After examining the wave motion on my and on the forum members’ prints, I could see a correlation between the waves and the temperature fluctuations.
The temperature of the PeoPoly heater is controlled by a two-position controller:
This control behavior leads to strong temperature fluctuations during control. The following figure shows the typical control behavior of the two-position controller (switches abruptly between two states):
The waves in the print image (in the direction of the Z axis) have the same cycle (and appearance) as the temperature fluctuations. The cause will be primarily the temperature-dependent the polymerization and the expansion of the cured resin and the entire Z-structure (see coefficients of thermal expansion).
The solution of the problem:
Elimination of temperature fluctuations by using a PID controller on the fan heater. This controller type is very adaptable and ideally suited for this application.
I chose the following experiment setup on my Moai 200 to test the PID controller:
This heater (900W) I have controlled with this PID controller (with thermocouple and Solid State Relay). During the heating up and the normal control operation I recorded the chamber temperature of both heating variants. Here are the results:
The temperature fluctuations of the PID controller during the print are <0.3 ° C. The heating phase is only about 4 minutes. Faults (opening the door, ventilating the room, sudden onset of winter, etc.) are compensated within a very short time.
Here is a sample print Raven Skull Fixed bottom by Grevan printed with the new heater (Nex Resin - Gray (HiTemp) at 30 ° C, Z height = 60um, FEP vat, total height = 70mm):
Another advantage of the PID controller with 230VAC PTC heating element is that it can do without a powerful switching power supply, thus causing less electromagnetic interference and also has a longer life expectancy.
Unfortunately, I have not found a ready-made plug-and-play version of such a small heater with integrated PID controller, which is why you have to build such a heater probably yourself or knows someone who can do that and has the appropriate expertise!
@peopoly: The optimal solution would be a in the Moai firmware integrated PID controller for heating.