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Problem homing X axis
« on: January 02, 2012, 03:12:08 PM »
Hi, I am in the process of bringing up a Denford Novamill that I bought without electronics.  I have built a driver system using drivers / PSU / BoB from fleabay and all seems to work pretty well but I seem to have hit a brick wall with homing.

All the home switches (installed at manufacture on the mill) work in the same way - a n/c switch that opens when activated by the axis reaching the end of its travel.  I have used the autosense feature on the config/ports&pins/inputs menu to set these up so I guess they should work OK.  On the Motor Home/Softlimits menu Autozero is unchecked for each axis; the X axis is checked for Home Neg but the other two axes are unchecked (all to correspond with which way they move).

Now I find that on a "reference" request the Y and Z axes function perfectly, running to their limit until the switch opens then reversing and running slowly until the switch closes.  However the X axis just moves a very short diatance, wherever it is, then stops and the green homed LED for it lights up.

I am wondering if there could be a noise problem on the X home switch wires.  Does this sound likely to the experts please?  At the moment the input debounce interval is set to zero, and I notice that in response to a home-related question Hood recommended that this should be set to around 1000, which would correspond to 40 ms - is this likely to be a possible fix please?

John.

Offline Hood

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Re: Problem homing X axis
« Reply #1 on: January 02, 2012, 03:52:31 PM »
Yes definitely noise or a bouncing switch, noise more likely.
2000 is normally what is recommended to try first then work down if it helps. Really though the best thing is to solve the problem by properly shielding and grounding the wires if not already.
Hood
Re: Problem homing X axis
« Reply #2 on: January 05, 2012, 06:38:23 AM »
Thanks Hood!  Having thought about this a bit I realised that it was quite likely that my wiring to the X limit switch could easily have reversed "live" and ground as one can't tell from outside the machine which pin on its multi-way connector is connected to the screen of the home switch wiring.  So I reveresed the connections on all the limit swutches (having followed the same convention on each one even if wrong) and this made a significant improvement though obviously still a problem.  Then I set the bounce parameter to 2000 as you suggested and it sprang into life.  I was able to reduce it to 1000 and still get reliable operation.  There is obviously still an issue that needs attention but I can now make progress.

Yet again I am very grateful for people sharing their experience and expertise on this forum!

John.
Re: Problem homing X axis
« Reply #3 on: January 05, 2012, 06:40:26 AM »
Oh, and another point is that for the X axis the home switch wiring runs with the drive wiring in a flexible conduit to the motor on the end of the slide, whilst for the other axes the switch and motors are well separated, so probably the X axis is more susceptible anyway.

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Re: Problem homing X axis
« Reply #4 on: January 05, 2012, 06:41:53 AM »
Are you using the screen as a ground wire?
Hood
Re: Problem homing X axis
« Reply #5 on: February 11, 2012, 03:39:54 PM »
Sorry Hood, only just seen your reply.  The answer is I don't know as I haven't dismantled the box where the wiring to the X drive motor is terminated - the X home switch is mounted on a bracket next to the motor on this machine.  All the commons on the home switches are brought back to my control box which is the only place that I have earthed them.  I must say that I've stuck with the debounce solution to this problem as everything seems to be working and I'm concentrating on learning to mill now.

Thanks, John.
Re: Problem homing X axis
« Reply #6 on: October 21, 2012, 03:41:57 PM »
Thanks JohnHaine and Hood....   I have also recently rebuilt my machine and had an issue with referencing stopping short.   The "debounce" setting seems to have worked for me.

Hood,  I have my switch shielding attached to my controller ground.   That is correct, isn't it?

 

Offline Hood

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Re: Problem homing X axis
« Reply #7 on: October 21, 2012, 04:19:36 PM »
That depends what you are meaning,  shielding from  all wires should be taken to a common point in your control cabinet and that point should be connected to what we call (at this side of the pond)  Earth.
Hood