Many industries must precisely measure the three-dimensional features of large objects. An increasingly popular way to do this is with the laser tracker, a device first introduced in the late 1980s. As its name suggests, the laser tracker measures 3D coordinates by tracking a laser beam to a retroreflective target held in contact with the object of interest.
Today, many instruments can measure coordinates. Each is best suited for certain applications. Traditional fixed coordinate measuring machines make repeated measurements rapidly and accurately but are immobile, limited in measurement range, and expensive for large applications. They are most popular for inspecting small to medium-sized (under one meter) production components where speed and accuracy are important.
For medium to large parts, portable CMMs are preferred. Until the advent of laser trackers, portable coordinate measurement was done mostly with theodolites, total stations (theodolites equipped with electronic distance measurement), articulated-arm CMMs and photogrammetry systems. Due to their high accuracy, high speed, and ease of use, laser trackers have replaced many of these earlier systems.
The operation of a laser tracker is easy to understand: It measures two angles and a distance. The tracker sends a laser beam to a retroreflective target held against the object to be measured. Light reflected off the target retraces its path, reentering the tracker at the same position it left. Retroreflective targets vary, but the most popular is the spherically mounted retroreflector (SMR). As light re-enters the tracker, some of it goes to a distance meter that measures the distance from the tracker to the SMR. The distance meter may be either of two types, interferometer or absolute distance meter (ADM).
Absolute distance measurement capability has been around for a long time. Within the last ten years, however, ADM systems have undergone dramatic improvement, offering accuracy comparable to interferometers. The advantage of ADM measurement over incremental distance measurement is the ability simply to point the beam at the target and shoot. The ADM system measures the distance to the target automatically, even if the beam has previously been broken. In a tracker with ADM, infrared light from a semiconductor laser reflects off the SMR and re-enters the tracker, where it’s converted into an electrical signal. Electronic circuitry analyzes the signal to determine its time of flight, multiplying this value by the speed of light in air to determine the distance from the tracker to the SMR.
Absolute distance meters first appeared in laser trackers in the mid-1990s. At that time, ADM units measured too slowly to permit scanning of surfaces. Because of this, all early laser trackers contained either an interferometer alone or an interferometer and an ADM. Today some absolute distance meters have been made fast enough to permit high speed scanning with negligible loss in accuracy. Hence some modern trackers contain only an ADM with no interferometer.
Today, many instruments can measure coordinates. Each is best suited for certain applications. Traditional fixed coordinate measuring machines make repeated measurements rapidly and accurately but are immobile, limited in measurement range, and expensive for large applications. They are most popular for inspecting small to medium-sized (under one meter) production components where speed and accuracy are important.
For medium to large parts, portable CMMs are preferred. Until the advent of laser trackers, portable coordinate measurement was done mostly with theodolites, total stations (theodolites equipped with electronic distance measurement), articulated-arm CMMs and photogrammetry systems. Due to their high accuracy, high speed, and ease of use, laser trackers have replaced many of these earlier systems.
The operation of a laser tracker is easy to understand: It measures two angles and a distance. The tracker sends a laser beam to a retroreflective target held against the object to be measured. Light reflected off the target retraces its path, reentering the tracker at the same position it left. Retroreflective targets vary, but the most popular is the spherically mounted retroreflector (SMR). As light re-enters the tracker, some of it goes to a distance meter that measures the distance from the tracker to the SMR. The distance meter may be either of two types, interferometer or absolute distance meter (ADM).Absolute distance measurement capability has been around for a long time. Within the last ten years, however, ADM systems have undergone dramatic improvement, offering accuracy comparable to interferometers. The advantage of ADM measurement over incremental distance measurement is the ability simply to point the beam at the target and shoot. The ADM system measures the distance to the target automatically, even if the beam has previously been broken. In a tracker with ADM, infrared light from a semiconductor laser reflects off the SMR and re-enters the tracker, where it’s converted into an electrical signal. Electronic circuitry analyzes the signal to determine its time of flight, multiplying this value by the speed of light in air to determine the distance from the tracker to the SMR.
Absolute distance meters first appeared in laser trackers in the mid-1990s. At that time, ADM units measured too slowly to permit scanning of surfaces. Because of this, all early laser trackers contained either an interferometer alone or an interferometer and an ADM. Today some absolute distance meters have been made fast enough to permit high speed scanning with negligible loss in accuracy. Hence some modern trackers contain only an ADM with no interferometer.
Laser trackers’ accuracy and speed distinguish them from other portable coordinate measuring instruments. Because an operator can make rapid measurements with a minimum of advance preparation, trackers are among the most versatile of the coordinate measuring instruments. Tracker software analyzes tracker data and presents the results in a useful form. Trackers are becoming increasingly popular, especially for large-scale manufacturing, where they assist in every stage of the manufacturing process.For more information about laser tracker technology, read the full whitepaper.
As with tactile coordinate measuring machines TRITOPCMM records the coordinates and their orientation in space for any feature of interest.
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