07-07-2012, 03:03 PM
Path Finding Mobile Robot incorporating Two Wheel Differential Drive coupled and Boolean Logic for Obstacle avoidance
Path Finding Mobile Robot incorporating Two Wheel Differential Drive coupled and Boolean Logic for Obstacle avoidance. (Size: 139.5 KB / Downloads: 38)
Abstract
Mobile robots have the capability to move around in their environment and are not fixed to one physical location. The robot could sense its surroundings with the aid of various electronic sensors while mechanical actuators were used to move it around. In this research work we are focusing on building a Obstacle Avoiding Robot using Boolean Logic by deducing a truth table. The design consisted of two main sections: Electronic analysis of the various robot sensors and Boolean logic used to interface the sensors with the robot’s actuators. The prototype is build using infra red sensor with comparator circuit and DC motor.In this paper it’s shown that obstacle detection using IR-Phototransistor sensors and motors act as actuators in turning to the next position. This system can be further enhanced by providing an external monitoring control to the robot.
Keywords: Robot, Obstacle Avoidance, Boolean logic.
Introduction
Obstacle avoidance is one of the most critical factors in the design of autonomous vehicles such as mobile robots. One of the major challenges in designing intelligent vehicles capable of autonomous travel on highways is reliable obstacle avoidance system. Obstacle avoidance system may be divided into two parts, obstacle detection
(mechanism, hardware, sensors) and avoidance control.
The traditional artificial intelligence approach to building a control system for an autonomous robot is to break the task into a number of subsystems. These subsystems typically include perception, world modelling, planning, task execution and motor control. The subsystems can be thought of as a series of vertical slices with sensor inputs on the left and actuator outputs on the right. The disadvantage of this approach, however, is that all of these subsystems must work correctly for the robot to function at all. To overcome this we provide an external monitoring control.
Differential Drive
Differential drive is a method of controlling a robot with only two motorized wheels. What makes this algorithm important for a robot builder is that it is also the simplest control method for a robot. The term 'differential' means that robot turning speed is determined by the speed difference between both wheels, each on either side of your robot. For example: keep the left wheel still, and rotate the right wheel forward, and the robot will turn left. If you are clever with it, or use PID control, you can get interesting curved paths just by varying the speeds of both wheels over time. Dont want to turn? As long as both wheels go at the same speed, the robot does not turn - only going forward or reverse.
The differential drive algorithm is useful for light chasing robots. This locomotion is the most basic of all types, and is highly recommended for beginners. Mechanical construction, as well as the control algorithm, cannot get any simpler than this.
Operating logic
pseudocode:
input sensor reading
make decision based on sensor reading
do one of below actions:
to drive straight both wheels move forward at same speed
to drive reverse both wheels move back at same speed
to turn left the left wheel moves in reverse and the right wheel moves forward
to turn right the right wheel moves in reverse and the left wheel moves forward
Circuit Design Sensor circuit
The Infrared emitter detector circuit is used for a robot with basic object or obstacle detection. Infrared emitter detector pair sensors are fairly easy to implement, although involved some level of testing and calibration to get right. They can be used for obstacle detection, motion detection, transmitters, encoders, and color detection (such as for line following).
Infrared Emitter Detector Basic Circuit
R1 is to prevent the emitter (clear) LED from melting itself. Look at the emitter spec sheet to find maximum power. Make sure you choose an R1 value so that
Vcc^2/R1 < Power_spec.
Or just use R1 = 120 ohms if you are lazy and trust me.
R2 should be larger then the maximum resistance of the detector. Measure the resistance of the detector (black) when it is pointing into a dark area and then choose the next larger resister. This means Vout is close to maximum when there is no signal. Or just use R2 = 11kohms
Or use a 20kohm Pot here in series with a100ohm resistor for white line following calibration.
In this work we have taken up 3 sensors SL,SR and SF where,
SL- Left Sensor
SR –Right Sensor
SF –Front Sensor
Control Logic Design
The output of the sensor circuit is taken and the truth table is built as follows,Where M+ and M- are the terminals of the motor.
Based on the above truth the logic expression for M+ and M- are deduced using any of the truth table minimization technique.
using Boolean logic deduced as above. The following fig shows the complete circuit for the Autonomous Mobile Robot
Conclusion
We have completed and tested the final circuit and analysed the results.
The Robot is found to of good mark unless and until it is not in the range of sunlight. This can be enhanced by using ultrasonic sensors. And also an external monitoring assistance can be given to avoid deadlock in unfriendly environments.