Wood material panel pressing device and method for monitoring a wood material panel pressing device

Abstract

The disclosure relates to a wood material panel pressing device for pressing a fibrous press cake in order to produce a wood material panel, including an inspection device that is designed to emit a signal in the event of a disruption. According to the disclosure, the inspection device has a camera and an evaluation unit, the camera is arranged in an intake region of the wood material panel pressing device and the evaluation unit is designed to automatically carry out a method featuring the steps: (i) continuous recording of images (B) of the intake region, (ii) continuous detection of measurement data for evaluation region pixels of images (B), which belong to a predefined evaluation region comprising at least one region bordering a target horizontal of the fibrous press cake at the top, such that evaluation data is obtained, and (iii) emission of a signal if the evaluation data changes by more than a predefined tolerance value (D.sub.T).

Claims

1. A wood material panel pressing device for pressing a fibrous press cake for producing a wood material panel, comprising: (a) an inspection device, which is designed to emit a signal in the event of a disruption, wherein: (b) the inspection device has a camera and an evaluation unit, (c) the camera is arranged in an intake region of the wood material panel pressing; and (d) the evaluation unit is designed to automatically carry out: (i) continuous recording of images (B) of the intake region, (ii) continuous detection of measurement data for evaluation region pixels of images (B), which belong to a predefined evaluation region comprising at least one region bordering a target horizontal of the fibrous press cake at a top, such that evaluation data is obtained, and (iii) emission of a signal if the evaluation data change by more than a predetermined tolerance value (D.sub.T).

2. The wood material panel pressing device according to claim 1, further comprising a spreading device for spreading the fibrous press cake onto a conveyor.

3. The wood material panel pressing device according to claim 1, further comprising: measurement data is recorded for a number of regions (B.sub.i), the regions (B.sub.i) border one another and together cover a full width (B) of the fibrous press cake.

4. The wood material panel pressing device according to claim 1, further comprising: a circulating press element for pressing the fibrous press cake, wherein continuous recording of measurement data for reference region pixels which belong to at least one predetermined reference region (R.sub.i), wherein precisely one reference region (R) is allocated to each evaluation region, said reference region being located in front of the evaluation region in terms of a direction of movement of the circulating press element, and wherein the continuous recording of measurement data for evaluation region pixels, which belong to at least one predetermined evaluation region, comprises a calculation of a deviation between: the measurement data of the evaluation region pixels; and the measurement data of the reference region pixels that have been shifted by a time delay, and wherein the time delay is the time needed for a section of the circulating press element to pass from the reference region to the evaluation region.

5. The wood material panel pressing device according to claim 1, wherein the wood material panel pressing device is a hot press and the press element is a press plate or the wood material panel pressing device is a pre-press and the press element is a press cloth.

6. The wood material panel pressing device according to claim 1, further comprising a lighting device for illuminating the intake region.

7. The wood material panel pressing device according to claim 1, wherein the inspection device is designed to automatically carry out a method according to claim 1.

8. The wood material panel pressing device according to claim 1, further comprising an optical axis (A) of the camera forms an axis angle () with a horizontal (H) that lies between 0 and 20.

9. A method for monitoring a wood material panel pressing device for pressing a fibrous press cake to produce a wood material panel comprising: (i) continuous recording of images (B) of an intake region, (ii) continuous detection of measurement data for evaluation region pixels of images, which belong to a predefined evaluation region that borders a target horizontal of the fibrous press cake at the top, such that evaluation data is obtained, and (iii) emission of a warning signal if the evaluation data change by more than a predetermined tolerance value (D.sub.T).

10. The method according to claim 9, further comprising: (i) grouping of evaluation pixels into a first region (G.sub.i) and at least one second region (G.sub.2), and (ii) for all regions (G.sub.i): detection of the pixels which feature one property that changes more drastically than a threshold value, calculation of a change parameter (D) from the number of these pixels and comparison of this change parameter (D) with the tolerance value (D.sub.T).

11. The method according to claim 9, wherein the evaluation region pixels are grouped into at least 20 regions (G).

12. The method according to claim 9, wherein the emission of the warning signal effects an adjustment of an intake angle, and wherein the intake angle is the angle between the horizontal plane and the press element of the wood material panel pressing device.

13. The method according to claim 9, wherein the emission of the warning signal effects an adjustment of a feed speed (v).

14. The method according to claim 9, further comprising: (i) calculation of a position of the actual horizontal of the fibrous press cake, and (ii) emission of a signal if the actual horizontal deviates from the target horizontal by more than one level error threshold value (Ahs).

15. The method according to claim 10, wherein the one property is color, brightness, contrast with at least one adjacent pixel.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) In the following, the invention will be explained in more detail by way of the attached drawings. They show

(2) FIG. 1 a schematic view of a wood material panel pressing device according to the invention,

(3) FIG. 2a a perspective detailed view of the intake region of the wood material panel pressing device according to FIG. 1 and

(4) FIG. 2b an image of the intake region in which the regions that are used for evaluation are depicted.

(5) FIG. 3 depicts an alternative embodiment of a wood material panel pressing device according to the invention which has a pre-press.

DETAILED DESCRIPTION

(6) FIG. 1 shows a wood material panel pressing device 10 according to the invention in the form of a hot press for pressing a fibrous press cake 12 to produce a wood material panel 14. The wood material panel pressing device has a spreading device 16 for spreading the fibrous press cake 12 on a conveyor 18.

(7) The wood material panel pressing device 10 features an inspection device 20, which comprises a camera 22 and an evaluation unit 24 that is connected to said camera. An optical axis A is oriented at an axis angle to the horizontal H, this angle generally lying between 0 and 45 and is =10 in the present case. A positive axis angle means that the camera is aimed downwards.

(8) The wood material panel pressing device 10 has a press element 26 in the form of a press plate, which forms a closed loop and is pressed onto fibrous press cake 12 by means of drums 28.1, 28.2, . . . with a press force F. Using a schematically depicted heater 29, the press element 26 is also brought to a predetermined temperature T.sub.26 by means of a hot thermal oil. In the present case, the wood material panel pressing device 10 also comprises a second press element 26, which is pressed against the fibrous press cake 12 from below via the drums 28.1, 28.2, . . . . The second press element 26 is also heated by heating elements 29.

(9) The press element 26 runs in the region in which it comes into contact with the fibrous press cake 10 for the first time, at an intake angle to the horizontal H. The intake angle is adjustable, as is indicated by the press plate depicted with a dashed line.

(10) The camera 22 captures images of an intake region 30 in which the fibrous press cake 12 comes into contact with the press element 26 for the first time. In the interior, the fibrous press cake 12 has an actual horizontal at a height h.sub.ist, which corresponds to a target height h.sub.soll in the situation shown in FIG. 1. A level error h lies below a level error threshold value h.sub.S.

(11) During operation, the fibrous press cake 12 moves in a direction of material flow M at a feed speed v. A trimming system 32 and/or other processing devices, such as a digital printing device for imprinting the wood material panel 14, may be arranged behind the wood material panel pressing device in the direction of material flow M.

(12) FIG. 2a shows a perspective view of the intake region 30 of the wood material panel pressing device. The fibrous press cake 12, the press element 26, a lighting device 34in the form of an LED light in the present casethe camera 22 and a humidification system 36 can be seen. The humidification system 36 can be used to spray a liquid mist, especially one made of water that contains surfactants, onto the fibrous press cake 12

(13) FIG. 2b shows an image B of the intake region 30 that has been captured using the camera 22. An actual horizontal H.sub.ist of the fibrous press cake 12, situated at the height h.sub.ist, can be seen in the lower partial image. An evaluation region 37 is also depicted which borders a target horizontal H.sub.soll of the fibrous press cake 12 at the top, said horizontal lying at the height h.sub.istsoll, wherein h.sub.ist=h.sub.soll in the present case.

(14) The evaluation region 37 is divided into N regions G.sub.i (i=1, 2, . . . , N), each of which has several pixels P. The regions G.sub.i may also be referred to as clusters.

(15) Each region G.sub.i relates to an image of a region B.sub.i of the evaluation region 37. In other words, regions indicate sections of the wood material panel pressing device, such as the press element 26, whereas the regions G.sub.i are groups of pixels P.sub.n,m, wherein n and m are the number indices of the pixels of the camera 22.

(16) For each pixel P.sub.n,m, a measured value P.sub.n,m(t.sub.j) is recorded at regular intervals, in particular the brightness b.sub.n,m(t.sub.j) and the color f.sub.n,m(t.sub.j). The brightness contrast, for example k.sub.n,m(t.sub.j)=b.sub.n,m(t.sub.j)b.sub.n1,m(t.sub.j), is also calculated as is the color contrast k.sub.n,m(t.sub.j)=f.sub.n,m(t.sub.j). Alternatively, the brightness contrast may be defined differently, for instance K.sub.n,m(t.sub.j)=b.sub.n,m(t.sub.j)b.sub.n+1,m(t.sub.j) or k.sub.n,m(t.sub.j)=b.sub.n,m(t.sub.j)b.sub.n,m1(t.sub.j) or k.sub.n,m(t.sub.j)=b.sub.n,m(t.sub.j)b.sub.n,m+1(t.sub.j) or a mean of these values. The same applies for the color contrast k.sub.n,m(t.sub.j). The measurement data of the evaluation pixels is referred to as evaluation data, as preferably only it is involved in the evaluation.

(17) At each point in time t.sub.j and for each region i, the evaluation unit 24 determines a change parameter D.sub.i to indicate whether the evaluation data b.sub.n,m(t.sub.j), f.sub.n,m(t.sub.j), K.sub.n,m(t.sub.j) and k.sub.n,m(t.sub.j) is in each case greater than a predetermined threshold value. It is thus examined for all n and m, for which the pixel P.sub.n,m lies in the region i, whether b.sub.n,m(t.sub.j)>b.sub.max, f.sub.n,m(t.sub.j)>f.sub.max, K.sub.n,m(t.sub.j)>K.sub.max and k.sub.n,m(t.sub.j)>k.sub.max applies. For each region G.sub.i, the pixels are counted for which at least one of the conditions is metthe corresponding number is the change parameter D. If the change parameter D.sub.i exceeds a tolerance value D.sub.T for at least one region G.sub.i, a signal is emitted.

(18) Alternatively, the temporal changes b(t.sub.j)b(t.sub.j1), f(t.sub.j)f(t.sub.j1), K(t.sub.j)K(t.sub.j1), k(t.sub.j)k(t.sub.j1) are used by the evaluation unit 24 to determine a change parameter D.sub.i at each point in time t.sub.j and for each region i, which is achieved as follows:
D.sub.i(t.sub.j)=.sub.n,m mtt P.sub.n,m.sub.tG.sub.i,({tilde over (b)}.sub.n,m(tj)+f.sub.n,m(tj)+K.sub.n,m(tj)+k.sub.n,m(tj)).

(19) The parameters , , , are real numbers that are identified in preliminary tests. If the change parameter D.sub.i exceeds a tolerance value D.sub.T, i.e. D.sub.i>D.sub.T, in at least one region Gi, a signal is emitted.

(20) FIG. 2b also shows that reference regions R.sub.i are captured in image B. The reference regions R.sub.i are preferably exactly as many pixels wide as the regions G.sub.i. The press element 26 moves at the feed speed v. In order to keep external influences on the measurement result as small as possible, the relative brightness {tilde over (b)} is preferably used over the absolute brightness B, wherein the relative brightness indicates the difference when compared with the same region on the press element 26 whilst passing through the reference region R.sub.i.

(21) Alternatively, the change parameter D is calculated using the method described above; however, before comparing it with the tolerance value T.sub.t, a reference change parameter D.sub.R is deducted, which is calculated from the corresponding pixels of the reference region R.sub.i at a point in time at which the corresponding area of the press element 26 has passed the reference region R.sub.i.

(22) FIG. 3 depicts a second embodiment of a wood material panel pressing system 42 according to the invention that features a pre-press 40 that is arranged in front of a hot press 38 as described above, said pre-press compacting the fibrous press cake 12 before it enters the hot press 38. The press element 26 of the pre-press 40 is designed to be a press cloth.