| Compared with wheeled,tracked and other common mobile equipments,the characteristics of floating base and discontinuous ground support make legged robot have higher mobility and environmental adaptability.Therefore,with the rapid development of science and technology,legged robot is becoming one of the first choices to perform mobile tasks in unstructured environments.Among all kinds of legged robots,hexapod robot with primordial self-stability is one of the key directions in the research field of legged robot.Compared with the small-size and medium-size hexapod robots which are developed for light load carrying and moving flexibility,the large-size heavy hexapod robot which is developed for large load carrying with environmental adaptability has more practical significance in real outdoor material transportations.However,some special problems in practical applications caused by the large mass,large inertia and unpredictable environment characteristics of a large-size hexapod robot can be easily seen,such as obvious deformation,large foot-ground contact impact,easy accumulation of body attitude deviation,and so on.The problems lead to more strict requirements of motion stability and flexibility of a large-size heavy hexapod robot.Therefore,to ensure the high requirements of motion stability,environmental adaptability,and motion compliance of a large-size heavy hexapod robot,it is of great significance to study the key motion control methods from the perspectives of motion stability,motion planning,and compliant control.To achieve this goal,the motion stability prediction,dynamic motion planning,and compliant control of a large-size heavy hexapod robot is studied in this paper.In this paper,a large-size heavy hexapod robot is studied.Aiming at the high requirements of the robot motion stability,the robot motion stability prediction method is studied.Based on the analysis of the actual kinematics model of the large-size heavy hexapod robot,the robot motion planning method considering the ground geometric parameter changes is studied first to realize the basic motion of the robot and reduce the adverse effect of the external ground geometric parameter changes on the robot leg motion.Furthermore,the typical influence factors of the robot motion stability are analyzed,and the FASM stability criterion is determined as the basic motion stability criterion of the robot.Aiming at the disadvantages of misjudgment and inability to quantitatively evaluate the motion stability trend of the robot,the unstable time frame in the single step motion time is proposed as the evaluation index of the motion stability trend of the robot.Finally,according to the historical multi-step unstable time frame information of the robot,a stability prediction method is proposed to fit the motion stability trend of the robot with quadratic curve and judge the future multi-step motion stability of the robot.The method proposed can solve the problem of lag in judging the motion stability of the hexapod robot,and the effectiveness of the method is verified through the virtual prototype simulation of the large-size heavy hexapod robot.In order to solve the problem of stable motion recovery of the large-size heavy hexapod robot under the instability trend,and improve the adaptability of the robot leg motion to the changes of the external environment,the dynamic motion planning method of the hexapod robot is studied in this paper.Based on the robot’s unstable step prediction and the analysis of the stable support states of the robot,an dynamic gait planning method for the hexapod robot is proposed in this paper using the stable support state searching method.Through this method,the robot motion stability can be regulated through realtime gait adjustment.In order to deal with the local obstacles existing on the external terrain,the classification and discussion of obstacle types are demonstrated,and a dynamic foot trajectory planning method of the robot inspired by the biological conditioned reflex mechanism is proposed.Through the motion simulations of the robot on different terrains,the effectiveness of the proposed dynamic motion planning method to improve the motion stability and environmental adaptability of the robot is verified.The compliant control method which conforms to the motion characteristics of the large-size heavy hexapod robot is studied to solve the robot’s motion problems,such as the overall deformation,large foot-ground contact impact and easy accumulation of motion attitude deviation.In order to adjust the attitude deviation of the robot in real time,a robot attitude angle trajectory planning method based on high-order interpolation curve is proposed,and the constraints of the key parameters during robot attitude angle trajectory planning under different walking gaits are analyzed.To further improve the foot-ground contact process,and reduce the influence of the robot deformation on the motion posture,a ”spring-muscle” model of robot leg inspired by the EPH hypothesis is established.Based on this model,a foot equilibrium point trajectory modification method is proposed.Through the foot equilibrium point trajectory modification method,both the overall force equilibrium and the foot-ground contact process of the robot during walking can be optimized.The simulation results show that the proposed compliant control method can reduce the difficulty of control system design and parameter adjustment on the basis of improving the overall motion compliance of the robot.Based on the research of the robot motion stability prediction method,the dynamic motion planning method and the compliant control method,and inspired by the idea of biological intelligent behavior decomposition,a hierarchical motion control framework of the large-size heavy hexapod robot is proposed in this paper.Through this control framework,the complex control logic of the robot can be simplified.Different walking experiments of the real large-size heavy hexapod robot in various environments are carried out.Through the quantitative analysis of the experimental results,it is verified that the motion control methods proposed in this paper have clear theoretical rationality and practical feasibility.The motion control methods proposed in this paper can effectively improve the actual motion performance of the large-sized heavy hexapod robot. |
