US 4,910,688 AGranted

On-machine sheet material property analysis

AssigneeDomtar Inc.

InventorJunis Amini

Life of this patent

Estimating the term…

Loading patent…

Abstract

A method and apparatus for determining on-machine, components of variances over an entire frequency range, of a property of a substantially continuous moving sheet material. At least two property-sensing detectors measure and each provide a signal Y(t) proportional to a sheet material property at a different location in the cross machine direction of a moving sheet material. Preferably a spectrum analyzer, determines the power spectral density function G(f) for each detector's signal, and the coherence function COH(f) between the two detectors' signals. On the basis of these results, the total variance, the machine direction variance, the residual variance and the contributions of the machine-directional cyclic and non-cyclic variances of the property of interest are determined, preferably by a computer. These contributions are generally indicative of process and/or machine upsets.

Claims18

Dependent claims

A method for automatically determining on-machine, components of the variance over an entire frequency range (f), of a property of a substantially continuous sheet material comprising:

(a) allowing said substantially continuous sheet material to travel in a machine direction (MD),
(b) scanning said sheet material along at least two longitudinally extending locations in a zone across said sheet material and automatically generating an output signal proportional to said property of said sheet material at each of said locations,
(c) transforming at least two of said output signals into their corresponding power spectral density functions,
(d) from a pair of said power spectral density functions, determining a coherence function,
(e) from said coherence function, computing a square root function of said coherence function,
(f) multiplying said square root function by a first power spectral density function of said pair in step (d), thereby obtaining a machine direction output power, MDOP(f),
(g) from said machine direction output power, MDOP(f), determining and generating data for the displaying of a machine direction variance over said entire frequency range, V.sub.MD, by ##EQU10## where MDOP(f.sub.i) is the machine direction output power at a frequency f.sub.i, and n is the number of frequencies in said entire frequency range, with the proviso that said machine direction variance is substantially pure and thereby does not include a residual variance.

4 more elements

An apparatus for automatically determining on-machine, components of the variance over an entire frequency range f, of a property of a substantially continuous sheet material, moving in a machine direction (MD), comprising:

(a) at least two detectors, each for scanning said sheet material in said machine direction and at a different longitudinally extending location in a zone across said moving sheet material,
(b) at least two of said detectors each generating a detector output signal proportional to said property of said sheet material at said location,
(c) means operatively connected to said detectors, for receiving at least two of said detector output signals, converting them and generating converted signals corresponding to their coherence function and at least a first power spectral density functions,
(d) means, operatively connected to said means for receiving, converting and generating, for receiving and processing said converted signals and generating a processed signal indicative of machine direction variance over said entire frequency range, V.sub.MD, of the property,
(e) means, operatively connected to said means for receiving, processing and generating, for receiving and displaying said processed signal indicative of machine direction variance, with the proviso that said machine direction variance is substantially pure and thereby does not include a residual variance.

2 more elements

Dependencies are inferred from the claim text.