Research On Adaptive Machining Technology Based On On-machine Measurement

In industrial production,many structural parts get the initial blank close to the theoretical design model first,and then finish machining the small allowance of the machined surface,so as to achieve the design size and requirements finally.However,the uneven machining allowance of blank surface will cause vibration and cutting force changes,resulting in machining errors.In addition,the different blank sizes challenge the precise positioning of workpieces,while the traditional manual alignment method is inefficient.In order to solve these problems,this paper studies the adaptive machining technology based on on-machine measurement,and strives to adjust the adaptability in time to improve the machining efficiency and quality in case of inaccurate workpiece clamping and uneven distribution of allowance.The main contents of this paper is as follows:(1)Based on the multi axis CNC machine tool,the overall scheme of on-machine measurement measurement is designed by integrating the industrial camera and the line laser sensor at the end of the machine tool spindle.The on-machine measurement method of using the industrial camera for preliminary positioning guidance and than using the line laser sensor for accurate scanning is proposed..(2)Based on the mathematical model of on-machine measurement system,the overall calibration technology of on-machine measurement system is studied.The camera imaging model is established,the internal and external parameters of industrial camera are obtained by Zhang Youzheng calibration method,and the measurement accuracy meets the initial positioning requirements.This paper analyzes the traditional calibration method of line laser based on spherical constraint.On this basis,an improved calibration method of line laser measurement system is proposed.The calibration method of line laser is realized by means of datum calibration and calculation of deflection angle.The experimental results show that the improved calibration method is more accurate and stable.(3)In order to realize the initial positioning with industrial camera,image preprocessing and edge detection algorithm are used to extract the contour information of the tested workpiece.Referring to the cutting path of the line cutting method in NC machining,a parallel measurement path planning method is designed to guide the line laser sensor to measure the actual surface of the workpiece quickly,so as to achieve the acquisition of point cloud measurement data.(4)Taking plane and hole as alignment features,using least square method,the fitting algorithm of plane and hole is designed.The size and position information of relevant features are calculated,and the coordinate transformation is carried out in combination with the calibration results to realize the automatic locating of workpiece based on the on-machine measurement system.(5)The surface reconstruction model of workpiece is obtained by using NURBS method.By using the method of three datum points initial registration and ICP precise registration,the accurate registration of workpiece surface reconstruction model and theoretical model is realized.On this basis,the calculation algorithm of machining allowance is designed and the distribution of allowance is obtained.According to the principle of uniform distribution of allowance,a path optimization method combining the original tool contact with the actual measurement point is proposed.The path is smoothed by using the three times Hermite interpolation method,and a new tool path is generated.Finally,it is verified by experiments.