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Author Topic: How to stop servo spindle gracefully on Estop or stop button?  (Read 708 times)

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Offline DMBGO

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How to stop servo spindle gracefully on Estop or stop button?
« on: October 09, 2019, 11:12:45 PM »
Hi, it's been a while since I posted, but there is a minor issue with my lathe that I have been meaning to ask for help about for a couple of years.
The issue is as follows: When I start and stop the servo spindle using M3 and M5, or the spindle on / off button, the spindle starts and stops gently, it takes a couple of seconds to stop.
If I panic for some reason and hit Estop or the stop button, the axis movement stops immediately and the spindle tries to stop immediately with a loud clunk. Unfortunately this overloads the servo controller and it comes up with the appropriate error.
I think the error is something like "what the hell did you just do to me?".
There is probably a setting somewhere in Mach3 to tell it to be more gentle when stopping the spindle, even in an Estop situation.
Cheers

David
Re: How to stop servo spindle gracefully on Estop or stop button?
« Reply #1 on: October 10, 2019, 12:29:11 AM »
I wouldn’t think there is a setting. If you push the EStop Mach3 tries to stop everything as quick as it can.
After all, it’s an Emergency Stop.

Cheers
Peter
----------------------------------------------------
Homann Designs
http://www.homanndesigns.com
email: peter at homanndesigns.com
Re: How to stop servo spindle gracefully on Estop or stop button?
« Reply #2 on: October 10, 2019, 01:25:58 AM »
Hi,
either <Stop> or <Estop> do not de-accelerate, they crash stop.

There is settings within your servo drive that limit current, or analogously torque, which will be a bit more graceful.

If you make this setting just a little more aggressive than the max acceleration you have set Mach to then it will not interfere
with normal operations but will effectively provide a max de-acceleration slightly in excess of that.

Craig
My wife left with my best friend...
     and I miss him!

Offline DMBGO

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Re: How to stop servo spindle gracefully on Estop or stop button?
« Reply #3 on: October 10, 2019, 04:05:36 PM »
Hi,
either <Stop> or <Estop> do not de-accelerate, they crash stop.

There is settings within your servo drive that limit current, or analogously torque, which will be a bit more graceful.

If you make this setting just a little more aggressive than the max acceleration you have set Mach to then it will not interfere
with normal operations but will effectively provide a max de-acceleration slightly in excess of that.

Craig
Thanks Peter and Craig,
Yes Peter I know it is an emergency stop, necessitating a stop as quickly as possible, and it does make sense to turn everything off immediately, regardless of the cost in mechanical terms.
However I did hope that there was perhaps an option for the stop button on M3, that perhaps wasn't quite so aggressive as an Estop.
Craig I think you have the answer with your suggestion about the decceleration period of the spindle motor being set within the servo controller, is the answer. I'll try it and get back to you with the result.
Thanks
Dave
Cheers

David

Offline DMBGO

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Re: How to stop servo spindle gracefully on Estop or stop button?
« Reply #4 on: October 10, 2019, 04:57:35 PM »
I have had a read through the manual (yet again) for the servo driver (GSK DA98B) from this link http://gskcnc.com/Support/DA98B_ACDriver.pdf
The terminology in the manual is a bit different to that which I have in my head, for example they use the terms "Pulse and Sign" which I interpret as "Step and Direction".
Perhaps someone on this forum has a better understanding than I of what they are saying in the manual?
To slow down the motor decceleration perhaps it is the PA05 setting?
Any advice / clarification here would be appreciated.
Cheers
Dave
Cheers

David
Re: How to stop servo spindle gracefully on Estop or stop button?
« Reply #5 on: October 11, 2019, 02:05:18 AM »
Hi,
as Chinglish goes that manual is atrocious!

The settings you should look at are PA34, PA 35 if you wish to set a torque limit under ALL circumstances
or PA36 and PA37 if you wish the limit to apply ONLY at those times when you excite an external signal.

Craig
My wife left with my best friend...
     and I miss him!

Offline DMBGO

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Re: How to stop servo spindle gracefully on Estop or stop button?
« Reply #6 on: October 11, 2019, 04:08:49 PM »
Thanks Craig, your suggestions are appreciated. I'll give that a try later this morning and let you  know.
Cheers

David

Offline DMBGO

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Re: How to stop servo spindle gracefully on Estop or stop button?
« Reply #7 on: October 11, 2019, 04:39:25 PM »
After looking at the options you suggest in the manual again, you are saying that I should set a torque limit. This can take 2 forms, either a global setting (PA34 CCW rotation and PA35 CW rotation), or only when the input pin 25 (FIL) is high, or on (PA36 CCW rotation and PA37 CW rotation).
I am interpretting this to mean that these settings shouldn't affect the motor torque in normal continous speed operation, but only alter the maximum torque applied to the motor when changing speeds.
This means that since I am using this motor as a lathe spindle, it shouldn't affect normal machining, but only affect speeding up and slowing down.

Do I understand this correctly?

Thanks

Dave
Cheers

David
Re: How to stop servo spindle gracefully on Estop or stop button?
« Reply #8 on: October 11, 2019, 07:00:12 PM »
Hi,

Quote
I am interpretting this to mean that these settings shouldn't affect the motor torque in normal continous speed operation, but only alter the maximum torque applied to the motor when changing speeds.

That is one interpretation.....is not particularly accurate but neither is it incorrect.

If a motor has to change speed, due to a speed change command for instance, and for our purposes the it could be an increase
in speed or a decrease, then the rotor has to accelerate, ie this requires torque. If you use PA34/35 then they set the maximum
torque under ALL circumstances. If you use PA36/37 then the torque limit applies ONLY when the 'torque limit input signal'
is active.

What happens however if you are machining at a constant spindle speed but the load increases due to cutting forces.....the
servo responds by increasing torque (analogous to current) to MAINTAIN speed. Under these circumstances you'd wish that
the servo had its maximum available torque (approx. 300% of rated torque). PA34/35 effectively imasculate your servo....
not desirable.

The alternative is to use PA36/37 so that the servo is at its most capable under normal circumstances. What would be required
than is that just prior to operating the <stop> or <Estop> button that you engerise the torque limit signal. That would require
you modify Mach to include the signal operation PRIOR to the <stop> or <Estop>. I don't know whether Mach3 can
do that but Mach4 can certainly be programmed to do that.

Craig
My wife left with my best friend...
     and I miss him!

Offline BR549

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Re: How to stop servo spindle gracefully on Estop or stop button?
« Reply #9 on: October 12, 2019, 11:05:34 AM »
The way we did this in the past was to simply disable teh Spindle drive when using teh Estop. You would first disable teh drive then ESTOP from code in teh estop button. You would do the same with teh STOP button.  This prevents teh spindle from an emediate stop which tends to unscrew teh chuck from teh spindle shaft. Or in your case faults teh spindle drive.

OR you could reduce teh spindle speed by code to a level that will not trip your drive THEN apply Estop or Stop.

Just a thought, (;-) TP