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alan.topcic@untz.ba. Abstract— Strong development and progress in the field of information technologies (IT) and manufacturing technologies, in.
The 1st International Virtual Conference on Advanced Scientific Results (SCIECONF-2013), Slovakia, Zilina, June 10. - 14., 2013

Comparative analysis of contact versus contactless methods of three-dimensional digitization of objects Sladjan Lovric

Dzemo Tufekcic

University of Tuzla Faculty of Mechanical Engineering Univerzitetska 4, 75000 Tuzla, BiH [email protected]

University of Tuzla Faculty of Mechanical Engineering Univerzitetska 4, 75000 Tuzla, BiH [email protected]

Adnan Mustafic

Alan Topcic

University of Tuzla Faculty of Mechanical Engineering Univerzitetska 4, 75000 Tuzla, BiH [email protected]

University of Tuzla Faculty of Mechanical Engineering Univerzitetska 4, 75000 Tuzla, BiH [email protected]

Abstract— Strong development and progress in the field of information technologies (IT) and manufacturing technologies, in the last decade, has provided performance and implementation of many activities that involve an interdisciplinary approach in solving of specific problems. By this way through synergy effect, based on achievements in various scientific fields, existing problems can be overcome, but it also open the doors to new applications in different areas of human activities. Threedimensional (3D) digitalization of physical objects is a multidisciplinary scientific-research area that combines a series of knowledge and practical skills in engineering and computer science. Result of 3D digitalization process is digital 3D CAD model with acceptable accuracy. Keywords- formatting; three-dimensional (3D) digitalisation, contact method, contactless method, cloud of points, CAD inspection

I.

INTRODUCTION

Three-dimensional digitalization is the initial step in implementation of contemporary approaches, based on usage of information technology in the manufacture of castings when as an input parameter of process the specimen was used. In cases when there is no the technical documentation of part that should pour off most often is foundry delivered samples of part, which requires making the appropriate technical documentation delivered of sample [1,2]. Unlike to conventional approaches where is this operation performed with conventional measuring equipment, approach based on modern methods of three-dimensional digitalization ensures creation of almost absolutely accurate copy of scanned part. In the framework of process of three-dimensional digitalization collecting of data with an of area of the physical object, as well as their transformation in digital form is carried out, and because of that comes the term three-dimensional (3D) digitalization [10]. The result of three-dimensional digitalization is the set of points, defined over the spatial

coordinates and because of the shape that occupies in the space are generally well known in a literature as a term "cloud of points”. There are a several methods that perform a threedimensional digitalization of geometric characteristics of objects, and depending on surface structure and complexity of part the appropriate method for three-dimensional digitalization is selected. In a case when the parts are made from materials with elastic properties application of contact methods for three-dimensional digitization is not appropriate [3]. Of course, if there is possibility of implementing contactless method of three-dimensional digitalization, it represent better choice because it provides generation of "cloud of points" with a large number of points scanned from a part in a very short period of time, with great accuracy of collected points. Generated "cloud of points" saved in a file represents a real physical description of the scanned object in three-dimensional virtual space [4,8,9]. II.

PROCESS OF CAD INSPECTION (CONTACT METHOD)

To determine the qualitative difference between „raw“ cloud of points versus generated 3D volume model of cross members of scraper conveyor obtained by contact method of 3D digitalization and pointed to the necessity of processing of „raw“ data presented in a cloud of points, CAD inspection of above mentioned data sets that generate the geometrical shape of the considered object was done. Phases of the CAD inspection process and its results are presented on Figure 1 and in table 1 [1]. When analyzing of critical cross section (Figure 1c) performed by CAD inspection (table 2) it can be concluded that the total number of points on the observed cross section is 334, from that 96 points deviate from the nominal value, and that the critical point with maximal distance (5.611 mm) from nominal value is located at the point of maximum radius (Figure 1d). Possible reason for the maximum deviation at the point of maximum radius is due to

TABLE II RESULTS CAD INSPECTION OF COMPARING

"slipping" of probe of tactile scanner on a circular surface and therefore collected points have significant deviation from the rest of sample [5,6].

a.

2D Comparison Reference model „Raw“ cloud of points Test model CAD-model 334 The total number of points 96 The points that deviate 2D deviation mm Measure 5.611 The maximum critical 2.074 The maximum nominal -2.074 The minimum nominal -5.611 The minimum critical Deviation 5.611 Maximum upper deviation -1.347 The least deviation

b.

The mean deviation The standard deviation

III. c. d. Figure 1. a) overlapping points, b) results of CAD inspection, c) critical cross section, d) most critical location at the cross section TABLE I DISPLAY THE RESULTS OF 3D-COMPARISON 3D Comparison „Raw“ cloud of points, method of Reference model contact CAD-model Test model 47973 The total number of points 11993 The points that deviate 3D deviation mm Measure 13.620 The maximum critical 0.681 The maximum nominal -0.681 The minimum nominal -13.620 The minimum critical Deviation 13.620 Maximum upper deviation -11.965 The least deviation 1.080/-0.438 The mean deviation

Analysis of the statistical distribution of errors in CAD inspection of two observed models (Figure 2) indicates that the highest number of points has a deviation of 0,681 mm, respectively, about 75% of total number of points [1].

Figure 2. Graphical representation of deviation

1.080/-0.438 1.852

PROCESS OF CAD INSPECTION (CONTACTLESS METHOD )

Identically as in the previous case in order to determine qualitative difference between "raw" cloud of points versus generated 3D CAD virtual model of cross members of scraper conveyor, and to point on necessary processing of „row“ data presented through a cloud of points access to with CAD inspection. Each phase of the CAD inspection and its results are presented on Figure 3 and table 3 [1,5,6,7].

a. b. c. Figure 3. a) overlapping of cloud of points and 3D CAD solid model, b) representation of the results of CAD inspection, c) critical cross section

Analysis of the results indicates that the total number of points of two overlapping models is 191860, from that in 724 points there are some variations (table 3). Maximum deviation from nominal value is 0,273 mm in critical point. Analysis of the critical cross section (table 4) indicated that the total number of observed points in cross section is 526, from that 276 points deviates from the nominal value, and the is maximum deviation is in critical point with distance of 0.158 mm from the nominal value [1].

TABLE III. RESULTS OF CAD INSPECTION 3D Comparison Reference model „Raw“ cloud of points, Test model CAD-model 191860 The total number of points 724 The points that deviate 3D deviation mm Measure 0.273 The maximum critical 0.068 The maximum nominal -0.068 The minimum nominal -0.273 The minimum critical Deviation 0.127 Maximum upper deviation -0.016 The least deviation 0.000/-0.000 The mean deviation The standard deviation

0.007

TABLE IV. RESULTS CAD INSPECTION OF COMPARING CROSS-SECTIONAL OBSERVED MODEL

2D Comparison Reference model „Raw“ cloud of points Test model CAD-model 526 The total number of points 276 The points that deviate

Measure The max. critical The maximum nominal The maximum nominal The min. critical Deviation Max. upper deviation The least deviation The standard deviation

IV.

2D deviation mm 0.158 0.015 -0.015 -0.158

0.158 -0.130 0.030

COMPARATIVE ANALYSIS OF THE RESULTS OF 3D DIGITIZATION

Once completed of partial analysis of „raw“ clouds of points (before processing) versus generated three-dimensional CAD virtual model of cross members of scraper conveyor obtained by contact and contactless methods of three-dimensional digitalisation a comparative analysis of the results was performed table 5. Based on the results presented on table 5, it can be concluded that by usage of contact digitalisation method maximal upper deviation from nominal value is 13,620 mm, while by usage of the contactless digitalisation method for the same model maximal upper deviation from nominal value 0,127 mm was obtained. The superiority of application of contactless method for 3D digitization in comparison to the applied contact method for 3D digitization can be viewed in comparative analysis of observed critical cross-section of the analyzed models (table 6) [1].

TABLE V.COMPARISON OF RESULTS OF THE CAD INSPECTION 3D Comparison

CAD model

„Raw „cloud of points, (contactless method) CAD model

47973

191860

32

mm 13.620 0.681 -0.681 -13.620

724 3D deviation mm 0.273 0.068 -0.068 -0.273

13.620 -11.965 1.0/-0.4 1.607

0.127 -0.016 0.001/-0.002 0.007

„Raw“ cloud of points, (method of contact)

Reference model Test model The total number of points The points that deviate

3D deviation Measure The max. critical The max. nominal The max. nominal The min. critical Deviation max.upper devia. max. least mdevia. mean deviation standard deviation

TABLE VI: COMPARISON OF THE RESULTS OF CARRY OUT CAD INSPECTION IN THE CROSS SECTION

2D Comparison

Reference model

Test model The total num. of points The points that deviate Measure The max. critical max. nominal max. nominal The min. critical Deviation max. upper devi. max. least devia. mean deviation standard deviati.

V.

„Raw“ cloud of points, (method of contact) CAD model 334 96 2D devia. mm 5.611 2.074 -2.074 -5.611 5.611 -1.347 1.0/-0.438 1.852

„Raw „cloud of points, contactless method CAD model 526 276 2D deviation mm 0.158 0.015 -0.015 -0.158 0.158 -0.130 0.001/-0.002 0.030

CONCLUSIONS

In this paper a comparative analysis of three-dimensional digitization of objects using contact and contactless methods was carried out. Although it is generally known that the process of contactless scanning results in better data quality i.e. obtaining better data on the one hand, the cost of these systems is much higher than the systems based on the contact approach. Finding the optimal scope of contact (tactile) and contactless (optical) methods of three-dimensional digitization usage is a goal of carried out analysis. In accordance with the derived measurements it is possible to conclude that tactile methods of three-dimensional digitization are less accurate at the circular crossing points on

the sample, at the openings, at the uneven surfaces, in the case of improper management of a probe, accuracy is a function of wear probe, etc. but application of contact methods is possible and justified in cases when the scan of geometrically simple surfaces is needed. On the other hand optical methods of three-dimensional digitalization have better accuracy due to the positioning of the sample for scanning, it is possible to collect more points than by tactile methods, quality of collected data is better, etc., but it is unreasonable to use those methods in the cases when the scan performs simple geometric surface (flat surface, without holes, Mitre etc.) [1]. REFERENCES [1] S. Lovric, Analysis of bottlenecks in integrated product developmen, Master thesis, Faculty of Mechanical Engineering Tuzla, University of Tuzla, 2011. [2] A. Topcic, E.Cerjakovic, Z. Babovic, E.Trakic, Implementation of systems for Reverse Engineering in product development, 1 st International conference VALLIS AUREA 2008, p.p. 969÷973, Pozega (Croatia), DAAAM International Vienna, Pozega, September 2008. [3] A. Topcic, Dž.Tufekcic, A. Fajic, E. Cerjakovic, Implementation of Three Dimenzional – 3DP printing process in casting, 5th international symposium, Faculty of Technical Science Novi Sad (Serbija), April 2008. [4] S. Lovric, Dž. Tufekcic, A.Topcic, M.Beganovic, Application of rapid prototyping and reversible engineering in casting in the sand, 38 Jupiter Conference, Belgrade (Serbija), May 2012th. [5] E. Trakić, B. Saric, A. Osmanovic, S. Lovric, Integration mechatric components of laser triangulation for 3D digitalization of the object” International Journal of Mechanical and Mechatronics Engineering IJMME/IJENS Vol: 11 No: 02, Haider Road, Saddar, Rawalpindiju Cantt Pakistan, april 2011 godine. [6] E. Cerjakovic, A. Topcic, S. Lovric, S. Ahmetbegovic, Aplication of Rapid Prototyping Technology in 3D visualization of relief surfaces” 2nd International conference VALLIS AUREA 2009, DAAAM International Vienna, Academy in Pozega, Croatia, September 2010. [7] Budak I.: Contribution to the analysis system for 3D scanning of parts in machine manufacturing, Seminar, University of Novi Sad, Faculty of Technical Sciences, Institute for Manufacturing Mechanical Engineering, graduate studies, Novi Sad, 2002; [8] Budak I., Hodolič J., Gatalo R.: Development of a System for Reverse Engineering Based Designof Complex Shapes with Emphasis on DataPoint Preprosessing, 11th International CIRP Life Cycle Engineering Seminar "Product Life Cycle – Quality Management Issues", Belgrade, Serbia, 2004. [9] Chen Y.H., Wang Y.Z.: Genetic algorithms for optimized re-triangulation in the context of reverse engineering, Computer-Aided Design 31, pp. 261–271, 1999. [10] J. Yan and S. L. De, "Reverse Engineering of Sheet Metal Parts Using Machine Vision", Proceedings of the- 10 -ASMEDesign Engineering Technical Conference, 2003, 1B, pp.1085 -1095;