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stepper motor of floppy disk

Discussion in 'Electronic Design' started by [email protected], Sep 11, 2007.

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  1. Guest

    Hello,

    I want to control stepper motor of sony floppy disk. I know that here
    is three pins on bus which are to control this motor. This is STEP
    pin, DIRECTION pin and MOTOR pin. I know that DIRECTION pin have
    influance just on direction of motor. MOTOR pin just starts/stops
    motor ( start - high and stop - low signal ? where high ~ 4.5 V ) .
    But I really don't know how I should control STEP pin. Can I assume
    that when STEP is high then motor is stepping?
    Or maybe then motor execute only one step?

    I would be very glad if someone would like to explain me how it
    works.

    Wiktor
     
  2. Tim Wescott

    Tim Wescott Guest

    Normal step/direction/enable functionality is that the enable (probably
    MOTOR in your case) turns the driver on, direction controls the
    direction, and step causes the motor to advance one step (or one
    microstep if it's such a driver) for each rising (or sometimes falling)
    edge on the step input.

    So to get the motor to go someplace you need a square wave on the step
    command.

    --

    Tim Wescott
    Wescott Design Services
    http://www.wescottdesign.com

    Do you need to implement control loops in software?
    "Applied Control Theory for Embedded Systems" gives you just what it says.
    See details at http://www.wescottdesign.com/actfes/actfes.html
     
  3. whit3rd

    whit3rd Guest

    A floppy drive has two motors, one that rotates the spindle and drives
    the disk , and another that positions the read/write head. It's
    probable
    that the MOTOR pin controls the spindle rotation (usually there's a
    multiphase
    AC motor for that) while the DIRECTION and STEP control the stepper
    motor that (through a screw-drive) moves the read/write head.

    Application notes on ICs for driving these motors might be
    illuminating (BA6980 seems
    to be the part number on the first Sony floppy drive I find). The
    'step' command
    in the drive interface is inherited from old 5.25" floppies, it might
    drive any number
    of steps on the actual motor interface after the control logic
    interprets the command.
    Steps are likely to occur on the high-to-low transition of the STEP
    signal.

    There's a bit of clucking from a disk drive at startup, when the step
    motor is
    moved to its end-of-travel; I'd expect another line on the interface
    that reports the
    end-of-travel condition after stepping.
     
  4. Guest

    maybe the step pin need a impulse,at the rising edge or falling edge
    of the impules.the the stepper motor can work
     
  5. Mark Zenier

    Mark Zenier Guest

    One step per pulse. See if you can find the datasheet for a floppy
    disk controller chip. There was even and ANSI standard for the
    interface, but that got superceded by industry practice (ie, it was
    ignored).

    I think newer disk drives will keep a count of the pulses so that
    they can be sent at a much faster rate than the mechanics will move.
    Older controllers had to set the rate at which the drive could step.
    Really old drives were quite slow.

    If you're driving the motor directly, this doesn't apply.

    There are a couple of types of stepper motor used for floppy head
    positioning.

    If the motor shaft spins freely (disconnected from any circuity), it's a
    Variable Reluctance stepper and usually has three motor windings. You get
    it to rotate by driving one (or two) of the three windings at a time,
    and the direction it goes depends on the sequence. Driving two windings
    at the same time gives it more power. Either case (one or two windings
    driven) have three possible drive combinations. They're indpendent of
    the polarity of the drive signal. They can be thought as a special kind
    of solenoid. These motors are usually cylindrical and used in drives
    with a lead screw mechanism.

    If the motor detents/cogs when you try to rotate it, it's a permanent
    magnet stepper. They have two sets of windings and the polarity
    (direction of current in the winding) matters. The two windings (often
    split into four seperate connections) end up with eight different
    combinations of positions. The buzzword here is Full Step, or Half
    Step (where you always drive two windings at once with four possible
    position sets). These are usually square (at least those used in 5 1/4
    inch drives) and used a metal ribbon to connect the drive to the head.

    (Anybody got the URL for Doug Jones' stepper motor web site?).

    Mark Zenier
    Googleproofaddress(account:mzenier provider:eskimo domain:com)
     
  6. Guest

    Thanks for help!

    Wiktor
     
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