Electricity: motive power systems – Motor-reversing – Armature or primary circuit control
Reexamination Certificate
1999-09-01
2001-08-21
Ro, Bentsu (Department: 2837)
Electricity: motive power systems
Motor-reversing
Armature or primary circuit control
C318S434000, C318S720000
Reexamination Certificate
active
06278251
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention relates to a permanent magnetically excited electrical rotary drive for a blood pump and to a blood pump with a rotary drive of this kind.
2. Description of the Prior Art
Blood pumps, which are usually designed as axial or as centrifugal pumps, serve for the forwarding of blood and are used, for example, in the framework of operations on the heart for maintaining the blood circulation. Furthermore, implantable blood pumps are known which are implanted into the body of the patient for the temporary or chronic support of the heart activity.
In blood pumps it must be ensured that no contamination of the forwarded blood arises. Therefore, the rotor of the electromagnetic drive and/or the pump rotor is preferably magnetically journalled in blood pumps. This magnetic journalling of the rotor can be realized either through separate magnetic bearings, that is ones which are different from the drive; or the magnetic journalling is realized through the stator of the drive.
A rotation pump which is suitable as a blood pump and which is designed as a so-called bearingless motor, which means as an electromagnetic rotary drive with a magnetically contactlessly journalled rotor, with no separate magnetic bearings being present for the rotor, is disclosed in WO-A-96/31934. For this, the stator is designed as a bearing and drive stator which comprises a drive winding and a control winding. With these two windings, a magnetic rotary field can be produced which, on the one hand, exerts a torque on the rotor and which, on the other hand, exerts a transverse force on the rotor which can be set as desired so that its radial position can be actively controlled.
Furthermore, blood pumps, in particular in the case of an implantation into the body, should be compact and space saving, but nevertheless achieve a pump performance which corresponds at least to that of the heart. For this it is e.g. proposed in WO-A-96/31934 to provide the rotor of the bearingless motor with vanes so that the rotor of the rotary drive is identical with the pump rotor, that is, forms an integral rotor. This rotor thus serves as a drive rotor, a bearing rotor and a pump rotor, through which a very compact and high performance blood pump can be realized.
Blood pumps are also known in which the pump rotor by means of which the blood is forwarded is different from the rotor of the rotary drive. The pump rotor is designed as a vaned wheel or rotor, which is set into rotation by the rotor of the rotary drive. For this, blood pumps of this kind can be designed, for example, in accordance with the principle of the gap tube motor or of the gap tube pump respectively; or the pump rotor can be magnetically coupled to the rotor of the rotary drive.
An essential importance, in particular in regard to implantable blood pumps, is assumed by the operating reliability. A problem in known rotary drives for blood pumps is that when faults arise, such as, for example, the failure of an amplifier circuit or the breakage of an electrical line in one of the phases of the drive winding of the stator, a correct functioning of the drive is no longer ensured. A failure of the drive of a blood pump resulting therefrom can, however, have very severe, possibly even fatal results. The invention is thus dedicated to the task of significantly reducing this safety risk.
SUMMARY OF THE INVENTION
The object of the invention is therefore to provide an electrical rotary drive for a blood pump which still enables a correct operation, which means, in particular, a reliable driving of the rotor, even when faults arise.
Thus, in accordance with the invention a permanent magnetically excited electrical rotary drive for a blood pump is proposed, comprising a permanent magnetic rotor and a stator, said stator comprising a drive winding having at least two loops for the production of a magnetic drive field which produces a torque on the rotor, with each loop belonging to a different electrical phase, furthermore comprising a setting device which supplies each loop in each case with a phase current or in each case with a phase voltage as a setting parameter, with the setting device comprising a separate power amplifier for each loop so that the setting parameter for each loop can be regulated independently of the setting parameter for the other loops.
Since the setting parameter, which means the phase voltages or the phase currents, is regulatable for each loop of the drive winding independently of the setting parameters for the other loops and since, in addition, a separate power amplifier is provided for each loop, each electrical phase, by which is meant in each case a loop of the drive winding and the part of the setting device supplying it, can be operated independently of the other electrical phases. Thus, the rotary drive can continue to be operated with a reduced number of phases in the event of a fault in a phase, e.g. the failure of the entire phase, without it being necessary to make concessions to the correct functioning of the rotary drive. Since the rotary drive in accordance with the invention can be operated with a reduced number of phases, it is in principle irrelevant where a fault arises in a phase. Thus, for example, a power amplifier can fail or a breakage in a line in a loop of the drive winding or in the connection between the power amplifier and a loop of the drive winding can occur, or a short circuit in a power amplifier or a winding loop of the drive winding can arise; and in spite of a fault of this kind a continued operation of the rotary drive is possible. As a result of this high fault tolerance, the rotary drive in accordance with the invention brings about a considerable increase in the operating reliability.
Depending on how many phases the rotary drive in accordance with the invention is designed with, it can even continue to be operated in the event of the failure of a plurality of phases. The minimum requirement for the capability of functioning of the rotary drive is that one phase, that is, a loop of the drive winding and the power amplifier supplying it, still operates without fault.
The rotary drive in accordance with the invention, with its design which is at least two-phased in its fault-free normal condition, is a permanent magnetically excited rotary field motor, thus, in particular, a permanent magnetically excited synchronous or a brushless d.c. motor (in spite of its generally usual name, the latter is in essence a rotary field motor). This means that the drive field which is produced by the stator is a magnetic rotary field which drives the permanent magnetic rotor. If only one fault-free phase still remains for operation through a fault in one or more phases, then the rotary field motor becomes a single phase a.c. motor.
Since an arbitrarily large supply of energy is in general not available for blood pumps, and in particular for implanted blood pumps, it is important for the rotary drive of a blood pump to operate as economically as possible and with as low an energy consumption as possible. Since the rotary drive in accordance with the invention is permanent magnetically excited, and thus has a permanent magnetically excited rotor, it is particularly suitable for blood pumps in contrast to field excited rotary drives, since no current and thus no energy is required for the field excitation in a permanent magnetically excited rotary drive.
In accordance with a first exemplary embodiment of the rotary drive in accordance with the invention a loadable star point is provided, which is connected to each loop of the drive winding. In usual multiple phase, e.g. three phase drive windings the three loops are in each case connected to a common star point, with it being necessary for the condition to be fulfilled that the sum of the phase currents is always zero at the star point. Through the measure of making the star point loadable, which means placing it at a loadable potential, this requirement can be omitted so that each phase current or each phase voltage
Ro Bentsu
Sulzer Electronics AG
Townsend and Townsend / and Crew LLP
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