Measuring and testing – Blower – pump – and hydraulic equipment
Reexamination Certificate
1999-07-22
2003-10-21
Williams, Hezron (Department: 2856)
Measuring and testing
Blower, pump, and hydraulic equipment
C415S118000, C416S043000
Reexamination Certificate
active
06634224
ABSTRACT:
BACKGROUND OF THE INVENTION
The invention relates to a method for the determination of the pressure in and/or of the through-flow through a pump with at least one magnetic bearing for the axial journaling of the pump rotor.
Pumps in which the pump rotor is magnetically journaled are nowadays already being used in a number of fields of application. In particular—but not exclusively—these are applications in which mechanical journallings of the rotor cannot be tolerated as a result of possible contamination of the medium to be forwarded, such is for example the case in blood pumps. Here magnetic journallings of the rotor are the rule.
Pumps with magnetic journallings of the rotor are for example known from DE-A-196 13 388 (U.S. Pat. No. 5,735,357) or from U.S. Pat. No. 4,781,525. Pumps can be described in more detail through several characteristic parameters. Two important characteristic parameters of this kind are the pressure in a pump and the through-flow through a pump. These parameters can be determined in principle with corresponding devices for the pressure measurement and the through-flow measurement respectively, but this typically has the result that corresponding sensors must be provided in the pump. Precisely in blood pumps, however, it is desirable if these parameters can be determined without sensors.
For this it is proposed in the already named U.S. Pat. No. 4,781,525 to determine the through-flow in such a manner that the torque by means of which the rotor is driven is determined (via the current by means of which the rotor is driven) at a constant viscosity of the liquid to be forwarded and at a predetermined speed of rotation of the rotor. At constant viscosity this torque is linearly related to the through-flow according to U.S. Pat. No. 4,781,525 (column 1, lines 57 ff., column 3, lines 50 ff.). The through-flow is determined with the help of various tables (see FIG. 2 of U.S. Pat. No. 4,781,525), each of which represents the linear relationship between the torque and the through-flow for a constant viscosity. It is noted that this linear relationship firstly holds only very approximately and secondly is valid only for limited through-flow amounts. Considered realistically, the relationship between the torque and the through-flow (at a predetermined speed of rotation) is not linear, however; this holds all the more above a certain through-flow amount.
SUMMARY OF THE INVENTION
It is an object of the invention to be able to determine the pressure in and/or of the through-flow through a pump of this kind without sensors (thus without special sensors for pressure and through-flow) and in this to obtain values for the pressure and the through-flow which are as realistic as possible without the need to measure the pressure and the through-flow directly. The present invention is dedicated to this object.
In accordance with the invention a method is proposed in which the pump used has at least one magnetic bearing for the axial journalling of the pump rotor, with axial forces acting on the rotor during the operation of the pump. For the determination of the pressure and/or of the through-flow, the axial forces which act on the rotor are utilized in the method in accordance with the invention. The axial forces which act on the rotor can be simply determined in various manners.
The axial forces (axial thrust) which act on the pump rotor are namely dependent on the pressure difference between the inlet side of the pump (e.g. centrifugal pump, diagonal pump, axial pump) and its outlet side. Therefore the axial forces (axial thrust) which act on the pump rotor can be used in order to determine this pressure difference—this pressure difference is generally designated as the “pressure” in the pump.
In a method variant the axial magnetic bearing of the pump rotor is designed as an active journalling. For the determination of the axial forces which act on the rotor then the bearing current which is required in each case for the axial journalling of the rotor is utilized.
In another method variant the axial magnetic bearing of the pump rotor is designed as a passive journalling. For the determination of the axial forces which act on the rotor the axial deflection of the rotor is then utilized.
Depending on the type of the axial magnetic journalling (active or passive respectively) different journalling currents which are required for the axial journalling of the rotor or different axial deflections of the rotor respectively at different speeds of rotation as well as the respective pressures resulting therefrom can in each case be stored in a look-up table. This look-up table is prepared prior to the practical use of the pump. During the operation of the pump the respective journalling current or the respective axial deflection of the rotor respectively and its speed of rotation are then determined, and with the help of this look-up table the pressure resulting therefrom is then determined.
Since larger item numbers of a pump type are regularly manufactured, the look-up table need be generated only a single time, insofar as it is ensured that the manufactured pumps remain within predetermined tolerances. Of course it is also possible to generate and store a look-up table of this kind for each individual pump, through which however the cost and complexity is increased; but the precision is also increased in return.
As an alternative to the look-up table the pressure in the pump can be determined—depending on the kind of the axial journalling (active or passive respectively)—with the help of a polynomial from the respective journalling current which is required for the axial journalling of the rotor or from the respective axial deflection of the rotor respectively on the one hand as well as from the respective speed of rotation on the other hand. A polynomial of this kind likewise permits the pressure in the pump to be determined with a sufficient precision.
The higher the precision requirements are in this situation, the higher will be the order of the polynomial as well, and the greater will be the computational effort. In this the coefficients of the polynomial are likewise determined prior to the practical use of the pump. Here as well it holds that the coefficients for a given pump type need only be determined a single time when predetermined manufacturing tolerances are observed. They can also be determined individually for each individual pump, however, which increases the precision, but also increases the cost and complexity.
In a further development of the above-named method variant the through-flow through the pump is determined from the already established pressure and the associated speed of rotation. The determination of the through-flow is done via the pressure-through-flow characteristics of the pump (also called “restrictor curves”).
These pressure-through-flow characteristics of the pump can again be stored in an electronic look-up table which has been generated prior to the practical use of the pump, either once for each pump type or for each pump separately. During the operation of the pump the through-flow through the pump is then determined with the help of this look-up table from the already established pressure.
Alternatively to the look-up table, the pressure-through-flow characteristics can be approximated by a polynomial so that during the operation of the pump the through-flow through the pump is then determined from the already established pressure with the help of this polynomial. The above considerations hold for the generation of the polynomial.
In a variant of the above-named method a pump with sensors for the determination of the direction of the magnetic field in the gap between the rotor and the stator is used. These sensors (typically Hall sensors) are also used in this method variant for the determination of the axial deflection of the rotor.
In this method variant the through-flow through the pump can be determined in that the torque which drives the rotor and the speed of rotation of the rotor are determined. For the determination of the to
Barletta Natale
Hahn Jürgen
Schöb Reto
Hynes William Michael
Levitronix LLC
Rogers David
Williams Hezron
LandOfFree
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