Boots – shoes – and leggings
Patent
1997-05-07
1998-04-28
Ruggiero, Joseph
Boots, shoes, and leggings
162263, 36447103, G06F 1900
Patent
active
057453659
DESCRIPTION:
BRIEF SUMMARY
The present invention relates to a method of and apparatus for web monitoring in paper making machines.
Paper making machines are complicated mechanical systems which are susceptible to a large number of problems, some of which can affect the quality or the consistency of the paper which is being produced. Looked at from one perspective, a paper machine can be thought of as a gigantic multi-channel tape recorder. The effects of mechanical vibrations, pulsations, control loop faults, non-uniform consistency of the pulp, together with a number of types of smaller scale random variation, all get written into the paper web. If not kept within bounds, they can affect the efficiency of the manufacturing process as well as the quality of the product. Their frequencies range from one cycle in about 6 minutes, or 0.003 Hz, up to almost 10,000 Hz.
In recent years, systems have become commercially available for permanent installation on paper machines to monitor the more common sources of disturbance.
Signal averaging is normally used to determine the contribution of the rotation of some roll, wet press felt or impeller either to the variations in the paper web or to the vibration of the end of a press roll.
Signal averaging, also known as signal extraction, is a method for discovering the contribution to some output signal of the cyclic variation associated with a steadily rotating or repeating source. To carry out signal averaging it is necessary to have a trigger signal in the form of a sharp pulse that indicates the commencement of each new rotation or repetition of the source of possible disturbance. When this trigger signal is received, sampling of the output signal is immediately commenced at a steady rate many times greater than repetition frequency of the source. Each sample is saved digitally in an array. The sampling continues until a further trigger pulse is received. It is then temporarily suspended. This process is repeated, with the difference that as each subsequent set of samples is obtained they are individually added to the values already saved in the array. After 100 or so sets of samples have been summed sampling ceases and each sum saved in the array is divided by the number of sets of samples taken, in order to obtain a time series representing the mean contribution of the input signal to the output.
Signal averaging works well within its limitations. It is only applicable to periodic inputs for which trigger signals can be obtained. It may be applied to rotating rolls and impellers, when it will give a result corresponding to the sum of the components of the output signal that have frequencies corresponding accurately to multiples of the trigger frequency. It will not detect the faults in the rollers of the bearings used to support the rotating element because these do not give rise to frequencies that are simple multiples of the trigger signal. It may be confused by periodic disturbances having harmonic frequencies that almost match the possible harmonic frequencies of the trigger signal. No statistical test has been devised to show whether or not the averaged signal has been contaminated by such unrelated periodics. It cannot, by its nature, be used to decide whether or not a randomly related signal is affecting another signal.
Before the introduction of the systems for permanent installation on paper machines, mentioned above, it was conventional to put sensors in place on an ad hoc basis and to take recordings, for example of the paper basis weight, for a total of several hours. Later these had to be analysed and studied off site in a laboratory for several days before the conclusions could be reported back to the mill. The long time required to report results was clearly a disadvantage, although it was accepted that considerable skill and experience was sometimes necessary to arrive at sound conclusions.
There are very many types of variation that can occur in paper webs, by no means all of which can currently be detected by conventional systems. FIG. 1 shows some examples of the patterns
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John Heyer Paper Ltd.
Ruggiero Joseph
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