04/833307

11/09/1971

06/16/1969

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Nucleonic Industries (Tucson, AZ)

250/359.100

250/389, 324/459, 250/424, 250/393, 324/457, 361/213, 250/395

H01T23/00; H05F3/06; H05F3/00; G21H5/00

250/44,106 317/2 250/49.5 (60)/ 250/45 324/32

Lawrence, James W.

Willis, David L.

What is sought to be protected by United States Letters Patent is

1. The method of applying regulated quantities of ions predominantly of selected polarity to a member of essentially nonconductive material for controlling the magnitude and polarity of a resultant electrostatic charge thereon, said method comprising the steps of:

2. The method according to claim 1 further comprising the steps of:

3. The method according to claim 2 wherein the member carries an initial charge and the step of

4. The method according to claim 3 wherein

5. The method according to claim 2 wherein the member carries an initial charge and the step of

6. The method according to claim 5 wherein

7. The method according to claim 2 wherein the member carries a substantially neutral initial charge and

8. The method according to claim 2 wherein

9. The method according to claim 2 wherein

10. The method according to claim 2 wherein

11. The method according to claim 2 wherein

12. The method of neutralizing the electrostatic charge accumulated on a running web to enable an operation to be performed upon the web in a substantially neutral zone on the path of the web which comprises:

13. The method according to claim 12 which further comprises the steps of

14. The method according to claim 12 wherein

15. The method according to claim 12 wherein

16. The method according to claim 12 wherein

17. The method according to claim 12 wherein

18. Apparatus for providing a supply of ions predominantly of selected polarity, comprising

19. Apparatus according to claim 18 wherein

20. Apparatus according to claim 18 wherein

21. Apparatus according to claim 18 wherein said polarity-determining means comprises

22. Apparatus according to claim 21 wherein said output-voltage-adjusting means comprises

23. Apparatus according to claim 18 which further comprises

24. Apparatus according to claim 23 wherein

25. Apparatus according to claim 23 wherein said ionization detector includes

26. Apparatus according to claim 23 wherein said control-signal-applying circuitry comprises

27. Apparatus according to claim 26 wherein

28. Apparatus according to claim 26 wherein

BACKGROUND OF THE INVENTION

In operations performed on members, especially moving sheets and continuous, running webs of essentially nonconductive material, static charges frequently develop on the material as it passes in frictional contact with other sheets or webs and with dissimilar materials, such as metal or rubber rollers, belts, cylinders and stationary surfaces, such as former boards, turning bars and the like. This has long presented a problem in the proper handling of such materials, particularly paper, paperboard, plastic films and sheets, elastomers and laminates of such materials. The problem is aggravated by the high speeds characteristic of modern equipment for the production, handling, processing, conversion and printing of such materials. Often it severely limits the production rates which otherwise could be achieved, necessitating slower web or sheet speed and frequently involving downtime, waste and inferior quality.

For many years it has been common practice partially to bleed off static charges on moving members by passing them in contact with such grounded conductors as metallic tinsel or soft wire brushes. Such expedients sometimes help on slowly moving members, but they have proven entirely inadequate in modern, high-speed operations.

More recently, ion-producing devices, such as electrically energized wires, needlelike protrusions, etc., have been used to induce or neutralize static charges on moving material brought into close proximity thereto. Such devices, to be effective, require the use of extremely high voltage and substantial amperage, usually accompanied by a corona discharge. While they are more effective at high material speeds than simple grounding devices, they create the hazard of electric shock to personnel and the danger of arcing. Fires are not uncommon when arcing or even an intense corona develops and in hazardous areas such as gravure pressrooms there is danger of explosion.

A safer but only partial solution to the aforementioned problems created by static charges resides in the use of so-called static bars, which employ a radioactive isotope in close proximity to the material. The isotope emits alpha, beta or gamma rays or combinations thereof, causing the generation of positive and negative ions in the atmosphere adjacent to the material. However, the emissions from the radioactive source produce both positive and negative ions in equal quantities. Therefore, these devices are only useful when the material carries a sufficiently high static charge that it will attract predominantly ions of the opposite polarity. These devices can neither induce a charge of either polarity on an uncharged material, nor enhance an existing charge. Neither can they completely neutralize nor reverse the polarity of an existing charge.

For the purpose of achieving neat and orderly sheet stacking and consistently good printing, winding, folding, cutting, laminating, collating, etc., it generally is required to keep the material being processed substantially free of static or to reduce its static charge to a relatively low level. Tests have indicated that, for example, in sheet cutting and stacking operations on relatively heavy (70 pound basis weight) coated paper, a static charge of up to about 3,000 volts, on a 48 inch-wide web may not be particularly detrimental at linear web speeds of some 300 to 400 feet per minute. However, at increased speed and sometimes even at these relatively low speeds the charge may build up to some 10,000 to 30,000 volts or more. This makes economical operation extremely difficult and it becomes impossible at speeds of 600 to 1,000 and more feet per minute, at which most modern equipment is intended to operate. Downtime and waste encountered at such speeds when the web carries a substantial static charge become intolerable and make profitable operation as impossible as it would be at slow speed.

SUMMARY OF THE INVENTION

By employing a suitable radioactive isotope as the source of energy for the production of ions, this invention obviates the hazards of electrical shock, fire and explosion which attend the use of high electrical energy devices such as those which produce a corona. By the use of field potentials which do not exceed 1,000 to 2,000 volts, with extremely low amperage, an electrostatic field is used in conjunction with a radioactive isotope and there is no corona discharge under these conditions.

Selectivity with respect to the predominant polarity of the ions imparted to the member undergoing treatment is a primary feature of the invention. This is accomplished by creating an electrostatic field in the immediate vicinity of the radiant energy source and the member. Preferably one pole of this field is within the ion emitter. The sign, positive or negative, as the case may be, of this pole is kept the same as that of the selected ions. Thus, it attracts ions of the opposite, unselected, polarity and repels ions of the selected polarity, making a predominance of the latter available for transmission to the member. The opposite pole of the field is so disposed in relation to the emitter and the member, that, in their inherent seeking of this pole, ions of the selected polarity, expelled from the emitter, are brought into contact with the member. Once in contact with the member the selected ions either impart to it a charge or their same polarity or, if the member is carrying an opposite charge, they will reduce, neutralize or reverse it, depending upon their quantity in relation to the magnitude of the preexisting charge.

By the provision for reversing, at will, the polarities being maintained in the electrostatic field, the selection of ions can be reversed to suit requirements. This accommodates and renders harmless to the intended results changes which may occur in the polarity of any preexisting charge on the member.

By suitably adjusting the potential maintained between the opposite poles of the electrostatic field as provided by the method and apparatus of this invention, the ratio between the quantities of selected to unselected ions transmitted to the member is controllable. This, in effect, gives control over the magnitude of any residual charge on the member as the result of its treatment. Increasing the potential of the field decreases the escape of unselected ions from the emitter and increases its proportionate output of selected ions, making a greater predominance of the latter available for application to the member. Conversely, decreasing the field potential reduces the proportion of the total unselected ions which are separated within the emitter from the selected ions, making a smaller proportion of the latter available for application to the member.

When it is desired to hold the treated member substantially neutral or to hold thereon a charge of relatively low magnitude, the potential of the field is increased as the resultant charge on the treated member increases above its desired value and vice versa. Thus, in such cases, the potential of the field is regulated in direct relation to the magnitude of the residual charge on the member.

When it is desired to impart a charge of predetermined magnitude to a member which either carries no charge, a lower charge than desired or a charge of the wrong polarity, the potential of the field is increased as the resultant charge on the member decreases to below its desired value, and vice versa. Thus, in such cases, the potential of the field is regulated in inverse relation to the magnitude of residual charge on the member. Regulation of the field potential is substantially proportional to changes in the magnitude of the residual charge on the member undergoing treatment and is accomplished automatically in response to continuous measurements of the magnitude of said residual charge.

The above and other aspects, achievements and objects of the subject inventive method and apparatus will become evident from the following.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates, in exploded, partly broken-away form, a preferred form of an ion generator and emitter useful in the invention;

FIG. 2 is a transverse section through the ion generator and emitter of FIG. 1, as assembled; and also illustrates the power source and general cross-sectional contour and nature of the electrostatic field maintained between the inner electrode of the emitter and the member undergoing treatment;

FIGS. 3A and 3B illustrate an ion detecting or sensing element suitable for use in the practice of the invention, FIG. 3B being a sectional view taken along the line A--A of FIG. 3A;

FIG. 4 is an exterior view of a control cabinet suitable for housing the power supply and automatic control equipment provided by the invention;

FIG. 5 is a circuit diagram of the power supply and control equipment housed within the cabinet of FIG. 4; and

FIG. 6 is a side elevation, broken partially away, of a rotary sheet stacker and illustrates the general physical relationship and interconnection between the major components of the system herein provided as applied to the specific use.

Referring now to FIGS. 1 and 2, the ion generator and emitter has an electrically conductive outer shell 11, formed of aluminum, steel or other suitable metal or metal-clad plastic material. Its upper portion is open faced and shaped to receive a nonconductive grill 12. Electrically conductive end caps 13 close the opposite ends of the shell 11. The electrical input end cap is provided with an opening 14 over which a socket 15 of a conventional shielded cable connector is attached.

A plug 16 mates with the socket 15 and receives a shielded cable 17, the shield 18 of which is soldered to the shell of the plug. The central conductor 19 of the cable 17 is insulated from both the shield 18 and the shell of the plug and is secured to a terminal 20 of an electrode 21. The electrode 21 is supported at two or more spaced locations within and along the bottom wall of the shell 11 by standoff insulators 22 which are attached to the base of shell. The electrode extends through substantially the entire length of shell 11, except for a sufficient airgap between its opposite ends and the end caps 3. The airgap prevents short circuiting and arcing. Inner rails 23, which are an integral part of the electrode 21, are shaped to receive and retain a channel-shaped foil holder 24, which is secured at its opposite ends to the base of the electrode.

In the case illustrated, the source of radiant energy from which ions are derived comprises a foillike metallic strip 25, having the central 50 percent or thereabouts of its width, along its entire length coated with a thin layer of radioactive substance 26. Foil-carrying isotopes such as polonium 210, americium 214 and tritium are commercially available to firms holding an appropriate license issued by the Atomic Energy Commission. The strip 25 constitutes a part of the electrode 21.

From FIG. 2 it will be apparent that the combination of the electrode 21, the foil holder 24, and the radioactive foil 25 forms one pole of an electrostatic field, when connected to a suitable source of direct current. The opposite pole of this field, which is insulated from the electrode 21 by the insulators 22, is formed by the outer shell 11 and its end caps 3. The grill 12, being nonconductive, quickly becomes saturated with the selected ions, thereafter permitting them to pass through its openings and, then being of the same polarity, actually repelling them outward.

The polarities indicated in FIG. 2 by the positive and negative signs are shown only as an example. They may all be reversed at will simply by reversing the polarities of the leads 18 and 19 from a power supply 27. Thus, the polarities of these leads determine the selected polarity of the ions to be imparted to the member 28 undergoing treatment.

With the connections to the power supply as shown in FIG. 2, namely the positive lead to the electrode 21 and the negative lead to the case of the emitter, the field created between the opposite poles is represented by dashed lines. Some of the negative ions may escape from the emitter and/or combine with a corresponding number of the positive ions generated. Equal quantities of positive and negative ions are produced and the percentage of the negative ions which find their way to the positively connected electrode 21 will depend upon the potential maintained between the opposite poles of the electrostatic field. Thus, this potential also determines the percentage of the positive ions which is made available for transmission to the member undergoing treatment.

The positive ions, seeking the negatively connected pole of the electrostatic field, follow different trajectories and, normally, in the absence of interference, can be detectable at a foot or more from the grill of the emitter. However, when a member of essentially nonconductive material is interposed in the path of positive ions seeking the opposite polarity of the field, they will be accumulated on the surface of this body, since an electrostatic charge is essentially a surface phenomenon. Since, the essentially nonconductive material or member 28 is interposed in the normal path of ions expelled from the ion generator and emitter, those ions which strike the member, do not penetrate it but their paths terminate on or slightly beneath its surface as indicated by the arrowheads 29.

When the member 28 is moving from left to right, as indicated by the arrow 30, and is negatively charged as it enters the field, as indicated by the negative sign 31 at the left end of the member 28, the positive ions which it attracts and captures will either reduce or neutralize this negative charge or, if they are sufficient in number, they will reverse the charge on the member. In the case illustrated, a substantially neutralized condition is indicated by the plus-minus designation 32 at the right end of the member 28.

If the member 28 carries a positive charge as it enters the electrostatic field, this positive charge will be enhanced when electrode 21 is employed as the positive pole of the field and the case or outer shell of the emitter is negatively connected. If the connections to these poles are reversed, as provided for herein, any positive charge carried by the member as it enters the field will either be reduced, neutralized or reversed, depending upon the number of negative ions applied to the member in relation to the magnitude of its initial, positive charge. This, in turn, is governed by the total ion output of the radioactive source employed and the potential maintained within the electrostatic field.

When the member to be treated carries little or no charge, the invention provides for applying to it a charge of either positive or negative polarity. Selection of the polarity of the charge to be imparted is dependent upon whether the positive or negative terminal of the power supply is connected to electrode 21 and will correspond to the polarity of the terminal so connected.

As previously indicated, regulation of the field potential to suit requirements for obtaining the desired resultant charge on the member is an important feature of the invention. Likewise, the provision for reversing the polarities of the field is an important feature.

Referring to FIGS. 3A and 3B, an ionization detector assembly 40 has a sensing element 41 which is a conductive, light-gauge metal tube that extends through a pair of mounting fixtures 42 provided at its opposite ends. These fixtures are similar except that one is provided with a connector 43 for a shielded cable 44, which has its shield grounded to the connector, and its central conductor coupled to the sensing tube 41. Suitable nonconductive sleeves 45 insulate the sensing tube from the mounting fixtures and a supporting framework 46.

In the illustration of FIGS. 3A and 3B, the member 28 undergoing treatment is a running web, moving in the direction of the arrow 30. Normally, the sensing tube would be spaced some 2 to 4 inches from the web and, in conjunction with that portion of the circuitry of FIG. 5 to which the cable 4 leads, it functions to detect the polarity and magnitude of the electrostatic charge on the web and provides electrical signals indicative of such polarity and magnitude.

Referring to FIG. 4, a cabinet 50 houses the power supply and control sections of the system and includes a hinged front panel 51 and a handle 52. Cable connectors 53 and 54 are provided for the shielded cables 17 and 44 leading to the ion generator 10 and to the ionization detecting means 40. A conduit 55 is also provided for a three-conductor cable, having one conductor grounded, which leads to any conventional source of 115-volt, 60 Hz. current. This powerline is suitably fused at 56.

Near the top of the front panel are three indicator lights 57, 58 and 59, respectively, labeled "Negative," "Normal" and "Positive," which operate in conjunction with a meter 60 to indicate when the signals received from the ionization detector signify that the member undergoing treatment carries either a negative or a positive charge which is greater than desired, or that the charge is within satisfactory, i.e., normal tolerance limits.

Also provided on the front panel are a power on-off switch 61 and a test switch 62, both can be of the pushbutton type. When the test button is depressed, it disconnects the signals of the ionization detector 40 from the meter 60 and the meter needle should come to rest at the exact center of the meter dial. If it does not, the meter can be properly zeroed by turning a potentiometer adjustment knob 63 in the direction opposite to that in which the meter needle is deflected from center. Also, by use of the potentiometer adjustment, the meter needle can be deflected to the left or right of center scale while the test button is depressed in order to induce a charge of either positive or negative polarity on the member undergoing treatment, instead of causing the member to become substantially neutral.

In FIG. 5, the electronic circuit which is contained in the cabinet 50 is illustrated. Basically, the circuit detects the residual or resultant electrostatic charge on the member 28 and produces an output for controlling the electrostatic field to select ions of the opposite polarity to the charge detected, and in an amount which will be proportional to the charge.

The various parts of the circuit are generally blocked off in broken lines to assist in an understanding thereof. As earlier stated, the power supply 27 is energized from a conventional 115-volt, 60 Hz. alternating current main. The power supply contains transformers, rectifiers, filters and the like, as needed to provide the several DC voltages for the circuit. Included in these voltages are two which are regulated, namely a +15 volts DC and a -15 volts DC, as for example by means of suitable zener diodes. The power on-off switch 61, fuse 56, circuit breakers, and the like are included in the power supply and need not be illustrated.

The detected charge on the member 28 will be transmitted to a comparison circuit 72 where polarity and magnitude of the charge are determined by comparing the same with a known DC voltage. In the absence of charge, the output of the comparison circuit, appearing on a line 74 will be zero, and the meter 60 should be centered at zero as well. The zero adjustment is provided by moving the wiper of a potentiometer R3 until the meter 60 reads zero. The wiper is connected to the adjustment knob 63. The ends of the potentiometer are connected to +18 volts and -18 volts. A test circuit 76 has provision for short circuiting the input 78 to the comparison circuit by means of the test switch 62. A neon tube Nel protects the comparison circuit, and an RC parallel network R7 and C1 averages the signals produced by the ionization detector 40. The heart of the comparison circuit is a differential amplifier 80 which has inverted inputs. A balanced condition is achieved by a network of resistors R3, R4, R5, R6, so that there will be no output on the line 74 when there is no signal to the input 78. An amplifier feedback through a resistor R9 assists in the balance, and the regulated power supplies of +15 volts and -15 volts promote the stability thereof. An RC network R8 and C2 controls the high-frequency response of the amplifier 80. A positive signal from the ionization detector on the line 44 will produce an amplified positive-going signal at the output 74 which is applied to the positive and negative output circuit blocks 81 and 82 and to an indicator circuit 84.

The three lamps 57, 58 and 59 in the indicator circuit are enabled according to the polarity of the signal on the output line 74 which can swing several volts plus and minus. A pair of transistors Q1 and Q2 have this signal applied to their bases by way of resistors R10 and R11. Since Q1 is an NPN-transistor, it will conduct when its input signal is positive going, while the transistor Q2 is in its normal, nonconducting state. With the transistor Q1 conducting, a pair of NPN-transistors Q3 and Q4 cannot conduct, since their bases are not positive. The only lamp which lights, therefore, is the lamp 57, since it is in series with the emitter and collector of the transistor Q1 and is connected between a 2.5-volt DC supply and ground.

If the signal on the line 74 goes negative, the transistor Q1 is held off, the transistor Q2 conducts, and resistors R13 and R14 supply sufficient voltage to the base of the transistor Q4 to cause it to conduct and the lamp 59 to light.

If the input signal is zero, both of the transistors Q1 and Q2 are off, the transistor Q3 is enabled through the resistor R12 and turns on the lamp 58, while at the same time the transistor Q4 is held off, by way of the resistor R14.

With respect to the operation of the output circuits 81 and 82, each has an input to a transistor through a resistor. In the case of the upper, negative output circuit 82, a resistor R15 is coupled to ground through a diode D4 and is connected to the base of an NPN-transistor Q5. The lower, positive output circuit has its input connected through a resistor R18, coupled to ground through a diode D5, and applied to the base of a PNP-transistor Q7. Thus, the circuits are protected from reverse signals, and each will pass only signals of one polarity. When the input signal is positive, the diode D5 conducts and shunts the signal to ground, the current being limited by the resistor R18. At the same time, the positive input signal is coupled through a resistor R15 to the base of the transistor Q5, since the diode D4 is blocked. With the transistor Q5 conducting, and acting as an emitter follower, +4.5 volts are applied through a resistor R16 and the lower half of the primary winding of a transformer T3 to the base of a transistor Q6. The resulting effect is that of a blocking oscillator, with the primary windings of the transformer T3 providing the inductance, capacitors C18 and C3 providing the capacitive reactance, and the resistance of the circuit serving to coact to achieve the oscillation. The signal, which is of the order of 1,000 Hz., is stepped up in the secondary winding, rectified and doubled by a pair of diodes D6 and D7 and a pair of capacitors C5 and C6 and filtered by another pair of capacitors C9 and C10 to appear across a resistor R22 as a negative voltage, considering the polarities of the diodes.

Following the same discussion, logic and explanation for the lower circuit 81, a positive output appears across its resistor R23 when there is a negative output from the amplifier 80 on the line 74.

The output from the positive and negative circuits 81 and 82 will be applied to the ion generator through the cable 17 to effect the magnitude and polarity control over the emission of the ions which impinge against the material 28, as has been explained previously.

FIG. 6 shows a rotary sheeter and sheet stacker 90 to which is coupled the control system of this invention. The continuous web 28 enters from the left of the figure and progresses in the general path indicated over conventional idler rollers 92, under the trolley 93 and beneath the ion generator and emitter 10 to a cutting cylinder 94. The resulting sheets are delivered to a sheet stack 95.

In the operation illustrated by FIG. 6, it is desired to reduce any electrostatic charge carried by the incoming web 28, as well as any charge which would otherwise build up on the web and the sheets, i.e., the members 28 as they travel through the machine, to a substantially neutral condition as the sheet members are delivered to the stack.

As here shown, the ion generator and emitter 10 can be mounted relatively close to the inlet end of the machine and, preferably, above and close to the web 28. Even when the incoming web carries little or no charge but a substantial charge ordinarily would be built up on it in traveling through the machine, the emitter 10 can be located at a point prior to such buildup. This is because when used as here shown, the control system will cause application to the web at the emitter ions of opposite polarity to that of the charge which, otherwise, would occur subsequently, neutralizing or substantially reducing it. This cannot be done in other systems of static neutralization which do not have the ion selectivity of the system herein provided.

Preferably the ionization detector 40 is located relatively close to the stack 95 at about the point where the top sheet begins to slide over the one beneath it in coming onto the stack. This usually is an area of highest static accumulation and makes the sheets tend to cling together, preventing their sliding into proper place on the stack.

The control cabinet 50 can be mounted on a side frame of the machine 90 or on a nearby wall or column. Preferably it is located on the same side of the machine as that on which the cable connectors of emitter 10 and the sensing element 41 are located. The cable 44 leads from the sensing element 41 to the control cabinet 50, and the cable 17 leads from the control cabinet to the ion generator and emitter 10. The power cable 55 leads to a suitable outlet box 96 for 115-volt, 60 Hz. current. The shielded wire or one of the conductors of each of the cables is well grounded at both ends, as previously explained.

When located and connected as shown in FIG. 6 and used for the purpose above mentioned the equipment functions as follows.

The residual or resulting charge on the members 28 coming onto the stack 95 is sensed by the detector 40, which transmits signals of the same polarity as the detected charge and of a magnitude related directly to that of the charge, to the control cabinet 50. Here these fed-back signals are amplified and utilized, as indicated in the description of the circuit diagram of FIG. 5, to indicate on the meter 60 and the lights 57, 58 and 59 the polarity and magnitude of the charge on the member adjacent the detector 40. In addition, the feedback signals determine the magnitude and polarity of the voltage applied to the electrode 21 of the ion generator and emitter, such that the magnitude is in direct relation to the magnitude of the measured residual charge on the members 28. This causes the meter, after it has been properly zeroed as explained in conjunction with FIG. 4, to seek its null, center position, indicating that the charge on members 28 are within a satisfactory charge tolerance with respect to polarity. Thus this invention accomplishes the originally designated goals in a fully automatic, continuous, and especially accurate manner.