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A. Grubinger, J. Fabiankowitsch, A. Eichhorn:
"A Laser Measurement System for he Investigation of Dynamic Tripod Deformation";
in: "Optical 3-D Measurement Techniques IX", A. Grün, H. Kahmen (ed.); Eigenverlag, Wien, 2009, (invited), ISBN: 978-3-9501492-5-8, 117 - 125.

The development of nearly fully automated tacheometer systems (`robot tacheometers´) aims at a significant progression in the automation of measurement processes
and an increasing accuracy and reliability of the measurement results. Robot tacheometers
enable the development of new fields of activity in engineering survey, e.g the establishment
of autonomous monitoring systems on construction sites and the precise control of industrial
manufacturing processes. They are not restricted to perform only static measurements but can
also observe highly kinematic processes. This is realised by electromechanic or
electromagnetic actuators at the tacheometer axes. The increase of automation, accuracy and
reliability also means higher requirements concerning the tacheometer equipment like tripods
and tribrachs. This includes the detection of static and dynamic deformations which may
occur during the measurement process (e.g. horizontal torsion and vertical tilt of a tripod) as a
basis for the development of compensation methods. In this paper the development and
application of a laser measurement system for the detection of static and dynamic
deformations of tripods is presented. The system basically consists of the combination of a
miniature laser with a position sensitive device. It is a lowcost system (< 3000 Euro) but
nevertheless enables the significant detection of tripod torsions and tilt within a range of 0.1
mgon up to theoretically 50 mgon and possible measuring rates up to 30 kHz. In the first part
the paper describes the configuration, the constructional compensation of disturbance
influences (like background radiation) and the calibration of the measurement system. One
focus is set on the achievement of a measurement accuracy of some micron on the position
sensitive device. In the second part the investigation of tripod deformations under variable
dynamic loading with different tacheometers TCA1800 (Leica), TCRP1201 (Leica) and S8
(Trimble) is discussed. The tacheometers have different masses, gravity centers and
electromechanic (TCA1800 and TCRP1201) respectively electromagnetic (S8) actuators.
They automatically perform different measurement processes like set measurements to target
groups and face changing. Using a standard tripod, deformations like short periodic (ca. 40
Hz) damped oscillations with amplitudes up to 4.5 mgon can be observed. It is also possible
to detect and distinguish the influence of tacheometer accelerations and decelerations. In some cases, hysteresis effects may occur and a significant dependency between tacheometer
direction and tripod tilt (up to 1.7 mgon) as an effect of unbalanced masses is observed and
discussed.