Electrical generator or motor structure – Dynamoelectric – Rotary
Reexamination Certificate
1999-08-04
2001-04-24
Ramirez, Nestor (Department: 2834)
Electrical generator or motor structure
Dynamoelectric
Rotary
C310S090500
Reexamination Certificate
active
06222290
ABSTRACT:
The invention relates to a sensor arrangement in an electromagnetic rotary drive which is designed as a bearing-free motor with a magnetically journalled, permanent magnetic rotor and a stator and to a method for the operation of a rotary drive of this kind.
A bearing-free motor with a permanent magnetic rotor is an electromagnetic rotary drive which comprises a permanent magnetically excited rotor and a stator, with the rotor being journalled without contact by means of magnetic forces. The characteristic to which the bearing-free motor owes its name is that it has no separate magnetic bearing for the rotor. For this the stator is designed as a bearing and drive stator and the rotor as a passive magnetic rotor which serves both as a bearing rotor and as a drive rotor. The stator is designed or provided with electrical windings respectively in such a manner that it produces an electromagnetic rotary field which exerts, on the one hand, a torque on the rotor which drives its rotation about the axis of rotation and which, on the other hand, exerts a transverse force on the rotor which can be set in any manner desired so that its radial position with respect to a plane perpendicular to the axis of rotation can be predetermined or actively controlled respectively. Thus in the operating state the rotor can be actively controlled and driven respectively by means of the electric windings of the stator with respect to three degrees of freedom, namely the rotation about the axis of rotation and the radial position in the plane perpendicular to the axis of rotation (two degrees of freedom).
With respect to three further degrees of freedom, namely tiltings with respect to the plane perpendicular to the axis of rotation (two degrees of freedom) and the axial position the rotor is passively magnetically stabilised, that is, not in a controllable manner, by reluctance forces. Thus in the operating state the rotor can be both driven and journalled without contact through the magnetic interaction between the bearing/drive stator and the rotor without separate magnetic bearings being present for this.
The term “bearing-free motor with a permanent magnetic rotor” is to be understood in this sense for the following explanations. With respect to further details of the design and of the excitation and regulation respectively of the bearing-free motor, reference is made here to Schoeb et al. U.S. Pat. No. 6,100,618 entitled Rotary Machine with an Electromagnetic Rotary Drive issued Aug. 8, 2000.
In Schoeb et al. U.S. Pat. No. 6,100,618 entitled Rotary Machine with an Electromagnetic Rotary Drive issued Aug. 8, 2000 a bearing-free motor of this kind is disclosed in the example of a rotation pump. In the latter the rotor of the bearing-free motor is provided with vanes and thus forms an integral rotor, which means that it takes over the function of the rotor of the pump in addition to the function of the rotor of the electric motor. Pumps of this kind are advantageous in particular for those uses in which the fluid to be forwarded must not be contaminated, for example for the forwarding of biological liquids such as blood or highly pure liquids such as purest water. In addition rotation pumps of this kind are suitable for the forwarding of aggressive liquids which would destroy mechanical bearings a short time.
In comparison with conventional pumps with a magnetically journalled rotor, pumps of this kind, which operate in accordance with the principle of the bearing-free motor, have the advantage of being extremely compact and space saving and nevertheless having all the advantages of the non-contact magnetic journalling of the rotor even at high performance or forwarding power respectively. This is one of the reasons why pumps of this kind are suitable among other things as blood pumps for uses inside and outside the body.
For the operation of a bearing-free motor with a permanent magnetically excited rotor, in particular for the regulation of the drive and the position of the rotor, which usually takes place by means of a vector regulation method or a field oriented regulation method respectively, it is necessary to know the direction of the rotor magnetisation, that is the momentary position of the magnetisation of the rotor relative to the stationary stator system. In accordance with Schoeb et al. U.S. Pat. No. 6,100,618 entitled Rotary Machine with an Electromagnetic Rotary Drive issued Aug. 8, 2000 it is proposed for this to arrange four magnetic field probes in the air gap between the stator and the rotor.
Even though this arrangement has proved its worth in practice, difficulties nevertheless result for several forms of the rotor magnetisation. If for example the rotor is magnetised in a block pattern, then the signal measured in the air gap by the magnetic field sensors varies only very little—if at all—over a relatively large rotational angle of the rotor so that a unique determination of the momentary direction of the rotor magnetisation is practically no longer possible. In such cases separate rotation sensors would then have to be provided.
One object of the invention is thus to propose a better sensor arrangement in a bearing-free motor with a permanent magnetically excited rotor which enables the direction of the rotor magnetisation and thus also the geometrical rotor angle to be determined. In accordance with a further aspect the axial position of the rotor is also to be determinable by means of the sensor arrangement. It is furthermore an object of the invention to propose a corresponding method for the operation of a bearing-free motor with a permanent magnetic rotor.
In accordance with the invention a sensor arrangement in an electromagnetic rotary drive is thus proposed which is designed as a bearing-free motor with a magnetically journalled, permanent magnetic rotor and a stator, said sensor arrangement serving for the determination of the direction of the rotor magnetisation and/or of the axial position of the rotor and comprising at least two sensors for the determination of a magnetic flux. The two sensors are arranged with respect to the rotor in such a manner that partial fluxes of that magnetic flux which the stray field of the permanent magnetic rotor produces can be determined with them.
In accordance with the invention the measurements for the determination of the position of the rotor magnetisation and/or of the axial position of the rotor thus take place in the stray field of the rotor. Through this the direction of the rotor magnetisation with respect to the stationary stator system—and thereby also the geometric angular position of the rotor—can also be determined in those cases in which the rotor magnetisation is not continuously distributed over the rotor, for example in a block-patterned rotor magnetisation. With the arrangement in accordance with the invention and the method in accordance with the invention respectively the momentary position and the direction of the rotor magnetisation respectively can be reliably determined during the operation of the motor for all rotor magnetisations which are relevant in practice. Since in addition no separate rotation sensor, that is, one that is different from the actual rotor, is required for this, the sensor arrangement in accordance with the invention is particularly simple in regard to the apparatus and in particular also in regard to the mounting technology and is thereby economical.
A further advantage lies in that the axial position of the rotor with respect to the stator can be determined with the arrangement in accordance with the invention or the method in accordance with the invention respectively without further sensors being required for this. This also reduces the cost and complexity of the apparatus for the bearing-free motor, especially the number of sensors required, because two measurement values which are required for the operation, namely the direction of the rotor magnetisation and the axial position of the rotor, can be measured by means of a single sensor system.
The sensors are preferably arranged
Barletta Natale
Schob Reto
Dinh Le Dang
Ramirez Nestor
Sulzer Electronics AG
Townsend and Townsend / and Crew LLP
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