Ask the expert: multisensor technology

How do you define multisensor measurement technology?

A multisensor system is one that integrates a combination of sensors, including touch trigger, scanning, laser and vision/video into one measurement platform, with all sensors being simultaneously calibrated and accessible through a single metrology software.

What factors should a manufacturer consider for implementing multisensor technology in a quality measurement process?

The first consideration is the size of the part to be measured and the measurement volume needed to accommodate it. The system must have a large enough measurement volume to accommodate the parts, and the accuracy to match the dimensions and tolerances that are called-out. Next, we look at the nature of the parts and features to select the best sensors to be used. For example, parts with a high proportion of “inside” dimensions, such as bore depth or diameter, will benefit from a combination of touch-trigger probe and laser, while parts which are very small or easily deformed when probed are more easily measured using video or an ultra-low force micro-probe. Overall, we focus on selecting the combination of sensors that provides accurate data most quickly. Finally, we look at what measurement challenges are likely to come up in the future, and configure a system so it is “ready” to accept additional sensors as future upgrades. With a little forethought, we can prepare a system so that its service life can be extended through multiple generations of a customer’s product.

Why choose multisensor measurement over stand-alone devices or other accurate measurement processes?

A multisensor system provides much more flexibility in measuring complex parts. Having a choice of sensors eliminates the need to set-up and measure parts on several systems to check all the critical dimensions. There is less handling of parts, fewer fixtures are needed, and all data is taken relative to a single system calibration. The ability to measure and construct dimensions using data from multiple sensors can enable measurements that wouldn’t be possible otherwise.  For example, a vision sensor can take edge data, while a touch-trigger probe can acquire points from perpendicular surfaces. A multisensor system can combine these data into a single measurement. Multisensor systems routinely achieve higher accuracy than single-sensor systems because you can always choose the best type of sensor for a particular feature—without having to compromise throughput or ease of use.

Does multisensor technology lend itself well to use in automated manufacturing cells?

Multisensor systems are often used in work cells to provide fast feedback for process adjustments. Because the output of the cell depends on getting accurate measurements quickly, the best measurement system is one with flexibility and speed. Having a combination of sensors in one system speeds up measurement— especially for complex geometries. Another key to efficiently processing parts through a work-cell is to use well designed tooling fixtures. When the parts can be loaded quickly and accurately—either by hand or by an automated handler—the throughput and reproducibility of the metrology system is vastly improved. The more quickly measurement data can be collected, the faster that data can be put to use in process control adjustments and decision making. Bottom line: multisensor measurement systems enable more measurements to be performed more quickly.

Is measurement data easily transferred to other data files in SPC systems?

Most multisensor system users monitor processes using SPC data. Using a well-integrated multi-sensor metrology software, measurement data is easily stored and exchanged with common SPC programs. Software modules, such as Smart Report Powered by QC-CALC, enable users to format measurement data into their preferred view, and to easily exchange that data with common SPC packages such as Minitab.

What does a manufacturer need to know about using multisensor measurement that may differ from how they handle existing measurement tools?

First, they should know that not all multisensor tools are created equal. In some systems, the addition of multiple sensors can impose limitations on working clearance or measurement volume. The ideal system has deployable sensors so that they can retract out of the way when not in use. Not all multisensor systems offer full access to all sensors through a common metrology software and datum reference set-up. It’s best to get a comprehensive demonstration on all sensors before purchase. Secondly, manufacturers should choose the appropriate sensors for the types of parts and dimensions they’ll typically be measuring, and be sure the users that will operate the system are trained in when and how to deploy a particular sensor. Some sensors, such as video and touch-trigger probes, are robust, while some others, such as micro-probes, can be fragile if not used with proper care. It’s easy to be impressed with high accuracy specs, but usually the best sensor to do a particular job is the simplest one.

What key technological advancements in multisensor technology do you foresee in the next five to ten years?

Vast numbers of parts and assemblies are getting smaller. Not just electronics—all kinds of components are shrinking. Micro-machined and micro-formed parts, EDM and modern machine tools are showing up in many industry sectors. As we encounter smaller and smaller dimensions and tolerances, the range and capabilities of sensors needed to measure them becomes more varied and complex. The challenge of keeping this range of sensors in simultaneous calibration is more difficult. More robust and fully-integrated calibration routines have become standard parts of the metrology software. Cycle time pressures also increase—not only in terms of measurement throughput, but in terms of providing the complete data set with analysis for decision making. We are continually working to shorten the cycle of data gathering, analysis and reporting.

Finally, we see ever increasing needs to analyze complex relationships between features and mating parts. Many parts today are designed to GD&T standards. Multisensor systems with advanced software compare measurements to CAD and apply advanced functions such as simultaneous requirements, to more completely characterize a part than would be possible by checking individual dimensions against their tolerances.

In spite of all these advancements, the machinist is still faced with the practical questions of “how much material should I remove?” and “where from?” We are continually developing our suite of metrology and analysis software to make it easier to get those answers.

The great benefit of multisensor systems is that they make the process of collecting the data, fitting it to a CAD model with full GD&T, and providing practical answers, faster and easier. CM

Nate Rose is the chief applications engineer at Optical Gaging Products, a Quality Vision International Co. based in Rochester, NY.

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