Patent Application
20240269776
The present invention relates to a laser engraving device for multiple laser beams for processing a target surface. The target surface may be for instance a non-patterned coating of a glazing unit installed on a train or in a building. By engraving the non-patterned coating by using the proposed device, a patterned coating can be obtained which would improve the penetration of electromagnetic waves through the coating in the radio frequency spectrum used for wireless communications.
In order to reduce energy consumption of for example trains and buildings, energy saving windows with better thermal properties are increasingly used. These energy saving windows are typically composed of two or more windowpanes. The thickness of the glass panes is selected to satisfy mechanical requirements of the glazing unit given by regulations. The gap between the glass panes suppresses acoustic noise, and it also improves thermal insulation. Energy saving windows typically comprise one or more coated glass panes. This coating has a low thermal emissivity and therefore reduces the heat transfer by radiation. It can also be a sun protection coating, reducing the transmission in the near infrared region. It is generally made of one to three layers of silver (Ag) along with some dielectric layers (zinc oxide (ZnO), silicon nitride (Si3N4), titanium dioxide (TiO2), etc.). Most trains and many modern buildings have a metallic structure, which when combined with the coating having one or more metallic layers on the windows, results in strong microwave attenuation inside the structure due to a Faraday cage effect. Electromagnetic (EM) waves used for telecommunications are thus strongly attenuated. This is problematic, as nowadays, wireless communications are increasingly used.
Solutions exist to perform a laser treatment on the electrically conductive coating to convert the coating to a frequency-selective surface (FSS). The FSS is a thin and repetitive surface designed to reflect, transmit or absorb electromagnetic fields. The FSS is able to make the coating, and thus the glazing unit substantially transparent to EM waves used in wireless telecommunications. The achieved effect is not limited to any specific frequency band, and the FSS makes it possible to achieve low attenuation for a large band of frequencies including the frequencies used in current wireless communication systems, such as global system for mobile communications (GSM), long-term evolution (LTE), multiple-input and multiple-output (MIMO), and future ones. However, the problem with the currently known laser treatment solutions is that they can only be applied at the production site, and the treatment can only be applied to a flat non-assembled glazing unit. This means that already installed energy saving glazing units, need to be replaced to benefit from the currently existing laser treatment solutions. This is a major limitation of the existing solutions.
It is also known to install repeaters in trains or buildings with poor indoor signal coverage. Repeaters consist of an antenna placed outside and another one placed inside, which is connected to an amplifier to increase the signal inside the train or building. This solution is technology-dependent, and a repeater works for a defined range of frequencies only. Since telecommunication standards evolve quickly, repeaters have to be often renewed (i.e., typically between 5 and 8 years). Furthermore, the repeater-based systems use a chipset and active components, which are prone to frequent failures. Moreover, repeaters have a high energy consumption. This reduces the energy savings achieved by modern windows.
Currently there is no reliable and well-functioning solution available to treat conductive coatings of glazing units that have been already installed in order to reduce their attenuation for EM waves used in telecommunications, and which would optionally improve their performance in terms of MIMO efficiency. More broadly, a reliable and well-functioning solution is needed to engrave or mark surfaces by using laser beam technology.
It is an object of the present invention to overcome at least some of the problems identified above related to engraving surfaces. More specifically, one of the aims of the present invention is to provide a device that can be used to engrave an electrically conductive coating to generate a patterned or structured coating. Compared with non-patterned coatings, the patterned coating would reduce the attenuation for EM waves used in telecommunications, and it would have an improved performance.
According to a first aspect of the invention, there is provided a laser engraving device as recited in claim 1.
The invention allows laser processing of any surface having any shape. For instance, the device may be used to process an assembled glazing unit, which may have any number of windowpanes, and this with a high focus positioning accuracy. This is not achievable with currently known existing laser engraving systems using a mechanical, capacitive, inductive or optical distance sensor. In the present invention, fast tracking of the target surface is achieved using an optical sensor, which has a response time of 0.002 ms or even less, and a high-speed focusing element, such as a tunable lens. The device may be placed on a motion system, which would allow a high displacement speed (e.g. up to 10 m/s) of the device. It is to be noted that the speed of a standard engraving system using imaging and detection technology is often limited by the response time, which is typically between 20 ms and 100 ms.
Furthermore, as the proposed device comprises a focusing element, there is no need to move the entire device to follow the target surface, which would usually induce a speed limitation due to a mechanical moving part. Moreover, the proposed device has the advantage that the desired pattern can be generated rapidly thanks to the possibility of simultaneously using a plurality of engraving beams to engrave the target surface. More specifically, the use of multiple beams reduces drastically the time of processing. The processing time can thus be reduced by a factor 2 to 20 or even more depending on the number of engraving beams. Standard systems accept only one engraving beam due to the used distance detection or scanning systems.
If the proposed device is used to engrave a coating of a glazing unit, then the processed glazing unit would have the advantage that it has energy saving capabilities and it is transparent or substantially transparent to broadband EM frequencies including the ones used in telecommunications. Thus, the processed glazing unit shows a low attenuation for broadband microwave frequencies.
According to a second aspect of the invention, there is provided a laser engraving system comprising the laser engraving device according to the first aspect, and further comprising a motion system.
According to a third aspect of the invention, there is provided a method operating the laser engraving device according to the first aspect.
Other aspects of the invention are recited in the dependent claims attached hereto.
Other features and advantages of the invention will become apparent from the following description of a non-limiting example embodiments, with reference to the appended drawings, in which:
Some embodiments of the present invention will now be described in detail with reference to the attached figures. The embodiments are described in the context of a laser engraving device used to post-process an insulating glazing unit for a train wagon, but the teachings of the invention are not limited to this environment. For instance, the teachings of the present invention could be used in other applications or environments, such as in buildings. Identical or corresponding functional and structural elements which appear in the different drawings are assigned the same reference numerals. It is to be noted that the use of words “first”, “second” and “third”, etc. may not imply any kind of particular order or hierarchy unless this is explicitly or implicitly made clear in the context. Furthermore, the word “between” when used to give a numerical range also includes the end points of the range.
The following definitions may be used in the context of the present invention:
The main motivation behind the present invention was to propose a device that can be used to obtain an improved glazing design for windowpanes, especially in situations in which the glazing unit has already been placed in its final installation location. The windowpanes should not only satisfy mechanical and tension requirements, but they should also provide low attenuation for broadband frequencies and optionally an advantageous path loss imbalance, particularly between the s (perpendicular) and p (parallel) polarisations, for a wide range of angles of incidence and broadband frequencies used for wireless telecommunication. The insulating glazing unit or window is typically assembled from two or more windowpanes. Each windowpane may contain polymer, such as polycarbonate or acrylic glass, and/or glass. A structured or patterned coating with low thermal emissivity, i.e., an emissivity value below 20% or approximately 20% (usually named low-e coating), applied to one or more surfaces of the glazing unit generally results in low attenuation for broadband microwave frequencies and optionally also in a small path loss imbalance between parallel and perpendicular polarisations, which may improve MIMO efficiency.
The beam splitter 7 is an optical device that is configured to split a beam of light in two or more beams of light. In this specific example, the beam splitter is a diffractive beam splitter, also known as a multi-spot beam generator or an array beam generator, which is a single optical element that divides an input beam into N output beams. Each output beam retains the same optical characteristics as the input beam, such as size, polarisation and phase. A diffractive beam splitter can generate either a 1-dimensional beam array (1×N) or a 2-dimensional beam matrix (M×N), depending on the diffractive pattern on the optical element. The diffractive beam splitter is used with monochromatic light such as a laser beam, and is designed for a specific wavelength and angle of separation between output beams. In the present example, the number of generated beams is between 2 and 20, or it could more specifically be between 6 and 20. These output beams are in the following text also referred to as engraving beams 27.
The laser head 1 further comprises a first optical focusing element 11 in the path of the beams coming from the beam splitter 7. The first focusing element is used to adjust the focal point of the laser beams that travel through it to minimise defocus aberration. The focusing element may comprise a lens, such as a mechanically movable lens, or alternatively, a tunable lens, also called a liquid lens, may be used. In the configuration of
In the example of
As is further shown in
The laser head 1 optionally also comprises a second optical focusing element 23, which in this example is a fisheye lens, and more specifically an f-theta lens, also known as a flat lens or a scanning lens, which is a type of fisheye lens. The f-theta lenses are designed to produce a focused spot in a flat field, the position of the spot being proportional to the focal length (f) of the lens and the angle (theta) of the beam entering the lens, giving them the name f-theta lenses. Ideally the size of the focused spot is constant throughout the field. As shown in
The laser head 1 may be placed on a motion system (not illustrated in the drawings), such as a robotic arm, that may be configured to rotate around any number of rotation axes, such as around three orthogonally arranged rotation axes. Furthermore, the motion system may be configured to translate the laser head 1 in any desired direction, optionally to move the laser linearly in the desired direction. Optionally, the beam splitter 7 is also arranged to rotate around one or more rotation axes. In this example, the beam splitter is arranged to rotate around a rotation axis, which is parallel or substantially parallel to the direction of the processing laser beam 25 entering the beam splitter 7. Optionally, a sub-entity formed by the beam splitter 7, the first optical focusing element 11, the second mirror 13, and the second optical focusing element 23 is also arranged to rotate around one or more rotation axes. In this example, the sub-entity is arranged to rotate around a rotation axis, which is parallel or substantially parallel to the direction of the engraving beams 27 traversing the first optical focusing element 11. In other words, the rotation axis of the beam splitter 7 would in this case coincide with the rotation axis of the sub-entity.
The operation of the laser head 1 is next explained in more detail. The laser head 1 is first placed in its desired start position and then the processing laser beam 25 is generated and directed to the dichroic mirror 5. The processing beam is reflected by the dichroic mirror 5 towards the beam splitter 7, which divides the processing beam into a given number of parallel engraving beams 27 or divided processing beams. The engraving beams 27 then propagate through the first optical focusing element 11 which dynamically adjusts its focal point based on the distance information received from the distance sensor 19. In this manner the engraving beams can be precisely focused on the target surface 17. To achieve this, the distance sensor 19 repeatedly, i.e., at given time intervals tracks the distance between the distance sensor and the target surface, which in this case is the surface of the coating 17. It is to be noted that the term “time interval” does not necessarily have to be a constant time interval, i.e. a constant time period, but it may instead be a non-constant time interval. In other words, the word “repeatedly” in the present description is understood to mean taking a given action a plurality of times, or “again and again” at regular or irregular time intervals. The distance sensor may receive as an initial input e.g. from the user of the laser head the position of the coating within the glazing unit, i.e., at which interface the coating is placed. Alternatively, the distance sensor determines the location of the coating by analysing the reflected wavelengths from the different interfaces of the glazing unit. In this example, the response time of the distance sensor 19 is between 0.5 us and 20 μs, or more specifically between 0.5 us and 10 μs, or between 1 us and 3 μs. The response time thus indicates how often the distance measurements can be taken and how often the distance information can be updated. The propagating engraving laser beams 27 are directed by the second mirror 13 towards the coating 17. Before the engraving laser beams reach the target surface, they propagate through the second optical focusing element 23, which refocuses the engraving beams so that they are all focused on one plane (i.e. the surface of the coating 17).
As mentioned above, the distance sensor 19 is arranged to communicate with the first optical focusing element 11 at given time intervals. These time intervals may be the same as the ones used for taking distance measurements. The first optical focusing element 11 then repeatedly adjusts its focal point depending on the received distance information. More specifically, if the distance sensor detects that the distance increases to the coating 17, then also the focal point of the first focusing element is moved further away from the laser head, or vice versa. In this manner, the focal point follows the surface of the coating. Here again the adjustment time intervals may be the same as the distance measurement time intervals. However, this does not have to be the case. It is to be noted that during the above engraving process, the laser head 1 moves along a pre-programmed path to generate the desired pattern on the coating 17. More specifically, thanks to the engraving process, the desired pattern of electrically conductive patches 29 (as shown in
Visible light gets then reflected from the coating 17. This light is then reflected by the second mirror 13 towards the dichroic mirror 5, which allows the light to pass through it to reach the vision system 9, such as a camera. The vision system 9 is aligned with the path of the incoming light beam and thus the technician can visually monitor the engraving process. Alternatively, or in addition, the vision system 9 may comprise an image recognition software tool to implement a computer-implemented monitoring framework of the engraving process.
The end result of the engraving process is thus a patterned coating, which advantageously has low thermal emissivity (a low-e coating). The coating may, for example, comprise a metal layer, such as a silver layer (to make it a silver-based coating), sandwiched between two oxide or dielectric layers, which may be any one of the following layers: zinc oxide (ZnO), silicon nitride (Si3N4), and titanium dioxide (TiO2) layers. The coating may be deposited onto a desired surface by applying sputter deposition, which is a physical vapour deposition (PVD) method of thin film deposition by sputtering. Alternatively, the coating may be a pyrolytic coating, which is a thin film coating applied at high temperatures and sprayed onto a glass surface, during the float glass process. The cross-sectional thickness of the transparent coating may be between 10 nm and 1000 nm, or more specifically between 50 nm and 300 nm, or more specifically between 100 nm and 200 nm.
Thus, in view of the above, the present invention proposes a laser processing head 1 allowing a real-time or substantially real-time adjustment of the focal points of the engraving beams 27, i.e., a real-time optical focus of multiple beams. The proposed solution is especially suitable for laser treatment of transparent conductive coatings in an assembled double/triple/curved, etc. glazing unit. By laser-treating the conductive coating(s) 17, a high transmittance for electromagnetic waves in the mobile communication spectrum can be achieved, while maintaining a low thermal emissivity, which is necessary for good thermal insulation by removing a small percentage of the total surface area of the coating, i.e., advantageously less than 20% or more specifically less than 5% of the total surface area. However, the teachings of the present invention may also be used for any other laser treatment, such as marking, engraving, etc. (e.g. a photovoltaic laser fired contact).
The first optical focal element 11, which may be composed of a composition of fast movable lenses or one or more tunable lenses, is controlled by using the signal from the distance sensor 19 measuring the distance from the distance sensor to the target surface 17 to be engraved. The distance measurement is performed with a fast response time, e.g. up to 200 kHz, in close vicinity of the laser treatment region, which is at least partially defined by the target surface, and which can be achieved through one or more transparent layers 151, 152, i.e. the windowpanes. The beam splitter 7, which may be a holographic/diffractive beam splitter, allows the number of processing laser beams to be multiplied to reduce the overall surface treatment time. The beam splitter 7 is advantageously rotated to follow the direction of movement of the laser head 1. This can be implemented for example so that the wavefront formed by the engraving laser beams is at an acute angle with respect to the movement direction of the laser head 1. The angle may for instance be substantially 90°. In other words, the wavefront would be substantially orthogonal to the direction of movement of the laser head 1. For this purpose, a data communication link may also be provided between the first optical focusing element 11 and the motion system so that the first optical focusing element may be rotated based on the movement information received from the motion system. Furthermore, the laser head 1 composed of the above-cited components can be rotated to follow a curved or tilted surface.
To summarise the above teachings, the present invention according to one example has the following elements or features:
In view of the above, a length or a length projection of one or more patches 29 along a first axis is greater than a height or a height projection of the one or more patches 29 along a second, different axis, wherein the first axis substantially horizontally follows a respective patch surface or its virtual extension, and the second axis follows the respective patch surface or its virtual extension orthogonally to the first axis. The first axis may be a horizontal axis, and the second axis may be a vertical axis.
In the design of
It is to be noted that the trajectory of the laser head is advantageously pre-programmed depending on the desired pattern shape. For example, the ditch lines that are parallel to each other can be first engraved with one or more laser head movements, and then the laser head may be reoriented, for instance by rotating it by 90 degrees (or by any desired amount) to engrave ditch lines having a different orientation.
While the invention has been illustrated and described in detail in the drawings and foregoing description, such illustration and description are to be considered illustrative or exemplary and not restrictive, the invention being not limited to the disclosed embodiments. Other embodiments and variants are understood, and can be achieved by those skilled in the art when carrying out the claimed invention, based on a study of the drawings, the disclosure and the appended claims. Further variants may be obtained by combining the teachings of any of the designs explained above.
In the claims, the word “comprising” does not exclude other elements or steps, and the indefinite article “a” or “an” does not exclude a plurality. The mere fact that different features are recited in mutually different dependent claims does not indicate that a combination of these features cannot be advantageously used. Any reference signs in the claims should not be construed as limiting the scope of the invention.
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/IB2020/062269 | 12/21/2020 | WO |
