| 1. |
- De Backer, Jeroen, 1987-, et al.
(författare)
-
Investigation of path compensation methods for robotic friction stir welding
- 2012
-
Ingår i: Industrial robot. - : Emerald Group Publishing Limited. - 0143-991X .- 1758-5791. ; 39:6, s. 601-608
-
Tidskriftsartikel (refereegranskat)abstract
- Purpose – Friction stir welding (FSW) is a novel method for joining materials without using consumables and without melting the materials. The purpose of this paper is to present the state of the art in robotic FSW and outline important steps for its implementation in industry and specifically the automotive industry.Design/methodology/approach – This study focuses on the robot deflections during FSW, by relating process forces to the deviations from the programmed robot path and to the strength of the obtained joint. A robot adapted for the FSW process has been used in the experimental study. Two sensor-based methods are implemented to determine path deviations during test runs and the resulting welds were examined with respect to tensile strength and path deviation.Findings – It can be concluded that deflections must be compensated for in high strengths alloys. Several strategies can be applied including online sensing or compensation of the deflection in the robot program. The welding process was proven to be insensitive for small deviations and the presented path compensation methods are sufficient to obtain a strong and defect-free welding joint.Originality/value – This paper demonstrates the effect of FSW process forces on the robot, which is not found in literature. This is expected to contribute to the use of robots for FSW. The experiments were performed in a demonstrator facility which clearly showed the possibility of applying robotic FSW as a flexible industrial manufacturing process.
|
|
| 2. |
- De Backer, Jeroen, 1987-, et al.
(författare)
-
Temperature control of robotic friction stir welding using the thermoelectric effect
- 2014
-
Ingår i: The International Journal of Advanced Manufacturing Technology. - : Springer. - 0268-3768 .- 1433-3015. ; 70:1-4, s. 375-383
-
Tidskriftsartikel (refereegranskat)abstract
- Friction stir welding (FSW) of non-linear joints receives an increasing interest from several industrial sectors like automotive, urban transport and aerospace. A force-controlled robot is particularly suitable for welding complex geometries in lightweight alloys. However, complex geometries including three-dimensional joints, non-constant thicknesses and heat sinks such as clamps cause varying heat dissipation in the welded product. This will lead to changes in the process temperature and hence an unstable FSW process with varying mechanical properties. Furthermore, overheating can lead to a meltdown, causing the tool to sink down into the workpiece. This paper describes a temperature controller that modifies the spindle speed to maintain a constant welding temperature. A newly developed temperature measurement method is used which is able to measure the average tool temperature without the need for thermocouples inside the tool. The method is used to control both the plunging and welding operation. The developments presented here are applied to a robotic FSW system and can be directly implemented in a production setting.
|
|
| 3. |
- Hagqvist, Petter, et al.
(författare)
-
Automatic detection of material phase transitions from spectroscopic data
- 2013
-
Ingår i: Proceedings of the IECON 2013. - : IEEE. - 9781479902231 ; , s. 2384-2389
-
Konferensbidrag (refereegranskat)abstract
- When using a temperaturemeasurementmethod which utilizes spectral information for measuring the temperature of varying emissivity measurands, there is a need for a temperature reference at some point in time. In this work, such a reference is created from the spectral radiance data already used by the temperature measurement method. A method of using knowledge of the measurand material's phase transitions and spectral radiance data as a temperature reference is presented. Through automatical identification of phase transitions from radiance spectra employing signal processing, the temperature is known at a certain instance in time, just like required by the temperature measurement method. Three methods for automatic identification of material phase transitions from spectroscopic data are examined and evaluated. The methods are, based on derivatives, steady-state identification and cross correlation respectively. They are introduced and evaluated using experimental data collected from a solidifying copper sample. All methods proved to identify the phase transitions correctly. The addition of automatic phase transition identification supplements the existing temperature measurement method such that it becomes a stand alone, reference free method for measuring the true absolute temperature of a measurand with varying emissivity.
|
|
| 4. |
- Hagqvist, Petter, 1986, et al.
(författare)
-
Emissivity compensated spectral pyrometry-algorithm and sensitivity analysis
- 2014
-
Ingår i: Measurement Science and Technology. - : IOP Publishing. - 0957-0233 .- 1361-6501. ; 25:2
-
Tidskriftsartikel (refereegranskat)abstract
- In order to solve the problem of non-contact temperature measurements on an object with varying emissivity, a new method is herein described and evaluated. The method uses spectral radiance measurements and converts them to temperature readings. It proves to be resilient towards changes in spectral emissivity and tolerates noisy spectral measurements. It is based on an assumption of smooth changes in emissivity and uses historical values of spectral emissivity and temperature for estimating current spectral emissivity. The algorithm, its constituent steps and accompanying parameters are described and discussed. A thorough sensitivity analysis of the method is carried out through simulations. No rigorous instrument calibration is needed for the presented method and it is therefore industrially tractable.
|
|
| 5. |
- Hagqvist, Petter, 1986-, et al.
(författare)
-
Emissivity estimation for high temperature radiation pyrometry on Ti–6Al–4V
- 2013
-
Ingår i: Measurement. - : Elsevier BV. - 0263-2241 .- 1873-412X. ; 46:2, s. 871-880
-
Tidskriftsartikel (refereegranskat)abstract
- The paper demonstrates a versatile procedure suitable for industrial implementation of temperature measurement on a hot titanium alloy. The driving force has been the need for an accurate temperature measurement during additive manufacturing using laser welding technology where Ti–6Al–4V-wire is melted. The challenges consider both industrial constraints and the varying emissivity of the surface. Measurements makes use of a narrow bandwidth spot radiation pyrometer and a calibration procedure for estimation of the surface temperature through spectral emissivity estimation. The theoretical results are validated through experiments. A number of difficulties in radiation temperature measurements for metals with varying surface properties are discussed; especially the case of surface oxidation. The uncertainty in temperature reading due to the uncertainty in the emissivity estimate is established along with a model that qualitatively describes surface oxidation. The procedure is expected to be useful for several manufacturing applications where it is important to control high temperatures.
|
|
| 6. |
- Heralic, Almir, 1981-, et al.
(författare)
-
Automatic in-process control of laser metal-wire deposition based on sensor feedback
- 2011
-
Ingår i: 30th Interantional Congress on Applications of Lasers & Electro-Optics, ICALEO 2011. ; , s. 211-220
-
Konferensbidrag (refereegranskat)abstract
- This paper describes alasermetaldepositionsystem that isbasedon robotizedlaserwelding andwirefiller material. The system has been found suitable for the manufacture of simple but large shapes with high metallurgical requirements such as bosses or flanges found on aero engine components. Several benefits have been identified with the usage ofwirefiller compared to powderized feedstock, such as betterprocessefficiency, higherdepositionrates, and cleaner working environment. Thewirebaseddepositionprocessis however sensitive to disturbances and thus requires continuous monitoring and adjustments.Inthis work a 3D scanning system is described forautomaticin-processcontrolof thedeposition. The goal is to obtain a flat surface for each deposited layerinorder to ensure stabledeposition. The deviationsinthe layer height are compensated by controlling thewirefeed rate. The system is tested throughdepositionof small cylindrical bosses and the results show that the proposedcontrolapproach is suitable forautomaticdepositionof such structures. The material consideredinthis paper is Ti-6Al-4V deposited on plates of same material. The paper presents the equipment and thecontrolstrategy and discusses practical issues regarding thesensorused.
|
|
| 7. |
|
|
| 8. |
- Heralic, Almir, 1981-, et al.
(författare)
-
Height control of laser metal-wire deposition based on iterative learning control and 3D scanning
- 2012
-
Ingår i: Optics and Lasers in Engineering. - : Elsevier BV. - 0143-8166 .- 1873-0302. ; 50:9, s. 1230-1241
-
Tidskriftsartikel (refereegranskat)abstract
- Laser Metal-wire Deposition is an additive manufacturing technique for solid freeform fabrication of fully dense metal structures. The technique is based on robotized laser welding and wire filler material, and the structures are built up layer by layer. The deposition process is, however, sensitive to disturbances and thus requires continuous monitoring and adjustments. In this work a 3D scanning system is developed and integrated with the robot control system for automatic in-process control of the deposition. The goal is to ensure stable deposition, by means of choosing a correct offset of the robot in the vertical direction, and obtaining a flat surface, for each deposited layer. The deviations in the layer height are compensated by controlling the wire feed rate on next deposition layer, based on the 3D scanned data, by means of iterative learning control. The system is tested through deposition of bosses, which is expected to be a typical application for this technique in the manufacture of jet engine components. The results show that iterative learning control including 3D scanning is a suitable method for automatic deposition of such structures. This paper presents the equipment, the control strategy and demonstrates the proposed approach with practical experiments.
|
|
| 9. |
- Ryberg, Anders, 1973-, et al.
(författare)
-
Analysis and evaluation of a general camera model
- 2011
-
Ingår i: Computer Vision and Image Understanding. - : Elsevier. - 1077-3142 .- 1090-235X. ; 115:11, s. 1503-1515
-
Tidskriftsartikel (refereegranskat)abstract
- A versatile General Camera Model, GCM, has been developed, and is described in detail. The model is general in the sense that it can capture both fisheye and conventional as well as catadioptric cameras in a unified framework. The camera model includes efficient handling of non-central cameras as well as compensations for decentring distortion. A novel way of analysing radial distortion functions of camera models leads to a straightforward improvement of conventional models with respect to generality, accuracy and simplicity. Different camera models are experimentally compared for two cameras with conventional and fisheye lenses, and the results show that the overall performance is favourable for the GCM.
|
|
| 10. |
- Ryberg, Anders, 1973-, et al.
(författare)
-
Stereo vision for path correction in off-line programmed robot welding
- 2010
-
Ingår i: Proceedings of the IEEE International Conference on Industrial Technology. ; , s. 1700-1705
-
Konferensbidrag (refereegranskat)abstract
- The paper describes a versatile machine vision system for correcting off-line programmed nominal robot trajectories for advanced welding. Weld trajectory corrections are needed due to slight variations in weld joints. Such variations occur naturally because of varying tolerances in parts and to heat induced deformations during earlier weld sequences. The developed system uses one camera and a weld tool mounted on the robot hand. As a first step, the whole system, including the camera, is calibrated. Then the system takes images of the weld joint from different positions and orientations, and determines the weld joint geometry in 3D using a stereo vision algorithm and a novel camera model. The weld trajectory is then updated in the robot control system, and weld operation is performed. These steps are repeated for all weld sequences of the work piece. The strategy has successfully been demonstrated for a standard industrial welding robot and a standard FireWire CMOS camera. The maximum deviation of the trajectory found by the system compared to a reference (coordinate measuring machine) is 0.7 mm and the mean deviation is 0.23 mm. Thus, the system shows high potential for industrial implementation. ©2010 IEEE.
|
|
