linear actuator circuit design

Discussion in 'The Projects Forum' started by max588, Aug 26, 2013.

  1. max588

    Thread Starter New Member

    Aug 26, 2013
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    Hello all,

    Let me first start off saying I am a half newbie with electronic projects so please pardon if i don't use the correct vocabulary.

    I have a project in mind that will require a circuit, but i need a little help designing it. It will contain the following:

    three limit switches
    one linear actuator
    one dial
    Power source (dc transformer)

    OK, so this is how this system would work:

    If limit switch A is triggered (linear actuator in home position) and limit switch B is triggered then upon release of limit switch B engage linear actuator. Once the linear actuator is engaged limit switch A will become disengaged, but this should not affect the actuator's travel. Once Limit switch C (linear actuator fully extended) is triggered then the actuator should stop. If at any time limit switch B is triggered during the actuators travel it must stop and reverse direction (back to home position). If limit switch C is triggered and limit switch B is triggered then upon release of limit switch B engage linear actuator in the opposite direction. I would need a dial in place to be able to set an amperage use ceiling for the actuator, this is intended to detect if the linear actuator is jammed. If a jam is detected the actuator should stop and switch its current direction, until either limit switch A or C is triggered.

    The whole system will be moving no more the 50lbs back and forth. If anybody has any suggestions on the design of this circuit and recommendations for components that can handle a bunch of cycles I would greatly appreciate it! I really cant wait to build it! :D

    Thanks
     
  2. MaxHeadRoom

    Expert

    Jul 18, 2013
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    Your switching sequence does not seem to make a lot of sense, Is the actuator itself tripping the limits or is there other mechanism involved?
    And presumably this has a DC motor on the actuator?
    Max.
     
  3. max588

    Thread Starter New Member

    Aug 26, 2013
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    Max,

    Limit switch A and C are at either end of the travel so the actuator is tripping these. Limit switch B rides along with the actuator and is meant to be used for collision detection and start button

    Yes the actuator will have a DC motor.

    Thanks,
    Max
     
  4. LDC3

    Active Member

    Apr 27, 2013
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    Similar to a garage door control with an edge sensor so things don't get crushed.
    Should be doable. ;) Oh wait, it is. You could buy it off the shelf.
     
  5. max588

    Thread Starter New Member

    Aug 26, 2013
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    Yes it is like one with the photoeye substituted with an edge sensor. I just need a miniature more quiet version. Plus what the fun of buying when you could build it!

    Does a garage door stop when it hits a limit switch or does it stop when is senses a spike in resistance (hits the floor or other hard object for that matter)?

    Max
     
    Last edited: Aug 27, 2013
  6. MaxHeadRoom

    Expert

    Jul 18, 2013
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    Both my garage door openers detect an increase in load, as in when/if they come down on a vehicle or other obstruction in the doorway.
    Which is a similar principle you are looking for, the L.S. operation is simple.
    The DC? motor current shut off might have to be built to suit?
    You would need a way to ignore the limit at switch on, to override the initial current, unless a slow start was employed?
    Max.
     
    Last edited: Aug 27, 2013
  7. LDC3

    Active Member

    Apr 27, 2013
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    There are 2 types of edge sensors for garage doors. Photoeye beams set just below the edge of the door and physical touch switches mounted on the door. Both can be set to either stop the door or reverse the direction. The physical switches must be ignored when the door is about to make contact with the floor. The photoeye beams are probably pushed out of the way.
     
  8. max588

    Thread Starter New Member

    Aug 26, 2013
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    hmm.. I guess next step is to search for a garage door opener wiring schematic..

    There will have to be a couple of modifications I'm sure so i will surely post when i have one!
     
  9. MaxHeadRoom

    Expert

    Jul 18, 2013
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    As I mentioned, the L.S. logic and reversing should be quite simple, most of the major O.H. Door Manuf such as Genie (Sears) are reluctant to hand out board schematics.
    If all else fails you could put a low Ohm resister in series with the motor to detect current and feed it in to an OP amp schmitt trigger to cut the motor if overloaded.
    You would need a way to either delay this until the motor was up to speed or bring the motor up slowly with another resister in series with the first and a relay contact to shunt this after a delay.?
    Max.
     
  10. THE_RB

    AAC Fanatic!

    Feb 11, 2008
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    strantor likes this.
  11. MaxHeadRoom

    Expert

    Jul 18, 2013
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    The initial motor current would have to be ignored somehow, either by slow acceleration or by a relay contact shunt if full voltage applied at start.
    Max.
     
  12. THE_RB

    AAC Fanatic!

    Feb 11, 2008
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    Thanks Maxheadroom, you are right the circuit I linked is not a total solution for driving a motor between current "limits". However it will detect the end of travel stall condition.

    For a total solution I like your suggestion of deliberately ramping up motor current during the start of travel, then end of travel can be detected by the over-current sensor.

    The best choice is of course a microcontroller, but it gets a bit boring saying the best solution in 95% of threads is to "just use a micro". ;)
     
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