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The Future of CMMs

Putting CMMs to Work in the 21st Century

by David H. Genest

Imagine this:

An additive in a resin mixture that automatically transmits dimensional data to a collector during the molding process and tells the press operator if specifications are being met.

A sampling device that checks the size, shape and color of chips produced during a turning operation and informs the machine operator that the cutting tool is worn to the point of producing out-of-tolerance parts.

Nanomachines ("measuring molecules") that inspect the critical dimensions of tiny electronic components, reporting any deviation from nominal.

A large, complex part -- an engine block, for example -- that is bathed in laser light to measure its critical features as it's machined on a transfer line.

Farfetched? Yes, for now. However, measurement and inspection technology is undergoing a significant change, and when the new century arrives, what we now know as coordinate metrology will not look and feel the same. Driving the change is the move to fully integrate measurement and inspection functions into the manufacturing process so that the data can help correct or modify operations and prevent the production of nonconforming parts. How full is fully integrated? Before "smart additives" and nanomachines, there are some predictable stops.

Precision measurement moves to the shop floor

Over the past several years, manufacturing engineers have discovered the power of dimensional data applied to process control. Dimensional inspection has always been used as a quality control and/or quality assurance tool to discover nonconforming parts before they were shipped to the customer. High-precision coordinate measuring machines, housed in environmentally controlled inspection laboratories, often were the measuring system of choice for these applications. With the introduction of statistical process control techniques, quality technicians could use the dimensional data gathered by CMMs to study trends in nonconformance and offer that analysis to manufacturing personnel. They, in turn, used the information to correct process variations that caused out-of-tolerance conditions. Unfortunately, the corrections often occurred after parts were scrapped or reworked to meet specifications.

To solve this, precision CMMs are put as close as possible to the manufacturing operation, to integrate them with processes so that corrections can approach real-time functionality. Putting measurement tools on the shop floor is nothing new. Fixed gages and precision measuring instruments such as calipers and micrometers have been used since the Industrial Revolution. However, using these devices takes time, and their accuracy often is subject to operator influence during the measuring process. Moreover, they don't provide the data analysis and documentation customers often require.

Real-time measurement data not only provides immediate feedback concerning the quality of individual parts but can serve as the basis for analyzing the machining operation's condition. By integrating measurement and design functions, manufacturers can improve overall productivity and fine-tune operations to account for production variables.

Traditionally, putting CMMs on the shop floor has represented a technological challenge for CMM manufacturers. They must guarantee high-accuracy performance while ensuring that throughput objectives are met.

The most dramatic problem is temperature -- specifically, temperature shifts compared with the calibration temperature as well as temperature gradients in time and space. Both the CMM and the workpiece are affected by these thermal conditions, and research into CMM behavior continues to focus on the problem. This research has resulted in adaptive compensation of temperature-induced variations (ACTIV) technology, now applied to shop-floor CMMs.

ACTIV technology compensates for both thermal expansion and thermal distortion errors with a mix of hardware and software solutions. For example, a web of up to 32 thermal sensors are placed at a machine's critical points and feed a complex algorithm with a huge amount of data in real time.

These sensors read the temperature on a machine's structure, and the algorithm extrapolates expansion and distortion values from the data. The software compensates each measured point so that the influence of temperature variations is virtually canceled over a wide range. Thus, dimensional inspection can be performed on the shop floor as accurately as in a lab.

Using a machine's structure to help solve the temperature variation problem is a technology whose time has arrived. To fully integrate measuring machines into manufacturing processes, machine structures must do more than simply hold workpieces and provide a mechanical means for moving the data-sensing device.

Increasing production throughput

Logistics is another concern when considering how measuring systems can be fully integrated with manufacturing. Can measuring systems keep pace with other manufacturing operations?

Most major automobile manufacturers worldwide have successfully integrated large measuring machines that can accommodate sheet metal assemblies and entire car bodies with materials handling equipment. For instance, a Volkswagen plant in Wolfsberg, Germany, has combined two large horizontal-arm measuring machines in a body-in-white inspection cell served by an automatic workpiece handling system. Parts are fed to the cell by two motorized shuttles from two load/unload stations, each of which is served by a crane that loads the parts from the welding line onto the loading station pallet. This system replaced fixed gages and has reduced overall inspection time at the facility.

Rapid measurement of car bodies underlies another coordinate metrology trend: the need for more quickly gathered data to measure such complex parts as turbine engine blades and sheet metal assemblies for the automotive industry. Automated     3-D measurement requires a CMM capable of scanning, which is simply a way of automatically collecting data points to accurately define a part's shape.

Scanning capability was once considered the exclusive province of the most high-tech manufacturers because sophisticated CMMs capable of scanning and the software to run them was expensive and not readily available. Today, even modest manufacturing operations can take advantage of the benefits scanning offers. Advances in software and sensor technology have made scanners more flexible and affordable.

Software and sensors unlock the future

While hardware is important for properly functioning CMMs, software and sensor technology may well prove the keys that unlock the future of coordinate metrology.

The next-generation software that will run CMMs and provide dimensional data analysis will differ significantly from today's versions. This new software's operator interface will be sensitive to the type of measuring device it runs. It will know if the operator uses a manual measuring instrument, such as an electronic caliper, or a full-featured CMM. The software will present only those interactions required for the specific application.

The new software also will be designed to work effortlessly with CAD/CAM and offline inspection systems to facilitate the inspection process and provide an advanced level of process control. It will seamlessly interface with these systems so that translating CAD models when they are downloaded to the measuring system will no longer be necessary. This will give users an accurate analysis of the tolerances that the process must maintain on the part for a complete assessment of design intent. Advanced SPC capability also will be part of new software programs.

How can this advanced software be so intuitive? The answer is in the object-modeling approach to software development. An object model is nothing more than a way to define a real-world system's fundamental components in a way that allows those components to simulate or perform tasks just like the real system. These components, called objects, are independent of each other but interact in a systematic way.

The internal combustion engine exemplifies a real-world system that can be object-defined. Pistons, connecting rods, valves, camshaft and crankshaft, fuel and cooling systems, and intake and exhaust manifolds all work independently but interact as a system to generate power. Individual elements, or objects, such as pistons can be combined with other objects to create a high-performance engine or one with improved emission control characteristics.

Hundreds of discrete objects make up measuring systems, including measuring devices such as CMMs; inspection paths that define an inspection device's motion; programs that define a sequence of measuring actions; and features such as planes, circles and cylinders. Virtually every element of a typical inspection process can be defined as an independent object.

Object modeling allows software developers to dissect an application into its fundamental objects, create those objects independently of others in the group and then quickly build applications based on independent objects. Once the object is developed and proven to behave like its real-world counterpart, the software development task is done, and that object is ready for use in any application.

For example, a set of inspection objects can be reused by any number of different design and manufacturing applications. Third-party developers can use them to design programs for unique inspection purposes such as part-specific SPC programs.

Object-oriented measurement and inspection software can accommodate a variety of inspection software and equipment, allow users to customize features for special inspection projects such as airfoil shapes or gears, and provide support for inspection equipment as well as real-time process control and materials handling  systems.

New sensors will combine elements of optical, video and laser technologies into devices that can rapidly scan complex shapes and surfaces, and accurately gather dimensional data. These sensors will change the way light is used as a data-gathering device. Powerful mathematical engines, combined with the sensors, will quickly analyze the billions of bits of dimensional data these systems can generate. Initial systems will be designed for turbine engine blade and electronic devices inspection applications.

This technology is scaleable for use in measuring complex contours in the aerospace and automotive industries as well. It will be powerful enough to look at entire car bodies and aerospace fuselage sections, and provide copious amounts of accurate dimensional data.

Dynamic challenges in electronics metrology

While much attention is paid to integrating measurement and inspection systems in the automotive and aerospace industries, the electronics industry offers a host of metrology challenges. For example, measuring the wide variety of pin grid array ceramic substrate components requires a machine capable of measuring the many critical features per component and with sufficient capacity to load multiple components on the measuring stage at one time. Multisensor CMMs, designed for measuring PGA pad diameters, pitch between pads and pad location, already are used in this industry. They uniquely use advanced image processing and scanning lasers to measure plane alignment of the component body and Z heights of wafer connection tracks, thus ensuring the lead frames have the required flatness and coplanarity.

Image analysis is taking on an increasingly important role in coordinate metrology. New systems, for the electronics industry and other manufacturing operations, will include extensive PC-based image analysis such as binary image processing, thresholding and image cleaning capabilities. These features, once considered out-of-reach technologically and economically unfeasible, will become standard in many measuring  systems.

As manufactured components become smaller and tolerances tighter, more data points must be collected and analyzed to help determine a manufacturing process's viability. This requires very high-speed, integrated data collection and analysis capability. Detailed knowledge of the application will be critical to metrology's success in the next century. Such knowledge will permit manufacturers to select appropriate sensor technologies and integrate the necessary hardware and software to interpret sensor output.

We also know that future metrology applications will link measurement systems to CAD systems. This will allow users to import CAD data for developing measurement programs and techniques, and to take measurement data and apply it to CAD models.

How soon we reach that point in metrology's evolution will depend upon the integration level the industry can reach. Whether CMMs become, in the form of smart additives and nanomachines, indivisible parts of the manufacturing process, or whether data-gathering sensors become ubiquitous, the art and science of metrology is undergoing a change that will inevitably enhance its value.

Metrology's ultimate value, of course, is its ability, through dimensional measurement, to link design intent and manufacturing capability. Such is the freedom possible with applied metrology and its true value to manufacturers.

About the author

For the past 22 years, David H. Genest has been involved in product engineering, development and marketing at Brown & Sharpe Manufacturing Co. in North Kingstown, Rhode Island. He is currently director of marketing and corporate communications for the company.

Genest's background in metrology system design and development includes the introduction of Brown & Sharpe's process control robot and other systems for shop floor measuring and inspection applications. He may be contacted by e-mail at


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