Design and control of a 6 DOF biped robot

Abstract

This thesis is composed of the following five parts: construction of a 6 Degrees of Freedom (DOF) biped robot, control system design, analysis of forward kinematics and inverse kinematics, walking pattern planning, and PID control implementation. The 6 DOF biped robot is built with aluminum plates, aluminum angles, wood, and rubber materials. It has two legs, two feet, and one trunk, each leg having three joints: hip, knee, and ankle. All joints are actuated by gear head DC motors with built-in encoders. A microcontroller-and-PC-computer-based control system is designed for the biped robot. The control system consists of actuators, sensors, controllers, and a PC computer. The actuators are the gear head DC motors with H-bridge circuits as drivers and the sensors are incremental encoders built in the DC motors. The controllers used are two microcontrollers, one for each leg. The microprocessors read and process joint angle measurements from the encoders and then transmit them to the PC computer. At the same time, the microcontrollers receive control signals from the PC computer and transfer them to the H-bridge circuits to control the robot joints. Data transfer between the microcontrollers and the PC computer is implemented by two RS232 serial communication channels. A control algorithm and walking pattern planning are carried out on the PC computer. Both forward kinematics and inverse kinematics are analyzed based on the D-H representation for the biped robot. Foot trajectories and hip trajectory are calculated by using the 3rd order spline interpolation method. Desired trajectories for joint angles are determined by the inverse kinematics. Simulation is performed to demonstrate the walking pattern. PID controllers are designed for controlling the biped robot to walk according to the designed walking pattern. The proposed PID controllers are implemented on the biped robot.