Query: In-situ measurement of surface roughness using chromatic confocal sensor

Candidate papers:

abstract: Abstract Surface roughness is an important characteristic which affects the quality, performance and lifetime of many types of industrial products, ranging from mechanical and biomedical parts to semiconductors and optics. In recent years, in situ measurement for surface roughness is increasingly demanded to provide real time feedback and reduce systematic errors of realignment and repositioning during manufacturing. Commercially available instruments, such as stylus profilometer, confocal laser scanning microscope and coherence scanning interferometer, are limited to a relatively low measurement speed and difficult for in situ measurement. In this paper, an in house developed surface measuring system using chromatic confocal sensor was integrated into a mass finishing cell to perform in situ and non contact surface roughness measurement. The surface roughness parameters are calculated and evaluated according to ISO 4287 and ISO 4288. From the preliminary experiments, it was verified that the relative error of surface roughness measurements can be kept within 5%
author_names: Shaowei Fu

Wei Sheng Kor

Fang Cheng

Leong Keey Seah
title: In situ measurement of surface roughness using chromatic confocal sensor
year: 2020

abstract: Roughness measurement is of highlighted importance in production for describing the quality control of manufacturing processes for the functional, tribological, etc. properties of the surfaces of parts. In the last 15 years or so the areal roughness studied on topographies has also become more common, as it provides a more accurate and detailed characterization of the surfaces. However, with relatively little experience and different technical conditions, topographies are analyzed differently. Sometimes 3D topography is used only as an illustration; however, spatial roughness measurement can provide much more information. The effect of measurement speed and point density during roughness measurement on the areal roughness was investigated using a confocal chromatic sensor.
author_names: Antal Nagy
title: INFLUENCE OF MEASUREMENT SETTINGS ON AREAL ROUGHNESS WITH CONFOCAL CHROMATIC SENSOR ON FACE MILLED SURFACE
year: 2020

abstract: Laser micromachining is a prominent method of fabricating microchannels on a wide range of metals, non metals, and polymers for biomedical, chemical, fuel cell applications for flow of liquids and gases in predefined path for microfluidic systems. In situ measurement of precise geometrical features on fabricated channels is required to avoid systematic errors. The geometrical parameters such as width, depth, aspect ratio of microchannels are the most important attributes which greatly influence quality of microchannels. This paper proposes in situ measurement of fabricated microchannels on EN 31 steel using LMM by integrating confocal sensor with micromachining system. Geometrical features have been measured with confocal sensor which is further employed to evaluate aspect ratio (AR) Obtained results are compared with microscopic images of the samples for geometrical features. Confocal sensor used to measure surface roughness. 3D profilometer is used to analyse MRR (based on measured cross section area) and oxidised zone width surrounded to microchannel.
author_names: Ashish Kumar Sahu

Faiz Iqbal

Aman Kumar

Sunil Jha
title: In situ geometric measurement of microchannels on EN31 steel by laser micromachining using confocal sensor
year: 2019

abstract: In this research a confocal chromatic point sensor was implemented in a desktop sized machine tool. The sensor was used to detect the surface in z direction. Data from the machine control of the x and y axes is extracted and combined with the z information of the sensor to directly scan surfaces. With the presented sensor, micro structures as small as 5 mm can be characterized. Based on the possibilities of this measuring system, face milling before the actual micro machining can be avoided by determining tilts and waviness of the workpiece. Also the effective tool diameter can be determined and compensated. After machining, the structure can be measured for quality control. Based on this measurement system, a micro machining process was developed broadening the potential for the use of desktop sized machine tools.
author_names: Christopher Muller

Ingo G Reichenbach

Martin Bohley

Jan C Aurich
title: In Situ Topology Measurement of Micro Structured Surfaces with a Confocal Chromatic Sensor on a Desktop Sized Machine Tool
year: 2016

abstract: The characterization of surface topographic features on a component is typically quantified using two dimensional roughness descriptors which are captured by off line desktop instruments. Ideally any measurement system should be integrated into the manufacturing process to provide in situ measurement and real time feedback. A non contact in situ surface topography measuring system is proposed in this paper. The proposed system utilizes a laser confocal sensor in both lateral and vertical scanning modes to measure the height of the target features. The roughness parameters are calculated in the developed data processing software according to ISO 4287. To reduce the inherent disadvantage of confocal microscopy, e.g. scattering noise at steep angles and background noise from specular reflection from the optical elements, the developed system has been calibrated and a linear correction factor has been applied in this study. A particular challenge identified for this work is the in situ measurement of features generated by a robotized surface finishing system. The proposed system was integrated onto a robotic arm with the measuring distance and angle adjusted during measurement based on a CAD model of the component in question. Experimental data confirms the capability of this system to measure the surface roughness within the Ra range of 0.2 7 mm (bandwidth lc/ls of 300) with a relative accuracy of 5%
author_names: Shaowei Fu

Fang Cheng

Tegoeh Tjahjowidodo

Yu Zhou

David Butler
title: A Non Contact Measuring System for In Situ Surface Characterization Based on Laser Confocal Microscopy
venue: Sensors
year: 2018

abstract: Introduction State of the art machining technologies enable the manufacturing of complex optical surfaces as aspheres and freeforms. To ensure the high quality demands of innovative optical surfaces, correction loops are implemented within the manufacturing process. These loops are based on metrology data. To avoid scratches on sensitive surfaces, non contact measurements are preferable. The classical approach of noncontact testing of optical surfaces is interferometry. However, the testing is complex because Computer Generated Holograms (CGH) have to be used to compensate the wave front differences between reference optic and test part [1] The results of these measurements are highly accurate, but not flexible and considerably more expensive, since each surface needs its own CGH. In situ measurements with alternative non contact measurement systems could reduce time and costs of the manufacturing process. Besides, tensions from clamping have no influence on the measurement, because in situ metrology without repositioning the workpiece works.
author_names: Confocal Sensor

Ralf Steinkopf

S Zwick

Andreas Gebhardt

Stefan Dr Risse

Ramona Eberhardt
title: IN SITU TESTING OF A FREEFORM OPTIC WITH A CHROMATIC
year: 2013

abstract: A chromatic confocal microscope (CCM) is a high dynamic range noncontact distance measurement sensor; it is based on a hyperchromatic lens. The vast majority of commercial CCMs use refractive based chromatic dispersion to chromatically code the optical axis. This approach significantly limits the range of applications and performance of the CCM. In order to be a suitable alternative to a laser triangulation gauge and laser encoder, the performance of the CCM must be improved. In this paper, it is shown how hybrid aspheric diffractive (HAD) lenses can bring the CCM to its full potential by increasing the dynamic range by a factor of 2 and the resolution by a factor of 5 while passively athermizing and increasing the light throughput efficiency of the optical head [M. Rayer, U.S. patent 1122052.2 (2011) The only commercially suitable manufacturing process is single point diamond turning. However, the optical power carried by the diffractive side of a hybrid aspheric diffractive lens is limited by the manufacturing process. A theoretical study of manufacturing losses has revealed that the HAD configuration with the highest diffraction efficiency is for a staircase diffractive surface (SDS) SDS lenses have the potential to reduce light losses associated with manufacturing limits by a factor of 5 without increasing surface roughness, allowing scalar diffraction limited optical design with a diffractive element.
author_names: Mathieu Rayer

Daniel Mansfield
title: Chromatic confocal microscopy using staircase diffractive surface.
venue: Applied optics
year: 2014

abstract: Evaluation of Surface Roughness is a crucial requirement in analyzing components life and performances. In analyzing Surface finish, Ra, Rz and Rq are the most widely used parameters in terms of 2D roughness and Sa,Sz and Sq with respect to 3D parameters. Assessment of Surface roughness involves various contact and noncontact methods. This work deals with a new surface inspection strategy applying a newly developed MATLAB algorithm for the BEMRF process. Conventionally the finished workpiece is unloaded for inspection thus generating a loss of production time and hindering the automation of the process. This work attempts to minimize the loss of time in frequent inspection of the finished workpiece by using a laser confocal chromatic sensor which is an integral part of the BEMRF setup. The laser confocal sensor measures the data points (i.e. heights of the surface asperities) of the surface there by aiding in surface finish evaluation. The Surface data points are analyzed by the proposed MATLAB algorithms. The MATLAB algorithms evaluated the data points, taking the data points as input and generated 2D parameters (Ra, Rz, Rq) and 3D parameters (Sa, Sq, Sz) as outputs. The results were compared with that of the standard methods of roughness measurement and were found to be marginally superior over them.
author_names: Radhik Rammohan

M Omkumar

Faiz Iqbal
title: Evaluation of 2D and 3D Surface Roughness Parameters by MATLAB Algorithm in Ball End Magnetorheological Finishing Machine
year: 2017

abstract: Chromatic confocal spectral interferometry (CCSI) is a hybrid method for fast topography measurement, which combines the advantages of the interferometric gain and accuracy with the robustness of confocal microscopy. The CCSI principle provides a single shot measurement of depth while offering a higher lateral resolution than commonly used spectral interferometers. This contribution is focused on the modeling and simulation of a CCSI sensor for measuring rough surfaces, based on sequential and non sequential ray tracing. With the simulation, the influence of surface roughness, surface reflectivity, and surface contamination on reliability of the sensor can be estimated.
author_names: Wolfram Lyda

David Fleischle

Tobias Haist

Wolfgang Osten
title: Chromatic confocal spectral interferometry for technical surface characterization
venue: Optical Engineering Applications
year: 2009

abstract: Both contact and non contact probes are often used in dimensional metrology applications, especially for roughness, form and surface profile measurements. To perform such kind of measurements with a nanometer level of accuracy, LNE (French National Metrology Institute (NMI) has developed a high precision profilometer traceable to the SI meter definition. The architecture of the machine contains a short and stable metrology frame dissociated from the supporting frame. It perfectly respects Abbe principle. The metrology loop incorporates three Renishaw laser interferometers and is equipped either with a chromatic confocal probe or a tactile probe to achieve measurements at the nanometric level of uncertainty. The machine allows the in situ calibration of the probes by means of a differential laser interferometer considered as a reference. In this paper, both the architecture and the operation of the LNE's high precision profilometer are detailed. A brief comparison of the behavior of the chromatic confocal and tactile probes is presented. Optical and tactile scans of an aspherical surface are performed and the large number of data are processed using the L BFGS (Limited memory Broyden Fletcher Goldfarb Shanno) algorithm. Fitting results are compared with respect to the evaluated residual errors which reflect the form defects of the surface.
author_names: E Nadim

Nouira Hichem

Anwer Nabil

Damak Mohamed

Gibaru Olivier
title: Comparison of tactile and chromatic confocal measurements of aspherical lenses for form metrology
year: 2014