Inspection device and method for inspecting an adhesive pattern on a substrate

Abstract

Inspection devices and methods for inspecting an adhesive pattern on a substrate are disclosed. The inspection device includes at least one sensor having a heat sensor head for detecting a pattern of the adhesive bead, and a controller. Reference data representing a desired adhesive pattern is initially provided to a controller. A predetermined tolerance range for the desired adhesive pattern is also provided to the controller. An adhesive bead is discharged onto a substrate from a nozzle. A pattern of the discharged adhesive bead is then detected by the sensor when the substrate moves. Signals representing the detected pattern are received from the sensor at the controller. Finally, the signals representing the detected adhesive pattern are compared to the tolerance range of the desired adhesive pattern.

Claims

1. A method for inspecting an adhesive pattern that is on a substrate, the method comprising: receiving, at a controller, a discharge signal including reference data representing a desired adhesive pattern to be applied to the substrate; calculating using the controller, based on the reference data, a tolerance range for the desired adhesive pattern; discharging, using a nozzle, the adhesive pattern on the substrate, wherein the reference data is data that is received independently of the discharging of the adhesive pattern on the substrate and the adhesive pattern is discharged based on the reference data; detecting, using a sensor arrangement, the discharged adhesive pattern on the substrate; and comparing, using the controller, the detected adhesive pattern with the tolerance range of the desired adhesive pattern; receiving the discharge signal for a first time or a change in the discharge signal; determining, using the controller, the desired adhesive pattern based on the received discharge signal or determining a changed adhesive pattern based on the received change in the discharge signal; and adjusting the tolerance range to a predetermined learning range based upon detecting that the discharge signal is received for the first time or detecting the determined changed adhesive pattern.

2. The method of claim 1, wherein detecting the discharged adhesive pattern comprises: determining an intensity or rate of change in intensity of a characteristic sensed by the sensor arrangement; determining that the intensity or rate of change in intensity exceeds a threshold; and determining, based on the determination that the intensity or rate of change in intensity exceeds the threshold, that a bead edge is present.

3. The method of claim 2, further comprising scaling the threshold based on a velocity of the substrate or a cooling rate factor.

4. The method of claim 1, further comprising determining, using a speed sensor of the sensor arrangement, a travelling speed and edge position of said substrate by: determining an intensity or rate of change in intensity of a characteristic sensed by the speed sensor; determining that the intensity or rate of change in intensity exceeds a threshold; and determining, based on the determination that the intensity or rate of change in intensity exceeds the threshold, that a substrate edge is present.

5. The method of claim 1, wherein the discharge signal is from a control unit of the nozzle for discharging the adhesive.

6. The method of claim 5, further comprising determining the desired adhesive pattern by calculating a desired bead beginning time and bead end time using at least one predetermined delay value.

7. The method of claim 6, wherein the predetermined delay value comprises: a valve delay time defining a delay between transmission of the discharge signal and a time when adhesive starts flowing out of the nozzle; an adhesive fly time defining a time between the adhesive exiting the nozzle and the adhesive contacting the substrate; or a travelling time of the substrate defining a time the substrate requires to move from the nozzle to the sensor arrangement.

8. The method of claim 1, wherein detecting the discharged adhesive pattern comprises detecting a width of the discharged adhesive pattern.

9. The method of claim 8, wherein the tolerance range comprises a width tolerance based on a travelling speed of the substrate.

10. The method of claim 1, further comprising: providing a centerline tolerance range for the desired adhesive pattern; calculating a centerline of the detected adhesive pattern; and comparing the calculated centerline with the centerline tolerance range.

11. The method of claim 1, further comprising calculating an area of the substrate which is covered by the discharged adhesive pattern.

12. The method of claim 11, further comprising: providing a value of a desired area covered by the discharged adhesive pattern; providing an area tolerance; and comparing the calculated area covered by the discharged adhesive pattern with the area tolerance.

13. The method of claim 11, further comprising: providing a thermal intensity tolerance; measuring or calculating a thermal intensity value of the calculated area of the substrate which is covered by the discharged adhesive pattern; and comparing the thermal intensity value of the calculated area with the thermal intensity tolerance.

14. The method of claim 1, further comprising: providing a maximum gap tolerance between two beads of the desired adhesive pattern; calculating a gap between two beads of the detected adhesive pattern; and comparing the calculated gap with the maximum gap tolerance.

15. The method of claim 1, further comprising: determining, based on the comparison of the detected adhesive pattern with the tolerance range, that the detected adhesive pattern not within the tolerance range; and outputting, in response to the determination that the detected adhesive pattern not within the tolerance range, a pattern-fault signal.

16. The method of claim 15, further comprising: receiving the pattern-fault signal at an alarm device; and outputting an alarm signal using the alarm device.

17. The method of claim 15, further comprising: receiving the pattern-fault signal at a discard device; and discarding the substrate.

18. The method of claim 1, wherein the sensor arrangement is configured to attach to an applicator head proximate the nozzle.

19. The method of claim 1, wherein said learning range is based on prestored values that correspond to predetermined adhesive patterns.

20. The method of claim 1, further comprising: discharging, using the nozzle, a discharged changed adhesive pattern onto another substrate; detecting, using the sensor arrangement, the discharged changed adhesive pattern on the other substrate; comparing the detected discharged changed adhesive pattern with the detected adhesive pattern to determine a deviation or deviation rate; and determining whether the deviation or the deviation rate since the change in the discharge signal is within a predefined tolerance.

21. The method of claim 20, further comprising: reaching a predetermined number of N−1 detected adhesives patterns, since reception of the change in the discharge signal; using the N detected adhesive pattern as the discharged changed adhesive pattern; and evaluating the adhesive patterns until a predetermined number N+x and calculating a desired pattern based on the N to N+x detected adhesive patterns.

22. The method of claim 1, further comprising setting back from the adjusted tolerance range to the tolerance range.

23. The method of claim 22, further comprising centering the tolerance range around the determined changed adhesive pattern.

24. An inspection device for inspecting an adhesive pattern on a substrate, the inspection device comprising: at least one sensor arrangement having a heat sensor head for detecting a pattern of an adhesive bead on the substrate; and a controller being in electrical communication with said sensor arrangement, the controller storing: reference data representing a desired adhesive pattern to be applied to the substrate; and a tolerance range for the desired adhesive pattern calculated based on the reference data, wherein the controller is configured to: receive signals representing the adhesive pattern detected by the sensor arrangement, wherein the reference data is data that is determined independently of the signals that represent the adhesive pattern detected by the sensor arrangement being received by the controller; and compare said detected adhesive pattern with the tolerance range of the desired adhesive pattern; receive a discharge signal that includes the reference data; detect if a change in the discharge signal occurs or if the discharge signal is received for a first time; and in case that the controller detects a change in the discharge signal, or that the discharge signal is detected for the first time, set the tolerance range for the desired pattern to a predetermined learning range.

25. The inspection device of claim 24, wherein the heat sensor comprises two or more heat sensor heads which are arranged offset in a direction substantially perpendicular to a direction of travel of said substrate for detecting a width or centerline position of said adhesive bead on said substrate.

26. The inspection device of claim 24, wherein the heat sensor comprises two or more heat sensor heads which are arranged offset in a direction substantially parallel to a machine direction of said substrate for detecting a travelling speed of said substrate.

27. The inspection device of claim 24, wherein the heat sensor comprises two or more heat sensor heads which are arranged offset in a direction substantially parallel to a machine direction of said substrate for detecting a cooling rate of the adhesive bead.

28. The inspection device of claim 24, further comprising a mask for the heat sensor head for constraining a sensing area of the heat sensor head.

29. The inspection device of claim 24, further comprising a speed detector for detecting an edge of the substrate or a velocity of the substrate.

30. The method of claim 1, wherein the tolerance range for the desired adhesive pattern is calculated before discharging the adhesive pattern on the substrate.

31. The inspection device of claim 24, wherein the sensor arrangement is configured to attach to an applicator head proximate a nozzle that discharges the adhesive pattern on the substrate.

32. A method for inspecting an adhesive pattern that is on a substrate, the method comprising: receiving, at a controller, a discharge signal including reference data representing a desired adhesive pattern to be applied to the substrate; calculating with the controller, based on the reference data, a tolerance range for the desired adhesive pattern; discharging, using a nozzle, the adhesive pattern on the substrate, wherein the reference data is not based on the discharged adhesive pattern; detecting, using a sensor arrangement, the discharged adhesive pattern on the substrate; and comparing, using the controller, the detected adhesive pattern with the tolerance range of the desired adhesive pattern; receiving the discharge signal for a first time or a change in the discharge signal; determining, using the controller, the desired adhesive pattern based on the received discharge signal or determining a changed adhesive pattern based on the received change in the discharge signal; and adjusting the tolerance range to a predetermined learning range based upon detecting that the discharge signal is received for the first time or detecting the determined changed adhesive pattern.

33. The method of claim 32, wherein detecting the discharged adhesive pattern comprises: determining an intensity or rate of change in intensity of a characteristic sensed by the sensor arrangement; determining that the intensity or rate of change in intensity exceeds a threshold; and determining, based on the determination that the intensity or rate of change in intensity exceeds the threshold, that a bead edge is present.

34. The method of claim 32, wherein the reference data comprises a discharge signal from a control unit of the nozzle for discharging the adhesive.

35. The method of claim 32, wherein the tolerance range for the desired adhesive pattern is calculated before discharging the adhesive pattern on the substrate.

36. The inspection device of claim 24, wherein the controller is configured to: receive the discharge signal, from a control unit of a nozzle for discharging adhesive.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) The invention shall now be described in greater detail with reference to the preferred embodiments and to the attached figures, in which:

(2) FIG. 1 shows a side elevation view of an applicator head adapted for use with the present invention;

(3) FIG. 2 shows an elevated view of the applicator head discharging fluid on a substrate together with an inspection device of the present invention;

(4) FIG. 3 shows an embodiment of an inspection device of the present invention;

(5) FIG. 4 shows a schematic view of four heat sensor heads together with a mask;

(6) FIG. 5 shows a second embodiment of nine heat sensor heads with a mask;

(7) FIG. 6 shows an inspection device attached to an applicator head by means of a mounting bracket according to a first embodiment in an elevated view;

(8) FIG. 7 shows the inspection device attached to the applicator head by means of the mounting bracket of FIG. 6 in a side view;

(9) FIG. 8 shows an inspection device attached to an applicator head by means of a mounting bracket according to a second embodiment in an elevated view;

(10) FIG. 9 shows the inspection device attached to the applicator head by means of the mounting bracket of FIG. 8 in a side view;

(11) FIG. 10 shows a block diagram illustrating an applicator head with an inspection device;

(12) FIG. 11 shows a signal logic diagram illustrating a method for inspecting an adhesive pattern on a substrate;

(13) FIG. 12 shows a signal logic diagram of a learning mode of the method for inspecting an adhesive pattern on a substrate;

(14) FIG. 13 shows a first diagram showing maximum tolerance curves for the learning mode;

(15) FIG. 14 shows a second diagram showing a learned tolerance curve;

(16) FIG. 15 shows a third diagram indicating a set narrow tolerance;

(17) FIG. 16 illustrated a signal output of the device according to the method for inspecting an adhesive pattern on a substrate;

(18) FIGS. 17a-17c show schematic views of three substrates with adhesive patterns; and

(19) FIGS. 18a-18b illustrate a max gap measurement.

DETAILED DESCRIPTION

(20) FIG. 1 shows an applicator head 1 for dispensing a fluid, in particular liquid adhesive material, in particular hot-melt adhesive. Although hot-melt adhesive is preferred, other fluids such as glue, sealants, fat or similar can be used. The applicator head 1 includes a basic body 4 and a valve 2 preferably a solenoid valve 2 that is mounted on the basic body 4. Basic body 4 accommodates inter alia internal fluid channels for the fluid to be guided through the basic body and a heater for heating the fluid. Applicator head 1 is designed as a pneumatic applicator head having valve 2 which is operated by means of pressurized gas. Valve 2 is preferably a solenoid valve.

(21) A module 6 provided with a nozzle 8 is attached to the basic body 4. A replaceable filter 10 is provided on an opposite side of basic body 4 from module 6. A tube connector 12 for supplying the fluid, in particular the hot-melt adhesive, is likewise disposed on the basic body 4. Tube connector 12 is therefore used as a fluid inlet connection and is connected in fluid communication to module 6 (in a manner not shown) via conduits inside the basic body 4.

(22) A holding device 14 for securing the applicator head 1 to a mounting rod or to similar elements is also disposed on the basic body 4.

(23) Solenoid valve 2 of applicator head 1 has one or more silencers 16, one of which is marked with a reference sign. Solenoid valve 2 is adapted to selectively release and close a pneumatic compressed air line in which compressed air is fed into applicator head 1 by means of a compressed air inlet 18. The valve 2 is actuated via a control signal which can be sent through port 20. Applicator head 1 also has an electrical connector 22 for coupling with a connection cable, which is used to supply electrical power to the heater located inside basic body 4.

(24) According to this embodiment, it is proposed that a controller module is connected to the signal port 20 of the solenoid valve 2 of the applicator head 1. The controller module has a signal input port and a signal output port. For more details regarding this controller module, reference is made to the published patent application EP 2 638 978 A1 in the name of Nordson Corporation, Westlake, Ohio. It should be noted that even though it is preferred that the controller module is formed according to the published patent application EP 2 638 978 A1 it is not necessary. Other embodiments without a stitching-function are also preferred.

(25) FIG. 2 shows an applicator head 1, having a nozzle 8. Even though applicator head 1 according to FIG. 2 is only shown schematically, it should be understood that applicator head 1 comprises the essential features of applicator head 1 shown in FIG. 1. Applicator head 1 is connected via its signal port 20 to a signal line 24, connected to a control box 26. The control box comprises a control unit for the nozzle 8, which sends control signals to solenoid valve 2 for opening and closing valve 2 to control the fluid flow in said nozzle 8. The control unit, provided in control box 26, may also comprise means for transforming a primary discharge signal into a secondary (“stitching”) discharge signal, as described in EP 2 638 978 A1.

(26) According to FIG. 2, an inspection device 30 is provided in preferably close relation to the nozzle 8 of the module 6 of applicator head 1 or as a part of the applicator head 1. In this embodiment the inspection device 30 is attached to the basic body 4 of the applicator head 1. The inspection device 30 is connected via a signal line 32 to the control box 26. The control box 26 also comprises a controller for controlling the inspection device 30 (see also FIG. 11).

(27) Both, the applicator head 1 and the inspection device 30 are shown relative to a substrate 34, in the illustrated exemplary embodiment above a substrate 34. The substrate 34 in this case is a continuous cardboard which is cut into pieces before or after application of adhesive. The substrate 34 moves into moving or machine direction 36 indicated by means of the arrow. When the substrate 34 moves relative to the applicator head 1, the nozzle 8 discharges adhesive and generates an adhesive pattern 37, consisting of beads 38, 39, 40 or other shapes (such as dots or films) of adhesive on the top surface of the substrate 34. The adhesive in this case is hot-melt adhesive radiating mainly infrared radiation.

(28) The inspection device 30 according to this embodiment (cf. FIG. 2) comprises a housing 31 and a sensor arrangement 43 having a heat sensor head 42 (cf. FIG. 3) which detects the irradiated infrared radiation 44 of the adhesive bead 38. According to FIG. 2, both, the sensor arrangement 43 and heat sensor head 42 (not shown in FIG. 2) are housed in a housing 31 of the inspection device 30.

(29) The controller, provided in the control box 26, receives the signals detected by the heat sensor head 42 via signal line 32 and compares the detected adhesive pattern with a desired adhesive pattern and outputs a pattern-fault signal when the detected adhesive pattern 37 is not congruent with the desired adhesive pattern. According to the embodiment shown in FIG. 2, the controller provided in the control box 26 receives information regarding the desired adhesive pattern from the control unit, provided in the control box 26 as well, which is the discharge signal pattern used for actuating the solenoid valve 2. Since the distance between heat sensor head 42 and nozzle 8 in the machine direction 36 is known, it is also known, when the heat sensor head 42 should detect or “see” the beads 38, 39, 40.

(30) The control box 26 is further connected to an input signal line 46, which connects the control box 26 with a controlling device for the whole machine. Furthermore, the control box 26 is connected to a signal line 48 for a pattern-fault signal output by the controller, in case the detected adhesive pattern 37 is not congruent with the desired adhesive pattern. The signal line 48 may be connected to an alarm device, outputting an audio or a visual signal in case a pattern-fault signal is received (cf. FIG. 13).

(31) While in the embodiment shown in FIG. 2, the sensor arrangement 43 and the heat sensor head 42 are integrated into the housing 31 of the inspection device 30, in the embodiment shown in FIG. 3, the heat sensor 43 is distally arranged from the heat sensor head 42. In FIG. 3, the housing 31 for housing the heat sensor head 42 also houses the sensor arrangement 43, which are not separately shown for simplifying the figure. Again an applicator head 1 comprises a solenoid valve 2, a basic body 4 and a nozzle 8. Adhesive beads 38, 39 are discharged on a substrate 34 by means of the nozzle 8. According to this embodiment, the sensor arrangement 43 comprises an infrared sensor. The heat sensor head is coupled to a fibre optic 52 comprised with a lens 50 for coupling infrared radiation into a fibre optic 52. The lens 50 is provided in a coupling means 49 haven a screw threaded portion such that the lens 50 can be attached to a support. The heat sensor head is arranged in the housing 31. Inside the housing 31 the sensor arrangement 43 is connected to the signal line 48 and the control line 46 for supplying the sensor arrangement 43 with electrical energy and control signals. Furthermore, the sensor arrangement 43 according to this embodiment is connected via a signal line 53 to the control unit (not shown) of the applicator head 1, for receiving control signals for the solenoid valve 2. As can easily be seen in FIG. 3, the sensor arrangement 43 is positioned with a distance to the lens 50, and thus may be arranged at a distance to the heated nozzle 8 and the hot-melt beads 38, 39, so that the sensor arrangement 43 does not receive excess heat.

(32) FIG. 4 shows a specific sensor arrangement 43 with four heat sensor heads 42, 52, 54, 56 which are comprised with a mask 60. The mask 60 in this embodiment is formed as a substantially flat housing portion of the housing 31 and comprises four recesses 62, 64, 66, 68 in which the respective heat sensor heads 42, 52, 54, 56 are arranged. Therefore, the heat sensor heads 42, 52, 54, 56 are recessed behind a surface 61 of the housing 31 in cylindrical recesses 62, 64, 66, 68 which in FIG. 4 extend into the plane of the figure. Openings of the recesses 62, 64, 66, 68 form sensor openings in this instance. Thus, the line of sight between the respective heat sensor heads 42, 52, 54, 56 and the adhesive beads 38, 39, 40 on the substrate 34 is restricted by means of the recesses 62, 64, 66, 68.

(33) As can be seen from FIG. 4, heat sensor heads 42, 52 and 54 are arranged substantially parallel to the machine direction 36 of the substrate 34 and heat sensor head 56 is arranged perpendicular to the machine direction 36 of the substrate 34. Heat sensor head 56 is used for measuring the length of a bead 38, 39, 40 in the machine direction 36 and heat sensor heads 42, 52, 54, are used to detect a width of application of adhesive in the machine direction 36. The single heat sensor heads 42, 52, 54, 56 are offset to each other in the machine direction 36 and perpendicular to the machine direction. Exemplary for heat sensor heads 42 and 52 the offset O.sub.1, O.sub.2 is depicted in FIG. 4. When for example the corresponding heat sensor of heat sensor head 56 indicates that a bead is detected and outputs a signal, and also the corresponding heat sensor for heat sensor head 52 outputs a signal indicating that an adhesive bead is measured, however the heat sensor corresponding to heat sensor head 42 does not, it is known that the edge of the bead parallel to the machine direction 36 is between heat sensor heads 52 and 42, thus in the range of offset O.sub.1.

(34) Offset O.sub.2, which is the offset in the machine direction 36, can be used to determine the travelling speed of the substrate 34. To this end, however, it is necessary that both, heat sensor heads 42 and 52, see the adhesive bead and the corresponding heat sensors for the heat sensor heads 42 and 52 output a signal indicating that a bead is detected. When e.g. the heat sensor corresponding to heat sensor head 52 first indicates a signal and afterwards the heat sensor corresponding to heat sensor head 42 indicates a signal, the time gap between these two signals can be measured and compared with the spacing between the two heat sensor heads, thus the offset O.sub.2, and subsequently the travelling speed can be measured.

(35) However, even though the heat sensors can be used to determine a travelling speed, it is even more preferred that the inspection device 30 comprises a separate speed detector. In this embodiment, an optical speed detector, such as two photocells (cf. FIG. 11), which are offset by O.sub.2, can be used.

(36) FIG. 5 shows another alternative of a mask 60 which can be provided for the inspection device 30, described above. In FIG. 5, similar and identical parts, already described with respect to FIG. 4, are depicted with identical reference signs and in so far reference is made to the above description of FIG. 4. According to FIG. 5, in total nine heat sensor heads 42, 52, 54, 56, 70, 72, 74, 76, 78 are provided and each connected with a corresponding heat sensor. Each heat sensor head 42, 52, 54, 56, 70, 72, 74, 76, 78 is provided in a respective recess 62, 64, 66, 68, 80, 82, 84, 86, 88, so that the line of sight between the respective heat sensor head 42, 52, 54, 56, 70, 72, 74, 76, 78 and the substrate 34 is restricted to focus the heat sensor head 42, 52, 54, 56, 70, 72, 74, 76, 78 on a specific area of the substrate 34.

(37) Again, in accordance with the embodiment of the mask 60 shown in FIG. 4, the mask 60 of FIG. 5 is formed in such a way that one heat sensor head 56 is arranged substantially perpendicular to the machine direction 36 of the substrate 34, and the further eight heat sensor heads 42, 52, 54, 70, 72, 74, 76, 78 are arranged substantially parallel to the machine direction 36 of the substrate 34. Due to this arrangement, the dimension of the heat sensor head 56 perpendicular to the direction 36 is much more extensive than the dimension of the heat sensor head 56 in the direction 36. Due to this arrangement, heat sensor head 56 is relatively tolerant regarding the width of an adhesive bead and also the lateral placement of the bead regarding the substrate 34, however using heat sensor head 56, the length of the bead can be detected within relatively small tolerances.

(38) The further eight heat sensor heads 42, 52, 54, 70, 72, 74, 76, 78 are arranged offset to each other perpendicular to the machine direction 36. All these heat sensor heads are arranged with an offset O.sub.1 to each other, and thus are evenly distributed over the width of the mask 60. Due to this arrangement, a detailed detection of adhesive bead width and presence in the width direction of the substrate is possible. Additionally, the heat sensor heads are arranged offset to each other in the direction 36, which is exemplarily shown with respect to heat sensor heads 56 and 42. Due to this offset O.sub.2, the travelling speed of the substrate can be detected.

(39) Reference is now made to FIGS. 6 to 9 which each show an applicator head 1 which substantially corresponds to the applicator head 1 shown in FIG. 1. In so far, reference is made to the above description. Similar elements in FIGS. 6 to 9 are indicated with identical reference signs. In contrast to the embodiment shown in FIG. 1, the applicator head of FIGS. 6 to 9 comprises a shell 100 enclosing the basic body 4 and the module 6 (in FIGS. 6 to 9 now shown).

(40) The applicator heads 1 of FIGS. 6 to 9 are provided with an inspection device 30 according to the present invention. The inspection device 30 comprises a housing 31 which houses both, the heat sensor heads and the heat sensor (in FIGS. 6 to 9 not shown in detail). Furthermore, a controller 102 is provided which is connected via a signal line 104 to the heat sensors, which are provided in the housing 31. According to this embodiment, the controller 102 is provided as a separate unit, while in the embodiment shown in FIG. 2 and described above the controller is provided within control box 26, which is connected to both, the housing 31 and the applicator head 1. In the embodiment of FIGS. 6 to 9, the control box of the applicator head 1 is not shown but would be connected to the connector 22. Furthermore, one of the signal lines 105, 106 is connected to the control box 26 (not shown in FIGS. 6 to 9).

(41) According to the embodiment shown in FIGS. 6 to 9, the housing 31 is attached to the applicator head by means of a mounting bracket 110. The mounting bracket 110 comprises a first engagement section 112 for engaging the applicator head 1 and a second engagement section 114 for engaging the housing 31. Both sections are substantially formed as arms which are provided rectangular to each other. The mounting bracket 110 is formed out of a thermo isolating material, such as plastics, so that the housing 31 is insulated against the nozzle 8. The first engagement section 112 according to the embodiment shown in FIGS. 6 and 7 is formed to engage a portion of the nozzle, in particular a circumferential outer surface of the nozzle 8. Therefore, the first engagement section 112 comprises a clamping means 116 for clamping the mounting bracket 110 against the nozzle 8. The second engagement section 114 comprises a dovetail-shaped recess 118 and the housing 31 comprises a correspondingly dovetail-shaped protrusion 120. Due to these matching forms, the housing 31 can be fixed against the mounting brackets 110 easily and without additional tools. When engaged, the geometric properties between housing 31 and nozzle 8 are known in a predetermined range.

(42) FIGS. 8 and 9 illustrate an alternative embodiment of the mounting bracket 110. The elements of the applicator head 1 and the inspection device 30 are substantially identical to those shown in FIGS. 6 and 7 and in so far reference is made to the above description and in the following in particular the difference between the two mounting brackets 110 of FIGS. 6, 7, 8 and 9 is described.

(43) The mounting bracket 110 again comprises a first engagement section 112 and a second engagement section 114. The first engagement section 112 engages the applicator head 1 and the second engagement section 114 engages the housing 31 of the inspection device 30. In contrast to the above embodiment shown in FIGS. 6 and 7, the first engagement section 112 is mounted against a portion 122 of the pneumatic solenoid valve 2, in particular two pipes connecting the basic body 4 with the valve 2. Fixing the first engagement section 112 against such a portion 122 can be beneficial in application of hotmelt adhesive, since there is no direct heat bridge from the nozzle 8 to the housing 31. Furthermore, it may be beneficial when for example the nozzle module 6 (see FIG. 1) needs to be changed, the mounting bracket 110 still can be maintained in place.

(44) The first engagement section 112 is substantially U-shaped having two legs 124, 126 running downwards from the portion 122 at two opposing sides of the basic body 4. At the lowermost portions, the legs 124, 126 are connected with the second engagement section 114. Also the second engagement section 114 is substantially U-shaped having two legs 128, 130. The legs 128, 130 are connected to the legs 124, 126 by means of a screw connection 132.

(45) Again, as also shown in FIGS. 6 and 7, the second engagement section 114 comprises a dovetail-shaped recess 118 and the housing 31 comprises a correspondingly dovetail-shaped projection 120. By means of the recess 118 and the projection 120, the housing 31 can be formfittingly connected to the second engagement section 114. Due to the mounting brackets 110 shown in FIGS. 8 and 9, the housing 31 is in a known and predetermined relationship to the nozzle 8, when engaged.

(46) FIG. 10 shows in a block diagram the principle arrangement of an inspection device according to the invention. Again, for identical parts identical reference signs are used and in so far reference is made to the above description.

(47) On the left hand side of FIG. 10, the applicator head 1 is shown having the valve 2, the basic body 4 and the nozzle 8. A discharge signal 200 is intercepted at 202 by the controller 102, before running at 204 to the solenoid valve 2. The solenoid valve 2 receives a supply of air 206 and provides air flow to the adhesive valve module 4. The adhesive valve module 4 receives an adhesive flow 208. The nozzle 8 discharges adhesive 210 on a substrate 34a, which travels in the machine direction 36. In FIG. 10 two more substrates 34b, 34c are shown, onto which an adhesive pattern 37 has already been discharged.

(48) The controller 102 intercepts the discharge signal 200 and determines based on the discharge signal 200 the desired adhesive pattern, using predetermined tolerances set by means of the tolerance dial 212. The tolerance dial allows an operator to set a desired tolerance within which the discharged adhesive pattern should be. The controller 102 is connected to a sensor arrangement 43, in this embodiment preferably formed as a heat sensor array as shown in FIG. 5. The sensor arrangement 43 provides a heat intensity data array signal 214 to the controller 102. The inspection device 30 furthermore comprises a speed detector 216 in this embodiment formed as two photo cells 218, 219, which detect a leading edge 220 of the substrate 34. The speed detector 216 provides a substrate presence and edge speed signal to the controller 102. The speed detector 216 and the sensor arrangement 43 are arranged in close proximity next to each other within the same housing (not shown in FIG. 10).

(49) The distance d.sub.GSO between nozzle 8 and sensor unit, comprising the speed detector 216 and the sensor arrangement 43, is known. Furthermore, process parameters, in particular delay times, are known. When the discharge signal 200 is generated at t.sub.0, it is provided to the solenoid valve 2. Until the solenoid of the solenoid valve 2 is energized, it takes a time t.sub.s. For the valve to react there is additional time t.sub.v, the actual delay for air flow into adhesive valve module. Dependent on the type of adhesive used, there is an additional delay time t.sub.a, for the adhesive to flow out of the nozzle tip. This delay is dependent on the type of valve, the adhesive pressure and viscosity, and wear in the valve over its lifetime. A high viscosity, low pressure and small nozzle orifice in general lead to a higher t.sub.a value. After the adhesive has been discharged, it flies through the air until it contacts the substrate 34. The time t.sub.f is the actual delay for adhesive flight from nozzle tip to substrate. The parameters t.sub.s, t.sub.v, t.sub.a, and t.sub.f may be determined experimentally. From the parameters t.sub.0, t.sub.s, t.sub.v, t.sub.a, t.sub.f, d.sub.GSO and the detected speed v.sub.s of the substrate, it is known when the respective heat sensor head should “see” the pattern 37, when the discharged pattern 37 is congruent to the desired pattern. If the detected pattern 37 is within the set tolerance, the adhesive pattern 37 is deemed to be congruent. Otherwise, it is detected as a faulty pattern and a pattern-fault signal 224 is outputted by the controller 102.

(50) FIG. 11 illustrates the signal logic of the inspection device 30. The controller 102 intercepts the discharge signal, as described above.

(51) When the controller determines in the step “Signal Active?” that no discharge signal is received and at the same time the speed detector 216 determines that no substrate is present, it is known that there is no substrate in the sensing field of the sensor arrangement 43. The detected heat intensity data array to this point of time is thus a “Background Heat Intensity Value” which is stored and used later on when determining the presence of a pattern. When the controller 102 determines that a discharge signal is present, it furthermore checks whether the pattern has changed in step “Has Pattern Changed?”. When the pattern has not changed, the normal running mode is operated. Otherwise, when the pattern has changed, the controller 102 switches into a learning mode (which will be described below with reference to FIG. 12). It should be noted that the learning mode is not entered due to an operator pressing a teach button, but based on the change in the pattern itself.

(52) By means of the tolerance dial 212, four different tolerance values can be set and/or adjusted. First of all a “start/end length tolerance” value is set, then a “width tolerance”, an “amount tolerance”, and a “center tolerance” value. The “start/end length tolerance” is used together with the determined speed, which has been determined in step “Calculate v.sub.s From Edge” and converted into a time value.

(53) For detecting the adhesive pattern 37, according to this embodiment (FIG. 11), a threshold value is used. Staring from the determined background heat intensity value, when a heat above a predetermined threshold value is reached at step “Start of Bead Detected?”, which is determined based on the background heat intensity value, it is deemed that a start of a bead is detected until the value sinks again below the threshold. The threshold value can be determined experimentally. From the detected substrate velocity, the threshold can be speed-adjusted using a known cooling rate factor which is dependent on the environmental temperature, the substrate speed, the type of adhesive, and potential other parameters. Furthermore it is determined whether the time of the start point is within the total estimated time and within the tolerance of the expected time at the step “Within Tolerance of Expected Time?”, and when it is not within this tolerance, a pattern-fault signal is outputted.

(54) When detecting a start of the bead at “Start of Bead Detected?” based on the heat intensity data array detected by the heat sensor 43, the “start/end length tolerance” is used to check whether the start time of a bead is within expected tolerance time. This is determined in the step “Within Tolerance of Expected Time?”. If not o.k., a pattern-fault signal is outputted.

(55) The width tolerance value may be used together with a “Width Speed Factor” to determine a speed adjust width tolerance. If the user selects a width tolerance with speed dependence, which would normally be used when the adhesive pressure is not adjusted depending on the machine speed and thus wider bead is expected at slower speeds, the width tolerance is scaled by the velocity and stored as a “Width/Speed Factor”, which is determined experimentally. Therefore, when the speed of the substrate is known it is possible to adjust the width tolerance based on the detected speed. Using the heat intensity data array, left and right edges of the pattern can be detected. From these the width of the pattern can be calculated and it can be checked whether this is within set tolerances. The last step is carried out at “Width Inside Tolerance?”. If these are not o.k., a pattern-fault signal is outputted.

(56) From the calculated width, the bead length and also a known array spacing of the heat sensor array, a bead area can be calculated. When calculating the bead area it can be determined whether the adhesive amount is within the set tolerance. This is checked at the step “Amount Within Tolerance?”. If the determined adhesive amount on the substrate is not within the set amount tolerance, a pattern-fault signal is outputted.

(57) Furthermore, the center of the pattern is determined. Therefore, the “Center Tolerance” value is used. When the left and right edges of the pattern are determined, the bead center can be calculated. Using the center tolerance value, it is determined whether the bead is within this tolerance. This is checked at step “bead of center?”. If the bead center is not within the predetermined tolerance, a pattern-fault signal is outputted.

(58) With reference to FIG. 12, the learning mode is now explained. When the controller 102 detects that a discharge signal has changed (see FIG. 11), or that a discharge signal has been detected for the first time, e.g. after starting the inspection device, the learning mode is entered. In the learning mode the status LED 211 is switched yellow, indicating that the controller 102 is in the learning mode. When the learning mode is entered, the set tolerance values are overwritten to the highest tolerance level 220 until N cycles have passed. The value N stands for the learning duration, that is the number of substrates which are used in the learning mode. For example, ten substrates are used for the learning mode. Dependent on the time of application also a smaller or higher number can be used. When in the learning mode, the controller tracks the average data array values of each of the N patterns. When it is determined that these values are stable, i.e. when the absolute change and the change rate between the detected patterns is within predefined tolerances, indicating there is no increasing/decreasing trend, the average of all or of a subgroup of the N detected patterns or of a following group of N+x patterns is used to adjust the threshold value and thus to determine a new adjusted desired pattern. After the new desired pattern has been set, the learning mode is ended and the controller returns to normal operation mode as shown in FIG. 11.

(59) As stated above, when in the learning mode, the tolerances (position, width, amount, center) set by the tolerance dial 212 are overridden to a stored highest tolerance level 220, preferably determined by experiments to cover a range such that the vast majority of plausible sensor values are included, both in terms of timing (position) and intensity of heat/infrared radiation (amount). In terms of timing, in one extreme, an application with an adhesive with a low viscosity applied at a high pressure through a small nozzle onto a close substrate, which will have fast valve actuation, fast flow through the valve and nozzle and a short time of flight to the substrate over the short distance, will have a short total delay. In the other extreme, a highly viscous adhesive at low pressure through a large nozzle to a substrate that is far away will have a long total delay. In terms of heat/infrared intensity, in one extreme, a high-temperature adhesive applied in large amounts onto a fast moving substrate will quickly reach the sensor with little cooling and will give a high and wide reading from the heat sensor array. In the other extreme, a low temperature adhesive applied in small amounts at slow speeds will give a narrow and low reading from the array. The verification nevertheless remains active during learning with these extended tolerances 220 in order to give a fault output if no or very atypical heat intensity data is received.

(60) An example of what the threshold intensity level could look like when in learning mode is shown in FIG. 13. To be recognized as present, the center of the bead preferably gives a reading of at least 100 (cf. FIG. 13, “sensor heat intensity value” on ordinate), and neighboring sensors in the array preferably give a reading of at least 65. This would correspond to a typical narrow, cool bead. The center of the bead (found by looking for the peak in the curve of array values) can also range almost the entire width of the sensor. Upper values could also exist particularly for the outer sensing elements to ensure the sensor is still seeing both edges of the bead.

(61) In FIG. 13, the abscissa indicates the sensor position across the width of the substrate. The ordinate indicates the sensor intensity normalized with an index value. The dashed vertical line 230 indicates an expected centerline of a pattern and/or a bead. This may be set by an operator or determined based on pre-stored values. The lower curve 232 shows a lower limit of the tolerance range and the upper curve 234 indicates the upper limit of the tolerance range. Every measured curve within the area defined between curves 232 and 234 would be within the tolerance in the learning mode.

(62) When the controller turns in the normal operation mode as shown in FIG. 11, the tolerance is set back to the normal mode. This is illustrated in FIG. 14. Again the ordinate indicates the sensor intensity normalized with an index value and the abscissa indicates the sensor position across the width of the substrate, as it was in FIG. 13. In this diagram the learned curve 236 of the desired adhesive pattern is shown. Two threshold curves are drawn, a first threshold level 238 for a tight sensitivity offset and a second, lower one 240 which is adjusted and adapted for slower speeds of the substrate and/or higher cooling rates, so that sensor heat intensity value is lower.

(63) To facilitate more accurate verification during the learning phase, a custom programming interface could be used to allow the user to enter their application data (bead width, setpoint temperature), which would result in the use of stored data from experiments that matches (or is interpolated to best match) the user conditions to be used to define a narrower learning range for the threshold. This is indicated in FIG. 15, which shows a lower curve 242 indicating a lower limit of the set tolerance range, and an upper curve 244 illustrating an upper limit of the tolerance range. Every detected pattern whose curve would fit in between those curves 242 and 244 would be considered congruent with the desired adhesive pattern.

(64) FIG. 16 illustrates an output logic of the controller 102. As shown in FIG. 10, the controller comprises two status LEDs, 211, 213. The status LED 211 according to this embodiment can switch between green and yellow and the status LED 213 can switch between white, blue and green. While status LED 211 is used to indicate whether the controller 102 is in learning mode (yellow) or in working mode (green), status LED 213 is used to indicate whether the last product is defect or not. As described above with reference to FIG. 11, it is checked whether the detected bead is within length tolerance, width tolerance, amount tolerance and center tolerance. Therefore, verification of a bead start/end position relative to substrate edge, verification of bead width, verification of bead position perpendicular to substrate travel, and verification of adhesive amount (bead area) are carried out. If any of these tolerances is not met, a fault counter is incremented. At the same time, the status LED 213 is switched to blue. Otherwise, when all tolerances are met, status LED 213 is maintained green. At the same time it may be provided that status LED 213 also flashes white, when a poor pattern is detected. Alternatively, at the end of the pattern cycle, status LED 213 may be switched white with a high voltage signal, in case the number in fault counter has reached a predetermined threshold.

(65) FIGS. 17a to 17c show different examples of adhesive patterns 37a, 37b, 37c. First reference is made to FIG. 17a. In FIG. 17a a row of three substrates 34a, 34b, 34c are shown, wherein the machine direction is to the left with respect to FIG. 6a. On substrate 34a an adhesive pattern 37a is discharged including an adhesive bead 38a and an adhesive bead 39a. Between these two beads 38a, 39a a gap 90 is provided. On the next substrate 34b again an adhesive bead 38b and an adhesive bead 39b is discharged. Between the two beads 39a and 38b, a gap 91 is provided. A gap 92 is provided between adhesive beads 38b and 39b, which is identical in length to the gap 90. Accordingly, a gap 93 is provided between beads 39b and 38c, which are discharged on the third substrate 34c. Gap 93 is identical in length as gap 91. When the substrate 34a moves along the inspection device 31 (s. FIGS. 2, 11), firstly bead 38a is detected by means of the heat sensor head. After gap 90, adhesive bead 39a is detected and after gap 91 adhesive bead 38b is detected. In case the controller, provided in the control box 26 of the heat sensor 43, receives the discharge signal of the control unit of the applicator head 1, detection of the adhesive pattern 37a and also in comparison of the detected adhesive pattern 37a with the desired adhesive pattern can directly be started based on the discharge signal.

(66) In a learning mode, the controller analyzes the detected adhesive pattern 37a for a recurrent pattern and sets the recurrent pattern as the desired pattern. The controller acts in such a case as follows: After bead 39a has been detected, it is compared with bead 38a and the controller analyzes that bead 39a is not identical to bead 38a. After detection of bead 39a, gap 91 is detected and then again bead 38b is detected. After detection of bead 38b, the controller analyzes that bead 38b is congruent with bead 38a. After bead 38b, gap 92 is detected and the controller analyzes that gap 92 is congruent to gap 90. The controller now expects that after this gap 92 a bead would follow that would be substantially identical to bead 39a. After detection of bead 39b this assumption can be verified. Bead 39b is again followed by gap 93 which is congruent to gap 91 and therefore a recurrent pattern has been identified. After detection of gap 93, thus with the start of bead 38c, the controller sets the detected adhesive pattern 37a as the desired adhesive pattern and thus starting from substrate 34c on, automatic detection and comparing of the detected adhesive pattern with the desired adhesive pattern, which is the recurrent pattern in this case, can be started. It can be provided that before a detected recurrent pattern is set as the desired pattern, one or more repetitions of the pattern must be detected. It can for example be provided that one repetition of a detected recurrent pattern is necessary. In this case, the automatic comparison between the detected pattern and the desired adhesive pattern can be started after substrate 34c, thus with a substrate 34d, which follows substrate 34c (which however is not shown in FIG. 17a).

(67) In FIGS. 17b and 17c, different alternatives of adhesive patterns 37b, 37c are shown. Regarding these two patterns 37b, 37c, the same as explained above with regard to pattern 37a is applicable. Pattern 37b consists of three adhesive beads 38a, 39a, 40a which are spaced by gaps, which are not shown with reference signs in FIGS. 17b and 17c. Even though the adhesive pattern 37b, 37c shown in FIGS. 17b and 17c are more complex than adhesive pattern 37a of FIG. 17a, the same method of detecting and analyzing the adhesive pattern 37b, 37c can be applied here.

(68) In FIGS. 18a and 18b schematically two adhesive patterns comprising adhesive beads 38, 39, 40, 41 are shown. While FIG. 18a illustrates a high tolerance for a maximum gap G.sub.1, FIG. 18b shows a low tolerance for the maximum gap G.sub.2. When applying the high tolerance as shown in FIG. 18a, the distance between the trailing edge 338 of the first bead 38 and the trailing edge 340 of the third bead 40 is measured. Thus, a pattern is within tolerances, in case the bead 39 is missing and also the leading portion of the bead 40 is missing. As long as the trailing edges 338 and 340 are detected, this pattern will be determined as being within the tolerance G.sub.1.

(69) In contrast thereto, FIG. 18b illustrates a low tolerance for the maximum gap G.sub.2. In this low tolerance, the trailing edge 338 of the first bead 38 and the trailing edge 339 of the second bead 39 are compared. When the second bead 39 is completely missing, this pattern will not be considered as being congruent with the desired adhesive pattern. However, it is still possible that the leading portion of the bead 39 is missing and the pattern as shown in FIG. 18b will be considered to be within the tolerance, when the trailing edges 338 and 339 are properly detected.