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Alexander Reiterer Fraunhofer Institute For Physical Measurement Techniques (IPM)
Laser Scanning Technology for Pavement Monitoring – A New Approach
Alexander Reiterer Fraunhofer Institute For Physical Measurement Techniques (IPM)
Laser Scanning Technology for Pavement Monitoring – A New Approach
Outline Fraunhofer IPM
Principle of a Laser Scanner
Concept of a Pavement Profile Scanner
Realized Technical Specification
Evaluation and Calibration
Examples of Implementation
Results
Conclusion and Outlook
© Fraunhofer IPM / Folie 3
Fraunhofer IPM The Institute
Services
Consulting – feasibility studies, technology-oriented market studies, technology assessment
Development – components, systems and pilot production
Support – implementing and maintenance of systems, technology transfer, coaching, workshops
Staff: 225 Employees Operating budget 2012 € 13.7 million, thereof € 4.8 million industrial proceeds
Dr. Alexander Reiterer - alexander.reiterer@ipm.fraunhofer.de
© Fraunhofer IPM / Folie 4
Fraunhofer IPM The Institute / Research Group “Laser Scanning LSC”
Contact Wire
Poles
Clearance Profile
Geometry
Road Pavement
Software
Dr. Alexander Reiterer - alexander.reiterer@ipm.fraunhofer.de
© Fraunhofer IPM / Folie 5
Pavement Monitoring Motivation
intact road infrastructure is an essential precondition for a functioning economy
One of the principal parameters of a road surface is its evenness
Based on the transverse profiles taken (generally in 1 m grids), the parameters of rut depth and theoretical water depth are calculated for the left and right wheel tracks.
→ Precise measurement / monitoring of the road surface necessary.
Dr. Alexander Reiterer - alexander.reiterer@ipm.fraunhofer.de
© Fraunhofer IPM / Folie 6
Pavement Monitoring (evenness, material characteristics) State of the Art
Measurement device for measurement of transverse profile with laser distance sensors mounted on a bar with a length of 3.3.m. → Dr. D. Wehrhan (Germany)
High-speed cameras, optics and laser line projectors to acquire high-resolution 3D profiles of the road. → e.g. Pavemetrics (Canada).
© Pavemetrics © Lehmann und Partner
Disadvantages: bulky, expensive and unsafe (Laser Class 3B!)
© Phoenix Scientific Inc.
Dr. Alexander Reiterer - alexander.reiterer@ipm.fraunhofer.de
© Fraunhofer IPM / Folie 7
Pavement Monitoring (evenness, material characteristics) State of the Art
Solution: Small, precise and safe (Laser Class 1!) device based on laser scanning technology.
Requirements:
relative precision of 0.3 mm.
max. point distance of 5 mm (transversal).
measurement independent from ambient light situation.
measurement independent from surface structure (color, roughness, etc.).
stable housing (IP67).
eye safe (laser class 1).
Dr. Alexander Reiterer - alexander.reiterer@ipm.fraunhofer.de
© Fraunhofer IPM / Folie 8
Laser Scanning Technology Principles
45°-Mirror Mirror as Polygon
Components of a laser scanner:
→ distance measurement module
→ angular measurement module
→ optical beam steering module
Dr. Alexander Reiterer - alexander.reiterer@ipm.fraunhofer.de
© Fraunhofer IPM / Folie 9
Laser Scanning Technology Principles
Technology (Distance Measurement)
Pros Cons
pulse-based - medium and long range (2 m – 5.000 m)
- less accurate - slower data aquisition - higher noise
phase-shift - more accurate - faster data aquisition - lower noise
- medium range only (~ 100 m)
Dr. Alexander Reiterer - alexander.reiterer@ipm.fraunhofer.de
© Fraunhofer IPM / Folie 10
Laser Scanning Technology Principles
Phase Shift Method
→ fast method for distance measurement (millions points per second)
→ precise method for distance measurement (e.g. sub-mm for distances up to 5 m)
→ method for close-range
Dr. Alexander Reiterer - alexander.reiterer@ipm.fraunhofer.de
© Fraunhofer IPM / Folie 11
Pavement Profile Scanner PPS Technical Specifications
Dr. Alexander Reiterer - alexander.reiterer@ipm.fraunhofer.de
© Fraunhofer IPM / Folie 12
Pavement Profile Scanner PPS Technical Specifications
relative precision of 0.3 mm.
max. point distance of 5 mm (transversal).
measurement independent from ambient light situation.
measurement independent from surface structure (color, roughness, etc.).
stable housing (IP67).
eye safe (laser class 1).
Dr. Alexander Reiterer - alexander.reiterer@ipm.fraunhofer.de
© Fraunhofer IPM / Folie 13
Pavement Profile Scanner PPS Technical Specifications
Mirror as Polygon
Dr. Alexander Reiterer - alexander.reiterer@ipm.fraunhofer.de
© Fraunhofer IPM / Folie 14
Pavement Profile Scanner PPS Technical Specifications
Polygon Mirror
Interfaces
- Modulator - DCDC-Board - FPGA - …
Laser and Detector
Dr. Alexander Reiterer - alexander.reiterer@ipm.fraunhofer.de
© Fraunhofer IPM / Folie 15
Pavement Profile Scanner PPS Tests and Calibration Procedure
Step 1: Evaluation of Distance Measurement Unit (Static Mode)
- Measurement section of 4 m is used as reference - Continuing measurement of distance between scanner and target - Evaluation for different reference targets (reflectivity) → functional test and evaluation of precision of the distance measurement unit.
magenta, cyan: intensity white, yellow: phase shift measurement plus distance green: difference between PPS and reference measurement
Dr. Alexander Reiterer - alexander.reiterer@ipm.fraunhofer.de
© Fraunhofer IPM / Folie 16
Pavement Profile Scanner PPS Tests and Calibration Procedure
Step 2: Evaluation of Scanner (dynamic mode, step-and-go)
- Measurement section of 10 m is used as reference - Continuing measurement of distance between scanner and target - Evaluation for different reference targets (reflectivity) - Evaluation of angular values (evaluation of the encoder) - Evaluation of the internal reference phase → calibration: non-linearity is considered by a lookup-table.
blue, magenta: distance (mean, standard deviation) red: intensity green: difference between PPS and reference measurement
Distance
Std
Dr. Alexander Reiterer - alexander.reiterer@ipm.fraunhofer.de
© Fraunhofer IPM / Folie 17
Pavement Profile Scanner PPS Tests and Calibration Procedure
Step 3: Evaluation of Scanner (dynamic mode, mounting height)
- Measurement of vertical profiles of different reflectivity - Continuing measurement of distance between scanner and target - Reference values are measured by a Laser Tracker (AT901) - Evaluation of reference and scanner values → calibration: non-linearity depending on angular values are considered by a higher-order (4th) polynomial function.
- Functional test under different light situation - Evaluation of air-sealed housing → functional test under real conditions.
Step 4: Indoor/Outdoor Test of the Scanner
Dr. Alexander Reiterer - alexander.reiterer@ipm.fraunhofer.de
© Fraunhofer IPM / Folie 18
Pavement Profile Scanner PPS Tests and Calibration Procedure
Calibration Protocol
PPS 101, SN: 114308-8 Light Grey 35% and 80% (*) Mean Grey 20% (*)
Noise (std. dev. < 0.2 – 0.3mm)
@ middle 0 deg. 0.17 mm 0.16 mm @ side 35 deg. 0.24 mm 0.24 mm
(*) on norm target, reference system = Leica Laser Tracker AT901B
Dr. Alexander Reiterer - alexander.reiterer@ipm.fraunhofer.de
© Fraunhofer IPM / Folie 19
Pavement Profile Scanner PPS Possible Implementations
Lehmann und Partner Germany
Dr. Alexander Reiterer - alexander.reiterer@ipm.fraunhofer.de
© Fraunhofer IPM / Folie 20
Pavement Profile Scanner PPS Possible Implementations
Lehmann und Partner Germany
Dr. Alexander Reiterer - alexander.reiterer@ipm.fraunhofer.de
© Fraunhofer IPM / Folie 21
Pavement Profile Scanner PPS Possible Implementations
Austria Institute of Technology Austria
Dr. Alexander Reiterer - alexander.reiterer@ipm.fraunhofer.de
© Fraunhofer IPM / Folie 22
Pavement Profile Scanner PPS Example (Schematic)
Dr. Alexander Reiterer - alexander.reiterer@ipm.fraunhofer.de
© Fraunhofer IPM / Folie 23
Pavement Profile Scanner PPS Results
Dr. Alexander Reiterer - alexander.reiterer@ipm.fraunhofer.de
© Fraunhofer IPM / Folie 24
Pavement Profile Scanner PPS Results
Dr. Alexander Reiterer - alexander.reiterer@ipm.fraunhofer.de
© Fraunhofer IPM / Folie 25
Pavement Profile Scanner PPS Results
- 2,5 %
- 2,3 %
- 2,0 %
Dr. Alexander Reiterer - alexander.reiterer@ipm.fraunhofer.de
© Fraunhofer IPM / Folie 26
Pavement Profile Scanner PPS Conclusion and Outlook
laser scanning device which is able to monitor the pavement with an (relative) precision of 0.1 – 0.3 mm.
eye safe technology (laser class 1).
robust technology.
used as a reference instrument by the German Federal Highway Research Institute (BASt)
Summery
Outlook
improvement of resolution of intensity channel (~1 mm).
improvement of measurement frequency up to 2 MHz.
→ measurement device for both geometry and crack monitoring.
Dr. Alexander Reiterer - alexander.reiterer@ipm.fraunhofer.de
© Fraunhofer IPM / Folie 27
Visit us on the Internet at www.ipm.fraunhofer.de/laserscanning
Good ideas for better solutions
Dr. Alexander Reiterer - alexander.reiterer@ipm.fraunhofer.de
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