Poll Question - Should Limit switches be hard stop.

[patchlead]

I have a question for the general.

My option of limit switches are, They are there for safety, and if you have hit them it is a problem. Because of this belief, I think the steppers should be told to stop, without any deceleration settings, just hard stop. gentle stops are for the soft limits set in the codes, and located on the homing function. So really you should never need the hard limits, unless the steppers have lost sync, and then there is bigger issues.

So, question is -

1. Hard limit switches should cause the cnc to stop all movement instantly. My cause the system to jerk, but at least it will not over run the switches
   
2. Hard limit switches should work like the soft limits, and bring the cnc to a stop gradually using the XYZ deceleration values. This will stop any sudden jerks to the cnc, but may run through the limit switch and into the bed or walls.
   

and yes this is a loaded question. I would like the hard limit to cause the steppers to jerk stop.

 

[psyko62]

Loaded Question much??

My vote goes with 1)

You have already moved past the soft stop, if you reach a hard stop limit switch you are somewhere you shouldn't be and all motion should immediately stop, equal to that big red button being hit.

 

[patchlead]

The big red button question is one on the next questions on my list ?

Just aiming for gentle movement towards a better masso future, without things hitting others lol

 

[gmarsh1]

My vote is for #1

The whole reason for 'limits' is to prevent doing serious damage to the machine. When a limit switch is hit, you want everything to stop as quickly as possible, including the spindle.

The purpose for the E-Stop (big red switch) is so when you're machine starts to cut and & it's plunging down a full inch deep when you expected a .01" depth of cut .. You can shut it down quickly yourself rather than let it get all the way to one of the limits and not only ruin your part but likely break an end mill & quite possibly put a very nice reminder of your mistake permanently on your vise.

Been there, done that!

 

[masso-support]

Yes option 1 is the right way to go, also you want to make sure this is not done in such a way that it is dependant on the software to stop because a software issue can mean that the motion is not stopped.

Its better to run the drive enable signal via switch/switches on the axis and this will guarantee that the axis is stopped when triggered.

 

[patchlead]

Great, of my highly loaded world wide survey, 100% agree.



Can we change the limit switch input to hard stop in the masso control software please master masso? (Or is the alpha software the only one that stops "softly")

??

 

[patchlead]

Latest software loaded (3.29.2a), and still MASO will not stop with the ESTOP or hard limit switchs!! I understand your comment about disabling the drivers external to the Software. I have this connected to Estop buttons as well. That's not the point of this issue.

The Software also needs to act safely. On E stop, the program needs to stop! Not just finish what it is doing. This is also an issue with Hard limit switches. The hard limit inputs do not stop the motion, just send a command to decelerate to stop. This is what soft limits are fore not hard limits!

 

[patchlead]

I triple checked the hard limits on the new version. They do work if activated during G0 or g1 commands. They do not stop instantly while jogging the head manually. It needs to stop without deceleration during Manual movement, just the same as during running code...

 

[masso-support]

• Even on hard limits the motion de-accelerate is applied, this is done because if you are running a heavy machine, putting a sudden stop on the motors can put a lot of load on the axis and damage something.
  
• Soft limits are used to make sure that all given motion commands are within your min and max axis travels and alarm if the motion is outside the range.
  
• Hard limits are supposed to be never reached, these are just as a second safety that for some reason the axis over travels then its stopped by the hard limits.
  

 

[patchlead]

Exactly, hard limits should never be hit, unless there is an issue (line stepper motor slip)! So then, even if there is a heavy machine, it should try to stop as quick as possible and not run into the physical end stop or try to kill something.

There is a reason you have a stop code input, AND Estop.. Estop is something is wrong, STOP NOW@! Please if people want a nice stop, don't use the Estop, use the other stop methods.

If you hit the hard limits or estop, it needs to stop. Soft limits and stop inputs are for gentle stops. Hard limits and Emergency Stops are for stop NOW...

Or if people want gentle stops in emergencies (hard limit, error input or Estop), have a extra acceleration setting for these types of stops, so to can have your gentle stops for people who use Estops for general use, and the rest can set it to 10000000 to stop now.

 

[masso-support]

Yes your points are valid, its just that different users have different opinion. It will be good to see what others say about this.

1. Also I think you have not wired the enable signals of the drives to the estops, if enable is wired to estop then drives will be disabled and motor will stop much faster and this will provide second safety.
   
2. Its also worth nothing that we prefer that the hard limits on both sides are not wired to MASSO and in fact wired to the enable signal of the drives, the same signal can also be wired back to the MASSO axis alarms so that when triggered MASSO will stop everything and show a message on the screen telling you which motor caused it.
   

 

[patchlead]

The problem with disabling the stepper drivers over stopping to send steps is; By disabling the steppers you disable the dynamic breaking ability of the motors and so it will not be able to stop as fast. It will just coast to a stop. Which is fine of a smaller or lighter router.

I will look at taking the hard limit control away form the MASSO, but this will require an external control system (because the above reason) for my setup, which seems silly when MASSO has more than enough power and inputs.

 

[masso-support]

So basically you need the motors to stop without ramping? maybe we can add an option in the settings to enable/disable ramping on hard limits and users can set as per their requirments.

 

[patchlead]

Yes stop without ramping.

Currently the software stops "without ramping" on a hard limit activation, which is great; But only while running g-code. It needs to do this while jogging also. E-stop as the name suggests, should stop without ramping also (on both G-code and Jogging)

 

[masso-support]

Ok, will try to add this feature in the next few days.

 

[irakandjii]

Was this feature implemented?

I too want the machine to come to an abrupt stop if a limit switch is hit. I consider limit switches to be safety devices.

Whilst, homing switches are operational devices, their purpose is fundamentally different.

In business terms, I save time and effort with homing. I avoid lawsuits with limit switches.

As a specific example, limit switches on a lathe that prevent a collision between the cutting tool (or cross bed) and the chuck. Sleepy moment on a pendent?