A biorobotic model of the sunfish pectoral fin for investigations of fin sensorimotor control

The efficiency and maneuverability that highly compliant, multiple degree of freedom fins lend to fish swimming is attractive to the development of a next generation propulsor for autonomous underwater vehicles. A critical component in the production and modulation of fin motions and forces is the sensorimotor system driving the fin; unfortunately little is known about the structures, organization and integration of this system. A biorobotic platform is proposed for the use in bluegill sunfish pectoral fin sensorimotor studies in conjunction with biological and neurobiological efforts. In order for a biorobotic platform to be an appropriate tool for sensorimotor studies, it must be capable of operating on par with the bluegill sunfish. The development of this biorobotic platform is based on multiple biorobotic pectoral fin prototypes that were proven capable of generating the motions, forces, and flows characteristic of individual gaits performed by the bluegill sunfish. This new platform integrates these prototypes to be capable of all the gaits studied and, with the appropriate motions, forces and flows generated, is providing the appropriate hydrodynamic information available to the biological sensory system. A preliminary sensory system, consisting of pressure sensors approximating the biological lateral line, and strain gauges approximating nerves intrinsic to the pectoral fin, captures some of this hydrodynamic information. This sensory information is correlated to propulsive force data to begin to formulate relationships between the production of force and sensor outputs; relationships that the biological entity may use for fin sensori-motor control. Initial results indicate that fin curvature may be an indicator of the direction of propulsive force generation and pressure may be an indicator of generated force magnitude and flow speed, but that more sensors and testing are necessary to completely reveal the complicated relationships between the sensory data and the generation of propulsive force. The initial set of data has revealed a clear path forward for future experimentation, and the performance of the test apparatus during experimentation indicates that the core design is sufficient for continued testing. As additional sensors are implemented and future testing is completed, a somatosensory map will be realized that will allow for the estimation of the fin-generated force direction and magnitude; this information is crucial to the development of a successful closed-loop fin control structure.