Design and Control of Turtle Locomotion-Inspired Robots Actuated By Antagonistic Shape Memory Alloy Springs

Inspired by turtle locomotion, a novel type of robot with flippers actuated by antagonistic shape memory alloy (SMA) springs is presented that can crawl based on two different variable friction mechanisms. First, unlike robots incorporating a variable friction mechanism based on weight, the turtle-inspired robot bends its flippers through “on-off” control of the SMA springs in an open-loop system and achieves high friction based on the electromagnet. It can crawl on a vertical surface under a load with a load ratio of 78.5% without accurate locomotion control. To achieve fast and accurate displacement for each locomotion sequence, a radial basis function (RBF) compensator based on the minimum parameter algorithm and a mechanical model of the flippers is used to control the antagonistic SMA springs. The robot can regulate the bending shape of its flippers using an RBF compensator and climb a nonmagnetic surface with an inclination angle of $72^\circ $ when it utilizes suction units in the foot for its variable friction mechanism. The robot can crawl forward along both the X- and Y-axis directions. In conclusion, antagonistic SMA actuation with an RBF compensator provides fast and accurate performance and is a feasible alternative to the disturbance of the control of the flippers. This article can be used to develop design guidelines for crawling robots.