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IndustryArena Forum > Mechanical Engineering > Linear and Rotary Motion > Moving across multiple axes at different speeds
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  1. #1
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    Jul 2019
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    Moving across multiple axes at different speeds

    Hi, please forgive the newbie question, but how do I move across multiple axes at different speeds? I'm working on a plotting machine, and need to cut an arc, and need to move X, Y, and C axes at different speeds to shape the arc.. Hope this is enough info, feel free to ask if you need to know more.

    Thanks in advance,

    Pete

  2. #2

    Re: Moving across multiple axes at different speeds

    What you are describing is a circular motion profile. It is point to point trigonometric function. Without going through all the math, the easy way to generate this is to just use a motion controller, could be a software controller like Mach3 or a hardware controller like a Galil Motion Control product. Both of these have all the hard work done for you. This is a common function of any CNC machine.

    Unless you intend to make a 3D arc, like a hemisphere, I'm not sure where the C axis comes into play. But in any case the C axis position would normally be tangent to the X/Y position. If the plot is only in the X/Y plane, then you would only need to describe the points along the arc by the angle (Ø), radius (r), X = r cos Ø, and Y = r sin Ø to do this manually would be rather tedious, that is where the software comes into play. The more points described the smoother the arc plot would be.

    Maybe a bit more information would be helpful. What are you using to drive the plotter?
    Jim Dawson
    Sandy, Oregon, USA

  3. #3
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    Thanks Jim, we're using a North TPT machine based on Siemens hardware and software (Sinumerik, Sinamics etc), laying prepreg carbon fibre. The cutter we're using is a 'pizza wheel' blade, which will need to rotate on the C axis while the head travels across the X and Y axes.

  4. #4

    Re: Moving across multiple axes at different speeds

    Ok, yes, I understand. In that case the C axis would need to be tangent to the X/Y point on the arc.

    The simple way to do this is with a ''drag knife'' Have the pizza cutter axle slightly offset from the spindle centerline and allow it to pivot naturally on bearings, similar to a shopping cart castor. That way it will always remain tangent to the direction of travel. The offset doesn't need to be more than 0.1mm or so. Doing it this way negates the need for actually driving the C axis with G code.

    Having said that, I believe that CamBam actually has a plugin that will control the C axis to do what you want, not sure if that feature is available in the more commercial CAM software offerings. Fusion 360 apparently does not.

    EDIT: I stand corrected, Fusion 360 does have drag knife support now.
    Jim Dawson
    Sandy, Oregon, USA

  5. #5
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    Thank you Jim, your help is greatly appreciated!

  6. #6
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    Aug 2009
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    168

    Re: Moving across multiple axes at different speeds

    Fusion 360 apparently does not.
    However, as the F360 post processors are JavaScript files; the post processor could be modified to emit the correct C axis code...

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