1 Introduction
2 Design of the on-machine FVM sensor
2.1 FVM working principle
2.2 Design of the on-machine FVM sensor
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Maximum travel is 20 mm.
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Encoder resolution is less than 25 nm.
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Positioning accuracy is less than 1 μm.
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Positioning repeatability is less than 250 nm.
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Maximum overall cylindrical dimensions are 80 mm diameter and 250 mm length.
3 Step height measurement and measurement noise comparisons with a calibrated artefact
Measurements | On-machine sensor | On-machine sensor operated in a controlled laboratory | Off-line FVM |
---|---|---|---|
Step height (mm) | Step height (mm) | Step height (mm) | |
1 | 0.9932 | 0.9994 | 0.9995 |
2 | 0.9954 | 0.9991 | 0.9995 |
3 | 0.9923 | 0.9993 | 0.9994 |
Standard error of the mean | 0.00092 | 0.00009 | 0.00003 |
Subtraction method (z) | On-machine sensor | On-machine sensor operated in a controlled laboratory | Off-line FVM |
---|---|---|---|
SqNoise (μm) | SqNoise (μm) | SqNoise (μm) | |
1 | 0.73 | 0.37 | 0.14 |
2 | 0.71 | 0.39 | 0.16 |
3 | 0.72 | 0.39 | 0.15 |
Standard error of the mean | 0.01 | 0.01 | 0.01 |
4 Experiment setup for on-machine measurement of micro-dimples and microchannels
Pattern | Pitch (μm) | Laser power (W) | Exposure time (s) | Feed rate (mm/min) |
---|---|---|---|---|
Dimple | 200 | 20 | 0.4 | 200 |
Channel | 200 | 20 | 0.4 | 200 |
5 On-machine measurement results and their comparison with off-line measurements
Patterns | Off-line FVM, depth (μm) | On-machine FVM, depth (μm) | Depth difference (μm) | |
---|---|---|---|---|
Channel | 1 | − 15.0 | − 14.9 | 0.1 |
2 | − 18.5 | − 16.5 | 2.0 | |
3 | − 18.0 | − 14.5 | 3.5 | |
4 | − 19.0 | − 15.5 | 3.5 | |
5 | − 8.6 | − 9.6 | 1.0 | |
6 | − 13.0 | − 17.5 | 4.5 | |
Mean (μm) | − 15.4 | − 14.8 | 2.4 | |
Std. dev. (μm) | 4.0 | 2.7 | 1.7 | |
Dimple | 1 | − 58.0 | − 52.0 | 6.0 |
2 | − 45.0 | − 43.0 | 2.0 | |
3 | − 38.5 | − 36.5 | 2.0 | |
Mean (μm) | − 47.2 | − 43.8 | 3.3 | |
Std. dev. (μm) | 9.9 | 7.8 | 2.3 |
6 Discussion on uncontrolled environmental noise during on-machine measurements
Measurements | On-machine FVM | Off-line FVM | |
---|---|---|---|
z position (μm) | z position (μm) | ||
1 | 0.094 | 0.008 | |
2 | 0.105 | 0.011 | |
3 | 0.054 | 0.017 |