Research On Focusing Method Of Tool Measuring Instrument Under Front-light Condition

As a high-precision tool parameter testing device,tool measuring instruments are more and more widely used in CNC machining.At present,the tool measuring instrument on the market measures the contour parameters of the tool under the condition of backlight illumination,and the non-contour features such as the angle of the spiral blade of the milling cutter cannot be accurately measured.This type of tool feature is also an important parameter affecting the quality of CNC machining.Therefore,this paper takes the spiral blade angle measurement of cylindrical milling cutter as the research object,and studies the focusing method of tool helix angle measurement under the pre-illumination condition.The main research contents are as follows:First of all,the imaging characteristics of different illumination modes can be accurately imaged around the spiral blade feature of the cylindrical milling cutter.The gray value contrast of the edge of the blade image in the parallel front illumination dark field illumination mode of diffuse front illumination bright field illumination,parallel front illumination bright field illumination,and three different illumination directions,easy to distinguish from the background and extract classification The front illumination scheme of the light source above the milling cutter was selected.Secondly,under the condition of front light,the cylindrical milling cutter can not be completely accommodated in the depth of field of the camera,and the whole image cannot be focused.A dynamic focus window setting method based on gray level change is proposed.According to the spatial spiral structure of the spiral blade of the milling cutter,the focusing window containing the cutting edge feature is established by the gray distribution of the blade,the tool body and the background in the image to reduce the influence of uneven distribution of depth information in the front image.Thirdly,under the condition of the pre-illumination measurement,a focusing method combining coarse and fine positioning is designed.Using the defocus depth method for coarse positioning,it is determined by experimental calculation that the precise focus interval can be twice the depth of field of the lens.The Brenner evaluation algorithm of the two-direction template is proposed,and the focus area of ??the algorithm is limited,and the image quality is evaluated by this algorithm.The Fibonacci search method is used together with the evaluation value to find the accurate optimal imaging position and complete the focus..Finally,using the tool measurement platform under the pre-illumination condition built in this paper,the experiment is carried out,the establishment and evaluation of the dynamic focus window,the calculation of the precise focus interval in the coarse positioning,and the convergence analysis of the full focus process are carried out.The tool helix angle was measured and the average deviation of the measurement deviation was 0.034%.It is proved that the focus method combined with the coarse and fine positioning proposed in this paper can effectively obtain an image with precise focus.The focus method of tool parameter measurement under the pre-illumination condition proposed in this paper,as well as the focus research on the pre-illumination condition,has certain theoretical and practical value.