Measuring and testing – Vibration – Resonance – frequency – or amplitude study
Patent
1996-01-30
1997-09-30
Williams, Hezron E.
Measuring and testing
Vibration
Resonance, frequency, or amplitude study
73159, G01N 2918
Patent
active
056728280
DESCRIPTION:
BRIEF SUMMARY
The invention relates to a method of determining strength and related mechanical properties of paper and similar products, both on-line and off-line, using an ultrasonic wave transmission and reception system. The invention also provides an apparatus for measuring the strength and related mechanical properties of paper and similar products.
It is generally desirable for manufacturers of paper and like products to measure the mechanical properties of their products to ensure that the product will meet the requirements of their intended uses. Until recently, in order to test these properties, it has been necessary to measure the desired properties from samples, cut from the paper sheet, in the laboratory. This method is particularly time consuming and the results obtained are in no way representative of the properties of the entire sheet or roll.
To overcome the problems associated with the off-line process, Baum and Habeger discuss in U.S. Pat. No. 4,291,572 the development of an on-line method and apparatus for measuring strength properties in paper and in particular an estimation of Young's modulus. Baum and Habeger disclose the use of applying a single ultrasonic pulse or a short burst of pulses of ultrasonic waves to the sheet product and measuring the "time of flight" for the pulse to reach the receiver. Knowing the distance between the transmitter and the receiver, the velocity of the wave can be calculated. Young's modulus can then be estimated from the velocity of the wave. However, there are a number of problems associated with the Habeger and Baum on-line method of measuring Young's modulus and other strength characteristics. In particular, because of the noise associated with an on-line system, it is difficult to segregate the extraneous noise from the transmitted pulsed signal and as such it is quite difficult to accurately identify the pulsed signal and thus calculate the "time of flight" of the pulsed signal. Apart from the problem of noise, there is additionally an interface problem where a mismatch of impedances between the material of the transmitter/receiver and of the product may cause problems with taking measurements. As is often the case, the impedance to the wave of the transmitter/receiver when compared to the impedance to the wave of the sheet product is quite different, resulting in losses of the actual energy transmitted to the sheet product. This results in a change of phase and distortion of the single pulse signal which once again makes it difficult to identify the transmitted signal and to calculate the "time of flight".
Another problem associated with the Habeger and Baum system, and hence the ability to accurately measure the "time of flight" of the pulsed signal, is the presence of reflections of the pulsed signal at the interfaces, (such as air/paper) and sample edges. Reflections as well as noise affect the ability to measure accurately the "time of flight" of a pulsed signal, since similarly the original pulsed signal is difficult to identify from the reflected signals.
Habeger and Baum have taken some steps to address the problems of their system and in particular in relation to the problems of noise, impedance mismatch, and reflections. Extra readings and manipulation of the data or in the case of reflections, waiting until the reflections have subsided, are steps which have been taken in an attempt to miniraise the problems associated with the Habeger and Baum system. However, all of these solutions require a significant amount of time which is not generally available in an on-line procedure. For example, it has been observed that it can take up to six minutes to provide an averaged measured result because of the noise and the measurement technique previously utilised. On a modern paper machine, six minutes on-line represents many kilometers and/or tonnes of paper resulting in significant wastage of product if the sheet product does not meet the strength requirements of the desired purpose.
Another type of instrument has been developed in an attempt to continuously mo
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patent: 4291577 (1981-09-01), Baum et al.
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patent: 5398538 (1995-03-01), Williams et al.
Derwent Abstract Accession No. 84-068158/11, Class S03, SU,A, 1019319 (Mosc Eng Phys Inst) 23 May 1983.
Patent Abstracts of Japan, P-154, p. 144, JP,A, 57-128844 (Mitsubishi Denki K.K.) 10 Aug. 1982.
Amcor Limited
Miller Rose M.
Williams Hezron E.
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