kopia lustrzana https://github.com/jbruce12000/kiln-controller
90 wiersze
2.9 KiB
Markdown
90 wiersze
2.9 KiB
Markdown
# PID Tuning Using Ziegler-Nicols
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This uses the Ziegler Nicols method to estimate values for the Kp/Ki/Kd PID control values.
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The method implemented here is taken from ["Ziegler–Nichols Tuning Method"](https://www.ias.ac.in/article/fulltext/reso/025/10/1385-1397) by Vishakha Vijay Patel
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One issue with Ziegler Nicols is that is a **heuristic**: it generally works quite well, but it might not be the optimal values. Further manual adjustment may be necessary.
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## Process Overview
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1. First of all, you will record a temperature profile for your kiln.
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2. Next, we use those figures to estimate Kp/Ki/Kd.
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## Step 1: Record Temperature Profie
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Ensure `kiln-controller` is **stopped** during profile recording: The profile must be recorded without any interference from the actual PID control loop (you also don't want two things changing the same GPIOs at the same time!)
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Make sure your kiln is completely cool - we need to record the data starting from room temperature to correctly measure the effect of kiln/heating.
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There needs to be no abnormal source of temperature change to the kiln: eg if you normally run with a kiln plug in place - make sure its in place for the test!
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To record the profile, run:
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```
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python kiln-tuner.py recordprofile zn.csv
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```
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The above will drive your kiln to 400 and record the temperature profile to the file `zn.csv`. The file will look something like this:
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```
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time,temperature
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4.025461912,45.5407078
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6.035358906,45.5407078
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8.045399904,45.5407078
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10.05544925,45.59087846
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...
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```
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## Step 2: Compute the PID parameters
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Once you have your zn.csv profile, run the following:
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```
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python kiln-tuner.py zn zn.csv
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```
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The values will be output to stdout, for example:
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```
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Kp: 3.853985144980333 1/Ki: 87.78173053095107 Kd: 325.9599328488931
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```
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(Note that the Ki value is already inverted ready for use in config)
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------
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## Sanity checking the results
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If you run
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```
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python kiln-tuner.py zn zn.csv --showplot
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```
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It will display a plot of the parameters. It should look simular to this .
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Note: you will need python's `pyplot` installed for this to work.
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The smooth linear part of the chart is very important. If it is too short, try increasing the target temperature (see later).
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The red diagonal line: this **must** follow the smooth part of your chart closely.
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## My diagonal line isn't right
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You might need to adjust the line parameters to make it fit your data properly. You can do this as follows:
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```
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python kiln-tuner.py zn zn.csv --tangentdivisor 4
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```
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`tangentdivisor` modifies which parts of the profile is used to calculate the line.
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It is a floating point number >= 2; If necessary, try varying it till you get a better fit.
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## Changing the target temperature
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By default it is 400. You can change this as follows:
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```
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python kiln-tuner.py recordprofile zn.csv --targettemp 500
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```
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(where the target temperature has been changed to 500 in the example above)
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