Immobilization-based control of spider-like robots in tunnel environments

This paper presents an immobilization-based control method for spider-like robots that move quasi-statically in tunnel environments. The control method is based on a recent immobilization theory of bodies in contact. This theory ensures that when a spider-like mechanism is bracing against the environment at an immobile posture, the naturally occurring compliance at the contacts stabilizes the mechanism as a single body. Based on this result, we present two versions of a position control law for general k-limbed robots. We show that if the controller's stiffness (i.e., proportional gain) is above a lower limit determined by the robot and environment parameters, stability of the closed-loop spider system is guaranteed. Next, we present dynamic simulations of a spider robot moving in a tunnel under the influence of the immobilization-based control law. The simulations show excellent convergence properties of the control algorithm. A four-legged spider prototype has been built, and we conclude with a description of initial experiments with this prototype.