TECHNICAL FIELD OF THE INVENTION The invention relates to a method and arrangement for analysing a property of a seam, and in particularly a weld seam. The analysing of a property relates for example to a seam or weld seam quality, cross-sectional profile, toughness, long-term sustainability or fatigue strength or opening angles, curvature, depth, full penetration, seam width, humping, or a degree of asymmetry during welding.

BACKGROUND OF THE INVENTION

Number of methods and techniques are known to analyse properties of a seam and weld seam, such as visually estimating or scanning or imaging by laser or X-ray or other radiating devices. The laser scanner devices are typically based on triangulation measurement, where the weld seam is scanned over with a predefined frequency so that the measurement can be determined for later use. Also a CMOS camera imaging is used for determining of the weld seam dimensions and shapes. It is also known to use cameras to take images or video-radiographic images of the cross section of the weld joint, for example, and to compare its parameters to a predetermined shape of desired weld in order to provide estimation about the quality.

There are however some disadvantages relating to the known prior art. Even if the optical imaging systems are typically relatively fast and noninvasive, their accuracy and resolution is not good enough to be able to generate so accurate surface profile in particularly of the weld seam that to overall quality could be estimated and determined in a reliable way enough. In addition e.g. using shorter wavelengths, such as x-rays or gamma-rays are not often suitable for accurate surface profile, as well as also the health risk in these techniques is significant. SUMMARY OF THE INVENTION

An object of the invention is to alleviate and eliminate the problems relating to the known prior art. Especially the object of the invention is to provide a system for analysing properties of a seam and especially weld seam in a reliable way enough and to get so accurate surface profile of the weld seam that all of the important surface shapes related to the weld seam that makes possible to predict its long-term sustainability or fatigue strength from the profile parameters can be achieved.

The object of the invention can be achieved by the features of independent claims.

The invention relates to an arrangement for analysing a property of a seam according to claim 1. In addition the invention relates to a method for analysing a property of a seam according to claim 17, as well as to computer program product according to claim 18. According to an embodiment of the invention at least one property of a seam and especially weld seam (weld seam hereafter) is analysed by providing a spectre of electromagnetic radiation band to an object representing the weld seam so that different wavelengths of said radiation are focused to different depths in a direction of a normal of the object. The object representing the weld seam is either the weld seam to be determined as such or alternatively a casting mould representing the weld seam, such as a silicone casting mould. According to the embodiment at least a wavelength focused on and reflected from the depth of the surface of said object is received and analysed. In analysing the wavelengths with intensities over a predetermined threshold value are selected, and one of which wavelength is then construed to represent the wavelength focused on and reflected from the depth of the surface of the object. The electromagnetic radiation band is advantageously continuous spectre and comprises ultraviolet spectral range, visible spectral range and/or infrared spectral range.

It is assumed that only the wavelengths reflected from the surface or some other point of the object are able to have intensity over the predetermined threshold value. In addition the wavelength travelled the shortest path is construed to represent the wavelength focused on and reflected from the depth of the surface of the object at a certain location to be determined. This is because no reliable wavelength can be reflected in the area between a device outputting said spectre of electromagnetic radiation band and the object (thus travelling more shorter path), and in other hand the wavelength travelled the longer path will represent wavelength either reflected behind or beyond the surface of the seam or having multiple reflections and being thus non-reliable.

Depending how the spectre is generated, so whether the shortest wavelengths are focused closer to the device and the longest behind the object or vice versa, the shortest or longest wavelength of said selected wavelengths determines the depth (or Z-coordinate) of the surface of the object at a certain point.

The length (or at least relative length) of the path of each wavelength can be deduced based on the wavelength, i.e. the colour of the wavelength, since the shortest and longest wavelengths of the radiation are focused to different depths so that the wavelength between the shortest and longest wavelengths is focused essentially to a depth of a median surface level of the object.

Additionally the spectre lines of the electromagnetic radiation band can be emitted so that a planar beam cone is provided of the wavelength and again to extend over the weld seam (or object) and further on at least two bodies (typically sheet or plates) to be welded by said weld seam. By providing a planar beam cone a cross-sectional profile can be better determined by one shot. In addition the planar beam cone is spread wider, a mutual disposition or placing, bending or alignment, such as linear or angular misalignment of the bodies to be welded can be determined based on the received wavelengths of the cone reflected from the bodies.

According to an embodiment the electromagnetic radiation, so typically at least partially visible light from the radiation source (advantageously not a point-like source, but with a circular emission), is divided to different wavelengths (colours), where each colour is focused to a certain own depth. Each colour is additionally spread and "extended" to a planar or line beam. As can be seen each colours are reflected, at least in principle, in a certain (own) direction (independently of each other wavelength), especially in the question of weld seam. The focused wavelength will be reflected at maximum intensity from a certain focus spot (on the surface of the object or weld seam) and non-focused will be reflected area located somewhere else that said objet or weld seam of interest. The receiving unit or detector is advantageously arranged (focused) to receive reflections reflected essentially and optimally from the profile cross-section. Because the non- focused wavelengths will be reflected from the area locating outside the area of the object or the weld seam, they will be reflected and passed by the side of the detector and additionally with smaller intensity than the beams focused on and reflected from the object or the weld seam. Again it might be that numbers of wavelengths focused outside the object or the weld seam (in addition to the desired wavelength focused on the object or the weld seam) may be received by the detector, whereupon the wavelength with the shortest path (top reflected) is selected.

According to embodiments of the invention a cross-sectional profile, comprising also joint or groove or notch areas, of the weld seam can be determined based on the determined depths. It is to be noted that when the spectre of electromagnetic radiation band (so the arrangement) and the object are moved in relation to each other, multiple images can be captured in real-time during moving and the longitudinal or overall profile or other properties along the length of the seam can be determined.

In addition it is to be noted that different exposure times can be used in order to achieve information from the points of the surface having e.g. different inclination angle in relation to the emitted spectre, namely with a first short exposure time a surface profile having front surface essentially perpendicular to the radiation beam will be exposed enough but the surface having inclined surface profile will be underexposed, and again with a second long exposure time the surface having inclined surface profile in relation to the radiation beam will be exposed enough but the surface profile having front surface essentially perpendicular will be overexposed. Furthermore the different exposure times can also be used for surface points having different degrees of gloss in order to achieve satisfying information. For example shorter exposure time is advantageously used for the glossier surface point in order to avoid overexposure and the longer for a matt surface point. By combining these images a satisfactory result can be achieved so that the whole surface profile of the object is imaged accurate enough. Naturally number of different exposure times can be used. According to an example using of number of different exposure times can be implemented in many ways. For example the reflected electromagnetic radiation can be received by number of diodes (or other receiving components, such as pixel in CCD or CMOS device), whereupon the first set of the diodes is used for receiving the reflected electromagnetic radiation for first time set (t-ι) and the second set of the diodes is used for receiving the reflected electromagnetic radiation for second time set (t ₂ ), which is longer than said first time set (t-ι). In this way two different exposure time can be applied and information from different portions with different inclination angles can be achieved. For example the shorter exposure time is advantageous for a surface essentially perpendicular to the radiation beam and the longer exposure time for a surface having steeper angle in relation to the radiation beam as well as shorter exposure time for the glossier surface and longer exposure time for the more matt surface. In particularly it is to be noted that also more than two different exposure times can be used. Different techniques can naturally be used for implementing different exposure times, such as reading different columns and/or rows of the detector (e.g. CCD or CMOS device) one-by-one or in a certain order or in a certain combination or at once. Additionally the different exposure times can also be mimicked by suitable software. The software can also be used for controlling the reading the detector or different columns and/or rows. Also a dedicated detector with suitable controlling capacity can be used. Furthermore, according to an exemplary embodiment, the different exposure times can also be implemented so to determine the degree of exposure in different pixels (or group of pixels) and whether any overexposure is determined in a certain pixels (or group of pixels), a data reading or gathering from a certain group of pixels, such as a certain row or column, is stopped in order to avoid overexposure of the whole group of pixels. This can be naturally achieved either by a hardware and controlling devices managing the reading of the pixels and/or by a software used for controlling the reading operation.

According to an embodiment the arrangement may also determine the steepness of the surfaces to be determined and thereby also configured to adjust and control different exposure times. Alternatively, or in addition to, the arrangement can apply and control (so change) the exposure time even for each single pixel based e.g. on the responses detected or received from the detector or receiving component in relation to the exposure, so whether the pixel tends to be overexposured or underexposured.

The properties, such as cross-sectional profile or the like described in this document, can be determined by comparing measured parameter, such as geometric parameter, like a cross-section profile, to a predetermined corresponding parameter or to respective reference value or respective tolerance interval of a reference weld seam, such as to a cross-section profile the reference weld seam. In generally the measured parameters are compared to a predetermined statistical distribution, which represent the corresponding parameters. These predetermined corresponding parameters or statistical distribution data are advantageously stored into a memory means.

According to an embodiment controlling information is generated to a weld seam manipulating device based on the measured parameters, in order to control the weld seam manipulating device to produce the weld seam so that the quality parameters correspond and match with a certain tolerance to the predetermined reference weld seam parameters. The controlling information can also be used for indicating the determined quality parameters to the user, such as especially indicating if the determined quality parameters does not fulfil the required level. The indication may be implemented e.g. by sound, visually and/or via tactile feedback, for example.

According to an embodiment the weld seam manipulating welding device is a welding device e.g. in a laser welding process, whereupon the controlling information is data used to controlling welding parameters of the welding device, such as current, length of arc, angle, position or speed, or even ON/OFF -type information to stop or start the welding process. By controlling the welding process by the welding parameters the welding device is advantageously controlled to produce the weld seam so that properties of the weld seams, such as cross-sectional profile, opening angles, curvature, depth, full penetration, seam width, humping, and a degree of asymmetry during welding among other, correspond and match with a certain tolerance to the predetermined reference weld seam parameters.

According to an embodiment the weld seam manipulating welding device is a marking or painting device, and wherein the generated controlling information is information used to control the marking or painting device to mark or paint a certain point of the weld seam if a certain parameter of said weld seam at said certain point does not correspond or match respective reference values or respective tolerance intervals of a reference weld seam. According to an embodiment the weld seam manipulating welding device is a sanding machine and wherein the generated controlling information is information to control said sanding machine to sand or polish a certain point of the weld seam if a certain parameter of said weld seam at said certain point does not correspond or match respective reference values or respective tolerance intervals of a reference weld seam.

The seam quality might be assessed as unsatisfactory for example if the geometric parameter determined does not correspond to a respective reference value or lies outside of a respective tolerance interval.

The method of the embodiments can be implemented by a handheld device or arrangement, or an arrangement being integrated into a production line (on-line installation) or being a portion of a welding arrangement. In addition at least some of the steps to implement the embodiments, such as especially for analysing the properties of the weld seam, can be implemented by running a computer program product on a data processing means. The computer program product code may be stored in a media run on the data processing means, or it may be stored into data cloud system. In addition the computer program product can be used, when run, to provide the control information to weld seam manipulating welding device. In addition the measured data can also be stored into the memory, e.g. to the cloud system, for possible later use or quality inspection purposes.

According to an exemplary implementation some embodiments of the invention can be implemented by a LCI (Lateral Chromatic Imaging) device which produces at least one light line (planar beam) over the weld seam. The LCI device is capable of creating an accurate line image of the cross section of the weld seam. Thus the three-dimensional course of the weld seam can be accurately detected and its geometrical data measured. Especially e.g. groove or notch in front of the weld seam can be seen and measured and the parameters of its shape can be determined, such as opening angles, curvature, depth, width etc. These are one of the most important parameters with which makes possible to accurately estimate the quality of the weld seam, such as toughness, long-term sustainability, fatigue strength or the like. The LCI device can be advantageously moved along the weld seam and similarly taking multiple images in real-time. These images can be transferred to a processing device, which analyses those using specified algorithms and gives an estimation of the weld seam quality. This result can be transferred to the welding robot or available to a person and thereby adjust the weld seam quality even during the welding process.

The present invention offers advantages over the known prior art, such as the possibility to measure very accurately the whole profile of the seam, also the groove or notch areas. For example LCI technology enables to have μιτι (micrometer) resolution image over the whole weld seam and all of its noteworthy surface shapes relating to it. Furthermore the embodiment of the invention also enables imaging a butt joint and T-connected parts (T-joints) because of its imaging technology, accuracy and mechanical size. The embodiments of the invention are also not sensitive to imaged weld seam vibration during measurement. In addition the invention enables measuring, analysing and feedback to the system in real time. Having this accurate image and fast analyse enables higher quality examination of the weld seam than before. Moreover the measurement and determination can be done in real-time which allows to produce feedback information to the welding system, for example, to adjust the welding parameters and therefore achieve higher quality weld seam.

BRIEF DESCRIPTION OF THE DRAWINGS Next the invention will be described in greater detail with reference to exemplary embodiments in accordance with the accompanying drawings, in which:

Figure 1 illustrates a principle of an exemplary arrangement for analysing a property of a weld seam (side view) according to an advantageous embodiment of the invention,

Figure 2 illustrates an exemplary arrangement for analysing a property of a weld seam (front view) according to an advantageous embodiment of the invention, Figure 3 illustrates an exemplary arrangement for analysing a property of a weld seam of t-connected parts (front view) according to an advantageous embodiment of the invention, and

Figure 4 illustrates a principle of reading the reflected beams and providing different exposure times according to an advantageous embodiment of the invention.

DETAILED DESCRIPTION

Figure 1 illustrates a principle of an exemplary arrangement 100 for analysing properties of a weld seam 101 (side view) according to an advantageous embodiment of the invention, wherein the arrangement 100 comprises an optical component 102, such as a prism, lens or optical lattice, for providing a spectre 103 of electromagnetic radiation band to the weld seam 101. The spectre 103 is spread so that different wavelengths 103A, 103B, 103C of the radiation are focused to different depths h-ι, h ₂ , h ₃ in a direction of a normal 104 of the weld 101. In addition the arrangement comprises also a receiving component 105 for receiving at least a wavelength 106B focused on and reflected from the depth h ₂ (level) of the surface of the weld seam 101 at a certain point of the weld seam. The receiving component comprises 105 a detector, such as a line detector, CCD device, or an imaging spectrometer. One example is e.g. a 2048x1088 matrix detector. The arrangement may also comprise a source 1 1 1 for generating the electromagnetic radiation band, such as a laser source.

Moreover the arrangement comprises also an analysing unit 107 for analysing the received wavelengths 106A, 106B, 106C and to select wavelengths having intensity over a predetermined threshold value. The analysing unit 107 is also configured to construe the wavelength travelled the shortest path to represent the wavelength 106B focused on and reflected from the depth h ₂ of the surface of the weld seam 101 and thereby configured to determine the depth h ₂ of the weld seam at said certain point of the weld seam.

The arrangement 100 may also provide, advantageously using the optical emitting components, the spectre lines 103 of said electromagnetic radiation band so that a planar line or beam 108 of each wavelength extend over the weld seam (see Fig 2, a front view) at a certain point in a direction of a cross axis line 109, which is perpendicular both to the normal 104 and longitudinal direction 1 10 of the weld seam.

In addition the arrangement is additionally configured to receive the reflections of the planar line or beam wavelengths 106A, 106B, 106C focused on and reflected from the different depths h-ι, h ₂ , h ₃ of the surface of the weld seam along the cross axis line 109. The arrangement is also configured to determine a cross-sectional profile (see the front view in Fig. 2) of the weld seam 101 at said certain point along of the elongated weld seam.

According to an embodiment the arrangement may also comprise, or is configured to communicate 1 13 with a welding device 1 12, whereupon the arrangement is configured provide controlling information to control the welding device 1 12 to produce the weld seam so that the parameters correspond and match with a certain accuracy to the predetermined reference weld seam parameters. It is to be noted that even if the welding device 1 12 is depicted as an example, the device 1 12 can be also other weld seam manipulating device controlled by the arrangement, as is disclosed elsewhere in this document. Figure 3 illustrates an exemplary arrangement for analysing a property of a weld seam 101 of t-connected parts (front view) according to an advantageous embodiment of the invention.

Figure 4 illustrates a principle of reading the reflected beams and providing different exposure times according to an advantageous embodiment of the invention by using an image sensor in connection with the receiving component 105. The receiving component 105 comprises a detector, such as a line detector, CCD or CMOS device as an image sensor, which comprises a pixel array of sensor elements used to create an image from the reflected beams of the measured surface of the object. In Figure 4 an example of the CCD / CMOS device 1 14 is depicted, where the device is used for providing number of different exposure times. The reflected electromagnetic radiation 106 are received by number of pixels in CCD or CMOS device 1 14. The device 1 14 can be controlled, for providing different exposure times, for example so that a first set of the pixels is used for receiving the reflected beams 106 for first time set (t-ι) and the second set of the pixels is used for receiving the reflected beams 106 for second time set (t ₂ ), which is longer than said first time set (t-i).

In addition, different columns and/or rows of the device 1 14 can be read in many ways and thereby different exposure times can be achieved. For example every row, column and/or pixel in the array can be read separately, or every row, column and/or pixel in the array can be read at different time (so in practice e.g. every row, column and/or pixel in the array can be turned on/off at different time). The device 1 14 may comprise suitable controller 1 15 for controlling the operation of reading the pixels, or the device 1 14 may comprise additionally also suitable components, such as a row addressing circuit 1 16 and column addressing circuit 1 17.

The invention has been explained above with reference to the aforementioned embodiments, and several advantages of the invention have been demonstrated. It is clear that the invention is not only restricted to these embodiments, but comprises all possible embodiments within the spirit and scope of the inventive thought and the following patent claims. In particularly it is to be noted that even if the determination of the physical weld seam is depicted in Figures, the arrangement and method of the embodiments according to the invention can also be used to analyse and determine a mould of the seam weld, such as a silicon casting mould.

Moreover it is to be noted that even if the weld seams are discussed in the description, they are only as examples and that the embodiments of the invention can also be used for analysing and determining properties of another seams or object representing also other types of seams.