How to measure surface roughness

1. Dept. of Mechanical Engineering, IISc
ME-255 : PRINCIPLES OF TRIBOLOGY
Surface Properties - Measurement Techniques
Profilometer
Presented by
Balasenthil D
Sr.No. 08993

2. CONTENTS
• Introduction
• Types of Profilometer
 Contact
 Non - Contact
• Working Principle
 Optical Principle Basics
 Modes of Operation
• System Performances
 Range , Resolution & Accuracy
• Surface Parameters
 Surface Topography & Amplitude Parameters
• Profilometers @ IISc
• Measurement Examples

3. INTRODUCTION
• Definition.
- A profilometer is a device used to measure the
roughness of a surface.
- Gives difference between the high and low point of
a surface in nanometres.
• Types of Profilometers.
 Non - Contact Profilometers
Contact Profilometers

4. • Optical Methods
 Vertical Scanning Interferometry
 Phase - Shifting Interferometry
 Differential Interference Contrast Microscopy
• Focus Detection Methods
 Intensity Detection
 Focus Variation
 Differential Detection
 Critical Angle
 Astigmatic Method
 Focault Method
 Confocal Microscopy
Contd…
Non - Contact Profilometer

5. • Pattern Projection Methods
 Fringe Projection
 Fourier Profilometry
 Moire
Non - Contact Profilometer
Contact & Pseudo – Contact Profilometer
• Stylus Profilometer
• Atomic Force Microscopy
• Scanning Tunneling Microscopy

6. Contact Profilometer
• Height from 10 nanometres to 1 millimetre
• Radius of diamond stylus from 20 nm to 25 μm
• Horizontal resolution is controlled by the scan speed
and data signal sampling rate.
Contd ...

7. Contact Profilometer
• Advantages & Disadvantages
 Acceptance & Easy to Use
Surface Independence
Resolution : The stylus tip radius can be as small
as 20 nanometres
 Direct Technique : No modelling required.
 Not suitable for very soft (or even liquid) and
easily damageable surface
 Very hard and damage surface can damage the
stylus
 Only 2D

8. Non - Contact Profilometer
• Uses beams of light to read a surface
• They shoot a beam out and measure the time it takes to
return.
• no wear since none of its parts touch anything
Contd …

9. • Advantages of optical profilometers
 Good Resolution: Vertical resolution is usually in the
nm level
 High Speed
 Reliability : cannot be damaged by surface wear or
careless operators
 Spot size or lateral resolution ranges from a few
micrometres down to sub micrometre.
Contd …
Non - Contact Profilometer

10. Non - Contact Profilometer
• Limitations:
 Limited by very high slopes, where the light is
reflected away from the objective, unless the slope
has enough texture to provide the light.
 Surface Modelling is required to convert the digital
code to human usable data.

11. Working Principle of Profilometer
(Non - Contact Optical Profilometer)
Contd …

12. • A light beam is split, reflecting from reference
(known/flat) & test material.
• Constructive and destructive interference occurs
• Forms the light and dark bands known as
interference fringes.
• The optical path differences are due to height
variances in the test surface.
Contd …
Working Principle of Profilometer
(Non - Contact Optical Profilometer)

13. Working Principle of Profilometer
(Non - Contact Optical Profilometer)
• Constructive interference areas as lighter and the
destructive interference areas as darker.
• Light to dark fringes above represents one-half a
wavelength of difference between the reference path
and the test path.
Contd …
Interference Image

14. Working Principle of Profilometer
(Non - Contact Optical Profilometer)
• From the above Interference Image:
 Lower portion is out of focus means less
interference.
 Greatest contrast means best focus.

15. • Phase Shifting Interferometry (PSI) Mode
• Vertical Scanning Interferometry (VSI) Mode
Contd …
Modes of Operation
(Non - Contact Optical Profilometer)

16. Modes of Operation
(Non - Contact Optical Profilometer)

17. • Range: Highest vertical distance the profiler can
measure.
• Resolution: Smallest distance the profiler can
accurately measure.
 Lateral Resolution
 Vertical Resolution
• Accuracy: How closely a measured value matches the
true value & can be obtained by frequent calibration.
System Performances

18. • Surface Topography: 3D representation of geometric
surface irregularities.
Contd …
Surface Parameters

19. • Roughness : Closely spaced irregularities
• Waviness : More widely spaced irregularities
• Error of Form : Long period & non cyclic deviations
• Flaws : Discrete & infrequent irregularities
• Roughness & Waviness comprise the Surface
Texture
Contd …
Surface Parameters

20. • Amplitude Parameters:
Contd …
Surface Parameters
Term Definition Use
Ra The roughness
average (mean
height)
Gives roughness of
the machine surface
Rq RMS roughness Describes the finish
of optical surface
Rp & Rv Max profile peak &
max profile valley
depth
Ra - info of friction &
wear
Rv - retaining of
lubricant
Rt Max height of
surface
Gives overall
roughness of the
surface

21. Surface Parameters
• Amplitude Parameters:
Term Definition Use
Rz Average max
height of the
profile
Evaluating
surface texture on
limited access
surfaces
Rsk Skewness -
measure of
asymmetry of the
profile about the
mean line.
Gives load
carrying capacity,
porosity &
characteristic of
non-conventional
machining
processes.

22. • Optical surface profilometer
 Make – Veeco NT1100
 Type – Non Contact type
 Principle of Operation
• VSI g interferometry (VSI)
• Phase-shifting interferometry (PSI).
 Range
• VSI – 2mm
• PSI – 160nm
 Resolution
• Vertical Resolution : PSI – 3Å & VSI – 3nm
 Lateral Resolution -- Function of magnification objective and
the detector array size you choose
Profilometers @ IISc

23. • Nanoscience Profilometer
 Film thickness measurement from 5 microns
down to 300 nm or less
 4 million pixel camera for high resolution
 Auto-range and auto-fringe-find for ease of use of
Single mode of operation over all scan ranges.
Profilometers @ IISc

24. Measurement Examples
• Some of the profiles obtained are shown below:
600 GRIT SIZE:
UPD (in 2D): UPD (in 3D)

25. • Surface of steel Block Reflection Intensity
• 3D Image
Measurement Examples

26. • Pit on a thin iron plate 2D image
• Plate thickness 0.7mm
• (Depth 0.14494mm)
Measurement Examples

27. • 3D image
Measurement Examples

28. • Research Papers :
 T.V.Vorburger, J.Raja.
Surface Finish Metrology Tutorial
June 1990
 WYKO Surface Profilers Technical Reference manual
September 1999, Version 2.2.1
• Webpage
 Profilometer, Wikipedia
http://en.wikipedia.org/wiki/Profilometer
References

29. THANK YOU