Stereolithographic 3D printer

1. A 3D printer comprising:

a vat for liquid photopolymer;

a print platform for extending into the vat;

a screen assembly having an arrangement of screens for providing an exposure of patterned electromagnetic radiation for selectively polymerising successive layers of photopolymer to build a 3D printed object on the print platform,

wherein each screen comprises an emissive pixel array for emitting the patterned electromagnetic radiation,

wherein the emissive pixel array comprises at least 2-by-2 pixels, and

wherein adjacent screens of the screen assembly are separated by a gap in which pixels are absent, and the gap between the adjacent screens is more than half the width or length of the screens; and

a control mechanism for controlling the separation of the print platform and the screen assembly parallel to a build direction;

wherein the control mechanism is configured to control the relative position of the print platform and the screen assembly perpendicular to the build direction; and

wherein the control mechanism is configured to provide a plurality of exposures of respectively patterned electromagnetic radiation for each layer, each exposure having a different relative position of the print platform and the screen assembly perpendicular to the build direction.

2. The 3D printer of claim 1 , wherein each screen comprises a visual display screen and the printer is provided with a light source for emitting the patterned electromagnetic radiation, which is patterned by selective transmission through the visual display screen.

3. The 3D printer of claim 1 , wherein the vat has a vat base that is substantially transparent to the electromagnetic radiation and the screen assembly is configured for providing the patterned electromagnetic radiation to the vat base.

4. The 3D printer of claim 1 , wherein each screen has a pixel pitch, and the control mechanism is configured to provide a plurality of exposures for each successive layer, having exposures with relative positions that differ by less than the pixel pitch.

5. The 3D printer of claim 1 , wherein an assembly of tapered fibre optic plates is provided between the pixel arrays of the screens and a vat base of the vat.

6. The 3D printer of claim 5 , wherein each of the tapered fibre optic plates has a bundle of optical fibres with a narrower end adjacent a respective screen of the screen assembly and a wider end adjacent the vat base, and the control mechanism is configured to selectively display pixels optically coupled into the fibre optical plate.

7. A 3D printer comprising:

a vat for liquid photopolymer;

a print platform for extending into the vat;

a screen assembly having an arrangement of screens for providing an exposure of patterned electromagnetic radiation for selectively polymerising successive layers of photopolymer to build a 3D printed object on the print platform,

wherein each screen comprises an emissive pixel array for emitting the patterned electromagnetic radiation,

wherein the emissive pixel array comprises at least 2-by-2 pixels, and

wherein each screen comprises a border in which pixels are absent surrounding the corresponding pixel array, wherein a gap between the pixel arrays of adjacent screens provided by the borders of the adjacent screens is more than half the width or length of the pixel arrays; and

a control mechanism for controlling the separation of the print platform and the screen assembly parallel to a build direction;

wherein the control mechanism is configured to control the relative position of the print platform and the screen assembly perpendicular to the build direction; and

wherein the control mechanism is configured to provide a plurality of exposures of respectively patterned electromagnetic radiation for each layer, each exposure having a different relative position of the print platform and the screen assembly perpendicular to the build direction.

8. The 3D printer of claim 7 , wherein each screen comprises a visual display screen and the printer is provided with a light source for emitting the patterned electromagnetic radiation, which is patterned by selective transmission through the visual display screen.

9. The 3D printer of claim 7 , wherein the vat has a vat base that is substantially transparent to the electromagnetic radiation and the screen assembly is configured for providing the patterned electromagnetic radiation to the vat base.

10. The 3D printer of claim 7 , wherein each screen has a pixel pitch, and the control mechanism is configured to provide a plurality of exposures for each successive layer, having exposures with relative positions that differ by less than the pixel pitch.

11. The 3D printer of claim 7 , wherein an assembly of tapered fibre optic plates is provided between the pixel arrays of the screens and a vat base of the vat.

12. The 3D printer of claim 11 , wherein each of the tapered fibre optic plates has a bundle of optical fibres with a narrower end adjacent a respective screen of the screen assembly and a wider end adjacent the vat base, and the control mechanism is configured to selectively display pixels optically coupled into the fibre optical plate.