Verification of the Effect of Light Source Intensity on Printing Accuracy
Voxel Size of a MSLA 3D Printer
The accuracy of MSLA(LCD/DLP) printers is affected by pixel size and layer height directly, they determine the size of the minimum printable unit: voxel. If you don't know how to calculate the size of a voxel, please check out this article.
Imaging Principle of MSLA(LCD/DLP) 3D printer
Now you know that the minimum voxel that can be generated by MSLA(LCD/DLP) 3D printer, let's explain how a MSLA(LCD/DLP) 3D printer can reproduce image. First, we need to know that the LCD screen is divided into 50 × 50µm pixels in the XY direction.
The light source generates an image on the LCD screen. If the pixel is white, the light source at this location cures the liquid resin, forming a solid cube. If the pixel is black, then there is no light source at this location, and the resin does not be cured.
Now, we have four 50 × 50 × 50µm cubes, and next to them, spaced at intervals, we have the same model made up of four 50 × 50 × 50µm cubes.
They can be 50µm, 100µm, 200µm or more apart.
But they have to be a multiple of 50µm apart. For example, we can't make them 175µm apart. Why? Because if our image is made up of pixels that are either pure white or pure black, there is no way to either expose them or not expose them to the fixed minimum grid on the LCD screen.
So if it's gray between white and black, is it possible to do half exposure and half no exposure? So where is the half exposure? Left half, right half, front half, back half, top half, or bottom half?
Autodesk’s Ember team shared a study of how a single voxel is made. They lined the pixels up from dark gray (nearly pure black) to pure white, then used the corresponding light source to cure the resin.
The research showed that the gray level is lower than a certain value, and there would be no cured reaction. However, from dark gray to a certain critical brightness, semi-circular bubbles started to be formed in the previous layer. With the increase of brightness, the bubbles became larger and larger, and then the height started to increase slowly, and the lateral development was rapid. This suggested that the size of the voxel could be controlled by the brightness of each pixel.
In practice, a gray pixel or hemivoxel would merge into adjacent voxels. So, if you have two white voxels from left to right plus one gray voxel (hemivoxel) plus one black voxel, you're going to have a hemivoxel near the two left voxels. By controlling the brightness of the pixel, any size of voxel can be produced.
So can this research actually be applied to the actual 3D printing? Now let's look at this experiment. Five squares consisting of 10 × 10 minimum voxels (i.e. 500 × 500µm (0.5 × 0.5mm)) were equally spaced from left to right between the two dividing lines. From left to right, the top row of pixels in each square decreased from pure white to pure black, and the bottom row of pixels increased from pure black to pure white.
As can be seen from the printing results below, the missing distance of the top row of pixels of each square from left to right is about 0µm, 12.5µm, 25µm, 37.5µm and 50µm respectively due to the increase of the grayscale of the light source. It showed that it was completely possible to break the limit of minimum feature size by controlling the intensity of light source and achieve more accurate size control.
Antialiasing Parameters in CHITUBOX
There are 3 parameters in CHITUBOX that give you controls of antialiasing:
- Anti-aliasing Level
- Gray Level
- Image Blur
Where Anti-aliasing Level is dedicated to the .cbddlp format only. Gray Level and Image Blur are dedicated to the .ctb format. Read CHITUBOX Docs to learn how to setup these parameters properly.