Microdosing system

Abstract

Microdosing system (100, 300) for dosing a quantity of fluid to be dispensed, comprising: a micropump (101) having an inlet (102) and an outlet (103) and designed to draw in the fluid (104, 105, 109) to be discharged through the inlet (102) and to discharge at least part of the fluid (104, 105, 109) from the outlet (103), a first flow sensor (106a, 106b) arranged on the inlet or outlet side, which has an opening (107a, 107b) and a flow meter (108a, 108b), wherein the flow meter (108a, 108b) is configured to determine the flow rate of the fluid (104, 105) passing through this opening (107a, 107b), and means (113, 313) for calibrating and / or interfering detection of the microdosing system (100, 300), wherein the means (113, 313) for calibrating and / or detecting disturbances of the microdosing system (100, 300) comprise a control device (302) configured to detect an actual sensor signal of the first flow sensor (106a, 106b) when the micropump (101) is inactive, and to correct subsequent sensor signals of the first flow sensor (106a, 106b) based on this in order to counteract sensor drift of the first flow sensor (106a, 106b) and to calibrate the microdosing system (100, 300).

Description

[0001] The invention relates to a microdosing system for dosing a quantity of fluid to be dispensed, comprising the features of claim 1, and to a method for dosing a quantity of fluid to be dispensed, comprising the features of claim 19.

[0002] There is a need for precise, cost-effective microdosing systems in various fields, such as drug or fragrance dosing. These microdosing systems typically consist of a fluid actuator, such as a pump (e.g., a microdiaphragm pump), and a fluid flow monitoring element, such as a flow sensor.

[0003] However, well-known microdosing systems are usually large and expensive.

[0004] For example, DE 698 27 952 T2 describes a microvolume liquid handling system with a microdispenser, a piezoelectric transducer, and a pressure sensor for measuring the liquid system pressure and generating a corresponding electrical signal. The pressure signal is used to verify and quantify the microvolume of the dispensed transfer liquid and to perform automatic calibration and diagnostics of the microdispenser.

[0005] EP 1 320 686 B1 describes a normally closed microvalve comprising a diaphragm, an actuating device, and a valve seal that is deformed by the controllable deformation of the diaphragm. The valve seal is located opposite the diaphragm and, in the valve's rest position, is positioned along a sealing lip located between the valve seal and the diaphragm. The valve seal can also be deformed in a second position to allow fluid communication between the outlet and the inlet port.

[0006] Microdiaphragm pumps with passive check valves are known, for example, from WO 03 / 095 837 A1. The microdiaphragm pump disclosed therein is combined with a nozzle chip arranged on the outlet side to generate a free jet.

[0007] For example, WO 98 / 48330 discloses a flow sensor in the form of a micro-dosing chip based on the technology of a piezoresistive pressure sensor. The micro-dosing chip has a membrane. The membrane has an opening that serves as an aperture for the flow to be measured.

[0008] Piezoresistive pressure sensors are inexpensive to manufacture, but very sensitive to stresses, especially those induced during assembly, for example by gluing, clamping, and the like. The micro-dosing chip known from the aforementioned WO 98 / 48330 exhibits the same behavior during assembly.

[0009] Due to such stresses induced during assembly, conventional pressure and flow sensors exhibit undesirable drift behavior when mounted in the traditional manner. High-quality pressure and flow sensors require complex, low-stress mounting to prevent sensor drift, which in turn increases costs.

[0010] Known methods for reducing sensor drift include, for example, aligning a glass wafer with the silicon wafer of the microdispensing chip. Alternatively, the microdispensing chip can be mounted using a very stress-free assembly process.

[0011] However, such stress-free assembly methods are very complex, which in turn prevents the use of such a micro-dosing chip in applications that require low manufacturing costs.

[0012] However, if microdosing pumps and microdosing chips are combined in a cost-effective manufacturing process, the sensor value of the microdosing chip will drift for the reasons mentioned above, i.e., due to the stresses induced during assembly, which prevents accurate dosing of the microdosing system.

[0013] There is therefore a conflict of objectives between the cost-effective production of a microdosing system in which the pressure or flow sensor still works accurately, i.e. without significant drift.

[0014] It is therefore desirable, and thus an object of the present invention, to provide a microdosing system in which the problem of sensor drift described above can be reduced or avoided despite cost-effective assembly.

[0015] This problem is solved according to the invention by a microdosing system having the features of claim 1 and by a method having the features of claim 19.

[0016] A microdosing system according to the invention for dispensing a quantity of fluid comprises, among other things, a micropump having an inlet and an outlet, configured to draw in the fluid to be dispensed through the inlet and to discharge at least a portion of the fluid from the outlet. The microdosing system further comprises a first flow sensor arranged on the inlet or outlet side, which has an opening and a flow meter, the flow meter being configured to determine the flow rate of the fluid passing through this opening. The flow sensor can measure or monitor the quantity of fluid dispensed by the micropump by means of the flow meter. The fluid to be dispensed flows through the opening provided in the flow sensor.For example, based on a pressure difference that occurs, the flow sensor can determine the flow rate of the fluid to be dispensed by means of the flow meter. The microdosing system according to the invention also includes means for calibrating and / or detecting disturbances. The means for calibrating and / or detecting disturbances are designed to calibrate the microdosing system by setting the sensor signal of the first flow sensor to a defined output value, e.g., zero, at any given time t0. The flow sensor can be calibrated or "zeroed" at any given time. If the flow sensor exhibits sensor drift, this drifting, i.e., time-varying, sensor signal can be reset or calibrated or "zeroed" at time t0.The microdosing system can thus be recalibrated at any time using the means for calibration and / or interference detection. In this way, a flow sensor manufactured using simple and cost-effective mounting methods, such as gluing with epoxy, can be used, since the mounting-related sensor drift is compensated according to the invention at time t0.

[0017] According to the invention, the means for calibrating and / or detecting disturbances of the microdosing system include a control device configured to detect an actual sensor signal of the first flow sensor when the micropump is inactive, and to correct subsequent sensor signals of the first flow sensor based on this.

[0018] It is conceivable that the control unit is configured to determine a correction value and subtract it from the magnitude of the measured actual sensor signal of the first flow sensor, with the resulting difference forming a corrected starting point for subsequent sensor signals from the first flow sensor. If the control unit detects that there is no flow (e.g., due to micropump inactivity), the first flow sensor is calibrated or "zeroed" using calibration and / or fault detection means. For example, the control unit can measure the current actual value of the flow sensor and correct it using a correction value to establish the resulting signal as the current "zero flow value," zero point, or starting point. The correction value is determined by the control unit and is based on the measured actual sensor signal. The correction value is subtracted from the measured actual sensor signal.The resulting difference value serves as a new starting point for subsequent sensor signals. In other words, the current actual sensor signal is defined as the new "zero signal." This new "zero signal" can be subtracted from the measured signal as an offset in an immediately following measurement of the flow sensor, provided the flow sensor has not yet drifted away again. For example, the correction value can correspond to the magnitude of the measured actual sensor signal and be subtracted from it. Thus, if, for instance, an actual sensor signal of ±50 mV is measured due to sensor drift when the pump is inactive, a correction value of 50 mV can be subtracted from the magnitude of the actual sensor signal. That is, the magnitude of the actual sensor signal of ±50 mV is corrected by the correction value of 50 mV. The drifting sensor signal is thus reset to zero.In other words, if the flow sensor signal is subject to time-varying sensor drift, the magnitude of the sensor drift can be set to zero at any given time t0 using the calibration and / or disturbance detection methods. The sensor drift is effectively suppressed or corrected at time t0, and the current zero point of the flow sensor at time t0 is redefined. However, the magnitude of the correction value does not have to correspond exactly to the magnitude of the actual sensor signal, as just described. It is also conceivable that the magnitude of the correction value has any value between zero and the actual value of the sensor signal. For example, if an actual sensor signal of ±50 mV is measured due to sensor drift, then a correction value with any value between 0 mV and 50 mV can be subtracted from the magnitude of the actual sensor signal.In this case, for example, it would be conceivable to subtract a correction value of 49 mV from the measured actual sensor signal of ±50 mV. This would result in a new difference value of 1 mV, which would be used as the new starting point or "zero point" for subsequent measurements. In the aforementioned cases, a low-cost sensor, which is not mounted using complex assembly methods and may even be housed under mechanical stress, can thus be used as a suitable, accurate flow sensor for the microdosing system according to the invention.

[0019] It is also conceivable that the correction value corresponds to a range of the magnitude of the actual sensor signal plus a tolerance value of ±10% of the actual sensor signal or plus a tolerance value of ±20% of the actual sensor signal. Thus, for example, with an actual sensor signal value of ±50 mV, a correction value x1 could be selected within the range of 50 mV ±10%, i.e., 45 mV < x1 < 55 mV, or a correction value x2 within the range of 50 mV ±20%, i.e., 40 mV < x2 < 60 mV.

[0020] According to another embodiment, the control unit can be configured to acquire the actual sensor signal of the first flow sensor and correct subsequent sensor signals before any or every pump stroke. A pump stroke includes both a suction stroke and a pressure stroke of the micropump. The new output value or "zero value" of the flow sensor can therefore be re-determined before each suction and / or pressure stroke of the pump; that is, the microdosing system can be recalibrated before each suction and / or pressure stroke of the pump.

[0021] It is conceivable that the microdosing system has the same pressure on the inlet side as on the outlet side, or a lower pressure than on the outlet side. For example, the microdosing system can have an inlet reservoir and an outlet reservoir, with the inlet and outlet reservoirs operating at the same pressure level. Because the same pressure prevails on the inlet and outlet sides, there is no free flow of the dispensed fluid in the forward direction, i.e., from inlet to outlet, also known as "free flow." If the pressure on the outlet side is higher than on the inlet side, check valves provided in the pump can prevent free flow in the reverse direction, i.e., from outlet to inlet, also known as leakage flow.Therefore, if it is ensured that there is no free flow in the forward direction and / or in the reverse direction, the control unit can measure the current actual value of the flow sensor and recalculate the current zero value taking sensor drift into account.

[0022] It is conceivable that the microdosing system has an inlet-side and / or outlet-side valve, wherein the valve is an active normally closed valve, an active normally open valve, a valve with a threshold pressure that closes below a threshold pressure, a double normally closed microvalve, and / or a safety valve. Such valves can be used, for example, when the inlet-side pressure is higher than the outlet-side pressure. In this case, free flow in the forward direction would occur. To prevent this, the aforementioned valves are used according to this embodiment. Such a valve is preferably arranged on the inlet side. It closes the inlet so that no free flow can take place. However, free flow can also be prevented by a valve arranged on the outlet side.For example, a valve known from EP 1 320 686 B1 can be used as an active normally closed valve and / or an active normally open valve. For example, a valve known from DE 10 2008 035 990 A1 can be used as a valve with a threshold pressure. For example, a valve known from EP 1 576 294 B1 can be used as a double normally closed microvalve. For example, a valve known from EP 2 220 371 B1 can be used as a safety valve.

[0023] According to one embodiment, the microdosing system can have a second flow sensor comprising an opening and a flow meter, the flow meter being configured to determine the flow rate of the fluid passing through this opening. The second flow sensor is located on the inlet side and the first flow sensor on the outlet side. Thus, the quantity of fluid flowing into the pump via the pump inlet and the quantity of fluid discharged from the pump via the outlet can be determined. These two values ​​can be compared using calibration and / or fault detection means, particularly by the control unit, to compare, for example, the quantity flowing into the pump with the quantity of fluid actually discharged by the pump. If the two values ​​do not match, the microdosing system can detect a fault, such as...close a leak from valves or a gas bubble in the pump chamber.

[0024] It is conceivable that the means for calibrating and / or detecting disturbances in the microdosing system include a control unit configured to actuate the micropump and the first outlet-side and second inlet-side flow sensors such that both the first and second flow sensors determine the flow rate of the fluid flowing through their respective openings when the micropump draws in the fluid to be dispensed. Furthermore, the control unit is configured to compare the flow rate determined by the first flow sensor with the flow rate determined by the second flow sensor. The two flow sensors can monitor each other in this process. For example, both flow sensors are recalibrated or "zeroed" by the means for calibrating and / or detecting disturbances before each suction stroke of the pump.During the suction stroke, the pump chamber is filled with the fluid to be discharged through the inlet valve. The inlet-side flow rate of the fluid is measured by the second flow sensor. Simultaneously, the outlet-side flow sensor measures whether fluid flow is detectable through its opening. This would indicate that fluid is escaping from the outlet, which should actually be fluid-tight during the pump's suction stroke. Thus, any potential leakage, including its leakage rate, can be detected. For example, a valve sealing the outlet might be leaking, which is detectable according to this embodiment. By comparing the measured inlet-side flow rate with the amount of fluid that may have escaped from an outlet-side leak during the same period, the actual suction rate of the pump can be precisely determined.

[0025] According to a further embodiment, the means for calibrating and / or detecting disturbances in the microdosing system can include a control device configured to control the micropump and the first outlet-side and second inlet-side flow sensors such that both the first and second flow sensors determine the flow rate of the fluid flowing through their respective openings when the micropump discharges the fluid from the outlet. The control device is further configured to compare the flow rate determined by the first flow sensor with the flow rate determined by the second flow sensor. The two flow sensors can monitor each other. For example, both flow sensors are recalibrated by the means for calibrating and / or detecting disturbances before each pressure stroke of the pump."Zeroed." The first flow sensor, located on the outlet side, measures the amount of fluid discharged through the outlet. Simultaneously, the second flow sensor, located on the inlet side, measures whether fluid flow is detectable through its opening. This would indicate that fluid is escaping from the inlet, which should actually be sealed fluid-tight during the pump's pressure stroke. Thus, any potential leakage, including its leakage rate, can be detected. For example, an inlet valve sealing the inlet might be leaking, which is detectable according to this embodiment. By comparing the measured amount of fluid discharged at the outlet with the amount of fluid that may have escaped from an inlet leak during the same period, the actual delivery rate of the pump can be precisely determined.

[0026] By integrating the flow sensor signal from the inlet-side flow sensor, the pump's stroke volume during the suction stroke can be determined. By integrating the flow sensor signal from the outlet-side flow sensor, the pump's stroke volume during the discharge stroke can be determined. The control device can compare both determined stroke volumes. Any differences in the stroke volumes indicate, for example, a measurement error.

[0027] It is conceivable that the micropump comprises a pump chamber arranged between the inlet and the outlet, a diaphragm arranged at least partially within the pump chamber, and a diaphragm deflection device, wherein the diaphragm deflection device is designed to deflect the diaphragm such that the volume of the pump chamber is increased to draw in the fluid to be discharged, and the volume of the pump chamber is decreased to discharge the fluid to be discharged. The micropump can be designed as a self-priming diaphragm pump.

[0028] The membrane deflection device can be a piezoelectric element designed to deflect the membrane depending on the voltage applied to the piezoelectric element. This allows low voltages to be sufficient to operate the pump. Furthermore, high operating rates of the micropump, such as 500 Hz, can be achieved with the piezoelectric element.

[0029] In another embodiment, the microdosing system can include a control unit configured to compare the flow rate determined by the opening of the first flow sensor with a predetermined flow rate reference value and to control the micropump until the flow rate determined by the opening of the first flow sensor is equal to or greater than the predetermined flow rate reference value. In this way, the micropump can advantageously deliver a desired or predefined quantity of fluid. If a delivery quantity greater than the quantity achievable with a single pump stroke is required, the control unit can control the micropump until the desired quantity is reached.

[0030] It is conceivable that fluid connecting elements with low fluidic capacitance are arranged between the micropump and the first and / or second sensor, particularly fluid connecting elements whose volume remains constant under varying operating pressure of the micropump and / or fluid connecting elements with low fluidic inductance. Advantageously, there are little to no fluidic capacitances between the micropump and the flow sensor, such as long, flexible plastic tubes or other elastic elements that would cause time delays before the flow comes to rest, as long, flexible tubes expand and thus increase their volume. That is, advantageously, there are no long, flexible lines between the micropump and the metering chip. Fluidic inductance essentially describes the inertia of the fluid column that must be accelerated during a pump stroke.The more sluggish the fluid column, the slower it follows the pump's movements. At high pump frequencies, a fluid column can no longer follow the pump's movements beyond a certain threshold frequency. This behavior essentially corresponds to low-pass filter behavior. Therefore, it is advantageous to provide fluid connecting elements with the shortest possible length and the largest possible cross-section.

[0031] It is conceivable that the inlet-side valve is located between the micropump and an inlet-side flow sensor, or upstream of an inlet-side flow sensor, and that the outlet-side valve is located between the micropump and the first outlet-side flow sensor, or downstream of the first outlet-side flow sensor. These are particularly advantageous positions for arranging the shut-off valves to prevent free flow.

[0032] It is conceivable that the first flow sensor is arranged on the outlet side and is in contact with the outlet of the micropump, at least partially. This creates a direct connection, at least in some sections, between the pump outlet and the flow sensor. The distance the fluid has to travel between the pump outlet and the flow sensor can thus be advantageously minimized. The pump pressure can therefore be transmitted to the flow sensor with virtually no loss.

[0033] According to one embodiment, the micropump can have a valve on its outlet side that is configured to close the outlet when the micropump draws in the fluid to be discharged, and that is configured to open the outlet when the micropump discharges the fluid. Such a valve prevents unwanted backflow, or leakage, of the discharged fluid. Thus, this valve allows the discharged fluid to exit through the outlet valve during the pump's discharge stroke. However, during the pump's suction stroke, closing the outlet is desirable to allow fresh discharged fluid to be pumped through the inlet into the pump chamber. Therefore, this valve closes the outlet and thus prevents unwanted backflow of the discharged fluid through the outlet during the micropump's suction stroke.

[0034] It is conceivable that the micropump has an inlet valve designed to open the inlet when the micropump draws in the fluid to be discharged, and designed to close the inlet when the micropump discharges the fluid from the outlet. This valve prevents unwanted backflow of the discharged fluid during the pump's discharge stroke, or backflow leakage, should, for example, the outlet pressure be higher than the inlet pressure. Thus, this valve allows the discharged fluid to enter through the inlet valve during the pump's suction stroke. However, during the pump's discharge stroke, closing the inlet is desired to build up pressure in the pump chamber. Therefore, this valve closes the inlet during the micropump's discharge stroke, thereby preventing unwanted backflow of the discharged fluid through the inlet.If, for example, the outlet pressure is higher than the inlet pressure when the pump is inactive, this valve can prevent unwanted backflow, i.e., towards the inlet.

[0035] It is conceivable that the second flow sensor is arranged in contact with the inlet of the micropump, at least in some sections. This would create a direct connection, at least in some sections, between the pump inlet and the second flow sensor. The distance the fluid has to travel between the second flow sensor and the pump inlet can thus be advantageously minimized.

[0036] According to one embodiment, the means for calibrating and / or detecting disturbances in the microdosing system can include a control device configured to actuate the micropump and the first flow sensor such that the first flow sensor determines the flow rate of the fluid flowing through its opening when the micropump is not actuated. This allows for the detection of any leakage from an inlet-side and / or outlet-side valve of the micropump when the pump is inactive, i.e., before a suction stroke and before a discharge stroke. When the micropump is at rest, i.e., when it is not actuated, the inlet-side and / or outlet-side valve is closed, and a certain amount of fluid remains in the pump chamber. Since the pump is not actuated, there is no overpressure in the pump chamber.If the first flow sensor, located on the outlet side, detects flow despite the outlet valve being closed and no overpressure being applied, the microdosing system can conclude that the micropump's outlet valve is not sealed or is leaking. Similarly, if the first flow sensor, located on the inlet side, detects flow despite the inlet valve being closed, the microdosing system can conclude that the inlet valve is not sealed or is leaking. The control unit can also detect leakage at the opening of the first flow sensor. To do this, the control unit measures the leakage flow rate at the opening of the first flow sensor when the pump is inactive. This leakage flow rate is stored as a differential value. When the pump is subsequently active, for example, during a pump pressure stroke, this differential value (i.e., the difference in flow rate) is recorded.The previously determined leakage current is then subtracted from the flow rate actually measured during the pump's pressure stroke. Thus, only the actual flow rate, i.e., without leakage current, is measured. Alternatively, it is also conceivable that the difference is subtracted from the flow sensor's previous zero point before each pump stroke. This establishes a new zero point, reduced or corrected by the previously determined amount of leakage current. In this way, if the first flow sensor leaks, the flow sensor can be recalibrated or zeroed before each pump stroke.

[0037] It is also conceivable that the means for calibrating and / or detecting faults in the microdosing system include a control unit designed to actuate the micropump and the first and / or second flow sensor in such a way that the first and / or second flow sensor determines the flow rate of the fluid flowing through its opening when the micropump is not actuated. This allows for the simultaneous detection of any leakage from both inlet-side and outlet-side valves before a suction stroke and before a pressure stroke. When the micropump is at rest, i.e., when it is not actuated, the inlet-side and outlet-side valves are closed, and a certain amount of fluid remains in the pump chamber. Since the pump is not actuated, there is no overpressure in the pump chamber.If the first flow sensor, located on the outlet side, detects flow despite the outlet valve being closed and no overpressure being applied, the microdosing system can conclude that the outlet valve is not sealing properly or is leaking. Similarly, if the second flow sensor, located on the inlet side, detects flow despite the inlet valve being closed, the microdosing system can conclude that the inlet valve is not sealing properly or is leaking.

[0038] According to one embodiment, the micropump can be designed as an intermittently operating pump. The pump generates a pressure pulse or a sequence of pressure pulses. This results in a transient, time-varying pressure signal at the flow sensors. A blockage of the opening of the respective flow sensor can be detected by analyzing this transient signal. With a static flow, the flow sensor cannot distinguish whether the opening is blocked. However, the transient, time-dependent signal at the flow sensor differs depending on whether the opening is blocked or not. If the opening is not blocked, the pressure pulse generated by the micropump will dissipate within a few milliseconds. If the opening is blocked, overpressure builds up, but cannot dissipate. This can be detected by analyzing the flow sensor signal.

[0039] Exemplary embodiments of the invention are shown in the drawing and are explained below. They show: Fig. 1A a micro-dosing system according to the invention, Fig. 1B a further embodiment of a micro-dosing system according to the invention, Fig. 2A a lateral sectional view of a micro-dosing system according to the invention in a further embodiment, Fig. 2B a lateral sectional view of a micro-dosing system according to the invention in a further embodiment, Fig. 3 a lateral sectional view of a micro-dosing system according to the invention in a further embodiment, Fig. 4 a block diagram of a method according to the invention, and Fig. 5 a diagram showing the pump chamber pressure as it changes over time.

[0040] Fig. Figure 1A shows a microdosing system 100 according to the invention for dispensing a quantity of fluid. The fluid to be dispensed can be, for example, a gas or a liquid. The fluid can have different rheological properties. For example, the fluid can have a low viscosity. The low-viscosity fluid can be, for example, a cream or a lotion. The fluid can contain pharmaceutically active ingredients. The fluid can also be, for example, a deodorant solution containing fragrances.

[0041] The microdosing system 100 includes a micropump 101. The micropump 101 has an inlet 102 and an outlet 103.

[0042] The micropump 101 is configured to draw in the fluid to be discharged, indicated by arrow 104, through the inlet 102. The micropump 101 is further configured to discharge at least a portion of the fluid, indicated by arrow 105, from the outlet 103.

[0043] The microdosing system 100 has a first flow sensor 106a, 106b. The first flow sensor 106a is located on the outlet side, i.e., it is situated on the side of the outlet 103 of the micropump 101. Optionally, the first flow sensor 106b can also be located on the inlet side instead of the outlet side, i.e., on the side of the inlet 102. Therefore, the optionally inlet-side first flow sensor 106b is shown in the figure below. Fig. 1A is indicated by dotted lines.

[0044] The first flow sensor 106a, 106b has an opening 107a, 107b. The fluid 104, 105 to be discharged can pass through this opening 107a, 107b. The first flow sensor 106a, 106b also has a flow meter 108a, 108b. The flow meter 108a, 108b is designed to determine the flow rate of the fluid 104, 105 passing through the opening 107a, 107b formed in the first flow sensor 106a, 106b.

[0045] The opening 107a, 107b can also be referred to as an orifice plate. The flow meter 108a, 108b can, for example, be a pressure sensor that measures the pressure upstream of the orifice plate 107a, 107b and the pressure downstream of the orifice plate, and can determine the differential pressure. Using the differential pressure, the flow rate passing through the orifice plate 107a, 107b can be determined, as described below. By integrating the flow rate over time, the flow rate or volume of the fluid passing through can be determined. Thus, the microdosing system can dispense the required amount of fluid.

[0046] The opening or aperture 107a, 107b presents a defined flow resistance to the fluid flowing through it. The volumetric flow rate, or mass flow rate, passing through this flow resistance is a function of the pressure applied to it. The volumetric flow rate Q is (for incompressible fluids with not too high viscosity, according to Torricelli's law) proportional to the square root of the pressure difference Δp between the pressure p1 measured before the aperture 107a, 107b and the pressure p2 measured after the aperture 107a, 107b, with a proportionality constant c. Q=c⋅p2−p1=c⋅Δp

[0047] Or more generally: Q=μA2Δpρ with the aperture area A and the density ρ of the liquid. The outflow coefficient µ is composed of the contraction coefficient λ (which describes the narrowing of the flow path at sharp aperture edges) and the velocity coefficient ς (which describes the influence of the (small) friction losses at the aperture). μ=λζ

[0048] The above root-shaped Toricelli relationship further requires that the aperture 107a, 107b is an "aperture," meaning that the diameter (or typical dimension in the case of a non-circular, e.g., square aperture) of the aperture 107a, 107b is significantly larger than the thickness of the aperture 107a, 107b. This is the case, for example, when the aperture 107a, 107b of the flow sensor 106a, 106b is realized, for example, by a dry etching step on a silicon pressure sensor membrane, which typically has a membrane thickness of 10–50 µm and a typical membrane side length of 1–3 mm, and the diameter of the aperture 107a, 107b has a value of 50–1500 µm. If the diameter of the aperture 107a, 107b is significantly larger than the thickness of the aperture 107a, 107b, the potential energy of the fluid is mainly converted into kinetic energy, resulting in the above law of Torricelli.In this case, the influence of friction on the orifice flow is small, which has the advantage that the liquid flow through orifices 107a, 107b is essentially independent of temperature, since density is essentially temperature-independent, whereas viscosity in liquids is highly temperature-dependent. The disadvantage here is that (due to the steep root characteristic curve at small sensor signals) the flow sensor 106a, 106b is less sensitive at low flow rates.

[0049] If the diameter of orifice 107a, 107b is not significantly larger than its thickness, the influence of friction increases. The root characteristic then acquires a linear component. However, this is irrelevant for the function of the microdosing system 100, as the relationship between pressure sensor signal and flow rate can still be determined. Since the influence of viscosity on temperature is also known, this temperature influence can be measured and compensated for by measuring the temperature (as previously described for gas flow). Furthermore, channel flow has the advantage that an approximately linear relationship results between flow rate and pressure drop, which is generally known for a round channel geometry due to Hagen-Poiseuill's law.

[0050] This makes it possible, for example, to realize aperture diameters that are equal to or smaller than the aperture thickness (whereby the aperture becomes the channel), and thus microdosing systems 100 can also be realized that can monitor and dose very small quantities.

[0051] The volume flow rate or flow rate Q is also the time derivative of the volume of fluid to be discharged flowing through the defined flow resistance (corresponding to the cross-section of the aperture 107a, 107b) during a unit of time. Q=V˙=dVdt

[0052] Integrating the volume flow rate Q yields the volume of the medium that flowed through during this period. V=∫t1t2Qdt

[0053] As mentioned previously, the fluid to be dispensed can also be a gas. In this case, the volume of the gas changes with temperature. Therefore, it can be advantageous for the microdosing system 100 to have a temperature sensor (not shown here) designed to determine the temperature of the gas passing through the aperture 107a, 107b, in order to determine the corresponding volume of the gas. Advantageously, the temperature sensor is integrated into the first flow sensor 106a, 106b. If the first flow sensor 106a, 106b is designed, for example, as a microflow sensor in the form of a semiconductor chip, the temperature sensor can also be integrated into this semiconductor chip.

[0054] The microdosing system 100 also includes means 113 for calibrating and / or detecting disturbances. These means 113 are designed to recalibrate the first flow sensor 106a, 106b as needed at any time, or to redetermine the current zero point as needed, in order to counteract unwanted sensor drift. The means 113 are also designed to detect disturbances in the microdosing system 100. The means 113 can be connected, for example, via signal lines 114, 115a, 115b to the micropump 101 and the first outlet-side or inlet-side flow sensor 106a, 106b.

[0055] The means 113 for calibrating and / or detecting disturbances in the microdosing system 100 comprise a control device 302. According to the invention, the control device 302 is configured to detect the prevailing actual value of the sensor signal from the first flow sensor 106a, 106b when the micropump 101 is inactive and to set it as the current zero value. The control device 302, as part of the means for calibrating and / or detecting disturbances in the microdosing system 100, switches the micropump 101 into an inactive state, i.e., the micropump 101 performs neither a suction stroke nor a pressure stroke. In this inactive state of the micropump 101, no fluid to be dispensed flows between the inlet 102 and the outlet 103.

[0056] However, it can happen that the sensor signal of the first flow sensor 106a, 106b drifts, i.e., the value of the sensor signal considered at time t1 changes over time, so that this sensor signal has a different value at a second time t2 than at the previous time t1. This can be induced, for example, by mechanical stress during the housing of low-cost sensors.

[0057] According to the invention, the control unit 302 can therefore acquire the current sensor value of the first flow sensor 106a, 106b at any given time t0 and set it as the new zero value. In other words, the current sensor value can be subtracted from the measurement signal as an offset in an immediately subsequent flow measurement of the first flow sensor 106a, 106b using the flow meter 108a, 108b. The microdosing system 100 is thus recalibrated before a measurement using the means for calibration and / or interference detection, according to the invention.

[0058] The control device 302 is configured to determine a correction value and to subtract this value from the amount of the detected actual sensor signal of the first flow sensor 106a, 106b, the difference value obtained forming a corrected starting point for the subsequent sensor signals of the first flow sensor 106a, 106b.

[0059] Therefore, if the control unit 302 detects that there is no flow (e.g., due to inactivity of the micropump and / or closed microvalves), the first flow sensor 106a, 106b is calibrated or "zeroed" using the calibration and / or fault detection means. For example, the control unit 302 can acquire the current actual value of the first flow sensor 106a, 106b and correct it using a correction value to define the resulting signal as the current "zero flow value" or zero point or starting point.

[0060] The correction value is determined by the control unit 302 and is based on the acquired actual sensor signal of the first flow sensor 106a, 106b. The correction value is subtracted from the acquired actual sensor signal. The resulting difference serves as a new starting point for subsequent sensor signals. In other words, the current actual sensor signal is defined as the new "zero signal." This new "zero signal" can be subtracted as an offset from the measurement signal in an immediately subsequent measurement of the flow sensor, in which the flow sensor has not yet drifted away again.

[0061] For example, the correction value can correspond to the magnitude of the measured actual sensor signal and be subtracted from it. So, if, for instance, an actual sensor signal of ±50 mV is measured due to sensor drift when the pump is inactive, then a correction value of 50 mV can be subtracted from the magnitude of the actual sensor signal. That is, the magnitude of the actual sensor signal of ±50 mV is corrected by the correction value of 50 mV. The drifting sensor signal is thus reset to zero.

[0062] The correction value can be subtracted from the previously acquired actual sensor signal before a measurement of the sensor signal from the first flow sensor 106a, 106b is carried out. This redefines the "zero point." However, it is also conceivable that the actual sensor value is initially stored as a correction value and only subtracted from this measured sensor signal after a measurement has been carried out. In this case, the correction value is therefore only subtracted from the obtained measured value as an offset after the measurement has been completed.

[0063] Regardless of whether the correction value is subtracted from the respective sensor signal before or after a measurement, if the flow sensor signal is subject to a time-varying sensor drift, the amount of the sensor drift can be set to zero at any desired time t0 using the calibration and / or disturbance detection methods. The sensor drift is effectively suppressed or corrected at time t0, and the current zero point of the flow sensor at time t0 is redefined.

[0064] The correction value does not have to exactly match the magnitude of the actual sensor signal. It is also conceivable that the correction value can be any value between zero and the actual sensor signal. For example, if an actual sensor signal of ±50 mV is measured due to sensor drift, a correction value of any value between 0 mV and 50 mV can be subtracted from the magnitude of the actual sensor signal. In this case, for instance, a correction value of 49 mV could be subtracted from the magnitude of the measured actual sensor signal of ±50 mV. This would result in a new difference of 1 mV, which would then be used as the new starting point, or "zero point," for subsequent measurements.

[0065] It is also conceivable that the correction value lies within a range of the magnitude of the actual sensor signal plus a tolerance value of ±10% of the actual sensor signal or plus a tolerance value of ±20% of the actual sensor signal. Accordingly, for example, with an actual sensor signal value of ±50 mV, a correction value x could be selected within the range of 50 mV ±10%, i.e., 45 mV < x1 < 55 mV, or a correction value x2 within the range of 50 mV ±20%, i.e., 40 mV < x2 < 60 mV.

[0066] The control unit 302 is designed to perform the calibration of the microdosing system 100 before each pump stroke. Accordingly, the control unit 302 can perform the calibration before a suction stroke and / or before a pressure stroke of the micropump 101, as described above.

[0067] Before calibrating the microdosing system 100, it should be ensured that there is no free flow, or only a negligible flow, of the fluid 104, 105, 109 between inlet 102 and outlet 103 in order to adequately compensate for the drifting sensor signal. This can be ensured, among other things, by the microdosing system 100 having a lower pressure on the inlet side than on the outlet side, according to the invention. For example, a pressure, described below with reference to the Fig. 2A and Fig. 2B, as described in more detail, provides for reservoir 201, whereby the fluid level in reservoir 201 must always be kept below the fluid level at the outlet. In this consideration, it is irrelevant whether the connecting fluid-filled fluid channels (e.g., 225) are above or below the fluid level at the inlet or the fluid level at the outlet. Thus, the hydrostatic pressure in the reservoir is insufficient to allow free fluid flow between inlet 102 and outlet 103. With this configuration, a reverse flow from outlet 103 back into inlet 102 would theoretically be possible with regard to the pressure conditions; however, the passive check valves 310, 311 of the micropump 101 (see Fig. 3) polarized in the blocking direction and prevent backflow, thus ensuring that no flow (or only a negligible leakage current) flows.

[0068] However, it is also possible to have both an inlet-side reservoir 201 and an outlet-side reservoir. The fluid pressures of the two reservoirs can be designed to be equal. In this case, the microdosing system 100 would therefore have approximately the same pressure on the inlet side as on the outlet side. This also prevents free fluid flow between inlet 102 and outlet 103.

[0069] If the microdosing system exhibits a higher pressure on the inlet side than on the outlet side, design measures can be taken to prevent free fluid flow between inlet 102 and outlet 103. According to the [document / section] Fig. In the embodiment shown in Figure 1B, an additional valve 140a, 140b can be provided. Valve 140a can be arranged on the outlet side. Alternatively, valve 140b can be arranged on the inlet side. It is also possible to have one valve 140a, 140b on both the outlet and inlet sides.

[0070] Valve 140a, 140 can be closed, thus preventing free fluid flow between inlet 102 and outlet 103. Valve 140a, 140 can be an active normally closed valve, as known, for example, from EP 1 320 686 B1. Valve 140a, 140b can be a valve with a threshold pressure that is leak-tight below a threshold pressure, as known, for example, from DE 10 2008 035 990 A1. Valve 140a, 140b can be a so-called double normally closed microvalve, as known, for example, from EP 1 576 294 B1. Valve 140a, 140b can also be a so-called safety valve, as known from EP 2 220 371 B1.

[0071] As in Fig. As shown in Figure 1B, the inlet-side valve 140b can be arranged between the micropump 101 and the inlet-side flow sensor 106b.

[0072] The inlet-side valve 140b can alternatively, and preferably, also be arranged upstream of the inlet-side flow sensor 106b. This is preferred because it prevents an increase in dead volumes, fluidic capacitances, and fluidic inductances between the flow sensor 106b and the micropump 101. The outlet-side valve 140a can be arranged as shown in Fig. As shown in Figure 1B, the valve 140a is arranged between the micropump 101 and the outlet-side flow sensor 106a. Alternatively, the outlet-side valve 140a can preferably also be arranged downstream of the outlet-side flow sensor 106a.

[0073] Alternatively or in addition to valves 140a, 140b, the micropump 101 can have passive check valves to prevent backflow of the fluid, i.e., from the outlet 103 to the inlet 102. These check valves 310, 311 are described below with reference to Fig. 3 described in more detail.

[0074] Alternatively or in addition to the valves 140a, 140b, the micropump 101 can have active inlet and outlet valves to prevent backflow of the fluid, i.e. from the outlet 103 to the inlet 102, by closing the active valves.

[0075] Such a micropump with an active inlet valve and an active outlet valve is known, for example, from the document DE 102 38 600 A1.

[0076] With the help of such a micropump, which has active valves, both the backflow and the forward flow of the fluid (free flow) can be prevented when one or both of the active valves are actively closed. First, it shows Fig. 2A another embodiment of a microdosing system 100 according to the invention. The microdosing system 100 has a micropump 101. The micropump 101 has an inlet 102 and an outlet 103.

[0077] More precisely, the inlet 102 has an inlet opening 102a and a rim section 102b surrounding the inlet opening 102a. The outlet 103 has an outlet opening 103a and a rim section 103b surrounding the outlet opening 103a. In the Fig. In the embodiment shown in 2A, the edge section 102b surrounding the inlet opening 102a and the edge section 103b surrounding the outlet opening 103a are formed in one piece.

[0078] The micropump 101 is configured to draw in the fluid to be discharged, indicated by arrow 104, through the inlet 102. The micropump 101 is further configured to discharge at least a portion of the fluid, indicated by arrow 105, from the outlet 103.

[0079] A reservoir 201, which stores the fluid 104 to be discharged, can be arranged on the inlet side of the micropump 101. The reservoir 201 is arranged such that the fluid level within the reservoir 201 is below the lowest edge of the fluid channel 225, which connects the inlet 102 with the outlet 103. Thus, the hydrostatic pressure of the fluid stored in the reservoir 201 is insufficient to allow a free fluid flow between the inlet 102 and the outlet 103.

[0080] In the Fig. In the embodiment shown in Figure 2A, the microdosing system 100 further comprises a first flow sensor 106a arranged on the outlet side. The first flow sensor 106a has an opening 107a through which the fluid 105 to be dispensed can pass. The first flow sensor 106a also comprises a flow meter 108a. The flow meter 108a is designed to determine the flow rate of the fluid 105 passing through the opening 107a formed in the first flow sensor 106a.

[0081] According to this embodiment, the first flow sensor 106a is arranged on the outlet side and is in contact with the outlet 103 of the micropump 101, at least partially. More precisely, the sections 203a, 203b of the first flow sensor 106a facing the micropump 101 are in contact with the edge section 103b of the outlet 103 surrounding the outlet opening 103a.

[0082] The microdosing system 100 includes means 113 for calibrating and / or detecting disturbances. The means 113 for calibrating and / or detecting disturbances comprise a control unit 302. The means 113 for calibrating and / or detecting disturbances correspond to those previously described with reference to the Fig. 1A and Fig. The means 113 discussed in Section 1B for calibration and / or fault detection are essentially the same and therefore have the same functionality. Among other things, they serve to calibrate the microdosing system 100 before a pump stroke by zeroing the flow sensor 106 located on the outlet side. For this purpose, the control unit 302 detects the current sensor signal of the flow sensor 106 when the micropump 101 is inactive and determines this sensor signal as the new zero value. This compensates for any drift in the sensor signal before each pump stroke.

[0083] Fig. Figure 2B shows an alternative embodiment of a microdosing system 100 according to the invention, in which the first flow sensor 106b is arranged on the inlet side.

[0084] The micropump 101 is configured to draw in the fluid to be discharged, indicated by arrow 104, through the inlet 102. The micropump 101 is further configured to discharge at least a portion of the fluid, indicated by arrow 105, from the outlet 103.

[0085] A reservoir 201, which stores the fluid to be discharged, can be arranged on the inlet side of the micropump 101. In this case, the first flow sensor 106b is arranged between the reservoir 201 and the inlet 102 of the micropump 101. Here, too, the reservoir 201 is arranged such that the fluid level within the reservoir 201 is below the lowest edge of the fluid channel 225, which connects the inlet 102 with the outlet 103. Thus, the hydrostatic pressure of the fluid stored in the reservoir 201 is insufficient to allow a free fluid flow between the inlet 102 and the outlet 103.

[0086] The micropump 101 draws the fluid to be dispensed from the reservoir 201. The first flow sensor 106b has an opening 107b through which the fluid 104 to be dispensed can pass. Subsequently, the fluid 104 to be dispensed enters the micropump 101 through the inlet opening 102a of the inlet 102.

[0087] The first flow sensor 106b further comprises a flow meter 108b. The flow meter 108b is designed to determine the flow rate of the fluid 104 passing through the opening 107b formed in the first flow sensor 106b.

[0088] According to this embodiment, the first flow sensor 106b is arranged on the inlet side and at least partially in contact with the inlet 102 of the micropump 101. More precisely, the sections 204a, 204b of the first flow sensor 106b facing the micropump 101 are in contact with the edge section 102b of the inlet 102 surrounding the inlet opening 102a.

[0089] Here too, the microdosing system 100 includes means 113 for calibrating and / or detecting interference of the microdosing system 100, which means 113 previously mentioned with reference to the Fig. 1A, Fig. 1B and Fig. 2A corresponds to the means described in 113 for calibration and / or interference detection.

[0090] The micropump 101 has a pump chamber 202 arranged between the inlet 102 and the outlet 103. The micropump 101 is designed to pump the fluid to be discharged through the pump chamber 202, as indicated here by arrow 109.

[0091] Fig. Figure 3 shows a further embodiment of a microdosing system 300 according to the invention, in which the first flow sensor 106 is arranged on the outlet side and a second flow sensor 110 is arranged on the inlet side.

[0092] The second flow sensor 110 has an opening 111 and a flow meter 112. The flow meter 112 is designed to determine the flow rate of the fluid 104 passing through this opening 112.

[0093] According to this embodiment, the second flow sensor 110 is arranged on the inlet side and is in contact with the inlet 102 of the micropump 101, at least partially. More precisely, the sections 304a, 304b of the second flow sensor 110 facing the micropump 101 are in contact with the edge section 102b of the inlet 102 surrounding the inlet opening 102.

[0094] The micropump 101 has a valve 310 on its outlet side, which is configured to close the outlet 103 when the micropump 101 draws in the fluid 104 to be discharged. The valve 310 is further configured to open the outlet 103 when the micropump 101 discharges the fluid 105 from the outlet 103.

[0095] The micropump 101 has an inlet side valve 311 which is configured to open the inlet 102 when the micropump 101 draws in the fluid 104 to be discharged, and which is configured to close the inlet 102 when the micropump 101 discharges the fluid 105 to be discharged from the outlet 103.

[0096] The microdosing system 300 includes means 313 for calibrating and / or detecting disturbances of the microdosing system 300, the function of which is essentially the same as previously described with reference to the Fig. The embodiments described in 1A to 2B correspond to the means 313 for calibrating and / or detecting disturbances in the microdosing system 300. These means comprise a control unit 302. The control unit 302 is configured to control the first outlet-side flow sensor 106 and / or the second inlet-side flow sensor 110. The control unit 302 can, for example, be a suitable microcontroller. The control unit 302 is connected to the microdosing system 300 via a wired or wireless connection 303. The control unit 302 is preferably connected to the micropump 101 and to the first and / or the second flow sensor 106, 110.

[0097] In addition to the aforementioned possibility of calibrating the microdosing system 300 by "zeroing" the inlet-side flow sensor 106 and / or the outlet-side flow sensor 110, the means 313 are designed for calibrating and / or detecting disturbances in the microdosing system 300 in order to detect a disturbance of the microdosing system 300. Such disturbances will be described in detail later in the text.

[0098] For example, a leak in the inlet-side valve 310 of the micropump 101 and / or the outlet-side valve 311 of the micropump 101 can be detected. A leak or malfunction in the inlet-side flow sensor 110 and / or the outlet-side flow sensor 106 can also be detected.

[0099] The control device 302 is designed, among other things, for such fault detection purposes, to control the micropump 101 as well as the first outlet-side flow sensor 106 and the second inlet-side flow sensor 110 in such a way that both the first and the second flow sensor 106, 110 determine the flow rate of the fluid 104, 105 flowing through the respective opening 107, 111 of the first and the second flow sensor 106, 110 when the micropump 101 draws in the fluid 104 to be discharged.

[0100] This means that during the intake stroke of the micropump 101, the fluid 104 located on the inlet side flows through the opening 111 of the second flow sensor 110 arranged on the inlet side. During the intake stroke of the micropump 101, the valve 311 arranged on the inlet side opens and the fluid to be discharged can flow into the pump chamber 202, as indicated by the arrow 109.

[0101] Simultaneously, the outlet-side valve 310 closes the outlet 103 during the suction stroke of the micropump 101. An intact valve 310 seals the outlet 103 fluid-tight. If the outlet-side valve 310 is defective, fluid flows back into the pump chamber 202 and also flows back through the outlet 103 and the first flow sensor 106. This escaped fluid flows back through the opening 107 of the outlet-side first flow sensor 106, and the flow rate of this escaped fluid is determined using the flow meter 108.

[0102] It should be noted here that the pressure sensor membrane of the flow meter 108 can also detect a reverse flow, since in this case the pressure difference at the orifice 107 of the flow sensor 106 is negative and a negative voltage is measured on the Wheatstone bridge.

[0103] The control unit 302 is aware that the pump 101 is in its suction stroke and therefore no flow should actually be measurable at the outlet-side flow sensor 106, since the outlet-side valve 310 should seal the outlet fluid-tight. If the control unit 302 nevertheless measures a flow at the outlet-side flow sensor 106, this indicates a defect, e.g., a leak at the outlet-side valve 310. The means 313 for calibrating and / or detecting faults in the microdosing system 300 can thus detect an outlet-side leakage flow. The control unit 302, as part of the means 313 for calibrating and / or detecting faults in the microdosing system 300, can therefore detect a fault in the microdosing system 300 during the suction stroke of the micropump 301.

[0104] The control device 302 is further configured to compare the flow rate determined by the first flow sensor 110 and the flow rate determined by the second flow sensor 106.

[0105] The microdosing system 300 can detect not only a leakage flow from the outlet-side valve 310 during the suction stroke of the micropump 101, but also a leakage flow from the inlet-side valve 311 during the pressure stroke of the micropump 101.

[0106] For this purpose, the control device 302 is designed to control the micropump 101 and the second flow sensor 110 arranged on the inlet side in such a way that the second flow sensor 110 determines the flow rate of the fluid 104 flowing through the opening 111 of the second flow sensor 110 when the micropump 101 discharges the fluid 105 to be discharged from the outlet 103.

[0107] This means that when fluid 105 is discharged, or during the pressure stroke of the micropump 101, the outlet-side valve 310 opens, and the fluid 109 to be discharged, located in the pump chamber 202, can flow from the pump chamber 202 towards the outlet-side first flow sensor 106 through the outlet 103, as indicated by the arrow 105. The fluid 105 to be discharged then flows through the opening 107 of the outlet-side first flow sensor 106. The flow rate of the fluid 105 to be discharged is determined by means of the flow meter 108.

[0108] Simultaneously, the inlet-side valve 311 closes the inlet 102 during the pressure stroke of the micropump 101. An intact valve 311 seals the inlet 102 fluid-tight. If the inlet-side valve 311 is defective, fluid flows from the pump chamber 202 back through the inlet 102 into the inlet-side second flow sensor 110. This backflowing fluid passes through the opening 111 of the second flow sensor 110, and the flow rate of this backflowing fluid is determined by the flow meter 112. The control unit 320 is therefore aware that the pump 101 is in its pressure stroke and that, consequently, no flow should actually be measurable at the second inlet-side flow sensor 110, since the inlet-side valve 311 should seal the inlet 102 fluid-tight.If the control unit 320 nevertheless measures a flow rate at the second flow sensor 110 located on the inlet side, this indicates a defect, e.g., a leak at the inlet-side valve 311. The means 313 for calibrating and / or detecting faults in the microdosing system 300 can thus detect an inlet-side leakage flow. The control unit 302, as part of the means 313 for calibrating and / or detecting faults in the microdosing system 300, can therefore also detect a fault in the microdosing system 300 during the pressure stroke of the micropump 101.

[0109] Furthermore, the microdosing system 300 according to the invention can detect leakage currents at the inlet-side valve 311 and / or at the outlet-side valve 310 when the micropump 101 is inactive or idling, i.e., is not performing a suction stroke or a pressure stroke.

[0110] For this purpose, the control device 302 is designed to control the micropump 101 and the first and / or the second flow sensor 106, 110 in such a way that the first and / or the second flow sensor 106, 110 determines the flow rate of the fluid 104, 105 flowing through the opening 107, 111 of the first and / or the second flow sensor 106, 110 when the micropump 101 is not actuated.

[0111] When the micropump 101 is inactive or not actuated, there is no negative or positive pressure in the pump chamber 202. The fluid to be discharged is therefore at atmospheric pressure in the pump chamber 202. In this state, both the inlet-side valve 311 and the outlet-side valve 310 are fluid-tight.

[0112] Should fluid contained in pump chamber 202 nevertheless escape from pump chamber 202, this escaped fluid flows, depending on which of the two valves is leaking, to the first or second flow sensor 106, 110 and through the opening 107, 111 of the first or second flow sensor 106, 110, respectively. The flow rate of the escaped fluid is determined by means of the respective flow meter 108, 112.

[0113] Since the control unit 302 is aware that the micropump 101 is in an inactive state, a fluid flow detected by the first and / or second flow sensor 106, 110 is recognized as a fault or malfunction of the microdosing system 300. The control unit 302, as part of the means 313 for calibration and / or fault detection, thus generates the information that the inlet-side valve 311 and / or the outlet-side valve 310 are leaking, and which of the two valves 310, 311 is leaking. Based on the flow rate of the escaped fluid determined by the respective flow meter 108, 112, the respective leak rate of a leaking valve 310, 311 can even be determined. The control unit 302, as part of the means 313 for calibrating and / or detecting disturbances of the microdosing system 300, can therefore also detect a disturbance of the microdosing system 300 when the micropump 101 is inactive.

[0114] The microdosing system 300 can determine the pump stroke volume during the suction stroke of the micropump 101 based on the fluid flow rate measured by the inlet-side flow sensor 110. The microdosing system 300 receives information about how much fluid flowed through the inlet-side flow sensor 110 during the suction stroke and is therefore located in the pump chamber 202.

[0115] The microdosing system 300 can determine the pump delivery volume during the pressure stroke of the micropump 101 based on the fluid flow rate determined by the outlet-side flow sensor 106. The microdosing system 300 receives information about how much fluid flowed out of the pump chamber 202 during the pressure stroke through the outlet-side flow sensor 110 and thus from the pump chamber 202.

[0116] If the flow rate measuring devices 108, 112 intended for determining the flow rate are designed as differential pressure sensors, the respective fluid volume can be determined by integrating the flow rate Q according to the formula given above. This is done by integrating the flow rate Q determined by the inlet-side differential pressure sensor 110. in The stroke volume of pump 101 during the suction stroke can therefore be determined. This is achieved by integrating the flow rate Q determined by means of the differential pressure sensor 106 located on the outlet side. out The stroke volume of pump 101 during the pressure stroke can be determined. The control device 302 can compare both determined stroke volumes. Any differences in the stroke volumes indicate, for example, a measurement error or leaks.

[0117] The leakage rate of a valve 310, 311, determined when the micropump 101 is inactive, can be used as a difference value compared to the determined pump stroke volume or the determined pump delivery volume to calibrate the microdosing system 300. That is, the determined value of a detected leakage rate can be used as an offset for a subsequent measurement of the flow rate of a fluid flowing through the opening 107, 111 of a flow sensor 106, 110. The control unit 302, as part of the means 313 for calibrating and / or detecting faults in the microdosing system 300, can thus calibrate the microdosing system 300 even if the inlet-side and / or outlet-side valve 310, 311 is leaking.

[0118] This type of calibration also works with a micro-dosing system 100, as described in the Fig. 1A, Fig. 1B, Fig. 2A and Fig. 2B is shown, where this microdosing system 100 is compared to the one with reference to Fig. The microdosing system 300 described in Section 3 has only one first flow sensor 106, which can be arranged on the outlet or inlet side. Accordingly, such a microdosing system 100, equipped with a means 113 for calibration and / or fault detection, can detect a leakage current from an inlet-side or an outlet-side valve 106, 110.

[0119] For this purpose, the microdosing system 100 has a control device 302 as part of the means 113 for calibrating and / or detecting disturbances of the microdosing system 100, which is configured to control the micropump 101 and the first flow sensor 106a, 106b in such a way that the first flow sensor 106a, 106b determines the flow rate of the fluid 104, 105 flowing through the opening 107a, 107b of the first flow sensor 106a, 106b when the micropump 101 is not actuated.

[0120] Furthermore, all embodiments of the microdosing system 100, 300 according to the invention have the advantage that they can be calibrated in order to compensate for any drift of the first and / or second flow sensor 106, 110, as described above.

[0121] For example, if the control unit 302 ensures that no fluid flow is taking place, e.g., when the micropump 101 is switched off, then the first flow sensor 106 is "zeroed," i.e., the flow meter 108 is read, and this value is taken as the "zero flow value," or zero point or starting point. This allows the zero point to be redefined before each suction stroke and / or pressure stroke of the micropump 101.

[0122] The first flow sensor 106 can therefore be recalibrated before each suction and / or pressure stroke of the micropump 101 or at specific intervals. This counteracts any potential sensor drift of the first flow sensor 106. Thus, even a low-cost sensor, which is not mounted using complex assembly methods and may even be housed under mechanical stress, can be used as a suitable, accurate flow sensor 106 for the microdosing system 100, 300 according to the invention. This applies both to a first flow sensor 106a arranged on the inlet side and to a flow sensor 106b arranged on the outlet side. The same applies to the second flow sensor 110.

[0123] According to one embodiment, the control device 302 is designed to compare the flow rate determined through the opening 107 of the first flow sensor 106 with a predetermined flow rate comparison value and to control the micropump 101 until the flow rate determined through the opening 107 of the first flow sensor 106 is equal to or greater than the predetermined flow rate comparison value.

[0124] The microdosing device 100, 300 according to the invention allows the amount of fluid to be dispensed to be precisely metered. For example, if a dispensing quantity of 1.0 µl of fluid is desired, and the micropump 101 can deliver a maximum of 0.25 µl per pump stroke, then the control device 302 activates the micropump 101 until the desired dispensing quantity of 1.0 µl is reached. With an intermittently operating micropump 101, this would require a total of four pump strokes.

[0125] For a more detailed description of the micropump 101, we refer again to the following: Fig. 2A and Fig. Reference is made to 2B. According to this embodiment, the micropump 101 of the microdosing system 100, 300 according to the invention has a pump chamber 202 arranged between the inlet 102 and the outlet 103.

[0126] The micropump 101 also has a diaphragm 222 arranged at least partially in the area of ​​the pump chamber 202 and a diaphragm deflection means 221. The diaphragm deflection means 221 is designed to deflect the diaphragm 222 such that the volume of the pump chamber 202 is increased to draw in the fluid 104, 105, 109 to be discharged, and the volume of the pump chamber 202 is decreased to discharge the fluid 104, 105, 109 to be discharged.

[0127] To perform a suction stroke of the micropump 101, the diaphragm 222 is lifted by the diaphragm deflection means 221, i.e. deflected upwards or in the direction of the end sections 240, 241 of the micropump.

[0128] To execute a pressure stroke of the micropump 101, the diaphragm 222 is lowered by the diaphragm deflection means 221, i.e. deflected downwards or in the direction of the flow sensors 106, 110.

[0129] Preferably, the membrane deflection means 221 is a piezoelectric element designed to deflect the membrane 222 depending on the voltage applied to the piezoelectric element 221.

[0130] The flow sensor 106, 110 described above is preferably designed as a semiconductor chip, for example made of silicon. A membrane 220 is embedded in the chip 106, 110, for example by conventional etching methods ( Fig. 2B). For example, four resistors 108 arranged in a Wheatstone bridge circuit are arranged on the membrane 220, two of which can be seen in each of the cross-sectional views shown in the figures. The Wheatstone bridge circuit serves as a flow meter 108. The opening 107, 111 provided in the flow sensor 106, 110 is preferably formed in the membrane 220 and serves as a flow resistor with a defined flow resistance. The opening 107, 111 can, for example, be introduced into the membrane 220 by dry etching.

[0131] The pump used in the microdosing system 100, 300 according to the invention is a micropump 101 with small dimensions. The lateral dimension of the pressure sensor diaphragm 220, for example, is preferably in the range of 2 x 2 mm. 2 up to 5x5 mm 2The membrane thickness is preferably in a range between 20 µm and 60 µm. The diameter of the opening can, for example, be in a range between 10 µm and 100 µm. A plurality of openings 107, 111 can also be provided in the membrane 220.

[0132] The flow sensors 106, 110 are designed to determine the amount of fluid flowing through the opening 107, 111 by means of the flow meter 108, 112 based on a transient, i.e., time-dependent, pressure signal. The flow sensor 106, 110 measures the pressure difference between the side of the diaphragm 220 of the flow sensor 106 facing the pump inlet 102 or pump outlet 103 and the side of the diaphragm 220 facing away from the pump inlet 102 or pump outlet 103.

[0133] The pressure difference changes over time. For example, with a flow sensor 106 arranged on the outlet side, at the beginning of a pump stroke there is a high initial pressure on the side of the diaphragm 220 facing the pump outlet 103, which is higher than the pressure on the side of the diaphragm 220 facing away from the pump outlet 103. The rising edge of the pressure profile on the side of the diaphragm 220 facing the pump outlet 103 thus rises steeply at the beginning of the pump stroke.

[0134] As the pump stroke approaches its end, more fluid has already flowed through the opening 107 formed in the diaphragm 220. Accordingly, the overpressure on the side of the diaphragm 220 facing the pump outlet 103 decreases continuously compared to the overpressure on the side of the diaphragm 220 facing away from the pump outlet 103. The pressure profile or pressure signal therefore exhibits a decreasing slope over time.

[0135] The flow sensor 106, 110 is designed such that the time-dependent fluid flow through the opening 107, 111 can be determined from the measured, time-dependent pressure signal and the static characteristic curve of the opening 107, 111. This fluid flow can then be integrated over time to determine the metered volume or flow rate.

[0136] Based on the pressure, the flow sensor 106, 110 determines the flow rate of the fluid to be discharged flowing through the opening 107, 111 of the flow sensor 106, 110 by means of the flow rate measuring device 108, 112.

[0137] To ensure that no fluid flows through micropump 101 even when it is switched off, the following must be observed. Firstly, no "free flow" may occur by ensuring that no back pressure develops. This can be achieved, for example, by ensuring that the reservoir 201 containing the fluid is always closed, as described in the Fig. 2A and Fig. As shown in Figure 2B, the reservoir 201 is located below the micropump 101. Furthermore, no overpressure should be exerted on the reservoir 201. The microdosing system 100, 300 according to the invention should generally operate at low pressures, for example, to allow its use in dosing patches.

[0138] Furthermore, no flow should occur through closed valves 310 and 311. If the outlet pressure is higher than the inlet pressure, these valves 310 and 311 close. If the inlet pressure is higher than the outlet pressure, these valves 310 and 311 open, and free flow, the so-called "free flow," can occur. To prevent this, additional valves 140a and 140b ( Fig. 1B). These valves 140a, 140b can, for example, be designed as one of the following valves: • Active valves • NO valve that closes • NC valve • Passive valves • Safety valve • DNC valve • Microvalve with operating threshold pressure

[0139] Furthermore, according to embodiments of the invention, it is advantageous that there are no "fluidic capacitances" (e.g., soft plastic hoses or other elastic elements) between the micropump 101 and the flow sensors 106, 110, which would cause time delays before the flow comes to a standstill. That is, it is advantageous that there are no long, flexible lines between the micropump 101 and the flow sensors 106, 110.

[0140] An advantageous arrangement would be, for example, a micropump 101 with a safety valve, in which the flow sensor 106, 110 is arranged directly before or after the micropump 101, e.g. by gluing, clamping (over a seal), or soldering the flow sensor directly onto the underside of the micropump at the outlet or inlet.

[0141] A major advantage of the microdosing system 100, 300 according to the invention is the fact that the flow measurement is very fast; pressure fluctuations and thus also flow fluctuations can be resolved down to less than one millisecond. This has already been demonstrated metrologically (Proceedings MEMS 99, Orlando / USA, January 17-21, 1999, pp. 118-123). Fault detection, pump diagnosis, valve diagnosis, etc...

[0142] This is particularly advantageous because fluctuations in pump chamber pressure and flow into and out of the pump chamber also occur very rapidly. Thanks to the very fast flow sensor 106, 110, not only can malfunctions be detected, but normal pump operation can also be continuously monitored.

[0143] Fig. Figure 5 shows a first diagram 501, in which the pump chamber pressure (y-axis) is plotted against time (x-axis), a second diagram 502, in which the flow at the inlet-side flow sensor 106b, 110 is plotted against time, and a third diagram 503, in which the flow at the outlet-side flow sensor 106a is plotted against time. In a first time interval I, the pump 101 is in a suction stroke. In a second time interval II, the pump 101 is in a pumping stroke or pressure stroke.

[0144] Fig. Figure 5 shows, as an example, the time-dependent pressure profile of the pump chamber 501 and the flows 502, 503 through the pump valves 310, 311, and thus the flow sensors 106a, 106b, 110 for different conditions. These conditions represent a micropump 101 without a gas bubble (solid line) and a micropump 101 containing one or more gas bubbles (dashed line). The time-dependent flow rates measured by the two flow sensors 106, 110 are also shown.

[0145] This illustrates the situation when a voltage signal is applied to the piezoelectric element 108, 112, where the voltage rises and falls very rapidly. For example, if the electrical capacitance of the piezoelectric ceramic C piezo If the capacitance is 10 nF and the charging resistance (or the internal resistance of a battery) is 1 kOhm, then the electrical voltage builds up or falls with a time constant τ = R*C = 1 kOhm*10 nF = 10 microseconds. τel=RelCpiezo

[0146] Furthermore, pressure signals can propagate very quickly. This occurs at the speed of sound, approximately 300 m / s in air or 1000 m / s in liquids or solids. With a typical micropump thickness and length of 1 to 10 mm, the pressure signal spreads throughout the entire micropump 101 within a few microseconds.

[0147] The pressure signal is therefore almost as fast as the electrical signal, in any case much faster than the fluidic equalization processes.

[0148] These times are therefore very fast compared to the fluidic times in the millisecond range. Consequently, the negative pressure during the suction stroke and the positive pressure during the pressure stroke build up very quickly. During this short time, no significant compensating flow can pass through the microvalves 310 and 311. This explains the large pressure amplitude in the pump chamber immediately after switching the voltage on or off.

[0149] The pressure signals then polarize the respective valves 310 and 311 in the flow direction or blocking direction, the valve flaps open, and fluid can flow into or out of the pump chamber. This equalization process can also be approximately described by a time constant, where the fluidic flow resistances R fl the microvalves 310, 311 (during the suction stroke essentially the resistance of the inlet valve 311, during the pressure stroke that of the outlet valve 310, if there are no leakage rates) and the pump chamber R PK and the fluidic capacities of the drive diaphragm C M and a potential gas bubble in pump chamber C gas take effect: τfl=(Rfl+RPK)(CM+Cgas)

[0150] The presence of a gas bubble in the pump chamber represents a disturbance that manifests itself (depending on the size of the gas bubble) as a greater or lesser fluidic capacitance. This has two consequences for the transient signals: the amplitude is reduced, and the compensation process for the respective pump stroke is prolonged. This effect depends on the magnitude of the fluidic capacitance and thus on the size of a gas bubble. Therefore, the flow sensors 106 and 110 can not only detect the presence of a gas bubble, but also quantify its size.

[0151] As long as the pressure amplitudes are large enough to open the microvalves 310 and 311 when a gas bubble is present, the full stroke can still be completed, it just takes a little longer. However, it is clear that if the operating frequency f = 1 / T of the micropump 101 becomes sufficiently high, the delays caused by the gas bubble may prevent the pump stroke from being completed if the available time for the suction and pressure strokes becomes less than the necessary compensation processes.

[0152] This would mean that the pumped volume per cycle at this higher operating frequency is greater without a gas bubble than with one. Therefore, at high operating frequencies, the gas bubble alters the flow rate per pump cycle and thus the pumping rate. Both of these factors can be precisely detected by the flow sensors 106 and 110. The microdosing system 100 can thus not only measure the reduction in flow rate but also determine its cause, namely the entry of a gas bubble into the pump chamber.

[0153] In Fig. Figure 5 shows the case where the inlet valve 311 is leaking, and during the pressure stroke per unit of time only about 60% is conveyed in the correct direction, but 40% is returned through the leaking inlet valve 311.

[0154] The advantage of transient analysis is further illustrated by the following example: When micropump 101 is inactive and / or microvalves 310, 311 are closed, no flow should actually pass through the microdosing system 100. However, if the flow sensor 106, 110 displays a different value compared to the last calibration, this can have two causes: firstly, sensor 106, 110 may have drifted in the meantime, or a leakage rate may have developed in the microvalve 310, 311 (e.g., due to particles). In the case of the inactive micropump 101, the flow sensor 106, 110 cannot distinguish between these possible causes. However, if a leakage flow is detected by the transient measurement described above (i.e.,If the inlet-side flow sensor 110 is detected during the pressure stroke for the inlet valve 311, and the outlet-side flow sensor 106 is detected during the suction stroke for the outlet valve 310, then the above causes can be clearly distinguished: because the drift of the sensor 106, 110 occurs on a long time scale, a corresponding sensor pulse on the millisecond time scale can therefore be assigned to a leak.

[0155] A diagnostic routine can also detect if one of the valves 140a, 140b (NC, NO, DNC...) in series has a leak (e.g., due to particles). In this case, pump 101 is activated with valve 140a, 140b closed. If valve 140a, 140b is sealed, then no flow should pass through the corresponding flow sensor 106, 110 during the corresponding pump stroke (depending on whether valve 140a, 140b is located in the suction line or the pressure line). If the flow sensor 106, 110 nevertheless detects a transient signal, a leak in this valve 140a, 140b can be clearly identified.

[0156] Fig.Figure 4 shows a block diagram of a method according to the invention for metering a quantity of fluid to be dispensed by means of a micro-dosing system 100. The individual process steps, and in particular the shown process step 404 for calibrating and / or detecting disturbances of the micro-dosing system 100, can also be carried out in a different sequence than the one shown according to the invention.

[0157] In step 401, a micropump 101, which has an inlet 102 and an outlet 103, is provided.

[0158] In step 402, the fluid to be discharged 104, 105, 109 is drawn in through the inlet 102 of the micropump 101.

[0159] In step 403, a first flow sensor 106a, 106b arranged on the inlet side or outlet side is provided, wherein the flow sensor 106a, 106b has an opening 107a, 107b and a flow meter 108a, 108b.

[0160] In step 404, the microdosing system 101, 301 is calibrated and / or faults are detected.

[0161] In step 405, at least some of the aspirated fluid 104, 105, 109 is discharged from the outlet 103 of the micropump 101.

[0162] In step 406, the flow rate of the fluid passing through the opening 107a, 107b of the flow sensor 106a, 106b is determined.

[0163] Some of the advantages of the microdosing system 100, 300 described above with reference to the figures are listed again below for overview: • The two flow sensors 106, 110 monitor each other • Before the suction stroke: both flow sensors 106, 110 are "zeroed" • Suction stroke: ◯ The filling of the pump chamber 202 through the inlet-side valve 311 is measured with the inlet-side flow sensor 110. ◯ Simultaneously, the outlet-side flow sensor 106 measures possible leakage rates of the outlet-side valve 310 using the flow rate measuring device 108 ◯ By integrating the flow sensor signal from both flow sensors 106, 110, the stroke volume can be accurately determined. • After the suction stroke: The flow sensor 106, 110 is reset to zero. • Pressure stroke: ◯ The discharge of the stroke volume through the outlet-side valve 310 is measured with the outlet-side flow sensor 106. ◯ Simultaneously, the inlet-side flow sensor 110 measures possible leakage rates of the inlet-side valve 311 using the flow meter 112 ◯ By integrating the flow sensor signal from both flow sensors 106, 110, the stroke volume can be accurately determined again. ◯ Any volume stroke differences compared to the suction stroke measurement still indicate the measurement error • After the pressure stroke: Flow sensors 106, 110 are reset to zero.

[0164] Advantageously, this allows not only the pump rate to be measured, but also the function of the pump drive and both valves 310, 311 including leak rates to be permanently monitored.

[0165] A further advantage of the microdosing system 100, 300 according to the invention lies in the possibility of detecting an orifice blockage, i.e., a blockage of the respective opening 107, 111 of a flow sensor 106, 110. Such detection of an orifice blockage can be carried out by transient signal analysis.

[0166] In static flow, the flow sensor 106, 110 cannot distinguish whether the orifice or the opening 107, 111 is blocked. However, the transient, time-dependent signal at an opening 107, 111 of a flow sensor 106, 110 differs depending on whether the opening 107, 111 is blocked or not.

[0167] If the opening 107, 111 is not blocked, the pressure pulse generated by the micropump 101 will dissipate within a few milliseconds. However, if the opening 107, 111 is blocked, overpressure builds up, which cannot escape. This can be detected by signal analysis of the respective flow sensor 106, 110.

[0168] Although some aspects have been described in connection with a device, it is understood that these aspects also constitute a description of the corresponding process, so that a block or component of a device can also be understood as a corresponding process step or as a feature of a process step. Similarly, aspects described in connection with or as a process step also constitute a description of a corresponding block, detail, or feature of a corresponding device. Some or all of the process steps can be performed by (or using) a hardware apparatus, such as a time-resolved sample-and-hold data acquisition system, a microprocessor, a programmable computer, or an electronic circuit.In some embodiments, some or more of the most important process steps can be carried out by such an apparatus.

[0169] Depending on specific implementation requirements, embodiments of the invention can be implemented in hardware or in software. The implementation can be carried out using a digital storage medium, for example, a floppy disk, DVD, Blu-ray disc, CD, ROM, PROM, EPROM, EEPROM, FLASH memory, hard disk, or other magnetic or optical storage medium, on which electronically readable control signals are stored. These control signals can interact with, or interact with, a programmable computer system in such a way as to execute the respective method. Therefore, the digital storage medium can be computer-readable.

[0170] Some embodiments according to the invention therefore comprise a data carrier which has electronically readable control signals which are able to interact with a programmable computer system in such a way that one of the methods described herein is carried out.

[0171] In general, embodiments of the present invention can be implemented as a computer program product with a program code, wherein the program code is effective in carrying out one of the methods when the computer program product runs on a computer.

[0172] The program code can also be stored on a machine-readable medium, for example.

[0173] The time-resolved data acquisition of the flow sensors, the data processing, the control of the micropump, the generation of the necessary high voltage for the e.g. piezo- or electrostatically driven micropump and the control algorithms can, for example, be housed on an ASIC (application specific integrated circuit), which allows the entire microdosing system micropump, flow sensors, control and ASIC to be realized in the smallest possible installation space (e.g. 10x10x2 mm3).

[0174] Other embodiments include a computer program for carrying out one of the methods described herein, wherein the computer program is stored on a machine-readable medium. In other words, an embodiment of the method according to the invention is thus a computer program that includes program code for carrying out one of the methods described herein when the computer program is executed on a computer.

[0175] Another embodiment of the methods according to the invention is therefore a data carrier (or a digital storage medium or a computer-readable medium) on which the computer program for carrying out one of the methods described herein is recorded.

[0176] Another embodiment of the method according to the invention is thus a data stream or a sequence of signals that represents the computer program for carrying out one of the methods described herein. The data stream or sequence of signals can be configured, for example, to be transferred via a data communication connection, such as the Internet.

[0177] Another embodiment comprises a processing device, for example a computer or a programmable logic device, which is configured or adapted to perform one of the methods described herein.

[0178] Another embodiment comprises a computer on which the computer program for performing one of the procedures described herein is installed.

[0179] Another embodiment of the invention comprises a device or system designed to transmit a computer program for carrying out at least one of the methods described herein to a receiver. The transmission can be, for example, electronic or optical. The receiver can be, for example, a computer, a mobile device, a storage device, or a similar device. The device or system can, for example, include a file server for transmitting the computer program to the receiver.

[0180] In some embodiments, a programmable logic device (for example, a field-programmable gate array, an FPGA) can be used to perform some or all of the functionalities of the methods described herein. In some embodiments, a field-programmable gate array can interact with a microprocessor to perform one of the methods described herein. Generally, in some embodiments, the methods are performed by any hardware device. This can be general-purpose hardware such as a computer processor (CPU) or method-specific hardware such as an ASIC.

[0181] The embodiments described above merely illustrate the principles of the present invention. It is understood that modifications and variations of the arrangements and details described herein will be obvious to other people skilled in the art. Therefore, it is intended that the invention be limited only by the scope of protection set forth in the following claims and not by the specific details presented herein by way of description and explanation of the embodiments.

Claims

[1] Microdosing system (100, 300) for dosing a quantity of fluid to be dispensed, comprising: a micropump (101) having an inlet (102) and an outlet (103) and designed to draw in the fluid (104, 105, 109) to be discharged through the inlet (102) and to discharge at least part of the fluid (104, 105, 109) from the outlet (103), a first flow sensor (106a, 106b) arranged on the inlet or outlet side, which has an opening (107a, 107b) and a flow meter (108a, 108b), wherein the flow meter (108a, 108b) is configured to determine the flow rate of the fluid (104, 105) passing through this opening (107a, 107b), and means (113, 313) for calibrating and / or interfering detection of the microdosing system (100, 300), wherein the means (113, 313) for calibrating and / or detecting disturbances of the microdosing system (100, 300) comprise a control device (302) configured to detect an actual sensor signal of the first flow sensor (106a, 106b) when the micropump (101) is inactive, and to correct subsequent sensor signals of the first flow sensor (106a, 106b) based on this in order to counteract sensor drift of the first flow sensor (106a, 106b) and to calibrate the microdosing system (100, 300). [2] Microdosing system (100, 300) according to claim 1, wherein the control device (302) is configured to determine a correction value and to subtract this from the amount of the detected actual sensor signal of the first flow sensor (106a, 106b), wherein the obtained difference value forms a corrected starting point for the subsequent sensor signals of the first flow sensor (106a, 106b). [3] Microdosing system (100, 300) according to claim 2, wherein the amount of the correction value corresponds to the amount of the detected actual sensor signal of the first flow sensor (106a, 106b), or wherein the amount of the correction value corresponds to a range of the amount of the detected actual sensor signal plus a tolerance value of ±10% of the measured sensor signal or plus a tolerance value of ±20% of the measured sensor signal. [4] Microdosing system (100, 300) according to claim 2 or 3, wherein the control device (302) is configured to subtract the correction value from the amount of the previously detected actual sensor signal before performing a measurement of the first flow sensor (106a, 106b), or to first store the amount of the previously detected actual sensor signal as a correction value and only after performing a subsequent measurement of the first flow sensor (106a, 106b) to subtract it from the amount of the sensor signal measured in that measurement, in order to subtract the stored correction value as an offset from the measured value only after the measurement has been carried out. [5] Microdosing system (100, 300) according to one of the preceding claims, wherein the control device (302) is configured to detect the actual sensor signal of the first flow sensor (106a, 106b) and to correct subsequent sensor signals before any pump stroke or before each pump stroke. [6] Microdosing system (100, 300) according to one of the preceding claims, wherein the microdosing system (100, 300) comprises means configured to provide the same pressure on the inlet side as on the outlet side or a lower pressure than on the outlet side in order to prevent a free flow of the fluid (104, 105, 109) to be dispensed through the micropump (101). [7] Microdosing system (100, 300) according to one of the preceding claims, wherein the microdosing system (100, 300) has an inlet-side and / or outlet-side valve (140a, 140b), wherein the valve (140a, 140b) is an active normally closed valve and / or an active normally open valve and / or a valve with threshold pressure that is closed below a threshold pressure and / or a normally double closed microvalve and / or a safety valve. [8] Microdosing system (100, 300) according to one of the preceding claims, wherein the flow rate measuring means (108a, 108b) is configured as a differential pressure sensor configured to measure the pressure applied before the opening (107a, 107b) and the pressure applied after the opening (107a, 107b) and to determine the differential pressure, and wherein the control device (302) is configured to determine the flow rate Q of the fluid (104, 105) by means of an integration according to the formula V=∫t1t2Qdt to determine the fluid volume V of the fluid (104, 105) that has flowed through the flow meter (108a, 108b). [9] Microdosing system (100, 300) according to claim 8, wherein the control device (302) is configured to determine the stroke volume of the micropump (101) in the suction stroke by integrating the flow rate determined by means of a differential pressure sensor (108b) arranged on the inlet side, and to determine the stroke volume of the micropump (101) in the pressure stroke by integrating the flow rate determined by means of a differential pressure sensor (108a) arranged on the outlet side. [10] Microdosing system (100, 300) according to claim 9, wherein the control device (302) is configured to compare the stroke volumes determined in the suction stroke and in the pressure stroke and to determine volume stroke differences in order to detect a malfunction of the micropump (100, 300). [11] Microdosing system (100, 300) according to one of the preceding claims, wherein the microdosing system (100, 300) has a second flow sensor (110) having an opening (111) and a flow meter (112), wherein the flow meter (112) is configured to determine the flow rate of the fluid (104) passing through this opening (111), wherein the second flow sensor (110) is arranged on the inlet side and the first flow sensor (106) on the outlet side. [12] Microdosing system (100, 300) according to claim 11, wherein the means (113, 313) for calibrating and / or detecting disturbances of the microdosing system (100, 300) comprise a control device (302) configured to control the micropump (101) and the first outlet-side flow sensor (106) and the second inlet-side flow sensor (110) such that both the first and the second flow sensor (106, 110) determine the flow rate of the fluid (104, 105) flowing through the respective opening (107, 111) of the first and the second flow sensor (106, 110) when the micropump (101) draws in the fluid (104) to be dispensed, and wherein the control device (302) is further configured to control the flow rate of the fluid (104, 105) detected by the first flow sensor (106) to compare the flow rate determined by the second flow sensor (110) so that the means for calibration and / or fault detection (113,313) can detect an outlet-side leakage flow at the outlet-side valve (310) during the suction stroke of the micropump (101). [13] Microdosing system (100, 300) according to claim 11 or 12, wherein the means (113, 313) for calibrating and / or detecting disturbances of the microdosing system (100, 300) comprise a control device (302) configured to control the micropump (101) and the first outlet-side flow sensor (106) and the second inlet-side flow sensor (110) such that the first and second flow sensors (106, 110) determine the flow rate of the fluid (104, 105) flowing through the respective opening (107, 111) of the first and second flow sensors (106, 110) when the micropump (101) dispenses the fluid (105) to be dispensed from the outlet (103), and wherein the control device (302) is further configured to to compare the flow rate determined by the first flow sensor (106) and the flow rate determined by the second flow sensor (110) so that the means for calibration and / or disturbance detection (113,313) can detect an inlet-side leakage flow at the inlet-side valve (311) during the pressure stroke of the micropump (101). [14] Microdosing system (100, 300) according to one of the preceding claims, wherein the micropump (101) has a pump chamber (202) arranged between the inlet (102) and the outlet (103), a diaphragm (222) arranged at least partially in the region of the pump chamber (202) and a diaphragm deflection means (221), wherein the diaphragm deflection means (221) is configured to deflect the diaphragm (222) such that the volume of the pump chamber (202) is increased to inflate the fluid (104, 105, 109) to be dispensed, and the volume of the pump chamber (202) is decreased to dispense the fluid (104, 105, 109). [15] Microdosing system (100, 300) according to claim 14, wherein the membrane deflection means (221) is a piezoelectric element configured to deflect the membrane (222) depending on the voltage applied to the piezoelectric element (221). [16] Microdosing system (100, 300) according to one of the preceding claims, wherein the control device (302) is configured to compare the flow rate determined by means of the first flow sensor (106) with a predetermined flow rate comparison value, and to control the micropump (101) until the flow rate determined by means of the first flow sensor (106) is equal to or greater than the predetermined flow rate comparison value. [17] Microdosing system (100, 300) according to one of the preceding claims, wherein fluid connecting means are arranged between the micropump (101) and the first and / or second flow sensor (106, 110), the volume of which remains constant when the operating pressure of the micropump (101) changes. [18] Microdosing system (100, 300) according to one of the preceding claims, wherein the flow sensor (106, 110) is arranged directly on a bottom surface of the micropump (101) at the outlet (103) or inlet (102) immediately before or after the micropump (101). [19] Method for metering a quantity of fluid to be dispensed using a micro-dosing system (100, 300), comprising: Providing a micropump (101) having an inlet (102) and an outlet (103), Suction of the fluid to be discharged (104, 105, 109) through the inlet (102) of the micropump (101), Providing a first flow sensor (106a, 106b) arranged on the inlet or outlet side, which has an opening (107a, 107b) and a flow meter (108a, 108b), Discharging at least part of the aspirated fluid (104, 105, 109) from the outlet (103) of the micropump (101), Determining the flow rate of the fluid (104, 105, 109) passing through the opening (107a, 107b) of the flow sensor (106a, 106b), and Calibrating and / or detecting interference of the microdosing system (100, 300) to counteract sensor drift of the first flow sensor (106a, 106b) and to calibrate the microdosing system (100, 300), wherein the step of calibrating and / or interfering detection of the microdosing system (100, 300) comprises the following steps: Acquiring an actual sensor signal from the first flow sensor (106a, 106b) when the micropump (101) is inactive, and Correcting subsequent sensor signals of the first flow sensor (106a, 106b) based on the acquired actual sensor signal. [20] Method according to claim 19, wherein the step of calibrating and / or interfering detection of the microdosing system (100, 300) comprises the following steps: Determining a correction value and subtracting the correction value from the magnitude of the recorded actual sensor signal of the first flow sensor (106a, 106b) to obtain a difference value, and Using the obtained difference value as a corrected starting point for subsequent sensor signals from the first flow sensor (106a, 106b). [21] Method according to claim 20, wherein the step of determining the correction value comprises the following step: Determining a correction value whose amount corresponds to the amount of the recorded actual sensor signal of the first flow sensor (106a, 106b), or Determine a correction value whose magnitude lies within a range of the magnitude of the detected actual sensor signal of the first flow sensor (106a, 106b) plus a tolerance value of ±10% of the detected actual sensor signal of the first flow sensor (106a, 106b) or a tolerance value of ±20% of the detected actual sensor signal of the first flow sensor (106a, 106b). [22] Method according to any one of claims 19 to 21, further comprising ensuring that when the micropump (101) is inactive, there is no free flow of the fluid (104, 105, 109) to be discharged from the inlet (102) to the outlet (103). [23] Method according to claim 22, comprising providing an inlet-side pressure and an outlet-side pressure, wherein the inlet-side pressure is equal to or less than the outlet-side pressure. [24] Method according to claim 22 or 23, comprising providing an inlet-side and / or outlet-side valve (140a, 140b), wherein the valve (140a, 140b) is an active normally closed valve and / or an active normally open valve and / or a valve with a threshold pressure that is closed below a threshold pressure and / or a normally double closed microvalve and / or a safety valve. [25] Method according to any one of claims 19 to 24, further comprising the following steps: Suction of the fluid to be discharged (104) through the inlet (102), Measuring the flow rate of the fluid flowing through the opening (111) of a second inlet-side flow sensor (110) and measuring the flow rate of the fluid flowing through the opening (107) of the first outlet-side flow sensor (106), and Comparing the two measured flow rates. [26] Method according to any one of claims 19 to 25, further comprising the following steps: Discharge of the fluid to be discharged (104) through the outlet (103), Measuring the flow rate of the fluid flowing through the opening (111) of a second inlet-side flow sensor (110) and measuring the flow rate of the fluid flowing through the opening (107) of the first outlet-side flow sensor (106), and Comparing the two measured flow rates. [27] Method according to one of claims 25 or 26 further comprising the following steps: Suction of the fluid to be discharged (104) through the inlet (102) and measurement of the flow rate of the fluid flowing through the opening (111) of the second inlet-side flow sensor (110), Dispensing the fluid to be dispensed (104) through the outlet (103) and measuring the flow rate of the fluid flowing through the opening (107) of the first outlet-side flow sensor (106), and Comparing the two measured flow rates.

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