US 4,301,366 A · Chatter detection in thickness measuring gauges and the like

Abstract

Process and apparatus for measuring variations in a stream of material, such as thickness in a strip from a mill. A radiation source and detector are positioned at a gauging station. The stream of material moves past the station providing an electrical signal varying as a function of material at the station which signal includes a lower frequency component, a higher frequency cyclical component, and a higher frequency noise component. A circuit for providing a thickness output varying as a function of the lower frequency component of the signal, and a circuit providing an output indicating chatter varying as a function of the higher frequency cyclical component. Digital and analog versions are disclosed.

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Claims17

Dependent claims

An apparatus for measuring thickness variations in a strip of material moving relative to a gauging station, including in combination:

a radioactive source positioned at said gauging station for directing radiation to said strip of material;
a radiation detector positioned at said gauging station for receiving radiation from said source transmitted or reflected by said strip;
first circuit means having the output of said detector as an input for producing a first electrical signal varying as a function of thickness along said strip, said first signal including a lower frequency component, a higher frequency cyclical component, and a higher frequency noise component;
a thickness measuring circuit having said first signal as an input and including low pass filter means for substantially removing said higher frequency components of said first signal, and calibration means for providing a second signal as an output varying as a function of said lower frequency component of said first signal;
a chatter detection circuit having said first signal as an input and including;
high pass filter means for substantially removing said lower frequency component of said first signal,
second circuit means having the output of said high pass filter means as an input for providing a third signal varying as a function of frequency of said higher frequency cyclical component,
a delay unit having said third signal as an input providing a delayed third signal as an output, and
a chatter indicating unit having said third and delayed third signals as inputs and providing an output indicating presence of chatter in said strip when there is coincidence in time of said third and delayed third signals.

6 more elements

A process for measuring thickness variations in a strip of material moving relative to a gauging station, including the steps of:

directing radiation onto said strip of material at said gauging station and detecting such radiation transmitted or reflected by said strip with the detected radiation varying as a function of thickness along said strip;
producing a first electrical signal varying in time as a function of said detected radiation, said first signal including a lower frequency component, a higher frequency cyclical component, and a higher frequency noise component;
in a first circuit removing substantially all of said higher frequency components of said first signal and providing a second signal varying as a function of said lower frequency component of said first signal and corresponding to the thickness of said strip of material;
in a second circuit removing substantially all of said lower frequency component of said first signal and providing a third signal varying as a function of frequency of said higher frequency cyclical component;
delaying said third signal a predetermined period of time providing a delayed third signal;
and
combining said third and delayed third signals and providing an output indicating presence of chatter in said strip when there is coincidence in time of said third and delayed third signals.

4 more elements

Dependencies are inferred from the claim text.

Description2,750 words

Summary839 words

#This invention relates to the detection of low frequency variations and high frequency cyclical variations in a signal, particularly those from on-line thickness measurement instruments.

#Continuous processing of strip products such as steel, aluminum, rubber, paper, etc., has grown enormously over the past three decades. The quality of on-line instrumentation has improved correspondingly, and manufacturers are able to measure and control their processes within tighter and tighter tolerance bands. In many processes there are prolonged regions of high frequency variations in the product. An example is the thickness variation that occurs in the cold rolling of steel--in particular the phenomenon known as "chatter". A common cause of chatter is a mechanical resonance in the rolling mill which makes the rolls bounce. This gives rise to a thick (or thin) spot in the steel for each bounce. The thickness variations are a quality defect which may render the steel unsuitable for an end use such as can making.

#Chatter may be characterized by the amplitude of the thickness variation and the spatial separation of the thick spots. For the roll bounce chatter described above, separations of 5-20 cm and amplitudes of 5-20 microns are found in 0.25 mm can stock. Such can stock is rolled at speeds from 600 to 2100 meters/minute, and finished on inspection, tinplating, and slitting lines at speeds from 300 to 600 meters/minute. The chatter shows up as high frequency variations in the range of 5 to 300 Hz. Regions of chatter may be as short as ten meters or as long as hundreds of meters. FIG. 1 shows an example of chatter, detected on a tinplating line with the strip of material moving at 500 meters/minute. The chatter is superposed on a much lower frequency variation in thickness, typically less than 2 Hertz.

Brief description of the drawings4 figures

#FIG. 1 is a recording of the output obtained with a thickness gauge measuring a nominal 0.25 mm thick steel can stock moving at 500 meters per minute on a tin plating line;

#FIGS. 2A and 2B is a block diagram illustrating a thickness and chatter measuring apparatus operating in analog style and incorporating the presently preferred embodiment of the invention;

#FIG. 3 is an algorithm for a digital embodiment of the apparatus of FIGS. 2A and 2B; and

Detailed description1,812 words

#Referring to FIGS. 2A and 2B, a stream of material such as a strip of steel 10 is moved past a gauging station 11 which provides an output V1 having a lower frequency component, a higher frequency cyclical component, and a higher frequency noise component, as illustrated in FIG. 1. This output signal V1 is connected to thickness measuring electronics indicated generally at 12 and chatter detection electronics indicated generally at 13.

#The gauging station may be a conventional on-line measurement unit such as a nuclear thickness gauge, a contacting thickness gauge, or any other type of instrumentation which produces the signal V1. The measuring instrument at the gauging station must have a response frequency which is greater than the frequency of the chatter to be detected. If a digital system is utilized to process the signals, the sampling rate must be high enough to prevent problems such as "aliasing".

#In the preferred embodiment illustrated, a radioactive source 16 directs radiation through the strip 10 to a radiation detector 17. The output of the detector is connected to a preamplifier 18 which in turn is connected to an amplifier/filter 19 which provides the output V1. An alternative configuration utilizing reflection rather than transmission is illustrated in FIG. 4, with the radiation source 16 directed to the strip 10 and with the detector 17 measuring reflected radiation rather than transmitted radiation as in FIG. 2A.

Chatter detection in thickness measuring gauges and the like

Life of this patent

Chatter detection in thickness measuring gauges and the like

Life of this patent

Life of this patent

Abstract

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Claims17

Description2,750 words

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Classification2 codes

Life of this patent

Description2,750 words