An overview

 Geometric Modelling is a technology that is already being used extensively in industry for designing new products. We think of Computer Aided Design (CAD) as a process that starts with ideas, progresses to shape models, and then feeds to get the real components using Rapid Prototyping and Computer Aided Manufacturing. By contrast, in Reverse Engineering, physical components are scanned and resulting digitized data are transformed into shape models, from which Rapid Prototyping and Computer Aided Manufacturing techniques can of course be used to make more components.
 

Many parts and objects, which are still in high demand today, were created before CAD had become mainstream. Another reason is that for certain disciplines such as toy manufacturing, the artist creates the original character or model in clay. It’s easier to sculpt the original rather then create in a Computer Aided Design modelling software. In other cases, even if the original part is created in CAD, it may get modified as it undergoes prototype feedback process. The only way to get changes into the CAD model is to Reverse Engineer them. In addition, the need for automated inspection and verification of rapid prototype and manufactured parts is also driving the field.

 Areas of Application
 

• It may be necessary to produce a spare part when no original drawings or specifications of components are available. Going further, it may be necessary to modify the design of such a part. In these cases a CAD model may be required to support processes such as Finite Element Analysis, so as to verify new uses and modifications.

• A different class of application of Reverse Engineering occurs in the design of components when appearance is important (Aesthetic Design). e.g., in the automobile industry, stylists still often use full-scale wood or clay model. Once these physical models are ready, they are reverse engineered to get the CAD model for many downstream activities.

• While modifying the design of an object, it is necessary to manufacture a prototype of it, so as to check its mechanical properties. Now a days, "Rapid Prototyping" is the fastest method to manufacture a prototype. Rapid Prototype machines can accept a CAD model constructed by a reverse engineering package. So the component can be scanned and a CAD model can be created.

• Reverse Engineering is very useful for inspection also. This inspection may be CAD to Part inspection or Part to Part inspection. In CAD to Part inspection Part is scanned then surface to cloud difference is interrogated for already existing CAD model and scanned data of component. Whereas in Part to Part inspection both the parts are scanned and registered and then cloud-cloud difference is interrogated.

• Reverse Engineering is applicable for modifying the CAD models also. Due to manufacturing limitations always there is difference between the CAD model and physical component obtained from this CAD model. So the results obtained during various types of analysis of this CAD model on computer and results obtained for the physical model will be different. So before beginning the analysis on computer this component should be scanned and CAD model should be obtained from this scanned data. This CAD model obtained from scanned data will more near to the physical component so results will be better.

• Reverse Engineering is the basic phase of "Image Processing". Image processing include scanning, edge detection, and surface construction, which are various operations performed in Reverse Engineering.

• Yet another application area, which is likely to become more important in future, is the generation of custom models for use in making just a single component. e.g., each human being is different; measuring individuals and modelling them allows items such as special helmets, protective suits etc, to be manufactured so as to fit exactly.

The procedure to construct geometric model (continuous representation) of a solid from its discrete representation can be characterized by the following
 

Data Capture

There are many different methods of acquiring shape data. Essentially, each method uses some mechanism or phenomenon for interacting with the surface or volume of the object of interest. There are non-contact methods of data capture, where contact type probes at the end of the robot arm uses light, sound or magnetic fields, while in others the surface is touched. Each method has its own strength and weaknesses, which require that data acquisition system is carefully selected for the desired shape, capture functionality.

Segmentation

 Segmentation is the process, in which, data points are grouped into sets to which an appropriate single surface can be fitted.

Surface Fitting

This process involves fitting or constructing a surface, by the use of a set of points, which are segmented in the segmentation process. Depending on the requirement and accuracy, different types of surface construction methods are used.

CAD Model Creation

The purpose of this final phase is to create a consistent and contiguous model of vertices, edges and faces, where both the adjacency relationship between the constituent elements and mathematical equations of underlying edges, curves and surfaces are explicitly stored. This constructed CAD model can be used for further modifications or analysis such as finite element analysis, rapid prototyping, gcode generation etc.
 

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