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

CONTENTS Introduction Types of Profilometer Working Principle 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 Profilometers Contact Profilometers

Non - Contact Profilometer 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 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 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

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 …

Non - Contact Profilometer 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 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 …

Working Principle of Profilometer (Non - Contact Optical Profilometer) 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) 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.

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

Modes of Operation (Non - Contact Optical Profilometer)

System Performances 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.

Surface Parameters 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 … Term Definition Use 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

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.

Profilometers @ IISc 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.

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

Measurement Examples 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

References Research Papers : Surface Finish Metrology Tutorial 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

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