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Author Topic: Soft stop at limit switches  (Read 13918 times)

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Offline Hood

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Re: Soft stop at limit switches
« Reply #40 on: September 16, 2010, 08:35:36 AM »
Because that is what a hard limit are for, it is a hardware last ditch safety feature.
What you are wanting is a soft limit that can be activated by physical switches. but these should never be instead of Hard Limits.  No machine would pass a safety inspection if there were not physical hardware switches, especially, I suspect, in Germany ;)

As said earlier you could make a Brain or Macropump to monitor switch inputs and do a feedhold and throw an on screen message if they are activated. Not a great option I know but the best you can hope for without changes to the programme coding, and the only one that can do that is Brian.
So instead of asking for hard limits to act as soft limits I suggest you request that work envelope switches can become an option.
Hood

Offline Jeff_Birt

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Re: Soft stop at limit switches
« Reply #41 on: September 16, 2010, 08:36:44 AM »
Because that is that a limit switch is! Simple as that. There is nothing stopping you from adding other switches to indicate various positions on your machine, but I'm not sure what the point would be.
Happy machining , Jeff Birt
 

Offline stirling

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Re: Soft stop at limit switches
« Reply #42 on: September 16, 2010, 08:39:23 AM »
Nicolas

Going back to one of your reasons for asking this. i.e. being kinder to the machine.
Do you agree that IF a decceleration curve were able to stop the axis more quickly than simply stopping the pulse train, then the crash/bang/jolt whatever we want to call it, would be increased? I ask again because for whatever reason, you didn't comment the last time I asked.

Ian
Re: Soft stop at limit switches
« Reply #43 on: September 16, 2010, 08:57:19 AM »
OK, let's make the question a bit more accurate:
"Why must the limit switch known by Mach be a last chance safety system?"
Re: Soft stop at limit switches
« Reply #44 on: September 16, 2010, 09:06:57 AM »
Nicolas

Going back to one of your reasons for asking this. i.e. being kinder to the machine.
Do you agree that IF a decceleration curve were able to stop the axis more quickly than simply stopping the pulse train, then the crash/bang/jolt whatever we want to call it, would be increased? I ask again because for whatever reason, you didn't comment the last time I asked.

Ian

Hello Ian,
I'm sorry when I missed the argument of your posting last time.
On the first glance, I would have said: "Yes, an improved deceleration would increase the load."
But on second thought: If you increase deceleration in a linear controlled process, you can chose if you want to increase, decrease or keep the load the same - the first profiting from shorter braking distance, the second profiting from less load and the third not changing anything. Of course, one never can have all at the same time. But one has the choice.

Many greetings
Nicolas



Offline stirling

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Re: Soft stop at limit switches
« Reply #45 on: September 16, 2010, 09:51:42 AM »
Nicolas - maybe it's a language thing but "load" has nothing to do with this. But if what you mean is in the realms of the rate of change of acceleration i.e. "jerk" or "jolt" then in my view we're getting far too theoretical for the sake of it and I'll try to explain why. If we do what you don't want and just take away the pulse train from a motor, lets say it then skips 8 steps (which in a screw system for example is actually a lot). Now lets say that your deceleration curve can stop it without skipping steps in say 4 steps. That would mean you would have to fit a 3rd order S curve deceleration profile into just 4 steps... bit of a raggedy assed curve don't you think.

Offline Hood

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Re: Soft stop at limit switches
« Reply #46 on: September 16, 2010, 09:56:58 AM »
OK, let's make the question a bit more accurate:
"Why must the limit switch known by Mach be a last chance safety system?"

I would say you should be asking if it is possible to set soft limits to act via a physical switch. This is possibly where things are getting confused, when talking about limits we normally think of Hard Limits and these should never rely on software to control them, software as well as the hardware is ok but both must work independently.
What you are wanting is soft limits which are activated by physical switches which can be moved if required.

That is not possible with Mach as is and would be a good feature to have for some BUT it should never be used instead of Hard Limits, they should always be present.

How easy it would be to do it in the code I have no idea and only Brian could answer that, I suggest you contact him now and ask for that feature to be added into Rev4 as it will likely be easier to add it now rather than after Rev4 comes out.
But please do not ask for Hard Limits to be turned into Soft Limits :)

Hood
« Last Edit: September 16, 2010, 09:58:41 AM by Hood »
Re: Soft stop at limit switches
« Reply #47 on: September 16, 2010, 10:03:15 AM »
Nicolas - maybe it's a language thing but "load" has nothing to do with this. But if what you mean is in the realms of the rate of change of acceleration i.e. "jerk" or "jolt" then in my view we're getting far too theoretical for the sake of it and I'll try to explain why. If we do what you don't want and just take away the pulse train from a motor, lets say it then skips 8 steps (which in a screw system for example is actually a lot). Now lets say that your deceleration curve can stop it without skipping steps in say 4 steps. That would mean you would have to fit a 3rd order S curve deceleration profile into just 4 steps... bit of a raggedy assed curve don't you think.


Hello Ian,
for me, "jerk" is a dimension for optimal control fetishists to have a reason for their optimality criteria  :). Especially in pulsed/time discrete systems.  And it's totally out of my scope. "Load" for me is always a "force" thing (second derivative to time, not third derivative to time like jerk :) ).

I only want a way to adjust acceleration - which is quite normal for rapid moves (G00 condition) - to limit stops.

Many greetings
Nicolas 




Re: Soft stop at limit switches
« Reply #48 on: September 16, 2010, 10:23:05 AM »
I suggest you contact him now and ask for that feature to be added into Rev4 as it will likely be easier to add it now rather than after Rev4 comes out.
But please do not ask for Hard Limits to be turned into Soft Limits :)
That's my plan. Nevertheless, this discussion is still a perfect source for justifying motivating arguments. :)

Better: That's the short form of my plan. I want my motivation being that good, that either
 - the feature gets added to Mach
 - the feature never gets added to Mach later, because no motivation never can be that convincing. Then I will develop a hardware filling that software gap. The only difficulty will be to make my first million before other axis controller hardwares include it :) .
« Last Edit: September 16, 2010, 10:31:32 AM by Nicolas S. »
Re: Soft stop at limit switches
« Reply #49 on: September 16, 2010, 10:40:44 AM »
By the way: Does anyone have experience with feature request? What's the best: Using the that named category of this board or sending an email?