Electrical generator or motor structure – Dynamoelectric – Rotary
Reexamination Certificate
2002-03-14
2004-03-16
Mullins, Burton S. (Department: 2834)
Electrical generator or motor structure
Dynamoelectric
Rotary
C310S06800R, C310S090000, C310S156050
Reexamination Certificate
active
06707201
ABSTRACT:
CROSS-REFERENCE TO RELATED APPLICATIONS
This application claims the benefit of German patent application 101 12 423.6 filed Mar. 15, 2001, herein incorporated by reference.
FIELD OF THE INVENTION
The present invention relates to a cylinder for guiding at least one yarn and to a method for vibration damping a rotatably seated cylinder jacket of a cylinder. More particularly, the present invention relates to such a yarn-guiding cylinder basically comprising a hollow-cylindrical cylinder jacket, a support on which the cylinder jacket is rotatably seated, at least one magnetic bearing having a plurality of bearing pole windings distributed on the support circumferentially relative to the cylinder jacket, and a plurality of sensors for determining an actual position of the cylinder jacket, with the sensors and the bearing pole windings being coupled with each other by a control unit.
BACKGROUND OF THE INVENTION
Cylinders of various types and shapes for guiding one or several yarns are employed in various textile applications, such as spinning installations or textile machines. For example, such cylinders are employed as godet rolls, which are used for conveying, drafting or heating of yarn. Cylinders are also known which serve as tension cylinders to conduct the yarn to a bobbin surface during winding of the yarn. It is common to all such cylinders that the cylinder jacket is rotatably seated for being operated at a circumferential speed which can essentially be equal to the yarn speed. The cylinder jacket may be seated on a support by means of bearings for this purpose. Cylinders in the form of godet wheels are known from European Patent Publication EP 0 770 719 B1 or German Patent Publication DE 197 33 239 A1, wherein the cylinder jacket is magnetically seated. At least one radially acting magnetic bearing is provided for this purpose, which bearing has a plurality of bearing pole windings distributed on the support. The bearing pole windings are evenly distributed over the circumference of the cylinder jacket. Sensors are associated with the bearing pole windings to monitor a bearing gap between the godet wheel jacket and the bearing pole winding. The sensors and the bearing pole windings are attached together on the support, so that the position of the cylinder jacket can be stabilized in relation to the support. However, with the known cylinders, the problem arises that externally produced resonances and machine vibrations cause the support to experience vibrations which have a negative effect on the control of the position of the godet wheel jacket. Under disfavorable conditions, there is even the possibility that the cylinder jacket is caused additional vibrational excitations, which lead to the instability of the bearing.
SUMMARY OF THE INVENTION
It is accordingly an object of the present invention to further develop a yarn guiding cylinder of the aforementioned type in such a way that the rotatable cylinder jacket is seated with as little vibration as possible.
It is a further goal of the present invention to prevent the danger of deformations of the cylinder as a result of sympathetic vibrations.
These objects are addressed by means of a yarn guiding cylinder of the basic type having a hollow-cylindrical cylinder jacket, a support on which the cylinder jacket is rotatably seated, at least one magnetic bearing having a plurality of bearing pole windings distributed on the support circumferentially relative to the cylinder jacket, and a plurality of sensors for determining an actual position of the cylinder jacket, with the sensors and the bearing pole windings being coupled with each other by a control unit. In accordance with the present invention, the sensors are fixed in place at a distance from the cylinder jacket and at a distance from the support for determining the actual position of the cylinder jacket in relation to a stationary reference position of the cylinder jacket.
The present invention further addresses these basic objects by providing a method for vibration damping of a cylinder jacket of a cylinder which is rotatably seated by at least one radially acting magnetic bearing, wherein the magnetic bearing is controlled as a function of an actual position of the cylinder jacket. Basically, the method of the present invention comprises the steps of:
a) determining the actual position of the cylinder jacket in relation to a stationary reference position of the cylinder jacket,
b) determining a chronological change of the actual position of the cylinder jacket as a function of a rotary frequency of the cylinder jacket,
c) determining a sequence of control signals for the magnetic bearing from the change of the actual position of the cylinder jacket at the rotary frequency and, via the control signals, causing bearing forces on the cylinder jacket counteracting the change in position of the cylinder jacket, and
d) controlling the magnetic bearing by the sequence of control signals at the rotary frequency.
The invention is distinguished in that the sensor arrangement and the actuating device are disengaged from each other. As a result, the vibrations in the support cannot have an effect on the position of the cylinder jacket. To this end, the sensors for determining an actual position of the cylinder jacket are fixed in place at a distance from the cylinder jacket and at a distance from the support in such a way that it is possible to determine the actual position of the cylinder jacket in relation to a stationary reference position of the cylinder jacket. In this case, the reference position of the cylinder jacket constitutes the position of the cylinder jacket which assures an optimal function of the cylinder during operation. Therefore, a position which is predetermined in a machine can be called the stationary reference position. In this case, there is also the possibility that the position of the cylinder defined in the machine changes in the course of operation, such as in connection with a tension cylinder, for example, which yields because of the increase in bobbin size. Here, each change of the position based on the function would constitute a stationary reference position. In this connection, it is important for the invention that the detection of the position of the cylinder jacket takes place independently of the reciprocal effect between the support and the cylinder jacket, and therefore independently of the bearing gap between the respective bearing pole windings and the cylinder jacket.
In order to allow a detection of the position of the cylinder jacket in connection with protrudingly seated cylinder jackets, it is suggested in accordance with an advantageous further development of the invention to fix the sensor in place by means of several protruding sensor supports. In this case, the end of each of the sensor supports is fixedly connected with the machine frame. A sensor, which has a defined position in relation to the stationary reference position of the cylinder jacket, is preferably fastened to the opposite protruding end.
A further embodiment of the invention is particularly advantageous in connection with godet wheels, wherein several yarns are guided on the circumference of the cylinder jacket. In this case, the sensor supports are arranged within an annular space between the cylinder jacket and the support, so that the exterior area of the cylinder remains completely free.
Here, the sensors and the bearing pole windings can be arranged together on a common bearing level, so that a very fast and precise positional regulation of the cylinder jacket by the magnetic bearing is possible.
However, it is also possible to arrange the sensors and/or the bearing pole windings on several adjacent levels. The arrangement of the bearing pole windings on several bearing levels has the advantage that a large bearing capacity and a particularly advantageous stiffness of the bearing is achieved. Such an arrangement is preferred in particular in connection with cantilevered cylinders. In this case, the bearing pole windings can be positioned on the support
Kennedy Covington Lobdell & Hickman LLP
Mohandesi Iraj A.
Mullins Burton S.
Neumag GmbH & Co. KG
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