Mach3 Spindle Speed Problem

[chrisjh]

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

[HimyKabibble]

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.

[chrisjh]

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

[chrisjh]

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

[Warp9TD]

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

[HimyKabibble]

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.

[jaja]

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

[chrisjh]

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

[Sparky_NY]

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.   

[chrisjh]

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