Machsupport Forum
Mach Discussion => General Mach Discussion => Topic started by: Nicolas S. on September 09, 2010, 09:19:48 AM
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Hello expert Mach users,
we had a long discussion about that at a german forum, but we did not conclude, so I'd like introduce myself with the following question:
Usually, when an end switch is triggered, Mach stops clock pulse immediately and sets status to emergency stop. Let there be a reason not to stop clock pulse immediately, being equivalent to a hit with a hammer to servo drives, but slowing down with a ramp, similar (but maybe much steeper) to that connected to the rapid move/motor tuning conditions. Is there a way to achieve that?
I'm sorry if this topic has been discussed here earlier and just my research at this board has not been accurate enough to find it.
Many greetings
Nicolas
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Set up soft limits and Mach will stop before you hit the physical limits. Physical limits are meant as a last defence and they need to stop instantly.
Hood
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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
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Using SoftLimits will avoid all the above situations so why not use them?
Hood
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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
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If you neglect to reference or you disable the softllimits then that is operator error in my opinion.
I am finding it hard to think of a situation where SoftLimits would need to be disabled, I dont think I have ever had them disabled on any of my mills since I set them up.
If you are in the habit of forgetting to reference your machine then I suggest that you make a new screen up so that you can not get to any controls until you have referenced the machine.
Having the limits ramp down when seen will mean that you lose working travel and is not a situation I would want and I suspect many others, using SoftLimits does not affect the working space.
If you feel strongly enough about this then probably it is best to contact Brian at Artsoft and ask him to write Mach to suit your needs but also make sure that he writes it as an additional option as I suspect most users will be happy with the way things are now, ie softlimits to do exactly what you are wanting hard limits to do.
Hood
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Nicolas - Let's go with your method for a moment. Suppose from max rapid your machine takes 10mm to come to a controlled stop. You'd have to place your limit switch at least 10mm from where the machine absolutely must be stopped. Now suppose for whatever reason the machine finds itself heading for a position at 5mm from end stop. It'll hit the switch at 10mm and come to your controlled stop. Now suppose you go with the soft limit method. Your machine heads for the 5mm position, hits the soft limit at 10mm, slows down, gets to the 5mm position and CARRIES ON with the job. Which is better? Now suppose it's heading to a position beyond the end stop. It goes into the slow zone and then hits the hard limit - but it does this at a speed set to NOT damage the machine. It's win win either way.
Now your E-Stop - you get your arm caught - would you prefer it to stop NOW or let it chew your arm for another 10mm or so in order not to possibly damage the machine?
And now a confession - Many moons ago I used to think the same as you - that was until a younger Hood and others put me right ;D
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stirling,
just a corrections if I may, you said
Now suppose it's heading to a position beyond the end stop. It goes into the slow zone and then hits the hard limit - but it does this at a speed set to NOT damage the machine.
What would actually happen, if Soft Limits are set correctly, is it would go into the slow zone and come to a stop before it actually triggers the Hard Limit. It will allow you to reposition and no Hard Limits will have been hit so no loss of position.
Hood
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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
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Hood - understood - thanks.
Nicolas - fair point - I can see in that case why you might want to introduce a brake on E-stop rather than just rely on the pulse train stopping - (don't these exist for heavy machines that would benefit?). Afraid I still can't see the limit thing though - given soft limits.
Ian
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The word "some" is there again and afraid that is the problem, one group of users want it one way and another want it another way.
One thing though that is for sure is Soft Limits when properly configured do exactly what you want (and actually more). It is the operators responsibility to ensure that the softlimits are active and if that cant be guaranteed because of forgetfulness then I suggest you set up additional measures such as the adapted first screen page as I mentioned earlier. Additional things that could be done are you could make the Cycle Start into a VB button which looks to see if the machine is Referenced and Soft Limits enabled before it will start the code. You could have a hidden Soft Limit button so an operator can not disable Soft Limits and I am quite sure it would not be beyond most people who know VB to have a password protected Soft Limit button.
If on a machine, say for example that has linear slides and very little friction, it may well travel further if pulses are removed. It should be noted however that Hard limits are an emergency feature so your machine should have proper means of stopping as fast as possible, motor brakes and braking resistors come to mind.
Hood
Hood
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I will also add that it is a common misconception that to reference the machine you need to first disable the soft limits. That is not true and if it is needed it is because soft limits have not been configured correctly in the first place.
Hood
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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
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As said Limit Switches are exactly that, and are a last form of defence and it is up to the system builder to use these in a way which best suits their machine.
If it was an option to have them set the way you want then I have no objection but if it was to be the way they had to be set then I would have a huge objection.
The way you want them is relying on software doing something, i.e. decelerating the axis when an input is seen, if the software fails to do that where are your limits now?
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.
Hood
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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
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Having the machine ramp to a stop when a limit is seen is purely a software feature and if that software fails then you dont have any limits.
Limits should not only be in software but should be mechanical and it is something you should think about.
Hood
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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
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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.
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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
In effect you are wanting two sets of Soft Limits and so will need additional switches to act as Hard Limits in case both SoftLimits fail or are you just going to rely on software?
I think it would be possible to do what you want by not having the switches set as limits but rather set as normal Inputs. You would then have a Brain or macropump monitor them and if seen to issue a feedhold.
100% Ack. But the same is for those limits already implemented.
I do not understand what you are meaning here.
Hood
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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
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What you are calling Hard Limits are really hardware activated Soft Limits, to be fair it is likely the way more than 90% of Mach users use and think of them. It is also the way two of my machines are set up.
So to answer your question, it is not possible to configure Mach to do as you wish through normal means but may be possible via macro pump or Brains but probably only to issue a feedhold.
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.
Hood
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Nicolas - If I understand you correctly, on the one hand you have concern over what I'll call the "bang" that a system suffers when the step pulses are simply "cut off" and you suggest that a ramp would be kinder. BUT on the other hand you suggest that a ramp could actually slow the machine down (deccelerate) faster than simply cutting off the step pulses.
But there surely is the contradiction. The "bang" is the result of rapid decceleration and you're wanting to INCREASE that deceleration.
Or have I missed something?
Ian
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@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
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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]
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Then you really need to eMail Brian and request that this is added to the list of things to do. There is a chance that it may be easy enough to do in Rev4 so the sooner you request the greater the chance of it happening :)
Hood
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Hi, when the axes touch the limit they should stop mechanically opening the motor contactor and brake with a low value resistor (resistive brake) while sending an alarm to the driver and the match for them to stop immediately. The limits of limit switch should stop the machine mechanically after out and then back to the reference.
I also think that the stop through the match should not have infinite deceleration but not a slowdown as low as 200 mm / s ยจ 2. Maybe 800-1200 would be a good option.
regards
Renato
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Nicolas
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.
OK - by replacing the word "crash" with deceleration. what you've just said is:
"I (for my own machine) want a ramp for slower deceleration, because at my machine, the deceleration to the dead stop is much softer than the stop made by Mach."
Therefore: why don't you just arrange your limit switches to be triggered towards the end of the deceleration caused by your "dead stop". So "at limit" your machine hits your dead stop - slows down with your "softer" deceleration and then hits the limit when it's almost stopped.
Others want a ramp because for their drive deceleration works faster with a ramp.
Then they're going to get a harder "crash" than at present. Do they understand this?
Ian
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Very interesting discussion. One thing that comes out is that Mach3 should have a way, in CONFIGURE---General settings, to set soft limits to default to ON at all times. Then no one would have to worry about forgetting them.
Regarding the "controlled stop" at E-Stop or hitting Limit Switches, many good points were made.
For some of us, I'm sure the main thing we wish Mach3 could do is NOT to lose knowlege of its location, even after those errors. With steppers (without encoders) , this can't be done if the step pulses stop, because it is the step pulses that update the DROS position. That's why we like soft limits, feedhold instead of STOP, etc. With servos, there are encoders. If Mach3 tracked the encoders and updated the position DROS at all times, even after stop or E-stop, it would be easy ( in absolute mode) to reset, and continue without having to rehome at all. Unfortunately, it doesn't, so a "controlled" stop could retain the position in some cases, namely hitting the STOP button on screen. As for hitting limits, the soft limits already somewhat do the "soft stop at limits" being asked for. The slow zone could be reduced making the axis decelerate faster. The minimum stop time is limited by the step motor capability. Early CNC's did in fact have two sets of limit switches. First one stopped all movement but retained position. Second one killed power, applied brakes (especially on Z-Axis where gravity would bring a thousand pound head crashing down, etc.) More later..if you don't drum me out of the corps.
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You CAN have mach turn on Softlimits through a script I believe BUT softlimits CANNOT work UNTIL the machine has been referenced(;-). Even a modern High $$$ cnc has to follow the same process. Yes I know some have linier encoders that retain the position values(;-) Mucho Bucks compared to mach.
LOOK at Rogers encoder board I think the latest version can recover the lost position or at least has the potential to do so AS LONG as the power has not been lost. You can also do it with MACH brains and shaft/linier encoders. I know in the past we could using Macros and the brains.
Just a thought, (;-) TP
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I just dont get why so many people crave Mach not losing position if a limit is hit, it only takes a few xeconds to reference and you are guaranteed to be back to a point you and Mach know.
Everyone to their own I suppose :)
Hood
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I agree with you Hood :)
If you hit a limit then something went very wrong. It is only safe to assume that the machine has no idea where it is at. The only way to always know your starting back off with the machine in the right place is to re-home it.
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hi guys
i was just reading this topic and i always try to use the softlimits but i am retrofitting a big cnc lathe with mach3 turn and some how i canot config the soft limits settings
i am working with the machine and i am trying to understand the soft limits settings
do you guys use softlimits in mach3 turn?
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They dont work in Turn, supposed to be getting fixed but will be Rev 4 before they are done.
Rev4 of Mill will be first then maybe the poor relation (Turn) will get looked at after that.
Hood
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do you know when rev4 is coming out ?
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No one does, not even Brian.
Hood
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If you hit a limit then something went very wrong.
Hello,
That's one point of view. Other points of view I wanted to explain in this thread. Anyway, the first question was a "how"-question. So I can read between the lines that there is no chance to achieve this behaviour in the current version (e.g. by a script or something) and this would be a totally new feature to be requested to the programmer.
So there is a two step solution:
1st On my own machine I removed all limit switches.
2n Now it's on to convince the programmer that this feature is absolutely necessary for a future release.
Thank you for this discussion.
Nicolas
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Can you remind me why there is a need for this other than forgetting that you have not enabled softlimits?
I looked back and I see this as your reasons.
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.
1. That may well be true but surely that would be up to the machine builder to provide a remedy for this? Especially when you remember that a Hardware Limit is an emergency situation so hardware means should be used rather than relying on software.
2. Mach is open loop so there will always be the high possibility that you have lost position when stopping in an emergency situation (Hardware Limits or E-Stop) It is no big deal to re-reference again, in my opinion, in the rare instance that soft limits have not protected you.
3a. Operator error and could be overcome with some VB in the cycle start button or hiding or disabling or requesting a password on the softlimits button to stop an operator disabling the soft limits.
3b. Dont understand this, Hard Limits are placed at the extent of the axis so how would the working area come into play. Hard Limits are a per axis thing and turning them into a software limit operated by physical switches is not going to help as far as I can see.
3c. That is the job of the soft limits or the operators programming responsibility. High End CAM and very expensive controllers have work envelope, fixture and tool awareness features but are complicated to set up and really only worth it if doing long production runs I would think.
3d. Not sure what you mean by that, softlimits are there to do exactly what you are wanting and why they would be useless when working is not understood by me.
4. Again use soft limits and only rely on your Hardware Limits for emergency situations when, in the unlikely event, Soft Limits fail.
Just my opinions of course ;)
Hood
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Can you remind me why there is a need for this other than forgetting that you have not enabled softlimits?
I looked back and I see this as your reasons.
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.
1. That may well be true but surely that would be up to the machine builder to provide a remedy for this? Especially when you remember that a Hardware Limit is an emergency situation so hardware means should be used rather than relying on software.
-> Of course, it's possible to add a hardware that will provide a "soft stop" when clock is interrupted. This would be a special hardware for dealing with a missing software feature.
2. Mach is open loop so there will always be the high possibility that you have lost position when stopping in an emergency situation (Hardware Limits or E-Stop) It is no big deal to re-reference again, in my opinion, in the rare instance that soft limits have not protected you.
-> No, it's no big deal to re-reference for many machines and situations. For other situations, it cost's you some minutes to re-reference. So operators ponder whether to hit "stop". Instead of "first hit stop, then think about if it whether it was necessary". This costs you some split-seconds in every maybe dangerous situation. So it's a security gain to make effort for a restart after "stop" as comfortable as possible.
3a. Operator error and could be overcome with some VB in the cycle start button or hiding or disabling or requesting a password on the softlimits button to stop an operator disabling the soft limits.
-> Better not. Constraining operators should have a very good reason. So better find another solution.
3b. Dont understand this, Hard Limits are placed at the extent of the axis so how would the working area come into play. Hard Limits are a per axis thing and turning them into a software limit operated by physical switches is not going to help as far as I can see.
It's about soft limits. They are only one pair (min/max) per axis - so working area by soft limits is always a rectangle or a cuboid or some hypercuboid in higher dimensions for four to six axis systems. But if the mechanics do not allow the same extrema on each axis for every position or all other axes, soft limits will not work.
3c. That is the job of the soft limits or the operators programming responsibility. High End CAM and very expensive controllers have work envelope, fixture and tool awareness features but are complicated to set up and really only worth it if doing long production runs I would think.
Yes, of course. And on the other hand, moving limit switches is very fast and simple on some machines.
3d. Not sure what you mean by that, softlimits are there to do exactly what you are wanting and why they would be useless when working is not understood by me.
If soft limits always did that thing they should, you would not need any limit switches. Machines have limit switches, so there's need of them. (Friedrich Nietzsche would have good arguments against this opinion, but I'm quite sure he will not visit this board.)
4. Again use soft limits and only rely on your Hardware Limits for emergency situations when, in the unlikely event, Soft Limits fail.
As I said before: On many machines, limit switches told to Mach are no emergency situation. Limit switches for emergency situation are behind them and stop machine by hardware when Mach failed to stop machine.
Just my opinions of course ;)
Hood
Many greetings
Nicolas
[Edit: Removed some typos]
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Yes, of course. And on the other hand, moving limit switches is very fast and simple on some machines.
And moving limits around is a VERY silly thing to do. Limit switches are a last chance safety system. Moving them around allows for the possibility of driving past one which is an open invitation for disaster as now there is no last line of defense between the moving bits and a very nasty hard stop.
Limit switches are there to protect an axis from being driven beyond its possible travel. Soft limits are there to provide an early warning system. If you have need to provide some safety around a given work envelope then you talking about a different subject entirely.
In complex robotic systems each axis has its limits of rotation (1), there are fixed physical limits and you don't screw with them. You most often also describe a safe position (2) by moving the robot to a position considered safe where other moving fixtures will not contact it. You also define a work envelope (3) by move the robot to various positions within its work cell that describe the limit of how far it should move whilst in operation.
1) is a physical limitation of each axis, the same as what a limit switch protects on a typical CNC machine. It has absolutely nothing to do with #2, or #3
2) is a simple 'move each axis to this position' type of thing.
3) is much more complex because it involves complex kinematics calculations to make sure no part of the robot protrudes from the work envelope. As Hood mentioned before, this work envelope stuff is something typically taken care of by the CNC programming software as it can take things like fixtures and other limitations in considerations where most CNC controllers do not have the capabilities to do so.
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Limit switches are a last chance safety system.
Why must every limit switch be a last chance safety system?
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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
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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.
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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
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OK, let's make the question a bit more accurate:
"Why must the limit switch known by Mach be a last chance safety system?"
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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
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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.
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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
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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
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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 :) .
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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?
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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.
#1 WRONG, if you stop the pulses to the drive while it is enabled THAT is the fastest you can stop the axis period. You will have FULL dynamic braking
#2 IF you run a program that has NOT been tested for clearance SHAME on you. You need to fire the operator DON't blame the machine. The machine is basically dumb as a box of rocks. It can ONLY do as it has been told. The operator on the other hand is suppose to be intelligent.
#3 The only time i have seen Soft limits fail is IF they were not turned on OR they were turned off. Operator error
#3a Retrain or fire the operator. The "second" time he turned OFF a "safety" he would be fired so fast he would think he had a stroke
#3b It has nothing to do with the subject. Soft limits are there to protect your "part" in the event you really screw up and have not tested for proper clearances. Hard limits are there to protect the machine.
#3c (;-) I have never seen a machine that could GROW. They all have a physical limit to movement
#3d Makes no sense(;-)
4. WRONG again it won;t happen. Worse case IF you hit the axis hardstop wide open you ARE going to tear up the machine. Best case it has to be inspected and retested for accuraccy even for a light tap. AND IF the operator hid from me a light tap hardstop see #3a
Sport I have been around this industry a long long time. What you are asking for is something to REPLACE an incompenent OPERATOR. In the old days yes there were slowdown switches on machines. they simply dropped the feedrate down. AND that was ONLY because there was NOT enought CPU power to do otherwise. Today you have very powerfull CPU and PLC to do the job. AND they do a much better job than the old mechanical machines ever did.
Full 6 axis control (;-). Mach can move on 6 axis BUT does not have any kenimatics as to KNOW where it is. It is just a GOOD low co$t pulse generator. That is why you cannot JOG in full 6 axis mode.
Now what exactly are you expecting for $175 there are limitations.
NOW IF you need all those bells and whistles they can be had but BRING your checkbook full of $$$$$$$$ cause it is a little MORE than $175.
(;-) TP
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Now what exactly are you expecting for $175 there are limitations.
NOW IF you need all those bells and whistles they can be had but BRING your checkbook full of $$$$$$$$ cause it is a little MORE than $175.
Mach is a good software for a good price. How much must a software be overpriced to give a reason for suggesting improvements?
Sorry, I'm not that expert in software development ethics.
Greetings
Nicolas