EP1240500A2

EP1240500A2 - Device for detecting the characteristics of a moving paper web using an ir-light source

Info

Publication number: EP1240500A2
Application number: EP00987140A
Authority: EP
Inventors: Ursula Schumacher
Original assignee: Metso Paper Automation Oy
Current assignee: Metso Paper Automation Oy
Priority date: 1999-12-11
Filing date: 2000-11-16
Publication date: 2002-09-18
Also published as: US20020179840A1; WO2001042765A2; US6696685B2; DE10056783A1; WO2001042765A3

Abstract

The invention relates to a device for detecting the characteristics of a moving paper web (20), in particular for controlling production during the manufacture of paper, comprising an IR-illuminating device (22) which is suitable for illuminating the paper web (20) with IR-light and a detector (28) containing a light receptor for the light which is reflected or transmitted from the paper web (20). The invention is characterised in that the IR-illuminating device (22) has a long, rod-shaped IR-light emitter (26) which forms the light source, that said light source is located in a housing (38), that the housing (38) has a front plate (40) which faces the paper web (20) and that an exit window (48) is sealed into the front plate (40), through which the light from the light source falls onto the paper web (20).

Description

Name: Device for detecting properties of a moving paper web with an IR light source

The invention relates to a device for detecting properties of a moving paper web, in particular for production control in paper manufacture, with an IR lighting device, which is suitable for illuminating the paper web with IR light and with a detection device for reflected from the paper web or transmitted light, which has a light receiving part.

In this device known from WO 98/40727, the paper web is illuminated by an unspecified IR light source. A light exit part of the IR illuminating device and a light receiving part of the detection device are located on a holding part, which is supported by a traverse. The light receiving part has a multiplicity of light guide fibers arranged next to one another in the form of optical fibers with a thickness which is typically in the range between 50 and 600 micrometers. The ends of these fibers are polished and directed towards the paper web, they are fixed to the holding part and protrude towards the paper web.

The area of the paper web to which the light receiving part is aligned should be sufficiently illuminated by the IR illuminating device

be tested. Reflected or transmitted light can be measured. The paper web should be illuminated as evenly as possible, the light used should be in the IR range, especially in the called near infrared, ie in the range above the visible light (> 800 nm) and in particular in the range 1.5 to 2.5 micrometers as intense and homogeneous as possible. Light in wavelength ranges outside the range that is detected by the detection device is not required.

The known device enables a large number of measurement spots next to one another on the paper web. In contrast to reciprocating slides on trusses, this device has the advantage that the light detection is stationary relative to the truss. Unchecked areas of the paper web are smaller than with a carriage. This is fundamentally advantageous and should be maintained.

The aim of the present invention is to provide a suitable IR illumination device which is particularly suitable for the specific measurement task. The effort should be as low as possible, in particular an adjustment and precise illumination of the areas in which the measurement spots of the detection device are located should be simple. In particular, a sufficient seal against dust and dirt should also be achieved. There is always a lot of dirt, dust, etc. in paper production. The IR lighting device should be designed so that it is contaminated as little as possible and can be easily cleaned if it is actually contaminated. Since paper machines often run continuously for many months, cleaning should also be possible while the paper machine is running.

Proceeding from this, the invention has set itself the task of creating an IR lighting device that is easy to assemble, requires relatively few parts, is reliable in operation and enables high, homogeneous illumination of those areas of the paper web on which the Measuring spots of the detection device are located.

Starting from the device of the type mentioned at the outset, this object is achieved in that the IR illumination device has a long, rod-shaped IR emitter as the light source, that this light source is arranged in a housing, that the housing has a front plate facing the paper web, and that an exit window is arranged sealed in the front panel, through which the light of the light source falls on the paper web.

A very long, rod-shaped IR emitter is used as the lighting device. This has the great advantage that a single illumination source is sufficient for a part of the paper web to be checked that is at least one meter wide, preferably at least two meters wide. With just one light source, a considerable part of the paper web, which is typically many meters wide, can already be detected. In contrast to many individual light sources for lighting, there is a considerable advantage. The number of components of the lighting device is significantly reduced, assembly is significantly simplified, and the same applies to service and maintenance. The illumination of the paper web is extremely good. An adaptation to different distances between the light exit part and the paper web is easily possible. Finally, the lighting device is easy to clean. As a result, it can always be brought back into a good starting state.

Typical IR radiators, such as those used for the invention, are offered by Heraeus Nobellight GmbH, Kleinostheim, Germany under the name IR tube radiators, for example under the product name ZKA. These are quartz glass tubes with at least an inner channel, in the channel there is an electrically heated coil. So-called twin tube emitters with gold reflectors have proven to be suitable. Round tube emitters with gold reflectors are also cheap. The manufacturer mentioned also manufactures these IR emitters in the halogen version, as well as in the version as short-wave infrared emitters. According to the company information, they are used practically exclusively in areas where heat is required, for example for drying paper and cardboard, drying printing inks, drying lacquers in painting lines, etc. An application in the field of measurement technology is not yet known.

This rod-shaped light source is arranged in a housing. Like the IR emitter, this housing is elongated. The housing is preferably sealed. This prevents dust and dirt from entering the IR emitter and its surroundings. The housing also allows the light from the IR emitter to exit only where it is desired to exit.

The housing has a front panel facing the paper web, an exit window is arranged in a sealed manner in this front panel, through which the light from the light source falls on the paper web. This exit window enables the housing to be made dustproof. The exit window can be easily cleaned from the outside. It stays clean from the inside because the housing is closed.

Overall, the device according to the invention specifies an IR illumination device which is outstandingly suitable for practical use in the detection device. By selecting the appropriate IR The desired length wave range for the detection can be obtained.

In a preferred development, the exit window is designed as a rod lens. This has essentially the length of the rod-shaped IR radiator. The rod-shaped IR radiator in connection with the rod lens achieves the essential parts of the lighting device for a part of the paper web that is at least one meter wide. This shows how few components are required for the lighting device.

In a preferred development, the rod lens has a cylindrical shape. The cylindrical shape has proven to be particularly suitable; a corresponding exit window can be arranged in a sealed manner in the front plate using simple means. Due to the circular cross-section, alignment is not necessary and the rod lenses also withstand high temperature changes. In the event of thermal expansion of the materials of the cylindrical rod lens and the front plate, a movement can take place transversely to the front surface. The downward projecting part of the exit window can be cleaned with simple means.

In a preferred development, the detection device has a large number n of spherical lenses. They are arranged in a sealed manner in the front panel and are each optically coupled within the housing to associated optical fibers of the light receiving part. The combination of this receiving part designed in this way with the IR illumination device described above has proven to be very favorable for measurement tasks. The measuring spot can be adjusted with simple means in the area that is illuminated by the IR illumination device on the paper web. The aperture of the optical fibers is corrected using the spherical lenses or the light is made in parallel. The size of the measuring spot on the paper web can thus be varied, for example the diameter can be changed between 5 mm and 10 mm. This allows paper to be measured with a sufficient cross-section resolution. Depending on the distance from the paper web, which is typically between 20 and 50 mm, and the size of the measurement spot and the cross-sectional resolution, balls made of sapphire or other spectroscopically transparent glasses with diameters of typically 2 to 10 mm are used. They are easier to manufacture than the usual lenticular collecting lenses, they are also easier to attach and seal than these.

The spherical lenses allow the optical images on the paper web to be specified and controlled much more precisely. Since the housing is sealed, the coupling area between the ball lenses and the light guides is protected. The parts of the ball lenses facing the paper web are easy to clean. The high hardness of sapphire is also noticeable here.

The ball lenses can be arranged interchangeably in the front plate, so that ball lenses of different diameters can be inserted into the front plate. In this way, different images can be achieved, depending on the measurement purpose. The same applies to the rod lens of the IR lighting device.

The distance between the housing and a paper web can be easily adjusted by changing the angle which the optical axes of the IR illuminating device and the light receiving parts form. The easiest way to do this is to set the angular position of the IR radiator. It has proven to be very advantageous to make the housing essentially elongated, in particular to make it at least one meter long and preferably at least two meters long. The IR radiator should be designed to be correspondingly long. With the usual widths of paper webs, only a few housings are then necessary, which are arranged next to one another and offset from one another on a fixed crossmember in order to illuminate the entire paper web. In order to be able to replace individual housings during ongoing paper production, at least some housings are connected to the crossbar via a longitudinal guide and can be displaced in relation to the crossbar. In this way, individual housings can be removed from the traverse in a targeted manner without disrupting paper production.

Finally, it has proven to be advantageous to provide a cleaning device which is designed to clean the partial areas of the exit window which are accessible from the outside and face the paper web, and their surroundings, during a cleaning process. In this way it is ensured that soiling which simply arises during normal operation of the paper machine does not restrict the optical conditions.

Furthermore, it is expedient to provide the rod-shaped IR radiator on its outside with a reflector layer, in particular a gold reflector layer, and to leave an exit region or exit gap in the latter which is open towards the exit window. In this way, the IR radiation is essentially concentrated or directed onto the exit window.

Further advantages and features of the invention emerge from the remaining claims and the following description of non-limiting to understand exemplary embodiments of the invention, which are explained in more detail below with reference to the drawing. The drawing shows:

FIG. 1: a schematic illustration in side view of a device for detecting properties of a moving paper web with an IR illumination device according to the invention,

FIG. 2: a representation corresponding to FIG. 1 for a different design of the IR radiator, other parts of FIG. 1 are not repeated,

FIG. 3: a representation in side view to explain the beam path,

FIG. 4: a representation corresponding to FIG. 3, but in another

Angular position, in connection with FIG. 3 the setting of the illumination spot can be seen,

FIG. 5: a sectional view through a front plate similar to FIG. 1 to show the arrangement and sealing of the exit window designed as a cylindrical rod lens,

FIG. 6: a perspective representation of a paper web onto which an IR illuminating device is directed and with light receiving parts corresponding to the design according to FIG. 1,

7: a representation similar to FIG. 3, but now in a different arrangement,

FIG. 8: a bottom view of a transported, dash-dotted paper web on a traverse and with three housings and

FIG. 9: a schematic illustration in side view of a cleaning device below a housing.

Figure 1 shows a device for detecting physical and / or chemical properties of a moving paper web 20, its movement is indicated by an arrow. It has an IR lighting device 22 which, in the specific exemplary embodiment, has a light exit part 24 with an IR light source 26 in the form of a rod radiator as far as an electrical control part 25. This rod radiator has a quartz tube housing which is closed at the end, the height is approximately 27 mm and the width is approximately 21 mm. A coil 27 is located in the quartz tube.

Furthermore, the device has a detection device 28, which has a light receiving part 30 and a downstream evaluation unit 32, the latter including, for example, a polychromator with a downstream IR photoconductor arrangement in the form of a matrix and electronics.

By means of the IR illuminating device 22, the paper web 20 is illuminated in the form of a very long, narrow line, which can also be referred to as a gap. A single illumination spot 34 of great length, in particular one meter above or even two meters and above, is thus generated. A multiplicity of light-receiving parts 30 are assigned to this single illumination spot, which capture the information from a measurement spot or image spot 36 which is located within the illumination spot 34. While the spot 34 is essentially in the form of a very long rectangle, the spots 36 are circular. This can be seen in particular in FIG. 6.

The complete IR lighting device 22 and the individual light receiving parts 30 are arranged in a housing 38, it is sealed off from the outside. It has a front plate 40 facing the paper web, which does not necessarily have to be plate-shaped, it can have any shape. It is located in the immediate vicinity of the paper web. As can be seen from the figures, in particular from FIG. 6, a large number of ball lenses 42 are arranged in a sealed manner in the front plate 40. The number of these ball lenses 42 is n. FIG. 6 shows a total of n = 19 such ball lenses 42, each of which the optical fibers of the detection device 28 are assigned. The arrangement is regular. Individual, smaller measuring spots 36 on the paper web 20 are obtained within the illumination spot 34.

The quartz tube of the IR radiator has a reflector 44, which in the exemplary embodiment shown is attached outside and consists of a gold layer. It completely covers the quartz tube except for a small gap in which the light is emitted. In Figure 1, the reflector 44 is shown according to its actual design by a solid line. In Figure 2 it is shown in dashed lines in order to better recognize it. However, this does not mean that it is designed in this way, rather it represents a closed layer.

An outlet window 48 is arranged in the housing 38 next to the individual spherical lenses 42, in FIG. 1 it is designed as a cylindrical rod lens, in FIG. 2 as a rod-shaped collecting lens. FIG. 5 shows how the exit window, there in the form of a cylindrical rod lens, as is offered, for example, by the Edmund Scientific Micro-Rod company, is inserted into the front plate in a sealed manner. For this purpose, sealing strips 46 are arranged in an opening of the front plate, which form an oblique contact surface. As a result, rod lenses of different diameters, as shown in FIG. 5, can be inserted tightly. In the case of thermal expansion, a movement relative to the front plate 40 is possible. It can be seen from FIGS. 3 and 4 that only by changing the angle setting of the IR radiator 26 is it possible to set the measuring device to different distances between the paper web 20 and the housing. FIG. 4 shows that by increasing the angle a the distance from the ball lenses 42 and the exit window 48 on the one hand and the paper web on the other hand can be changed, FIG. 3 shows the state with a large distance d, FIG. 4 shows the state with a small distance d.

The exit window 48 is accessible from below, in some cases it projects downward from the underside of the housing 38. The ball lenses 42 also project downward.

FIG. 7 shows an arrangement similar to that of FIGS. 3 and 4, but the position of the IR emitter 26 and the individual light receiving parts 30 is now reversed. The exit window 48 again has optical properties; it is designed as a converging lens, in this case as a cylindrical rod lens. This almost parallelizes the light, so that an elongated, approximately 5 to 10 mm wide illumination spot 34 is achieved. Because of its more spherical, highly symmetrical shape, the rod lens is less prone to breakage under thermal stresses than a plate as shown in FIG.

FIG. 8 shows a bottom view through a dash-dotted paper web 20 onto a fixed crossmember 50 which is connected to a dash-dotted part of a paper machine. Rails 52 are arranged on the underside of the crossmember 50. Elongated housings 38, in which light exit parts 24 and light receiving parts 30 corresponding to FIGS. 2, 6 or 7 are arranged, hang on these. The configuration according to FIG. 8 is preferably provided for the rod-shaped IR light sources 26 according to FIGS. 6 and 7. seen. To bridge a paper web 20 that is many meters wide, a plurality of housings 38 are arranged offset, so that a continuous detection of the entire width of the paper web 20 is possible.

Figure 9 shows a cleaning device, which is shown here only in principle. A housing 38 is shown, from which ball lenses 42, 44 or a rod lens 48 protrude slightly below. The cleaning device 54 has a circumferential belt 56, which is supported and driven on the left and right by two rollers, the drive takes place in the direction of the arrow. On the belt there are, for example, brushes 58 for cleaning the lower surface of the front plate 40 and in particular the parts of the ball lenses 42 which are visible downwards. Drying devices etc. are also provided on the belt 56. For cleaning, cleaning fluid is sprayed against the front surface 40 from below by means of a spray device 60, and the fluid is sucked off again via a suction device 62. So that no contamination of other parts occurs, there is a trough 64 below the cleaning device 54.

Claims

Description: Device for detecting the properties of a moving paper web with an IR light source

1. Device for detecting properties of a moving paper web (20), in particular for production control in paper manufacture, with an IR lighting device (22), which is suitable for illuminating the paper web (20) with IR light and with a detection device ( 28) for light reflected or transmitted from the paper web (20), which has a light receiving part (30), characterized in that the IR lighting device (22) has a long, rod-shaped IR emitter (26) as the light source, that this Light source is arranged in a housing (38), that the housing (38) has a front plate (40) facing the paper web (20) and that an exit window (48) is arranged in a sealed manner in the front plate (40) through which the light of the Light source falls on the paper web (20).

2. Device according to claim 1, characterized in that the exit window (48) is formed by a rod lens which has essentially the length of the rod-shaped IR radiator (26).

3. Device according to claim 2, characterized in that the rod lens has a cylindrical shape.

4. The device according to claim 1, characterized in that in the front plate (40) a plurality of n-ball lenses (42) is further arranged sealed, which are each optically coupled within the housing (38) with associated optical fibers of the light receiving part (30).

5. The device according to claim 1, characterized in that the housing (38) is elongated, in particular at least 1 meter long.

6. The device according to claim 5, characterized in that the housing (38) with a plurality of identical housings (38) is arranged side by side on a crossmember (50) which extends transversely to the moving paper web (20) and that the housing (38 ) is held in a longitudinal guide and is displaceable in the longitudinal guide relative to the crossmember (50).

7. The device according to claim 1, characterized in that a cleaning device (54) is provided, which is designed to clean the areas of the exit window (48) accessible from the outside and their surroundings during a cleaning process on the front plate (40).

8. The device according to claim 1, characterized in that the rod-shaped IR radiator (26) has on its outside a reflector layer (44), in particular a gold reflector layer, which is only interrupted towards the exit window (48) for the outlet of IR light ,

9. The device according to claim 1, characterized in that the IR radiator (26) is at least one meter long, preferably that it is at least two meters long.