Machsupport Forum
Mach Discussion => General Mach Discussion => Topic started by: chrisjh on October 28, 2008, 08:12:21 PM
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I am using Mach3 V3.041 with a Smooth Stepper in PWM mode. Base Frequency is 1000 (but the problem persists whatever Base Frequency I use).
The problem is very consistent and it doesn’t matter what method of requesting any Spindle Speed. (MDI using M and S commands or from any Spindle Toggle Buttons on any Mach3 Tab).
The problem with the spindle speed is as follows:
Select a speed (say 1000rpm). Spindle Override reads 1000 same as Spindle Speed and SRO reads “00”.
Toggle the spindle on. The actual speed of the spindle always starts at a slightly higher speed than that requested.
Pressing “Reset” under the Spindle Speed Tab always brings the speed back to correct requested speed and subsequent requests for speed changes (via Spindle Override or actual commands for a different speed) from there on are correct and consistent.
It appears that Mach3 is in some form of Spindle Override (approx +10%) when first started. I first noticed this problem a couple of years ago but ignored it and learned to live with it with my mill. However I and building a cnc lathe with a VFD controlled Spindle Motor and want better control over spindle speed.
Also there is another dialogue Tab under the Spindle Speed Tab labeled RPM. It always reads “0” regardless of what I do with Spindle Speed and it does not accept any characters typed into it even though it changes background when selected. So I ignore it. What is the purpose of this “RPM” Box and should it indicate something?
Regards
Chrisjh
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Chris,
Your spindle is open-loop, right? i.e. - you do not have a spindle speed encoder? I believe the "RPM" DRO will only be active if you have a spindle encoder, and it will show the actual spindle RPM, which is not necessarily exactly the same as the commanded RPM.
I have a sort-of similar problem with mine, and I also have a SmoothStepper. At low spindle speeds, when I turn the spindle on, it comes on too fast (sometimes 2X), then over a period of several seconds settles down to the correct speed. Mine is open-loop - no encoder (yet).
Regards,
Ray L.
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Hi Ray,
I am currently testing all of my electronics on the bench open loop. Thanks for the pointer in the right direction. That would explain why the RPM box always displays "0". I often wondered about it but now makes sense. My intention is to run closed loop with a spindle pulse from a slotted disc or Hall effect sensor. I will trial a fully fedback system ASAP.
Thanks and Kind Regards
Chris
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I have done some more experimentation and Mach3 definitely has a bug in the Spindle Speed Control. The problem has nothing to with whether you use open or closed loop. I have tried 2 different computers using both Mach3 and Quantum with exactly the same repeatable results on my mill and my mockup of my lathe in progress. In both cases I am using PWM to control the spindle motors. The Mill uses a PWM to Analogue Converter Board and Motor Control Board to control the 1000W DC Brushless Motor. The lathe uses my own PWM to Analogue Converter to control a Danfoss Microdrive VFD to a conventional 3 phase AC Motor.
I am also using a Smooth Stepper (what a great leap forward in technology, I love it).
If you are using PWM, try this to see the problem:
Command Mach3 to go to any speed (say 750RPM) via the Spindle Speed Dialogue Box or MDI
When the spindle is running, press the "Reset" Button. You will notice a destinct drop in RPM.
You get the same results if you:
Command Mach3 to go to any speed (say 750RPM) via the Spindle Speed Dialogue Box or MDI
When the spindle is running, press the override "up" arrow twice. You will notice a destinct drop in RPM on the first press of the arrow and then the spindle will respond normally on the second and subsequent presses.
I have monitored the PWM steam out of Mach3 with my CRO and the PWM mark to space ratio (duty cycle) changes accordingly so the problem is definitely with Mach3.
Any hints as to how to correct or overcome this would be greatly appreciated.
Regards
Chrisjh
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Hi Chris and Ray,
I played around with it a little, but I didn't see that happen. There are a number of variables though, and it would help me if you could e-mail your XML (and screen set if it is different (if you'd like)) to me so that I can run with the same exact parameters as you. Please send them to me support@warp9td.com if you want me to take a look.
Thanks,
Greg
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Greg,
On mine, it's really not a problem, since it always settles to the right speed before any movement takes place (I have a 5-second dwell on spindle start) and I've done nothing to determine if it's the SS or the CNC4PC analog output that causes that initial "surge". The spindle has been behaving well lately, after the problems a couple of weeks ago, so I'm afraid to touch it! :-)
Regards,
Ray L.
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Command Mach3 to go to any speed (say 750RPM) via the Spindle Speed Dialogue Box or MDI
When the spindle is running, press the override "up" arrow twice. You will notice a destinct drop in RPM on the first press of the arrow and then the spindle will respond normally on the second and subsequent presses.
I have monitored the PWM steam out of Mach3 with my CRO and the PWM mark to space ratio (duty cycle) changes accordingly so the problem is definitely with Mach3.
Any hints as to how to correct or overcome this would be greatly appreciated.
Regards
Chrisjh
Chrisjh,
Did you ever solved this problem from October 2008?
I have exactly the same problem. Command a lower speed, and the spindle speed will drop much to low before climbing up to the desired speed , and also hitting the override up button first drop the speed.
Found an answer???
gr jaja
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Hi Jaja,
The problem is not associated with Smoothstepper. It is a Mach3 bug.
I overcome the problem by inserting the following lines of code (or something similar) into every program.
This code is a soft start routine for my mill spindle.
G00 G17 G21 G40 G49 G50 G64 G69 G80 G90 G94 F1000
M6 T6 (Ø5mm Spot Drill)
M3 S750 (Start spindle at 750rpm but spindle goes to approx 850rpm)
G04 P100 (Dwell for 0.1secs)
S1000 (Increase speed to 1000rpm. Spindle goes to correct speed from here on)
G04 P100
S1500
G04 P100
S2000
G04 P100
S2500
M8 (Coolant on)
G00 Z10
G00 X0 Y0 Z3
Regards
Chrisjh
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I have the exact same problem, and found other reports of it but no fixes. Ver 3.043.040 here but apparently the bug has been around a while. I have seen at least 3 unrresolved reports of it.
Is there a fix? I see the workaround in the post above but that won't do any good from the MDI or just clicking the spindle on button.
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Hi George,
The problem still persists. I believe that this bug does not cause most users any problems so a fix doesn't get high priority.
You and I seem to be the only ones concerned.
I continue to use my extra lines of code in cnc programs or, when in manual mode, I am in the habit of automatically hitting spindle override reset to achieve the correct rpms.
Regards
Chrisjh
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Thanks for the reply. I was afraid it was never fixed. I reported it in the yahoo group but it is only getting responses that don't comprehend what is happening, the responses go into how to setup and tune a PWM spindle. I knew that would happen. Its pretty obvious that it is a bug in mach but until that is realized a fix will never happen. I have gone down the same path before with other bugs, they always seem to be initally dismissed as "operator" errors. Its not like mach hasn't had a "few" bugs before.
I have a hunch that this might have happened a year or so back when Art fixed the threading code in machturn OR when he fixed the spindle calibration routine. Its pretty common for one item to get fixed and cause another bug in the process.
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We are not alone !! http://www.machsupport.com/forum/index.php/topic,17064.0.html
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Its fixed ! Link to fix:
http://groups.yahoo.com/group/mach1mach2cnc/message/125366
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Hi All,
I am happy to report that the spindle speed problem that I have been witnessing for years now is FIXED!!!
I am also happy to report that Page 3 of my document describing PWM Control of Spindles using Mach3 is now inaccurate.
I have downloaded and tested Mach3_Rev3_043_030 from the yahoo site on two different machines as follows:
1. A CNC Mill under Parallel Port Control from a Desktop PC, and
2. A CNC Lathe under Smoothstepper USB Control from an older Dell Laptop.
When I request 500rpm from any input (MDI, From a G Code program, etc.), the spindle now goes to 500rpm as requested, and not some speed slightly higher as in all previous versions of Mach3 that I have used.
Pressing the Spindle Speed Override reset button now has no effect, unless the spindle speed override is set to other than 100%.
Thanks to Sparky whose tenacity is to be envied. Like a bloody bloodhound!!! If ever you are in Queensland, Australia, I owe you a carton of my favourite local brew, *********X Gold.
And thanks to Brian who found the pesky problem and corrected it.
Regards
Chrisjh
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Its fixed ! Link to fix:
http://groups.yahoo.com/group/mach1mach2cnc/message/125366
The message does not show up, just the Yahoo page, how do I see message?
Its fixed ! Link to fix:
http://groups.yahoo.com/group/mach1mach2cnc/message/125366
Cannot see the message, just get the Yahoo page when I click the link?
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Hi,
this post dates back to 2011, do you suppose the links have expired?
Craig
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So I guess my question is anyone know the contents of the message?
Or the answer supplied?
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I have the entire yahoo mach3 database stored somewhere here. When I get time I will try to look it up.
(;-) TP