Gauging: Made to Measure

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by Andrew Brooks

Advances in automated gauging


The goals of automation are the same in pretty much any industry: reducing human error, increasing speed, and enhancing the accuracy and uniformity of the output—whether that output is in the form of information or a tangible, solid product.

When it comes to measurement in tight-tolerance applications like machining, accuracy is probably the paramount consideration, but in an industrial setting, that accuracy also needs to be combined with productivity. In other words, the need for accuracy can’t compromise the pace of production any more than is absolutely necessary. Automation offers the possibility of increasing accuracy and the pace at the same time by reducing the need for human intervention.

“Users are looking for something where they can get away from having the operator doing measurement manually,” says David Chang, business manager for measurement and automation products, Renishaw. “They want repeatability and reproducibility. And in terms of ease of use, they always want something that they can just click and go—they don’t want the operator to do too much on the shop floor in terms of the actual measurement itself.”

Blum-Novotest's bore gauge BG 60 for in-process measurement of bore diameters in mass production for automatic measurement of bores greater than 3 mm.Users can derive huge benefits from inline gauging if the systems can be integrated as seamlessly as possible into the manufacturing or machining process, with the ultimate goal being reduced dependence on human operators and, ultimately, true lights out operation. The ideal gauging system can be used manually or integrated into a fully automated cell, which means automating not just the actual gauging itself but also the physical handling of the parts that are being measured.

That’s what Renishaw has done recently with its Equator automatic transfer system (EQ-ATS), an adjunct to its Equator flexible gauging system. EQ-ATS allows parts to be loaded and unloaded automatically.

“The auto transfer system is basically an automatic slider,” Chang says. “When, for instance, a robot loads a part onto the fixture and initiates the gauging cycle, this auto transfer system will slide the fixture and the part into the work volume of the Equator and start the gauging cycle.”

Renishaw has also recently added the Intelligent Process Control (IPC) feedback system to its Equator offering. The system is designed to interface with current CNC controllers. IPC allows offset values to be updated, compensating for tool wear, thermal drift and other causes of process instability. 

“Say that a part has been measured on a gauge for the critical dimensions the user wants to control,” Chang says. “With IPC the actual volume is calculated against the nominal to determine the trend offset. This will then send it to the CNC control automatically, to a specific tool and specific offset. This corrects the deviation, and ideally this allows the user to do lights out manufacturing. They don’t have to take the inspection results to the CNC and make the tool offset adjustment manually.”

In most shop floor environments, there is still a broad range of measuring devices in play, from handheld gauges to large coordinate measuring machines. These devices are all capable of generating measurement data to very high tolerances and a very high degree of accuracy. 

One potential source of error or omission arises in how that measurement data is relayed to the CNC control so the machining process can be adjusted to compensate for drift and deviation in the machining process. If manual data entry is part of that process, it’s inevitable that human error will occur sooner or later, so the key is to automate data entry across as wide a range of devices and systems as possible.

Renishaw's Equator gauging system features the Equator automatic transfer system (EQ-ATS), which allows parts to be loaded and unloaded automatically.One system that incorporates the full gamut of shop floor gauges and measurement devices, from micrometers, wireless gauges to vision systems and full fledged CMMs into an integrated automated gauging system is AutoComp, which was developed by Caron Software and is offered by Blum-Novotest. 

“This is an interface between anyone’s digital gauge and the CNC control,” says Jamie King, regional manager, Canada for Blum-Novotest. “You set up a part in AutoComp with the features that you will be measuring, the tolerances for each feature and the limits that you want it to be able to compensate.” 

As King explains, the idea is to enable one or many devices—spindle probes, CMMs, digital micrometers, height stands or other kinds of gauges—to create a csv file. AutoComp reads the file and provides onscreen feedback and logs historical data for the measured dimensions. Based on the conditions, it makes offset adjustments automatically on the machine to continue producing good parts. It will send the operator a warning when tool compensation exceeds a user-defined threshold so the operator can change the tool. It can also tell the CNC control to call a redundant tool automatically or to stop the machine before the next cycle is engaged. 

“To effectively close the loop on machining, you need to have more control of all aspects of your process,” King says. “The ability to inspect critical features before the part leaves the machine has advanced so far in recent years. The goal is always to have good parts leaving the machine the first time.” SMT

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