Nowadays, biped robots have attracted the attention of many researchers and many studies have been focused on this subject. Most of the essential parameters of the human walking can be captured with a seven-link planar biped robot. In this thesis, dynamics modeling, dynamic stability, trajectory planning, control and implementation of a seven-link planar biped robot, walking on a level ground with a ditch or stairs, are studied. Each walking step may include two phases, the single support phase and the double support phase. Dynamic equations of the biped were derived in both phases. The generalized coordinates are chosen so that the final form of dynamic equations could be expressed in a simpler form. Zero moment point (ZMP) which was first introduced by Vukobratovic is used as the criterion to evaluate the stability of the biped robot. To generate smooth hip and foot trajectories and continuous ZMP, it is necessary that the velocity and acceleration terms of foot and hip joint trajectories be continuous all the times. To this end, with having the kinematics constraints for foot and hip joints, we can generate smooth trajectories for foot and hip joints in Cartesian space using polynomials with suitable orders such that the first and the second time derivatives are continuous all the times. The hip and foot trajectories are designed such that impact effect of feet with ground eliminated. If hip and ankle joints trajectories of each leg are known, all other joint trajectories will be determined using inverse kinematics. The key parameters of the hip joint trajectory in walking direction of the robot are obtained using boundaries of biped stable region during the walking to satisfy dynamic stability of robot. Using this method, we can also plan trajectories for walking on slope surfaces and stairs. Then the highest position of the swing foot ankle joint in sagittal plane is optimized with two different fitness functions. For walking in environments with different obstacles and ditches, the robot has to change its step length. Hence, a novel method for trajectory planning of walking with different step lengths, uses for online trajectory planning, is proposed. The effectiveness of the proposed method is verified by simulation and experimental results. We have used the proposed method to our small-size biped robot to verify the validation of simulation results. Experimental results prove the stability of our biped robot during walking on the level ground with different step lengths. Finally, with adding a joint as trunk joint, ZMP of the biped is controlled by trunk compensation to achieve stable walking. key Words: Biped robot, dynamic stability, zero-moment point, walking pattern generation, ZMP control
