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lnt J Adv Manuf TechnolFig. 12 (a) Unwom cutting tooltip, (b) wom cutting tool tipafter 40 minutes of machining,(c) wear area obtained bysubtractiona b c3.3 11m/pixel and 2.8 11m/pixel, respectively. The field-ofviewof the CCD camera is 1.06 mm x 0.672 mm.Four different cutting tool tips were used to verify theresults of the on-line measurement. A grinding machinewas used to deliberately introduce 'wear' on the cuttingtool tips for the verification purpose. Images of fourdifferent cutting tool tips were captured before and aftergrinding using the on-line vision method and the opticalmicroscope. Comparison of the wear areas of cutting tooltips determined using the algorithm developed in this studyand those measured using the microscope showed amaximum deviation of 6.8%.5 Results of wear measurementThe results of wear measurement are presented in threeparts. In sub- section 5.1, the system elTor before and afterapplying the confonning algorithm developed in this studyis presented. In sub-section 5.2, results of the study on theeffect of ambient light intensity and ambient vibration onsystem elTor is discussed, and in sub-section 5.3 the resultsof on-line measurement of the wear area of cutting toolusing the system developed in this work is presented.5.1 System elTor evaluationThe algorithm developed was used to determine the effectof tool holder and machine parts clearance on themisalignment error of the cutting tool. The images capturedusing backlighting comprises two regions-the backgroundand the tool tip. Since the images are in grayscales, theintensity of the background and tool tip varied between 0and 255. Intensity histograms of the images were used tofind the threshold T for thresholding (binarizing) the image.Thresholding changes the intensity of background to I andthat of the cutting tool to 0 and, therefore, effectivelyremoves the effect of ambient lighting that causes nonunifonnintensity distlibution in the image. The two imagesof one cutting tool insert were subtracted before and afterapplying the conforming method as described earlier.Figure 13 shows the results of subtracting 20 di ffcrcntimages of one cutting tool before and after applying theconfonning method. In each case, the tool was removedand refastened onto the tool holder. Each of the images wassubtracted from the first image (reference). The maximumand minimum elTors (in pixels) were, respectively, 25,924and 51,696 before applying the algorithm consisting offiltering, morphological and conforming operations. Byapplying the scaling factors, these enol'S correspond to10° n==============;,-..--..----,,...--,........ Before applying algorithm-- After filtering (withont conforming)- - Arter filtering and conforming10·4'--_'-_'--_'-_'--_'--_'--_'--_'------JL----..Jo 2 4 6 8 10 12 14 16 18 20Test numberFig. 13 The system error before and after applying the conformingalgorithm1.4 2'---'-3--4'----'-5--6'---'-7--'----'-----'10-----'11Filter mask sizeFig. 14 System error of subtracting two images of one cutting toolusing different filter mask size%l Springer
Int J Adv Manuf Techno!Table 2 Wear area of cutting tools (x 10- 6 mm 2 )Cutting speed (m/min)191163134Machining duration (min)1031496161761693.85xlO- 3 mm 2 and 187.14xlO- 3 mm 2 respectively. Theminimum and maximum errors after applying the algorithmare 0.95X 10- 3 mm 2 and 1.71 x 10- 3 mm 2 , respectively. Themaximum reduction in error using the proposed algorithmis 99.4%. Figure 13 also shows that there is a slightreduction in the pixel area in the subtracted image as aresult of the filtering and morphological operations. This isdue to the removal of noise and dust particles in the image.The number of pixels remaining after applying theproposed algorithm is suspected to be due to other systemelTors, such as vibration and limitation of camera resolution.The mean error due to the remaining pixels is 1.45 x10- 3 mm 2 .In this work, Median and Wiener filtering wereemployed to remove noise, and morphological operationswere used to remove the micro-dusts particles. The largerdust particles can be removed using compressed air, butremoval of micro-dusts in the workshop area is difficult.The subtraction results were found to be influenced bydifferent mask sizes used in the filtering operations.Therefore, it was necessary to use an iterative approach toget the optimum result using median and Wiener filtering.The optimum result is considered achieved when thesubtracted area is a minimum. A program wtitten in Matlabwas used to change the mask size automatically to find theoptimum result. Figure 14 shows the results of subtractingtwo images of one cutting tool using different square masksizes after applying the confonning algorithm to correctmisalignment. The results show that the system error variesrandomly using either median or Wiener filter, both withand without the morphological operations. The minimumerror occurs with Wiener filtering using a 6 x 6 mask. In allcases, a 3 x 3 structuring element was used for themorphological operations. The study was repeated for 20different images of one cutting tool insert. The data plottedin Fig. 13 was obtained using the filter mask that gave theoptimum result.5.2 Effect of ambient lighting and ambient vibration5.2.1 Effect ofambient lighting503265859213306136108201943697851361126879To study the effect of ambient lighting on the system error,two different images of one cutting tool tip were captured2040under different ambient light intensity. A light meter (LxlOlA,LT Lutron) was used to record the ambient lightintensity. The light intensity of the ambient was 16 lux and1321 lux when capturing the first image and second image,respectively. The images were subtracted to determine thesystem error in the presence of different ambient lightintensities. The system error due to different ambient lightintensity was found to be 1.48 x 10- 3 mm 2 . Since this errorfalls within the range of minimum and maximum errorunder the same lighting condition, the system can beconsidered relatively insensitive to environmental lightintensity, provided the intensity is not too high.5.3 Effect of ambient vibrationTo study the effect of ambient vibration on the system error,21 different images ofone cutting tool tip were captured underthe same ambient light. Each ofthe 20 images was subtractedfrom the first image one at a time. The system error due toambient vibration was found 2x 10- 3 mm". Since this erroralso falls within the range of minimum and maximum errorunder the same lighting condition, the system can beconsidered relatively insensitive to environmental vibration.5.4 Measurement of nose wear areaTo determine the nose wear area of cutting tools, uncoatedcarbide inserts were used to machine low-carbon steel rodsusing a conventional lathe machine. Images ofthe cutting toolinselts were captured on-line before machining. The inseltswere then used to machine the work piece. The cutting speedswere changed for each machining duration as shown inTable 1. Images of the worn inselts were then captured onlinefor different machining durations. Each of the images0.03 r;=--+-==cC::::u=tt=i=n=g::=s=p=e=e=d::':==1=3=4=m=:O::/=m=i=n=;-~---10.025~ 0.02('6S'" 0.015~....'"'l)~0.Q10.005--- Cutting speed=163m/min-+- Cutting speed=191 m/mino'-__'---__"--__-'--'--__-'--_---.-.J10 15 20 25 30 35 40Machining duration (min)Fig. 15 Wear area of cutting tools for various machining time andcutting speed~ Springer
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