Winding – tensioning – or guiding – Tension control or brake – Supply controlled
Reexamination Certificate
2000-05-23
2002-10-29
Walsh, Donald P. (Department: 3653)
Winding, tensioning, or guiding
Tension control or brake
Supply controlled
C226S015000, C226S093000
Reexamination Certificate
active
06471153
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an apparatus for controlling the vibration of a steel sheet being driven along the running surface of a processing facility in a steel rolling line or surface treating line in a steel mill.
2. Description of the Related Art
FIG. 27
shows a schematic diagram of a conventional apparatus for controlling the vibration of a steel sheet
101
being processed, by placing opposing electromagnets
102
A,
102
B on the front and back sides across the steel sheet
101
.
In such an apparatus, sensors
107
A,
107
B are placed inside the electromagnets
102
A,
102
B, respectively, for detecting the distances from the steel sheet
101
to respective electromagnets
102
A,
102
B, and the excitation currents passing through the coils in the electromagnets
102
A,
102
B are controlled according to the distances detected by the sensors
107
A,
107
B, so that the magnetic attraction forces can be adjusted in such a way to reduce the vibrations.
This vibration control apparatus comprises a plurality of pairs of electromagnets
102
~
105
arranged transversely to the running direction of the steel sheet, as seen in a plan view of the steel sheet
101
shown in FIG.
28
. Pairs of sensors
107
~
110
are placed in paired electromagnets
102
~
105
so that the magnitudes of the excitation current can be adjusted according to respective separation distances detected by the paired sensors.
In such a vibration control apparatus, because of bowing in the steel being rolled, the path of the steel sheet can sometimes show a tendency to be closer to one or the other electromagnet depending on the type of steel being processed and the running speed. If the control of electromagnets is started under such a condition, the control apparatus, in its effort to correct bowing of the steel sheet, tries to deliver more current to the electromagnet that is farther away from the sheet. However, a considerable force is required when the steel sheet is thick so that it is necessary to supply a high current to develop the necessary magnitude of force. Under such a circumstance, excitation current may become saturated due to factors such as inadequate capacity of the amplifier for the electromagnet, which may result in virtual loss of vibration control.
Also, when starting or stopping the vibration control action of the apparatus, if the apparatus is simply turned on or off, the excitation current changes suddenly to cause the steel sheet to hunt for a balancing position thus resulting in wild oscillation, and in extreme cases, the surface of the steel may collide with the surface of the magnetic poles to cause scratches on the steel sheet.
Also, when starting the control action, if the steel sheet is vibrating with such a large amplitude that the electromagnets cannot be brought into a proper range for control action, it may be considered that the electromagnets may be brought into proper positions after starting the process line. However, if the gap is large and the steel sheet is outside the range of detection of the sensors and the sensors are not able to detect the sheet position properly, there is a possibility that the steel sheet can be induced into oscillation.
Also, in the control apparatus described above, the relationship between the electromagnet pairs and the running sheet is subject to continual change because of such factors as the variations in the sheet thickness and width of the steel roll to be processed. For this reason, if the gain of the control apparatus is fixed at a constant value, changes in thickness, for example, may make the steel sheet susceptible to vibration to such an extent that the sheet surface may touch the pole surfaces of the electromagnets, in some cases.
Also, widthwise snaking of the steel sheet may occur in such a way that the edge of the steel sheet
101
swings to the position shown by the dotted line in FIG.
28
. In such a case, the steel sheet
101
positions itself in an ambiguous-location between the pair of electromagnets
102
so that, in spite of the fact that the sensor pair
107
inside the electromagnet pair
102
cannot detect the distances to the steel sheet, the control action in this case would be based on the detected distance of the sensor pair
107
to the steel sheet, therefore, control action on the electromagnet pair
102
becomes impossible. Under such a circumstance, the steel sheet may undergo vibration or the surface of the sheet
101
may touch the pole surfaces of the electromagnet pair
102
to cause scratches on the sheet
101
.
Also, if the steel sheet moves completely out of the detection range of the pair of electromagnet placed near the edge of the steel sheet, power will be wasted by the pair of electromagnets that are out of the range of detecting the steel sheet.
All of the foregoing problems may also be caused by changes in the width of the steel sheet being processed, for example.
Also, this type of control apparatus is normally operated so that the steel sheet would pass through the center line between the pair of opposing electromagnets. But, when the type of steel being processed changes in a given roll, that is, when a welded joint is passing through, the electromagnets are sometimes moved away from their normal detection position to a standby position to avoid collision of the welded section with the electromagnets. If the move is made while the electromagnets are turned on, even though the position of the steel line has not changed, the relative distances between the steel sheet and the electromagnets would increase, so that the control apparatus judges that the steel sheet has moved in a direction away from the sensors, and increases the excitation current to the electromagnets.
In this case, because the electromagnets are moving away from the steel sheet, the current increases as the electromagnets are moved away, and ultimately the control apparatus capability reaches its saturation limit, and the apparatus becomes inoperable. In the worst case scenario, the magnets may be overheated and destroyed.
To avoid such phenomena from happening, power to the conventional apparatus is turned off when the electromagnets are to be moved to the standby position. In the absence of vibration control action, vibration can be introduced in the processing line, and particularly during the initial stage of preparing for the standby operation, in other words, while the distance of separation between the electromagnets and the steel sheet is small, there is a danger that the steel sheet may contact the electromagnets.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide an apparatus for controlling vibration of a steel sheet being processed in a steel processing line, so that the processing line can be operated in a stable manner without having operational problems such as sheet vibration or loss of vibration control caused by such factors as snaking of the steel sheet or changes in the conditions of the sheet such as varying sheet thickness and width in the running sheet.
Also, it is another object of the present invention to provide a vibration control apparatus that permits the electromagnets to be retreated to a standby position without causing a line instability or excessive heating and damage to the electromagnets.
The object has been achieved in an apparatus for controlling vibration comprised by: electromagnet means for generating magnetic forces acting at right angles on the steel sheet; sensor means for detecting separation distances between the steel sheet and the electromagnet means; control means for controlling a flow of excitation current through the electromagnet means according to separation distances detected by the sensor means; and actuator means for adjusting the separation distance between the steel sheet and the electromagnet means; wherein the separation distance is adjusted by the actuator means when a specific condition is attained in a positional relationship between the steel sheet and the electromagnet mea
Kato Kazumichi
Kimura Tetsuyuki
Muragishi Yasushi
Rodriguez Joseph C
Shinko Electric Co. Ltd.
Walsh Donald P.
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