Abstract: A device for the continuous determination of a surface state index for a ing sheet, creped in the form of undulations, comprising a light source, a first optical system, a cell intended to receive the back-scattered beam and a system for processing the beam, wherein: the light source is a laser source; the first optical system is an astigmatic system, intended to adapt the size of the laser beam at the point where it meets the sheet to the average pitch of the said undulations in the moving creped sheet; the cell is an optoelectronic cell whose sensitive surface receives at least part of the back-scattered light, concentrated by a second convergent optical system; and the processing system comprises a means for determining a surface state index for the sheet from the electrical signals.

Abstract: Device for detecting insipient cracks or tears on the edges (4) of a moving heet (5), of the type comprising:a light source (6),and a receiving cell for picking up the light transmitted by the source (6) through the sheet (5) moving between the source (6) and the cell,characterized in that:on the one hand, the light source (6) is a laser source;and on the other hand, the receiving cell (17) is an optoelectronic cell placed in such a way that the solid angle under which the serviceable surface of said cell (17) or of its image by an optical system, can be seen from the sheet, is less than 0.01 steradian.

Abstract: This invention relates to an apparatus for continuously measuring the state of formation of a sheet of paper which comprises: --means for moving a sheet of paper at a predetermined speed; --a light source directing a laser beam through said sheet; --a means for picking up the laser light transmitted, then for converting it into an electrical signal; --electronic processing means for separating this electrical signal into two components; --means for calculating from these components the index I representative of the state of formation; --a means for displaying the value of this index I; wherein the laser beam is polarized, and the apparatus further comprises, between the sheet and the means for picking up the laser light transmitted, a polarizer of which the axis of polarization is perpendicular to the axis of polarization of the laser beam transmitted.

Abstract: For continuous measurement of the linear speed of relative travel of an object 11 in front of a measuring device 10 two fixed zones 21,22 in the path of the object are illuminated by means of two parallel laser beams emitted by a single source 15, images of the two zones illuminated are formed upon one and the same transducer 17 the output signal from which is processed electronically by autocorrelation in order to determine the time of travel of a point on the object in going from one illuminated zone to the other.