Electric heating – Heating devices – With power supply and voltage or current regulation or...
Reexamination Certificate
1999-12-17
2001-01-23
Paschall, Mark (Department: 3742)
Electric heating
Heating devices
With power supply and voltage or current regulation or...
C219S483000, C219S508000, C219S501000, C219S497000, C065S384000, C065S488000, C065S162000
Reexamination Certificate
active
06177656
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates in general to the control of glass fiber forming bushings and, more particularly, to an improved method and apparatus for controlling one or more segments of a multiple segment bushing to extend the range of control utilizing a given auxiliary power level by controlling both the heating and cooling of one or more segments of the bushing.
Glass fibers are commonly produced by drawing multiple streams of molten glass through nozzles or holes located in a heated container known in the industry as a bushing. The bushing is electrically resistance heated by passing high currents through it. Since the temperature of the bushing is one important factor in determining the characteristics of the glass fibers which are produced using the bushing, a variety of temperature control arrangements have been devised. All known fiber glass bushing control circuits are based on either current diversion around all or one or more segments of a multiple segment bushing or current injection into one or more segments of a multiple segment bushing.
Temperature control using current diversion around a bushing or one or more segments of a multiple segment bushing is disclosed, for example, in U.S. Pat. No. 4,594,087. In the disclosed arrangement, a controller diverts current around a bushing or segments of a bushing using variable impedance circuits. The diverted current reduces the temperature of the bushing or segment of the bushing from which current was diverted. An improved bushing controller utilizing an auxiliary transformer in each of the variable impedance circuits of the '087 controller to increase the current capacity of the controller is disclosed in U.S. Pat. No. 4,931,075.
Temperature control using current injection into a bushing is disclosed, for example, in U.S. Pat. No. 4,780,120. In the disclosed arrangement, current is injected into all but one segment of a multiple segment bushing and adjusts the supply of electrical energy to the entire bushing to control the temperature of each segment of the bushing.
Many of the known prior art arrangements are able to control fiber glass bushings to produce high quality glass fibers. Unfortunately, all known prior art arrangements require partial activation, preferably approximately 50%, during initial start-up and balancing of a fiber glass bushing which complicates these procedures.
There is an ongoing need for improvement in controlling fiber glass bushings to improve their operation and efficiency. Preferably, an improved bushing controller would not interfere with initial start-up and balancing operations, would provide increased range of bushing control without increasing the size of an auxiliary bushing power supply and would improve the coefficient of variation of glass fibers produced by controlled fiber glass bushings.
SUMMARY OF THE INVENTION
This need is met by the invention of the present application wherein a supplemental controller for a fiber glass bushing actively performs heating and cooling of a connected segment of the bushing which is otherwise controlled by a primary controller. In one embodiment of the supplemental controller of the present application, heating is performed by means of current injection into a connected bushing segment and cooling is performed by means of current diversion from or around the connected bushing segment. In another embodiment of the invention, heating is performed by injecting current into a segment in which the injected current is in-phase with current from a primary bushing controller while cooling is performed by injecting current which is out-of-phase with current from the primary bushing controller. With this improved positive control of both heating and cooling, initial start-up and balancing operations can be performed without activation of the supplemental controller. Since auxiliary power for heating does not have to be applied at approximately 50% during start-up and balancing operations, the effective control range is expanded. The control range is in fact approximately doubled over prior art arrangements with the same size auxiliary power supply.
In accordance with one aspect of the present invention, a method for supplemental control of a segment of a fiber glass bushing controlled by a bushing primary controller comprises the steps of: coupling a heating and cooling circuit to the segment of the fiber glass bushing; generating a control signal for the segment of the fiber glass bushing; determining whether the control signal commands heating or cooling of the segment of the fiber glass bushing; and, operating the heating and cooling circuit to heat and cool the segment of the fiber glass bushing in accordance with the determined requirements of the control signal.
The step of determining whether the control signal commands heating or cooling of the segment of the fiber glass bushing may comprise the step of comparing the control signal to a threshold. The step of generating a control signal for the segment of the fiber glass bushing may comprise the steps of determining the temperature of the segment of the fiber glass bushing, and utilizing the determined temperature of the segment of the fiber glass bushing in a temperature controller to generate the control signal. In one embodiment of the invention, the step of operating the heating and cooling circuit to heat and cool the segment of the fiber glass bushing in accordance with the determined requirements of the control signal may comprise the steps of connecting in-phase current to the segment of the fiber glass bushing for heating the segment, and connecting out-of-phase current to the segment of the fiber glass bushing for cooling the segment.
The step of coupling a heating and cooling circuit to the segment of the fiber glass bushing may comprise the steps of coupling a current diversion circuit to the segment of the fiber glass bushing and coupling a current injection circuit to the segment of the fiber glass bushing. The step of operating the heating and cooling circuit to heat and cool the segment of the fiber glass bushing in accordance with the determined requirements of the control signal may comprise the steps of operating the current diversion circuit for cooling of the segment of the fiber glass bushing, and operating the current injection circuit for heating of the segment of the fiber glass bushing.
The heating and cooling circuit is controlled to conduct portions of cycles of ac electrical energy to the segment of the fiber glass bushing for heating and to conduct portions of cycles of ac electrical energy from the segment of a fiber glass bushing for cooling. And the step of operating the heating and cooling circuit to heat and cool the segment of the fiber glass bushing in accordance with the determined requirements of the control signal comprises the steps of determining current flow in the heating and cooling circuit, generating a current flow signal corresponding to the current flowing in the heating and cooling circuit, combining the current flow signal and the control signal to generate a control error signal, determining a conduction control signal for the heating and cooling circuit in response to the control error signal, and operating the heating and cooling circuit in response to the conduction control signal.
Where the heating and cooling circuit comprises a first current control switch for connecting supplemental current to the segment of the fiber glass bushing and a second current control switch for diverting current around the segment of the fiber glass bushing, the step of operating the heating and cooling circuit in response to the conduction control signal comprises the step of controlling an onset of current conduction through the first and second current control switches for controlling heating and cooling of the segment of the fiber glass bushing, respectively.
In accordance with another aspect of the present invention, a supplemental controller is provided for a segment of a fiber glass bushing controlled by a primary bushin
Sanik Paul S.
Varrasso Eugene C.
Advanced Glassfiber Yarns, LLC
Alston & Bird LLP
Paschall Mark
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