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Working in 3D: Increase your measure of success

Based on the idea that 3D information can be used in real-time applications, Neptec is proving that its smart processing sensor systems can gather relevant information quickly, while eliminating redundant data.

DesignFax Online
31 October, 2006 by Maureen Campbell,
Neptec, Staff Writer

Neptec Design Group is proving that its Intelligence in Three Dimensions approach is fundamental to making 3D systems work in today's manufacturing environment. Based on the idea that 3D data can be used in real-time applications, even over relatively modest bandwidth data links, Neptec developed real-time object recognition and tracking systems that were designed for and tested onboard the space shuttle. Neptec is now bringing its latest offering, the Laser Metrology System (LMS), to the manufacturing industry.

"Because three-dimensional data represents actual measurements of the world, it contains more information than two-dimensional imagery," says Iain Christie, vice president of research and development. "This results in a significant data management problem when working in 3D." Neptec's approach centers on finding ways to extract the maximum amount of this information from the minimum amount of data. "The key to making real-time 3D work is to be intelligent about how to acquire and exploit it," says Christie.

At the heart of Neptec's Intelligence in Three Dimensions approach is the MILD principle — More Information, Less Data. Adhering to this principle means that Neptec's LMS only extracts and reports on useful information rather than inundating operators with an abundance of data. Using it's ability to locate and recognize objects and features, LMS determines what data to acquire, when to acquire it, and how to process the data to extract the required information — the result is efficient, timely data acquisition and easy-to-understand information presented without the need to transmit or store extraneous data to other computers and systems in a manufacturer's facility.

Say for instance you require the outside diameter of a hole or the distance between hole centers. A typical 3D scanning approach would scan the entire part, transmit all of the 3D data over the network, store the data, create a model based on the data, and then import the model into visualization and modeling software that would finally extract the measurement. Not only is this daunting, but it is time consuming as well. Using Neptec's LMS, the same measurement becomes more efficient. The LMS identifies the feature to be measured, an optimal scan pattern is calculated, data is collected, the desired measurement is made, and ONLY information that has to be transferred and stored externally is sent (in this case, the measurement itself). No external workstations or software applications are needed to process the data. The result is an overall measurement process that is much more efficient and cost effective.

The LMS relies on software that was originally developed for the military and space program to accomplish similar tasks. The software is designed to rapidly recognize objects using only a small amount of 3D data. Once an object is recognized; its exact location and orientation are also calculated. Typically this requires less than one second to run on a Pentium-level processor.

Once the object is recognized, positioned, and oriented, the LMS consults an internal database to determine what features should be measured. This internal database is set up and maintained by the manufacturer to ensure that all critical features of any given part are measured. Once LMS identifies a feature to be measured, it determines how to steer its laser beam to generate an optimized scan pattern for the feature. In a fraction of a second, this data is acquired and analyzed to extract critical dimensions of the measured feature. These critical dimensions can then be passed directly to the operator or compared to preset tolerances. In the latter case, the only data that needs be passed to the operator is a simple list of pass/fail determinations based on the 3D measurements. Assuming the operator does not wish to retain any of the measured data for more detailed analysis, the 3D measurements are deleted and the process starts again. Typically, the elapsed time for the whole measurement process is several seconds.

Of course, this extra efficiency would be pointless if the LMS did not meet industry standards for accuracy and precision. With high-precision metrology systems, dealing with noise and other sources of error is always an issue. Measurement errors can arise from a number of sources such as roughness or high-reflectivity of the object, thermal drift in the equipment, vibrations, or even electrical interference from other machinery. The LMS implements a number of design features to address these issues, including an athermalized optical design, simple calibration routines, and a Steerable Laser Beam (SLB) that allows the operator to use the LMS much like a point-and-shoot camera. This allows the operator to quickly gather only the information that is of interest, mitigating the effects of low-frequency vibrations.

The LMS offers a different approach to the current 2D and 3D inspection systems currently on the market. For instance, one popular technique is 2D stereovision, which has the advantage of being relatively inexpensive with fairly rapid data acquisition times. 2D stereovision determines the distance to each point by measuring the parallax shift (the apparent shift of a point when viewed from two pre-set locations). Similar to human vision, in that it uses two imagers instead of one, it also has similar limitations, the biggest being susceptibility to poor lighting conditions. Shadows and similar part colors can cause a lot of noise in scan results. This can lead to the construction of custom lighting for each type of part to be inspected. This reduces the flexibility and efficiency of the system. The LMS does not require specialized lighting setups for each part that is to be measured because it uses an active illumination source.

A popular family of 3D digitizers is white light scanners. White light scanners are generally used for large scan areas and to generate 3D surface models. A sampling sensor using white light projects a pattern of lines on an object and through triangulation. Based on the distortion of the surface object, the senor measures the deviation of the original pattern and calculates the surface of the target area. Typically, these units scan fairly small adjacent areas and concurrently record registration marks to build a full 3D model from several successive scans. These systems are capable of producing very accurate 3D models, however, they also tend to be victims of their own high resolution — typically producing huge data files to record the wealth of detail that they are capable of measuring. The issue for operators is that this level of detail is not always needed over the entire surface of the part, especially if only a few critical tolerances are measured.

The LMS delivers precision comparable to a white light scanner without the need to digitize (and store the model of) a whole part in order to make a single measurement. Whereas a white light scanner produces a digital model as an end product, the LMS makes measurements directly from the part. The LMS makes an initial low-resolution scan of the object, then, using built-in object recognition routines, the LMS identifies the part under inspection, determining how it is oriented. The LMS then plans a second round of data acquisition to measure only those features that are required. This whole process typically takes a few seconds, and no further processing is required.

Touch or "near-touch" point measurement techniques using a high-precision arm or coordinate measuring machines are also utilized in the manufacturing industry. These systems acquire very high-precision data and only acquire the data that an operator specifies. These systems are designed to make point-to-point measurements of a single feature. However, these systems are operator intensive and are disadvantaged when performing tasks where large amounts of data must be collected. Neptec's LMS combines the ability to make single-feature measurements with the ability to also collect large amounts of data autonomously.

Today's industries require speed and accuracy in order to expedite rather than impede processing and manufacturing times. As technologies advance and products mature, convergence happens, allowing products and processes to be faster and more efficient. Neptec's LMS offers the best features and capabilities of both non-contact metrology systems as well as point measurement systems in one self-contained, easy-to-use unit. With Neptec's LMS, you choose how much or how little information you need.