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Author Topic: "Goto Zero" getting Soft Limits Error  (Read 880 times)

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"Goto Zero" getting Soft Limits Error
« on: May 10, 2018, 08:43:35 PM »
Hello Everyone!  Smiley  This is my first post. Hate to be so short, but I'm in the middle of a Project and the issue I'm having has brought me to a Halt!

Problem: I can manually move the spindle to an area with the "Soft Limits" ON with no problems! However, as soon as I press the "Goto Zero" button the spindle will head to that area and when it gets close the machine will stop! Mach 3 will give me a "Soft Limits exceeded" error. I can then still manually move the spindle past that area once again no problem. There are NO Limit Switches of any kind on this machine!


Hopefully Someone out there has had this issue before! All Help is Greatly Appreciated! Thank You  Smiley
Re: "Goto Zero" getting Soft Limits Error
« Reply #1 on: May 10, 2018, 10:33:42 PM »
Hi,
soft limits have nothing to do with limit switches. They are a programmable way of doing the same thing.
On the screen there should be a button 'Soft Limits'. Find it, hit it, and now soft limits should be disabled.
If you crash its your own fault. Ideally you would have home switches which allow you to usefully employ softlimits
which are a boon to the CNCer.

Craig
My wife left with my best friend...
     and I miss him!
Re: "Goto Zero" getting Soft Limits Error
« Reply #2 on: May 11, 2018, 04:38:08 AM »
Hi,
just under the DRO block.

Craig
My wife left with my best friend...
     and I miss him!
Re: "Goto Zero" getting Soft Limits Error
« Reply #3 on: May 11, 2018, 10:21:59 AM »
Yes I know where the button is. I set my "ZERO" (soft limits ON) then when I move the machine away and then click "Goto Zero" the machine heads towards my "ZERO" point and when it gets close, it stops and and gives me a "Soft Limits Exceeded" error. At that time, i can still move the machine with the "Soft Limits" on over to my "ZERO".

Why am I getting a soft limits error? I am still able to move the machine to the boundaries set in my homing/limit tab which are "PAST" where the machine stops and says I exceeded.

If my "Zero" was past the "REF ALL HOME" would it cause this?

Offline TPS

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Re: "Goto Zero" getting Soft Limits Error
« Reply #4 on: May 11, 2018, 11:33:44 AM »
Soft limits act like limit switches the only difference is, that they are defined in software (Mach3) and don’t need actual switches. It is recommended that you have homing switches properly setup before you configure the soft limits. The soft limits will only work if the machine is properly initialized (homing procedure is completed) and limits are defined.

Homing and Zeroing is a big differnce.
anything is possible, just try it.
if you find some mistakes, in my bad bavarian english,they are yours.
Re: "Goto Zero" getting Soft Limits Error
« Reply #5 on: May 11, 2018, 05:27:34 PM »
Hi,
if you do not have home switches or have some other means of referencing your machine Soft Limits are useless, in fact as you've discovered worse than useless, they keep faulting.

As Thomas says 'Zeroing' is different to 'Referencing'. Note that most people use 'Homing' interchangeably with 'Referencing'. 'Homing has a number of connotations which increases confusion
so 'Referencing' is preferred.

Without referencing your machine you have to turn 'Soft Limits' off as I've showed you.

Craig
My wife left with my best friend...
     and I miss him!
Re: "Goto Zero" getting Soft Limits Error
« Reply #6 on: June 06, 2018, 02:56:42 AM »
You may have a tool offset trying to push beyond the work envelope of the machine.
Re: "Goto Zero" getting Soft Limits Error
« Reply #7 on: June 06, 2018, 03:30:48 AM »
Hi,
that may be happening also but the basic problem it without accurate and repeatable referencing SoftLimits are useless.

Question: 'When Mach is first powered up how does it know where the machine is?'
Answer: 'It doesn't know where the machine is'.
Explanation: Mach is an OPEN LOOP controller. It has no real facility to accept feedback from the machine as to where it is and even if it were to be pressed that way
our machines DO NOT HAVE ABSOLUTE ENCODERS. Such things are available but they are rare and expensive well beyond the means of hobbyists.

Say you have boundaries programmed into the Soft Limits page, your machine has 1m travel in X and 1,2m travel in Y. It might be reasonable to have the X- softlimit = -500mm
and the X+ softlimit=500mm, the Y- softlimt= -600mm and the Y+ softlimit=600mm.

When you turn your machine on if it were perfectly centered on the table the SoftLimits would be fine, Mach would know that the X+ boundary is 500mm to the right and the X- boundary 500mm to the left.
What happens however when you turn your machine on and its not in the center, lets say its 200mm to the right of center. If Mach assumed that the boundary is X+ is 500mm to the right
your about to crash because you started not in the center but somewhere else and the soft limit data is correct if Mach starts in the center only.

This is the secret to how SoftLimits  work, the boundary data is relative to a particular point and at the beginning of each session you must jog to that location and tell Mach, 'This is the sweet spot,
all the boundaries are relative to this location'. Mach is very good about tracking where it is ONCE you've told it where it started from and it can keep in mind where the boundaries are IF AND ONLY IF
it knows where it started from. This is the reason for home switches, and good, accurate home switches are worth their weight in gold.

Craig
My wife left with my best friend...
     and I miss him!