Fraunhofer Chalmers Research Center

Göteborg, Sweden

Fraunhofer Chalmers Research Center

Göteborg, Sweden
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Shellshear E.,Fraunhofer Chalmers Research Center
Visual Computer | Year: 2014

Detecting self-collision for cables and similar objects is an important part of numerous models in computational biology (protein chains), robotics (electric cables), hair modeling, computer graphics, etc. In this paper the 1D sweep-and-prune algorithm for detecting self-collisions of a deforming cable comprising linear segments is investigated. The sweep-and-prune algorithm is compared with other state-of-the-art self-collision detection algorithms for deforming cables and is shown to be up to an order of magnitude faster than existing algorithms for cables with a high proportion of segments moving. We also present a multi-threaded version of the algorithm and investigate its performance. In addition, we present worst-case bounds for 1D sweep-and-prune algorithms whereby the colliding objects do not exceed a certain object density, and apply these results to deforming cables. © Springer-Verlag 2013.


Warmefjord K.,Chalmers University of Technology | Carlson J.S.,Fraunhofer Chalmers Research Center | Soderberg R.,Chalmers University of Technology
Journal of Computing and Information Science in Engineering | Year: 2016

In the auto body assembly process, fixtures position parts during assembly and inspection. Variation in the positioning process propagates to the final assembly. To control the assembly fixtures, repeatability studies are used. Those studies are, however, usually done with long intervals and the fixtures might be afflicted with variation between studies. There are also other sources of variation in the final assembly, such as variation in parts due to previous manufacturing steps. To separate variation caused by fixtures and the variation caused by previous manufacturing processes, a multivariate fixture failure subspace control chart is proposed. Copyright © 2016 by ASME.


Tafuri S.,Fraunhofer Chalmers Research Center | Shellshear E.,Fraunhofer Chalmers Research Center | Bohlin R.,Fraunhofer Chalmers Research Center | Carlson J.S.,Fraunhofer Chalmers Research Center
Proceedings - Winter Simulation Conference | Year: 2012

Collision free path planning is a key technology for assembly analysis, robot line optimization, and virtual assessment of industrial maintenance and service. The ability to compute collision free paths relies on the ability to quickly and robustly query the proximity of the planning object to its surroundings. Path planning with triangulated models is a well studied problem, however, hybrid models comprising both points and triangles present new and difficult challenges. Working directly with point clouds is becoming more relevant because it allows one to scan existing industrial installations and path plan with the scan data instead of possibly incorrect planned layouts. In this paper we implement and analyze a new hybrid path planning interface on a case study in robot line manufacturing and demonstrate its feasibility in comparison to an existing CAD model of the work environment and show that triangulating the original point cloud is undesirable for path planning. © 2012 IEEE.


Warmefjord K.,Chalmers University of Technology | Carlson J.S.,Fraunhofer Chalmers Research Center
ASME International Mechanical Engineering Congress and Exposition, Proceedings (IMECE) | Year: 2012

In the auto body assembly process, fixtures are used to position parts during assembly and inspection. If there is variation in the positioning process, this will propagate to the final assembly. There are also other sources of variation in the final assembly, such as variation in parts due to previous manufacturing steps. To facilitate the separation of the different sources of variation, and thereby also improve fault diagnosis, a fixture failure subspace control chart is proposed. This control chart is based on a multivariate T 2-chart, but only variations in the fixture failure subspace are considered. The method is applied to two industrial case studies with satisfying results. Copyright © 2012 by ASME.


Shirvany Y.,Chalmers University of Technology | Shirvany Y.,MedTechWest Center | Edelvik F.,Fraunhofer Chalmers Research Center | Jakobsson S.,Fraunhofer Chalmers Research Center | And 3 more authors.
Applied Soft Computing Journal | Year: 2013

Surgical therapy has become an important therapeutic alternative for patients with medically intractable epilepsy. Correct and anatomically precise localization of an epileptic focus is essential to decide if resection of brain tissue is possible. The inverse problem in EEG-based source localization is to determine the location of the brain sources that are responsible for the measured potentials at the scalp electrodes. We propose a new global optimization method based on particle swarm optimization (PSO) to solve the epileptic spike EEG source localization inverse problem. In a forward problem a modified subtraction method is proposed to reduce the computational time. The good accuracy and fast convergence are demonstrated for 2D and 3D cases with realistic head models. The results from the new method are promising for use in the pre-surgical clinic in the future. © 2012 Elsevier B.V. All rights reserved.


Rundqvist R.,Fraunhofer Chalmers Research Center | Mark A.,Fraunhofer Chalmers Research Center | Edelvik F.,Fraunhofer Chalmers Research Center | Carlsson J.S.,Fraunhofer Chalmers Research Center
Fluid Dynamics and Materials Processing | Year: 2011

Multiphase flow simulation using Smoothed Particle Hydrodynamics (SPH) has gained interest during recent years, mostly due to the inherent flexibility of the method and the physically rather intuitive formulation of extra constitutive equations needed when dealing with for instance non-Newtonian flows. In the work presented here, simulations based on an SPH model implemented in the flow solver IBOFlow has been used for simulation of robotic application of sealing material on a car body. Application of sealing materials is done in order to prevent water leakage into cavities of the body, and to reduce noise. In off-line programming of the robots in the automotive paintshop it is of great interest to predict shape and appearance of sealing material without having to resort to trial and error procedures. The flow of sealing material in the air between applicator and target (car body) is relatively uncomplicated, as the material mostly moves at constant velocity until impact on target. The flow of the material on the target is however more complex, applied material flows at the target surface due to inertia, gravity and pressure and in order to predict the appearance of the applied material, flow equations for a non-Newtonian fluid with an open surface needs to be solved. The sealing material is both thixotropic and viscoelastic; the material is shear thinning but needs to be sheared for some time before the structure of the material is broken down. Conversely, the regain of structure of the material, and thereby also the increase of viscosity when shearing is stopped or reduced, is also connected to a delay time. In the model used, the local viscosity is considered obeying a first order differential equation where the stationary limit is determined by a Bingham relation. The simulation model was built by comparing simulations and experiments at three different stages of complexity. In the most fundamental stage the material properties were determined. Using a rotational rheometer, yield stress, plastic viscosity and thixotropy time constant was determined and implemented in the simulation model. To verify the numerical behaviour of the rheology, simulated rheometer experiments were carried out and compared with the physical experiments. In the second stage, simulation of application of sealing material with a stationary hollowcone nozzle was carried out. To verify the simulations, the resulting thickness, width and shape of applied material as a function of time were compared to experiments. In the third stage a moving applicator of the same type was considered, here thickness width and shape of applied material as a function of applicator to target distances were compared between experiments and simulations. At all three stages the number of SPH particles, i:e: grid points, in the simulations was varied in order to verify that the simulations were resolution independent. Results of the simulations show good agreement between experiments and simulations in all stages using no artificial tuning of the models, i.e. all parameters used in the models are based on physical considerations. Furthermore, simulation time on a desktop computer indicates that computational power required for industrially relevant cases is not prohibitively large, for the most complex cases in this work the simulation time did not exceed six hours. © 2011 Tech Science Press.


Warmefjord K.,Chalmers University of Technology | Soderberg R.,Chalmers University of Technology | Carlson J.S.,Fraunhofer Chalmers Research Center
ASME International Mechanical Engineering Congress and Exposition, Proceedings (IMECE) | Year: 2010

The repeatability of the assembly fixtures influences the geometrical outcome of an assembly. To control the fixtures, capability studies are conducted. Those studies give however just information about the variability in a number of inspection points. In this paper, a method for transforming the variation in inspection data to variation in the contacts between workpiece and locators is described. By doing this, the fault localizing of the fixture is facilitated. Further, the accuracy of the variation simulations used to evaluate different concepts and designs can be improved. Usually, when data from a repeatability study are used as input to a variation simulation, the tolerances are only applied in the points that actually were inspected. The suggested methodology makes it possible to transform the tolerances containing the repeatability of the fixture to tolerances on the locating scheme, and they are thereby affecting every point in the simulation model, not only the inspected ones. The method is tested on a case study and the effect of including fixture repeatability in a variation simulation is investigated. ©2010 by ASME.


Segeborn J.,Volvo Car Corporation | Segerdahl D.,Fraunhofer Chalmers Research Center | Carlson J.S.,Fraunhofer Chalmers Research Center | Carlsson A.,Volvo Car Corporation | Soderberg R.,Chalmers University of Technology
ASME International Mechanical Engineering Congress and Exposition, Proceedings (IMECE) | Year: 2010

The balancing of weld work load between executing stations and its robots has a significant influence on achievable production rate and equipment utilization. However, no automatic simulation based method for line balancing has been formulated up to this point. In practice, it is still manually conducted. Therefore in this work we propose two novel methods for load balancing of welds in multi station sheet metal assembly lines to minimize line cycle time. The methods are based on superimposition of the scenes/geometries of all line stations, with maintained robot positioning relative to the work piece, creating a "multi station". The weld load is balanced between all multi station robots, whereupon the individual robots are combined into stations and coordinated station wise for simultaneous operation. Furthermore one of the proposed methods reduces the subsequent need for robot coordination, by introducing some restrictions on the load balancing: Firstly, for each robot, the weld load is balanced over the other station robots such that the working envelopes are maximally separated. Secondly, for each robot, the weld load is balanced over equivalently positioned robots in other line stations, based on previous station load balancing techniques. The proposed line balancing methods are applied on two industrial case studies which each involves the balancing of about 200 automotive stud welds between 3 stations, each of 4 robots. One of the proposed methods produces line cycle times close to that of the slowest uncoordinated robot, which can be considered a theoretical optimum of the line cycle time. Corresponding algorithm running time is about 30 minutes on an Intel Core 2 Quad with 8 GB RAM. ©2010 by ASME.


Shirvany Y.,Chalmers University of Technology | Mahmood Q.,Chalmers University of Technology | Edelvik F.,Fraunhofer Chalmers Research Center | Jakobsson S.,Fraunhofer Chalmers Research Center | And 2 more authors.
IEEE Transactions on Neural Systems and Rehabilitation Engineering | Year: 2014

One of the most important steps in presurgical diagnosis of medically intractable epilepsy is to find the precise location of the epileptogenic foci. Electroencephalography (EEG) is a noninvasive tool commonly used at epilepsy surgery centers for presurgical diagnosis. In this paper, a modified particle swarm optimization (MPSO) method is used to solve the EEG source localization problem. The method is applied to noninvasive EEG recording of somatosensory evoked potentials (SEPs) for a healthy subject. A 1 mm hexahedra finite element volume conductor model of the subject's head was generated using T1-weighted magnetic resonance imaging data. Special consideration was made to accurately model the skull and cerebrospinal fluid. An exhaustive search pattern and the MPSO method were then applied to the peak of the averaged SEP data and both identified the same region of the somatosensory cortex as the location of the SEP source. A clinical expert independently identified the expected source location, further corroborating the source analysis methods. The MPSO converged to the global minima with significantly lower computational complexity compared to the exhaustive search method that required almost 3700 times more evaluations. © 2001-2011 IEEE.


Shellshear E.,Fraunhofer Chalmers Research Center | Carlson J.S.,Fraunhofer Chalmers Research Center | Bohlin R.,Fraunhofer Chalmers Research Center | Tafuri S.,Fraunhofer Chalmers Research Center
IEEE International Conference on Automation Science and Engineering | Year: 2015

A new multi-threaded memetic algorithm (genetic algorithm with local optimizations) for the ISO 3832 luggage packing standard is presented. Apart from producing high-quality results, the algorithm also exploits the highly parallel computer architectures that are becoming more common as well as packing more boxes than other state-of-the-art algorithms. We also provide the first comparison of state-of-the-art packing algorithms for a real world trunk geometry. © 2015 IEEE.

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