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Thread: Line follower sensor dilemna

  1. #21

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    I have an emitter but I am not measuring the specular reflection (for which the angles have to be matched), I am measuring the uniform diffused reflection. Basically I have the emitter and the sensor (photodiode) pointing at the same point, parallel to each other.

    I can cover my sensors but I prefer to use modulation to reduce the effect of ambient light.

    I am not keeping the sensors in the middle of the line (obviously the bot has to follow the line), I keep the sensors near the edge of the line and due to the variation of the response I know when I have moved slightly inside or outside the edge of the line (basically the error from the set position which is the edge of the line) which allows me to use a PD controller (instead of the simple ON/OFF controller) so as to be able to go faster without losing track of the line. I haven't tried with acute angles though, only tried up to right angles.

  2. #22
    Super Moderator T-1000 docel's Avatar
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    Karthik!!
    You are saying now, ALL that you should have said in your first post.
    The guy who started this thread has some serious problem. If you have a solid justified solution and suggestion, make it. It should be in a position to help the OP, since it is his thread.

    You are just confusing issues without direction or anchor.
    The argument about "diffused" light, in your words and justification, cannot be a reliable Line Following technique for a simple design. i have mentioned , in my reply, that it is possible only with modulated light. You own up NOW that you are using mod. light with multiple sensors. This does not add up as solution to the question in hand.
    I have been using " " for "diffused" for the same reason Allbits has pointed out- because i myself dont understand your justification for the Diffused light.

    Let me tell you this: your argument ignores the basic sensor response to light. Ie., the digital state. It is actually the converse of it. The sensor will see the difference between dark and light, with the source being the most intense in the surrounding area. I use LDRs for sensing and White Leds as source. This works beautifully, as the LDR attains some 100 to 5 million intermediate states and is easy to set the relevant threshold, unlike the Photodiode. Now do'nt tell us you are using Photo-transistors!!!
    Besides, any sensor aligned between black and white demarkations will still give a slope, as will your "diffused" reflection (whatever that means).

    The "look-forward" sensor is used to detect lines before the Robot actually touches the line- like in the Autonomous Sumo Robot. This does not apply well to Line following.
    Besides, the sense range will be small and the motors will actually modulate in speed. This may be ok but is not reliable with a single sensor per side.

    Now the worst thing is: black surfaces also "diffuse" light quite well. So :?:

    We will accept your argument when you convince us about the term "diffuse" reflections with respect to the sensor. The diagram does not do this.

    Why talk about "expert" solutions to a newbie with a simple problem? You are talking about multiple sensors, without saying so till the last post, as the solution to a minimum sensors scenario.

    I'm not saying you are wrong, but you are'nt being correct either. We can probably thrash this out here as good as anywhere. This is a public Forum and the posts are read widely, although the participants are less. They should not go off at a tangent with some unexplained theory.

    ....reminds me of the old adage:
    " Are you here with the solution or are you a part of the Problem..? "
    docel
    ^Anything is possible..
    after YOU prove it!!

    http://bangalorerobotics.tripod.com

  3. #23

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    Yeah, the solution is definitely not for newbies which I have mentioned in my earlier post.

    Black surfaces diffuse light but due to their low reflectivity the amount of light diffused (which is just a form of reflection) is lower than a white surface.

    Regarding the multiple sensors thing, that was an assumption at the back of my mind which I thought was obvious, so was not mentioned,

  4. #24

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    if you have an emittre inside, and you only want to use the 'reflectivity' of the surface, then why do you want to use diffused light?? just put the sensor emitter in a proper direction to get the reflected beam! maximum output!!

  5. #25

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    hey i think on the turning acute part a lot will depend on the algorithm u use rather than if u using reflected or diffused light besides if the surface is too reflective bith of these techniques usually arent very reliable so i would saywe use an array to detect the path and to turn lets put our minds to developing a stronger algo which sadly in all the competitions i have been too was seriously lacking!!!




    "The end is Inconsequential"

  6. #26

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    and as for ur earlier querry i would still recommend i.r. sensors though u cud check if the condns u testing ur sensors is too hot which might trigger them or u cud also try decresing the height of ur sensors from the ground so that ur pot wud be placed somewhere in the midle giving a better resolution..

  7. #27

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    Quote Originally Posted by shreek1123581321
    if you have an emittre inside, and you only want to use the 'reflectivity' of the surface, then why do you want to use diffused light?? just put the sensor emitter in a proper direction to get the reflected beam! maximum output!!
    With the reflected beam (specular reflection) the problem is that you get a small "cone" of high sensitivity but if something like the floor angle changes, the reflected beam no longer falls on the sensor and you loose all the sensor information.

  8. #28
    Super Moderator T-1000 docel's Avatar
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    Quote Originally Posted by kartikmohta
    With the reflected beam (specular reflection) the problem is that you get a small "cone" of high sensitivity but if something like the floor angle changes, the reflected beam no longer falls on the sensor and you loose all the sensor information.
    :arrow: Kartikmohta:
    This cannot happen. You are talking about what will happen with your "diffused" light. How can a 1cm round 'cone' dissappear at ANY angle seen by a Line Follower sensor :?: :?:

    Have you tried this or is it just theory?

    You are again confusing the issues here.

    I suggest that you start a different thread for more discussions on this. I also suggest that you practically try these things out first and commit yourself in text.

    :arrow: Jaabis:
    It is not the Algo thats important but rather the sensor(s) placement. The bot has to simply do 'some' move for a specific sensor combo output, as a binary word. And you dont need a Microcontroller to solve OUR LFR tracks!!
    docel
    ^Anything is possible..
    after YOU prove it!!

    http://bangalorerobotics.tripod.com

  9. #29

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    karthik! if your floor angle keeps changing, then your diffused light alos cannot help you! nothing can help you... we assume floor to be sufficiently smooth, and it is, in most of the competitions!

    and have you ever tried using diffused light? its was such a pain to work with even reflected light, i just cannot imagine how are you going to work with diffused light coz it gives so less intensity!.

    and one more point, diffused light is 'diffused'! i think at any point of time reflected beam deserves more trust than diffused... tell me if floor angle changes what will happen to your diffused beam? as diffused light also follows the angle rule, its presence is because of the roughness of the surface...now tell me if the roughness also changes what will happen? and i think roughness change is more probable than surface angle chage...
    "if roughness changes all the info is gone!" in your words!

    i think in line following we assume uniform surface angle...

  10. #30
    Super Moderator T-1000 docel's Avatar
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    ...You have put that very beautifully Shreek!!

    I wonder: why is Kartik bent on using a negligible ("diffuse") percentage of light when an ample ( Reflected) amount of light is available..... :?

    Besides , the trigger threshold can always be set with a Preset in the voltage divider. Or with the Light..... intensity ! This has been the problem and the reason for this thread.
    docel
    ^Anything is possible..
    after YOU prove it!!

    http://bangalorerobotics.tripod.com

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