1、One end fixed, one end free
One end of the screw rod is fixed, and the other end is free. The fixed end bearing and axial force and radial force, the support for a short trip or for a small screw closed loop machine, because the structure of the mechanical positioning accuracy is the most unreliable, especially for the large aspect ratio of screw (ball screw, relatively slender) thermal denaturation is obvious, different 1.5m long screw in cold and hot under the change of 0.05~0.10mm is normal. However, because of its simple structure and convenient installation and debugging, many high precision machine tools still use this structure, but the grating must be installed with full closed loop feedback.
2、One end is fixed, the other end is supported
One end of the screw rod is fixed, and the other end is supported. The fixed end and the axial force and radial force; bearing end only bear radial force, and can trace the axial float, can reduce or avoid bending caused by the weight of the screw, the screw thermal deformation free to end elongation. This kind of structure is most widely used. At present, this kind of structure is adopted in small and medium-sized CNC lathes and vertical machining centers in china.
3、Both ends fixed
Both ends of the screw are fixed. The fixed end bearing can bear axial force at the same time. This kind of support way can apply the proper pretightening force to the screw rod, and improve the supporting rigidity of the screw, and can partly compensate the thermal deformation of the lead screw.
Such schemes are often applied to large machine tools, heavy machine tools, and high-precision boring and milling machines. However, the adjustment of this kind of screw is rather complicated. If the pretightening force at both ends is too large, the final stroke of the lead screw will be longer than the design stroke, and the pitch of the screw will be larger than the designed pitch. If the preload of both ends of the lock is not enough, it will lead to the reverse result, and will easily cause vibration of the machine tool and reduce the accuracy. Therefore, this type of screw in the disassembly must be adjusted in accordance with the instructions of the original manufacturers, or with the aid of instruments (dual frequency laser measuring instrument) adjustment.
