Abstract:
The invention relates to a device for detecting the location of an edge ( 2 ) of a transparent, anisotropic material ( 3,3 ′) comprising at least one sensor ( 1 ) with a light source ( 4 ), two polarization filters ( 6,7 ) with transmission axes ( 8,9 ) meeting at a 90° angle as well as a light detector ( 10 ), whereby the light source ( 4 ) and one polarization filter ( 6 ) are located on one side of the edge ( 2 ) to be detected and the second polarization filter ( 7 ) and the light detector are located on the other side. 
     This type of device is to be configured in such a way that it can be used for detecting material ( 3,3 ′) with optical axes ( 14 ) in various directions without requiring assembly. This is achieved by at least one of the sensors ( 1 ) being configured and/or adjustable so that various angles ( 32 ) between the transmission axis of the first polarization filter ( 6 ) and the optical axis ( 14 ) of the transparent, anisotropic material ( 3,3 ′) are possible. In addition, the invention is equipped for a web control edge ( 16 ) and printing press with such a web edge control.

Description:
FIELD OF THE INVENTION 
     The invention relates to a device for detecting the location of an edge of a transparent, anisotropic material, comprising at least one sensor with a light source, two polarization filters with transmission axes meeting at a 90° angle as well as a light detector, whereby the light source and one of the polarization filters are located on the edge to be detected and the second polarization filter and the light detector are located on the other side. 
     The invention further relates to a web edge control with such a device, a control device and a web edge adjustment device as well as a printing press with such a web edge control. 
     BACKGROUND OF THE INVENTION 
     A device for detecting the location of the edge of a transparent material is known from U.S. Pat. No. 5,751,443, whereby such light is to be directed on the transparent material so that it is reflected and then the reflected light is detected, in order to determine the location of an edge. The problem with a sensor using this method is that, if the material is soiled, the reflection properties are weakened, and thus the detection of the location of the edge is inaccurate or impossible. This is particularly true of continuous webs that transport goods, as well as printing presses, particularly electrophotographic printing presses that are equipped with a transparent web to convey printing substrates. Such web edges must, however, be detected, in order to adjust the location of the web. 
     A device from DE 199 06 154.8 of the type mentioned at the beginning was suggested to solve this problem. Its operating principle is based on the fact that polarization filters with transmission axes meeting at a 90° angle allow no penetration of light, since such polarized light passes only through the first polarization filter, which is blocked by the second polarization filter. If an anisotropic material with an excellent optical axis is introduced between the polarization filters, a beam or partial bean may occur, whose polarization direction is turned to 90°. This light penetrates the second polarization filter, so that a clear image of the material edge is produced on the light detector. This image is basically much more resistant to soiling than the image based on a reflection. However, the problem with this suggestion is that a beam or partial beam with a turned polarization direction does not occur if the light along the optical axis of the transparent material enters into this material. The light must then form an angle to the optical axis, which ensures that there is an easily detectable amount of light that is turned in its polarization direction. However, due to the manufacturing procedure and stress, the optical axis of transparent, anisotropic materials also has different alignments with a material of the same chemical composition. Such a device must thus be aligned with the respective optical axis in which the beam is turned in its polarization direction with an easily detectable intensity. Due to the above-mentioned reasons, this alignment must, however, be repeated with each piece of material to be detected. Where a wet to convey a product is concerned, each change of the web to a new web requires an alignment of the sensor with the optical axis of the new web. This problem may also well occur with an increase or decrease of the stress of the web. 
     SUMMARY OF THE INVENTION 
     In contrast to this suggestion, the task of the invention is to configure a device for detecting the location of an edge of a transparent, anisotropic material that does not require assembly for the detection of material with optical axes in various directions. 
     This task can be achieved by having at least one sensor of this type that can be arranged and/or is configured, so that various angles between the transmission axis of the first polarization filter and the optical axis of the transparent, anisotropic material are possible. 
     Thus a device would be provided that can detect the edge of a transparent, anisotropic material and whereby, by means of a simple tilting motion or another change of position with change in the angle direction of the polarized light, a position can be achieved in which the alignment to the optical axis of the respective material required to detect the material is possible. In this manner, it is possible to obtain the exact location of this type of material edge, which is relatively resistant to soiling and which thus solves the problem stated at the beginning, particularly where continuous web edge controls and webs transporting material, such as the web edge control for transparent, anisotropic webs of electrographic printing presses, are concerned. 
     The problem of the different optical axes occurs primarily because the optical axes of webs have various directions as a result of the manufacturing process and that the detection and adjustment of the location of such a web is difficult. The device according to the invention provides a web edge control in which the optical path is directed or can be directed to the edge of a transparent, anisotropic web to be detected in such a way that all possible courses of optical axes as a result of the change of the optical axes of the/a web can be adjusted, without requiring assembly. To this end, a sensor can be arranged such that it can be tilted, and several sensors can be arranged at various angle positions and the corresponding sensor can be selected or the optical path of one sensor of this type can be configured so that it is adjustable, and thus it and the polarized light can take various angle positions to the material to be detected and thus to its optical axis. 
     Particularly in the case of printing presses, the device according to the invention can reduce the maintenance costs, the use of assembly staff, and the machine downtime during a change of the web. Also with a change in the stress of a web and a concordant change of the location of the optical axis, the device can be aligned with the direction of the optical path without great expense. Another use for the invention is the detection of the edge of individual piece of material, since in this case as well, the different course of the optical axes must be taken into account. 
     The device according to the invention provides a simple means such that the polarized light takes an angle position to the material, in which a turn of the light emitted from the first polarization filter passes through the material to be detected to a sufficient degree to detect an edge, whereby an angle between the transmission axis of the first polarization filter and the optical axis of the transparent, anisotropic material is preferably selected, in which the best possible image of the edge on the light detector can be achieved. An optimum is achieved with a 45° angle, although an angle within the range of 25° and 65° will suffice to show an image of an edge. 
     There are various ways to configure the placement of the sensor in various positions to achieve the above-mentioned angle or another alignment of various angle positions of the polarized light to the material to be detected. It can be set up so that the angle between the transmission axis and the optical axis is exactly positioned or so that an angle position of a sensor is selected that lies in the 25° to 65° angle range. It is often sufficient to use two defined angle positions and that the angle position to the respective material is selected in which the edge is better shown. However, a plurality of multiple defined angle positions can also be envisaged, whereby the angle position to the respective material is selected in which the edge is better shown. The latter or an exact positioning of the angle is useful if the directions of the optical axes of the material to be detected is not limited to a particular angle range, but the optical axes can take all the various directions possible or, if a good image of the edge requires that the most optimal angle be selected, that the best optimal angle is selected, such as when a material of reduced transparency, caused by soiling, for example, is to be detected. 
     The sensor may also be tilted manually into the various positions and locked in this position. This can be implemented with any simple mechanics. A drive may also be used, which places a sensor in the most optimal position of possible positions with various angle positions. This is an advantage if the sensor is mounted on a part of the machine that is difficult to reach. In addition, a control can be used that is connected with the light detector and that the angle position for the image of the edge is selected on the light detector. This can, for example, permit the placing of a sensor in its optimal position. For example, the control can ensure that several positions are switched through and that the most contrasting image of the edge is selected. But it can also select the most optimal optical path from angle positions of several optical paths installed in any manner, or adjust an optical path in a corresponding manner. This type of device is very comfortable, since no further operating effort is required. If the material to be detected concerns individually transporter pieces that have optical axes in various directions, then this type of control is a very useful solution, since it automatically ensures very good detection of the edges. 
     In addition, a control can be further configured so that it adjusts the intensity of the light source and/or the responsivity of the light detector. The advantage of this control is that the device reacts automatically to a change of conditions and thus ensures a flawless image of the edge. Such changes may be due to some contamination, or because materials of various intensities of transparency are to be detected. 
     The control can adjust the set points on the basis of a corresponding algorithm of a program, or it is possible that the control has programmed set points for defined positions. In this manner, an optimal positioning is ensured. 
     The light detector may comprise several optical receiving components: for example, it may be configured as rows of optical receiving components, e.g., forming a CCD row, or it is possible that the light detector is configured as a flat receiver. With such arrangements, digital set points for further processing in an electronic control have been produced. In this sense, a flat receiver has the advantage that, by means of a single receiver, the inclined position of an edge can be detected. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     In the detailed description of the preferred embodiment of the invention presented below, reference is made to the accompanying drawings, in which: 
     FIG. 1 an exemplary embodiment of a web edge control according to the invention with a device according to the invention, which is configured as a swiveling sensor 
     FIG. 2 the operating principle of such a sensor 
     FIGS. 3 a ,  3   b  and  3   c  The effects of various angle positions of the polarized light on a material with various angle positions of the optical axis with respect to the degree of effectiveness of a sensor and 
     FIG. 4 an example for various angle positions of the optical axis of a web caused by the manufacturing process. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     FIG. 1 illustrates an exemplary embodiment of a web edge control  16  according to the invention with a device according to the invention that is configured as a swiveling sensor  1 . The sensor  1  is used to detect an edge  2  of a transparent anisotropic material  3 , for example, a transparent web  3 ′. 
     The sensor  1  consists of a light source  4  and two polarization filters  6 ,  7 , whose transmission axes  8 ,  9  meet at a 90° angle. In addition, a light detector  10  is arranged that may be configured as a CCD row, for example, or as an array of receiving components. The light source  4  and the first polarization filter  6  are located on one side with respect to the edge  2  of the transparent, anisotropic material  3  or  3 ′ to be detected, and the second polarization filter  7  with the light detector  10  is located on the other side of the material  3 ,  3 ′. 
     The invention recommends that the light source  4 , the polarization filters  6 , 7  as well as the light detector  10  be configured in such a manner that the sensor  1  can take various positions  11 ,  11 ′,  11 ″, . . . in which the polarized light  5  can take various angle positions  12 ,  12 ′,  12 ″, . . . to the material  3 ,  3 ′ to be detected, in order to find an angle  32  of the transmission axis  8  of the first polarization filter  5  at the optical angle  14  of the material  3 ,  3 ′ (see FIG.  2 ), in which an accurate detection of the edge  2  is possible. To this end, the sensor  1  is configured in such a way that the light source  4 , the polarization filters  6 ,  7  as well as the light detector  10  are located on a common carrier  30 , which can be swiveled around a swivel axis  19 . This swiveling capacity is configured in such a way that the sensor  1  can be moved from the position  11  indicated into other positions  11 ′,  11 ″, . . . in order to select a position  11 ,  11 ′,  11 ″, . . . in which the polarized light  5  with its optical axis  14  of the material  3 ,  3 ′ forms an angle that is wide enough to ensure a portion of the light, whose polarization direction  22  is turned is taken, and which is sufficiently intensive that it can be detected with the light detector  10 . To this end, the sensor  1  and thus the polarized light  5  can take the angle positions  12 ′ or  12 ″ illustrated in the exemplary embodiment. As a result, it is possible to envisage both of the illustrated positions  12 ′,  12 ″, or any of the angle positions  12  within the mechanically possible swiveling range can be envisaged as possible positions. 
     This type of sensor  1  may be configured in such a way that it may be manually swiveled and locked in various positions  11 ,  11 ′,  11 ″, . . . . In the exemplary embodiment illustrated, a drive  13  is used that can place the sensor  1  in the various positions  11 ,  11 ′,  11 ″, . . . . For this purpose, a control  15 , which is connected by a connecting line  20  to the light detector  10  and which selects a position  11 ,  11 ′,  11 ″, of sensor  1  and which can take a position  11 ,  11 ′,  11 ″, . . . in which the edge  2  is clearly shown on the light detector  10 . If such a clear image is achieved, then the control  15  allows a positioning movement  17 , based on the values, determined by the light detector  10 , to obtain the targeted position of the edge  2  by means of a web edge control device  18 , which is likewise connected to the control  15  by means of a connecting line. The drive  13 , the control  15  and the web edge control device  18  constitute a principal drawing. This component may be any configuration, whereby such a drive as well as the control can also be positioned in the above-mentioned vertical axis. 
     FIG. 2 shows the operating principle of the sensor  1 . The light source  4  emits unpolarized light  21 , whereby the only polarized light  5  passes through the first polarization filter  6  that has a polarization direction  22  lying in its transmission axis  8 . In the illustrated example, the transmission axis  8  is located on a coordinate system x, y, z at an angle of +45° on the y-axis in the y-z plane. As long as this polarized light  5  is not hitting a transparent, anisotropic material  3  or  3 ′, the polarization direction  22  is maintained and hits the second polarization filter  7 , whose transmission axis  9  is turned so that it lies at a 90° angle to the transmission axis  8  of the first polarization filter  6 , thus forming a 45° angle to the y axis appearing in the y-z plane. This prevents the polarized light  5  of the rays passing over the top half of the transparent material  3  from penetrating the second polarization filter  7 . The rays of the polarized light  5  act differently, in that they hit the transparent, anisotropic material  3 . With respect to a portion of the light  5 , during the course of the optical axis  14  of the material  3 , the polarization direction  22  is turned, which causes this portion of the light  5  to be polarized in the direction of the transmission axis  9  of the second polarization filter  7 , thus permitting this portion of light  5  to penetrate the second polarization filter  7 . The polarized light  5  penetrating the polarization filter  9  is detected by a light detector  10 . An illuminated surface  23  is thus produced by this polarized light  5 . As a result, the edges  2  of the material  3  are also shown as edges  24 . Thus the location of the transparent material  3  and its edge  2  are accurately detected. The remaining surface of the light detector stays dark, since the turned polarized light  5  that did not penetrate the transparent material  3  in its polarization direction  22  is blocked by the second polarization filter  7 . 
     The invention uses the setup of the transmission axis  8  of the first polarization filter  6  at the optical axis  14  to ensure, by means of the selected angle position  12 , that the polarized light  5  approaching the light detector  10  has the proper intensity to be able; to detect the edges  2  as clearly shown by edges  24 . The swiveling of the angle position  12  makes it possible to obtain the dash and dot axis  19  in the direction of the dash and dot arrow indicating the angle positions  12 , as illustrated in FIG.  1 . Since the swiveling occurs in the y-z plane, the angle position  12  changes between the polarized light  5  and the material  3 ,  3 ′ to be detected, and thus between the transmission axis  3  and optical axis  14 . If the change of the angle position  25  of the optical axis  14  of the material  3 ,  3 ′ likewise occurs in the y-z plane, as illustrated by the dash and dot arrow, symbolizing the angle position  25 , then within this plane, a coordination of the course of the transmission axis  8  to the optical axis  14  can be obtained, which ensures that the turning of the polarization direction  22  is sufficient. 
     FIGS. 3 a ,  3   b  and  3   c  show the effects of different angle positions  12 ,  12 ′,  12 ″, of the polarized light  5  to a material  3 ,  3 ′ with various angle positions  25 ,  25 ′,  25 ″, . . . of the optical axis  14  with respect to the degree of effectiveness  26  of a sensor  1 . 
     In addition, FIG. 3 a  shows the various angle positions  25  of the optical axis  14  of the material  3 , whereby the angle position  25 ′ is located at −35° and the angle position  25 ″ is located at +35° The area in between is the customary swiveling space of angle positions  25  of optical axis  14  during the manufacturing of the transparent web  3 ″. 
     FIG. 3 b  shows swiveling motions of the sensor  1  that are set up so that the sensor  1  can detect the edge  2  of a material  3 ,  3 ′, although different angle positions  25  of the optical axis  14  of the transparent materials  3 ,  3 ′ appear. The exemplary embodiment of FIG. 3 b  recommends in this case that the sensor  1  take an angle position  12 ′ of −17° or an angle position  12 ″ of +17°. It is thus not located in the dot and dash area of the 0° position  11 , but in one of the position  11 ′ or  11 ″ facing the material  3  or  3 ′ to be detected. Thus the swiveling of the sensor  1  is only an example that the polarized light  5  can take various angle positions  12 ,  12 ′,  12 ″, . . . to the material  3 ,  3 ′ to be detected. Further possibilities, such as placing the polarized light  5  in various angle positions  12 ,  12 ′,  12 ″, . . . are conceivable. 
     FIG. 3 shows the effect of the angle positions  12  or  12 ′ on the degree of effectiveness  26  of the sensor  1 . Here, the curve  27  is shown in comparison with the degree of effectiveness  26  of the sensor  1 , which is located in the dot and dash area of position  11  in FIG. 3 b . Here the polarized light  5  in the point  31  takes an angle position of 0° to the material  3 , whereby, by means of the relocation of the transmission axis  8  at 45° to the optical axis  14  (see FIG.  2 ), the maximum possible effectiveness  26  of 100% is achieved. This type of positioning has the disadvantage, however, that the effectiveness up to the angle  25  of the optical axis  14  drops from −35° or +35° to 0 and sensor  1  cannot function. 
     The exemplary embodiment thus recommends that it must be possible to place the sensor  1  in the second position  11 ′ and  11 ″, as illustrated in FIG. 3 b . The effect is plotted by means of the curves  28  and  29  in FIG. 3 c . Here the curve  28  shows the effectiveness of a sensor  1 , wherein the polarized light  5  is located in the angle position  12 ′, thus at −17° with respect to the perpendicular line on the surface of the material  3 . By contrast, the other curved portion  29  extends to the curved portion  28  in the positive area and represents the effectiveness  29  of a sensor  1 , wherein the polarized light  5  in the angle position  12 ″ is located at +17° with respect to the perpendicular line on the surface of the material  3 . Here both angle positions  12 ′ and  12  ′are laid out in such a way that the optimal effectiveness  26  in these angle positions and thus with 17° or +17 is ensured In these points  31  and  31 ′, 100% of the possible effectiveness  26  can be achieved, so that in the angle positions  12 ′ and  12 ″ of the polarized light  5  respectively, the transmission axis  8  is located at an angle of 45° to the optical axis  14  (see FIG.  2 ). It can thus be seen how already, by taking two possible angle positions  12 ′ and  12 ″, it is possible for a transparent material  3 ,  3 ′ to be detected whose optical axis  14  moves in an angle range  25  of way over +40° to −40′, whereby with an angle of 35° of the effectiveness  26  always still lies at a minimum of 80°. Thus there are materials of ±45° with respect to the 0° position that can still be clearly detected up to the angle deviations  25  of the optical axis  14 , which at the position  12  is not possible. 
     FIG. 4 shows an example for angle positions  25  of the optical axis  14  of transparent, anisotropic webs  3 ′ resulting from the manufacturing process. When such webs  3 ′ are produced, wide webs are often are manufactured for economic reasons, from which several  3 ′ webs are then cut. Due to the manufacturing process, a course of angle positions  25  of the optical axis  14  occurs, which corresponds to the course plotted. Thus the course of the optical axis  14  may vary between 0° and a maximum of ±45, for example, whereby certain angle differences can be found across the entire width of the individual webs  3 ′. The sensor  1  must thus be adjusted to the angle position  25  of the optical axis  14  in the area of a web  3 ′ in which the edge  2  is supposed to be detected. This can easily be done by means of swiveling the sensor  1  according to the invention or by means of another change of the angle position  25 ,  25 ′,  25 ″, . . . of the polarized light  5 , and it is possible to accurately detect such webs  3  and adjust the position of the webs  3 ′ by a positioning movement  17  based on this detection. This is of particular importance with the electrophotographic printing press, since in this case, webs  3 ′ are used in the manner illustrated in FIG.  4  and that, with a change of a web  3 ′, it must be possible to immediately align a web edge control  16  with the new course of the optical axis  14 , in order to continue operating the press with minimum downtime. In addition, the invention makes it possible for the operator to change the web  3 ′ himself, since the setting of sensor  1  takes no effort. 
     The illustrations are, of course, only examples; they show one way in which a sensor  1  and a web edge control  16  can be produced and explain the operating principle of the invention. Various positions of a sensor  1  can not only be achieved by swiveling motions around a swivel axis  19 , best it is also possible to achieve an even larger positioning area with other mechanical devices for positioning the sensor  1  in various positions  11 ,  11 ′,  11 ″, . . . . In addition, it is also possible to use any position  11  of the sensor  1  or a defined number of several positions  11 ,  11 ′,  11 ″, . . . . The respective embodiment shows how such a sensor  1  can be concretely used. 
     Of course, instead of a mechanical positioning—as mentioned above—an arrangement of several sensors  1  can also be used, or the angle positions  12 ,  12 ′, &#39; 12 ″, . . . may be determined by means of a selection of a sensor  1  from positioned sensors  1  in various angle positions  12 ,  12 ′, &#39; 12 ″. It is also possible to use a sensor  1  with optical means with various angle positions  12 ,  12 ′, &#39; 12 ′, . . . from which one is selected to detect the edge  2  of a material  3 ,  3 ′. Adjustable optical means may also be envisaged. 
     The invention has been described in detail with particular reference to certain preferred embodiments thereof, but it will be understood that variations and modifications can be effected within the spirit and scope of the invention. 
     Parts List 
       1  Sensor 
       2  Edge 
       3   3 , 3 ′ Transparent, anisotropic material 
       3 ′ Transparent web 
       4  Light source 
       5  Polarized light 
       6  First polarization filter 
       7  Second polarization filter 
       8  Transmission axis of the first polarization filter 
       9  Transmission axis of the second polarization filter 
       10  Light detector 
       11 ′  11 ″, . . . Position of the sensor 
       12 ′  12 ″, . . . Angie positions of the polarized light to the transparent material, e.g., as angle positions of a sensor 
       13  Drive of the sensor 
       14  Optical axis of the transparent material/transparent web 
       15  Control 
       16  Web edge control 
       17  Positioning movements for the web edge 
       18  Web edge control device 
       19  Swivel axis 
       20  Connecting lines 
       21  Unpolarized light 
       22  Polarization direction 
       23  Illuminated surface of the light detector 
       24  Edges shown 
       25 ′,  25 ″ Angle positions of the optical axis of the transparent, anisotropic material 
       26  Degree of effectiveness of the sensor 
       27  Degree of effectiveness of a sensor with an angle position  25  of the optical axis  14  between −40° and +40°, if the angle position of the sensor at 0° produces the optimum (i.e., the transmission axis  8  forms an angle of 45° to the optical axis  14 ) 
       28  Degree of effectiveness of a sensor with an angle position  25  of the optical axis  14  between −40° and 0°, if the angle position of the sensor at −17° produces the optimum (i.e., the transmission axis  8  forms an angle of 45° to the optical axis  14 ) 
       29  Degree of effectiveness of a sensor with an angle position  25  of the optical axis  14  between 0° and +40°, if the angle position of the sensor at +17° produces the optimum (i.e., the transmission axis  8  forms an angle of 45° to the optical axis  14 ) 
       30  Common carrier 
       31 , 31 ′ Points of the maximum effectiveness (100%) by means of a location of the transmission axis  8  with an angle of 45° to the optical axis  14   
       31  Point with one possible angle position 
       31  ′ Points with two possible angle positions 
       32  Angle between the transmission axis  8  of the first polarization filter and the optical axis  14  of the transparent, anisotropic material