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Hot end auto-tuning failed due

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  • undefined
    resam
    last edited by 6 Jun 2018, 11:33

    Hi,

    I tried re-tuning my hot end heater today, a 40W 24V unit heater cartridge (cheap clone).
    My current heater model is: M307 H1 A539.5 C221.2 D3.2 S0.80 V24.1 B0
    It is working just fine for PLA the last months, but now I'm starting to print PETG which requires a bit higher temps, so I wanted to re-tune at 245C:
    M303 H1 P0.85 S245

    But it fails, because just as it hits the max temp, the heater cuts out for a second, causing this weird kink.
    And then during the cool-down phase, the auto-tune fails with: failed due to bad curve fit.
    I tried different PWM settings, 1.0, 0.9, 0.85, 0.5 - always the same error.

    0_1528284689898_Screen Shot 2018-06-06 at 13.31.03.png

    I can heat-up manually to 245C via DWC just fine without getting this kink, so something in the auto-tuning process must be causing it...
    I think DWC plots the kink in the graph before displaying the "Heater off" message, but it is all happing within a few seconds, so it is hard to tell.

    The the existing heater PID model affect the re-tuning in any way? should I reset the values before running the auto-tune (to which values)?

    Firmware Name: RepRapFirmware for Duet 2 WiFi/Ethernet
    Firmware Electronics: Duet WiFi 1.02 or later
    Firmware Version: 1.21 (2018-03-21)
    WiFi Server Version: 1.21
    Web Interface Version: 1.21

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    • undefined
      dc42 administrators
      last edited by 6 Jun 2018, 12:55

      That heater cut-out is causing the problem. What temperature limit did you set with M143?

      Duet WiFi hardware designer and firmware engineer
      Please do not ask me for Duet support via PM or email, use the forum
      http://www.escher3d.com, https://miscsolutions.wordpress.com

      undefined 1 Reply Last reply 6 Jun 2018, 12:57 Reply Quote 0
      • undefined
        resam @dc42
        last edited by resam 6 Jun 2018, 13:01 6 Jun 2018, 12:57

        @dc42 I don't have a M143 in my config.
        I just tried with M143 H1 S270 - no difference, I still get the same kink & auto-tuning error.

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        • undefined
          dc42 administrators
          last edited by dc42 6 Jun 2018, 13:18 6 Jun 2018, 13:18

          If you increase or decrease the target temperature by 5C or 10C, does the kink move with the target temperature or remain at the same temperature?

          What type of temperature sensor are you using?

          Stick with PWM 1.0.

          Duet WiFi hardware designer and firmware engineer
          Please do not ask me for Duet support via PM or email, use the forum
          http://www.escher3d.com, https://miscsolutions.wordpress.com

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          • undefined
            resam
            last edited by 6 Jun 2018, 13:29

            I'm using a v6-clone hot end, 40W 24V heater, no silicone sock, and an old-style glass thermistor bead:
            M305 P1 S"Hotend" R4700 T100000 B4725 C0.0000000706.

            I just completed a successful auto-tuning with P0.85 S210, although I also saw a tiny kink at roughly 210C (smaller kink, and close to the expected target temp).

            Tuning with P1.0 S245 now resulted in a Auto tune cancelled because temperature peak was not identified and a kink close to 245C (and a pesky warning - which I can ignore 🙂 )

            This weird kink feels like the auto-tuning state machine is switching too soon into the peak-detect or turns off the heater too early...

            undefined 1 Reply Last reply 6 Jun 2018, 13:35 Reply Quote 0
            • undefined
              dc42 administrators @resam
              last edited by 6 Jun 2018, 13:35

              @resam said in Hot end auto-tuning failed due:

              This weird kink feels like the auto-tuning state machine is switching too soon into the peak-detect or turns off the heater too early...

              That's why I want to know whether the position of the kink moves up and down with target temperature.

              Duet WiFi hardware designer and firmware engineer
              Please do not ask me for Duet support via PM or email, use the forum
              http://www.escher3d.com, https://miscsolutions.wordpress.com

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              • undefined
                dc42 administrators
                last edited by 6 Jun 2018, 13:37

                PS - which firmware version are you using?

                Duet WiFi hardware designer and firmware engineer
                Please do not ask me for Duet support via PM or email, use the forum
                http://www.escher3d.com, https://miscsolutions.wordpress.com

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                • undefined
                  resam
                  last edited by 6 Jun 2018, 14:03

                  Firmware Name: RepRapFirmware for Duet 2 WiFi/Ethernet
                  Firmware Electronics: Duet WiFi 1.02 or later
                  Firmware Version: 1.21 (2018-03-21)
                  WiFi Server Version: 1.21
                  Web Interface Version: 1.21

                  And yes, the kink moves up and down.
                  Tuning for 210C causes a kink at roughly 205-210.
                  Tuning for 245C causes a kink at roughly 240-245.

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                  • undefined
                    dc42 administrators
                    last edited by 7 Jun 2018, 11:30

                    Thanks, this is now on my list to investigate for the next firmware release. Meanwhile, I suggest you either use your existing model (it shouldn't change much with temperature), or else tune at the highest temperature that works but be prepared to increase the dead time parameter if the temperature oscillates.

                    Duet WiFi hardware designer and firmware engineer
                    Please do not ask me for Duet support via PM or email, use the forum
                    http://www.escher3d.com, https://miscsolutions.wordpress.com

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                    • undefined
                      resam
                      last edited by 15 Jun 2018, 13:35

                      Well, now I'm printing at 257C - and the fluctuations get quite big now... up and down of almost 10C in total.
                      I found another forum post with a similar issue, but no answer there either: https://forum.duet3d.com/topic/3279/pid-autotune-fails

                      I'm doing a rather long print at the moment, but I will try a few more auto-tune runs this weekend. Maybe I get lucky once.
                      I also suspect my PSU to be a bit weird, because the speed of the internal fan somehow oscillates as well... maybe it's related.

                      undefined 1 Reply Last reply 15 Jun 2018, 20:59 Reply Quote 0
                      • undefined
                        Dougal1957
                        last edited by 15 Jun 2018, 17:33

                        If it is a clone V6 then it is likely to have a thermistor with a B Value of 3950 specified at 25/50 degrees and not the same as the E3D ones maybe thats the issue?

                        undefined 1 Reply Last reply 15 Jun 2018, 17:36 Reply Quote 0
                        • undefined
                          resam @Dougal1957
                          last edited by 15 Jun 2018, 17:36

                          @dougal1957 I performed a successful auto-tuning about 8-9 months ago, and I didn't change my thermistor settings since then...
                          Next thing on my list to check is wiring and the thermistor itself - and maybe replace it.

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                          • undefined
                            Dougal1957
                            last edited by 15 Jun 2018, 17:36

                            fair do's

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                            • undefined
                              dc42 administrators @resam
                              last edited by dc42 15 Jun 2018, 20:59

                              @resam said in Hot end auto-tuning failed due:

                              Well, now I'm printing at 257C - and the fluctuations get quite big now... up and down of almost 10C in total.

                              If the fluctuations are regular oscillations (not caused by e.g. the print cooling fan turning on), increase the dead time (D parameter in M307) until they stop. The kink you are getting in the tuning temperature curve is causing the dead time to be under-estimated.

                              Dead time should be independent of temperature, so try the 3.2 seconds that you were using before.

                              Duet WiFi hardware designer and firmware engineer
                              Please do not ask me for Duet support via PM or email, use the forum
                              http://www.escher3d.com, https://miscsolutions.wordpress.com

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                              • undefined
                                resam
                                last edited by 15 Jun 2018, 22:13

                                I now tried various combinations of parameters and configs - no luck.
                                The kink goes down too quickly to be caused by actual cooling - so I'm guessing this must be some other non-heat-related measurement error...0_1529099981641_Screen Shot 2018-06-15 at 23.58.00.png

                                PSU voltage stays fairly constant at 24.1 - 24.2V.
                                30mm hotend cooling fan comes on at full power at 50C and does not blow on the heater block. No part cooling fans are active.

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                                • undefined
                                  dc42 administrators
                                  last edited by 16 Jun 2018, 12:57

                                  I agree, the kink looks like a firmware artefact. It's on my list to see if I can reproduce it.

                                  Duet WiFi hardware designer and firmware engineer
                                  Please do not ask me for Duet support via PM or email, use the forum
                                  http://www.escher3d.com, https://miscsolutions.wordpress.com

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                                  • undefined
                                    resam
                                    last edited by 17 Jun 2018, 08:47

                                    I didn't find any wiring issues or other obvious faults, but I did manage to play with the model parameters to get a stable temperature while printing. I do get a big initial overshoot of 10-15C when heating up from a cold state, but after that has settled down, I get a stable 257C with +/- 0.5C.

                                    My old model was M307 H1 A539.5 C221.2 D3.2 S0.80 V24.1 B0
                                    (auto-tuned a few months ago).

                                    My new model is M307 H1 A560.0 C130.0 D10.0 S1.0 B0
                                    (tweaked by hand until I saw a flat temp curve).

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                                    • undefined
                                      dc42 administrators
                                      last edited by 17 Jun 2018, 14:23

                                      The initial overshoot suggests that you have set the gain too high or the time constant too low. I find it suspicious that your new time constant is half the value you had from auto turning. Also your dead time is very high and will prevent the PID from reacting very fast.

                                      Duet WiFi hardware designer and firmware engineer
                                      Please do not ask me for Duet support via PM or email, use the forum
                                      http://www.escher3d.com, https://miscsolutions.wordpress.com

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                                      • undefined
                                        resam
                                        last edited by 18 Jun 2018, 08:20

                                        @resam said in Hot end auto-tuning failed due:

                                        M307 H1 A560.0 C130.0 D10.0 S1.0 B0

                                        I didn't fine tune it yet - I just tried with D5.0 and it was even better, less initial overswing, and also stable at 255C.
                                        I did notice another oddity, when I used DWC to set the heater to 0C (i.e., OFF), I got another weird kink (far right)!
                                        0_1529309932158_Screen Shot 2018-06-18 at 10.16.50.png

                                        Is my 24V 40W heater somehow affecting the thermistor reading when I turn it off? Voltage drop on the ADC reference?

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                                        • undefined
                                          dc42 administrators
                                          last edited by 18 Jun 2018, 08:35

                                          Yes I think there is an interaction between your hot end heater being powered and the temperature sensor. But it's unlikely to be the ADC reference. What type of temperature sensor are you using?

                                          Duet WiFi hardware designer and firmware engineer
                                          Please do not ask me for Duet support via PM or email, use the forum
                                          http://www.escher3d.com, https://miscsolutions.wordpress.com

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