Soft Limit Setup

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28 May 2024 00:30 #301627 by Project_Hopeless
I'm working with a sim at present prepping for the real machine.  If I jog into a limit the sim/machine faults and I cannot reverse direction to get out of the limit.

Is there a way to setup soft limits so the machine stops motion at the limit, doesn't fault, and can still reverse motion without needing to disable limits or re-home?

 

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28 May 2024 00:37 #301628 by pippin88
Replied by pippin88 on topic Soft Limit Setup
Limit switches should never be hit in normal function and will only occur because of a fault (in a properly configured setup).

I don't believe a function to not fault when limits triggered exists (nor should it)

There is the maximum physical travel of the machine (usually with limit switches close to either end of this).
Then there are the 'soft limits'/ axis travel defined in your ini file.

E.g. real max physicial travel 320mm.
Limit switches 5mm from either end = 310mm between limit switches
Axis travel 300mm
Then you need to tell LinuxCNC where the axis is (in relation to the actual allowable physical travel / limits)
Usually done with a home switch inside limits, or using on limit switch as home+limit

If axis not homed correctly, then you can end up hitting limits

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28 May 2024 01:02 #301629 by cmorley
Replied by cmorley on topic Soft Limit Setup
Did you home the machine?
There is usually a button to 'override limits' to back away off the limit switches.

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28 May 2024 01:18 #301630 by Project_Hopeless
Replied by Project_Hopeless on topic Soft Limit Setup
There are no limit switches, I'm in Sim mode presently.  So over travel should not be possible. 

So isn't the Min_Limit and Max_Limit the travel limits, and not fault limits?

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28 May 2024 01:19 #301631 by tommylight
Replied by tommylight on topic Soft Limit Setup
I just tested Axis sim mm, it does not exceed limits, so how are you able to exceed them?

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28 May 2024 02:24 #301636 by cmorley
Replied by cmorley on topic Soft Limit Setup
Please answer the questions explicitly.
Did you home the machine?

You don't need home switches or limits switches or a real machine to home the machine.
Homing sets the reference for the machine origin which sets the soft limits.

If you didn't home - the machine doesn't know where it is.

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28 May 2024 12:23 - 28 May 2024 12:58 #301669 by Aciera
Replied by Aciera on topic Soft Limit Setup
If this for your robot and you are using custom kinematics/ switchable kinematics you will need to switch the axis limits from cartesian to joint when switching from 'World' to 'Joint' mode (and the other way around).
For an example have a look at the 'millturn' sim config.
M428/M429 will call 'M128/M129' respectively which is where the axis limits are switched between the two sets defined in the ini.

[edit]
Here is the melfa-sim config with axis limit switching added:
 

File Attachment:

File Name: melfa-sim.tar.gz
File Size:34 KB
Attachments:
Last edit: 28 May 2024 12:58 by Aciera.
The following user(s) said Thank You: Project_Hopeless, DPFlex

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28 May 2024 13:03 #301672 by Aciera
Replied by Aciera on topic Soft Limit Setup
Note that when jogging in WORLD mode you will still be able to jog into the joint limits. That is a limitation of the current state of linuxcnc.
The following user(s) said Thank You: DPFlex

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29 May 2024 00:29 #301711 by Project_Hopeless
Replied by Project_Hopeless on topic Soft Limit Setup

Aciera post=301669 userid=25994If this for your robot and you are using custom kinematics/ switchable kinematics you will need to switch the axis limits from cartesian to joint when switching from 'World' to 'Joint' mode (and the other way around).
 

Yes exactly, my 5-DOF robot.

I reset the robot, Home the robot, select World jog mode.  Then if I jog into a limit I can't back out without disabling the axis limits or re-homing the arm. 

All axis are rotary joints, so I thought when any individual joint approaches its limit it would soft stop.  I really only need axis limits not Cartesian for a maximum usable envelope.

 

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29 May 2024 00:57 #301713 by Project_Hopeless
Replied by Project_Hopeless on topic Soft Limit Setup

[edit]
Here is the melfa-sim config with axis limit switching added:
 

File Attachment:

File Name: melfa-sim.tar.gz
File Size:34 KB

 

Thanks for the example.  It will take me a while to grasp how this works.

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