Gas-mixing device for the controlled mixing of two different gases

Abstract

The invention relates to a gas-mixing device (1) for the controlled mixing of two different gases, the gas-mixing device (1) having a first inlet (2) for a first gas which is under pressure, a second inlet (3) for a second gas which is under pressure, and an outlet (4) for the mixed gas. The gas-mixing device (1) also has two gas-conducting lines (5a, 5b); the first line (5a) connects the first inlet (2) to the outlet (4), and the second line (5b) connects the second inlet (3) to the outlet (4). In each line (5a, 5b), an upstream valve (6a, 6b), a proportional valve (7a, 7b) and a flow sensor (8a, 8b) are provided. The gas-mixing device (1) additionally has at least one electronic control unit (9) for controlling the two proportional valves (7a, 7b) and is designed such that the proportional valve (7a) of the first line (5a) acts as a pressure regulator and the proportional valve (7b) of the second line (5b) acts as a flow regulator.

Description

[0001] Gas mixing device for the controlled mixing of two different gases

[0002] The present invention relates to a gas mixing device for the controlled mixing of two different gases, in particular for mixing two different gases at high pressure of greater than 10 bar, wherein the gas mixing device has a first inlet for a first pressurized gas, a second inlet for a second pressurized gas and an outlet for the mixed gas.

[0003] For various technical applications, such as laser cutting, plasma cutting or plasma welding of metals, it can be advantageous to carry out the respective process in a special atmosphere.

[0004] In this context, it is already known from the prior art according to EP 2 344 296 B1, for example, that in a machine for processing a workpiece by means of a laser beam, in particular for laser cutting metals, a gas supply device is provided with which gas is discharged from a gas source under high pressure by means of a gas nozzle in the area of ​​the laser processing unit of the machine, the output pressure being adjusted by means of a specifically designed pressure control valve.

[0005] Practice has shown, however, that in the above-mentioned applications not only the choice of a particular gas and a specific initial pressure can be advantageous, but that, particularly in laser cutting, plasma cutting or welding, the use of a gas mixture produced from two different gases with a specific mixing ratio can also bring about additional improvements (e.g. with regard to the cutting or welding quality and the maximum possible cutting or welding speed). Typically, in the prior art, the desired gas mixture is produced in a first step at low pressure and stored in a buffer tank, which is then compressed to a high pressure in a suitable manner for further use. However, this entails a comparatively high expenditure on equipment.

[0006] Furthermore, devices for mixing gases at high pressures are already known from the prior art, although they also all have a comparatively complex structure and in which the high-pressure gas mixture is also typically stored in a buffer tank.

[0007] Against this background, it is the object of the present invention to provide a gas mixing device of the type mentioned at the outset which is as simply constructed as possible and at the output of which a mixture of two different gases at high pressure which can be adjusted with regard to the desired mixing ratio can be provided.

[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 embodiments as well as preferred developments of the present invention.

[0009] The gas mixing device according to the invention for the controlled mixing of two different gases has a first inlet (or connection) for a first gas under (preferably high) pressure, a second inlet (or connection) for a second gas under (preferably high) pressure and an outlet for the mixed gas. According to the invention, the gas mixing device has two gas-carrying lines, the first line connecting the first inlet to the outlet and the second line connecting the second inlet to the outlet. A pilot valve, a proportional valve and a flow sensor are arranged in each line.The gas mixing device according to the invention further comprises at least one electronic control unit for controlling the two proportional valves and is configured such that the proportional valve of the first branch functions as a pressure regulator and that the piezo proportional valve of the second branch functions as a flow regulator.

[0010] In this way, using comparatively simple means and parallel or simultaneous control of the two proportional valves in the various strands at the outlet of the gas mixing device, a gas flow with a constant outlet pressure - mixed from two different gases - can be generated, whereby at the same time the mixing ratio of the two gases can be precisely adjusted.

[0011] This is possible because the proportional valve in the first branch acts as a pressure regulator and the proportional valve in the second branch acts as a flow regulator. When the proportional valve in the first branch is operated as a pressure regulator according to the invention, in an expedient embodiment of the invention the pressure prevailing at the outlet of the proportional valve can be regulated to a desired pressure. Due to the simultaneous regulation of the gas flow by the proportional valve in the second branch, for the regulation of which the measured values ​​from the two flow sensors in both branches can be used in an advantageous manner, a defined outlet pressure at the outlet of the gas mixing device and a defined mixing ratio of the two gases at the outlet of the gas mixing device then results at the outlet of the gas mixing device - i.e. after the two gas flows have been brought together.

[0012] Clearly, the pressure at the outlet of the gas mixing device can only be set or regulated to a value that is lower than the minimum of the two gas pressures provided on the inlet side. It is advantageous that, in this case, 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 storage for the mixed gas is required.

[0013] Thus, the mixing ratio of the gases can be changed during operation of the gas mixing device according to the invention without having to vent a gas mixture already stored in a buffer tank with a previously selected mixing ratio. In this respect, the device according to the invention also allows for particularly economical operation with regard to gas consumption when changing the mixing ratio of the gases to be mixed.

[0014] The flow sensors provided according to the invention in each branch can be any desired measuring device for determining the gas flow through the respective branch, wherein the flow sensors can be designed, for example, as mass flow or volume flow sensors. Further below it is also explained that when using proportional valves with pressure sensors provided on the inlet and outlet sides and when the characteristics of the two proportional valves are known, the gas flow in each branch can also be determined by evaluating the pressures measured on the inlet and outlet sides of the respective proportional valve, which typically enables a faster, but somewhat less accurate, measurement of the flows compared to the use of separate flow sensors.A flow sensor in the sense of the invention can therefore also be realized in that the flow (with knowledge of the characteristics of the proportional control valves) is determined from pressures measured on the inlet and outlet sides of the proportional valve by means of pressure sensors provided there. At the outlet of the gas mixing device according to the invention, a pressure control valve known from the prior art can be connected, if necessary, by means of which the mixed gas is fed to a gas outlet (e.g. 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. This pressure control valve and the downstream gas outlet can also be part of the gas mixing device according to the invention, if necessary.

[0015] The pilot valves provided in both lines of the gas mixing device according to the invention serve to prevent any air or gas consumption when the gas mixing device is not active. Furthermore, the pilot valves can be used, if necessary for circuitry reasons, to prevent a potential backflow of the respective gas into another line. Operation of the pilot valves as pressure or flow regulators is neither necessary nor intended within the scope of the present invention.

[0016] The pilot and proportional valves used in the gas mixing device according to the invention can, in principle, be of any design, provided they are suitable for this purpose in terms of their switching characteristics. In particular, a design as solenoid valves could be considered, for example.

[0017] In a particularly preferred embodiment of the invention, the proportional valves provided in both strands are each a piezo proportional valve with a piezopneumatic pre-stage and a pneumatic power stage actuated by the latter. Such piezo proportional valves have a switching behavior suitable for the present purpose and are sufficiently known from the prior art, with the pre-stage of the piezo proportional valve connected to a compressed air supply typically containing an electrically actuated piezo bending transducer with which the output of the pre-stage can be optionally pressurized with compressed air or vented. The pre-stage can then be used to actuate the downstream power stage of the piezo proportional valve. The two pre-valves can also advantageously be designed as piezo valves with a piezopneumatic pre-stage and a pneumatically actuated power stage.

[0018] In an expedient embodiment of the invention, it can be provided that the proportional valve of the first branch (functioning as a pressure regulator) is advantageously designed as a 3 / 3-way proportional valve, in which in particular switching states for venting, for venting and for maintaining a certain pressure can be set.

[0019] The proportional valve of the second branch (functioning as a flow regulator) can preferably be designed as a 2 / 2-way proportional valve and advantageously has an integrated position sensor for precisely setting a specific flow rate. Identical functionality can also be achieved using a 3 / 3-way proportional valve in the second branch, provided that one input of the valve is deactivated in a suitable manner and only two switching states are achieved. Thus, identical 3 / 3-way proportional valves can also be used in the first and second branches of the gas mixing device.

[0020] Furthermore, it can preferably be provided that the proportional valves of the first and second strand (each) have integrated pressure sensors with which the pressure prevailing at the input and output sides of the respective proportional valve can be measured.

[0021] The measured values ​​of these pressure sensors are then fed in a suitable manner (e.g., via a CAN bus) to at least one electronic control unit in order to take these measured data into account when generating suitable control signals for the two proportional valves. The same naturally applies to the measured values ​​of the two flow sensors provided according to the invention in the two lines of the gas mixing device according to the invention.

[0022] Furthermore, it should be mentioned that the gas mixing device according to the invention can either have a single electronic control unit for the simultaneous and parallel control of both proportional valves or that a separate electronic control unit is provided for each proportional valve to control the respective proportional valve, wherein control algorithms which are sufficiently known from the prior art can be used for the actual control of the two proportional valves.

[0023] A PID controller, for example, can be used to control the mixing ratio. The controller uses the measured flow rates of the two gases to calculate the current actual mixing ratio. The controller uses the resulting control deviation to determine a corresponding control signal for the flow control valve. In an expedient development of the present invention, if the characteristics of the two control valves are known, this controller can also use the pressures measured on the inlet and outlet sides of both valves in order to enable a typically faster, but less accurate measurement of the flow rates. If necessary (e.g. in the case of rapid changes in the flow rates), these can be used instead of the measured values ​​from the typically slower, but more accurate flow sensors.

[0024] In order to improve the controllability of the system and to provide the highest possible output pressure, the gas mixing device and the at least one control unit can advantageously be designed to determine a corresponding setpoint for the output pressure at the pressure control valve from the pressure measured on the inlet side of the flow control valve, which setpoint can be selected, for example, to be 1 bar lower than the input pressure at the flow control valve. A PID controller, for example, can then be used for the pressure control itself. This controller uses the pressure measured on the outlet side of the pressure control valve and the setpoint to determine the control deviation and from this the control signal for the pressure control valve. This controller can additionally use the pressure measured on the input side to improve the control speed, for example to select various control parameters.

[0025] When using two separate electronic control units, it may also be provided that these are connected to one another in a suitable manner (e.g. by means of a CAN bus), whereby, for example, the measurement data supplied by individual pressure and flow sensors to a first of the two control units can also be transmitted to the second of the two control units.

[0026] In an advantageous embodiment of the invention, it can further be provided that the control unit of the gas mixing device controlling the flow regulator is designed to determine the actual mixing ratio of the two gases from the measured values ​​of the flow sensors provided in both strands.

[0027] Particularly when using the gas mixing device according to the invention on a laser cutting device, a plasma cutting device, or a welding device, it can preferably be provided that the first gas is nitrogen and the second gas is oxygen. For the aforementioned applications, the provision of a high-pressure gas mixture of oxygen and nitrogen in a specific mixing ratio proves to be particularly advantageous, since this can positively influence the cutting or welding quality as well as the maximum possible cutting or welding speed.

[0028] It can be expediently provided that each gas is provided at its assigned inlet at a pressure of greater than 10 bar. For this purpose, the respective gas is typically provided in a gas reservoir under appropriate pressure and connected to the respective inlet of the gas mixing device by means of suitable high-pressure connections.

[0029] Furthermore, the gas mixing device is advantageously designed to regulate the pressure of the mixed gas at the outlet of the gas mixing device to a value greater than or equal to 10 bar, preferably in the range between 15 and 40 bar or in the range between 15 and 30 bar.

[0030] Furthermore, within the scope of the invention, it can preferably be provided that the first and second gases are mixed at the outlet in a ratio in which the first gas has a proportion of between 80 and 99 vol . -% and the second gas has a proportion of between 1 and 20 vol . -% ha, the sum of the two proportions obviously adding up to 100%.

[0031] And finally, it proves to be particularly expedient if the gas mixing device and the at least one control unit are designed to be operated optionally in an operating mode for the passage of only one gas, in which only a pressurized gas is connected to one of the two inlets, while the line connected to the other inlet is closed by means of the upstream valve there and / or by means of the proportional control valve there.

[0032] In this case, only the gas connected to one inlet flows through the branch connected to the respective inlet towards the outlet, while no gas flows in the other branch. Optionally, if there is no separate pressure control valve downstream of the outlet, pressure control could be achieved by means of the proportional control valve provided in the respective branch. Two exemplary embodiments of the invention are explained in more detail below with reference to the drawing. The drawing shows:

[0033] Fig. 1 is a schematic circuit diagram of a first embodiment of a gas mixing device according to the invention and

[0034] Fig. 2 is a schematic, but somewhat more detailed, circuit diagram of a second embodiment of a gas mixing device according to the invention.

[0035] The first exemplary embodiment of a gas mixing device 1 according to the invention for the controlled mixing of two different gases, shown in Fig. 1 in the form of a schematic circuit diagram, has a first inlet 2 for a first pressurized gas, a second inlet 3 for a second pressurized gas, and an outlet 4 for the mixed gas. Two gas-carrying lines 5a, 5b are provided in the gas mixing device 1, the first line 5a connecting the first inlet 2 to the outlet 4, and the second line 5b connecting the second inlet 3 to the outlet 4.

[0036] In each branch 5a, 5b there is arranged a pilot valve 6a, 6b (for opening and closing the connection to the respectively assigned inlet 2, 3), a proportional valve 7a, 7b and a flow sensor 8a, 8b connected downstream of the proportional valve, so that the flow sensors 8a, 8b detect the gas flow through the respective branch 5a, 5b fluidically behind the respective proportional valve 7a, 7b.

[0037] Furthermore, an electronic control unit 9 is provided for controlling the two proportional valves 7a, 7b, which is set up in such a way that the proportional valve 7a of the first branch 5a acts as a pressure regulator (for setting a specific pressure at the output of the proportional valve 7a located in the first branch 5a) and that the proportional valve 7b of the second branch 5b acts as a flow regulator (for setting a specific flow rate through the proportional valve 7b located in the second branch 5b).

[0038] Due to the parallel control of both proportional valves 7a, 7b in the aforementioned sense, the pressure of the gas mixture at the outlet 4 as well as the mixing ratio of the two gases at the outlet 4, which can be determined from the measured values ​​of both flow sensors 8a, 8b, can be controlled to a specific value.

[0039] Each of the two proportional valves 7a, 7b in the two branches 5a, 5b is assigned a pressure gauge 10a, 10b fluidically connected upstream in the respective branch 5a, 5b and a pressure gauge 11a, 11b fluidically connected downstream in the respective branch 5a, 5b, with which the pressures prevailing on the inlet and outlet sides of the respective proportional valves 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 transmitted in a suitable manner to the control unit 9, which is not shown in Fig. 1 for the sake of clarity.

[0040] The two strands 5a, 5b, each initially carrying a gas, are fluidically brought together behind the respective flow sensor 8a, 8b at the location of the reference symbol 12, so that in the area between the reference symbol 12 and the outlet 4, in which the two strands 5a, 5b share the same fluid path, a gas flow mixed from two different gases with a defined mixing ratio and defined pressure flows.

[0041] The gas mixing device can, with the exception of the connections to be provided on the inlet and outlet sides, be accommodated completely or partially within a housing (not shown). In this case, for example, the outlet 4 for the mixed gas can be formed by a connection provided on the housing of the gas mixing device 1, to which a high-pressure line can be connected, which then leads, for example, to a laser cutting device and has a gas outlet nozzle (or other gas outlet) for the mixed gas at its other end. In an alternative design of the gas mixing device 1, the two gas-carrying strands 5a, 5b can be brought together in the area of ​​the reference number 12, if necessary also outside the housing (e.g. in the area of ​​the laser cutting device).For this purpose, two outlet-side connections must be provided on the housing, to which two high-pressure lines that are only joined outside the housing can then be connected.

[0042] Fig. 2 shows a circuit diagram of a second embodiment of a gas mixing device 1 according to the invention, in which identical reference numerals are used to designate the same components.

[0043] In the second embodiment, the gas mixing device 1 also has two gas-carrying strands 5a, 5b, the first strand 5a connecting the inlet 2 for a first pressurized gas to the outlet 4 and the second strand 5b connecting the inlet 3 for a second pressurized gas to the outlet 4.

[0044] In each branch 5a, 5b there is arranged a respective upstream valve 6a, 6b (for opening and closing the connection to the respectively assigned inlet 2, 3), a proportional valve 7a, 7b designed as a piezo proportional valve and a flow sensor 8a, 8b connected downstream of the proportional valve, so that the flow sensors 8a, 8b detect the gas flow through the respective branch 5a, 5b fluidically behind the respective proportional valve 7a, 7b.

[0045] The flow sensors 8a, 8b provided in the two branches 5a, 5b are advantageously designed as mass flow sensors, since the actual mixing ratio of the two gases downstream of the gas junction 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 the pressure sensors 8a, 8b (downstream of the two proportional control valves 7a, 7b).

[0046] In the second exemplary embodiment, there is no common electronic control unit, but rather a separate electronic control unit 9a, 9b for controlling the respective proportional valve 7a, 7b for each (piezo) proportional valve 7a, 7b, wherein the two control units 9a, 9b are set up in such a way that the proportional valve 7a of the first branch 5a is operated by means of the first control unit 9a as a pressure regulator (for setting a specific pressure at the output of the proportional valve 7a located in the first branch 5a) and that the proportional valve 7b of the second branch 5b is operated by means of the second control unit 9b as a flow regulator (for setting a specific flow rate through the proportional valve 7b located in the second branch 5b).

[0047] Each of the two proportional valves 7a, 7b in the two branches 5a, 5b has two integrated pressure gauges 10a, 11a and 10b, 11b, respectively, with which the pressures prevailing on the inlet and outlet sides of the respective proportional valves 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 transmitted to both control units 9a, 9b via the CAN bus 13 shown.The two strands 5a, 5b, each initially carrying a gas, are in turn fluidically brought together behind the respective flow sensor 8a, 8b at the location of the reference number 12, so that in the area between the reference number 12 and the outlet 4, a gas flow mixed from two different gases flows with a defined mixing ratio and defined pressure.

[0048] Initial investigations by the applicant have shown that maximum pressures of 30-40 bar can be regulated with the gas mixing device according to the invention. By using two-stage piezo pre-valves and two-stage piezo proportional valves, adjustment times of less than 1 second can be achieved at flow rates of up to 5,000 rpm and an output pressure in the range of approximately 20 bar.

Claims

Patent claims Gas mixing device (1) for the controlled mixing of two different gases, in particular for mixing two different gases at a high pressure of greater than 10 bar, wherein the gas mixing device (1) has a first inlet (2) for a first pressurised gas, a second inlet (3) for a second pressurised gas and an outlet (4) for the mixed gas, characterized in that the gas mixing device (1) has two gas-carrying strands (5a, 5b), wherein the first strand (5a) connects the first inlet (2) to the outlet (4) and the second strand (5b) connects the second inlet (3) to the outlet (4), wherein in each strand (5a, 5b) a pilot valve (6a, 6b), a proportional valve (7a, 7b) and a flow sensor (8a, 8b) are arranged, and wherein 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 such that the proportional valve (7a) of the first branch (5a) functions as a pressure regulator and that the proportional valve (7b) of the second branch (5b) functions as a flow regulator. Gas mixing device (1) according to claim 1, characterized in that the proportional valves (7a, 7b) provided in both branches (5a, 5b) are each a piezo-proportional valve with a piezo-pneumatic pre-stage and a pneumatic power stage actuated by the pre-stage. Gas mixing device (1) according to claim 1 or 2, characterized in that the proportional valve (7a) of the first branch (5a) is designed as a 3 / 3-way proportional valve. Gas mixing device (1) according to one of the preceding claims, characterized in that the proportional valve (7b) of the second branch (5b) is designed as a 2 / 2-way proportional valve. Gas mixing device (1) according to one of the preceding claims, characterized in that the proportional valves (7a, 7b) of the first and second branches (5a, 5b) have integrated pressure sensors (10a, 11a; 10b, 11b) with which the pressure prevailing at the inlet and outlet sides of the respective proportional valve (7a, 7b) can be measured.Gas mixing device (1) according to one of the preceding claims, characterized in that the gas mixing device (1) either has a single electronic control unit (9) for the simultaneous and parallel control of both proportional valves (7a, 7b) or that a separate electronic control unit (9a, 9b) is provided for each proportional valve (7a, 7b) for controlling the respective proportional valve (7a, 7b). Gas mixing device (1) according to one of the preceding claims, characterized in that the control unit (9; 9b) of the gas mixing device (1) controlling the flow regulator is designed to... The mixing ratio of the two gases is to be determined from the measured values ​​of the flow sensors (8a, 8b) provided in both strands. Gas mixing device (1) according to one of the preceding claims, characterized in that the first gas is nitrogen (N2) and the second gas is oxygen (O2). Gas mixing device (1) according to one of the preceding claims, characterized in that each gas is provided at its associated inlet (2, 3) with a pressure of greater than 10 bar. Gas mixing device (1) according to claim 9, characterized in that the gas mixing device (1) is designed to regulate the pressure of the mixed gas at the outlet (4) of the gas mixing device (1) to a value greater than or equal to 10 bar, preferably in the range between 15 and 40 bar or in the range between 15 and 30 bar.Gas mixing device (1) according to one of the preceding claims, characterized in that the first and second gases are mixed at the outlet (4) in a ratio in which the first gas has a proportion of between 80 and 99 vol.% and the second gas has a proportion of between 1 and 20 vol.%. Gas mixing device (1) according to one of the preceding claims, characterized in that. that the gas mixing device (1) and the at least one control unit (9; 9a, 9b) are designed to be operated optionally in an operating mode for the passage of only one gas, in which only a pressurized gas is connected to one of the two inlets, while the branch connected to the other inlet is closed by means of the upstream valve there and / or by means of the proportional control valve there.

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