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Column gages - holding their own.

Judging from all the ink that coordinate measuring machines (CMMS) have been receiving in the trade press, you might get the impression that older forms of gages already have gone the way of the dinosaur. You might, that is, unless you've been watching the evolution of gages in general. Thanks mostly to application of electronics, older forms of gages have become amazingly versatile and powerful.

Take, for example, the column gage. Fifteen years ago, it was strictly an air-operated readout, a way to get a quick visual indication of readings from snap or bore gages. Ganged up, column gages were-and still are, for that matter-an excellent means for taking simultaneous readings from several, simultaneous gaging operations. You can't beat this method for picking measurements off shafts and bores.

Back then, however, the air-operated column gage gave little or no usable output in the form of electrical signals. It was strictly a visual aid for the inspector. Now, though, we expect and demand usable output for statistical analysis and process control.

Though it still strongly resembles its ancestors, today's column gage is a vastly improved animal. If you haven't looked at it yet, you'll certainly find it worthwhile to do so. Hail to the chip

Most notably, the controls, readouts, and other outputs of today's column gages are all based on the microprocessor. "This makes using the gages simple, fast, and easy for all involved, " says Jack Gaughan of Edmunds Gages, Farmington, CT. "Older forms used purely analog logic such as that in PLCs and electrical relay panels. With microprocessors and digital logic, you can program-in a lot more, and do it quickly and easily."

Another, more recent advance is the adoption of digital display. "This is a tremendous boon to users," points out Walter Funke of Sheffield Measurement's Gaging Systems Operation, Dayton, OH. "Digital LCD readout makes the gage easier to use, and therefore promotes higher quality."

Not only do the latest column gages have digital readouts, but they show actual size. "Digital display is now standard on all our columns," Funke adds. "With statistical process control (SPC) being adopted in most plants, we realized it is important to be able to read actual size. Many people doing statistics today are familiar with numbers but not with gaging. So they need a gage that is easy to read and displays actual sizes. "

Another key point is that digital display facilitates work being done by people performing R&R (repeatability and reproducibility) studies. "These days, most major gages must be able to repeat and reproduce under actual plant conditions," Funke notes. "People doing the studies want to look at actual numbers, rather than counting lights or studying a scale. Also, use of digital display helps do away with transposition errors and other kinds of errors. "

Much of the gaging function is being transferred from inspection rooms and departments, out to machine stations on the factory floor. Here, digital display proves very convenient for machine operators.

"LED and LCD displays are easy to read, and are quite easy to use by operators who do their own gaging, " says Funke. "There's less chance they'll make errors in reading these displays, than they would in reading analog scales and interpreting them. "

Another advantage of the latest column gages lies in their ability to communicate electronically. In one new unit, for example, there's a remote input capability. By pressing a button when measuring a part, an operator automatically stores the measured dimension in the column's memory. Later, collected dimensions can be polled and sent by RS-232 to a computer for analysis. Simpler controls

Still another recent advance in column gages is simplification of controls. "In column gages we're building today, we try to present as few controls to the operator as possible," says George Schuetz of Federal Product Corp's Instrumentation Group, Providence, RI. "At the same time, the column must be intelligent enough to perform a variety of tasks. For instance, it must do signal sharing and multiplication of signals. This is accomplished by internal switches. The operator shouldn't have to get involved.

"We find that once a column gage is put on a fixture to do something," he continues, "it does that one task until the company no longer makes the part. We don't want an operator to have to go through a long setup subroutine, throw a lot of switches for each part-run, or be overwhelmed by a large number of controls. So we keep the gage simple, and put many switches inside."

Yet another advance is that of higher resolutions. "Five years ago, many gages had 50 LEDs representing the full scale," points out Walter Funke. "Now most columns have 100 LEDs."

And then there's automatic mastering. This is important to gage setup personnel because it automatically adjusts for gain, mastering the minimum and maximum. Here to stay

With all these advances, what lies ahead for column gages?

"First off, let me stress that the column gage isn't going to roll over and die in the path of CMMS," says George Schuetz. "There will always be a need for column gages, especially for measuring parts with multiple diameters such as on shafts or complex parts."

Jack Gaughan sees recent advances broadening the applications of column gages. "All these improvements and new capabilities make the column gage a more versatile, useful instrument," he states. "Today you can put in multiple inputs, where you couldn't before. Moreover, you can generate output signals in digital as well as analog, and talk to computers and printers.

"In addition, now you can perform dual-circuit air gaging, or check multiple features simultaneously. For example, you can look at a diameter for size and roundness Introduced in January, this Universal Electronic Column from Sheffield Measurement does the work of three ordinary columns. Equipped with microprocessor control, the unit handles amplifier/splitter, summation, or mixer applications in one unit. It accepts both LVDT and half bridge transducers. The digital display shows actual size or variations. at the same time, or in one column, and give the operator over-all status of good or bad. You couldn't do these things with the old column gages. "

Like Schuetz and Gaughan, Walter Funke feels column gaging will continue to be useful. "True, the column gage and its allied gages and fixtures are more dedicated to one part or family than is the CMM," he admits. "Further, justifying the use of this equipment requires precision work and high production volumes.

"We see some plants coming back to column gaging," Funke continues. "They got away from it because the purely-air column had no output capability. Now, though, with the air/electronic column, you can output electrical signals, but still use air for gaging. You gain the advantages of both media in one instrument. "

For the future, Jack Gaughan forecasts more integration of gaging into processes to achieve real-time process control. "We see SPC largely as the generation and study of historical documents," he maintains. "Real advances will come when we achieve real-time control, and provide continuous updating to machine operators so they can quickly adjust their machines."

Walter Funke believes the apparent conflict between proponents of CMMs and gages is largely fallacious. For the future, he sees a better definition of roles played by the two forms of equipment.

"Our company sells both CMMs and column gages," he says. "When training new salesmen, I tell them that CMMs do their best work measuring positions, center distances, and co-planar areas.

"On the other hand, column gaging works best on sizes such as the ID or OD of a part, and on relationships on a single axis. Examples are bores, and concentricity of bores on one axis.

"The size of a bore is usually more accurate than its position on a part," Funke continues. "As fine as CMMs are, many are not accurate enough to measure precision bore sizes, or to pass R&R studies.

"So, as others have said, column gages will be around for a long time. " 9
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Publication:Tooling & Production
Date:Apr 1, 1990
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