26-12-2012, 02:23 PM
Command Based Line Following Robot using RF Technology
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ABSTRACT
This research paper demonstrates a prototype development of an Intelligent Command Based Line Follower Robot (LFR) using Radio Frequency (RF) Technology. Mostly the LFR are build by using microcontroller chips. One of the basic and most fundamental problems with LFR based upon microcontroller chips is that they are preprogrammed. Due to these preprogramming limitations LFR cannot accept any instruction and command in real time from outside users other than what is already fixed. The proposed prototype systems is designed and demonstrated to recognize, understand and modify the actual performance and the movements of the robot following the path by getting information in real time from three Light Dependent Resistor (LDR) sensors via Parallel Port Interface Circuit (PPIC) connected to PC. A computer program is implemented in C-language to accept user commands and also control the robot autonomously according to the received signals.
Introduction
LFR is a tool or machine that can follow a specified path. Historically the most LFR are build using the microcontroller chips (Roman et al. 2006; Nolfi .and Floreano, 2001). The chip is preprogrammed and embedded within the robot. One of the basic problems with microcontroller based designs is the acceptance of commands from the user in real time from outside world.
The second problem with LFR is wired connections, and the length of wire is the main constraint. As the length of a wire increases, the signal strength attenuate and along with signal strength attenuation delay in timings also increases. To overcome these problems, RF is used as it provides a convenient way of transmitting signals without conductors and hence eliminating the attenuation and time delay. The current approach solves the problem of controlling LFR with the added functionality of command mode. The command mode LFR is controlled using PC based instructions developed in C-programming language. Some work based on Radio Frequency Identification (RFID) systems has been reported in (Finkenzeller, 2003; Microchip Micro Guide).
System Development
Two different RF chips have been used for transmitting and receiving the signals between the robot and the PC. The RF of 35 MHz is used for controlling robot movement and 27MHz for transmission of information.
The construction of a command based LFR using RF technology, a RF based Car of 35 MHz was selected that works as a robot. The reasons for selecting this type of RF car are:
a. It works on wireless system
b. Easy to assemble, configure and control
c. Low cost
The main advantage of using RF technology is that it does not require line of sight, which makes this device more useful as compared to one that uses the wired or infrared based wireless technology.
The elements involved during the physical design of robot are:
Sensor Placement
Sensors are place at the front bumper of a robot. The main objective of the robot is to position its B (middle) sensor on the tape line and other two sensors A (left) and C (right) off the tape line. If the tape line ever ventures past these two extreme sensors, then the robot corrects by turning in the appropriate direction to maintain tracking. Sensors are positioned between 1/16" to 1/8" above the ground as shown in Fig.3
Sensor Transmission
The Red LED is used to transmit the light on the tape (line) and the LDR is used to sense the reflected light of LED as shown in the Fig.5. The output of the sensors is an analog signal which depends on the amount of light reflected back. This analog signal is sent by RF based transmitter of 27MHz which transmits these signals to sensor receiver circuit which is connected to PPIC.
Then PPIC fed these three signals to PC via three PC input pins as mentioned in Table 3. Table 6 shows the description of Sensors transmitted signal and Table 7 shows the pin description of Sensor received signals at PC.
Curve Line Analysis
The action of a robot is decided according to received signals via PPIC through sensor receiver circuit. The robot movement according to Curve Line behavior of the Robot is shown in Fig.7.
If A (Left Sensor) reads 1, B (Middle Sensor) reads 0, and C (Left Sensor) reads 1, then the S1 and S2 signals are generated from RC transmitter and the robot moves in forward direction as shown in Fig.7 case: 1.
In contrast if A (Left Sensor) reads 1, B (Middle Sensor) reads 1, and C (Left Sensor) reads 0, then the S2 signal is generated from RC transmitter and the robot moves in right (Clockwise) direction as shown in Fig.7case: 2.
And finally if the Robot moves in the left direction (anticlockwise), then the Relay number 2 is triggered, to generate signal S2 as shown in Fig.7 case: 4.
Conclusions And Recommendations
The problem with microcontroller based LFR’s was the acceptance of commands from the user in real time environment, so this problem was solved by the replacing the microcontroller with PC to provide additional facility. To overcome this problem RF was used to provide a convenient way of transmitting signals without conductors and hence eliminating the attenuation and time delay. These additional facilities provide users to control the robot wirelessly as well as it allows user to work at such places which are too dangerous to explore.
Further range finder modules (ultrasonic or infrared) and a gripper could be used. Such modules will allow variety of different and more complex algorithms to be implemented on the robot. Furthermore, adding a gripper will allow more sophisticated algorithms to be implements in robot to carrying objects, play soccer and various industrial applications.