Note: Descriptions are shown in the official language in which they were submitted.
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A ROTARY TYPE ELECTROSTATIC SPRAY PAINTING DEVICE
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BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a rotary type
electrostatic spray painting device.
2. ~ Descrip~ion of the Related Art
In a known rotary type electrostatic spray
painting device, a rotary shaft thereof is supported by
static pressure air bearings within the housing of the
device. A spray head is fixed to the outer end of the
rotary shaft, and a turbine wheel for driving the rotary
shaft is fixed to the inner end of the rotary shaft. An
air injection nozzle which provides a rotational force
in one direction for the turbine wheel is arranged in
the housing of the device to provide a driving force for
rotating the rotary shaft (hereinafter referred to as
the drive nozzle), and another air injection nozzle
which provides a rotational force in the other direction
for the turbine wheel is also arranged in the housing of
the device to provide a braking force for the rotary
shaft (hereinafter referred to as the brake nozzle).
Air under pressure is fed into the static pressure air
bearings (hereinafter referred to as the air bearings)
so that the rotary shaft is supported by these air
bearings in a non-contact state. When a painting
operation is carried out, air under pressure is injected
towards the turbine wheel from the~air injection drive
nozzle, and the rotary shaft is thus rotated at a high
speed. When the painting device is to be cleaned, to
enable a~change of the color of the paint to be sprayed,
air under pressure is injected towards the turbine wheel
from~the~air injection brake nozzle so that the~rotating
~speed of the rotary shaft is~quickly reduced (Japanese
~Unexamined Utility Model Publication No. 58-124254).
~ In~this rotary type~electrostatic spray painting
device,~a certain amount of~air under pressure is
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necessary to support ~he rotary shaft hy means of the
air bearings in a non-contact state, ana to keep this
pressure to a minimum, the clearance between the bearing
faces of the air bearings and the outer circumferential
wall of the rotary shaft is very small, i.e., about
~0 ~m to 70 ~m. In addition, to prevent a seizure
between the rotary shaft and the air bearings, a surface
hardening treatment such as flame spraying ceramic
material and the like is applied to the outer circum-
feren~ial wall of the rotary shaft.
However, in this rotary type electrostatic spraypainting device, since the amount of air fed into the
air bearings is relatively small, the force supporting
the rotary shaft is weak. In addition, the clearance
between the bearing faces of the air bearings and the
outer circumferential wall of the rotary shaft is very
small as mentioned above. Therefore, if an insufficient
amount of pressurized air is fed into the air bearings
when the rotary shaft is rotated, or when the rotating
speed of the rotary shaft is quickly reduced, the rotary
shaft comes into contact with the bearing faces of the
air bearings during rotation, and as a result, when the
rotating speed of the rotary shaft is low, although
there is no danger of a seizure between the rotary shaft
and the bearing faces of the air bearings~ a problem
occurs in that a large frictional force is generated
between the rotary shaft and the bearing faces of the
air bearings, and thus the rotating speed of the rotary
shaft is reduced. When the rotating speed of the rotary
shaft is high, even if a surface hardening treatment has
- been applied to the outer circumferential wall of the
rotary shaft, a seizure will occur between the rotary
shaft and the bearing faces of the air bearings, and
thus a problem occurs in that the rotary shaft cannot be
35 rotated.
SUMMARY OF THE INVENTION
An object of the present invention is to provide a
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rotary type electrostatlc spray painting device capable
of obtaining a stable rotating motion of the rotary
shaft.
According to the present invention, there is
S provided a rotary type electrostatic spray painting
device comprising: a housing; a rotary shaft rotatably
arranged in the housing and having an inner end portion
and an outer end portion; a spray head fixed to the
outer end of the rotary shaft and having a cup shaped
inner wall; a feeding means for feeding a paint onto the
cup shaped inner wall; a means for generating a negative
high voltage and applying same to the spray head; static
pressure air bearings arranged in the housing an~
supporting the rotary shaft in a non-contact state; a
turbine wheel fixed to the inner end portion of the
rotary shaft; a first air injection nozzle injecting air
under pressure towards the turbine wheel to cause the
rotary shaft to rotate in one direction; a second air
injection nozzle injecting air under pressure towards
the turbine wheel ~o provide a rotational force in the
other direction for the rotary shaft and thus reduce thP
rotating speed of the rotary sha~t; an air source
producing air under pressure; a first air supply conduit
interconnecting the air source to the static pressure
air bearings; detecting means arranged in the first air
supply conduit for detecting the amount of air under
pressure fed into the static pressure air bearings; a
second air supply conduit interconnecting the air source
to the first air injection nozzle; a first valve means
arranged in the second air supply conduit; a third
our supply conduit interconnecting the air source to the
second air injection nozzle; a second valve means
arranged in the third air supply conduit; a drive
control means producing output signals denoting that the
first valve means and the second valve means should be
open; and a valve control means actuating the first
valve means and the second valve means in response to a
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signal ou~put from the de~ecting means and ~he signals
output from the drive control means to selectively open
the first valve means and the second valve means in
accordance with the signals output from the drive
control means when the amount of air under pressure fed
into the static pressure air bearings is larger than a
predetermined-amount.
The present invention may be more fully understood
from the description of a preferred embodiment of the
invention set forth below, ~ogether with the accompanying
drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
In the drawings:
Fig. 1 is a cross-sectional siae view of a
rotary type electrostatic spray painting device according
to the present invention; and
Fig. 2 is a cross-sectional view of the spray
painting device, taken along the line II-II in Fig. 1.
DESCRIPTI~N OF A PREFERRED EMBODIMENT
Referring to Figures 1 and 2, a rotary type electro-
static spray painting device generally designated by
reference numeral 1 comprises a hollow cylindrical front
housing 2 made of metallic material, and a hollow
cylindrical rear housing 3 made of metallic material.
The housings 2 and 3 are firmly connected to each other
by means of bolts (not shown). A rotary shaft 4 is
inserted into the front housing 2. The rotary shaft 4
comprises a hollow cylindrical portion 4a located at the
central portion thereof, an outer end portion 4b
integrally formed with the hollow cylindrical portion
4a, and an inner end portion 4c fixed to the hollow
cylindrical portion 4a. A spray head 5 made o metallic
material is fixed to the outer end portion 4b of thé
rotary shaft 4 by means of a nut 6. The spray head 5
35 ~comprises~a spray head supporting body 8 defining an
annular space 7 therein, and a cup shaped spray head
body 9~ flxed to the spray head supporting body 8. A
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plurality of paint outflow bores 12 are formed in an
outer cylindrical portion 10 of the spray head supporting
body 8. Each of the paint outflow bores 12 is open to
the annular space 7 on one hand and is smoothly connected
to the cup shaped inner wall 11 of the spray head
body 9. An end plate 13 is fixed to the front end of
the front housing 2, and a paint injection nozzle 14 is
mounted on the end pla~e 13. The paint injection nozzle
14 is connectea to a paint tank 16 via a paint feed
pump 15, and a nozzle mouth 17 of the paint injection
nozzle 14 is directed towards an inner cylindrical wall
of the outer cylindrical portion 10.
As illustrated in Fig. 1, a pair of static pressure
radial air bearings 18 and 19 (hereinafter referred to
as the radial air bearings) are arranged in the front
housing 2, and the rotary shaft 4 is rotatably supported
by the radial air bearings 18 and 19 in a non-contact
state. The radial air bearings 18 and 19 have annular
air chambers 20 and 21 formed therein, respectively, and
a plurality of air outflow bores 22, 23 connected
respectively to the corresponding annular chambers 20,
21 are formed on the bearing faces of the radial air
bearings 18, 19. An air inlet 24 of the air chamber 20
and an air inlet 25 of the air chamber 21 are connected
to a pressurized air source 26 formed by an air feed
pump.
As illustrated in Fig. 1, a pair of disc shaped
runners 27, 28 are rigidly fixed to the inner end
portion 4c of the xotary shaft 4 via a spacer 29, a
30 drive turbine wheel 30, a spacer 31, and a braking
turbine wheel 32 by means of a nut 33. A stationary
annular plate 34 is arranged between the runners 27 and
28, and:the runners 27, 28 and the annular plate 34
together form a non-contact type static pressure ~hrust
35 air bearing (hereinafter, thrust air b:earing). The
runners:27~ 28 are slightly spaced from the annular
plate 34. The annular plate 34 is airtightly fixed to
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the front housing 2 via O rings 35, 36. As illustrated
in Figs. 1 and 2, an annular groove 37 e~tending along
the outer circumferential wall of the annular plate 34
is formed in the front housing 2 and connected to the
air feed pump 26 via the air inlet 38 formed in the
front housing 2. A pluralit~ of air passages 39~ each
extending radially inwardly from the annular groove 37,
are formed in the annular plate 34, and a plurality of
air outflow bores 40, 41 extending towards the corre-
sponding runners 27, 28 from the inner end portions ofthe air passages 39 are also formed in the annular
plate 34.
A pair of turbine nozzle holders 42, 43 are arranged
in the front housing 2. An annular air chamber 44 is
formed between the turbine nozzle holder 42 and the
front housing 2 and connected to the air feed pump 26
via an air inlet 45. The air chamber 44 has an air in-
jection nozzle 46 in which a plurality of guide vanes
(not shown) are arranged. The air injection nozzle 46
is arranged so that the turbine blades 47 of the drive
turbine wheel 30 face the air injection nozzle 46. Air
under pressure introduced into the air chamber 44 from
the air feed pump 26 is injected from the air injection
noæzle 46 into a housing interior chamber 48. At this
time, the injecting air provides a rotational force for
the drive turbine wheel 30, and thus the rotary shaft 8
is rotated at a high speed. Air in the housinq interior
chamber 48 is then discharged ~rom a discharge part 49.
An annular air chamber 50 is formed between the turbine
nozzle holder 43 and the front housinq 2 and connected
- to the air feed pump 26 via an air inlet 51. The air
chamber 50 has an air injection nozzle 52 in which a
plurality of guide ~anes (not shownJ are arranqed. The
air injection nozzle 52 is arranqed so that the turbine
blades 53 of the braking turbine wheel 32 face the air
injection noæzle 52. Air under pressure introduced into
the air chamber 50 fr~m the air feed pump 26 is injected
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from the air injection nozzle 52 into a housing interior
chamber 54. At this time, the in~ec~ed pressurizea air
provides a rotational force in a direction which causes
the braking turbine wheel 32 to act as a brake on the
rotary shaft 4. This direction is opposite to the
direction of rotation of the rotary shaft 4, which
rotation is caused by pressurized air injected from the
air injection nozzle 46 towards the turbine blades 47 of
the drive turbine wheel 30, causing the drive turbine
wheel 30 to rotate the rotary shaft 4. Air in the
housing interior chamber 54 is then discharged from a
discharge port 55.
The rotary type electrostatic spray painting
device 1 is connected to a high voltage generator 56
generating a negative high voltage of -60 KV to -90 KV,
and this negative high voltage is applied to the front
housing 2 and the rear housing 3. The negative high
voltage is then applied to the rotary shaft 4 via an
electrode 57, and thus is applied to the spray head 5.
As illustrated in Fig. 1, a main air supply con-
duit 60 sonnected to the air feed pump 26 is aivided
into three air supply conduits 61, 62, and 63. The
first aix supply conduit 61 is connected to the air
inlet 38 of the ~hrust air bearing and the air inlets 24,
25 of the radial air bearings 24, 25. The second air
supply conduit 62 is connected to the air inlet 51 of
the turbine nozzle holder 43. The third air supply
conduit 63 is connected to the air inlet 45 of the
turbine nozzle holder 4~. An air heating device 64 for
vaporizing water droplets contained in the pressurized
air is arranged in the main air supply conduit 60, and a
regulator 65 for maintaining the pressurized air at a
predetermined pressure is also arranged in the main air
supply conduit 60. In addition, a stop valve 66 is
arranged in the main air supply conduit 60 upstream of
the air heating device 64, and another stop valve 67 is
arranged in the main air supply conduit 60 downstream of
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the regulator 65. A detector 68 for detecting the
pressure or the flow rate of the pressurized air flowing
within the first air supply conduit 61 is arranged in
the first air supply conduit 61 and, in addition, a stop
valve 69 is arranged in the first air supply conduit 61.
A stop valve 71 and a solenoid valve 70 actuated in
response to the output signal of the detector 68 are
arranged in the second air supply conduit 62, and a stop
valve 73 and a solenoid valve 72 actuated in response to
the output signal of the detector 68 are arranged in the
third air supply conduit 63. The solenoid valve 70 is
connected to the output terminal of an AND gate 75 via a
drive circuit 74, and the solenoid valve 72 is connected
to the output terminal of an AND gate 77 via a drive
circuit 76. One of the input terminals of the AND
gate 75 and one of the input terminals of the AND
gate 77 are connected to the output ~erminal of the
detector 68, and the other input terminals of the AND
gates 75, 77 are connected to the output terminals of a
drive control device 78. The output voltage of the
detector 68 becomes high when the pressure or the flow
rate of the pressurized air flowing within the first air
supply conduit 61 exceed a predetermined level, and the
solenoid valves 70 and 72 are opened when the output
voltages of the corresponding AND gates 75 and 77 become
high.
- The drive control of the d~ive turbine wheel 30 and
the braking turbine wheel 32 is automatically carried
out in response to the signals output from the drive
control device 78. When the output voltage appearing in
the output lead 79 of the drive control device 78
becomes high, in order to dxive the drive turbine wheel
30, if the pressure or the flow rate of the pressurized
air flowing within the firs~ air supply conduit 61 is
higher or larger than the predetermined level, the
output~voltage of the A~D gate 77 becomes high, and thus
the solenoid valve 72 is caused to open. When the
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output voltage appearing in the output lead 80 of the
drive control device 78 becomes high, in order to drive
the braking turbine wheel 32, if the pressure or the
flow rate of the pressurized air flowing within the
first air supply conduit 61 is higher or larger than the
predetermined level, the output voltage of the AND
gate 75 becomes high, and thus the solenoid valve 70 is
caused to open. When the output voltage appearing in
either the output lead 7g or the output lead 80 becomes
high, if the pressure or the flow rate of the pressurized
air flowing within the first air supply conduit 61 is
lower or smaller than the predetermined level, the
output voltages of the AND gates 75, 77 are low, and
thus, the solenoid valves 70, 72 remain closed. In the
embodiment illustrated in Fig. l, the output voltages
appearing in both the output leads 79 and 80 do not
become high at the same time, and therefore, the solenoid
valves 70 and 72 do not open at the same time.
As mentioned previously, the rotary shaft 4 is
supported by a pair of radial air bearings 18, 19 and by
a thrust air bearing constructed by the runners 27, 28
and the annular plate 34. In the radial air bearings 18,
l9, when the pressure or the flow rate of the pressurized
air is higher or larger than the predetermined level
when the air flows from the air outflow bores 22, 23, an
air layer is formed between the outer circumferential
wall of the hollow cylindrical portion 4a of the rotary
shaft 4 and the bearing faces of the radial air bearings
18, 19. Consequently, at this time~ the rotary shaft 4
is supported in a non-contact state by this air layer.
In the thrust air bearing, when the pressure or the flow
rate of the pressurized air is higher or larger than the
predetermined level when the air is fed from the air
out10w bores 40, 41 into the clearances between the
annular plate 34 and the runners 27, 28, an air layer is
formed between the annular plate 34 and the runners 27,
28. ConsequentLy, at this time, the runners 27, 28 are
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supported in a non~contact state by this air layer.
That is, if a sufficient amount of pressurized air i5
fed into the radial air bearing.s 18, 19 and the thrust
air bearing, the rotary shaft 4 is supported by these
air bearings in a non-contact state due to the interven-
tion of the air layers therebetween.
When the electrostatlc spray painting device 1 is
operated, all of the stop valves 66, 67, 69, 71, 73 are
open, and pressurized air is fed into the radial air
bearings 18, 19 and the thrust air bearing. When the
painting operation is carried out, the output voltage
appearing in the output lead 79 of the drive control
device 78 becomes high. At this time, if an amount of
pressurized air sufficient to support the rotary shaft 4
lS in a non-contact state is fed into the radial air
bearings 18, 19 and the thrust air bearing, the solenoid
valve 72 is caused to open. As a result, since pres-
surized air is injected from the aix injection nozzle 46,
the rotary shaft 4 is rotated at a high speed.
When it is necessary to quickly reduce the rotating
speed of the rotary shaft 4, in order to, for example,
carry out the cleaning operation required for changing
the color of the paint, the output voltage appearing in
the output lead 80 of the drive control device 78
becomes high. At this time, if an amount of pressurized
air sufficient to support the rotary shaft 4 in a
non-contact state is fed into the radial air bearings 18,
19 and the thrust air bearing, the solenoid valve 72 is
closed, and the solenoid valve 70 is opened. As a
result, pressurizea air injected from the air injection
nozzle 52 provides a ro~ational force in a direction
which causes the turbine wheel 32 to act as a brake on
the rotary shaft 4. This direction is opposite to the
direction of rotation caused by pressurized air injected
from the air injection nozzle 46, and thus the rotating
speed of the rotary shaft 4 is rapidly reduced.
Where an amount of pressurized air sufficient to
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support the rotary shaf-t 4 in a non-contact state is not
fed into the radial air bearings 18, l9 and the thrust
air bearing, the solenoid valves 70 and 7~ remain
closed, regardless of the output voltage appearing in
the output leads 79, 80. As a result, at this time, the
injection of pressurized air from the air injection
nozzles 46, 52 is stopped, and thus the rotation of the
rotary shaft 4 is stopped. Consequently, it will be
understood that, according to the present invention, the
rotary shaft ~ is rotated only when it is supported by
the radial air bearings 18, 19 and the thrust air
bearing in a non-contact state.
In the operation of the rotary type electrostatic
spray painting device of the present invention, when the
rotary shaft 4 is rotated at a high speed, paint injected
from the nozzle mouth 17 of the paint injection nozzle 14
onto the inner circumferential wall of the outer cylin-
drical portion 10 of the spray head 5 flows out onto the
inner wall 11 of the spray head body 9 via the paint
outflow bores 12, due to the centrifugal force caused by
the corresponding rotation of the spray head 5. The
paint then spreads over the inner wall 11 of the spray
head body 9 and flows on the inner wall ll in the form
of a thin film, until the paint reaches the tip 9a of
the spray head body 9. As mentioned previously, a
negative high voltage is applied to the spray head 5.
Consequently, when the paint i5 sprayed from the tip 9a
of the spray hea~ body 9 in the form of fine particles,
the particles of the sprayed paint are charged with
electrons. Since the surface to be painted is normally
grounded, the paint particles charged with electrons are
attracted towards the surface to be painted due to
electrical force, thus forming a layer of paint on the
surface to be painted.
According to the present invention, when an amount
of pressurized air sufficient to support the rotary
shaft in a non-contact state is not fed into the radia].
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air bearings and the thrust air bearing, the rotation of
the rotary shaft is stopped. As a result, it is possible
to prevent a seizure between the rotary shaft and the
bearing faces, and thus ensure that the rotary shaft
will be able to rotate. In addition, when the rotary
shaft is rotated, the rotary shaft is always supported
in a non-contact state. Consequently, since it is
possible to rotate the rotary shaft at a predetermined
regular speed, a uniform and aesthetically pleasing
painted surface can be obtained.
While the invention has been described by reference
to a specific embodiment chosen for purposes of illus-
tration, it should be apparent that numerous modifi-
cations could be made thereto by those skilled in the
art without departing from the basic concept and scope
of the invention.
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