Hardware-Efficient CPG Model Based on a Ring of Unidirectionally Coupled Oscillators With Perturbation of State Transition Timing

Abstract

A ring of unidirectionally coupled phase oscillators is simple and easy to implement but not suitable for application to central pattern generators (CPGs) owing to the presence of coexisting stable equilibria corresponding to a gait and useless pattern. In this study, we propose a novel approach to applying a ring of unidirectionally coupled phase oscillators to CPGs by incorporating additional circuitry that alters state transition timing. This circuitry comprises a linear-feedback shift register and comparator. Our proposed model successfully generated typical hexapod gait patterns, such as wave and tripod gait patterns, as well as transition patterns between them. The projected Poincarè map was numerically derived to reveal that the proposed model possesses a unique stable equilibrium corresponding to these desired patterns. Furthermore, we implemented the proposed model on a field-programmable gate array (FPGA) to experimentally validate its effectiveness in generating gaits for a hexapod robot. Finally, the proposed model is demonstrated to require fewer FPGA resources compared with conventional and state-of-the-art CPG models.