Study On Deformation Detection And Reconstruction Of Gantry Structure On Heavy-duty CNC Machine Tools

Heavy-duty CNC machine is a processing machine tool in large-scale equipment manufacturing industry,its technical performance represents a country's comprehensive national strength and industrial modernization.So it is of great significance to study how to improve the accuracy of heavy-duty CNC machine tools and reduce the processing error.At present,the deformation of important structures like machine beam and stand,caused by the change of temperature or load,is an important factor which restricts the further improvement of the machining accuracy.Long-span gantry structure is one of the key components of the large gantry machining center,since it is an important load-bearing structure of the whole machine.The deformation of the gantry structure will lead to the machining error,and it is significant to compensate the error for improving the machining precision of the heavy-duty CNC machine.In actual processing,working condition of the long-span gantry structure is complex.The gantry structure have to bear not only the force load from other components but also the heat load of various heat sources around the machine,what's worse,these loads are constantly changing.Therefore,the deformation of this structure shows a time-varying and non-linear characteristics and it is difficult to be measured and quantitative analyzed.As a new type sensor,fiber grating sensor has the characteristics of light weight,small size,easy to install,little impact of the measured structure and a strong anti-electromagnetic interference.So it has been widely used in the field of large structure deformation detection.This paper introduces a new method for measuring gantry structure of machine tool based on distributed fiber Bragg grating sensor.A reconstruction algorithm is also proposed for calculating the deformation.Eventually,the validity of the measurement method and the reconstruction algorithm are verified by experiments.The main contents are as follows:(1)The research on force and thermal deformation of gantry structure of heavy-duty CNC machine tool is carried out.The characteristics of the gantry structure of heavy-duty CNC machine tool and the deformation characteristics caused by the force and thermal load of the gantry structure are analyzed.In order tofacilitate the analysis,the gantry structure is simplified as a physical model of three-time statically indeterminate continuous beam,and the mathematical model of the theory combined deformation of bending and compression is established considering the knowledge of material mechanics.(2)A deformation reconstruction algorithm of gantry structure based on FBG technology is studied.First,the principle of strain sensing in distributed fiber grating sensors is introduced.Second,referring to classical KO displacement theory,and the theory for non-uniform distributed strain is deduced.Then,the layout of fiber Bragg grating sensor used in measuring bending strain and tension strain of uniform beam structure is researched.At last,the reconstruction algorithm just for bending-tensioncompression combined deformation of this structure is also proposed.(3)Experimental study on deformation detection of gantry structure based on FBG is carried out.First,the gantry structure test system of Heavy NC machine tool is built,including the establishment of experimental platform and layout determination of fiber Bragg grating sensors.Second,A series of loading experiments are carried out on the heavy-duty CNC machine tool bench with fiber grating sensor including multi-position at the same load and multi-load at the same location.Then,the experimental strain and the theoretical deduction are compared,the results show that the three kinds of strain values are basically consistent,which verifies the accuracy of the proposed fiber grating measurement strain method.Finally,the strain measured by the experiment is substituted into the deformation reconstruction algorithm,and the deformation reconstruction curve is obtained,the characteristic is consistent with the calculated deformation curve,which shows that the proposed reconstruction algorithm is feasible.