Design and control of a 6 DOF biped robot

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

Design, analysis and passive balance control of a 7-DOF biped robot

Biped robots have many advantages than traditional wheeled or tracked robots. They have better mobility in rough terrain and can travel on discontinuous path. The legs can also provide an active suspension that decouples the path of the trunk from the paths of the feet. Furthermore, the legs are able to step over considerably bigger obstacles compared to wheeled robots. However, it is difficult to maintain the balance of biped robots because they can easily tip over or slide down. To be able to walk stably, it is necessary for the robot to walk through a proper trajectory, which is the goal of this research. In this research, a complete 7-DOF biped walking trajectory is planned based on human walking trajectory by cubic Hermite interpolation method. The kinematics and dynamic model of the biped are derived by Denavit-Hartenberg (D-H) representation and Euler-Lagrange motion equations, respectively. The zero moment point of the robot is simulated to check the stability of the walking trajectory. The setpoint sampling method and sampling rate for trajectory tracking control are investigated by studying sinusoidal curve tracking on a single link robot arm. Two control sampling time selection methods are introduced for digital controllers. A 7-DOF biped is designed and built for experiments. Each joint has its own independent microcontroller-based control system. PD controllers are used to control the biped joints. Simulations are performed for the walking trajectory and zero moment point. Simulation results show that the walking trajectory is stable for the 7-DOF biped. Experiment results indicate that the sampling time is proper and the PID controller works well in both setpoint control and trajectory tracking. The experiment for the marching in place shows the trajectory is stable and the biped can balance during the marching process

A Foot Placement Strategy for Robust Bipedal Gait Control

This thesis introduces a new measure of balance for bipedal robotics called the foot placement estimator (FPE). To develop this measure, stability first is defined for a simple biped. A proof of the stability of a simple biped in a controls sense is shown to exist using classical methods for nonlinear systems. With the addition of a contact model, an analytical solution is provided to define the bounds of the region of stability. This provides the basis for the FPE which estimates where the biped must step in order to be stable. By using the FPE in combination with a state machine, complete gait cycles are created without any precalculated trajectories. This includes gait initiation and termination. The bipedal model is then advanced to include more realistic mechanical and environmental models and the FPE approach is verified in a dynamic simulation. From these results, a 5-link, point-foot robot is designed and constructed to provide the final validation that the FPE can be used to provide closed-loop gait control. In addition, this approach is shown to demonstrate significant robustness to external disturbances. Finally, the FPE is shown in experimental results to be an unprecedented estimate of where humans place their feet for walking and jumping, and for stepping in response to an external disturbance