ON LINE VIDEOOPTICAL SYSTEM FOR WELD GROOVE ANALYSIS Tadeusz Mikolajczyk1,a *, Mikolaj Mikolajczyk2,b, Andrzej Skibicki 1,c 1
Faculty of Mechanical Engineering, University of Technology and Life Sciences Kaliskiego 7 str.85-796 Bydgoszcz, Poland 2 a
Erplast, Olowiana 12 str., 85-461 Bydgoszcz, Poland
[email protected], b
[email protected], c
[email protected]
Keywords: picture recognition, weld groove, intelligent robot control
Abstract. The article shows the video-optical system for to recognition of location and size of weld groove. Was used special system equipped with two USB cameras (VGA resolution) and red laser. First of camera was used to recognition of groove location and second one with laser as mobile scanner was used to size of groove analyse. For proposed conception was prepared in Visual Basic 6.0 special software WELD_REC, which calculate the angle of groove location and the groove parameters: width, depth and angle of opening. Presented system is used for experiments using PC controlled IRb –60 industrial robot. The differences of location of groove: between well-known and video-optical measured have the highest of 3%. Introduction Industrial robots are improved very quickly [1]. Their control systems are better and better. New modules used may modernize existing older robots [2]. They can be practically used real production and sometimes replace humans. In this case we may observe more often application of artificial intelligence. Also in industrial and humanoid robots. Industrial robots was used in many tasks of manufacturing especially as machines equipped with tool for machining [3]. Welding represents one of the single largest applications of robots in manufacturing engineering, as approximately a quarter of all industrial robots are being used in connection to welding tasks [4]. The development of digital technique and software make possible the recognition and analysis of image [5-14]. It is also practical in technological uses. In many tasks in technological processes has used cameras as informative input. Now digital camera is cheap element which may be connected to PC USB port. Capture pictures from this camera are used by the author in many solutions, for example: system of tool wear recognize using neural networks [5], measurement of tools angles [6], measurement of temperature (in infrared range) [7], measurement of drill diameter in adaptive system [8]. Increase using of videoptical system equipped with USB camera for industrial robots: for scanning systems [9,10] especially for welding [14,15], for system of surface roughness measuring [10,11], analyse of picture for making surface relief [12], indication of machining area [13], RobScan - Robot-guided remote scanner for laser beam welding [14] - is a new laser beam welding process. It represents a new approach to laser beam welding using the known advantages of laser welding and extending it with new possibilities in process technology and a new control system to utilize all the possibilities of the remote scanner. Authors of presented paper was shown video optical system for research of weld groove in welding process [16]. This article shows the modernized video optical system for the diagnostics weld groove direction and size. It is applied for industrial robot IRb-60. This study was made on Faculty of Mechanical Engineering University of Technology & Life Science, Bydgoszcz, Poland.
Concept solution An idea of presented system was search of weld groove location and after of robots head rotation to groove direction automation measurement of groove parameter for calculation of welding process parameter. According to conception for recognition and analysis of weld groove, the intelligent system concept has been worked out, which has the procedures of image analysis (Fig. 1). The system should have measuring arrangement, which can recognize the image. This way it will qualify the datum feature of the location and dimensions of weld groove. Measuring and robot steering systems are mutually linked. The generated signals steer the shoulder and end of arm tooling (EOAT) of robot. Next, the results of this dimensions' analysis of weld groove can control the process of welding, but it need some development of used software.
Laser
Camera #1
Camera #2
Axis of head
rotation Laser ray
Weld groove
Intersection of laser light with workpiece surface
Fig. 1. Conception of measuring system for finding and the measurement of weld groove
Fig. 2. The first phase of system functioning: finding the groove and qualification of dislocation and rotation parameters of weld robot EOAT Subsequently, it is possible to think about the assessment of the quality of the executed joint. In this conception the arrangement has to have: camera #1 for determining the groove location (Fig. 2), the flat ray of red laser to show weld groove profile (Fig. 3), camera #2 for registration the groove section (Fig. 3). The direction of groove is the straight line going by groove centre and tilted for some angle. It in next step there is a calculation of the perpendicular angle and distance of groove from rotation axis of the EOAT of robot (Fig. 4).
1. dislocation of analysed crossection
Fig. 3. The measurement of section of light groove - the view from camera #2
Fig. 4. The diagram of distance calculation: from the groove to rotation axis of EOAT
y
yB xB
y
a x h
b
yB xB
yA x xA xA
yA xA xA
yA
(1)
(2)
yA
(3)
Next the rotation axis of EOAT is calculated, as equation of more suitably straight line. The software then solves the arrangement of equations in relation to axis X and Y for both straight lines. That gives the intersection to the straight lines. Because yP= y0 will suffice to find yP for straightline s: yp b xp (4) a Now follows the translocation of the camera, in the direction to groove of weld. This is necessary to obtain the slits of groove and axis of camera. The module of steering receives these results. The EOAT is then shoved and turned over. This is realized, together with installed here the arrangement of diagnostics of groove. Now follows the verification of current location. If camera #1 is in axis of groove then camera #2 begins working. This camera #2 is 150 mm away from axis of laser and is under the angle. The view of triangulation of laser in groove is now recorded and analysed (Fig. 3).
Investigative stand Investigative stand (Fig. 1) consists of: industrial robot IRb-60, PC with operating system and programming environment. The control system of the robot is modernized and connected to personal computer [2]. Old manual control system [17] was replaced by special arrangement of relays and connected through LPT interface to PC and with special software control the robot [2] and make possible many advanced tasks [9-11]. Measuring arrangement has been worked out (Fig. 5) according to conception (Fig. 1). It contains: special holder camera #1: vertical, camera #2: horizontal, laser (little pointer), diverging cylindrical lens (Fig.6).
Laser ray
lens
Fig. 5. The view on measuring arrangement
Fig. 6. Scheme of scanner lens
Two USB cameras with VGA resolution and CMOS matrices were used. In system was used low cost USB camera (Fig. 5) with VGA resolution (640x480), up to 15 frames/s, number of colours: 24 bit true colour, depth of field: min. 50 mm to infinity, viewing angle 52 o, interface: USB 1.0, 1.1, 2.0, connection hot plug & play, running operating systems: Win XP, Win 2000, Win ME. The source of lighting for scanning arrangement is LED laser (little pointer with red light, about 660 nm). The arrangement has the lens especially made of plastic plexiglas. It generates thin light line on studied surface. This idea is new and considerably simpler than rotary 3D scanner or arrangement with gyratory mirror. The length of line depends on the distance from weld groove. Here, 12 mm was applied. Software for recognition and measurement of the weld groove Special software for conception (Fig. 1 and Fig. 2) was prepared in Visual Basic 6.0 using algorithm presented on Fig. 7. This software is called WELD_REC (WELDing RECognition) (Fig. 8). It functions in two steps: • First: qualification of direction of groove and calculation of necessary dislocation of robot. The algorithm has the loop of verification of the new location of robot. • Second stage comes after positive verification of the first. It is the measurement of weld groove with the help of the image analysis of laser light section. Main form this software have some specialized panels for realize two steps of task picture recognition, control of robot and to save the results of caliper measurements.
Fig. 7. The algorithm of special WELD_REC software The works accomplished in first stage are shown on Fig. 8. They demonstrate the further sequences of finding the groove location (in the visual field from upper camera). The recognition of location of groove is possible thanks to the analysis of colour the pixel of image: in upper and bottom sections, in direction from the left as well as from the right.
Fig. 8. View of main form of WELD_REC software. Presented Groove location panel
Software finds the outline of groove through the analysis, checking the pixels for the colour of laser ray (R > 240). Section creates 4 lines and this defines groove. Software calculates the dimensions of groove: the width, depth and angle of opening (Fig. 9).
Fig. 9. View of groove profile measurement panel For the unfailing measurement of groove it is necessary to adjust the arrangement of cameras to current parameters: external lighting and kind of surface of groove. The software gives the possibility of modifying the brightness and contrast. This optimises the signal designed to analysis. Verification of system Samples for verification were made of N10E steel. Dimensions: 43x60x3.1 mm, V-grove with angle of 2x26,6 º . Upper surface is almost black, the banks of groove are after grinding. Sample was situated in the field of vision of camera #1 and analysed with software WELD_REC. The differences of location of groove: between well known and measured have at most 3%. This is enough if we compare this with the accuracy of location of sample (+/- 0.5°). After the measurement of angle, the dislocation was calculated. Later, the groove was observed and measured. The results from the analysis of groove are approximate to the results of mechanical measurements. This refers to the thickness of sample and the width of groove. Estimated, standard deviation for measurement of thickness is 0.186 mm for camera and 0.008 mm for slide caliper. For measurement of the groove width the standard deviation amounts 0.158 mm for camera and 0.013 mm for optical microscope. The accuracy of video-optical measurements is not very high, because the measured object (the groove) is small in comparison to camera resolution. In such conditions this is about 0.176 mm/pixel. It is possible of it increase using of subpixel analysis [18]. This is enough for the measurement of groove in workshop conditions, because the aim is the preparation of welding procedure. The use of camera with greater resolution and with the suitable optical magnification can indeed improve the precision of measurements.
Conclusions Accomplished results of investigations, along with their analysis and the review of literature, enable to present the following conclusions: the diagnostics of weld groove location with use of image analysis is possible. This image should be the subject for suitable transformation, for the unfailing diagnostics of welding groove location, it is essential to use the suitable lighting and special setting for the cameras parameters, has been found that the applied method of visualization of weld groove section with the use of laser distracted beam from diverging cylindrical lens is handy and convenient to measure the width of groove and thickness of material, achieved accuracy of measurement is connected with the resolution of the camera and zoom of its optical arrangement, the worked out software can find the practical use as a part of application for supervising welding by industrial robot, it is essential to conduct additional works over the use of video-optical method for positioning the groove and the measurement of its section basing on the research carried out, it is possible to work out the practical WELD_REC application to recognition the position of industrial robot during real welding. Need for further improvement of the scanner construction and also software towards the practical application of the presented idea. For scanner need to use camera with more resolution and best optical zoom to increase the accuracy of system. Based on the recognized shape and size of the weld groove should be developed algorithm for the welding of the terms accuracy. Developed scanner to measure the groove after the addition of the analysis can be used to examine the state of the weld. References [1] M. Vagaš, M. Hajduk, J. Semjon, L. Koukolová, R. Jánoš, View to the Current State of Robotics, Advanced Materials Research, vol. 463 - 464, (2012), 1711-1714 [2] Mikolajczyk T., Modernisation of IRb60 industrial robot steering system. OPTIROB'2007, Predeal Romania, University "POLITEHNICA" of Bucharest, 149-152 [3] Mikolajczyk T., Manufacturing Using Robot. Advanced Materials Research, vol. 463-464, (2012), 1643-1646 [4] European Commssion Report, 2003. Smart, Sustainable Manufacturing: EU Research Sparks Revolution in Machine Tools, Robots and Automation, Research and Innovation Report, Brussels, 2003 [5] Miko ajczyk T., Nowicki K.: Ocena obrazu zu ycia ostrza z wykorzystaniem sieci neuronowych. (Recognition of Edge Wear Using Neural Networks). Mechatronika, Warszawa, 1997, 829-833 [6] Miko ajczyk T., Zastosowanie analizy obrazu w badaniach obiektów i procesów (Implementation of Picture Analysis in Research of Objects and Process), Diagnostyka, vol. 33, (2005), 123-128 (in polish) [7] Mikolajczyk T., Polasik R., High Temperature Diagnosis with Infrared CMOS Camera. Journal of Polish CIMAC, vol. 6, no 2, (2011), 161-167 [8] Mikolajczyk T., Olaru A., Krainski P., Adaptive Control System for Drill Machine. Applied Mechanics and Materials, 2013, vol. 436, 445-450
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