Messages

11

General Mach Discussion / Re: Soft stop at limit switches

« on: September 10, 2010, 03:54:16 PM »

Should it be an option in Mach, in my opinion only if its an additional option using separate inputs from the limit switches. Reason is I want my limit switches to act as true limits, ie my E-Stop circuitry is invoked via hardware but in addition Mach is told to cut pulses. That way  I have both hardware and software activated Limits from the same switch.
Then if wished additional switches could be input to Mach to act as ramp down hardware activated soft limits via  another input, called maybe something along the lines of Ramping Limit Inputs.

Having the possibility to separate between "ramp stop inputs" and "cut-off inputs", maybe even with two separate stop conditions, would be the Rolls Royce solution. Having the choice between an adjustable ramp and a cut-off for the one existing stop condition would be the Toyota Yaris solution. When having none at all, implementing the Toyota would be enough.

Greetings
Nicolas

[Edit: correcting some stupid false friends in vocabulary]

12

General Mach Discussion / Re: Soft stop at limit switches

« on: September 10, 2010, 03:34:22 PM »

@stirling:
No, Ian, you did not miss the point- as I told in the first post, we have been discussing this topic in a german board for a while. I (for my own machine) want a ramp for slower deceleration, because at my machine, the "crash" to the dead stop is much softer than the stop made by Mach. Others want a ramp because for their drive deceleration works faster with a ramp.

@bob888:
OEM code for Reset is "1021", have a look here:
http://www.artsoftcontrols.com/MachCustomizeWiki/index.php?title=OEM_Buttons

Greetings
Nicolas

13

General Mach Discussion / Re: Soft stop at limit switches

« on: September 10, 2010, 09:19:51 AM »

OK, perhaps my vocabulary maybe insufficient:
I'd like to say:
Hard limits which are security issues, of course have to be casted in hardware. Something having nothing to do with Mach at all. Mach only gets a notice that an emergency stop has occured. And, maybe if it makes sense, that a limit switch has been triggered. Anyway, it's not Mach to decide to stop the machine because this has already been done by hardware.

Hard limits I talk about in this discussion are those limit switches connected to a breakout board and to Mach which decides to stop motion by cutting clock when they're triggered. However, these limits stop motion by software anyway - so they're as reliable as every software thing, regardless if they're implemented with a ramp or not.

Soft limits I do not want to talk about at all. They're fine.

Many greetings
Nicolas

14

General Mach Discussion / Re: Soft stop at limit switches

« on: September 10, 2010, 08:54:18 AM »

Limits should not only be in software but should be mechanical and it is something you should think about.

100% Ack. But the same is for those limits already implemented.

15

General Mach Discussion / Re: Soft stop at limit switches

« on: September 10, 2010, 08:51:31 AM »

So afraid it is up to you to petition Brian to add that feature for you and as said I have no objection as long as it is an option and not the only way.

Of course, every "adjustable ramp" implies the possibility of a sudden stop. In fact, it's exactly the point that either I want to know how to implement this in existing Mach or want to pose a feature request for future release. But before the second, I'd like to discuss its usefulness, otherwise I don't see any chance of implementation if its reason is not as clear as day.

Many greetings
Nicolas

16

General Mach Discussion / Re: Soft stop at limit switches

« on: September 10, 2010, 08:43:40 AM »

Here is my personal list of arguments why it makes sense to care about the possibility of a controlled slowdown at a limit switch on in an emergency condition (some of them are not my own ideas):

1. Some machines stop faster when there is a controlled stop instead of killing the drive clock.
2. On stepper drives, hitting "stop" usually results in lost steps, causing the need to re-reference position. So operators usually ponder whether it's really necessary to hit "stop" but maybe "line feed" does as well. That's not the sense of a "stop" button to ponder before hitting it!
3. Sometimes, soft limits simply don't work.
  3a) Sometimes soft limits just are switched off by operator
  3b) Some machines do not have a rectangular working area!
  3c) Some machines have changing dimensions of working area.
  3d) If soft limits always worked, they would be useless.
4. At some machines (usually smaller ones), the impact on the machine by the abrupt stop when triggering the limit switch is even harder than that one caused by crushing into the elastic dead stop.

I think every single reason itself is enough to motivate for having an adjustable ramp for "emergency slowdown".

Many greetings
Nicolas

17

General Mach Discussion / Re: Soft stop at limit switches

« on: September 10, 2010, 08:25:04 AM »

I better should have titled this thread with "softer stop at emergency condition or limit switches".
When soft limits are applied and work, limit switches are not needed, anyway. When limit switches are not needed, the whole discussion is futile. i think we all agree that limit switches are useful- if we could omit their use totally by using soft limits we could save a some money and construction effort. So why is the response to the question: "How can I make my stopping process more effective?" - "Don't come to a situation where it's needed!" ?

Many greetings
Nicolas

18

General Mach Discussion / Re: Soft stop at limit switches

« on: September 10, 2010, 07:30:11 AM »

Hello Stirling,
your argumentation is based on the idea, that there is a possibility to stop NOW. In fact, it always takes time to decelerate any moving mass. So instant stop is impossible. So the closest position to "now" being physically achievable is: "I want to stop as fast as possible!"

Starting from the "as fast as possible" point of view, please allow me an analogy:
When braking your car in front of an obstacle, for some cars it's the the best way to decelerate just making all four wheels block - you use sliding friction for your wheel on the ground. In many other situations, not to make all four wheels block but keep your wheels rolling on ground, use the sticking friction of your wheels, and slow down with a defined traction results in shorter braking distance.  

Back to my servo drives: There exist some servo drives and also stepper drives, where stopping drive clock leads directly to lost steps resulting in much longer deceleration path than stopping with a defined ramp.

Greetings
Nicolas

Edit: Minor typos

19

General Mach Discussion / Re: Soft stop at limit switches

« on: September 10, 2010, 04:16:19 AM »

Of course, limit switches become interesting when soft limits either have not applied, e.g. machine has not been referenced or have been switched off intentionally.
Also, points 2 and 3 are interesting not only when limit trigger is applied, but also on any emergency stop condition.

Many greetings
Nicolas

20

General Mach Discussion / Re: Soft stop at limit switches

« on: September 10, 2010, 04:01:37 AM »

The problem is, that when hitting limit trigger, Mach3 stops immediately drive clock. This has some major disadvantages:

1. At some machines, the limit switches which are reported to Mach are not the last security instance because that one is realized in hardware. So when limit trigger is reported to Mach, it would be convenient to slow down with a steep ramp instead of killing drive clock for a more gentle treat of the mechanic components.

2. At some machines with servo drives, namely those where the servo controllers have no separate input for emergency-stop, slowing down with a ramp leads to faster stop than just clock interrupt.

3. Same is at some machines with stepper drivers, where instant interrupt of drive clock leads to lost steps, resulting in a slower slowdown than possible.

At all these cases, slowing down the drives with an adjustable ramp would be beneficial either for security reasons or for a considerable treatment of hardware.

Many greetings
Nicolas