Abstract: The research of quadruped robot has become one of the hottest spots of robotics. A review of current status and development of quadruped robot is given; the serial architectures of leg mechanism are listed. Hybrid leg mechanism is advantageous to achieve needs of high-payload, energy consumption and high mobility. Three type of hybrid leg mechanism are designed. For each of them, a 2-DOF planar parallel mechanism is designed for lifting up a heavy load and providing trot trajectory and a four-bar link is used to swing the planar part while the robot steps on irregular terrain or balances outer strike. Design concept of leg and kinematic modeling method of robot are introduced. The workspaces are analyzed to maintain robot mobility. The load capabilities are given and a trot trajectory with the pace of 300 mm.The isotropy criterions are shown for back-and-forth with left-and-right locomotion. The third type is the best and furthermore compared with classic serial leg. A prototype is build to verify all the results through trotting experiment.

Key words: Heavy load transportation, Hybrid leg mechanism, Planar parallel mechanism, Quadruped robot