Abstract: An additive manufacturing apparatus for building a product according to a planned geometry by successive solidification of a radiation-curable fluid in a solidification layer extending in a vertical direction from a surface of the fluid to a surface of the product. The apparatus includes: a vat holding the fluid; a support holding the product; a mechanism to control feeding of fluid to the solidification layer; a curing radiation source to generate a 2D exposure pattern of curing radiation in the solidification layer. The exposure pattern is defined by a curing radiation pattern geometry and/or curing radiation intensity. A radiation sensor receives radiation from the solidification layer. The radiation sensor generates a sensor signal having information indicative of a solidification process status. A control system is connected to the feed control mechanism and the curing radiation source.