Homing update and new question


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  1. #1
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    Default Homing update and new question

    First, turning off the home inputs in Mach3 works. However the buttons in the 1024 lset have the wrong OEM codes assigned to the home buttons. I was able to kludge a workaround while I developed a more elegant solution.

    My new question has to do with quadrature encoding.

    My home brew spindle encoder has a few shortcomings.

    I use a pair of Opti Interrupters on the spindle. The wave form is reasonably crisp as I have shaped it with a Schmidt trigger.

    But the duty cycle is a bit of an issue as is the offset between the two signals.

    The duty cycle of each wave form is in the 60 % range.

    But the big potential issue is the offset. The two wave forms are more like 120 degrees offset instead of 180.

    My objective is single point threading and possibly rigid tapping.

    Any thoughts? Do I need to rework quadrature? And if so, which is more important, duty cycle or offset?

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  2. #2
    Gold Member TomKerekes's Avatar
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    Default Re: Homing update and new question

    Hi netboss,

    which is more important, duty cycle or offset?
    The bottom line is where the quadrature transitions occur. Each transition should occur at 25% intervals through the cycle. Deviations from those points would correspond to position measurement error and introduce "jitter" in the position measurement.

    But I doubt if it would be a big problem. A perfect encoder would still have 25% jitter where there is no change for a while and then the position suddenly changes by 1 (quantization error). So your case might be similar to having a perfect encoder with half the resolution (slots). I don't think you mentioned how many slots you have.

    The parameters for Threading have a Tau Parameter where you specify how much smoothing is made to the measured encoder position to reduce jitter. A normal value is 0.1 seconds. A larger value will reduce the effect of jitter but increase the time it takes to correct for a speed change.

    HTH
    Regards

    TK
    http://dynomotion.com


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    Default Re: Homing update and new question

    Hello,

    I have a kdlop with close loop steppers. It is closing the loop with linear glass scale encoder.
    I'm using home reference from the index of linear glass scale but the problem is that the index mark is not at the end of the table. So instead of zero coordinate and zero encoder on mach3 i need to have 81,5mm on macine coordinate and encoder read witch is the distance from the table end and index mark. Please tell me how to do that.

    Another question is how to store machine coordonate and restore it on boot. Do i need external flash card atached to kflop?

    Thanks and best regards,
    Cris



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    Gold Member TomKerekes's Avatar
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    Default Re: Homing update and new question

    Hi Cris,

    I have a kdlop with close loop steppers. It is closing the loop with linear glass scale encoder.
    I'm using home reference from the index of linear glass scale but the problem is that the index mark is not at the end of the table. So instead of zero coordinate and zero encoder on mach3 i need to have 81,5mm on macine coordinate and encoder read witch is the distance from the table end and index mark. Please tell me how to do that.
    You can set the Encoder Position and Enable the Axis at the same Destination with the following C Code:

    #define XAXIS 0
    #define COUNTS_PER_MM_X 1000.0
    #define HOME_POSITION_X 81.5

    chan[XAXIS].Position = HOME_POSITION_X * COUNTS_PER_MM_X;
    EnableAxisDest(XAXIS, HOME_POSITION_X * COUNTS_PER_MM_X);

    note its KFLOP btw

    Another question is how to store machine coordonate and restore it on boot. Do i need external flash card atached to kflop?
    You normally need to re-home after a power loss as there isn't any way to tell if an axis moved when power is off. KFLOP does have a 1 MByte Flash memory available for User Use.

    Another issue is to know when to save the positions. The Flash memory does have a limited number of erase/write cycles. I believe it is 100,000 times. There is an example C Program \FlashNonVolatile\FlashAxisDestinations.c that monitors PC activity and whenever there is no status communication for a while and the axis destinations haven't changed in a while saves the Destinations of the axes.

    Regards

    TK
    http://dynomotion.com


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    Default Re: Homing update and new question

    yes, Kflop )

    Thank you. It is working. But if i enable the soft limits it doesn't work anymore. I use SimpleHomeIndexFunctionTest.c and i think the code dose not disable the soft limits. I set the positive limits + 220x2000 (i have 2000 counts/mm) and negative limits 4x2000.
    What do you think? What i do wrong? I use Mach3.

    Thanks,
    Cristian



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    Gold Member TomKerekes's Avatar
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    Default Re: Homing update and new question

    Hi Cristian,

    Yes you should disable the Soft Limits before homing by setting them to huge values. Then set the normal values after homing has completed.

    Regards

    TK
    http://dynomotion.com


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    Default Re: Homing update and new question

    Hi Tom,

    I have disable the soft limits and everything is working ok. I have set the same soft limits in Mach3 and now i get a warning message about the limits witch is very nice.
    Now about saving and restore axis coordinates. I was thinking to save the axis coordinates to a file on the pc on every 5 seconds, even if the axis is moving, and when the Kflop is booting to read axis coordinate from that file and restore them.
    Do you think is is possible? How?

    Best regards,
    Cristian



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    Gold Member TomKerekes's Avatar
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    Default Re: Homing update and new question

    Hi Cristian,

    Now about saving and restore axis coordinates. I was thinking to save the axis coordinates to a file on the pc on every 5 seconds, even if the axis is moving, and when the Kflop is booting to read axis coordinate from that file and restore them.
    Do you think is is possible? How?
    I don't think it would be proper to save the coordinates while the axis is moving because they would be immediately incorrect.

    What exactly are you hoping to achieve? How would you know if the saved coordinates are correct after a power cycle?

    Regards

    TK
    http://dynomotion.com


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