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Initial Speed control issue
« on: May 30, 2014, 08:25:23 AM »
Hi,
Have a lathe with VFD drive running via PWM.
When initially launch Mach3 and after an S command M3 or M4 drive motor at max revs. Reissuing S and then M5 then M3 or M4 bring it back under proper control.
Assume this is a known bug, what is the fix?

Offline Hood

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Re: Initial Speed control issue
« Reply #1 on: May 30, 2014, 07:57:32 PM »
Never used PWM or for that matter a VFD controlled by Mach but I have never heard of that issue so I think it unlikely to be a bug, but nothing is impossible ;)
If you attach your xml I can have a look to see if I can figure out your problem.
Hood
Re: Initial Speed control issue
« Reply #2 on: May 31, 2014, 08:42:24 AM »
XML attached.

Seems to be more of a problem of reading the initial setting that that of set-up, but be interested if you see any issues in it.

Offline Fastest1

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Re: Initial Speed control issue
« Reply #3 on: May 31, 2014, 02:29:13 PM »
Do you use a charge pump or its feature? My understanding is that it doesnt allow any motion until the signal is received from the PC, meaning communication with Mach is successful.
I want to die in my sleep like my grandfather, not like the passengers in the car! :-)
Re: Initial Speed control issue
« Reply #4 on: May 31, 2014, 04:05:38 PM »
Yes I use the charge pump, but only into the BOB.
Pins on that drive a digispeed board which gives the 0-10v to the VFD invertor. The volts for that from the VFD.

so I would tend to input something like this first time you run the spindle, remembering to clear out any spindle over OV% increment, so it is not that.
S750
M3   : at which point motor will hit around a 1000 rpm
S750 : and speed reduces to within 20 rpm
M5
next time you run it tracks oK

From then on it hits the calibrated curve OK.


Good linearity of control

Offline Hood

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Re: Initial Speed control issue
« Reply #5 on: June 01, 2014, 04:21:08 AM »
You said first it hits Max rpm then now say 1000rpm, is that the case that it is just 1000rpm if you call S750 initially?

Can you measure the voltage output from the speed controller to see what its outputting.

Couple of things I notice is you have spindle pulleys set to 3250 max and motor tuning set to 4500rpm, try setting both the same.

Hood
Re: Initial Speed control issue
« Reply #6 on: June 01, 2014, 08:28:02 AM »
OK,
I will rephrase the issue.

Remember this is PWM control, not pulse frequency via steps, so the motor tuning is not relevant. Proved this by setting all the values for spindle to zero. The relevant control for PWM are in the spindle setup tab:- motor control  ( step and dir NOT ticked, PWM freq 1000 and 5% min) and special features ( ticked feedback in sync and Averaging) as you have seen in the XML.

From cold start or from a reset, MDI a S word  "n"  ( where n= 500-2000, just happens to be limit of tests)
start spindle from screen button or a M3/M4 ( this is slant lathe so turn in reverse)
Spindle rotates at approx. 120-125% above set speed, speed stable at this speed ( if you implement the PID feature then speed will slowly crawl down to setting, but there are other issues with PID control and so are advised to not enable.)
do another S word and Mach 3 reads correctly the speed and spindle revolves at calibrated revs for that speed.  ( PWM control is  not infinitely variable, integer frequencies,  so will work at nearest speed which normally within 20 rpm)

(to clear the other red herring :IF you forget to reset the OV% then you can get jump to max speed, which I clarified and have now instated in my start up sequence.)

I have seen mention of this limitation, but have failed of later to track the thread and/or any fix, other than writing programs that double issue the speed at the start of the programme after spindle live.

Hope now clarified?
Re: Initial Speed control issue
« Reply #7 on: June 01, 2014, 08:34:47 AM »
Re: Initial Speed control issue
« Reply #8 on: June 02, 2014, 05:07:53 AM »
Hood,
Appears you already answered this?
Communicated with Chris
"The problem in Mach3 was eventually fixed in Feb 2011 in Rev 3.043.030.  I currently use (on Hood’s recommendation) R.043.056.  Later versions of Mach3 have reported issues, so I no longer update.  I am happy with, and will continue to use R043.056 on both my mill and lathe.

 

Here is a link to my thread in the Mach3 forum which outlines the history and subsequent fixing of the problem:

 

http://www.machsupport.com/forum/index.php/topic,9314.10.html
"

Regards