Measuring and testing – Volume or rate of flow – Using rotating member with particular electrical output or...
Reexamination Certificate
2000-04-20
2003-06-24
Williams, Hezron (Department: 2855)
Measuring and testing
Volume or rate of flow
Using rotating member with particular electrical output or...
Reexamination Certificate
active
06581476
ABSTRACT:
FIELD OF THE INVENTION
The invention relates to a measuring apparatus for fluids, it being understood that under “fluids”, both a gas and also a liquid are encompassed.
BACKGROUND OF THE INVENTION
In the state of the art, measuring apparatuses have been developed in which a rotor is maintained in an equilibrium position within a carrier tube by magnetic field forces. Thus in DE-A-29 19 236, a turbine wheel counter is described for the flow-through measurement of liquids in which the rotor has, for radial stability, two spaced apart rotor magnets formed as permanent magnets which are juxtaposed pairwise with stator magnets also formed as permanent magnets, which surround the carrier tube. Thus the rotor magnets and stator magnets are magnetized in the axial direction so as to repel one another.
Between the stator magnets, an electromagnet coil is arranged which surrounds the carrier tube in an annular manner. The magnet coil cooperates with a ferromagnetic flux conductive piece on the rotor which is arranged between the rotor magnets.
Additionally, a sensor is provided that detects the axial position of the rotor and cooperates with a control unit which regulates the electric current flow in the magnet coil. As soon as the field forces of the rotor magnets and the stator magnets are engendered by an axial shift of the rotor to accelerate the rotor out of the equilibrium position in the axial direction there is generated a signal of the axial shift of the rotor as measured by the sensor which produces in the magnet coil a counteracting stabilizing field force. The rotor is thus, upon an axial shift in position in one or the other direction, always returned to its setpoint position. The stabilizing axial force countering the axial shift is so phase-shifted in time in a known manner that the rotor is held stably in its setpoint position by restoring as well as damping forces.
A drawback of the aforedescribed measuring device is that the rotor has only a relatively limited positional stiffness in the radial direction. The origin of that problem is the large distance between the stator and rotor magnets because of the annular channel between the support pipe and the rotor for the throughflow of the fluid.
In DE-A-24 44 099, a magnetic bearing for rapidly movable bodies is described. This magnetic bearing has a sleeve-shaped rotor whose ends have pole pieces provided with permanent magnets and whereby, based upon tractive forces on the rotor, the latter is held in a stable position. By means of a contactless position sensor, deviations from the equilibrium position are determined. Such deviations are compared by a powerless electromagnetic stray field control for which annular coils are provided which are arranged proximal to the gaps on the pole pieces of the rotor. Such a magnetic bearing is not suitable for disposition in a carrier tube through which a fluid is conducted on spatial grounds.
Magnetic bearings have also been used for blood pumps. Thus in U.S. Pat. No. 5,695,471, a blood pump is known which is formed as a radial pump with a radial rotor. The radial rotor is disposed within a carrier tube and has in an inlet side extension, a multiplicity of rotor magnets which are juxtaposed with stator magnets on the carrier tube. Additionally the radial rotor has distributed over the periphery a multiplicity of rod-shaped rotor magnets extending in the axial direction and which are juxtaposed with ring-shaped stator magnets on both sides of the radial rotor toward the carrier tube. These rotor and stator magnets should support the radial journaling in the region of the extension of the rotor. In the axial direction, the rotor is held purely mechanically with one end on a ball and another end on a point journal. The rotor is driven by a brushless rotary field motor. On sides of the carrier tube a coil is arranged which cooperates with a spoked-wheel magnet set into the radial rotor. A drawback of this blood pump is that the bearing stability in the radial direction is not optimal and that the pump because of the multiplicity of rotor and stator magnets has a high spatial requirement and high weight. In addition, the purely mechanical bearings give rise to wear in the axial direction.
The are also axial blood pumps. Here the journaling is effected exclusively mechanically in impeller wheels which are arranged at fixed locations in the carrier pipe ahead of and behind the rotor (Wernicke et al., A Fluid Dynamic Analysis Using Flow Visualization of the Baylor/NASA Implantable Axial Flow Blood Pump for Design Improvement, Artificial Organs 19(2), 1995, Pages 161-177). Such mechanical bearings are subject to wear and have an unsatisfactory effect on sensitive liquids, especially body liquids like blood.
OBJECT OF THE INVENTION
An object of the invention is to provide a measuring device of the type described at the outset which has a substantially higher bearing stiffness, especially in the radial direction, and which therefore has numerous applications.
SUMMARY OF THE INVENTION
This object is achieved by the following features in accordance with the invention:
a) the measuring device has a carrier tube;
b) a rotor is journaled rotatably in the carrier tube;
c) the rotor is configured for interaction with the fluid found in the carrier tube;
d) the rotor has at both ends axially magnetized permanent magnet rotor magnets;
e) the ends of the rotor are juxtaposed with axially opposite permanently magnetic stator magnets connected to the carrier tube;
f) each stator magnet has such axial magnetism that it attracts the neighboring stator and rotor magnets; and
g) the measuring device has a magnetic axial stabilizing device for the rotor.
Alternatively, the object is achieved by a measuring device with the following features:
a) the measuring device has a carrier tube;
b) a rotor is rotatably journaled in the carrier tube;
c) the rotor is configured for the interaction with the fluid found in the carrier tube;
d) at the ends of the rotor there are respective axially magnetized permanently magnetic magnets opposite a flux conductive member whereby the magnets are either mounted on the rotor as rotor magnets or are connected to the carrier tube as stator magnets; and
e) the measuring device has a magnetic axial stabilizer unit.
The basic concept of the invention is thus, by means of rotor magnets and stator magnets arranged at the ends of the rotor, to generate a magnetic field in the axial direction respectively bridging the gaps between the rotor and stator magnets which respectively draws the opposing pairs of rotor and stator magnets in opposite directions toward one another. As a result, a bearing stiffness with the same geometry with respect to the magnet bearing of DE-A-29 19 236 can be obtained, but increased by at least one power of ten without thereby significantly affecting the annular passage between the carrier tube and the rotor hub. The aforedescribed effect also can be obtained when each magnet assembly has a magnet on one side and a flux-conducting device on the other side, as opposed to a system where each magnet assembly consists of two magnets, such as the rotor and stator magnets, which are juxtaposed. Thus, as an alternative, the magnet can be a rotor magnet mounted on the rotor and the flux-conducting member can be connected to the carrier tube or the flux-conducting member can be arranged on the rotor and the magnet fixed as a stator magnet on the carrier tube. For generating a high bearing stiffness, additional electric magnet coils can be provided for amplifying the magnetization of the flux-conducting member in the sense of increasing the attractive force between the magnets and the flux-conducting members.
To the extent that rotor and stator magnets pairwise are disposed opposite one another, they should preferably be composed of at least two interfitted partial magnets whereby respectively radially neighboring partial magnets are oppositely magnetized. Through this configuration of the rotor and stator magnets, a further increase in the bearing stiffness by a factor
Dickens C
Dubno Herbert
Forschungszentrum Julich GmbH
Williams Hezron
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