US 3599038 A
Description (OCR text may contain errors)
Unite States Patent ELECTROSTATIC CHARGING OF PARTICLES Primary Examiner-J. D. Miller Assistant Examiner-Harry E. Moose, Jr. Arlorney- Bryan, Parmelee Johnson & Bollinger ABSTRACT: Apparatus and systems for high-voltage electrostatic charging of particles are disclosed which are compact and lightweight so as to be truly portable. High-voltage electrostatic particle charging tools are disclosed for performing the useful function of propelling charged particles toward a desired object incorporating a high-voltage supply as part of the handling tool, the illustrative high-voltage supplies being l2 Chims 8') win voltage multiplier rectifier networks, The voltage multiplier m g [83' sections are stacked within the barrel structure of the handling U.S. to l to rovide rogres ively higher voltages toward the muz- 118/621, 321/15 zle end thus minimizing electrical leakage and reducing [511 1nt.Cl B05b 5/02 hazar A nf naranepspaced Stacks f capacitors with  Field of Search 317/2, 3; diode rectifiers selective, interconnected between the 118/621; 321/ es ective capacitors of the stacks are encapsulated within solid insulating material to form a rigid barrel structure. A  Reerenm Cited portable setup transformer is positioned emote from the tool UNITED STATES PATENTS the transformer being adapted to be worn by the user, as by 2,302,289 11/1942 Bramston-Cook 317/3 X mounting on his belt, and the tool being connected to the 2,526,763 10/1950 Miller 317/3 X secondary winding of the transformer by a flexible insulated 2,989,241 6/1961 Badger 1 18/621 X electrical cable. Air-atomizing as well as hydraulic-atomizing 3,273,015 9/1966 Fischer 317/3 systems may be employed with the invention.
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SHEET 1 OF 5 INVENTOR DONALD D. SKIDMORE W 'POJWKDQLL & WW1.
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INVENTOR DONALD D. SKIDMORE BY @wmfl 2, ATTOR EYS PATENTEU Abs 1 0 |97| SHEEI l 0F 5 wOmE VEOZ,
INVENTOR DONALD D. SKIDMORE BY RUQQJIM 'PATENIEB AUG 1 0 Ian SHEET 5 0F 5 mOm n vEO NmwT INVENTOR DONALD D. SKIDMORE ATT NEYS JOKFZOO w APPARATUS AND SYSTEMS FOR HIGH-VOLTAGE ELECTROSTATIC CHARGING OF PARTICLES DESCRIPTION This invention relates to apparatus and systems for highvoltage charging of particles, and more particularly relates to compact, lightweight apparatus and systems for high-voltage electrostatic charging.
An advantage of a high-voltage electrostatic particle charger incorporating a high-voltage supply as part of the particle propelling tool in accordance with the invention is its easy to handle, lightweight, compact structure obtained with the location of the electrostatic voltage supply in the vicinity of the region where it is used for charging of particles emerging from the apparatus.
This invention provides a truly portable high-voltage electrostatic particle charger for the first time, so far as I am aware. All of the prior so-called portable equipment com mercially available of which I have knowledge cannot be conveniently carried by a man while using the equipment and thus have required a vehicle to carry the weight of the high-voltage power supply. If the user wished to move to a new location he walked over and picked up the equipment to move it or moved the vehicle to transport it.
A further advantage of a particle charger made in accordance with the invention resides in a reduction of electrostatic voltage attenuation and leakage such as may be encountered in conventional high-voltage particle charger apparatus utilizing lengthy and cumbersome high-voltage cables. There is a reduction in the voltage carried by the electrical cable connected to the particle charger and a consequent reduction in hazard as compared with prior conventional devices. Also, the size of the cable is reduced and it is more flexible and easier to handle.
It is among the advantages of the illustrative embodiment of this invention that the high-voltage components of the electrical power supply are associated with and incorporated in the particle-handling tool that performs the useful function of propelling the particles to be charged.
Other advantages and objects of the invention will be understood from a description of an embodiment described as follows in conjunction with the drawings wherein FIG. 1 illustrates an apparatus and system for high-voltage electrostatic charging of particles embodying the invention, with portions of the apparatus and system being shown in section;
FIG. 2 is a top plan view as seen in the direction 22 in FIG. 1, showing a high-voltage increasing and insulating structure utilized with the particle charger apparatus and system in accordance with the present invention, this high-voltage struc-- ture being shown as incorporated with a particle-charging paint spray barrel;
FIG. 3 is a cross-sectional view of the high-voltage barrel structure of FIG. 2 taken generally along the line 3-3 in FIG.
FIG. 4 is a front view, i.e. muzzle end view, of the high-voltage barrel structure of the particle charger of FIG. I as seen in the direction 4-4 in FIG. 1;
FIG. 5 is a partial top view of the high-voltage barrel structure taken along the line 5-5 in FIG. 4;
FIG. 6 is a back end view of the high-voltage barrel structure used with the particle charger taken along the line 6-6 in FIG. 2;
FIG. 7 is a schematic electrical diagram of a circuit employed with the high-voltage electrostatic particle charger apparatus and system embodying the invention as shown in FIGS. 1-6, inclusive; and
FIG. 8 is a schematic electrical diagram of an alternative electrical control network for use with an alternative embodiment of the high-voltage electrostatic particle charger apparatus and system in accordance with the invention.
With reference to FIG. 1, a high-voltage electrostatic particle charger structure 10 is illustrated for issuing and propelling a spray of particles, such as paint, from a nozzle 12. The paint is supplied under pressure from a reservoir 14 (illustrated in a different drawing scale from that used for the particle charger 10). The reservoir 14 is pressurized by a source 16 of compressed pressure air applied to the reservoir 14 through a conduit 18 and a shutoff control valve 20. The paint is conducted through a supply tube 22 connected to a paint-supplying hose 24 having a shutoff valve 26, the hose 24 being attached to a suitable hose connector 28 for operative connection with the particle charger 10. A return hose 30 and shutoff valve 31 are provided for return flow circulation to maintain the paint passages in the tube 22, hose 24 and connector 28 free from accumulation of any undesired dirt, and allows cleaning of those passages.
The high-voltage electrostatic particle charger structure 10 is shown in the form of a spray gun 10 for electrostatically charging paint spray particles issuing therefrom by supplying a very high direct current voltage to an electrically conducting metal electrode 32 located in the nozzle 12 and extending beyond the end of the nozzle at the paint-spraying end of the particle charger 10 so that the electrode 32 charges the particles issuing from the nozzle 12. The high direct current voltage for the electrostatic charging of the paint particles is produced by initially stepping up an alternating current (AC) voltage to a desired level and thereafter in a remote location by rectifying the AC voltage into a direct current (DC) voltage which is increased in a voltage multiplier network to a desired higher level for use.
The alternating current is supplied from a suitable AC voltage source of conventional voltage, such as is available from conventional l15-volt AC power lines 33-33, this AC line voltage being applied to a step-up high-voltage transformer 34. The AC voltage line 33' is directly connected to the primary winding 92 (FIG. 7) of the transformer 34, but the line 33 is connected to the primary of the transformer 34 through an onoff switch 35 and through a normally open manual control switch 36 located on the particle charger 10 in operative relationship with a manual trigger 38 used to actuate the highvoltage electrostatic particle charger 10. With the switch 36 closed by pulling the trigger 38, AC power is applied to the transformer 34 to generate a high AC voltage in the secondary winding 94 (FIG. 7) of this transformer. The step-up characteristic of the transformer 34 is selected to produce a high AC voltage which can be conducted safely to the particle charger 10 through an insulated cable 40 that is flexible, light and safe to handle. In this illustrative system the transformer 34 produces 10,000 volts AC (root means square value) which may be safely conducted to the particle charger 10 through the center conductor 39 of an insulated coaxial cable 40, th conductive shield braiding 41 of the coaxial cable 40 being grounded. It is to be understood that an AC voltage of 10,000 volts RMS means that a peak value of l4,000 volts occurs twice across the secondary winding 94 during each full cycle of the alternating current. The step-up transformer 34 is of a size and weight such that it may be conveniently carried about by an operator, with only the line-voltage volts) cord 33-33 being trailed along behind him. In this illustrative embodiment the transformer 34 may be adapted to be supported from the operator's belt.
This high AC voltage is rectified into a DC voltage which is increased to a much higher DC voltage level in a voltage multiplier high-voltage DC supply 42 which is incorporated in the particle charger 10. This high-voltage DC supply 42 is incorporated in a barrel section 44 of the particle charger spray gun 10. The high-voltage supply 42 provides the high DC electrostatic voltage to the electrode 32 in the vicinity of the region where the spray of particles issues-preferably in the center of the nozzle 12 so that the high-voltage field associated .with the electrode 32 will encompass and enclose the issuing spray.
The particle charger 10 includes in the barrel 44 a paintconducting tube 46 made of an insulating material and which extends longitudinally along the barrel. The tube 46 communicates with the supplying hose 24 through an elbow section 48 and the connector 28. The tube 46 is provided with a particle discharge opening 50 which is closable by a ball valve 52. The ball valve 52 is positioned between an insert 54 having a spherical valve seat 56 sized to accommodate in sealing relationship a ball 52 attached to the end of an operating rod 58 made of insulating material. The rod 58 extends through the length of the tube 46 and protrudes through an opening lined with a sleeve seal 59 for operation of the rod 58 by the trigger 38 and a biasing spring 60. The trigger 38 is pivotally attached to the frame 61 of the particle charger at a pivot 62 and is connected at 64 to the rod 58 so as to move the rod in response to trigger motion. The rod is urged by compression spring 60 located in a recess 66 in the handle 68 of the particle charger to normally close the ball valve 52.
The trigger 38 is further provided with a switching actuator 70 operatively engaging the switch 36, which is of the normally open pushbutton type. The switch 36 is adjusted in operative relationship with the trigger 38 by use of an adjusting mechanism 72. The adjusting mechanism 72 include a switch mounting 74 slidingly mounted in a recess 76 in the handle 68. The mounting 74 is retained by a stud 78 having an enlarged plunger portion 79 located in a bore 80 opposite to the recess 76. The plunger is driven into the bore 80 against a spring 82 by a screw 84 until the switch 36 is actuated when the trigger 38 is squeezed.
A trigger stop 86 is provided opposite trigger 38 to limit the opening of the ball valve 52 to a maximum determined as desired by the operator of the particle charger 10. A squeezing of the trigger 38 is thus accompanied with an opening of the ball valve 52 and a closing of the normally open switch 36 to thus essentially simultaneously electrostatically charge the stream of particles issuing from the barrel nozzle 12.
The handle 68 and barrel 44 are interconnected to one another with a pair of clamps 8890 as will be described in relation to FIGS. 4 and 5. The structure of the barrel 44 including the high-voltage DC supply 42 may best be appreciated with initial reference to the schematic electrical circuit diagram of the voltage supply illustrated in FIG. 7. FIG. 7 shows'the trigger 38 and the associated switch 36. The switch controls the supply of AC power to the primary 92 of the stepup transformer 34. The secondary 94 of the step-up transformer 34 is connected through the center conductor 39 and shield braid 41 of conductor 40 to a series of rectifier voltage multipliers interconnected to form a sextupler network. The sextupler network includes a plurality of capacitors 96-1, 96- 2, 96-3, 96-4, 96-5 and 96-6 and diodes 98-1, 98-2, 98-3, 98-4, 98-5 and 98-6 selectively interconnected to generate a high DC voltage at the junction 100 of capacitor 96-6 and diode 98-6, this voltage being of approximately six times the peak voltage of the AC voltage appearing across the secondary 94 of transformer 34. In this illustrative embodiment, the high DC voltage at the junction 100 in the absence of any current flow through the resistor 102 is 84,000 volts. This electrostatic voltage is applied to the electrode 32 (see FIG. 2) of the particle charger through the current-limiting resistor 102 of approximately 50 megohms. A bleedoff resistor 104 is provided of approximately 5,000 megohms to discharge the high DC voltage from junction 100 in a relatively short time when the particle charger is not being energized.
FIG. 2 illustrates the advantageous structural arrangement of the capacitors 96 and diodes 98. The capacitors 96 (as seen in FIGS. 2 and 3) are each of cylindrical configuration and are each provided with concentrically located terminals 106 and 108 at opposite sides of a cylindrical capacitor structure containing ceramic dielectric. The capacitors are serially arranged in two parallel stacks 110 and 112 commencing at ground terminal 114 and at input terminal 116 and terminating at junctions 118 and 100. The junction 100 is shown connected through the current-limiting resistor 102 to an annular conducting collar 120 surrounding the base portion of the insulating nozzle 12. This collar 120 is electrically connected to the electrode 32 as illustrated in FIG. 1 and is connected to one lead of the bleedoff resistor 104. The high-voltage diodes 98 are cylindrically shaped and are selectively connected to the junctions'between the capacitors in accordance with the physical arrangement shown in FIG. 2 and in accord with the circuit diagram shown in FIG. 7.
The capacitors 96 are physically and electrically connected one to another by means of sleeve 122 sized to snugly enclose a pair of adjacent terminals 106-l08, of adjacent series-connected capacitors. The sleeves 122 are soldered to the leads from the respective diodes 98 to form a positive connection. Four end terminal sleeves 114, 116, 124 and 125 are employed. As shown in FIG. 2, the two end terminals 114 and 116 at the inner (left) end of the barrel structure 44 are female threaded, while the two end terminals 124 and 125 near the muzzle end of the barrel structure are used to form the electrical junctions and 118 (FIG. 7). A machine screw 121 (FIG. 5) serves to connect the low voltage terminal 114 to the grounded metal frame 61 of the metal handle 68. A stud 123 is soldered onto the end of the center conductor 39 of the coaxial cable 40, and this stud is screwed into the terminal 116. An insulating bushing 1 27 surrounds the connection between stud 123 and terminal 116 to increase the insulation against leakage. As shown in FIG. 2 the lead from the current-limiting resistor 102 is soldered to the junction 100.
Parallel spacing of the stacks and 112 of capacitors 96 is provided by employment of a yoke 128 supported by the particle supplying tube 46 visible below the several interconnected diodes 98. The yoke 128 (FIG. 2) is formed of insulating material and includes a pair of capacitor stack gripping arms 130 and 132 sized to maintain the capacitor stacks I10- 112 in parallel-spaced relationship during encapsulation. The yoke 128 includes an opening snugly surrounding the tube 46 and an opening in each arm 130 and 132 snugly enclosing end sleeves 124, 125 as the entire high-voltage supply 42 and tube 46 are encapsulated in an insulating material to form an integral insulated barrel structure 44 which is shaped as illustrated. A preferred encapsulating material for the barrel structure 44 is epoxy resin, and the yoke 128 is made of the same material so that it becomes an integral part of the encapsulant. Generally speaking, the barrel structure has an isosceles triangular configuration having rounded vertices as seen in FIG. 3 in cross section. Thus the integral insulated barrel structure 44 has a streamlined triangular configuration with the capacitor stacks therein lying above and offset on opposite sides of the paint feed tube 46, as seen clearly in FIGS. 3 arid 4.
Application of power from the conductor 39 extending from the high-voltage step-up transformer is obtained through a stud 123 screwed into the terminal 116, while the protective braid 41 is grounded to the handle 68 as indicated at 152 (FIG. 1). The low voltage terminal 114 (FIG. 2) is also grounded by the screw 121 (FIG. 5) to the handle 68 of the particle charger 10. The reader's attention is directed to the longitudinal size of the discharge resistor 104 which interconnects the high-voltage collar to ground located at the input terminal 114. Since the voltage does progressively increase at the respective voltage multiplier stages along the barrel 44 as generated by the power supply, the spacing and location of the capacitors and diodes within the barrel is predetermined to provide the proper amount of insulating material between them. It is to be noted that the entire assembly is potted in a rigid insulating material in a form of the general shape as indicated for the barrel to enhance electrical safety and prevent corona discharges from the side of the supply. The highest level of the DC voltage is preferably generated as close as possible to the point where the paint is to emerge and to be electrostatically charged. A particular advantage of the construction of the barrel may be appreciated in view of the rather short conducting path needed to make connection to the collar 120 and to the electrode 32. This construction for progressively increasing the voltage in successive stages from the handle out toward the muzzle end of the barrel is most efficient as regards electrical power because it advantageously limits the voltage losses and thus permits a minimum power construction and consequently providing a compact lightweight structure suitable for portability in a manner as illustrated in FIG. 1.
FIG. 3 illustrates the elevational height of the barrel. The barrel is essentially isosceles triangular shaped in cross section but rounded at the comers to prevent any inadvertent and undesirable discharges along the side of the barrel. It is to be noted that the paint supplying tube 46 is located near the rounded apex on the bottom of the triangular barrel as distant from the parallel stacks of spaced capacitors as possible. Likewise, the diodes are stacked in elevation as illustrated.
It is seen in FIG. 2 that there is a circumferential groove 140 located near the low voltage end of the barrel structure 44. This groove 140 is used in conjunction with complementary fitting tongues M2 and 144 located in the clamps 88 and 90 to firmly secure the barrel 44 to the handle 68 as will be explained.
FIGS. 4 and 5 illustrate the clamps 88 and 90 referred to with relation to FIG. 1. The clamps are formed of an electrically conductive material, such as aluminum and engage one another with screws 146. Each of the clamps is provided with suitable tongues 142 and 114$ shaped to fit within the previously mentioned groove 1140 located in the low voltage end of the barrel. The tongues shown in dotted form since they are not normally visible in the view of FIG. 4. As indicated in FIG. 5, the upper clamp 88 is further attached to the handle grip 68 formed of electrically conductive material with suitable screws 148 to assure rigid attachment of the grip 68 to the barrel. Similar screw-mounting arrangements are provided at 150 on the underside of the lower clamp 90 so as to form an integrally connected spray gun particle charger including the grip and barrel with the barrel structure 44 in effect being a standoff insulator projecting from the handle structure 68, 88 and 90 which is formed of electrically conductive material, Thus, the whole handle structure 68, 88 and 90 is at ground potential as provided by the grounding connection at 152. The conductive collar 120 is at a DC voltage of approximately 84,000 volts, and the voltage of the components within the barrel structure progressively increases from kilovolts AC to the high DC voltage. Corona effects are minimized by the cylindrical sleeves 122 of substantial diameter.
FIG. 8 illustrates a schematic electrical diagram of an alternative embodiment including control circuitry for use with a system similar to FIG. 1. The circuit illustrated in FIG. 8 ineludes an overload protection network, generally indicated at 1160. In this embodiment the workpiece is grounded through a lead 162 and a potentiometer 1164, and the wiper contact arm 166 of the potentiometer is connected to the overload protection and control circuit 160. This circuit is electrically connected by leads 167 and 168 to the manual control switch 36 operated by the trigger 38. In response to an overload condition caused by placing the electrode 32 too close to the workpiece so as to cause a corona discharge therebetween, a relay coil 170 becomes energized by the circuit 160 to open a switch 172 in series with a resistor 174. The switch 172 is connected to the control electrode 176 of an electronic switch 178, shown as a triac, and thus opening the switch 172 serves to interrupt power flow through the electronic switch 178 which is placed in series with the primary 92 of the step-up transformer 34. A detailed description of the overload protection and control circuit and system 160 may be found in the copending patent application recently filed by Anthony J. Pellegrino and entitled lnterlocked Operation Control and Overload Protective Circuit System and assigned to the same assignee as the present application which issued on Dec. 1, 1970, as U.S. Pat. No 3,544,844.
In the illustrative embodiment the pressure of the paint is used to produce an atomized spray of particles propelled from the nozzle 12. It is to be understood that the applications of the present invention are not limited to such hydraulic pressure systems; this invention can be applied to advantage in airatomizing systems. In air-atomizing systems the particle charger 10 includes another passage for feeding air under pressure to the spray nozzle where such air serves to atomize the paint into suitable particles which are electrostatically charged by the electrode 32.
What I claim is:
l. a portable, compact, lightweight electrostatic particlecharging system comprising a particle-handling tool for issuing a spray of particles, said tool including a longitudinal barrel including a longitudinally extending particle-supplying tube formed of an insulated material and having a particle discharge nozzle coupled to an end thereof, said barrel further including a high-voltage supply longitudinally extending along near said tube, said tube and said supply being encapsulated with an electrically insulating material, with said supply being arranged to provide successively increasing voltages building up to a high DC voltage provided in the vicinity of the particle discharge nozzle, an electrode located in the vicinity of issuing particles, said electrode being connected to said supply for charging said particles.
2. A portable, compact, lightweight electrostatic particle charger system as claimed in claim 1 including a step-up transformer having a primary winding adapted to be connected to a low AC voltage source and a secondary winding sized to generate a higher AC voltage, said step-up transformer being located remote from said tool, a flexible insulated cable connecting the secondary winding to said high-voltage supply located in the barrel, said high-voltage supply being formed of longitudinally stacked voltage multipliers, the number of said voltage multipliers being chosen to determine the level of voltage generated at said electrode for the charging of said particles.
3. A portable, compact, lightweight electrostatic particle charger system as claimed in claim 2 in which said tool has an electrically conducting handle adapted to be held in the user's hand and said step-up transformer is adapted to be mounted on the users body, said system including a grounding connection for grounding said handle.
4. A portable, compact, lightweight electrostatic particle charger system as claimed in claim 3 in which said flexible in- 'sulated cable includes a conductive braid surrounding and spaced from an inner conductor, said conductive braid being grounded to said handle and being connected to one side of the secondary winding of said transformer and also being connected to the low voltage side of an initial one of said voltage multipliers.
5. A portable, compact, lightweight electrostatic particlecharging system as claimed in claim 2 in which said high-voltage supply located in the barrel is formed of a pair of parallelspaced stacks of capacitors with rectifiers selectively interconnected between the capacitors in the respective stacks to rectify and multiply the AC voltage up to high level of DC voltage suitable for electrostatic charging of the particles.
6. A portable, compact, lightweight electrostatic particlecharging system as claimed in claim 5 in which said pair of stacks of capacitors extend within said barrel parallel to said particle-supplying tube.
7. A compact, lightweight hand-held high-voltage electrostatic particle charger comprising a particle-handling tool for performing the useful function of propelling particles toward the desired object, and having a handle with a barrel body pro jecting from the handle, a high-voltage supply incorporated in the barrel body of said particle-handling tool, said barrel body having a muzzle end portion from which the particles are propelled, said barrel body being insulated from said handle, said high-voltage supply including a voltage multiplier rectifier network including a plurality of capacitors interconnected with a plurality of rectifiers for producing progressively higher voltage levels at progressively greater distances from said handle toward said muzzle end portion from which the particles are propelled.
8. A compact, lightweight, high-voltage particle charger as claimed in claim 7 in which said voltage multiplier rectifier network includes a pair of spaced-parallel stacks of capacitors with said rectifiers being interconnected between said stacks of capacitors.
9. A compact, lightweight hand-held high-voltage electrostatic particle charger as claimed in claim 7, in which said capacitors are cylindrical with concentrically located terminals at opposite ends, said capacitors being stacked in endto-end relationship in said barrel body, and electrically conductive sleeves positioned between the successive adjacent capacitors, said sleeves snugly engaging and interconnecting the adjacent terminals of successive capacitors in the stack.
10. A compact, lightweight hand-held high-voltage electrostatic particle charger system comprising a hand-held particlehandling tool for performing the useful function of propelling particles toward the desired object, a step-up transformer having a primary winding adapted to be connected to a source of AC voltage, said step-up transformer being located remote from said hand-held tool, said step-up transformer having a high-voltage secondary winding for supplying a high AC voltage, a flexible insulated electric cable extending from said secondary winding to said handheld too], said hand-held tool having an electrically conductive handle with a barrel structure extending from the handle, a voltage-multiplier capacitor and rectifier network including in said barrel structure, said network being connected to said electric cable for rectifying said high AC voltage from said secondary winding and for increasing the resultant DC voltage to a high level suitable for electrostatically charging the particles, an electrode connected to said voltage multiplier rectifier network, said electrode being positioned near the muzzle end of said barrel structure to charge the particles issuing from said muzzle end, said voltage-multiplier capacitor and rectifier network including a plurality of capacitors distributed longitudinally along said barrel structure toward said muzzle end with rectifiers interconnected therebetween for providing successively increasing voltages along said barrel structure in the direction away from said handle and toward the muzzle end thereof, said high-voltage supply being integrally joined with an insulating encapsulating material to form a rigid barrel structure, and the high-voltage end of said voltage-multiplier network being connected to said electrode.
1 l. A compact, lightweight hand-held high-voltage electrostatic particle charger system as claimed in claim 10, in which a bleedofi' resistor having a high-resistance value extends longitudinally in said barrel structure with one end of said bleedoff resistor being electrically connected to said electrode and the other end being electrically connected to said handle,
12. In a portable, charged particle generating tool for emitting an electrostatically charged stream of particles with a high-voltage electrode placed in the vicinity of the emitted particles for electrostatically charging them, a longitudinal barrel structure providing said particles at a muzzle end thereof, said barrel including longitudinally stacked high-voltage multipliers arranged to supply a high particle charging voltage to said electrode at said muzzle end to electrostatically charge the stream of particles, said stack of high voltage multipliers including a plurality of series-connected high-voltage capacitors, each capacitor being cylindrically shaped and having concentrically located terminals, with said cylindrical capacitors being axially stacked with their terminals arranged along the longitudinal dimension of the barrel and with adjacent terminals conductively connected.