Calibration and Obtaining Optimum Performance.
Portable measuring arms are becoming commonplace in today's manufacturing facility. It’s true that they bestow many benefits on the users, but there are also many pitfalls to overcome when utilizing this highly effective and sophisticated tool.
Design and Measurement Range
The articulating arm coordinate measuring machine uses a series of rotating components around a generally perpendicular axis. It consists of three joints: the wrist, the elbow and the shoulder. Both the shoulder and the elbow are generally two axes; on seven-axis machines (typically scanning arms), the wrist has three axes of movement. Arm sizes are determined by spherical measuring ranges and are usually available in sizes from 2 m to as large as 5 m.
Portable measurement arms can be used anywhere in the modern factory. They can be attached to a portable measurement stand, directly on a fixture or on a surface plate in the inspection room. It's also not unusual to find them mounted on the bed of the machine tool! It is little wonder, then, that their popularity is on the rise. The latest arms have both Bluetooth and wireless integrated technology enabling them to be completely cable-free. Combine this with battery operation and they become a highly mobile device that is used anywhere inside or out.
As we come to rely more and more on the portable arm, it's important to monitor your arm’s accuracy through regular calibration. The current standard for calibration is ASME B89.4.22-2004. For a successful evaluation of the arm, your calibrator must follow the standard. There are essentially three parts to the calibration procedure:
- Single point accuracy test.
- Volumetric ball bar test.
- Effective diameter performance test.
These tests must be performed at an accredited lab with traceable artifacts, ideally a lab certified to ISO 17025 standards.
Request your portable arm calibration quote here or call us at 1.800.606.9266
It is a generally accepted fact that arm performance degenerates at a much faster rate than that of a stationary coordinate measuring machine. There are several reasons for an arm not to perform to specifications: poor clamping and unstable mounting platforms are two of the biggest culprits. Any kind of instability will magnify itself to the probe tip and create major accuracy issues. Care must also be taken during probing: make sure the probe is in constant contact with the area to be measured and always be on the lookout for points that are taken out of range. Finally, use the gauge with care; portable arms do not tolerate rough usage well. Remember, should an arm be damaged it will usually have to go back to the USA for repair and in most cases this means you will be out of action for several weeks!
Laser Scanner Integration
Laser scanners are now becoming a popular add-on for seven-axis and sometimes six-axis articulating arms. In most cases, the scanner is calibrated independently of the arm. The scanner essentially has its own coordinate system separate from the measurement arm and it’s therefore important to ensure the scanner is in calibration. This is done using the measurement of a non-reflective calibrated sphere. The resultant Maximum Permissible Error (MPE) value is a direct indication of the scanner’s precision in the localized area.The beauty of using an integrated seven-axis arm with probing and a scanner is that you have the ability to utilize the higher accuracy of the probe during the alignment phase of the measurement. This allows you to use the tremendous data collecting capability of the scanner combined with the precision of the probe. In fact, new software products allow the user to switch back and forth between scanning and tactile probing during the same program.
Your portable measuring arm can give you high-quality service and provide accurate measurements. Treat it with care, calibrate often, apply good metrology practices and it will reward you with many years of trouble-free service.
We want your feedback! What is your experience with portable arms? Do you find them easy to use and learn? How are you using these versatile measuring machines in your shop?