Apr 30, 2011 - instead of a laser line generator for high measurement tasks. MEASUREMENT 2011. 8th Conference on Measurement. 27 to 30 April, 2011, ...
MEASUREMENT 2011 8th Conference on Measurement 27 to 30 April, 2011, Smolenice castle, Slovakia
Using a structured LED linear light instead of a laser line generator for high measurement tasks Matthias Rückwardt ILMENAU UNIVERSITY OF TECHNOLOGY
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MEASUREMENT 2011
Agenda 1. Back round – spectacle frame measurement 2. The Triangulation principle for 3D measuring 3. Creation of a structured LED linear light 4. Results and Conclusion
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Back round – spectacle frame measurement -
humans take up nearly 90% of all sensation with the eyes
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ca. 60% of all adults have spectacle frames in Germany [1]
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11 million pieces of spectacle frames are sold each year
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the disposal of eyeglasses is about 34.5 million
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the business volume is about 4.8 billion Euro [2]
Fig. 1: Business volume of optician in Germany 2009 [2]
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Back round – spectacle frame measurement -
the costumer choses his spectacle frame and his defective vision is checked out each spectacle frame is measured by the optician to get its form with a tracer the eyeglasses are grinded the measurement is needed, because of the huge range of the different designs and their manufacturing inaccuracies.
- Each tactile measurement depends on a contact force and this force is able to warp the spectacle frame.
Fig. 2: Nidek LT900
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Fig. 3: Nidek LT900 during measurement
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Back round – spectacle frame measurement Idea of an optical measuring method for spectacle frames The groove of the frame has to be known very well
Fig. 5: Parameter of the groove (negative procedure)
Fig. 4: metal spectacle frame
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The Triangulation principle for 3D measuring
Fig. 6 Triangulation principle
- beam (send out) is a point - structured beam, at least a line
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distance measuring surface measuring
MEASUREMENT 2011
The Triangulation principle for 3D measuring
Problems with speckle: depends on the material (high reflective metal and transparent plastics) and on the coherence of the light
Fig. 7: A plastic and a metal frame with its groove, illuminated with a laser line generator (from left to right)
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huge influence on sharpness of the contour and homogeneity of the linear line and its width no correct measurement
MEASUREMENT 2011
Creation of a structured LED linear light Table 1: Typical Properties of LEDs and Laser diodes. property
Laser diode
Wave length
NIR, red, blue, UV
Power (typical)
visible: 50mW
Spatial coherence
single transversal modus (speckle)
Time coherence
coherent (Δλ < 0,1 nm) (speckle)
Dimming
not linear, Laser Threshold
Modulation
GHz
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What is needed? a sharp line with a known width a define depth of focus a large working distance
MEASUREMENT 2011
Creation of a structured LED linear light Table 1: Typical Properties of LEDs and Laser diodes. property
Laser diode
LED
Wave length
NIR, red, blue, UV
NIR, red, yellow, green, blue, UV, white
Power (typical)
visible: 50mW
500mW
Spatial coherence
single transversal modus (speckle)
highly multi-mode
coherent (Δλ < 0,1 nm) (speckle)
incoherent (Δλ > 10 nm)
Dimming
not linear, Laser Threshold
linear
Modulation
GHz
MHz
Price
Expensive
Very cheap
Time coherence
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MEASUREMENT 2011
Creation of a structured LED linear light But the illumination of a LED is shared in all directions high power LED are needed for this measuring task
better to use attachment optics for building a powerful point light source
Fig. 8: Light emission of a LED without and with attachment optic.
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MEASUREMENT 2011
Creation of a structured LED linear light There are different basic setups to generate a light line:
projection of a split
beam moulding with a cylindrical lens
beam moulding with a parabolic reflector
a combination of them
Fig. 9: Basic set up to generate a light line.
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Creation of a structured LED linear light
split with width of 300 µm and a length of 12 mm the cylindrical lens is used to the beam expansion (due to this the illuminance is reduced)
Fig. 10: Beam rum with split and cylindrical lens.
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Results
Fig. 11: Line width.
Fig. 12: Line length.
Fig. 13: False Color DV – line width 336µm. 30.04.2011
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Results Table 2: Specification for groove measuring and realised criteria. Criterion
Specification
realised criteria
light source
LED white coloured
LED Vishay (TLCR5100-white)
width
≤ 500 µm
336 µm
length
10 mm
9,4 mm
depth of focus
≥ 5 mm
6 mm
illuminance
0,1 lm/mm²
0,03 lm/mm²
low cost
< 350 €
145 €
working distance
< 50 mm
40 mm
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Results and Conclusion This study shows, that it is possible to use a structured LED linear light instead of a Laser line generator for high measurement tasks. But therefore the specification of the measuring task has to be known exactly and the measuring system has to be optimised for it. Here it is brought out of detecting the ground of the frame groove. The best results are achieved with an optical system out of a split and a cylindrical lens.
Fig. 13: False Color DV – line width 336µm. 30.04.2011
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Thank you for your attention This work is funded by the Federal Ministry of Economics and Technology Germany within the framework of the InnoNET program.
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REFERENCES [1] [2] [3]
http://www.zva.de/brillen/ (3.3.2011). http://www.zva.de/getfile/content/28/ (3.3.2011) M. Rückwardt, “A novel proceeding for optical coordinate measuring machines to locate deviations behind an undercut”, Measurement 2009 - 7th International Conference on Measurement, pp. 373-376, Smolenice, Slovakia, May 2009
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