GB2185105A

GB2185105A - Velocity measurement

Info

Publication number: GB2185105A
Application number: GB08700276A
Authority: GB
Inventors: Sabyasachi Bhattacharya; Ernest Paul Shuttleworth
Original assignee: BICC PLC
Current assignee: Balfour Beatty PLC
Priority date: 1986-01-07
Filing date: 1987-01-07
Publication date: 1987-07-08
Also published as: GB8700276D0; GB8600239D0

Abstract

The velocity of a moving elongate element such as a cable 1 is measured by illuminating at least a part of the element at first and second positions spaced a known distance along the axis of movement thereof. A variation in the physical configuration of the element, e.g. its width or the profile of one surface of the element, changes the amount of illuminating radiation obscured by the element. The radiation at the first and second positions is detected by two detectors 5, 6, and the signals therefrom are cross-correlated to calculate the velocity of the moving elongate element. <IMAGE>

Description

SPECIFICATION Velocity measurement This invention relates to the measurement ofthe velocity of a moving elongate element. The invention is particularly, but not exclusively, suitable for measuring the velocity of electric cables, conductors, etc but the generic term "elongate element" is herein meantto include flat sheet-like items such as paper or metal.

It is desirable to measure the velocity of an element such as a cable as it emerges from a production process, in orderaccuratelyto determine the length of cable dispensed onto a receptacle such as a spool or reel. The applicants co-pending European application 8530813.3 relates to apparatus for measuring the velocity, and hence length, of a moving cable by contacting the cable with rollers having dif ferentresponsesto changes in velocity. The present invention relates to a non-contact method of velocity measurement which avoids many problems known to be associated with contact techniques.

Accordinglythere is provided a method of measur ingavelocityofa moving elongate elementcomprising the steps of illuminating, with one or more sources of electromagnetic radiation, at least a part of the elongate element at first and second positions spaced a known distance one from another along an axis of movement of the element,the illumination being such that variation in the physical configuration ofthe element will cause a change in the amount of radiation obscured by the element; detecting the radiation incident upon first and second detectors situated on the opposite side of the element from the one or more sources such that a variation in the physical configuration ofthe element will cause a sequential change in the amount of radiation detected by the first and second detectors; and cross correlating signals obtained from the first and second detectors to calculatethe velocity of the element.

Preferablythe element is illuminated with one or more lightsources and thefirstand second detectors are photodetectors. There is conveniently one light source associated with each of the first and second detectors. In one convenient arrangement there is provided two lig htsources each adapted to produce a substantially collimated beam of light.

The "physical configuration" monitored is preferably eitherthe width of the element, or the profile of one surface thereof. Where the monitored configuration is the width of the element, the one or more sources will be arranged to illuminate the entire cross section of the elements such that changes in its width will vary the amount of radiation reaching the detectors. Alternatively, where the configuration monitored is the profile of one surface ofthe el ement,thesources maybearrangedtosupplya focused beam of radiation illuminating only a part of the element containing the said one surface. Irre gularities on the surface will obscure the incident radiation to a differing amount, and produce a change in the amount of radiation reaching the detectors.

The invention further relates to apparatus for carrying out the above described method. In particular, apparatus for measuring the velocity of a moving elongate element comprises one or more sources of electromagnetic radiation adapted toil- luminateatleasta partoftheelongateelementat first and second positions spaced a known distance one from another along an axis of movement ofthe element, the illumination being such that a variation in the physical configuration of the element will cause a change in the amount of radiation obscured by the element; first and second detectors situated on the opposite side of the element from the one or more sensors such that a variation in the physical configuration of the element will cause a sequential change in the amount of radiation detected bythe first and second detectors; and electronic processing means adapted to receive electronic signals from the first and second detectors, and cross correlaqte said signals to calculate the velocity of the moving element. The electronic processing means is prefer ably a microprocessor.

The invention will now be further described, by way of example only, with reference to the accompanying drawings in which; Figure 1 is a schematic diagram of apparatus accordingly to the present invention; Figure 2 is a schematic cross-sectional view of one arrangement ofthe apparatus of figure 1; and Figure 3is a schematic cross-sectional view of an alternative arrangement ofthe apparatus of figure 1.

Referring to Figure 1 a cable 1 is moved longitudinally past a velocity measuring station shown generally at 2. Situated on one side ofthe cable 1 are two lightsources 3, 4 each capable of i(luminating the cable with a beam of collimated light. Each light source has an associated photodetector 5,6 situated on the opposite side ofthe cable 1 and positioned so as to detect the remains of the beams of light after they have illuminated the cable. Signals from the photo detectors 5,6 are transferred via lines 7,8 to a microprocessor 9, which cross correlates the two signals to calculate the velocity ofthe cable.

Cross correlation techniques are well known for measuring the velocity of a moving entity, usually a fluid or suspension of particulate material. The signalsfromthe photodetectors5and6arepro- cessed by the microprocessor to compare them to find the maximum correlation therebetween. The delay to the signal from photodetector 5, necessary to produce the maximum correlation with the signal from the photodetector 6, is an indication of the velocity of the cable. The micro processor 9 establishesthe delay required and, preprogrammed with the known distance 'x' between the photo det ectors5and6,calculatesthevelocityofthecable1.

The signals ofthe photodetectors 5 and 6 vary due to random variations in the configuration of the cable 1. Figure 2 shows an arrangement whereby vari- ations in the width of the cable are detected and used as a parameter for cross correlation. The output from the light source 3 is passed through a slit formed by two plates 10to produceacollimated beam of iight 11, of a width slightly greaterthan that of the cable 1.

The beam is incident on the cable which obscures much ofthe beam from reaching the associated photodetector 5. Anyvariations in the width, 'a' of the cable as it moves past the source 3 will alterthe amount of light which is able to reach the photodetector 5, thereby producing fluctuations in the output signal therefrom. A similar downstream arrangement with source 4 and photodetector 6 will produce a similarly fluctuating signal, delayed bya factor depending on the speed ofthe cable and the distance 'x' between the two photodetectors.

Figure 3 shows an alternative arrangement whereby variations in the profile of one surface of the cable 1 are detected for use as a parameter for cross correlation. In this arrangement the collimated beam 11 is directed to make a grazing illumination of one surface 12, rather than illuminating the whole of the cable 1. Any variation in the profile ofthe surface 12 as the cable is moved past the source 3will again varytheamountoflightwhich isableto reach the photodetector 5. As before, by detecting the variations in profile at two positions with a known spacing therebetween, the velocity of the cable 1 can be calculated by cross correlation.

One advantage of the present invention is that it may be employed to detect the velocity of elements regardless ofthe reflectivity ofthe surface thereof.

Therefore elements such as electric cables, which are coated with a sheath of generally non reflective material buy which contain random fluctuations in their physical configuration, are especially suited to the technique described herein.

Claims

1. A method of measuring the velocity of a moving elongate element comprising the steps of illuminating, with one or more sources of electromagnetic radiation, at least a part of the elongate element at first and second positions spaced a known distance onefrom another along an axis of movement of the element, the illumination being such that a variation in the physical configuration of the element will cause a change in the amount of radiation obscured by the element; detecting the radiation incident upon first and second detectors situated on the opposite side of the element from the one or more sources such that a variation in physical configuration ofthe element will cause a sequential change in the amount of radiation detected by the first and second detectors; and cross correlating signals obtained from the first and second detectors to calculate the velocity of the element.

2. A method according to claim 1 wherein the el ement is illuminated with one or more lightsources and the first and second detectors are photodetectors.

3. A method according to claim 1 or 2 wherein the configuration monitored is the width of the elongate element.

4. A method according to claim 1 or claim 2 wherein the configuration monitored is the profile of one surface of the elongate element.

5. A method according to any of claims 1 to 4 and substantially as hereinbefore described.

6. Apparatus for carrying outthe method of any one of claims 1 to 5.

7. Apparatus for measuring the velocity of a moving elongate element comprising one or more sources of electromagnetic radiation adapted toil- luminate at least a part of the elongate element at first and second positions spaced a known distance one from another along an axis of rnovement ofthe element, the illumination being such that a variation in the physical configuration of the element will cause a change in the amount of radiation obscured by the element; first and second detectors situated on the opposite side ofthe element from the one or more sources such that a variation in the physical configuration of the element will cause a sequential change in the amount of radiation detected by the first and second detectors; and electronic processing means adapted to receive electronic signals from the first and second detectors, and cross correlate said signals to calculate the velocity of the moving element.

8. Apparatus according to claim 7 wherein the one or moresources are lightsources and thefirst and second detectors are photodetectors.

9. Apparatus according to claim 8 wherein there is provided two light sources each adapted to produce a substantially collimated beam of light.

10. Apparatus according to any of claims 7 to 9 wherein the first and second detectors are adapted to produce electronic signals which vary in accordance with variations in the width ofthe elongate element.

11. Apparatusaccordingtoanyofclaims7to9 wherein the first and second detectors are adapted to produce electronic signals which vary in accordance with variations in the profile of one surface ofthe elongate element.

12. Apparatus according to any of claims 7 to 11 wherein the electronic processing means is a microprocessor.

13. Apparatus substantially as hereinbefore described with reference to the accompanying drawings.