Controlling temperature of reprap extruder hot-end
hydraraptor.blogspot.com/2007/10/measuri...rature-easy-way.html
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I also found the XR4151, a very simple to use VCO, to convert the thermistor value in pulses. As said, these pulses will be read by the encoder module (set in counter mode).
What frequency range do you suggest to use for encoder good reading? Is 100Hz enough? Better use higher frequency? The frequency will only vary in a 2:1 ratio...
Thanks,
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What frequency range do you suggest to use for encoder good reading? Is 100Hz enough? Better use higher frequency?
I think the frequency cancels out (more pulses with less temporal accuracy v fewer pulses and more temporal accuracy). Just make sure that you are significantly lower than the base thread frequency (assuming you are using a parport)
For example, if the base thread is 30,000nS (30uS, 33kHz) then 1.5kHz would be as high as I would go.
You do need to bear in mind the thermal reaction time of your extruder. A lower frequency will give slower feedback.
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The thermal reaction is pretty slow, so no problem for EMC. I will just have to tune the pid.
I think I will also need to use a slipping average on the temperature reading (ie encoder speed). Is there a way to do that, using standard modules?
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I think I will also need to use a slipping average on the temperature reading (ie encoder speed). Is there a way to do that, using standard modules?
Yes, have a look at www.linuxcnc.org/docview/html/man/man9/lowpass.9.html
(It doesn't actually describe the effect, just gives the equation used, but that is a rolling average)
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At which frequency would you use this filter? Does it need a slower thread than the servo thread?
How do you determine the gain for a given frequency and rolling period (~1s)?
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For a 1 second response, use a gain of 0.001 if the servo thread rate is 1mS
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Thanks.
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BTW, does anybody have worked on a fuzzy logic component?
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In the Ziegler & Nichols or Broïda methods, they compute Kp, Ti and Td params.
How do I determine Ki and Kd for the hal pid component, from Ti and Td (integration time and derivative time)?
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