DMD Based Resin Printer
The second technology is based on the curing of specially developed resins by ultraviolet (UV) light. In these printers, the building surface is located within a tank containing the resin. One layer of the object is created by exposing the resin to UV light at all locations where the object is to exist. This exposure cures or solidifies the resin, and if carried out properly will allow the newly curing resin to bond strongly with the previous layer. To print each successive layer, the building surface is moved one layer thickness within the tank. Common approaches include lowering the building surface into the resin or lifting the building layer out of the resin, the latter case effectively building the object upside down. Among existing printers, UV exposure is accomplished by either sweeping a laser beam or by imprinting the layer pattern onto the optical beam and writing the entire layer at once. The former case is functionally equivalent to FFF, except that the sweeping is accomplished using tilting mirrors with higher sweep speeds than for FFF. The latter case typically uses a DMD, consisting of an array of very small mirrors that can direct light towards or away from the build tank. Light from the optical source is directed to the DMD, and only those points that are to be part of the object have light directed to them by the corresponding mirror and imaging optics. An advantage of the DMD method is reduction in layer writing time, even when creating a solid layer. Precision of construction is dictated by the number of mirrors in the DMD, the transfer function of the optics, and the object dimensions.