I lastly managed to get to a ebook that has been on my “to learn” record for fairly some time: “Past Measure: The Hidden Historical past of Measurement from Cubits to Quantum Fixed” (2022) by James Vincent (Determine 1). It traces the evolution of measurement, its makes use of, and its motivations, and the way measurement has formed our world, from historic civilizations to the trendy day. On a private be aware, I discovered the primary two-thirds of the ebook a fantastic learn, however for my part, the final third wandered and meandering off subject. Regardless, it was a worthwhile ebook total.
Determine 1 This ebook gives an enchanting journey by way of the historical past of measurement and the way totally different advances mixed over the centuries to get us to our current ranges. Supply: W. W. Norton & Firm Inc.
A number of chapters take care of the way in which measurement and the nascent science of metrology have been utilized in two main manufacturing entities of the early 20th century: Rolls-Royce and Ford Motor Firm, and the manufacturing variations between them.
Earlier than trying on the variations, it’s important to “reset” your body of reference and acknowledge that even low-to-moderate quantity manufacturing in these days concerned plenty of handbook fabrication of element components, because the “mass manufacturing” equipment we now take as a given typically didn’t exist or might solely do tough work.
Rolls-Royce made (and nonetheless makes) effective motor automobiles, in fact. A lot of their high quality was not simply within the end and equipment; the automobile was totally mechanical aside from the ignition system. They featured a finely crafted and tuned powertrain. It’s not a fantasy that you could possibly steadiness a crammed wine glass on the hood (bonnet) whereas the engine was working and never see any ripples within the liquid’s floor. Moreover, you could possibly barely hear the engine in any respect at a time when automobiles have been pretty noisy.
They achieved this stage of efficiency utilizing cautious and laborious handbook changes, trimming, submitting, and balancing of the suitable elements to attain that near-perfect steadiness and operation. Clearly, this was a time-consuming course of requiring expert and skilled craftspeople. It was “mass manufacturing” solely by way of quantity, however not by way of manufacturing circulation as we perceive it immediately.
In distinction, Henry Fiord targeted on mass manufacturing with interchangeable components that might work to design goal instantly when assembled. Doing so required advances in measurement of the elements at Ford’s manufacturing facility to weed out incoming substandard components and statistical evaluation of high quality, conformance, and deviations. Ford additionally despatched specialists to suppliers’ factories to enhance each their manufacturing processes and their very own metrology.
These have been the times
In fact, these have been totally different occasions by way of industrial manufacturing. When Wright brothers wanted a gasoline engine for the 1903 Flyer, few “commonplace” engine selections have been out there, and none got here near their measurement, weight, and output-power wants.
So, their in-house mechanic Charlie Taylor machined an aluminum engine block, fabricated most components, and assembled an engine (1903 Wright Engine) in simply six weeks utilizing a drill press and a lathe; it produced 12 horsepower, 50% above the 8 horsepower that their calculations indicated they wanted (Determine 2).
Determine 2 Maybe in an final do-it-yourself undertaking, Charlie Taylor, mechanic for Wright brothers, machined the aluminum engine block and fabricated many of the components after which assembled the entire engine in six weeks (reportedly working solely from tough sketches). Supply: Wright Brothers Aeroplane Firm
Which strategy is healthier—effective adjusting and trims, or use of a greater design and superior elements? There’s little doubt that the “high quality by elements” strategy is the higher tactic in immediately’s world the place even personalized automobiles make use of many off-the-shelf components.
Furthermore, the required quantity for a profitable car-production line mandates avoiding hand-tuning of particular person autos to make their elements plug-and-play correctly. Even Rolls-Royce now makes use of the Ford strategy, in fact; the choice is impractical for contemporary autos aside from particular trim and equipment.
Single unit “perfection” makes use of each approaches
In some instances, each calibration and use of higher topology and superior elements mix for a singular design. Not surprisingly, a traditional instance is likely one of the first EDN articles by late analog-design genius Jim Williams, “This 30-ppm scale proves that analog designs aren’t useless but”. Sure, I’ve cited it in earlier blogs, and that’s no accident (Determine 3).
Determine 3 This 1976 EDN article by Jim Williams set a typical for analog signal-chain technical experience and perception that has not often been equaled. Supply: EDN
Within the article, he describes his step-by-step design idea and fabrication course of for a transportable weigh scale that might provide 0.02% absolute accuracy (0.01 lb over a 300-pound vary). But, it might by no means want adjustment to be put into use. Despite the fact that this text is sort of 50 years outdated, it nonetheless has related classes for our very totally different world.
I imagine that Jim did a follow-up article about 20 years later, the place he revisited and upgraded that design utilizing newer elements, however I can’t discover it on-line.
At present’s necessities have been unimaginable—till not too long ago
Use of in-process calibration is advancing as a consequence of methods akin to using laser-based interferometry. For instance, the positional accuracy of the carriage, which strikes over the wafer, must be within the sub-micrometer vary.
Whereas this stage of efficiency could be achieved with friction-free air bearings, they can’t be utilized in extreme-ultraviolet (EUV) programs since these function in an ultravacuum setting. As a substitute, high-performance mechanical bearings should be used, though they’re inferior to air bearings.
There are micrometer-level errors within the x-axis and y-axis, and the 2 axes are additionally not completely orthogonal, leading to a system-level error sometimes higher than a number of micrometers throughout the 300 × 300-mm aircraft. To compensate, producers add interferometry-based calibration of the mechanical positioning programs to find out the error topography of a mechanical platform.
For instance, with a 300-mm wafer, the grid is scanned in 10-mm steps, and the interferometer determines the precise place. This worth is in contrast in opposition to the motion-encoder worth to find out a corrective offset. After this mapping, the system accuracy is improved by an element of 10 and may obtain an absolute accuracy of higher than 0.5 µm within the x-y aircraft
Perhaps too sensible?
In fact, there are occasions once you is usually a little too intelligent within the number of elements when working to enhance system efficiency. A few years in the past, I labored for an organization making controllers for giant machines, and there was one circuit perform that wanted coarse adjustment for modifications in ambient temperature. The apparent method would have been to make use of a thermistor or the same element within the circuit.
However our lead designer—a circuit genius by any measure—had a “higher” thought. Because the design used plenty of low cost, 100-kΩ pullup resistors with poor temperature coefficient, he determined to make use of a type of as an alternative of the thermistor within the stabilization loop, as they have been already on the invoice of supplies. The bench prototype and pilot-run items labored as anticipated, however the common manufacturing items had poor efficiency.
Lengthy story brief: our good designer had based mostly circuit stabilization on the deliberate poor tempco of those re-purposed pull-up resistors and related loop dynamic vary. Nonetheless, our in-house buying agent obtained an excellent deal on some resistors of the identical worth and measurement, however with a a lot tighter tempco. Moreover, getting a greater element that was functionally and bodily similar for much less cash appeared like a win-win.
That was effective for the pull-up position, nevertheless it meant that the switch perform of temperature to resistance was severely compressed. Figuring out that downside took plenty of aggravation and time.
What’s your most well-liked strategy to reaching a high-precision, correct, secure analog-signal chain and front-end? Have you ever used each strategies, or are you inherently partial to 1 over the opposite? Why?
Invoice Schweber is a degreed senior EE who has written three textbooks, tons of of technical articles, opinion columns, and product options. Previous to turning into an writer and editor, he spent his whole hands-on profession on the analog facet by engaged on energy provides, sensors, sign conditioning, and wired and wi-fi communication hyperlinks. His work expertise consists of a few years at Analog Gadgets in purposes and advertising.
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