Gas mixing device for controlled mixing of two different gases

Abstract

The invention relates to a gas mixing device (1) for the controlled mixing of two different gases, comprising a first inlet (2) for a first gas held under pressure, a second inlet (3) for a second gas held under pressure, and an outlet (4) for a mixed gas. According to the invention, the gas mixing device (1) has two gas supply branches (5a, 5b), a first branch (5a) connecting the first input (2) to the output (4) and a second branch (5b) connecting the second input (3) to the output (4). Pilot valves (6a, 6b), proportional valves (7a, 7b), and flow sensors (8a, 8b) are provided in each branch (5a, 5b). The gas mixing device (1) has at least one electronic control unit (9) for controlling the two proportional valves (7a, 7b) and is arranged such that the proportional valve (7a) of the first branch (5a) acts as a pressure regulator and the proportional valve (7b) of the second branch (5b) acts as a flow regulator.

Description

[0001] The invention relates to a gas mixing device for the controlled mixing of two different gases, in particular for mixing two different gases at a high pressure greater than 10 bar, wherein the gas mixing device has a first input end for a first gas kept under pressure, a second input end for a second gas kept under pressure, and an output end for the mixed gas.

[0002] For various technical applications, in particular laser cutting, plasma cutting or plasma welding of metals, it can be advantageous to carry out the corresponding process in a special atmosphere.

[0003] By way of example, in this respect it is already known from the prior art according to EP 2 344 296 B1 that a machine for processing workpieces by means of a laser beam, in particular for laser cutting of metals, is provided with a gas supply device, by means of which gas from a high-pressure gas source is discharged by means of a gas nozzle in the region of the laser processing unit of the machine, wherein the output pressure is regulated by means of a specially configured pressure regulating valve.

[0004] However, practice shows that not only the selection of a specific gas and a specific output pressure may be advantageous in the above-mentioned applications, but also, especially in the case of laser cutting, plasma cutting or welding, the use of a gas mixture generated from two different gases and having a specific mixing ratio may also require additional improvements (for example in terms of cutting or welding quality and the maximum possible cutting or welding speed).

[0005] Typically, in such prior art, the desired gas mixture is produced at low pressure in a first step and kept in a buffer tank, and the gas is then suitably compressed to high pressure for further use. However, this is associated with relatively high equipment costs.

[0006] Furthermore, devices for mixing gases under high pressure are also known from the prior art, but they also have a relatively complicated construction, and the gas mixture maintained under high pressure is also usually retained in a buffer tank.

[0007] Against this background, the object of the present invention is to provide a gas mixing device of the initially mentioned type, which has the simplest possible construction and at whose output a gas mixture from two different gases can be supplied with high pressure and which can be adjusted according to the desired mixing ratio.

[0008] This object is achieved by a gas mixing device according to claim 1. The following description, the drawings and the dependent claims explain advantageous aspects and configurations of the invention as well as preferred further developments.

[0009] The gas mixing device for controlled mixing of two different gases of the present invention has a first input end (or port) for maintaining a first gas under (preferably high) pressure, a second input end (or port) for maintaining a second gas under (preferably high) pressure and an output end for the mixed gas. According to the present invention, a gas mixing device is also provided with two gas delivery branches, wherein the first branch connects the first input end with the output end, and the second branch connects the second input end with the output end. A pilot valve, a proportional valve and a flow sensor are arranged in each of these branches. The gas mixing device of the present invention also has at least one electronic control unit for controlling the two proportional valves, and is arranged so that the proportional valve of the first branch is used as a pressure regulator and the piezoelectric proportional valve of the second branch is used as a flow regulator.

[0010] Therefore, by using a relatively simple manner and adjusting two proportional valves in different branches in parallel or simultaneously, a gas flow mixed together from two different gases with a constant output pressure can be generated at the output of the gas mixing device, wherein at the same time the gas mixing ratio of the two gases is also precisely adjustable.

[0011] This is possible because the proportional valve of the first branch acts as a pressure regulator and the proportional valve of the second branch acts as a flow regulator, in other words as a flow regulator. During the inventive operation of the proportional valve arranged in the first branch as a pressure regulator, in an advantageous configuration of the invention, the pressure prevailing on the output side of the proportional valve can be adjusted to a desired pressure. Due to the simultaneous regulation of the gas flow by the proportional valve present in the second branch, it is advantageously possible to use the regulation of the measured values ​​of the two flow sensors in the two branches, and what is then obtained at the output of the gas mixing device (i.e. downstream of the junction of the two gas flows) is a defined output pressure at the output of the gas mixing device and a defined mixing ratio of the two gases at the output of the gas mixing device.

[0012] Obviously, in this case the pressure at the output of the gas mixing device can only be adjusted or regulated to a value below the minimum of the two gas pressures supplied on the input side.

[0013] It has proven to be advantageous in the present case that only one proportional valve operating as a flow regulator and one proportional valve operating as a pressure regulator are required and that within the scope of the invention no buffer tank for the mixed gas is required.

[0014] Thus, the mixing ratio of the gases can be changed during operation of the gas mixing device of the invention without having to blow out from the buffer tank for this purpose the gas mixture already retained in the buffer tank and having a previously selected mixing ratio. Thus, in this respect, the device of the invention also allows a particularly economical operation from the point of view of gas consumption during a change in the mixing ratio of the gases to be mixed.

[0015] The flow sensor provided in each branch according to the invention can be any desired measuring device for determining the gas flow through the corresponding branch, respectively, wherein the flow sensor can be constructed as, for example, a mass flow sensor or a volume flow sensor. In the further description, it will be additionally explained that during the use of a proportional valve with pressure sensors arranged on the input side and the output side, and in the case where the characteristics of the two proportional valves are known, the gas flow in each branch can also be determined by evaluating the pressure measured on the input side and the output side of the proportional valve in question, thus generally allowing faster, although slightly less accurate flow measurement compared to the use of separate flow sensors. Therefore, a flow sensor in the sense of the present invention can also be obtained by determining the flow (given knowledge of the characteristics of the proportional control valve) according to the pressure measured on the input side and the output side of the proportional valve by means of pressure sensors arranged on the input side and the output side of the proportional valve.

[0016] If necessary, a pressure regulating valve known from the prior art can be attached to the output of the gas mixing device according to the invention, through which the mixed gas is fed to a gas outlet (for example, in the form of a gas outlet nozzle), via which the mixed gas can be discharged, for example, in the working area of ​​a laser cutting device, a plasma cutting device or a welding device. If necessary, this pressure regulating valve and the downstream connected gas outlet can also be part of the gas mixing device according to the invention.

[0017] The pilot valves provided in the two branches of the gas mixing device of the invention serve to prevent possible consumption of air or gas when the gas mixing device is not in operation. In addition, a potential backflow of the respective gas into the other line can be prevented by the pilot valve, as this may be desirable from a circuit design point of view. Within the scope of the invention, the operation of the pilot valve as a pressure or flow regulator is neither necessary nor intended.

[0018] The pilot valve and the proportional valve used in the gas mixing device of the present invention can be of any desired design type in principle, as long as they are suitable in terms of their switching characteristics. In particular, for example, for this purpose, a configuration as a solenoid valve can be conceivable.

[0019] In a particularly preferred configuration of the invention, the proportional valves arranged in the two branches are respectively piezoelectric proportional valves having a piezoelectric pneumatic preparatory stage and a pneumatic power stage actuated thereby. Such a piezoelectric proportional valve exhibits a switching behavior suitable for the purposes of the invention and is sufficiently known from the prior art, wherein the pilot stage of a piezoelectric proportional valve attached to a compressed air supply source generally contains an electrically actuable piezoelectric bending transducer, with which the output of the pilot stage can be optionally pressurized or discharged with compressed air. The power stage of the piezoelectric proportional valve connected downstream can then be actuated with the pilot stage. The two pilot valves can also advantageously be configured as piezoelectric valves having a piezoelectric pneumatic pilot stage and a pneumatically actuated power stage.

[0020] In an advantageous configuration of the invention, it can be provided that the proportional valve of the first branch (acting as pressure regulator) is advantageously configured as a 3 / 3-way proportional valve, wherein in particular the switching state can be adjusted for admitting air, for ventilation and for maintaining a specific pressure.

[0021] The proportional valve of the second branch (used as a flow regulator) can preferably be configured as a 2 / 2-way proportional valve and is advantageously provided with an integrated actuation sensor system for precisely regulating a specific flow rate. Incidentally, the same function can also be achieved by using a 3 / 3-way proportional valve in the second branch, setting one input of the valve and then appropriately deactivating it and establishing only two switching states. Therefore, a 3 / 3-way proportional valve of the same construction can also be used in the first branch and the second branch of the gas mixing device.

[0022] Furthermore, it can preferably be provided that the proportional valves of the first branch and of the second branch (in each case) have an integrated pressure sensor, by means of which the pressure prevailing at the input side and at the output side of the respective proportional valve can be measured.

[0023] The measured values ​​of these pressure sensors are then fed to at least one electronic control unit in a suitable manner (e.g. by means of a CAN bus) in order to generate suitable regulating signals for the two proportional valves taking into account these measured data. This naturally applies to the measured values ​​of the two flow sensors provided according to the invention in the two branches of the gas mixing device according to the invention.

[0024] Incidentally, it should be mentioned that the gas mixing device of the present invention can have a single electronic control unit for adjusting two proportional valves simultaneously and in parallel, or, for each proportional valve, a separate electronic control unit is respectively provided for adjusting the corresponding proportional valve, wherein, the regulation algorithm fully known from the prior art can be used for the actual regulation of the two proportional valves. As an example, a PID regulator can be used to adjust the mixing ratio. The regulator uses the measured flow of two gases and calculates the current actual mixing ratio based on them. According to the resulting regulation deviation, the regulator determines the corresponding actuation signal for the flow regulating valve. In an advantageous further development of the present invention, and in the case of the known characteristics of the two regulating valves, the regulator can additionally use the pressure measured at the input side and the output side of the two valves to realize a generally faster, although less accurate, flow measurement. If necessary (for example, in the case of rapid changes in flow), these values ​​can be used instead of the measured values ​​of the generally slower but more accurate flow sensor.

[0025] In order to improve the adjustability of the system and make the highest possible output pressure available, the gas mixing device and at least one control unit can advantageously be arranged to determine, for the pressure at the output side of the pressure regulating valve, a suitable set point according to the pressure measured at the input side of the flow regulating valve, which set point can be selected, for example, to be 1 bar lower than the pressure at the input side of the flow regulating valve. As an example, a PID regulator can then be used for appropriate pressure regulation. The regulator determines the regulation deviation according to the pressure measured at the output side of the pressure regulating valve and the set point and according to the actuation signal of the pressure regulating valve. In order to increase the regulation speed, the regulator can additionally use the pressure measured on the input side, for example, in order to select various regulation parameters.

[0026] In the case of using two separate electronic control units, it can also be provided, if necessary, that these electronic control units are connected to each other in a suitable manner (for example, by means of a CAN bus), whereby, for example, measurement data fed by separate pressure sensors and flow sensors of the first of the two control units can also be transmitted to the second of the two control units.

[0027] In an advantageous configuration of the invention, it can further be provided that the control unit controlling the gas mixing device of the flow regulator is arranged to determine the actual mixing ratio of the two gases based on the measured values ​​of the flow sensors arranged in the two branches.

[0028] In particular, when the gas mixing device according to the invention is used on a laser cutting device, a plasma cutting device or a welding device, it can be preferably provided that the first gas is nitrogen and the second gas is oxygen. In fact, for the above-mentioned applications, supplying a gas mixture of oxygen and nitrogen kept at high pressure and having a specific mixing ratio proves to be particularly advantageous, since thereby the cutting or welding quality and the maximum possible cutting or welding speed can be positively influenced.

[0029] It can be advantageously provided that each gas is supplied at a pressure greater than 10 bar at the input assigned to it. For this purpose, the respective gas is usually supplied by a gas cylinder which is kept at an appropriate pressure and is attached to the respective input of the gas mixing device via an appropriate high pressure port.

[0030] Furthermore, the gas mixing device is advantageously arranged to adjust the pressure of the mixed gas at the output of the gas mixing device to a value greater than or equal to 10 bar, preferably in the range between 15 bar and 40 bar or in the range between 15 bar and 30 bar.

[0031] Furthermore, it can preferably be provided within the scope of the present invention that the first gas and the second gas are supplied to the output end in a mixing ratio in which the first gas has a ratio between 80 and 99 volume percent (Vol.%) and the second gas has a ratio between 1 and 20 volume percent (Vol.%), wherein the sum of the two ratios obviously amounts to 100%.

[0032] And, finally, it proves to be particularly advantageous when the gas mixing device and the at least one control unit are arranged such that, optionally, they can also be operated in an operating mode for delivering only one gas, in which only one gas kept under pressure is attached to one of the two inputs, while the branch connected to the other input is closed by means of a pilot valve therein and / or by means of a proportional control valve therein.

[0033] In this case, only the gas attached to the input then flows in the direction of the output through the branch in question connected to the input, while no gas flows in the other branch. Alternatively, if a separate pressure regulating valve has not been connected downstream of the output, the pressure regulation can be carried out by a proportional regulating valve arranged in the branch in question.

[0034] Two exemplary embodiments of the invention will be explained in more detail below based on the accompanying drawings, in which:

[0035] Figure 1 A schematic circuit diagram of a first exemplary embodiment of a gas mixing device of the present invention is shown.

[0036] Figure 2An equally schematic but slightly more detailed circuit diagram of a second exemplary embodiment of the gas mixing device of the invention is shown.

[0037] Figure 1 A first exemplary embodiment of a gas mixing device 1 according to the invention for controlled mixing of two different gases, shown in the form of a schematic circuit diagram, has a first input 2 for a first gas held under pressure, a second input 3 for a second gas held under pressure and an output 4 for the mixed gas. Two gas supply branches 5a, 5b are provided in the gas mixing device 1, wherein the first branch 5a connects the first input 2 with the output 4 and the second branch 5b connects the second input 3 with the output 4.

[0038] In each branch 5a, 5b, a pilot valve 6a, 6b (for opening and closing the connection with the corresponding assigned input ends 2, 3), a proportional valve 7a, 7b and a flow sensor 8a, 8b connected downstream of the proportional valve are respectively configured, so that the flow sensor 8a, 8b records the gas flow passing through the corresponding branch 5a, 5b in a fluid manner downstream of the corresponding proportional valve 7a, 7b.

[0039] In addition, in order to control the two proportional valves 7a and 7b, an electronic control unit 9 is provided, which is configured so that the proportional valve 7a of the first branch 5a is used as a pressure regulator (for adjusting the specific pressure at the output end of the proportional valve 7a existing in the first branch 5a), and the proportional valve 7b of the second branch 5b is used as a flow regulator (for adjusting the specific flow through the proportional valve 7b existing in the second branch 5b).

[0040] Since the two proportional valves 7a and 7b are adjusted in parallel in the above sense, the pressure of the gas mixture at the output end 4 can be adjusted simultaneously and the mixing ratio of the two gases at the output end 4 can be adjusted to a specific value, which can be determined based on the measurement values ​​of the two flow sensors 8a and 8b.

[0041] Each of the two proportional valves 7a, 7b in the two branches 5a, 5b is assigned a pressure gauge 10a, 10b connected fluidically upstream in the respective branch 5a, 5b and a pressure gauge 11a, 11b connected fluidically downstream in the respective branch 5a, 5b, with which the pressure prevailing at the inlet side and the outlet side of the respective proportional valve 7a, 7b can be determined. The measured values ​​of the four pressure sensors 10a, 10b, 11a, 11b and the measured values ​​of the two flow sensors 8a, 8b are supplied to the control unit 9 in a suitable manner, for the sake of clarity, Figure 1 The control unit 9 is not shown.

[0042] The two branches 5a, 5b that initially transport one gas are each fluidly joined together at the position of reference numeral 12 downstream of the corresponding flow sensors 8a, 8b, so that a gas flow mixed by two different gases and having a defined mixing ratio and a defined pressure flows in the area between reference numeral 12 and the output end 4, wherein the two branches 5a, 5b share the same fluid path.

[0043] In addition to the ports provided on the input side and the output side, the gas mixing device can be completely or partially installed in a housing not shown. As an example, the output end 4 of the mixed gas can then be formed by a port, which is provided on the housing of the gas mixing device 1, and a high-pressure pipeline can be attached to the port, which then leads to a laser cutting device, for example. And at its other end there is a gas outlet nozzle (or other gas outlet) for the mixed gas. In an alternative configuration of the gas mixing device 1, if necessary, the junction of the two gas delivery branches 5a, 5b in the area of ​​reference numeral 12 can also be formed only outside the housing (for example, in the area of ​​the laser cutting device). For this purpose, two ports can then be appropriately provided on the output side of the housing, and two high-pressure pipelines connected only outside the housing can be attached to the two ports.

[0044] Figure 2 A circuit diagram of a second exemplary embodiment of a gas mixing device 1 of the invention is shown, wherein the same reference numerals are used to denote the same components.

[0045] In the second exemplary embodiment, the gas mixing device 1 also has two gas delivery branches 5a, 5b, wherein the first branch 5a connects the input end 2 for the first gas kept under pressure to the output end 4, and the second branch 5b connects the input end 3 for the second gas kept under pressure to the output end 4.

[0046] A pilot valve 6a, 6b (for opening and closing the connection with the corresponding assigned input terminals 2, 3), a proportional valve 7a, 7b configured as a piezoelectric proportional valve and a flow sensor 8a, 8b connected downstream of the proportional valve are respectively arranged in each branch 5a, 5b, so that the flow sensor 8a, 8b records the gas flow passing through the corresponding branch 5a, 5b in a fluid manner downstream of the corresponding proportional valve 7a, 7b.

[0047] The flow sensors 8a, 8b arranged in the two branches 5a, 5b are advantageously designed as mass flow sensors, since the actual mixing ratio of the two gases upstream of the gas connection 12 can then be determined directly from the measured values ​​of the two flow sensors. If the flow sensors 8a, 8b are designed as volume flow sensors, which is also possible, the actual mixing ratio of the two gases can be calculated by additionally taking into account the gas pressures measured by means of pressure sensors 8a, 8b (connected downstream of the two proportional control valves 7a, 7b).

[0048] In a second exemplary embodiment, there is now no common electronic control unit, but instead a separate electronic control unit 9a, 9b is provided for each (piezoelectric) proportional valve 7a, 7b for controlling the respective proportional valve 7a, 7b, wherein the two control units 9a, 9b are arranged so that the proportional valve 7a of the first branch 5a is operated by means of the first control unit 9a acting as a pressure regulator (for regulating a specific pressure at the output end of the proportional valve 7a present in the first branch 5a), and the proportional valve 7b of the second branch 5b is operated by means of the second control unit 9b acting as a flow regulator (for regulating a specific flow through the proportional valve 7b present in the second branch 5b).

[0049] Each of the two proportional valves 7a, 7b in the two branches 5a, 5b has two integrated pressure gauges 10a, 11a and 10b, 11b, by means of which the pressure prevailing at the input side and the output side of the respective proportional valve 7a, 7b can be determined. The measured values ​​of the pressure sensors 10a, 10b, 11a, 11b are fed directly to the control unit 9a, 9b assigned to the respective proportional valve 7a, 7b and can also be exchanged between the two control units 9a, 9b via the CAN bus 13 shown. Furthermore, the measured values ​​of the two flow sensors 8a, 8b can be fed to the two control units 9a, 9b via the CAN bus 13 shown.

[0050] Furthermore, the two branches 5a, 5b that initially transport one gas are each fluidly joined together at the position of reference numeral 12 downstream of the corresponding flow sensors 8a, 8b, so that a gas flow mixed by two different gases and having a defined mixing ratio and a defined pressure flows in the area between reference numeral 12 and the output end 4.

[0051] Preliminary studies by the applicant have shown that the gas mixing device of the present invention can regulate a maximum pressure of 30 to 40 bar. In this way, and using a two-stage piezoelectric pilot valve and a two-stage piezoelectric proportional valve, a regulator response time of less than 1 s can be achieved at a flow rate of up to 5,000 L / min and an output pressure in the range of about 20 bar.

Claims

1. A gas mixing device (1) for the controlled mixing of two different gases, in particular for mixing two different gases at a high pressure greater than 10 bar, in, The gas mixing device (1) has a first input (2) for a first gas kept under pressure, a second input (3) for a second gas kept under pressure and an output (4) for the mixed gas. It is characterized in that The gas mixing device (1) has two gas delivery branches (5a, 5b), wherein the first branch (5a) connects the first input terminal (2) with the output terminal (4), and the second branch (5b) connects the second input terminal (3) with the output terminal (4), wherein a pilot valve (6a, 6b), a proportional valve (7a, 7b) and a flow sensor (8a, 8b) are arranged in each branch (5a, 5b), and The gas mixing device (1) has at least one electronic control unit (9, 9a, 9b) for controlling the two proportional valves (7a, 7b), and is configured so that The proportional valve (7a) of the first branch (5a) acts as a pressure regulator, and The proportional valve (7b) of the second branch (5b) acts as a flow regulator.

2. The gas mixing device (1) according to claim 1, It is characterized in that The proportional valves (7a, 7b) arranged in the two branches (5a, 5b) are respectively piezoelectric proportional valves having a piezoelectric pneumatic pilot stage and a pneumatic power stage actuated thereby.

3. A gas mixing device (1) according to claim 1 or 2, It is characterized in that The proportional valve (7a) of the first branch (5a) is configured as a three-way proportional valve.

4. The gas mixing device (1) according to claim 1, It is characterized in that The proportional valve (7b) of the second branch (5b) is configured as a 2 / 2-way proportional valve.

5. Gas mixing device (1) according to one of the preceding claims, It is characterized in that The proportional valves (7a, 7b) of the first branch (5a) and the second branch (5b) have integrated pressure sensors (10a, 11a, 10b, 11b) by means of which the pressure prevailing at the input side and the output side of the respective proportional valve (7a, 7b) can be measured.

6. Gas mixing device (1) according to one of the preceding claims, It is characterized in that The gas mixing device (1) has a single electronic control unit (9) for simultaneously and parallelly adjusting two proportional valves (7a, 7b), or a separate electronic control unit (9a, 9b) is provided for each proportional valve (7a, 7b) for adjusting the corresponding proportional valve (7a, 7b).

7. Gas mixing device (1) according to one of the preceding claims, It is characterized in that The control unit (9, 9b) of the gas mixing device (1) controlling the flow regulator is arranged to determine the actual mixing ratio of the two gases according to the measurement values ​​of the flow sensors (8a, 8b) arranged in the two branches.

8. Gas mixing device (1) according to one of the preceding claims, It is characterized in that The first gas is nitrogen (N2), and the second gas is oxygen (O2).

9. The gas mixing device (1) according to claim 1, It is characterized in that Each gas is supplied at an input (2, 3) assigned to it at a pressure of more than 10 bar.

10. The gas mixing device (1) according to claim 9, It is characterized in that The gas mixing device (1) is configured to adjust the pressure of the mixed gas at the output end (4) of the gas mixing device (1) to a value greater than or equal to 10 bar, preferably in the range between 15 bar and 40 bar or in the range between 15 bar and 30 bar.

11. Gas mixing device (1) according to one of the preceding claims, It is characterized in that The first gas and the second gas are delivered to the output end (4) at a mixing ratio in which the first gas has a ratio between 80 and 99 volume percent and the second gas has a ratio between 1 and 20 volume percent.

12. Gas mixing device (1) according to one of the preceding claims, It is characterized in that The gas mixing device (1) and the at least one control unit (9, 9a, 9b) are arranged so that, optionally, they can also be operated in an operating mode for delivering only one gas, in which only one gas kept under pressure is attached to one of the two input ends, while the branch connected to the other input end is closed by means of the pilot valve therein and / or by means of the proportional control valve therein.

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