Taufiq Widjanarko | The University of Nottingham (original) (raw)

Papers by Taufiq Widjanarko

A new approach to the absolute measurement of two-dimensional optical path differences is present... more A new approach to the absolute measurement of two-dimensional optical path differences is presented in this thesis. The method, which incorporates a white light interferometer and a hyperspectral imaging system, is referred to as Hyperspectral Interferometry. A prototype of the Hyperspectral Interferometry (HSI) system has been designed, constructed and tested for two types of measurement: for surface profilometry and for depth-resolved displacement measurement, both of which have been implemented so as to achieve single shot data acquisition. The prototype has been shown to be capable of performing a single-shot 3-D shape measurement of an optically-flat step-height sample, with less than 5% difference from the result obtained by a standard optical (microscope) based method. The HSI prototype has been demonstrated to be able to perform single-shot measurement with an unambiguous 352 (m depth range and a rms measurement error of around 80 nm. The prototype has also been tested to perform measurements on optically rough surfaces. The rms error of these measurements was found to increase to around 4× that of the smooth surface. For the depth-resolved displacement field measurements, an experimental setup was designed and constructed in which a weakly-scattering sample underwent simple compression with a PZT actuator. Depth-resolved displacement fields were reconstructed from pairs of hyperspectral interferograms. However, the experimental results did not show the expected result of linear phase variation with depth. Analysis of several possible causes has been carried out with the most plausible reasons being excessive scattering particle density inside the sample and the possibility of insignificant deformation of the sample due to insufficient physical contact between the transducer and the sample.

Epj Web of Conferences, 2010

We propose a method that we call Hyperspectral Interferometry (HSI) to resolve the 2π phase unwra... more We propose a method that we call Hyperspectral Interferometry (HSI) to resolve the 2π phase unwrapping problem in the analysis of interferograms recorded with a narrow-band light source. By using a broad-band light source and hyperspectral imaging system, a set of interferograms at different wavenumbers are recorded simultaneously on a high resolution image sensor. These are then assembled to form a three-dimensional intensity distribution. By Fourier transformation along the wavenumber axis, an absolute optical path difference is obtained for each pixel independently of the other pixels in the field of view. As a result, interferograms with spatially distinct regions are analysed as easily as continuous ones. The approach is illustrated with a HSI system to measure 3-D profiles of optically smooth or rough surfaces. Compared to existing profilometers able to measure absolute path differences, the single shot nature of the approach provides greater immunity from environmental disturbance.

Measurement Science and Technology, May 25, 2010

We propose a method that we call Hyperspectral Interferometry (HSI) to resolve the 2 phase unwra... more We propose a method that we call Hyperspectral Interferometry (HSI) to resolve the 2 phase unwrapping problem in the analysis of interferograms recorded with a narrow-band light source. By using a broad-band light source and hyperspectral imaging system, a set of interferograms at different wavenumbers are recorded simultaneously on a high resolution image sensor. These are then assembled to form a three-dimensional intensity distribution. By Fourier transformation along the wavenumber axis, an absolute optical path difference is obtained for each pixel independently of the other pixels in the field of view. As a result, interferograms with spatially distinct regions are analysed as easily as continuous ones. The approach is illustrated with a HSI system to measure 3-D profiles of optically smooth or rough surfaces. Compared to existing profilometers able to measure absolute path differences, the single shot nature of the approach provides greater immunity from environmental disturbance.

Journal of the Optical Society of America, Aug 19, 2020

Metal powder bed fusion (PBF) methods need in-process measurement methods to increase user confid... more Metal powder bed fusion (PBF) methods need in-process measurement methods to increase user confidence and encourage further adoption in high-value manufacturing sectors. In this paper, a novel measurement method for PBF systems is proposed that uses multi-view fringe projection to acquire high-resolution surface topography information of the powder bed. Measurements were made using a mock-up of a commercial PBF system to assess the system's accuracy and precision in comparison to conventional single-view fringe projection techniques for the same application. Results show that the multi-view system is more accurate, but less precise, than single-view fringe projection on a point-by-point basis. The multi-view system also achieves a high degree of surface coverage by using alternate views to access areas not measured by a single camera.

Augmented and Mixed Reality promises another leap forward in productivity and lifestyle, offering... more Augmented and Mixed Reality promises another leap forward in productivity and lifestyle, offering benefits with a magnitude and impact matching that of the introduction of smartphones. However, to enable this, many significant technical challenges must be overcome. Here we review the state of the art, identifying key challenges established in the literature to consumer-wearable devices. In particular, we discuss: vergence-accommodation conflict (the detrimental effect of overlays that are optically inconsistent with the real-world objects they augment), the need to present overlays visible against the vast dynamic range that the human eye can process, and constraints surrounding the scalability and cost of manufacture of optics. We demonstrate that digital holography as a display mechanism not only provides an effective solution to the aforementioned challenges, but also that various hardware requirements become far less stringent. By operating in the Fourier Domain, holographic dis...

Laser (profile) scanners (LS) have been widely used in industry for 3D shape measurement. However... more Laser (profile) scanners (LS) have been widely used in industry for 3D shape measurement. However, commercially available scanners are costly. They are also less flexible as the components of the device are permanently fixed in a sealed housing, whereas altering setup geometry can improve the device’s height resolution. This paper describes the design and construction of a LS setup from generic off-the-shelf components; a digital camera, laser line module, optical bandpass filter and a machine vision library software for image to 3D point cloud conversion. The performance of the setup is assessed by measuring a set of step height samples ranging from 50 μm to 1 mm. LS measurement performance is determined by comparing measurements of the step heights with those taken from a Coordinate Measurement Machine (CMM). Average measurement difference between the setup and CMM is 20.29 μm with repeatability of 0.60 μm. The highest percentage error for the smallest tested step height suggests ...

2014 13th International Conference on Control Automation Robotics & Vision (ICARCV), 2014

ABSTRACT Recent advances in automation and sensor technology have enabled the use of industrial r... more ABSTRACT Recent advances in automation and sensor technology have enabled the use of industrial robots for complex tasks that require intelligent decision making. Vision sensors have been the most successfully used sensor in many high value industrial applications. Over the recent years, weld seam tracking has been a topic of interest, as most of the existing robotic welding systems operate on basis of pre-programmed instructions. Such automated systems are incapable of adapting to unexpected variations in the seam trajectory or part fit-up. Applications such as tungsten inert gas (TIG) welding of aerospace components require high tolerances and needs intelligent decision making. Such decision making procedure has to be based on the weld groove geometry at any instance. In this study, a novel algorithm along with an automated system was developed for estimating the joint profile and path tracking of a three dimensional (3D) weld groove. A real-time position based closed-loop system was developed with a six axis industrial robot and a laser triangulation based sensor. The system was capable of finding the 3D weld joint profile and position in real-time, and make intelligent decisions accordingly. Raw data from a vision sensor was processed through a novel algorithm to obtain X and Z co-ordinates at an accuracy of 8.3μm and 43μm respectively at an acquisition speed of 2.5 profiles per second. The algorithm was also capable of measuring the weld gaps with an accuracy of 28μm. Finally, the developed system was successfully used for three dimensional seam tracking, and demonstrates an accuracy of ±0.5mm at a tracking a speed of 2mm/s.

2014 13th International Conference on Control Automation Robotics & Vision (ICARCV), 2014

ABSTRACT Recent advances in automation and sensor technology have enabled the use of industrial r... more ABSTRACT Recent advances in automation and sensor technology have enabled the use of industrial robots for complex tasks that require intelligent decision making. Vision sensors have been the most successfully used sensor in many high value industrial applications. Over the recent years, weld seam tracking has been a topic of interest, as most of the existing robotic welding systems operate on basis of pre-programmed instructions. Such automated systems are incapable of adapting to unexpected variations in the seam trajectory or part fit-up. Applications such as tungsten inert gas (TIG) welding of aerospace components require high tolerances and needs intelligent decision making. Such decision making procedure has to be based on the weld groove geometry at any instance. In this study, a novel algorithm along with an automated system was developed for estimating the joint profile and path tracking of a three dimensional (3D) weld groove. A real-time position based closed-loop system was developed with a six axis industrial robot and a laser triangulation based sensor. The system was capable of finding the 3D weld joint profile and position in real-time, and make intelligent decisions accordingly. Raw data from a vision sensor was processed through a novel algorithm to obtain X and Z co-ordinates at an accuracy of 8.3μm and 43μm respectively at an acquisition speed of 2.5 profiles per second. The algorithm was also capable of measuring the weld gaps with an accuracy of 28μm. Finally, the developed system was successfully used for three dimensional seam tracking, and demonstrates an accuracy of ±0.5mm at a tracking a speed of 2mm/s.

A rigorous two-dimensional (2D) model of electromagnetic surface scatter has been developed, base... more A rigorous two-dimensional (2D) model of electromagnetic surface scatter has been developed, based on a boundary element method (BEM) established by Simonsen [1]. Simulated far-field scatter is compared to that measured from a laser scatterometer for a sinusoidal grating, with a mean difference of 3% of the peak intensity.

The combination of white light interferometry with hyperspectral imaging ('hyperspectral interfer... more The combination of white light interferometry with hyperspectral imaging ('hyperspectral interferometry') is a recently proposed technique for single-shot measurement of 3-D surface profiles. We consider for the first time its application to speckled wavefronts from optically rough surfaces. The intensity versus wavenumber signal at each pixel provides unambiguous range information despite the speckle-induced random phase shifts. Experimental results with samples undergoing controlled rigid body translation demonstrate a measurement repeatability of 460 nm for a bandwidth of approximately 30 nm. Potential applications include roughness measurement and coordinate measurement machine probes where rapid data acquisition in non-cooperative environments is essential.

Journal of the Optical Society of America A

Metal powder bed fusion (PBF) methods need in-process measurement methods to increase user confid... more Metal powder bed fusion (PBF) methods need in-process measurement methods to increase user confidence and encourage further adoption in high-value manufacturing sectors. In this paper, a novel measurement method for PBF systems is proposed that uses multi-view fringe projection to acquire high-resolution surface topography information of the powder bed. Measurements were made using a mock-up of a commercial PBF system to assess the system's accuracy and precision in comparison to conventional single-view fringe projection techniques for the same application. Results show that the multi-view system is more accurate, but less precise, than single-view fringe projection on a point-by-point basis. The multi-view system also achieves a high degree of surface coverage by using alternate views to access areas not measured by a single camera.

Symmetry

The authors would like to make the following addenda and correction to their paper [...]

Symmetry

We consider the interactions of traveling localized wave solutions with a vertex in a star graph ... more We consider the interactions of traveling localized wave solutions with a vertex in a star graph domain that describes multiple Josephson junctions with a common/branch point (i.e., tricrystal junctions). The system is modeled by the sine-Gordon equation. The vertex is represented by boundary conditions that are determined by the continuity of the magnetic field and vanishing total fluxes. When one considers small-amplitude breather solutions, the system can be reduced into the nonlinear Schrödinger equation posed on a star graph. Using the equation, we show that a high-velocity incoming soliton is split into a transmitted component and a reflected one. The transmission is shown to be in good agreement with the transmission rate of plane waves in the linear Schrödinger equation on the same graph (i.e., a quantum graph). In the context of the sine-Gordon equation, small-amplitude breathers show similar qualitative behaviors, while large-amplitude ones produce complex dynamics.

In this report two binary image thresholding methods are briefly described. Both methods assume t... more In this report two binary image thresholding methods are briefly described. Both methods assume that the image consists only two major parts: object (foreground) and background. First method is Otsu method. Threshold value in this method is calculated by minimizing the within-group variance. This method, however, has a possibility to falsely detect the background as foreground. Second method reported in

Optics Letters, 2012

Received Month X, XXXX; revised Month X, XXXX; accepted Month X, XXXX; posted Month X, XXXX (Doc.... more Received Month X, XXXX; revised Month X, XXXX; accepted Month X, XXXX; posted Month X, XXXX (Doc. ID XXXXX); published Month X, XXXX

Laser (profile) scanners (LS) have been widely used in industry for 3D shape measurement. However... more Laser (profile) scanners (LS) have been widely used in industry for 3D shape measurement. However, commercially available scanners are costly. They are also less flexible as the components of the device are permanently fixed in a sealed housing, whereas altering setup geometry can improve the device's height resolution. This paper describes the design and construction of a LS setup from generic off- The-shelf components; a digital camera, laser line module, optical bandpass filter and a machine vision library software for image to 3D point cloud conversion. The performance of the setup is assessed by measuring a set of step height samples ranging from 50 μm to 1 mm. LS measurement performance is determined by comparing measurements of the step heights with those taken from a Coordinate Measurement Machine (CMM). Average measurement difference between the setup and CMM is 20.29 μm with repeatability of 0.60 μm. The highest percentage error for the smallest tested step height suggests the setup can measure objects with feature variation down to 0.1 mm.

Authors: Taufiq Widjanarko, John R.Hodgson, Peter Kinnell and Michael R.Jackson

Proceedings of the 13th International Conference on Control Automation Robotics & Vision (ICARCV), 2014 pp.1368,1372, Singapore 10-12 Dec. 2014

Recent advances in automation and sensor technology have enabled the use of industrial robots for... more Recent advances in automation and sensor technology have enabled the use of industrial robots for complex tasks that require intelligent decision making. Vision sensors have been the most successfully used sensor in many high value industrial applications. Over the recent years, weld seam tracking has been a topic of interest, as most of the existing robotic welding systems operate on basis of pre-programmed instructions. Such automated systems are incapable of adapting to unexpected variations in the seam trajectory or part fit-up. Applications such as tungsten inert gas (TIG) welding of aerospace components require high tolerances and needs intelligent decision making. Such decision making procedure has to be based on the weld groove geometry at any instance. In this study, a novel algorithm along with an automated system was developed for estimating the joint profile and path tracking of a three dimensional (3D) weld groove. A real-time position based closed-loop system was developed with a six axis industrial robot and a laser triangulation based sensor. The system was capable of finding the 3D weld joint profile and position in real-time, and make intelligent decisions accordingly. Raw data from a vision sensor was processed through a novel algorithm to obtain X and Z co-ordinates at an accuracy of 8.3μm and 43μm respectively at an acquisition speed of 2.5 profiles per second. The algorithm was also capable of measuring the weld gaps with an accuracy of 28μm. Finally, the developed system was successfully used for three dimensional seam tracking, and demonstrates an accuracy of ±0.5mm at a tracking a speed of 2mm/s.

Authors: R.P.Manorathna, P.Phairatt, P.Ogun, T.Widjanarko, M.Chamberlain, L.Justham, S.Marimuthu and M.R.Jackson

The measurement of surface profile is a vital quality control procedure in many industries. For s... more The measurement of surface profile is a vital quality control procedure in many industries. For small objects (dimensions below ~10 mm) with rough or discontinuous surfaces, scanning white light interferometry (SWLI) is currently the method of choice. However, with a resolution of ∼1 nm, vibration during the scan induces motion artifacts and prevents its routine use on the production line. We present a system that avoids temporal scanning by spectrally splitting the white light interferogram into a set of interferograms at different wavenumbers which are recorded simultaneously on an image sensor. The system essentially consists of an interferometer coupled to a single-shot hyperspectral imaging system. Fourier transformation along the wavenumber axis provides an absolute optical path difference for each point in the field of view, a procedure which is robust even on optically rough surfaces. Height maps with a spatial resolution of 19×19 pixels and a measurement accuracy of ∼460 nm are demonstrated.

A new approach to the absolute measurement of two-dimensional optical path differences is present... more A new approach to the absolute measurement of two-dimensional optical path differences is presented in this thesis. The method, which incorporates a white light interferometer and a hyperspectral imaging system, is referred to as Hyperspectral Interferometry. A prototype of the Hyperspectral Interferometry (HSI) system has been designed, constructed and tested for two types of measurement: for surface profilometry and for depth-resolved displacement measurement, both of which have been implemented so as to achieve single shot data acquisition. The prototype has been shown to be capable of performing a single-shot 3-D shape measurement of an optically-flat step-height sample, with less than 5% difference from the result obtained by a standard optical (microscope) based method. The HSI prototype has been demonstrated to be able to perform single-shot measurement with an unambiguous 352 (m depth range and a rms measurement error of around 80 nm. The prototype has also been tested to perform measurements on optically rough surfaces. The rms error of these measurements was found to increase to around 4× that of the smooth surface. For the depth-resolved displacement field measurements, an experimental setup was designed and constructed in which a weakly-scattering sample underwent simple compression with a PZT actuator. Depth-resolved displacement fields were reconstructed from pairs of hyperspectral interferograms. However, the experimental results did not show the expected result of linear phase variation with depth. Analysis of several possible causes has been carried out with the most plausible reasons being excessive scattering particle density inside the sample and the possibility of insignificant deformation of the sample due to insufficient physical contact between the transducer and the sample.

Epj Web of Conferences, 2010

We propose a method that we call Hyperspectral Interferometry (HSI) to resolve the 2π phase unwra... more We propose a method that we call Hyperspectral Interferometry (HSI) to resolve the 2π phase unwrapping problem in the analysis of interferograms recorded with a narrow-band light source. By using a broad-band light source and hyperspectral imaging system, a set of interferograms at different wavenumbers are recorded simultaneously on a high resolution image sensor. These are then assembled to form a three-dimensional intensity distribution. By Fourier transformation along the wavenumber axis, an absolute optical path difference is obtained for each pixel independently of the other pixels in the field of view. As a result, interferograms with spatially distinct regions are analysed as easily as continuous ones. The approach is illustrated with a HSI system to measure 3-D profiles of optically smooth or rough surfaces. Compared to existing profilometers able to measure absolute path differences, the single shot nature of the approach provides greater immunity from environmental disturbance.

Measurement Science and Technology, May 25, 2010

We propose a method that we call Hyperspectral Interferometry (HSI) to resolve the 2 phase unwra... more We propose a method that we call Hyperspectral Interferometry (HSI) to resolve the 2 phase unwrapping problem in the analysis of interferograms recorded with a narrow-band light source. By using a broad-band light source and hyperspectral imaging system, a set of interferograms at different wavenumbers are recorded simultaneously on a high resolution image sensor. These are then assembled to form a three-dimensional intensity distribution. By Fourier transformation along the wavenumber axis, an absolute optical path difference is obtained for each pixel independently of the other pixels in the field of view. As a result, interferograms with spatially distinct regions are analysed as easily as continuous ones. The approach is illustrated with a HSI system to measure 3-D profiles of optically smooth or rough surfaces. Compared to existing profilometers able to measure absolute path differences, the single shot nature of the approach provides greater immunity from environmental disturbance.

Journal of the Optical Society of America, Aug 19, 2020

Metal powder bed fusion (PBF) methods need in-process measurement methods to increase user confid... more Metal powder bed fusion (PBF) methods need in-process measurement methods to increase user confidence and encourage further adoption in high-value manufacturing sectors. In this paper, a novel measurement method for PBF systems is proposed that uses multi-view fringe projection to acquire high-resolution surface topography information of the powder bed. Measurements were made using a mock-up of a commercial PBF system to assess the system's accuracy and precision in comparison to conventional single-view fringe projection techniques for the same application. Results show that the multi-view system is more accurate, but less precise, than single-view fringe projection on a point-by-point basis. The multi-view system also achieves a high degree of surface coverage by using alternate views to access areas not measured by a single camera.

Augmented and Mixed Reality promises another leap forward in productivity and lifestyle, offering... more Augmented and Mixed Reality promises another leap forward in productivity and lifestyle, offering benefits with a magnitude and impact matching that of the introduction of smartphones. However, to enable this, many significant technical challenges must be overcome. Here we review the state of the art, identifying key challenges established in the literature to consumer-wearable devices. In particular, we discuss: vergence-accommodation conflict (the detrimental effect of overlays that are optically inconsistent with the real-world objects they augment), the need to present overlays visible against the vast dynamic range that the human eye can process, and constraints surrounding the scalability and cost of manufacture of optics. We demonstrate that digital holography as a display mechanism not only provides an effective solution to the aforementioned challenges, but also that various hardware requirements become far less stringent. By operating in the Fourier Domain, holographic dis...

Laser (profile) scanners (LS) have been widely used in industry for 3D shape measurement. However... more Laser (profile) scanners (LS) have been widely used in industry for 3D shape measurement. However, commercially available scanners are costly. They are also less flexible as the components of the device are permanently fixed in a sealed housing, whereas altering setup geometry can improve the device’s height resolution. This paper describes the design and construction of a LS setup from generic off-the-shelf components; a digital camera, laser line module, optical bandpass filter and a machine vision library software for image to 3D point cloud conversion. The performance of the setup is assessed by measuring a set of step height samples ranging from 50 μm to 1 mm. LS measurement performance is determined by comparing measurements of the step heights with those taken from a Coordinate Measurement Machine (CMM). Average measurement difference between the setup and CMM is 20.29 μm with repeatability of 0.60 μm. The highest percentage error for the smallest tested step height suggests ...

2014 13th International Conference on Control Automation Robotics & Vision (ICARCV), 2014

ABSTRACT Recent advances in automation and sensor technology have enabled the use of industrial r... more ABSTRACT Recent advances in automation and sensor technology have enabled the use of industrial robots for complex tasks that require intelligent decision making. Vision sensors have been the most successfully used sensor in many high value industrial applications. Over the recent years, weld seam tracking has been a topic of interest, as most of the existing robotic welding systems operate on basis of pre-programmed instructions. Such automated systems are incapable of adapting to unexpected variations in the seam trajectory or part fit-up. Applications such as tungsten inert gas (TIG) welding of aerospace components require high tolerances and needs intelligent decision making. Such decision making procedure has to be based on the weld groove geometry at any instance. In this study, a novel algorithm along with an automated system was developed for estimating the joint profile and path tracking of a three dimensional (3D) weld groove. A real-time position based closed-loop system was developed with a six axis industrial robot and a laser triangulation based sensor. The system was capable of finding the 3D weld joint profile and position in real-time, and make intelligent decisions accordingly. Raw data from a vision sensor was processed through a novel algorithm to obtain X and Z co-ordinates at an accuracy of 8.3μm and 43μm respectively at an acquisition speed of 2.5 profiles per second. The algorithm was also capable of measuring the weld gaps with an accuracy of 28μm. Finally, the developed system was successfully used for three dimensional seam tracking, and demonstrates an accuracy of ±0.5mm at a tracking a speed of 2mm/s.

2014 13th International Conference on Control Automation Robotics & Vision (ICARCV), 2014

ABSTRACT Recent advances in automation and sensor technology have enabled the use of industrial r... more ABSTRACT Recent advances in automation and sensor technology have enabled the use of industrial robots for complex tasks that require intelligent decision making. Vision sensors have been the most successfully used sensor in many high value industrial applications. Over the recent years, weld seam tracking has been a topic of interest, as most of the existing robotic welding systems operate on basis of pre-programmed instructions. Such automated systems are incapable of adapting to unexpected variations in the seam trajectory or part fit-up. Applications such as tungsten inert gas (TIG) welding of aerospace components require high tolerances and needs intelligent decision making. Such decision making procedure has to be based on the weld groove geometry at any instance. In this study, a novel algorithm along with an automated system was developed for estimating the joint profile and path tracking of a three dimensional (3D) weld groove. A real-time position based closed-loop system was developed with a six axis industrial robot and a laser triangulation based sensor. The system was capable of finding the 3D weld joint profile and position in real-time, and make intelligent decisions accordingly. Raw data from a vision sensor was processed through a novel algorithm to obtain X and Z co-ordinates at an accuracy of 8.3μm and 43μm respectively at an acquisition speed of 2.5 profiles per second. The algorithm was also capable of measuring the weld gaps with an accuracy of 28μm. Finally, the developed system was successfully used for three dimensional seam tracking, and demonstrates an accuracy of ±0.5mm at a tracking a speed of 2mm/s.

A rigorous two-dimensional (2D) model of electromagnetic surface scatter has been developed, base... more A rigorous two-dimensional (2D) model of electromagnetic surface scatter has been developed, based on a boundary element method (BEM) established by Simonsen [1]. Simulated far-field scatter is compared to that measured from a laser scatterometer for a sinusoidal grating, with a mean difference of 3% of the peak intensity.

The combination of white light interferometry with hyperspectral imaging ('hyperspectral interfer... more The combination of white light interferometry with hyperspectral imaging ('hyperspectral interferometry') is a recently proposed technique for single-shot measurement of 3-D surface profiles. We consider for the first time its application to speckled wavefronts from optically rough surfaces. The intensity versus wavenumber signal at each pixel provides unambiguous range information despite the speckle-induced random phase shifts. Experimental results with samples undergoing controlled rigid body translation demonstrate a measurement repeatability of 460 nm for a bandwidth of approximately 30 nm. Potential applications include roughness measurement and coordinate measurement machine probes where rapid data acquisition in non-cooperative environments is essential.

Journal of the Optical Society of America A

Metal powder bed fusion (PBF) methods need in-process measurement methods to increase user confid... more Metal powder bed fusion (PBF) methods need in-process measurement methods to increase user confidence and encourage further adoption in high-value manufacturing sectors. In this paper, a novel measurement method for PBF systems is proposed that uses multi-view fringe projection to acquire high-resolution surface topography information of the powder bed. Measurements were made using a mock-up of a commercial PBF system to assess the system's accuracy and precision in comparison to conventional single-view fringe projection techniques for the same application. Results show that the multi-view system is more accurate, but less precise, than single-view fringe projection on a point-by-point basis. The multi-view system also achieves a high degree of surface coverage by using alternate views to access areas not measured by a single camera.

Symmetry

The authors would like to make the following addenda and correction to their paper [...]

Symmetry

We consider the interactions of traveling localized wave solutions with a vertex in a star graph ... more We consider the interactions of traveling localized wave solutions with a vertex in a star graph domain that describes multiple Josephson junctions with a common/branch point (i.e., tricrystal junctions). The system is modeled by the sine-Gordon equation. The vertex is represented by boundary conditions that are determined by the continuity of the magnetic field and vanishing total fluxes. When one considers small-amplitude breather solutions, the system can be reduced into the nonlinear Schrödinger equation posed on a star graph. Using the equation, we show that a high-velocity incoming soliton is split into a transmitted component and a reflected one. The transmission is shown to be in good agreement with the transmission rate of plane waves in the linear Schrödinger equation on the same graph (i.e., a quantum graph). In the context of the sine-Gordon equation, small-amplitude breathers show similar qualitative behaviors, while large-amplitude ones produce complex dynamics.

In this report two binary image thresholding methods are briefly described. Both methods assume t... more In this report two binary image thresholding methods are briefly described. Both methods assume that the image consists only two major parts: object (foreground) and background. First method is Otsu method. Threshold value in this method is calculated by minimizing the within-group variance. This method, however, has a possibility to falsely detect the background as foreground. Second method reported in

Optics Letters, 2012

Received Month X, XXXX; revised Month X, XXXX; accepted Month X, XXXX; posted Month X, XXXX (Doc.... more Received Month X, XXXX; revised Month X, XXXX; accepted Month X, XXXX; posted Month X, XXXX (Doc. ID XXXXX); published Month X, XXXX

Laser (profile) scanners (LS) have been widely used in industry for 3D shape measurement. However... more Laser (profile) scanners (LS) have been widely used in industry for 3D shape measurement. However, commercially available scanners are costly. They are also less flexible as the components of the device are permanently fixed in a sealed housing, whereas altering setup geometry can improve the device's height resolution. This paper describes the design and construction of a LS setup from generic off- The-shelf components; a digital camera, laser line module, optical bandpass filter and a machine vision library software for image to 3D point cloud conversion. The performance of the setup is assessed by measuring a set of step height samples ranging from 50 μm to 1 mm. LS measurement performance is determined by comparing measurements of the step heights with those taken from a Coordinate Measurement Machine (CMM). Average measurement difference between the setup and CMM is 20.29 μm with repeatability of 0.60 μm. The highest percentage error for the smallest tested step height suggests the setup can measure objects with feature variation down to 0.1 mm.

Authors: Taufiq Widjanarko, John R.Hodgson, Peter Kinnell and Michael R.Jackson

Proceedings of the 13th International Conference on Control Automation Robotics & Vision (ICARCV), 2014 pp.1368,1372, Singapore 10-12 Dec. 2014

Recent advances in automation and sensor technology have enabled the use of industrial robots for... more Recent advances in automation and sensor technology have enabled the use of industrial robots for complex tasks that require intelligent decision making. Vision sensors have been the most successfully used sensor in many high value industrial applications. Over the recent years, weld seam tracking has been a topic of interest, as most of the existing robotic welding systems operate on basis of pre-programmed instructions. Such automated systems are incapable of adapting to unexpected variations in the seam trajectory or part fit-up. Applications such as tungsten inert gas (TIG) welding of aerospace components require high tolerances and needs intelligent decision making. Such decision making procedure has to be based on the weld groove geometry at any instance. In this study, a novel algorithm along with an automated system was developed for estimating the joint profile and path tracking of a three dimensional (3D) weld groove. A real-time position based closed-loop system was developed with a six axis industrial robot and a laser triangulation based sensor. The system was capable of finding the 3D weld joint profile and position in real-time, and make intelligent decisions accordingly. Raw data from a vision sensor was processed through a novel algorithm to obtain X and Z co-ordinates at an accuracy of 8.3μm and 43μm respectively at an acquisition speed of 2.5 profiles per second. The algorithm was also capable of measuring the weld gaps with an accuracy of 28μm. Finally, the developed system was successfully used for three dimensional seam tracking, and demonstrates an accuracy of ±0.5mm at a tracking a speed of 2mm/s.

Authors: R.P.Manorathna, P.Phairatt, P.Ogun, T.Widjanarko, M.Chamberlain, L.Justham, S.Marimuthu and M.R.Jackson

The measurement of surface profile is a vital quality control procedure in many industries. For s... more The measurement of surface profile is a vital quality control procedure in many industries. For small objects (dimensions below ~10 mm) with rough or discontinuous surfaces, scanning white light interferometry (SWLI) is currently the method of choice. However, with a resolution of ∼1 nm, vibration during the scan induces motion artifacts and prevents its routine use on the production line. We present a system that avoids temporal scanning by spectrally splitting the white light interferogram into a set of interferograms at different wavenumbers which are recorded simultaneously on an image sensor. The system essentially consists of an interferometer coupled to a single-shot hyperspectral imaging system. Fourier transformation along the wavenumber axis provides an absolute optical path difference for each point in the field of view, a procedure which is robust even on optically rough surfaces. Height maps with a spatial resolution of 19×19 pixels and a measurement accuracy of ∼460 nm are demonstrated.