PeoPoly heater problem, analysis and solution

#1

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):

unstet3
(Source)

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:

PID-Heater%20V1

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:

Heating%20comparison%20V1

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.

6 Likes

#2

I have four heaters with PID controllers and have gone through 5-6 different ones that all got stuck on from the relay fusing from having too fine a control enabled. I have settled on ±1.5C. For this reason, and stopped buying any PID controller where I could not set the thresholds, and set wider thresholds on the ones that I have. The thermal mass of the printer smooths it out.

If someone really wants ±1.0C or finer control, I would get a controller with a solid state relay. They do cost a lot more though.

0 Likes

#3

love your work. now we have found the problem, lets see if Peopoly can come up with a solution.

I am not great with DIY electronics, so building a heater myself is not something I would do, but purchasing an off the shelf solution would be.

I would like to see a vat direct heating solution rather then wasting energy on heating the entire build volume, which is the cause of this wave artifact is that the printed part expands and contracts.

A direct vat heating solution would somewhat mitigate this as it only keeps the resin at higher temps by heating the metal vat.

The overall ambient temperature of the build volume would still fluctuate, but I imagine it would be a much smoother and wider curve.

0 Likes

#4

can you measure the gap between each way and see if it matches the time of temperature fluctuation.

There are hundreds of these heaters out there and the problem is not universal so we are getting several backs to test. It is possible the temperature flucation has effect on print but since when you switched heater, you switched not just the controller but also power supply and heating block. There are 3 moving parts, not just one so let’s see if we can narrow down further.

1 Like

#5

Thanks @johnchen . Heating the vat frame (Alu) directly is a good approach. This is e.g. made in the form2 and the wiper distributes the heat in the resin evenly. The Moai does not (yet) have a wiper … // I’m working on it, later

The hot air generator was only a test of the influence of temperature fluctuations on the print result. At the moment I am working on an infrared heater, which heats the glass plate evenly from below. That is a bit more complicated and there is still much to do…

1 Like

#6

There is still an unclear point in your test, and that is is the peopoly heater really not perturbing the galvos.
Would it be easy for you to use the Peopoly heater with the original PSU and use an arduino/tinkerforge or another similar board for the PID funtction ? Or maybe just use your current setup but adjust the PID to create a big temperature swing and see if you get lines ?

Most of my experience with SLA is using Formlabs machines but my guts tell me a 3°C temperature swing shouldn’t have such an impact on curing parameters, especially since the resin itself has quite a bit more thermal capacity than the air in the printer so it might not actually change that much.

0 Likes

#7

Thank you John for your request.

In my short contributions, I have summarized only the most important information about my experiments. Only if I’m pretty sure (>90%) that I’m not mistaken, I publish my findings.

For your questions and concerns:

There is still an unclear point in your test, and that is the peopoly heater really perturbing the galvos.

Before I installed the PID controller, I had a 230V heater with two-position controller (fluctuation: about 5 ° C, period: 85 s). This has switched much faster than the PeoPoly heater and caused a corresponding pattern:

The wave pattern only became visible in higher layers and stronger after the building board was out of the resin and the support structure was exposed. The heat capacity of the aluminum plate and the liquid resin will probably have smoothed the temperature fluctuations:

The carriers react very quickly to temperature fluctuations as they have a low volume and a large surface!

Theoretically, with a temperature change of 3 ° C, a change in length of approximately 12 μm results for only one carrier (assumed: 80 10-6 m / m / K). The geometric structure of the support structures also has a great influence on the layer displacements due to leverage.

For undisturbed printing results, a constant ambient temperature is a condition !!!

Would it be easy for you to use the Peopoly heater with the original power supply and use an Arduino / Tinkerforge or other similar board for the PID function? Or just use your current setup, but do you adjust the PID to create a large temperature swing and see if you get any lines?

At the moment I can not print and I do not have much time, because I’m 99% involved in other projects.

Also, I can not imagine how the simple 24VDC heater from PeoPoly could electrically affect the galvos. Do you have a theory?

0 Likes

#8

Hello Mark, aka @peopoly!

I would like to measure the grooves exactly and compare with the switching cycles of the heater, but I miss the exact total printing time, as this is unfortunately deleted after a print of the firmware from the display :confused: (firmware change request).

However, I have not the slightest doubt (see above) that the temperature fluctuations are the cause of the shift shifts. There are so many pictures of users who prove this. See especially The Peopoly Heater problem from @Whazaa:

Each groove corresponds to approx. 12 minutes. The piece shown has 25 waves and will therefore have been printed in about 5 hours. With a bit of phatasia you can even see the sawtooth from the temperature curve. Is not it?

0 Likes