1. Computer Automation of a Tribometer
Michael Eng, TJHSST
With Nimel Theodore, Kathy Wahl
NRL Code 6176

2. Objective Main goal- integrate positional data w/ friction collection
Using LabVIEW program
Can be applied to microscopic or spectroscopic analysis of frictional events

3. Implementation Develop LabVIEW data collection program
Interface w/ tribometer
Strain gauges, circuit board, etc.
Integrate w/ FTIR
In situ to minimize contamination of samples

4. Implementation Ff Tribometer arm bends Tribometer + stage move
Signal board converts signal to data
Computer- LabVIEW program reads, graphs data
Microsoft ClipArt Ff M
Tribometer + stage move

5. Outline Reciprocating stage Tribometer Circuit board Program structure
Sample output
Applications

6. Controller transforms
Stage and Controller
Aerotech ALS stage
Moves tribo arm
Soloist motion controller
Processes stage’s digital voltage signal into position
Stage sends voltage
signal to controller
Controller transforms
signal into position
value
Computer receives
position value via USB

7. Tribometer Arm + probe 4 strain gauges
Moving stage/platform- 1-D motion
Motion controller sends position to computer as +V M

8. Strain Gauges Insulating flexible backing around an electric conductor
Change in strain = deformity  change in resistance
Wheatstone bridge measures change, signal board transmits voltage

9. Wheatstone Bridges Full bridge used- R1=R2=R3=R4=R
Vg = [(# used arms)/4] * GF * ε * Vin
GF * ε = ΔR/R
Vg = (ΔR/R) * Vin
For example,
If R = 1000 Ω, Vin = 2.5 V, then
Vg = 1 mV for a 500g force
Lower resistance = higher output
Figure1.gif

10. Wheatstone Bridges Full bridge used- R1=R2=R3=R4=R
Vg = [(# used arms)/4] * GF * ε (strain) * Vin
GF * ε = ΔR/R
Vg = (ΔR/R) * Vin
Lower resistance = higher output
Figure1.gif

11. Signal Conditioning Board
Figure 2-1. SC-2043-SG Parts Locator Diagram- NI manual
Powers strain gauges, receives strain signal from strain gauges
Excitation voltage (Vin) controlled via potentiometers ( V)‏
Output voltage (Vg) nulled via potentiometers
Int/ext excitation jumpers
Vin potentiometer
+Vin
Cable to PCI
+Vg
Vg Potentiometer

12. Computer- LabVIEW programFf
Bending  ΔR
Computer- LabVIEW program
Signal board- Wheatstone bridge
Microsoft ClipArt
ΔR  ΔV
ΔV  Ff
Ff / FN = μ

13. LabVIEW Programming environment Data acquisition/analysis focus
Logging, graphing, etc.
Graphical programming language
Human-Machine Interface

14. Data structure Input voltage signals Position data Friction data
stage and
signal conditioning board
Position data
Friction data
Convert w/ calibration
Converted by
motion controller

15. Program structure alt Run Stage/controller: Oscillate DAQ card:
Collect
Receive, convert
positional data
frictional data
Record as (x, y) pts,
graph

16. Program Structure Run Stage/controller: Oscillate DAQ card: Collect
Receive, convert
friction data
Calculate position data
w/ # data points collected, start point
Record as (x, y) pts, graph
Re-sync every half-cycle

17. Calibration Arm turned on side Multiple loads applied
Linear regression
Y-intercept, slope convert voltage to friction

18. Friction vs. cycle Friction (y) vs. cycle (x)
Allows analysis over many cycles
Account for debris, reactions, etc.

19. Friction vs. position Friction (y) vs. position (x) Updates real-time
Provides coordinates of friction anomalies

20. Intensity plot Pseudo-3D
Friction (color) vs. position (y) vs. cycle (x)
Combines previous two graphs

21. Conclusion LabVIEW program Integrates positional and frictional data
Extracts data as CSV and TXT files
Graphs friction vs. cycle, friction vs. position, friction vs. position vs. cycle

22. Future Applications Integrate with microscopy or spectroscopy
Use coordinates of frictional event in other analysis instrument
Example- FTIR of nanocrystalline diamond films

23. Acknowledgements Nimel Theodore Kathy Wahl Irwin Singer Jeffrey Weimer
SEAP
ONR

24. Error analysis
1 cycle
50 mm track
20 micron intervals
Loop structure?

25. FTIR Fourier Transform Infrared Spectroscopy Multiple reflection ATR
Time domain  wavelength domain
I0, If measured- (I0 – If)/I0 = %Absorbance
Multiple reflection ATR
Enables solid/liquid samples to be measured while maximizing sample reproducibility and minimizing preparation
Detects bonds - C-H, C-O, H-O, etc.

26. Current status Implementations Strain gauges
Oscillation
Position/configuration/voltage logging
Pause/resume
Improved UI
Strain gauges
Wiring, hooking up, calibrating, etc.
Position and voltage logging
Running tests to optimize speed and accuracy
Time calculator
Graphing VI

27. Plans Run tests- get graphs Data logs in binary and .csv formats
Optimize settings for speed and accuracy
Maximize data resolution- ~1 micron
Implement FTIR