A CAD Based Off-line Programming of Painting Robots

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1 A CAD Based Off-line Programming of Painting Robots [1] Kadam Bhagyashree Jayarjun, [2] S.S.Gaonkar, Sinhgad Institute of Technology and Science, Narhe, Pune, Abstract-Nowadays, robot programming is used to complete various task. Teach Pendant, a most popular robot programming language is time consuming and requires training to learn and program. New method developed for robot and human communication is off-line programming. It requires high level programming language. In Teach Pendant as operator has to operate the robot for programming, it would be dangerous. This paper presents off-line programming using CAD models. Off-line programming is done without stopping the robot production. In off-line programming robot can be programmed through CAD software. Operator need not to operate the robot manually. The program can be downloaded directly from CAD software to robot. This paper introduces the off-line robot programming used in spray painting, welding, etc. A post-process is important element of an off-line robot programming that allows robot simulation system to be used as robot programming tool. The robot was programmed to paint alphabets using its Flex Pendant. The Flex Pendant was used to manually teach the robot how to follow paths for specific targets of letter. For effective painting task, end effector (painting tool) was choosen and mounted on robot. The Computer Aided Design (CAD) of system work-objects and end effector was programmed based on solidworks software. With simulation and experiments off-line programming has improved efficiency of production and quality of products. Keywords-CAD, off-line robot programming, painting robot I. INTRODUCTION Modern industries are developing on industrial robots. Robots are widely used in spray painting application. Robot programming through Teach Pendant is time consuming and requires training to learn and program. The sequence of motion and data required to drive robot can be transmitted through use of serial or parallel data link, between an off-line computer (where proposed system is designed and simulated) and robot controller[3]. Robot programming is done from CAD drawing and not by CAM software or commercial off-lone programming. The robot is 6-axis industrial robot, designed specifically for an industry that uses flexible robot based automation. The robots have an open structure that is adapted for flexible use and communicate extensively with external systems[2]. As robot has flexible movements, it can achieve a projection on complex andfree form workpiece. The accurate programming of robot is required to ensure painting properties that require low tolerance concerning thickness, roughness, hardness, porosity and coating structure [4]. There are two basic robot movements in control system, manipulator movement in terms of manipulator end effector location and the movement in terms of manipulator joint angle. Advances in CAD/CAM methods and growing interest in off-line robot programming led to this technique being applied for painting robots, which led to better quality coating and decrease of paint loss [3]. The efficiency of 179

painting process is increased by off-line programming than the current practice (efficiency is defined as being ratio of paint usefully applied to total consumed). II.

2 painting process is increased by off-line programming than the current practice (efficiency is defined as being ratio of paint usefully applied to total consumed). II. OFF-LINE PROGRAMMING OLP involve manual editing of robot code. The advantage is that robot can be programmed without stopping robot production. While limitation is high investment in software and worker s training. Three most common OLP packages are Delmia from Dassault systems, RobCAD from Technomatix Technologies and Robomaster from Jabez Technologies. Every robot manufacturer has its own OLP software. Example: KUKA.Sim from KUKA, Robot studio from ABB Robotics and Motosim from Motoman. Figure 1. OLP concept[1] A. Graphics Programming It is advanced process called off-line programming. It provides complete solution for spray painting from path generation, parameter choice to procedure simulation and trajectory optimization[4]. To guarantee path precision robot trajectory can always be generated by geometrical data Acquisition of the CAD files First step is to acquire 3D geometric model. If there is no original CAD model available, it must create the simple model that describes the surface to spray in CAD software such as: Catia, Solidworks, Pro/Engineer, etc. The geometrical information of the workpiece can be obtained by the coordinated measuring machine or laser scanner system. This method is particularly effective for complex workpieces without CAD files. 180

3 Reverse engineering CAD files Obtain workpiece s form Select operating parameters Analyze workpiece Generate curves on surface Create points on the curves Generate robot path Process simulation No Adapted? Yes Robot program Download to robot controller Calibration Yes Collision detection No Apply to the system Figure2. Procedures for generating an off-line trajectory [1, 4] 181

4 Selection of operating parameters Parameters are classified into several groups according to published studies: the energy parameters, powder injection parameters and kinematic parameters. In order to lead to desired and optimized coating properties, operating parameters should be chosen and kept constant during spray painting. Trajectory generating The aim is to find the coordinates of points which define the scanning curve and orientation of each point. The first method is to generate the mesh of the CAD model, then find out the trajectory from the mesh points and normal vectors to the surface. There are many file formats of geometric models available for this operation such as STL, IGES, STEP, ASCII and ACIS [4]. The STL file describes the workpiece with triangular mesh and every triangle is defined by three vertices and normal vector to surface in three-dimensional Cartesian coordinate system. The trajectory can be generated by this method using software such as Matlab, Catia etc. The advantage of this method is that it is possible to generate trajectories on all types of complex workpieces. The second method involves the use of orthogonal planes to cut the surface to be coated, and then a series of scanning curves will be generated [4]. This method is simpler than the method of mesh generating, but if the workpiece is very irregular and asymmetrical, it is difficult to obtain a satisfactory trajectory with this method. Figure3. Coordinate frames [1] Simulation The process simulation method involves two parts: simulation of the robot kinematics and heat transfer. Robot kinematics: Industrial robots are manufacturers are now offering simulation software tailored specifically to their robots, for example the RobotStudio for ABB robots, the Robotguide for Fanuc robots etc. This software can import 3D models of workshops, robots, and workpieces to generate the desired trajectory invirtual workspace. Heat transfer: It consists of studying the temperature distribution at the substrate s surface and the stresses to which the piece will be subjected during the coating process. 182

5 Calibration If the results of kinematic and thermal simulations are satisfactory, the robot program can be loaded to the site of projection. An off-line program cannot be executed correctly in real robot without calibration. This process permits to synchronize the definition of the TCP (Tool Center Point) and the position of workpiece between the virtual and real robot [4]. Collisions It should be predicted by the designer during the creation of the CAD model of the cell. The designer should ensure that there should be no collisions between the robot and other objects within the workspace [1]. If the robot end effector is linearly moved from the initial to the target pose a collision occurs. Apply to the system After collision test, the robot program is tested at low speed and at last it will be used for real spray painting process. If simulation result is not satisfactory, it is necessary to return to previous steps to verify and modify the robot program. Figure4. Collision [1] Figure 5. Avoiding an obstacle [1] 183

III. CAD BASED ROBOT PROGRAMMING CAD technology has become economically attractive and easy to work. In 1980s, CAD was seen as technology that could help in development of robotics [1].

Diverse solution is proposed for spray painting and coating processes. Robotics system defines mechanics, control, sensor and design of robot.

6 III. CAD BASED ROBOT PROGRAMMING CAD technology has become economically attractive and easy to work. In 1980s, CAD was seen as technology that could help in development of robotics [1]. It is now possible to get information from CAD drawing to create robot program for different applications. Human and robot communication is generated using CAD studies. Diverse solution is proposed for spray painting and coating processes. Robotics system defines mechanics, control, sensor and design of robot. Mechanics includes design and structure of manipulator, arms, end-effector and energy storage. The other components that played vital role in project are the design of robot work object, air compressor and paint used in spraying process [2]. A CAD guided robot path generator is proposed for process of spray painting of compound surfaces commonly seen in automotive manufacturing [1]. Chenetal presented review of CAD-based robot path planning for spray painting. While Arikan and Balkan proposed CAD based robotic system addressing spray painting process of curved surfaces [1]. Many researchers have been conducted in field of CAD/CAM based OLP. There is no effective solution for low cost and intuitive OLP solutions using CAD drawing. Figure 6. Opening Autodesk Inventor (coded in VB)[1] Figure 7. Opening an Autodesk Inventor document and extracting their properties (coded in VB) [1] 184

Figure 8. Extracting data from a selected Work Point (coded in VB) [1] Figure 9.

Extracting the transformation matrix of a selected item (coded in VB)[1] The IRB1410 robot is

Actuators are like muscle of manipulator. They convert stored energy into movement.

7 Figure 8. Extracting data from a selected Work Point (coded in VB) [1] Figure 9. Extracting data from a selected virtual line (coded in VB)[1] Figure 10. Extracting the transformation matrix of a selected item (coded in VB)[1] The IRB1410 robot is used for spray painting. It has payload of 5kg and 1.44m working envelop[2]. Actuators are like muscle of manipulator. They convert stored energy into movement. The device called as end-effector is placed at end of robot manipulator to interact with environment. In this spray gun is used as an end-effector for 185

8 painting robot. Paint is any liquid, liquefiable or mastic composition which after application to subtract in a thin layer is converted to an opaque solid film[2]. Figure 11. Simplified tool models defining the robot end-effector pose in each path segment [1] IV. SOFTWARE DEVELOPMENT The end-effector should be choosen correctly for painting application. The spray gun and work object is designed in Solidworks software and imported to Robotstudio as CAD file for programming of path and target[2]. The backup system of painting program is created and saved in flash drive. Flex Pendant of IRB1410 robot connected to IRC5 controller contains backup painting program[2]. The flow of air to actuate spray gun is controlled when ON signal is given by controller to directional control valve. The Flex Pendant generates its program according to how robot is taught. V. PATH PLANNING AND ROBOT TRAVELLING TIME To program robot motion and find travelling time for spray painting is time consuming and really challenging task. Computer model of robot or physical robot can be used for programming. The joystick is used to control the motions of robot to specify robot program. OLP has many advantages such as better equipment utilization, fast introduction to new product model, reduce the programming time and improve program by math-based algorithms for motion planning[6]. 186

VI. METHODOLOGIES OF DOWNLOADING OFF-LINE PROGRAMS TO THE ROBOT CONTROLLER When post-processing is complete, the program may be transmitted to the robot controller in following possible ways: a.

9 VI. METHODOLOGIES OF DOWNLOADING OFF-LINE PROGRAMS TO THE ROBOT CONTROLLER When post-processing is complete, the program may be transmitted to the robot controller in following possible ways: a. The robot program can be downloaded via robot specific medium (such as magnetic tapes, paper tapes, floppy diskettes, etc.) which can be transferred manually from design office to the shopfloor[3]. Figure 12. Download to robot controller [1] b. If it is desired to load program electronically through an available robot specific medium interface, then a communication protocol must be implemented in software in order to interface o the robot controller. The use of an RS-232 link to facilitate the communication between the CAD system and the robot controllers is quite commonly used in industry[3]. c. A more flexible approach could be based upon the use of the MAP/TOP. This new enabling technology provides control data, monitoring status transmission, etc. And potentially there is much reduced need to write specific protocol conversion for each robot. MAP broadband network and advanced internet facilities enable users and programmers to transmit off-line robot programmers to transmit off-line simulation workstation and the actual robot cell for calibration[3]. VII. CONCLUSION The use of off-line programming will increase widely in the application of spray painting. The cost of painting is reduced by using less paint. New methods are developed to optimize geometry stations with respect to dimensional quality and cycle time and also to make robot programming easy in spray painting. The quality of painting and safety was improved. Post processors are system-dependant or application-dependant. The main disadvantage is initially high investment in software and skill operators are required during off-line programming. 187

10 VIII. REFERENCES [1] Pedro Neto, Nuno Mendes, Direct off-line robot programming via a common CAD package,in:robotics and Autonomous Systems 61 (2013) [2] Ijeoma W. Muzan, Tarig Faisal, H M A A Al-Assadi, Mahmud Iwan, Implementation of Industrial Robot for Painting Applications, in: Procedia Engineering 41 (2012) [3] S.F.Chan, Reggie Kwan, Post-processing methodologies for off-line robot programming within computer integrated manufacture, in: Journal of Materials Processing Technology 139 (2003) [4] SiHao Deng, ZhenuHua Cai, DanDan Fang, HanLin Liao, Ghislain Montavon, Application of robot offline programming in thermalspraying,in: Surface and Coatings Technology 206 (2012) [5] Wenlei Xiao, Ji Huan, Shuxiang Dong, A STEP-complaint Industrial Robot Data Model for robot off-line programming systems, in: Robotics and Computer Integrated Manufacturing 30 (2014) [6] John S. Carlson, Domenico Spensieri, Kristina Warmefjord, Johan Segeborn, Rikard Soderberg, Minimizing Dimensional Variation and Robot Travelling Time in Welding Station, in: Procedia CIRP 23 (2014)

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