profilometer

Dept. of Mechanical Engineering, IISc

ME-255 : PRINCIPLES OF TRIBOLOGY

Surface Properties - Measurement TechniquesProfilometer

Presented by Balasenthil D Sr.No. 08993

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

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 ProfilometersContact Profilometers

• 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

• Pattern Projection Methods Fringe Projection Fourier Profilometry Moire

Non - Contact Profilometer

Contact & Pseudo – Contact Profilometer

• Stylus Profilometer• Atomic Force Microscopy• Scanning Tunneling Microscopy

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 ...

Contact Profilometer

• Advantages & Disadvantages

Acceptance & Easy to UseSurface IndependenceResolution : 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

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 …

• 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

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.

Working Principle of Profilometer(Non - Contact Optical Profilometer)

Contd …

• 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)

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

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.

• Phase Shifting Interferometry (PSI) Mode• Vertical Scanning Interferometry (VSI) Mode

Contd …

Modes of Operation(Non - Contact Optical Profilometer)

Modes of Operation(Non - Contact Optical Profilometer)

• 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

• Surface Topography: 3D representation of geometric surface irregularities.

Contd …

Surface Parameters

• 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

• Amplitude Parameters:

Contd …

Surface Parameters

Term Definition UseRa 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 & wearRv - retaining of lubricant

Rt Max height of surface

Gives overall roughness of the surface

Surface Parameters

• Amplitude Parameters:

Term Definition UseRz 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.

• 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

• 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

Measurement Examples

• Some of the profiles obtained are shown below: 600 GRIT SIZE:

UPD (in 2D): UPD (in 3D)

• Surface of steel Block Reflection Intensity

• 3D Image

Measurement Examples

• Pit on a thin iron plate 2D image

• Plate thickness 0.7mm• (Depth 0.14494mm)

Measurement Examples

• 3D image

Measurement Examples

• 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

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