Design and Development of a Low-Cost Prototype of a Modular Robot Platform to be Used in the Control Engineering Laboratory by Paul Saade, Alfred Gemayel, and Michel Owayjan, M.E.M. Senior undergraduate student, senior undergraduate student, and Lecturer Department of Computer and Communications Engineering, American University of Science & Technology (AUST) 16-6452, Beirut, Lebanon
[email protected] Products Used NI USB 6008 DAQ® NI LabVIEW ™ 8.0 Student Edition (National Instruments, Inc., Austin, TX, USA). The Challenge i) To provide a practical demonstration platform for the Control Engineering Laboratory students. ii) To reduce the equipment overhead cost, by providing a low-cost modular robot platform with different modules. iii) To improve the quality of control engineering education and demonstrate data acquisition, analysis, and display. The Solution Building a low-cost modular robot platform that can embody many sensory input modules. The robot is connected (by cable or wireless) to the NI USB 6008 DAQ that is interfaced with LabVIEW. Students can design virtual instruments on LabVIEW to control the robot’s motors. Abstract This project aims to design and develop a low-cost prototype of a modular robot platform to be used in the Control Engineering Laboratory using the National Instruments™ (NI) 6008 USB Data Acquisition and LabVIEW. The objective of this project is to demonstrate different control concepts, such as sensor input, position control, velocity control, feedback, stability, controllers, etc. The robot platform contains different modules (sensors, motors, etc.) that can be controlled through cable or wireless by virtual instruments developed with LabVIEW using the NI 6008 USB Data Acquisition. Introduction In the CCE undergraduate curriculum, the Control Engineering Laboratory course provides the students with practical hands-on experience in control. Students have to demonstrate their understanding of the control concepts using various instruments such as analog computers, sensors, tacho-generators, etc. Often these instruments are expensive, and many institutions cannot afford buying them. Using NI hardware and software, we can build a modular robot platform that can be used in many experiments at a fraction of the cost of one of the above instruments. Moreover, the rapid development in today’s technology has facilitated the use of computers in different control applications. The robot platform, as one such application, allows the students to experiment control using the computer. This is done by sending input sensory signals from different modules into the PC, and the robot’s motors receiving orders to move.
This is executed through simple and efficient programming using NI LabVIEW via different functional modules and control techniques. The Modular Robot Platform The robot, depicted in Figure 1, was built using low-cost material that is available in the Lebanese market. The body of the robot is composed of two plexiglass sheets fixed together with long metallic screws. Two motors are fixed at the back of the robot and a free-driving wheel is fixed at the front. The robot moves and changes direction using the tank technique, i.e., one motor stops while the other spins in order to allow the robot to turn right or left.
Figure 1: The Modular Robot Platform.
Different sensory input modules can be built onto the robot. They include, but are not limited to tentacle switches used for obstacle avoidance, ultrasonic sensors used also for obstacle avoidance, light dependant resistors (LDR) or light sensors used for light tracking. In addition to photodiodes mounted at the bottom of the robot used for either black or white line tracking, and temperature sensor used to measure the ambient temperature. Two of these sensory inputs (tentacle switches for obstacle avoidance and light sensors for light tracking) were implemented, while the rest can be easily employed. Even though electronic circuits can be built on the robot platform to control the robot from sensory input, the aim of the robot is to send all sensor input data to the computer and let the students design programs that send orders to the motors on the robot to control its movements. Interfacing the robot with the serial or the parallel ports, and writing lengthy codes on high level languages such as Java (Sun Microsystems Inc., Santa Clara, CA, USA) or C++ is a time-consuming procedure and not guaranteed to work. However, using the NI hardware and software will make this procedure more efficient and productive. The NI USB 6008 DAQ is very user-friendly and easy to communicate with, using simple TTL logic. The graphical programming language of LabVIEW makes writing control codes easy, fun, and less prone to errors. The robot is connected to the NI USB 6008 DAQ that has 12 digital I/O channels, 8 analog input channels, 2 analog output channels, and one counter input, by a simple UTP cable. But the connection can be easily converted into a wireless connection using two remote control circuits with 5-bit transmission/reception capability at a low cost (few dollars). Data encoders/decoders may then be needed. A functional block diagram is shown in Figure 2
explaining the connection between the robot platform and the computer using Virtual Instruments written with LabVIEW.
Figure 2: The Connection between the Robot Platform and the Computer Running LabVIEW.
The LabVIEW Control Program LabVIEW 8.0 (Student Edition) was used to acquire sensor input from the NI USB 6008 DAQ unit, perform control techniques, and store the acquired data (to simulate and model the robot’s environment). The computer used was an IBM X60s (IBM Corporation, Armonk, NY, USA) notebook with a 1.6 GHz Centrino™ (Intel, Santa Clara, CA, USA) processor, 1 GB of RAM and a 12 in. screen. The notebook operated on a Microsoft Windows XP platform (Microsoft Corporation, Redmond, WA, USA). A simple robot control virtual instrument (VI) was developed for two modules in the platform: the obstacle avoidance using two tentacle switches, and the light tracking using three LDRs. In addition, users of this VI can control the motors using switches on the front panel. The obstacle avoidance program is very simple. The robot senses obstacles using two switches, a left and a right one. If for example there is an obstacle on the left, the left switch closes and a signal is transmitted to the VI indicating the existence of an obstacle on the left. The VI then sends an order to robot to turn right, away from the obstacle. Moreover, the light tracking is done through three LDRs: a left LDR, a right LDR, and a center LDR. A comparative circuit built with simple 741 operational amplifiers, compares the inputs of the left and center LDRs as well as the right and center ones. If the light is on the right for example, the comparative circuit transmits input to the VI indicating logic 1 for light on the right and logic 0 for light on the left. Then the VI controls the motors of the robot to turn it to the right and make it chase the light source. Figure 3 illustrates a sample block diagram for the robot control application on LabVIEW. And Figure 4 shows a simple front panel with simple indicators and control switches. Students will be asked in the laboratory to add more sensor input modules and write VIs and Sub VIs to control the robot. The students can also add other indicators to display the sensory inputs (Charts, Graphs, etc.); they can write modules to save the inputs to files, so that the data can be used later on for analysis, and for the robot’s environment modeling and simulation.
Figure 3: Block Diagram for the Robot Control VI using LabVIEW.
Figure 4: Block Diagram for the Robot Control VI using LabVIEW.
Results and Conclusions The modular robot platform was designed and built for the control laboratory experiments. The NI USB 6008 DAQ and LabVIEW made the interfacing of the robot with the computer very simple and straightforward without wasting a lot of time. This will help students focus more on control techniques and algorithms that can be easily implemented using the graphical programming language of LabVIEW. A set of experiments are designed for this robot platform, so as to help students be up-to-date in the control industry while utilizing state of the art tools. In conclusion, NI hardware and software proved to be indispensible for control. Contact Information For more information, contact: Michel Owayjan American University of Science and Technology (AUST)
Ashrafieh, Alfred Naccache Street, P.O.Box: 16-6452 Beirut – Lebanon Telephone: +961-1-218716/7 Fax: +961-1-339302 Mobile: +961-3-523418 E-mail:
[email protected]
