Leica s Pinpoint EDM Technology with Modified Signal Processing and Novel Optomechanical Features Fadi A Bayoud Ph.D. Geomatics Engineering
Contents Leica s Total Stations and Telescope ATR PS Leica s EDM System Analyser Comparison with other EDM s New Optomechanical features Conclusions
Leica s Total Station Functionality Accuracy
Leica s Telescope High quality optics Accurate reflector, reflector-less and long range EDM Automated prism finding Automatic Target Recognition (ATR) Power Search (PS) Small and coherent laser spot Emitted Guiding lights (EGL)
ATR Emits infra-red light while video-imaging is on Locates reflected light Steers the cross-hair to the lightened spot until the angular offset is less than 50 cc (16 arcsec) Measures angle and distance In case there are more than one reflecting spot, the emitter goes on and off to find the activated prism Emitter on Emitter off
Power Search (PS) ATR come in Scanning duration (sec) Plausibility volume: 0.1 upper tolerance limit A foreign object: e.g. traffic sign A foreign object: e.g. traffic sign Received signal Amplitude Target object: a prism Plausibility volume: upper tolerance limit Plausibility volume: lower tolerance limit Target object: a prism 0.01 1.10-3 Plausibility volume: lower tolerance limit 1m 10m 100m 1000m Distance 1.10-4 1 0 10 20 30 40 50 60 70 80 90 100 Distance [m]
EDM Current Technologies Time of Flight (TOF) & Phase Shift Time of Flight OK > 500 m but less accurate multi-target realisation, but needs excellent laser coherence (expensive) Phase Shift Difficult > 400 m multi-target realisation not possible (inseparable signals) Highly affected by environmental conditions
Leica s EDM Technology - System Analyser Permit accurate (in the mm range) RL measurements to objects over large distances (> 500 m) within few seconds (< 12 sec). Permit identification (and correct surveying) of multiple targets. Permit distance measurements independently of general atmospheric influences, such as, dust, smoke, mist, rain or snowfall, etc. Make on-board distance calibration available which runs simultaneously with the distance measurement to avoid thermal drifts and interrupts of measurement flow.
System Analyser Large number of high frequencies (100MHz) are emitted to collect distance information with exclusively high resolution Every frequency contributes to the final result giving high accuracy (λ~1.5m) Sub-mm distance resolution is achievable No time is wasted for ambiguity resolution. Selective w r t hard targets and blind w r t soft targets that have low-pass behaviour: 1 to 5 MHz Large number of frequencies causes redundancy: any interruption in the signal path can be detected and neglected Ultra short laser pulses in sub-nsec range within pulse-trains of 100MHz Energy s emitted at higher harmonics (1GHz) supporting high distance resolution Noise is minimised due to the steepness of the wave
System Analyser After sampling the received signals, a merit-function (which is comparative to a time-of-flight signal) is constructed based on using all the incoming signal information Thus, all the information between the EDM and Target is included in a quasi-continuous system Advanced algorithms perform a System Analysis to get the function whose maximum is the sought distance Number of used modulation frequencies depends on the received signal strength At high signal levels 4 frequencies are sufficient At low signal levels up to 10 frequencies are emitted and analysed
System Analyser 100 50 0 0 50 100 150 200 250 Amplitude 150 100 50 0 0 50 100 150 200 250 300 D (m)
Leica s EDM Accuracy (1) Comparison with an Interferometer: up to 60 meter with a 30 cm step 12 10 8 6 mm 4 2 Le ica TOF 1 TOF 1 w/out off-set TOF 2 TOF 2 w/out off-set Phase Shift P ha s e S hift w/out off-s e t 0-2 -4 0 10 20 30 40 50 60 m
Leica s EDM Accuracy (2) ISO range measurements; max.dist.: K1 = 500m, K2 = 1000 3 Std. Dev. [mm] 2.5 2 1.5 1 0.5 0 K1 Combination K2 Leica TOF1 TOF2 Phase Shift [ppm] 6 5 4 3 2 1 PPM value Leica TOF1 TOF2 Phase Shift 0 K1 K2 Combination
Range and Speed Range Range [m] 450 400 350 300 250 200 150 100 50 0 1 Kodak grey card 18% reflective Leica TOF1 TOF2 Phase Shift [m] 800 700 600 500 400 300 200 100 0 1 Kodak grey card 90% reflective Leica TOF1 TOF2 Phase Shift 25 Speed [sec.] 20 15 10 5 Leica TOF1 TOF2 Phase Shift 0 Typical max.
New Optomechanical Design 3 1 2 4 5 6 7 1. Laser Diode 2. Collimation lens 3. Tilted mirror 4. Revolver Wheel 5. Adjustable filter wheel 6. Negative lens 7. Tilted mirror 8. Deflection prism 9. Main objective lens 9 8
New Optomechanical Design Movable parts Reflectorless position Calibration position Reflector position It intelligently takes a position that depends on the strength of the reflected laser
Design Improvements Thus: Improving optical beam path Due to the reduced number of parts in the optical path Improving beam stability Due to the lack of moving mirrors/lenses and improvements of the geometric coupling Improving the MTF (Modulation Transfer Function) Sharper optical picture/impression for optical sighting through telescope Eliminating the need for user adjustment of the laser beam Allowing no misalignments or deviations between the reflector and reflectorless beam
Laser Spot 5 m 35 m 55 m
Effectiveness of Laser Spot Leica EDM TOF EDM
Conclusions Leica s EDM System Analyser is superior to existing technology Able to measure accurate distances with 4 to 6 times lower signals than with a conventional phase-method. Measures routinely to distance > 650 m with maximum time of 12 sec Further investigations are carried out to improve the maximum likelihood approach model in order to measure ranges to more than 1000m on bright diffusive targets. A new optomechanical design that overcomes potential disadvantages found in the old design, especially in terms of beam stability, image quality, laser beam spot geometry, etc.
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