Electric heating – Metal heating – Cutting or disintegrating
Reexamination Certificate
1999-03-01
2001-07-10
Evans, Geoffrey S. (Department: 1725)
Electric heating
Metal heating
Cutting or disintegrating
C219S069160, C219S069180
Reexamination Certificate
active
06259053
ABSTRACT:
TECHNICAL FIELD
The present invention relates to a method and apparatus for controlling the position and power of electrodes in an electric-discharge texturing machine.
BACKGROUND ART
Electric-discharge machining which is conventionally referred to as EDM has been performed by generating a voltage between an electrode and a workpiece through a dielectric fluid such that a spark momentarily generated removes a portion of the workpiece surface to perform machining. EDM has more recently evolved into electric-discharge texturing (EDT) wherein the surface of a workpiece is textured. For example, rolls used in steel mills to roll steel that is to be painted cannot be too smooth or the paint adhesion will be improper. Texturing of the rolls provides the rolled steel with a textured surface to which paint adheres better. This texturing is performed by an EDT apparatus wherein a head having a bank of electrodes traverses the roll surface as the roll rotates. Actuators move the electrodes towards and away from the roll so as to achieve the correct gap between the electrodes and the roll. The actuators ensure that the electrodes are properly spaced with respect to the roll surface so as to be close enough to generate momentary sparks through dielectric fluid, but not too close so as to generate a continuous current flow without any sparks to perform the texturing operation.
A problem with a typical EDT apparatus is that the actuators are controlled with the same gain irrespective of whether the electrodes are to be moved toward or away from the roll. Using the same gain equally weights open and short circuited voltage conditions at the interface between the electrodes and the roll interface. This is disadvantageous because the difference in magnitude between the voltage associated with an open circuit condition and a discharge voltage is typically much larger than the difference in magnitude between the voltage associated with a short circuit condition and the discharge voltage. The discharge voltage is the voltage between the electrodes and the roll when sparking occurs.
Another problem with a typical EDT apparatus is that the spark periods during discharge are inconsistent. This occurs because the power switching control in the typical EDT apparatus switches on and off the power supply with a constant pulse train. Using a constant pulse train does not take into account that the time between pulse application and spark initiation varies depending upon operating conditions. In essence, the resultant spark period is variable depending upon the period between pulse application and spark initiation and a typical EDT apparatus does not account for this variability. The uneven spark period is a source particularly troublesome in EDT where consistent surface finishes are sought.
A further problem with a typical EDT apparatus is that of haphazard sequencing between power channels. An EDT apparatus includes numerous independently operating power supplies. To maintain consistency, the power output current must be the same across all power supplies. This is traditionally accomplished by generating a central on-off time control pulse train and distributing it to all the power supplies. This haphazard sequencing causes back electromotive forces to be generated as the power system is fully loaded at one time instant and then has no load at all at another time instant.
DISCLOSURE OF INVENTION
Accordingly, it is an object of the present invention to provide a method and apparatus for an electric-discharge texturing (EDT) machine in which the actuators for moving the electrodes are controlled with different gains depending upon whether the electrodes are to be moved toward or away from the roll.
It is another object of the present invention to provide a method and apparatus for an EDT machine in which the actuators for moving the electrodes have a forward gain if the electrodes are to be moved toward the roll and a reverse gain if the electrodes are to be moved away from the roll.
It is a further object of the present invention to provide a method and apparatus for an EDT machine in which the spark periods during discharge are consistent.
It is still a further object of the present invention to provide a method and apparatus for an EDT machine in which pulse application is continued until discharge and then terminated after the expiration of a selected discharge period.
It is still another object of the present invention to provide a method and apparatus for an EDT machine in which the sequencing between power channels is synchronized to minimize the power load of the EDT machine at any given time.
It is still yet another object of the present invention to provide a method and apparatus for an EDT machine in which the on period of a power channel is synchronized to start a selected time period after any other power channel has been turned off.
In carrying out the above objects and other objects, the present invention provides an electric-discharge texturing (EDT) apparatus for texturing a roll. The apparatus includes an electrode and an actuator associated with the electrode for moving the electrode away from and towards the roll to maintain a desired spacing between the electrode and the roll. A power source applies a voltage to the electrode for promoting a spark between the electrode and the roll to remove particles from the roll and produce a textured finish thereto. The spark between the electrode and the roll occurs when spacing between the electrode and the roll is equal to a sparking gap while voltage is being applied to the electrode. A gap voltage monitor is operable with the electrode to provide a gap voltage monitor signal indicative of the voltage between the electrode and the roll. A processor determines the spacing between the electrode and the roll from the gap voltage monitor signal. The processor is operable with the actuator to move the electrode away from and towards the roll to increase and decrease the spacing between the electrode and the roll until the spacing between the electrode and the roll is equal to the sparking gap. The processor controls the actuator to move the electrode at different speeds as a function of the spacing between the electrode and the roll with respect to the sparking gap.
Further, in carrying out the above objects and other objects, the present invention provides another EDT apparatus for texturing a roll. This apparatus includes an electrode and a power source. The power source applies a voltage pulse to the electrode for promoting a spark between the electrode and the roll. A gap voltage monitor is operable with the electrode to provide a gap voltage monitor signal indicative of the voltage between the electrode and the roll. A processor controls the power source to apply a voltage pulse to the electrode and processes the gap voltage monitor signal to determine when a spark is promoted between the electrode and the roll. The processor controls the power source to apply the voltage pulse until spark initiation and then controls the power source to maintain the voltage pulse for a selected time duration after spark initiation to provide a spark having the selected time duration between the electrode and the roll.
Still further, in carrying out the above objects and other objects, the present invention provides a further EDT apparatus for texturing a roll. This apparatus includes first and second electrodes. First and second power sources apply voltages to the respective first and second electrodes for promoting an electrical discharge between the first electrode and the roll to remove particles from the roll. A switching controller is operable with the first and second power sources for applying respective voltages to the first and second electrodes. The switching controller controls the first and second power sources such that the first power source applies a voltage to the first electrode while the second power source is off and the second power source applies a voltage to the second electrode while the first power source is off.
The objects, features
Brooks & Kushman P.C.
Evans Geoffrey S.
Modern Hard Chrome Service Company
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