We’re all familiar with the way machined parts can be inspected: using a flat surface like a granite measurement base, establishing a zero datum, and using a bridge CMM or laser scanner to collect x,y,z data on the part. But what about large or irregularly-shaped products, such as a bent tube?
For objects like bent tubing, it’s much easier to use a portable arm with a non-contact probe than it is to use a touch-based method like a ball probe. As you can imagine, contact with thin tubing can cause vibrations that make accurate measurement a massive headache. As you can see in the video, portable arm systems are designed to make tube measurement faster and simpler.
How it Works: Portable Arm Tubing Measurement
In this case, using the Hexagon Romer Absolute Arm, the software—called TubeShaper—accepts nominal data in the form of x,y,z coordinates. Alternately, the data can be imported in the form of a CAD file. The part must be securely clamped in any orientation, such that it does not move during measurement and all the sections of the part are accessible to the probe. Of course, the arm must also be securely mounted so that it does not move during the test.
To begin the measurement, the software prompts the operator to pass the probe’s infrared light beam over each section of the part, as shown in the video. If the operator misses, or probes the incorrect section, the software will beep an alert, requiring the operator to scan again. After the probing is complete, the machine shows the measured data both in x,y,z coordinate measurements as well as length, rotation, angle (LRA) data and any deviations.
This data can then be compared to the nominal data, exported for reporting, or fed back into a bending machine to correct the next part. Due to this feature, and the overall speed and usability of the arm, this process is ideal for in-process measurement. A portable arm such as this does not require extensive training to use. It can be used by machine operators directly on the line, and in dirty or harsh conditions.
Thermal expansion is a non-factor in the accuracy of the machine due to the carbon fiber construction, said Scott Martin, regional manager at Hexagon Manufacturing Intelligence. According to Martin, he was set to demonstrate the product in northern Minnesota in the middle of the winter. He left the arm sitting in his truck overnight at -30F. Only a few minutes later, Martin did a demonstration measuring a ring gauge in an 80F shop. The arm hit the measurement within two tenths of a thousandth of an inch.
For more on CMM and metrology, check out An Introduction to Metrology and Quality in Manufacturing.