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The Effects of Interference Motion of Rolling Elements in a Ball Screw
|關鍵字:||ball screw;滾珠螺桿;preload;interference;free-zone;預壓力;干涉;空迴||出版社:||機械工程學系所||引用:||H. Hertz, ”The Contact of Elastic Solids,” J. Reine Angew. Math., Vol. 92, pp. 156-171, 1881. B.J. Hamrock and D. Dowson, Ball Bearing Lubrication –The Elastohydro- dynamics of Elliptical Contacts, Wiley-Interscience, New York, 1981. T.A. Harris, Rolling Bearing Analysis, John Wiley & Sons, New York, 1981. P.H. Markho, ”Highly Accurate Formulas for Rapid Calculation of the Key Geometrical parameters of Elliptic Hertzian Contacts,” ASME J. of Tribology, Vol. 109, pp. 640-647, OCT. 1987. M. C. Lin, S. A. Velinsky, and B. Ravani, ”Design of the Ball Screw Mechanism for Optimal Efficiency,” ASME J. of Mechanical Design, Vol. 116, pp. 856-861, Sept. 1994. B.J. Hamrock, Fundamentals of Fluid Film Lubrication, Chapter 19, pp. 402-416. 1994. J.F. Cuttino, T.A. Dow, and B.F. Knight, ”Analytical and Experimental Identification of Nonlinearities in a Single-Nut, Preloaded Ball Screw,” ASME J. of Mechanical Design, Vol. 119, pp. 15-19, Mar. 1997. H.T. Huang and B. Ravani, ”Contact Stress Analysis in Ball Screw Mechanism Using the Tubular Medial Axis Representation of Contacting Surfaces,” ASME J. of Mechanical Design, Vol. 119, pp. 08-14, Mar. 1997. K. Miyaguchi(宮口和男), M. Ninomiya, Y. Watanabe, S. Arai, M. Hamamura, and Y. Kakino, “A Study on the Friction Torque Variation of a Ball Screw at Motion Direction Change-Friction Torque Variation due to the Change in Ball Contact Points,” 精密工學會誌, Vol. 68, No. 6, pp. 833-837, 2002. 魏進忠，”單螺帽雙圈滾珠螺桿在預負荷及潤滑作用條件下運動機制與機械性能的理論分析及實驗印證”，國立成功大學機械工程學系博士論文，2003. 曹博涵，”滾珠螺桿預壓力、軸向剛性與尺寸及公差關係之探討”，國立中興大學機械工程學系碩士論文，2005. 黃惠琪，”單螺帽歌德牙型滾珠螺桿之尺寸干涉量對預壓力影響之探討”，國立中興大學機械工程學系碩士論文，2006. 上銀科技股份有限公司，滾珠螺桿技術型錄，2006.||摘要:||
滾珠螺桿為線性傳動的核心，其優良傳動效率及精密定位的特性，於精密機械的平移運動扮演重要角色。在客戶服務經驗中，常有客戶提及螺桿異常温升、反向運動時的預壓力消失現象。它常常會被客戶誤以為是“螺桿背隙”(本研究稱為 ”空迴” )。本研究以實驗觀測及動態模擬的方式，了解螺桿正反轉時預壓力變化的原因，並得到相關的數據。
本文亦進行偏位式預壓螺桿的動態模擬，以填入不同的鋼珠尺寸6.340mm, 6.345mm,…, 6.352mm等，進行動態受力分析，讀取相同時間點的鋼珠受力進行比對，由動態模擬正向和反向的運動結果，可印證實驗觀測的成果。在正反轉的運轉過程，左右螺帽因為螺旋角度的關係，個別螺帽的鋼珠受力角度並不對稱，所以在轉向的過程中，由受力的改變而產生鋼珠調整位置的空迴現象。
Ball screw is known as the core of linear motion technology. The significance of its role in a precision linear motion comes from its distinguished characteristics of excellent transmission efficiency and precise positioning. Many customers mentioned the problem of losing preload while ball screw performing reverse motion. This phenomenon is expressed as “backlash” by customers (referred as “free-zone” in this thesis.) In this thesis, we use dynamic simulation and running test to study the main cause of preload variation while a ball screw travels forward and backward. Some data are presented for reference.
A double-nut ball screw was a specimen for studying. Two types of experiment are conducted: (i) adjusting preload by spacers for nut with same size of balls; (ii) Changing the size of balls but maintaining the same preload of nut by spacer. The outcomes of the experiments prove that free-zone and preload are irrelevant, however, free-zone and the size of balls are correlated in someway. As the size of balls get larger, free-zone value tends to get smaller, yet there is a limit to it and it's unlikely to lose all free-zone completely. The recirculation system was disassembled for observing the ball movement on both forward and reverse free-zone occurrence. When the size of ball is 6.340mm, there are only two points of contact regardless of moving direction. Nevertheless, when the size of ball is increased to 6.352mm, forward and reverse spinning axis is located at 45° or 90°, respectively. When the spinning axis is at 90°, the third point of contact will happened in the system. In the high speed running test, the ball screw with 90° spinning axis has higher temperature increase.
Dynamic simulations on the ball screw with offset preload are also performed. Several different sizes of balls were inserted, respectively, in the nut to compare their dynamic stress under same position of ball. The results from dynamic simulations are to be used for corroborating the actual running test. While the nut is traveling back and forth on the shaft, the stress vector of the ball is asymmetric on each re-circulating system due to the helix angle. The contact position of ball is changed due to the variation of stress vector, that's how the “free-zone” phenomenon is generated.
The main purpose of this study is to clarify the “free-zone” phenomenon on a ball screw. It can be used as an illustrative material for customer questions. Definitely, the results can provide as an excellent checking point to avoid temperature increase and wear out rate.
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