Student Projects
Line Tracer Robot
By
Choong Sze Min, Student
Christy Lim You Sun, Student
Rodney Tan, Advisor
UCSI University
Malaysia
Product Used:
NI USB-6008 DAQ
National Instrument LabVIEW 8.6
The Challenge:
To educate the young generation who do not have any programming background on mastering the skills of controlling line tracer robot and to understand the basic operation of a line tracer robot.
The Solution:
Creating a line tracer robot which can perfectly move follow the black line no matter how curve is the track by acquiring the signal from sensor and also generate the output for the motor using NI DAQ and display the voltage when the sensor senses the black line with LabVIEW.
Abstract
With National Instrument LabVIEW 8.6 and NI USB-6008 DAQ, we were able to analyze the input signal more accurately and this contributes a lot especially in our troubleshooting process. In addition, we were able to shorten our development time and avoid using excessive electronic components by selecting the appropriate tools on LabVIEW which could actually replace some certain electronic components. Thus, the cost had been greatly reduced.
Introduction
Line tracer robots are widely accepted in various industry for the purpose of moving objects. Feasibility of using line tracer robots under disaster situation is studied as the line tracing capability may be useful in case of disaster. A small scale line tracer robot is designed, implemented, and tested under disaster situation. Specifically, the MCU based robot hardware including sensor, motor, and power supply is designed and implemented. In our case, NI USB DAQ-6008 played the role as the MCU. Also, the software for receiving sensor signal, for driving motor and for implementing line searching algorithm is designed. The software that we used was NI LabVIEW 8.6.
By using the infrared sensors with the transmitter and receiver, a black colour track could be detected. The detection was based on the different voltages that appear when the sensors sense between the black colour track and white space. If we would to use MCU to control this line tracer robot, the nature of the different voltages inputs could not be analyzed properly. With the help of NI USB DAQ-6008 on acquiring input signals and NI LabVIEW 8.6 on displaying the output, a better judgment and a wiser decision can be made.
System Overview
The complete system overview of Line Tracer Robot is shown with block diagram in Figure 1.
Sensors acquire signal as input Laptop with NI LabVIEW installed displaying input wave form
Figure 1. Line Tracer Robot System Overview Block Diagram
The line tracer consisted of three parts. The first part was the NI USB DAQ-6008 which actually acted as the microcontroller unit (MCU) of the robot. Secondly was the sensor part which acted as the input of the robot and thirdly was the motor controller part. Three of them made up a full complete line tracer robot. The infrared sensor which contained a matched infrared transmitter and infrared receiver pair was used. The signal sensing process started with the transmitter emitting the light and receiver receiving the light. The signal will then be sent to the NI DAQ-6008 if the receiver receives certain amount of light. The line tracer robot was working based on measuring the amount of light that was reflected into the receiver by the transmitter. L293D chip which was basically an integrated circuit motor driver was used for simultaneous and bi-directional control of two small motors. The two small motors that mentioned were none other than the brushed DC motor and the current flowing through L293D was limited to 600mA.
Results and Discussion
The user interface of the Line Tracer Robot in LabVIEW 8.6 is shown in Figure 2 below.
Figure 2. Line Tracer Robot User Interface
The user interface of the line tracer robot consists of a waveform chart, indicator for right and left sensor, sliders, two LEDs and numeric indicator. The waveform chart was used to display the input signal of the sensors and also the voltage limit that being set on the slider. When the sensors sense the black colour track, the input signal voltage that appears would be higher than 1V. Thus by adjusting the voltage limit of the slider, the tasks that the line tracer has to perform vary according to the programming. The indicator and numeric indicator display the exact value of the input signal voltage. The two LEDs used in the user interface are to tell which sensor senses the black track. If the sensor senses the black track, the LED will be turned on. The line tracer robot will only move forward when the two sensors sense the white surface. If both sensors return black, then the robot was properly positioned over the track. When the left sensor “sees” a white whereas the right sensor still “sees” black, then the robot will veer off to the right and vice versa.
Only two sensors were used for this line tracer robot. Adding on the number of the sensors would certainly push our line tracer robot towards perfection. The line tracer robot with more sensors will move more smoothly and consistently stick to the track as it had more “eyes”. Another enhancement with great potential was changing the NI USB DAQ-6008 to the wireless DAQ card. It was because NI USB DAQ-6008 connected the line tracer robot with cable. This had actually limited the moving distance of the line tracer robot and was troublesome for the users while controlling the line tracer robot. So, changing to wireless DAQ card can help us avoid some unnecessary troubles.
Besides that, the receiver was very sensitive to the ambient light. So, when the receiver was well shielded from ambient light, the line tracer robot will move smoother in following the tracks. Thus, it is better to adjust the sensor board as low as possible so that it can become well shielded better. When the distance between the sensor and the reflective surface was small which less than 5mm, the line tracer robot will also work in the best condition. In a nutshell, the infrared sensor is often used to detect white and black surfaces where white surfaces generally reflect well and black surfaces reflect poorly.
In real time L293D can only handle much smaller currents unless we do some serious heat sinking to keep the temperature down. Basically they were two types of the chip which were L293 and L293D. The “D” version was chosen because it had built in fly back diodes to minimize the inductive voltage spikes.
Figure 3 shows the line tracer robot connected to the laptop through NI USB DAQ-6008. The complete system setup of the line tracer robot is shown in Figure 3.
Figure 3. The Complete Setup of Line Tracer Robot Moving On Track
The track had to be designed on the white surface to maximize the desired output which means that the surface had to be a reflecting surface. Mahjong paper was considered to be a good reflecting surface in use. As for the black line, the printed line or the electrical tape can either be used due to the reasons where these two things can optically absorbing the light. The following important point was the contrast between the white surface and the black line. The contrast between the white background and the black line had to be large enough so that the sensor can easily determine whether the robot is over white or black part.
Conclusion
LabVIEW is a programming system with block diagrams and thus stimulated so much interest of the people who program. The process of creating this line tracer robot had become more exciting and challenging for us. Besides that, by using LabVIEW, the process of learning to create and program a line tracer robot will become less dull for a person who does not have any programming background or knowledge. In addition, the connection among blocks would easily tell us the flow of the program and the errors could be identified faster and more accurately. Above all these, the best part was that the signal could be acquired in different form as users desired and the output waveform could be captured instantaneously. Through the study on the pattern of the output, we could wisely plan our programming and decide our next-step decision with more ideas coming into mind.
For more information, contact:
Rodney Tan
Deputy Head of Embedded System Research Group (ESRG)
Senior Lecturer
UCSI University, Malaysia
No 1, Jalan Menara Gading, UCSI Heights, 56000 Kuala Lumpur Malaysia
Tel: +6017-3078955
Fax: +603-91023606
Email: rodneyt@ucsi.edu.my
