Methods For Improving The Positioning Accuracy Of The Main Spindle Of CNC Machine Tools

Positioning accuracy of CNC machine tools is the accuracy from actual position of main spindle to the final setting point that NC program.Main spindle is the core component of the machine tools,of whi ch positioning accuracy may directly effect on the whole accuracy.Hence,it is critical to improve the positioning accuracy.Nowadays many researches on the positioning accuracy of machine tools are made by research agencies and manufacturers both in dome stic and abroad,however,there are few researches on the positioning accuracy of the main spindle of CNC machine tools.This article takes the main spindle of the TK6920 CNC floor type milling and boring machine as the studying object.The close-loop transmission servo system is adopted by all the other spindles meanwhile the open-loop servo system is applied by the spindle due to its structure limit,hence,the deflection deformation and thermal deformation and so on cannot be effectively controlled when the main spindle is extending,which make the positioning errors large(the performing components of the other spindles are located on the guide ways and supporting base).It analyzes on the three kinds of servo systems of the main spindle,and gets out a common problem of these three systems from the studies on the main spindle body errors such as the bedding-in of the symmetric keys,the fit tolerance confirmation between milling spindle and main spindle,and milling spindle and bearings,spindle transmis sion system assembly and open-loop backlash adjustment of main spindle,and on the operating errors from temperature and dynamic balance aspects.Finally,the positioning accuracy can be compensated by the mod eling of multi-body system and thermal error as well as the addition of testing element to outstandingly improve the positioning accuracy of the main spindle.