Ball screw pair is the feed transmission chain of NC machine tool. Its assembly method and precision determine the positioning accuracy of NC machine tool, and also affect the stability of feed shaft interpolation operation.

一、滾珠絲杠副安裝方法及受力

I. Installation Method and Force of Ball Screw Pair

控機(jī)床進(jìn)給軸常見(jiàn)的絲杠支撐有如下幾種方法：

There are several common methods of screw support for feed shaft of CNC machine tools:

1、一端固定一端自在

1. One end fixed and one end free

絲杠一端固定，另一端自在。固定端軸承一起接受軸向力和徑向力，這種支承方法用于行程小的短絲杠或者用于全閉環(huán)的機(jī)床，由于這種結(jié)構(gòu)的機(jī)械定位精度是較不可靠的，特別是關(guān)于長(zhǎng)徑比大的絲杠，熱變性是很明顯的，1.5m長(zhǎng)的絲杠在冷、熱的不同環(huán)境下變化0.05~0.10mm是很正常的?？墒怯捎谒慕Y(jié)構(gòu)簡(jiǎn)單，安裝調(diào)試便利，許多高精度機(jī)床依然選用這種結(jié)構(gòu)，可是必須加裝光柵，選用全閉環(huán)反應(yīng)。

One end of the lead screw is fixed and the other end is free. Fixed end bearings accept both axial and radial forces. This support method is used for short lead screw with small stroke or machine tool with full closed loop. Because the mechanical positioning accuracy of this structure is the most unreliable, especially for the lead screw with large aspect ratio, the thermal variability is very obvious. It is normal that the lead screw with 1.5m length varies from 0.05 mm to 0.10mm in different cold and hot environments. However, because of its simple structure and convenient installation and debugging, many high-precision machine tools still choose this structure, but grating must be installed, and full-closed-loop response must be selected.

2、一端固定另一端支承

2. One end is fixed and the other end is supported.

絲杠一端固定，另一端支承。固定端一起接受軸向力和徑向力；支承端只接受徑向力，并且能作微量的軸向起浮，可以削減或防止因絲杠自重而出現(xiàn)的彎曲，一起絲杠熱變形可以自在的向一端伸長(zhǎng)。這種結(jié)構(gòu)使用較廣泛，目前國(guó)內(nèi)中小型數(shù)控車(chē)床、立式加工中心等均選用這種結(jié)構(gòu)。

One end of the lead screw is fixed and the other end is supported. The fixed end receives both the axial force and the radial force together; the supporting end receives only the radial force, and can make a small amount of axial buoyancy, which can reduce or prevent the bending caused by the self-weight of the lead screw, and the thermal deformation of the lead screw can extend freely to one end. This structure is the most widely used. At present, this structure is used in small and medium-sized CNC lathes and vertical machining centers in China.

3、兩頭固定

3. Fixation at both ends

絲杠兩頭均固定。固定端軸承都可以一起接受軸向力，這種支承方法，可以對(duì)絲杠施加適當(dāng)?shù)念A(yù)緊力，提高絲杠支承剛度，可以部分補(bǔ)償絲杠的熱變形。

Both ends of the lead screw are fixed. Fixed end bearings can accept the axial force together. This support method can exert appropriate preload on the screw, improve the support stiffness of the screw, and partly compensate the thermal deformation of the screw.

關(guān)于大型機(jī)床、重型機(jī)床以及高精度鏜銑床常選用此種計(jì)劃。可是，這種絲杠的調(diào)整比較繁瑣，假如兩頭的預(yù)緊力過(guò)大，將會(huì)導(dǎo)致絲杠終究的行程比規(guī)劃行程要長(zhǎng)，螺距也要比規(guī)劃螺距大。

This plan is often used for large machine tools, heavy machine tools and high precision boring and milling machines. However, the adjustment of this kind of screw is rather tedious. If the pre-tightening force at both ends is too large, the final stroke of the screw will be longer than the planned one, and the pitch of the screw will be larger than that of the planned one.

假如兩頭鎖母的預(yù)緊力不行，會(huì)導(dǎo)致相反的結(jié)果，并簡(jiǎn)單引起機(jī)床震動(dòng)，精度降低。所以，這類絲杠在拆裝時(shí)一定要按照原廠商說(shuō)明書(shū)調(diào)整，或憑借儀器（雙頻激光測(cè)量?jī)x）調(diào)整。

If the pre-tightening force of the lock mother at both ends is not good, it will lead to the opposite result, and simply cause the vibration of the machine tool, and reduce the accuracy. Therefore, this kind of screw must be adjusted according to the manufacturer's instructions or by means of instruments (dual-frequency laser measuring instrument).

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