Ball screw is the most commonly used transmission element on machine tools and precision machinery. It belongs to a classification of machine tool bearings. It is composed of screw, nut and ball. Its function is to convert rotary motion into linear motion, or the ideal machine tool bearing product that transforms linear motion into rotary motion.
The main function of the ball screw is to convert rotary motion into linear motion, or convert torque into axial repetitive force, and at the same time have the characteristics of high precision, reversibility and high efficiency.
The ball screw is a further extension and development of the ball screw. The important significance of this development is to change the bearing from sliding action to rolling action. Because of its small frictional resistance, ball screws are widely used in various industrial equipment and precision instruments.
There are three main ways to install the ball screw, namely, one section is fixed, one end is free to install; one end is fixed, the other end is supported by the installation method; Fixed installation at both ends.
One end is fixed, the other end is free
One end is fixed and the other end is freely installed. The fixed end bearing can bear axial force and radial force at the same time. The ball screw bearing is mainly used for short screw bearings with small strokes or fully enclosed bearings. For machine tools, when the mechanical positioning method of this structure is adopted, its accuracy is the most unreliable, especially for screw bearings with a large aspect ratio (the ball screw is relatively slender), and its thermal deformation is very obvious. However, if it is a 1.5-meter-long lead screw, it is a normal phenomenon that it changes from 0.05 to 0.1 mm under different cold and hot environments. Nevertheless, due to its simple structure and convenient installation and debugging, most high-precision machine tools still adopt this structure; however, one thing that needs special attention is that when adopting this structure, a grating must be installed and a fully enclosed ring is used. Feedback in order to be able to take full advantage of the performance of the screw.
One end is fixed, the other end is supported
One end is fixed and the other end supports this installation method. The bearing at the fixed end can also withstand axial force and radial force at the same time, while the supporting end only bears radial force, and can do a small amount of axial floating, and can reduce or avoid the bending of the screw due to its own weight, and the thermal deformation of the screw can freely extend to one end. Therefore, this is the most widely used structure. For example: At present, domestic small and medium-sized CNC lathes, vertical machining centers, etc. all adopt this structure.
Fixed at both ends
Both ends of the screw are fixed. In this way, the fixed end bearing can bear the axial force at the same time, and an appropriate pre-tightening force can be applied to the screw to improve the supporting rigidity of the screw, and at the same time, the thermal deformation of the screw can be partially compensated. Therefore, most large-scale machine tools, heavy-duty machine tools, and high-precision boring and milling machines adopt this structure. Of course, it also has shortcomings, that is, the use of this structure will make the adjustment work more cumbersome; in addition, if the pre-tightening force at both ends is too large during installation and adjustment, the final stroke of the screw will be longer than the design stroke. , The pitch will also be larger than the design pitch; and if the pre-tightening force of the nuts at both ends is not enough, it will cause the opposite result, which will easily cause the machine tool to vibrate and reduce the accuracy. Therefore, if the structure is fixed at both ends, it must be adjusted strictly in accordance with the instructions during disassembly or assembly, or adjusted with the aid of an instrument (dual-frequency laser measuring instrument) to avoid unnecessary losses.