| 1. |
- Kinell, Lars, et al.
(författare)
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Component forming simulations validated using optical shape measurements
- 2003
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Ingår i: Optical Measurement Systems for Industrial Inspection III. - Bellingham, Wash. : SPIE - International Society for Optical Engineering. - 0819450146 ; , s. 409-419
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Konferensbidrag (refereegranskat)abstract
- For validation of forming simulations a methodology, using optical shape measurements, is here presented. In this work, the shape of a sheet metal component with complex geometry is measured using projected fringes. The component in consideration is a closed section steel profile that is formed using a forming tool. The shape is measured using the reduced temporal phase unwrapping scheme and calibration data for the calculation of absolute coordinates in the local coordinate system. Local 3-D coordinates from several measurements of this long object are merged together through a feature based stitching program. To validate the finite-element model, the final shape of the forming simulation is compared to the results from the shape measurements. Since no computer aided design model exists for the formed beam, the features in shape of the measured object are used as references when comparing results
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| 2. |
- Kinell, Lars
(författare)
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Multichannel method for absolute shape measurement using projected fringes
- 2004
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Ingår i: Optics and lasers in engineering. - 0143-8166 .- 1873-0302. ; 41:1, s. 57-71
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Tidskriftsartikel (refereegranskat)abstract
- The multichannel approach is combined with the reduced temporal phase unwrapping scheme for rapid shape measurement. The shape is measured using projected fringes and optical triangulation. Fringes are projected using a colour video projector and recorded by a CCD-camera. Using a colour video projector and a colour video camera makes it possible to use the red, green and blue channels individually. This is the multichannel method. In each channel, the blue, green and red carries fringe maps with different fringe pitch. A short sequence of phase-stepped images is projected and acquired sequentially in time. This reduces measurement time by a factor of three when compared to using one channel. From the acquired images, it is possible to calculate absolute phase using the reduced temporal phase unwrapping analysis scheme. For each channel, it is also possible to calculate fringe contrast and fringe amplitude. Therefore, it is possible to retrieve the colour of an object without acquiring an extra image. The method is demonstrated by measuring the shape of two generally coloured and complex shaped objects.
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| 3. |
- Kinell, Lars
(författare)
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Optical shape measurements using temporal phase unwrapping
- 2003
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- This doctoral thesis is devoted to optical shape measurements using an analysis scheme called temporal phase unwrapping. This scheme makes it possible to determine the absolute distance from a detector (usually a camera’s CCD-detector) to an object. Two different optical methods are considered for this 3-D sensing. The other first is a new interferometric method, which uses wavelength scanning. The other one is a classical triangulation method, which uses projected fringes. Both are whole field active measuring methods. The temporal phase unwrapping strategy requires a projection and acquisition of a sequence of fringe maps. In the present work, we formulate the reduced temporal phase unwrapping scheme and investigate the performance of it. With this scheme, we can calculate the phase (shape) from an arbitrary number of fringe frequencies. We found expressions that relate the physical quantities to phase errors. We also found expressions that relate the measurement accuracy and the unwrapping reliability, respectively, to the reduction in fringe sequence length. As expected, the measurement accuracy is unaffected by a shorter fringe sequence while a significant reduction in the unwrapping reliability is found, as compared to the complete negative exponential sequence. We consider both a single-channel and a multi-channel approach, letting different channels carry different phase-stepped image. In these simulations, the single channel approach proves to be the most robust one. The strength of reduced temporal phase unwrapping is demonstrated experimentally, in a projected fringe three-channel system. Instead of letting each channel carry phase-stepped images, each channel carries images with a change in fringe pitch. This significantly reduces noise, but requires an acquisition of at least three phase-stepped images. A spatio-temporal approach for real time absolute shape measurements is formulated. We experimentally show that absolute shape is measurable with a reduced number of fringe maps in exchange of spatial resolution. In combination with the multichannel-approach one need only to project and acquire one static image. The solution can therefore become a powerful measurement method for automation and assembly line work. For validation of forming simulations a methodology using projected fringes and reduced temporal phase unwrapping is presented. In this work, the shape of a long object is measured using projected fringes, reduced temporal phase unwrapping and calibration data. Local 3-D coordinates from several measurements are merged together through a feature based stitching program. The features in shape of the forming simulation are compared to the results from the shape measurements. It is also shown that the temporal phase unwrapping analysis scheme can be used to evaluate experimental data from wavelength scanning interferometry. Two unwrapping strategies are considered: fitting to a reversed exponential sequence and complex Fourier-transform ranging. The achievable accuracy for both methods ultimately depends on the tuning width, the speckle correlation, and random noise in the optical setup.
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| 4. |
- Kinell, Lars, et al.
(författare)
-
Robustness of reduced temporal phase unwrapping in the measurement of shape
- 2001
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Ingår i: Applied Optics. - 1559-128X .- 2155-3165. ; 40:14, s. 2297-2303
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Tidskriftsartikel (refereegranskat)abstract
- The predictions of success rate and depth uncertainty for the negative exponential sequence used for temporal phase unwrapping of shape data are generalized to include the effect of a reduced sequence and speckle noise in single-channel and multichannel systems, respectively. To cope with the reduction of the sequence, a scaling factor is introduced. A thorough investigation is made of the performance of this algorithm, called the reduced temporal phase-unwrapping algorithm. Two different approaches are considered: a single-channel approach in which all the necessary images are acquired sequentially in time and a multichannel approach in which the three channels of a color CCD camera are used to carry the phase-stepped images for each fringe density in parallel. The performance of these two approaches are investigated by numerical simulations. The simulations are based on a physical model in which the speckle contrast, the fringe modulation, and random noise are considered the sources of phase errors. Expressions are found that relate the physical quantities to phase errors for the single-channel and the multichannel approaches. In these simulations the single-channel approach was found to be the most robust. Expressions that relate the measurement accuracy and the unwrapping reliability, respectively, with the reduction of the fringe sequence were also found. As expected, the measurement accuracy is not affected by a shorter fringe sequence, whereas a significant reduction in the unwrapping reliability is found as compared with the complete negative exponential sequence
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| 5. |
- Kinell, Lars
(författare)
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Shape measurements using temporal phase unwrapping
- 2000
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- This licentiate thesis is devoted to shape measurements using two different optical methods. The first one is a classical triangulation method, which uses projected fringes. The second one is a new interferometric method, which uses wavelength scanning. Both are whole field measuring methods. The main goal of the project has been to analyse the performance of an analysis scheme for absolute shape measurements called temporal phase unwrapping. This method permits the user to determine the absolute distance from the detector (usually a CCD-detector) to the object. A generalised version of the temporal phase unwrapping scheme is called reduced temporal phase unwrapping. The scheme uses an arbitrary number of fringe maps with varied fringe pitch, to calculate phase (shape). A thorough investigation is made of the performance of this algorithm. A single channel and a multi channel approach is considered. Expressions are found that relates the physical quantities to phase errors. In these simulations the single channel approach was found to be the most robust one. Expressions that relate the measurement accuracy and the unwrapping reliability, respectively, to the reduction of the fringe sequence were also found. As expected the measurement accuracy is not affected by a shorter fringe sequence while a significant reduction in the unwrapping reliability is found, as compared to the complete negative exponential sequence. The strength of reduced temporal phase unwrapping is demonstrated experimentally, in a projected fringe three-channel system. Instead of letting each channel carry phase-stepped images each channel can carry images with a change in fringe pitch. This significantly reduces noise, but at least three images needs to be acquired. It is also shown that the temporal phase unwrapping analysis scheme can be used to evaluate experimental data from wavelength scanning interferometry. Two unwrapping strategies are considered: fitting to a reversed exponential sequence and complex Fourier-transform ranging. The achievable accuracy for both methods ultimately depend on the tuning width, the speckle correlation, and random noise in the optical setup.
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| 6. |
- Kinell, Lars
(författare)
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Spatiotemporal approach for real-time absolute shape measurements by use of projected fringes
- 2004
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Ingår i: Applied Optics. - 1559-128X .- 2155-3165. ; 43:15, s. 3018-3027
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Tidskriftsartikel (refereegranskat)abstract
- A spatiotemporal approach for fast absolute shape measurements is formulated. In principle, the Takeda method is used in combination with the reduced temporal phase-unwrapping scheme to calculate the absolute phase. Three different measurements are performed: a flat surface, steps, and a curved beam with varying cross sections. The performance in standard deviation is improved, and the success rate is approximately the same as that obtained with a strict temporal solution for which a four-bucket phase algorithm is used. The multichannel approach is also used. Then only one static image is needed. It should therefore be possible to measure objects in motion
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