Patent Application
20130003047
1. Field of the Invention
The present invention relates to a method for contactless determination of the thickness of a material web, for example, a fibrous material web, with a sensor arrangement including at least two optical measurement plates between which the web can be guided, whereby an air cushion is generated respectively between each measurement plate and the web so as to keep the measurement plates at a distance from the web.
2. Description of the Related Art
Hitherto a magnetic or optical method was used for contactless measurement of the thickness of a material web. Both methods however, permit only measurements of thicker papers, in particular papers having a thickness of >50 micrometers (μm), since—based on the method—the required accuracy is not achieved with thinner papers.
Optical thickness sensors for contactless determination of the thickness of a material web, especially a fibrous web are known from publications EP 1 855 082 A1 and EP 1 855 083 A1.
In contactless measuring of paper thickness the distance between the optical measuring units, or respectively measurement plates which are arranged on opposite sides of the material web is to be determined on the one hand and on the other hand the distances between these measuring units or respectively measurement plates and the material web are to be determined, whereby the distances between the 3 measuring units and the material web occurs by means of an optical measurement. The optical measuring units, which are arranged on opposite sides of the material web, must be positioned in precisely the same optical axis in order to eliminate faulty measurements due to a paper web which is not progressing perpendicular to the optical axis.
In particular, due to the air build-up of the moving web tilting can occur between the optical measuring units or measuring heads arranged on opposite sides of the web, resulting in an erroneous measurement.
Such tilting between an upper and a lower optical measuring unit or respectively their measurement plates 12, 14 caused for example by the air build-up of the moving web or respectively fibrous web 10 can be seen in
What is needed in the art is a method for accurate contactless determination of the thickness of a material web with which also on thinner webs or respectively papers and on webs or respectively papers having a thickness of <50 μm are obtained.
The present invention provides a sensor arrangement used for determining a thickness of a material web which includes at least one magnetic sensor as well as also optical distance measuring devices whereby the distance between the measurement plates which are arranged on opposite sides of the web, and the distance between a respective measurement plate and the web is measured through optical distance measurement devices which are provided on the measurement plates which are arranged on opposite sides of the web. According to the present invention a magnetic and an optical measuring method are therefore combined with each other. The measurement plates can always be kept at a constant distance from the web by means of air cushions.
In order to adjust the measurement plate distance to a constant value, the magnetically determined measurement plate distance may also be utilized. Magnetic determination of the distance between the measurement plates which are arranged on opposite sides of the web occurs, for example, through a magnetic measurement on at least three different locations.
The optical determination of the distance between a respective measurement plate and the web may occur respectively through at least three optical distance measuring devices provided on a respective measurement plate.
According to a first embodiment of the present inventive method, the thickness of the web is established from the magnetically determined distance between the measurement plates which are arranged on opposite sides of the web and the optically determined distances between the measurement plates which are arranged on opposite sides of the web, and the web. For this purpose an evaluation unit can be used with an appropriate algorithm in order to calculate the web thickness.
Since the magnetic sensors and the optical sensors cannot be arranged in the same location on the measurement plate, the magnetically determined distance values between the measurement plates which are arranged on opposite sides of the web are converted from the location of the magnetic sensors to the location of the optical sensors, whereby the required accuracy is achieved through the conversion of the magnetic measured value to the location of the optical sensors.
An additional improvement in the accuracy is achieved in that always all magnetically determined distance values between the measurement plates which are arranged on opposite sides of the web are used at the locations of the magnetic sensors to calculate the respective distance value at the location of the optical sensor. The magnetic determination of the distance between the measurement plates which are arranged on opposite sides of the web occurs, for example, through at least one magnetic sensor provided on the measurement plate on one side of the web. For the purpose of such magnetic determination of the measurement plate distance through the at least one magnetic sensor provided on one side of the web, the measurement plate on the opposite side of the web is at least partially formed of ferrite.
According to second embodiment of the inventive method, the magnetic determination of the distance between the measurement plates which are arranged on opposite sides of the web occurs through at least three magnetic sensors which are provided on the measurement plate on one side of the web.
A respective optical distance measuring device or respectively optical sensor of the inventive sensor arrangement may moreover be configured in particular as described in EP 1 855 082 A1 or EP 1 855 083 A1.
An optical sensor with a device to determine the distance to an object is known for example from EP 1 855 082 A1, whereby at least one lens arrangement is provided in order to focus light from a light source, such as a laser light source onto the object and to collect light reflected and scattered from the object, whereby an aperture element with a circular aperture is provided in order to form a circular light beam from the reflected and scattered light, and a detector system structured and arranged to receive the circular light beam, wherein the detector system is sensitive to the light beam diameter, whereby determination of the distance to the object is based upon signals from the detector system. An analyzer, allocated to the detector system can be configured for determination of the thickness of the object. Hereby a lens arrangement can be provided on both sides of the object and the lens arrangements provided on different sides may feature a defined distance from each other. The thickness of the object may in this case be determined in particular in that the respectively defined distances between lens arrangements provided on both sides of the object are added to the object and the thus obtained sum is subtracted from the defined or respectively determined distance between the lens arrangements.
EP 1 855 083 A1 describes a comparable optical sensor with which a light source of low coherence is used which can include a super-luminescence diode. An optical window may be provided between a respective lens arrangement and the object.
The above-mentioned and other features and advantages of this invention, and the manner of attaining them, will become more apparent and the invention will be better understood by reference to the following description of an embodiment of the invention taken in conjunction with the accompanying drawings, wherein:
Corresponding reference characters indicate corresponding parts throughout the several views. The exemplification set out herein illustrates one embodiment of the invention and such exemplification is not to be construed as limiting the scope of the invention in any manner.
Referring now to the drawings, and more particularly to
According to the present invention therefore, a method for contactless determination of the thickness of a material web, such as a fibrous web material with a sensor arrangement including at least two optical measurement plates between which the web can be guided is cited, whereby an air cushion is generated respectively between each measurement plate and the web so as to keep the measurement plates at a distance from the web. The fibrous web may be a paper or cardboard web.
A sensor arrangement is hereby used which includes at least one magnetic sensor 121-123, as well as also optical distance measuring devices 141-143. The distance between the measuring plates which are arranged on opposite sides of the web is hereby measured, and the distance between a respective measurement plate and the web is determined through optical distance measuring devices 141-143 which are provided on the measurement plates which are arranged on opposite sides of the web. The measurement plates can be kept at a constant distance from the web through the air cushions.
As indicated in
The optical determination of a distance between a respective measurement plate and the web can—also as indicated in FIG. 2—occur respectively through at least three distance measuring devices which are provided on a respective measurement plate, whereby in the current example respectively only three optical distance measuring devices 141-143 are provided on the measurement plates which are arranged on opposite sides of the web.
The thickness of the web can be established from the magnetically determined distance between the measurement plates which are arranged on opposite sides of the web and the optically determined distances between the measurement plates, which are arranged on opposite sides of the web, and the web. Here, in the first instance the magnetically determined distance values in positions 12k, 122, 123 are computed onto positions of optical sensors 14k, 142, 143. The geometric distances which are used for the calculation of the positions of the optical sensors are also defined in
H12=H1+(C1/A1)*[H1−(H2+H3)/2]+[(B2/2)/B1]*(H2−H3)
H13=H1+(C1/A1)*[H1−(H2+H3)/2]+[(B2/2)/B1]*(H2−H3)
H11=(H2+H3)/2+(C2/A1)*[(H2+H3)/2−H1]
H1: Magnetic measurement on 121
H2: Magnetic measurement on 122
H3: Magnetic measurement on 122
H11: Magnetic values calculated on 141
H12: Magnetic values calculated on 14
H13: Magnetic values calculated on 143
To calculate the actual thickness value of the web an evaluation device with an appropriate algorithm can be provided which suitably combines all determined measured values or respectively through which the web thickness is accordingly calculated.
As already explained, the magnetic determination of the distance between the measurement plates which are arranged on opposite sides of the web occurs, for example, through at least one magnetic sensor 121-123 provided on measurement plate 10 on one side of the web.
For the purpose of magnetic determination of the measurement plate distance through at least one magnetic sensor 121-123 provided on one side of the web, the measurement plate on the opposite side of the web can be formed partially or totally of ferrite.
The magnetic determination of the distance between the measurement plates which are arranged on opposite sides of the web can occur through at least three magnetic sensors 121-123 provided on measurement plate 10 on one side of the web, whereby in the embodiment of the referenced measurement plate 10 illustrated in
While this invention has been described with respect to at least one embodiment, the present invention can be further modified within the spirit and scope of this disclosure. This application is therefore intended to cover any variations, uses, or adaptations of the invention using its general principles. Further, this application is intended to cover such departures from the present disclosure as come within known or customary practice in the art to which this invention pertains and which fall within the limits of the appended claims.
This is a continuation of PCT application No. PCT/EP2010/057887, entitled “METHOD FOR THE CONTACTLESS DETERMINATION OF THE THICKNESS OF A WEB OF MATERIAL”, filed Jun. 7, 2010, which is incorporated herein by reference.
| Number | Date | Country | |
|---|---|---|---|
| 61222634 | Jul 2009 | US |
| Number | Date | Country | |
|---|---|---|---|
| Parent | PCT/EP2010/057887 | Jun 2010 | US |
| Child | 13339472 | US |
