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Author Topic: Mach Turn Index Pulse and IPR question  (Read 20325 times)

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Mach Turn Index Pulse and IPR question
« on: January 01, 2013, 09:07:20 PM »
 Good evening,

I've just finished a control retrofit on an old Crusader Anilam CNC lathe. It has turned out very nice and I'm almost finished working through the bugs. My experience with Mach Turn is very limited and it appears to be far more buggy than Mill has been in years. This evening I was doing a bit of testing with G95 and IPR feed rates. It seemed to be working fine (I have a spindle index pulse which seems to be working with good stability) and then my VFD cut out due to an unrelated issue. I would assume that as the spindle index slowed to a stop as a result of the faulted VFD, the feed rate would also go to 0. This isn't what happened. The feed rate continued along happy as usual, both through the completion of that particular move, and then right on through to the end of the program (I was cutting air, so I let it continue running with the spindle stopped). I find this rather disturbing. Is the IPR just based on the programmed "S1500" and not looking at the index pulse? I haven't messed around with CSS yet, but if this thing isn't reading the actual index pulse than I suspect it won't work as I had hoped. I'm interested to know whether this is a problem others have experiences or whether maybe I'm doing something wrong....?? I do have the "Use Spindle Feedback in Sync Modes" checked.

Thanks

SG

Offline Hood

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Re: Mach Turn Index Pulse and IPR question
« Reply #1 on: January 02, 2013, 04:24:55 AM »
If you have Use Spindle Feedback in Sync mode chosen (Ports and Pins, Spindle Setup) then every time you command a feedrate Mach will look at the spindles RPM and feed accordingly. If you change RPM between feed calls then Mach will not change the feedrate and that is what has happened to you.
 For situations like you had there should be  a fault signal from your VFD to Mach to tell Mach to E-Stop. There may or may not be a fault signal output from your VFD for that but I would think there would be. I had a macropump that would look at commanded RPM and actual RPM and if different by, I think, 10% then it would fault Mach, unfortunately at the time it would only work if I disabled modbus and as I needed that for the turret I couldnt. Now I have a servo on the spindle  so I can set up the fault signal to tell Mach if the spindle has faulted so I dont need the macropump.
  Adding to the feed question if you had the feed call on each line of code then the next line of code would not have fed at the normal speed, however it probably still would have fed along at a creep.
I hope the latter will be fixed in Mach4, we will see.

Regarding CSS, it doesnt work correctly I am afraid and never will in Mach3 when using G95. Mach Rev4 will , I am assured, fix this, again we will see.
Its been a while but if I recall what happens in Mach 3 is the feedrate will start out correct but as the spindle increases the feedrate will stay constant with respect to time but slow with respect to per rev and vice versa.

Hood
« Last Edit: January 02, 2013, 04:26:48 AM by Hood »
Re: Mach Turn Index Pulse and IPR question
« Reply #2 on: January 02, 2013, 08:33:12 AM »
 Interesting. So when threading it is also just looking at the speed at the beginning of the cycle or is it looking at it with a higher sampling rate? I was playing around with threading last night as well and during a 10 pass threading cycle I noticed the Z axis was stuttering from time to time. I was once again cutting air but I'm certain these hessitating moves would have trashed the thread. The Z axis doesn't demonstrate this behavior any other time. I have noticed that my index readout on the screen periodically blips to a much higher RPM reading, and then quickly returns. I suspect I have noise somewhere but also need to make sure the slots in my disc are wide enough.  Debounce doesn't seem to help the issue in any significant way. If what you're saying is true than maybe I have something else going on because once the threading starts a blip on the RPM readout shouldn't have any effect on feed rate.

It is remarkable how different Turn is from Mill given that they are technically the same program. I feel like a newbie even though I've been using Mach Mill for nearly a decade.

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Re: Mach Turn Index Pulse and IPR question
« Reply #3 on: January 02, 2013, 09:02:44 AM »
Threading is different, it is done in the driver and feedrate is altered with respect to the spindle speed. The more steady your spindle is the better your threading will work but it will follow increases or decreases of spindle speed, within reason.
Index Debounce is the one for the Index signal but I have found zero to be what I needed, increasing has made things worse and going above 10 made it totally unreadable. A good clean signal is required so make sure your index cable is shielded and properly grounded, especially if it is 5v.
Hood

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Re: Mach Turn Index Pulse and IPR question
« Reply #4 on: January 02, 2013, 09:06:39 AM »
Regards the differences, yes there is a big difference but I think the major difference is the Turn screen. I dont like it, never have and also have never used it, I just altered my mill screenset for my lathes.
Hood
Re: Mach Turn Index Pulse and IPR question
« Reply #5 on: January 02, 2013, 09:57:54 AM »
 Good info Hood. I'm using a CNC4PC C3 index pulse board with a H21A2 phototransistor and a slotted disc. I've done the slot calcs and I'm at around 600us pulse width at 3000rpm. The sensor comes with a 6' lead already soldered on which is touted as being shielded, but it isn't. I need to swap it out for a shielded wire and ground it to the star point. The sensor wire is running right next to a bunch of power wires between 12V and 200V, so this is an issue. Thanks

SG
Re: Mach Turn Index Pulse and IPR question
« Reply #6 on: January 03, 2013, 08:35:17 AM »
 I seemed to have fixed the issue last night. I ended up rewiring the optic sensor with shielded cable to the C3 board which actually made the problem worse. I then rerouted the data cable which was running in the same cable way as the spindle VFD output (I know....stupid) and with some debounce I was able to get a very steady RPM signal in the DRO. I monitored the spindle running for half an hour or so without a single spike in RPM, and the threading cycle which was hessitating now cycles smoothly. I'm hoping to actually do some cuts on metal tonight to confirm, but I suspect I'm all good. Once again, improper machine wiring protocol to blame.

SG

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Re: Mach Turn Index Pulse and IPR question
« Reply #7 on: January 03, 2013, 10:30:35 AM »
Good you got it, hopefully threading will work well when you actually get to cut some metal :)
Hood
Re: Mach Turn Index Pulse and IPR question
« Reply #8 on: January 12, 2013, 01:51:31 AM »
 I'm STILL messing with my index pulse on this lathe conversion of mine. Per some recommendations off this board I converted the signal from the C3 into differential to the BoB due to some potential noise issues. I painted the index wheel flat black to avoid any optical errors. Mach is configured to allow syncing and has spindle speed averaging. The RPM readout seems to be very stable and doesn't hop around at all. I tried to thread for the first time tonight. The test piece was delrin and I was attempting to cut a RH 1x8 UNC thread 2" long. The first 3/4" or so of thread looks great, but then it looks like maybe one of the index pulses got dropped and the rest of the pitch is shifted over 1/2 of the thread pitch. It seems to correct at the beginning of each new cut since literally the first 3/4" or so looks perfect. It seems to be exactly half the pitch so a dropped index signal makes sense except for the fact that I've got averaging checked. It seems like the first few passes are great, but into the 3rd or 4th pass the thing starts buggering up. It has consistently done it 3 times now. I have noticed that I am getting a very consistent pulse out of the index LED on the C3 board and on the input in the BoB LED, but often times when I'm rotating by hand the LED on the diagnostic screen misses pulses here and there. I suspect there is something going on related to this but at this point I don't know where to look. I'm really desperate to get this machine threading due to a job I need to get out of here ASAP.

AAAAHHHHH!@#!@$!
Re: Mach Turn Index Pulse and IPR question
« Reply #9 on: January 12, 2013, 02:38:07 AM »
 Correction: The Index LED in the mach diagnostic screen is sporadically being triggered. The LED's on the boards appear to trigger very consistently but the Mach LED is getting maybe 1 in 10 when the spindle in running @ 500 RPM. I've tried all sorts of debounce settings but I don't think that would have any effect on this anyway.

So, index signal getting to the BoB but inconsistently being reported to Mach through the ESS. The RPM readout on Mach is getting its info from somwhere, but if the LED needs to be very consistent for threading to work than this is my issue.