Coating apparatus – Projection or spray type – Moving projector
Reexamination Certificate
2003-10-16
2004-12-28
Edwards, Laura (Department: 1734)
Coating apparatus
Projection or spray type
Moving projector
C118S326000, C427S421100, C901S043000
Reexamination Certificate
active
06835248
ABSTRACT:
FIELD OF THE INVENTION
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
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.
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.
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. Pat. 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 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
The robotic paint applicator and method of this invention begins with the electric motor which, as set forth above, is preferably an electric 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.
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 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.
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 a
Frey Marcus
Haas Jürgen
Hezel Thomas
Behr Systems, Inc.
Edwards Laura
Howard & Howard
LandOfFree
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