Development And Testing Of An Integrated Rotating Dynamometer Based On Fiber Bragg Grating For Cutting Force Measurement

Nowadays,real-time on-line monitoring of cutting force is important for the development of machine tool condition evaluation.Cutting force is of great significance for optimization of tool status information,management of status information,surface quality of workpieces,tool vibration measurement and so on.As to the cutting force measurement methods,it can be divided into installation on the spindle and mounted on the table.Compared with the measurement method installed on the table,the dynamometer mounted on the spindle has advantages that dynamic performance of the dynamometer isn't affected by the mass of the workpiece and the sizes of the workpieces aren't limited.In contrast to other electric sensors,fiber Bragg grating(FBG)has advantages of small volume,good long-term stability,free from electromagnetic interference.So it is more suitable for cutting force measurement.Therefore,this paper provides a novel integrated cutting force measuring device based on FBG.The two mutual-perpendicular semi-octagonal rings has superiority of higher rigidity and more affixation of FBGs.The selecting-point method can realize the decoupling of multi-axis loads.Based on the analysis of the cutting process,the four-dimensional loads have been abstracted.The theoretical model between the four-dimensional loads and six-dimensional loads has been established.The load of the arched beam end face connected with the flange has been accomplished under the six-dimensional loads.The functional relationship between the stress and loads at different positions of the arched beams under the six-dimensional loads has been analyzed using the statically indeterminate theory in material mechanics.Meanwhile,the relationship between the four-dimensional loads of the blade tip and the wavelength of FBGs has been established.The size of the elastic structure and the range of the load in each direction have been determined through the analysis of the elastic strength and stiffness of the dynamometer.By analyzing the surface strain of the elastic structure,the layout of the FBGs used to bring the decoupling of the multi-axis load was determined.Moreover,the relation of the decoupling function was obtained.The static performance such as sensitivity,linearity,repeatability,hysteresis,and coupling between dimensions were obtained by static calibration in all directions of the dynamometer.Through the study of knocking tests,the first-order natural frequency and critical speed of the dynamometer were obtained.Besides,the relationships between the different FBGs' wavelengths and the time under different speeds and directions were got by studying the rotation experiments of the dynamometer.The parameters such as amplitude,angular velocity,coefficient of determination,offset distance were fitted by sine function.What's more,the relationship between different parameters was analyzed.It has been proved that the dynamometer was suitable for cutting force measurement through the analysis of the static and dynamic experimental results.