Maybe an obscure bug

[AMDlloydsp]

I'm training some new folks, teaching them to set up the tool offsets for a new batch of tooling. Because they often make mistakes, I have them "sneaking up" on each new tool's plunge to the clearance plane by turning down the feed rate override until they can verify that the cutter is the correct distance above the stock surface.

I have one fellow who 'twiddles' the feedrate, rather than just turning it down really low. If he repeatedly drops the rate to zero then turns it up to about 20% (I don't know, maybe two to four times), the job will often lock up in a 'pause' state (just as if the knob were all the way to zero), where it appears to be running just fine, but will never move the axes again. Doing a feed hold or a tool check will not restore this state again -- only starting the job over works.

It sort of feels - to an old-school programmer - like he's overwhelming an interrupt routine which never again sees the change in the rate knob.

???
Thanks,
Lloyd

[diycncscott]

Lloyd,

"Pause" sounds like a feedhold condition. Parameter 146 defines the level of the feedrate override % at which the control is put into feedhold. If the override is turned down to that point, or below, the control is put into feedhold.

If he presses Cycle Start does it resume?

[AMDlloydsp]

Scott, thanks.

No, it's not a feed hold pause due to getting the knob below the hold threshold. Many times, the trainees will stop the feed with the feedrate knob in order to guestimate the distance from the stock. This is the only guy who 'twitches' the knob. The others move smoothly to a low rate, then stop when they want.

Once stopped by these multiple excursions above and below the pause threshold, advancing the knob back to a positive value won't restore motion, nor will pressing Cycle Start. FWIW, the feed hold light does not come on.

I've tried this, wanting to make sure he wasn't misinterpreting the condition, and I, too, can make it fail if I really joggle the feed override up and down below and above the feed hold threshold. Once 'stuck', nothing.... not even a tool check will free it up again; nothing except stopping the job and restarting.

I think this is not a situation a 'normal' user would challenge often, if at all. My programming background says, "missed interrupt, never cleared", but since I know nothing of your code, that's a pretty broad assumption. <G>

Lloyd

[cncsnw]

This is a known issue, related to allowing the override to go to 0%.

The fix is to use a newer PLC program, which prohibits the override from going below 1%, and which supports Parameter 146 as a Feed Hold threshold. Then set P146 = 3, so turning the override down to 2% or 1% will activate Feed Hold.

[AMDlloydsp]

I have that fix, so far as I know (have to check, but I have a pretty new unit). I turn down the speed knob any time I want until motion entirely stops, and "Feed Hold" is displayed. Then I can neatly run it back up from there. Never a problem until this guy showed me 'how'.

This ONLY happens when you repeatedly jog the knob up and down to zero.

LLoyd

[cncsnw]

A fixed PLC program would not allow the override percentage to go down to 0%. It would stop at 1%.

For example, the attached is a corrected allin1dc-basic program for mills. See the references to the constant "MIN_FROR_PCT".