Development of Low-Cost, Root Collar Diameter Measurement Devices for Pine Seedlings

1. Development of Low-Cost, Root Collar Diameter Measurement Devices for Pine Seedlings Tony E. Grift; Roberto Oberti ABE425Engineering

2. Agenda Root Collar Diameter measurement of seedlings • Machine vision attempts • Time of flight measurement • Parallel light beams, constant velocity • Diverging light beams, constant velocity • Diverging light beams, constant velocity, sliding edge • Counterbalanced arrangement with a diverging beam and constant receiver acceleration • Results • Conclusions

3. Machine vision attempts • Determine length and diameter from images • Length is hard to determine • Diameter inaccurate • Slow operation • Lighting issues Shoot section Root collar diameter (RCD) Root section

4. Relationship between the motion of an object passing through a dual light beam sensed by receivers and output timing (right)

5. Measurement configuration with a diverging light beam

6. Lab-scale, sliding-edge diameter measurement device

7. Measurement configuration with diverging light beam and object sliding along a guide at a distance S from the receivers

8. Counterbalanced diameter measurement device bottom view

9. Counterbalanced diameter measurement device Top view

10. Analysis shows that the acceleration is constant by approximation (for small motions)

11. Assuming a constant acceleration, we can use basic equations of motion to see how b,D are related to time

12. Assuming a constant acceleration, the equations of motion can be used to derive expressions for b,D

13. Some basic math is needed to come up with an equation that relates the diameter D to the timing information Solving this equation gives an expression for the acceleration a Substitution of a in the following equation gives an expression for the diameter D p,b are constants: c = constant

14. The counterbalanced device has diverging light beams. An adaptation is needed to incorporate this

15. Comparison of true and measured diameters using sliding-edge device (12 repetitions per diameter)

16. Comparison of true and measured diameters using sliding-edge device (12 repetitions per diameter)

17. Comparison of true and measured diameters using counterbalanced device (24 repetitions per diameter)

18. Comparison of true and measured diameters using counterbalanced device (24 repetitions per diameter)

19. Conclusions • 1) a parallel light beam arrangement with constant object velocity, • 2) a diverging light beam arrangement with constant object velocity, • 3) a diverging light beam arrangement with constant object velocity and a sliding edge for guidance and • 4) a counterbalanced arrangement with a diverging beam and constant receiver acceleration • 1), 2) are not artificial concepts (not realizable)

20. 3) Diverging light beam arrangement with constant object velocity and a sliding edge for guidance • Simple in design • Depends on human capability to keep constant velocity during detection • Accuracy better than expected, but insufficient due to human operator

21. 4) Counterbalanced arrangement with a diverging light beams and constant receiver acceleration • Design more complicated • Model is valid • Dimensions and weight can be chosen arbitrarily • Measurements obtained solely from timing information • Friction is subsumed in timing and therefore not a factor!

22. What should you learn from this ? • Automate where you can • Make people’s lives easier • Get more reliable results • Costs are usually not a factor (compare wages!) • Model and analyze your system • Use model to analyse your data • This shows that your model is valid • You now really understand your instrument • you can design/optimize your instrument with the model! • You do not need calibration, just instrument characterization (that is determine constants for the model) • Keep everything digital! No more errors downstream • Find people smarter than yourself and work with them: multidisciplinary work always pays off

23. The End