| The thermal error caused by thermal deformation of machine tool parts is one of the most important factors affecting the accuracy stability of high-end CNC machine tool.Error compensation method has the advantages of low implementation cost and wide range of application,and is the most commonly used method to restrain the thermal error of machine tool.The establishment of a prediction model with high precision and strong robustness is the basis of error compensation.Compared with the spindle of machine tool,the heat source composition of feeding axis is more complex,and the law of thermal deformation is more elusive,so it is more difficult to model and compensate.For the thermal error modeling of feeding axis,compared with the data-driven modeling method,the mechanism-driven modeling method has the advantages of fewer sensors and strong robustness.Therefore,in this paper,a novel adaptive compensation method for the thermal error of machine tool’s feeding axis was studied based on the mechanism-driven modeling method,in order to further enhance the robustness of thermal error compensation technology.The main research work is as follows:Research on thermal deformation mechanism of feeding axis based on numerical analysis.The thermal deformation of feeding axis is caused by the common excitation of multiple heat sources,and there is a very complex thermo-mechanical coupling effect in the process of thermal deformation.For this reason,in this paper,through the method of numerical analysis,the thermal elongation response process of the screw excited alone by different heat sources,the thermal elongation response process and thermo-mechanical coupling effect of the screw excited together by different heat sources,and the thermal elongation response process of the screw after pre-stretching treatment was revealed respectively.Thermal error modeling of feeding axis excited by multiple time-varying dynamic heat sources.The difficulty of modeling thermal error based on the mechanism-driven modeling method is how to more accurately reflect the dynamic process of the heat transfer and thermal deformation of feeding axis.Therefore,based on the analysis of transient heat transfer mechanism of screw microelement,an iterative thermal error prediction model of screw under the multi-time-varying dynamic heat sources excitation was established.When the boundary conditions are determined,the temperature values collected from at most two temperature sensitive measuring points are introduced into the model,and the error compensation of the screw at any position and at any time can be calculated by iteration.Adaptive compensation method for thermal error considering the change of short-term friction characteristics of screw and nut pair.In the established thermal error prediction model,there is a single-time friction heat generation coefficient of screw and nut pair Q,which reflects the friction heat generation capacity of the screw and nut pair.After Q is determined by the method of parameter identification,it can not be adjusted in real time according to the change of machine tool state.For this reason,an adaptive adjustment model was established.And combined with the thermal error prediction model driven by heat transfer mechanism,a novel adaptive compensation method for thermal error of feeding axis was proposed.When the adaptive function of this method is enabled,Q can be adaptively modified in real time according to the change of short-term friction characteristics of screw.Experimental verification of the adaptive compensation method for thermal error.The compensation effect of the thermal error prediction model of feeding axis excited by multiple time-varying dynamic heat sources was verified by experiments on a vertical machining center,and the adaptive function of the proposed adaptive compensation method was verified by experiments and simulation analysis.The test results show that the adaptive compensation method reduced the fluctuation range of the machine tool Y-axis error from-25.1~-0.6μm to-6.8~0.6μm,with a decrease of 70%.At the same time,the problem of reducing the accuracy of compensation for thermal error caused by the change of the short-term friction characteristics of screw and nut pair was effectively solved. |
