US3864603A

US3864603A - High voltage safety apparatus

Info

Publication number: US3864603A
Application number: US415096A
Authority: US
Inventors: David A Kozinski; Bernard W Siczek; Kenneth L Carlson
Original assignee: Graco Inc
Current assignee: Graco Inc
Priority date: 1973-11-12
Filing date: 1973-11-12
Publication date: 1975-02-04
Anticipated expiration: 1992-02-04

Abstract

Apparatus for discharging residual high voltage charge associated with electrostatic paint spraying equipment, including a safety enclosure for confining equipment which becomes highly voltage-charged and which discharges such voltage when entry is made into the safety enclosure.

Description

United States Patent [1 1 Kozinski et a1.

Feb. 4, 1975 HIGH VOLTAGE SAFETY APPARATUS Inventors: David A. Kozinski, Palatine;

Bernard W. Siczek, Chicago; Kenneth L. Carlson, Wheeling, all

of Ill.

Assignee: Graco Inc., Minneapolis, Minn. Filed: Nov. 12, 1973 Appl. No.: 415,096

US. Cl. 317/9 R, 118/12, 239/15,

317/3 Int. Cl. H02h 3/00 Field of Search 118/12, 620, 621;

117/93.4 R, 93.4 A, 93.4 NC; 309/92, 94; 239/3, 15; 317/3, 9 R

[5 6]. References Cited UNlTED STATES PATENTS 2,895,083 7/1959 Quinlan 307/94 3,740,612 6/1973 Gauthier et a1 l17/93.4

Primary Examiner-J. D. Miller Assistant ExaminerHarry E. Moose, Jr.

[57] ABSTRACT Apparatus for discharging residual high voltage charge associated with electrostatic paint spraying equipment, including a safety enclosure for confining equipment which becomes highly voltage-charged and which discharges such voltage when entry is made into the safety enclosure.

8 Claims, 3 Drawing Figures /l|0 V. POWER SUPPLY PATENTEDFEB 4W5 SHEET 10F 2 /HO V. POWER SUPPLY AIR REG AIR XMER V 5 0 6 v f 2 MM 3 m 5 7 2 5 mw 2 3 S 0 4 fi 1 T M l f I I L I m 0.. L r I 3 FIG, 1

PATENTEDFEB M 3.864.603

' sum 20F 2 GUN TO PAINT SUPPLY 25 ;ro owen SUPPLY H.V. CABLE VOLTAGE POWER SUPPLY FIG, 3

1 HIGH VOLTAGE SAFETY APPARATUS This invention relates to a novel apparatus for insuring the complete electrical discharge of high voltage apparatus used in connection with electrostatic paint spraying. The invention automatically provides a mechanical interlock between ground and a paint supply container which becomes highly voltage-charged during paint spraying operations, both when an electrostatic spray gun trigger is released and when a person comes into close proximity to the highly charged paint supply.

In electrostatic paint spraying systems the paint is applied to a work piece by means of a spray gun which atomizes the paint and includes a circuit which applies an electrostatic charge potential to the paint particles. Typically, the work piece is grounded so that the charged paint particles are attracted to the work piece and tend to uniformly cover all exposed areas of the work piece. The electrostatic charging of the paint particles is either accomplished directly by contact with a spray gun electrode as the particles are emitted, or indirectly by passing the particles through a region of ionized air whereby the particles become charged while passing through the ionized air region. In either event, the spray gun typically has a high voltage needle, probe, or other charging means associated therewith, and this high voltage charging means is maintained at a voltage ranging from several thousand to 100,000 volts. The high voltage potential is generally provided by means of a cable extending to a remotely located power supply.

When conductive paints are used in an electrostatic paint spraying system, the high voltage charge at the spray gun becomes transferred to the paint itself and, because the paint is conductive, is transferred to the paint container all objects conductively attached to it. Therefore, when conductive paints are sprayed in this manner, it becomes necessary to insulate the paint container from its surrounding area and to provide protective shielding to prevent people from coming into contact with the charged apparatus. One of the simplest ways of providing this protection is to construct an enclosure around the paint supply. However, since frequent access to the paint supply must be provided for, it becomes necessary to build a gate into the enclosure for this purpose.

One of the inherent characteristics in utilizing high voltages for electrostatic paint spraying operations is the retention of voltage charge after the high voltage power has been turned off. This charge retention is caused by the capacitive effects of the high voltage cable, power supply. and other apparatus together with the extremely high resistances to ground found in circuits of this type. Because of the voltage charge retention, it is possible for an operator to be severely shocked even though the high voltage power supply has been turned off, and therefore a safeguard against this possibility must be provided. The present invention achieves this safety feature by means of a mechanical interlock connection which automatically grounds the voltage-charged equipment whenever the paint sprayer is not being used. This mechanical interlock is connected to the gate into the enclosure surrounding the paint supply, and serves to ground the paint supply whenever the gate is opened. In this manner the opera- I tor is protected against residual charge after he releases vertent-contact with the otherwise highly charged paint supply whenever he enters the enclosure surrounding the paint supply.

Briefly, the invention comprises an enclosure surrounding the paint supply, said enclosure having as an integral part a closed pneumatic link such that when the gate to the enclosure is open the pneumatic link is broken. A pressure switch is connected into the closed pneumatic link to sense drops in pressure caused by opening the gate, and this pressure switch controls a mechanical switch between the incoming power line and the high voltage supply. When the gate is opened, the pressure switch becomes deenergized, cutting off the incoming line voltage to the high voltage power supply. This causes the high voltage to be cut off, which in turn activates a solenoid-operated grounding arm to solidly connect the paint supply container to ground potential. The solenoid-operated grounding arm is also activated whenever the spray gun trigger is released, thereby draining any residual voltage charge from the paint supply.

It is the principal object of this invention to provide a system for safeguarding against high voltage shock when operating an electrostatic paint spraying apparatus.

It is another object of this invention to provide an apparatus for draining residual electrostatic charge from the high'voltage circuits whenever the electrostatic spray gun is not being used.

It is another object of this invention to provide a positive mechanical connection between the highly charged paint supply of an electrostatic paint spraying system and ground to eliminate shock hazards.

These and other objects will be described in the following specification and drawings in which:

' FIG. 1 is a schematic illustration of the entire apparatus of this invention;

FIG. 2 illustrates the high voltage discharging arrangement; and

FIG. 3 shows the mechanical interlock and solenoid apparatus of this invention.

Referring first to FIG. I, the invention is shown in schematic representation. A high voltage power supply 10 generates the electrostatic voltage required for the paint application, typically of magnitude 50,000l00,000 volts. This high voltage is conveyed via high voltage cable ll to a spray gun 20. High voltage cable is constructed from materials suitable for the transfer of the extremely high voltages required in electrostatic painting applications, and has an outer conductive sheath which is solidly connected to ground potential. The grounded cable sheath is connected to the body of spray gun 20 in order to insure that all exterior metal parts of spray gun 20 are securely electrically grounded. The high voltage conveyed thereby is connected within spray gun 20 to a suitable electrostic ionizing means, using any of the concepts available for this purpose and known in the prior art.

A source of compressed air is required for use in conjunction with the invention. Air is introduced into the system at inlet 30 and is conveyed via air lines and hoses, shown as solid lines in FIG. I, to the various system components. The incoming air pressure may be reduced through an air transformer or regulated through an air regulator as desired. The air is used generally for two purposes: to supply the transfer medium for deliv- 3 ering and atomizing paint at the spray gun outlet, and for providing the safety interlock means to be hereinafter described. If the invention is used with a paint system that does not require air for delivering and atomizing paint, the air may still be used as a part of the safety interlock means. Alternatively, another source such as an interruptible light beam with appropriate optical sensing means, may be used to provide the safety interlock means which forms a part of the invention.

The electrical lines used with the invention are illustrated in FIG. 1 as broken lines, and the paint delivery hose 26 is illustrated as a double line.

A paint container 25 is connected to a paint hose 26 which feeds paint from container 25 to the spray gun 20. The paint feed mechanism 50 may be a pumping device for transferring the paint from the container 25 to the hose 26 under suitable pressure. Among the types of paint which may be used with this apparatus are conductive paints, such as water-based paint composition. Because of the conductive nature of these paints, paint container 25 is insulated from earth ground by means of an insulated stand 27.

Surrounding the paint supply is an enclosure which includes an air hose 31. Air hose 31 is coupled to a source of compressed air ,via inlet 30 and provides a complete closed path around the paint supply. Hose 31 is also attached to a gate 32 in the enclosure surrounding the apparatus. Typically, the enclosure is constructed of electrically grounded steel mesh material and gate 32 is a conventional hinged gate providing access into the enclosure from without. Hose 31 is fitted with a quick-disconnect coupling 33 at the point where gate 32 may be opened. Therefore, the opening of gate 32 will cause the coupling 33 to disconnect and thereby relieve the air pressure in hose 31. A pressure switch 35 senses the drop in air pressure caused by opening gate 32 and activates an electrical contact which opens the electrical circuit for deenergizing a solenoid within solenoid container 12. The solenoid is deenergized by means of a voltage cutoff, and a solenoid spring return grounds the paint supply 25. The detailed mechanical operation of the solenoid will be described hereinafter. With respect to the other elements in this circuit path, pressure switch 35 may be any of a number of wellknown switches which are responsive to pressure drops to cause an electrical contact to activate, such as switch type 69GBR7, manufactured by Furnas Electric Co., Batavia, Ill. Spray gun trigger 21 is mechanically connected to an air valve located within gun 20; when the trigger is depressed the air valve opens and causes air to flow through hose 51 and gun 20. This air flow is detected by a flow switch of conventional design located in power supply 10, to cause the activation of electrical switch contacts when air is flowing in hose 51. When air flow stops the flow switch contacts open and cause the high voltage power supply to deenergize its high voltage output. This also causes the solenoid energizing voltage on lines 41 to be removed, thereby deenergizing solenoid within container 12.

FIG. 2 illustrates the high voltage discharge arrangement. High voltage is delivered to the spray gun ionizing means via cable 11, which cable develops and retains a voltage charge because of its inherent distributed capacitance. The ionizing means contacts the conductive paint as it is sprayed. and the voltage charge is thereby conducted back to the paint supply system via the paint in delivery hose 26. The paint supply system thus becomes highly voltage-charged. and is required to be insulated from ground by insulated stand 27. However, a conductive path is provided between the paint supply system 25 and solenoid container 12 via line 42. This conductive path terminates within container 12 at contact plate 16. Contact plate 16 serves as a conductive striking plate for solenoid arm 13 when solenoid 15 is deenergized. Insulated cover plate 29 is sealably fitted into the top of solenoid container 12 in a manner which isolates the insideof container 12 from the exterior. Because of this isolation, any sparkling that occurs when solenoid arm 13 comes into contact with contact plate 16 is contained entirely within container 12, thus eliminating the possibility of the spark igniting paint or solvent vapors which may exist exterior to container 12.

A pair of wires 41 are used to energize and deenergize solenoid 15 as hereinbefore described. Solenoid 15 is rigidly mounted on a metal conducting base 17. Base 17 is, in turn, electrically connected to ground potential through suitable conductors (not shown).

FIG. 3 illustrates the mechanical interlock and solenoid apparatus of this invention. Solenoid 15 has a coil of wire 18 wrapped around a slidable solenoid plunger 19. The ends of coil 18 are brought out and connected to wires 41 as previously described. When a suitable voltage is applied to wires 41 a current flows through coil 18 and creates an electromagnetic field which causes plunger 19 to slide into the body of solenoid 15 as illustrated in FIG. 3. In this energized position, coil spring 14, which is connected between the frame of solenoid 15 and an extension of plunger 19, is constrained inwardly from its normally quiescent position. This causes the spring 14 to develop a force in opposition to the electromagnetic force of solenoid 15 but of insufficient magnitude to oppose the inwardly sliding motion of plunger 19 when the coil 18 is energized.

When -the voltage on the wires 41 is removed, the electromagnetic field generated within coil 18 disappears and the spring tension of spring 14 causes solenoid plunger 19 to slide outwardly in the direction indicated by arrow 43 of FIG. 3. Since the outerextension of plunger 19 is pivotally connected to bracket 48 at pivot pin 46, the outward motion of plunger 19 causes bracket 48 to pivot to the left about its pivot pin 49. Solenoid arm 13 is rigidly connected to bracket 48 by bolt or rivet 50. Therefore, the motion of plunger 19 is transmitted to solenoid arm 13 to cause arm 13 to move sharply to the left. The positioning of the relative pivot points illustrated in FIG. 3 creates a snap-action effect at the end of solenoid arm 13 to cause a decisive contact to be made by the end of solenoid arm 13 against contact plate 16, as shown in FIG. 2. This decisive contact insures a solid connection between contact plate 16 and ground, which, as hereinbefore described, is connected to base plate 17.

It is possible to modify the general configuration of solenoid 15 within the spirit of this invention. Any solenoid configuration which can insure a positive electrical contact between contact plate 16 and ground may be suitably used in this invention. Similarly, the means for energizing and deenergizing solenoid 15 may be accomplished by wiring in ways different from that shown herein{ it being necessary to the invention only that the solenoid be activated to discharge the high voltage potential when the spray gun trigger is released and also when the enclosure gate is open.

It would be possible to substitutefor the air hose surrounding the apparatus of this invention, an electrical analogous circuit. The preferred embodiment illustrates an air hose for the reason that the use of a nonelectrical means to accomplish this function is believed to constitute less of a fire hazard. Most available electrical devices which might be utilized for this purpose have some risk of sparking when circuits are broken. Because of the likelihood of paint and solvent vapors being found in the immediate vicinity of the apparatus, an airdisconnect system was preferably selected for this invention. However, other safe devices, such as an interruptable light beam, could be equally well suited for this purpose.

In operation, solenoid remains energized and solenoid arm 13 remains retracted from contact with contact plate 16 for so long as both of two conditions exist. These conditions are: the air pressure in hose 31 remains pressurized; and the trigger 21 on spray gun is depressed. If either the air pressure drops or the trigger is released, solenoid 15 becomes deenergized and thereby causes solenoid arm 13 to come into contact with contact plate 16 to ground the high voltage potential present on the paint supply. Because the invention operates in this manner, it is a completely fail-safe apparatus. Failure of the air supply, of the solenoid power supply, or of the spray gun trigger mechanism will all cause the solenoid 15 to become deenergized and will ground the high voltage potential. It is to be assumed that the high voltage power supply has a built-in overload circuit breaker which detects instances when high voltage has been shorted to ground. In these instances the internal overload circuit will become activated to shut off the high voltage power at the supply, cutting the power to the solenoid, thus deactivating the solenoid, and directing the stored voltage charge to ground.

What is claimed is:

1. Safety apparatus for confining voltage-charged paint spraying equipment and for discharging components thereof retaining residual voltage charges, comprising:

a. enclosure means for enclosing said voltagecharged equipment, including an access gate for entry and exit;

b. pneumatic alarm means, attached to said enclosure means, for providing a pneumatic signal when said access gate is opened, said pneumatic alarm means including an interruptable pressurized connection at said gate opening point;

0. pneumatic signal receiving means connected to said alarm means for receiving said pneumatic signal indicating an open access gate and for generating a corresponding first voltage signal;

d. a sealed container having therein a spring-biased solenoid, said solenoid having a first solenoid arm position in electrical contact with said components retaining residual voltage charges and a second solenoid arm position displaced from electrical contact, said solenoid being activated by the first 6 voltage signal from said pneumatic signal receiving means, and said solenoid arm being electrically connected to ground potential.

2. The apparatus of claim 1, further comprising a trigger-actuated electrostatic paint spray gun having a circuit for detecting the position of said trigger and for generating a second voltage signal responsive thereto, and means for connecting said second voltage signal to activate said solenoid.

3. Apparatus as claimed in claim 2 wherein said first and second voltage signals are caused to energize said solenoid when said gate is closed and said trigger depressed respectively, and said solenoid arm correspondingly remains in said second position, and said solenoid spring bias causes said solenoid arm to travel to its first position when said solenoid is deenergized.

4. Apparatus as claimed in claim 3 wherein said sealed container further comprises an internal conductor forming the solenoid first arm position electrical contact, and a conductive path to the container exterior; and means for connecting said internal conductor to said conductive path.

5. Apparatus as claimed in claim 4 wherein said alarm means further comprises a pressurized air line and said interruptable connection comprises an air line coupling.

6. Apparatus as claimed in claim 5 wherein said signal receiving means further comprises a pressuresensitive switch.

7. Apparatus as'claimed in claim 6 wherein said enclosure means further comprises an electricallygrounded wire mesh fence.

8. Apparatus for electrically discharging voltagecharged components in a paint supply system, comprising:

a. a fenced enclosure surrounding said paint supply system, said enclosure having a hinged gate;

b. a pressurized air line attached to said enclosure and extending across said enclosure gate, said air line having a disconnectable coupling at said gate opening point;

e. a pressure switch connected to said air line and responsive to pressure drops in said line to activate electrical contacts;

d. a power supply switch connected to said electrical contacts and responsive to activation thereof to disconnect said source of voltage of said voltagecharged components;

e. a solenoid having its energizing coil connected to said power supply switch and having a movable solenoid arm electrically grounded and movable upon deenergization of said solenoid coil into electrical contact with said voltage-charged components; and

. a scalable housing enclosing said solenoid, said housing having electrical connections therethrough for connecting to said solenoid coil, said solenoid arm deenergized position, and electrical ground.

Claims

1. Safety apparatus for confining voltage-charged paint spraying equipment and for discharging components thereof retaining residual voltage charges, comprising: a. enclosure means for enclosing said voltage-charged equipment, including an access gate for entry and exit; b. pneumatic alarm means, attached to said enclosure means, for providing a pneumatic signal when said access gate is opened, said pneumatic alarm means including an interruptable pressurized connection at said gate opening point; c. pneumatic signal receiving means connected to said alarm means for receiving said pneumatic signal indicating an open access gate and for generating a corresponding first voltage signal; d. a sealed container having therein a spring-biased solenoid, said solenoid having a first solenoid arm position in electrical contact with said components retaining residual voltage charges and a second solenoid arm position displaced from electrical contact, said solenoid being activated by the first voltage signal from said pneumatic signal receiving means, and said solenoid arm being electrically connected to ground potential.

6. Apparatus as claimed in claim 5 wherein said signal receiving means further comprises a pressure-sensitive switch.

7. Apparatus as claimed in claim 6 wherein said enclosure means further comprises an electrically-grounded wire mesh fence.

8. Apparatus for electrically discharging voltage-charged components in a paint supply system, comprising: a. a fenced enclosure surrounding said paint supply system, said enclosure having a hinged gate; b. a pressurized air line attached to said enclosure and extending across said enclosure gate, said air line having a disconnectable coupling at said gate opening point; c. a pressure switch connected to said air line and responsive to pressure drops in said line to activate electrical contacts; d. a power supply switch connected to said electrical contacts and responsive to activation thereof to disconnect said source of voltage of said voltage-charged components; e. a solenoid havIng its energizing coil connected to said power supply switch and having a movable solenoid arm electrically grounded and movable upon deenergization of said solenoid coil into electrical contact with said voltage-charged components; and f. a sealable housing enclosing said solenoid, said housing having electrical connections therethrough for connecting to said solenoid coil, said solenoid arm deenergized position, and electrical ground.