Slow down before endstop?

sinned6915

@thekm the probe and type already have the functionality that you want built into it.

how is using what you already have to use of more complicated than a NEW G1 parameter?

cjm

@sinned6915 The suggestion of using a mode 1 Z-probe certainly sounds an interesting solution.

However, are we absolutely certain that it does give a controlled deceleration, rather than just forcing a stop like all the other Z-probe options?

I ask because this appears to be an undocumented feature, although I might well have misread the Duet dictionary!

theKM

@sinned6915 ...so, your less complicated solution is to set up the circuitry of the switches so that it emulates the analog output of an IR probe...

(pregnant pause)

...clearly we have different definitions of what "more complicated" means.

fcwilt

@sinned6915 said in Slow down before endstop?:

@thekm the probe and type already have the functionality that you want built into it.

I looked at the docs but I cannot figure out how to connect a given probe to a given axis.

This states a probe is to be used for the X axis:

M574 X2 S2

This configures a switch type probe:

M558 P5 C"io8.in" H300 F300 T300 R0.0 A1 S0.01
G1 P500 X0 Y0 Z0

But what connects the two?

Frederick

sinned6915

But what connects the two?

G38

fcwilt

@sinned6915 said in Slow down before endstop?:

But what connects the two?

G38

Thanks. I will give it a try.

But it is more complicated than just changing the behavior of an existing endstop.

Frederick

theKM

@sinned6915

...I see the two feedrates in 558 that I wasn't seeing before (nor someone nicely saying "you can provide both the fast and slower rates with 558")...

M558 F600:120

...so, voltage dividers to 1 or 2 volts on the first switch to emulate the initial analog, then send it high with the endstop?

...I guess I'll go play a little. Thanks for the help, generally appreciated.

sinned6915

@fcwilt said in Slow down before endstop?:

But it is more complicated than just changing the behavior of an existing endstop.

I dont see how a probing command is any more complicated than homing or controlled move command.

G38.2 K5 X0

sinned6915

@thekm that might work of you wire them in parallel, not sure of the voltage divider though. voltage dividers are 'dirty signals'. if the MCU tolerates it you might be ok.

you might have more consistent repeatability with an opamp instead of the voltage divider.

fcwilt

@sinned6915 said in Slow down before endstop?:

@fcwilt said in Slow down before endstop?:

But it is more complicated than just changing the behavior of an existing endstop.

I dont see how a probing command is any more complicated than homing or controlled move command.

G38.2 K5 X0

Assume. The endstops of the kind discussed previously are in place and working. The new goal is to have the first movement slow to a stop, the last stop immediately as done now.

; as done now for a Xmax endstop
G91
G1 H1 Xmax Ffast
G1 X-25
G1 H1 X30 Fslow

; with new parameter
G91
G1 H5 Xmax Ffast
G1 X-25
G1 H1 X30 Fslow

theKM

@fcwilt ...with an extra line to change the endstop switches from the proximity to the endstop?

fcwilt

@thekm said in Slow down before endstop?:

@fcwilt ...with an extra line to change the endstop switches from the proximity to the endstop?

Sorry but I don't understand what you are saying.

Frederick

theKM

@fcwilt there's two switches, so it's not just two lines of G1 at different rates, as it needs to change from the switch indicating it's close, to the endstop switch.

fcwilt

@thekm said in Slow down before endstop?:

@fcwilt there's two switches, so it's not just two lines of G1 at different rates, as it needs to change from the switch indicating it's close, to the endstop switch.

Depending on the breaking distance there may not be a need for two switches.

My IR beam break endstop sensors are positioned some 25mm away from the end of the axis. The part that breaks the beam will keep the beam broken all the way to the end of the axis.

So it would provide 25mm to slow to a stop. If 25mm was not enough I could move them and print a new part that breaks the beam to handle the longer distance.

Frederick

theKM

@fcwilt there's a move that's interrupted by the IR beam breaking, how does it change to using a different interrupt on the second move when it hits the endstop?... G1 is "move until trigger", doesn't something have to change to let the second G1 stop on something different than the first G1?... the little backup on my machine would be much less than the distance needed to decelerate, and would still be true.

fcwilt

@thekm said in Slow down before endstop?:

@fcwilt there's a move that's interrupted by the IR beam breaking, how does it change to using a different interrupt on the second move when it hits the endstop?... G1 is "move until trigger", doesn't something have to change to let the second G1 stop on something different than the first G1?... the little backup on my machine would be much less than the distance needed to decelerate, and would still be true.

The proposed H5 parameter would work that same as H1, H3 and H4 - terminating the move.

The only difference is that H5 would respect the M204 setting (acceleration) as opposed to the immediate stop of H1, H3 and H4.

Clearly the "backup" move needs to move enough so the sensor is no longer triggered. Perhaps I should have pointed that out.

Frederick

theKM

@fcwilt ...always fascinates me how geeks typing to each other can be such a struggle

My machine wouldn't be backing up at all... it would pass the proximity switches, slow down, stop, then disable the proximity switches change to use the actual endstop switches for the second move. This way the endstop switches will still work as endstop switches, and the proximity switches in use for this procedure as needed.

fcwilt

@thekm said in Slow down before endstop?:

@fcwilt ...always fascinates me how geeks typing to each other can be such a struggle

My machine wouldn't be backing up at all... it would pass the proximity switches, slow down, stop, then disable the proximity switches change to use the actual endstop switches for the second move. This way the endstop switches will still work as endstop switches, and the proximity switches in use for this procedure as needed.

That is certainly one way to do it if you don't mind having two sensors instead of one. It would save a small amount of time by adding the additional hardware and wiring.

Is there a particular reason why you want to avoid the backup?

Frederick

theKM

@fcwilt ...it's not the backup, just that using only one trigger would reduce the effective working area, and no longer are the estops representing the absolute max of travel.

Once there was such a feature I could measure the deceleration distance... if it's small enough single switch would be fine.

fcwilt

@thekm said in Slow down before endstop?:

@fcwilt ...it's not the backup, just that using only one trigger would reduce the effective working area

Then I did a rotten job of explaining.

Having a endstop sensor some distance away from the end of the axis doesn't have to result in a change to the working area.

Homing is simply a means of the firmware determining where things are. The fact the a G1 H1 move sets the position to the min/max value in M208 is a not an issue.

Let's say my X axis min/max are 0 and 300. And that the sensor is at 275.

So I do a normal G1 H1 move and it stops at 275 but the logical position is set to 300 because of the M208 settings. All I have to do is include a G92 275 after the last G1 H1 and now the logical position matches the physical position.

And movement to 300 is retained.

It is required that the endstop activation is done in such a way that it remains activated from, in this case, 275 to 300. This is usually easily done.

In my case of using IR beam break sensors I simply make the moving part that breaks the beam long enough that it keeps the beam broken until the end of travel.

Frederick