Everything Old Is...
OK. Whether it is a car or truck or a piece of metrology equipment, we all tend to want the latest, the newest. But the reason why lots of us are still moving along in cars that no longer have the new-car smell is because, well, our budgets just won't make it at the dealer.
|What you see on a Virtual DMIS screen: the machine, the part, the fixture, and the probe, a display useful for programmers and nonprogrammers alike.|
According to the people at International Metrology Systems (IMS; Livonia, MI), there are on the order of 100,000 coordinate measuring machines (CMMs) that are being used right now that aren't necessarily up to snuff requirements-wise. It is not that there is anything wrong with the hardware per se (face it: most CMMs have structures that provide a long-lived capability), but there are, the folks at IMS suggest, limitations vis-à-vis such things as integrating with CAD.
So to accommodate these vintage CMMs, IMS coders and control engineers have developed an upgrade package for virtually any CMM out there, manual and CNC alike. It's called "Virtual DMIS." In addition to providing graphical programming, measuring, surfacing, SPC, and 3D CAD data linkage, the software includes an error-correction system that enhances the machine accuracy. Even though it may not be the newest CMM on the floor, this package promises to soup it up.
On the Beam
On a recent visit to the Chrysler Technology Center in Auburn Hills, MI, we were led down to the Pilot Plant facility that resides within that massive structure. The Pilot Plant has a staff of about 200 people, yet as a program is getting close to launch, that number can swell to more than 400.
A fundamental function of the Pilot Plant is to identify problems before, well, they become problems vis-à-vis building cars and trucks. So within the plant, there are what can be considered "practice builds" with real parts and the actual equipment that will be used in the factories to make the vehicles. And, of course, there are tools and fixtures on site at the Pilot Plant before they are moved to the Actual Plant.
One of the ways that the tooling is checked is through a laser scanning device from SMX Corp. (Kennett Square, PA). SMX calls this equipment "Laser Tracker" systems. At the DCX Pilot Plant there are three systems being used.
|Using AM signals for assured assembly. Gages, artifacts and masters can be measured with minimal uncertainty with an LMM.|
Apparently, the key benefit of these systems is the fact that they are portable: They can be moved to the work, not vice versa. In the past, the approach was that tooling would be moved via hi-lo to a coordinate measuring machine (CMM) room (which, incidentally, is still in operation, equipped with gear from Brown & Sharpe and even layout plates and checking fixtures; all of this is being used for a variety of panels and smaller components).
Now, the large tools are measured out on the factory floor; the SMX units provide a working volume up to 34 m x 270o x 120o. The elements of the system are a laser interferometer, two precision encoders, proprietary software, and a mirrored target, or probe. Essentially, an operator starts the measuring process by creating a three-point coordinate system for the object being measured with the target (aka, a Spherically Mounted Retroreflector), then moves the target over the features that are to be measured. The tracker tracks the movement of the reflector; the encoders report the horizontal and vertical angles; the interferometer reads the distance.
For the SMX Tracker4000 model, the transverse (i.e., angular control of the laser encoders) resolution is 0.25 arc seconds; the repeatability is 3 microns +1 micron/meter; the accuracy is 18 microns +4 micron/meter. With regard to the lineal control of the laser interferometer, the resolution is 0.16 microns; the repeatability is 1 micron +1 micron/meter; and the accuracy for radial distance is 10 microns +0.8 microns/meter.
One advantage of the tracker system is that a single person can perform the measuring. However, it was pointed out that one of the reasons why the DEA System 5 setup in the CMM room is still used on an on-going basis (it is a system that combines a CMM with a programmable fixturing system) is because it lends itself to automated measuring.
|Gages, artifacts and masters can be measured with minimal uncertainty with an LMM.|
Nowadays it goes—or should go—without saying that when fasteners are being applied to assemblies, they need to be torqued to a measured level and, moreover, that they should be monitored. One supplier of such instrumented torque wrenches has come up with a new twist: wireless monitoring.
It's called the "Torque Activated AM Signal" (TAAMS) wrench; it is available from Mountz Inc. (San Jose, CA). Yes, that's "AM Signal" as in a radio broadcast signal. The wrench's handle is fitted with a battery-powered transmitter that's activated when the preset torque is reached on a fastener. According to the people from Mountz, AM signals are superior to FM signals because they are not as susceptible to signal breakup. Each transmitter has a unique signal, so even if there are multiple tools in a given area, there is clear identification of what's what.
The wrench itself is a cam-over style, which means that once a preset torque is attained, the wrench cannot provide more torque: it cams over.
An additional benefit of the TAAMS wrench from the operator's point of view: there are no wires to trip over.
CAD & CMM
It seems as though CMM vendors are really concentrating on bringing their machines more into alignment with the math data that are part and parcel of today's programs as in that generated during computer aided design. . .such as LK Metrology Systems (Brighton, MI) bringing out a new module for its 3D DMIS-based CMM software suite, CAMIO, CAMIO Studio. The software generates inspection programs from solid, surface or wire-frame CAD files. Nowadays, it is all about designing, making and measuring.
|When you need to see it: the optical comparator helps to measure it.|
Although it is fairly widely acknowledged that CMM is the acronym for coordinate measuring machine, LMM, we must admit, is a new one on us: length measuring machine. The LMM was brought to our attention by the people at American SIP Corp. (Elmsford, NY—the American arm of the known-for-quality Geneva-based Société Genevoise d'Instruments de Physique), which provides a line of LMMs, which are highly accurate—to put it mildly. The measurement uncertainty of the instruments is 0.18 + 0.4L µm; the resolution is 0.01 µm; the repeatability is 0.1 µm. Facilitating use of these instruments is a Windows-based PC control.
J&L Metrology is a venerable company in the world of measurement; it was founded in 1919 and it is said to have produced the world's first optical comparator. And it is still producing them. Witness the new ICON MC-14. It is equipped with a 5 x 18-in. table that can handle parts up to 55 lb. It provides axis travels of 12 in. X and 6 in. Z; the helix swivel is ±15o. Glass scales with 0.000050-in. resolution are used in both positioning axes. There is a 14-in. viewing screen that uses telecentric optics, which means that there is no distortion from edge-to-edge.