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Projects frequently require the creation of a 3D CAD model from existing parts for further work or modifications. Various reverse engineering technologies (RE) now exist that can produce 3D CAD information from real parts. There are two main phases in the RE process. The first phase, digitizing or measuring, the second phase, 3D modeling and data manipulation. Some of the main applications of RE are listed below:
· making an electronic model from a handcrafted clay model;
· making a product that fits onto some part of the human body;
· providing 3D data when insufficient data is available;
· when the original CAD data are not usable;
· if the design changed from the initial design;
· medical applications
· using existing hand crafted product geometry to produce production tools
Several RE methods are available. Every system has some strong and weak points. The selection of an RE system depends largely on the nature of the project, namely the final requirement. RE methods can be generally classified into two groups, namely contact and non-contact.
To read more about RE, look at the following MS Word document:
Contact us for more information on other publications:
· Novel Combination of Reverse Engineering and Rapid Prototyping in Medicine; Journal of Science 95, August 1999
· RP for Reconstructive Surgery; RCFAO 15/2000 - Rapid Production
Co-ordinate Measurement Machines (CMM) can be used to digitize the shape of a part. These machines normally have touch probes, but laser probes can also be fitted. CMM have either a gantry or an arm that accommodates the probe. Only a few points can be sampled per time interval, in comparison with other RE systems. Skilled meteorologists are very often required to drive the CMM systems efficiently.
Manual devices have more degrees of freedom. The user places the probe at the desired location and samples 3D co-ordinates. Manual devices are not as accurate as CMM systems.
Laser systems can measure a large number of points in a very short period of time without touching the surface of the article. Measurements are based on the reflection of a laser point or a laser line range on the surface. The system uses a charged-coupled device (CCD) camera and triangulation method to determine the co-ordinate position. The sensor (a CCD) can also be attached to a machine tool. Most laser systems are non-destructive and not as accurate as CMM equipment.
In Computer Tomography (CT) methods, penetrable X-rays are used for digitizing. The part is scanned in order to produce a series of 2D slices that is used to generate 3D models. The main advantage of this method is that it is non-destructive and can capture internal geometry.
The Moiré Interferometer system is based on the projection of a grid of contrast lines onto a work piece. When the reference grid overlies the grid, interference lines are generated. The interference lines are used to calculate the geometry of the surface. A huge amount of data can be collected without making contact with the part.
The Capture Geometry Inside (CGI) slicing method is a destructive method that can measure internal, as well as external, geometry.
Manipulation of the captured data requires computer power and proper software programs. Several software packages are available on the market. A short description of each of the RE techniques follows.
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