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lnt J Adv Manuf TechnolFig. 3 Flow chart ofalgorithm used for tool wearmeasurementStage 1Stage 2Stage 3I Capturing of images~I Noise removal using median and Wiener filtering I~I Dust removal and smoothing using morphological operationsIIStage 4Stage 5~I Image thresholding (binarization)~Conforming of two images: 1) Rotate images ofcutting tool2) Move two contours of cutting tool using cropping methodI...Stage 6Determining wear area by subtracting the imagesFig. 4 Intensity profile acrosstoo I: (a) Before fittering(original), (b) after medianfiltering (non-optimum),(c) median filtering (optimum)and (d) Wiener filtering(optimum)300r----.,....----...----~25.0100300.-----~---~---__.250,C.~ 200£;~ 150::J10050 0L..-.--- 2-'0...0----4-"0-0-----'600DIStance along profilea500L..-.----20.L.O---~4~OO--------'600Distance along profileb30ilr--~-~-~--~-~--,300r----~---~---__,250~-ell·i 200~150::;~250~·200£;~ 150:::;100 100500~-1~O-=-0--=2~OO:---3:-00'"='O--:4~OO:---5:-'Oc::-0--:-l600Distance along profilec50 0L-----=-20....,O,-------:-40....,0,---------::-:600Distance along profiled~ Springer
Int J Adv Manuf TechnolFig. 5 Subtracted images:(a) Before removing noise,(b) after removing noise bymedian filtering and (c) afterremoving noise by Wienerfilteringa b cthe closing operation. For both operations a 3 x3 structuringelement was found to be sufficient to remove the dustparticles.3.4 SegmentationIn stage 4, the image was segmented to separate the tool tipfrom the background using the thresholding method.Thresholding produces a binary image by setting all pixelsin the input image for a given range of gray values to 1 andthe remaining values to O. A thresholding parameter (T) isused to define the range of gray scale pixels that are set tovalue 0 and 1. The simple thresholding method can bedefined byg(x,y) = {1!ff(x,Y)2:T}or{Oi[ f(x,y) < T}where f(x,y) is the input image. Twas detennined from theimage gray level histogram.3.5 COnfot111ingIn stage 5, a confonning method was used to correctmisalignment of the tool insert. In the offline measurement,a tool holder was used to fix the cutting tool in the fixhtreshown in Fig. 2. After capturing the image ofunworn cuttingtool, it was necessary to remove the cutting tool from thetool holder to use it on the lathe machine. After machining,the worn cutting tool was refastened onto the holder tocapture an image of the worn tool. Due to a small clearance(2)in the tool holder, rotational and translational misalignmentbetween the unworn and worn tool occur when the tool isremoved and refastened. In the on-line measurement,movement of cutting tool during machining causes similarmisaligmnent due to machine parts clearance. For accuratetool wear measurement it is necessary to COITect themisalignment. To achieve this, an unworn cutting tool wasfastened in the tool holder and an image was captured. Thetool was removed, refastened and a second image wascaptured. The effect of cutting tool movement caused by theclearance in the tool holder is shown in Fig. 7 obtained bysubtracting two successive images.To investigate the effect of tool holder clearance onpositioning error, 21 images were captured from one cuttingtool, each time the tool was removed and refastened in itsholder. Each image was subtracted from the first image andthe results of 20 subtractions were recorded as test results.The rest of this section describes the algorithm used todecrease the misalignment elTor using the confonningmethod. In this work, 'conforn1ing' means rotating andtranslating two images of cutting tool contour to nullifymisalignment of the tool when the images are captured.The orientation of the cutting tool tip can be detectedautomatically by software method in order to move andconfonn the first caphlred image ofcutting tool to the second.Figure 8 shows two binary images of tool tip where themisalignment is clearly visible. 0:1 and 0:2 are the angles ofthe upper left side of the tool tip from the vertical as shownin the figure. One of the conditions for the two images toconform together is 0:1 =n2. The other condition is that theAa b c dFig. 6 Removal of micro-dust using opening and closing operations: (a) Cutting tool tip, (b) area A before opening, (c) area A after opening,(d) area A after opening and closing%! Springer
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