Laser Cutting Machines

The Related Art The invention is related to a laser cutting system and method comprising an adaptive focus control unit associated with cutting heads, which are used at laser cutting machines.

The invention particularly is related to laser cutting system and method which was developed to eliminate the focus position shifting problem as the cutting laser is focusing on the working area via lenses at laser cutting machines. The Prior Art

When laser cutting heads which is used in laser cutting machines, are examined, it is shown that maintaining optics clean in industrial environment is highly difficult and the temperature value of optics rises and for that reason focus position does not remain constant, in other words, "thermal lens" effect occurs. Optics absorb laser in a very low quantity due to their core structure. The increase in temperature due to absorption, depends on quality of lenses (materials and coating) although it is just a couple of degrees. The increase in temperature due to heat (Q) absorption in optics stops when ambient temperature is balanced. The main reason for the increase in temperature in lenses and protective glasses which are used in optical cutting heads, is contaminations. Contamination on optics is usually caused by sludge splashing from working area, dirt, dust and other visible and invisible particles as well as smoke that occurs during the process or due to the ambience. When these factors are taken into account, the optics that is used in optical cutting heads may be contaminated in several ways. As a result, in addition to the absorption occurring due to the core structure of the optics, temperature value increases due to environmental factors too.

In Figure 2, representative view of focusing lens (8) that is used in laser cutting head (1 ), when focus shifting occurs and when it does not occur, is given. As seen, the contaminated lens (8') creates focus shifting distance (d ₃ ). In Figure 3, representative view of the quantity of the heat (Q) that is emitted from the focusing lens (8) that is used in laser cutting head (1 ), in clean and contaminated conditions, is given. Similarly, in Figure 4, representative view of the quantity of the heat (Q) that is emitted from protective glass that is used in laser cutting head (1 ), in clean and contaminated conditions, is given. As seen, the contaminated lens or glass is more heated.

It is a fact that ambient contamination always occurs on optic cutting heads and optics are hotter than normal value all the times. When the problem is considered from this point, the optic design to be made, should be made while considering the increase in temperature from ambient factors, is not reflected to cutting parameter and the quality is maintained constantly. In the optic designs to be made while not considering ambient factors, the optics need to be frequently cleaned or replaced. When looked from the perspective of the customer, this situation is difficult to be accepted because it causes time and money loss. When all of them are considered, in addition to self-absorption of the optics, increase in temperature caused by ambient factors, causes thermal lens and leads to focus shifting.

Thermal lens effect caused by optics at high temperature is a serious problem. Because thermal lens effect adversely affects the cutting quality.

Various types of optic cutting heads are used in laser cutting machines. Some of them focuses laser beam onto working area with use of mirrors. On the other hand, some performs focusing with use of lenses. The purpose of using different methods is to improve the quality of cutting parameter caused by thermal effect. The focus position shifting in optic cutting heads caused by thermal effect, is known as thermal lens. In former embodiments, some methods were used to reduce thermal lens effect with use of passive methods. However, none of these methods managed to eliminate thermal lens effect fully.

One of the solutions suggested in optic cutting head designs in order to eliminate said adverse effects is the double lenses system to focus laser beam onto work area as disclosed under patent numbered US8274743B2. In the optical design one of the selected lenses has positive index of refraction and other has negative index of refraction and optical materials having same expansion coefficients and thus intended to reduce the thermal lens effect. However, this approach has only reduced thermal lens effect arising from main structure of the lenses (material from which lens is made and coating). From the gained experiences, it is seen that lenses absorb laser beam mostly because of contamination and the lens temperature rises. This case causes thermal lens effect when one of the lenses is contaminated and temperature rises while other lens is not contaminated and temperature remains constant. For that reason, it has not been possible to fully eliminate the thermal lens effect with use of the method explained above. Since the lower focus point of lenses group is shortened in double lens system, lower protective glass comes closer to work area and as a result, the lower protective glass is influenced by the adverse effects (sludge, Dirt, temperature, smoke etc.) in the work area much more.

Another approach disclosed to diminish thermal lens effect is selection of materials having high thermal conductivity or lenses and absorption of lenses as disclosed under document numbered EP2473315B1 . In this method water is passed through the body where lenses are placed and the temperatures of the lenses are maintained constant. As a result of very nature of lenses, the laser beam is absorbed and as a result thereof, the temperature rises to a certain value and remains constant there. In this case the removal of heat on the lenses at constant temperature can be achieved successfully by water cooling method. Although thermal conductivity coefficients of the materials from which the lenses are made are selected from materials with high ones, in general, thermal conductivity of glass materials is not of the value capable to remove fully the heat on the lenses. For that reason, it is seen that it fails to stop temperature rise arising out of contamination but just slows down the temperature rising speed. Therefore, thermal lens effect encountered due to contamination is not fully controlled. Since optic cutting head has moving mechanism conducting focus position setting, applying directly water cooling method to the body where lenses are placed causes complication of optic cutting head structure and difficulty in production, which will be another adverse effect.

One of the methods applied to minimize thermal lens effect is an active control system disclosed under patent application numbered EP1600241 B1 . When optics are contaminated, the splashing rate thereon increases some folds of normal value. Taking advantage of this characteristic, the photo detector is placed onto optic cutting head and thermal lens effect is actively controlled. However, since optic cutting head consists of more than one optics, it is difficult to distinguish whether it is the lenses or protective glasses getting contaminated. Photo detector will read the same value after the splashing in the ambience due to contamination of the optics exceeds threshold value. It is considerably difficult to apply this method for each optic. Because in such case, the optics are to be put in separate compartments. Mobility of some optics make the situation much difficult. This proposed method fails to fully eliminate the thermal lens effect because the contaminated optics cannot be distinguished in the system consisting of multiple optic.

In the patent application numbered US7605342B2, in the systems consisting of mirror method to reduce thermal effect, one face of the mirror is used as reflective while other face is cooled down to remove the heat. The reflection rates of the metal mirrors selected to reflect the wavelength (1 micron) of solid state lasers are not very high, the temperature effect cannot be entirely eliminated. For that reason, radius of sphere mirrors cannot be controlled fully. Wavelength of carbon dioxide (10 microns) work better with mirror cutting heads. Since optic materials working at 10 microns wavelength absorb laser beams too much, today mirror focus systems are preferred in carbon dioxide lasers. As seen, this method does not cover all lasers. Since absorption rate of short wavelength (1 micron) laser beam at metal materials is high, in industry mostly solid state lasers are used. Mirror cutting heads are not solution for short wavelength solid state lasers.

The patent application numbered US20150144607A1 tries to find out solution with use of peltier technology in order to control thermal lens effect. In conventional method water is passed through optic holders located in optics in order to cool down the optics. Mechanical design of this method is considerably complicated as it contains moving lens systems on z- axis of optic cutting head and lens requiring adjustment on x-y axis. The heat on the optics is removed by use of peltier method to solve the thermal lens problem. However, while one side is cooling down the other side heats because of nature of peltier. This causes humidity in the optic cutting head over time. Sensitivity of optics to water condensation causes deformation in optics structure over time. Method of cooling down optics cannot eliminate thermal lens effect completely. Because heat conductivity coefficients of materials used in manufacture of the optics are very low.

As a result, the need for problems that mentioned above, and inadequacy of the existing solutions have made necessary to make a development in the related art. Purpose of the Invention

This present invention is related to a laser cutting system and method developed to eliminate disadvantages which are mentioned above, and provide new advantages in the related art.

Main purpose of the laser cutting system and method subject of the invention, is to actively control and eliminate "thermal lens" effect. Under the invention, temperatures of all optics (beam collimating lens, focus lens and protective glass) are measured by temperature sensors and moved as per position value according to temperature of each lens by predefined control software. By moving the lens whose focus is adjustable, focus position value is moved to previous place and controlled actively. Thus thermal lens effect is reset continuously by being kept under control. Another purpose of the invention is to provide accurate reading of temperature of lens by using single lens and to reduce the difference between mechanical axis and optical axis seen in double lens embodiments. Another purpose of the invention is to place the lower protective glass in upper position as the lens lower surface is far to working area in single lens using design when compared to multi-lens using designs, and thus to provide less contamination as it remains far from working area. In addition, when different lens materials are used in multi-lens configurations, thermal stress effect is experienced on the lens since expansion coefficients and absorption values are different. Such problem will not be experienced in single lens method.

Another purpose of the invention is to determine the lens heating up, by measuring the temperatures at lenses via temperature sensors and to take action without damaging the lens. Thus actions may be taken before the lens is over heated and may be re-used by cleaning.

Another purpose of the invention is to adjust the focus position with collimating lens and be less affected by particles such as dirt, sludge splashing from working ambience. Having movement mechanism on the lens in the top (collimating lens) facilitates mechanical accessories of the focusing lens in the lower part, and enables lifting lower protective glass upper and thus provides less contamination.

A further purpose of the invention is to move lens less by adjusting focus position via collimating lens and thus adjust focus position. This enables design of mechanical body in a more compact structure.

In order to achieve the advantages mentioned above, in the most general manner, the invention relates to a laser cutting system comprising a laser cutting head that focuses the laser beam onto processed material in laser cutting machines, which comprises following features;

• at least one collimating lens collimating the laser beams emitted from laser beam source, and transmitting at a given diameter and, · at least one focusing lens that is used to focus the laser beams to working area, is located.

The invention is characterized in that in order to solve the problem of focus point shifting while focusing the laser beams onto working area, it comprises an adaptive focus control unit comprising; · temperature sensors that is located in said laser cutting head, measuring the temperature of said collimating lens and/or focusing lens, • sensor reading circuit converting temperature values measured at said temperature sensors, into electrical value,

• processor receiving temperature values converted into electrical values, from said sensor reading circuit and where control software containing algorithm specifying the locations where the collimating lens and/or focusing lens should be for temperature values of collimating lens and/or focusing lens, is installed,

• at least one driving unit locating the collimating lens and/or focusing lens to the specified locations while being controlled by said processor.

In order to achieve said advantages in the most general manner, the invention is related to a method achieved by said laser cutting system.

The invention is characterized in that, in order to solve the focus point shifting problem which occurs during focusing the laser beams onto working area, comprises following procedure steps;

• measuring the temperature of said collimating lens and/or focusing lens by temperature sensors located in said laser cutting head,

• converting the temperature values measured at said temperature sensors into electrical value with sensor reading circuit located in an adaptive focus control unit,

• receiving the temperature values converted into electrical value, from said sensor reading circuit, with processor where control software containing algorithm specifying the locations where the collimating lens and/or focusing lens should be for collimating lens and/or focusing lens temperature values, is installed and

• controlling at least one driving unit controlled by said processor, bringing the collimating lens and/or focusing lens to the specified locations.

The structural and characteristic features and all advantages of the invention will be understood better in the figures given below and the detailed description by reference to the figures. Therefore, the assessment should be made based on the figures and the detailed descriptions. Brief Description of the Drawings

Figure 1 is a representative view of an alternative of the laser cutting system subject of the invention.

Figure 2 is a representative view of focusing lens that is used in laser cutting head, when focus shifting occurs and when it does not occur.

Figure 3 is a representative view of the quantity of heat that is emitted from the focusing lens that is used in laser cutting head, in clean and contaminated conditions.

Figure 4 is a representative view of the quantity of heat that is emitted from protective glass that is used in laser cutting head, in clean and contaminated conditions. Figure 5 is the view showing cutting machines together with the laser cutting system of the invention.

Description of Part References

1 . Laser cutting head

2. Fibre optic cable 3. Connector

4. Protective glass holder

5. Upper protective glass

6. Lens holder

7. Collimating lens 8. Focusing lens

9. Lower protective glass

10. Temperature sensor

1 1 . Driving unit

12. Laser output aperture 13. Focus point 14. Processed material

15. Adaptive focus control unit

15.1 Sensor reading circuit

15.2 Processor 15.3 Motor driver

16. Optic axis

17. Laser cutting machine 20. Laser cutting system

Q: Heat d ₃ : focus shifting distance 8': Contaminated lens 4': Contaminated glass Detailed Description of the Invention

In this detailed description, the preferred alternatives of the laser cutting system (20) subject of this invention, have been disclosed solely for the purpose of better understanding of the subject and described in a manner not causing any restrictive effect.

Figure 1 is a representative view of an alternative of the laser cutting system (20) subject of the invention. Accordingly, laser beams that is focused onto the processed material (14) from focus point (13) is transmitted from laser beam source to the laser cutting head (1 ) by cable (2). Said cable (2) is a fibre optic cable. In order to connect said fibre optic cable (2) to the laser cutting head (1 ) the connector (3) is used. In the inner part of said laser cutting head (1 ) upper protective glass (5) collimating lens (7) focusing lens (8) and lower protective glass (9) are located at certain intervals from top to down. The components located from top to down are on the same optic axis (16). Lower part of the laser cutting head (1 ) where laser beams leave at high pressure has the laser output aperture (12).

Said upper protective glass (5) and lower protective glass (9) are held inside said laser cutting head (1 ) by the protective glass holder (4). Said upper protective glass (5) is used to prevent penetration of dust particles that might come from connector (3) gap into internal parts of the cutting head (1 ), while said lower protective glass (9) is used to protect the focusing lens (8) against contamination particles that might come from working area, and ensure that the focusing lens (8) is not affected from high gas pressure. Said collimating lens (7) and focusing lens (8) are mounted to lens holders (6) and located inside the laser cutting head (1 ). The main body (20) is cooled down with water flowing through channels provided on main body (20). Since lens holder (6) and protective glass holder (4) are in contact with the main body (20), the lens holder (6) and protective glass holder (4) assist to discharge the heat (Q) on the optics.

Said collimating lens (7) is a collimator lens. Said collimating lens (7) lets the laser beams emitted from fibre optic cable (2) to progress in a certain diameter by collimating. Said focusing lens (8) is used to focus the laser-beam onto the working area. The temperature sensors (10) are located inside laser cutting head (1 ) at certain points. The temperature sensors (10) measure the temperatures at collimating lens (7), focusing lens (8), lower protective glass (9) and upper protective glass (5).

At least one driving unit (1 1 ) is connected to the laser cutting head (1 ). Said driving unit (1 1 ) is preferably associated with collimating lens (7), to adjust focus and moves the lens.

There is an adaptive focus control unit (15) in the laser cutting system (20). Accordingly, said adaptive focus control unit (15) comprises a sensor reading circuit (15.1 ), a processor (15.2) and a motor driver (15.3). Said sensor reading circuit (15.1 ) converts temperature value measured at the temperature sensors (10) into electrical value. The control software is installed onto said processor (15.2). The control software has the algorithm specifying the locations where moveable lens (collimating lens (7)) should be as per temperature values of collimating lens (7) and/or focusing lens (8) and/or lower protective glass (9) and/or upper protective glass (5). Said motor driver (15.3) controls the motion of driving unit (1 1 ) upon command received from the processor (15.2).

Operating principle of the invention is as follows:

Temperature sensors (10) in the laser cutting head (1 ), measures the temperature of the upper protective glass (5), the collimating lens (7), the focusing lens (8) and the lower protective glass (9) while working, and sends to the adaptive focus control unit (15). The temperature values received from the temperature sensors (10), are converted into electrical values by sensor reading circuit (15.1 ) in the adaptive focus control unit (15), and transmitted to the processor (15.2). Said processor (15.2) specifies the location where the moveable lens (collimating lens (7)) should be according to the related temperature values, with control software installed therein, and provides control over the driving unit (1 1 ). Upon the received command the driving unit (1 1 ) starts working and drives moveable lens and relocates it. Thus the moveable lens is located to the location specified by the control software of the processor (15.2) according to the temperature values measured by the temperature sensors (10), and operate without any focus shifting. Thus thermal lens effect is reset continuously by being kept under control.

The deviation of the focus positions at various temperature values, of each optic is calculated by control software installed onto said processor (15.2), and the magnitude and direction of the motion to move the moveable lens in order to bring the focus onto the same point again, is found out.

In the invention, preferably, management of the driving unit (1 1 ) is provided by the motor driver (15.3) upon command received from said processor (15.2).