ABSTRACT

Objective ......................................................................................................................................... 94 3.1 Introduction .......................................................................................................................... 95 3.2 Laser Trackers: Concept of Operation ............................................................................... 95

3.2.1 From Fixed 3D to Portable 3D ................................................................................ 95 3.2.2 Tracking Mechanism ............................................................................................. 101 3.2.3 Leveled and Non-Leveled Operation .................................................................. 102 3.2.4 Range Measurement: In Brief ............................................................................... 103 3.2.5 Reflector ................................................................................................................... 104

3.2.5.1 Reflector Offsets ...................................................................................... 106 3.2.5.2 Target Adapters ....................................................................................... 107 3.2.5.3 Virtual Reflector (Mirror Probe) ........................................................... 109 3.2.5.4 Hidden Point Rods .................................................................................. 109

3.3 Line of Sight and Measurement Networks .................................................................... 110 3.3.1 6D Probing .............................................................................................................. 112 3.3.2 6D Tracking: Leica Geosystems ........................................................................... 116 3.3.3 6D Tracking: Automated Precision, Inc. ............................................................. 117

3.4 Laser Tracker: Range Measurement Details .................................................................. 119 3.4.1 Relative Range Measurement by Interferometer .............................................. 119 3.4.2 Absolute Distance Meter ....................................................................................... 122 3.4.3 Range-Dependent Accuracy................................................................................. 124

3.5 Targeting: Retroreflector Design Details ........................................................................ 125 3.5.1 Air-Path Corner Cube Retroreflectors ................................................................ 127 3.5.2 Break-Resistant Reflectors..................................................................................... 129 3.5.3 Solid Glass Prism Reflectors ................................................................................. 130 3.5.4 Tooling Ball Reflectors ........................................................................................... 131 3.5.5 Repeatability Targets ............................................................................................. 131 3.5.6 Cat’s Eye Retroreflectors ....................................................................................... 132 3.5.7 Reflector Housing .................................................................................................. 133

3.6 Environmental Compensation ......................................................................................... 134 3.6.1 Wavelength Compensation for Accurate Range ............................................... 134 3.6.2 Bending of Light Due to Temperature Variations ............................................. 135

The objective of this chapter on laser trackers is to offer a concise and practical guide to laser tracker measurement technology and techniques. It should serve as a desk reference resource for those that need a better understanding of laser tracker metrology, its accessories, and targeting requirements in order to make informed decisions and application choices. It should also act as a “how-to” guide for laser tracker use on site and applications in general.