Reverse Engineering Approach for Object with Free-Form Surfaces Using Standard Surface-Solid Parametric CAD System Andrzej Łukaszewicz 1,a, Kanstantsin Miatliuk 1,b 1
Faculty of Mechanical Engineering, Bialystok Technical University, ul. Wiejska 45c, 15-351 Białystok, Poland a
[email protected],
[email protected]
Keywords: reverse engineering, feature-based design, parametric CAD
Abstract. In this paper the reverse modelling process for mapping and reconstructing the geometric characteristics of element with free-form surfaces as virtual CAD model is described. The basic approach in reverse modelling process in middle range standard parametric 3D modeler such as SolidWorks system is presented. The digitizing process was performed on the coordinate measuring machine. Using surface-solid modelling tools the virtual solid models were created. They are based on prepareing 3D curves from cloud of points as a sectional profiles. As the next step, it is possible to realize various CAx applications based on 3D feature-based model. In our case an abrasive wear of rotor blade was estimated. Introduction The virtual reconstruction of real object from various contact or non-contact measurement methods is a very hard problem, not completely solved and problematic in case of incomplete, noisy and sparse data. The goal is always to find a way to create a computer model of an object which best fits the reality. The use of reverse engineering techniques for conversion of an existing physical object, described by surfaces of complicated 3D forms, to virtual model simplifies the procedures of design process and in this way accelerates the construction and technologies preparation process [1]. This approach allows also evaluating geometric changes which take place in operation process in comparison with geometric characteristics of the object being tested before its introduction to the running. A current trend in reverse engineering is the use of feature-based models and methodology [2]. In the case of measurement of an object with 3D complex form the object should be digitized, i.e. the object’s surface to be scanned. For this aim the coordinates measurement technique is used [3]. In this case the geometric data of the object are obtained as a collection of coordinates of measured points (mostly unorganized) called usually as „point clouds”. After the virtual CAD model creation of real element, it could be analysed and modified as common editable 3D the surface or solid model. Reverse engineering procedures allows fast correcting of shape and improvement of functionality, ergonomic and esthetical qualities of the element. It is widely used in numerous applications, such as tools, moulds and press tolls manufacturing or reconstruction, medical diagnosis or else 3D work of art reproduction were it is necessary to collect the data of a indefinite surfaces representation. Measurement of the object There are many methods of acquisition of digital information about real object. In the general case 3D-scanners can be grouped into contact and non-contact device. We can used reverse engineering techniques to reconstruct, preserve and collect information for the future or make it available for the public access (e.g. by internet network) of wide range of technical, anatomic or artistic existing things.
analysed surface profile
Fig. 1 Testing object
The measurement of the blade surface of exhaust fan rotor (Fig. 1) used in the chipboard industry, with evident erosion wear degree (Fig. 2), was executed on contact coordinates measurement machine (CMM) Mistral 070705 (Fig. 3) produced by Brown&Sharpe with PC-DMIS software. Measuring accuracy of the machine is 3,5 µm. After setting up and fixing the object on the measuring table the measurements of the blade surface profile were performed. Concerning the element shape the measurement was executed by the surface scanning along 22 measuring lines parallel to the radial direction of rotor. Distances between neighbouring lines were adjusted to the variability of geometrical characteristic degree of the analysed surface. The distance between each measuring points of measuring line was about 5 mm.
Fig. 2 Zoom of fragment of the analysed blade
Fig. 3 View of measuring position and sensor
Surface-solid modelling of the blade The results of measurements, presented as the set of 3D points and saved in “igs” format, were imported to the parametric environment of SolidWorks CAD system. The curves which correspond to individual measuring lines were created using the coordinates of the measured points (Fig. 4). The surface was stretched on the generated curves using loft feature. Real thickness of blade in the initial state was 10 mm. However to show clearly the erosive change in CAD model it is defined that the lower bound of analysed fragment is increased 10 mm from real surface. The contour of previously generated surface was projected on that plane as 2D sketch. Next, the solid object was created by extruding this sketch to the existent surface (Fig. 5). To create continuous cutting planes of the same sizes the solid object was trimming by two parallel planes and two ones perpendicular to the radial direction of rotor (Fig. 6) [4].
Fig. 4 View of 3D curves
Fig. 5 Solid bodies creation by extruding to surface
Fig. 6 Trimmed model by two parallel and two perpendicular planes
Determining of blade erosion using cross cutting Figure 7 shows the orientation of cutting planes in analysed fragment of blade. Marks (A-J) and (a-k) denote the planes parallel and perpendicular to the radial direction of rotor correspondently. Flat cross-sections were created in module “Drawing” of SolidWorks using cutting planes. Figure 8 shows the blade cross-sections according to indication of cutting planes (the same as in Fig. 7) and the top view of analysed surface with the use of the tool for curvature analysis „zebra stripes” in SolidWorks. This view mode allows easy seeing of wrinkles or defects in a surface, and a user can verify if that two adjacent faces are in contact (G0), are tangent (G1), or have continuous curvature (G2). It is possible to evaluate the abrasive wear by using the procedure described in previous work [5].
Fig. 7 Orientation of cutting planes
Fig. 8 Cross-sections on the cutting planes and „zebra stripes” in the top view of blade virtual model
Summary The techniques of reverse engineering in widely used in various branches of industry where it is necessary to collect the data about indefinite 3D surfaces. Measured data could be used for the generation of CAD model of analysed real object. Using such virtual model it is possible, for instance, to evaluate the geometric changes of various objects being operated or to generate CNC code with the aim of manufacturing analogous product or generating of geometric variant of the primary virtual model.
References [1] Varady T., Martin R.R., Cox J.: Reverse Engineering of Geometric Models – An Introduction, Computer-Aided Design, Vol. 29 (1997), p. 255-268. [2] Ke Y., Fan S., Zhu W., Li A., Liu F., Shi X.: Feature-based reverse modeling strategies, Computer-Aided Design, Vol. 38 (2006), p. 485-506. [3] Ratajczyk E.: Co-ordination Measurement Technique, PW, Warsaw, Poland, (2005) (in Polish). [4] Lukaszewicz A.: Hybrid Modeling Application in Parametric CAD System for Forms Representation of Elements with Curve Surfaces, In: V Conference „Energy in Science and Engineering”, WPB, Bialystok, Poland, (2006), p. 117-122 (in Polish). [5] Lukaszewicz A.: Utilization of co-ordination measurement technique and geometric modeling for evaluation of exploitation wear degree, In: II Workshop „Computer Aided Technique in Science and Engineering” CAX’2005 Duszniki Zdrój, ATR, Bydgoszcz, Poland, (2005), p. 6467 (in Polish). This paper was performed within a framework of W/WM/05/06 realised in Bialystok Technical University.
