| Today,with the continuous development of science and technology,the process of industrial automation is deepening,and the popularity of robots is also improving.Among them,mobile robot is widely used in transportation,search and rescue,measurement,military and other aspects,so it has become a hot topic in global research.There are three typological common mobile robots which are divided into wheeled,tracked and feet.Wheeled and tracked robots have continuous landing points,which makes it difficult to play a large role on relatively steep roads.The foot robot can complete the walking task on rugged road,because of its discrete landing points,which has profound research significance and application prospect.At present,most foot robots have a single foot trajectory,and the phase difference of the trajectory needs to be used to realize gait planning and the turning process is complicated.In the case of narrow or limited space,the turning task cannot be completed.Because the landing point of omnidirectional mobile robot is any point in three-dimensional space,it can realize multi-direction movement through different trajectories.However,the research of omnidirectional mobile robot is mostly wheeled,and the leg mechanism of omnidirectional foot robot is also mostly series mechanism,which has some shortcomings such as poor bearing capacity and poor stability.To sum up,this paper proposes an omnidirectional walking robot with parallel mechanism legs,which can realize omnidirectional movement while maintaining the same attitude,and can effectively solve the problem of being unable to turn in a narrow space.Firstly,the movement form of cheetah leg was analyzed,and the structure form that can realize three-dimensional movement of foot was determined according to bionics principle.A kind of parallel mechanism leg based on functional bionics was designed according to screw theory,and a quadruped omnidirectional walking robot was proposed and a 3D model was drawn.Then,the screw theory was used to determine the driving joint of the mechanism and verify the degree of freedom of the mechanism.The forward and inverse kinematics solutions are analyzed by the method of geometric and the Jacobian matrix and acceleration matrix are calculated by the method of influence coefficient.Secondly,the performance of the parallel mechanism leg was studied and analyzed,including the reachable workspace was obtained by the method of searching inverse solution,the static torque of the driving joint was calculated by virtual work principle,and the static stiffness of the mechanism was analyzed according to the Jacobian matrix.Thirdly,the omnidirectional gait and foot trajectory of the quadruped robot are planned by integrating three methods: quintic polynomial,cosine programming and inverted pendulum,and the kinematic stability of the mechanism is analyzed.Multi-objective structure optimization was carried out based on genetic algorithm,and the rod length data with the best performance was obtained.Finally,the simulation analysis of virtual prototype is completed and the principle prototype is made,and the gait experiment and freedom experiment of the prototype are verified.Through the theoretical analysis and research of omnidirectional mobile robot,it is verified that the mechanism designed in this paper has good motion characteristics and acceleration continuity.The foot has 2R1 T three degrees of freedom motion characteristics,realizing omnidirectional motion can effectively solve the problem of unable to complete the steering in the case of limited space,and can meet the work requirements under extreme conditions.The robot foot has the motion characteristic of2R1 T three degrees of freedom,which can realize omnidirectional motion,effectively solves the problem that the turning cannot be completed in the case of limited space,and can satisfy the work requirements under extreme conditions. |
