Getting the most accurate measurements with your FARO® Laser Tracker is a matter of set up, warm-up, Compensation and regular checks during long duration measurements.
Getting the best result from your tracker requires a warm-up time and laser stabilization period. This can take anywhere between 45 – 80 minutes depending on Tracker temperature. Inadequate thermal stabilization is a common cause of accuracy issues such as CompIT failures or poor overall reproducibility in the early stage of measurements.
If immediate measurement is required there is a possibility to Skip the Warm-Up. If this is done, then regular Compensation should be run.
For details, refer to your Tracker User Manual, Thermal Stabilization section.
- Basic Compensation
When you are measuring in a small area where you do not plan on using the full range of the tracker it is recommended to run the Basic Compensation (Quick Compensation and Angular Accuracy Check)
- Full Pointing Compensation
If you plan on utilizing the full range of the tracker or measure longer ranges and you are looking for the most accurate measurements you will want to run a full pointing compensation (Quick Compensation, Angular Accuracy Checks, Pointing Compensation, and Axis Non Squareness).
If you are failing Angular Accuracy Checks, it is recommended to run a full Pointing Compensation.
Quick/Self Compensation adjusts parameters in the Laser Tracker to improve its accuracy. Its purpose is to provide Angular Accuracy Results that are within your Laser Tracker’s specifications for the current working range of the system, or lower than the Laser Tracker’s Maximum Permissible Error (MPE) based on the published specifications.
Quick/Self Compensation is the preferred compensation for most applications, however Pointing Compensation from the Advanced tab of CompIT can yield lower back sight error or improved Angular Accuracy results, especially at longer distances, or when the full range of the system is required.
Laser Tracker Quick Compensation Video
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Laser Tracker Angular Accuracy Check Video
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Full Pointing CompIT
Pointing CompIT allows you to check the accuracy of the tracker and compensate if necessary. The standard Pointing CompIT takes three interim test points to check accuracy and six points to compensate. The compensation points are at 2, 4 and 6 meters and will bring the Tracker into specification at all ranges.
For the highest accuracy at ranges over 20 meters, Pointing CompIT can be customized to use the maximum range required for the measurement job.
Pointing CompIT should be run immediately before starting a measurement job. The interim test will report whether the Tracker is within specification. For the highest accuracy, the compensation can be performed even if the interim test passes.
If the Pointing Compensation is not bringing the tracker into tolerance after the 6 points are measured, then it will recommend continuing onto the Squareness Compensation, which consists of a few more points on the floor.
The Squareness parameter is a very stable parameter and does not change with temperature. Its changes are typically a result of shock, vibration or shipping. Some operators who ship the tracker to each inspection location may choose to go straight to the Advanced Tab of CompIT and run a full Pointing Compensation continuing onto the Squareness portion of the compensation despite the passing results up to that point to re-optimize the Squareness parameter for any small changes that may have occurred during transit.
A Pointing Interim Test or Backsight Check can be run at any time to determine whether the tracker is measuring within specification. These tests provide a pass/fail result that is based on the Tracker specifications. A detailed report of the results can be viewed and saved.
Long Duration Measurements
Long duration measurements, jobs that last more than two hours, typically experience global drift. This drift can be caused by vibration or temperature changes in the environment. Changes in temperature can affect the part being measured, the floor, the tracker stand and the Tracker. Because of these environmental effects, drift must be checked throughout the duration of a measurement job.
At the beginning of a measurement job, several fixed reference points should be measured over the full volume of the part. These points should be checked periodically for drift. When drift is noticed, a device position move (Relocation in Insight) should be done to re-fit the tracker back into the coordinate system. The device position move should be executed with auto-scale to allow for growth or shrinkage of the part. This allows the Tracker to continue to measure a part accurately over a long measurement session.
Backsight Checks or a Pointing Interim Test should be run periodically throughout a long duration measurement job to verify accuracy. If the checks do not meet specification, a 5-minute Pointing CompIT should be run.
Surveys are used to measure a set of targets repeatedly. The most accurate method for running a survey is to use Relocation between each cycle and frontsight/backsight averaging on each point (Insight only). Relocation eliminates part, environment, and tracker drift during the survey, and the frontsight/backsight cancel out any beam and gimbal errors.
Frontsight-Backsight averaging is a method of measuring points in frontsight and backsight mode and averaging them. This method can only be used in jobs that measure individual points, features cannot be measured with this method. When measuring a frontsight-backsight job, every point must be measured in both frontsight and backsight. This method is only used beneficial on an Un-compensated Tracker.
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