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Welcome to DREAMLINE TECHNOLOGY
ELECTRONICS
COMMUNICATION ENGINEERING:
Communication engineering a major field of electronics and electrical engineering. basically communication engineering applied the knowledge of electronics to the field of communication for instence- old age telegraphy to modern age telephone or satellite, mobile phone, mobile radio, television, networking.
My project
2. Summary:
The purpose of this report was to build a micro mouse that followed and raced on a circuit where the road pattern changes at different parts of the circuit. We were allowed to use as many sensors as chosen with no restrictions.
The robot built during the eleven weeks would be raced on week twelve.
We went for something simple and understandable. As long as it worked and raced on the day for the number of laps set we were happy. They were our main goals.
After a lot of research and testing on a parts of a digital circuit, having had no success and also concerned on the power losses we decided to try an analogue circuit.
We chose something simple to connect and test with, not like some other circuits, it would take more time to check and improve it if necessary.
It didn’t work the first time but we understood this circuit better and after some checks at different parts of it we found that current was not enough for driving our motors. We changed the resistor values and the circuit worked. This was only half of the job done as the colour pattern changes during the race. The opposite of this circuit needed to be built as the pattern changes to the opposite. All this needed to be connected together somehow and make it work.
Having built the opposite of the first circuit we tested it separately. It worked and did what we predicted. We were concerned that more circuit components (second circuit) would loose us power for the motors. It took us a while to come up with the right connection between circuit one and two but in the end after different tests our mouse robot was working fully with only 0.5 volts more than the original and that could be minimized further by adjusting the variable resistors in the circuit.
Finally the two circuits were connected in parallel. Some modifications were made to the second circuit where the motor connections were to save power and only one pair of diodes is used for both circuits.
We did the tests on our completed circuit and results showed us that our circuit design is correct. In theory our robot goes through the whole circuit. This was shown when we did the tests. Adjusting the response time was a bit of a problem as more light was needed for faster motor response.
If problems occurred during this method a sensor switching between the two circuits would be used.
3. Introduction:
In this report we present our design of an autonomous mobile robot. UEL group project emphasize student to work in small group. We were assigned to design the robot in team 3. The robot is capable of following a race surface track. The track is consisting of black and white squares. On the black square the track is white and on the white square the track is black.
The most important part of this project is the navigation system of the robot that helps it to navigate around the race. The navigation part is consists of sensors and controlling the wheel of the robot through the circuitry of the motor drive controller. In this case the sensors are non visual. The high intensity red LED reflects light on the track. Depending on the colour of the edges and middle track photo resistor cell detect reflected light from the track and increase or decrease its resistance. When the photo resistor cell change its resistance the input voltages of the motor changes. For motors, gripes are important so that the robot responds accurately when stopping and turning. In this design rubber tyres and screw skid are used to ensure the fast moving capabilities of the robot.
Key points:
· The power consumption of the moving robot should be kept at minimal because of the limited resource of the on board facility.
· The physical size and weight of the robot should be practical.
· The electronics circuitry should be simple, easy to maintain and possibility to adapt with evolutionary upgrade.
4. Constructional ideas:
Two complete way of constructing of the micro mouse are possible. One is the conventional method or the analogue circuit with sensors and control circuit that control the motors of the robot. The second one is a digital method using logic gates and A/D or D/A converter or using microprocessor.
In order to select a method to apply to the design a trial and error method was applied. The opportunities to use digital method are understandable but for its complex logic unit the construction of digital circuit was abandoned.
So we have used analogue method for its simplicity and availability. The simple analogy of the circuit could be more understandable from the overall system structure.
The analogue circuit designed is simple and convenient to build. It is mainly a sensor information dependent circuit which get information from the sensors that sense the colure difference of the race track. The information is feed to the control part of the circuit. Which is very simple and only contain a
5. Mechanical construction:
The mechanical construction is key element in building successful mobile robot. The mechanical construction of the mobile robot is given in Appendix 3. The body of the robot was provided. Everything on the chassis was mounted in a way that we could get as close as possible to the track ground to get the centre of gravity down. A sensor holder was built to provide the sensor fixed position. Ball bearing were used in front of the vehicle for better turning and speed. The circuits were placed directly above the battery holder.
The manual gear holder consists of gears to manage the speed of the robot. The speed at which the robot operate is important for better response from the sensor. Adding gears to the holder decrease the speed of the robot. Adding one gear reduce the revolution ratio of 9.6 to 1. In total 5 gears were added to the box. So the ratio found is 777.6 and output shaft RPM is 7.7.
The DC motors provided require
6. The race track and the race:
The figure below shows the race track of the race. It has white and black background on different places and the robot sensors have to response according to the colure in the track. There are three lines to be followed. Depending on the position of the robot the track changes as black- white- black and white-black – white. The robot has to do certain number of laps as fast as possible from the starting point in order to complete and win the race.
Figure 1: Picture of the race track.
7. Overall system structure:
Sensor circuit Unit Control Circuit unit
Sensor
Input Sensor output
Control signal
Motor Drive 1
Manual set gear
Motor drive output
Motor Drive 2 Manual set gear
Motor drive output
Wheel 1 Wheel 2
Figure 2: Overall system structure of mobile robot.
The overall system structure is shown above. The sensor circuit unit senses the track and feed information to the control part of the circuit. The control circuit controls the level of voltage according to the feeded information and send to motor drives. The motor drive turns the manual gear box which in turns moves the wheel of the robot.
8. Electrical construction:
The electronics of the circuit is divided in to two parts:
1. The sensor unit.
2. The control unit.
8.1. The sensors unit:
The navigation of the mobile robot is important. In this assignment the robot use local navigation system in order to find its way in a relatively small area. In the race track the robot will sense white and black background. In order to work reliably the robot speed have to be relatively slow. Because if the robot operates at full speed then it could go off the track. So the motors speed has to be controlled. In order to decrease the speed the gear ratio of the robot increased by adding gears.
The sensors used in this case are simple Cadmium Sulphide sensors photo resistive cells. An LDR is an input transducer which converts brightness to resistance. The resistance for darkness can be found using a multimeter. In darkness the maximum resistance is about 1M ohm and the minimum resistance is about 100 ohm for very bright light.
In this design, the sensor positions are fixed and the sensing capability also fixed for different background. In other words, the sensor which sense black edge only sense black surface and sensor for white edge only sense white surface of the track.
The sensor cell reduces its resistance in presence or absence of light depending on the type of the sensor. Hence allows the motor control circuit to pass current to the motor drive. When the sensor which sense white surface is in the black surface of the track, it increases resistance. This is a signal to the motor control to decrease speed of the wheel. Again if the sensor which sense black surface is in black part of the racing track, it reduces resistance. This is a signal to the control circuit to turn the wheel and increase speed. While in the white surface the white surface detector decrease resistance, so the control unit increase speed. But if the sensor is in the black surface then it decrease the speed.
Photo detector cell
(a) (b)
Figure 3: Photo detector circuit.
(a)White sensor. (b) Black sensor
The area under the photo cells is illuminated by high intensity LEDs and viewed by the photo cells. The adjustment of the line detector is very critical. It is control by the variable resistor of the circuit.
Figure 4: Position of the sensors.
The position of the sensors is very crucial. Otherwise the sensors wouldn’t be able to move straight and turn at the corner of the track. There are four sensors used in this circuit. Two sensors used for white and other two for black surface.
From the circuit diagram, a 330 ohm resistor is used in conjunction with the LED. The value of the resistors R1, R2, R3, R4 are chosen as that the LED current is about 180 mA from 6v supply. In order to control the photo resistors sensitivity variable resistors are connected with each sensor. For white sensor the value of the variable sensor is 10K and for black sensor its 100K. For white sensors the LEDs and photo resistors are connected to the power supply and the black sensor circuit LEDs and photo resistors are connected to the ground reference.
Testing sensor circuit:
Having designed the sensors circuit, it was built on proto board and tested with 6 v supply. The proto type of the racing track was tested by means of covering sensors with white and black card board. For the circuit to work as a line follower a large variation of voltage is required. By testing with a multimeter the level of voltage found for the sensors are as follows:
|
Type of Sensor |
Surface colour |
Level of voltage |
|
Black sensor 1 |
Black |
4.8V |
|
Black sensor 1 |
White |
.86V |
|
White sensor 1 |
Black |
.91V |
|
White sensor 1 |
White |
4.75V |
|
Black sensor 2 |
Black |
4.67V |
|
Black sensor 2 |
White |
.84V |
|
White sensor 2 |
Black |
.92V |
|
White sensor 2 |
White |
4.76V |
Table 1: Level of voltage across the sensors.
The algorithm for the sensor circuit was derived from the testing.
The sensor algorithm is given below:
|
Sensor A (Response to light) |
Sensors B (Response to absence of light) |
Sensors C (Response to light) |
Sensors D (Response to absence of light) |
Direction of robot |
|
0 |
0 |
0 |
1 |
Turn left |
|
0 |
0 |
1 |
0 |
Turn right |
|
0 |
0 |
1 |
1 |
Go straight |
|
0 |
1 |
0 |
0 |
Turn right |
|
0 |
1 |
0 |
1 |
Go straight |
|
0 |
1 |
1 |
0 |
Turn left |
|
0 |
1 |
1 |
1 |
Go straight |
|
1 |
0 |
0 |
0 |
Turn right |
|
1 |
0 |
0 |
1 |
Turn right |
|
1 |
0 |
1 |
0 |
Go straight |
|
1 |
0 |
1 |
1 |
Go straight |
|
1 |
1 |
0 |
0 |
Go straight |
Table 2: Sensor algorithm.
Here, 1 represents the on condition of the sensor.
0 represents the off condition of the sensor.
8.2. Control circuit unit:
Control is a control strategy in which the robot exhibits behavior as reactions to events. The control circuit unit is important part of the mobile robot as it is used to control the wheel. This control unit use low level control over the wheel.
The control unit is very simple and consists of 4 darlington pairs of transistor. The transistors used in this circuit are BC 109 and TIP 31A. The single transistor does not amplify the current to the motor. As a result the motor does not ‘spin’. So darlington pair method was chosen to amplify the current. Darlington Pair is made up of two transistors and when they are arranged as shown in the circuit they are used to amplify weak signals.
The figure below shows the darlington pair:
Figure 5:
The TIP31A transistor’s emitter feeds in to the BC 109 transistor’s base. Collectors of the transistor also connected together. The end result is the input signal is amplified by the time it reaches the out put. The gain of the circuit is vary high and sufficient to drive the motor. The base current provided to the TIP31A is almost 180-200 ma. After amplification the control unit supply 1-1.2 ma to the motor driver.
Testing of control circuit:
An oscilloscope was used to test the control unit. By attaching the leds of the oscilloscope to the out put of each control circuit and turning the power on, it was seen that there was huge noise at the display. This was adjusted by varying the resistor of the sensor unit to give sufficient information to the control unit.
9. How the circuit works:
The circuit concept is an edge follower. It consists of a simple emitter follower circuit.
Looking at the circuit from left to right (Appendix 1) first we notice the resistor in series with the light emitting diode (LED). Its purpose is to protect the LED from high currents, acting like a limiter.
Continuing in this direction we see the LDR connected in series with a variable resistor. Its purpose is to adjust the sensitivity and sharpness of the sensor by adding or decreasing the resistance that controls the current going into the motor.
The current in our motor during our first tests was not enough so we decided to amplify it using a Darlingtons pair of transistors. Both transistors had different pin connections because they were different from each other. We had to look at their data sheets and resources on books “Tower s….” and websites of similar content to help us understand better their best use and limits.
Pictures of the TIP31A and BC109 pin connections are shown below. The simple circuit diagram of how we connected them to amplify the current (
Figure: Transistor TIP 31A and BC 109.
The base of the transistor controls the current between the collector and emitter and in our case the LDR sensor let the appropriate current trough to matching the surface colour for the
BC109 transistor base current could support the TIP 31A that is why it is connected first in the
We then connected diodes across the motor to stop any negative feedback from the motors into the circuit damaging the transistors.
The other part of the circuit was the same except for the LDR position.
Being positioned below the variable resistor instead of up as before it could control the electrons in the negative terminal. This made it work in the reverse as it could run the motor when the sensor sensed black instead of white.
The rest of the circuit is the same as this but with the black sensing circuit connected first and the white sensing circuit following.
(Black sensing circuit = motor rotate when sensor is in black).
(White sensing circuit = motor rotates when sensor is in white).
All the circuit is connected in series having one common positive and ground terminal.
Our circuit uses 4 LDR’s all together and 4 LED’ to support it with enough light in dark conditions.
10. Overall circuit testing:
The sensor and control stage of the circuit was designed to drive the motor driver stage clock wise rotation. For driving straight ahead or at the turning both unit of the circuit has to control the motor driver.
In order to go straight on the track, the control circuit has to provide same amount of current to both motor drive.
While the middle track is white the control circuit provides current to the motor drive as shown below:
Sensor Motor drive Current
Sensor 1 Motor drive 1 .95 amp
Sensor 2 Motor drive 2 .95 amp
While in the middle track colored black:
Sensor Motor drive Current
Sensor 3 Motor drive 1 .86 amp
Sensor 4 Motor drive 2 .86 amp
Some time problem may occur with different level of current. This could be adjusted by varying the variable resistor.
To turn left or right on the track, current level of the wheels have to be different. As the sensors follow the inner edges, the current level of the left wheel motor drive have to be higher then the right wheel motor drive.
While the middle track is white:
Sensor Motor drive Current
Sensor 1 Motor drive 1 .86 amp
Sensor 2 Motor drive 2 .23 amp
While the middle track is black:
Sensor Motor drive Current
Sensor 3 Motor drive 1 .86 amp
Sensor 4 Motor drive 2 .25 amp
This testing prove that both unit of the circuit work and interact with each other.
11. Cost of the project:
The cost of any project is an important factor when designing and building products to mach their purpose. In this case our micromouse didn’t just have to work; we had to race it with the other teams.
Cost anticipated for the micromouse in the beginning of this project could be increased by the quality of the components. This increases the price.
As speed is a big concern on this project the sharp response of the sensors would help us win.
Having a simple circuit with not a lot of components makes our circuit not expensive.
The circuit includes:-
4 BC109 transistors
4 TIP 31 transistors
4 330Ω resistors,
4 LDR’s,
4 LED’s,
2 VR 10 KΩ resistors
2 VR 100 KΩ resistors
2 6v D.C motors
2 (130-96) PCB (Printed Circuit Board)
The price of the components comes to £5.00 all together. This cost value was approximately what we anticipated it to be because of our simple approach technique of building the circuit. The cost of the whole project including the materials and the body of the robot come to ≈ £14.00. We did a lot of testing on the components and parts of the circuits had to be rebuilt increasing the actual cost to £16.00 for the whole project.
If I was to do this project again I would choose a better type of sensor. The circuit and controller for the mouse would be a micro processor. This would be the simplest and fastest method of making a robot or machinery to respond like expected.
12. Conclusion:
This project was a very interesting project that required many skills. Some of those skills include, planning and following it, group leading and setting of targets but most important of all was working as a group with people that you don’t know much about, their strength and weaknesses.
Sometimes it was hard making decisions on one specific topic or idea as the rest of the group had to be convinced that it would work.
Splitting the work up into section made it less stressful for us because everyone had a certain task to complete. The time spent on each part of our plan was crucial as we knew that we could face more problems in testing. It was hard to keep to the plan in the end as members of the group were not attending regularly causing time losses.
Taking a project from an idea on the paper and accomplishing it is very different and unexpected problems can come up. Resistor values had to be changed from the original value was current was an issue in the end. Even connecting a switch in the circuit took us time as we connected the supply leads together causing our batteries to heat up (short circuit). Simple things like this took us a long time that if thought properly and with some more research could have been avoided.
At first our micromouse was turning and we had some difficulties positioning the sensors however it managed to go around the track. Speed was a problem for us as it was a bit high during corners. Quick decisions taken by group members during testing of varying the speed form the variable resistor, which wasn’t designed for that, cost us a lot of time needing a complete readjustment of the circuit and other components. Parts of the circuit were not working when tested again leading to one final half of the circuit being rebuilt, checked and tested. We also thought it would be a good idea to build a new sensor mounting unit to keep the sensors stable. We designed it to be adjustable in length giving us an edge in the race as position would be crucial.
In the end the project was successful members managed to work harder. Our robot was the fasting moving robot in the track. We raced our micromouse robot and achieved reasonable result.
13. Further improvement:
The basic idea of this circuit was to focus on the sensor surface detector and control unit. Sensor circuit was formed with a voltage divider by a fixed resistor and a variable resistor. If the fixed resistor is replaced by a constant current source then the given change in the resistance will result in a much larger voltage out put to the control unit. The constant current source could be formed using two pnp transistor and a resistor by connecting as current mirror.
Bette quality LDRs were possible to order and super bright LEDs with small current could have been used this circuit. But as the time was worst enough for these components to arrive in time member were agreed to use to the components
from the lab with light intensity.
Differ types of motor like stepper motor would behave better in the race and be more precise in braking when the sensor sensed a change of colour in the track. The quick and precise response time of these type of motor would not let any room for error in our micro mouse performance during the race.
The mobile robot designed faces some problem at the turning track. With the knowledge of actual position of sensor on the track and the acceleration the improvement of the circuit could be achieved. The acceleration, braking and turning process of the motor drive could be sped up by slowly acceleration at the beginning then at maximum speed before the starting of the turning track. Capacitors could be used for this purpose. Charging process of the capacitor slow down and while discharging slowly increase the speed.
If we assigned to do this robot project again, we would use microprocessor with software programming in conjunction with digital circuitry. The software and the circuit will be designed to solve similar type of race track with different background color.
12. Achievement from the group design:
Working in a group is the real engineering world. Engineers have to be team player in order to solve problems and develop ideas. The UEL group design project of autonomous mobile provides each individual with experience of working in a team. This is important to all employers. Also the role of the supervisor was understood.
Group design enhance the problem solving capability as we faced many obstacle on many stages of the task. The group was very useful for this purpose. The problems were discussed with members and reached to the level best solution of our capability. Working on team takes time and patience as members could have disagreement. In this case the problems were discussed with supervisor of the group. Discussion helps the members to learn from supervisors experience and knowledge. If any group member was not able to contribute much, rest of the group try to help the person to keep on track of the project.
The entire work load was divided among the group members. But close contact to each other were maintained in order to ensure the members working the task given. The plan of the group design was updated on regular basis by judging the amount of work finished by the time.
Appendix 1:
The circuit
Appendix 2:
Technical data
§ 4 to 6 operating voltages.
§ LDR sensor unit.
§
§ Average speed 18 cm/s.
§ Compact size.
§ Light weight.
§ Power efficient.
Appendix 3:
Mechanical construction of the robot.
Appendix 4:
Plan Of group design of autonomous mobile robot.
Appendix 5:
Picture of mobile robot components
Appendix 6:
Contribution of work of the group members
Members:
1. Sk. Asif Bari Akash, student no- 0300719
Percentages of work – 35%.
( overall report writing, worked on sensor circuit, help to build the circuit )
Agreed by the group member-
Eldi Alilaj –
Romeo KENMOE
2. Eldi Alilaj, Student no- 0302323
Percentages of work- (Circuit building and soldering)
Agreed by the group member-
Sk. Asif
Romeo KENMOE
3. Romeo KENMOE, Student no-0308157
Percentage of work-
Agreed by the group member-
Sk. Asif
Eldi Alilaj-
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Reference:
1. Brooks, R.A. 1986. A robust layered control system for a mobile robot. IEEE Journal of Robotics and Automation. RA-2: 14-23.
2. Craig, J. J., Introduction to Robotics: Mechanics and Control, 2nd ed.,
Wesley,
3. Williamson, M. M., Series Elastic Actuators, Master’s Thesis, Massachusetts Institute of Technology Artificial Intelligence Lab, Cambridge, MA, 1995.
4. UEL handout: university of east
Bibliography:
1. Brooks, R.A. 1989. A robot that walks: emergent behavior from a carefully evolved network.
2. Neural Computation. 1(2): 253-262. Ferrell, C. 1993. Robust agent control of an autonomous robot with many sensors and actuators.
3. MIT Artificial Intelligence Laboratory Technical Report 1443.
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