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Offline dresda

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Re: Another dumb question
« Reply #20 on: January 30, 2011, 06:25:49 PM »
I don't get it. I can rapid the slides at 200inch/min and they will stop dead, isn't that just like putting a feed hold on? Am I missing something?
Anyway, that's a minor problem, I've just spent all day trying to get an analog voltage out to my VFD with no look.
I don't have anything connected yet, just commanded 100rpm m03 spindle light flashes, I think I setup the DSPMC correct.
Ray.

Offline Hood

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Re: Another dumb question
« Reply #21 on: January 30, 2011, 06:39:14 PM »
Afraid you will have to talk to Rufi regards the analogue voltage, I know nothing of the DSPMC's workings.
Hood
Re: Another dumb question
« Reply #22 on: January 30, 2011, 11:27:47 PM »
Yes DSPMC is closed loop just like my servo drives close the loop to my AC motors but if the pulse is stopped immediately without the deceleration then the motors may end up out of position from where Mach thinks they are.
Hood

With servos, this should not be a problem, unless you're moving fast enough that when the step pulses stop the axis coasts far enough, due to inertia, to trigger a servo fault due to exceeding the maximum allowable following error.  Barring that, it should overshoot, then quickly return to the position Mach3 thinks it's in.  On my servo-driven knee mill, I can usually hit Stop without losing position, even when doing a rapid.  The same is NOT true of steppers, however.

Regards,
Ray L.
Regards,
Ray L.

Offline dresda

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Re: Another dumb question
« Reply #23 on: January 30, 2011, 11:43:42 PM »
Yes, I think I will try the stop function and check postion. I just spoke with rufi and he said the DSPMC is fixed at the moment and they will change it run it in mach3. I am running a knee mill with 30inch/lb SEM motors and at 20inch/min  you can see it winding down to a stop when hitting the feed hold, that's no good when trying to run a first off in close tight corners.
Ray.

Offline Hood

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Re: Another dumb question
« Reply #24 on: January 31, 2011, 03:50:59 AM »
Yes, I think I will try the stop function and check postion. I just spoke with rufi and he said the DSPMC is fixed at the moment and they will change it run it in mach3. I am running a knee mill with 30inch/lb SEM motors and at 20inch/min  you can see it winding down to a stop when hitting the feed hold, that's no good when trying to run a first off in close tight corners.
Ray.

That is where a FRO pot is very useful, you slow the axis down as it approaches any danger point on first runs and get ready to fully stop it by turning the pot to zero. The way Mach is at the moment it will never actually go to zero with the FRO, it will still crawl along. I have mine set up in such a way that if the pot  sets the FRO below 1% then a feedhold is automatically called and again if its wound up the Start button will be automatically pressed and it works very well. I am in hopes that in Rev4 Mach will actually do this internally but whether that will be the case I do not know, I have asked Brian for it now just have to see if he does it or can do it.

Regards the following error as Ray mentioned, well I suppose that depends on how tight you have the following error set up. I know on my lathe I have a following error set to 20 counts from 8000 counts per 5mm so that is only a distance of 0.0125mm (0.00049") Added to that my saddle on the lathe is in the region of 1/2 tonne then pressing the stop would I imagine make it travel a bit more than that distance.
 With Rays setup I think he uses Geckos and I believe they have a fixed following error of 128 counts, I assume Ray has 500 line encoders and  0.2 pitch screw, so even assuming he has as much as 4:1 reduction that is still a distance of 0.0032" (0.08128mm) and with a relatively light axis with relatively high friction such as in  is on a mill then it may well be fine to press Stop and not lose position due to following error.

That then throws up another point, I believe the buffers are cleared in Mach with a stop, is it then safe to just press cycle start again or would it be safest to do a RFH?
For me personally I will stick to my FRO pot. :)

Hood

Offline dresda

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Re: Another dumb question
« Reply #25 on: February 01, 2011, 10:49:47 PM »
You are right Hood, The FRO should be used at all times and I don't have a problem with that. By the way, my motors are SEM.
My problem is that my next system that I put together will be for a customer and all there machines are Fanuc, Mits, and alike and some guys like to set the parameters up so when using the FRO it only controls the feedrate and not the rapid moves, now they can distinguish between rapids and feedrates in the program.
I did email Rufi at Vital systems re: DSPMC and this could be the problem, This is what he said: "ok.  the slow down time is fixed right now, which may be quite high for your mill.  but we plan to change that to use the actual decel setting in mach3 motor tuning screen." 
 
Ray.

Offline Hood

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Re: Another dumb question
« Reply #26 on: February 02, 2011, 02:31:52 AM »
and alike and some guys like to set the parameters up so when using the FRO it only controls the feedrate and not the rapid moves, now they can distinguish between rapids and feedrates in the program.

 Then just unlink the SRO from the FRO ;)

I did email Rufi at Vital systems re: DSPMC and this could be the problem, This is what he said: "ok.  the slow down time is fixed right now, which may be quite high for your mill.  but we plan to change that to use the actual decel setting in mach3 motor tuning screen." 
 
Ray.

I presume you are talking about the feedhold here?
Hood

Offline dresda

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Re: Another dumb question
« Reply #27 on: February 02, 2011, 06:00:12 PM »
This is not right, the acc & dec is way off. My motors are only 30in/lb SEM, small knee mill a when I input an MDI move at 40"/min and press the feedhold you can actually see the motor winding down to a stop, then press the cycle start and it starts to ramp up, it looks stupid, The motors respond good and in rapid at 120in/min they stop dead.
If my machine was a router running at 100in/min I bet it would about 3-4inchs, to stop.
I'm not talking high speed machining here. I have a Milltronics mill with a 386SX, and I have no problems with the feedhold.
Hood, what was on about re: debounce?
Ray.

Offline Hood

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Re: Another dumb question
« Reply #28 on: February 02, 2011, 06:10:36 PM »
Feedhold is not instant in Mach as its an buffered  system so has to decel and recalculate but it does sound like yours is taking longer than normal which would seem is the DSPMC. How long in time does a Feedhold take to stop from your 40IPM?

Not sure what you are asking with this
Quote
Hood, what was on about re: debounce?
Hood

Offline dresda

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Re: Another dumb question
« Reply #29 on: February 02, 2011, 06:27:34 PM »
I thought you had mentioned something about de-bounce? I think I'm loosing my mind right now and It's snowing like a bugger outside...
I am going to take a video of my motor coming to a stop so you can see it.
Ray.