Need help with Rotation Sensor on Automatic tool change router.

Discussion in 'The Projects Forum' started by slimneill, Aug 6, 2014.

  1. slimneill

    Thread Starter New Member

    Aug 6, 2014
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    Hi, I'm new to electronics. I am currently building a CNC router from scratch and have incorporated an automatic tool change (ATC) spindle into the build. The manual for the ATC states that there are 3 sensors.
    1. to detect the presence of the tool
    2. to detect that the tool holder is open to allow for a new tool to be inserted or the present tool to be released.
    3. a sensor that detects rotation.

    I need these sensors to all work together to ensure that the spindle can't eject a tool accidently when rotating at 20000 RPM.

    The last sensor that detects motion is the one that i can't figure out how to only send a signal to the machine when the tool is motionless.
    The way the sensor is explained in the manual is that the sensor will send a high signal for 1/4 of the spindles rotation followed by a low signal for 1/4, so the high signal gets sent twice per revolution. Once the spindle is spinning fast enough it will appear as if the sensor is sending a constant high signal.
    The problem i see is that the sensor could come to a stop on either a high or low signal 50% of the time. How do i build some sort of a signal that will only send out a high signal when the spindle is at a stand still. Does it have to be time based or comparative?

    Thanks for all your help. I'm mechanically inclined, and average at best with electronics.
    The manual states:
    -The sensor S3 supplies two on pulses and two off pulses for every rotation of the shaft.
    Above a certain speed range the sensor may appear to send a permanent on signal returning to normal once speeds reduce.
    -Ignore the tool change sensor during the tool change phase as it may appear to be on either of the two states
     
  2. MaxHeadRoom

    Expert

    Jul 18, 2013
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    2,381
    So what is the means of controlling the T.C. ?
    Is this a stand alone operation or part of the machine main controller.
    One way is with a timer, the pulses would constantly reset the timer preventing time-out, if the pulses stop, the timer times out and indicates a stationary position, just one way of doing it, there are others depending on more details of the system used.
    Do you need spindle orientation?
    Max.
     
  3. alfacliff

    Well-Known Member

    Dec 13, 2013
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    that switch is usually called a plugging switch it detects stopped spindle for tool change and what ever requires the spindle to stop, gear changes, reversal, and such.
     
  4. slimneill

    Thread Starter New Member

    Aug 6, 2014
    2
    0
    Thanks for the help Max!

    I am building a CNC router from scratch. So as i build the machine i'm adding functionality. The tool release on the spindle is one area where i don't want to skimp on safety.

    The draw bar on the spindle is air operated. I have two pneumatic valves that open when they recieve a signal which allows air to pass the valve and presurize the cylinder which allows the tool holder to be relased.

    Right now i just want to get it working manually, (there is an electic button on the spindle which when pushed sends the signal to the air valves and allows the tool to be released.

    Eventually i would like to automate the tool change process, but not yet.

    Spindle orientation/rotation isn't important.

    Is there some sort of a circuit drawing which would show me how to do this?
     
  5. MaxHeadRoom

    Expert

    Jul 18, 2013
    10,571
    2,381
    Still a little vague, manual operation means everything operated by a P.B. etc, but your first post indicates some kind of logic such as feedback from sensors.
    If I was to implement this in a very basic manner, I would be tempted to use either a small PLC or a Smart Relay, in fact many CNC controllers often hand over the job of T.C. to a PLC or M/S/T code handler.
    Very often the T.C. is the trickier of M or T code commands.
    Another thing to consider is what type of spindle is it? for e.g. a VFD or similar spindle controller has the ability to output At-Zero-Speed condition that could be used for this.
    Max.
     
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