Note: Descriptions are shown in the official language in which they were submitted.
ELECTROSTATIC SPRAY COATING A _ARATUS
This invention relates to electrostratic spray coat-
ing systems wherein the deposition of coating materials upon
a workpiece is enhanced through the application of electro-
static forces and, more particularly, to an improved spray
gun apparatus incorporating an entirely self-contained elec-
trical power supply.
Electrostatic spray coating systems of both the
air-atomized and airless types are widely utilized in paint
spraying and for deposition of other coating materials.
Spray gun apparatus conventionally employed therein is gener-
ally constituted by an insulating barrel member having a
grounded handle or mount disposed at one end thereof and a
selectively sized and shaped high voltage electrode extending
from the other end thereof disposed adjacent to the locus of
atomization. Such electrode is usually charged to a poten-
~;tial in the neighborhood of from 30 to 85 kilovolts, and incertain installations as high as 150 kilovolts, to create a
corona discharge condition and a concomitant electric field
of appreciable magnitude. Under such conditions, the corona
dl~scharge current flowing from the high voltage eléctrode
creates a region adjacent to the locus of atomization rich in
unlpolar ions that attach themselves to and charge the paint
or other coating material sp~ray droplets. Alternatively, for
conductive coating materials ~ontact charging of the spray
~droplets will occur in the high field strength region around
the fluid orifice. The charged droplets are then displaced,
under the conjoint influence of their own inertial forces and
the~ electrostatic field extant in the spray region, toward a
grounded workpiece. In accord with conventional practice,
maximum paint savings are g~nerally effected by maintaining
:
~ 1~204 ~
the charging voltage as high as possible and of such magni-
tude as to produce an average depositing field strength of at
least 5,000 volts/inch, and preferably as high as 10,000
volts/inch, between the spray gun and the workpiece. As a
concomitant thereto, the spray velocity in the vicinity of
the workpiece should be of minimal magnitude consistent with
the demands of adequate atomization and paint flow.
The requisite charging voltages are conventionally
obtained either through the utilization of externally located
standard electronic high voltage power supplies or by the
incorporation of an electrogasdynamic high voltage generator
within the spray gun body. The standard electronic high
voltage power supplies are relatively large, heavy and expen-
sive and are so constituted as to inherently function with
essentially "constant voltage" type characteristics. In
addition thereto and because of the magnitude of the poten-
tials involved, the high voltage cable interconnecting such
power supply with the spray gun is heavy, bulky and relative-
ly inflexible, adding undesired weight to the gun assembly
which, because of the concomitant high voltage insulation
requirements is rendered unduly large, complex, and, in most
instances, not field serviceable.
While the electrogasdynamic powered spray coating
apparatus is possessed of several advantageous features as
compared to the standard high voltage power supplies, such
conventionally require external generation of the relatively
low, but still multi-kilovolt, excitation potentials for the
spray apparatus-contained electrogasdynamic generator and as
such, require utilization of an external power supply con-
nected to the spray head as well as requiring the use of
pre-conditioned or ~Iseeded~l air for reliable operation
thereof.
~,
l 16~4 ~
The avoidance of dependence upon a "seededt' air sup-
ply and the minimization, if not elimination, of all external
power supplies and associated electrical connections to the
electrostatic spray apparatus has been a long-sought ob~ec-
tive in this field. However, the antithetical requirements
of required high operating potentials with attendant current
limiting or constant current characteristics, the required
utilization of conventionally available compressed air sup-
plies, and the avoidance of deleterious discharge potentials,
all within the framework of lightweight, small size and ex-
tended trouble-free operation over long periods of time, have
effectively precluded, despite various suggested solutions,
practical realization of this objective.
This invention may be briefly described as an im-
proved construction for a lightweight electrostatic spray
coating apparatus incorporating an entirely self-contained
electrical power supply and which includes, in its broadest
aspects, means for converting the energy of a fluid under
pressure into electrical energy suitable for use as a power
source for the spray apparatus and/or appropriate for appli-
cation to the spray apparatus charging electrode. In its
broadest aspects, the present invention also contemplates
means for converting the kinetic energy of a moving air
stream into kinetic energy of a rotating solid and means for
converting the latter into electrical energy suitable for use
as a power source for the spray apparatus and/or appropriate
for application to the spray apparatus charging electrode.
Pursuant thereto, the invention broadly includes an air
driven low voltage alternator, a rectifier and voltage regu
lator for converting the alternator output into a substanti-
~ally constant DC voltage input Eor a high frequency oscillat-
or and a multi-stage voltage multiplier for further increas-
ing the magni~ude of the transformed output voltage of the
high frequency oscillator and converting the same to the
,
i 162~ l
30-100 kilovolt potential level conventionally required to
effect the electrostatically enhanced deposition of coating
materials. Further, in its broad aspects, the subject inven-
tion also includes an energy conversion unit for electrostat-
ic spray coating apparatus comprising a selectively sized and
arranged lightweight high speed impulse type air motor di-
rectly driving a compatible magnetic armature low voltage
alternator adapted to provide an effectively instantaneous
voltage output in response to demand for power.
In its narrower aspects, the subject invention in-
cludes the provision of a spray head incorporating a light-
weight~ self-contained power supply made up of a high speed,
impulse-type low-inertia air motor directly driving a magnet-
ic armature low voltage alternator, a solid state rectifier
and voltage regulator for converting the alternator output
into a substantially constant DC voltage input for a high
frequency oscillator adapted to provide a stepped up or
transformed essentially square or sine wave output of about
2.5 kilovolts peak and a solid state multi-stage voltage mul-
tiplier employing standard 5 kilovolt components for increas-
ing the magnitude of the transformed output voltage of the
high frequency oscillator to the 30 to 100 kilovolt level
required to effect the electrostatically enhanced deposition
of coating materials.
In a still narrower aspect, the subject invention
includes the selective combination of diminutive and light-
weight components operative within a framework of mechanical
and electrical opera-ting parameters that provide an operative
lightweight electrostatic spray gun unit adapted to utilize
conventional plant compressed air supply as the prime movant
and to deliver conventionally required output voltages for
paint spraying and the like at acceptably low current levels.
Among the advantages of the subject invention is the
provision of a lightweight diminutively sized and readily
1 16~
manipulatable electrostatic spray gun that dispenses with all
external electrical connections thereto and the provision of
a self-contained electrical power generating system for elec-
trostatic spray coating apparatus that derives its electric
power solely throu~h direct conversion of the kinetic energy
of a moving air stream. Other advantages of the subject in-
vention include the provision of a self-contained high volt-
age power supply for electrostatic paint spray guns that is
drivable from conventionally available compressed air sources
and employs readily available electrical components; the pro-
vision of a diminutive high voltage power supply of enduring
and reliable character adapted to produce output voltages of
30-100 kilovolts at a current level in the order of 50 micro-
amperes; and the provision of a reliable high voltage power
supply adapted to be contained within a hand-holdable spray
coating apparatus without materially increasing the weight
thereof. Still further advantages of the subject invention
include the provision of electrostatic spray coating appa-
ratus that is completely free of any external electrical
power connections and requires only an available conventional
source of compressed air for operability. Yet another advan-
tage of the subject invention is the provision of a
cartridge-type multi-element power supply made up of essenti-
ally monolithic subassemblies that are assemblable and are
individually replaceable for easy field servicing thereof.
In more particularity, the practice of the herein-
disclosed invention provides an electrostatic spray gun
assembly having an entirely self-contained electrical power
supply that is devoid of e~ternal electrical connection
thereto and which is characterized by conventional opera-
tional parameters of a re~uired 30-100 kilovolt output at
approximately 50 microamps; a power level of approximately 3
watts; a total weight of between about 1-1/2 to 3 pounds and
the utilization of conventionally available compressed air
supply of between about 20 to 80 psig at flow rates no great-
er than 5 scfm.
The primary objective of this invention is the pro-
vision of improved electrostatic spray coating apparatus in-
corporating an entirely self-contained electrical power
supply.
Among the further objects of the invention is the
provision of an improved power supply construction for elec-
trostatic spray coating operations of such diminutive size as
to be disposed within the spray head apparatus and drivable
by compressed air.
Still another object of this invention is the pro-
vision of a self-contained and improved cartridge-type power
supply for electrostatic spray coating devices that is readi-
ly field replaceable.
Other objects and advantages of the subject inven-
tion will be apparent from the following portions of this
specification and claims and from the appended drawings which
illustrate a presently preferred construction incorporating
the principles of this invention.
Referring to the drawings:
FIG. 1 is a schematic side elevational view, partly
in section, showing the disposition of the elements of the
power supply disposed within a hand manipulatable spray gun
of the air atomizing type;
FIG. lA is a schematic flow diagram indicative of
the nature of flow of the gaseous prime movant in the dis-
closed system;
FIG. 2 is a schematic vertical section of a suitable
air motor configuration;
FIG. 3 is a schematic sectional view of a suitable
air motor-alternator subassembly construction;
FIG. 4 is a schematic representation of the typical
performance characteristics of the air motor;
~- 1 16~0~ ~
FIG. 5 is a schematic circuit diagram of a
rectifier-voltage regulator ircuit;
FIG. 6 is a schematic circuit diagram of an
oscillator-transformer circuit;
FIG. 7 is a schematic circuit diagram of a suitable
long chain series voltage multiplier;
FIG. 8 is a schematic vertical section of an air
pressure regulator device; and
FIG~ 9 (on the s~eet of FI~. lA~ is a schematic vertical
section of another embod~ment of a pressure regulator device.
Referring to FIG. 1, there are generally and sche-
matically illustrated the components of a hand manipulatable
type of electrostatic spray gun 10 for paint spraying and the
like embodying the principles of this invention. The spray
gun 10 includes a generally cylindrical and elongate barrel
portion 12 formed of insulating material and a pistol grip
type handle 14 formed of conducting material and whose upper
portion encircles the rear end of the barrel portion 12. An
air hose 16 connectable to a remote source of compressed air
(not shown), suitably a conventional compressed plant air
supply capable of supplying air at a pressure range of from
20 to 80 or more psig and at a flow rate of at least about 3
scfm, and more preferably at least 10 scfm, is connected to
the base of the handle 1~ through a suitable fitting 18.
: As shown in FIG. 1, the spray gun 10 constructed in
accordance with the principles of this invention differs from
those conventionally employed in both air-atomized and air-
less electrostatic spray coating systems in that it has con-
nected thereto only a~paint supply line 38, an air supply
line 16 and a ground connection and is totally devoid of
:external electrical power supply connections theretor The
subject construction thus completely dispenses with the here-
tofore required large and heavy floor-supported electronic
0~
power supply units and the associated heavy and relatively
inflexible insulated cables required to transmit the exter-
nally generated charging potentials to the gun, as well as
also dispensing with the seeded air supply and the insulated
electrical cable conventionally required to transmit the
excitation potentials to electrogasdynamically powered spray
gun assemblies.
Disposed within the handle 14 is an air flow conduit
20 connected to a flow control valve 22 operable through dis-
placement of a trigger 24 by the user of the gun. The output
side of the flow control valve 22 is connected to a conduit
26 which fluidly connects with a control valve and regulator
assembly 27 schematically shown in FIG. 1. Exiting from the
assembly 27 is a primary air flow conduit 30 and an auxiliary
air flow conduit 28. The primary air flow conduit 30 serves
(in an air-atomized gun of the type described) to convey a
flow of compressed air to an air cap assembly 32 wherein, as
indicated by the further subdivided air flow conduits 34 and
36, such air may be used for conventional air-induced atomi-
zation of the coating material introduced from a remote sup-
ply through the hose 38 and fitting 40 and conveyed to the
air cap assembly 32 via conduit 42 and/or may be employed as
"fan" air for shaping the emitted spray of the atomized coat-
ing material.
: : ~ The structure and configuration of the air cap
assembly 32 and the internal design of the air and coating
material conduits therewithin may be essentially conventional
in nature and U.S. Patents 3,645,447: 3,693,877; and
3,843,052 are exemplary of suitable constructions therefor.
The electrode system incorporated in the air cap 32 may also
be con~entional, as is the grounding of the conductive handle
portion 14, by means of a conductive sheath 44 disposed
around the air hose 16 or by means of a suitable ground lead
associated there~ith.
,
1:l62043
Disposed within the barrel portion 12 and the upper
section o~ the handle portion 14 of the gun 10 is an elongate
removable power supply cartridge member ~5. The cartridge
member 45 contains the hereinafter-described operative com-
ponents of the power supply and is of generally cylindrical
configuration having a rear section 46 of appreciably greater
diameter than its forward section 48.
When the cartridge 45 is properly seated within its
complementarily contoured receiving bore within the gun bar-
rel 12, the auxiliary air flow conduit 28 is directly con-
nected to an input nozzle 50 of a diminutive air motor
assembly 52 to rotatably drive the rotor 56 thereof at high
speed. The air flow through the air motor 52 may suitably be
vented to the atmosphere through an exhaust channel 54 at the
rear of the gun barrel 12. The rotor 56 of the air motor 52
is mounted on a common shaft 58 with the armature 60 of an
adjacent alternator 62 to form an effectively integral low
inertia assembly capable of rapid acceleration to high speeds
with a concomitant long life. The armature 60 is disposed
within a cylindrical epoxy-coated sleeve type stator 64,
preferably of tape wound construction. The air motor 52 and
the alternator 62 comprise an essentially integral sub-
assembly that is both of small size, lightweight and low
~inertia. The described direct coupling of the air motor 52
with the alternator 62 operates to effect a direct conversion
of kinetic energy available in the moving air stream in con-
dui~t 28 into electrical energy in the nature of an alternat-
ing voltage suitably of about 8-20 volts r.m.s. at a frequen-
cy sf about 250 to 350 cycles/sec.
The alternating voltage output of the alternator 62
is introduced, through leads 68, into a rectifier 70 and
voltage regulator 72 wherein it is converted into a substan-
tially constant DC voltage, suitably of about 8 to 20 volts
in magnitude. The regulated output voltage of rectifier 72
.:
' :
2~ ~
drives a high frequency oscillator 74 to produce a low volt-
age sine or square wave output suitably at a frequency in the
range of from 10 to 50 kilohertz. The high frequency but low
voltage output of the oscillator 74 is then raised by a
transformer 76 which comprises an integral part of the oscil-
lator circuit, to provide a + 2,500 volt square or sine wave
output at the specified frequency range.
The high frequency, high voltage output of the
transformer 76 is introduced into a long chain multiplier 80,
suitably a series multiplier of about 20 or more stages, to
elevate the input voltage into a desired 30 to 100 kilovolt
rectified output voltage which is fed to the electrode
assembly in the air cap 32 via lead 84 and a limiting resist-
ance 82. A major part of limiting resistance 82 may alter-
natively be placed between the low voltage end of cartridge
45 and the grounded handle 14.
The critical size and weight limitations herein
attendant for electrostatic spray coating apparatus, and par-
ticularly for hand manipulatable spray guns, can be effec-
tively satisfied by utilization of a prime movant air supply
and flow system of the type schematically illustrated in FIG.
lA. As there shown, the prime movant source comprises a con-
ventional plant compressed air supply 85 that normally sup-
plies clean air at pressures greater than 70 ps.ig and at
available flow rates in excess of 15 scfm. Such compressed
air is initially introduced into an externally located, con-
ventional and commercially available pressure regulator 86
adapted to provide a fixed and regulated supply of compressed
air at 70 psig. A suitable regulator may, for exa~ple, be
Binks No. 85-201 as manufactured and sold by Binks Manufac-
turing Company of Franklin Park, Illinois. Such regulated
air at 70 psig is introduced via the air hose 16 to the gun
10. Previous limitations on the effective length of air hose
for electrostatic spray apparatus, which was about 25 feet,
~ ~2~ 1
are now effectively removed and any length of air hose can
now be employed. Air flow within the gun is primarily con-
trolled by actuation of the trigger 24 and shift of the flow
control valve 22 disposed within conduit 20 in the handle 14
from fully closed to fully opened condition. Downstream of
trigger 24 the primary air flow within conduit 26 is intro-
duced into the control valve and regulator assembly 27. Such
control valve and regulator assembly 27 is operative to
selectively and independently regulate the flow of air via
conduit 30 to the air cap for both atomization of the coating
fluid and fan width control, while also effecting a selective
control of the flow of air at substantially fixed pressure to
conduit 28 to the energy conversion unit.
As mentioned earlier, spray guns of the type herein
of concern employable in commercial electrostatic paint
spraying or other coating operations must satisfy and fall
within a practical and established framework of mechanical
and electrical parameters. In general, hand-holdable
electrostatic spray guns desirably should weigh less than
three pounds, should provide an operating potential of from
30 to 100 kilovolts at a current level of about 50 micro-
amperes, and should be operable with conventional plant
supply of compressed air at pressures from about 20 to 80
psig. In addition, such guns must include means for limiting
the current flow to prevent deleterious arc-type discharge
when the high voltage electrode approaches a grounded object.
The following portions of this specification will
describe, in more detail, a presently preferred embodiment of
a self-contained electrical power supply for electrostatic
spray guns that (a) weighs about 1/2 pound, (b) is operable
from conventionally available compressed air supplies of from
20 to 80 psig at a flow rate no greater than 5 scfm, (c) pro-
vides a 50 kilovolt minimum output at 50 microamperes with a
maximum current flow of about 200 microamperes at short
1 1~20~ ~
circuit, and (d) is conveniently formed as a replaceable
cartridge to facilitate field servicing of the spray
equipment--all of which permit ready cartridge-type incorpo-
ration within hand-holdable spray guns and concomi~ant satis-
faction of the currently accepted and recognized mechanical
and electrical parameters therefor.
Further, there is also described a presently pre-
ferred embodiment of a lightweight energy conversion assembly
for electrostatic spray guns that (a) is operable from con-
ventionally available compressed air supplies of about 70
psig at flow rates of about 3 scfm, (b) provides an 8-20 volt
alternating output at 5-10 watts/ (c) provides desired output
voltage to satisfy electrostatically enhanced deposition of
spray coating material, and (d) is conveniently formed as a
separable component of a replaceable cartridge assembly to
facilitate field servicing of the spray equipment.
The air motor 52, alternator 62, rectifier 70 and
voltage regulator 72 subassembly preferably is desirably con-
structed to provide exemplary operating characteristics such
as (a) relatively constant output voltage of 5-10 volts DC at
a power level of 5-10 watts from a 20-80 psig oil-free air
supply utilizing less than 5 scfm of compressed air exhaust-
ing at atmosphere pressure, (b) acceleration of the air motor
rotor 56 and armature 60 to 80% of full speed within a maxi-
mum of about 0.2 second from trigger actuation, and (c) a
light weight, in the order of 3 ounces, with a concomitant
structural durability to provide for long operating life.
As best shown in FIGS. 2 and 3, a presently pre-
ferred construction for the air motor 52 comprises a simple
impulse type air motor wherein the rotor 56, when exposed to
an entering air stream through nozzle 50 moving at about 300
meters/sec., has a theoretical maximum speed of about 300,000
r.p.m. so as to conveniently and readily permit operation at
speeds in the order of 10,000 to 30,000 r.p.m. while provid-
ing the necessary torque to drive the alternator 62 in such
~ I~62~41
manner as to provide the desired power output from the avail-
able kinetic energy in the moving air stream.
Compressed air flowing at about 4 scfm at a pressure
of 40 psig has a theoretical power capability of about 200
watts, and at flow conditions of about 3 scfm at a pressure
of 70 psig, it has a theoretical power capability of about
250 watts. Since the desired output of the alternator 62 and
the rectifier 70 are in the order of about 10 watts or less,
the described system renders the full pressure drop available
to drive the air motor 52 and associated alternator 62.
~dditionally, the above described preferred impulse turbine
type of air motor avoids the utilization of sliding seals and
permits the use of ball bearings, oil-impregnated bushings or
other suitable bearing elements, suitably of the type em-
ployed in dentists' drills and the like for long-lived high
speed operation.
In order to obtain the desired rapid acceleration of
the~armature 60 of the alternator 62, the inertia of the air
motor rotor 56 and armature 60 must be kept as small as pos-
sible.
To the above ends, the rotor 56 of the air motor 52
is about 2~5 cm. in diameter, about 0.6 cm. thick and is con-
veniently of lightweight, high strength resin such as "Delrin"
(a trademark), manufactured by E.~I. DuPont de Nemours & Co.,
Inc. The rotor 56 is mounted adjacent one end of shaft 58
which is terminally supported in sealed ball bearings 59.
The ball bearing-mounted rotor 56 is disposed in close
peripheral clearance within a chamber 61 formed in a shell
~houslng 63. The prime movant air from conduit 28 is intro-
duce~d through a selectively located and sized orifice 50 that
is e~ssentially tangentially oriented relative to the rotor
periphery and is about 0.15 cm. in diameter. The diameter of
the aperture 50 is selected to provide air exiting into cham-
ber 61 in the vicinity of sonic velocity and to limit flow to
0~1
14
approximately 3 scfm. After impingement on the blade sur-
faces of rotor 56, such air is vented from chamber 61 through
one or preferably a number of ports 54. Disposed downstream
of the ports 54 is a muffler plate 67 disposed in peripheral
engagement with an o-ring 69, for venting such exiting air to
the atmosphere from the rear of the gun with minimal noise.
A suitable muffler 67 comprises a sintered ceramic or metal
disc of about 0.3 cm. thickness.
As shown in FIG~ 4, the torque speed characteristic
of the described impulse type turbine, shows that output
torque is essentially inversely proportional to speed of
rotation. As such, desirable torque levels are achieved at
speeds of less than 30,000 r.p.m. as represented by the
shaded portion under the curve. Such torque-speed limitation
poses a further operating parameter upon the design of the
alternator 62.
The alternator unit functions to convert the rota-
tional kinetic energy of the air motor rotor 56 into electri-
cal energy, which in turn serves as the electrical power
source for the high voltage for the electrostatically en-
hanced deposition o~ the spray coating material. As previ-
ously described, such alternator unit should provide a power
output of from 5 to 10 watts at an output voltage of at least
5, and preferably greater than 10 volts, and should do so
with low losses and internal dissipation and in a highly
reliable manner through avoidance of any brushes, wipers or
other commutating means. The above ob]ectives must be satis-
fied in an assembly that is both small in size and weight and
is possessed of minimal inertia.
To the above ends, the alternator 62 is disposed
immediately adjacent to the rotor 56 and within the common
housing 63. The armature 60 is mounted on shaft 58 and is
directly driven by rotor 56. Such armature 60 preferably
comprises a high energy permanent magnet 100 about 5/8 inch
204 ~ `~
long and about 1/2 inch in diameter, magnetized across a
diameter thereof. Present knowledge indicates that magnet
diameters in excess of 1/2 inch are attended by unaccep~able
inert~a charactexistics. Alinc~ 8 Ca tradem~xk~ is a preferred
material for such magnet armature although ~t~er mater~als
including Aln~co 5 (a trademark) can also be used.
As best shown in FIG. 3, the stator 64 of the alter-
nator 62 consists of a hollow cylindrical tape wound core 71
of high permeability alloy steel to minimize hysteresis and
eddy current losses. Toroidally wound about the core 71 are
a pair of coils 73 serving as the stator winding. Such coils
are selected to provide an output voltage as previously indi-
cated and to match the impedance requirements of the down-
stream electrical components such as the rectifier 70, volt-
age regulator 72 and oscillator 74. The entire stator and
winding assembly is encapsulated or potted to provide a mono-
lithic type structure. The above described alternator 62 is
of simple and rugged construction and is characterized by a
low starting torque that permits the rapid attainment of an
operating speed of about 15,000 r.p.m. in less than 1/4
second to effect delivery of 5 to 10 watts of power at a
voltage level of about 12 volts.
The remaining components of the power supply are
electrical in nature and are constituted of essentialIy con-
ventional circuitry and circuit elements with the values of
thé circuit eIements being selected to operate within the
heretofore and hereinafter identified parameters. By way of
illustrative example, FIG. 5 delineates a suitable circuit
arrangement for the rectifier 70 and voltage regulator 72
that serves to convert the 8-16 volts r.m.s. alternating
voltage output of alternator 62 into a constant DC voltage of
about 8-12 volts in magnitude. As there shown, the alter-
nator 62 is connected across a bridge rectifier 110 made up
of solid state diodes 112. The bridge output is connected
,~
1 1620~ ~
across a zener diode 114 and a filtering capacitor 116 to
provide a substantially constant DC output across terminals
118.
As described earler, the high frequency oscillator
74 is preferably designed to provide a square wave type out-
put in the frequency range of from 10 to about 50 kilohertz
at a voltage level commensurate with the previously indicated
8 to 12 volt DC input thereto. The high frequency alternat-
ing output of the oscillator is then transformed up to a plus
or minus 2,500 volt square wave for introduction into the
first stage of the multiplier 80.
~ IG. 6 schematically illustrates a suitable circuit
for such oscillator 74 and transformer 76. As shown, the
output terminals 118 of the regulator 72 are connected across
a resistor 120 and diode 122. The oscillator circuit in-
cludes a pair of transistors 124, 126 having the output
thereof connected across the primary winding 128 of trans-
former 76. The stepped up voltage output of about + 2,500
volts at a frequency of from 10 to 50 kilohertz is delivered
by the secondary winding 130 of the transformer.
Such preferred ~ 2,500 ~olt square wave output from
the transformer 76 is applied to the input terminals of the
long chain multiplier 80. Figure 7 schematically illustrates
a suitable circuit for a multistage (suitably about 24
stages) series multiplier to provide a 60 kilovolt output.
Since the size and weight of any such unit is determined by
the size and weight of the electrical elements, i.e~, capaci-
tors and rectifiers, forming the multiplier chain, the plus
or minus 2,500 volt input permits the utilization of standard
5 KV components which are diminutive in size and light in
weight. As shownr such chain conventionally includes a plur-
ality of stages each formed of series-connected capacitors
132 bridged by diodes 13~. Any type of series or parallel
long chain multiplier may be employed although a series
multiplier is presently preferred.
~ ;~
~ :l620~ ~
The air motor 52 and alternator 62 comprise a first
subassembly of the cartridge 45 which is detachably electri-
cally connected to a second subassembly comprising the recti-
fier 70, voltage regulator 72, oscillator 74, and transformer
76. The long chain multiplier 80 (when potted) comprises a
third subassembly which is detachably electrically connected
to the transformer 76. The subassemblies may form separable
monolithic-type structures that compositely form parts of the
cartridge 45 and together are readily field-replaceable.
In order to limit the voltage output and to prevent
over driving of the air motor 52l the air regulator assembly
27 is preferably included in line with the auxiliary air flow
conduit 28 in handle 14. FIG. 8 schematically illustrates a
simple air regulator assembly. As shown, a sleeve 150 defin-
ing an elongate central bore 152 of markedly reduced air flow
cross section is placed in the conduit 28. The bore 152 is
capped by a displaceable valve member 154. The base portion
156 oE the valve member 154 is disposed in sliding inter-
facial enga~ement with the walls of an enlarged portion of
conduit 28 where suitable O-rings 158 are desirably inter-
posed to prevent leakage of air therepast. The upper portion
160 of the valve member 154 is of reduced transverse extent
to provide a chamber 162 thereabout. The chamber 162 is also
bounded by a plug 164 having a central bore 166 of reduced
air flow cross section. The plug 164 is located to limit
upward displacement of the valve member 154 which is normally
biased in closed inter~acial engagement therewith by the
spring 168. Also included in the valve member 15~ are a
~plurality of angularly disposed conduits or channels 170
which permit air flow from the bore 152 to the chamber 162
when the dependent ends thereo~ are not closed by the end of
the sleeve 150.
In operation of the subject unit, the valve member
154 is normally biased into sealing relation with the bore
, .
1 ~620~ J
18
166 of the plug 16~. Air pressure extant within the chamber
162, howeverp will displace the valve member downwardly
against the action of the biasing spring 168 serving to open
the bore 166 and to partially or fully close the channels
170. The closure or partial closure of the channels 170
reverses the action and permits the spring 168 to control and
move the plug upwardly. As will be apparent, proper dimen-
sioning of the elements will serve to limit the effected
pressure on the upstream side to a predetermined value inde-
pendent of the pressure in the downstream line and thus regu-
late the air input to the air motor.
Referring to FIG. 9, a modified air regulator
assembly 27' is operative to selectively and independently
regulate the flow of air via conduit 30 to the air cap Eor
both atomization of the coating fluid and fan width control,
while also effecting a selective control of the flow of air
at substantially fixed pressure to conduit 28 to the energy
conversion unit. The critical size and weight limitations
attendant hand manipulable electrostatic spray guns narrowly
confine permitted operating parameters necessary for high
reliability and high efficiency operations. For example, the
ability of the system to absorb and dissipate excess energy
resulting from higher air supply pressure to the energy con-
version unit is necessarily limited. Similarly a drop in
supply air pressure results in less than desirable output
voltages. Commensurately therewith, and because of the
necessity of providing a constant pressure source of prime
movant gas to the energy conversion unit, it is an equal
necessity to provide a variable and controlled source of air
~or atomizing purposes. The control valve and regulator
assembly 27' is adapted to be disposed within the gun for
performing such necessary functions and it is readily con-
trollable by the operator. Thus, the control valve and regu-
lator assembly 27' serves the dual functions of regulating
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19
the flow of air fed, via conduit 30~ to the delivery end of
the spray gun for use in atomization of the coating material
and in fan spray pattern control and second of supplying air
in controlled volumetric amounts and at substantially con-
stant pressure to the air motor assembly.
As diagrammatically shown in FI5. 9, the control
valve and regulator assembly 27' is adapted to be mounted
within a bore 180 within the rear of the gun barrel, with
such bore 180 being in fluid communication with air inlet
conduit 26 and air conduits 28 and 30. Such assembly is
formed of a selectively shaped cylindrical sleeve 182 thread-
edly mounted in the bore 180, as at 184. The exposed end of
the sleeve 182 terminates in a knob 186 for effecting longi-
tudinal displacement of the sleeve 182 within bore 180 in
response to rotation thereof. The forward end of sleeve 182
is tapered to provide a variable sized annular entry orifice
188 to the bore 180. The sleeve 182 includes a plurality of
vent ports 190 near the forward end thereof.
Threadedly mounted, as at 192, within sleeve 182 is
an elongate valve stem 1~4. The rear exposed end thereof
terminates in a knob 196 for rotation relative to sleeve 182
and consequent longitudinal displacement of the pointed for-
ward end 198 thereof relative to a restricted orifice 200
within the end of sleeve 182. Suitable O-rings 202 and 204
serve to selectively isolate air conduits 28 and 30 from each
other.
In operation of the described assembly actuation of
the trigger 24 results in air being supplied, from a remote
source thereof and at a constant pressure, typically 70 psig,
to air conduit 26. A portion of the air flows through the
annuIar entry orifice 188, in an amount and at a pressure
dependent upon the position of sleeve 182, and into conduit
30 for passage to the air cap for atomi~ation and fan control
usage. The remainder of said air flows through the
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restricted orifice 200, when open, through ports 190 into the
bore 180 and outwardly thereof through conduit 28. The flow
through conduit 28 will be essentially at the pressure of the
air source, typically 70 psig, and its volume rate of flow
will be controlled by the size of the aperture 50 adjacent
the air motor 52.
Rotation of knob 186 displaces the assembly forward
or backward permitting a greater or lesser flow of air
through the annular orifice 188 which exits through the port
connecting with conduit 30 in the barrel of the spray gun and
thereinafter to the air cap for atomization purposes. Inde-
pendently of the operation of knob 186 just described rota-
tion of knob 196 acts to move the inner concentric valve stem
194 back or forth opening or closing the second air passage
200. When knob 196 is rotated anticlockwise, the valve is in
the open position and air at the full inlet pressure, typi-
cally 70 psig/ is fed to the air motor via chamber 206. The
screw threads and the fit of the O-rings 202 and 204 are
preEerably designed so that rotation of knob 196 rotates only
valve stem 194 and not the body 182, thus permitting control
of power for electrostatic spraying without affecting the
setting of air for atomization. Similar rotation of knob 186
to control atomization does not affect the relative setting
of the valve stem 194 and valve seat 208 and so does not
simultaneously actuate the air supply to the air motor via
port 188.
A prototype system constructed in accord with the
foregoing principles readily provides a 55 KV output at 3
watts DC from a 20 psig regulated compressed air input at 4.2
scfm. The following operational and physical parameters were
attained:
Air Mot_r - Alternator Subassembly
.
Air Input 20 psig; 4.2 scfm
Output 8.6 watts at 12.1 volt
rms and 250 hertz
Dimensions (D x L) 1.375" x 1.355"
Weight 2.4 oz.
Rise Time less than 0.1 sec. to
90~ of rated power
Rectifier-Regulator-Oscillator-Transformer
Input as above
Output 5.1 KV (peak) at 20 KHz
and 5.4 watts
Dimensions 1.375" x 1.0l'
Weight 2.25 oz. (encapsulated)
High Voltage Multiplier
Input as above
Output 55 KV at 3 watts DC
Dimensions (D x L) 0.875" x 4.75"
Weight 4.0 oz. (encapsulated~
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