Metal working – Method of mechanical manufacture – Electrical device making
Patent
1990-09-14
1992-02-25
Echols, P. W.
Metal working
Method of mechanical manufacture
Electrical device making
29593, 29618, 72378, 242 712, H01F 706
Patent
active
050901125
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE INVENTION
The present invention relates to methods and apparatus for manufacturing coils and, in particular, to methods and apparatus for manufacturing coils of resistance wire.
BACKGROUND OF THE INVENTION
Coils having a preselected resistance value are used for various applications, such as current coils for injection valves. One problem in manufacturing these types of coils with conventional automatic winding machines, is that the resistance value of the wire typically does not remain constant along the entire length of the coil. For example, there may be variations in the alloy of the base material, or various conditions during the process of drawing the wire, that may cause the resistance of the wire to vary. The resistance of a wound coil is also influenced by the ambient conditions during the process of winding the coil, such as the room temperature.
It is an object of the present invention, therefore, to overcome the problems of known methods and apparatus for manufacturing coils and to provide coils having substantially predetermined electrical resistance characteristics.
SUMMARY OF THE INVENTION
The present invention is directed to a method of manufacturing coils having substantially predetermined resistance characteristics. The method comprises the following steps the resistance of at least one wire section forming a coil is measured and a measuring signal is generated indicative thereof; the measuring signal is supplied to an evaluating configuration; the measured resistance value is compared to a preselected desired value; if the measured resistance value exceeds the preselected desired resistance value, a braking signal is generated and transmitted to a braking element of the winding machine, in order to correspondingly decrease the braking action, and if the desired value is undershot, a braking signal is generated and transmitted to a braking element to correspondingly increase the braking action.
In known automatic winding machines, an increase in the braking action typically causes greater stretching of the wire due to the continued drawing of the wire, whereby the wire diameter is reduced As a result, the resistance of a length of the wire, and thus the resistance of a coil which is wound from that length of wire, increases. Accordingly, depending on the resistance of the wire used, the formation of areas of increased resistance within the wire is promoted by increasing the braking action and, in turn, stretching the wire. On the other hand, a reduction in the braking action decreases the amount that the wire is stretched and, thus, increases the wire diameter. This brings about a reduction in the formation of areas of increased resistance within the wire.
Thus, one advantage of the method of the present invention, is that it provides finished coils made of resistance wire, wherein each coil's electrical resistance falls within a narrow predetermined tolerance range, regardless of fluctuations in the resistance of the base wire used.
The method and apparatus of the present invention provide a relatively simple control loop which compensates for fluctuations in the resistance of the wires. Thus, it is possible to manufacture coils with precisely defined resistance characteristics. In accordance with one method of the present invention, while the resistance is measured, the coil temperature and/or the room temperature is measured. Based on the temperature measurement, the measured resistance value of the evaluating configuration is corrected. Thus, one advantage of the present invention is that it is possible to consistently produce coils with a desired resistance, regardless of the existing room temperature, which can otherwise have a considerable influence thereon.
The measurement of the coil temperature as such provides particularly accurate information which can be used to make corrections in the evaluating configuration. Due to the tensile stress and deformation caused by drawing the wire, the temperature of the wire can increase relative to the room temperature dur
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Bensch Gunther
Schmidt Martin
Schneider Markus
Walch Bert
Echols P. W.
Robert & Bosch GmbH
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