courtesy of the author
As an editor, I don't see the inside of a factory as part of my everyday life. Nonetheless, as a man with a workshop (albeit a small one), I believe it a natural necessity to own a good set of callipers. This comes in addition to the range of other measuring instruments I have at my disposal. As I was sorting out things in the workshop to make it ready for use through the winter, as opposed to a storage shed that won't be touched until next June, I put together all the different measuring devices that I own. It made me look back at what I've learnt about the industrial side of measurement so far in this job.
From the simplest to the most advanced
The devices that I have to my disposal are by no means very specialised or advanced. From the most basic, there's some hand forged, mediaeval style tools: a compass and a set of callipers. Not very accurate at all by today's standards, but they're a nice item to have and they're perfectly fine for plenty of 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. Open the callipers or compass to the size of the object measured, leave them in that position and you will replicate that same measurement with decent precision on another part. The absence of markings and their historic design is the only reason I chose these as the most basic, even before a ruler.
Of course a ruler is 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 I will list the solutions I have learned of so far, from the simplest to the most complex, as well as going from the small to the larger capabilities (roughly):
The micrometer:
One of my previous posts was concerned with these tools; mainly with how little they have changed over time. I would describe it as the more intelligent brother of callipers. It works to a similar concept, just much, much more precise: it clamps around an object and you adjust it until it touches. There are analogue and digital versions, again much like callipers. These are manual tools and don't require much training. They're best for small measurements, though not miniscule (think golf ball, not ants), simply because the tool is hand held.
Touch-probes and Coordinate Measuring Machines (CMM):
There are plenty of machines that fall under this category, but as this is a summary, I will keep it brief. Touch-probe machines are essentially machines that have a little finger (the probe), that will touch the points that need to be measured. The computer that is connected with the probe knows exactly where the probe is at any point, because of its movement. These machines can be operated by hand if they're attached to a robot arm, in which case the robot arm's movement registers the location of the probe for the computer. For more advanced (and often larger) machines, a Coordinate Measuring Machine, or CMM, is likely going to be the solution. These have the advantage of being fully automated. That means, that you can program the machine to measure a part according to the CAD file, and leave it to its routine. There are plenty of different types of CMMs, ranging from small machines that would fit on a desk (except they need a very stable surface to be mounted on), up to much larger machines that are built into the factory foundations. I'm likely to write an article about all the different types of CMM in the future, so keep following us if you're interested.
Photogrammetry:
There comes a point where the components you're measuring are too large for a CMM. Although there are work-arounds for this, such as having a custom probe 3D-printed for extra reach, if you need to measure something complex that simply won't fit in the work envelope of a CMM, photogrammetry is an option. Photogrammetry is essentially measuring using picture technology. It can be done for fairly small objects, at extreme accuracy, with the help of reference markers. This means you basically put some stickers on your object, which the camera is then able to recognise, and software will then be able to work out very accurately 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 advantage of photogrammetry is that it can be very 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:
Okay this one is very closely related to photogrammetry, and it may be a cop-out, but there are so many different versions of 3D scanning that it would take up most of this article if I were to discuss all of them. 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/LADAR scanners and they range from small, handheld devices, to big factory installations. I'll probably do another article on 3D scanning alone, so keep an eye out for that. 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 you set up to let it do its thing, or whether 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 look inside a patient, whether it's for examining bone structure or the brain, CT scans and X-rays are commonplace. In industrial measurement, these machines are also invaluable. They are highly specialised instruments that do two things particularly well: looking at hollow spaces inside objects, and looking at the composition of materials. If you manufacture parts that have hollow insides that need to be accurate for whatever reason, you're probably not going to be able to measure it any other way than with a CT scanner or an X-ray machine. But the properties of materials, such as the porosity and density of a component, can also be accurately measured.
Nuclear Magnetic Resonance (NMR):
Finally, we arrive at a type of machine that measures the smallest things on this list. In fact, it can't actually measure any 'thing' as such. Nuclear Magnetic Resonance, or NMR, is a technique for analysing compounds. Chemists in olden days used techniques such as distillation or simply smelling a substance to try and determine what it consisted of. In the modern world, you can use some very complicated magnets to check at what frequency molecules vibrate, which will give a pretty accurate analysis of what that substance contains on a molecular level. It's not as commonly used as the other machines on this list, perhaps, but it's an interesting type of technology that is invaluable in countless fields.
Conclusion
I can 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. Although this is only a very brief look at what's out there, and by no means comprehensive, it covers most of the industrial measurement needs. Whether it's molecular analysis, or entire landscapes, one of the techniques described here is bound to suit your personal need.