Additive Manufacturing

What is PID tuning and how it works

First, we printed a calibration cube, and we identified that there appeared to be inconsistent layer heights, and after verifying the Z screws were moving freely and without a problem, we the first weakness of our printer, the fluctuating temperatures, so we used the PID tuning feature of Klipper (see Pranav, 2022) to solve this issue.

Fig. 1 Bed temperature fluctuations (blue)

PID controller stands for Proportional Integral Derivative Controller and in our case, it’s a digital temperature controller application, and its job is to take and maintain a steady state for a particular function (Microcontrollerslab, n.d.). It’s a closed-loop feedback system that continuously measures the error in your system and tries to correct it (Microcontrollerslab, n.d.). An error like the one seen in Fig. 1, where the temperatures fluctuate above and below the target.

Fig. 2 Klipper PID tuning routine

After running the PID_CALIBRATE

HEATER=heater_bed TARGET=60 and 

SET_HEATER_TEMPERATURE HEATER=extruder TARGET=210 commands in the console, as 210°C for the extruder and 60°C for the bed are the temperatures we’re usually printing at, the software runs a heat cycle routine (seen in Fig. 2) for the heated bed and the extruder that will generate the PID values and correct the fluctuations seen before while trying to hold a steady temperature (Klipper 3D Printer Firmware, n.d., b).

After saving the generated values by the commands in the configuration of the printer, we tested to see if it held a steady temperature, and it did. As that wasn’t enough proof we printed another calibration cube after the changes to see if there is any visible quality improvement.

Fig. 3 Cube before PID (left) next to cube after PID tuning (right)

The tuning has completely removed the horizontal rings that appeared on the cube on the left, as shown in Fig. 3, but this enabled another printing error to be more visible. The repeated horizontal patterns and lines are known as ringing or ghosting. That 3D printing quality issue results from vibration in layers, too high of a printing speed, high acceleration, or a displacement in the printing area (Klipper 3D Printer Firmware, n.d., e). …