Apparatus for detecting faults in the inherent flatness of a stretched strip in movement

Claim 1

Apparatus for detecting faults in the inherent flatness of a stretched moving strip, comprising (a) a deflector roll (3) over which the strip passes, said roll comprising an inner cylinder covered by a thin cylindrical casing (12); (b) cavities (14, 15, 16, 17) of small dimension machined in the side surface of said cylinder so as to constitute at least one group of apertures arranged discontinuously over said surface, the centers of said cavities being located on a helix coaxial with said roll and in angular positions spaced apart by 2π/n, with n an integer, if one rotation of the roll about its axis is concerned; (c) each said cavity containing a displacement sensor (41, 42) having a moving part (43, 44) in contact with the inner surface of said thin casing (12) for radial displacement with respect to said roll; (d) said sensors being connected by means (6) for collecting and processing signals which they emit when said moving part moves under the action of the stresses exerted by said strip on said thin casing; (e) said sensors (41, 42) each comprising a primary winding and a secondary winding through which a moving ferromagnetic core passes, solid with said moving part (43, 44) of said sensor, modifying by its displacements the signal emitted by said secondary winding when said primary winding is supplied with electric current; (f) an optical encoding system (50) for very precise marking of the angular position of said roll (3); and (g) a programmable apparatus using data supplied by said optical encoding system (50) for emitting a current pulse to said primary winding of each sensor once under load when said strip is at said sensor and once not under load; (h) said means (6) for collecting and processing the signals emitted by said sensors (41, 42) at their secondary windings comprising (i) means for measuring the value of the secondary current at a moment predetermined with respect to the beginning of the pulse; (ii) means for converting this value into numerical form; (iii) means for storing all the numerical values; (iv) means for callculating the differences in said numerical values corresponding to each of said sensors under load and not under load; and (v) means (9) for displaying the results relating to each sensor.