Problem How do I get Mach3 to keep a pin low.


Results 1 to 2 of 2

Thread: How do I get Mach3 to keep a pin low.

  1. #1
    Registered
    Join Date
    Dec 2013
    Posts
    9
    Downloads
    1
    Uploads
    0

    Default How do I get Mach3 to keep a pin low.

    Hi All,
    The gist of my problem starts with a modification I did to my controller and the statement that follows in it. The situation is made even less clear by the Mach3 settings suggested by the chinese geniuses in their machine manual. These settings are very short pulses (3 us) and even shorter (1 us) direction set up time. Furthermore the signal level is such that Mach3 pulses are effectively inverted at the TB6560 chip input. In this way, the step signal is inverted and therefore the ON time is very long (basically it's ON most of the time except during the Mach3 3 us pulse). The problem with this is that it violates another datasheet constraint, i.e. that the duty cycle of the input pulses should be no more than 50%). And in addition, the slow rising edge affects the direction pin too, so whenever the direction inverts from low to high at the TB6560, a step is taken in the wrong direction.

    The reason why some people have some improvement with filtering capacitors is that due to reduced noise, some margin could be recovered. However this is still not ideal. I have tested two workarounds, one software and one hardware.

    The software workaround: 1) make sure that the Mach3 signal level is such that when there is no step, pin 5 of the TB6560 (named CLK in the datasheet) is low. 2) Use 1/2 step Sherline mode, with kernel running at 25 or 35 kHz. The effect of Sherline mode is that the pulse will stay high for the entire duration of the kernel cycle, and reset on the next cycle. 3) Set the Direction pulse timing to the maximum (15 us - note the GUI indicates 1 to 5 but it will accept up to 15). The net effect is a long pulse (40 us for 25 kHz kernel, 28.5 us for 35 kHz), with the limitation that the maximum pulse rate is reduced to one half of the kernel frequency. This is not a problem given the fact that in any case the TB6560 maximum allowable step frequency is only 15 kHz.

    The hardware workaround: replace R4 to R9 with lower value (470 or 1k). This will make the rising edge sharper and gain some pulse width margin. You can't go too low with the value, otherwise the falling edge will become too slow, reducing the margin. You still need to make sure the Mach3 signal level is as in point 1 above. You can then either use Sherline mode as above, or normal mode. In the latter case, just make sure both step and direction timings are set to their maximum (15 us) and don't exceed 35 kHz (there is no point and all it will do is reduce your pulse times, this eating the margin).
    What I need to know is how to set up the software to control this input in Mach3. Any help in this would be deeply appreciated.


    Thanks,
    Lindsey

    Similar Threads:


  2. #2
    Member ger21's Avatar
    Join Date
    Mar 2003
    Location
    Shelby Township
    Posts
    35538
    Downloads
    1
    Uploads
    0

    Default Re: How do I get Mach3 to keep a pin low.

    Does the Step active low setting do what you want?

    Gerry

    UCCNC 2017 Screenset
    [URL]http://www.thecncwoodworker.com/2017.html[/URL]

    Mach3 2010 Screenset
    [URL]http://www.thecncwoodworker.com/2010.html[/URL]

    JointCAM - CNC Dovetails & Box Joints
    [URL]http://www.g-forcecnc.com/jointcam.html[/URL]

    (Note: The opinions expressed in this post are my own and are not necessarily those of CNCzone and its management)


Tags for this Thread

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •  


About CNCzone.com

    We are the largest and most active discussion forum for manufacturing industry. The site is 100% free to join and use, so join today!

Follow us on


Our Brands

How do I get Mach3 to keep a pin low.

How do I get Mach3 to keep a pin low.