Radiant energy – Photocells; circuits and apparatus – With circuit for evaluating a web – strand – strip – or sheet
Reexamination Certificate
2000-05-24
2002-02-19
Porta, David P. (Department: 2882)
Radiant energy
Photocells; circuits and apparatus
With circuit for evaluating a web, strand, strip, or sheet
C250S559120
Reexamination Certificate
active
06348696
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention relates to a method for detecting the position of a moving material web, as well as to a device for carrying out the method.
2. The Prior Art
A photoelectric sensor system is described in German Patent No. DE 34 23 308 C2, in which a light source is disposed opposite a plurality of independently acting receiver components. The receiver components are formed by semiconductor photocells, which are optically coupled to the surfaces of plastic panels. Each of the receiver components detects a defined zone of the material web, and the photocell sends out a signal that is proportional to the coverage by the material web. The position of the edge of the material web is determined by comparing the signals emitted by the photocells with a threshold value. This method has the drawback that the resolution achievable with such a sensor system substantially corresponds with the width of the plastic panels. Therefore, to obtain a high resolution combined with a large measuring range, a very large number of photocells is required, which makes such a sensor system expensive. Furthermore, a very large number of photocells must be interrogated in each measuring cycle, which leads to intolerably long measuring times.
A device for detecting the position of the edge of a moving material web is described in German Patent No. DE 42 09 546 C2, which shows a receiver component disposed opposite each of a plurality of separately controllable light sources. The receiver components emit a signal that is proportional to the coverage by the material web, and which is compared with a threshold value. The result of this comparison is supplied to a microcomputer that controls the light sources and the receiver components depending on the result of the comparison according to a successive approximation, to determine the position of the edge of the material web. To carry out this successive approximation, it is necessary to store a number of comparative values of the receiver components with the threshold value in a memory unit of the microcomputer.
SUMMARY OF THE INVENTION
It is therefore an object of the invention to provide a method of the type specified above that achieves high resolution in a short measuring time period.
It is another object of the invention to provide a device for implementing this method at a favorable cost.
These and other objects of the invention are accomplished by a method for detecting the position of an edge of a moving material web, in which the material web is scanned by a plurality of sensors distributed transversely to the moving direction of the web. In this process, each sensor generates a signal that depends on the amount that the web covers the sensor. The signal generated by the sensor is preferably proportional to the coverage by the material web. In this way, each sensor supplies a signal that depends on the position of the edge of the material web, and the individual sensors are arranged in different zones in the measuring direction.
The material web is preferably scanned without the web coming into contact with the sensors, so that even webs consisting of a sensitive material will not be damaged by the sensors. Furthermore, the sensors themselves are prevented from interfering with the detection of the edge, as compared to a mechanical edge sensor that is pressed against the edge of the material web by spring force. With the edge of the material web being in about the mean position, the inner sensors viewed from the center of the web are completely covered by the material web, and emit a constant idle signal. The outer sensors are not covered by the material web at all, and generate a maximum signal. The sensors located in the zone around the edge of the material web supply signals that are between the idle signal and the maximum signal.
Therefore, the function of the signals generated by the sensors from the sensor locations have two constant ranges of different signal intensities when the edge is in about the mean position, with a constant transition range between the two ranges. If the edge of the material web is in an extreme position, i.e., near the innermost or outermost sensor, one of the constant ranges may also be missing, so that the determination of the edge via threshold values becomes very inaccurate. It is therefore proposed according to the invention that the position of the edge be determined based on the turning point of the function of the signals generated by the sensors from the sensor locations. This turning point can also be determined when the edge of the web is in an extreme position even if the sensor signals can no longer be determined with complete coverage or complete release of a sensor by the material web.
The individual sensors are preferably distributed equidistantly transversely to the direction of movement of the material web, so that the sensor location can be determined in a particularly simple way by numbering the sensors. In this way, the detection of the turning point can also be determined based on the function of the sensor signals by th e sensor number. The result of the search for the turning point is multiplied by the mutual spacing of the sensors. The turning point can also be generally determined based on a function of the sensor signals of values that are proportional to the sensor sites. In order to obtain a correctly scaled web edge position, the detected turning point has to be subsequently multiplied by the proportionality factor. In those cases in which only a signal proportional to the edge position is required, which is the case with web guiding devices, it is possible to eliminate a corresponding correction of the determined reversing point.
The sensor integrates its signal from a predetermined area, so that deposits with small-sized surface areas resting on the surface of the sensor have only a minor influence on the signal generated by the sensor. This is important in connection with material webs that lose a lot of fluffy matter in the form of lint, because the lint originating from the material web may directly deposit on the surface of the sensor. If the sensor had an effective width below about 1 mm, each individual lint fragment could cause complete coverage of a sensor, which would be erroneously interpreted as an edge of the material web.
Due to the design of the sensor with a large effective surface area, lint deposits may only lead to a uniform dampening of the signals of all sensors, which has no influence on the position of the turning point. Increased insensitivity to dirt of the edge-sensing system is therefore achieved. Since the turning point can be determined with substantially greater accuracy than the spacing of the individual sensors, this measure will not become a burden on the accuracy of the detection of the edge.
The methods for detecting the coverage of the material web work without contact with the web, and consequently do not interfere with the movement of the web. It is also possible to safely scan webs of particularly sensitive materials without the risk of damaging the material web, or the risk of any falsification of the measured values. The coverage by the material web is optically detected either by the reflection method or based on the light barrier principle.
The material web is illuminated by at least one light source, with light-sensitive receivers either on the side opposite the material web, or next to the light source. Alternatively, the coverage of the material web could be scanned pneumatically by air jets. This requires pressure-sensitive sensors. With acoustic scanning of the material web, sound waves are aimed at the material web, which are then detected with the help of microphones.
The function of the signals originating from the location of the sensor are differentiated two times numerically and a zero coefficient is determined based on the second derivative. The zero coefficient of the second derivative conforming to the edge position is located in the area of the greatest ascent, thus at a maximum
Alt Gerhard
Brunner Gerhard
Häussler Harald
Seibold Hans
Collard & Roe P.C.
Erhardt + Leimer GmbH
Porta David P.
Yun Jurie
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