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which kind of sensor should i use ???

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mohmoh

New Member
hi, i'm very new in building robots and i should build robot that can follow black line and also i should use (IR) sensor so, can any one advice me which the simplest sensor can i use, with all regard :roll:
 

falleafd

New Member
For line following, they usually use IR sensor, but I used red led, and it worked better than IR. If you got better skills on computer programming, you may get a camera to track the line, and using fuzzy logic to follow the line. Espeacially, as the line is not perfect (it may be build from multi discrete points) using camera can make advantages.
 

steveshy

New Member
How can I use camera to follow a line?

I am interested in following white lines using camera. I am currently involved in a robots contest(ABU), I have tried several methods to track meshs made by white lines. I tried using four BANNER D11 sensor coupled the information acquired from encorder. However it is not stable enough for our demands.

Can you provide me more information about tracking lines based on cameras? And is it possible to implement it in a short peroid of time?
 

falleafd

New Member
Are you going to come to Robocon? which will be held on Korea next April?

Congratulation.

No, as I know, the floor is green, and the line is white. There are many tracking board working quite good on this kind of floor. Perhaps your circuits are not good enough.

As I took place with my friend in the last contest, our circuits worked good. Unfortunately, my data was lost as I left school, and I cannot send the circuits to you. However, perhaps, some kind men in this forum will help you for the suitable circuits. We discuss muchie about this kind of line trackers, you may take a look to old topics.

Perhaps, its subject is "mobile robot".

The problem is that you have to use a good algorithm to move and remember where you are on the floor.

You may use 2 or 3 sensor in front of your robot to detect the line and go on it. You then can put 2 sensor on 2 sides to detect if you come to a cross.

And in your program, you should remember if you are on horizon or vertical. Each times you pass a cross, you will know exactly where you are.

The problem will happen as you come to the coner and turn around, your robot may lost the position of the coner (the sensor may not detect the line after turning around in some cases). But if so, you can use more sensors like a square.

x__x_
..|..........|
x|..........|x
x|..........|x
..|_x_x_ |

where x is your sensors. At a time, you always can see the white lines.

You can also use a compass if you want to know the direction, and it cost about 50$ for Devantech compass.


There are many method to detect the line, and know your positions. But if the problem comes from your circuits, try reading the old topic I suggested, and you may make your circuit works better.

Good luck on the contest.

Don't try with camera, because camera is quite difficult as the contest is coming so close.
 

falleafd

New Member
To protect your robot from noises and interferences, there are many way to do
1) You can cover your robot with clothes or black papers.
2) You can use rheostat at receiver LED
3) You can cut a black sheet and a white sheet, then detect it
as reference with a visible light transceiver.
Hide it inside your robot, and use this receiver reading
as reference for other ones.

I wrote this.

I'll send a picture later if you care of it. I have to go now.
 

steveshy

New Member
Thank you very much for your help.

Dear falleafd,

I am very moved by your help. Your tips is very useful. I have made several clothes for my sensors.:)

Yes, I will represent PR China to the Robocon in Koera if our team beat other univeritis this July.

From our last year's experience, the noise is the strong light reflection of the ground as it is broadcasted by TV. The sensor is unable to detect white line and green ground in some places. Also, the ground is not clean enough. Some black noise(foot print) may lead to unfavorate behavor of the robots. So the utmost important work for me is to shift the stability of our robot.

Another problem for me is that due to mechanic design and the sensor we choose( Banner D11 photoelectroic sensor) , it is hard for me to put the sensor in the front and back of the robots. I can only put the sensor in the sides of the robot.

| |
| |
XO OX
| |
| |
where X is the position of the sensor(I place two sensor in one position to provide more reliable information) and O is the position of the wheel.

By using a lit more complex algrothim, I now can achieve the line tracking by adjusting position in the cross( every 500mm will be a cross) where the robot will turn. During two adjustions, the robot moves according to the encords. It may be hard to explain, if you want to know the detail, I may send you my program.

I think our circuit is very good which has updated for 9 times. It based on a powerful Cygnal C8051f040 runs at 24.5mhz which intergrate A/D,D/A, Can controller, compartor.SPI,SMBUS and 8 ports.

I think my current problem is
(1), to count whitelines corrected. Currently I use two sensors as one, that is when the two sensor both detect a white, I think it is a white . both detect black I think it is a black. Else(one black one white) then it is determined by previous condition. However it detects wrong number of lines from time to time. As for my adjust algrothim, it is very important to detect the right number of whitelines.

(2) How can I find my position if in case the robot lost because of a bang of some other accedents. How can I re-position myself?

(3)To use a compass. As in this year's competition, there is no lines in a part of the ground. We have tried several methods to position in this area. We have try some expensive gyros, however it doesnot work good enough after one or two minutes. As for compass, we are afraid that it may be affected by the cameras and other electrical equippments in the TV station where we will compete. Have you got any good idea about this?

BTW, falleafd, which university did you represent in last year's Robocon? I may see you at TV:).

pls post the picture about your circuit, thank you.
 

falleafd

New Member
From our last year's experience, the noise is the strong light reflection of the ground as it is broadcasted by TV. The sensor is unable to detect white line and green ground in some places. Also, the ground is not clean enough. Some black noise(foot print) may lead to unfavorate behavor of the robots. So the utmost important work for me is to shift the stability of our robot.

Have you ever take a picture of the floor? You can use a the role of film to take the picture of the floor. You know, it's the negative film. And if the light of boardcasting is go through your cloths and come to the sensors. You cover the sensor by the film taken from the floor. The light out side is white light, it reflex on the green floor, so the film will intercept the green light (because the film is negative.).

Try it.

Besides, you should make pulse to your tranceiver, it's bout 40KHz, and it can intercept the noise. Because the light of boardcasting is about 50Hz or continuous.

The third way you can use is that,

You put a sample of the floor and the line into your robot. You cover it up. Use the same sensors with your sensors, the receivers will get a voltage as it receive reflextion from the sample, it's reference voltages. And you use the reference voltages to detect the sensors which is used to detect the line and the floor.


--|\
| >----
--|/

this is an opamp

you can compare if the reference voltage as detecting on green sample is equal, little smaller, or higher than the voltage you receive from the sensors or it's large difference from it. Then you can recognize if it's green or white.

Another problem for me is that due to mechanic design and the sensor we choose( Banner D11 photoelectroic sensor) , it is hard for me to put the sensor in the front and back of the robots. I can only put the sensor in the sides of the robot.

No, the stable control for line tracker is that the sensors have to put in front the robot. This was proved. You can do some changes, but it'll make your robot better.

(1), to count whitelines corrected. Currently I use two sensors as one, that is when the two sensor both detect a white, I think it is a white . both detect black I think it is a black. Else(one black one white) then it is determined by previous condition. However it detects wrong number of lines from time to time. As for my adjust algrothim, it is very important to detect the right number of whitelines.


The floor is green and white (lines). Therefore, as you get good detection, you will know where you are. Note that the start area of robocon have a different colors from the green floor. You have to take care of as the robot start, it cannot know the floor is green or white if you only use 2 status of the floor. Give your robot 4 status to detect the floor. RED, GREEN, BLUE and WHITE. The start area is usually RED and BLUE.

In this case, if you use 2 sensors, you will see that, if there is something wrong, your 2 sensors will go wrong in the same way, and it's no effect, because your 2 sensors will be so close.


(2) How can I find my position if in case the robot lost because of a bang of some other accedents. How can I re-position myself?

Close your eyes and move around, then do you know where you are?

If you got better sensors, and algorithms, you may know where you are all the time. But with IR sensor like this only, it seems cannot.

But if you lost your position for a short distance, and you wanna to find it again. You may use the sensors arranged as I told you. At the conner, as you lost your position, the conner is still inside the ring of sensors. Therefore, you can re-find it.


3)To use a compass. As in this year's competition, there is no lines in a part of the ground. We have tried several methods to position in this area. We have try some expensive gyros, however it doesnot work good enough after one or two minutes. As for compass, we are afraid that it may be affected by the cameras and other electrical equippments in the TV station where we will compete. Have you got any good idea about this?

well, if the gyro does not work good, it's from your program or your circuit. The gyro is much better than the compass. However, both of them have an limited accuracy. You should take it in account.

You don't have to worry about it. You only need the compass for large inaccuracy. For example, you turn 90 deg, but the compass show that you turn only 80 deg. It's oki... Use the encoder on your motor to compute it. And use the white line on the floor to fix the noises.

I'm in Vietnam. And in the last contest, my team lost from the national contests. My page is at www.99a1.net/vp99/doanhiep/falleaf.htm

But it's in vietnamese.
 

Donny_maybe

New Member
Ask bout robotics

Hy excuse me,.
I wanna ask bout robotic,.
I wanna join rob0t contest line follower in my country,.
I use AVR for microprocesor,.
Is there any one had used it before??
I wanna find the reference or the listing programs for my AVR,.
Is there anyone can help me here??
Thanks before,.
 
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