Pitching attitude closed loop control of wheel-legged all terrain mobile robot with active suspension

With the attention of agricultural robot research and development in recent years, many kinds of agricultural robots have been developed according to the different focus of the problem solving. Because the wheel-legged robots have excellent obstacle surmounting ability, low energy consumption and stable terrain adaptability compared with other mobile platforms, it has been widely used in various fields of precision agriculture, military investigation, resource exploration and so on. The position and attitude will be inevitably changed when the wheel-legged robots in operation, and the working accuracy and working performance will be affected due to the complexity of the working environment. In order to control the position and attitude, reduce the influence of the non paved pavement to the robot's attitude and position, ensure the stability of the robot, a new type of wheel-legged all terrain mobile robot with active suspension was designed in this study based on the multi-link independent suspension system of the vehicle. Multi-link independent suspension had mature application experience in automobile manufacture, but seldom applied in wheel-legged robot. The suspension system was the general name of the device that connected the body and the wheel. It can be roughly divided into the independent suspension system and the dependent suspension system, of which the non independent suspension system referred to the connection between the two wheels, and the pulsation of one side of the wheel affected the beat of the other side, while the wheels in the multi-link independent suspension system had their respective suspension mechanisms, which were independent of each other and did not interfere with each other, this improved the stability and comfort of the robot. By the suspension system, the vibration of the robot can be effectively reduced, the impact between the parts of the robot was buffered, and the economy and reliability of the robot can be improved. Then on the basis of establishing the kinematics model of wheel-legged robot, the inverse kinematic equations was established by Vector method and Euler formula, and the relationship between actuator stroke and suspension rotation angle was obtained, meanwhile, the position and attitude control of wheel-legged robot was decoupled. In order to ensure the reliability and correctness of the inverse kinematics and kinematics control model of the robot, the 1/4 robot test rig was manufactured and a 1/4 bench model test was carried out on the basis of theoretical analysis. The simulation results were basically consistent with the bench test data, and the maximum error was within 1.5%, the correctness of the relationship between the motion pitch angle of the robot body and the rotation angle of each leg joint was verified under the condition of the participation of the kinematic model. Then, a robot pitching attitude control strategy was built in MATLAB with proportional control to realize the closed loop control under the condition that the center of robot centroid was fixed, Finally, the robot virtual model was built in ADAMS, and MATLAB and ADAMS were used to establish the joint simulation. The simulation results showed that the pitch attitude and the centroid position of the robot had a good tracking effect, and the position error and attitude error of the centroid were 0.2% and 2%, respectively. Therefore, the correctness of the closed-loop attitude control strategy of the wheel-legged robot was verified. The algorithm can maintain the position and attitude of the wheel-legged robot and reduced centroid offset when crossing obstacles, it enhanced the performance of wheel-legged robot as the agricultural robot, the performance of the all terrain mobile robot with active suspension provides a reference for the design of the motion position and attitude control of the modern agricultural robot.