The invention relates to a device and a method for structuring the surface of floor coverings which have already been laid. With this method and device, it is possible to provide virtually any materials used for floors with structures on their upper, preferably smoothed surface, these structures increasing and improving the nonslip properties and, if appropriate, the aesthetic appearance.
Various methods are known for increasing the nonslip properties of floors in which the surface is machined or influenced by wet-chemical means, in order to influence the nonslip properties of floors, in particular made from natural stone, artificial stone, plastics or other plastics-sealed or coated coverings of the desired form.
In addition, DE 195 18 270 C1 has described a nonslip floor covering and a method for producing it. A floor covering of this type, which is to have a highly polished surface, is provided with lenticular and sharp-edged microcraters by pulsed laser firing, the intention being that the microcraters should have a sucker action and these microcraters being made in a size which means that they are not visible to the human eye. The microcraters are to be randomly distributed and produced in an irregular arrangement. These microcraters are said to increase the coefficient of friction of a floor covering of this type to over 0.4.
This prior publication reveals that the microcraters are to be formed on the surface of in particular mineral floor covering materials in a stationary installation by means of a pulsed Nd:YAG laser. Consequently, it is only possible for suitably treated coverings to be fitted in new buildings or as newly laid floors, while the potential danger which exists on floors which have already been laid remains. Moreover, it is customary for floor coverings which have already been laid to be remachined, i.e. ground down after prolonged periods, in particular in the case of stone floor coverings, in order to restore the visual appearance and, in particular, the shine. This naturally leads to the desired effect of the microcraters, as a result of their dimensions in terms of shape and depth being at least reduced, being eliminated together with the desired nonslip effect.
Furthermore, Wo 97/48536 A1 describes how various jointing materials and mortars can be removed from joints between tiles and bricks by means of laser beams using a mobile unit. The mobile unit with a housing can be moved both manually and using a robot. To effect the movement, wheels are present on the housing by means of which a laser beam in protected form is directed onto the jointing material to be removed, which is situated in joints between tiles, for example, and is to be removed again.
Therefore, the object of the invention is to propose a possible solution for providing floor coverings which have already been laid with a structure on their surface, which structure at least increases the nonslip properties on the surface even when a slip-promoting medium, such as for example water, is present.
According to the invention, this object preferably is achieved by means of the characterizing features of the invention. Advantageous embodiments and refinements of the invention will be apparent from the description provided herein.
The device according to the invention and the corresponding method can be used for virtually any floor coverings which consist of a very wide range of materials, and shaping the one or more laser beam(s) are accommodated.
According to the invention, it is possible to use laser light sources which operate either continuously or in pulsed manner. In this context, it is certainly expedient to use a continuously operating laser beam if linear structures are to be formed in the surfaces of the floor covering and to use a pulsed laser beam if punctiform structures are to be formed. The appropriate laser light source may be selected appropriately according to the floor covering material and in particular taking into account its absorption properties for the wavelengths of the laser used.
In addition to CO2 lasers, these lasers include Q-switched pulsed lasers, such as an Nd:YAG laser, which is preferably diode-pumped.
To guide and shape the beam, it is possible to use optical elements which are known from laser technology, such as mirror systems, beam-widening lenses, planar field optics, scanners or polygon wheels, these optical elements preferably being designed or arranged in such a way that it is possible to control in particular the laser beam intensity on the surface of the floor covering. Systems of this type are known from laser marking.
It is particularly advantageous to use optical fibers to transmit the laser beam or a plurality of laser beams from one or more laser light sources to the point of action. This is particularly expedient if the device comprises a plurality of parts and that part of the device in which the laser light source together with the additional components required for its operation, such as for example the cooling system and the power supply, are separated from the mobile part of the device. Designing the device according to the invention in this way is particularly advantageous for machining steps, since the flexibility and ease of handling of the mobile part of the device which contains the elements for guiding and shaping the laser beam(s) can be made correspondingly small both in terms of mass and in terms of volume.
In this case, this mobile part may have its own drive, by means of which it can be moved at a predeterminable speed over the surface to be structured, so that deflecting the laser beam(s) in only one dimension is sufficient to form the desired structure pattern on the surface of the floor covering. In addition, however, it is possible to carry out a speed measurement, for example using an undriven wheel, as is known from Peixcex2ler, and to take the speed measurement signal into account when controlling the laser beam. If the device according to the invention is designed in this way, it is possible to achieve continuous operation. The procedure should be similar for manual operation without a dedicated drive for the mobile part.
However, the procedure using the invention may also involve certain areas of the surface being structured one by one, after the mobile part has been suitably positioned, in a so-called step-by-step process. In this case, it is necessary to deflect the laser beam in two dimensions. A procedure of this nature is recommended in particular when a floor covering which is to be treated accordingly, comprising individual elements (slabs) of virtually identical dimensions which are separated from one another by joints, is to be structured.
To control the movement or the positioning of the mobile part, it is possible to provide a guidance, navigation and/or image-processing system on the mobile part of the device according to the invention, which may be operated in conjunction with an electronic data-processing unit. An electronic data-processing unit of this type can store corresponding data about the dimensions, geometric configuration and material of the floor covering, and this data can be taken into account for controlling the movement of the mobile part of the device according to the invention and the laser intensity. Moreover, an electronic control unit of this nature can also be used to influence the shape and dimensioning of the structure formed on the surface of the floor covering. It is therefore readily possible to design structuring in the form of microcraters which act as displacement space for slip-promoting media of a size which is not visible to the human eye at a distance of at least 1 meter and therefore scarcely affects the visual appearance of the surface.
However, to achieve the desired nonslip effect, the structuring does not have to be formed over the entire surface of the floor covering, but rather it is possible to form structured regions in the form of a raster, in which structured areas are separate from unstructured areas. The shape of the structured areas may, for example, be square or circular. However, the distances between the structured areas should be selected in such a way that the safety when the floor covering is walked upon is almost as great as if the entire surface were to be structured. An embodiment of this nature reduces the machining time required for a floor covering to be structured.
Moreover, the machining speed can be increased if a plurality of laser beams are used. In this case, for cost reasons it is particularly expedient for the laser beam from a single laser light source to be split into at least two laser beams which can be used for structuring, using at least one beam splitter. Recently, beam splitters which enable a laser beam to be split not just into two part-beams, but rather into three individual beams or, with beam splitter systems, into even more individual beams, have recently become known. In any event, however, the part-beams have to be deflected and shaped separately in order to form the structuring in the desired shape.
However, in addition to the virtually invisible microstructuring, it is also possible to form structuring which is visible to the human eye and may be formed, for example, as a regular pattern or in the form of predeterminable pictorial representations. Pictorial representations of this type may be used, for example, for advertising purposes. By suitably influencing the laser beam machining with regard to intensity and machining time, it is readily possible to obtain pictorial representations on the floor covering surface which, through a variable structure size and structure depth, give the impression of a three-dimensional effect.
At least one proximity sensor should be present on the device according to the invention, at least on the mobile part, which sensor measures the distance from the surface to be structured, in particular for focusing the laser beam, and this measurement signal is used to guide and shape the beam and/or to control the laser power.
This proximity sensor or at least one additional proximity sensor may moreover be used to monitor or control the movement of the mobile part of the device according to the invention. In this case, proximity sensors of this type are used to continuously or discontinuously measure the distance from walls, parts of buildings (e.g. columns) or other objects arranged on a floor. The actual distance measured can be compared to the stored values and used for navigation and controlling the movement.
However, at least one proximity-measuring device may also be used for an emergency switch-off, for example if the mobile part is kiltered by a certain angle, so that there may be a risk to people and objects situated in the vicinity. In this case, when a predetermined limit value is exceeded, as measured with a proximity-measuring device of this type, the laser light source can be switched off.
However, it is also possible for other additional sensors or switches, such as for example inclination sensors, to be used for this purpose. However, safety switches may also be arranged on a protective guard surrounding the actual working area, these switches preventing the device from operating when the protective device is open or has been removed.
If only one or only two proximity sensor(s) is/are used, at least one should be rotatable about at least one axis and, in addition, the corresponding angle should be determined by means of a conventional rotation-angle sensor and should be taken into account when evaluating the proximity signal.
Since, in particular for structuring mineral materials, such as the wide range of natural stones, solid particles break off and are thrown outward under considerable acceleration, it is expedient for a protective device for the optical elements for guiding and shaping the laser beam(s) in the beam direction to be arranged on the mobile part of the device according to the invention. In this case, the protective panels which are transparent to the particular laser radiation used and are preferably exchangeable may be used. It may also be expedient to use a protective panel in which there is a longitudinal incision through which the laser beam which has been deflected in one dimension is directed unimpeded, i.e. without transmission losses, onto the surface to be structured.
The thickness of the protective panel and the width of a longitudinal incision of this nature should be dimensioned in such a way that it is impossible for any particles of the floor covering material which is to be structured to be able to reach and damage the optical elements.
Another possible option for protecting these elements consists in using a sheet which is conveyed continuously by being wound up onto and unwound from reels. A transparent sheet of this type is sufficiently strong, and its flexibility ensures that the kinetic energy of the particles is absorbed and there is no possibility of the particles breaking through the sheet. The use of a continuously moving sheet of this type has the additional advantage that the transmission remains virtually constant and there is no possibility of deterioration caused by scratches and dirt, as may be the case with transparent protective panels.
It is also possible, on its own or in addition, to use a suction system for these particles, in which case it is possible, for example, to use a so-called cross-jet suction system.
It may also be advantageous to set a pressure which is above ambient pressure in the closed area in which the optical elements for guiding and shaping laser beams are arranged, in order to at least limit contamination caused by penetrating dust.
Moreover, the invention may also be formed by providing or using a separate image-processing system or the image-processing system which has already been mentioned for controlling the movement of the mobile part of the device to record the structure which is formed by means of the laser machining and to carry out a corresponding quality control.
Particularly in the case of relatively highly reflective materials, to increase the machining speed it may be appropriate to provide a surface of this type with a layer of a medium of higher absorption for the laser radiation used before the structures are formed. In this case, it is possible for sheets, liquid or pasty media to be temporarily applied in a relatively smaller layer thickness to the floor covering which is to be structured.
It is advantageous not only in this case for the device according to the invention to be provided with an integral cleaning device which can also be used to remove the particles which have broken off the floor covering material.
The cleaning may be achieved by using liquid cleaning agents in conjunction with conventional mechanical elements, such as brushes or sponges, or on their own or in combination with wet cleaning by means of a suitable suction device, which in turn may act in combination with the cross-jet system which has already been mentioned.
In the case of wet cleaning, it may be advantageous to utilize the thermal energy of the cooling water and/or of the cooling air for the laser light source, in which case either heat exchangers which are already present or heat exchangers which are to be additionally fitted should be used for this purpose.
For process control, it is possible to provide plasma monitoring on the mobile part of the device according to the invention, which is used to measure the temperature and/or the size of the plasma formed by the laser beam on the surface and to control in particular the intensity of the laser beam.
It is possible to set or control the laser parameters, such as the laser power, pulse energy, pulse frequency and/or the laser beam parameters, such as beam widening, focal length, active spot diameter, on their own or in combination with the machining speed (line feed) and the feed rate of the device. Since fluctuations in the reflective or absorption properties over the surface to be structured occur in particular when machining natural or artificial stones, it is expedient to provide an additional optical measuring system on the mobile part of the device according to the invention, which is used to determine the reflection or absorption in a positionally-resolved manner, and this measurement is taken into account when controlling the intensity of the laser beam(s).