| Offset press is a kind of printing equipment with great bulk, complex structure and sophisticated motion, and the gear transmission system is an important part of the mechanical transmission system of multi-color offset press. With the high requirements for the efficiency and quality of printing, offset press develops along the high-speed, multi-color and high-precision lines. The native and foreign scholars have proved some conclusions by experiments:(i) the dynamic excitation created by the gear transmission system is the main source of vibration at high speed, and (ii) the reduction in printing quality caused by nonlinear vibration of gear transmission system becomes the most concerned and urgent issue. The highest printing speed of abroad advanced high-speed multi-color offset press have exceeded 18000r/h (revolutions per hour), while that of the domestic corresponding products only reach 15000r/h. Therefore, the nonlinear dynamics behavior of gear transmission system have turned into an urgent issue waiting for solving in vibration theory and engineering applications.The lubrication technology of gear can significantly affect tooth surface friction, life span, load capacity and reliability. In engineering applications, the textural characteristic of tooth surface have a great influence on lubricating performance such as the pressure distribution, film thickness distribution and friction coefficient, however, there have been few corresponding theoretical model, causing ineffective guidance on the lubrication system design of gear. The latest findings obtained from foreign scholars show that there exists coupling effect between the tooth surface friction and the gear dynamics. Thus, it is necessary to establish and develop gear tribo-dynamic theory to deeply analyse the coupling relationship between the lubrication characteristics and the dynamics behavior, thereby revealing the mechanism of film lubrication which have an important influence on reliability. The results of the study have great theoretical significance and practical value to the cognition of lubrication characteristics and the lubrication system design.The dissertation, supported by the transformation of scientific and technological achievements foundation of Jiangsu province, made an exhaustive research on nonlinear dynamics and elastohydrodynamic lubrication (EHL) for the gear transmission system of domestic high-speed multi-color offset press. A series of progresses and accomplishments have been made on the key issues, for example, (i) to establish a nonlinear dynamic model of offset press gear-cylinder-bearing system and the analysis of nonlinear dynamics behavior, (ii) to establish a dynamic model of offset press gear transmission system and the parameter optimization, (iii) the analysis of mixed EHL for spur gear of form inking roller and (iv) the analysis of tribo-dynamic characteristics for involute gear. The major works of this dissertation are listed as follows:(1) The nonlinear dynamic model of gear-cylinder-bearing system, included time-varying meshing stiffness, transmission error, backlash, shoulder iron and rubber contacts and so forth, was established in this dissertation. The dynamic equations of system were solved by direct integral Newmark-β method, and then the natural frequency, dynamic factor and effective value of acceleration were also investigated detailedly. According to the numerical results, the nonlinear dynamic characteristics of gear-cylinder-bearing system were studied by the dynamic response of acceleration in time domain, FFT spectrum, phase-plane diagram, Poincare map and the largest Lyapunov exponent.(2) The dynamic model of multistage parallel-axes helical gear and spur gear were proposed by using the lumped parameter method, respectively. Therefore, the dynamic model of offset press gear transmission system was established by integrating two sub-models. The dynamic equations of gear transmission system were solved by fourth-order Runge-Kutta method, accordingly we obtained a series of dynamic response such as the acceleration, dynamic meshing force and relative sliding velocity of cylinder. The parameter optimization of gear transmission system was carried out by using sequential quadratic programming (SQP), then the effect of parameter optimization could be verified by comparing the optimization to the origin, for example the contact ratio, dynamic meshing force, equivalent dynamic factor, individual tooth force and equivalent stress.(3) Under the consideration of axial velocity and textural characteristic of tooth surface, the lubricating performance of spur gear of form inking roller was investigated based on finite line contact mixed EHL theory. The numerical results for the mixed EHL model of spur gear of form inking roller were calculated by using multigrid method. In addition, we discussed the influence of axial velocity and textural characteristic of tooth surface on lubricating performance along the line of action, such as the pressure distribution, film thickness distribution, asperity load ratio and friction coefficient.(4) A dynamic model of involute spur gear and a transient mixed EHL model were proposed based on dynamics and tribology theory, respectively, then we developed a tribo-dynamic model of a spur gear pair that contained the coupling effect. An integrated iteration incorporated Runge-Kutta method and multigrid method to predict numerical results. According to the numerical results, the variations of kinematic characteristics, fluid film stiffness, individual tooth force, central film thickness, time-varying meshing viscous damping, sliding friction force, friction force, friction coefficient, meshing power loss were studied along the line of action. In addition, we also discussed gear transmission efficiency under static and dynamic conditions, respectively.(5) Dynamic response testing for offset press was carried out by using electrometric method, with the result that the vibration acceleration of several key parts were obtained at different printing speeds. On the basis of experiment, the experimental data were investigated in time domain, frequency domain and effective value space by signal analysis technique. Finally, the experimental results revealed the main source of vibration and ascertained the optimizing direction.This dissertation is innovative in the following aspects:(1) According to finite element method, the gear-cylinder-bearing system can be divided into the gear meshing pair element, the cylinder and elastic shaft element, the bearing element, the shoulder iron and rubber contacts element. The assemblies of elements are performed by using the continuity condition and displacement compatibility condition between nodes, accordingly a nonlinear dynamic model of gear-cylinder-bearing system is established at the end.(2) On the basis of establishment of dynamic model of offset press gear transmission system, the gear mesh model with multiple degrees of freedom (MDOF) is translated into single degree of freedom (SDOF) model. In addition, the approximate analytic formula of maximum meshing force is deduced and the equivalent dynamic factor is selected as objective function in optimum design.(3) A new model for spur gear of form inking roller that contains two-dimensional velocities is proposed to deal with lubrication problem, using the finite line contact mixed EHL formulas, then we investigate the influence of axial velocity and rough surface pattern on lubricating performance.(4) A tribo-dynamic model of a spur gear pair included dynamic meshing force, dynamic boundary conditions, time-varying meshing viscous damping, time-varying friction force and time-varying friction torque is established to study the coupling effect between the lubricating performance and the dynamics behavior, besides, to reveal the mechanism of film lubrication for gear system. |
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