Online trajectory generation in an amphibious snake robot using a lamprey-like central pattern generator model

Abstract

Abstract-This article presents a control architecture for controlling the locomotion of an amphibious snake/lamprey robot capable of swimming and serpentine locomotion. The control architecture is based on a central pattern generator (CPG) model inspired from the neural circuits controlling locomotion in the lamprey's spinal cord. The CPG model is implemented as a system of coupled nonlinear oscillators on board of the robot. The CPG generates coordinated travelling waves in real time while being interactively modulated by a human-operator. Interesting aspects of the CPG model include (1) that it exhibits limit cycle behavior (i.e. it produces stable rhythmic patterns that are robust against perturbations), (2) that the limit cycle behavior has a closed-form solution which provides explicit control over relevant characteristics such as frequency, amplitude and wavelength of the travelling waves, and (3) that the control parameters of the CPG can be continuously and interactively modulated by a human operator to offer high maneuverability. We demonstrate how the CPG allows one to easily adjust the speed and direction of locomotion both in water and on ground while ensuring that continuous and smooth setpoints are sent to the robot's actuated joints.

Adaptive creeping locomotion of a CPG-controlled snake-like robot to environment change

“…Many researches have studied the snake-like robot locomotion controlled by CPG, like Conradt and Varshavskaya (2003), Inoue et al (2004), Matsuo et al (2007), and Ijspeert and Crespi (2007). However, how the CPG parameters affect snake-like robot locomotion and how the adaptive motion is generated to the change of environment by CPG-based control is little discussed.…”

A novel mechanism for caterpillar-like locomotion using asymmetric oscillation

“…Last, Ijspeert et al use a high-level abstraction of CPG activity. Their model is designed to display a limit cycle corresponding to a circle in a cartesian plane [13]. The nonlinear oscillator is provided with amplitude, frequency and phase difference parameters to shape the body wave.…”

Direct programming of a central pattern generator for periodic motions by touching

“…(1) chain [22,9,23,24], used mainly for snake robots (2) star [25,26,5,27,28], that is a "pacemaker"/ "clock" oscillator which provides a synchronizing signal to the other oscillators (3) tree [29][30][31], where essentially the oscillators are connected as a tree, from proximal to distal joints (4) connection between homologous joints [32][33][34][35][36][37][38][39][40], i.e. joints with a similar function (5) full connection between the oscillators [41][42][43] Our purpose is to let the user modify the behavior of the robot by changing (through touching) the oscillator parameters.…”

“…However, systems similar to animal CPGs, often realized as weakly coupled oscillators, have been proposed for the control of many kinds of robots, such as hexapods [1], quadrupeds [2,3], bipeds [4][5][6][7], snake robots [8], etc. CPGs offer several advantages in terms of simplicity and the ease with which sensory feedback can be introduces [9] as well as in the adaptability and robustness [10] of the system. As reported in [10] the determination of CPG parameters is still difficult because they depend both on the robot and on the environment.…”