EMBEDDED | INTEGRATED | CONNECTED Smart Factory Metrology

As factories get “smarter”, Autodesk and FARO Technologies believe that measurement is playing an even more essential role in speeding up operations without losing the accuracy and rigor that many final products are required to exhibit.

Measurement is the first building block of engineering. Without validation, there can be no certified components and therefore, for many high accuracy industries, no final products. As factories get more connected and “smarter”, metrology, the science of measurement, is playing an essential role in speeding up operations without losing the accuracy and rigor that many final products are required to apply.

The main focus for factory metrology is to move from the status quo of machining parts in batches and relying on “tailgate measurement” verification on a coordinate measurement machine (CMM), to a system where the measurement is fully embedded in the manufacturing process. Each part is measured in real-time and companies achieve 100% verification of parts rather than a sample rate.

The future factory will also produce less waste. Despite well-honed “Industry 3.0” practices to avoid this, scrappage still occurs. This incurs high material costs, manufacturing delays and is bad for the environment. In the factory of the future using clever metrology that incorporates new technologies and applications like cobots for combined working, “right first time every time” fabrication of bespoke products is the objective.

The National Physical Laboratory, Britain’s national measurement institute, says that “future metrology will be used to assess and guarantee the fit, performance and functionality of every part and support the targets of zero waste and carbon neutrality.” It goes further to link measurement to the whole connected supply chain. “Metrology will also support the interconnection of these new factories to form an industrial base that is independent of the scale of production and combines R&D with production, while achieving the lowest energy consumption and impact on the environment.”

The three key words for inspection in the smart factory are: EMBEDDED | INTEGRATED | CONNECTED

As with the proposition for Industry 4.0 and connected factories, the purpose of smart factory metrology is to give a company greater visibility of the whole enterprise, including its suppliers. And it’s the exactly same for a small company as for a global corporation, says Markus Grau, Director 3D Machine Vision at FARO, “you want to know what’s going on everywhere especially related to measurement technology, you can give an OEM the ability to see the values of the supplier globally in time, the quality of their parts and what the OEM will receive in two weeks – what condition the parts are in, what cycle times they have, also what parts are bad. To have the complete overview of the complete production process from the raw material to the final item.”

Smarter, quicker but equally reliable metrology is arguably the most important aspect of the future factory. A factory could have banks of industrial robots and automated material handling, but without quick verification, delivery of the approved part i.e. productivity will be little better than today’s business-as-usual system.

Work at the UK’s Future Metrology Hub and complimentary work at the PhysikalischTechnische Bundesanstalt in Germany and other
global measurement institutes are focused on new measurement techniques to power the 4th industrial revolution.

Two of the Grand Challenges are to:

  • Overcome the formidable physical barriers of the optical diffraction limit, high dynamic range measurement and dynamic (multi-physical
    time-discontinuous) data acquisition for implementation of embedded metrology systems to maximize manufacturing productivity and efficiency
  • Close the gaps and divergences in metrology information between different stages in manufacturing value-chains to fully facilitate customized digital/autonomous manufacturing.

Embedded Metrology, with measurement built into or alongside machines, measuring parts in-process, have several advantages over the traditional, separate CMM verification stage.

  • Speed, as the operator avoids having to remove and measure the part.
  • The advantage of measuring every part being made provides 100% verification, rather than a sample rate.
  • It makes rework redundant. “For parts machined up to 100 microns scale, not only must you remove it and measure it you then have to bring it back and re-machine it,” says Christian Young, Hub Manager at the UK’s Future Metrology Hub in Huddersfield. “Validating
    it on the machine means you cut out the corrective machining stage.”

There are a variety of measurement techniques available today that provide in-line measurement, including contact, non-contact and robotically operated solutions. The prevailing view in industry is that in-line measurement is not as accurate as the huge CMM in
the climate controlled temperature regulated quality lab, and won´t replace it with current technologies, says Faro’s Markus Grau. “But embedded metrology can give an indication of the production line is running well or not and identify fails early,” he adds.

Could “tailgate” CMM be replaced wholesale?

This depends on the accuracy. To measure microns the air condition and humidity must be controlled. CMMs need a big granite table
for a stable set up. Normally this is in a clean room environment and cannot be omitted for sub-30 micron industries. But in the 100 microns plus area, for complete assemblies, more measurement can be achieved on the line and this envelope, where the tolerances of many industrial parts reside, and will be where the most metrology automation is applied.

Non-contact metrology is a catch-all terms that covers a range of techniques that can be broadly split into:

  • Capacitive sensors, using electro-magnetic fields
  • Laser/structured light scanning
  • Microscopy – both confocal and infinite focus
  • Optical interferometry – which uses interference in light waves to measure
  • Photogrammetry – analysis of captured images by mathematical methods
  • X-ray CT scanning

Manufacturing non-contact metrology primarily, not exclusively, deal with optical interferometry, laser scanning and X-ray CT. Non-contact metrology is crucial to the smart factory solution because a measuring device does not have to be manouvered in to measure or touch the part. This can be done at distance with no interruption to manufacturing operations.

The two popular factory technologies are laser scanners and optical systems.

Laser scanning is typically based on the time of flight principle. This measures a distance by shooting a laser beam to an object and measuring how long it takes that laser beam to bounce back. By knowing the speed of the laser beam, and measuring the time, the distance is computed by multiplying the time divided by two and multiplying it by the constant for the speed of light.

Phase based laser scanning uses a constant beam of laser energy emitted from the scanner. The scanner then measures the phase shift of the returning laser energy to calculate distances, but the rest of the process is the same as the “time of flight” scanner.

Optical interferometers are a more recent metrology technology being adopted to assist precision engineers with some practical challenges in factory measurement. Interferometry uses electromagnetic waves that are superimposed causing the phenomenon of interference in order to extract information. It is used industry for the measurement of small displacements, refractive index changes and surface irregularities and is well-suited to some factory applications.

The challenge is that, counter-intuitively perhaps, non-contact metrology tends to be much slower, requiring manual and accurate positioning during manufacture. The strobe angle of the optic can be affected by reflections – known as optical diffraction – and there are other practical challenges.

How to speed this up?
One project at the Metrology Hub is to increase the capability for high dynamic range measurement, the ability to move equipment away from the work piece and measure from distance. “We are looking at methods to move the equipment further away, potentially up to several metres, while still maintaining the capability for micron level accuracy” says the Hub’s Christian Young.

However, the rise of non-contact does not mean manufacturing is ejecting the touch probe and traditional CMM. “It entirely depends on the
application,” says Fikret Kalay, Technical Consultant Manager at Autodesk in France. “When we scan parts of course it will take less them than moving a touch probe into place. But until the accuracy and speed issues of non-contact are resolved, touch probes have a strong place in the smart factory.”

How much precision do you need?
Robots have several big advantages over humans that are well documented. Robot operations are:

  • Accurate and reliable
  • Repeatable
  • Tireless
  • Able to work in any shift pattern

For smart metrology with robotics, another advantage is flexibility. “Human operation is more flexible than robotics in general but robotic inspection can be a real advantage for high volume production,” says Faro’s Markus Grau. ”Automated robotic measurement is better than a static system on a fast production line and can be set up to measure multiple points. This gives you a high level of flexibility to be able to react to different parts with the movement of the sensor, for example. The repeatability, flexibility and reliability of the robotic system are the top three benefits.”

Robots are not designed to measure parts or cut metal. Fikret Kalay of Autodesk says “industry is asking them to do things they are not optimized to do – but metrology can help here to increase robot utility. They were first designed for pick-and-place movement, but we now want robots for machining, welding, cleaning and so on. This creates a lot of production problems because if you try to get a robot to behave like a machine tool it is not as accurate.”

“What we try to achieve from measurement with robots is to make the robot more accurate,” Fikret adds. “For example, if we probe a part before milling, we will get the precise position of the tool in the working area and improve the accuracy of the operation.

Repeatability is Essential
The sweet spot for robotic inspection is the 100 micron tolerance area and above. Here, errors of a robot machining system can be compared with a normal machine tool in a fair comparison. “The trend is going to be to perfect more accurate robotic systems in the future,” says Grau. “There are many improvements being made – from each lifecycle to the next, it gets more accurate. The dynamic accuracy improvement in robotic will have a big influence for on the fly robotic measurement applications as well.”
Bigger robots can have 30 micron repeatable position precision, which is already very accurate. But the key aspect is the application. The main factor is the degree of precision an application needs for it to be robot-compatible or not.

What’s Next?

“The field of metrology is moving as quickly as any engineering field in the “Industry 4.0” evolution. Companies are developing new sensors with better measurement capabilities, at a smaller size and higher operational accuracy than ever. Expect to see new, smarter and possibly more affordable measurements tools in the future, as sensor costs fall. Software is getting far more powerful. For example, Autodesk is improving its PowerInspection tool that will incorporate a dual device manager, allowing you to probe one part with two devices, to increase accuracy. We are also improving the algorithms, taking in new features from CAD models, such as GDT information,” says Autodesk’s Kalay.

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