Pressure Equalizer scales improperly

[n8bot]

Description of the bug

Pressure equalizer says it takes mm^3/s^2. However, when the feedrate is increased, the pressure equalizer dramatically reduces the allowed volumetric acceleration.

Project file & How to reproduce

Load up any print profile, and set slopes to 1 mm^3/s^2. Slice, notice the print time, and the speed visualization. Then, increase the infill speed to something like 180 mm/s. Notice that the print time is actually LONGER.

The infill will now take longer to hit the same feedrate as before.

Checklist of files included above

• [ ] Project file
• [x] Screenshot

Version of PrusaSlicer

2.5.0

Operating system

win 10

Printer model

any prusa profile

[murk-sy]

You should share your project file, because I can't reproduce this with default Mini 0.20 SPEED profile. It seems to behave as it should.

[n8bot]

1. Load mini 0.2 quality profile.
2. Add a cube, scale it to 80x80x80 mm.
3. Configure positive and negative slope of 1 mm^3/s^2
4. Slice. See this:

Note that the requested feedrate of 80 mm/s is achieved around this point where the nozzle is shown. (Ignore the fact that the feedrate fluctuates -- this is due to single precision float usage instead of double precision. Easy fix.)

5. Now, change the infill feedrate to 180 mm/s.
6. Slice. See this:

Note that the requested feedrate of 180 mm/s is never achieved. Not even 80 mm/s is achieved by the time the infill starts to "decelerate" due to the pressure equalizer. (Ignore the fact that the deceleration phase is abrupt -- this is due to the lookback value of 128. Expected.)

If the acceleration is equivalent, then both toolpaths should achieve 80 mm/s at close to the same spot in the infill.

I suspect that the acceleration rate is greatly reduced because the "time estimate" used by the pressure equalizer to determine the acceleration rate is not quite right. I haven't confirmed this, just a suspicion.

[murk-sy]

Okay, yeah, important discovery: this happens on Prusament PLA, but not on Prusament PETG @ MINI profile due to max volumetric speed. I forgot to even check actual speed reached, was only looking at volumetric speed view.