Machine Design

A different spin on CMM


One might think that after more than 50 years of adances in coordinate-measuring machines (CMMs), the field would be exhausted of innovation. Current devices include gantry-type structures for measuring large objects such as car bodies, where the movements of the CMM’s X, Y, and Z axes fully describe the measuring envelope, as well as manually operated lightweight articulated arms with six or seven rotary axes for such nonrepetitive applications as reverse engineering.

But now comes what’s called a direct computer-control coordinate-measuring machine (DCC CMM), the zCAT from Prrrfect Technologies LLC, Carlsbad, Calif. The portable device weighs only 26 lb. It can repetitively measure parts to accuracies of 8 microns, either on or off the machine tool, and needs only 10 W of power. zCat has no air bearings, comes with a 5-hr lithium-ion battery, and connects to computers through the same Wi-Fi connection laptop owners might use to access the Internet — the 801 B standard. This eliminates the need for cables.

One way to use the DCC CMM is on a surface plate. Here, the machinist brings the machined part to the surface plate, pushes a button on the zCAT touchscreen, and the CMM measures the part using a programmed procedure. While the zCAT measures the part, the machinist can begin cutting another one.

Many CMMs robotics are controlled with a joystick. Autodrive on zCAT lets users toggle between robotic and manual operation. Users can flip a switch on the screen to go into manual mode, which lets them grab the probe tip and move it to take measurements or do referencing. Flipping the switch again initiates automated operation.

Another way to use the zCAT is on a base inside the machine tool. The device can thereby measure each part while it is still chucked. This is traditionally done via on-machine probing. However, on-machine probing has problems, says Prrrfect’s Hank Kraus and zCAT inventor. Many CMMs are programmed with a standard code called DMIS while a machine tool uses a completely different language — G code. “Thus, programming of part measurements is in a language most machinists are unfamiliar with,” says Kraus.

The zCAT eliminates this problem because it comes with onboard software which lets users measure basic geometries such as spheres, cones, planes, and points, and compare distances between them. Users can also communicate with the device through third-party metrology software such as PC-DMIS. It uses a standard communication protocol called I++. The ZCAT works with all I++-capable software. So using PC-DMIS on the DCC CMM would just be a matter of opening PC-DMIS on your laptop along with a Wi-Fi connection to the zCAT.

© 2011 Penton Media, Inc.

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