Machsupport Forum
Mach Discussion => General Mach Discussion => Topic started by: Stuart_H on May 19, 2012, 11:58:07 PM
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Good evening all,
I have just completed building a 1300mm X 900mm router table with rack and pinion gantry drive design. I am very happy with the operation of the table and have had great success with the accuracy of it but I am now faced with this frustrating problem.
Subsequent to the initial design I have connected 5 limit/ home switches all wired in series and connected to pin 10 on the breakout board. Also a dedicated Emergency stop switch to pin 12 on the breakout board. Both work exactly as expected, however as soon as I start the spindle motor, it triggers a limit switch activation and the machine stops. If I reset it, the machine will run for about another 10 seconds or so before doing the same. On the diagnostic page, all five limit switch LED's illuminate for about half a second each time the interference occurs. The spindle is a Chinese HY brand 1.5 kw unit and it appears to operate without any issues very smoothly. The spindle is totally electrically isolated from the breakout board. I.e. control is only achieved through the operation of the touch panel on the front of the VFD.
This is what I have tried so far to overcome the problem:
All wiring to the stepper motors, limit switches and spindle motor has been replaced with shielded wire and all shielding taken to a common ground.
The spindle carrier frequency has been changed throughout its entire range with no change.
The config debounce has been set to a figure of up to 2000 ms with no change.
Short of pulling what little hair I have left out, I am stumped with how to fix this.
Any help appreciated
Stuart
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how close is the e stop wire and limit wires to the vfd and power wires had same problem just moved e stop wire and separated all power wires from control wires and all problem disappeared
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E stop wire is some distance away but the limit switch wiring runs in the same cable chain as the wiring from the VFD to the spindle. I had been advised this was OK if I used screened cable all around, but I am starting to think otherwise. Was just looking to see if there were any other possible causes or remedies before ripping the wiring out.
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Hi Stuart,
This is worth trying before doing any major work....
Connect one 0.1uF capacitor between each used input to you BoB and GND. This will mostly suppress noise spikes which may be triggering you stop condition.
Tweakie.
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Thanks Tweakie,
This was something I was also thinking about doing but wanted to hear from others first. So I am clear, we are talking about a normal Ceramic Cap (not electrolytic)??
Appreciate your good advice.
Stuart
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Have you got the screen connected at one end only and all screens to the same point
Hood
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Thanks Tweakie,
This was something I was also thinking about doing but wanted to hear from others first. So I am clear, we are talking about a normal Ceramic Cap (not electrolytic)??
Appreciate your good advice.
Stuart
Hi Stuart,
Yes, the miniature ceramic disc caps are OK (don't forget to sleeve the leads, if necessary, so they cannot short to each other)
Tweakie.
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Have you got the screen connected at one end only and all screens to the same point
Hood
Hi Hood,
At each Microswitch I have taken the Screen to a lug and connected it to the Aluminium frame of the machine. At the other end of the cables (where they come together at the breakout board) I have joined them all as a common connection and it is connected to the table ground (which is also connected to the supply earth).
Stuart
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Thanks Tweakie,
This was something I was also thinking about doing but wanted to hear from others first. So I am clear, we are talking about a normal Ceramic Cap (not electrolytic)??
Appreciate your good advice.
Stuart
OK. Shall give this a try in the morning when I can get a couple of caps.
Thanks.
Stuart
Hi Stuart,
Yes, the miniature ceramic disc caps are OK (don't forget to sleeve the leads, if necessary, so they cannot short to each other)
Tweakie.
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Have you got the screen connected at one end only and all screens to the same point
Hood
Hi Hood,
At each Microswitch I have taken the Screen to a lug and connected it to the Aluminium frame of the machine. At the other end of the cables (where they come together at the breakout board) I have joined them all as a common connection and it is connected to the table ground (which is also connected to the supply earth).
Stuart
I would try cutting the shield connection at the switch end, having it earthed at both ends may set up a loop.
Do you also have the VFD and motor wires shielded? If not you may want to also do that.
Hood
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The cable from the VFD to the spindle is shielded and connected to earth at the VFD end and not connected at the Spindle end. The supply cable to the VFD is not shielded but is only about 300mm long. Also the machine runs without a problem with the VFD powered. It is only when the spindle is running that I get the problem so I suspect more to do with the output wiring or some sort of harmonic being generated within the VFD when in the run mode.
Stuart
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Hi Tweakie,
Just to give you a heads up on where I am at. I tried the two 0.1mf caps and it made a substantial difference. Good advice.... Thanks. The machine will run for about 10 minutes or more before the system detects a limit switch activation. I have been onto the BOB manufacturers today and they have suggested to move the position of the VFD and give it a try as they feel it is a little close. At the moment the VFD is about 300mm from the BOB and stepper drivers.
I am overseas at the moment with work so wont get to try it before the end of the week, but shall let you know the outcome.
Cheers,
Stuart
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Did you unhook the shield connections at the switch end?
Hood
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Hi Stuart,
Pleased to hear you are making some progress.
As Hood has suggested your shields must only be connected at one end (preferably the controller end).
Tweakie.
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Shall disconnect them when I get back home in a couple of days. Thanks again for your help.
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Hi Guys,
Some further success last night. Cutting the shield wires at the micro switches made little difference, but when I also cut the shields at the stepper motor ends I think may have fixed my problem. I only have the one piece of code to run the machine on at the moment, which runs for about 15 minutes. Today I plan to slow the feed rate right down and see if I can run it for over half an hour or so to see how it performs.
Good advice hood, thank you to both of you for your help.
Stuart
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Hopefully that is the end of the problems.
Hood