Level Controlling a actuator.

Discussion in 'The Projects Forum' started by Allfive, Jan 10, 2013.

  1. Allfive

    Thread Starter New Member

    Jan 10, 2013
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    Hi,
    I’m new here at this forum. I’m an mechanic of background, and have worked with electronics before but I have rarely worked with actuators. I have tried to use the search bar but I haven’t found any threads to mach my needs.

    - How can I level control a actuator (Length)?

    As I have understood there are normally 2 internal switches in a actuator as below.
    These need to be there for the electric engines safety.
    Actuator.png

    On my configuration I need some way to control the length of the arms extent. This way I can control witch positions the actuator is in with a couple of buttons as under:
    Actuator 2.png

    In other words I’m looking for hints and tricks to make this work. The actuator is in a tight spot so size is of the essence, and I think it is difficult to place a limit switch on each location for indication.
    I’m hoping to have a control box separate from the box above, with individuale potentiometers that will able me to move the locations (1, 2, 3, and 4) around to be able to insure that the actuator arm is the correct length.


    - Is it possible to make it so that I’m able to press from 1->3?
    Lets say I’m in number 1, and want number 3, press on it and it slowly goes there, and then the same from 3->2 and 2->4 etc etc


    My index finger has blisters all this Googling. :)
     
  2. Allfive

    Thread Starter New Member

    Jan 10, 2013
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  3. panic mode

    Senior Member

    Oct 10, 2011
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    add position feedback for the actuator and trigger output when position exceeds preset (value set by potentiometer).
     
  4. mcgyvr

    AAC Fanatic!

    Oct 15, 2009
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    string pots (basically a string connected to a potentiometer.. pull the string out and the resistance of the pot changes.. A table of resistance to distance can be constructed and the resistance simply monitored to know how far its out..

    or linear encoders,etc..

    Depending on the accuracy required even just stopping/starting based on time "could" work.. Turn on for X seconds yields X amount of movement.. But its more than likely not very accurate at all..
     
  5. BillB3857

    Senior Member

    Feb 28, 2009
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    I built a unit to self level my travel trailer front to back using the landing gear. Two IR LEDs and two IR photo detectors set across a bubble level. Positioned so that when level, IR is either on both or blocked on both. Detectors feed comparators and output of comparators feed XOR gates. Output of XORs feed relay drivers. Unit knows whether front is high or low and reacts accordingly. Stops when level.
     
  6. Allfive

    Thread Starter New Member

    Jan 10, 2013
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    Thanks for the replys.

    (Is there a pre-made box out there?)


    - The potensiometer will give me a feedback in Ω that is different on every length? And how do I "trigger" output?

    - The string pot I assume is needed to "ad on" as a extra external part?
     
  7. KMoffett

    AAC Fanatic!

    Dec 19, 2007
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    Can you post a link to the spec's for the actuator you're using? If it has an internal encoder or pot, it will be a lot easier

    Ken
     
  8. Allfive

    Thread Starter New Member

    Jan 10, 2013
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    My intention was to highlight the control box here, and then let the controller determine the actuator.
    - But the aim was to produce controller for a small actuator, and I've looked at this one:

    This will probably be small enough, and since its location is in a confined space. The stroke needs to be exact and adjustible.
     
  9. Allfive

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    Jan 10, 2013
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  10. Allfive

    Thread Starter New Member

    Jan 10, 2013
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    Now I feel like I'm spamming my own thread here, but I'm curious how this will work.
    All drawing is made ​​of a simplified assumption of how this is hooked up.
    As the picture suggests:
    Actuator 3.png

    How can I make a intellectual control box that will run this actuator to the correct posistion?


    * - I want(but dont need) to get the potentiometer to adjust them from point 0 to 4 (ie from 0Ω to 30Ω) on each.
    They will have to be adjusted to the exact position, and then you have to maybe take away the ability to adjust potentiometer from point 1->4 to get a more accurate potentiometer at each point?

    Such as:
    If point 1 is preset to be 3mm from the actuator. But I want it to do it by 4mm from the actuator instead, will have to be able to adjust it.
     
  11. Allfive

    Thread Starter New Member

    Jan 10, 2013
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    I'm guessing this is how I will connect it.
    Actuator 3.png
     
  12. BillB3857

    Senior Member

    Feb 28, 2009
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    Looks like a plan! What kind of "smarts" will you use in your control box? Microprocessor would be one way but it could be done with discrete components as well.
     
  13. KMoffett

    AAC Fanatic!

    Dec 19, 2007
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    That actuator has an internal position potentiometer. Good. Though it doesn't state the resistance, they are usually 1KΩ or 10KΩ. You will use the pot as a voltage divider. The output voltage will be proportional to the ram position. A microprocessor will be to best way to set positions and control the direction and speed of movement.

    Ken
     
  14. Allfive

    Thread Starter New Member

    Jan 10, 2013
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    @BillB3857:
    Discrete components you say, how?

    @KMoffett:
    I'm reading up on microprocessors as we speak.
    Are they usually from 0Ω->1/10KΩ?
     
  15. KMoffett

    AAC Fanatic!

    Dec 19, 2007
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    Yes. Ground to one end and supply voltage to the other. The wiper will output ~0V to ~ Supply voltage. Many microprocessor have an analog voltage input to read this position-relative voltage.

    You will also need an H-bridge circuit/module/relays to control the motor power and direction.

    Ken
     
  16. Allfive

    Thread Starter New Member

    Jan 10, 2013
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    From what I'm gathering the H-Bridge is for use to revers the polarity of the engine.
    Or do I need this one to control the signal to external cables from my relays?
     
  17. KMoffett

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    Dec 19, 2007
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    Do you intend the "motor" in the actuator to run at full speed from stop to stop? If yes, then the microcontroller can drive two transistors that can drive two relays that control the power and direction of the motor.

    Ken
     
  18. Allfive

    Thread Starter New Member

    Jan 10, 2013
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    I'm not sure. I believe the actuator will be used at slow speed everywhere, so I can get the right length. - Do you have a microcontroller to recommend?

    Thanks for all the help so far!
     
  19. KMoffett

    AAC Fanatic!

    Dec 19, 2007
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    Allfive,

    There are lots of choices for microcontrollers. Everyone has their favorites. I like PICAXE for simple, low speed control projects like this. The chips start at ~$3.50 and the BASIC software and manuals are free online. It just takes a 3-wire serial cable (homebrew) from a PC, a 5V supply, and two resistors to program the chips. And, they have a very supportive and civil forum (http://www.picaxeforum.co.uk/). The system was designed for middle and high school classes. But, others will have their reasons for their choices.

    Since you are not sure about the speed, I think we should take a step back. What's the real purpose of the project? This can bring up variables that you might not be aware of, but can be critical to a control design.

    Ken
     
    Last edited: Jan 12, 2013
  20. Allfive

    Thread Starter New Member

    Jan 10, 2013
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    A little late response... But the project is for my work space, its still in its early fantasy stages but I want to learn so I can understand how I can make a "smart" controll box.

    - It will be used for a mechanical arm. This one has about 4 positions, and is normally on board operated by hand. It is about 1cm in between the positions.
     
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