Automatic Obstacle Removing Robot

1.    INTRODUCTION

            Avoiding obstacles efficiently is a commonly encountered problem during the design of moving robots. The model described below will provide a cheap and efficient solution for the problem. It uses infrared sensors for detecting the obstacles in its path. Two separate DC are employed for driving the two tires. The system is so simple that the use of microcontroller is eliminated for the current control to DC motors according to the obstacle sensed.

                               This motor is also called the differential drive steering method, which use two independent motors mounted in fixed positions on the left and right side. This mean by slowing the rotation speed of the left DC motor will make the robot to arc to the left and slowing the rotation speed of the right DC motor will make the robot to the right. If both motor rotate at the same speed then the robot will go straight.

2.    BLOCK DIAGRAM

          INPUT                                                                                                        OUTPUT

Sensor circuit

LM741 circuit

Sensor circuit

Motor circuit R

Motor circuit L

Gear motor

Gear motor

 

                                                                                                           

 

                                                                                                       OUTPUT

        INPUT                                                                                           

Fig: 1

3.    BLOCK DIAGRAM DESCRIPTION

3.1 SENSOR CIRCUIT

The circuit consists of two infrared transmitters and two infrared receiver circuits. The output from the receiver is fed to a transistor switching circuit which is a comparator. The output of the comparator circuit can control the current fed into the motors according to the object sensed by the sensor circuit.

 Transmitter section uses an IR led. We use an astable multivibrator for the transmitter stage. It generates a pulse with frequency of 38-40 KHz. This pulse is fed into a transistor and the out of transistor to an IR led which transmit the signal.

3.2 COMPARATOR CIRCUIT

   The Receiver contains anIR diode and preamplifier in one package, the output of the two receivers is fed to the transistor switches. They will switch between low and high according to the presence or absence of the obstacle in the range of the transmitters. The output of each transistor switch will give to the driver circuit of the DC motor.

3.3 MOTOR CIRCUIT

            The motor is the part helps in the motion of the vehicle. The motor receives the output from the comparator circuit and it rotates according to the input received by the comparator from the sensor.

4.    CIRCUIT DIAGRAM

Fig: 2

5.    CIRCUIT DIAGRAM DESCRIPTION

            Here the circuit consists of a triangular wave generator which provides the input for two comparator. Here we use a LM 741 op amp as the comparator circuit. The triangular wave generator produces an output around a range of 15 KHz which is the basic feed input for the logic. We give another comparator voltage from a voltage divider circuit which consists of a 10k pot and an IR diode. At present there occur no voltage drop across the diode and there present a drop only across the pot. In this stage there will be a PWM output across the comparator. The output is fed into a transistor (BD 139).

            The BD 139 NPN Bipolar Transistor is designed to operate as the current gainer amplifier; this means we operate the BD 139 in its linear region. The advantages of using the transistor in its linear region is; the transistor collector current passed through the DC motor will varying according to the base current which controlled by the IR diode and 10K trimmer potentiometer (trim pot). Therefore the current through the DC motor will vary according to the IR diode. We use BD 139 because it allows current of range 1.5 A (dc) max at its collector which can rotate the dc motor of range 12V, 150mA and 40 RPM. We should use a low RPM geared dc motor. The lower RPM is required because the IR diode has a slow response.

       

            We use a 555 timer IC here working as a multivibrator. The output required frequency is designed in a range of 40 KHz which is the required range for the IR diode to sense. The output of this multivibrator lights the IR led. These IR led requires an input of the range 20mA. So the transistor BC 547 is used to amplify the output current from the multivibrator which is of the range 10mA. 

             

            Using this simple principal we could easily identify the presence of obstacle in front of the vehicle in such as that the IR diode will receive the reflected IR rays when the corresponding IR diode is in front of the obstacle and this will make the DC motor to turn slowly or off. Otherwise IR diode will not receive the IR ray; this will make the motor to turn. When an obstacle is produced in front of on IR diode the reflected IR rays which is emitted by the IR led is received or sensed by it. When the diode senses the IR ray it becomes active and there occur a voltage drop across it. Thus the voltage drop at the negative comparator input reduces. Thus the output of that comparator will become zero and the base current of the transistor BD 139 becomes zero which turns off the motor.

   

             The 2^nd comparator will be active at this stage since there is no obstacle at the other end and there is no change in the 2^nd comparator output. So the 2^nd motor continues in on state. Now from this principle when an obstacle is present at one side the motor at opposite side turns off and the motor at the same side continues to rotate which rotate the vehicle away from the obstacle. When the obstacle is removed the IR diode will become deactivated and there will be no voltage drop across the diode and thus both motor works and the vehicle continues to move. When there occur an obstacle at the other side the reverse process takes place.

6.    COMPONENTS LIST

COMPONENTS	SPECIFICATION	QUANTITY
RESISTORS	56K 47K 22K 18K 10K 1K 330Ω	1 4 1 1 2 4 2
CAPACITORS	1F	4
POT	10K	2
IC	555	1
OP AMP	LM 741	4
DIODE	IR DIODE (TSOP)	2
LED	IR LED	2
TRANSISTORS	BD 139 BC 547	2 2
MOTOR	DC GEAR MOTOR	2
BATTERY	6V	1

7.    COMPONENT DESCRIPTION

7.1 GEAR MOTOR

           In a gear motor, the magnetic current (which can be produced by either permanent magnets or electromagnets) turns gears that are either in a gear reduction unit or in an integrated gear box. A second shaft is connected to these gears. The result is that the gears greatly increase the amount of torque the motor is capable of producing while simultaneously slowing down the motor's output speed. The motor will not need to draw as much current to function and will move more slowly, but will provide greater torque.

7.2 NE555 IC

            The 555 monolithic timing circuit is a highly stable controlled capable controlled with two external resistors and one capacitor. The circuit free running frequency and the duty cycle are both accurately may be triggered and reset on falling waveforms, and the output mode of operation, the time is precisely controlled by one external of producing accurate time delays, or oscillation. In the time delay resistor and capacitor. For a stable operation as an oscillator, the structure can source or sink up to 200mA.

7.3 RESISTORS

              A resistor is a two-passive electronic component which implements electrical resistance as a circuit element. When a voltage V is applied across the terminals of a resistor, a current I will flow through the resistor in direct proportion to that voltage. This constant of proportionality is called conductance, G. The reciprocal of the conductance is known as the resistance R, since, with a given voltage V, a larger value of R further "resists" the flow of current I as given by

7.4 LM 741

            The LM741 series are general purpose operational amplifierswhich feature improved performance over industry standards like the LM709. They are direct, plug-in replacements for the 709C, LM201, MC1439 and 748 in most applications. The amplifiers offer many features which make their application nearly foolproof: overload protection on the input and output, no latch-up when the common mode range is exceeded, as well as freedom from oscillations. The LM741C is identical to the LM741/LM741A except that the LM741C has their performance guaranteed over a 0°C to +70°C temperature range, instead of −55°C to +125°C.

7.5 IR LED

            The light emitting diode (LED) is a semiconductor light source. IR LED emits IR rays which are invisible. When an light emitting diode is forward biased electrons are able to recombine with electron holes within the device, releasing energy in the form of photons. This effect is called electroluminescence. IR LED is used in remote as an emitter for sensing, Televisions, DVD players and other domestic appliances.

7.6 CAPACITORS

            A capacitor is a electrical/electronic device that can store energy in electric field between a pair of conductor called plates. The process of storing in the capacitor is known as “Charging”, and involves electric charge of an equal magnitude, but opposite polarity, building upon each plate. They can also be used to differentiate between high frequency and low frequency signal. This property makes them useful in electronic filters.

7.8 TRANSISTORS

            A transistor is a semiconductor device used to amplify and switch electronic signals. It is

made of a solid piece of semiconductor material, with at least 3 terminals for connection of an  external circuit. A voltage or current applied to one pair of the transistors terminals changes the current flowing through another pair of terminals. Because the controlled (output) power can be much more than the controlling (input) power, the transistor provides amplification of the signal. Today some transistors are packaged individually, but many more are fond embedded in integrated circuits.

8.    PCB FABRICATION PROCESS

                                                                                                                                      

            The heart of any electronic project is the Printed Circuited Board on which component connections are done. The materials used for making PCB are

·         Hand drill

·         Drill bits 0.8mm & 3mm

·         Mirror hacksaw

·         Rat tail file

·         Clamp

·         Enamel paint

·         Ferric chloride

·         Fine painting brush

·         Vero board of 0.1 inch holes(VB)

·         Copper Clad Board (CCB)

·         Transparent foot rule

               The components are mounted on the Vero board after bending their lead as required. The holes through which the leads are protruding are marked using a pencil. Place VB on CCB such that copper foil on CCB and the marking on VB are facing up.

            The CCB is adjusted to be exactly at the center of the layout on the VB.Then both boards are placed on a wooden plank and tightened. Using a hand drill CCB is drilled at required places for power supply, outputs and interstate couplings.

            

            A thin coat of enamel paint applied on the pencil tracks using a fine tipped brush. A small blob of paint is applied at the holes so that the copper at the soldering

point is not lost during etching. The unused portion of CCB is painted without touching the other tracks and connected to main ground.

           

              The CCB half dried paint is immersed in solution of ferric chloride. When etching is over the paint is wiped off with dipped in kerosene. The holes are cleaned and a coat of varnish is applied to the CCB to prevent corrosion.

8.1 Soldering Process

            Each component is taken and there leads are scraped with a blade for removing any oxide coating around the holes in the PCB has to be removed. This will help to get proper contact between the component leads and the copper tracks on PCB. A 25W soldering iron is used. Flux helps removing oxide coating early from the leads of the components.

9.    PCB LAYOUT

10.        ADVANTAGES

1.      Avoid obstacles.

2.      Cheap in construction

3.      Simple logic

4.      Simple circuitry

5.      Highly locative

6.      Highly controllable

7.      Easy installation

8.      Weightless design

9.      Compact size

11.        DISADVANTAGES

1.      Circuit is poor

2.      Sensing capability is less

12.     APPLICATION

1.      Advanced sensor with the logic is used in motor vehicles

2.      Used in modern underground  resource  locater

3.      Used in robot

4.      Used in the field of defence for bomb searching

5.      Used in pipe failure detection 

13.        CONCLUSION

             Obstacle avoiding robot is a simple and efficient method to avoid obstacles in its path. This circuit can be modified by using an ultrasonic module. So that can avoid the robot efficiently according to the distance of the object as used in tracking radar system.

14.  FUTURE SCOPE

Ø   As we know that sensing of an obstacle helps to avoid it, as a simple human logic it is being introduced in mechanical and electrical application for the modern world.

Ø  An obstacle avoiding robot or a circuit can be modified into an advanced one using microcontroller which includes a number of logics in a small circuitry.

Ø  Developed logics are now familiar to us in the high end luxurious car.