Method and apparatus for measuring stress in a band subjected to tension and applications thereof, in particular for the measurement of the state of planarity of such a band

A method for measuring the state of planarity of a band subjected to tension, comprising producing a disturbance in the band transversely of the band in a plurality of longitudinal regions of the band, which regions are parallel to the longitudinal direction of the band and arranged transversely of the band between one lateral edge and an opposite lateral edge of the band, measuring the times that the disturbance takes to travel through a predetermined distance in each one of said longitudinal regions of the band, and comparing said measured times, which comparison represents the state of planarity of the band according to the formula:

• ##EQU3## which characterises a planarity defect in the band and wherein:
• a is the half-amplitude of a corrugation of a band whose middle part is taut and whose edges have corrugations;
• .lambda. is the wavelength of one corrugation;
• E is Young's modulus;
• p is the volumic mass of the band;
• l is said predetermined distance;
• t is the time that the disturbance takes to travel through said predetermined distance in one of said longitudinal region;
• .DELTA.t is the difference of time of propagation from said region to another.

A method for measuring the state of planarity of a band subjected to tension, comprising producing a disturbance in the band transversely of the band in a plurality of longitudinal regions of the band, which regions are parallel to the longitudinal direction of the band and arranged transversely of the band between one lateral edge and an opposite lateral edge of the band, calculating the velocity of propagation c of said disturbance in each one of said longitudinal regions of the band from a known value of said predetermined distance and comparing the calculated speeds of propagation, which comparison represents the state of planarity of the band according to the formulae c = l/t and ##EQU4## which characterises a planarity defect in the band and wherein:

• a is the half-amplitude of a corrugation of a band whose middle part is taut and whose edges have corrugations;
• .lambda. is the wavelength of one corrugation;
• E is Young's modulus;
• p is the volumic mass of the band;
• l is said predetermined distance;
• t is the time that the disturbance takes to travel through said predetermined distance in one of said longitudinal region;
• .DELTA.t is the difference of time of propagation from said region to another.

A method for measuring the state of planarity of a band subjected to tension, comrising producing a disturbance in the band transversely of the band in a plurality of longitudinal regions of the band, which regions are parallel to the longitudinal direction of the band and arranged transversely of the band between one lateral edge and an opposite lateral edge of the band, calculating the tensil stress .sigma. in each one of said longitudinal regions and comprising said calculated stresses, which comparison represents the state of planarity of the band, according to formulae .sigma. = p. l.sup.2 /t.sup.2 and ##EQU5## which characterises a planarity defect in the band and wherein:

• a is the half-amplitude of a corrugation of a band whose middle part is taut and whose edges have corrugations;
• .lambda. is the warelength of one corrugation;
• E is Young's modulus;
• p is the volumic mass of the band;
• l is said predetermined distance;
• t is the time that the disturbance takes to travel through said predetermined distance in one of said longitudinal region;
• .DELTA.t is the difference of time of propagation from said region to another.

An apparatus for measuring the tensile stress in a band subjected to tension, comprising means for producing a disturbance in the band transversely of the band, detecting means comprising a first detecting device and a second detecting device disposed at a given distance from each other along said band and capable of producing in succession a first electric pulse and a second electric pulse in response to the disturbance of the band in their respective region, and an electric measuring circuit capable of measuring the time t that elapses between said pulses, said time being related to the tensile stress .sigma. in the band by the formulae:

• .sigma. = p.c.sup.2 and c = l/t wherein:
• p is the volumic mass of the band;
• c is the velocity of propagation of said disturbance;
• and
• l is said given distance.

An apparatus for measuring the planarity state of a band subjected to tension comprising means for producing a disturbance in the band transversaly of the band, a set of detecting means each associated to a respective one of a plurality of longitudinal regions of the band arrangeged, parallel to the longitudinal direction of the band, between one edge and the other edge of the band, each detecting means comprising a first detecting device and a second detecting device disposed at a given distance from each other along said respective region of said band and capable of producing in succession a first electric pulse and a second electric pulse in response to the disturbance of the band adjacent said first and second detecting devices respectively, an electric measuring circuit capable of measuring the time t that elapses between said first and second pulses, and means for comparing the times measured in each one of said longitudinal region, which comparison represents the state of planarity of the band according to the formulae:

• ##EQU6## which characterises a planarity defect in the band and wherein:
• a is the half-amplitude of a corrugation of a band whose middle part is taut and whose edges have corrugations;
• .lambda. is the wave length of one corrugation;
• E is Young's modulus;
• p is the volumic mass of the band;
• l is said predetermined distance;
• t is the time that the disturbance takes to travel through said predetermined distance in one of said longitudinal region;
• .DELTA.t is the difference of time of propagation from said region to another.