FEED HOLD (Stop Motion)

[Techman2930]

Hi All, I'm a 40+yr vet of developing hardware and software for automated equipment, CNC, Pick&Place, Etc. Lately I have been purchasing Duet PCAs with RepRap Firmware loaded for motion control applications.

The Only thing I can't find that I need on every application is an equivalent to "FEED HOLD". What I mean by feed hold is, during any movement pressing feed hold decelerates all motion in a coordinated fashion. leaving the spindle going. when a continue button (sometimes the same feed hold button) is the machine Accelerates in a coordinated fashion from where it left off.

I do realize all of this was originally designed for printing but these controllers are proliferating into many other applications.

As far as I have observed this function is a hardware feature of CNC equipment. I do not know of a G or M code for this function

How can I accomplish this? I can't be the only one needing to pause motion.
Perhaps using an I/O bit and an addition to the firmware.

[dc42]

RRF 3.3 (the latest stable release) supports something close to feed hold already. You just need to enable segmentation in the M669 command. You can use segmentation to break up long moves into a sequence of shorter moves, for example 1mm long. You can then pause the print between segment boundaries, provided that the feed speed is no greater than the maximum configured jerk - which is likely to be the case in CNC applications. The stop will be sudden rather than smooth, but as the speed is less than the jerk limit there will be no loss of position, if you have set the jerk limit correctly.

In release 3.4 (under development) we intend to provide more pause options, so that you will be able to define a feed-hold type of pause that is different from a normal pause.

Feed hold (and other applications of instant pause) at any speed with smooth deceleration is planned for release 3.5 or later.

[lee7670]

@dc42 is there more detail on how segmentation works? If I pause mid move with segmentation on, move a motor, G92 a couple axes and then resume, will it resume mid segment?

[tom33]

Hi @dc42 any news about this subject ?

Thanks !

[T3P3Tony]

@lee7670 said in FEED HOLD (Stop Motion):

@dc42 is there more detail on how segmentation works? If I pause mid move with segmentation on, move a motor, G92 a couple axes and then resume, will it resume mid segment?

The pause happens on segment boundaries, not on move boundaries so that's the advantage of segmenting the moves. The interaction with G92 is an interesting question, will need to ask @dc42 about that.

[rjenkinsgb]

Feed hold is an interesting addition, especially for CNC use.

With that in mind, for machining a separate "spindle hold" is also useful - however than needs to be interlocked with feed hold, so the spindle cannot be stopped until the feed it stopped, and vice versa the spindle must be started before (and with a delay or "at speed" signal) before the feed hold can be released.

If the spindle is not controlled by the Duet board, then just a three position switch so feed hold must be set before reaching spindle hold is a simple alternative.

For 3D printing, an option stop at the end of the current layer could be useful, so the head can be moved out of the way to inspect the job or replace filament without the hotend being close enough to the piece to block the view or cause distortion??

(Just throwing suggestions in, while the subject of temporary stops is on peoples minds).