FaroArm - Lifetime Calibration
The FaroArm was designed to endure the typical stress and impact loads of a “factory floor” measuring tool, as well as survive multiple transportation cycles while maintaining its accuracy throughout its useable life. In order to fully appreciate what is meant by “Lifetime Calibration”, one must first understand several basic concepts of measurement equipment.
In this document, we will explain these concepts in common terms, as well as explain how the FaroArm is able to maintain its certified accuracy throughout its lifetime.
Calibration versus Certification
In most cases the terms “calibration and certification” are used together, and are often mistakenly used interchangeably. This generally occurs since traditional Coordinate Measuring Machines are often calibrated every time they are certified.
In reference to the FaroArm, there are two types of calibration: the arm calibration and the probe calibration.
Calibration is the procedure by which a measurement device is optimized to perform accurate measurements. This may be done through mechanical adjustments, as well as software corrections.
Specialists at the Faro production facility perform the factory calibration. This calibration utilizes patented hardware and software (not available to the user) to determine the true dimensions and kinematics of the FaroArm . The results of the factory calibration are imprinted on the EEPROM chip located in the arm. The FaroArm is permanently calibrated, such that it does not require mechanical adjustments during normal operation.
The FaroArm will only lose its calibration (stop functioning within Faro’s published standards) if one or more of the following occurs: bending of the transfer cases (long, tube sections), damage to the encoder-bearing interface joints (where tubes, bearings and encoders are mated) , or failure of the encoder-electronics system (changes motion into electrical data). Physical (plastic) deformation can occur in the arm after excessive impact with another object or an end-stop. The impact may cause the transfer cases to bend, the joint housings to deform, or the encoder-bearing interface pin system to loosen. Encoder-electronics system failure will occur based on standard probability theory and testing by the original equipment manufacturer. Both of the aforementioned cases require Faro’s Service Department to disassemble the arm, repair the necessary item(s), and perform a factory calibration. A factory calibration is necessary because the physical nature of the arm has been changed.
Since the FaroArm will always require repair if it loses calibration, and will only lose calibration if it is damaged, there is never a need for a field or user-site calibration.
Since the FaroArm can accept a variety of probe tips or end effector configurations, the user is given the ability to calibrate the probe tip.
The probe calibration routines determine the location of the probe tip relative to the intersection of the last two axes of the FaroArm.
Since the probe tip is the component in contact with the measurement piece, it is subject to the most damage and wear. Therefore, the probe tip is not considered to be permanently calibrated.
Certification is the process by which one proves that a device is performing within specification. The FaroArm is certified at the factory in accordance with the ANSI B89 standard.
Although the FaroArm is certified at the factory, it should be periodically re-certified in order to verify that its calibration is still valid.
Every company has its own standard for periodic certification of measurement equipment. If your organization does not yet have a standard, FARO can provide procedures that can be used as a basis for the development of such a standard.
Single point repeatability can be determined by the following test to ensure that the FaroArm is performing within specification. This test is not meant to replace a full certification as required by such standards ISO9000, but rather to provide an additional degree of confidence to the operator that measurements will be within specification.
Single Point Ball Bar - Repeatability test.
Note: This is NOT a single hole probe calibration.
- Calibrate a ¼” probe.
- Select BALL BAR from the CERTIFICATION menu.
- Digitize 50 points in a .200” machined hole. Measure the hole twice from 25 different directions and be sure to rotate all the FaroArm joints. Remove the ¼” probe from the hole each time a point is taken.
- The results of this test are used to analyze single point repeatability. The measured X, Y, Z and the bar values are analyzed. Each of these values should be within the specified bandwidth of your FaroArm.
- If the test results do not meet the required specifications, please repeat the test. If the data from both tests are outside the bandwidth of your FaroArm, please send the data to the Customer Service Department for review.
A truly portable measurement device should be fully operable right “out of the box” and should not require time consuming calibration procedures to be performed at the measurement sight. Such a device should also provide the software and hardware tools required to prove or “certify” that it is performing within specification.
The FaroArm meets all these criteria, as should any portable measurement device you purchase.