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Offline kolias

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Adjusting Limit Switch
« on: December 14, 2009, 12:42:41 PM »
I installed a limit switch on my Z axis to prevent uncontrolled plunges but have problem adjusting the trigger lever.

When I go to test the adjustment of the trigger lever, mack3 says “Limit Switch Triggered” and before I press the Reset button I have to release the limit switch lever but I can’t do that because the CNC axis is locked by mack3.

Is there some kind of “by-pass” to this problem?

Nicolas
Nicolas

Offline Hood

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Re: Adjusting Limit Switch
« Reply #1 on: December 14, 2009, 02:15:11 PM »
There is Auto Limit override, think its on Settings page. When you have that enabled you just press the reset and you can jog off a limit, be aware though that you can jog either direction so make sure you go the right way.
 You say you have uncontrolled plunges, this seems to tie in with your problems with limits on the other thread. It would seem maybe you are suffering from very bad noise issues and to me it would be better to cure them than try to use limit switches to bandage up the problem.
Hood

Offline kolias

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Re: Adjusting Limit Switch
« Reply #2 on: December 14, 2009, 03:08:57 PM »
There is Auto Limit override, think its on Settings page. When you have that enabled you just press the reset and you can jog off a limit, be aware though that you can jog either direction so make sure you go the right way.
 You say you have uncontrolled plunges, this seems to tie in with your problems with limits on the other thread. It would seem maybe you are suffering from very bad noise issues and to me it would be better to cure them than try to use limit switches to bandage up the problem.
Hood

Yes I know about the Limit Override I just was not sure the purpose of it, now I get it and thanks.

In 6 months I have operated my CNC router, the Z axis plunged uncontrolled to the stock I was working on ONLY 3 times and always at the middle or towards the end of the gcode. All the other times my CNC has been working perfectly. I have tried to find the source of the problem and the only thing I found was a bad connection in my XLR connector for the Z axis. So I fixed that plus I now have grounded the three motor cables to the DC ground bar to eliminate any noise.

In addition and following your advice I have now set the Debounce Interval parameter to 2000.

The limit switch on the Z axis is an extra safety and it is not intended to fix the problem of the uncontrolled plunges. Since the machine is working well most of the time, it will take some time of work to assure me that this problem is gone.

I have started another thread in another forum to find out of curiosity why when I ground the limit switch cable I get too much noise that even the Debounce Interval is not working

Thank you Hood for your excellent help

Nicolas
Nicolas

Offline Hood

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Re: Adjusting Limit Switch
« Reply #3 on: December 14, 2009, 03:26:15 PM »
It would seem to me that you are causing some sort of ground loop by  connecting the shield. Its hard to say without seeing your wiring why this would be but the general rule is to have all shield wires connected at one end only and all connected to the same point if at all possible. Also never use a shield as a 0V line, dont think you have done that but thought I better mention it.
 Try as much as possible to route high voltage wires well away from signal wires and even putting small capacitors across the signal wires can help
 Maybe if you could post some pics of your wiring someone would see a problem, I think Jeff Birt is very knowledgeable about noise and grounding, so hopefully he will chime in.
Hood

Hood

Offline kolias

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Re: Adjusting Limit Switch
« Reply #4 on: December 14, 2009, 06:30:42 PM »
Here are some pics of my control box and the wiring inside.

All ground wiring connections are soldered

Nicolas
Nicolas

Offline Hood

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Re: Adjusting Limit Switch
« Reply #5 on: December 14, 2009, 07:21:38 PM »
Looks good and neat, only thing I would do is shorten the shield for the limits and maybe try and route it away from the motors. A small capacitor on the BOB between the limits wires may also help, think the norm is around 0.1uF.

The Step/Dir wires from BOB to drives may possibly be where your occasional z plunge comes from, is there any way you can shield the ribbons? Is the Z axis the one that runs nearest the motors wiring?


Hood

Offline kolias

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Re: Adjusting Limit Switch
« Reply #6 on: December 14, 2009, 11:30:21 PM »
Looks good and neat, only thing I would do is shorten the shield for the limits and maybe try and route it away from the motors. A small capacitor on the BOB between the limits wires may also help, think the norm is around 0.1uF.

The Step/Dir wires from BOB to drives may possibly be where your occasional z plunge comes from, is there any way you can shield the ribbons? Is the Z axis the one that runs nearest the motors wiring?


Hood


That gets kind of complicated for me Hood because I only have basic electronics experience, but I like to learn.

No problem to shorten the shield for the limits.

Route it away from the motors? Do you mean the motor wires?

Can you tell me where to connect the capacitor? Between the limit wire ground and where on the BOB?

How can I shield the ribbons? Perhaps put masking tape? Or take them to the ground bar?

I don’t understand when you say “Is the Z axis the one that runs nearest the motors wiring? I attach another picture indicating the drives which may be of help.

Nicolas
Nicolas

Offline Hood

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Re: Adjusting Limit Switch
« Reply #7 on: December 15, 2009, 03:19:38 AM »
Yes I was meaning the motors wires, normally things should be fine the way you have them but for some reason you are picking up noise in your system, especially the limit. Thing that gets me is that you connect the shield for the limit and it gets worse, that could be down to the coil of shield wire but I am no where near an expert on this (or any :D ) subject, so take it with a pinch of salt.
 Ok well that new pic blows my theory out of the water LOL. I was thinking that possibly the Z axis was the one on the left in your pic and was picking up noise from the motor wiring, again it shouldnt really as the motor wiring is shielded. You could use foil to shield the ribbons but might not be worth the effort as again it shouldnt really be a problem.
 The capacitor will go between the two limit wires where they connect to the breakout board.

Hood

Offline kolias

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Re: Adjusting Limit Switch
« Reply #8 on: December 15, 2009, 10:20:14 AM »
Have a snow storm here and the power went out, now is back

ok I cut the excess ground wire from the limit switch cable as you suggested and noticed a big improvement. Now the message “Limit Switch Triggered” comes on once in a while, like I can move the X axis back and forth and the message will appear once. If I set the Debounce Interval to zero the message is always on. So I still have to do some work to eliminate that.

I also cut the ribbons from the motor cables (the ones you said to put some foil over). I see no use for them.

I will go to the store today and get the 0.1uF capacitor. Is there a polarity on these capacitors to be carefull?

Nicolas
 
Nicolas

Offline Hood

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Re: Adjusting Limit Switch
« Reply #9 on: December 15, 2009, 10:28:38 AM »
Capacitors can be polarised but think that its electrolytic that are. The type you want are suppresion capacitors and are usually ceramic I think.


Not sure what ribbons you are talking about, I was meaning the multi coloured ribbon cables that go between your Bob and drives.

Hood