Note: Descriptions are shown in the official language in which they were submitted.
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ROBOTIC PAINT APPLICATOR AND METHOD
OF PROTECTING A PAINT ROBOT HAVING
AN EXPLOSION PROOF ELECTRIC MOTOR
FIELD OF THE INVENTION
[00001] This invention relates to a robotic paint application system for
use in a potentially explosive atmosphere, such as a paint booth, and a method
of
protecting a paint robot having an electric motor in such atmosphere.
BACKGROUND OF THE INVENTION
[00002] A conventional paint application system for mass production
applications typically includes a plurality of rotary atomizers which are
mounted on
various fixtures to apply paint or other coatings to a substrate. The
substrate, such an
automotive body, is typically mounted on a conveyor which traverses the paint
booth
and is sprayed by the paint applicators. In one typical application, a
plurality of
overhead and side mounted rotary atomizers are mounted on a U-shaped frame
assembly which moves on tracks with the vehicle body. The paint applicators,
which
may be conventional rotary atomizers or other conventional spray devices, may
be
mounted on robot arms to apply paint to all areas of the vehicle body as the
vehicle
body traverses the paint booth on a conveyor. The paint booth is generally
enclosed
because of the overspray and the potentially explosive atmosphere which may be
created by the paint overspray. One example of a potentially explosive
atmosphere is
volatile organic compounds or vocs, including volatile organic solvents
utilized as a
solvent for paint. The paint overspray and solvents are continuously removed
from
the atmosphere of the paint spray booth by various recovery systems.
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[00003] More recently, true robotic paint application systems are being
used in mass production applications. A typical robotic paint applicator
includes a
base member, which may be mounted on the floor of the paint spray booth or
mounted on a rail to traverse with the substrate mounted on a conveyor, an
intermediate section or housing, typically pivotally or rotatably mounted on
the base
member, and a generally horizontal robot arm pivotally mounted on the
intermediate
member having a paint applicator, generally a rotary paint atomizer, at its
distal end.
.The intermediate section and the robot arm are then manipulated by motors
generally
connected to a computer, to continuously move the paint applicator to apply
paint
over the substrate as the substrate is moved through the paint booth. The
movement
of the intermediate section and the robot arm may be controlled by hydraulic
motors.
However, hydraulic controls are expensive, complicated and subject to failure.
Electric motors, particularly servomotors, have replaced hydraulic controls
because
servomotors provide better control at less cost and servomotors have less
service
problems. However, electric servomotors have a potential for sparking and thus
create potential safety issues in a potentially explosive atmosphere, such as
a paint
booth applying liquid paint having an organic solvent. Conventional sealed
explosion
proof servomotors are not practical in this application because of the bulk
and weight
of such explosion proof motors.
[00004] The prior art has proposed flooding the section compartments
or enclosures containing "non-explosion proof motors" with an "inert gas,"
such as air
or nitrogen, to prevent entry of the potentially combustible atmosphere in the
paint
booth, such as disclosed, for example, in U.S. Patent No. 4,984,745. However,
this
approach has several problems. First, there are typically compartments within
the
enclosures, particularly including the housing of the servomotor. That is,
this patent
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proposes to use conventional or "non-explosion proof' servomotors having a
housing
which is not sealed or explosion proof. As will be understood by those skilled
in this
art, a conventional paint application system does not run continuously. That
is, the
paint application system is periodically shut down for shift changes,
maintenance,
etc., and the paint application line may be shut down for one or more eight
hour shifts.
Thus, potentially combustible gas from the paint booth will enter the robot
housing
enclosures and the compartments within the housing enclosures, including the
motor
housings, when the supply of non-combustible gas supplied to the base member
is
turned off, such as when the paint application system is idle. When the
combustible
gas enters the housing enclosures containing the non-explosion proof
servomotors, the
combustible gas may also enter the housings of the servomotors creating a
potential
explosion hazard. However, flooding the housing enclosures containing the
servomotors with a non-combustible gas will not necessarily purge combustible
gas in
the servomotor housings, creating a potentially explosive atmosphere in the
motor
housings. Further, circulating the non-combustible gas to the base or lower
housing
enclosures to the other enclosures of the robot may not thoroughly purge the
components within the enclosures. Thus, there is a need for an improved
robotic paint
applicator and method of protecting a paint robot having electric motors from
explosion in an enclosed paint booth having a potentially combustible
atmosphere.
The robotic paint applicator system and method of this invention solves this
problem
in a simple, cost effective manner.
SUMMARY OF THE INVENTION
[00005) The robotic paint applicator and method of this invention
begins with the electric motor which, as set forth above, is preferably an
electric
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servomotor to provide accurate and fast control of the robotic paint
applicator. The
electric motor includes the conventional components of an electric motor,
including a
stator, rotor and drive shaft. The explosion proof electric motor utilized in
the paint
applicator of this invention includes a relatively air-tight housing
surrounding the
electrical components of the motor, wherein the housing includes a gas inlet
and a gas
outlet spaced from the gas inlet. A source of non-combustible gas under
pressure is
connected to a gas inlet of the motor housing and the non-combustible gas thus
creates a positive pressure of non-combustible gas within the motor housing,
purging
the motor housing and preventing entry of potentially combustible gas into the
motor
housing. Thus, the servomotors utilized in the robotic paint applicator of
this
invention are explosion proof. Further, the enclosures of the sections of the
robotic
paint applicator containing the explosion proof motors are generally or nearly
air
tight, such that the non-combustible gas is received from the gas outlet of
the motor
housings into the robot housing enclosures, providing those housing enclosures
with
non-combustible gas, thereby creating explosion proof robot housing
enclosures.
[00006) As set forth below in regard to the method of this invention, the
non-combustible gas, such as air, is initially supplied to the motor housings
with
sufficient pressure, such as 4 bar, to purge not only the motor housing, but
also the
robot section enclosure containing the electric motor and the further
electrical parts or
components contained within the enclosure. Following purging, the non-
combustible
gas is supplied to the motor housing at a lesser pressure, preferably at least
0.8 mbar,
to maintain a positive pressure of non-combustible gas greater than
atmospheric in the
motor housings and the robot section enclosures. In a preferred embodiment,
the
motor housing includes an inlet which receives the non-combustible gas and a
tube
which communicates with the electrical components of the electric motor
including
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the windings and rotor, and an outlet or exit port preferably having a
diameter greater
than the inlet. In the disclosed embodiment, the gas outlet is "a flame
restrictor"
filter. As used herein, the term "explosion proof electric motor" means a
conventional electric motor, particularly including an electric servomotor,
including
an enclosed housing having gas inlets and outlets as described above, but
excludes
"non-explosion proof' electric motors.
[00007] The robotic paint applicator of this invention includes a
housing enclosure, preferably a substantially or nearly air tight robot
housing
enclosure, containing an explosion proof electric motor and a robot arm
mounted on
the robot enclosure having a paint applicator on a distal end of the robot
arm. As set
forth above, the robot arm of the paint applicator generally also includes a
wrist or
wrist mechanism and the applicator is typically a rotary paint atomizer, but
may be
any type of applicator. The robot paint applicator is typically located in an
enclosed
paint booth having a potentially combustible atmosphere including, for
example, a
solvent containing vocs. As described above, the explosion proof electric
motor
includes a motor housing having a gas inlet, a gas outlet and a source of non-
combustible gas under pressure, preferably located outside the paint spray
booth,
connected to the gas inlet of the motor housing, pressurizing the motor
housing with
non-combustible gas for purging and preventing the potentially combustible
atmosphere from entering the motor housing. The gas outlet of the motor
housing
directs non-combustible gas into the nearly air-tight robot enclosure
containing the
electric motor, creating a positive pressure of non-combustible gas within the
robot
enclosure and preventing the potentially combustible gas from entering the
robot
enclosure, thereby protecting other electrical components within the robot
enclosures,
such as wires, switches and the like, from being exposed to the potentially
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combustible atmosphere of the paint spray booth. In a typical application of
the
robotic paint applicator of this invention, each of the robot enclosures or
section
components of the base, the intermediate sections or members and the robot arm
includes at least one electric motor for manipulating the paint applicator and
at least
one of the robot enclosures may include a plurality of explosion proof
electric motors.
In such embodiments, each of the explosion proof electric motors include a
motor
housing having a gas inlet and a gas outlet and the robotic paint applicator
includes a
plurality of conduits, each of which is connected to the source of non-
combustible gas
under pressure, such that each of the motor housings is directly flushed or
purged with
clean non-combustible gas directly from the source and each of the robot
enclosures
or compartments is maintained at a positive pressure of non-combustible gas
received
through the gas outlet of the motor housings. In one preferred embodiment, the
robot
enclosures containing the explosion proof electric motors are in fluid
communication,
having conduits between adjacent enclosures, such that non-combustible gas
received
from the explosion proof motors is directed from one robot enclosure to the
next robot
enclosure to an outlet in the lower enclosure or base member, assuring
complete
purging and maintenance of a positive pressure of non-combustible gas within
each of
the enclosures.
[00008] The preferred method of protecting a paint robot having an
electric motor from explosion in an enclosed paint spray booth having a
combustible
atmosphere of this invention includes first enclosing an explosion proof
electric motor
or electric motors and controls in a substantially air-tight enclosure. As
used herein,
the term "substantially air-tight" means that the enclosure or compartment is
substantially completely enclosed as is conventional for such enclosures, such
that a
positive gas pressure may be maintained in the robot housing enclosure. The
method
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of this invention further includes providing an explosion proof electrical
motor with a
substantially air-tight motor housing having a gas inlet and a gas outlet
preferably
spaced from the gas inlet as described above.
[00009] The method of this invention then includes purging the motor
housing and the robot enclosure containing the explosion proof electric motor
by
supplying a non-combustible gas, preferably air, under pressure to the gas
inlet of the
motor housing under sufficient pressure to circulate the non-combustible gas
through
the motor housing and through the gas outlet into the robot section enclosure,
purging
the motor housing and the robot section enclosure of potentially combustible
gas. In a
preferred embodiment, during the purging step, air is supplied to the motor
housing at
a pressure of about 4 bars and the volume of air supplied to the motor housing
is
preferably at least 5 times or between about 5 and 10 times the volume of the
motor
housing and the robot housing enclosure which contains the explosion proof
electric
motor. This volume and pressure assures complete purging of combustible gas
from
the motor housing and the robot housing enclosure. The explosion proof
electric
motors can then be safely operated to control the paint robot. Finally, the
method of
this invention includes continuing to supply the non-combustible gas to the
inlet of
each of the motor housings at a lesser pressure sufficient to maintain the
motor
housings and the robot housing enclosures at a positive pressure, thereby
preventing
combustible gas from entering the housing enclosures and the motor housings. A
pressure of about 0.8 mbar is generally sufficient to maintain a positive
pressure of
non-combustible gas in the motor housings and the robot enclosures containing
the
motor housings. As set forth above, where the paint robot includes a plurality
of
explosion proof electric motors, the method of this invention includes
separately
purging each of the motor housings and the robot housing enclosures by
delivering
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non-combustible gas under pressure from a source of non-combustible gas,
preferably
located outside the paint booth, separately connected to each of the inlets of
the motor
housings as described above.
[00010] The robot paint applicator and method of this invention will be
more fully understood from the following description of the preferred
embodiments,
the appended claims and the drawings, a brief description of which follows.
BRIEF DESCRIPTION OF THE DRAWINGS
[00011] Figure 1 is a side cross-sectional view of one embodiment of an
explosion proof servomotor utilized in the robotic paint applicator of this
invention;
[00012] Figure IA is an end elevation of the explosion proof
servomotor shown in Figure 1;
[00013] Figure 2 is a side view partially cross-sectioned of one
embodiment of a robotic paint applicator of this invention;
[00014] Figure 3 is a side partially cross-sectioned view of the robotic
paint applicator shown in Figure 2 with schematics illustrating the purging
system;
[00015] Figure 4 is partially cross-sectioned side view of an alternative
embodiment of the robotic paint applicator of this invention;
[00016] Figure 5 is an end view of the robotic paint applicator
illustrated in Figure 4 including schematics illustrating the purging system;
[00017] Figure 6 is a schematic illustration of the purge system utilized
in the robotic paint applicators of Figures 2 to 5; and
[00018] Figure 7 is a partial schematic illustration of an alternative
embodiment of the purge system which may be utilized in the robotic paint
applicators of Figures 2 to 5.
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DESCRIPTION OF THE PREFERRED EMBODIMENTS
[00019] Figure 1 illustrates one embodiment of an explosion proof
electric motor 20 adapted for use in a robotic paint applicator of this
invention as
described below. In a preferred embodiment, the explosion proof electric motor
20 is
an electric servomotor including a conventional stator 22, rotor 24 and drive
shaft 26.
The explosion proof electric motor 20 utilized in the robotic paint applicator
of this
invention includes a substantially air-tight motor housing 28 including a gas
inlet 30
and a gas outlet 32. As described above, the motor housing 28 should be
sufficiently
air-tight to maintain a positive gas pressure upon receipt of a non-
combustible gas.
Thus, the gas inlet 30 preferably has a smaller diameter opening than the gas
outlet 32
to maintain a positive non-combustible gas pressure within the housing. The
gas
outlet 32, preferably includes a disc-shaped flame restrictor filter. The gas
inlet 30 is
connected to a source of non-combustible gas under pressure 36 which, in a
preferred
embodiment, is air. The source of non-combustible gas 36 is connected to the
inlet 30
through a valve 38 which is connected to a control (not shown) which, as
described
below with regard to the method of protecting a paint robot from explosion of
this
invention, may be utilized to control the volume or pressure of non-
combustible gas
received by the gas inlet 30 or may be turned off during maintenance or when
the
paint applicator is idle for an extended period of time. The gas inlet 30 is
connected
to a tube 34 having an outlet within the electric motor to purge the primary
components of the servomotor including the stator 22 and rotor 24 as shown by
the
arrows in Figure 1. The non-combustible gas thus circulates through the
components
of the electric servomotor including the stator 22 and rotor 24 and returns
through a
junction box 35 containing further electrical components, such as relays,
switches and
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the like. Figure IA is a perspective view of the explosion proof servo
electric motor
20 described above illustrating the non-combustible gas inlet 30 to the motor
housing
28 and the outlet 32. The illustrated embodiment further includes a plurality
of
conventional electrical connectors 37 which receive the wires to the
electrical
components of the explosion proof servomotor 20 (not shown), preferably in
sealed
relation to avoid entry of combustible gas into the motor housing.
[00020] As described below, the explosion proof electric motor 20 is
initially purged of potentially combustible gas by directing air or another
non-
combustible gas, such as nitrogen, from the source 36 through the valve 38 to
the inlet
30 of the electric motor 20. The air under pressure is initially received in
the junction
box 35 by tube 34 which communicates with the stator 22 and rotor 24 and the
air is
then circulated through the junction box and discharged through the outlet 32
into a
robot enclosure containing the electric motor, also purging the enclosure as
described
below. Following purging, the explosion proof electric motor 20 may be
actuated and
the air pressure is then reduced by valve 38 to maintain a positive pressure
of non-
combustible gas in the housing 28 during operation of the robot as described
below.
Thus, the motor 20 is properly classified as an explosion proof motor under
the
Standard for Purged and Pressurized Enclosures for Electrical Equipment in
Hazardous (Classified) Locations, NFPA 496-7 for Class I, Division 1 Locations
in
which ignitable concentrations of flammable gases or vapors exist under normal
operating conditions, such as a paint spray booth, because the motor housing
is
purged with a non-combustible gas and then maintained at a pressure greater
than
atmospheric pressure pursuant to Chapter 2, 2-2.3.1, supra. Thus, the
explosion proof
servomotors utilized in the robotic paint applicator of this invention are
nonhazardous.
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{00021] Figures 2 and 3 illustrate one suitable embodiment of a robotic
paint applicator 40 of this invention. In describing the robotic paint
applicator 40,
reference will also be made to Figure 6, which is a schematic illustration of
the
primary electrical components of the robotic paint applicator and the air
circulation
and purging system of this invention. The robotic paint applicator 40
illustrated in
Figures 2 and 3 includes a base housing enclosure or section 42, an
intermediate
housing enclosure or section 44 mounted on the base housing enclosure 42 and a
robot arm enclosure 46 mounted on the intermediate housing enclosure 44. The
robot
arm includes a wrist 48 at its distal end which receives a conventional rotary
paint
atomizer 49, In this embodiment, the base housing enclosure 42 is mounted on a
support section 50, which is supported by the floor of the paint booth 52, As
will be
understood by those skilled in this art, the paint booth 52 is an enclosed
work area
including a potentially explosive atmosphere separated and enclosed from the
remainder of the paint shop by a wall 54 shown in Figure 2, This embodiment of
the
robotic paint applicator 40 includes six to seven explosion proof electric
servomotors
labeled MI through M7 in Figures 2, 3 and 6. Electric servomotors M1 and M2
are
located in the base housing enclosure 42, explosion proof electric servomotor
M3 is
located in the intermediate housing enclosure 44 and electric servomotors M4
to M7
(where the robot includes seven servomotors) are located in the robot arm
enclosure
46 as shown in Figures 2 and 3 and also in Figure 6. Bach of the explosion
proof
servomotors Ml to M7 is enclosed within the substantially or nearly air-tight
enclosures provided by the housings of the robot enclosures 42, 44 and 46
which, as
described above, are sufficiently air-tight to permit purging and maintain a
positive
pressure of a non-combustible gas within the enclosure. Thus, explosion proof
electric servomotors M1 and M2 are enclosed within the base housing 42,
explosion
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proof electric servomotor M3 is enclosed within the intermediate housing
enclosure
44 and explosion proof electric servomotors M4 to M7 are enclosed within the
robot
army enclosure 46, each forming a substantially air-tight enclosure.
[000221 As will be understood by those skilled in this art, a robotic
paint applicator of the type 40 illustrated in figures 2 and 3 includes
numerous
components and controls which do not form any part of this invention and will
not,
therefore, be described in any detail. However, as will be understood by those
skilled
in this art, the intermediate housing enclosure 44 is pivotally supported on
the base
housing enclosure 42 by a pivot joint 62 and the robot arm enclosure 46 is
pivotally
supported by the pivot joint 64. The base housing enclosure 42 may be
rotatably
supported on the support section 50. The electric servomotors Ml through M7
control the movement of the robotic paint applicator 40 including the wrist
48, Thus,
a paint atomizer 49 mounted on the wrist 48 may be moved and controlled by the
electric servomotors M1 to M7 during application of paint or other coating to
a
substrate (not shown), such an automotive body, which is typically transferred
through the paint booth 52 on a conveyor (not shown),
[00023] In a typical application, the robotic paint applicator 40 is
substantially in continuous motion during operation to apply paint to an
entire surface
of a large substrate, such as an automotive body. As will also be understood,
the
housing enclosures 42, 44 and 46 will include other electrical components,
such as the
solenoid valves S1 and S2 in the robot arm enclosure 46 shown in Figure 6,
wires,
switches, etc. which are maintained in a non-combustible or explosion proof
atmosphere in the robotic paint applicator of this invention as described
below.
Figures 2, 3 and 6 illustrate schematically the air purge and pressurizing
system for
the rdbotic paint applicator 40 of this invention. As best shown in Figure 6,
the purge
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and pressurizing system includes a source of non-combustible gas or air source
66
which is located outside the paint booth 52 as shown in Figure 2. The air
under
pressure is received by a valve 68 which is controlled by the control unit 70.
As set
forth above and further described below, the proportional valve 68 may be
controlled
by the control unit 70 to control the pressure and, therefore, the volume of
air received
by the first transfer block 72 which may be located in the base housing
enclosure 42
of the robotic paint applicator. The transfer block 72 divides the air or
other non-
combustible gas into a first line or conduit 74 and a second line or conduit
76. The air
received from the first transfer block 72 is then received through line 74 to
a second
transfer block 78 and the air through line 76 is received by a third transfer
block 80.
The second transfer block 78 divides the air under pressure into three lines
82, 84 and
86. Line 82 is connected to the gas inlet 30 (see Figure 1) of the first
electric
servomotor Ml, line 84 is connected to the inlet of the second electric
servomotor M-
2 and line 86 is connected to the inlet of the third servomotor M3. In this
embodiment, explosion proof electric servomotors M1 and M2 are located in the
base
housing enclosure 42 of the robotic paint applicator and explosion proof
electric
servomotor M3 is located in the intermediate housing enclosure 44 of the
robotic
paint applicator. Line 76 from the first transfer block 72 is connected to the
third
transfer block 80 which divides the air flow between the remaining electric
servomotors M4 to M7 by lines 90, 92, 94, 96, 98, respectively. Thus, the
inlet of
each of the electric servomotors M1 to M7 are individually or separately
connected to
the source 66 of clean non-combustible gas.
[000241 Further, the air or another non-combustible gas is discharged
from the motor housing 28 through gas outlet 32 as shown in Figure 1 into the
housing enclosures 42, 44 and 46 also shown in Figures 2 and 3. In one
preferred
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embodiment of the robotic paint applicator 40, the upper section housing or
robot arm
enclosure 46 is connected by a flexible hose 56 to the intermediate housing
enclosure
44 and the intermediate housing 44 is connected by a flexible hose 58 to the
base
housing enclosure 42. The base housing is connected with a flexible hose 60 to
a
fourth transfer block 61 which may be located in the support section 50 or any
convenient location. As shown in Figure 6, the fourth transfer block 61
includes the
control unit 70 which is connected to the proportional valve 68, such that if
the
pressure in the housing enclosures 42, 44 and 46 fall below a predetermined
minimum
greater than atmospheric, the valve 68 is controlled to increase the pressure
or air flow
through the valve 68 to the first transfer block to maintain the pressure of
non-
combustible gas in the housing enclosures 42, 44 and 46 above atmospheric
pressure
to prevent the entry of combustible gas into the section housings and the
electric
servomotors. Thus, the air pressure is controlled by valve 68 to first purge
the electric
servomotors and then maintain a positive pressure of non-combustive gas within
the
explosion proof motors Ml to M7 and robot section enclosures 42, 44 and 46.
[000251 The robotic paint applicator 140 illustrated in Figures 4 and 5
may be identical to the robotic paint applicator 40 illustrated in Figures 2
and 3,
except that the base housing enclosure 142 is supported on a base 150
supported on a
rail 100 for movement with the substrate to be painted (not shown). As set
forth
above, the robotic paint applicator of this invention may be mounted on the
floor of
the paint booth 52 as shown by robotic paint applicator 40 shown in Figures 2
and 3
or the robotic paint applicator 140 shown in Figures 4 and 5 may be mounted on
a rail
100 best shown in Figure 4 to traverse the paint spray booth as the substrate
(not
shown) is moved through the paint spray booth on a conveyor. The air supply
and
purge system shown in Figure 6 may also be utilized in the robotic paint
applicator
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140 shown in Figures 4 and 5. All other components of the robotic paint
applicator
140 may be identical to the robotic paint applicator 40 described above and
have,
therefore, been numbered the same in Figures 2 and 3 and no further
description is
required for a complete understanding of this embodiment.
1000261 Having described preferred embodiments of the robotic paint
applicator, the method of protecting a robotic paint applicator having an
explosion
proof electric motor from explosion in an enclosed paint booth may now be
described.
As will be understood from the above description of the preferred embodiments,
the
method of this invention includes enclosing an electric motor and controls in
a
substantially air-tight enclosure. In a typical application, the enclosure
comprises the
housings of the base and intermediate section and the robot arm housing
enclosure 42,
44 and 46, respectively, wherein the enclosure is sufficiently air-tight to
maintain a
positive pressure of non-combustible gas, such as 95%. The method of this
invention
then includes providing an explosion proof electric motor in a substantially
air-tight
motor housing, such as the electric servomotor 20 illustrated in Figure 1
having a
substantially air-tight motor housing 28, including a gas inlet 30 and a gas
outlet 32.
The method of this invention then includes purging the motor housing 28 and
the
enclosure by supplying a non-combustible gas under a first pressure to the gas
inlet 30
of the motor housing 28 under sufficient pressure to circulate the non-
combustible gas
through the motor housing and through the gas outlet 32 into the enclosure,
purging
the motor housing and the enclosure of potentially combustible gas. In a
preferred
embodiment, air is supplied to the inlet 30 of the motor housings 28 under a
pressure
between 3 and 5 bars, preferably about 4 bars, and the volume of air supplied
to the
explosion proof electric servomotor during purging is between 5 and 10 times
the
volume of the motor housing and the enclosure, assuring complete purging of
CA 02446479 2011-03-18
potentially combustible gas from both the motor housing and the enclosure. Of
course, where the enclosure includes a plurality of electric servomotors, the
volume of
air supplied to the electric servomotor may be adjusted accordingly. The
explosion
proof electric servomotors may then be operated with safety, The final step in
the
method of this invention includes continuing to supply non-combustible gas to
the gas
inlets of the electric servomotor housings at a second pressure less than the
first
pressure used during purging, but sufficient to maintain a positive pressure
of non-
combustible gas in the motor housings and the enclosure. An air pressure of
about 85
mbar will be sufficient in most cases to assure maintaining a positive air
pressure in
the motor housings 28 and the housing enclosures 42, 44 and 46 containing the
electric servomotors, preventing entry of potentially combustible gas into the
enclosures and the electric servomotor housings.
[00027] More specifically, the method of protecting a paint robot in an
explosion atmosphere of this invention, wherein the robotic paint applicator
includes a
plurality of substantially air-tight housing sections, each having an
explosion proof
motor including a motor housing having a gas inlet and a gas outlet, includes
separately supplying a noncombustible gas under pressure to the inlet 30 (see
figure
1) of each of the explosion proof electric motors 20 which circulates through
the
motor housing 28 and is received from the gas outlet 32 into the housing
enclosures
42 or 142, 44 and 46 or 146 as described above. In a preferred embodiment, the
housing enclosures are substantially sealed as described above and
interconnected by
conduits or flexible hose 58 and 56 and one of the housing members 42 is
connected
by a conduit or tube 60 to a transfer block 61 including a pressure activated
control 70
connected to the inlet valve 68, from source 66, 166 wherein the method of
this
invention further includes sensing the pressure in the housing members and
increasing
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the pressure by regulating the inlet valve 68 in the event that the pressure
in the
housing members falls below a predetermined minimum, such as 85 mbars.
Further,
as described
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above, the method of this invention includes first purging or flushing the
motor
housings by directing a non-combustible gas, preferably air, under pressure
into the
components of the electric motor, purging the motor housing and the robot
housing
members prior to actuation of the explosion proof motors, such that both the
electric
motors and the robot housing enclosures are explosion proof.
[00028] As will be understood by those skilled in this art, a commercial
embodiment of the robotic paint applicator of this invention will include
numerous
other electrical and pneumatic components including the servo valves S 1 and
S2
shown in Figure 6, a brake and brake valve, also shown in Figure 6, filters
and the like
which are shown in the drawings to complete the disclosure of the robotic
paint
applicator, but not described, because they do not form part of this
invention.
[00029] Figure 7 illustrates in schematic form an alternative
embodiment of the control and purge system which may be utilized in the
robotic
paint applicators illustrated in Figures 2 to 5 which includes a pressure
regulator 71
between the valve 68 and the transfer block 72 which regulates the pressure of
the
non-combustible gas delivered from the source 66. As will be noted from Figure
7,
the pressure regulator 71 is in parallel with the line 69 between the source
of non-
combustible gas and the transfer block 72 providing further optional control
of the
pressure of non-combustible gas to the robotic paint applicator. The control
70 in the
third transfer block 61 may be optionally connected to the main control valve
68 as
described above with reference to Figure 6. The robotic control and purge
system
illustrated in Figure 7 may be otherwise identical to the system disclosed in
Figure 6.
[00030] Having described preferred embodiments of the robotic paint
applicator and method of this invention, it will be understood that various
modifications may be made within the purview of the appended claims. For
example,
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the robotic paint applicator of this invention and method is not limited to
the disclosed
embodiments. The robotic paint applicator may include any number of housing
sections or modules and each section may include any number of explosion proof
electric motors depending upon the application. Further, the purge and
pressurizing
system may be utilized with any electric motor and is, therefore, not limited
to an
electric servomotor as disclosed and described. As will be understood, the
embodiment of the explosion proof electric servomotor disclosed in Figure 1 is
a
modification of a conventional electric servomotor to include a housing having
gas
inlet and outlet ports and the housing has been enlarged to assure circulation
of non-
combustible gas and purging of the electrical components. Further, the gas
inlet and
outlet may be located in various portions of the motor housing, but are
preferably
spaced to assure complete purging. As used herein, the term "paint" is
intended to
cover any coating which may be applied to a substrate and is not limited to
color
coatings or conventional paint. However, a purge and circulation system will
not be
required for coatings which do not include a potentially explosive carrier or
solvent.
Finally, non-combustible gas may be any suitable non-combustible or non-
explosive
gas including an inert gas, such as nitrogen or a noble gas, but air is
preferred for
reasons of cost and convenience.
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