Abstract: A stereolithography apparatus comprises a fixed, vat (401) or a holder for receiving a removable vat for holding resin for use in a stereolithographic 3D printing process, a build platform (402), a moving mechanism (2003) configured to move said build platform in a working movement range be-tween a first extreme position proximal to said vat (401) and a second extreme position distant from said vat (401), a working region between said vat (401) and said second extreme position of said build platform (402), an optical imaging detector (501) having a field of view, installed and directed so that at least a part of said working region is within said field of view when said optical imaging detector is in an operating position and a controller (502, 2001) coupled to said optical imaging detector (501) for receiving optical image data from said optical imaging detector (501). Said controller (502, 2001) is configured to use said optical image data in controlling operation of the stereolithography apparatus.

Abstract: A stereolithography apparatus comprises a fixed vat (401) or a holder for receiving a removable vat for holding resin for use in a stereolithographic 3D printing process, an optical radiator (901) configured to project a pattern upon a portion of said vat (401), an optical imaging detector *501 (field of view, installed and directed so that said portion of said vat (401) and/or a surface onto which the projected pattern is reflected—is within said field of view when said optical imaging detector (501) is in an operating position, and a controller (502, 2001) coupled to said optical imaging detector (501) for receiving optical image data from said optical imaging detector (501). Said controller (502, 2001) is configured to use said optical image data to calculate an amount of resin in said vat (401).

Abstract: A stereolithography apparatus comprises a fixed, vat (401) or a holder for receiving a removable vat for holding resin for use in a stereolithographic 3D printing process, a build platform (402), a moving mechanism (2003) configured to move said build platform in a working movement range be-tween a first extreme position proximal to said vat (401) and a second extreme position distant from said vat (401), a working region between said vat (401) and said second extreme position of said build platform (402), an optical imaging detector (501) having a field of view, installed and directed so that at least a part of said working region is within said field of view when said optical imaging detector is in an operating position and a controller (502, 2001) coupled to said optical imaging detector (501) for receiving optical image data from said optical imaging detector (501). Said controller (502, 2001) is configured to use said optical image data in controlling operation of the stereolithography apparatus.

Abstract: A procedure for measuring the formation of paper, wherein through a paper sample is passed radiation and the radiation that has passed through the paper is observed with a .beta. radiation detector for establishing a spectrum characterizing the formation of the sample, for radiation source being used a liner .beta. radiation source, and the .beta. radiation that has passed through the sample being observed in one dimension with a position-sensitive wire chamber detector operating in limited streamer mode.