Extruder Heat Control

Hi

What is the software method of controlling the heater?

Is it open loop with the purpose of the thermistor to give a temperature readout or is it closed loop actually referencing the thermistor and adjusting the heater command accordingly?

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Regards

Ian

Closed loop

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[www.hydraraptor.blogspot.com]

Many thanks

As it is closed loop why do you have to run the Extruder Heat Profiler?

I ask because I am using Arduino electronics and the profiler does not seem to work with the Arduino firmware so I am going to try to get the profile empirically if it is needed.

I also want to change to a thermocouple as the fine wires on the thermistor are giving me trouble and RS will be out of stock soon if I break any more!

Out of interest would the thermocouple have to be electrically isolated from the metal parts of the extruder?

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Regards

Ian

I think the host s/w works out two PWM values to give approximately the correct temp and then switches between them. IMHO, far too complicated. I just turn mine on when the value from the thermistor is too low and off when too high. I get +-1 C temp swing which is very good.

Its a good idea to insulate them from the barrel as it might pick up a bit of noise from it. I must be insulated from the heater wires otherwise it will blow up the processor and it would be fairly easy for the heater to short to the barrel.

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[www.hydraraptor.blogspot.com]

I modified the Arduino G code to give bang bang control of the heater and like nophead's it gave +- 1

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Ian
[www.bitsfrombytes.com]

the arduino gcode calls extruder_manage_temperature() after every dda_step, so yes it will keep temperature controlled during a move =)

In my hacked together arduino firmware I first tried a "bang bang" approach but ended up with way to much over/under-shoot. +- 10 to 15 degrees I think.

After a little bit of poking at it I settled on a 3 level PWM value for heating (based on the difference between actual and desired) and full off for cooling.

It works ok for now, but that is simply with me pushing feed stock through by hand... I also don't have insulation around the heater barrel yet, could that make that much of a difference?

In the back of my mind I'm carrying the assumption that it will eventually need PID control.

Hmm, very odd. I get +-1 or 2C with bang bang and Ian Adkins got the same I think with Arduino hardware.

The variation depends on how fast it switches which is determined by the thermal time constant. Have you got the normal extruder heater, barrel and thermistor arrangement?

I have had three different heaters and barrels and the variation was between +-1C and +-3C depending how far the thermistor was from the heater.

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[www.hydraraptor.blogspot.com]

I attempted to make a standard barrel/heater/thermistor setup.

I just realized that my first algorithm stepped up the PWM value on each loop. That means that it actually scaled up and then back down. That's probably the problem. I originally assumed that the clock rate of the Arduino was high enough that that wouldn't make a difference.

I'll change it to proper bang bang and leave it at that.

Hi, I am trying to do a Extruder Heat Control, I already made it with Simple Conditionals Control, but I would like to implement a PID or FeedForward control, which probably will work better. If you have any idea o can suggest me which one is better to use, I will apreciate it.

Thanks...!