METHOD AND APPARATUS FOR MONITORING A MOVING WEB

Abstract

A monitoring apparatus (8) for monitoring a moving web (5), especially for defects (F), using analyzed image data of the web (5) comprises at least two camera elements (14, 140) that may be positioned adjacent one another perpendicular to the direction of transport (T) of the web (5). Said device comprises a control and evaluating unit (20, 200) and at least one serial communication link (21, 22) that connects at least one camera element (14, 140) to the control and evaluating unit (20, 200). Each camera element (14) comprises an area scan element (15) for capturing raw data (BI).

The monitoring apparatus (8) comprises at least one camera module (13, 130, 131) that contains at least one camera group (G1, G2) having at least two camera elements (14, 140) and a housing (17). The camera elements (14, 140) of a camera group (G1, G2) are connected to a serial communication link (21, 22). They are designed to forward the raw data (BI) captured by the area scan elements (15) over the serial communication link (21, 22) to the control and evaluating unit (20, 200). The control and evaluating unit (20, 200) is designed for the generation of image data from the raw data (B1) and for analyzing the image data from the camera element (14, 140) of the camera groups (G1, G2).

Claims

1. In an apparatus for monitoring a web moving in a transport direction using analyzed image data of the web, the apparatus having at least two camera elements adjacent one another perpendicular to the direction of transport of the web, a control and evaluating unit, and at least one serial communication link that connects at least one camera element and the control and evaluating unit, each camera element having an area scan element for recording raw data, the improvement comprising: at least one camera module, that comprises at least one camera group having at least two camera elements and a housing, the camera elements of each camera group being connected to a serial communication link, the camera elements in each camera group transmitting the raw data captured by the area scan elements over the serial communication link to the control and evaluating unit; and the control and evaluating unit generating image data from the raw data and analyzing the image data from the camera elements of the camera groups.

2. The monitoring apparatus according to claim 1, wherein at least one of the camera elements of a camera group comprises two data links and a multiplexer, one of the data links being a camera data link extending to the area scan element of the camera element, the other of the data links being a through data link passing through the camera element and connectable to a data link of a further camera element of the camera group the two data links of the camera element are connectable via the multiplexer to the serial communication link.

3. The monitoring apparatus (8) according to claim 1, wherein each camera module (13, 130, 131) comprises at least two of the camera groups (G1, G2) and the control and evaluating unit effects parallel processing of the raw data from the camera groups (G1, G2).

4. The monitoring apparatus according to claim 3, wherein the camera elements of the camera groups are positioned alternating adjacent each other in the housing.

5. The monitoring apparatus in accordance with claim 1, wherein one of the camera modules is a master camera module and contains the control and evaluating unit.

6. The monitoring apparatus in accordance with claim 1, wherein at least two camera modules are provided whose housings are connected together.

7. The monitoring apparatus according to claim 1, wherein the area scan element comprises an area scan sensor and an optical element.

8. The monitoring apparatus according to claim 1, wherein adjacent array elements are spaced from one another at a camera interval of 0.3 m to 2.0 m.

9. The monitoring apparatus in accordance with claim 1, further comprising: an illuminating device that comprises at least one illuminating element for each camera element having LEDs arranged on a connection line of the area scan elements.

10. In a method of monitoring a moving web wherein the web is transported in a direction of transport, image data of the web is analyzed, the image data is generated and analyzed with the aid of at least two camera elements positioned adjacent one another and perpendicular to the direction of transport of the web, of a control and evaluating unit and of at least one serial communication link that connects at least one camera element and the control and evaluating unit, and raw data for the image data is captured by an area scan element of each camera element, the improvement comprising the steps of: capturing the raw data by at least one camera module having at least one camera group having at least two camera elements and a housing, the camera elements of a camera group being connected to a serial communication link, transmitting in each camera group by the respective camera elements the raw data captured by the area scan elements over the serial communication link to the control and evaluating unit, and generating image data from the raw data by the control and evaluating unit and analyzing the image data from the camera elements of the camera groups.

11. The method in accordance with claim 10, further comprising the steps of: passing raw data from the area scan elements of at least two camera elements of the camera group through at least one camera element of a camera group provided with two data links and with one multiplexer over two data links to the serial communication link passing raw data from the area scan element of the camera element through a data link designed as a camera data link and passing raw data from the area scan element of at least one further camera element through a data link designed as a through data link to the serial communication link by the two data links of the camera element connected in sequence to the serial communication link through the multiplexer.

12. The method in accordance with claim 11, further comprising the step of: processing the raw data from the camera elements of at least two camera groups in parallel in the control and evaluating unit.

Description

[0066] The invention will be explained in more detail on the basis of examples illustrated diagrammatically in the drawing. In the figures:

[0067] FIG. 1 is a side view of a diagrammatic arrangement of a knitting machine with a monitoring apparatus according to the invention;

[0068] FIG. 2 is a diagrammatic front view of the knitting machine with the monitoring apparatus;

[0069] FIG. 3 is a diagrammatic function sketch of the monitoring apparatus of a first example;

[0070] FIG. 4 is a simplified block diagram of camera elements of the monitoring apparatus;

[0071] FIG. 5 is a simplified block diagram of the monitoring apparatus;

[0072] FIG. 6 is a simplified block diagram of a control and evaluating unit of the monitoring apparatus;

[0073] FIG. 7 is a simplified block diagram of a camera element of the monitoring apparatus;

[0074] FIG. 8 is a simplified block diagram of an illuminating element of the monitoring apparatus;

[0075] FIG. 9 shows graphs relating to image analysis in the monitoring apparatus;

[0076] FIG. 10 is a flow chart of the transmission of raw data to the control and evaluating unit;

[0077] FIG. 11 shows a monitoring apparatus of a second example using a very simplified exploded drawing; and

[0078] FIG. 12 is a simplified cross-section through the monitoring apparatus of FIG. 11.

FIRST EXAMPLE

[0079] FIG. 1 shows in diagrammatic presentation a knitting machine having a machine frame 1 with knitting tools, for example a warp knitting machine with guide bars 2 for warp yarns 3 and with slider needles 4, of which only one is shown. The web 5 produced on the knitting tools is guided over rollers 6a, 6b, 6c, for instance to a winding device not illustrated.

[0080] A monitoring apparatus 8 of the first example according to the invention for monitoring the moving web 5 is arranged above the web 5. The cross-section through the apparatus 8 is indicated in FIG. 1 by a circle. The monitoring apparatus 8 extends transversely to the web. The apparatus 8 is fastened to the machine frame 1 by a fastening device 9. It is arranged after the knitting tools and before the deflection rollers 6a, 6b, 6c in the transport direction T. The apparatus 8 comprises an illuminating device, the light beams 10 from which are aimed at the web 5.

[0081] FIG. 2 shows a front view of the knitting machine with the apparatus 8. The machine frame 1 comprises a frame, in which in this example six sectional warp beams 11, the monitoring apparatus 8, guide rails 2 for the needle bars (with slider needles) 4 and the rollers 6b, 6c and a winding-on roller 7 are mounted. The web 5 can be seen in FIG. 2 as it leaves roller 6b and as rolled finished goods on the winding-on roller 7.

[0082] The monitoring apparatus 8 extends parallel to the axes of the rollers 6, 7, for example, i.e. transversely to the web 5, on both sides as far as the machine frame 1.

[0083] FIG. 3 shows a function sketch of the monitoring apparatus 8. The monitoring apparatus 8 comprises, in this example, a camera module 13 with camera elements 14, of which three may be seen in FIG. 3. The camera elements 14 each comprises an area scan element 15 with an area scan sensor 15a and an optical element 16.

[0084] The camera module 13 is provided with a housing 17.

[0085] The camera elements 14 are positioned next to each other as a result of the arrangement of the apparatus 8 perpendicular to the direction of transport T of the web 5, i.e. transversely to the web 5. The area scan elements 15 are here arranged in the housing 17 at a camera interval Ka from each other and each in the middle of a camera element 14 extending transversely to the web 5.

[0086] The apparatus 8 is arranged at a distance A from the web 5. Distance A is 0.2 m to 2.0 m, particularly from 0.6 to 1.1 m, from the web 5.

[0087] The monitored width I, i.e. the width of a section of the web 5 to be monitored, of an area scan element 15 is dependent on distance A and on the camera interval Ka between the area scan elements 15.

[0088] The camera interval Ka of the area scan elements 15 is 0.3 m to 2.0 m, preferably 0.5 m to 0.8 m. In this example the area scan elements 15 are arranged next to each other at a camera interval Ka of approximately 0.6 m.

[0089] FIG. 3 shows the camera interval Ka between two area scan elements 15, a corresponding width B of a section of the web 5, to which a camera element 14 is assigned and the monitoring width I. The monitoring width I is greater than the width B assigned to a camera element 14. That is to say, the monitoring regions I monitored by two adjacently arranged area scan elements 15 overlap each other somewhat.

[0090] The optical element 16 comprises an objective lens that is designed as an S-mount lens, for example. In this example the lens is displaceable in its distance from the area scan sensor 15a and hence the focus of the optical element is adjustable. The focal length is 3 mm to 16 mm, preferably 6 mm to 8 mm.

[0091] In an alternative the objective lens comprises at least one lens the lens curvature of which is variable. Lenses with variable lens curvature and hence with variable focal length are liquid lenses.

[0092] The focal length of the objective lens is selected as a function of the distance A from the web at a desired camera interval A and a desired monitoring width I.

[0093] A housing section of the continuous connector housing 17 is assigned to each camera element 14, wherein the transition from one housing section to the next is shown in FIG. 3 by a dashed line. The width of a housing section of housing 17 of the camera elements 14 corresponds to the width B and is likewise 0.6 m.

[0094] The camera elements 14 each comprise, for example a circuit board element with the area scan element 15 not illustrated in the drawing. The optical element 16 is likewise mounted on the circuit board element.

[0095] The housing 17 of the camera module 13 comprises light-permeable areas in front of the area scan elements 15 and in front of the LEDs 19.

[0096] The housing 17 comprises a section of a housing profile and at least one cover. The housing profile and the cover are produced from aluminum extruded profiles. The housing profile, and hence the housing 17, is provided with a circumferential surface area that is at least partially cylindrical. The diameter of the housing 17 is 7 cm to 18 cm, preferably 10 cm to 15 cm. In this example the diameter is approximately 11 cm, for example 11.2 cm.

[0097] In this example the apparatus 8 for monitoring the web is provided with an illuminating device. The illuminating device comprises for each camera element 14 at least one lighting element 18 having a fixture and having, for example, six LEDs 19. The LEDs 19 are arranged on a connection line between the area scan elements 15 or its extension on outer area scan elements 15. Six LEDs 19, three on each side of the area scan element 15, are assigned to the camera elements 14 shown in FIG. 3. The light beams 10 from the six LEDs 19 illuminate the width I to be monitored.

[0098] FIG. 4 shows a simplified block diagram of camera elements 14 for the monitoring apparatus 8. The monitoring apparatus 8 of this example comprises the camera module 13 referred to above that comprises two camera groups G1 and G2 each with three camera elements 14. That is to say, the camera module 13 is provided with six camera elements 14 that are divided into two camera groups G1, G2.

[0099] The monitoring apparatus 8 is provided with a control and evaluating unit 20 and a serial communication link 21, 22 for each camera group G1, G2. The communication links 21, 22 each connect the camera elements 14 of the camera groups G1, G2 with each other and with the control and evaluating unit 20. The control and evaluating unit 20 is designed for the parallel processing of the raw data recorded by the area scan elements 15.

[0100] The serial communication links 21, 22 comprise bus lines for the transmission of data, clock signals and control signals. In this example the data links are designed as LVDS lines. The control links are designed as IC2 bus lines. In a further alternative, the control links are designed as CAN bus lines.

[0101] In this example with one camera module 13, said module comprises the control and evaluating unit 20 and the serial communication links 21, 22.

[0102] The camera elements 14 of each camera group G1, G2 are designed to pass the raw data recorded by the area scan elements 15 over the associated serial communication link 21, 22 to the control and evaluating unit 20. The control and evaluating unit 20 is designed to generate image data from the raw data and to evaluate it. It can be connected to a machine control system for the knitting machine by a communication line 23.

[0103] At least two camera elements 14 of each camera group G1, G2 having three camera elements 14 are provided with two data links and a multiplexer 26. One of the data links is designed as a camera data link 24 that is fed to the area scan element 15 of the camera element 14. The second data link connection is designed as a through data link, a section of a data link 21a of the serial communication link 21 that is passed through the camera element 14. The two data links from the camera element 14 can be connected to the relevant serial communication link 21, 22 in series using the multiplexer 26.

[0104] FIG. 5 shows a simplified block diagram of the monitoring apparatus 8. As indicated in FIG. 5, the camera elements 14 of the two groups G1 and G2 are positioned alternating adjacent each other. The serial communication link 21 of the first group G1 connects, seen from left to right, the first, third and fifth camera element 14 with each other and with the control and evaluating unit 20. The serial communication link 22 of the second group G2 accordingly connects the second, fourth and sixth camera element 14 with each other and with the control and evaluating unit 20.

[0105] The monitoring apparatus 8 is provided with links 27, 28 to control the illuminating elements 18 of the illuminating device. The link 27 connects the illuminating elements 18 that are assigned to the camera elements 14 of the first camera group G1, to each other and to the control and evaluating unit 20. The same applies correspondingly to link 28.

[0106] The links 27, 28 comprise bus lines for control signals.

[0107] In this example the links 27, 28 comprise 12C bus lines. In an alternative, the links 27, 28 comprise CAN bus lines.

[0108] The control and evaluating unit 20 is designed to switch the LEDs 19 of the control elements 18 on and off individually or in groups by means of control signals.

[0109] FIG. 6 shows a simplified block diagram of a control and evaluating unit 20 for monitoring apparatus 8. The control and evaluating unit 20 comprises at least one microprocessor 29 (CPU) and a one control element 30, 31 each with an output 32, 33 for each of the camera groups G1, G2.

[0110] The control element 30 for the first camera group G1 comprises sections of the communication link 21 with sections of, for instance, a data link 21a for the transmission of the raw data, a timing link 21b for timing the transmission and a control link 21c for controlling the transmission. The control element 30 comprises a first repeater 34, i.e. a signal amplifier and processor for increasing the range that is connected to the timing link 21b, and a second repeater 35 that may be switched off and that is connected to the control link 21c. The second repeater 35 can be activated by the microprocessor 29 over a control line 36. The control element 30 comprises sections of a power supply link 37.

[0111] The power supply link 37 and the control link 21c, the timing link 21b and the data link 21a are connected to output 32. The camera elements 14 of the first camera group G1 can be connected to the control and evaluating unit 20 through this output 32.

[0112] The control element 31 for the second camera group G2 is constructed correspondingly. The control element 31 for the second camera group G2 comprises sections of the communication link 22 with sections of, for instance, a data link 22a for the transmission of the raw data, a timing link 22b for timing the transmission and a control link 21c for controlling the transmission. The control element 31 comprises a first repeater 38 that is connected to the timing link 22b, and a second repeater 39 that may be switched off and that is connected to the control link 22c. The second repeater 39 can be activated by the microprocessor 29 over a control line 40. The control element 31 comprises sections of a power supply link 41.

[0113] The power supply link 41 and the control link 21c, the timing link 21b and the data link 21a are connected to output 33. The camera elements 14 of the second camera group G2 can be connected to the control and evaluating unit 20 through this output 33.

[0114] The control and evaluating unit 20 comprises one supply element 42, 43 with an output 44, 45 each for the illuminating elements 18 of each of the camera groups G1, G2.

[0115] The supply element 42 for the first camera group G1 comprises sections of the communication line 24 to the illuminating elements 18. The communication line 24 is designed as a control link. The supply element 42 comprises a repeater 46 that can be switched off and that is connected to the communication line 24. The repeater 46 can be switched off and can be activated by the microprocessor 29 over a control line 47. The supply element 42 comprises sections of a power supply link 48.

[0116] The power supply link 48 and the communication line 24 are connected to the output 44. The illuminating elements 18 of the first camera group G1 can be connected to the control and evaluating unit 20 through this output 44.

[0117] The supply element 43 for the second camera group G2 is constructed correspondingly. The supply element 43 comprises sections of the communication line 25 to the illuminating elements 18. The communication line 25 is designed as a control link. The supply element 43 comprises a repeater 49 that can be switched off and that is connected to the communication line 25. The repeater 49 can be switched off and can be activated by the microprocessor 29 over a line 50. The supply element 43 comprises sections of a power supply link 51.

[0118] The power supply link 51 and the communication line 25 are connected to the output 45. The illuminating elements 18 of the second camera group G2 can be connected to the control and evaluating unit 20 through this output 45.

[0119] FIG. 7 shows a simplified block diagram of a camera element 14 of the monitoring apparatus 8. The camera element 14 shown in FIG. 7 is, for example the first camera element 14 of the first camera group G1 having the area scan element 15 that is designed as a CMOS sensor.

[0120] The camera element 14 is provided with an input 52 and with an output 53 for the following camera element 14, for example the second camera element 14 of the first camera group G1. It comprises sections of the power supply link 37 and the serial communication link 21, that is to say the data link 21a, the timing link 21b and the control link 21c that are each connected to the input 52 and the output 53.

[0121] The camera element 14 comprises an addressing switch 54, an IO expander 55, a repeater 56 and an activatable repeater 57. The IO expander 55 is connected to the control link 21c and linked to the addressing switch 54. The control link 21c can be connected to the area scan element 15 by the activatable repeater 57. The activatable repeater 57 can be switched by the IO expander 55 via a line 58. The repeater 56 is connected into the control link 21c.

[0122] The section of the data link 21a forms the through data link of the camera element 14.

[0123] The camera element 14 comprises a serializer 59, to which the outputs of the area scan element 15 are connected. It comprises the multiplexer 26 referred to above which is connected into the data link 21a. The serializer 59 is connected to the multiplexer 26 through the camera data link 24. The multiplexer 26 can be switched by the IO expander 55 via a line 62 or multiple lines.

[0124] The camera element 14 comprises a repeater 63 that is connected into the timing link 21b. The area scan element 15 is connected by a line 64 to the repeater 63 and hence to the timing link 21b. The area scan element 15 can be controlled by the IO expander 55 via a line 65 or multiple lines.

[0125] The camera element 14 comprises a voltage regulating unit 66 that is connected into the power supply link 37.

[0126] The camera element 14 comprises one or more position lighting elements, in this example red LEDs 67 that may be switched on by the IO expander 55 over a line 68. They indicate the position of the product defect detected.

[0127] FIG. 8 shows a simplified block diagram of an illuminating element 18 of the monitoring apparatus.

[0128] The illuminating element 18 is assigned to the camera element 14 described above. It is provided with an input 69 and an output 70. It comprises sections of the power supply link 48 and the communication line 24 that are each connected with the input 69 and the output 70.

[0129] The illuminating element 18 comprises an addressing switch 6671, an IO expander 67 and a repeater 73. The IO expander 72 is connected to the communication link 24 and linked to the addressing switch 71. The repeater 73 is connected into the control link 24.

[0130] The illuminating element 18 comprises a driver 74 for the LEDs 19 that is connected between the power supply link 48 and the LEDs 19. The driver 74 can be controlled by the IO expander 72 via a line 75.

[0131] The illuminating element 18 comprises a voltage regulating unit 76 that is connected into the power supply link 48.

[0132] In an alternative the position elements described above can be controlled by the IO expander 72 of the illuminating element 16. In this case they are connected to the IO expander 72 and not to the IO expander 55.

[0133] FIG. 9 shows graphs relating to image analysis by the control and evaluating unit 20 in the monitoring apparatus.

[0134] Raw data B1 of all image sections are recorded over a width X (in millimeters) of a narrow illuminated strip of the web 5. Data B1 (image data) of a brightness profile over the width X of the web 5 is derived from the raw data B1 of each image section. To this end, the raw data BI of the image section is collated into blocks and average values are determined. A block comprises a few pixels transverse to the direction of transport and a few pixels in the direction of transport, three each, for instance. Its average value is a value for the data B1 of the brightness profile of the lower graph in FIG. 9.

[0135] In the course of evaluation by the control and evaluating unit 20, the data B1 of the brightness profile is normalized and filtered into data B2 (evaluated image data). Normalization compensates for intensity losses of the brightness profile in the edge region of the web caused by lens curvature of the optical element 16.

[0136] The normalized and filtered data B2 of the brightness profile can be seen in the upper graph in FIG. 9. Both the graph with the data B1 and the graph with the data B2 show the impact of a brighter, defect area between 950 and 1000 mm.

[0137] In an alternative an apparatus 8 according to the invention for monitoring the moving web 5 is located beneath the web 5.

[0138] In an alternative the monitoring apparatus comprises at least two camera modules. The housings 17 of the camera modules are here connected with one another.

[0139] In an alternative, a monitoring apparatus comprises the camera module 13 described above that comprises the control and evaluating unit 20 and a further camera module having two camera groups each having two camera elements. The camera module 13 is also identified as the master camera module. Further camera modules are identified as expansion modules.

[0140] The expansion module(s) comprise the same number of camera groups as the master camera module.

[0141] In operation, the moving web 5, which is being transported in the direction of transport T, is monitored by the monitoring apparatus 8, especially for defects. Image data of the web 5 is analyzed to this end. The image data in this example is generated and analyzed with the aid of a plurality of camera elements 14 positioned next to each other perpendicular to the direction of transport of the web 5, the control and evaluating unit 20 and the communication links 25 that connect the camera elements 14 and the control and evaluating unit 20. The raw data for the image data is captured by the area scan elements 15 of the various camera elements 14.

[0142] The raw data is captured by the camera module 13 that comprises the camera groups G1, G2 and the housing 17. The raw data captured by the area scan elements 15 is passed by the camera elements 14 of each camera group G1, G2, which are connected to the associated serial communication link 21, 22, through the serial communication link 21, 22 to the control and evaluating unit 20. Image data is generated from the raw data by the control and evaluating unit 20. The image data from the camera elements 14 of the camera groups G1, G2 is evaluated by the control and evaluating unit 20.

[0143] The raw data from the area scan elements 15 of the camera elements 14 of one of the camera groups G1, G2 is passed via the camera elements 14 of the camera group G1 or G2 to the corresponding serial communication link 21, 22.

[0144] As mentioned, the camera elements 14 are provided, to this end, with two data links, specifically the data link configured as a camera data link 24 and the data link configured as a through data link, i.e. to the section of the data link 21a, and with the multiplexer 26.

[0145] The raw data from the area scan element 15 of the camera element 14 under consideration is passed via the camera data link 24 and the raw data from the area scan elements 15 of further camera elements 14 in camera group G1, G2 is passed via the through data link, i.e. to the section of the data link 21a, to the serial communication link 21, 22. The two data links for the camera element 14 are connected in sequence to the appropriate serial communication link 21, 22 through the multiplexer 26.

[0146] The raw data from the camera elements 14 of the camera groups G1, G2 is processed in parallel in the control and evaluating unit 20.

[0147] FIG. 10 shows a schematic flow chart for the transmission of the raw data from the camera elements 14 of a camera group G1, G2 to the control and evaluating unit 20 by the control and evaluating unit 20.

[0148] Here initially, for each camera group G1, G2 the first camera element 14[0], to which the index i=0 is assigned within its group, is connected to the control and evaluating unit 20. Once the link is made, a memory area is made available in the control and evaluating unit 20. The raw data from the camera element 14[0] is transmitted and written to the memory as soon as an image start is detected. The next time an image start is detected, the raw data from the camera element 14[0] is forwarded from the memory for analysis. The index i is incremented by 1 and the corresponding next indexed camera element 14[i] of camera group G1, G2 is connected to the control and evaluating unit 20. The procedure is repeated for the further camera elements 14[i] until the raw data of the last camera element (the third, in the case of three camera elements 14 per camera group G1, G2) is read and forwarded. The index is then reset to 0 and the first camera element 14[i0] of camera group G1, G2 is thereby connected again to the control and evaluating unit 20.

[0149] As long as the web is being monitored, for example as long as the knitting machine (see FIG. 1) producing the web is in operation, data transmission is repeated. It ends after the end signal.

SECOND EXAMPLE

[0150] The second example corresponds to the first example apart from the features described below. The monitoring apparatus of the second example is illustrated in FIGS. 11 and 12. It comprises two camera modules, one master camera module 130 and one expansion camera module 131.

[0151] The master camera module 130 comprises a control and evaluating unit 200 and six camera elements 140, three each to a camera group G1, G2. The first, third and fifth camera element belongs to the first camera group G1 and the other camera elements 140 belong to the second camera group G2. The expansion camera module 131 comprises two camera elements 140, wherein the first camera element belongs to the first camera group and the second camera element 140 belongs to the second camera group.

[0152] FIG. 12 shows a cross-section through, for example, the housing 17 of the master camera module 130 in the region of a camera element 140. The housing 17 comprises a housing profile 170 extending over the length of the master camera modules 130, the outer contour of which profile takes the form of a cylinder open on one side. In its half opposite the open side, the housing profile 170 comprises partition walls 171a, 171b and 171c that form an approximately square opening 172 extending over the length of the master camera module 130. The housing profile 170 is provided with a center wall 173 extending over the length of the master camera module 130. The camera elements 140 are mounted on the center wall 173. In this example the center wall 173 is interrupted. The cavity thereby created is used as a cable duct.

[0153] The housing 17 of the master camera module 130 comprises a plurality of covers 174a, 174b, 174c, 174d closing the open side. The control and evaluating unit 200 is mounted on the cover 174 on the left in the figure. The control and evaluating unit 20 is accessible by simply releasing the cover 174.

[0154] FIG. 11 shows two end covers 176a, 176b for the two ends of housing profile 170 for the housing 17 of the master camera module 130, for example for an application without expansion camera modules.

[0155] Seals 175 are provided at the points at which the covers 174a to 174d butt against one another. Further seals 177 are provided between the housing profile 170 and the end covers 176a, 176b. The seals 175, 177 are disc-shaped. Sealing strips 178 are provided extending along between the housing profile 170 and the covers 174 to 174d.

[0156] The housing profile 170 is provided with a plurality of longitudinal slots 179. A plurality of brackets 180 for the monitoring apparatus 8 are each secured in two of the longitudinal slots 179 at a distance from each other in the longitudinal direction. The longitudinal slots 179 and the slotted holes that cannot be seen in the brackets 180 are arranged in such a manner that the monitoring apparatus 8 can be positioned in different inclinations to the web 5.

[0157] The expansion camera module 131 is constructed the same as the master camera module 130 in the region of the camera elements 140. Its housing 17 comprises a housing profile 170 and a cover 174e. The housings 17 of the two camera modules 130 and 131, specifically their housing profiles 170, are connected with one another. The ends of the housing profiles 170, against which the camera modules 130, 131 butt, are open, i.e. have no end cover 176. A longitudinally extending profile 190, made of steel for instance, is arranged in the openings 172 of the housing profiles 170 of the two camera modules 130, 131. The profile 190 stabilizes the connection of the two camera modules 130, 131. Its length corresponds to at least one camera interval Ka. In this example the length of the profile 190 is approximately twice the camera interval Ka.

[0158] In this example the monitoring apparatus is executed without illuminating device. The light-permeable regions of the housing 17 are formed by transparent windows 150 in the covers 174. The area scan elements 15 record the images of the web through the windows 150.

[0159] In an alternative monitoring unit with illumination, windows extending over the entire length are provided in the covers 174, for example. In an alternative the monitoring apparatus comprises a larger expansion module that comprises four camera elements, of which the first and third belong to the first camera group and the second and fourth belong to the second camera group.

[0160] In further alternatives the monitoring apparatus comprises a plurality of expansion modules of the same size or of different sizes.

TABLE-US-00001 List of reference numbers 1 Machine frame 2 Guide rail 3 Warp yarn 4 Needle bars (with slider needles) 5 Web 6 Roller 7 Roller 8 Apparatus 9 Mounting device 10 Light beam 11 Warp beam 13 Camera module (master camera module) 14 Camera element 15 Area scan element 15a Area scan sensor 16 Optical element 17 Housing 18 Illuminating element 19 LED 20 Control and evaluating unit 21 Communication link 22 Communication link 24 Camera data link 26 Multiplexer 27 Link 28 Link 29 Microprocessor 30 Control element 31 Control element 32 Output 33 Output 34 First repeater 35 Second repeater 36 Control line 37 Power supply link 38 First repeater 39 Second disconnectible repeater 40 Control line 41 Power supply link 42 Supply element 43 Supply element 44 Output 45 Output 46 Disconnectible repeater 47 Line 48 Power supply link 49 Disconnectible repeater 50 Line 51 Power supply link 52 Input 53 Output 54 Addressing switch 55 IO expander 56 Repeater 57 Activatable repeater 58 Line 59 Serializer 62 Line 63 Repeater 64 Line 65 Line 66 Voltage regulation unit 67 Red LED 68 Line 69 Input 70 Output 71 Addressing switch 72 IO expander 73 Repeater 74 Driver 75 Line 76 Voltage regulation unit 130 Master camera module 131 Expansion camera module 140 Camera element 150 Window 170 Housing profile 171a, b, c Partitions 172 Opening 173 Center wall 174a-e Cover 175 Seal 176a, b End cover 177 Seal 178 Seal strip 179 Slot 180 Bracket T Direction of transport A Distance B Width of camera module D Housing diameter I Width of region captured X Width of web G1 Camera group G2 Camera group BI Raw data for an image B1 Processed data B2 Normalized data F1 Error signal F1 Noise signal