[SOLVED] Heated bed PID auto tune failed.

dc42 · 26 Aug 2018, 18:51

The problem is that the measured dead time is negative. I suggest you use the gain and time constant values given by auto tuning, but measure the dead time manually. It is approximately the time between turning the heater on and seeing the temperature start to rise significantly. It's typically 2 seconds for a hot end, somewhat more for a bed heater.

vapvap · 30 Aug 2018, 23:06

Sorry, but I'm new to these settings.
Could you show an example of such a code command?
I'm afraid that without you I will not deal with this.

dc42 · 31 Aug 2018, 07:25

Your tuning run reported:

G=118.2, tc=794.1, td=-0.6

So the M307 command you need based on these values would be:

M308 H0 A118.2 C794.1 D-0.6

However, the dead time can't be negative. So measure the time it takes from turning the bed heater on to the indicated temperature starting to rise. For example, if it is 4 seconds, use:

M308 H0 A118.2 C794.1 D4.0

I have it on my work list to improve the measurement of dead time during auto tuning.

HTH David

deckingman · 31 Aug 2018, 07:37

@dc42 said in Heated bed PID auto tune failed.:

I have it on my work list to improve the measurement of dead time during auto tuning.

I've always struggled in that respect with my big thick lump of aluminium tooling plate and have to manually change the auto tune value. No big deal as it's not something that needs to be done often, but it would be nice to see that improved if it's possible.

dc42 · 31 Aug 2018, 07:42

@deckingman said in Heated bed PID auto tune failed.:

@dc42 said in Heated bed PID auto tune failed.:

I have it on my work list to improve the measurement of dead time during auto tuning.

I've always struggled in that respect with my big thick lump of aluminium tooling plate and have to manually change the auto tune value. No big deal as it's not something that needs to be done often, but it would be nice to see that improved if it's possible.

Can you tell me what value auto tuning reports, what happens if you use that value, and what value you actually use to get good results?

deckingman · 31 Aug 2018, 09:43

@dc42 said in Heated bed PID auto tune failed.:

@deckingman said in Heated bed PID auto tune failed.:

@dc42 said in Heated bed PID auto tune failed.:

I have it on my work list to improve the measurement of dead time during auto tuning.

I've always struggled in that respect with my big thick lump of aluminium tooling plate and have to manually change the auto tune value. No big deal as it's not something that needs to be done often, but it would be nice to see that improved if it's possible.

Can you tell me what value auto tuning reports, what happens if you use that value, and what value you actually use to get good results?

Now you've got me. I made a note in my config of the date I last ran auto tune and it was 17-08-2017, so over a year ago. Thinking about it, (and my memory is a bit hazy) I seem to remember that prior to that time, I really struggled to get a successful tune, but you made some changes which fixed the problem that I had - it was something to do with the check it makes after the heater turns off (can't remember what that check is). So now that I think about, you may have fixed the dead time issue too.

I'll run another auto tune when I get chance - bed is hot at the moment and it'll take about 3 to 4 hrs to get down to ambient. I can say that I'm using D16.4 so that would indicate that it came from auto tune and not a post tune manual entry (I'd have rounded it to a whole second).

vapvap · 1 Sept 2018, 19:00

@dc42
I'm sorry, but I think I'm doing something wrong...

7:43:07 PM
Warning: Auto tune of heater 0 failed due to bad curve fit (A=133.8, C=839.5, D=-0.5)
7:30:11 PM
Auto tune phase 3, peak temperature was 90.0
7:30:04 PM
Auto tune phase 2, heater off
7:22:08 PM
Auto tune phase 1, heater on
7:22:02 PM
M303 H0 S90
Auto tuning heater 0 using target temperature 90.0°C and PWM 1.00 - do not leave printer unattended
7:21:45 PM
M307 H0 A83.9 C552.1 D20.0
6:46:16 PM
Warning: Auto tune of heater 0 failed due to bad curve fit (A=83.9, C=522.1, D=-0.3)
6:38:16 PM
Auto tune phase 3, peak temperature was 90.1
6:38:09 PM
Auto tune phase 2, heater off
6:31:45 PM
Auto tune phase 1, heater on
6:31:39 PM
M303 H0 S90
Auto tuning heater 0 using target temperature 90.0°C and PWM 1.00 - do not leave printer unattended
6:31:15 PM
M307 H0 A102.6 C642.0 D17.0
6:22:21 PM
Warning: Auto tune of heater 0 failed due to bad curve fit (A=102.6, C=642.0, D=-0.1)
6:12:29 PM
Auto tune phase 3, peak temperature was 90.2
6:12:22 PM
Auto tune phase 2, heater off
6:05:14 PM
Auto tune phase 1, heater on
6:05:08 PM
M303 H0 S90
Auto tuning heater 0 using target temperature 90.0°C and PWM 1.00 - do not leave printer unattended
6:04:45 PM
M307 H0 A102.0 C633.4 D15.0
5:48:31 PM
Warning: Auto tune of heater 0 failed due to bad curve fit (A=102.0, C=633.4, D=-0.9)
5:38:47 PM
Auto tune phase 3, peak temperature was 90.0
5:38:40 PM
Auto tune phase 2, heater off
5:31:40 PM
Auto tune phase 1, heater on
5:31:34 PM
M303 H0 S90
Auto tuning heater 0 using target temperature 90.0°C and PWM 1.00 - do not leave printer unattended
5:31:22 PM
M307 H0 A163.0 C1031.9 D12.0
5:21:56 PM
Warning: Auto tune of heater 0 failed due to bad curve fit (A=163.0, C=1031.9, D=-0.3)
5:06:05 PM
Auto tune phase 3, peak temperature was 90.1
5:05:58 PM
Auto tune phase 2, heater off
4:57:09 PM
Auto tune phase 1, heater on
4:57:04 PM
M303 H0 S90
Auto tuning heater 0 using target temperature 90.0°C and PWM 1.00 - do not leave printer unattended
4:56:48 PM
M307 H0 A78.8 C487.0 D10.0
2:26:11 PM
Warning: Auto tune of heater 0 failed due to bad curve fit (A=78.8, C=487.0, D=-0.9)
2:18:43 PM
Auto tune phase 3, peak temperature was 90.2
2:18:36 PM
Auto tune phase 2, heater off
2:12:24 PM
Auto tune phase 1, heater on
2:12:19 PM
M303 H0 S90
Auto tuning heater 0 using target temperature 90.0°C and PWM 1.00 - do not leave printer unattended
2:12:01 PM
M307 H0 A141.7 C892.4 D7.0
2:08:46 PM
Warning: Auto tune of heater 0 failed due to bad curve fit (A=141.7, C=892.4, D=-0.7)
1:55:02 PM
Auto tune phase 3, peak temperature was 90.0
1:54:55 PM
Auto tune phase 2, heater off
1:46:39 PM
Auto tune phase 1, heater on
1:46:33 PM
M303 H0 S90
Auto tuning heater 0 using target temperature 90.0°C and PWM 1.00 - do not leave printer unattended
1:45:29 PM
Connection established!
1:45:29 PM
Page Load complete!

deckingman · 1 Sept 2018, 20:10

@vapvap It's the negative dead time that's screwing it up but I don't know why you are getting that. Are you starting from a low ambient or are things really hot in your part of the world?

vapvap · 1 Sept 2018, 22:32

@deckingman Normal room temperature (~20C).

dc42 · 3 Sept 2018, 09:00

What happens if you use a lower target temperature such as 70C?

The bed needs to be allowed to cool down completely to room temperature between tuning attempts.

vapvap · 4 Sept 2018, 22:22

@dc42
11:20:51 PM
M307 H0 A181.2 C1041.0 D4.0 P0.5
Warning: Heater 0 appears to be over-powered. If left on at full power, its temperature is predicted to reach 206C.
11:20:43 PM
M307 H0 A181.2 C1041.0 D4.0 P0.6
Warning: Heater 0 appears to be over-powered. If left on at full power, its temperature is predicted to reach 206C.
10:39:52 PM
M307 H0 A181.2 C1041.0 D4.0 P0.7
Warning: Heater 0 appears to be over-powered. If left on at full power, its temperature is predicted to reach 206C.
10:39:27 PM
M307 H0 A181.2 C1041.0 D4.0 P0.8
Warning: Heater 0 appears to be over-powered. If left on at full power, its temperature is predicted to reach 206C.
10:38:52 PM
M307 H0 A181.2 C1041.0 D4.0
Warning: Heater 0 appears to be over-powered. If left on at full power, its temperature is predicted to reach 206C.
10:21:55 PM
Warning: Auto tune of heater 0 failed due to bad curve fit (A=181.2, C=1041.0, D=-0.8)
10:05:55 PM
Auto tune phase 3, peak temperature was 70.3
10:05:48 PM
Auto tune phase 2, heater off
10:00:36 PM
Auto tune phase 1, heater on
10:00:30 PM
M303 H0 S70
Auto tuning heater 0 using target temperature 70.0°C and PWM 1.00 - do not leave printer unattended
10:00:00 PM
M307 H0
Heater 0 model: gain 90.0, time constant 700.0, dead time 30.0, max PWM 1.00, calibration voltage 0.0, mode PID, inverted no, frequency default
Computed PID parameters for setpoint change: P46.3, I0.319, D971.8
Computed PID parameters for load change: P46.
9:59:31 PM
Connection established!
9:59:31 PM
Page Load complete!

dc42 · 5 Sept 2018, 16:35

Try with those M307 settings. The warning message is usual when using a high-power bed heater.

vapvap · 12 Sept 2018, 20:16

This post is deleted!

Phaedrux · 12 Sept 2018, 20:25

What type of heated bed is it?

vapvap · 12 Sept 2018, 20:53

@phaedrux Aluminum disc 220mm (Delta Printer).

vapvap · 12 Sept 2018, 20:55

@dc42

In the end, I achieved a positive value.
But what to do next?
After all, the "auto tune" still does not work.

7:20:11 PM
Warning: Auto tune of heater 0 failed due to bad curve fit (A=183.8, C=1042.4, D=0.1)
7:04:11 PM
Auto tune phase 3, peak temperature was 70.3
7:04:04 PM
Auto tune phase 2, heater off
6:58:52 PM
Auto tune phase 1, heater on
6:58:46 PM
M303 H0 S70
Auto tuning heater 0 using target temperature 70.0°C and PWM 1.00 - do not leave printer unattended
6:58:30 PM
M307 H0
Heater 0 model: gain 188.4, time constant 1070.6, dead time 5.0, max PWM 1.00, calibration voltage 0.0, mode PID, inverted no, frequency default
Computed PID parameters for setpoint change: P202.9, I2.773, D710.0
Computed PID parameters for load change: P2
6:58:23 PM
M307 H0 A188.4 C1070.6 D5.0
Warning: Heater 0 appears to be over-powered. If left on at full power, its temperature is predicted to reach 213C.