Dynamics Research And Robust Desing Of Web Offset Press's Folding Mechanism With Clearance

High speed, high precision and high stability are the important features and inevitable requirement of modern printing machinery. Web offset press is the highest speed large equipment, but the folding mechanism is one of the critical factors to restrict the printing speed of web offset press. In this paper, combined with the characteristics and development tendencies of modern printing machinery, and around with improving the accuracy and stability of folding mechanism, dynamics of mechanism with clearance and robust design to the folding mechanism are studied.To the nonlinear dynamic response of folder system caused by the pair clearance and the bearing stiffness, the hypothesis of rigid role and spring combination is put forward, and the dynamics model of folder mechanism with clearance is established. According to the actual situation of folding mechanism's pair, rigid pole hypothesis is quoted to the pair clearance, and the roller is assumed as a spring to it's deformation, by defined the roller radial stiffness. The hypothesis makes folder system to be a multi-freedom complex mechanical system by adding four broad freedoms and eight local freedoms. The dynamics model consists of three parts:kinematics analysis which can draw the relationship of kinematics output to input, the clearance angle, the spring deformation and angle, dynamics equations which is established by Lagrangian equation to solve the clearance angles, and each component's balance equationg which is derived by D'alembert's principle to solve the clearance's constrain forces and the spring's deformation and angle. The dynamics model which contains second order partial differential equations, is solved by Longur-Coulthard method. The dynamic model is verified by the dynamic testing to the folding machainism.The quantitative relation between dynamic responses to the working speed and the clearance is gotten, and folding mechanism's response differentiation point and dynamic load coefficient, are provided. The response differentiation point can be used to analysis the folding mechanism's highest speed in different clearance. Dynamic load coefficient can be used to analysis the maximum allowable clearance in working speed. The fold cutter's lateral deformation is the key factor to influence the folding precision. The cutter's lateral deformation model is established to research the relationship of the folding precision to the working speed and the clearance, by the finite element method and the analysis to the deformatin of folding stem.Considering the design variables and processing error influence on the performance of folding mechanism, the sensitivity analysis method and variance analysis method are firstly used to research the robustness of folding mechanism. The sensitivity analysis model and variance analysis model are derived by folding mechanism's clearance dynamics model. The response sensitivity can intuitivey reflect the affect degree of each design variables to the folding mechanism's performance. The response variance can analysis the performance deviation probability of folding mechanism caused by the random factors such as processing error.Based on the robustness analysis, the robust design mothed is studied. Used the minimization of folding deviation and sensitivity as the goals, the robust design model to the mean design variables is established. Based on the variance analysis, and combined with the relationship of processing cost and tolerance, the robust design model to the design variables'tolerance is derived. Combined with the advantages of two models, the folding mechanism robust design integrated model is constructed. The robust design integrated model can simultaneously solved the mean design variables and the design variables'tolerance, which can solved the no-consistency problem of the mean design variables and the design variables'tolerance, and avoid the complex calculation in the robust design model to the design variables'tolerance. A contrast test, which is to the results of the original scheme and robust design scheme, is done on the device. The test result confirms the validity and feasibility of robust desigh mothed.