Laser trackers are instruments that accurately measure large objects by determining the positions of optical targets held against those objects. The accuracy of laser trackers is of the order of 0.025 mm over a distance of several metres. Some examples of laser tracker applications are to align aircraft wings during assembly and to align large machine tools. To take measurements the technician first sets up a laser tracker on a tripod with an unobstructed view of the object to be measured. The technician removes a target from the base of the laser tracker and carries it to the object to be measured, moving smoothly to allow the laser tracker to follow the movement of the target. The technician places the target against the object and triggers measurements to be taken at selected points, sometimes by a remote control device. Measurements can be imported into different types of software to plot the points or to calculate deviation from the correct position.
The targets are known as "retroreflective" because they reflect the laser beam back in the same direction it came from (in this case, back to the laser tracker). One type of target in common use is called a spherically mounted retroreflector (SMR), which resembles a ball bearing with mirrored surfaces cut into it.
History
The first laser tracker was invented in 1987 by NIST and commercially available instruments were first produced by Leica in 1991. Currently, there are three well known manufacturers of Laser Trackers; API, Faro and Leica.