Research On Key Technologies Of Precision Camshaft Measurement Based On Line Scan Camera

Geometric accuracy measurement is one of the critical links in the manufacturing process of automobile engine camshafts.Traditional contact measurement has the advantage of high accuracy,but it also has the deficiency of low efficiency and possible damage to the measurement surface.In view of this,the key technologies of camshaft measurement based on the combination of image and coordinate methods are studied,including the measurement system scheme,geometric error compensation technology,image edge detection technology,etc.,which provides technical support for efficient camshaft geometric dimension measurement.Firstly,the overall scheme of a camshaft measurement system is designed.According to the main characteristics of a camshaft,the requirements of the measurement system are analyzed.The measurement method of combining image and coordinate measurement is adopted,and the traditional contact probe is replaced by a linear array camera.According to the design requirements,the hardware selection of the optical imaging system is completed.The calibration method of the measurement system is proposed to realize unit conversion and edge calibration.Secondly,the geometric error compensation technology of the measurement system is studied.By analyzing the mechanical structure of the measurement system,the geometric error model of the coordinate measurement system using a line array image probe is established based on the theory of multi-body kinematics and homogeneous coordinate transformation matrix theory.The sensitivity analysis of the geometric error of the measurement system is carried out,and the mathematical model is established using the matrix differentiation method to find out the key error terms affecting the accuracy of the measurement system.The error compensation is carried out for the key error terms,and on this basis,the form and position error evaluation model is established,and the error compensation simulation analysis is carried out.Thirdly,the image processing algorithm is studied,and the efficiency of image processing is improved by preprocessing the camshaft image to extract the region of interest in the image and discarding the redundant pixels.In order to obtain the grayscale values of the pixel points in the image edge region,a suitable pixel-level edge detection algorithm is selected for the initial localization of the part edges.A fitting function is used to fit the gray edge curve,and the position of the edge point on the edge curve is determined by combining the edge calibration results,so that the sub-pixel edge point of the part to be measured can be accurately extracted.Finally,a prototype of the camshaft measurement system is built,and standard shafts with different diameters are used for calibration experiments,and the relationship between the diameter size and the calibration results is obtained.On this basis,measurement experiments of camshaft characteristic parameters were conducted,and the measurement results of the ADCOLE 911 type measuring instrument were used as the reference value for comparison to test the measurement accuracy of the camshaft measurement system studied in this paper.The results show that the measurement error of the camshaft measurement system studied in this paper is less than 1.7μm,and the repeated measurement accuracy can reach 0.9μm,which meets the requirements of camshaft detection accuracy.