Advanced Materials Research Online: 2012-10-08 ISSN: 1662-8985, Vol. 576, pp 777-780 doi:10.4028/www.scientific.net/amr.576.777 2012 Trans Tech Publications, Switzerland Parallel Manipulator for Auto Tracking System: Virtual Prototyping using LabVIEW- Solidworks Zalifah Ramli a, Asan G. A. Muthalif b, Amir A. Shafie c, Hasmawati Antong d Department of Mechatronics Engineering, International Islamic University Malaysia Jalan Gombak, 53100, Kuala Lumpur, Malaysia a zalifah_ramli@yahoo.com, b asan@iium.edu.my, c aashafie@iium.edu.my, d hasmawati@iium.edu.my Keywords: FSO, tracking system, Parallel manipulator, SolidWorks, LabVIEW. Abstract. Free-space optics (FSO) communication is a technology that uses light to transmit data through free space. The most important part in FSO communication is the alignment between transmitter and telescope s receiver. However, since the transmission medium of FSO is atmosphere, it will give misalignment between the transceivers. Hence, auto tracking system is required to solve the problem between the transmitter and receivers. The 3-RPS parallel manipulator has been designed as an auto tracking system for the alignment between transceivers. First, a prototype of the system is designed in SolidWorks and integrated with LabVIEW software to perform virtual prototyping. Then, the result of virtual prrotyping is discussed. Introduction Free-space optics (FSO) communication is a technology that uses laser beam to transmit data through air as transmission medium. The transmitter, the propagation channel and the receiver are the three basic components in transferring data through FSO [1]. The transmitter and receiver are placed on the rooftop or behind the window to get clear line of sight. Therefore, FSO system can reach over distances of several kilometers. In FSO, the laser beam must be transmitting through light of sight (LOS) direction between transmitter and receiver. In order to achieve successful data transmission, it is crucial to have the alignment of transmitter and receiver in the whole duration of communication. However, there is also certain problem that can occur in FSO such as the misalignment between transmitter and receiver which are caused by weather conditions and vibrations. For instance, the alignment of the transceiver can be effected by the building sway. Building sway can interrupt the light of sight (LOS) direction between transmitter and receiver, so the received signal will be reduced and consequently increases the bit errors probability (BEP) [2]. Hence, the auto tracking system is considered to overcome this problem. The auto tracking system can be divided into two parts: auto focusing and alignment part. In this project, the alignment part is considered. Therefore, to overcome this issue, parallel manipulator for auto tracking sytem is proposed since it has low inertia, high stiffness, high speed motions and low cost as compared to serial manipulator [3]. As to mantain alignment of the laser beam between transmmitter and receiver, the mechanical model of parallel manipulator will be designed and fabricated. The rest of the paper is organized as the following. Section 2 gives an overview of parallel manipulator system and kinematics analysis of parallel manipulator. Section 3 describes virtual prototyping using SolidWorks and LabVIEW. Section 4 shows the results of yirtual prototyping, followed by summary in Section 5. Parallel Manipulator Parallel manipulator is a type of parallel robot that can move in the space and can also be placed in any desired locations within the workspace of the system [4]. A parallel manipulator typically consists of a moving platform and a base platform, connected by several limbs. The spherical joint connects the limb with the moving platform whereas the revolute joint connects the limb with the base platform. The moving platform is to be used as the end- effector as shown in All rights reserved. No part of contents of this paper may be reproduced or transmitted in any form or by any means without the written permission of Trans Tech Publications, www.ttp.net. (ID: 130.203.136.75, Pennsylvania State University, University Park, USA-12/05/16,09:11:02)
778 Advances in Manufacturing and Materials Engineering Fig.1. The limbs (L1, L2,L3) of the parallel manipulator used here are linear actuator. The moving platform can be manipulated by varying the limb lengths with respect to the base platform. In this project, the receiver telescope will be placed on the moving platform and the linear actuator of the parallel manipulator will be controlled by the controller. Thus, the receiver telescope can track the laser beam from the transmitter and consequently enables the receiver telescope to be placed at the desired position and orientation. The number of degrees of freedom (DOF) of the moving platform is usually equal the number of limbs of parallel manipulator. One actuator is required for each limb and all actuators can be mounted at fixed base. Three DOF parallel manipulators with revolute-prismatic-spherical joints structure are considered in this project. As mentioned above, this structure of manipulator was known as Stewart Platform since Stewart introduced a platform manipulator in the middle of 1960 to use as an aircraft simulator [5]. A parallel manipulator is differed from the serial manipulators in terms of their kinematics structure. Parallel manipulator can perform at high-speed motions as it has close kinematic structure and the actuators fix to its base enable it to have low inertia with the addition of end-effector that allows movement with higher acceleration. Kinematics Analysis of the 3-RPS parallel manipulator Spherical joint P3 w h u v P2 L2 Moving platform Prismatic joint P1 Revolute joint L3 A3 Z g O L1 X A2 O Base platform Y Fig 1. 3-RPS parallel robot geometry Kinematic analysis of robot is divided into two parts, which are known as forward kinematics and inverse kinematics analysis. The forward kinematics problem involves the calculation of the position and orientation in which the limb length and joint angles of the robot are known. Meanwhile, the inverse kinematics problem involves a calculation of the link lengths and joint angles which given the position and orientation of the robot. The position vector of A1,A2,A3 and P1,P2,P3 in coordinate system {A} and {P} are given by: A1. (1)
Advanced Materials Research Vol. 576 779 The rotation matrix of the moving frame {p} with respect to the fixed frame {A}can be expressed in term of Euler angles [4]. By using the direction cosines and orthogonal conditions, the values of u1, u2, u3, v1, v2, v3, w1, w2, w3 can be solved. (2). (3) Virtual Prototyping using SolidWorks-LabVIEW. (4) Virtual prototyping is a technique that used computer simulation to design, optimize, validate, and visualize physical products before incurring the cost of physical prototypes [6]. In this paper, LabVIEW and SolidWorks are used to do the virtual prototyping. Solidworks is the computer-added design (CAD) that is used to design the mechanical structures of parallel manipulator. A 3D model in SolidWorks is shown in Fig.2 (a). Afterwards, NI LabVIEW is used to communicate with SolidWorks to perform the virtual prototyping as shown in Fig.2(b). Fig. 2: (a) SolidWorks 3D CAD model Fig.2: (b) Contour move in LabVIEW Since this project is still at the design stage, virtual prototyping is used to observe the motion of the moving platform at joint P1 when the value of limb length (L1) is given. The motion of the manipulator is given in term of contour move by using Contour Move Function in LabVIEW. A table containing a vector of [20 40 60 80 100] which repeated for 10 times is provided. The limb and moving platform will move in accordance to these points. The resulting displacements of the moving platform (P1) due to contour movement is shown in Fig. 3 (b).
780 Advances in Manufacturing and Materials Engineering Fig.3: (a) Displacement of limb (L1) in SolidWork Fig.3: (b) Displacement of the moving platform Results By referring to Fig.3 (a), when the value of the limb lengths (L1) is given, the moving platform can be orientated at the certain points. Fig.3 (b) shows the displacement of the moving platform along z- axis. It shows that the physical parameter of the 3D model can work when it is applied in real prototype. Summary Auto tracking system based on 3-RPS parallel maipulator is proposed to improve FSO communication. Virtual prototype using LabVIEW and SolidWorks allows the 3-RPS parallel manipulator to be designed according to the required specifications. By using the LabVIEW Softmotion module, physical parameters of parallel manipulator such as displacement can be observed from SolidWorks without having to develop the real prototype. References [1] S. Bloom, E. Korevaar, J. Schuster, and H. Willebrand. Understanding the performance of freespace optics [Invited]. Journal of Optical Networking. Vol.2(6) (2003), p.178-200. [2] S. Arnon. Optimization of urban optical wireless communication systems. IEEE Transactions on Wireless Communications. Vol. 2(4). (2003). [3] L. W. Tsai, The Enumeration of a Class of Three-DOF Parallel Manipulators, IO t h World Congress on the Theory of Machine and Mechanisms, Olulu, Finland, June 20-24. [4] Niku S.B, Introduction to Robotics Analysis,Systems,Applications. New Jersey,2001 [5] Stewart D. A platform with six degrees of freedom. Proceedings of the Institution of Mechanical Engineers.1965,pp.371-386 [6] R. McHugh and H. Zhang. Virtual Prototyping of Mechatronics for 21st Century Engineering and Technology, Proceedings of American Society for Engineering Education 2010, Illinois - Indiana Section Conference, (2010), Purdue University, West Lafayette, IN,USA.
Advances in Manufacturing and Materials Engineering 10.4028/www.scientific.net/AMR.576 Parallel Manipulator for Auto Tracking System: Virtual Prototyping Using LabVIEW- Solidworks 10.4028/www.scientific.net/AMR.576.777