MDI Commands and Soft Limits

[hkinkade]

Today I mistakenly enetered a MDI command - G0 G54 x0 y0 z1 - the machine moved to the commanded postion, which for z was past a soft limit. I have Z zero set to the top of the travel just below the soft limit switch. Of course I mistakenly set Z to a positive vs negative number, which drove the z axis up AND past the soft limit. Why is this? I assumed soft limits would protect against this mistake. I was able to repeat this with safe excursion past the soft limit to confirm this behavior.

The machine is a three axis router, Mach 3 control, Pokeys57 machine controller board.

 

[Mtndew]

Some machines will overtravel if commanded to while inside of the soft limit zone.
If you're way outside of the zone and command that same move, it would hit the soft limit instead of the hard limit.

 

[hkinkade]

Mtndew, thank you

OK I moved to G54, then moved my Z well below the soft limit by jogging. Then used the MDI command - G0 G54 X0 Y0 Z.2 - it again moved past the soft limit. I couldn't manually jog any higher, but could jog outside (lower) the soft limit. Any more ideas? When below the soft limit I can't manually jog past it.

 

[Mtndew]

Mtndew, thank you

OK I moved to G54, then moved my Z well below the soft limit by jogging. Then used the MDI command - G0 G54 X0 Y0 Z.2 - it again moved past the soft limit. I couldn't manually jog any higher, but could jog outside (lower) the soft limit. Any more ideas? When below the soft limit I can't manually jog past it.

Are you just trying to send the machine to the soft limits without overtravelling?
If so , then try G91G28X0Y0Z0.
Be sure to command a G90 on the next line though.

 

[sinha]

I do not know about your control, but some overshoot beyond the soft limit happens on Fanuc also.There is typically an overrun of F/7500 mm at the prohibited boundary, before the tool stops (F is the current feedrate of the tool in mm/min). If this is unacceptable, set parameter 1300#7 = 1 which suppresses the overrun, forcing the tool to stop on or before reaching the boundary.
There might be a similar parameter on your control.

 

[hkinkade]

I'm going to try to see if this happens at other boundaries (X/Y). I don't think it's a small overrun. I think it's not seeing the STOP sign at all. I'll let everyone know what happens at the other limits, as I have more room to run before the machine hits the brick wall :-/

 

[hkinkade]

I have confirmed all soft limits (XYZ) are ignored when using MDI commands. When jogging soft limits work, G-code programs are limited, but not MDI commands. After the gantry goes past a soft limit jogging won't go deeper into the limit, but I can jog out of the soft limit towards the safe area. Anyone with any ideas why this is happening. I'm not a fan of miss typing a command and end up crashing the gantry ;-/

 

[sinha]

Reading the posts of various users, I have come to the conclusion that MDI behavior might be different from memory-mode (AUTO) behavior, in some cases. This can be an MTB thing, and may not be parameter-controlled. You may need to ask your MTB.

 

[604Pook]

I have confirmed all soft limits (XYZ) are ignored when using MDI commands. When jogging soft limits work, G-code programs are limited, but not MDI commands. After the gantry goes past a soft limit jogging won't go deeper into the limit, but I can jog out of the soft limit towards the safe area. Anyone with any ideas why this is happening. I'm not a fan of miss typing a command and end up crashing the gantry ;-/

Pretty sure this is also the case on our CrOnsrud wood router with Fanuc control. Jogging it won't go past the limits, MDI it can a little ways. For tool changes it ignores it completely and goes way outside of what the soft limits are for jogging. You can jog out of the soft limit, but not further into it.

 

[hkinkade]

Reading the posts of various users, I have come to the conclusion that MDI behavior might be different from memory-mode (AUTO) behavior, in some cases. This can be an MTB thing, and may not be parameter-controlled. You may need to ask your MTB.

I'm sorry what is MTB?

 

[sinha]

Machine Tool Builder who manufactured the machine.