Finite Element Modeling And Damping Control Strategy For Boom Of Plant Protection Machine

The single-side boom of a large-scale plant protection machine can be as long as 20 meters.Besides,it is light and soft.During the operation,the external excitation generated by the road surface will likely lead to the boom's obvious elastic deformation.Even if the deformation is not serious(less than 20cm),it may result in re-spray or missed spray.In addition,in the complicated environment of the farmland,the deformed boom will likely scratch the crop or even touch the ground by the end.This will cause serious damages to the crops and sprayers and reduce the durability of the boom.Therefore,the key factors affecting the uniformity of the spray deposition distribution are how to construct an effective boom system and manage the vibration control.This thesis explained the establishment of a strain-based finite element model.This model can accurately simulate the nonlinear deformation of the boom during operation with the least degree of freedom.The stiffness matrices and mass matrices of the boom were calculated and incorporated into the nonlinear beam.Because of the non-rigid connection between the spray boom and the fuselage of a large-scale plant protection machine,the Lagrange multiplier method were used to simulate the node displacement constraint at the connection.And,the principle of virtual work was drawn upon to establish the entire spray boom kinematics equations.Through the ANSYS platform,this article analyzed the vibration characteristics of the boom model.The 12m-long single-sided boom was divided into 13 nodes.In the affected low frequency situations,the boom's free vibration analysis was performed,and the four modes were obtained and dynamic characteristics were simulated.Then,the deformation analysis was made,the displacement graphics was used to find the element with larger deformation degree,and the largest deformation node is Node No.13.After that,in the MATLAB finite element structural dynamics analysis platform,vertical vibration analysis was performed of these specific nodes.Finally,the node with the largest degree of deformation in this direction was found,and the balance of the end points of the boom is used as the control target.For the established control model,the linear quadratic optimal control method was adopted in this article.The LQR controller was designed to control the vibration suppression in the vertical direction for the specific node of the boom.Considering the actual operating conditions and the realization of the project,the researcher compared the control effects of these specific nodes and finally selected Node No.4 as best control point.At the same time,the designed controller was used to control the selected node in different external disturbances.Afterward,the effectiveness of this control method was simulated and verified.