courtesy of the author
On Manufacturing Quality, we often discuss the high-tech, industrial measurement solutions that manufacturing companies have at their disposal. However, metrology devices of all shapes and sizes are used in our everyday lives. For example, as a man with a workshop (albeit a small one), I believe it a natural necessity to own a good set of callipers, as well as a range of other measuring instruments.
As I take my time sorting out my workshop, I put together all the different measuring devices that I own. This made me reminisce about the industrial metrology technologies I have learnt about in recent months.
From the simplest to the most advanced
Of course, comparing my basic measurement tools to those we discuss daily on Manufacturing Quality, the contrast is quite astounding. From the most basic, there are some hand-forged, mediaeval-style tools: a compass and a set of callipers. Not very accurate by today's standards, but they're a nice item to have and are robust for woodwork. In fact, the absence of markings makes them terrifically easy and fast to use: they work without numbers or regulation, simply by reproducing an observation.
Looking at my other measurement devices, rulers are standardised, which is a very modern thing and requires extreme precision. Other than the straight metal ruler, I've got several ruler-like devices at different levels of complexity, serving different needs: a tape measure, a triangle protractor, a very large set square and a smaller set square with a level included. Finally, the most advanced piece of equipment by far is the modern set of callipers, mainly because of the inclusion of a Vernier scale.
But compared to any of the devices used in industrial metrology, this is nothing. So, let's explore the technologies and devices available to metrology companies.
Touch-probes and Coordinate Measuring Machines
Touch-probe machines are used to touch specific points (with the probe) that need to be measured. The machine will also be connected to the probe, which will be able to identify where the probe is at any point. These machines can be operated by hand if they're attached to a robot arm, in which case the robot arm's movement will register the location of the probe for the computer.
For more advanced (and often larger) requirements, a Coordinate Measuring Machine (CMM), maybe a better solution. This solution can be fully automated, meaning that it can be programmed to measure a part according to the CAD file, and then be left to complete its task automatically. There is a large variety of CMMs available on the market, ranging from small machines that would fit on a desk, to much larger machines that are built into the factory foundations.
Photogrammetry
If the component is too large for a CMM, photogrammetry may be the next best option. While there are workarounds like 3D-printed custom probes, they might not be able to handle complex tasks.
Photogrammetry is essentially completing measurement tasks using picture technology. The solution can also measure small objects with extreme accuracy, with the help of reference markers. This means the user will place sticker-like items on the object, which the camera will recognise, and then the software will be able to analyse how far apart the stickers are, as well as the shape and size of everything surrounding it, including to some degree, the surface texture.
One of the biggest advantages of photogrammetry technology is that it is portable and easy to use. Another is that you can upscale photogrammetry to almost anything you can think of, such as with satellite photography. Photogrammetry can also be used to improve the accuracy of laser scanning.
3D scanning
While it is closely related to photogrammetry, there are so many different versions of 3D scanning. Photogrammetry is, in a way, a type of 3D scanning, although it technically uses 2D photographs to compile a 3D image.
Some of the most common types are laser scanning, including LiDAR and LADAR scanners. These devices can also range from small, handheld devices, to big factory installations. Some of the advantages of 3D/laser scanning include not only its accuracy and versatility but specifically its potential in automation. Whether it's a scanner on a tripod that the user sets up to manually scan an object, or if it's a compact scanner mounted on a robot dog, the future of 3D scanning definitely will see a lot of autonomous robotic activity.
CT scanning and X-rays
In the medical world, if doctors need to take a non-intrusive, internal examination of a patient, whether it's for examining bone structure or the brain, Computed Tomography (CT) scans and X-rays are commonplace. In industrial measurement, these machines are also invaluable.
These solutions are highly specialised instruments that excel in looking at hollow spaces inside objects and looking at the composition of materials. When manufacturing parts with a hollow inside, that require accurate measurements, these types of technologies will help you achieve this. Additionally, the properties of materials, such as the porosity and density of a component, can also be accurately measured.
Nuclear Magnetic Resonance
Finally, we arrive at a type of machine that measures the smallest objects on this list. Nuclear Magnetic Resonance, or NMR, is a technique for analysing compounds. In time gone by, chemists used techniques such as distillation, or simply smelling a substance, to try and determine what it consists of. Now, chemists can utilise complex magnets to check at what frequency molecules vibrate, providing an accurate analysis of what that substance contains on a molecular level. Perhaps this type of technology isn't the most commonly used solution on this list, but it's an interesting type of technology that is invaluable in countless fields.
Circling back around to my personal collection of measurement devices, while I may be able to measure down to 0.02mm using the Vernier scale on my callipers, that's nothing compared to the accuracy levels of any of the machines listed above. While this is only a very brief look at what's available on the market, and by no means is comprehensive, we have covered a wide selection of industrial measurement needs. Whether it's molecular analysis or entire landscapes, one of the techniques described here is bound to fit the bill.