Paper Example on Reverse Engineering Applying Contact Techniques

Introduction

Reverse engineering is a growing industrial market for manufacturing and development. Various individuals and groups have developed new techniques, which have been improvements to the current existing techniques available.

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The second technique we visit is that of (Yu Zhang, 2003). This research focuses on the engineering application of reverse engineering. The system employed is built with a coordinate measurement machine and CAD/CAM software. By scanning the physical object, the measurement data is essential. The basic principles of reverse engineering applied to the design and manufacturing of the die of a diesel engine. The process described in the paper is the object digitization and CAD model reconstruction to NC machining.

The die's geometric shape is measured, and data is acquired using a CMM in conjunction with KUM measurement software that has a linear scan mode. The number of points measured is determined automatically by the CMM according to the curvature change of the surface. This is a measurement on the rear end. The CMM that is used can measure about 1600 points for each scanned curve.

Usually, a machining tracing process results in a structured point of sequences with a large number of points and a line structure. The result of Zhang's system is a self-developed program to realize the transformation of the format of the measured data information from the CMM and KUM. First, the size of the measured data is transformed into an acceptable form for the software used. Then the data is filtered out and processed in a visualized way. The processed information is directly used for the creation of the die CAD model. After the CAD model of the die is complete, the NC machining process planning can generate the location for cutting the manufacturing application. The die is finally machined by the NC machine tool using the created CAD model.

Non-Contact Data Acquisition Techniques

Optical methods of shape capture are probably the broadest and growing in popularity over contact methods. This is because they have relatively fast acquisition rates. There are five essential categories of optical methods: laser triangulation, time-of-flight, interferometers, structured lighting, and stereo analysis. This section will discuss the various principles of each technique.

Laser Triangulation is a method, which uses location and angles between light sources and photo sensing devices to deduce position. A high-energy light source is focused and projected at a pre-specified angle at the surface of interest. A photosensitive device, usually a video camera, senses the reflection of the surface and then by using geometric triangulation from the known angle and distances, the position of a surface point relative to a reference plane can be calculated. The light source and the camera can be mounted on a traveling platform which then produces multiple scans of the surface. These scans are therefore relative measurements of the surface of interest. Various high-energy light sources are used, but lasers are the most common.

Triangulation can acquire data at rapid rates. The accuracy is determined by the resolution of the photosensitive device and the distance between the surface and the scanner. (Motavalli et al., 1991) presents a reverse engineering strategy using laser triangulation. (Moss et al., 1989) Present a detailed discussion of a classic laser triangulation system used to capture shape data from facial surfaces. The use of laser triangulation on a coordinate measuring machine is presented by (Modjarred, 1988). These references give a broad survey of methods, approaches, and limitations of triangulation.

Measuring distance by sensing time-of-flight of the light beams emitted is the way a ranging system works. Practical methods are usually based on lasers and pulsating beams. For example, in laser rangefinders, the time-of-flight is used to determine the distance traveled, and in the stereo analysis, the relative locations of landmarks in multiple images are related to the position. Interferometer methods measure the distance regarding wavelengths using interference patterns. This can be a very accurate method of measurement since visible light has a wavelength of the order of hundreds of nanometers, while most reverse engineering applications distances are in the centimeter to meter range. In principle, other parts of the electromagnetic spectrum could also be used. In practice, a high-energy light source is used to provide both a beam of monochromatic light to probe the object and a reference beam for comparison with the reflected light. (Moring et al., 1989) Describe a range finder based on time-of-flight calculations. The article presents some information on accuracy and performance. (Jarvis, 1983) offers an in-depth report on time-of-flight range finders giving detailed results and analysis.

Structured lighting involves projecting patterns of light upon a surface of interest and capturing an image of the resulting model as reflected by the cover. The image must then be analyzed to determine the coordinates of data points on the surface. A popular method of structured lighting is shadow Moire, where an interference pattern is projected onto a surface producing lighted contour lines. These contour lines are captured in an image and are analyzed to determine distances between the lines. This distance is proportional to the height of the surface at the point of interest, and so the coordinates of surface points can be deduced. Structured lighting can acquire large amounts of data with a single image frame, but the analysis to determine positions of data can be somewhat complicated. (Will and Pennington, 1972) use grids projected onto the surface of objects to identify point locations. (Wang and Aggarwal, 1987) use a similar approach but use stripes of light and multiple images.

The final optical shape capture method of interest is stereo image analysis. This is similar to structured lighting methods in that frames are analyzed to determine coordinate data. However, the report does not rely on projected patterns. Instead, typically, stereo pairs are used to provide enough information to determine the height and coordinate position. This method is often referred to as a passive method since no structured lighting is used. Active processes are distinguished from passive methods in that artificial light is used in the acquisition of data. Correlation of image pairs and landmarks within the images are significant difficulties with this method, and this is why effective ways are preferred. Another stereo image analysis approach deals with lighting models, where an image is compared to a 3D model. The model is modified until the shaded images match the real pictures of the object of interest. Finally, intensity patterns within images can be used to determine coordinate information.

The final types of data acquisition methods we will examine are acoustic, where the sound is reflected from a surface, magnetic, where a magnetic field touches the surface and a hybrid of both contact and non-contact. Acoustic methods have been used for decades for distance measuring. Sonar is used extensively for this purpose. Automatic focus cameras often use acoustic methods to determine range. The technique is necessarily the same as time-of-flight, where a sound source is reflected off a surface, and the distance between the source and surface is determined knowing the speed of sound. Acoustic interference or noise is often a problem as well as deciding focused point locations. Dynamic imaging is used extensively in ultra-sound devices where a transducer can sweep a cross-section through an object to capture material data internal to an object.

Magnetic field measurement involves sensing the strength of a magnetic field source. Magnetic touch probes are used which usually detect the location and orientation of a stylus within the field. A trigger allows the user only to record specific point data once the knife is positioned at a point of interest. Magnetic resonance is used in similar applications to ultra-sound when private material properties are to be measured. MRI (magnetic resonance) activates atoms in the material to be measured and then measures the response.

To conclude this section, all measuring methods must interact with the surface or internal material using some phenomenon, either light, sound, magnetism or solid surface contact. The speed with which the aspect operates as well as the rate of the sensor device determines the frequency of the data acquisition. The sensor type selected also determines the amount of analysis needed to compute the measured data and the accuracy.

Reverse Engineering Applying Non-Contact and Hybrid Techniques

The first non-contact techniques that we explore are that of (Fan and Tsai, 2001). They present a measurement system that includes the combination of two CCD cameras, a line laser, and a three-axis motion stage. They formed an optical non-contact scanning setup that works with the mathematical method of right shape error analysis for engineering purposes. The profile measurement of free-form objects can be analyzed. Matching the images of the free-form surfaces with sufficient efficiency and accuracy is the final result.

The effects of ambient lighting are discussed for non -contact systems. Whether or not the system can measure the ambient lighting depends on the projected color of light on the object. Clark summaries by writing that if a system projects laser light, then the unwanted frequencies can be filtered out. If the system projects white light, then no particular wavelengths can be blocked out. This is because it might be carrying the information required to measure the object. Therefore, white light area-based systems will be limited in their ability to regulate ambient lighting versus laser-based systems.

The results from Clark are of that model using a water pump. The water pump was scanned using both contact and non -contact system. The results were compared based on the surface quality and the point cloud data obtained. He demonstrates that non-contact techniques in conjunction with advanced surfacing and inspection software yield sufficient results for the mechanical design process.

(Chow et al., 2000) Developed an integrated laser-based reverse engineering and CAM machining system called RECSI (Reverse Engineering and CAM System Integration). They evaluate the feasibility of using concurrent engineering and reverse engineering methods with the data from laser scanning to remanufacture complex geometrical parts.

The first phase of their research demonstrates that laser scanning and CAD model reconstruction can duplicate aircraft structural components accurately and efficiently within a given tolerance. The second phase is the actual development of the system. The system utilizes NC coding generated from the software. The goal of the system is to show that an integrated reverse engineering and CAM machining system can make the remanufacturing process more automatic and efficient.

To summarize this section, (Fan and Tsai, 2001) implemented a non-contact system that utilizes CCD cameras and laser triangulation for reverse engineering. (Clark, 2000) Implemented a non-contact system that works in conjunction with surfacing and inspection software. He also discussed some of the issues regarding the implementation of such policies for manufacturing purposes. (Chow et al., 2000), developed and implemented a process planning system that interfaces with a tightly coupled CAD modeling system and CAM tooling path. They demonstrate the accuracy and efficiency of their laser-based reverse engineering system.

References

A. Modjarred, "Non-Contact Measurement Using a Laser Scanning Probe," P...