Brakes – Operators – Electric
Reexamination Certificate
1999-01-13
2001-06-12
Oberleitner, Robert J. (Department: 3613)
Brakes
Operators
Electric
C188S164000, C188S158000, C310S103000
Reexamination Certificate
active
06244395
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to an electromagnetic hysteresis brake, especially as a yarn brake for textile machines, with a stationary brake magnet having an inner and an outer pole ring part and a magnet winding, and with a rotating armature, which is attached to a hysteresis ring of permanent magnetic material, wherein the hysteresis ring projects into an annular air-gap of the brake magnet, which is formed between the inner and outer pole ring parts.
BACKGROUND OF THE INVENTION
Known hysteresis brakes (DE 4 424 457 A1) are used as yam brakes in textile machines for example. The feature typical of such machines is a plurality of production units which are arranged in a row and run the same processing cycle in parallel. The individual yarn brakes are under central electrical control, in that current from a DC voltage source is applied to the magnet windings of the hysteresis brakes. The braking moment is provided exclusively by the magnetic flux created by the electromagnetic winding in the air-gap, which is dependent on the current applied to the winding at the time. If there is no current, there is no magnetic flux and the braking moment created by the previously known hysteresis brake would be equal to zero in this case. This means that the yarn has no tension when using the hysteresis brake as a yarn brake, should the current supply fail.
This can have fatal results in textile machines. The yarns of all spindles lose tension. If in ply twisting for example the yarn brake of the outer yarn lacks braking moment, yarn will be drawn out of the creel until the yarn is completely lacking tension. On account of the twist imparted by the twisting or ply twisting process, the yarns have an internal torsional moment. If there is no longer any yarn tension, this leads to the formation of loops. These can no longer be stretched out as the machine runs on. An unacceptable fault develops in the finished product. In order to avoid such faults, the textile machine has to be completely cleared down and set up again. Half-finished spools cannot be further processed as a rule. Also the remainders of the supply spools not yet processed create problems. As well as the high costs of unusable casualty spools of ply and supply material, high down times of the textile machines result. In order to counter these problems caused by loss of current, the textile machines are equipped with an emergency current supply from batteries. The demands of space, cost and servicing this emergency current supply are however substantial. Moreover the emergency current supply and thus the braking moment only lasts until the capacity of the batteries is exhausted which is normally the case after about 20 minutes.
SUMMARY OF THE INVENTION
The invention is based on the object of providing an electromagnet hysteresis brake, especially as a yarn brake for textile machines, wherein a sufficiently large braking moment is available in the case of loss of current, even without an emergency current supply.
This achieved according to the invention in that at least one permanent magnet is so arranged in shunt with the magnetic circuit of the magnet winding, that the magnetic field in the air-gap is formed by cooperation of the magnetic fluxes of the electromagnet (magnet winding) and the permanent magnet, and in that the magnetic flux of the electromagnet is so adjustable in magnitude and direction in the gap by corresponding poling that it assists or counteracts the magnetic flux of the permanent magnet.
The invention thus develops from the concept of creating the magnetic flux in the air-gap in part by the magnet winding of electromagnet and in part by the permanent magnet and superimposing the magnetic fields created by the electromagnet and by the permanent magnet. By suitable adjustment of the current applied to the electromagnet the superimposition can be so effected in the region of the hysteresis ring that the total magnetic flux in the gap tends to zero or is only used in part or is completely aligned in parallel in the gap.
By suitable current control of the electromagnet it is thus possible to adjust the hysteresis brake to any desired torque between 0 and 100%. Furthermore, on loss of current, the electromagnet does indeed become ineffective, but a magnetic field remains indefinitely through the permanent magnet, which is fully enough to generate a sufficiently high braking moment while the machine runs or when it stops. The braking force for keeping the yarn taut in the case of loss of current is insignificant; a small braking moment is already sufficient since it does not have to work against the yarn tensions during the production process. This means that only a braking moment of at least 20% has to be available, which is easily achieved by the permanent magnet. It is thus possible to dispense with an emergency current supply entirely and accordingly servicing the emergency current supply is obviated. As a side effect, the permanent magnet relieves the electromagnet during normal production. Accordingly this does not have to be energized with such a high current The output power of the normal current supply to the electromagnet can be made smaller. This affects the DC voltage source, the power output of the controller and the cable cross-sections through the machine.
The permanent magnet is advantageously so designed that the braking moment which can be created by it alone amounts to about 50% of the maximum braking moment. The electromagnet then only has to create the difference in magnetic flux which is needed to attain the specific braking moment. If less than the average braking moment is required, then the electromagnet operates with reverse polarity to the permanent magnet. If a braking moment between 50% and 100% is required, the electromagnet strengthens the magnetic flux of the permanent magnet through corresponding polarity. In normal operation of the textile machine the braking moment is therefore created by the magnetic fluxes of the two magnets. The adjustment of the required braking moment is effected by opposing or adding together the magnetic fluxes of the permanent magnet and the electromagnet. Only when current is lost and the textile machine correspondingly stops is the braking moment determined solely by the permanent magnet.
REFERENCES:
patent: 2765878 (1956-10-01), Pierce
patent: 3512618 (1970-05-01), Schafer
patent: 4560895 (1985-12-01), Zahner
patent: 4594844 (1986-06-01), Muzila
patent: 5121018 (1992-06-01), Oldakowski
patent: 5238095 (1993-08-01), Pedu
patent: 5490583 (1996-02-01), Anderson et al.
patent: 5873436 (1999-02-01), Schneider
patent: 1 613 034 (1971-04-01), None
patent: 3 628 285 (1987-03-01), None
patent: 4 424 457 (1996-01-01), None
Flynn ,Thiel, Boutell & Tanis, P.C.
Oberleitner Robert J.
Saurer-Allma GmbH
Sy Mariano
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