Flow Dynamics Calibration

What is Flow Dynamics Calibration ?

From fluid mechanics, when a newtonian fluid flow through a hole, it needs pressure, and the pressure is proportional to the flow rate .

As the filament is not rigid body, when the extruder starts to extrude, the filament will be compressed to generate the pressure. The compression process will delay the response of the real flow, as the extruder only provides the amount of the filament that needs to extrude, no extra.

So we implemented the flow dynamic control to solve the problem, similar to the “Pressure advance” in Klipper or the “Linear advance” in Marlin, with some non-linear effect compensation added. When executing a flow rate cmd, the printer will do a fast extra extrusion to generate the pressure as fast as possible , to make the respond of the flow can catch the respond of the toolhead movement.

But how much “extra” extrusion is needed for a specific filament? As different filament has different stiffness and viscosity, under a certain flow rate, different filaments will need different amount. That’s why flow dynamics calibration is needed.

Previously, we do the calibration before every print, but there is some problem:

1. If the new print uses the same filament as before, the printer will still do the calibration (unless the user cancels it manually), which costs time and print space;

2. When doing multi color or multi material print, the printer only calibrates the first print filament and uses the parameter for the whole print, which may not be applicable for other filaments.

When to do the Flow Dynamics Calibration?

We now have added the auto-calibration for different filaments, which is fully automated and the result will be saved into the printer for future use. In the following cases, you will need to do the calibration:

1. If you introduce a new filament of different brands or models ;

2. if the nozzle is worn out, as the friction in the nozzle will change;

3. If you replace a new nozzle, as there is tolerance in the manufacturing;

4. If the filament is damp. Moisture will change the viscosity of the filament.

5. If the max volumetric speed or print temperature is changed in the filament setting.

What if I don’t do the calibration?

Well, there are two cases:

1. You start a single color/material print, if “Dynamic Flow Calibration” is checked in the print start menu. In this case, the printer calibrates the flow before printing as before. If “Dynamic Flow Calibration” is not checked, it will adopt the default extrusion compensation parameters. In most cases, using the default parameters can also get good printing results.

2. You start a multi-color/material print. In this case, during every filament switch, the printer will use the default extrusion compensation parameters for uncalibrated materials.

Is the calibration reliable?

It depends. There are a few cases that will make the calibration result not reliable:

1. Using a texture plate to do the calibration ;

2. The filament is damp, which will make the calibration result not suitable for fresh filament ;

3. The filament is transparent ;

4. The build plate is not sticky (please wash the build plate or apply gluestick) ;

Except for the above cases, the calibration result is reliable in our test.

Why are my calibration results not the same in each calibration?

The calibration results have about 10% jitter in our test. We are still investing the root cause.

Two modes of calibration

Flow Dynamics Calibration has two modes: manual and automatic.

Automatic mode: the user only needs to start the calibration, and the printer will return the calibration results to after the printing is finished.

Manual mode: the user needs to judge which parameter to use by observing the quality of the calibration line on the printed board.

How to start a calibration?

Automatic mode

(1) How to start

The printer must be connected before calibration.

(2) Select the material to be calibrated

We will select all the necessary parameter information by default, and you can also modify some of the parameters according to your own situation.

Select the nozzle diameter of your printer

(Note: calibration on different nozzle sizes needs support from the printer firmware. For OTA version, only 0.4mm nozzle is supported)

Select the plate type of your printer

Synchronize filament list information from ams

Select the filament you want to calibrate, and you can select the filament preset for printing through the filament combo box.

When you have set the required information, you can start the calibration by pressing the “calibration” button.

(3) Calibration printing in progress.

After the printing is finished, you can click the next button to go to the next step.

(4) Save calibration results

After the printing is finished, the machine will return the results, and you can save the returned results. Each set of parameters can record a name, and you can modify this name.

All saved results can be viewed by clicking the “Manage Result” button on the homepage, 

 and you can set the K value you want to use for each slot in the material dialog on the device page.

Manual mode

(1) How to start

(2) Select the material to be calibrated

The same with Automatic mode, but manual mode can only calibrate one material at a time.

(3) Calibration printing in progress.

(4) Save calibration results

By observing the calibration line, select the number corresponding to the calibration line with the best printing effect. Fill in the K value edit box with the number, and you can also view the saved history in the history dialog box after saving.

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