Method for monitoring the state of a gear pump of an apparatus for extracorporeal blood treatment and apparatus for extracorporeal blood treatment

Abstract

Method for monitoring the condition of a gear pump (1) of a device (100) for extracorporeal blood treatment, comprising the steps of: - determining a normalization characteristic map, wherein the normalization characteristic map for a new reference gear pump (1) relates a volume flow (Q) of a fluid (2) generated by the reference gear pump (1), a pressure (Δp) of the fluid (2) at the reference gear pump, a torque (M) generated by the reference gear pump (1), and a speed (n) of the reference gear pump (1) to one another, - during operation of the gear pump (1), determining an operating characteristic map, wherein the operating characteristic map for a gear pump (1) used during a specific operating period relates a volume flow (Q) of the fluid (2) generated by the gear pump (1), a pressure (Δp) of the fluid (2) at the gear pump (1),a torque (M) generated by the gear pump (1) and a speed (n) of the gear pump (1) are related to each other, and - determining the state of the gear pump (1) as a function of the normalization characteristic map and the operating characteristic map.,

Description

[0001] The invention is based on the object of providing a method for monitoring the condition of a gear pump of a device for extracorporeal blood treatment and a device for extracorporeal blood treatment which enable simple and reliable condition monitoring.

[0002] The method is used to monitor the condition of a gear pump of a specific type of extracorporeal blood treatment device, for example in the form of a dialysis machine.

[0003] The gear pump or transmission pump can be, for example, an external gear pump, an internal gear pump, a gerotor pump (also known as a gerotor pump or Eaton pump), or a screw pump. For further information, please refer to the relevant technical literature.

[0004] According to the invention, a normalization characteristic map is determined, wherein the normalization characteristic map for a new reference gear pump of the same type mathematically or formulaically relates a volume flow of a fluid generated by the reference gear pump, a (differential) pressure of the fluid at the reference gear pump, a (shaft) torque generated by the reference gear pump or its electric motor, and a speed of the reference gear pump to one another. The torque generated by the reference gear pump is in particular the torque acting on the driven gear of the reference gear pump. The speed of the reference gear pump is in particular the speed of the driven gear of the reference gear pump. A new gear pump of the device can form the reference gear pump. Alternatively, the reference gear pump is a new gear pump whose type corresponds to the type of gear pump of the device.The normalization map can be determined in advance, for example by the manufacturer of the gear pump, and stored in a memory assigned to the control system of the device.

[0005] During operation of the device's gear pump, an operating characteristic map is determined, whereby the operating characteristic map for the gear pump used during a specific operating period relates the volume flow of the fluid generated by the gear pump, the pressure of the fluid at the gear pump, the torque generated by the gear pump and the speed of the gear pump to one another mathematically or by formula.

[0006] Finally, a (wear) condition of the device's gear pump is determined depending on the normalization map and the operating map.

[0007] The condition can be assessed, for example, in the categories "good," "still usable," and "no longer usable." Quantification using a wear index with a predefined value range is also possible, for example, a value range between 0 and 10, where the value 0 represents a defective or completely worn gear pump and the value 10 represents a new or unused gear pump.

[0008] In one embodiment, the state of the gear pump of the device is determined depending on a difference between the normalization map and the operating map.

[0009] In one embodiment, the normalization characteristic map describes the torque generated by the reference gear pump as a function of the volume flow of the fluid generated by the reference gear pump, the pressure of the fluid at the reference gear pump, and the speed of the reference gear pump.

[0010] In one embodiment, the operating characteristic map describes the torque generated by the gear pump of the device as a function of the volume flow of the fluid generated by the gear pump of the device, the pressure of the fluid at the gear pump of the device, and the speed of the gear pump of the device.

[0011] In one embodiment, in addition to the condition of the device's gear pump, a forecast for the remaining service life of the device's gear pump is determined based on the normalization map and the operating map. The remaining service life is also referred to as the Remaining Useful Lifetime (RUL).

[0012] In one embodiment, the remaining service life of the device's gear pump is calculated using a gear pump-specific regression model. The remaining service life, for example, forms the regression criterion. The difference between the normalization map and the operating map, for example, forms the predictor.

[0013] The device according to the invention for extracorporeal blood treatment with a gear pump is designed to carry out a method described above.

[0014] The invention is based on the finding that a difference between the normalization characteristic map and the operating characteristic map is characteristic of an (aging) condition or aging of the gear pump, whereby a prognosis for the remaining service life (RUL) of the gear pump can be derived from this difference. In principle, an increasing difference reflects a deteriorated condition of the gear pump and suggests a shorter remaining service life.

[0015] The normalization characteristic map can, for example, be determined for a given type of gear pump using type-specific measurement technology and / or read from a manufacturer database of the gear pump.

[0016] According to the invention, the degradation of gear pumps is evaluated to predict their remaining service life. The evaluation of the current wear state is based on a change in the characteristic map.

[0017] In general, the efficiency η based on the first law for gear pumps or positive displacement pumps as follows: η = Q Δ p P s = Q Δ p 2 πM s n

[0018] Here, Q the pumped volume flow, Δ p the pressure increase of the gear pump, M s the (shaft) torque and n the speed. P s describes the shaft power.

[0019] This relationship is valid under the assumption of an incompressible pumping fluid and negligible play in the mechanical parts, as well as no heat flow. These assumptions can be considered approximately valid for the pumping fluid in a dialysis machine. The values ​​for Q , Δ p, M s , n are measured using associated sensors and stored if necessary.

[0020] First, the normalization map is M N = f ( Q, Δ p, n ) for a new reference gear pump of the specific type at a defined fluid reference temperature.

[0021] Furthermore, for example experimentally, lower limits of an operating map that has changed due to ageing phenomena M B determined.

[0022] The normalization map M N and the operating map M B describe the (shaft) torque generated by the gear pump M s depending on the volume flow Q of the fluid generated by the gear pump, the pressure Δ at the gear pump p of the fluid and the speed n of the gear pump.

[0023] During operation of the dialysis machine, the operating characteristic map is determined M B First, the fluid temperature is adjusted to the fluid reference temperature on the dialysis machine. Then, the operating map is measured at characteristic predefined points. M B = f ( Q, Δ p, n ) scanned.

[0024] The operating map determined in this way M B is approximated using a suitable function, for example a piecewise linear function or nonlinear function.

[0025] Age-related wear leads to a change in the operating characteristic map. The wear or condition of the gear pump can be quantified using a detection function, such as a difference, a squared deviation, etc. The detection function compares the operating characteristic map with the normalized characteristic map. The result of the comparison is, for example, a wear index that reflects the condition of the gear pump.

[0026] Future wear behavior can be predicted using a machine-specific regression model.

[0027] For example, the wear index of an initially unused gear pump can be determined over time at a constant fluid reference temperature. The determined time curve can be approximated by an nth-order function using conventional mathematical methods.

[0028] To estimate the remaining service life of the gear pump in relation to its function, a current wear index is determined. Based on the current wear index and mathematically inverting the function, the point in time at which a specified threshold value is exceeded is calculated. The time until this point in time is reached is, by definition, the remaining service life of the gear pump. The threshold value is selected such that it accurately reflects a typical wear limit. Using statistical methods, an uncertainty range for the calculated remaining service life can be calculated.

[0029] The invention is described in detail below with reference to the drawings. Fig. 1 highly schematically shows a device for extracorporeal blood treatment in the form of a dialysis machine with a gear pump, Fig. 2 shows a wear characteristic of an unused gear pump of Fig. 1 over time and Fig. 3 schematically shows an exemplary normalization characteristic map and an exemplary operating characteristic map of a gear pump.

[0030] Fig. 1 shows a highly schematic illustration of a device 100 in the form of a dialysis machine with a conventional gear pump 1.

[0031] A condition monitoring of the gear pump 1 is described in detail below.

[0032] First, a normalization map is created, especially once. M N = f ( Q, Δ p, n ) for a new reference gear pump 1 of a type corresponding to the type of gear pump 1 of device 100, at a defined fluid reference temperature. An exemplary normalization map M N is in Fig. 3 shown.

[0033] The normalization map M N describes a (shaft) torque generated by a reference gear pump 1a M s depending on a volume flow Q of a fluid 2 generated by the reference gear pump 1, a pressure Δ at the reference gear pump 1 p of the fluid 2 and a speed n of the reference gear pump 1.

[0034] During operation of the dialysis machine 100, an operating characteristic map is determined M B First, the fluid temperature is set to the fluid reference temperature on the dialysis machine 100. Then, the operating map M B at characteristic predefined points M B = f ( Q, Δ p, n ) are sampled. The operating map M B describes the (shaft) torque generated by the gear pump 1 of the dialysis machine 100 M s depending on the volume flow Q of the fluid 2 generated by the gear pump 1 of the dialysis machine 100, the pressure Δ at the gear pump 1 of the dialysis machine 100 p of the fluid 2 and the speed n of the gear pump 1 of the dialysis machine 100. An exemplary operating map M B with sampling points M B 1 to M Bk is in Fig. 3 Furthermore, for example experimentally, lower limits of an operating map that has changed due to ageing phenomena M B determined.

[0035] The operating map determined in this way M B is approximated using a suitable function, for example a linear function or non-linear function.

[0036] Age-related wear leads to a change in the operating map M B . The wear or the condition of the gear pump 1 is quantified by means of a detection function, which, for example, can be a difference, a quadratic deviation, etc. between the normalization map M N and the operating map M B The detection function calculates a wear index VK, which reflects the (wear) condition of gear pump 1.

[0037] Future wear behavior is predicted using a machine-specific regression model.

[0038] Fig. 2 shows a curve of the wear index VK of an initially unused gear pump 1 over time t at a constant fluid reference temperature. The determined curve over time is approximated by an nth-order function using conventional mathematical methods.

[0039] In order to estimate the remaining service life of gear pump 1 in conjunction with its function, a current wear index VK is first determined. Then, based on the current wear index Vk and mathematically inverting the function, it is calculated at what point in time tA the wear index VK falls below a threshold value VS. The time period until this point in time tA is reached is, by definition, the remaining service life of the gear pump. The threshold value VS is selected such that it accurately reflects a typical wear limit. Using statistical methods, an uncertainty range for the calculated remaining service life can be calculated.

Claims

1. Method for monitoring the condition of a gear pump (1) of a specific type of device (100) for extracorporeal blood treatment, comprising the steps of: - determining a normalization characteristic map ( M N ), where the normalization map ( M N ) for a new reference gear pump (1) of the specific type, a volume flow (Q) of a fluid (2) generated by the reference gear pump (1), a pressure (Δ p ) of the fluid (2), a torque (M) generated by the reference gear pump (1) and a speed (n) of the reference gear pump (1) are related to each other, - during operation of the gear pump (1), determining an operating characteristic map ( M B ), where the operating map ( M B ) for the gear pump (1) used during a certain operating time, the volume flow (Q) of the fluid (2) generated by the gear pump (1), the pressure (Δp ) of the fluid (2), relating the torque (M) generated by the gear pump (1) and the speed (n) of the gear pump (1) to each other, and - determining the state of the gear pump (1) as a function of the normalization characteristic map ( M N ) and the operating map ( M B ) .

2. Method according to claim 1, characterized in that - the state of the gear pump (1) depending on a difference between the normalization map ( M N ) and the operating map ( M B ) is determined.

3. Method according to one of the preceding claims, characterized in that - the normalization map ( M N ) the torque (M) generated by the reference gear pump (1) as a function of the volume flow (Q) of the fluid (2) generated by the reference gear pump, the pressure (Δ p) of the fluid (2) and the speed (n) of the reference gear pump (1).

4. Method according to one of the preceding claims, characterized in that - the operating map ( M B ) describes the torque (M) generated by the gear pump (1) as a function of the volume flow (Q) of the fluid (2) generated by the gear pump, the pressure (Δp) of the fluid (2) at the gear pump (1) and the speed (n) of the gear pump (1).

5. Method according to one of the preceding claims, characterized in that - in addition to the condition of the gear pump (1), a prognosis for the remaining service life of the gear pump (1) depending on the normalization map ( M N ) and the operating map ( M B ) is determined.

6. Method according to claim 5, characterized in that - the remaining service life of the gear pump (1) is calculated using a gear pump-specific regression model.

7. Device (100) for extracorporeal blood treatment with a gear pump (1), which is designed to carry out a method according to one of the preceding claims.

Images