Ball screw, belonging to one of the classifications of machine tool bearings, is an ideal machine tool bearing product that can convert rotary motion into linear motion.Ball screw consists of screw, nut, reversing device and ball,and it has the characteristics of high precision, reversibility and high efficiency at the same time.
There are three main ways to install ball screw, namely, one end fixed, one end free installation method; one end fixed, the other end support installation method; both ends fixed installation method.
1、One end fixed, one end free method
One end fixed, the other end free installation method: fixed end of the bearing can simultaneously withstand axial force and radial force, while the ball this support method is mainly suitable for small stroke short screw bearings or fully enclosed machine tools, because when using this structure of mechanical positioning method, its accuracy is the most unreliable, especially the long-diameter ratio of large screw bearings (ball screw is relatively slender), its thermal deformation is very obvious. The However, for a 1.5m long screw, the variation of 0.05~0.1mm under different conditions of cold and heat is normal. Nevertheless, due to its simple structure and easy installation and commissioning, most high-precision machine tools are still using this structure. However, there is a point that needs special attention is that the use of this structure must be added to the grating, using a fully enclosed ring to feedback, in order to be able to fully screw performance.
2, one end fixed, the other end support mode
One end is fixed and the other end is supported: the bearing at the fixed end can also withstand both axial and radial forces, while the supporting end only withstands radial forces and can do a small amount of axial float, as well as reduce or avoid the bending of the screw due to its self-weight. In addition, the thermal deformation of the ball screw support bearing of the screw is free to elongate toward one end. Therefore, this is the most widely used structure. For example, domestic small and medium-sized CNC lathes, vertical machining centers, etc. are all using this structure.
3、Fixed at both ends
Both ends of the screw are fixed: In this way, the bearing at the fixed end can bear the axial force at the same time, and the appropriate preload can be applied to the screw to improve the support stiffness of the screw, and the thermal deformation of the screw can also be partially compensated. Therefore, large machine tools, heavy machine tools and high-precision boring and milling machines are mostly used in this structure. Of course, there are shortcomings, that is, the use of this structure will make the adjustment work more tedious; in addition, if the installation and adjustment of the two ends of the preload is too large, it will lead to the final stroke of the screw than the design stroke, the pitch will also be larger than the design pitch; and if the two ends of the nut preload is not enough, it will lead to the opposite result, which will easily cause machine vibration, resulting in reduced accuracy. Therefore, if the structure is fixed at both ends, then the disassembly must be adjusted in strict accordance with the instructions, or with the help of the instrument (dual frequency laser interferometer) to adjust, so as not to cause some unnecessary losses.
Post time: Dec-19-2022
