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

Objective Main goal- integrate positional data w/ friction collection Using LabVIEW program Can be applied to microscopic or spectroscopic analysis of frictional events http://www.rpi.edu/dept/materials/COURSES/NANO/oja/nanocrys.gif

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

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 http://sine.ni.com/images/products/us/1sc567a1m.jpg

Outline Reciprocating stage Tribometer Circuit board Program structure Sample output Applications

Controller transforms Stage and Controller Aerotech ALS 130- 150 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

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

Strain Gauges Insulating flexible backing around an electric conductor Change in strain = deformity  change in resistance Wheatstone bridge measures change, signal board transmits voltage http://upload.wikimedia.org/wikipedia/en/4/40/StrainGaugeVisualization.png

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 http://i.cmpnet.com/planetanalog/2007/10/C0215- Figure1.gif

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 http://i.cmpnet.com/planetanalog/2007/10/C0215- Figure1.gif

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 (1.25-2.5 V)‏ Output voltage (Vg) nulled via potentiometers Int/ext excitation jumpers Vin potentiometer +Vin Cable to PCI +Vg Vg Potentiometer

Computer- LabVIEW program Ff Bending  ΔR Computer- LabVIEW program Signal board- Wheatstone bridge Microsoft ClipArt ΔR  ΔV ΔV  Ff Ff / FN = μ http://sine.ni.com/images/products/us/1sc567a1m.jpg

LabVIEW Programming environment Data acquisition/analysis focus Logging, graphing, etc. Graphical programming language Human-Machine Interface http://www.mathworks.com/company/newsletters/news_notes/dec04/images/mlint_srccode_wl.gif http://www.mezintel.com/LVCode01.png

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

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

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

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

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

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

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

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

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

Acknowledgements Nimel Theodore Kathy Wahl Irwin Singer Jeffrey Weimer SEAP ONR

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

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. http://www.uweb.engr.washington.edu/images/research/atrtutorial3.jpg

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

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