Connect BOB To Servo Drives

Discussion in 'Plasmacam Retrofit' started by SignTorch, 4/28/14.

  1. SignTorch

    SignTorch Artist

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    Location:
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    Now we can connect the axis drive output pins on the BOB to the servo drive inputs.

    Turn everything off. Do not connect a motor at this time.

    On both servo drives turn all the DIP switches on, except turn switches 7 and 10 off.

    Connect each step, dir, and gnd from the BOB to step, dir, and com on each servo drive as shown below.

    Connect the reset button from ENC 5V to ERR/RST on each servo drive.

    Connect motor power to terminals 1 and 2 on the servo drive.

    Connect motor power ground to 5 V ground on BOB.

    Power up, start Mach3 and press reset in Mach3.

    Set step jog mode with .1" jog increment.

    That will send about 212 step pulses per jog.

    So that if we jog once we get a warning, and if we jog twice we get a fault because the number of steps taken will exceed the 256 step following error limit that is set by DIP switches 4 and 5.

    The servo drive power light should be on.

    The servo drive fault light should be on.

    Press the reset button on each servo drive.

    The fault light should go off and the IN POS light should come on.

    Now jog each axis once by pressing an arrow key once.

    When the drive gets the first step signal, the IN POS light should go off and the WARN light should come on.

    If you jog twice, it exceeds 256 step signals in the same direction, the WARN light will go off and the FAULT light will come on.

    At that point the servo drive shuts down because it is out of position. Press the servo reset button to reset, and IN POS light comes on.

    Jog once, the WARN light comes on. Jog once in reverse direction. IN POS light comes back on.

    Test both drives by jogging their respective axis. X and Y should both behave the same way.

    Now we know that the BOB is sending the step/dir signals and the drives are receiving them.

    servo-signals.
     
  2. SignTorch

    SignTorch Artist

    Roles:
    • Vinyl CuttingVinyl Cutting, CNC RouterCNC Router, Designer / ArtistDesigner / Artist, Hobby / PersonalHobby / Personal
    Brands:
    • Corel DrawCorel Draw, Adobe PhotoshopAdobe Photoshop, V-Carve ProV-Carve Pro
    Location:
    Vidor, TX
    normally - when the servo drive gets a step signal, it sends power to the motor, the motor starts to turn, which turns the encoder, and the encoder wheel has a thousand slots in it, as it turns, each slot causes the encoder to send a step signal back to the drive, and the drive keeps up with how many step signals it recieved, and it keeps up with how many encoder step signals it gets back, when both counts are even, the drive is IN POSITION. When the drive is getting step signals and the motor is running and the encoder is independently sending step signals back to the drive - unlike a stepping motor - the servo step count can be different from the encoder count - and the difference is called the position error - and the larger that error, the harder the drive pushes the servo to get into position with zero error - so the servo follows the step signal as close as possible but it is not a one to one exact position like with a stepper where each step moves the motor one detent

    actually - the servo never locks into a step position - it sort of hovers in a position and if anything pushes it out of position, it knows because the encoder knows, and it applies opposite force to hold that position, and if anything knocks it way out of position, it will still move right back to position, based on encoder feedback, the drive knows the exact motor shaft position and whether it matches the commanded position or not

    if the position error gets too large, that indicates that something is wrong and the motor is unable to keep up with the step signals - in this case we get a warning at 127 steps of error and a fault at 256 steps of error

    if you see the warning during normal operation, that means you're pushing the motor too hard to maintain postion accurately, whether that means you need to slow down or get more power or refine the gantry, you should not be getting position warnings during normal operation

    normally - the amount of actual accumulated position error during motion is very small within +/- one encoder step - so overall, the machine position is always accurate - and it never misses or loses a step - and it recovers from position errors as quickly as electronically possible
     

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