by Andrew Brooks
As technology advances, portable metrology requires fewer and fewer compromises
Until relatively recently, achieving portability in metrology meant accepting compromise, whether it meant reduced accuracy, restricted functionality or the negative effects of the rough, contaminant, and noise-filled operating conditions found on any active shop floor.
But the technology has advanced steadily since the mid-90s, when hand scanners were first added to portable articulated arms, and has logged impressive milestones even since the middle years of the first decade of this century, when laser tracking was incorporated into hand scanner systems.
The paradox is that while functionality and accuracy have actually increased, along with ease of use, the size and weight of portable metrology systems have been constantly shrinking.
“Laser trackers and structured light scanners used to be the kind of systems you’d fit into the back of a van,” says Joel Martin, product manager, laser tracker software for Hexagon Manufacturing Intelligence, which manufactures structured light scanners and portable articulated measuring arms, in addition to laser trackers.
“We used to call these devices ‘portable’ when they were really just ‘transportable,’” Martin says. “You needed a large vehicle to move them from Point A to Point B.” Today’s portable devices, such as laser trackers, really are portable–to the point that they’ll fit inside airline carry-on luggage.
Gone too are the days when the laser operator was held in awe as the possessor of highly specialized skills. “They were like magicians,” Martin says. “Nobody really knew how they made the technology work, but somehow they got these magical numbers. And when the guy decided to take a vacation and you wanted somebody else to fill in, they’d get on the system and go ‘I don’t know how he makes this thing work the way that he does.’” Operators required days of training to get the best use out of the technology, with the predictable result that the company became heavily dependent on the operator.
It’s really in the last five years that the most significant advances in ease of use have come, Martin says. “Now with laser trackers, as well as structured light scanners and even on the articulated arm side, the technology is such that anybody can pick it up and use it. We’ve gone from training classes that used to take two or three weeks to get an operator up to speed, to one day or a couple of days to give the people the specifics they need to get going.”
Data acquisition rates are also increasing, having passed the 20 kHz level a few years ago, radically reducing the amount of time required to scan large surfaces. Flying-dot technology, which automatically adjusts the intensity of a collimated laser beam to compensate for variations in the reflectivity and contours of the surface being scanned, has reduced or eliminated the spurious measurements scanners can sometimes return when conditions aren’t optimal. It has also greatly expanded the variability and degree of contours that can be accurately measured.
In sum, Joel Martin, like many others in the industry, believes the accuracy of portable metrology is about as good as it can get, at least for now.
“As for accuracy in portable metrology – I’m thinking specifically in 3D, and a little bit in scanning–we’ve sort of hit a wall,” Martin says. “Until there’s some game-changing technology that’s going to take us into the micro space, I don’t see accuracy being the driving decision-maker. Essentially we’ve gotten to the point where the equipment is more accurate than the environment we use it in. Making equipment even more accurate is no longer the limiting factor.”
That means that advances in portable metrology will come, for the foreseeable future, in other areas such as ease of operation and training, lighter weight and smaller size, modularity/interchangeability, and the constant struggle to “ruggedize” or adapt measuring tools to challenging shop floor conditions.
The development of smart machines and the continuing evolution of the automated enterprise also mean that portable metrology devices will increasingly be expected to integrate seamlessly with other metrology instruments, on the shop floor and in the QC lab. In a job shop, something as small as a digital micrometer has an important potential role to play in monitoring tool performance and wear, and the data that it gathers can be critical in maintaining product quality.
“Obviously, larger shops have more money to spend on the automation side, but even in the smaller shops, everybody’s trying to automate things as much as they can,” says Jamie King, regional manager, Canada for Blum Novotest. “With automated cells, where one robot is loading the machine and another is unloading newly made parts, automated gauging is already relied on to sort good parts from faulty ones. But that’s just a start.”
The next step, says King, is to integrate the gauging data–whether it’s gathered directly within the cell or by means of something as simple as a handheld digital micrometer–back into the machine control to program tooling offsets to compensate for tool wear, and to keep track of tool wear as a way of making better informed decisions when it comes to preventive maintenance and, ultimately, tool replacement.
“Automated gauging can tell you whether a part is good or bad, and sort it accordingly,” King says, “but beyond that, you ultimately want to be able to register changes on the machine itself so that it continues to make good parts for as long as possible.”
New Windows-based software packages are arriving that enable data gathered by any type of gauge, from a full shop-floor CMM through portable vision systems to handheld digital micrometers, to be displayed on a PC or even routed directly to the machine control to input offsets to compensate for tool wear. It sounds complicated, but a system like AutoComp, produced by Caron Engineering, can use data from any metrology instrument that can produce a common CSV-format file, King says.
“This eliminates the human error in the process of deciding when offsets are needed and then programming them into the machine,” King says. “You can also track the tool life based on those measurements. When the measurements start to exceed predetermined tolerances, AutoComp can prompt you to let you know its time to change out the tooling.”
Most shops need to track part sizes and maintain product data for quality control purposes. “They can use something as simple as a height stand to record the data, and as long as it’s digital they can even transmit it wirelessly,” King says. “The beauty of it is that as they’re taking that step to track that data, they’re also taking out the element of human error because they’re not relying on an operator to do the measurements and then decide how much to offset the part.”
In smaller shops, many tasks that can potentially be automated are still done manually, and even when an automated system, whether for metrology, machine control or data collection, is introduced, it has to be able to function in a hybrid environment where a high proportion of the work may still be performed by human operators.
“In this case there’s the option of manually inputting the data if the customer wants, so they can actually have a system like AutoComp as a data-tracking system, and correlate the data to the part number,” King says. “Now you’ve got a history of the part, so if the customer ever comes back and questions something, you’ve got a history of it; you can track it back in your system.” SMT