leg of the robot) that use only sensory feedback local to each subsystem. Each subsystem has its own processing unit and controller to make its own decisions based on its own measurements.
For legged locomotion, decentralization is desirable for several reasons. For prosthetics, where the purpose is to replace a lost natural limb, it is impractical to wire the user with a profusion of sensors. Therefore the prosthetic device must primarily rely on its own built-in measurements. Another advantage of decentralization is the management of complexity. As robots become more sophisticated, the number of variables that must be monitored for a complete description of the system status becomes so large that top-down controllers are costly or infeasible to implement. The challenge of decentralized control is made substantially more difficult because walking and running are hybrid dynamic behaviors, that is, the dynamics follow a completely different set of rules when, for example, a foot is planted on the ground, compared to when it is swinging in the air.
This NSF project will advance the state-of-the-art in advanced lower limb prosthetics, as well as in locomotion for the next generation of legged robots. Dr. Akbari Hamed (PI) and Dr. Gregg (Co-PI) will investigate the systematic design of decentralized feedback controllers that coordinate low-dimensional subsystems to achieve robust legged locomotion, overcoming the curse of dimensionality in legged robots and enabling cooperative human-machine walking with powered prosthetic legs. They will create innovative computational algorithms to systematically design robust stabilizing decentralized controllers for cooperative subsystems. Finally, they will transfer the decentralized control framework into practice with SQ1, an experimental quadruped robot at SDSU (see Fig. 1), and a powered prosthetic leg at the UT Dallas (see Fig. 2).
More information about the project is available in the NSF award posting.
Fig. 1 (left) SQ1, a quadruped robot at SDSU, designed and manufactured by “Wonik Robotics” for the validation of feedback control algorithms. Fig. 2 (right) The UTD powered prosthetic leg, a testbed for the implementation of feedback controllers. Dr. Akbari Hamed (SDSU) and Dr. Gregg (UTD) will transfer the theoretical innovations from this NSF grant into practice through experiments with SQ1 at SDSU and the UTD powered prosthetic leg.