Possible Patent Infringement By Non-Planar Slic3r Development?

Example of non-planar 3D printing showing smooth surfaces [Source: University of Hamburg]

We’ve been tipped to a potential patent infringement in 3D printing, involving the popular Slic3r software tool.

The nature of the controversy revolves around the master’s thesis by Daniel Ahlers, a visiting scientist at the University of Hamburg, where his thesis “3D Printing of Nonplanar Layers for Smooth Surface Generation”, published late in 2018, describes methods of slicing 3D printer models in a non-planar fashion to improve surface quality.

3D Print Stair Stepping Surfaces

This is a highly desirable approach, as anyone who has 3D printed a not-quite-flat object will notice severe “stair stepping” patterns on the top surfaces. This occurs because virtually all 3D print slicers, which generate specific machine actions, “slice” the 3D model into a series of adjacent horizontal planes.

Printing takes place one plane at a time. While this works very well and is the basis for virtually all 3D printing taking place today, it is problematic when a surface happens to be at a slight angle to the layer plane. This results in highly noticeable “steps” appearing on the surface.

Some have resorted to post-processing techniques to eliminate these unsightly structures. But others have resolved to print differently to solve the problem.

Non-Planar 3D Printing

The answer, it seems, is called “non-planar” 3D printing. In this concept, the 3D model is not printed plane by plane. Instead the surfaces are analyzed and the 3D printer is directed to move along the path of the model’s surface geometry in an attempt to match the non-planar surface. This can result in far smoother surfaces.

However, it’s ridiculously complicated to design a slicing system that does so. Ahlers brilliantly explains the issues in his Master’s thesis, and develops approaches to resolve them.

Some of the issues involve collisions. In a fully-planar slicing scenario collisions are not possible because each layer is printed independently; layer 3 cannot collimate with anything on layer 2 or lower because it’s already higher and cannot go lower.

But that guarantee is not present in a non-planar scenario, where, in theory, the extrusion action can be located anywhere in 3D space during the print.

Non-Planar 3D Printing Challenges

In practice, however, “anywhere” is not possible due to collisions with previously extruded material. Slicers would have to carefully map what’s been printed and somehow navigate around them. And that means taking into account the size of the moving nozzle and accompanying sensors, fans and other bits that could collide, which vary by machine.

In some cases the object’s geometry could be pathological and not allow a smooth non-planar extrusion due to collisions.

Another challenge is that of the nozzle itself; the nozzle in a three-axis motion system 3D printer does not itself tip, and thus there is a maximum angle of deposition determined from the angle of the nozzle’s shape itself.

Ahlers has all this and much more figured out. I encourage you to read his thesis, as it is quite enlightening.

Meanwhile, there is work taking place in the open source community to build non-planar functionality into a fork of the Slic3r software. A considerable amount of code has been deployed to GitHub, where anyone can participate in the project.

It’s not clear to me whether Ahler’s specific approach has been used for the non-planar printing code of this software fork. Indeed the dates of the non-planar contributions seem to be prior to the date of his thesis publication. However, the contributor of the non-planar code seems to be GitHub user “Zip-o-mat”, described as a “Computer science student at University of Hamburg.” Coincidence?

Autodesk Patent For Non-Planar 3D Printing

Image from Autodesk’s patent on “Systems and methods for improved 3D printing” [Source: Google Patents]

Meanwhile, it turns out that Autodesk seems to have patented a non-planar approach in 2015!

According to their patent, US10005126B2:

”A system for fabricating an object, the system comprising:

an extruder for one or more deposition materials, the extruder comprising at least one nozzle having a nozzle tip that includes an exit orifice, the tip having a width that is equal to or larger than a width of the exit orifice; and

a controller coupled with the extruder, the controller configured and arranged to apply a correction factor that has been calculated for a path of the nozzle based on a slope of a surface of an object to be fabricated, the correction factor for a positive slope being different from the correction factor for a negative slope;

wherein the extruder is configured and arranged to cause movement of the nozzle along the path to deposit a material on the slope of the surface of the object, and

wherein the controller is configured to remove differences in thickness of the deposited material caused by the slope in relation to the path by applying the correction factor to thereby adjust a vertical position of the nozzle relative to the path by an amount dependent on the slope of the path.”

That sounds to me a lot like a non-planar extrusion.

In fact, many of the images from the Autodesk patent are extremely similar to those appearing in Ahlers’ thesis. This is understandable, as the same problems seem to be under exploration.

Image from Ahlers’ thesis showing non-planar 3D printed nozzle challenges [Source: University of Hamburg]
Image from Autodesk’s patent on “Systems and methods for improved 3D printing” [Source: Google Patents]
Image from Ahlers’ thesis showing non-planar 3D printed surfaces [Source: University of Hamburg]
Image from Autodesk’s patent on “Systems and methods for improved 3D printing” [Source: Google Patents]

Autodesk Patent Infringement?

Are these approaches legally overlapping? That is a very large question, and one that patent lawyers are very good at interpreting. When patents are struck, the wording is often made sufficiently vague in order to catch subsequent developments, and that could be the case here. On the other hand, new developments need only be suitably different from the first patent claim to be considered an original work. Often new work is specifically engineered to “be different” in this way.

One question is, who knows about this? Do any of the involved parties — Autodesk, Slic3r, Ahlers or the University of Hamburg — have any awareness of this potential patent conflict?

Another question is whether there actually is a patent infringement taking place. That largely depends on Autodesk, who could choose to enforce their patent, or not, and whether the specific details of the process are legally considered overlapping. That’s a matter for lawyers to determine, not me.

And a final question is if there is an infringement, what happens next? Could Autodesk as the Slic3r fork project to cease and desist? Could Autodesk demand licensing payments from the University of Hamburg?

None of this is clear at this point. What do you think?

Via University of Hamburg (thesis, PDF), GitHub and Google Patents (Hat tip to Justin)