Diaphragm pump drive

Abstract

The present invention relates to a diaphragm pump drive for driving the pump chamber of a diaphragm pump, comprising at least one pressure sensor and a control unit, wherein the control unit controls the diaphragm pump drive and evaluates values measured by the pressure sensor; the control unit is designed to determine a basic compressibility value of the diaphragm pump; and the basic compressibility value is determined according to at least one and preferably more measurements during which a liquid is present in the pump chamber.

Description

[0001] Diaphragm pump drive

[0002] The present invention relates to a diaphragm pump drive.

[0003] Diaphragm pumps are often used in medical technology, particularly in dialysis technology, for pumping medical fluids such as dialysate or blood. A diaphragm pump typically has a pumping chamber enclosed by a diaphragm. By pushing the diaphragm into the pumping chamber, fluid can be expelled from the pumping chamber, and by pulling the diaphragm out of the pumping chamber, fluid can be drawn into the pumping chamber. In conjunction with appropriate valves, this allows fluid to be pumped through the pumping chamber.

[0004] The pump chamber is usually arranged in a disposable device, for example a pump cassette, which is coupled to a diaphragm pump drive. The diaphragm pump drive usually has a drive chamber which is also closed off by a diaphragm. The pump chamber and drive chamber are then coupled to one another in such a way that the diaphragm of the pump chamber follows the movement of the diaphragm of the drive chamber. In a piston diaphragm pump, the drive chamber is hydraulically connected to a piston-cylinder unit. By moving the piston, hydraulic fluid can be pushed into or sucked out of the drive chamber, which results in a corresponding movement of the diaphragm of the drive chamber. Such an arrangement has the advantage that the pump pressure can be controlled by appropriately controlling or regulating the pressure in the hydraulic part.Furthermore, diaphragm pumps enable easy balancing of the pumped liquids, since the volume change of the pump chamber and thus the liquid displacement during a pump stroke corresponds to the volume change of the control chamber (with the opposite sign), whereby this can be precisely determined via the position of the piston of the piston-cylinder unit pressure.

[0005] However, sources of error can arise here: Firstly, air accumulation in the pump chamber can lead to the volume of fluid pumped through the pump chamber not exactly corresponding to the volume change in the drive chamber. Furthermore, due to a certain basic compressibility of the diaphragm pump, the volume change in the drive chamber can deviate from the volume change caused by the movement of the piston in the piston-cylinder unit. In particular, air accumulating in the hydraulic fluid can lead to a certain compressibility of the hydraulic system. Furthermore, hoses connecting the piston-cylinder unit to the drive chamber, for example, can exhibit a certain degree of flexibility and therefore expand under increased pressure. Other drive mechanisms can also have a certain basic compressibility, which influences the values ​​recorded for balancing.Further influences arise from the disposable and its coupling.

[0006] DE 19919572 A1 discloses a method for determining the air content in the liquid pumped through a pump chamber. For this purpose, the pump chamber is first filled gravimetrically, and the resulting outlet pressure is measured. The shut-off valves of the pump chamber are then closed, resulting in a liquid volume enclosed within it. With the shut-off valves closed, the piston-cylinder unit is then actuated to apply a predetermined final pressure to the enclosed liquid volume. The volume change of the liquid volume in the pump chamber associated with this pressure change is directly related to the proportion of air in the enclosed liquid volume. Therefore, the air content can be determined based on the volume change generated by the pressure difference, which is determined by the piston movement.In DE 19919572 A1, the influence of the basic compressibility of the diaphragm pump drive, which is referred to there as system compressibility, is taken into account by a fixed constant. However, the basic compressibility can change, for example, due to the accumulation of air in the hydraulic fluid during pump operation, which is not taken into account in DE 19919572 A1.

[0007] DE 102011105824 B3 therefore discloses a method for determining the basic or system compressibility of a diaphragm pump drive. The system compressibility of the gas-filled pump device is determined by adjusting a starting and final pressure with a pressure sensor and recording the corresponding pump positions or pressure sensor values. Based on these pairs of values, the spring constant is determined, which is equated with the basic or system compressibility.

[0008] Document DE 10 2014 013 152 A1 describes a method for determining a base or system compressibility value of a medical diaphragm pump drive. During the determination of the base or system compressibility value, the diaphragm of the diaphragm pump drive rests against a rigid surface, for example, the rear wall of the pump chamber or the drive chamber. In this case, the pump chamber is empty or not even connected.

[0009] The object of the present invention is to provide an improved diaphragm pump drive.

[0010] This object is achieved by a diaphragm pump drive according to claims 1 and 2. Preferred embodiments of the present invention are the subject of the dependent claims. According to a first aspect, the present invention comprises a diaphragm pump drive for driving the pump chamber of a diaphragm pump, having at least one pressure sensor and a controller, wherein the controller controls the diaphragm pump drive and evaluates measured values ​​from the pressure sensor, wherein the controller is configured to determine a basic compressibility value of the diaphragm pump. It is provided that the basic compressibility value is determined based on at least one and preferably several measurements in which liquid is present in the pump chamber.

[0011] The present invention thus allows the basic compressibility to be determined after upgrading the diaphragm pump and / or during ongoing operation. Furthermore, the present invention allows the basic compressibility to be determined more precisely, as the flexibility of the diaphragm pump, which is due to the pump chamber itself, is also taken into account. Furthermore, the present invention takes into account that the basic compressibility has different effects on varying chamber volumes. Since the measurement is performed with liquid in the pump chamber, the inventive procedure better represents the basic compressibility over the diaphragm pump's operating cycle.

[0012] Furthermore, in cases where the pump chamber is designed as a component of a disposable and is coupled to the diaphragm pump drive, the flexibility of the disposable and its coupling is also taken into account.

[0013] According to a second aspect, the present invention comprises a device for driving the pump chamber of a diaphragm pump, comprising at least one pressure sensor and a controller, wherein the controller controls the diaphragm pump drive and evaluates measured values ​​from the pressure sensor, wherein the controller is configured to determine a basic compressibility value of the diaphragm pump and / or an air content in the pumped liquid. It is provided that the determination of the basic compressibility value and / or the air content in the pumped liquid is carried out on the basis of at least two measurements, between which the chamber volume of the pump chamber was changed by suction and / or pumping out liquid.

[0014] This approach also takes into account the fact that the basic compressibility has a different impact on varying chamber volumes. Since at least two measurements are taken, between which the chamber volume of the pumping chamber was changed by suction and / or pumping of fluid, the inventive approach better represents the basic compressibility over the working cycle of the diaphragm pump.

[0015] The diaphragm pump drives according to the first and second aspects are each independently subject of the present invention. However, in a preferred embodiment, the two aspects are combined.

[0016] Preferred embodiments of both the first and second aspects are described in more detail below.

[0017] The basic compressibility value according to the invention can be any parameter by which a compressibility property or the compliance of the diaphragm pump and / or the diaphragm pump drive during pressure changes can be characterized and preferably quantified.

[0018] According to a possible embodiment, it is provided that in each of the measurements a total compressibility value of the overall system formed by the diaphragm pump and the liquid in the pump chamber is determined.

[0019] According to one possible embodiment, the base compressibility value of the diaphragm pump and / or the air fraction is determined by means of a regression analysis of the total compressibility values, in particular by means of a regression analysis of the total compressibility values ​​as a function of the pump chamber volume and / or by linear regression. According to one possible embodiment, the total compressibility value is determined as the value resulting from the regression analysis for a pump chamber volume of zero.

[0020] According to a possible embodiment, it is provided that the air fraction is determined on the basis of a change in the total compressibility values ​​as a function of the chamber volume of the pumping chamber and in particular from a slope of a regression line.

[0021] According to a possible embodiment, it is provided that the basic compressibility value is determined and used to determine the air content of the liquid to be pumped in a subsequent measurement, in particular in a later pumping cycle, wherein the air content is preferably determined based on only one measurement of the total compressibility value of the overall system formed by the diaphragm pump and the liquid in the pumping chamber, in particular by correcting the measured value by the basic compressibility value.

[0022] According to a possible embodiment, it is provided that the basic compressibility value is initially determined, in particular within the framework of an initial test routine.

[0023] According to one possible embodiment, the basic compressibility value and / or the air content is determined during operation.

[0024] According to a possible embodiment, it is provided that the basic compressibility value and / or the air fraction is determined repeatedly, and in particular is determined in each pumping cycle.

[0025] According to one possible embodiment, the diaphragm pump drive comprises at least one valve drive for driving at least one valve to control the fluid flow into and / or out of the pump chamber, wherein the controller of the diaphragm pump drive controls the at least one valve drive. According to one possible embodiment, the controller is configured to control the at least one valve drive to perform the at least one and preferably several measurements for determining the basic compressibility value and / or the air fraction according to one of the preceding claims.

[0026] According to one possible embodiment, the diaphragm pump drive comprises a coupling surface to which a pump cassette can be coupled, which comprises the pump chamber and preferably one or more valves.

[0027] According to a possible embodiment, it is provided that the diaphragm pump drive has a drive chamber which is closed off by a diaphragm, wherein the diaphragm is deflected outwards out of the drive chamber by overpressure in the drive chamber and inwards into the drive chamber by negative pressure in the drive chamber.

[0028] According to one possible embodiment, the pressure sensor determines the pressure in the drive chamber.

[0029] According to one possible embodiment, the pressure in the drive chamber is generated via a piston-cylinder unit connected to the drive chamber.

[0030] According to one possible embodiment, it is provided that a length sensor is provided which detects the position of the piston, and / or that the transmission of the pressure to the membrane preferably takes place hydraulically, wherein preferably the piston-cylinder unit and the drive chamber are filled with hydraulic fluid.

[0031] According to one possible embodiment, it is provided that the controller is configured to approach a first and a second pressure level by controlling the diaphragm pump drive with the pump chamber closed and to record associated operating parameter values ​​of the diaphragm pump drive and / or to approach a first and a second operating parameter value by controlling the diaphragm pump drive with the pump chamber closed and to record associated pressure levels in order to carry out a measurement.

[0032] According to one possible embodiment, it is provided that the total compressibility value is determined on the basis of the operating parameter values ​​and / or pressure levels, wherein the operating parameter values ​​are preferably position values ​​of the diaphragm pump drive.

[0033] In one possible embodiment of the present invention, the controller is configured to approach a first and a second pressure level by controlling the diaphragm pump drive with the pump chamber closed in order to carry out a measurement and to record associated operating parameter values ​​of the diaphragm pump drive.

[0034] To access the first and second pressure levels, the diaphragm pump drive is preferably operated until the pressure of the diaphragm pump and / or the diaphragm pump drive reaches the first pressure level. The first operating parameter value of the diaphragm pump drive is then determined. The diaphragm pump drive is then operated until the pressure of the diaphragm pump and / or the diaphragm pump drive reaches the second pressure level, and then the second operating parameter value is determined. The pressure of the diaphragm pump drive and / or the diaphragm pump can be measured via the pressure sensor.

[0035] The first and second pressure levels can be predefined pressure levels. In particular, these can be stored in a control system of the diaphragm pump drive.

[0036] In one possible embodiment of the present invention, the controller is configured to perform a measurement by controlling the diaphragm pump drive with the pump chamber closed and to detect the associated pressure levels. The first and second operating parameter values ​​can be predefined values. In particular, they can be stored in a controller of the diaphragm pump drive.

[0037] The operating parameter can be determined using a corresponding operating parameter sensor, such as a position and / or motion sensor. The operating parameter values ​​are preferably position values ​​of the diaphragm pump drive.

[0038] Preferably, the overall compressibility value is determined based on the operating parameter values ​​and / or pressure levels.

[0039] The present invention further comprises a medical device, in particular a blood treatment machine, in particular a dialysis machine, in particular a peritoneal dialysis machine, with a membrane pump drive according to the invention.

[0040] In particular, the medical device has a pump cassette holder and / or an air cushion for pressing the pump cassette against a coupling surface of the diaphragm pump drive. Preferably, the control of the diaphragm pump drive is integrated into the control of the medical device, in particular the blood treatment machine.

[0041] Preferred embodiments of the present invention will now be described in more detail with reference to figures and exemplary embodiments:

[0042] Showing:

[0043] Fig. 1 : a schematic representation of a diaphragm pump drive according to the invention with coupled pump chamber,

[0044] Fig. 2: a section through the coupling area of ​​a diaphragm pump drive according to the invention with a coupled pump cassette, and Fig. 3: an embodiment of a pump cassette as it can be coupled to a diaphragm pump drive according to the invention, and

[0045] Fig. 4 is a diagram in which several measured values ​​of the total compressibility are shown as a function of the pump chamber volume, to explain the present invention.

[0046] Fig. 1 shows an embodiment of a diaphragm pump drive 30 according to the invention for pumping a liquid through the pump chamber 4.

[0047] The diaphragm pump drive has a drive chamber 1, on which a flexible diaphragm 2 is arranged. The flexible diaphragm 2 is arranged in a coupling surface 3 of the diaphragm pump drive, so that a diaphragm of the pump chamber 4 (not visible in Fig. 1) can be coupled to the diaphragm 2 of the drive chamber in such a way that it follows the movements of the diaphragm 2 of the drive chamber. By moving the diaphragm 2 out of or into the drive chamber 1, the volume of the pump chamber 4 can therefore be changed. By appropriately switching valves (not shown in detail in Fig. 1), which control the inflow and outflow to the pump chamber 4, fluid can be pumped by moving the diaphragm 2 with the pump chamber 4.

[0048] The pump chamber 4 is typically part of a pump cassette (not shown in detail in Fig. 1), which is preferably a disposable device that can be coupled to the diaphragm pump drive. The pump chamber is typically formed by a correspondingly shaped hard part of the pump cassette, which is covered by a flexible film forming the diaphragm of the pump chamber.

[0049] However, the present invention could also be used in the same way in diaphragm pumps in which the drive chamber and the pump chamber are firmly connected to one another or integrated into a common pumping device. The exemplary embodiment shown in Fig. 1 is a piston diaphragm pump having a piston-cylinder unit 7 which is hydraulically connected to the drive chamber 6 via the hydraulic line 12. The piston-cylinder unit 7 is driven by a drive 10 which acts on the piston 8 of the piston-cylinder unit 7 and moves it in the cylinder 9. The distance traveled by the piston 8 in the cylinder 9 is detected or measured by a length sensor 11 assigned to the piston-cylinder unit 7.

[0050] The pressure side 25 of the piston-cylinder unit 7 is fluidly connected to the drive chamber 1 via the fluid line 12, wherein the pressure side 25, the fluid line 12, and the drive chamber 1 are filled with hydraulic fluid. As a result, the actuating movement of the piston 8 is transmitted to the diaphragm 2 of the drive chamber 1. Therefore, with a corresponding change in the hydraulic volume of the piston-cylinder unit 7, the diaphragm 2 of the drive chamber 1 is convexly curved outward or drawn concavely into the interior of the drive chamber by the movement of the piston 8.

[0051] The volume change of the drive chamber 1 required to pump fluid into the pump chamber 4 is accordingly brought about by actuating the piston-cylinder unit 7. By actuating the piston 8, the hydraulic fluid is forced into or sucked out of the drive chamber 1. This actuates the diaphragm 2, whose movement is transmitted to the pump chamber 5, changing its volume.

[0052] The diaphragm pump drive further comprises a pressure sensor 13, via which the pressure of the hydraulic fluid in the hydraulic system, and thus the pressure in the drive chamber 1, can be measured. The pressure prevailing in the drive chamber 1 corresponds - except for any counterpressure of the diaphragm 2 - to the counterpressure prevailing in the pump chamber 4, so that the pressure in the pump chamber 4 can also be determined simultaneously via the pressure sensor 13. The diaphragm pump drive further comprises a control unit (not shown), which is connected to the length sensor 11 and the pressure sensor 13 and evaluates the measurement signals. Furthermore, the control unit controls the drive 10 of the diaphragm pump drive and the valves for controlling the fluid flow in and out of the pump chamber 4. For this purpose, the diaphragm pump drive preferably comprises valve actuators, which act on valves that are preferably also integrated into the pump cassette.

[0053] Such a piston diaphragm pump has the advantage that it pumps liquid with very high precision, whereby the total pumped quantity can be precisely balanced, since the pump volume corresponds to the stroke volume of the piston-cylinder unit 7 and can be precisely measured by the length sensor 11.

[0054] The mechanical structure of an embodiment of a diaphragm pump drive according to the invention, to which a pump cassette can be coupled, is shown in more detail in Fig. 2. The diaphragm pump drive has a machine block 20, on which the coupling surface 3 for coupling the pump cassette 14 is arranged. The drive chamber 1, provided with the flexible diaphragm 2, is embedded in the coupling surface 3 and is hydraulically connected to the piston-cylinder unit 7 (not shown here) via the hydraulic line 12.

[0055] The pump cassette 14 is inserted into a pump cassette receptacle 15 for coupling to the coupling surface 3, so that the rear side of the pump cassette rests against a receiving surface of the pump cassette receptacle 15. The receiving surface has a corresponding dome-shaped recess in the area of ​​the pump chamber 4, which is designed as a bulge on the rear side of the pump cassette.

[0056] After inserting the cassette 14, the cassette holder 15 is pressed against the coupling surface 3 by an air cushion 18 arranged at the rear, which in turn is supported on a device wall 17. For this purpose, the air cushion is subjected to an appropriate operating pressure, which can be, for example, between 1,500 and 2,500 mbar.

[0057] In the exemplary embodiment, the pump cassette holder 15 is designed as a drawer that can be moved in and out in direction 21 to insert a cassette. Furthermore, the machine block 20 can be placed on the pump cassette 14 in the direction of movement 22. After the drawer 15 is pushed in and the machine block 20 is placed on it, the air cushion 18 is then pressurized to ensure a secure coupling of the pump cassette 14 to the coupling surface 3.

[0058] As an alternative to the design shown in Fig. 2, the pump cassette holder 15 could also be designed, for example, as a door that is opened to insert the pump cassette 14 and closed to apply the pump cassette to the coupling surface. In this case, the air cushion 18 would be integrated into the door.

[0059] Fig. 3 shows an embodiment of a pump cassette 14 having two pump chambers 4 and 4'. The pump cassette consists of a hard part in which the fluid-carrying channels and the pump chambers are embedded, and is covered by a flexible film toward the coupling surface. The pump cassette includes, among other things, valves 23 and 24, via which the fluid flow into or out of the pump chambers 4 and 4' can be controlled. The valves are also actuated by actuators arranged in the machine block 20.

[0060] In one possible embodiment, the control of the diaphragm pump drive has a function that allows the air content in the fluid pumped by the diaphragm pump to be determined. This function can prevent air bubbles present in the pump chamber 4 from distorting the balance of the fluid pumped through the pump chamber 4.

[0061] To determine the air content or air quantity, a measuring phase can be provided, which can be inserted between the pumping process and each stroke. First, fluid is sucked into the pumping chamber 4 by moving the diaphragm 2, as is usual in the pumping process. The shut-off valves of the pumping chamber 4 are then closed, resulting in a sealed fluid volume, and a first, predetermined pressure level p is achieved by actuating the drive 10. a and the corresponding position of the piston 8 is determined. Then, by actuating the drive 10, a second pressure level p eapproached, and also determines the corresponding position of piston 8. If the liquid enclosed in the pumping chamber 4 contains a certain amount of gas, this gas is compressed by the increase in pressure, which corresponds to a corresponding change in the volume of the pumping chamber 4. This volume difference can be determined by the positions of piston 9 at the initial and final pressure.

[0062] From the values ​​thus obtained, the control calculates the amount of air contained in the pump chamber, ie the air volume V contained therein a t at atmospheric pressure. For this purpose, the control is based on the Boyle-Mariotte law, which, for an isothermal change of state, i.e., neglecting a temperature change, states: px V = constant.

[0063] Based on this, different states of the measurement phase can be equated:

[0064] Vat X Pat = Va X Pa = Ve X p e .

[0065] Taking into account the relationship that the differential volume Vdiff is determined by the difference between the initial volume and the final volume, i.e. Vdiff = V a - V e , the actual gas volume at atmospheric pressure V a t can be obtained:

[0066] Depending on the specific pumping process used, it must be taken into account in this formula that the pressure measured on the hydraulic side of the diaphragm pump via the pressure sensor 13 may not exactly correspond to the pressure in the pump chamber 4, but deviates from this pressure by a certain value due to the residual stress of the diaphragm 2.

[0067] In a first variant of the method, however, the air fraction can be determined with the membrane 2 not deflected, so that the influence of the membrane is negligible. In a second variant, the output pressure p aon the other hand, a differential pressure p due to the membrane m em between the hydraulic side and the pump side can be corrected. This can be stored, for example, in the control system. This makes it possible to determine the air content while the diaphragm 2 is pulled very far or completely into the drive chamber 1, so that the entire pump volume is utilized. If necessary, the differential pressure p attributable to the diaphragm can be m em between the hydraulic side and the pump side must be determined during the setup phase. Depending on the relationship between the pressures on the hydraulic side and the differential pressure p attributable to the diaphragm m em and the required accuracy, the differential pressure pmem can also be neglected.

[0068] The volume difference used in the above formula is determined by the pressure level p a to the pressure level p edistance traveled by the piston Sdirr and its area AK.

[0069] However, it must be taken into account that the movement of the piston 8 during the pressure change of p a after p e is not exclusively due to the air volume in the pump chamber 4. This is because the diaphragm pump drive and the pump chamber itself also exhibit a certain degree of flexibility or basic compressibility under pressure changes. Factors here include, in particular, the air that can accumulate in the hydraulic system and a certain degree of flexibility in the hydraulic line 12. Therefore, the piston 8 would be displaced by a pressure change of p a on p e Even if there were no air at all in the pump chamber 4 and it were therefore incompressible, it would move a certain distance So solely due to this basic compressibility.

[0070] The actual volume V at of the air contained in the pumping chamber 4 is thus obtained, taking into account the basic compressibility value So characterizing the basic compressibility, as:

[0071] In one possible embodiment, the control of the diaphragm pump drive according to the invention has a function by which the basic compressibility value So can be determined. This function is used in particular with a diaphragm pump as described above. However, the function can also be used independently of the specific design of the diaphragm pump described above.

[0072] The relevant embodiment of the present invention is based on the following considerations, which are particularly relevant for the use of the membrane pump drive in medical applications such as peritoneal dialysis, but are also generally applicable to membrane pump drives.

[0073] The administration of fluid using a diaphragm pump places the following demands on this process: The administered amount must meet a specified dosing accuracy. The fluid may only be mixed with air to a certain degree. The fluid can be pumped, for example, using one or two piston diaphragm pumps operating in parallel, such as those described above. The piston diaphragm pumps are moved by motors, and the pressures and positions are recorded using suitable sensors.

[0074] This arrangement makes it possible, as described above, to determine the compressibility of the enclosed fluid of a piston stroke using two pressure levels.

[0075] The determination of the air content of the liquid can be derived from the measured compressibility.

[0076] The actually measured total compressibility is composed of various factors: compressibility of the solution in the pump chamber and device properties.

[0077] The device properties are derived from the components involved in the pumping system. These include

[0078] - the remaining air in the hydraulic oil

[0079] - the remaining air between the pump membrane and the set foil

[0080] - the movement of the counter bearing (drawer)

[0081] - the hydraulic hoses expanding under pressure

[0082] These factors form the basic compressibility of the system and negatively impact the accurate determination of the air content of the fluid to be pumped. It should also be considered that the basic compressibility has varying effects on varying chamber volumes.

[0083] The present invention aims to incorporate these effects into the calculation. The following approaches, some of which are already known, are conceivable: a) Introducing a device constant for the entire series. b) Determining a compensation factor for an interval. c) Compensating the device properties by differential measurement within a chamber stroke. d) Combining approaches a), b), and c) to achieve greater system reliability.

[0084] These approaches are described below: a) The basic compressibility arises from device properties, which may be design-related. These device properties could be determined once for the series devices as a device constant. This device constant could be applicable to all devices.

[0085] The advantages of this state-of-the-art method are that a teach-in process within the machine is not necessary and no measurement errors occur. The disadvantage, however, is that the factor must be selected conservatively, otherwise overcompensation occurs, and in order to include all series variations, the method would fail to detect air content in the solution.

[0086] The present invention therefore takes a different approach and therefore comprises the embodiments described below: b) Determination of a compensation factor by a learning process:

[0087] The following procedure is followed:

[0088] Step 1: The pump chamber is filled with fluid. Step 2: The total compressibility is determined.

[0089] Step 3: The chamber volume is reduced by forcing fluid out of the pump chamber.

[0090] Step 4: Steps 2 and 3 are repeated several times.

[0091] Step 5: The basic compressibility is calculated from the total compressibility of steps 2 to 4.

[0092] The determination of the basic compressibility is most accurate when performed at the operating point or with the working fluid. However, a determination at the zero point is also conceivable.

[0093] The determination of the total compressibility is preferably carried out as already described above with regard to the function for determining the air content, ie in particular by approaching two pressure levels with the pump chamber volume closed and determining the corresponding pump positions.

[0094] The proportion of air bound in the liquid behaves deterministically. This fact allows the basic compressibility to be determined from at least two measurements of the total compressibility with different chamber volumes.

[0095] As shown in Fig. 4, the basic compressibility of the device can be determined from a regression line of the measurement results at the intersection point of the Y-axis and is referred to as dead volume, see area G in Fig. 4. The upper area L is the compressibility of the solution at measurement point 1.

[0096] Through this multiple measurement with different chamber volumes, the result of the determination can be verified.

[0097] The inventive procedure allows, on the one hand, the direct determination of the air fraction, already corrected for the base compressibility, from the slope of the resulting regression line or the range L above the intersection with the Y-axis. On the other hand, the base compressibility can be determined and used to correct the conventionally determined air fraction in a method as described above.

[0098] The determination of the baseline compressibility can be carried out using the disposable device and the dialysis solution during treatment and during each pump stroke.

[0099] The measurements can be performed multiple times with different chamber volumes and the compressibility can be extrapolated.

[0100] The advantages of this approach are the following:

[0101] ■ Individual determination of the factor for each device and each disposable item.

[0102] ■ The inclusion of series variation places lower demands on the device components and their tolerances.

[0103] ■ A more precise balancing and dosing of the dialysis solution can be carried out.

[0104] ■ Leaks in the disposable item, in the connections or in the pump hydraulics can be detected and quantified in each pump stroke.

[0105] This increases patient safety.

[0106] A disadvantage to consider is that the dosing inaccuracy or the air content of the dialysis solution depends on the reliability of the learning process. c) Compensation of the device properties by differential measurement within a chamber stroke

[0107] Procedure:

[0108] Step 1: The pump chamber is filled with liquid.

[0109] Step 2: The total compressibility is determined.

[0110] Step 3: The chamber volume is reduced by forcing fluid out of the pump chamber.

[0111] Step 4: Steps 2 and 3 are repeated several times. Step 5: The base compressibility is calculated from the total compressibility of steps 2 to 4.

[0112] The drain can be generated when emptying the chamber (as described in steps 1-5) or when filling the chamber by swapping the liquid volumes.

[0113] The advantage of this design lies in the individual determination of the device properties for each device, each disposable item and at each point in the treatment, as well as in the fact that the inclusion of series variation places lower demands on the device components and their tolerances.

[0114] A disadvantage of this approach, however, is that the multiple measurements of compressibility are time-consuming and reduce the device performance data.

[0115] Regardless of the variant used according to the invention, the following advantages arise: a) Less waste, since the air volume limits are now related to the solution. Small chambers are no longer overestimated. b) Better dosing accuracy. c) Since the air detection result no longer depends on the chamber size, a better balance is achieved.

[0116] The basic compressibility value determined according to the invention can therefore, as described above, be used to determine the air volume of the pumped medical fluid. It allows for a more precise balancing of the fluids moved by the diaphragm pump, since the air volume in the pumped fluids can be determined more precisely.

[0117] Determining the base compressibility value can also be used to verify the quality of the hydraulic system's degassing. For example, degassing of the hydraulic system can be initiated or indicated as soon as the base compressibility value exceeds a certain threshold.

[0118] The diaphragm pump drive according to the invention is preferably used in a blood treatment device for pumping medical fluids, in particular for pumping blood or dialysate. The diaphragm pump drive according to the invention is particularly preferably used in a dialysis machine, wherein the diaphragm pump is used for pumping the dialysate into the patient's abdominal cavity or withdrawing the dialysate from the patient's abdominal cavity.

Claims

Diaphragm pump drive for driving the pump chamber of a diaphragm pump, comprising at least one pressure sensor and a controller, wherein the controller controls the diaphragm pump drive and evaluates measured values ​​from the pressure sensor, wherein the controller is configured to determine a basic compressibility value of the diaphragm pump, characterized in that the determination of the basic compressibility value is based on at least one and preferably several measurements in which liquid is present in the pump chamber. Diaphragm pump drive, in particular diaphragm pump drive according to claim 1, for driving the pump chamber of a diaphragm pump, comprising at least one pressure sensor and a controller, wherein the controller controls the diaphragm pump drive and evaluates measured values ​​from the pressure sensor, wherein the controller is configured to determine a basic compressibility value of the diaphragm pump and / or an air content in the pumped liquid. characterized in that the determination of the basic compressibility value and / or the air content in the pumped liquid is based on at least two measurements, between which the chamber volume of the pumping chamber was changed by suction and / or pumping out liquid. Diaphragm pump drive according to claim 1 or 2, wherein, for each of the measurements, an overall compressibility value of the overall system formed by the diaphragm pump and the liquid in the pumping chamber is determined. Diaphragm pump drive according to claim 3, wherein the basic compressibility value of the diaphragm pump and / or air content is determined by means of a regression analysis of the overall compressibility values, in particular by means of a regression analysis of the overall compressibility values ​​as a function of the chamber volume of the pumping chamber and / or by linear regression.Diaphragm pump drive according to claim 4, wherein the total compressibility value is determined as the value which results from the regression analysis for a chamber volume of the pumping chamber of zero. Diaphragm pump drive according to one of claims 2 to 5, wherein the air proportion is determined on the basis of a change in the total compressibility values ​​as a function of the chamber volume of the pumping chamber and in particular from a slope of a regression line. Diaphragm pump drive according to one of the preceding claims, wherein the basic compressibility value is determined and used to determine the air proportion of the liquid to be pumped in a subsequent measurement, in particular in a later pumping cycle, wherein the air proportion is preferably determined based on only one measurement of the total compressibility value of the. by the diaphragm pump and the fluid in the pump chamber, in particular by correcting the measured value by the basic compressibility value. Diaphragm pump drive according to claim 7, wherein the basic compressibility value is initially determined, in particular as part of an initial test routine. Diaphragm pump drive according to one of the preceding claims, wherein the basic compressibility value and / or the air fraction is determined during ongoing operation. Diaphragm pump drive according to one of the preceding claims, wherein the basic compressibility value and / or the air fraction is repeatedly determined, and in particular is determined in each pump cycle.Diaphragm pump drive according to one of the preceding claims, wherein the diaphragm pump drive has at least one valve drive for driving at least one valve for controlling the fluid flow into and / or out of the pump chamber, wherein the controller of the diaphragm pump drive controls the at least one valve drive. Diaphragm pump drive according to claim 11, wherein the controller is configured to control the at least one valve drive for carrying out the at least one and preferably several measurements for determining the basic compressibility value and / or the air fraction according to one of the preceding claims. Diaphragm pump drive according to one of the preceding claims with a coupling surface to which a pump cassette can be coupled, which comprises the pump chamber and preferably one or more valves. Diaphragm pump drive according to one of the preceding claims, wherein the diaphragm pump drive has a drive chamber which is closed off by a diaphragm, wherein the diaphragm is deflected outwards out of the drive chamber by overpressure in the drive chamber and inwards into the drive chamber by negative pressure in the drive chamber. Diaphragm pump drive according to claim 14, wherein the pressure sensor determines the pressure in the drive chamber. Diaphragm pump drive according to claim 14 or 15, wherein the pressure in the drive chamber is generated via a piston-cylinder unit connected to the drive chamber, wherein preferably a length sensor is provided which detects the position of the piston, and / or wherein the transmission of the pressure to the diaphragm preferably takes place hydraulically, wherein preferably the piston-cylinder unit and the drive chamber are filled with hydraulic fluid.Diaphragm pump drive according to one of the preceding claims, wherein the controller is configured to carry out a measurement by controlling the diaphragm pump drive with the pump chamber closed and to record associated operating parameter values ​​of the diaphragm pump drive and / or to control the diaphragm pump drive with the pump chamber closed and to record associated pressure levels, wherein the total compressibility value is preferably determined on the basis of the operating parameter values ​​and / or pressure levels, wherein the operating parameter values ​​are preferably position values ​​of the diaphragm pump drive. Medical device, in particular a blood treatment machine, in particular a dialysis machine, in particular a peritoneal dialysis machine, with a. Membrane pump drive according to one of the preceding claims, wherein the blood treatment machine preferably has a pump cassette holder and / or an air cushion for pressing the pump cassette against a coupling surface of the membrane pump drive.

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