Method for dosing a quantity of liquid and dosing device

Abstract

The invention relates to a method for metering a quantity of liquid using a metering device (100) comprising the steps of: pressurizing the liquid reservoir (160) with compressed air by means of the compressed air source (140), so that the liquid (161) is moved by pressurization in the first (121) and second channel sections (122); moving the valve element (112) from the closed position to the open position at the beginning of a metering period, so that the liquid (161) is moved into the third (123) and fourth channel sections (124) and flows out of the metering tip (130); moving the valve element (112) from the open position to the closed position at the end of the metering period; determining an outlet pressure profile during and / or after the metering period with the outlet pressure sensor (152); and / or determining an inlet pressure profile during and / or after the metering period. Dosing time with the inlet pressure sensor (151),wherein the processing device (170) processes the outlet pressure profile and / or the inlet pressure profile with a viscosity characteristic of the liquid (161) and with a geometry characteristic of the metering tip (130).

Description

The invention relates to a method for metering a quantity of liquid and to a metering device.DE 10 2019 134 804 A1 discloses a measuring arrangement for detecting fluid properties, comprising a micromechanical sensor, an annular channel which has at least a first throttle element, a second throttle element and a third throttle element, a first and a second fluid line which open into the annular channel between the first and the second throttle element or between the third and the first throttle element, respectively, three pressure sensors for detecting pressure measurement values between in each case two adjacent throttle elements, a measurement and operating circuit which is configured to determine the at least one property of the fluid on the basis of the measurement values of the micromechanical sensor, and to detect a fluid flow between the second and the third throttle element on the basis of pressure measurement values, wherein the micromechanical sensor is arranged in the annular channel between the first and the second fluid line in series with at least one throttle element other than the first throttle element.It is an object of the present invention to enable a reliable metering of a liquid.The object is achieved by a method as follows:A method according to the invention for metering a quantity of liquid is carried out using a metering device having a fluid channel which has a first channel section, a second channel section, a third channel section and a fourth channel section, wherein the first channel section is fluidically connected to the second channel section, the second channel section is fluidically connected to the third channel section and the third channel section is fluidically connected to the fourth channel section, and having a valve in which the second and the third channel sections are arranged and which has a valve member which is arranged between the second and the third channel section and which can be moved into an open position in which the fluidic connection of the second channel section to the third channel section is enabled and into a closed position in which the fluidic connection of the second channel section to the third channel section is closed, and having a liquid reservoir, in which a liquid is accommodated and which is connected fluidically to the first channel section, and having a metering tip, which is connected fluidically to the fourth channel section and acts as a throttle, and having a compressed air source, by means of which the liquid reservoir can be supplied with compressed air, and having an output pressure sensor, which is assigned to the fourth channel section, and / or an input pressure sensor, which is assigned to the first channel section, and having a processing device.The method according to the invention is carried out with the steps: supplying the liquid reservoir with compressed air by means of the compressed air source, such that the liquid is moved by pressurizing in the first and second channel sections, moving the valve member from the closed position into the open position at the beginning of a metering time, such that the liquid is moved into the third and fourth channel sections and flows out of the metering tip, moving the valve member from the open position into the closed position at the end of the metering time, ascertaining an output pressure profile during the metering time and / or after the metering time with the output pressure sensor, and / or ascertaining an input pressure profile during the metering time and / or after the metering time with the input pressure sensor, wherein the processing device processes the output pressure profile and / or the input pressure profile with a viscosity characteristic of the liquid and with a geometry characteristic of the dosing tip in order to determine a volume of the liquid dosed from the dosing tip during the dosing time.The liquid is moved in the fluid channel. The numbering of the channel sections corresponds to the direction of movement of the liquid within the fluid channel during the dosing process. Accordingly, the liquid enters the fluid channel via the first channel section and flows from there into the second channel section, the third channel section and the fourth channel section, in order subsequently to flow out of the dosing device via the dosing tip.The movement of the liquid in the fluid channel is initiated by compressed air which is pressed into the liquid reservoir. As a result, compared to an environment surrounding the dosing device, an overpressure results in the liquid reservoir, which is reduced in the direction of the dosing tip. In an operating state, the liquid reservoir has only a first opening, via which compressed air is fed in, and a second opening, through which the first channel section protrudes from the liquid reservoir. On the side of the first channel section facing away from the second channel section, the first channel section dips into the liquid. In this way, it is possible on the one hand to prevent compressed air from penetrating into the fluid channel and on the other hand to ensure that the liquid flows into the fluid channel when an overpressure is present in the liquid reservoir.In the sense of the present invention, the fluid channel is divided into channel sections in order to be able to clearly identify and assign the different functions or areas of the fluid channel. Preferably, the first and / or the fourth channel section are designed hose-like and furthermore preferably connected to the valve by means of a hose coupling. The second and the third channel section are preferably formed as part of the valve and are furthermore preferably bounded by housing components of the valve.The valve is preferably designed as a solenoid valve, so that the movement of the valve member is effected by energizing an electromagnet. By the movement of the valve member, a valve seat formed between the second channel section and the third channel section can be selectively released or blocked.If the valve member is in the closed position, the valve member seals off the fluid channel in a fluid-tight manner, so that a transfer of the liquid from the second channel section to the third channel section is prevented. This also prevents liquid coming from the liquid reservoir from flowing out of the dosing tip.The valve is preferably designed in the manner of a media-separated diaphragm valve. Alternatively, the valve can be designed in the manner of a piston slide valve or in the manner of a seat valve.Suitable liquids are, in particular, liquids used in the field of biotechnology, for example substrate solutions, active substance solutions, sample liquids or similar liquids. These are usually aqueous, i.e. low-viscosity, in particular water-based or organic, for example alcohol-based, liquids or liquid mixtures.The dispensing tip has a known internal geometry in contact with the liquid. On the basis of dimensions of the internal geometry of the dosing tip, the geometric characteristic value of the dosing tip is determined. The internal geometric dimensions of the dosing tip are preferably known within a certain tolerance range, so that the geometric characteristic value of the dosing tip can be determined without a prior separate measurement of the internal geometry of the dosing tip. Preferably, the inner geometry of the dosing tip is rotationally symmetrical, optionally circular cylindrical in sections, and conically tapered towards a dosing opening. Furthermore, the radius and / or the length of the cavity of the dosing tip is preferably taken into account in the determination of the geometric characteristic value of the dosing tip. Particularly preferably, the geometric characteristic value G of the dosing tip is obtained as a quotient of a divisor and a divisor end, wherein the divisor end corresponds to the fourth power of the radius of the cavity of the dosing tip and wherein the divisor corresponds to the length of the cavity of the dosing tip.In principle, all components of the metering device through which the liquid is moved act as a throttle because of friction and / or because of changes in cross section. In this case, in addition to the metering tip, the fluid channel is also of importance. However, the dosing tip, which typically tapers to the dosing opening, preferably opposes the movement of the liquid with a resistance which is at least twice as great as the other components of the dosing device. Thus, the metering tip is deliberately used as a throttle, while the throttling action is to be accepted naturally in the other components. The throttling effect of the metering tip can be influenced by its internal geometry. For example, by increasing the length of the cavity of the dosing tip and / or by reducing the radius of the cavity of the dosing tip, the resistance applied to the liquid can be increased and thus the throttling effect can be increased. In addition, for example, by reducing the length of the cavity of the dosing tip and / or by increasing the radius of the cavity of the dosing tip, the resistance applied to the liquid can be reduced and thus the throttling effect can be attenuated.The output pressure sensor is preferably designed as a relative pressure sensor. Thus, the output pressure is directly measured as a relative pressure to the atmosphere, that is, as an output relative pressure. Furthermore, the output pressure sensor is preferably designed as a piezoresistive pressure sensor. Alternatively, the output pressure sensor is designed as a piezoelectric or capacitive pressure sensor.The compressed air source is preferably designed as a decentralised compressed air generator, so that the compressed air source can be directly assigned to the liquid reservoir. The compressed air source has a compressor, a voltage supply and, in particular, a proportional pressure control.Preferably, a pressure regulating valve, in particular a proportional pressure regulating valve, is arranged between the compressed air source and the liquid reservoir, with which pressure regulating valve the pressure with which the liquid reservoir is subjected can be regulated. The pressure regulating valve is preferably arranged directly upstream of, particularly preferably in, the liquid reservoir. As a result, the pressure of the compressible compressed air can be regulated in the immediate vicinity of the location at which the liquid is moved into the first and second channel sections with the compressed air. In this way, a rapid, i.e. high-frequency, control of the pressure of the compressed air can be effected with which the liquid is moved into the first and second channel sections. This allows a controlled movement of the liquid in the fluid channel and a controlled outflow of the liquid from the dosing tip. In particular, it can be achieved in this way that towards the end of the dosing process a drop separation of the liquid at the dosing tip takes place in the desired manner.The processing device is configured to execute the method according to the invention. For this purpose, the processing device preferably has at least one electrical circuit, in particular a microprocessor or microcontroller, on which a computer program code for executing the method according to the invention is stored and / or with which the computer program code for executing the method according to the invention can be executed. Furthermore, the processing device is preferably configured to detect the output pressure profile detected by the output pressure sensor during the metering time and to store it, in particular in the processing device. Particularly preferably, the processing device is configured to determine the viscosity characteristic value and / or the viscosity characteristic value is stored in the processing device. Furthermore, the geometric characteristic value of the dosing tip is preferably stored in the processing device.The method of the invention is intended for use in high level automation environments, for example. By providing, according to the invention, to determine the volume of the liquid metered from the metering tip during the metering time with the initial pressure profile, the viscosity characteristic value and the geometry characteristic value of the metering tip, further measuring means can be dispensed with for determining the volume, in particular balances or measuring cylinders.A time difference or a time interval between the time at the beginning of the dosing and the time at the end of the dosing is referred to as the dosing time. The time at which the second channel section and the third channel section are fluidically connected after the movement of the valve member from the closed position into the open position has been initiated is considered as the time at the beginning of the metering. This is, for example, when using a valve designed as a diaphragm valve, the time at which the diaphragm lifts from a valve seat due to the movement of the valve member. The time at which the fluidic connection between the second channel section and the third channel section is interrupted after the movement of the valve member from the open position into the closed position has been initiated is considered as the time at which the metering ends. This is, for example, when using a valve designed as a diaphragm valve, the time at which the diaphragm again rests sealingly on the valve seat.Preferably, the volume of the liquid metered from the metering tip during the metering time is determined taking into account the integral of the output pressure over time. Furthermore, the volume of the liquid V metered from the metering tip during the metering time is preferably determined according to the following formula in which p Ausgang is the initial relative pressure, i.e. the absolute initial pressure minus the ambient pressure, K Viskosität is the viscosity characteristic value, t 0 is the time at the beginning of the metering, t Ende is the time at the end of the metering and G is the geometry characteristic value:Preferably, the viscosity characteristic refers to the dynamic viscosity or kinematic viscosity of the liquid. The dynamic viscosity of the liquid corresponds to the product of the kinematic viscosity of the liquid and its density. Further preferably, the viscosity characteristic is proportional to the dynamic viscosity or the kinematic viscosity of the liquid. The viscosity characteristic value is preferably specific for a liquid type and / or liquid class of the liquid or conclusions can be drawn about the liquid type and / or liquid class. With the use of the viscosity characteristic value, when determining the volume of the liquid metered from the metering tip during the metering time, it is possible to dispense with taking into account or using the liquid type and / or liquid class. The viscosity characteristic value K Viskosität is particularly preferably obtained as eight times the dynamic viscosity according to the following formula, in which η is the dynamic viscosity:Further features which develop the invention are the subject matter of the dependent claims with the features listed below:Preferably, immediately after the valve member has been moved from the closed position into the open position or immediately after the valve member has been moved from the open position into the closed position, an output pressure oscillation profile is determined with the output pressure sensor, wherein the viscosity characteristic value is determined on the basis of the output pressure oscillation profile. The movement of the valve member influences the movement of the liquid in the fluid channel. After the valve member has moved from the closed position into the open position, an abrupt increase in pressure occurs in the fourth channel section, by which a pressure wave is generated in the fourth channel section. If this pressure wave impacts an obstacle, in particular the metering tip acting as a throttle, the pressure wave is at least partially reflected at the obstacle, resulting in a pressure oscillation. The time profile of this pressure oscillation is referred to as the output pressure oscillation profile with respect to the output pressure. The output pressure oscillation profile is determined by the output pressure sensor and is preferably a time-related part of the output pressure profile, which is in particular located directly after the valve member is moved from the closed position into the open position, i.e. at the beginning of the metering time, or is located directly after the valve member is moved from the open position into the closed position, i.e. at the end of the metering time.Likewise, a pressure oscillation occurs when the valve member is moved from the open position to the closed position. In this case, an abrupt pressure drop occurs. In the region of the third channel section facing the second channel section, a lower pressure then occurs at least briefly than in the remaining region of the third channel section and in the fourth channel section. This pressure difference leads to a pressure equalization which is directed counter to the direction of movement of the liquid formed during the metering.Accordingly, the output pressure oscillation profile can be determined both after the valve member is moved from the closed position into the open position and after the valve member is moved from the open position into the closed position.The output pressure oscillation profile is dependent on the dynamic and / or kinematic viscosity of the liquid and thus on its viscosity characteristic value. Kinematic viscosity is a measure of how the liquid flows under the influence of gravity. Dynamic viscosity is a measure of which resistance the liquid applies to deformation. Since the pressure vibration pattern results from an influence on the motion of the liquid as described above, a liquid having a high dynamic viscosity exerts a greater resistance to the influence of the motion than a liquid having a low dynamic viscosity. Thus, the pressure curve of a liquid with a high dynamic viscosity is less strongly influenced than the pressure curve of a liquid with a low dynamic viscosity. This is manifested firstly in the fact that lower pressure amplitudes are achieved in the case of a liquid having a high dynamic viscosity than in the case of a liquid having a low dynamic viscosity. On the other hand, this is manifested in the fact that the frequency of the pressure amplitudes is greater for a liquid having a high dynamic viscosity than for a liquid having a low dynamic viscosity. This is also manifested in the fact that, in the case of a liquid having a high dynamic viscosity, the decay rate of the amplitudes of successive pressure extremes is greater, that is to say the pressure oscillation is attenuated to a greater extent than in the case of a liquid having a low dynamic viscosity.Additionally or alternatively, immediately after the valve member has been moved from the closed position into the open position or immediately after the valve member has been moved from the open position into the closed position, an input pressure oscillation profile is determined with the input pressure sensor, on the basis of which the viscosity characteristic value is determined. Furthermore, it can be provided to determine a further input pressure oscillation profile directly after the movement of the valve member from the open position into the closed position. The discussion above regarding the output pressure oscillation profile, in particular in connection with the dynamic and / or kinematic viscosity, applies analogously to the input pressure oscillation profile. The input pressure oscillation profile is determined with the input pressure sensor and is preferably a time-related part of the input pressure profile, which is located in particular directly after the movement of the valve member from the closed position into the open position, i.e. at the beginning of the metering time, or directly after the movement of the valve member from the open position into the closed position, i.e. at the end of the metering time.With respect to the input pressure, an abrupt pressure increase results in the second channel section when the valve member is moved from the open position to the closed position and an abrupt pressure decrease when the valve member is moved from the closed position to the open position.The viscosity characteristic value can be determined on the basis of the output pressure oscillation profile and / or on the basis of the input pressure oscillation profile. If the viscosity characteristic value is determined on the basis of the output pressure oscillation profile and the input pressure oscillation profile, these two pressure oscillation profiles enter in parallel into the determination of the viscosity characteristic value.The viscosity characteristic value is preferably determined with at least one characteristic value from the group: amplitude of the first extreme value, amplitude of the second extreme value, amplitude of the third extreme value, time difference between the first extreme value and / or the second extreme value and / or the third extreme value, decay rate of the amplitude of at least two consecutive extreme values, which is determined on the basis of the output pressure oscillation profile. Taking into account the mechanisms described above, conclusions can be drawn about the dynamic and kinematic viscosity from the aforementioned amplitude-related characteristic values.The numbering of the amplitude-related extreme values follows the temporal occurrence of the relevant extreme values, i.e. the first extreme value occurs first, followed by the second extreme value. The third extreme value then occurs. It is possible to use the amplitudes of further extreme values as characteristic values for determining the viscosity characteristic value, for example the amplitude of the fourth, fifth, sixth, seventh, eighth, ninth and / or tenth extreme value. The extreme values can be designed as maximum or minimum.As time intervals between the extreme values, the time interval between the first and the second extreme values, the time interval between the first and the third extreme values and the time interval between the second and the third extreme values can be used, among other things. If further extreme values are determined or taken into account, further temporal distances can be iteratively taken into account, for example the temporal distance between the first and the fourth extreme value, the temporal distance between the second and the fourth extreme value and the temporal distance between the third and the fourth extreme value and so on.The decay rate of the amplitude of at least two successive extreme values is a measure of how fast the amplitude values of successive extreme values decrease. In the case of a large decay rate, the amplitude values decrease more or more quickly than in the case of a low decay rate.Alternatively or in addition, the viscosity characteristic value is determined with at least one characteristic value from the group: amplitude of the first extreme value, amplitude of the second extreme value, amplitude of the third extreme value, time difference between the first extreme value and / or the second extreme value and / or the third extreme value, decay rate of the amplitude of at least two consecutive extreme values, which is determined on the basis of the input pressure oscillation profile.Alternatively or in addition, the viscosity characteristic value is determined with at least one characteristic value from the group: amplitude of the first extreme value, amplitude of the second extreme value, amplitude of the third extreme value, time difference between the first extreme value and / or the second extreme value and / or the third extreme value, decay rate of the amplitude of at least two consecutive extreme values, which is determined on the basis of the output pressure oscillation profile and the input pressure oscillation profile.Preferably, the processing device is parameterized before the determination of the volume of the liquid by the input pressure sensor determining a maximum feed pressure provided by the compressed air source while the valve member is in the closed position, wherein, in addition, for at least one test liquid having known dynamic viscosity, the following steps are carried out: moving the test liquid in the fluid channel by means of moving the valve member from the closed position to the open position and subsequently moving the valve member from the open position to the closed position, wherein an output pressure oscillation profile of the at least one test liquid is determined with the output pressure sensor immediately after the valve member has been moved from the closed position to the open position or immediately after the valve member has been moved from the open position to the closed position, wherein the viscosity characteristic value of the at least one test liquid is determined on the basis of the output pressure oscillation profile of the at least one test liquid, or wherein immediately after the valve member has been moved from the closed position into the open position or immediately after the valve member has been moved from the open position into the closed position, an input pressure oscillation profile of the at least one test liquid is determined with the input pressure sensor, on the basis of which the viscosity characteristic value of the at least one test liquid is determined, wherein the viscosity characteristic value of the at least one test liquid is determined with at least one characteristic value from the group: amplitude of the first extreme value, amplitude of the second extreme value, amplitude of the third extreme value, time difference between the first extreme value and / or the second extreme value and / or the third extreme value, decay rate of the amplitude of at least two consecutive extreme values, wherein subsequently at least one viscosity class is determined taking into account the determined viscosity characteristic value of the at least one test liquid and the feed pressure, wherein the at least one viscosity class is assigned to the subsequent determination of the volume given a corresponding match of the liquid, wherein the volume of the liquid metered from the metering tip during the metering time is determined with this assigned at least one viscosity class.By determining the viscosity characteristic value of the at least one test liquid and determining a viscosity class based thereon, it is possible to dispense with the direct determination of the viscosity characteristic value of the liquid metered from the metering tip during the metering time, for example on the basis of the input pressure oscillation profile and / or the output pressure oscillation profile. Rather, the assigned viscosity class required for determining the volume of the liquid metered from the metering tip is used according to the above preferred development of the invention. This assigned viscosity class, once it has been determined and stored in the processing device, for example, can be replaced by the viscosity characteristic value of the liquid metered from the metering tip, or can be used as a corresponding viscosity characteristic value, with respect to subsequent metering processes in time. If reference is made to the viscosity characteristic value of the liquid metered from the metering tip, an associated viscosity class can therefore be meant, but also a viscosity characteristic value determined, for example, on the basis of the input pressure oscillation profile and / or the output pressure oscillation profile without prior knowledge of viscosity classes can be meant.Preferably, the assignment of a viscosity class to the liquid metered from the metering tip is less complicated than the determination of a relevant viscosity characteristic value without prior knowledge of viscosity classes. In particular, the assignment to a viscosity class takes place on the basis of fewer amplitude-related characteristic values, optionally on the basis of only one amplitude-related characteristic value, while the viscosity characteristic value of the relevant test liquid is determined on the basis of more amplitude-related characteristic values.If the input pressure oscillation profile is determined after the valve member has been moved from the open position into the closed position, the time between the movement of the valve member from the closed position into the open position and the movement of the valve member from the open position into the closed position can be minimized. Alternatively or in addition, a test dosing time can be used as the time between the movement of the valve member from the closed position into the open position and the movement of the valve member from the open position.The processing device is preferably parameterized with a plurality of test liquids having respectively known, different dynamic viscosities, wherein a plurality of viscosity classes are determined taking into account the viscosity characteristic value determined in each case for the plurality of test liquids. This allows the accuracy of the volume determination for the liquid metered from the metering tip to be increased. Furthermore, a viscosity characteristic value is preferably determined multiple times for each test liquid, wherein the corresponding viscosity class is determined in each case on the basis of the multiple viscosity characteristics of a test liquid.Preferably, the different viscosity classes are determined using a viscosity characteristic related model for machine learning. The viscosity characteristic-related model for machine learning is a model in which at least one statistical learning algorithm is stored and with which functional relationships between at least one viscosity characteristic as input variable and possibly other input variables and at least one viscosity class as output variable can be determined. This makes it possible to dispense with the need to acquire complicated knowledge of physical relationships relating to the liquid and the metering device, as a result of which, in particular, the parameterization of the processing device is simplified.A test volume is preferably determined for at least one test liquid, wherein a comparative volume is determined for the at least one test liquid, wherein a volume-related model for machine learning is trained taking into account the test volume and the comparative volume. The volume-related model for machine learning is a model in which at least one statistical learning algorithm is stored and with which functional relationships between the determined test volume as input variable and possibly other input variables and the comparison volume as output variable can be determined. The test volume is determined by means of the aforementioned method and the comparative volume is determined by means of classic volumetric methods, for example by means of measurement with a measuring cylinder.Preferably, the volume-related model is trained for machine learning after the at least one viscosity class has been determined. Furthermore, the comparative volume is preferably determined using a direct measurement method, for example using a measurement cylinder. Particularly preferably, after the volume-related machine learning model has been trained, the volume of liquid metered from the metering tip is determined taking into account the trained volume-related machine learning model.Preferably, a test volume is determined for a plurality of test liquids and a comparison volume is determined, wherein the volume-related model for machine learning is trained taking into account the test volumes and the comparison volumes. As a result, any measurement errors which occur during the determination of the comparative volume or during the measurement with the output pressure sensor can be compensated for, as a result of which the accuracy of the volume determination for the liquid metered from the metering tip can be increased.Preferably, the viscosity characteristic related machine learning model and / or the volume related machine learning model is based on a multi-layered machine learning model, a so-called deep learning model. The multilayer machine learning model uses multiple intermediate layers between an input and an output layer. Artificial neural networks are formed between the layers.Preferably, the viscosity characteristic related model for machine learning and / or the volume related model for machine learning is trained with at least one test liquid for which a viscosity characteristic and a density are known. Furthermore, the viscosity characteristic-related model for machine learning and / or the volume-related model for machine learning is preferably trained with a plurality of test liquids for which in each case a viscosity characteristic and a density are known, wherein in particular the viscosity characteristics and / or the densities of the test liquids differ from one another. At least one of the following features is preferably used in the training: amplitude of the first extreme value, amplitude of the second extreme value, amplitude of the third extreme value, time difference between the first extreme value and / or the second extreme value and / or the third extreme value, decay rate of the amplitude of at least two consecutive extreme values. The features can be determined on the basis of the output pressure oscillation profile and / or on the basis of the input pressure oscillation profile.Particularly preferably, several of the features are used during the training. In this way, more accurate results can be achieved in the so-called inference (inference).Preferably, the viscosity characteristic value and the volume of the liquid metered from the metering tip are used to determine a mass of the liquid metered from the metering tip. Furthermore, preferably, a density characteristic value of the liquid is determined with the viscosity characteristic value, on the basis of which the mass of the liquid metered from the metering tip is determined. In particular, the mass of the liquid m metered from the metering tip is determined according to the following formula, in which the density characteristic value is:The object of the present invention is also achieved by a metering device having the features listed below:The metering device has a fluid channel which has a first channel section, a second channel section, a third channel section and a fourth channel section, wherein the first channel section is fluidically connected to the second channel section, the second channel section is fluidically connected to the third channel section and the third channel section is fluidically connected to the fourth channel section, a valve in which the second and the third channel sections are arranged and which has a valve member which is arranged between the second and the third channel section and which can be moved into an open position in which the fluidic connection of the second channel section to the third channel section is enabled and into a closed position in which the fluidic connection of the second channel section to the third channel section is closed, a liquid reservoir in which a liquid is accommodated and which is fluidically connected to the first channel section, a dosing tip which is fluidically connected to the fourth channel section and acts as a throttle, a compressed air source by means of which compressed air can be applied to the liquid reservoir, an output pressure sensor which is assigned to the fourth channel section, and a processing device which is configured to carry out a method described above.The invention is explained in more detail below with reference to the attached drawings and shown therein: FIG. 1 shows a metering device with a valve member in an open position, FIG. 2 shows the metering device illustrated in FIG. 1 with the valve member in a closed position, FIG. 3 shows a dosing tip of the dosing device shown in FIGS. 1 and 2, FIG. 4 shows a method for metering a quantity of liquid, FIG. 5 shows an initial pressure curve with a short metering time, FIG. 6 shows an initial pressure curve with a long metering time, FIG. 7 shows an input pressure curve of a slightly influenced input pressure, and FIG. 8 shows an input pressure curve of a strongly influenced input pressure.FIG. 1 shows a metering device 100 with a valve member 112 in an open position. The dosing device 100 has a fluid channel, which has a first channel section 121, a second channel section 122, a third channel section 123 and a fourth channel section 124. The first channel portion 121 is fluidically connected to the second channel portion 122. The second channel section 122 is fluidically connected to the third channel section 123. The third channel section 123 is fluidically connected to the fourth channel section 124.The metering device 100 has a valve 110 in which the second channel section 122 and the third channel section 123 are arranged. The valve 110 has a valve member 112 which is arranged between the second channel section 122 and the third channel section 123. The valve member 112 is movable into an open position in which the fluidic connection of the second channel section 122 to the third channel section 123 is enabled (cf. FIG. 1 ). The valve member 112 can also be moved from the open position into a closed position in which the fluidic connection of the second channel section 122 to the third channel section 123 is closed (cf. FIG. 2 ).The dosing device 100 has a liquid reservoir 160 in which a liquid 161 is accommodated. The liquid reservoir 160 is fluidically connected to the first channel section 121 by the first channel section 121 being immersed in the liquid 161. The dosing device 100 has a dosing tip 130, which is fluidically connected to the fourth channel section 124 and acts as a throttle.The dosing device 100 has a compressed air source 140, by means of which the liquid reservoir 160 can be supplied with compressed air. For this purpose, the compressed air source 140 is connected to the liquid reservoir 160 by means of a compressed air channel 142.The dosing device 100 further comprises an output pressure sensor 152 associated with the fourth channel portion 124. In addition, the dosing device 100 has an inlet pressure sensor 151 which is associated with the second channel section 122.The dosing device 100 comprises a processing device 170 electrically connected to the input pressure sensor 151, the output pressure sensor 152 and the valve 110, respectively.Below the dosing tip 130, a sample container 180 is arranged, into which the liquid 161 dosed from the dosing tip 130 can be accommodated.FIG. 3 shows the dosing tip 130 of the dosing device 100 shown in FIGS. 1 and 2. The dosing tip 130 has an internal geometry 131 that is in contact with the liquid 161. Purely by way of example, the inner geometry 131 is of circular cylindrical configuration and has a length 134 and a radius 132. Purely by way of example, the outer geometry of the dosing tip 130 is conical. Moreover, different external geometries of the dosing tip 130 are possible; for example, the external geometry of the dosing tip 130 can be circular cylindrical.The processing device 170 is configured to execute the method 200 illustrated in FIG. 4. The method 200 is carried out using the metering device 100 described above. It is assumed here that venting of the fluid channel has been carried out in advance, so that the entire fluid channel is filled with the liquid.The method 200 begins with a first step 210, in which the liquid reservoir 160 is supplied with compressed air by means of the compressed air source 140, such that the liquid 161 is moved by pressurization in the first and second channel sections 121, 122.A second step 220 follows, in which the valve member 112 is moved from the closed position into the open position at the beginning of a metering time, so that the liquid 161 is moved into the third and the fourth channel sections 123, 124 and flows out of the metering tip 130.A third step 230 follows, in which the valve member 112 is moved from the open position into the closed position at the end of the metering time.A fourth step 240 then follows, in which an output pressure profile is ascertained during the metering time using output pressure sensor 152.Finally, a fifth step 250 follows, in which a volume of the liquid 161 metered from the metering tip 130 during the metering time is determined by means of the processing device 170 with the initial pressure profile, a viscosity characteristic value and with a geometry characteristic value of the metering tip 130.FIG. 5 shows an output pressure curve 310 with a short metering time and FIG. 6 shows an output pressure curve 310 with a long metering time. The output pressure curve 310 corresponds to a temporal profile of an output pressure plotted on a pressure axis 340 over a time axis 330. The output pressure is determined with the output pressure sensor 152 (see FIGS. 1 and 2 ).At the beginning, the output pressure curve 310 runs along a first output pressure 311, which corresponds purely by way of example to the ambient pressure. At a point in time at the beginning of the metering 331, the output pressure jumps from the first output pressure 311 to a second output pressure 312, which is formed by the fluidic connection between the second channel section 122 and the third channel section 123 having been released by the valve member 112 (cf. FIG. 1 ). After a time at the end of the metering 332, the output pressure falls back to the first output pressure 311. At the time at the end of the metering 332, the fluidic connection between the second channel section 122 and the third channel section 123 is separated again (cf. FIG. 2 ). The area below the output pressure curve 310, which is between the time at the beginning of the metering 331 and the time at the end of the metering 332, is proportional to the volume of the liquid 161 metered from the metering tip 130.The short metering time is manifested in the fact that the distance between the time at the start of metering 331 and the time at the end of metering 332 is shorter (cf. FIG. 5 ) than in the case of a long metering time (cf. FIG. 6 ). Accordingly, assuming an identical second output pressure 312, the volume of the liquid 161 metered from the metering tip 130 in the metering operation, the output pressure curve 310 of which is illustrated in FIG. 5, is smaller than the volume of the liquid 161 metered from the metering tip 130 in the metering operation, the output pressure curve 310 of which is illustrated in FIG. 6.FIG. 7 shows an input pressure curve 320 of a weakly influenced input pressure and FIG. 8 shows an input pressure curve 320 of a strongly influenced input pressure. Assuming otherwise identical conditions, in particular an identical metering device 100 and an identical pressure provided by the compressed air source 140, the inlet pressure curve 320 shown in FIG. 7 corresponds to a liquid 161 which has a greater dynamic and / or kinematic viscosity than the liquid 161 which is associated with the inlet pressure profile 320 shown in FIG. 8.The input pressure curve 320 corresponds to a temporal profile of an input pressure plotted on a pressure axis 340 over a time axis 330. The input pressure is determined with the input pressure sensor 151 (see FIGS. 1 and 2 ). Initially, the input pressure corresponds to a first input pressure 321. At the point in time at the beginning of the metering 331, a pressure oscillation results, which is manifested in the input pressure dropping abruptly and then settling at a fifth input pressure 325. The fifth input pressure 325 is slightly below the first input pressure 321. The difference between the first inlet pressure 321 and the fifth inlet pressure 325 is due to the fact that in the open position, i.e. between the time at the beginning of the metering 331 and the time at the end of the metering 332, a pressure loss occurs via the metering tip 130.After the time at the end of the metering 332, a pressure oscillation results, which is manifested in the input pressure abruptly rising until a maximum is reached as an extreme value with a second input pressure 322. Thereafter, the input pressure falls until a minimum is reached as an extreme value with a third input pressure 323. Thereafter, the input pressure rises again until a maximum is reached as an extreme value with a fourth input pressure 324. Finally, the input pressure oscillates again at the first input pressure 321, wherein in this case a few further extreme values each designed as a maximum or as a minimum are achieved, which for the sake of clarity are not provided with reference symbols in FIGS. 7 and 8.FIGS. 7 and 8 also each show a time difference 338 between the time at which the input pressure reaches the second input pressure 322 and the time at which the input pressure reaches the third input pressure 323. This time difference 338 is dependent on the dynamic viscosity of the liquid 161. The time difference 338 shown in FIG. 7 is larger than the time difference 338 shown in FIG. 8.The deviations of the amplitude of the input pressure between the pressure peak values 322, 323, 324 and the first input pressure 321 is smaller in the input pressure curve 320 shown in FIG. 7 than in the input pressure curve 320 shown in FIG. 8. In addition, a decay rate 328 of the amplitudes of successive pressure extremes 322, 324 in the input pressure curve 320 shown in FIG. 8 is greater than the decay rate 328 of the input pressure curve 320 shown in FIG. 7.References included in the specificationThis list of documents cited by the applicant has been produced in an automated manner and is only included for the better information of the reader. The list is not part of the German patent application or utility model application. The DPMA does not take any adhesion for any faults or omissions.Patent Literature citedDE 10 2019,134 804 A1

[0002]

Claims

Method (200) for metering an amount of liquid using a metering device (100) having a fluid channel which has a first channel section (121), a second channel section (122), a third channel section (123) and a fourth channel section (124), wherein the first channel section (121) is fluidically connected to the second channel section (122), the second channel section (122) is fluidically connected to the third channel section (123) and the third channel section (123) is fluidically connected to the fourth channel section (124), and having a valve (110) in which the second (122) and the third channel section (123) are arranged and which has a valve member (112) which is arranged between the second (122) and the third channel section (123) and which is in an open position, in which the fluidic connection of the second channel section (122) to the third channel section (123) is enabled and can be moved into a closed position in which the fluidic connection of the second channel section (122) to the third channel section (123) is closed, and comprising a liquid reservoir (160) in which a liquid (161) is accommodated and which is fluidically connected to the first channel section (121), and comprising a metering tip (130) which is fluidically connected to the fourth channel section (124) and acts as a throttle, and comprising a compressed air source (140) by means of which the liquid reservoir (160) can be supplied with compressed air, and comprising an output pressure sensor (152) associated with the fourth channel section (124) and / or an input pressure sensor (151) associated with the first channel section (121), and having a processing device (170), having the steps of: supplying the liquid reservoir (160) with compressed air by means of the compressed air source (140), such that the liquid (161) is moved by pressurization in the first (121) and second channel sections (122), moving the valve member (112) from the closed position into the open position at the beginning of a metering time, such that the liquid (161) is moved into the third (123) and the fourth channel section (124) and flows out of the metering tip (130), moving the valve member (112) from the open position into the closed position at the end of the metering time, determining an output pressure profile during the metering time and / or after the metering time with the output pressure sensor (152) and / or determining an input pressure profile during the metering time and / or after the metering time with the input pressure sensor (151), wherein the processing device (170) processes the output pressure profile and / or the input pressure profile with a viscosity characteristic value of the liquid (161) and with a geometry characteristic value of the metering tip (130) in order to determine a volume of the liquid (161) metered from the metering tip (130) during the metering time.Method (200) according to Claim 1, characterized in that an output pressure oscillation profile is determined with the output pressure sensor (152) directly after the valve member (112) has been moved from the closed position into the open position or directly after the valve member (112) has been moved from the open position into the closed position, wherein the viscosity characteristic value is determined on the basis of the output pressure oscillation profile.Method (200) according to Claim 1, characterized in that, directly after the valve member (112) has been moved from the closed position into the open position or directly after the valve member (112) has been moved from the open position into the closed position, an input pressure oscillation profile is determined with the input pressure sensor (151), on the basis of which the viscosity characteristic value is determined.Method (200) according to claim 2 or 3, characterised in that the viscosity characteristic value is determined with at least one characteristic value from the group: amplitude of the first extreme value, amplitude of the second extreme value, amplitude of the third extreme value, time difference (338) between the first extreme value and / or the second extreme value and / or the third extreme value, decay rate (328) of the amplitude of at least two consecutive extreme values, which is determined on the basis of the output pressure oscillation profile and / or the input pressure oscillation profile.Method (200) according to Claim 4, characterized in that, before the volume of the liquid (161) is determined, the processing device (170) is parameterized by the input pressure sensor (151) determining a maximum feed pressure provided by the compressed air source (140) while the valve member (112) is in the closed position, wherein, in addition, the following steps are carried out for at least one test liquid having a known dynamic viscosity: moving the test liquid in the fluid channel by means of moving the valve member (112) from the closed position to the open position and then moving the valve member (112) from the open position to the closed position, carrying out the additional method steps according to Claims 4 and 2 and / or 3, wherein subsequently at least one viscosity class is determined taking into account the determined viscosity characteristic value of the at least one test liquid and the feed pressure, wherein the at least one viscosity class is assigned to the subsequent determination of the volume given a corresponding match of the liquid (161), wherein the volume of the liquid (161) dosed from the dosing tip (130) during the dosing time is determined with this assigned at least one viscosity class.Method (200) according to claim 5, characterised in that the processing device (170) is parameterized with a plurality of test liquids having respectively known, different dynamic viscosities, wherein a plurality of viscosity classes are determined taking into account the viscosity characteristic value determined in each case for the plurality of test liquids.The method (200) of claim 5 or 6, characterized in that the different viscosity classes are determined using a viscosity characteristic related machine learning model.Method (200) according to one of Claims 5 to 7, characterized in that a test volume is determined for at least one test liquid, wherein a comparative volume is determined for the at least one test liquid, wherein a volume-related model for machine learning is trained taking into account the test volume and the comparative volume.Method (200) according to Claim 8, characterized in that a test volume is determined in each case for a plurality of test liquids and a comparison volume is determined, wherein the volume-related model for machine learning is trained taking into account the test volumes and the comparison volumes.Method (200) according to one of Claims 2 to 9, characterized in that a mass of the liquid (161) metered from the metering tip (130) is determined using the viscosity characteristic value and the volume of the liquid (161) metered from the metering tip (130).Dosing device (100) having a fluid channel which has a first channel section (121), a second channel section (122), a third channel section (123) and a fourth channel section (124), wherein the first channel section (121) is fluidically connected to the second channel section (122), the second channel section (122) is fluidically connected to the third channel section (123) and the third channel section (123) is fluidically connected to the fourth channel section (124), and having a valve (110) in which the second and the third channel section (123) are arranged and which has a valve member (112) which is arranged between the second and the third channel section (123) and which is in an open position in which the fluidic connection of the second channel section (122) to the third channel section (123) is released, and can be moved into a closed position, in which the fluidic connection of the second channel section (122) to the third channel section (123) is closed, and with a liquid reservoir (160) in which a liquid (161) is accommodated and which is fluidically connected to the first channel section (121), and with a dosing tip (130), which is fluidically connected to the fourth channel section (124) and acts as a throttle, and with a compressed air source (140), by means of which the liquid reservoir (160) can be supplied with compressed air, and with an output pressure sensor (152), which is associated with the fourth channel section (124), and / or an input pressure sensor (151), which is associated with the first channel section (121), and with a processing device (170), which is configured to carry out a method (200) according to one of the preceding claims.

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