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Author Topic: Spindle RPM feedback, not low enough.  (Read 14646 times)

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Offline Katoh

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Spindle RPM feedback, not low enough.
« on: January 22, 2013, 09:04:31 AM »
G'Day Friends
Just going through little problems on this lathe build one by one. Have solved many a problem but there is one recurring at present.
I have a slotted disk on the spindle with an opto, (recommended by Hood) in a previous thread, all is good there wiring is fine and all shielded to BOB. I'm using a Homman BOB and the little led next to the input flash's every time that slot passes through the opto without fail, even to turn by hand, 1rpm lets say it will flash on the board. Now I don't know why but when you go into Mach, on the diagnostic page it wont show the index input the way it shows up on the board? The spindle input light is actually always activated it shows the rpm but erratically, Now my spindle can turn right down to 30rpm, there is no chance I can get that reading in Mach, anything under 100 is unstable, I have tried the debounce settings to some very high numbers, it will then read down to 46 rpm but then at higher rpms the readings play up, and I have read its best to keep the debounce as low as possible.
I have read also to turn off spindle relays, this is unacceptable as I will loose my M3/M4 command to the Homman DC03 Digispeed which is working correctly. I have had to add a capacitor to the E-Stop and Limit switch inputs to stop noise setting them off and also to the 0-10v control to the VFD which gives me a very stable motor speed controller.

Question
Firstly when the led on the BOB registers the slot passing the pto, should it not show up on the inputs on the Mach screen on every pass not just every now and then?
Would adding more slots to the spindle disk help?
Is this a noise problem ?
Or is a config problem?

I realize this has being posted before but there solutions in prior threads have not worked in my case.

Thanks
Katoh

Cheers
Katoh

Offline Hood

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Re: Spindle RPM feedback, not low enough.
« Reply #1 on: January 22, 2013, 09:13:28 AM »
Dont worry about the index LED on the diagnostics page, that is due to the refresh rate of the screen and the update rate of Mach, it is just an indication.
Regarding Debounce, it is the Index Debounce you adjust, probably what you were meaning but just saying in case ;)
Set the Index debounce to 0, also go to ports and pins, spindle setup and disable averaging and see if that helps.
Hood

Offline Katoh

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Re: Spindle RPM feedback, not low enough.
« Reply #2 on: January 23, 2013, 01:54:33 AM »
Sorry for the late response, I have not had a chance till now to test  those things.
Disabling/ enabling speed-average did not do much if anything, the Index debounce if set to 200 will read down to 42rpm (great)  but will not read over 150rpm (bugger) actually the faster you go the slower it says it is, Go figure. Go the other way with the debounce minimum 50 will give me good rpm higher but nothing under 100rpm.
tried a cap between input pin 15 from opto to 0v think it made things worse. I have wired the opto as described in previous thread,
Black and green connected to pin 0v
blue input pin 15 (index)
White +5v from BOB
Red  + 5v from common power source with a inline 220Ohm resister to limit current.

Thanks
Katoh
Cheers
Katoh

Offline Hood

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Re: Spindle RPM feedback, not low enough.
« Reply #3 on: January 23, 2013, 02:57:32 AM »
I am not sure how the parallel port behaves regards reading the Index at low revs nowadays. It has seen a lot of changes since I used it many years ago so it may just be these changes have made it react that way.
 I tested out yesterday with the smoothstepper and set the spindle to 1rpm and the DRO read 1 then 0 then 1 then 0 etc, same up to 25 rpm, it went 25/0 but over that it sat at a steady rpm. When however I enabled averaging then I got the numbers jumping around when under 30, eg the 25rpm would move around from maybe 12 to 25 continually counting up and down.
 This however likely has no similarities with the parallel port way of doing things especially if you say averaging makes things worse.
sorry cant be much more help other than to say its unlikely a problem with your input.
Hood

Offline Katoh

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Re: Spindle RPM feedback, not low enough.
« Reply #4 on: January 23, 2013, 03:27:12 AM »
Hood  many Thanks again for input, from what you describe I don't seem to have the same issue with the low rpm, mine just is stable and 42rpm, that is the lowest it goes, even though as mentioned earlier the Led on the BOB flashes without fail ever time that slot goes past the opto.
Do you think adding extra slots would help?
Or did I  put the capacitor in the wrong place Maybe should have been between the red and Blue or the red and black or the White and blue, I should just check the lot and see what works.

Thanks Muchly
Katoh
Cheers
Katoh

Offline Hood

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Re: Spindle RPM feedback, not low enough.
« Reply #5 on: January 23, 2013, 03:54:22 AM »
Adding more slots will not help as you can only use a single slot in Mach now, well not strictly true so I will elaborate.
Previously you could use a disc with many slots but have one wider as the index, this was set up as a timing signal rather than the Index. It was found however to be no better and likely even worse with regards threading so it was abondoned and now the only valid setup is the Index.
 You could have a disc with two or more accurately milled slots and use the spindle pulleys ratio to make Mach read the rpm as 1 per rev. Would it help? I have no idea but it may at the lower revs, the problem you may have however is at higher revs the parallel port input is not fast enough to see the multiple slots and thus you get erroneous readings.
 I do not think it is a problem with your input, I think it is likely the way Mach does things in the driver but hopefully Rich or someone else that uses the parallel port can confirm or deny that.
Hood

Offline Katoh

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Re: Spindle RPM feedback, not low enough.
« Reply #6 on: January 23, 2013, 06:12:24 AM »
Adding more slots will not help as you can only use a single slot in Mach now, well not strictly true so I will elaborate.
Previously you could use a disc with many slots but have one wider as the index, this was set up as a timing signal rather than the Index. It was found however to be no better and likely even worse with regards threading so it was abandoned and now the only valid setup is the Index.
 You could have a disc with two or more accurately milled slots and use the spindle pulleys ratio to make Mach read the rpm as 1 per rev. Would it help? I have no idea but it may at the lower revs, the problem you may have however is at higher revs the parallel port input is not fast enough to see the multiple slots and thus you get erroneous readings.
 I do not think it is a problem with your input, I think it is likely the way Mach does things in the driver but hopefully Rich or someone else that uses the parallel port can confirm or deny that.
Hood

I can understand that, cannot really understand how one slot makes it just as accurate as multiple slots, but that's not why we are here at the moment. You would think with the Bob identifying every pulse sent by the opto switch that it really should be a piece of cake, but something is screwy somewhere.
I read  that earthing the computer chassis to the machine earth helps also in dealing with noise, but maybe this is not a noise problem and the pulsed signal is not actually even reaching the Mach?
Its all speculation at present but something has got to work surly.

Cheers
Katoh.
Cheers
Katoh

Offline Hood

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Re: Spindle RPM feedback, not low enough.
« Reply #7 on: January 23, 2013, 06:46:30 AM »
I dont think its a problem with your signal it is, I think, likely to be the way the parallel port driver processes the signal.
Hood

Offline Katoh

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Re: Spindle RPM feedback, not low enough.
« Reply #8 on: January 23, 2013, 08:45:28 AM »
Hood
Just doing some further research I came across this thread from 08, with particular reference to page 3 post by SimonD,
http://www.machsupport.com/forum/index.php/topic,6707.20.html

Do you think I'm looking down the barrel of the same sort of thing, maybe?

Cheers
Katoh
Cheers
Katoh

Offline Hood

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Re: Spindle RPM feedback, not low enough.
« Reply #9 on: January 23, 2013, 09:44:51 AM »
I am not unerstanding what you are meaning? Your index is being seen fine abve 30rpm and you will not be threading anything at anything like these RPMs so dont think you will have a problem in that respect. Maybe that is not what you are meaning?

I will see if I can find the info Art posted regards the Timing via Index.
Hood