Design and Implementation of a Three-Link Brachiation Robot with Optimal\n Control Based Trajectory Tracking Controller

Abstract

This paper reports the design and implementation of a three-link brachiation\nrobot. The robot is able to travel along horizontal monkey bars using\ncontinuous arm swings. We build a full order dynamics model for the robot and\nformulate each cycle of robot swing motion as an optimal control problem. The\niterative Linear Quadratic Regulator (iLQR) algorithm is used to find the\noptimal control strategy during one swing. We select suitable robot design\nparameters by comparing the cost of robot motion generated by the iLQR\nalgorithm for different robot designs. In particular, using this approach we\nshow the importance of having a body link and low inertia arms for efficient\nbrachiation. Further, we propose a trajectory tracking controller that combines\na cascaded PID controller and an input-output linearization controller to\nenable the robot to track desired trajectory precisely and reject external\ndisturbance during brachiation. Experiments on the simulated robot and the real\nrobot demonstrate that the robot can robustly swing between monkey bars with\nsame or different spacing of handholds.\n