Date post: | 01-Jan-2016 |
Category: |
Documents |
Upload: | cecily-hardy |
View: | 216 times |
Download: | 1 times |
Pietro Craighero
Laboratory of Optoelectronics, University of Brescia
2D Vision Course
Telecentric Measurement System
Pietro Craighero
Problem definition
Measurement of the inner and outer radius
• Set up for inner radius • Set up for outer radius
Pietro Craighero
System Engineers vision have to face these problems:
1. Alteration of the magnification (due to object displacement)
2. Image distortion
3. Perspective errors
4. Low image resolution
5. Uncertainty of the position of the boundary (due to lighting geometry)
Pietro Craighero
Hardware available
Telecentric technology addresses the need to have high-contrast images and almost no distortion
Telecentric lenses reduce or even cancel most of these problem, and for this reason have become a key component for any high accuracy gauging applications
Pietro Craighero
Alteration of the magnification(telecentric lenses)
dH = ds * theta = 1 * 0.0017 mm = 0,0017 mm
With telecentric lenses the image size is left unchanged with object displacement, provided the object stays within a certain range often referred to as “depth of field” or “telecentric range”
In a telecentric lens the magnification change is
determined by the “telecentric slope”
theta = 0,0017 rad ds = 1 mm
Pietro Craighero
Perspective errors
Telecentric lenses eliminate the perspective effect
This effect is due to the specific path of the rays
Non telecentric lens Telecentric lens
Pietro Craighero
Good image resolution
The resolution provided by telecentric lenses is compatible with very small pixel sizes and high resolution cameras thus increasing the measurement resolution.
• Frame rate : 11.2 fps• Sensor type : CMOS• Pixel size : 3.2 um• Optical size : 6.554 x
4.915 mm• Resolution : 2048 x 1536• Optical class : ½”• Resolution class : 3.15
Mpix
RSx = FOVx/(#pixel) = 46.5 mm / 2048 pixel = 0.022 mm/pixelRSy = FOVy/(#pixel) = 34.9 mm / 1536 pixel = 0.022 mm/pixel
Pietro Craighero
Imaging system set up
Working Distance : 182,3 (+/-) 5 [mm] Field of View (with ½” detector) : 46,5 x 34,9 [mm]
WD
46.5 mm
34.9mm
Pietro Craighero
Software structure
State machine
User choises
Init / Idle /Calibrazione offline /Calibrazione online / Acquisizione online / Acquisizione offline / Misura Raggi InterniMisura Raggi Esterni
Calibration & Acquisition
Pietro Craighero
Inner radius
ROI selection?
• Default mode • Manual mode
ROI Cluster
Compute inner radius and display
Pietro Craighero
Outer radius
While(stop == false){..
If(new ROI drawn == false) {..
}}
Pietro Craighero
Outer radius
While(stop == false){..
If(new ROI drawn == false) {..
}}
30,33 mm
30,33 mm
Pietro Craighero
Conclusion
• set and choose the right hardware• friendly interface design
• Thank you for your attention