EP2395895B1

EP2395895B1 - Cleaning device with rotating brushes

Info

Publication number: EP2395895B1
Application number: EP09787355.8A
Authority: EP
Inventors: Bastiaan J. De Wit; Fokke R Voorhorst; Johannes T. Van Der Kooi
Original assignee: Koninklijke Philips Electronics NV
Current assignee: Koninklijke Philips NV
Priority date: 2008-10-07
Filing date: 2009-10-05
Publication date: 2013-07-24
Anticipated expiration: 2029-10-05
Also published as: EP2395894A1; CA2753156A1; EP2395895A1; WO2010041185A1; CA2753157A1; WO2010041184A1; CA2753156F; EP2191763A1; CA2753157C; CA2753156C; EP2395894B1

Description

FIELD OF THE INVENTION

The invention relates to a cleaning device for cleaning a surface, the cleaning device comprises at least one brush rotatable in a rotation direction about a rotating axis and movable over the surface to be cleaned, the cleaning device also comprises at least one deflector extending parallel to the rotating axis and contacting the bristles of the brush at a location, seen in the rotation direction, before the location where the bristles contact the surface to be cleaned.
The invention also relates to a vacuum cleaner.

BACKGROUND OF THE INVENTION

By such a device which is known from WO 2005/053498 a rotatable brush is being used to aid in the loosening and removal of dirt and foreign material from the surface to be cleaned. To perform the cleaning action the brush is pressed against the surface. To improve the cleaning of the surface, a cleaning liquid is being used. The cleaning liquid is removed from the surface by means of the rotating brush, together with the dirt. Droplets of the cleaning liquid on the inside of the housing of the brush are guided back to the brush by means of the deflector. To ensure that no droplets will fall back on the cleaned floor, the deflector must be pressed firmly against the brush. The known cleaning device has the disadvantage that the ends of the brush leave very distinctive lines on the floor indicating the transition from a strip of cleaned surface and a surface located next thereto. This is especially disadvantage when the surface located next to the strip of cleaned surface has just be cleaned as well. The drops and stripes will be visible on the surface.

SUMMARY OF THE INVENTION

It is an object of the invention to provide a cleaning device whereby the contact between the brush and the surface to be cleaned improved so that better cleaning results are being obtained.
This object is achieved by the cleaning device according to the invention in that the cleaning device is provided with at least one side deflector extending at an angle to the rotating axis and contacting the bristles of the brush located near an end of the brush, wherein the bristles are bent by the deflector and/or side deflector to an extend that suction between the bristles when losing contact with the deflector is larger than the expellation of air from between the bristles when contacting the surface to be cleaned.
In case that the cleaning device is being used for cleaning a surface with liquid whereby the water or cleaning liquid must be removed from the surface, the side deflector which can be attached to the housing of the cleaning device will prevent water against the inside of the housing from dripping on the surface. Also water on the outside of the housing will flow in the direction of the deflector and will be guided back into the brush. The water guided back into the brush by the side deflector will be used again for the cleaning action before moving upwards and away from the surface to be cleaned. Due to the side deflector a smooth transition zone from a cleaned surface and a surface located next thereto will be obtained and no stripes or droplets will occur on the cleaned surface and the transition to the surface next thereto.
Since the bristles are pressed together by the deflector and the side deflector air will be pushed out of the area between the bristles. Between the deflector and the side deflector and the surface to be cleaned, the bristles will be moved apart and the area between the bristles will increase so that air will be sucked into the brush. Because the air is sucked into the brush close to the position where the brush is pressed together by the surface to be cleaned, the blowing of air from between the bristles near the surface to be cleaned is compensated for. Such blowing of air in a direction away from the cleaning device is detrimental to the cleaning action since dirt will be blown away. Due to the side deflector and deflector this is being prevented. The side deflector will prevent blowing away of dirt by cleaning a surface by means of the cleaning device with or without using cleaning liquid.
In case that the cleaning device comprises a vacuum source for creating a vacuum above the brush, the flow of air will be limited since the brush is in contact with the side deflectors and deflector at other sides. Due to the limited area along the brush where the flow of air can occur the filtering device for filtering the air as well as the vacuum source can be relatively small.
An embodiment of the cleaning device according to the invention is characterized in that the side deflector has a rounded shape, extending around the end of the brush.
The rounded side deflector provides the brush with a rounded shape near the end during rotation due to which a very smooth transition zone from a cleaned surface and a surface to be cleaned is obtained. The rounded shape of the side deflector can be semi-circular or oval-shape, for example.
Another embodiment of the cleaning device according to the invention is characterized in that the cleaning device comprises at least two brushes rotatable in opposite directions directed towards each other at the surface to be cleaned, at least two deflectors located at opposite sides of the two brushes and at least two side deflectors contacting the bristles of the brushes located near the ends of the brushes.
Due to the two brushes rotating in opposite direction a very effective cleaning operation is obtained since each location on the surface to be cleaned will be contacted by both brushes. Furthermore the dirt will be collected between the brushes and can easily be moved in an upwards direction to a debris collecting chamber.
A further embodiment of the cleaning device according to the invention is characterized in that the side deflectors extend between the deflectors, forming a closed loop shaped deflector around the two brushes.
Such a closed loop shaped deflector can easily be provided in the cleaning device. Due to the closed loop shaped deflector dripping of water back to the surface is effectively prevented. Also the blowing of air away from the brushes due to pressing the brushes against the surface to be cleaned is prevented by the closed loop shaped deflector. Furthermore, the flow of air into the housing of the brushes, either created by a vacuum source or between the two brushes rotating in opposite directions, will only be present between the two brushes, where the dirt is being picked up by the brushes and not along other parts of the brushes.
Yet another embodiment of the cleaning device according to the invention is characterized in that the side deflector partly extends between the two brushes.
In this manner, the side deflector will also presses against the brushes between the brushes, so that also at this location no dripping of water and/or blowing away of air will occur.
Another embodiment of the cleaning device according to the invention is characterized in that the cleaning device comprises a plate shaped element located near an end of the brush and extending, in use, parallel to the surface to be cleaned at a distance between 0,5 and 5 mm thereof.
Air will flow under the plate shaped element towards the brushes, which air will picks up dirt located aside of the brushes. Such a plate shaped element can be used to clean a surface out of reach of the brushes, for example near walls or plinths.
Another embodiment of the cleaning device according to the invention is characterized in that the side deflector comprises at least one protrusion extending towards the surface to be cleaned when using the cleaning device.
Such a protrusion element will reduce the distance between the side deflector and the surface to be cleaned so that less air will be sucked in along the sides of the brushes. However, the speed of the air being sucked in will be enlarged due to which dirt located aside of the brushes will be moved towards the brushes. The protrusion may be connected to the plate shaped element at a location between the brushes.
Yet another embodiment of the cleaning device according to the invention is characterized in that the deflector and/or side deflector is movable against spring force when the bristles of the brush are getting in contact with the deflector and/or side deflector when the brush is being rotated.
The side deflector, deflector and the bristles of the brush will be moved when getting in contact with each other when the brush is being rotated. If the brush is worn or deformed, the side deflector and/or deflector is will still keep in touch with the brush, although in this situation the side deflector and/or deflector will be moved less. In case that the diameter of the brush is larger than expected, for example due to production tolerances, the side deflector and/or deflector will be moved more.
By the movable side deflector and/or deflector an optimal balance between a sufficient contact with the brush and a minimum power dissipation by the motor due to the contact between the brush and the side deflector and/or deflector can be obtained.
Another embodiment of the cleaning device according to the invention is characterized in that the deflector and/or side deflector comprises at least one flexible plate-shaped element being bendable against spring force of the plate-shaped element.
Such a flexible plate-shaped element can easily be manufactured. The plate-shaped element can be made of a plastic like silicon rubber, a polymer or any other suitable material like natural rubber.
The cleaning device according to the invention is characterized in that the bristles are bent by the deflector and/or side deflector to an extend that suction between the bristles when losing contact with the deflector is larger than the expellation of air from between the bristles when contacting the surface to be cleaned.
With such bending of the bristles by the deflector and side deflectors a net air flow towards to the brush will occur near the surface.
Another embodiment of the cleaning device according to the invention is characterized in that the bending of the bristles by the deflector and/or side deflector is larger than the bending of the bristles by the surface to be cleaned.
Also in this situation the net air flow by the brush will be directed towards the brush.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will be explained in more detail with reference to the drawings, in which

Fig. 1 is a side view of a rotatable brush according to the prior art,
Fig. 2 is a perspective view of a cleaning device according to the invention,
Fig. 3 is a schematic side view of a part of the cleaning device as shown in Fig. 2,
Figs. 4A and 4B are respectively a schematic side view of a brush with a deflector according to the invention and a graph indicating the volume of air between the bristles of the brush while rotating the brush,
Figs. 5A-5C are a schematic side view and bottom views of the cleaning device according to the invention,
Figs. 6-8 are bottom views of the several other embodiments of the deflectors according to the invention,
Figs. 9-11 are perspective views of other embodiments of the deflector according to the invention,
Fig. 12 is a schematic side view of another embodiment of a cleaning device according to the invention as shown in Fig. 2.

Like parts are indicated by the same reference numbers in the figures.

DETAILED DESCRIPTION OF EMBODIMENTS

Fig. 1 is a side view of a rotatable brush according to the prior art. As is schematically illustrated, air will be expelled from the rotating brush in the direction indicated by arrow P1 when contact is made at position A with the surface to be cleaned. The air will be expelled from the brush from the position A to position B. From position B, air will be sucked in a direction indicated by arrow P2 into the brush to compensate for the increasing volume between the bristles, until the bristles have lost contact with the surface (position C). The airflow in the direction indicated by arrow P2 towards the brush aids the cleaning action of the brush. However the airflow in the direction indicated by arrow P1 away from the brush is detrimental to the cleaning action since dirt will be blown away.
Fig. 2 shows a perspective view of a cleaning device 1 according to the invention, comprising a housing 2 in which two brushes 3, 4 are rotatably mounted around axles 5, 6. The brushes 3, 4 are driven by a motor (not shown). The motor might be located on any suitable position whereby via gears of belts the brushes 3, 4 are being rotated with a speed of 5000-0,000 rotations per minute. The axle of the motor can also be directly connected to the axle of the brush, whereby the motor can be placed inside the brush, for example. The diameter of the brushes for example is 4 cm à 6 cm. The length of the brush is for example about 25 cm. Brush 3 is rotatable in a clockwise direction, indicated by arrow P3 and brush 4 is rotatable in a counter clockwise direction, indicated by arrow P4 around the respective axles 5, 6. The housing 2 is provided with wheels (not shown) keeping the axles 5, 6 at a predetermined distance of the surface to be cleaned. The housing 2 is connected via a steering joint to a stick 7 which is provided on a side remote of the housing 2 with a handle 8. The cleaning device 1 is furthermore provided with a tank 9 for water or other cleaning liquid. A power cord 10 enters the handle 8 and is guided through the stick 7 to the motor for rotating the brushes 3, 4 and the device (not shown) for feeding water from the container 9 into a brush from which it is spread on to the surface to be cleaned.
The housing 2 comprises a debris collecting chamber 11, the entrance 12 of which is located between the brushes 3, 4. The brushes 3, 4 are fully enclosed except at the bottom by the housing 2. For sake of clarity the side cover has been removed. Near the bottom of the housing 2 two longitudinal deflectors 13, 14 are provided extending parallel to the axles 5, 6 and partly into the brushes 3, 4. The deflectors 13, 14 are connected to each other near their ends by side deflectors (see fig. 5B, 6, 7 8). The function of the deflectors 13, 14 and the side deflectors will now be explained with reference to the drawings 3, 4A and 4B.
As can be seen in fig. 3 the brushes 3, 4 rotate in opposite directions P3, P4, which directions are directed towards each other near the surface to be cleaned 16. The bristles 17 of the brushes 3, 4 rub over the surface to be cleaned 16 and the dirt and other materials are being disconnected from the surface to be cleaned 16 and are being moved upwards in the direction of arrow P5 into the entrance 12 of the debris collecting chamber 11. When the bristles 17 of the brushes 3, 4 reaches the deflectors 13, 14 or side deflectors the bristles 17 are pressed together whereby the volume between the bristles is being reduced. Hereby air is being expelled from the brushes 3, 4, which air is guided along the walls 18 of the housing 2. By further rotating of the brushes 3, 4 the bristles 17 lose contact with the deflectors 13, 14 or side deflectors whereby the area between the bristles is being enlarged and air will be sucked into the brushes 3, 4. By further rotating the bristles 17 will be pressed against the surface to be cleaned 16 whereby air will be expelled from the area between the bristles 3,4. The net air flow between the deflectors 13, 14 or side deflectors and the surface to be cleaned 16 is in the directions indicated by the arrows P6, P7 towards the brushes 3, 4 respectively. Such a net air intake by the brushes 3, 4 will for example occur if the bending of the brushes 3, 4 by the deflectors 13, 14 or side deflectors is greater than the bending of the brushes 3, 4 by the surface to be cleaned 16. The bending by the deflectors 13, 14 or side deflectors of the brushes 3, 4 is for example 5 mm while the surface to be cleaned 16 bends the brushes 3, 4 for example only 3 mm. The deflectors press against the bristles of the brush at a location before the location where the bristles contact the surface to be cleaned as seen in the direction of rotation.
Fig. 4A shows brush 3 and different angles ϕ whereby the bristles come in contact with the deflector 13 (near ϕ = a), lose contact with the deflector 13 (ϕ = b), start with losing contact with the surface to be cleaned 16 (ϕ = c) and have fully lost contact with the surface to be cleaned 16 (ϕ = d). When moving from ϕ = b to ϕ = d the volume between the bristles is at its minimum at ϕ = c.
Fig. 4B shows a graph whereby the volume between the bristles 17 is indicated at different angles ϕ. As is clearly visible in the graph the volume between the bristles 17 is being reduced between the angles ϕ = a and ϕ = b whereby air is blowing in the direction indicated by arrow P8 along the walls 18 of the housing 2. Between the angles ϕ = b and ϕ = c air is being sucked towards the brush 3 in the direction indicated by arrow P6. Also between the angles ϕ = c and ϕ = d air is being sucked towards the brush 3 however now in the direction indicated by arrow P7.
The cleaning device 1 according to the invention can be used for cleaning soft surfaces with carpet and hard surfaces. It can be used by only rotating the brushes 3, 4 but the cleaning can be supported by sucking vacuum by means of vacuum device in the entrance 12. Furthermore the device 1 can be used for wet cleaning of for example hard surfaces whereby water or a cleaning liquid is guided from the container 9 towards the brushes 3, 4 and the surface 16 is being wetted by the brushes 3, 4. It is also possible to spray water on the surface by means of a separate device in which case the cleaning device need not to be provided with a container 9. It is important that as little as possible water or cleaning liquid remains on the surface 16. The water or cleaning liquid will be removed by the brushes 3, 4 and guided into the entrance 12 towards the debris collecting chamber 11. As can be seen in fig. 5A some of the water droplets 19 will be collected against the wall 18 of the housing 2 and will flow back along the wall 18 and over the deflectors 13, 14 or side deflectors into the brushes 3, 4. Hereby the water droplets 19 are prevented from being dropped back on the surface to be cleaned 16. Also water on the outside of the housing 2 will be guided back to the brushes 3, 4 due to the shape of the housing, whereby the ends of the deflectors 13, 14 and side deflectors are located in the brushes 3,4 and form the lowest part of the housing.
The deflectors 13, 14 form part of a bottom plate 21 as indicated in Fig. 5B. To prevent water droplets 19 to fall back on the surface 16 near ends 20 of the cylindrical brushes 3, 4 the bottom plate 21 also comprises side deflectors 22 extending perpendicular to the deflectors 13, 14. The distance between opposite side deflectors 22 is shorter than the length of the brush 3,4. The bottom plate 21 forms a closed loop shaped deflector. Water droplets 19 will either be guided by the side deflectors 22 of the bottom plate 21 towards a V-shaped nose 23 of the side deflector 22 from which the droplets 19 will fall between the brushes 3, 4 and will be picked up by the brushes 3, 4 during a next passage of the brushes 3, 4 or the droplets will be picked up by the brushes when moving towards the V-shaped nose 23. The V-shaped nose 23 can also be another kind of element extending between the brushes.
Fig. 5C shows a bottom plate 24 similar to bottom plate 21 except for the shape of the side deflectors. The side deflectors 25 of the bottom plate 24 comprises semi-circular parts 26 located around ends 20 of the brushes 3, 4. The semi-circular parts 26 are connected to each other by a semi-circular part 27 extending towards the semi-circular part 27 of the other side deflector 25.
Fig. 6 shows a bottom view of another embodiment of the cleaning device 31 according to the invention whereby U-shaped deflectors 32 are connected to each other at their side edges by means of adjusting mechanisms 34. Each U-shaped deflector 32 comprises a deflector 13, 14 extending parallel to the rotation axis of the brushes and two side deflectors 22. The deflectors 13, 14 are preferably flexible. The side deflectors 22 may be flexible or relatively rigid. Each adjusting mechanism 34 comprises a rod 35 and an adjusting knob 36 whereby by rotating the adjusting knob 36 in or opposite to a direction indicated by arrows P9, P10 the U-shaped deflectors 32, 33 will be moved apart or towards each other in the direction indicated by the double arrow P11. By adjusting the distance between the U-shaped deflectors 32, 33 the pressure exerted on the brushes 3, 4 can be amended depending on the desired amount by which the bristles are pressed together. If the bristles are firmly pressed together no unwanted blowing will occur. However this might lead to extensive wear of the brushes and to an increase in the power needed to rotate the brushes. In case that the U-shaped deflectors 32, 33 do not press together the bristles enough to prevent all unwanted blowing, an additional fan can be used to apply vacuum near the surface 16, which vacuum will prevent together with the deflectors that unwanted blowing will occur.
Fig. 7 shows another embodiment of the cleaning device 41 according to the invention whereby the U-shaped deflectors 32, 33 are connected near the side deflectors 22 by means of springs 42. These springs 42 will determine the force by means of which the U-shaped deflectors 32, 33 are pressed against the brushes 3, 4. In case for example that the brushes 3, 4 are replaced and the diameter of the brushes 3, 4 is slightly different due for example to production tolerances, the U-shaped deflectors 32, 33 can be moved towards each other in the directions indicated by arrows P12, P13 under the influence of the forces exerted by the springs 42 or can be moved apart against the forces exerted by the springs 42.
Fig. 8 shows a further embodiment of a closed loop shaped deflector 51 according to the invention comprising deflectors 52, 53 and side deflectors 22. The deflectors 52, 53 and part of the side deflectors 22 are being made of flexible elements which can accommodate the differences in the diameter of the brushes 3, 4 according to for example production tolerances.
Fig. 9 shows another embodiment of a (side)deflector 61 of a cleaning device according to the invention which (side)deflector 61 comprises a holder 62 which is connected with the housing 2 of the cleaning device 1 and flexible pens 63 extending parallel to each other. The pens 63 are pressed against the brushes 3, 4 with their ends remote from the holder 62. Depending of the thickness of the pens 63 and the distance between the pens 63 the (side)deflector 61 will only function to prevent water being dropped back on the surface to be cleaned 16 or also for preventing unwanted blowing.
Fig. 10 shows another embodiment of a (side)deflector 71 according to the invention whereby a holder 72 is provided with flexible wires 73 along which water is guided back to the brushes 3, 4. If the distance between the wires 73 is relatively small and the wires are stiff enough, the wires 73 will also diminish the unwanted blowing.
Fig. 11 shows an embodiment of a (side)deflector according to the invention whereby a holder 82 is provided with rigid pens 83. Also this (side)deflector 81 will prevent the dripping of water and will diminish the unwanted blowing.
Fig. 12 shows a side view of a part of a cleaning device according to the invention comprising two plate shaped element 91, one near each pair of ends of the brushes 3, 4 and extending, in use, parallel to the surface to be cleaned at a distance X1 between 0,5 and 5 mm thereof, preferably about 2 mm. The plate shaped element 91 extends between the axes 5,6 in a direction perpendicular to the axes 5, 6 and extends over a distance of 25 to 40 mm, for example, in a direction parallel to the axes 5,6. Due to the limited distance between the plate shaped element 91 and the surface to be cleaned the speed of the flow of air will increase due to which also dirt located near ends of the brushes will be sucked towards the brushes rotating at high speed. The distance X2 between the deflectors and the side deflectors on both sides of the axes 5,6 and the surface to be cleaned is preferably about 5 mm or more.
Preferably the plate shaped element 91 comprises a protrusion located between the brushes and extending further towards the surface to be cleaned to guide liquid towards the brushes. Due to the plate shaped element 91 the air flow from the side towards the brushes 3, 4 is being limited.
The side deflector may be relatively wide, so that the side deflector itself comprises the plate shaped element 91.
The bottom plate, the deflectors and side reflectors can be made from any suitable material like metal or plastic. The deflectors and side deflectors can be formed as a strip connected to or integrated with the housing 2.
It is possible to make the distance between the surface and the axles of the brushes 3, 4 adjustable to be able to amend the amount by which the bristles are pressed together. Preferably also the deflector and side deflectors are adjustable with respect to the brush to adjust the pressure between the deflector and the brush.
It is also possible to suck the debris and water away from the entrance 12.
For the bristles of the brush any kind of fibre, hair, wire-shaped element or other kind of element is suitable which will be pressed together when contacting a surface to be cleaned.
If the deflector does not press firmly enough against the bristles of the brushes, the airflow away from the brush might also be prevented by means of a vacuum system. In such a case the deflector still prevents the leakage of water and limits the power needed by the fan.
It is also possible to connect each deflector with a spring to the housing. The forces exerted by the spring can be in vertical direction, horizontal direction or a combination thereof.

Claims

Cleaning device (1, 31, 41, 51) for cleaning a surface, the cleaning device comprises at least one brush (3, 4) rotatable in a rotation direction about a rotating axis and movable over the surface to be cleaned, the cleaning device also comprises at least one deflector (13, 14, 52, 53, 71, 81) extending parallel to the rotating axis and contacting, during use, the bristles (17) of the brush at a location, seen in the rotation direction, before the location where the bristles contact the surface to be cleaned (16), characterized in that the cleaning device is provided with at least one side deflector extending at an angle to the rotating axis and contacting, during use, the bristles of the brush located near an end of the brush, wherein the bristles (17) are bent by the deflector (13, 14, 52, 53, 71, 81) and/or side deflector to an extend that suction between the bristles when losing contact with the deflector is larger than the expellation of air from between the bristles when contacting the surface to be cleaned.
Cleaning device (1, 31, 41, 51) according to claim 1, characterized in that the side deflector has rounded shape, extending around the end of the brush.
Cleaning device (1, 31, 41, 51) according to one of the preceding claims, characterized in that the cleaning device comprises at least two brushes (3, 4) rotatable in opposite directions directed towards each other at the surface to be cleaned (16), at least two deflectors (13, 14, 52, 53, 71, 81) located at opposite sides of the two brushes and at least two side deflectors contacting the bristles of the brushes located near the ends of the brushes.
Cleaning device (1, 31, 41, 51) according to claim 3, characterized in that the side deflectors extend between the deflectors, forming a closed loop shaped deflector around the two brushes.
Cleaning device (1, 31, 41, 51) according to claim 3 or 4, characterized in that the side deflector partly extends between the two brushes.
Cleaning device (1, 31, 41, 51) according to one of the preceding claims, characterized in that the cleaning device comprises a plate shaped element located near an end of the brush and extending, in use, parallel to the surface to be cleaned at a distance between 0,5 and 5 mm thereof.
Cleaning device (1, 31, 41, 51) according to one of the preceding claims, characterized in that the side deflector comprises at least one protrusion extending towards the surface to be cleaned when using the cleaning device (1, 31, 41, 51).
Cleaning device (1, 31, 41, 51) according to one of the preceding claims, characterized in that the deflector (13, 14, 52, 53, 71, 81) and/or side deflector is movable against spring force when the bristles of the brush are getting in contact with the deflector and/or side deflector when the brush is being rotated.
Cleaning device (1, 31, 41, 51) according to claim 8, characterized in that the deflector and/or side deflector comprises at least one flexible plate-shaped element being bendable against spring force of the plate-shaped element.
Cleaning device (1, 31, 41, 51) according to claim 7, characterized in that the bending of the bristles (17) by the deflector (13, 14, 52, 53, 71, 81) and/or side deflector is larger than the bending of the bristles by the surface to be cleaned (16).
Cleaning device (1, 31, 41, 51) according to one of the preceding claims, characterized in that the cleaning device (1, 31, 41, 51) comprises a cleaning fluid chamber (9).
Cleaning device (1, 31, 41, 51) according to one of the preceding claims, characterized in that the cleaning device (1, 31, 41, 51) comprises a debris collecting container (11).
A vacuum cleaner comprising at least a vacuum source and a cleaning device (1, 31, 41, 51) according to one of the preceding claims.