US3424895A - Electrical spark perforator for moving web - Google Patents

Description

Jan.2s,1969 Komm l 3,424,895

ELECTRICAL SPARK PERFORATOR FOR MOVING WEB Jan. 28, 1969 A. K. OLSON 3,424,895

ELECTRICAL SPARKPERFORATOR FOR MOVING WEB Filed Dec. 2, 1966 sheet 3 of; 76. 624 F/G. 65

I F/c7165 l H6714 F/G 7.5

United States Patent O 1S Claims ABSTRACT OF THE DISCLOSURE An apparatus and method for electrically perforating a moving web are disclosed wherein the web is guided between a first electrode which continually slideably engages the web and a second electrode, the web being supported a predetermined distance from the second electrode by a pressurized moving fluid film; and the discharge of the electrodes being synchronized with the rate of web advance. i

This invention relates to apparatus and method for perforating a moving length of strip material and in one aspect to apparatus and method for electrically perforating a rapidly moving web supported by a fluid film between a pair of electrodes.

Perforation of a rapidly moving web by means of an electrical discharge across a pair of electrodes adjacent a moving web is known.

In one known spark recording system a web moving at a uniform rate is perforated as a means of recording information. The web is moved within a spark gap formed between a pointed electrode, which is positioned normal to and adjacent one surface of the moving web, and a rotating electrode, which physically contacts the moving web and is in spaced alignment With the pointed electrode. When a spark is produced across the electrodes, the moving web is perforated in the vicinity of the pointed electrode at the instant the spark is produced. The web is advanced at a uniform rate and the spark is produced at intervals independent of the rate of advance of the web.

Other known devices feed the moving web between an anvil and a die wherein the anvil supports a pair of electrodes adjacent the web surface. A high-voltage highcurrent electrical spark having a duration in the order of microseconds is discharged across the electrodes. The gases produced by the spark are confined between the anvil and die. The force produced by the rapid expansion of the gas due to the electrical discharge causes the moving web to be embossed or perforated in a desired manner. Improved spark discharge control means have been developed to control more than one pair of electrodes thereby permitting several web perforations to be accomplished simultaneously.

Spark perforation of microscopic holes in stationary dielectric materials is known. The spark perforation is accomplished by a pair of pointed electrodes placed in pressure contact, one on each side of the dielectric material to be pierced. Additionally, one of the pointed electrodes is immersed in a dielectric fluid such that when an electrical discharge is produced, the discharge travels .directly through the material being pierced thereby permitting holes to be placed in close proximity to each other. The fluid is utilized to prevent the spark discharge from occurring at any other location other than at the tip of the pointed electrode.

The known prior art apparatus and methods have certain disadvantages. A disadvantage of the spark recording system is that the rotating electrode contacting the surface of the moving web has a large mass and a high 3,424,895 Patented Jan. 28, 1969 heat transfer coefficient. When an electrical discharge occurs between the electrodes, one of which is the large rotating electrode, the resulting perforations have a nonuniform axial diameter. This occurs because the rotating electrode, contacting the web surface, absorbs a substantial portion of the thermal energy produced by the electrical discharge, which thermal energy would otherwise produce a perforation of uniform diameter.

The apparatus employing a die and an anvil has a disadvantage in that separate machined components are required to vary the diameter of the perforations. Further, the high voltage pulses require high currents in the order of hundreds of amps. Because of the large current magnitudes and short burning times associated with such discharges, the resulting perforations have ragged edges and burrs.

The apparatus for electrically piercing microscopic holes in dielectric materials has the disadvantage that the electrodes must be brought into pressure engagement with the surface of the material to be pierced and one of the electrodes must be immersed in a dielectric fluid to prevent flashover. Thus, the apparatus must include means for fixing the electrode and workpiece together to prevent movement therebetween at the time of the electrical discharge. A further disadvantage of this apparatus is that the perforations cannot be continuously made on a moving dielectric material.

Other problems of the prior art devices are that certain of spark perforators are energized by direct current voltage or by a fixed alternating current voltage such that a variance in the speed of the moving web results in a nonuniform density of holes per unit area as a function of web speed. Further, a pointed electrode, when placed normal to and in continual contact with the material to be perforated, wears and 'becomes rounded. As the electrode becomes rounded, hole placement in the dielectric material becomes uncontrollable. Thus, it is necessary that fboth electrodes be sharply pointed and disposed opposite each other. If point electrodes are utilized to contact a rapidly moving web, the pointed electrodes must be continually replaced or sharpened to insure controllable perforations in the moving web.

This invention overcomes the disadvantages of the prior art by providing a sprak perforator utilizing a fluid film. The fiuid film supports a rapidly moving web in a spark gap between two electrodes and provides a thermal barrier for the discharge. One electrode is positioned at an angle to slideably contact one surface of the moving web. The other electrode, which is disposed in spaced v alignment from the one electrode to form the spark gap therebetween, has the moving web spaced therefrom by means of the fluid film. The fiuid film serves a dual function as an air bearing and as a thermal barrier. The thermal barrier function of the uid film insures perforations of uniform axial diameter throughout the entire web thickness.

Another advantage of this invention is that the frequency of the electrical discharges between the electrodes can, as desired, be synchronized with the rate of advance of the moving web such that perforations of a uniform density are produced in the longitudinal direction of web movement at any web speed.

A further advantage of the present invention is that one of the electrodes is preferably a pointed or needle electrode which is self-sharpening and need not be replaced even though the tip thereof is worn by the abrasive effect between the electrode and rapidly moving web.

Another advantage of this invention is that the diameter of the perforations may be precisely controlled by varying the duration, the voltage and current of the electrical discharge. By utilizing the teachings of this invention, perforations having a wide range of diameters can be made in a web wherein the web can be either stationary or moving over a wide range of speeds from substantially zero feet per minute up to and in excess of 800 feet (244 meters) per minute.

Yet another advantage of the present invention is that a method of perforating a moving web is provided wherein the perforations may be of uniform axial diameter and without ragged edges and burrs.

Briefly, the apparatus for perforating a rapidly moving web includes a first and a second electrode. The first electrode is positioned at an angle to the longitudinal direction of web movement and continually slideably contacts one surface of the web. The second electrode is spaced from the first electrode. The second electrode, or an auxiliary source, comprises means for forming a fluid film in the spark gap which supports the web a predetermined distance from the second electrode. A power means is connected between the first and the second electrodes and produces an electrical discharge lacross the spark gap which perforates the web. The apparatus further includes means which are connected to the power means for synchronizing the electrical discharge with the rate of advance of the web.

The above and further advantages of the present invention will become fully apparent when considered in light of the following detailed description and drawing.

FIGURE 1 is a diagrammatic illustration partially in block form showing one embodiment of a spark perforator utilizing the teachings of this invention;

FIGURE 2 is 'a graph illustrating a waveform of the current as a function of time of the electrical discharges of the spark perforator;

FIGURE 3 is a side view of a needle electrode used in one embodiment of the spark perforator;

FIGURE 4 is a diagrammatic illustration showing the relationship between the moving web and electrodes across which an electrical discharge is produced;

FIGURE 5 is a side view of a needle electrode support assembly;

FIGURES 6A, 6B and 6C are diagrammatic illustrations of the electrical discharge between a needle electrode and a plenum at various stages during web perforation;

FIGURES 7A and 7B are diagrammatic illustrations of the wearing of a needle electrode which slideably engages a rapidly moving web; and

FIGURE 8 is a schematic diagram partially in diagrammatic illustration showing a high voltage supply and a triode vacuum tube for synchronizing the electrical discharge with the rate of advance of the web.

In the diagrammatic illustration of the spark perforator of FIGURE 1, a rapidly moving web 12 is guided along a predetermined path around a journalled roller 14. The moving web 12 is driven around the roller 14 by means of a web drive 16 operatively coupled to a first set of rollers includingl a driving roller 18 'and an idling roller 20. The roller 20 forms a nip with driving roller 18 such that counterclockwise rotation of roller 18 advances the web across the surface of roller 14. A second set of guide rollers 22 and 24 direct the moving web such that it follows the arcuate surface of roller 14.

The roller 14, in one preferred embodiment, is secured in a predetermined position and the moving web 12 slideably advances across the surface thereof. However, the roller 14 is constructed such that when it is unclamped it is permitted to freely rotate as the web 12 advances thereacross.

The roller 14 has a thin cylindrical outer wall 26 enclosed by end members 28, only one being shown due to cross sectioning of the roller 14. The outer wall 26 and the end members 28 form a fluid chamber 30 within the interior of roller 14. Each of the end members are journalled at support members 32 to permit either clamping or rotation of roller 14. Further, the roller 14 is constructed such that about one-half of the outer wall 26, or about a 180 sector, has a plurality of apertures 34 extending therethrough between the external periphery of outer wall 26 and chamber 30. This 180 sector forms a plenum 36. It is anticipated that more or less than a sector may contain the apertures 34. For example, some applications may require that the plurality of apertures 34 be provided about the entire periphery of the roller 14. In this application, the apertures would be aligned relative to the electrodes such that a portion of the roller surface is always positioned in spaced alignment with the electrodes, to be described hereinafter, to insure perforation of the web.

When the roller 14 is clamped or secured from rotation, the plenum 36 is positioned adjacent the moving web 12. A source of positive fluid pressure 38 is operatively connected via a line 40 to the support member 32 such that a positive pressure is introduced into the chamber 30. The positive pressure in chamber 30 forces fluid through apertures 34 against the undersurface of the web 12. Hereinafter, the side of the moving web 12 near the outer wall 26 shall be referred to as the undersurface while the opposite side thereof shall be referred to as the outer surface. The fluid directing through apertures 34 of plenum 36 is confined between the undersurface of the moving web 12 and the outer wall 26 and forms a fluid film 42.

As mentioned hereinbefore, the roller 14 can be unsecured such that the roller freely rotates as the web 12 advances across the surface thereof.

When the roller 14 is permitted to freely rotate together with the rapidly moving web 12, the rapidly moving web 12 generates a laminar flow of fluid due to the frictional interaction between the moving web and the surrounding fluid. 'Ihe rapidly moving web 12 causes the laminar flow of fluid to be directed between the outer wall 26 of roller 14 and the moving web 12. The laminar flow of fluid creates a hydrodynamic force which resiliently supports the web 12 a predetermined distance from the periphery of outer wall 26 forming the fl-uid film 42. Concurrently, the roller 14 is rotated by the force of the moving fluid. rIlhe peripheral velocity of the outer wall 26 is substantially the same as the linear velocity of the advancing web 12. Further, in some applications it may be desirable to permit the roller 14 to freely rotate while the source of positive pressure is utilized to aid in forming the fluid film 42. In this instance, the roller 14 would have a plurality of apertures 34 about its entire periphery.

In any application, i.e. when the roller 14 is secured in a predetermined position with plenum 36 adjacent the web 12 and a positive source of fluid pressure is utilized, or when roller 14 is permitted to freely rotate, or when the roller 14 is permitted to freely rotate and a positive source of fluid pressure is utilized, the confined fluid forms the fluid bearing or fluid film 42 between the outer wall 26 or roller 14 and the undersurface of moving web 12. 'I'he fluid filmI 42 spaces the moving web 12 a predetermined distance from. the roller 14. The spaced distance of web 12 from roller 14 is a function of tension produced by the web drive 16 in cooperation with driving roller 18 and idling roller 20.

It is anticipated that equivalent apparatus could be used in performing the function of the roller in various modes of operation. The use of a roller member in cooperation with a posit-ive pressure source is intended to be only an illustrative embodiment of one mode of this invention.

A needle electrode 44 having a conical tip member 46 and a conductive resilient support means 48 is positioned to slideably engage the moving web 12, said needle electrode being positioned at yan angle 9 to the longitudinal direction of web movement. In this embodiment, the needle electrode 44 forms a first electrode and the roller 14 forms a sec-ond electrode. It is anticipated that the second electrode could be pointed with the tip thereof positioned frotm the surface of roller 14 and into the fluid film 42. Such an arrangement would increase the voltage gradients between the electrodes for perforation of materials having highkilovolt dielectric strength. The needle electrode 44 and the roller 14 are spaced to form a spark gap therebetween through which the web advances. The conductive resilient support means 48 permits the needle electrode tip 46 to yieldably slideably engage the outer surface of the web 12. The needle electrode 44 is electrically connected in series circuit to a resistor 50 having a high ohmic value.

Hereinafter, the remainder of the discussion will be directed to the operation of the spark perforator wherein the roller is seoured or clamped such that the plenum 36 of outer wall 26 is adjacent the moving web 12. Thus, the flulid llrn 42 is formed by the liuid directed through aperture 34 and between the under side of web 12 and wall 26. The principles of operation described in connection with this condition are equally applicable when the roller 14 is permitted to freely rotate either with or without the source of positive pressure 38 aiding in the formation of the fluid iilm 42.

The source of positive lluid pressure 38 is selected to be of suicient pressure to form the fluid nlm 42 in the spark gap beween the needle electrode 44 and the roller 14 to space the web a predetermined distance from the wall 26. p

An electrical discharge is produced across the tip 46 of needle electrode 44 to plenum 36 by applying a high voltage pulse across the resistor 50. The electrical discharge or spark burns a hole through the web 12 beginning at a point at the end of the electrode tip 46. As the web advances, the electrical discharge burns a perforation, having a preselected uniform axial diameter, through the thickness of the web 12.

The electrical energy for producing the high voltage pulse is obtained from power means 52 which may be a high voltage power supply. The power means 52 is connected via line 54 to the roller 14 establishing a common reference potential therebetween. A switching means 56 is electrically connected between the power means 52 via a conductor 58 and the resistor 50 by means of a conductor 60. When the switching means 56 is actuated, an electrical cirouit is completed between power means 52, conductor 58, switching means 56, conductor 60, resistor 50, resilient means 48, tip |46, and across the spark gap to the roller 14, conductor S4 back to the power.

means 52. The resulting electrical discharge in the spark gap between needle electrode 44 and roller 14 perforates the moving web 12.

Switching means 56 is controlled in synchronism with the Vrate of advancement of the web 12. Thus, the spark perforator is capable of perforating the moving web 12 at a unifonm density regardless of web speed. This synchronization is accomplished, in this embodiment, by connecting a pulse generator 62 to guide roller 24. The pulse generator 62 produces a series of output pulses as a function of the rate of advance of the web, which is determined by t'he rotations per minute of the guide roller 24. The output pulses produced by the pulse generator 62 are `applied to a counter 64. Counter 64 produces a control pulse after receiving a predetermined number of output pulses from the pulse generator 62. The counter 64 applies the control pulses to a control means 66. The control means 66 conditions switching means 56 with a switching pulse in response to each control pulse. The switching means 56, when triggered by switching pulse, connects the power means 52 to the resistor 50. By synchronizing the electrical discharge across electrode 44 and roller 14 with the rate of advance of the web, the density of perforations per unit area on the web will be uniform regardless of the rate of advance of the web.

The electrical discharge produced by switching means 56 in synchronism With the advancing web is determined 'by the control means 66. An important feature of the spark perforator is that the resulting electrical discharge produced by switching means 56, in response to a switching pulse from the control means 66, is of a relatively low power level. This feature is important since the prior art devices required pulses having current magnitudes in the order of hundreds of amps and extremely short time durations in the order of microseconds.

In the present invention, the pulses have current magnitudes in the order of milliamps and pulse durations in the order of milliseconds. A typical waveform of the spark perforator discharge current as a function of time is illustrated in the graph of FIGURE 2. The graph of FIGURE 2 comprises two electrical discharge waveforms 68 and 70 wherein the time interval therebetween is a function of web speed. If the web is advancing at a high rate, the duration between pulses is extremely short. Inversely, if the web is advancing at a slow rate, the time interval between the pulses is greater thereby maintaining uniform perforation density regardless of web speed.

Referring now, for example, to waveform 68 illustrated in the graph of FIGURE 2, at the beginning of the electrical discharge, particularly with the leading edge thereof occurring at time T1, the discharge current may be in the order of about six milliamps. The eract current magnitude is a function of discharge voltage, the material to be perforated and the thickness of the fluid film. The pulse duration may be about two and one-half milliseconds and the trailing edge of the discharge is illustrated at time T2. At time T2 the current may decrease to a magnitude less than the original starting current. The diameter of the resulting perforation can be made larger by increasing the pulse duration. When the pulse duration is increased, the difference between the beginning discharge current magnitude and the dischar-ge current magnitude at the end thereof increases. Thus, the maximum pulse duration would be dependent upon the minimum current required to burn the moving web 12 after the initial perforation is accomplished by the leading edge of the discharge pulse at time T1.

The power consumption required for perforating each hole in the moving web is substantially decreased due to the uid film 42 which functions as a thermal barrier between the web 12 and the roller 14. The fluid film 42 prevents the roller 14 from absorbing thermal energy from the electrical discharge thereby permitting substantially all of the thermal energy of the portion of the arc passing through the web to be utilized in perforating the web 12.

In one embodiment, the web drive 16 provides a tension in the range of `about two pounds per inch (about .36 kilograms per centimeter) of web width while moving the web at speeds up to about 800 `feet (about 244 meters) per minute. The clamped roller 16 had a diameter of about ve inches (about 12.7 centimeters). The web was a .00125 inch (32 micron) thick paper. The iluid lilm 42 may be, for example, an air bearing, an inert gas bearing or the like of up to about .030 inch (about .75 millimeter) thickness but may be normally in the range of about .001 to .005 inch (about .O3 to .13 millimeter). An air pressure of about two to five pounds per square inch (about to 350 grams per square centimeter) was used to space the pap-er from the roller 14, which roller was made from one-eighth inch (3.2 millimeter) metal. The needle electrodes `were constructed of stainless steel. A spark perforator having the above typical characteristics is capable of perforating holes which are less than one micron in diameter at a density of about 64 holes per square inch (about 10 holes per square centimeter). In one operation, perforations of about .0016 inch (about 40 microns) were made in the moving web 12. The power means 52 was about 6,000 volts and the pulse duration would vary from about 1.3 to 4.5 milliseconds. The angle 9 may vary from normal to the outer surface of the web 12 down to about less than ten degrees with an angle of 45 degrees being preferred.

FIGURE 3 is a front view of the needle electrode 44 illustrating that the conductive resilient support means 48 may be a stainless steel coiled spring soldered to a stainless steel tip46. The soldering was accomplished by using a solder comprising 60 percent tin and 40 percent lead and a soldering flux for stainless steel. v.

Referring now to FIGURE 4, the operation of the spark perforator is illustrated vwith the electrical discharge 74 at an intermediate point when the electrical discharge is perforating-the web 12. The needle electrode 44 is supported in aneedle electrode support 76 which is circular in cross-section. The support 76 has an elongated opening 78 extending therethrough into ,which the needle electrode 44 is inserted. The support 76 has a tapped opening 80 which is normal to opening 78. Thetapped opening 80 receives a set screw 82 which is advanced into contact with spring 4 8 to removably support the needle electrode 44 in opening 78. The spring 48 permits the tip 46 of needle electrode 44 to yieldably engage the outer surface of web 12.'

The fluid film 42 is an important part of this invention in that it functions as a thermal barrier between the web 12 and the roller 14. The fluid film 42 provides a reduced coefficient of sliding .friction between-the web 12 and roller 14 such that the web can be driven in a longitudinal direction at speeds in excess of 800 feet I(244 meters) per minute. In the absence of the uid film 42, the moving web 12 would be urged into slideable engagement with the roller 14 with the tip 46 ofthe needle electrode 44 slideably engaging the outer surface of web 12. If an electrical discharge occurs between electrode tip 46 and roller 14 undersuch conditions, a perforation would be made in the web 12. However, the axial diameter of the perforation of the undersurface of web 12 contacting roller 14 would be substantially less than the axial diameter of the perforation onthe outer surface of the web 12 adjacent the ti-p 46 ofthe needle electrode 44.

By placing the lluid lm 42 between themoving web 12 and roller 14, perforations of uniform axial diameter without burrs and ragged edges are formed. The iiuid film V42 acts as a thermal barrier and the heat generated by an electrical discharge 74 occurring between the tip 46 of electrode 44 .and roller 14 is retained within the localized larea of the web being perforated. In the absence of the fluid film 42, the roller 14 absorbs thermal energy from the electrical discharge 74 such `that only a part of the thermal energy can be used for perforating the web 12 thereby resulting rin the taperedhole.I Thus, introduction of a liuid lilm 42.between the rapidly moving ,web 12;,and the second electrode or roller 14 not onlyreduces the coeicient of sliding friction therebetween but. also provides a thermal barrier such that a rapidly moving `web, 12 can be perforated at a uniform density with perforations of uniform axial diameter throughout the entire thickness of the web 12.

The sizeof the perforation in the moving web can be controlled by varying both the magnitude of current flowing between needle electrode 44 and roller 14 and the duration of the pulse. The maximum high voltage pulse duration is limited by the length to which the electrical discharge 74'can be extended as the web 12 advances before the discharge is extinguished. The length of the electrical discharge 74 is determined by the maximum ionized path which can be sustained by the source of potential through a perforation which is continually moving` away from the electrode tip 46. If the high voltage pulse duration exceeds this limitation, the electrical discharge 74 could possibly restrike and perforate the web 12 in an undesired location.l

`FIGURE isl a side viewtof a needle electrode assembly ,84 having a housing l86 which encloses the needle electrode support 7 6. The needleelectrode support 76 is an insulating elongatedmember having a circular cross-section as described in FIGURES and includes a plurality of spaced elongated openings 78 therethrough such that a plurality of needle electrodes can be disposed along the width of the moving web 12.

A longitudinally extending member 88 having an 8 g elongated opening thereinwith arcuate edges is fastened to the housing 86 by means of fasteners such asscrews 90. The member 88 receives thesupport 76 therein such that the electrode tip 46 extends through its opening. When the screws 90 are advanced into the housing 86, the member 88 secures the support A76 in the desired position such that electrode tip 46 yieldably slideably engages the outer surface of web 12. An arcuate-shaped member 92 isvtixedly connected to the housing 86 by means of ,screws 94, one of which terminates in an electrode terminal 96. Further, the arcuate-shaped member 92 is positioned around the periphery of support 76 to slideably contact and complete an electrical.circuitbetween the portion of spring 48 ex-` tending from opening 78 opposite the tip 46 and resisto 50.

The entire needle electrode assembly. 84 iswrigidly supported by means of housing support member 98 which member is fastened by a fastener 100` against la channel member 102. The channelmember 102 is ,constructed to have a plurality of individual wiringV terminals 104 which wiring terminalsare subsequently connected to the resistor 50. Separate high voltage conductors 106 elec. trically connect each wiring terminal 104 to electrode terminal 96.l .v As indicated hereinbefore, electrode tip 46 slideably engages the outer surface of the moving web 12 at an angle 9 to the longitudinal direction of movementof the web. The angle 9 can be adjusted by withdrawing screws 90 froml the housing 86 such that the member 88 is loosened to allow the needle electrode support 76 to be rotated therein. As the support 76 is rotated to position theelectrode tip 46 at any desired angle and the screws 90 retightened, the spring 48 slideably contacts the arcuate-shaped member 92 thereby insuring a complete electrical connection between the needle electrode 44 and the remainder of the high voltage circuit. FIGURES 6A, 6B and 6C are diagrammatic representations Of the electrical discharge V74. The electrical discharge isv shown in FIGURE 6A as it commences, `in FIGURE 6B at approximately Athe mid-point of the e1ectrical discharge and in FIGURE 6 C just' prior to termination ofthe electrical discharge. In FIGURE 6A, when the electrical discharge is produced,ia perforation 108 having an initially small diameter is produced in the web 12 located at the electrode tip `46 of electrode 44. When the electrical discharge 74 occurs, the dielectric strength of the moving web 12 and the portion of the iiuid film 42,between the web 12 and outer wall 26 ofv roller 14 isexceeded forming an ionized conductive path for the discharge 74from electrode tip 46 to outer wall 26. As the electrical discharge v74 continues, the diameter of the perforation 108 increases as the web moves relative to the outer wall 26.

This can be seen by referring to FIGURE 6B wherein the perforation 108 is disposed lfrom the electrode tip 46of needle electrode 44 and the length of the electrical discharge 74 is increased. As the length of the electrical discharge 74 increases, the discharge 74 continually ionizes the localized portions of the liud film 42 between web 12 and outer wall 26. The diameter of perforation 108 of FIGURE 6B is increased compared to that of FIGURE 6A. FIGURE 6C illustrates the final position of the perforation 108 just prior to extinction of the discharge 74. The length of the discharge 74 is substantially longer thanY that of FIGURE 6B, and when terminated the perforation 108 will be spaced from the electrode tip 46 of electrode 44. When a subsequent high voltage pulse is applied to electrode 44, perforation 108 will be spaced sufficiently from electrode tip 46 of electrode 44 such that a subsequent perforation is made in web 12 by a subsequent discharge 74. If perforation 108 is not spaced sufficiently from electrode tip 46 of electrode 44 at the time of a subsequent electrical discharge, the discharge would ionize a path to outer wall 26 through the same perforation 108 whereupon web 12 would not be perforated.

Since the electrode tip 46 continually slideably engages the rapidly moving web 12, the sharp point of the tip 46 illust-rated in FIGURE 7A will subsequently be Worn to a tapered point illustrated in FIGURE 7B. However, the electrode 44 is disposed at an angle G relative to the longitudinal direction of movement of the web 12 and as electrode tip 46 is Worn, the tip 46 forms a sharp trailing edge 110 which eng-ages the outer surface of web 12. When the discharge 74 is produced, it ernanates from trailing edge 110 which functions as a pointed electrode. This is an important feature of this invention in that as the needle electrode wears, the resulting tapered point will still operate properly and the electrode need not be replaced.

Referring now to the schematic diagram of FIGURE 8, each needle electrode 44 is connected through a resistor 50 having a high ohmic value of about one megohm. A second resistor 112 having a substantially lower ohmic value, in the range of about 27,000 ohms, is connected in series circuit with resistor 50. Connected in parallel to the second resistor 112 is a neon lamp 114, -which lamp is connected in series circuit with a current limiting resistor 116. Resistor 112, resistor 50, needle electrode 44 and neon lamp 114 are energized by a conductor 118, which conductor is electrically connected to a switching means, particularly a high voltage triode vacuum tube 120. The resistor 116 is inserted in series circuit with the resistor 50 to provide a small voltage drop of sufficient magnitude to ignite neon lamp 114. Each neon lamp 114 is ignited providing a visual indication that a spark is being produced each time an electrical discharge occurs between each needle electrode 44 and the second electrode or outer wall 26. In the event that one of the needle electrodes fails to produce an electrical discharge when energized, neon lamp 114 will not be ignited thereby providing a visual indication of the malfunction.

Tube 120 is connected to a high voltage power supply 124. When tube 120 is rendered conductive, the tube 120 electrically connects the high voltage power supply 124 to conductor 118. Conductor 118 applies the high voltage across the parallelly connected needle electrodes 44 causing the electrical discharge between each needle electrodev 44 and outer wall 26 of roller 14. Outer wall 26 is electrically connected to the high voltage power supply 124 by means of conductor 126 thereby completing the high voltage circuit.

The conduction of the 120 may be controlled by a oneshot rnonostable multivibrator 128 in response to a control pulse applied thereto via an input 130. The high voltage pulse duration is determined by the reset time of multivibrator 128.

When the high voltage `pulse is applied via resistors 112 and 50 to the needle electrodes 44, the capacitance between each high voltage lead and ground stores a charge. This charge is removed by means of a bleeder resistor 132, which resistor is electrically connected between conductor 118 and the high voltage power supply 124.

The high voltage -pulse duration is controlled by varying the on time of the multivibrator 128. The interval between pulses is determined by the frequency of control pulses applied to input 130 from a pulse generating and counting circuit such as that of FIGURE l. The resistors 50 are necessary in this spark perforator so that each of the needle electrodes will generate an electrical discharge regardless of whether or not the other electrodes are discharged. After an electrode has producer a discharge, its resistor 50 develops a voltage drop thereacross of sufiicient magnitude to keep the voltage on conductor 118 at a high voltage level such that the other electrodes can produce a discharge. In the absence of resistors 50, if one of the electrodes discharged prior to the other electrodes, the voltage on conductor 118 would be reduced substantially to ground potential such that the other electrodes could not produce an electrical discharge.

Having thus described the inventive spark perforator, it is to be understood that various modifications will be apparent to one having ordinary skill in the art and all such modifications are contemplated as within the scope of the appended claims.

What is claimed is:

1. Apparatus for electrically perforating a moving web comprising a first electrode positioned at an angle to the longitudinal direction of web movement for continually slideably engaging one surface of said web;

a second electrode spaced from said first electrode for forming a spark gap therebetween through which said web advances;

means for supporting said web on a moving fluid film having sufiicient pressure to space said web a predetermined distance from said second electrode;

power means connected between said first and second electrodes for producing an electrical discharge thereacross having a potential sufficient to at least perforate said web; and

means connected to said power means for synchronizing said electrical discharge with the rate of advance 0f said web.

2. The apparatus as set forth in claim 1 wherein said first electrode includes a conical tip member which slideably engages said one surface of the web such that as said tip becomes worn the trailing edge thereof remains pointed independent of electrode wear, and wherein said second electrode is a continuous surface.

3. The apparatus of claim 1 wherein said iirst electrode is a stainless steel needle electrode supported by a conductive resilient means which yieldably urges the tip of said needle electrode into continual slideable engagement with said one surface of the web, and wherein said second electrode is a metal plenum having an outer surface formed with a plurality of apertures therethrough, said apparatus further including a source of positive iiuid pressure communicating with said web supporting means to direct fiuid under pressure through said apertures for producing a iiuid film which supports said web a predetermined distance from said plenum outer surface.

4. The apparatus of claim 1 wherein said first electrode is a stainless steel needle electrode supported by a conductive resilient means which yieldably urges the tip of said needle electrode into continual slideable engagement with said one surface of the web, and wherein said second electrode is a metal roller having a metal outer Wall and adapted to freely rotate as said web is advanced thereacross whereupon said advancing web in cooperation with said roller causes a laminar fiow of fiuid to be confined therebetween which supports said web a predetermined distance from said roller outer wall.

5. The apparatus of claim 4 wherein said metal roller outer wall includes a plurality of apertures extending therethrough and wherein said metal roller outer wall encloses a hollowed-out area therein for forming a fluid chamber, said apparatus further including a source of positive fluid pressure communicating with said fluid chamber to direct fluid under pressure through said apertures for producing a fluid film which supports said web a predetermined distance from metal roller outer wall.

6. The apparatus of claim 5 wherein said metal roller incudes means for clam-ping said roller in a predetermined position whereby the advancing web slideably advances thereacross.

7. The apparatus of claim 1 wherein said synchronizing means includes pulse generating means responsive to said moving web for producing output pulses which are a function of the rate of advance of said web;

counting means operatively connected to receive said output pulses from said pulse generating means for producing a control pulse upon receiving a predetermined number of output pulses;

control means operatively connected to said counting means for producing a switching pulse in response to said control pulse, said switching pulse having a duration which determines the high voltage electrical discharge duration which occurs between said electrodes; and

switching means connected between said power means and said iirst electrode which is responsive to said control means for connecting said power means to said rst electrode in response to and for the duration of said switching pulse.

8. Apparatus for perforating a rapidly moving web comprising a plurality of aligned spaced needle electrodes positioned at an angle to the longitudinal direction of web movement for continually slideably engaging one surface of said moving web;

a continuous surface second electrode having a plurality of apertures therethrough, said second electrode being spaced from said plurality of needle electrodes for forming a plurality of spark gaps between each of said needle electrodes and said second electrode and for directing said web along a predetermined path through said spark gaps; K

means including a source of fluid under a positive pressure operatively connected to said second electrode and communicating with said apertures for forming a fluid lm which supports said moving web a predetermined distance from said second electrode;

means including a high voltage power supply yconnected between each of said needle electrodes and said second electrode for simultaneously producing a high voltage electrical discharge across said spark gaps of a sufficient potential to perforate said web; and

means connected to said power supply means for synchronizing said plurality of electrical discharges With the rate of advance of said web.

9. The apparatus of claim 8 wherein said plurality of needle electrodes are supported in an electrode assembly support member by means of conductive. resilient means which yieldably urge the tips of the electrodes into continual slideable engagement with said one surface of the web.

10. The apparatus of claim 8 further including web driving means for advancing the web in a longitudinal direction of movement between said needle electrodes and said second electrode, said web driving means being capable of selectively driving said web from a slow speed to a rapid speed.

11. The apparatus of claim 8 wherein said synchronizing means includes pulse generating means responsive to said moving web for producing output pulses which are a function of the rate of advance at which said web driving means advances said web;

counting means operatively connected to receive said output pulses from said pulse generating means for producing a control pulse upon receiving a predetermining number of out-put pulses from said pulse generating means; control means operatively connected to said counting means for producing a switching pulse in response Y Y 12 l to said control pulse, said switching pulse having a duration which determines the electrical discharge duration which occurs between ,each of said needle electrodes and said second electrode; and switching means connected lbetween said high voltage power supply andV each of ysaid needle electrodes which is responsive to said control means for connecting said high voltage power supply simultaneously to.ea ch of said needle electrodes in response t0 and for the duration of said switching pulse. 12. The apparatus of claim 8 further including a plurality of high ohmic value resistors one of each of which is electrically connected in series `circuit relationship with one of said needle electrodes. 13. The apparatus of claim 12 further including a plurality of low ohmic value resistors one of each of which is electrically connected in series circuit relationship with each of said high ohmic value resistors and said needle electrodes; and a plurality of neon lamps one of each of which is electrically connected in parallel circuit relationship witheach of said low ohmic Vvalue resistors, said low ohmic value resistors producing a voltage drop thereacross of suicient magnitude toenergize said neon lamps toprovide a visual indication when its associated needle electrode produces an electrical discharge. 14. A method for perforating a moving web comprising the steps of guiding `said web between a rst electrode, which slideably engages one surface thereof, and a second electrode spaced from said `lirst electrode forming a spark gap therebetween; producing a, moving fluid lm between said web and said second electrode under sucient pressure for supporting said web a predetermined distance from said second electrode;- generating a high voltage electrical discharge between said iirst and second'electrodes of a potentialsucient to atleast perforate said advancing web; and synchronizing the generating of said high voltage elecktrical discharge with the rate of advance of said web. 15. The method of claim 14 wherein said moving web is guided between a plurality of ne'edle electrodes and a second electrode over a lluid film which supports said web a predetermined distance from said second electrode, and further comprising the step of t driving said web over said uid iilm between said needle electrodes and said second electrode over a range of web speeds.

References Cited UNITED STATES PATENTS BERNARD A. GILHEANY, Primary Examiner. V. Y. MAYEWSKY, Assistant Examiner.

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