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"Why Tacho Feedback is Necessary?"

Discussion in 'Electronic Basics' started by Nick, Dec 27, 2005.

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  1. Nick

    Nick Guest

    Hi,

    Please let me know why tacho feed back is necessary?? Without Tacho the
    Servo motor runs..

    Help me..
     
  2. Pooh Bear

    Pooh Bear Guest

    Yeah - it'll run - but not at any speed you can control ! That's what the
    tacho is for.

    Graham
     
  3. Jamie

    Jamie Guest

    Feed back is needed to maintain a steady output verses
    input reference which is called Tach/Reference feed back otherwise
    , its called armature feed back which really does nothing
    more than maintain the output voltage to the input voltage
    reference ratio. in the case of the second, this is not a
    steady reliable way to maintain speed because the motor may
    require more voltage on to maintain speed depending on shaft
    load&load Swing variations.
    Simply put, armature feed back can maintain the output
    voltage but not the actual shaft speed on load..
    etc...
    there are the cases where you have a feed back from some
    other reference point inputting to a Trim controller which then
    can regulate the input reference to the drive, this would then
    be regulated from the Trim control by simply biasing the input
    reference of the drive which is in armature mode.
    this all applies to DC PM/Shunts and the like motors.
     
  4. Fred Abse

    Fred Abse Guest

    Armature feedback can make a pretty fair job of it, if you use good IR
    compensation. What it won't do is allow you to run the motor above base
    speed using field weakening.
     
  5. Bob Eldred

    Bob Eldred Guest

    The function of the tach depends on the kind of servo it is. In its simplest
    case, the tach provides velocity or speed feedback and it is the speed that
    is controlled. The tach element provides a voltage or count frequency that
    represents the actual speed of the motor or system it is connected to.

    In a position servo where a physical position is the controlled element, a
    tach is often used to feedback the differential of the position, dx/dt. This
    is a velocity or rate term and helps to stabilize the servo by controlling
    the motion.

    Thirdly, tach outputs can be integrated or counted to provide position
    information. Line tacks of this kind are used on all kinds of numerically
    controlled machine tools. Even the lowly mouse on your computer works this
    way.
     
  6. Nick

    Nick Guest

    Thanks to you all guys...
     
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