Expert's Desk: OASIS Alignment Services

by Hubert Meagher on October 17, 2016 From Ask The Experts

OASIS Shares Why OTG is Important in Industrial Applications

Orient-To-Gravity (OTG) is a standard feature on the Leica AT960 laser tracker and it is arguably one of the most important for us at OASIS Alignment Services. As a service company providing 3D metrology services to many different industries, we often have applications that require a reference level-to-Earth. With more traditional optical alignment technologies, level-to-Earth was not only a requirement for the object of the inspection, but it was essential in order to use the instruments properly. For most machinery, being level-to-Earth is normally a best practice, if not outright essential, for proper function, whereas certain tooling could be out of level and still be in tolerance and perfectly operable. Most tooling is still specified to be level-to-Earth whether by best practice or just by design legacy.   

When using traditional optical tooling, precision levelling has always been a part of utilizing the instruments. When laser trackers were first used in manufacturing, they did not have level-to-Earth capabilities and so were mainly used to inspect parts, assemblies, and tooling after the fixture was leveled by other means.  

Once laser trackers began to incorporate precision levels in order to expand their capabilities in general industry outside of aerospace and automotive, the process of levelling was a separate measurement step that needed to be taken. The data was then incorporated into the metrology software to compensate coordinate systems in order to show objects relative to a level plane.  

With the Leica AT960 Absolute tracker’s OTG, the laser tracker has truly become a seamless 3D measurement device that is compensated for level from within. Much like traditional optics, after the instrument is “levelled”, the data and readings coming from the device are based on coordinates that are compensated. What that means for us is three fold:

  1. The operator no longer has to be concerned with creating a level coordinate system from a level plane derived from a level measurement process. The operator simply has to ensure the laser tracker is rough levelled within tolerance and the OTG option is checked in our metrology software.  
  2. When OTG is activated on the first device position of a project, by definition the World coordinates become level-to-Earth. No longer is there a confusing difference between device coordinates, level coordinates, and World coordinates.
  3. Since each new device can be compensated level-to-Earth, we now have a very real constant between device positions. We can now constrain device position moves to their respective “level planes” or “Z” axis. Gone are the days where drifting reference targets (in the vertical attribute) would create havoc on a project. Also gone are the very real concerns about translating devices down long and narrow corridors or machine alleys. By constraining to level at every device position along a very long machine, we can ensure that the cross-machine level is constant at every device position.  
We here at OASIS are very pleased to have a fleet of laser trackers with level capabilities that not only allows us to level machines, equipment, and tooling, but also make the measurement process itself even more accurate. 

Hubert Meagher

Hubert Meagher, B. Eng, spent years in the field as an Alignment Engineer specializing in precision measurement prior to his role as Director of Metrology Services at OASIS Alignment Services (OASIS). He is an expert in using both optical tooling and portable metrology tools in manufacturing facilities. Mr. Meagher was instrumental in researching and developing the 3-Dimensional Metrology Services segment of OASIS and has been heavily involved with testing the use of laser trackers, coordinate measuring arms and laser scanners in industrial environments.