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« on: January 11, 2010, 12:29:19 PM »
Hi Barry,
Sorry to be bit of a killjoy on this but although your limit switches are the manifestation of the problem they are not the root cause or source of the problem which, in my opinion, is definitely noise related and your limit switch wiring is just the antenna. Increasing the debounce setting may well mask the noise but, as Hood has said, you must consider that this is the time interval taken by Mach to recognize any limit switch being triggered and if the limit switch is mounted too close to the machine’s mechanical stop it will not perform it’s intended function.
I have recently fitted a VFD and can vouch for their noise potential but if it is correctly fitted there should be no problem. Although it is a vast subject here are a couple of easy things you could try before getting in too deep.
1. Check you have a proper and good ground connection coming into your machine.
2. Check that the VFD is grounded in accordance with the makers installation instructions.
3. Check that you have no ground loops on the machine (screened cables grounded at both ends etc.). A single point ground (with all shields and ground connections terminated at this one point) would be an ideal situation.
4. VFD driven motors can build up a charge on their rotor shafts (caused by stray flux) which will discharge to ground through the bearings and in so doing cause electrical noise. This can be tested for by temporally connecting the spindle shaft to ground with a carbon brush or similar. (large motors often have more than one brush in contact with the shaft to achieve this and prevent the bearings from pitting).
5. Your computer ground and your machine ground should not form a loop. (again only connected at one end, which is usually at the incoming mains supply). This may be particularly difficult to test for due to the many signal connections and their ground returns.
Waffled on a bit but I hope this helps.
Tweakie.
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