Could one detect filament jams via nozzle heater duty cycle?

General Discussion
14

This is an interesting idea. I watched my average heater power consumption at 215°C without printing which was around 47% and during a print it was at 74%, so there is a clear difference for my printer at this Temperature. I only have a 20W heater, which is why the difference is so big. Mainsail show the average power consumption when you hover over the power percentage.

I looked at the thermodynamics of this and found that the heating power should be depended on the mass flow, which is connected with the volumetric flow. From the first law of thermodynamics with the systems boundaries set outside of the heater block, i got this:

\dot{E} = 0 = \dot{Q_{add}} -\dot{Q_{off}}+ \dot{M}(h_1-h_2)

Where h_1 is the enthalpy of the filament coming in and h_2 out. Q_add comes from the heater and Q_off is the heat which goes in the environment. Assuming the filament is incompressible the enthalpy can be calculated like this:

h_{i} = c_{i}*T_{i}+ v_{i}*p

Where T_1 is the room temperature and T_2 is the nozzle temperature. Pressure p, specific heat capacity c and specific volume v (inverse density).
When we take a look at the formula we can see the that the heater power is depended on the flow. With a clog the flow would be 0. So we could calculate the Mass flow, which we get from the formula and if it is close to 0 for a longer time detect a clog.

\dot{M} = \frac{\dot{Q_{add}}-\dot{Q_{off}}}{h_2-h_1}

I’m not sure if all of these assumptions can be made, since we don’t live in an ideal world and in addition we get measurement errors.
I would determine Q_off by heating and holding a temperature for a few minutes, without filament loaded. However there might be a significant difference with a still standing and moving printhead and fan setting.

I think this could work if you print with high flowrate, but it would need to be properly tuned and you need different values for every material and experimentally determine Q_off at every temperature. I don’t know if this method would be reliable.

It definitely worth a try, but i don’t think it would be something for everyone and can’t be used universally, since it would need to be tuned carefully to your printer/print settings.

This is a really interesting idea and i will probably give it a go this summer break. I will definitely share my experience if i’m successful or find some interesting results.