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Limit switch to control motor

Discussion in 'Electronic Design' started by Norman Pirollo, Nov 17, 2004.

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  1. Need some advice..

    I am designing a small feed system for lumber grading.
    This feed system is part of a lumber grading system.

    There is a motor drive feeding the individual boards along a
    horizontal surface using rubber wheels or rollers.
    The feed motor is started manually with a magnetic switch.

    At a certain point the piece of lumber should activate a limit or
    proximity switch indicating the lumber is correclty against the
    horizontal surface of the grading component ( very important to
    correctly grade)

    If the board rises above the surface , even as little as 1/3 in., the
    limit or proximity switch should shut the feed motor down using the
    same magnetic switch used to start it..(severly warped board, etc..)

    I wish to use one limit/proximity switch to do this.
    The difficult part is that the switch is normally open while the board
    is being fed through, then becomes closed, then open if there is a

    The open switch then needs to shut the feed motor down...

    I have been looking at metal roller ball type switches, preferably
    dust-proof and rugged.

    How to perform this trickery?

  2. Rock

    Rock Guest


    Most micro switches such as the one you describe have three contacts so that
    you can wire them as normally open or normally closed. If I understand your
    problem correctly you would connect it in series with the coil of a relay
    controlling the motor and wire the switch in the normally closed condition.

  3. Ross Herbert

    Ross Herbert Guest

    You will need to use an industrial limit switch such as the 9007AW
    shown here$file/HeavyDutyIndustLimits.htm

    the SPDT and DPDT types have changeover contacts (single or double
    contact) so that you can use the NO or NC side of the switch for your
    purpose. You can obtain application information from the technical
    library here
  4. Thx for the links....
    I'm still stumped on how to toggle the switch, then monitor same
    switch if piece rises above surface. Toggling the limit switch on
    should do nothing, but if the switch turns off, then it will release
    the motor dricve
    at the mag. switch

    Looks like I'll need a circuit which is normally set, then if unset,
    will release the magnetic switch powering the motor.
  5. John Fields

    John Fields Guest

    The circuitry required to do what you want isn't difficult to come up
    with, but what's confusing (to me, anyway) is the sequence of events
    leading up to the piece of lumber engaing the switch and then the
    criteria used to determine if/when the feed motor should stop.

    Could you describe the grading process in greater detail and how the
    lumber is handled from start to finish, please?
  6. Norman

    Norman Guest

    Thank You all, looks like I need to look at this design a little
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