|Ario Sunar Baskoro||Department of Mechanical Engineering, Faculty of Engineering, Universitas Indonesia, Kampus Baru UI Depok, Depok 16424, Indonesia|
|Reggi Prasetyo Kurniawan||Department of Mechanical Engineering, Faculty of Engineering, Universitas Indonesia, Kampus Baru UI Depok, Depok 16424, Indonesia|
|Haikal||Department of Mechanical Engineering, Faculty of Engineering, Universitas Indonesia, Kampus Baru UI Depok, Depok 16424, Indonesia|
The development of technology in fabrication and manufacturing systems is increasing nowadays. The use of robots as mediators to assemble all kinds of product has become a new challenge in this era, and robotic welding technology is now the choice for certain automotive industries to produce their vehicle products. This research will develop an artificial robot welder with a type of gantry robot as a training prototype to gain more in-depth knowledge of industrial robots. The purpose of the paper is to develop an initial welding robot system, focusing on evaluation of the 2-axis movement of X and Y. The robot’s movement will be controlled by a microcontroller, and its level of accuracy and repeatability will be measured a by Faro Arm Portable Coordinate Measuring Machine (PCMM) with an error of around 0.02 mm. This measurement method will consist of five speed characteristics, which make the robot move for a constant distance of 125 mm. The results show that the best level of accuracy is 0.83%, at 2.5 mm/s of velocity. The X and Y axes produce movement with the best repeatability of 96 ?m and 108 ?m, respectively. Based on the results, the gantry robot displays good performance in repeatability and accuracy, proving it can work effectively.
Accuracy; Gantry robot; Repeatability; Welding application
Many industries have recently used robotic assistance in their industrial processes, such as welding, tasting and stamping. In addition, the demand for robots in industry has also increased, in line with better levels of accuracy and repeatability (Nubiola & Bonev, 2013). Many types of robots are used in industry, such as arm robots and gantry robots. The gantry robot is a robotics system that is widely used in industrial manufacturing processes, due to the larger workspace area that can be achieved and high levels of stiffness. Since 1998, such robots have used for precision manufacturing and materials handling in the electronics, nuclear and automotive industries (Baicu et al., 1998). Nowadays, they are not only used for materials handling, but also for welding applications such as arc and spot welding. The requirements for robots that are suitable for use in industry include at least good accuracy and repetition rates (Zaeh et al., 2010).
Welding is an important technique and is often used in industry to join metals quickly, strongly and economically. Robotic welding technology has been implemented in many industrial sectors to increase the level of production. In addition, using such technology can improve weld quality and the consistency of weld results, and reduce associated costs and product defects (Kah et al., 2015). Friction stir welding (FSW) is an advanced welding technology to join light materials used in gantry-type CNC system manufacturing processes in the aircraft, aerospace and automotive industries. Another process for welding similar light materials is to use aluminum to aluminum resistance spot welding (RSW) (Baskoro et al., 2017) and for dissimilar materials aluminum to steel RSW (Muzakki et al., 2018). Using FSW to join aluminum has several advantages compared to fusion welding and riveting processes (Baskoro et al., 2015).
The development of gantry robots has been researched for a considerable time; Ji-Hyoung et al. (2001), for example, developed a multi-axis gantry type welding robot system for automated fabrication of shipbuilding and steel bridge line subassemblies. It was reported that using a PC-based controller on the gantry robot was more compatible than a robot controller and that cost efficiency could be reduced. However, using a gantry robot as a robotic mechanical system faces certain problems, especially related to movement. Meressi (1998) created sliding mode and fuzzy scheduled linear controllers to minimize the rope angle oscillations of a three-dimensional gantry robot during travel and transverse motion in reasonably high-speed maneuvers. Recently, many types of research approach have been undertaken to develop FSW welding tool technology from gantry type CNC systems with industrial robots (Von Strombeck et al., 2001; Smith, 2004; Soron & Kalaykov, 2006; Mendes et al. 2016). Nevertheless, several problems have arisen because industrial robots have the limitation of only being able to join aluminum materials of up to 8 mm thickness (Voellner et al., 2008). Furthermore, high lateral force emerges during the FSW process, so a mechanism with high stiffness is needed (Guillo & Dubourg, 2016).
The accuracy of robots is important if applied to an offline program, but if they are taught manually at the end-effector of the robot, the accuracy is not important. Several issues can cause errors in robot accuracy, such as ones linked to computation, measurement, application, the environment or parameters. Another important aspect of robots is their level of repeatability. In industry, robots used have a better repeatability rate than level of accuracy. The calibration method was one method to increase the level of robotic accuracy if the robot already had a good level of repeatability (Nubiola & Bonev, 2013).
A gantry robot is more compatible than a jointed arm robot for FSW applications which need a high-performance machine. Previous studies by Guillo and Dubourg (2016) and Samhouri et al. (2005) have focused on the gantry robot, but have been limited to the 3-axis type. This paper develops a 5-axis gantry robot system for FSW welding applications, but this preliminary study will focus on evaluation of the 2-axis movement of X and Y. One of the applications of this robot is that it can be used to make honeycomb structures (Cohal, 2017). Robot testing was conducted by its movement, which measured the suitability of the repeatability and accuracy of the target.
In this paper, a gantry robot system has been successfully developed for robotic FSW applications. This preliminary research has focused on the 2D axis movement of the gantry robot to determine its level of accuracy and repeatability. Measurement of X and Y axes was made to evaluate the ability of the gantry robot with several variations in feed rate. The results show that the best level of accuracy was 0.83% at a velocity of 2.5 mm/s, while the repeatability rate produced on the X and Y axis was 96 ?m and 108 ?m, respectively. Future work will focus on the remaining three axes and the application of the gantry robot for FSW welding, and will also examine the 3-axis movements that have not been discussed in this paper, and their application in welding.
The author would like to express his sincere gratitude for the financial support of the Directorate Research and Public Service, Universitas Indonesia, through contract number 1753/UN2.R12/PPM.00.00/2016, with the title of “Pengembangan Mesin Tungsten Inert Gas Welding Otomatis Berbasis Machine Vision dan Neural Network”.
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