Deformation Analysis Of Tripods Under Static And Dynamic Loads
Deformation Analysis of Tripodsunder Static and Dynamic LoadsAndreas EICHHORN, GermanyJohannes FABIANKOWITSCH and Daniel NINDL, AustriaFIG Working Week, Eilat3-8 May, 2009Contents1. Motivation2. Theoretical simulations3. Static tripod deformations4. Quasi-static tripod deformations5. Dynamic tripod deformations6. Conclusions and outlookTS 8C, Eichhorn et al., Deformation Analysis of Tripods14. Mai 2009 2 1
1. Motivation Short term precise monitoring tasks (no pillars / consoles available) flexibleuse of tripods Temporal stability of tripods is essential precondition for accurate resultsMinimization of random and systematic errors by tripod head movements Tripod stability height stability ( z) and horizontal stability ( x, y) ‘Stability’ must be referred to the length of the measurement process External loads (e.g. sun, wind, soil instability and vibrations) System tripod Ù tacheometer also affected by tacheometer itself- robot tacheometers: typical mass 5 - 8 kg and rot. speed up to 128 gon/s- static and dynamic loads by mass, accelerations resp. decelerations elastic or plastic tripod deformationsTS 8C, Eichhorn et al., Deformation Analysis of Tripods31. Motivation Increasing number of tripod types available on the market Introduction of new materials in tripod manufacturing (e.g. fibreglass: NanjingSurvey / Crain Inc.) Cooperation between TU Vienna and Leica Geosystems for investigation ofstandard tripods (diploma thesis) Investigations realised at Leica labs / Heerbrugg Focus on- interaction tacheometer load Ù tripod (no external disturbances): lab- at first: inner height stability and quasi-static drift reactions- later: also dynamic effects (like horizontal torsional rigidity)TS 8C, Eichhorn et al., Deformation Analysis of Tripods14. Mai 2009 4 2
1. Motivation Investigation of 7 different standard tripod types:- companies Leica, Nanjing Survey and Crain Inc.- material: wood, aluminum, fibreglass- light and heavy tripods (different admissible load) LeicaGST120-9 HCTP101 H/LGST05 LGST05L LWoodTS 8C, Eichhorn et al., Deformation Analysis of TripodsCTP103 L CrainTrimax HAluminumS40 HFibreglass52. Theoretical simulations First step: theoretical simulations for expected deformation range Simple Finite Element model (FEM) of tripod- each tripod leg is system of three homogenous and isotropic beams- rigid connection (neglection of clamps)- legs connected in single knot (tripod head)- supported by non-elastic ground Restricted to static vertical loads ( height stability) For simulation: geometrical parameters derived from Leica GST120-9 (H) Young’s modulus from dry hardwood ‘Loaded’ with typical test mass m 30 kg (F 300 N)TS 8C, Eichhorn et al., Deformation Analysis of Tripods14. Mai 2009 6 3
2. Theoretical simulations Static reaction of tripod head: z 0.02 mm Model verified by following measurements( zmeas 0.02 – 0.03 mm) FE-model enables calculation of failure ( 240 kg)TS 8C, Eichhorn et al., Deformation Analysis of Tripods73. Static tripod deformations Investigation of height stability under static loading Required accuracy for monitoring system derived from FEM results Monitoring system:- combination of precise levelling instrument (Leica DNA03) and shortlevelling rod (Leica GWLC60)- inner accuracy for repetition measurements (small cutout): s h 0.01 mm- automated registration of measurements- measuring frequency restricted to f 0.25 Hz (compensator influence) Experimental setup under controlled environmental (lab-) conditions Tripod legs fully extended, spaced (1 m), clamps tightened with torque spanner Controlled loading with Leica test masses (m 30 kg for H and 10 kg for L)TS 8C, Eichhorn et al., Deformation Analysis of Tripods14. Mai 2009 8 4
3. Static tripod deformationsExperimental setupSteel CableTest unterbalanceTS 8C, Eichhorn et al., Deformation Analysis of Tripods93. Static tripod deformationsLeica GST120-9: static load m 30 kgCrain Trimax: static load m 30 kgH / WoodH / FibreglassDeformation z [0.01 mm]00220 min446 z 0.03 – 0.04 mm 620 min z 0.05 mmHyst. 0.01 – 0.02 mmHyst. 0.02 – 0.03 mmNo. of measurements t 4 sNo. of measurements t 4 sTS 8C, Eichhorn et al., Deformation Analysis of Tripods14. Mai 2009210 5
3. Static tripod deformationsResults for vertical static loadsHeight stability (H heavy / L light tripod)TS 8C, Eichhorn et al., Deformation Analysis of Tripods114. Quasi-static tripod deformations Investigation of quasi-static drift behaviour slow long-term effect Horizontal torsion of tripod more critical than vertical movement- time-dependent error in tacheometer orientation- systematic error in measured horizontal directions One main reason (indoor): continous stress decomposition in tripod Requires another kind of monitoring system:- Leica autocollimator and autocollimation mirror (accuracy σΘ 2cc)- automated registration of measurements (integrated PSD)- measuring frequency f 16 Hz Experimental setup under controlled environmental (lab-) conditions Static tripod loading with tacheometer Leica TCA2003 (m 8 kg)TS 8C, Eichhorn et al., Deformation Analysis of Tripods14. Mai 2009 12 6
4. Quasi-static tripod deformationsExperimental setupAutocollimatorTripod withautocollimation mirrorTS 8C, Eichhorn et al., Deformation Analysis of Tripods134. Quasi-static tripod deformationsLeica GST120-9: loaded withLeica TCA2003Nanjing Survey S40: loaded withLeica TCA2003 (cutout)H / WoodH / Fibreglass0Drift [cc]51015 min / 1.5cc015 min / 7cc1545 h 7cc205 h 23cc8Time [s]Time [s]TS 8C, Eichhorn et al., Deformation Analysis of Tripods14. Mai 2009 14 7
4. Quasi-static tripod deformationsResults for quasi-static deformations( TCA2003 σr 1.5cc )Horizontal drift investigationTS 8C, Eichhorn et al., Deformation Analysis of Tripods155. Dynamic tripod deformations Tacheometer rotation (esp. accelerations and decelerations) also inducestorsional moments to tripod up to MT 60 Ncm New task: investigation of horizontal torsional rigidity (resistance of tripodagainst torsional moments) Short-term effects with high frequencies (more than 50 Hz) Autocollimator (16 Hz) not suitable for investigation Development of a monitoring system at TU Vienna Just an outlook to first results Monitoring system consists of combination highspeed PSD and miniature laser- measuring frequency up to 30 kHz- relative position accuracy laser spot on PSD s Y s X 5 µmTS 8C, Eichhorn et al., Deformation Analysis of Tripods14. Mai 2009 16 8
5. Dynamic tripod rea Laser on NIRO plate- fixed on tripod- performs tripodrotation- weight 200 g sPSDNIRO plate PSD fixed on pillar Distance 8 mαTripodheadr sα Compensatedbackground radiationLaserαTS 8C, Eichhorn et al., Deformation Analysis of Tripodsr175. Dynamic tripod deformations Tripod Leica GST120-9 (H) Movement clockwise 0 50 gon Loading: rotating Leica TCA1800 Movement counterclockwise 50 0 gon PSD meas. frequency f 1 kHz Acceleration - constant vel. - deceleration0 50 gonHz [mgon]630-3-6 1.6 s 45time [s]TS 8C, Eichhorn et al., Deformation Analysis of Tripods14. Mai 2009 50 0 gon 1.6 s 61314time [s]1518 9
6. Conclusions and outlook Inner height stability is no real problem for short-term monitoring tasks Small amplitudes and hysteresis effects / wood best & fibreglass worst behaviour Quasi-static drift is much more critical Aluminum and fibreglass: drift influence cannot be neglected (in relation tospecified tacheometer accuracy) / wood shows acceptable amplitudes Recommendation: tripod relaxation of min. 1-2 hours after tacheometer mounting Dynamic torsional moments may induce tripod torsions up to 3 mgon (and more) Only short phases, mainly in acc. and dec. phases / face changes May have significant influence esp. on kinematic measurements New PSD-laser-system: further investigation of dynamic tripod deformations(e.g. influence of unbalanced tacheometer masses) diploma thesisTS 8C, Eichhorn et al., Deformation Analysis of Tripods19Thank you very muchfor your attention !Special thanks tofor equipment, lab facilities and local adviceTS 8C, Eichhorn et al., Deformation Analysis of Tripods14. Mai 2009 20 10
3. Static tripod deformations DNA03 Pillar Tripod Steel Cable Test Weight Counterbalance Levelling-rod GWLC60 Swivel Experimental setup TS 8C, Eichhorn et al., Deformation Analysis of Tripods 10 3. Static tripod deformations Leica GST120-9: static load m 30 kg H / Wood Crain Trimax: static load m 30 kg H / Fibreglass No. of measurements .
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