Mentor II DC drive, e-stop deceleration

[BWCMaint]

It was brought to my attention that one of our machines decels significantly faster with the regular stop button than with the E-Stop. I want it the other way around, but I can't seem to control the EStop. There are two Decel parameters but they control the Run Stop and Inch Stop.

From the wiring diagram, I see that the Regular stop button opens the Run Fwd signal only, whereas the EStop opens both Run Fwd AND Start signals. Is there any way to control the EStop Decel when wired this way?

Thank you in advance for any help. This is my first post here, but I'm going to be tweaking and updating several motor control systems in the near future. If I find this site to be helpful I will become a regular user.

 

[Skogsgurra]

If the E-stop is the same thing as a safe stop, then you don't have any torque to brake the motor with. The motor just coasts to standstill. Opening the Start circuit points to that.

There has been some confusion about E-stop and safe stop and how they are defined for many years. I do not have access to the manual. How is E-stop defined for the drive?



Gunnar Englund

http://www.gke.org

--------------------------------------
Half full - Half empty? I don't mind. It's what in it that counts.

 

[BWCMaint]

It looks like the drive doesn't recognize any EStop. After looking further into it, it looks like my only option would be to install a timer, so that the EStop functions the same as the regular stop but then removes power from the drive once the motor reaches zero speed. But even then I cannot make the EStop Decel any different from regular stop. They want the EStop to be relatively immediate and regular stop to coast down to a stop. Unless there's something I'm not seeing, I'm not going to be able to do that with this drive.

What I don't get though, is that there are similar machines with the same drive, and this is the only machine that has this issue. At this point, I'm guessing that the other machines are just facing more resistance and doesn't coast as much. But I am going to dig deeper and would appreciate any more help.

 

[itsmoked]

Often your drive will have a parameter that describes which various inputs allow controlled deceleration. It may be that parameter is set to cause coasting if, say, the start input is opened.

Why are you bothering with both? Most machines I work on only have one. The big red mushroom. They use the mushroom to stop the machine normally. This has the advantage of testing the stop dozens of times a day. VFD run devices often use the VFD in the e-stop function because it's always the fastest way to stop the motion.

Consider rewiring your e-stop to use the same stopping method as your 'normal' button uses. If there are other machine functions involved in the e-stop not normally operated with the normal stop, then add another contact block to the e-stop to additionally signal those other functions.

Keith Cress
kcress -

http://www.flaminsystems.com

 

[BWCMaint]

My boss asked my to make the EStop slow the machine down faster than the normal stop, as well as "drop the power to the drive." As it is now, it opens the "start" signal which acts like an enable. Which forfeits all control of the motor and it coasts to a stop.

When my boss gets back from vacation I'm going to tell him that I can make the EStop Decel at the same rate as the normal stop, and then disable the drive when it comes to zero speed using a timer (or maybe a zero speed aux contact if i have one). Or we can buy a new drive that has the functions he's requesting. Those are my only options as I see it.

 

[itsmoked]

Or clearly explain to him the reality of the physical logic you're faced with so he can alter his request rather than pouring a ton of money in to a desire that's just off from an easy, available solution.

BTW I would never include any kind of timer in an e-stop function. It can fail or take too long or....

Keith Cress
kcress -

http://www.flaminsystems.com

 

[jraef]

My boss asked my to make the EStop slow the machine down faster than the normal stop, as well as "drop the power to the drive."...

Pick one.

You are asking it to be in control, with power removed. Think about that...

You have two options:
[ol ]
[li]Come up with a way of living with the drive's braked stop capability as the fast "E-stop" and forgo the "drop the power" requirement[/li]
[li]Add a mechanical safety brake to the motor shaft that is immediately released when power is applied, so that if you kill the power with the E-stop, the mechanical brake engages.[/li]
[/ol]

What old drives like that one usually offered was an E-Stop option that immediately ignored all Accel / Decel commands and immediately cut power to the motor, often by shorting out the power control device logic circuits (i.e. "base block" on transistors). They would have a set of input terminals that were supposed to be closed, but when opened, as in an E-Stop button, the command line in the logic goes low and the power components are immediately shot with tranquilizer darts powerful enough to stop an elephant.Under "normal" stopping conditions, the drive REQUIRES power, AND it must continue applying power to the motor in order to create the braking effect, in whatever way it does that (there are several).

Your timer idea most likely would not stand the scrutiny of any reasonable safety assessment, too much risk of failure. You would be better off just going with option 1 above.

"Will work for (the memory of) salami"

 

[Marke]

If you have the four quadrnt version, then you can brake quicker than when you just drop the power. Otherwise, you need to add some external braking device.

Mark Empson
Advanced Motor Control Ltd

 

[BWCMaint]

"Your timer idea most likely would not stand the scrutiny of any reasonable safety assessment, too much risk of failure. You would be better off just going with option 1 above."

But your option 1 and my timer idea would stop the machine in the exact same way. In the event of a failed timer there would be no difference at all. Using an off delay timer would just allow me to disable the drive after a few seconds. It wouldn't bring anymore risk only more protection.

 

[BWCMaint]

The timer wouldn't control the stop. Pressing the EStop would stop the machine with or without it. The timer would keep the enable signal on for a few seconds (enough time for the motor to come to a complete stop) and then disable the drive.

 

[ozmosis]

Hi BWCMiant,
Welcome to eng-tips.
Relating to the particular description of 'the machine'. When you say this, do you mean just the mentor dc drive or the whole machine it is connected to? The reason I ask; an emergency stop connected to a machine should relate to the overall integrity of the machine stopping in a common manner, and not being able to restart again individually.
There is a very different definition of stopping and braking when looking at an emergency function. It depends on what the intention is when you hit the estop. If braking is itself a safety requirement,i.e.if the braking does not operate then there is an unacceptable risk of injury,then a fail-safe brake must be provided,such as a mechanical brake with electrical hold off.
Stopping, when it comes to an estop, is generally looking at the inability to restart again.
Introducing timers into a safety system would generally require defined safety relays from my experience.
There are various standards relating to safety and, depending on where you are in the world, should always be checked beforehand.
Finally, when it comes to safety (especially), please understand that the information provided here are tips only from various parts of the world. You have the benefit of being in front of the machine..
Having said that, you have available in this forum, some of the best motor control experts you will find, some have already contributed.

 

[mikekilroy]

IEC 60204 defines various stop modes, including e-stop. A good simple 1 page description of these stop categories 0,1,& 2 is on page 50 of this drives manual:

http://www.kollmorgen.com/en-us/pro...ollmorgen-akd_installation_guide_en-us-rev-k/

I am old fashion and would not want to rely on a timer or software for stopping an E-stop situation, but seems I am old fashion and it is allowed today....

Just had yet another customer decide it met code to NOT disable the drive but instead send software "quick stop" command to drive so it decelled to stop fast, ThEN turn off... For safety. Guess we gotta get with the 90's.... I at least talked them into pulling the 3ph input power at same time as sending the software stop command so once it decelled it had no juice left to malfunction.

 

[cswilson]

I'm a little late to this party, but I have puzzled over conflicting desires and demands for E-stops for many years now, watching the fashions in regulations and suggested practices swing back and forth like a pendulum (with different continents often out of sync with each other). Lately, I have been digging into the myriad overlapping and cross-referencing national and international standards.

The standard IEC 61800-5-2 defines several categories of "safe stopping functions". Category 0 is immediate removal of power, either bus power, or increasingly, gate drive power (known as "safe torque off"). Without mechanical braking, the motor will coast. (Leads of servo motors can also be shorted together, but this does not help with induction motors.)

A Category 1 stop is a controlled deceleration to a stop, followed by power removal after a fixed time interval. This is the method that the poster wants to use.

A Category 2 stop is a controlled deceleration to a stop, with control maintained at stop, not permitting commands to start up again.

If the reason that the E-stop needs to be invoked is that the drive has lost control, then attempting a controlled stop will not help. That said, I believe I see a trend now that drives can usually tell if they have lost control and shut themselves down, so people increasingly want the quick controlled stop, with a timer relay dropping out power (especially now that most new drives allow you to drop out gate-drive power) after a couple of seconds, which acts (among other things) as a backup in case the drive has truly lost power.