Lamprey Robots

We have developed a biologically based underwater, autonomous vehicle modeled after a simple vertebrate, the sea lamprey. The robot consists of a cylindrical Plexiglas electronics bay with a polyurethane undulator actuated by shape memory alloy artificial muscles. Sensors include a compass, pitch and roll inclinometers and sonar rangers, the signals of which are quantized into a labeled line code. Behavioral parameters are reverse engineered from the behavior of the target organisms. Fig. 1 Lamprey Robot Prototype Introduction We have implemented a lamprey-based robot based on biomimetic neurotechnology (Fig. 1). Lamprey swim by rhythmic lateral undulations of the body axis. The propagating lateral axial undulations increase in amplitude from nose to tail. Similar waves travelling from tail to nose can propel the lamprey backward (Ayers, 1989). Rhythmic propagating muscle activity alternating on either side of the body axis underlies this propulsive wave. Lamprey swimming is uncomplicated by pectoral, pelvic, or anal fins. Endurance rather than high speed is characteristic of Anguillform swimming. Kinematics of Swimming To quantitatively analyze the undulatory behavior of the lamprey, we employed a computer program (Ayers et al., 1983) uses stop-frame analysis of video images to establish the dynamics of body flexion’s (Fig. 2). Filmed sequences of swimming were then digitized and analyzed on a frameby-frame basis (Ayers, 1989). Kinematic analysis of body curvature demonstrates swimming behavior is organized into lateral flexion waves that propagate either from nose to tail or tail to nose. During swimming, the propagation time of flexion waves down the body axis is equal to the period so specimens always maintain an S-shape during swimming. 1 This work is supported by DARPA/DSO through ONR Grant N00014-98-1-0381. 2 Ayers, J., Wilbur, C., Olcott, C. (2000) Lamprey Robots. In: Proceedings of the International Symposium on Aqua Biomechanisms. T. Wu and N, Kato, [eds]. Tokai University. 2 Variations in period and curvature of flexion differentiate lamprey behavior acts (Table I. Ayers, 1989). Thrust occurs when a propulsive wave travels backward over the body at a velocity greater than the speed of forward swimming. Kinematic analysis demonstrates lamprey generate a peak of thrust as each flexion wave passes the cloaca (Fig. 2d-e). The thrust peaks at approximately sixty percent of the body and there are two peaks of thrust for every swimming cycle. Fig. 2. Kinematic Analysis of Swimming (A). Images of the lamprey body axis as digitized from sequential frames of a movie We evaluated how swimming movements are effected by hydrodynamic load by analyzing high frequency forward swimming of the lamprey in a wet shallow pan. The analysis demonstrates the active segments during swimming are located in the middle two thirds of the body (curvature vs locus), the mid-region of the body constitutes the propulsor for locomotion, and a passive role for the tail. As a result, our vehicle has three separate functional sections: head, body axis and tail. Neuronal-circuit based Controller We adapted a command neuron, coordinating neuron, central pattern generator based controller originally developed as a controller for a lobster robot (Ayers and Crisman, 1992, Jalbert et al. 1995) as the controller for the undulator. The controllers generates control signals for each of 5 body segments which alternate on the two sides and propagate down the body axis such that the propagation time is equal to the period of the undulation (Fig. 2). Modulation of the amplitude and timing of these propagating waves generates the complete behavioral repertoire (Table I).