Simulation and experiment of legs-stride forward and overcoming obstacle gait of walking robot based on double 6-UPU parallel mechanism

Abstract: In order to expand the application of hexapod robot and improve the adaptability and flexibility of hexapod robot to the working environment, a walking robot based on double 6-UPU parallel mechanism is proposed. The walking robot that has a total of 18 degrees of freedom, which is composed of two 6-UPU parallel mechanism legs and 6 feet equipped with auxiliary legs. The auxiliary leg enhances the adaptability to overcome obstacles and the environment by changing the body height of the walking robot. Firstly, the kinematics of the 6-UPU parallel mechanism is analyzed, and the kinematics inverse solution is applied to obtain the status of each branch of the parallel leg. Secondly, according to the results of inverse kinematics solution, 2 gait modes of legs-stride forward gait and overcoming obstacle gait are designed. And then, the model of the hexapod robot is built in the ADMAS, and the materials of model are set according to the prototype material, to simulate two kinds of gaits. In simulation, it takes 23.734 2 s for the leg-stride forward gait cycle and the body of hexapod walking robot advances forward 400 mm, with the average walking speed of 1 011.2 mm/min. While it takes 18 s for overcoming obstacle gait cycle and the body of hexapod walking robot advances forward 100 mm, with the average walking speed of 333.3 mm/min. Finally, the control system is designed with two pieces of STM32 microprocessor chip for data collection and PID algorithm calculation, and the data transmission between two chips is by serial communication. In experiment, it takes 24.85 s for the leg-stride forward gait cycle and the body of hexapod walking robot advances forward 385 mm, with the average walking speed of 929.6 mm/min, for what in overcoming obstacle gait are 20.8 s, 90 mm, and 259.6 mm/min. In leg-stride forward gait cycle, the deviation of the time taken and the average walking speed between simulation and experiment results are 5% and 8%, respectively, while that in overcoming obstacle gait cycle, are 13% and 22%, respectively. The simulation planning trajectory and experimental trajectory of the central points of 2 moving platforms for parallel legs are drawn in the walking stage, and the experimental trajectory lag behind the simulation for two kinds of gaits. Though affected by the characteristics, the assembly accuracy of each electric cylinder and quality errors of material in the experimental prototype, the prototype can complete walking task by the set gait, thus the correctness of the simulation analysis is verified. The research could provide a reference for further investigation on hexapod parallel walking robots, achieving stable walking on unknown environment.