What are some relatively simple improvements to FDM 3D printers that cannot be sold however because they are under patent?
I know a heated build chamber is one such thing: According to the RepRap Wiki Heated_Build_Chamber:
The disclosure on how to fabricate a heated build chamber might also be illegal as it is protected by patent.
So I wonder if there are similar "simple" FDM printer upgrades for which it currently would be forbidden to sell (or even promote?) parts due to patent infringement.
This is exactly the question I am interested in. This is not about a specific printer. A heated build chamber is a simple upgrade that would benefit pretty much any FDM printer. I am interested in other relatively simple upgrades which you won't find on most commercial 3D printers despite their simplicity for the reason that the feature is patented.
What other simple improvements are there, that are protected by patents?