Fully automated absolute distance interferometer with micrometer accuracy

1. Fully automated absolute distance interferometer with micrometer accuracy using a Michelson interferometer and the iterative synthetic wavelength principle Liverpool John Moores University General Engineering Research Institute GERI Coherent and Electro-Optics Research Group CEORG Khaled Alzahrani

2. Research problem Large-scale manufacturing demands high accuracy measurements over long-range distances.

3. Research objective • Design, implement and automate an absolute distance interferometer with large nonambiguity range (NAR) (mm) and micrometer accuracy.

4. Optical absolute distance measurement methods

5. Relative optical interferometry ∆L

6. Absolute optical interferometry (ADI) ∆L FSI or MWI λa &λb = nm &λs=mm

7. ADI methods based on synthetic wavelength principle

8. The proposed algorithm (IVSWI)-1 • Basic principle? • Advantages of the system: • 1-Begins with a high uncertainty range (4mm) • 2-No target movement or continuous LoS is required. • 3-A single tunable laser used to reduce uncertainty from 4mm to 4μm. • 4-Multi-point and surface measurement capability. • 5-Can be adapted to the required uncertainty and accuracy. • 6-Uses commercially low cost equipment. Uncertainty range ±ɛ

9. The proposed algorithm steps (IVSWI)-2 ±𝜀 ±𝜀 ±𝜀 λs1 λs2 λs3

10. -𝜀 +𝜀 Nλs (N+1)λs f f f f ∆ϕ

11. Results-1 • Measurements Convergence 1 μm

12. Results-2 • Measurements Repeatability ±1.6 µm over 340mm

13. Results -3 • Measurements Accuracy 1.6 µm over 340mm

14. Results-4 • System Sensitivity

15. Optical isolator Beam splitter Screen Target arm Tunable laser head Reference arm Mt CCD camera Mr Motorized stage System Realisation • New Focus TLB-6309 ECDL (680.3-690.12 nm) • Bristol 621A Laser wavelength meter (0.0001 nm accuracy) • Prosilica GE 1380 CCD camera. • New Focus Linear Motor Stages XMS160 with ± 0.75 µm accuracy & XPS-8 motion controller with ± 0.5 µm accuracy. • Michelson interferometer.

16. Conclusion • A novel algorithm to measure absolute distance was designed, built and tested. • Measurement accuracy of 1.6µm over 340mm under uncontrolled lab conditions. • Measurements repeatability with ± 1.6 µm over 340mm. • Measurement sensitivity of 1 µm recorded with ± 0.5 µm. • Convergence time of 25 seconds.

17. Thank you