Methods and apparatus for three-dimensional fabrication by tomographic back projections

A system for producing a three-dimensional object from a photoresponsive material, the system comprising:

• a first projection unit capable of emitting controlled spatial patterns of light;
• a means for computing a sequence of back-projections describing the three-dimensional object to be formed from different orientation angles of said object;
• and said back-projections being used to define said controlled patterns of light;
• a vessel optically transparent to said patterns of light, said vessel intended to contain a volume of photoresponsive material, and said vessel and the intended photoresponsive material defining a build volume;
• whereby the first projection unit is arranged in the system to irradiate said build volume with said controlled patterns of light;
• and
• a direction varying means operatively associated with said first projection unit, for controllably varying a direction of incidence of said patterns of light relative to said build volume, either by rotating the build volume within a field of illumination of the first projection unit, or by rotating the first projection unit relative to the build volume, or a combination of both of these rotations, and for executing the computed sequence of back-projections by irradiating the photoresponsive material with the controlled patterns of light from directions corresponding to the different orientation angles thereby creating a three-dimensional distribution of alterations of the photoresponsive material, and creating the three-dimensional object, wherein the system is further configured so that the alterations of said photoresponsive material are recorded during the irradiation with said patterns of light and these recordings are used as feedback to correct or adjust subsequent patterns of light in order to produce said three-dimensional object with improved accuracy.