The Research of Thermal Displacement Analysis of Ball Screw's Nut

• Main Authors: Ting-Chia Kang, 康庭嘉
• Other Authors: Kuo-Ming Chang
• Format: Others
• Language: zh-TW
• Published: 2011
• Online Access: http://ndltd.ncl.edu.tw/handle/25384133360178915547

碩士 === 國立高雄應用科技大學 === 機械與精密工程研究所 === 99 === Ball screw is widely used in transmission components of the precision engineering industry. In the cycle of the periodic circular motion, the ball between nut and screw generates the heat and thermal stress, which may result in temperature rise and thermal displacement problems in ball screw system. Therefore, the precision positioning of ball screw is a very important issue. This thesis numerically investigates the temperature distribution and the displacement of nuts affected by heat and stress with the change in load and rotational speed. In addition, to improve the stiffness and remove the backlash of the ball screws, a preload was added on them in practice. Thus this work solves the true axial force under various stages, taking into consideration of the preload function and the acceleration /deceleration of ball screw. Based on the kinematic theory, the average heat flux and the hertz contact stress are evaluated with changes in viscosity and temperature. This work presents a three-dimensional model for calculating the thermal displacement, and applies the finite element method for discretization. Full-coupled system equations of motion and heat conduction are solved in the iteration process, then this work establishes the database used in numerical simulation with a change in convection heat transfer coefficient. Thus employing the least root mean square error method on the experimental temperature and calculating temperature, the effective convective heat transfer coefficients can be efficiently predicted at various rotational speeds. Therefore, this work directly evaluates the temperature field and the strain by substituting the effective convective heat transfer coefficients to the thermal-displacement analysis model. This study experimentally validates the numerical results by utilizing the hatchback machine of a ball screw system, which is divided into two categories: no-oil cooling system and oil cooling system. This work puts the thermal couples inside and outside the nut to instantaneously measure the variation of temperature, then it is able to compare the temperature difference and the cooling effect in these two systems. Moreover, this study adopts the steady temperature data of no-oil cooling system to build the numerical simulation. The comparison of numerical results and experimental results displays that the agreement is very good. Thus, the proposed model incorporating thermal displacement is capable of easy analysis in practical industry and reducing the trial-and-error time in the design process.