Patent Publication Number: US-2023152171-A1

Title: Force Measuring Device for Measuring Web Tensions of a Running Material Web

Description:
The present invention relates to a force measuring device for measuring web tensions of a running material web that comprises a longitudinal direction defined by the running direction, and a transverse direction perpendicular thereto. Here, the force measuring device comprises an axle and, supported on the axle, a measuring roll wrapped around by the material web. 
     In systems for manufacturing or further processing web-shaped materials, for example paper, plastic foils or aluminum foils, the material webs are processed at the beginning of the processing operation with web widths of a few meters. Often, for further processing, for example in label printing or packaging manufacture, considerably narrower webs are required and for this, the material webs are cut into narrower longitudinal strips of the desired width on slitter winders. Conventional force measuring devices measure the web tension of the entire material web over the full roll width, but for the further processing of cut webs, it would be advantageous to obtain more precise information about the distribution of the web tension along the transverse direction of the running web. 
     This is where the present invention begins. The object of the present invention, as characterized in the claims, is to specify a force measuring device of the kind mentioned above with which the distribution of the web tension along the transverse direction of a running material web can be measured. 
     Said object is solved by the features of the independent claims. Developments of the present invention are the subject of the dependent claims. 
     According to the present invention, in a generic force measuring device, it is provided that
     the measuring roll is formed as a segmented measuring roll having two or more measuring segments that are separately slidable on the axle and lockable in a measuring position on the axle in order to position the measuring segments in the transverse direction of the material web in accordance with desired measuring positions such that longitudinal sections of the material web wrap around one measuring segment each,   the measuring segments each comprise a load cell that serves to determine the web tension of the longitudinal section of the material web wrapped around the respective measuring segment and that provides a mount with which the measuring segment sits on the axle, and   the axle is furnished with electrical conductors that extend substantially in the axial direction across the entire width, that are contactable at every position axially and with which the measuring signals supplied by the load cells of the measuring segments are conductible to an evaluation unit arranged at an axle end.   

     The electrical conductors of the axle can be arranged in an inner axial chamber, for example the guide chamber described in greater detail below, but they can also be arranged on the exterior of the axle, for example in an axial exterior groove of the axle. Here, it is important only that the electrical conductors are contactable at every position axially at which measuring segments are lockable, that is, substantially at every position along the width of the axle, such that, regardless of the respective measuring positions of the measuring segments, they can conduct to the evaluation unit the measuring signals supplied by the load cells. 
     Here, the measuring segments expediently comprise, in addition to the load cell, a roll shell and, supported by the load cell, a bearing for the roll shell. 
     In one preferred embodiment, the load cell includes in each case, lying on the axle, an inner ring that provides the said mount. The load cell further comprises a concentric outer ring that is slidable with respect to the inner ring upon the application of force, and a measuring section that connects the inner ring and outer ring in a connecting region. When measuring the web tension, due to the application of force, the outer ring is slid radially relative to the inner ring and, as a result, tensions are produced in the measuring section that can be measured by means of strain gauges. 
     The inner ring particularly advantageously comprises an indentation in which the connecting region with the outer ring is accommodated. The indentation can extend radially up to half the radius of the inner ring, preferably even to the middle of the inner ring. The load cell is advantageously guided in an axial guide chamber of the axle with the indentation of the inner ring. In this way, a particularly compact architecture of the load cell and the force measuring device is achieved and, moreover, the load cell is integrated with the axle of the force measuring device. 
     According to one advantageous variant of the present invention, the inner ring and the outer ring are arranged radially nested and are connected in a radial connecting region by the measuring section. As overload protection, the inner ring and the outer ring are preferably separated outside the connecting region by a narrow radial gap whose width is dimensioned such that, in the event of overload, the movable outer ring rests against the inner ring fixed on the axle. The gap width corresponds, for example, to 110% of the measuring path at nominal load and is typically in the range of a few tenths of a millimeter. 
     In another, likewise advantageous embodiment, the inner ring and the outer ring are arranged spaced apart axially and are connected in an axial connecting region by the measuring section. 
     The load cell is advantageously furnished with strain gauges for measuring the web tension. Preferably, the measuring section that connects an inner ring and outer ring is furnished with the said strain gauges for measuring the mechanical tension produced in the measuring section. 
     In one advantageous embodiment, the measuring section is formed in the form of a double-bending beam. 
     The inner ring, the outer ring and the measuring section of the load cell are particularly advantageously formed to be one piece. 
     According to one preferred embodiment, the axle is formed as an extruded profile. The extruded profile preferably comprises a vertical ridge and two horizontal guide rails that extend from the vertical ridge, such that the vertical ridge and the two guide rails form a U-shaped axial guide chamber in the extruded profile of the axle. 
     Alternatively, the axle can also be formed as a milled axle, in which the axial guide chamber and, if applicable, further indentations, such as an axial groove for an air hose and a pressure strip, are milled into a round bar. The manufacture of the axle as a milling element is simple and inexpensive, but permits no radially closed hollow spaces and thus generally entails a higher weight than extruded profiles of the same bend resistance have. 
     The axle is advantageously furnished in a guide chamber with axially running power rails that are contactable at an arbitrary axial position of current collectors in the load cells of the measuring segments and that form said electrical conductors. Particularly advantageously, in the axial guide chamber, both the load cell is guided with the indentation of the inner ring, and the axially running power rails are arranged. 
     The measuring segments preferably each include an electronics unit for supplying the strain gauges and for receiving, for preamplifying, preferably in addition to digitalizing, and for discharging the preamplified and, if applicable, digitalized measuring signals into the electrical lines, especially the power rails in the axle. A digitalization of the measuring signals is advantageous especially when the segmented measuring roll comprises a larger number of measuring segments, for example four or more or six or more measuring segments, since the digitalized measuring signals can then, using a bus protocol, be conducted to the evaluation unit via a few, typically two, power lines. Especially when the segmented measuring roll includes only a small number of measuring segments, the measuring signals can, of course, also be conducted to the evaluation unit in analog form, each via its own power line. 
     For measuring the rotational speed, every measuring segment is advantageously furnished with a device for measuring the rotational speed, the device preferably comprising one or more magnets that rotate with the roll shell, and a static Hall effect generator connected with the load cell. From the Hall voltage produced upon rotational, the rotational speed of every measuring segment can be determined in the manner known to the person of skill in the art, and conducted to the evaluation unit via the electronics unit. The individual determination of the rotational speed of every measuring segment permits especially the determination whether slip occurs in one or more measuring segments in operation. 
     In one preferred embodiment, the axle includes, in an axial groove, an air hose and a pressure strip for locking the measuring segments on the axle. Here, the evaluation unit preferably includes a pressure sensor for monitoring the air pressure of the air hose. In the event of a deviation of the air pressure from the target value, the evaluation unit can, for example, emit a warning signal or initiate other suitable measures. 
     In one advantageous embodiment, the measuring segments are each furnished with lateral spacers whose size is coordinated with the size of the respective roll shell in such a way that the measuring segments can be slid together on the axle in such a way that the roll shells lie next to one another practically without gaps, but without touching one another. In practice, this means clearances of the roll shells in the slid-together state of a few tenths of a millimeter up to about one millimeter. 
     On the axle are advantageously positioned and locked two or more, especially three or more, four or more or even six or more measuring segments, such that the measuring roll is formed as a segmented measuring roll having two or more, three or more, four or more or even six or more measuring segments . 
     In one advantageous embodiment, the measuring segments are each positioned and locked on the axle with spaced apart roll shells, such that the segmented measuring roll is adapted and configured especially for measuring the web tensions of the longitudinal strips of a cut running material web. The number and the positions of the measuring segments and the width of their roll shells are expediently adapted to the number, the positions and the widths of the cut longitudinal strips of the material web. 
     In another, likewise advantageous embodiment, the measuring segments are positioned and locked on the axle in such a way that their roll shells are adjacent practically without gaps without touching each other. The segmented measuring roll is then adapted and configured especially for measuring the web tensions of the longitudinal sections of an uncut running material web and thus for the measuring of a tension profile in the transverse direction of the material web. The number and the positions of the measuring segments and the width of their roll shells are expediently adapted to the resolution requirements for the measuring of the tension profile. 
     The force measuring device according to the present invention enables the measuring of the web tensions in the transverse direction of a running material web both in the individual longitudinal strips of a cut web and locally in the longitudinal sections of an uncut web. It is understood that, during operation of the force measuring device, the slidable and lockable measuring segments are each locked in a certain position that corresponds to the location of the desired web tension measurement. If another tension profile or the web tension of another longitudinal strip configuration is to be subsequently measured with the force measuring device, the lockings are disengaged and the measuring segments are slid on the axle accordingly and relocked. If another number of measuring segments is required, or if measuring segments of another width are required, measuring segments can also be removed from the axle and/or additional or different measuring segments of desired width pushed onto the axle. The described force measuring device can thus be adapted very flexibly to the respective measuring job and the measuring requirements. 
     By measuring the web tensions of the longitudinal strips of a cut web, it becomes possible to individually control the winding process and thus avoid a lot of waste due unsuitable tension conditions in individual longitudinal strips. Knowing the tension profile is often of great benefit with uncut material webs, as well. For example, when manufacturing blown films, by measuring the tension profile of the film tube produced, the cooling profile of the molten tube can be readjusted to obtain a uniform tension profile of the film tube. 
     Further exemplary embodiments and advantages of the present invention are explained below by reference to the drawings, in which a depiction to scale and proportion was dispensed with in order to improve their clarity. 
    
    
     
       SHOWN ARE 
         FIG.  1    schematically, a material web, cut into longitudinal strips, in which the web tensions of the longitudinal strips are to be measured individually, 
         FIG.  2    schematically, a force measuring device according to the present invention, 
         FIG.  3    a cross section through a force measuring device according to the present invention in a direction corresponding to the line III-III in  FIG.  2   , 
         FIG.  4    the load cell of a measuring segment of the force measuring device in  FIG.  3    separately, in cross section, 
         FIG.  5    a perspective view of the load cell in  FIG.  4   , 
         FIG.  6    the axle of the force measuring device in  FIG.  3    separately, in perspective view, 
         FIG.  7    in (a) the axle in  FIG.  6    in cross section, in (b) a milled axle according to a further exemplary embodiment of the present invention, 
         FIG.  8    the load cell in  FIG.  4    with the electronics circuit board and the contact regions with the strain gauges and the power rails of the axle drawn in, 
         FIG.  9    a load cell according to the present invention having a measuring section that runs in the axial direction, in cross section, 
         FIG.  10    schematically, a force measuring device according to the present invention configured for recording the tension profile of an uncut material web, and 
         FIG.  11    schematically, a tension profile of an uncut material web, measured with the force measuring device in  FIG.  10   , in which the force F is plotted over the dimension x in the transverse direction. 
     
    
    
     The present invention will now be explained using the example of a force measuring device for measuring web tensions of a cut running material web. 
       FIG.  1    shows, by way of example, a material web  10  whose running direction defines a longitudinal direction L and a transverse direction Q perpendicular thereto. In the exemplary embodiment, the material web  10  is cut into n=6 longitudinal strips, namely having one longitudinal strip  12 - 1  of average width, two wider longitudinal strips  12 - 2 ,  12 - 3  and three narrower longitudinal strips  12 - 4 ,  12 - 5 ,  12 - 6 . 
     For the subsequent winding process of the longitudinal strips, it is advantageous to know the web tension in each of the strips individually. While conventional measuring devices permit only a measuring of the web tension of the entire web  10  over the full roll width, the inventive force measuring device  20  described below enables separate measuring of the web tension in every single one of the plurality of longitudinal strips  12 - i  (i=1...6) of the material web  10 . 
       FIG.  2    shows, diagrammed schematically, a force measuring device  20  according to the present invention. The force measuring device  20  includes a bend-resistant axle  22  that lies at both of its ends on an on-site substructure, not shown. Supported on the axle  22  is a measuring roll  30  that, in operation, is wrapped around by the material web  10  to be measured. 
     According to the present invention, the measuring roll is formed as a segmented measuring roll  30  that, in the exemplary embodiment, serves to measure the web tension of the 6 longitudinal strips  12 - i  of the material web  10  in  FIG.  1    and thus consists of n = 6 measuring segments  32 - i , where i = 1...6, adapted to the longitudinal strips  12 - i . 
     As in  FIG.  2   , the measuring segments  32 - i  can differ in their width, especially the width of their roll shell, but otherwise they are preferably formed identically with their structural features. The following description of a measuring segment thus pertains to all measuring segments  32 - i  of the measuring roll  30 , such that, for the sake of simplicity, the index i is usually omitted. 
     The measuring segments  32  are separately slidable on the axle  22  and lockable in a measuring position on the axle to be able to position them in the transverse direction Q of the material web  10  in accordance with the desired measuring positions in such a way that the longitudinal strips  12 - i  of the material web  10  each lie on a roll shell  34  of an associated measuring segment  32 - i  and wrap around said roll shell. The roll shell  34  of the measuring segments is, in each case, connected via a rolling bearing  38  with a load cell  36  that serves to determine the web tension of the longitudinal section  12  of the material web  10  wrapped around the respective measuring segment. Moreover, the load cell  36  provides a mount with which the respective measuring segment  32  sits on the axle  22 . 
     The width of the roll shells  34  of the measuring segments  32  is adapted to the width of the associated longitudinal strips  12  of the material web, as depicted in  FIGS.  1  and  2   . In the exemplary embodiment, the measuring roll  30  thus consists of a measuring segment  32 - 1  having a roll shell of average width, two measuring segments  32 - 2 ,  32 - 3  having wider roll shells and three measuring segments  32 - 4 ,  32 - 5 ,  32 - 6  having narrower roll shells. 
     The axle  22  is furnished with electrical conductors  26  that extend substantially in the axial direction across the entire width, that are contactable at every position axially and with which the measuring signals supplied by the load cells  36  of the measuring segments  32  are conducted to an evaluation unit arranged at an axle end  28 . Here, the electrical conductors  26  can be arranged on the exterior of the axle  22 , for example in an axial groove, but they can advantageously also be present in a guide chamber in the axle, described in greater detail below. The measuring segments  32  are further furnished with spacers  40  whose function is explained in greater detail at  FIG.  10   . 
     One advantageous development of the measuring segments  32  and the axle  70  of a force measuring device according to the present invention will now be described in greater detail with reference to  FIGS.  3  to  7   . Here,  FIG.  3    shows a cross section through the force measuring device  20  in a direction corresponding to the line III-III in  FIG.  2   . The load cell  36  of a measuring segment  32  alone is depicted in  FIG.  4    in cross section and in  FIG.  5    in perspective view, the axle  70  alone is shown in perspective view in  FIG.  6   , and in  FIG.  7    in cross section. 
     With reference first to  FIG.  3   , the measuring segment  32  includes, radially from exterior to interior, a roll shell  34 , a rolling bearing  38  and a load cell  36 . The longitudinal strip  12  of the material web  10 , wrapped around the measuring segment  32 , is indicated with dashed lines. 
     Here, the load cell  36 , which is depicted again separately in  FIGS.  4  and  5   , comprises an outer ring  50 , a concentric inner ring  52  and a measuring section  54  having an H-shaped recess  56 . The outer ring  50  comprises notches  58  ( FIG.  5   ) for retaining the rolling bearing  38  via retaining rings, not shown, the inner ring  52  lies on the axle  70  and provides the above-mentioned mount. In the exemplary embodiment, the inner ring  52  and the outer ring  50  are arranged radially nested and connected in a radial connecting region by the measuring section  54 . For this, the inner ring  52  comprises an indentation  66  that extends radially to the center of the inner ring  52 . On one hand, the indentation  66  accommodates the connecting region with the outer ring, on the other hand, it serves to securely guide the load cell in the axial guide chamber  80  ( FIG.  7   ) of the axle  70 . 
     The outer ring  50 , the inner ring  52  and the measuring section  54  are formed to be one piece, the different hatchings in  FIGS.  3  and  4    serve merely to illustrate the different functional regions  50 ,  52 ,  54  of the load cell  36 . 
     Outside the connecting region, the inner and the outer ring are separated by a radial gap  60  whose width is dimensioned such that, in the event of overload, the movable outer ring  50  rests against the inner ring  52  fixed on the axle  70  and, in this way, avoids a plastic deformation and thus a destruction of the load cell  36 . In the exemplary embodiment, the width of the gap  60  is adapted for 110% of the measuring path at nominal load. 
     Due to the H-shaped recess  56 , the measuring section  54  forms a double-bending beam in which, in the exemplary embodiment shown, strain gauges  62  are arranged on its top side for measuring the mechanical tension on the material surface produced by the application of force. It is understood that strain gauges  62  can also be provided on the bottom side or on both the top and bottom side of the double-bending beam. 
     The wrapping around of the measuring segment  32  with a longitudinal strip  12  of the material web produces a force  64  that is dependent on the wrap angle and the web tension and that pushes the movable outer ring  50  of the load cell  36  downward with respect to the fixed inner ring  52  and, in this way, leads to a bending of the double-bending beam of the measuring section  54 . This bending is measured by the strain gauges  62  and a corresponding electrical signal is produced that is preamplified by an electronics unit in the measuring segment  32  and transmitted in suitable form via the power rails of the axle  70  to the evaluation unit  28 . 
     With reference to  FIGS.  3 ,  6  and  7   (a), in the exemplary embodiment shown, the axle  70  is formed as an extruded profile that can accommodate multiple individually measuring measuring segments  32  across its width, as shown schematically in  FIGS.  2  and  10   . The formation of the axle  70  as an extruded profile enables a bend-resistant formation of the axle, which does not deform, or deforms only minimally, even in the event of maximum load due to high web tensions, and thus does not influence either the geometric arrangement of the measuring segments across the width or the web tension measurement. 
     In the exemplary embodiment, the extruded profile axle  70  is formed having a circular cross-sectional circumference  75 . It includes a central vertical ridge  72  that ensures the stability of the axle, and from which two horizontal guide rails  74 , 76  and a guide curve  78  extend. Together with the ridge  72 , the horizontal guide rails  74 , 76  form in the axle  70  a U-shaped, axial guide chamber  80  that is open on one side and into which the indentation  66  of the inner ring protrudes for guiding and for electrically connecting the load cell ( FIG.  3   ). The guide curve  78  and the radial outer surfaces of the guide rails  74 ,  76  are adapted in their curvature to the curvature of the inner ring  52  with tight tolerance such that, on the one hand, the measuring segments  32  are easily slidable on the axle, but on the other hand, are also easily and securely lockable by a, for example, mechanical or pneumatic locking mechanism. 
     To conduct the electrical signals produced by the strain gauges  62  of the load cell of a measuring segment  32  to the evaluation unit  28 , the lower horizontal guide rail  76  of the axle  70  is furnished in a recessed region with axially running power rails  82  that facilitate the power supply and the electrical contact with the measuring segments  32  regardless of their position on the axle  70 . It is understood that the power rails can also be provided at another location in the guide chamber, for example on the upper guide rail  74  or also on both guide rails  74 ,  76 . 
     Instead of an extruded profile, the axle can also be formed as a milled axle  170 , as depicted in  FIG.  7   (b), into which a U-shaped, axial guide chamber  80  and an axial groove  84  are milled. Here, the axle body  172  includes a central vertical supporting structure that ensures the stability of the axle and from which two horizontal guide rails  174 ,  176  extend to form, together with the axle body  172 , within the cross-sectional circumference  175 , a U-shaped, axial guide chamber  80  in the axle  70  into which the indentation  66  of the inner ring projects for guiding and for electrically connecting the load cell. 
     As illustrated in  FIG.  8   , the load cells  36  include, in addition to the mechanical elements already described, a circuit board  90  having an electronic coupling that, for supplying and receiving the measuring signal, is connected in a contact region  92  with the strain gauges  62  and that, via current collectors  94 , can establish contact with the power rails  82  at any arbitrary axial position of the axle  70 . In the exemplary embodiment shown, the electronic coupling of the circuit board  90  includes, for processing the signals, a preamplifier that amplifies and digitalizes the measuring signals of the strain gauges  62  and relays the digitalized measuring signal to an internal bus. 
     Arranged at an end of the axle is the evaluation unit  28  that communicates with the measuring segments  32 - i  on the axle  70  and receives and further processes their measured values. For this purpose, in the exemplary embodiment, the power rails  82  include, in addition to two power rails for the power supply, two further power rails for a data transmission to the evaluation unit  28 , for example according to the RS-485 standard. If a measuring roll includes only a few measuring segments, or if no digitalization is to occur for other reasons, the preamplified measuring signals can, of course, also be conducted to the evaluation unit in analog form, each via its own power rail. 
     For its part, the evaluation unit  28  communicates via a standardized bus protocol with a higher-level controller that triggers suitable actions based on the measured values provided by the different measuring segments  32 , for example causes the drives to run slower or faster, emits an alarm signal, or the like. 
     The secure locking of the measuring segments  32  on the axle  70  is done in the exemplary embodiment with the aid of an axial air hose  86  and an axial pressure strip  88  ( FIG.  3   ) that are both embedded in a groove  84  formed in the guide curve  78  of the axle  70 . 
     In the slackened state of the air hose  86 , the measuring segments  32  are freely slidable on the axle and can be arranged in the desired number at the desired positions on the axle. If the air hose  86  is then inflated, it presses with an air-pressure-dependent force against the pressure strip  88 , which is thus pushed radially slightly out of the groove  84 . As a result, the pressure strip  88  clamps the positioned measuring segments  32  against a defined stop on the axle  70  and, in this way, simultaneously locks all measuring segments  32  in their correct position. Through a slackening of the air hose  86 , the locking is disengaged again and the measuring segments can be slid and/or exchanged. The air pressure of the air hose  86  is monitored by a pressure sensor arranged in the evaluation unit  28  at the end of the axle. 
     In another variant of the present invention, instead of the air hose and the pressure strip, it is provided that the measuring segments  32  are each furnished with a mechanical locking device through which they can be individually fixed on the axle. 
     In the exemplary embodiment described in  FIGS.  3  to  8   , the measuring section  54  runs between the inner and outer rings in the radial direction, which is currently preferred due to the simpler construction and high positive tension. However, it is likewise possible to have the measuring section of a measuring segment run in the axial direction, as explained below with reference to the exemplary embodiment in  FIG.  9   , in which a measuring segment  100  according to the present invention is shown schematically in side view. 
     The measuring segment  100  includes a load cell  102  that comprises an outer ring  110 , a concentric inner ring  112  arranged spaced apart axially and an axial measuring section  114 . The inner ring  112  sits with little tolerance on the axle  22 , indicated in the figure with dashed lines, such that it can be slid along the axle in the untensioned state. The outer ring  110  bears exteriorly the bearing retainer for the rolling bearing  38 , on whose exterior circumference the roll shell  34  is attached. 
     The outer ring  110  and the inner ring  112  are connected by an axial measuring section  114  that, in the exemplary embodiment, comprises a substantially H-shaped recess  116  and forms a double-bending beam that is furnished with strain gauges  62  for measuring the tensions of the measuring section  114 . The tolerance of the outer ring  110  with respect to the axle  22  is dimensioned such that, in the event of overload, the outer ring rests against the axle  22  and, in this way, prevents any destruction of the load cell  102 . 
     If, due to the web tension, a force  64  presses on the roll shell  34  of the measuring segment  100 , the force is transmitted via the rolling bearing to the outer ring  110 , which rests on the inner ring  112  via the measuring section  114 . The tensions produced in this way in the measuring section  114  are measured by the strain gauges  62 , and the electrical signals produced are, as already generally described above, preamplified, if applicable digitalized, and passed into the power lines of the axle  22 . The fixation of the measuring segments  100  on the axle can occur, for example, mechanically or pneumatically, as likewise already described above. 
     In addition to the measuring of the web tensions of cut longitudinal strips of a material web, the force measuring device according to the present invention permits, through the independent web tension measurement of the measuring segments, also the recording of a tension profile of an uncut material web. 
     For this, with reference to  FIG.  10   , the measuring segments  32  of the force measuring device  20  are positioned and locked on the axle  22  in such a way that their roll shells  34  are adjacent practically without gaps without touching each other (reference sign  120 ). To ensure this, the measuring segments  32  are furnished with lateral spacers  40  ( FIG.  5   ) whose size is coordinated with the size of the respective roll shell  34  in such a way that, when the measuring segments  32  are pushed together, the desired side-by-side arrangement  120  practically without gaps with mutual clearances of the roll shells of a few tenths of a millimeter is achieved. 
     Since every measuring segment  32  measures the local web tension BZ(x) at the location x of the respective measuring segment along the transverse direction Q of the material web, a tension profile  122  of the material web can be measured with the plurality of measuring segments  32 , as depicted schematically in  FIG.  11   . In the tension profile diagram shown there, the local web tension Bz(x) is plotted over the spatial coordinate x in the transverse direction of the material web. From the knowledge of the tension profile, suitable measures can then be derived, for example for a non-uniform profile, control measures can be taken that lead to a more uniform tension profile. If the temporal progression of the local web tension is displayed, for instance, in a waterfall diagram, also periodic signals, such as non-round supply reels, periodic wrinkling and the like can be easily identified. 
     The width of the measuring segments  32  used for the tension profile measurement can be identical, as in the exemplary embodiment in  FIG.  10   , but it can also be expedient to use measuring segments  32  of different widths. For example, in the middle region of the material web, measuring segments having narrower roll shells than at the edge regions of the material web can be used. 
     It can be determined whether slip occurs in one or more measuring segments by measuring the rotational speed of the individual measuring segments  32 . Here, the fastest-rotating segment in each case provides the reference value. To determine the rotational speed of the measuring segments  32 , there can, for example, be mounted in each measuring segment, via a mount  130  on the roll shell  34 , two magnets  132  offset from each other by 180°, as depicted in  FIG.  3   . The load cell  36  is furnished at a suitable location with a Hall effect generator which the magnets  132  periodically run past when the roll shell  34   rotates and produce in the Hall effect generator a Hall voltage from whose temporal progression the rotational speed of the measuring segment can be determined. The signals of the Hall effect generator are conducted to the evaluation unit via the electronics unit ( FIG.  8   ) and evaluated. For example, the rotational speed of the fastest rotating measuring segment is defined as the reference value, and for a measuring segment whose rotational speed falls below the reference value by a predetermined threshold value, a slip is displayed.