Virtual Robot Kinematic Learning System: A New Teaching Approach

Transcription

1 Virtual Robot Kinematic Learning System: A New Teaching Approach 1 Haslina Arshad, 2 Khor Ching Yir, 3 Lam Meng Chun 1,2,3 School of Information Technology, Faculty of Information Science and Technology, Universiti Kebangsaan Malaysia, UKM Bangi, Selangor, Malaysia has@ftsm,ukm.my Abstract Computer assisted learning systems for robotics can assist students to understand topics on robot modeling, direct and inverse kinematics, join motions, trajectories, and also workspace limitations. This paper presents a virtual robotic kinematic learning system as a new teaching approach of robotics class which will assist and promote better students understanding of robotics. From the virtual system s interface, basic structure and movement of Cartesian, Cylindrical, Spherical and Articulated robot can be visualized. The transformation matrix exercises allow students to write down the formula of translation and rotation matrix and then see the movements of the virtual robot based on the input. In this virtual system, a Lynxmotion Arm Robot was used to teach kinematics for the manipulator movement using Denavit Hartenberg representation. The system is developed using Unity 3D for the animation and for the calculation of robot kinematic, C-Sharp and Java script programming language were used. The system will be evaluated with the students to determine its effectiveness in providing a new teaching approach. 1. Introduction Keywords: Virtual Teaching Systems, Robot Kinematics Robotics has become a very important field for engineering and manufacturing due to flexibility in executing a variety of tasks or executes a given task in a variety of ways. Universities have included robotics in their curriculum and research. Current textbooks and robot manuals include only pictures of the robot, description of robots motion and the tasks that the robot can do along with the programming samples. For an effective learning in robotics, it requires the basic equipment which is the robot. It is expensive for the university to make it available to every student to perform robot experiments. Robots are very fragile and require careful handling. During learning process, improper handling and operation by inexperienced students may damage the robots. Since robots are expensive, designing virtual robotic system with useful visualization tool and instructions of operation can overcome these problems. The virtual robot laboratory concept is that it provides visualization and simulation of a robot in a virtual environment. It also provides facility to work off-line programming of actual working robot. Now it is possible to visualize a complex, expensive, or dangerous system safely. The traditional teachings are directly aimed at the average student, often ignoring the faster and slow learners. Virtual reality technology would fulfill the learning process to fit with individual learner. This paper presents a virtual learning system for robotic course. It will provide a new teaching medium to teach students on forward kinematic of an arm robot. The system development and techniques used in this system will be discussed. 2. Related work Research has shown that virtual reality techniques have been used in computer assisted learning systems such as in robotics [10], language course [11], surgery [12,13] and many others. Nowadays there are many new software tools available to help in the development of virtual reality models. Virtual reality model can now be integrated with common graphical programming languages such as Visual Basic, Visual C++, OpenGL[9], Labview, Java or other [1]. Simulation using VRML (Virtual Reality Modeling Language) by using robot with six rotational joint is described in [2]. Java and VRML s External Authoring Interface (EAI) were integrated for the visualization of the simulation. Manseur [3] used Spazz3D as VRML writer to model a virtual model of PUMA robot. This allows Journal of Convergence Information Technology(JCIT) Volume 7, Number 14, Aug 2012 doi : /jcit.vol7.issue

2 student to rotate, translate, zoom-in, or zoom-out the robot model. The students can move virtual robot s joint separately or in combined motion in 3D space. Animation was developed to assist student to understand about robot modeling, direct and inverse kinematics, join motions, trajectories, and also workspace limitations [3]. Wirabhuana et.al[4] developed a robot simulation system using Virtual Reality Modeling Languages (VRML) and Simulink toolbox of MATLAB software of Mitsubishi RV 2AJ Industrial SCARA Robot. The virtual robot can be moved by using two ways of input data either by using scrollbar or by keying in the angular values. Belousov et.al [5] produced a dynamic, 3D virtual environment for on-line robot control in real-time. Education and training of robot includes offline usage of virtual environments for task planning [6]. Lecture materials which are organized in the form of multimedia contents, and also a 3D robot simulator can be used to perform virtual robot experiment. In this way student can understand the command and parameters of the robot easily without any risk of damaging the robot. Virtual instructors used in mixed reality environment can provide effective instruction to increase conceptual learning and increase robotic construction accuracy and assembly task repeatability [7,8]. 3. Virtual Kinematic System In this work, a stand-alone virtual system is developed where the users can run this system on their own computer without worrying about the Internet connection. Lynxmotion arm robot with 6DOF (Degree of Freedom), 5 rotational joints and 1 moving griper, is used as a model. Figure 1 shows the Lynxmotion arm robot used in a robotic lab for third year student of Faculty of Information Science and Technology (FTSM), Universiti Kebangsaan Malaysia. In the class, students learn forward kinematic, Denavit-Hartenberg Convention and are taught on how to program the robot using Visual Basic to see the movements of the robot s link. Figure 1. Lynxmotion robot A set of transformation matrix exercise is created to make sure students are able to write down the formula of translation and rotation matrix before they can apply it. User interface shown in Figure 2 allows the user to key in the corresponding formula, the system will check the formula entered by the user and prompted a message for incorrect answer. 55

3 Figure 2. Formula of Transformation Matrix Figure 3 presents an example question of forward kinematic and the users are required to apply the formula that they have learned before for solving the question. The question is randomly generalized by clicking the reset question button that allows the user to try the formula on different questions. Figure 3. Example of Question This virtual system also allows the students to visualize different types of robot which are Cartesian, Cylindrical, Spherical and Articulated robot to help the students understand its basic structure, movement of each robot and their workspace. 4 types of the virtual robot are as shown in Figure 4. 56

4 Figure 4. Four types of virtual robot The virtual robot is created using 3DStudioMax which is then converted into OpenGL code and a.dll file for easy manipulation by using VB.NET language. To demonstrate the movement of each robot s link, an interface is created using VB.NET which allows the user to input data to the servo by using scrollbar to select the angle for each joint such as in Figure 5. From these input values, the robot s link will move from the initial value to the end. From there, the user will know the minimum and maximum servo value for every servo. The visual can be controlled by the user, where the user can choose each servo movement. A commonly used convention for selecting frames of reference in robotics applications is the Denavit Hartenberg convention. There are four important parameters in DH convention which are generally given the name joint angle (θ i ), joint distance (d i ), link length (a i ) and link twist angle (α i ). In order to help student understand about it, a set of question was created as in Figure 6 where the students will input the four parameters. Figure 5: Screen to input servo values 57

5 Figure 6. Denavit-Hartenberg user interface The representation of the joints and links of the Lynxmotion Robot are as shown in Figure 7. Figure 7: Joints representation of Lynxmotion Arm Robot The kinematics equation for the manipulator movement is based on the DH representation as shown in Table 1. 58

6 Table 1. Kinematics parameter based on DH representation Link θ i α i d i (cm) a i (cm) 1 θ 1 90 d θ a 2 3 θ a 3 4 θ a 4 5 θ a i =distance between two joint axes. the mutual perpendicular is designated the x-axis d i =distance between two perpendicular measured. α i =the relative twist circular angle θ i =joint angle about the z axis measured. The matrix representations of the kinematic equation used are as the following: Matrix transformation 0 A 1 (Rotation): 0 A 1 = Matrixs transformation 1 A 2 (Transformation): 1 A 2 = Matrixs transformation 2 A 3 (Transformation): 2 A 3= Matrixs transformation 3 A 4 (Transformation): 3 A 4 = Matrixs transformation 4 A 5 (Transformation): 59

7 4 A 5 = Forward kinematics of the arm robot is the product of all the matrices: 0 T 5 = 0 A 1 * 1 A 2 * 2 A 3 * 3 A 4 * 4 A 5 0 T 5 = where Ci = cos θi Si = sin θi Cij = cos (θi+θj) Sij = sin (θi+θj) Sin (α+β) = sin α cos β +cos α sin β Sin (α- β) = sin α cos β cos α sin β Cos(α + β) = cos α cos β sin α sin β Cos(α - β) = cos α cos β +sin α sin β The virtual robot can be controlled by the user, where the user can choose each servo movement from first joint to the 5 th joint. Fig. 8 to Fig.13 demonstrate the output of the application after the user select the joint angle for each joint. Figure 8. Initial position of Lynxmotion Arm Robot 60

8 Figure 9. Output after user selects the first joint angle Figure 10. Output after user selects the second joint angle 61

9 Figure 11. Output after user selects the third joint angle Figure 12. Output after user selects the fourth joint angle 62

10 Figure 13. Output after user selects the fifth joint angle The other function of this virtual robotic system is to allow the users to test their off-line programming code. By using this application the user can test their coding and see the movement of the robot based on their coding without the need to link to the actual robot. This part is still in the preliminary stage and under development. 4. Conclusion and Future Work Advances in computer graphic hardware and software tools make it possible to develop a 3D graphic model, visualization, simulation and also an interactive animation. Virtual Robotic system was designed to provide students with not only a 3D viewing but also an operation procedure of the virtual robot. It makes learning robotics interesting. There is no doubt that a simple interface with a good visualization really help student to understand and can also save students time in learning the concepts of robotic. A good and fast system developed with suitable programming language can facilitate better student s understanding of the concept of forward kinematics of robot. A module will be added to the system for offline programming to allow the users to test their offline programming code. By using this application the user can test their coding and see the movement of the robot based on their coding without the need to link to the actual robot. This work will continue with the evaluation of the system with the students from the robotics class to determine its effectiveness as a new teaching approach. 5. References [1] R. Manseur, Vitual Reality in Science and Engineering Education, in Proceedings of the 35 th ASEE/IEEE Frontier in Education Conference, pp8-13, [2] M. Rohrmeir, Web Based Robot Simulation Using VRML, In Proceedings of the 2000 Winter Simulation Conference, pp , [3] R. Manseur, Modeling and Visualization of Robotic Arms, In Proceedings of IASTED International Conference on Graphics and Visualization in Engineering, pp. 1-6, [4] A.Wirabhuana, H. Harun and Jasril, Industrial Robot Simulation Software Development Using Virtual Reality Modeling Approach (VRML) and Matlab - Simulink Toolbox, In Proceedings of the Simposium National IV RAPI, pp ,

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