M191 not waiting as expected

SpoonUnit

Thanks for the input. To add, I use this at the start of the file to await heating, rather than cooling.

; Wait for bed thermistor (chamber P0) to report reasonable temp
M191 P0 R70
; Ignore thermistor now
M141 P0 S0

; Home
M98 P"homeall.g"

This does work. The job waits at M191 until the chamber reports 69 degrees and then moves forward. That's why I don't understand it not working correctly at the end of the file.

SpoonUnit

Now attempting to narrow down the problem, I have created the following separate GCODE test file:

; Home
M98 P"homeall.g"
; Measure Mesh
G29

T0
G0 Z10

G0 X150 Y100
M140 S50
M191 P0 R40

G0 X150 Y0
M140 S30
M191 P0 R30

G0 X150 Y100
M140 S50
M191 P0 R40

G0 X150 Y0
M140 S30
M191 P0 R30

G0 X150 Y100
M140 S50
M191 P0 R40

G0 X150 Y0
M140 S30
M191 P0 R30

T-1

The behaviour I observe is

Homing
Mesh Measurement
Tool collection
Move to bed center
Pause for chamber temp to be reached
Repeated moves back and forth after temp reached
Tool docked

The behaviour I expect is

Homing
Mesh Measurement
Tool collection
Move to bed center
Pause for chamber temp to be reached
Move to second position
Pause for temperature to be lowered
Move to first position
Pause for temperature to be reached
Repeat
Dock

What am I doing wrong that this works once and then not subsequently?

SpoonUnit

OK - I just spotted this on M190 documentation:

Note: M190 will not wait for temperatures below 40c because in many cases they may never be reached due to ambient temps. So if you want to wait for a bed to cool, use 41c or higher.

This isn't specified for M191, but I'm going to assume it's the same limit. If I'm working in Antarctica, or space, perhaps lower ambient temps are perfectly reasonable to expect. Will verify if this impacts M191 also. In my case, I'm trying to wait for a print to detach fully from the heated bed, which is coated with PEI. I find this happens around 35 degrees. If M191 will not permit me to wait for lower than 41 I'll be forced to insert a blind pause to accommodate the extra wait. Ambient bed temp when the bed isn't heated is current 23C, which is far lower than 40.

SpoonUnit

Verified.

This works as expected:

; Home
M98 P"homeall.g"
; Measure Mesh
G29

T0
G0 Z10

G0 X150 Y100
M140 S60
M191 P0 R45

G0 X150 Y0
M140 S41
M191 P0 R41

G0 X150 Y100
M140 S60
M191 P0 R45

G0 X150 Y0
M140 S41
M191 P0 R41

G0 X150 Y100
M140 S60
M191 P0 R45

G0 X150 Y0
M140 S41
M191 P0 R41

T-1

M191 should reflect this limit of 41. Would be nice to be able to specify this, perhaps in the same breath as we can specify the max limit using M143.

deckingman

@SpoonUnit I thought maybe you could use M116 instead of M191 https://duet3d.dozuki.com/Wiki/Gcode#Section_M116_Wait

But when I checked the wiki, I see it has the same comments about temperatures<= 40.

I guess the firmware developers are between a rock and hard place with this because if they changed the limit to be say 35, then they would no doubt get complaints from people who live in warmer climes with M191 waiting forever and never reaching (cooling down) to the set point because the ambient is (say) 38.

SpoonUnit

@deckingman It's fair to say that you can't please all the people all of the time :). 41 seems like a strange default, but there it is. It would be nice to be able to configure it though. At present, I now have a wait to 41 followed by a 5 minute blind pause, and that works just fine for now.

SpoonUnit

@dc42 is there any chance to permit configuration of this bottom limit of 41 described above? While it might be a sensible default, individual users may decide it doesn't work for them.

My blind wait of 5 mins today was not good enough due to the UK heat wave. As such, after 5 mins, the chamber temp had not got to 36 and my PETG item had not released from the bed. There was an almighty PING when the sweep finally applied enough pressure to release the item and it shot across the room. A blind wait of 10 mins might work, or maybe 15, but the neater answer would be able to simply put M191 P0 R36. Sadly all values of R below 41 result in the command returning instantly with no error.

dc42

@spoonunit I agree that the documentation should be updated. Also it would be a good idea to generate a warning message if the requested temperature is below 40C.

However, if you really want to wait for a heater to reach temperatures below 40C and you are sure that the ambient temperature is low enough for this to be possible, then you can call a macro containing a while-loop to achieve this. If we change the code to always respect the requested temperature, I think that will increase the load on our support engineers.

SpoonUnit

@dc42 Macro !. Brilliant. Thanks. I'd started looking at the code and was thinking of recompiling, but this will be much quicker. Cheers.

SpoonUnit

@spoonunit For anyone else having a similar requirement, this can be inserted into GCODE

M98 P"0:/macros/waitForChamberTemp" A36

Where param A with a value of 36 is the temperature you wish to wait for.

Now create this macro:

waitForChamberTemp

echo "starting"
while true
	if heat.heaters[6].current < param.A
                G4 S30 ; wait 30 seconds until next reading
		break
echo "bed temp reached"

Note: Check the object model for your version so ensure the exact coordinates of the heater you're interested in as they have been known to move around. The above example works with RRF 3.3beta2.