| One of the key bottlenecks to achieve ultra-precision machining technology is how to get an accurate, stable and reliable micro displacement by the tool or work piece during machining process, that is precision positioning technology. The precision positioning system plays an important role in precision measurement, precision machining and so on. Due to the impact of low speed creeping phenomenon of electromechanical system inherent attribute to the conventional electromechanical transmission system structure and working mode, and the impact of low-speed nonlinear creeping phenomenon, so it is difficult to achieve precise micro displacement and uniform feed control, and can not meet the high precision manufacturing and processing equipment before the urgent need of micro displacement is an important way to realize the ultra precision machining. From the results of domestic and international research, a typical microfeed is realized with a macro-micro double drive, which usually uses a precision ball-screw single drive for macro movements and then uses the magnetostrictive effect of piezoelectric ceramics to achieve micro movements. But the macro-micro double drive has obvious disadvantages:small stiffness, creep, hysteresis nonlinearity, and especially a hysteresis phenomenon, resulting in greatly reduced positioning accuracy. The dual servo feed system presented in this paper is on the two "macro feed motions" ("motor drive screw" and "motor drive nut")through the same transmission of "rotary nut drive type" structure, which are nearly equal in speed and the same in turning direction, and it could obtain the "micro feed". Because it's higher than the two high-speed "macro motions" under the critical speed generating crawling, and obtains "micro action " through the rigid drive of the same "rotation-line" rolling screw transmission vice, we can relieve the unavoidable effect of low speed nonlinear creeping phenomenon caused by the inherent property of the traditional electromechanical servo system structure, so as to realize high precision micro feed.In this paper, based on Hertz contact theory, the contact raceway control theory, analysis of multi body dynamic and static friction, and the thermodynamics theory, based on the analysis of Pro/E, ABAQUS, MATLAB and other software, construct the kinematics model, kinetics model and thermodynamic coupling model of the dual drive micro feed mechanism of the dynamic characteristics of the main content including:(1)This paper analyzes the state of motion of working ball by the principle of differential geometry, calculates the friction at the contact points, establishes the balance equation of force and moment, studies the influence of the screw and nut on the kinematic parameters of ball at different velocities and the differences of the state of motion of ball under different driven mode, and calculates the mechanical efficiency of dual driven ball screw mechanism. The results of theoretical analysis lay the foundation of the design-calculation and the finite element analysis of the micro feed mechanism.(2)The rotary-nut-ball-screw double-drive system is modeled on the basis of Hertz theory and the lumped-mass method. Then, the frequency-response characteristics are calculated using the Lagrange equation and the state-space method. Finally, the frequency-response characteristics of macro-macro double-drive and single-drive systems are compared via numerical analysis, and the influence of changes in the preload, torsional rigidity, and workbench's total mass on the frequency-response characteristics is studied. The dynamic model and simulation results provide an important theoretical foundation for developing the novel drive system and controller.(3)Because the friction nonlinearity will cause crawling, oscillation and other erratic behavior to the system, we use the mature lumped parameter method to establish a dynamics model of feed system considering the friction.We use the block diagram of transfer function to describe the motion relations of dual-motor servo feed system, and use Simulink simulation to analyze the effect of friction on the output of the table under different driving mode and the effect of the combination of different speeds of dual motors on the output of the table at the same feed speed. The results show that whether in uniform or variable speed the fluctuation of the table of dual servo system is significantly less than the single-drive system's when both are micro-feed.(4)The establishment of the theory of heat transfer conduction and convection system components in thermal resistance model based on the heat balance heat node analysis, using thermal network method to establish the feed system of the heat balance equations of heat balance equations using Newton Raphson method to obtain temperature distribution model of feed system; combined with the deformation theory mechanical thermal, thermal error prediction of axial double ball screw driven by temperature field model. Two single/double drive dynamic thermal performance under the condition of the numerical analysis results show that in the same way and different driving speed, single/dual drive system of the distribution of temperature field and thermal error is different, comparative analysis also shows the variation of thermal dynamic characteristics of the system driven by two different feed speeds.(5)Based on modern sensing, signal processing and computer modern numerical control technology, a dual drive micro feeding characteristic comprehensive experimental platform is developed. Experimental research on dynamic characteristics of the experimental platform to build, including the frequency response test, experiment table in different driving conditions of the critical creeping speed test system, temperature rise and thermal elongation measurement experiment. The theoretical model is verified by experiments, and the experimental results are in agreement with the simulation results, which shows that the theoretical calculation and analysis results of the dual drive feed system are correct. |
PDF Full Text Request