Dynomotion

Group: DynoMotion Message: 871 From: Ross Ferguson Date: 1/14/2011
Subject: ESTop needs a rethink
I had occasion, just recently, to have to use the EStop when a 1 metre long piece of 35mm bar got a
bit of a shake on in the lathe spindle, at 1100rpm.
The lathe has a 14" diameter three jaw chuck which gathers quite a bit of momentum.
The EStop worked but the spindle no longer had any braking effect, and it ran on for quite a while,
with the bar still thrashing around.

Would it be possible to connect the earth leg of the DAC - VFD supply as per the diagram attached.
That would allow the use of just one relay connection rather than having to connect to both forward
and reverse legs.

When the motor is powered up the connections at "Simple orientation/Start Command/Stop Command" have
no effect.

The only problem we can see with disconnecting the earth is that there may be potential for back EMF.
Would this effect the Kanalog board?

Your thoughts/advice would be, as usual, much appreciated.

Ross

P.S I am NOT doing any more long bars without supporting the outer end - no matter what diameter the
bar is :(
   @@attachment@@
Group: DynoMotion Message: 872 From: Tom Kerekes Date: 1/14/2011
Subject: Re: ESTop needs a rethink [1 Attachment]
Hi Ross,
 
I'm confused.  You mention DAC - but then the diagram shows Opto Output conections?
 
I don't see any problem with putting a relay contact in the ground leg for the optos.
 
My understanding is that you are trying to arrange things so that Estop actively brakes the spindle to a stop by leaving power to the VFD but switiching both forard and reverse off?  How was it wired before? 
Regards
TK
 

Group: DynoMotion Message: 873 From: william Carrothers Date: 1/14/2011
Subject: Re: ESTop needs a rethink
Wondering if a config in the VFD would be avaliable to enable dynamic brakeing when estop IO is triggered to it..  I'll have to look at mine for that,  I've estoped my system to watch my spindle cost to a stop but have not had to watch it coast during a Oh S^!T moment..
 
b./


--- On Fri, 1/14/11, Tom Kerekes <tk@...> wrote:

From: Tom Kerekes <tk@...>
Subject: Re: [DynoMotion] ESTop needs a rethink
To: DynoMotion@yahoogroups.com
Date: Friday, January 14, 2011, 5:20 PM

 
Hi Ross,
 
I'm confused.  You mention DAC - but then the diagram shows Opto Output conections?
 
I don't see any problem with putting a relay contact in the ground leg for the optos.
 
My understanding is that you are trying to arrange things so that Estop actively brakes the spindle to a stop by leaving power to the VFD but switiching both forard and reverse off?  How was it wired before? 
Regards
TK
 

Group: DynoMotion Message: 874 From: Ross Ferguson Date: 1/14/2011
Subject: Re: ESTop needs a rethink
Sorry Tom - my mistake.
The DAC are connected to the Frequency Adjust Potentiometer in that diagram.
The Optos are connected to the Forward/stop command and Reverse/stop command.
We'll try the relay on the Opto ground leg.

It turns out that it wasn't wired at all previously - bit of an oversight in my rush to play with the machine :)
The EStop was turning off the servos but not the spindle.
We had tested the EStop but not under operating conditions and we could find no wiring circuitry to tell us how it had been done previously.

Thanks again for you help - I'll let you know how it works out.

Ross

On 15/01/2011 11:20 AM, Tom Kerekes wrote:
 
Hi Ross,
 
I'm confused.  You mention DAC - but then the diagram shows Opto Output conections?
 
I don't see any problem with putting a relay contact in the ground leg for the optos.
 
My understanding is that you are trying to arrange things so that Estop actively brakes the spindle to a stop by leaving power to the VFD but switiching both forard and reverse off?  How was it wired before? 
Regards
TK
 

Group: DynoMotion Message: 893 From: miguels244 Date: 2/1/2011
Subject: Re: ESTop needs a rethink
Hi...
The safest way to configure this is to add two contacts to the E-Stop button and use them to ground the FWD/REV terminals. Use one to tell the controller that E-Stop has been invoked and to execute the E-Stop routine for the servos. Depending on your servo/stepper drives there may be an E-Stop system as well. After everything stops THEN disable the power circuits. You can do this with safety timing relays ideally, or with a routine in the controller.

Note that your VFD has a braking resistor that could overheat, the VFD will freewheel after that happens. You need to do some calculations on the inertia of the system to find out of the VFD can brake the load. If not, then you may be able to add an outboard braking resistor to help. Failing THAT there are other strategies to safe your machinery.

Please do not rely on software for safety!

Miguel
Group: DynoMotion Message: 901 From: Ross Ferguson Date: 2/2/2011
Subject: Re: ESTop needs a rethink
Thanks Miguel.
That is what we have done, in effect, and it works well.
The servos are depowered and the spindle brake works.
The power off main switch is handy so that is not a problem.
The problem was in stopping all motion as quickly as possible and we have achieved that by using the relay to break the circuit which signals the spindle to run.
Ross

On 2/02/2011 7:14 AM, miguels244 wrote:
 

Hi...
The safest way to configure this is to add two contacts to the E-Stop button and use them to ground the FWD/REV terminals. Use one to tell the controller that E-Stop has been invoked and to execute the E-Stop routine for the servos. Depending on your servo/stepper drives there may be an E-Stop system as well. After everything stops THEN disable the power circuits. You can do this with safety timing relays ideally, or with a routine in the controller.

Note that your VFD has a braking resistor that could overheat, the VFD will freewheel after that happens. You need to do some calculations on the inertia of the system to find out of the VFD can brake the load. If not, then you may be able to add an outboard braking resistor to help. Failing THAT there are other strategies to safe your machinery.

Please do not rely on software for safety!

Miguel


-- 
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New Zealand.  0882
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