Paint delivery and application system and method

A paint delivery and application system including a color changer, at least two paint canisters and a paint applicator, a first pair of supply lines connected between the color changer and the paint canisters and a second pair of supply lines connecting the paint canisters and the paint applicator, wherein the paint canisters operate in tandem permitting delivery of a first paint to one of the paint canisters while a second paint canister is electrically isolated from the color changer and is delivering paint to the applicator. In one disclosed embodiment, the delivery line from the paint canisters to the applicator includes two pigs and solvent is delivered between the pigs, such that this system is self purging.

FIELD OF THE INVENTION

The present invention relates to paint or coating delivery and application systems using pigging technology and methods of delivering and applying paint which significantly reduce cycle time between applications to a substrate or a plurality of substrates using multiple coating materials or colors and substantially eliminating waste of paint.

BACKGROUND OF THE INVENTION

The prior art discloses numerous paint delivery and application systems including systems using pigging technology. Such systems may be used to apply seriatim paints of different colors, for example, to a plurality of substrates, such as vehicle bodies on a moving conveyor in a paint spray booth. The term “paint,” as used herein, includes solvent or water base paints used to paint or coat a substrate and generically any coating, including protective coatings, which may be applied to a substrate using an applicator, such as a sprayer or rotary atomizer. Depending on its function in the coating delivery system, pigs or pigging elements are variously referred to in the prior art as shuttles, separating elements, terminating pistons, plugs, etc. Generally, a pig or pigging element is utilized in the prior art paint delivery systems to push paint either toward the applicator to apply the paint, separate different paints or solvent, scrape or clean the paint supply lines or push paint in the supply line back to the paint supply switching device or color changer. Pigs or pigging elements have also been used to separate fluids in a delivery line including paints of different colors, solvents, etc. which may be driven through the delivery line by pneumatic pressure or other fluid.

A conventional paint supply and application system includes a source of paint under pressure, an applicator, such as a rotary atomizer, generally at high voltage, sprayer or the like, a source of solvent under pressure, and a supply line connecting the source of paint and solvent to the applicator. Where the source of paint and solvent includes a color changer or paint supply switching device, the paint supply and application system may also include a paint canister which may be mounted on a robot, for example, and the color changer is generally at ground potential. When a second paint is to be applied, the canister may be switched for a canister filled with a different paint or the canister may be connected to a source of a different paint. As used herein, the term “canister” or “paint canister” includes any container suitable for receipt and delivery of paint.

A paint delivery and application system using pigging technology for application of different paints, as disclosed in the prior art, includes a color changer or paint supply switching device, including sources of different paints and solvent under pressure, a paint applicator, a supply line connecting the color changer and the applicator and a pigging element or pig which is received in the supply line to push paint through the supply line either toward the paint applicator to apply paint to a substrate or from adjacent the paint applicator to the color changer to recover paint in the supply line. As the pigging element moves through the supply line, it pushes paint or solvent through the supply line and cleans or scrapes paint or solvent from the supply line. In one embodiment disclosed in the prior art, a pigging element is inserted into the supply line to push paint from a color changer to the applicator and the pigging element is then removed. In another embodiment disclosed in the prior art, the supply line between the paint supply switching device and the applicator includes two pig receiver stations, including a first station adjacent the paint supply switching device or color changer and a second pig station adjacent the paint applicator. The pig receiver stations are defined by a chamber which permits paint or solvent to flow around the pigging element. The pigging element is releasably retained in the first receiver station by a clamping means and then released to push paint from the first pig receiver station adjacent the paint applicator to push paint in the supply line to the paint applicator. The pigging element is then driven back under pneumatic pressure to the first receiving station to push paint in the supply line back to the paint supply and switching device or color changer to recover paint in the supply line.

There are several problems associated with the prior paint delivery and application systems described above, particularly in mass production applications, wherein the part to be painted is generally supplied to the applicator in a paint spray booth by a conveyor requiring a short cycle time. As will be understood by those skilled in this art, the longer the cycle time, that is the time required to change from a first paint to a second paint, the greater the expense. At present, the cycle time of a conventional paint supply and application system is at least about 30 seconds. To accommodate this cycle time, the manufacturer can either slow the conveyor through the paint booth or add additional paint application equipment. It would therefore be desirable to reduce the cycle time which is one object of this invention.

Another problem is associated with the electrical or electrostatic charge applied to the electrically conductive paint by the paint applicator during application, particularly with rotary electrostatic paint atomizers of the type commonly used in mass production applications. In a typical application, the color changer is at ground potential and thus the electrically charged paint applicator must be electrically isolated from the color changer during application of paint. This presents a particular problem when attempting to reduce cycle time. Other problems with conventional paint supply and application systems include waste of paint, cycle time for cleaning and flushing of the paint applicator and paint lines and changing of paint colors, particularly including but not limited to robotic paint systems.

Other problems associated with paint delivery and application systems of the type described herein, particularly for mass production applications, including automotive applications, generally relate to the precise metering of liquid coating or paint applied to the part because of differences in the temperature and viscosity of the liquid coating and different parts may be painted in the same line. Where paint canisters are utilized, it would also be desirable to use a nonconductive cylinder which does not expand or contract under varying conditions. In certain applications, for example, it would be desirable to provide an excess of available paint to compensate for variations in temperature and viscosity and return the excess paint to the color changer.

The paint delivery and application systems and methods of this invention solve the above-identified problems, including reduced cycle time, automatic switching of paint and rapid flushing of the paint applicator between applications and electrically isolates the color changer from the applicator permitting use of electrically conductive paint, including but not limited to water based paints. The paint delivery and application systems of this invention also eliminates waste of paint. The paint delivery and application systems and method of this invention is also easily adapted for robotic paint application systems using a rotary atomizer and applying electrically conductive paint.

SUMMARY OF THE INVENTION

As set forth above, the paint delivery and application systems and methods of this invention may be utilized to apply electrically conductive paint utilizing a conventional electrostatic rotary atomizer and is particularly, but not exclusively, adaptable to robotic paint applicators and overhead and side mounted paint applicators. The paint delivery and application systems and methods of this invention significantly reduce cycle time and substantially reduces or eliminates waste paint.

One preferred embodiment of the paint delivery and application system of this invention includes a color changer or paint supply switching device at ground potential preferably having at least two sources of paint under pressure, at least two paint canisters, a paint applicator, a first pair of separate supply lines connecting the paint supply switching device and the paint canisters, and a second pair of separate supply lines connecting the canisters to the paint applicator (in most cases an atomizer). Thus, with this embodiment of the paint delivery and application system of this invention, a first paint may be supplied from a first paint canister to the paint applicator while a second paint is supplied from the paint supply switching device to a second canister, significantly reducing the cycle time. As will be understood, the cycle time may be further reduced by utilizing three or more paint canisters connected in parallel between the paint supply switching device and the paint applicator. However, one preferred embodiment of this paint delivery and application system of this invention includes at least two paint canisters connected in parallel by paint supply lines between the color changer or paint supply switching device and the paint applicator.

Where the paint delivery and application system of this invention is utilized to deliver and apply electrically conductive paint, particularly with an electrostatic paint applicator, such as a conventional rotary electrostatic paint atomizer, at high voltage, the second paint canister receiving paint from the paint supply switching device must be electrically isolated from the paint applicator to avoid sparking or shorting of the pumps, etc. Similarly, the first canister supplying paint to the paint applicator must be electrically isolated from the paint supply switching device or color changer at ground potential. This is accomplished in one preferred embodiment of the paint delivery and application system of this invention by utilizing a unique pigging technology and the method of this invention as now described.

In one preferred embodiment of the paint delivery and application system of this invention utilizing pigging technology, the system includes a first supply line connecting the paint supply switching device or color changer and a first paint canister including a first pigging element movable in the first supply line between a first station adjacent the paint supply switching device and the first paint canister. The system further includes a second supply line connecting the first paint canister and the paint applicator including at least one second pigging element movable in the second supply line between a first station adjacent the first paint canister and a second station adjacent or within the paint applicator. The system further includes a third supply line connecting the paint supply switching device and a second paint canister including a third pigging element movable in the third supply line between a first station adjacent the paint supply switching device and a second station adjacent the second paint canister. Finally, this system includes a fourth supply line connecting the second paint canister and the paint applicator including a first station adjacent the second paint canister and a second station adjacent or within the paint applicator. With this system, the first canister may be electrically isolated from the paint supply switching device during application of the paint from the first canister through the paint applicator and the second paint canister may be electrically isolated from the paint applicator as the second canister is filled from the paint supply switching device by the method of this invention.

The methods of this invention utilizing the pigging technology described above include delivering a predetermined quantity or volume of a first paint from the paint supply switching device to the first canister through the first supply line. When the first paint canister has received substantially a full charge of paint, for example about 95% of the paint required for the application, the first pigging element is released into the first supply line, pushing the remainder of paint in the first supply line into the first paint canister. The pigging element thereby removes paint through the first supply line and electrically isolates the first paint canister from the paint supply switching device. In the disclosed embodiment, the pigging element is driven through the first supply line by a nonconductive fluid, such as air, creating a voltage block between the color changer and the first paint canister. The first paint is then delivered from the first paint canister to the paint applicator through the second supply line while the second paint canister is electrically isolated from the paint supply switching device by the pigging technology of this invention. The first paint may be delivered through the second paint line to the applicator by actuating a piston, for example, of the first paint canister. In one of the disclosed embodiments of the paint delivery and application system of this invention, the paint remaining in the second supply line between the first paint canister and the paint applicator is delivered to the paint applicator by a second pigging element by driving the second pigging element through the second supply line. That is, upon delivery of most of the paint from the first paint canister has been completed, the second pig is driven through the second supply line to deliver the remainder of the paint through the paint applicator. In another disclosed embodiment, wherein the first paint canister contains an excess of paint to accommodate variations in temperature and viscosity of the paint, the excess paint is returned to the first paint canister by a pigging element and the piston is again extended to return the remaining paint to the color changer to eliminate waste of paint as described further below.

While the first paint is being delivered to the paint applicator from the first paint canister, as described above, a second paint is delivered from the paint supply switching device to a second canister which is then electrically isolated from the paint applicator by the same method. That is, a second paint is delivered from the paint supply switching device to the second paint canister through the third supply line. In one disclosed embodiment, a third pigging element is then driven from the first pig station to the second pig station, thereby pushing the remainder of a predetermined quantity of second paint to the second paint canister and electrically isolating the second canister from the paint supply switching device as described. In the alternative embodiment described further below, the excess paint in the fourth paint supply line between the applicator and the second canister is returned to the second canister by the fourth pigging element and the piston is then extended to drive the remaining paint back to the color changer. The sequence is then repeated indefinitely.

As will now be understood, the paint canister receiving paint from the paint supply switching device is always electrically insulated from the paint applicator during filling, and the paint canister delivering paint to the paint applicator is always electrically isolated from the paint supply switching device, thereby avoiding arcing or damage to the pumps, etc. of the paint supply switching device, which is at ground potential. Further, the simultaneous application of one paint from a first paint canister while filling a second paint canister substantially reduces the cycle time by at least one half. In the first embodiment described above, substantially no paint is wasted because each canister is charged or filled with only a predetermined volume as required for each application. In the second embodiment, wherein the paint canisters are filled with an excess of paint, the excess paint is returned to the paint canisters and the piston of the paint canisters drive the remaining paint back to the color changer eliminating any waste of paint as described above.

The paint delivery and application systems of this invention may also be conveniently flushed with solvent. As will be understood, the preferred solvent will depend upon the paint or coating. When applying a water based paint, for example, the preferred solvent is deionized water. In one preferred embodiment of the paint delivery and application system of this invention, the paint supply switching device includes a source of solvent under pressure. Upon completion of the delivery of paint from the first paint canister, for example, the pigging elements are both located in the second station, wherein fluid can flow around the pigging elements. Solvent is then delivered through the first and second supply lines to the paint applicator to flush the supply lines and the paint applicator. The third and fourth supply lines may also be flushed by the same method. In a another preferred embodiment of the paint delivery and application system of this invention, a separate source of solvent is connected to the paint applicator through a solvent supply line for flushing the paint applicator, particularly when the second paint is identical to the first paint, further reducing the cycle time. Alternatively, in a second preferred embodiment of the paint delivery and application system of this invention, the second supply line between the first paint canister and the paint applicator and the fourth paint line between the second paint canister and the paint applicator each include at least two pigging elements and solvent is delivered between the pigging elements, such that upon delivery of the pigging elements to the applicator, the solvent between the pigging elements first flush the paint lines between the canister and the applicator and the paint is then delivered to the applicator through the clean lines.

In a preferred embodiment of the paint delivery and application system of this invention, the pigging elements are shuttled between the first and second pig stations by a nonconductive fluid such as pneumatic pressure to deliver paint, and electrically isolate the components of the system as described above. As will be understood, the pneumatic pressure may include any suitable non-conductive fluid. In one preferred embodiment, the first pig station is defined by a trunk line communicating with the supply or delivery line which receives the pigging element, such that paint or solvent may flow past the pigging element in the first station without flowing around the pigging element. A source of pneumatic pressure is then connected to the trunk line to drive the pigging element from the trunk line or first pig station to the second pig station. The pigging elements may be conventional in this type of system, such as a dumbbell-shaped pigging elements including resilient rings or the pigs may include opposed skirt portions which as described in a copending patent application wipe paint or solvent from the supply lines. In one preferred embodiment, the pigging elements include an encapsulated magnet and the pigging stations include a sensor which senses the location of the pigging element.

The paint delivery and application system of this invention may be utilized to deliver a predetermined volume of solvent to the delivery line between the paint canister and the paint applicator to flush the delivery line following application of paint. In the prior systems, solvent was delivered to the delivery lines in a timed sequence by opening the valve from a source of solvent under pressure to the delivery lines. However, the precise volume of solvent cannot be controlled by this method. In one described embodiment of the paint delivery and application system of this invention, wherein the paint canisters each include a reciprocable piston, paint is delivered from the paint canisters to the paint applicator through a delivery line by movement of the piston in the paint canister, thereby creating a continuous stream of paint in the delivery line from the paint canister to the paint applicator in the delivery line. The system further includes a source of solvent under pressure connected to the delivery line adjacent the applicator. The method of delivering a predetermined volume of solvent then includes delivering a predetermined volume of paint from the paint canister to the applicator by extending the piston in the paint canister creating a continuous stream of paint between the paint canister and the applicator, then delivering a predetermined volume of solvent to the delivery line by retracting the piston in the paint canister. As will be understood, the volume of solvent can thus be accurately controlled.

In one disclosed embodiment, the paint canisters are located on the arm of robotic paint applicators and the color changer is located outside the paint booth at ground potential. In a second embodiment, the paint canisters are located in a voltage block module located outside the paint booth permitting maintenance or service of the paint canisters without entering the paint booth as disclosed in a copending application. In a preferred embodiment of the piston-type paint canisters, the piston is gear driven by a servomotor providing precise metering of the paint, thereby eliminating the requirement for a metering pump on the robot and reducing cost. In a preferred embodiment of the paint delivery and application system of this invention utilizing a rotary atomizer which, as set forth above, applies a high voltage to an electrically conductive paint, the rotary atomizer includes at least one and preferably two pig stations which are referred to in this description as the second pig stations. Further, in a preferred embodiment of the paint canisters having a reciprocable piston, the first pig stations may be located in or on the paint canister.

As mentioned above, the piston-type paint canister driven by dosing or metering drive means eliminates the requirement of a metering pump (usually a gear pump) adjacent the atomizer. This makes it possible to place the second pig station within the atomizer, thereby reducing paint and solvent losses to a minimum. Reference is made in this regard to EP 1314480.

Other advantages and meritorious features of the paint delivery and supply systems and methods 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.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

The schematic or fluid diagram ofFIG. 1illustrates the components of one embodiment of the paint delivery and application system of this invention. The paint delivery and application system illustrated inFIG. 1includes a color changer or paint supply switching device20at ground potential including a plurality of ports each connected to a source of paint under pressure22, a port connected to a source of solvent under pressure24, ports connected to a source of air or pneumatic pressure26and a solvent recovery port28. The color changer20in this embodiment of the invention may be generally conventional except that in the disclosed embodiment, the color changer20is divided in two identical components in parallel, wherein the second component includes the suffix “A” for ease of reference. The number of components will depend upon the number of paint canisters. As will be understood, the number of ports22which receive paint under pressure will depend upon the number of paints to be applied by the paint delivery and application system of this invention and the color changer may include any number of ports depending upon the application. Further, the embodiments of the paint delivery and application system of this invention may be utilized to apply any coating or paint, as defined above, wherein the second paint may either be identical to the first paint or a different paint, such as a different color paint. The paint delivery and application system and method of this invention is also particularly, but not exclusively, adapted for application of an electrically conductive paint, such as a water based paint, now utilized in many automotive and appliance applications.

The paint delivery and application system disclosed inFIG. 1further includes a paint applicator30, such as a conventional electrostatic rotary atomizer at high voltage having a rotary bell cup32which applies an electrostatic charge to an electroconductive paint applied to a substrate at ground potential (not shown). As will be understood, however, any paint applicator or paint gun may be utilized with the paint delivery and application system of this invention. The system further includes at least two piston-type paint canisters34and36. However, as set forth above, the paint delivery and application system of this invention may include three or more paint canisters to further reduce the cycle time. In the disclosed embodiment, the paint canisters34and36each include a piston37which reciprocates within the chamber of the paint canisters34and36to receive or discharge paint as will be understood by those skilled in the art. The paint canisters34and36may also include a pressure transducer35which measures the pressure of the paint in the paint canister and the transducers may be connected to a control module (not shown) of the paint delivery and application system of this invention.

The color changer or paint supply switching device20in this embodiment is connected by a first supply line38to a first paint canister34. As will be understood, the designation of paint canister34as the first paint canister is for purposes of description only. The first paint canister34is then connected to the paint applicator30by a second supply line40. Similarly, the color changer20is connected to the second canister36by a third supply line42and the second paint canister36is connected to the applicator30by a fourth supply line44. As will be understood by those skilled in this art,FIG. 1is a schematic illustration of one preferred embodiment of a paint delivery and application system illustrating the method of this invention and the description thereof does not include details which would be understood by those skilled in the art and are not relevant to the method or apparatus of this invention. For example, the color changer20or more particularly the ports22,24,26and28, are connected to the first delivery line38by a delivery line38aand from the second pig receiver station54by line38binFIG. 1. Similarly, the paint canister34is connected to the second delivery line40by delivery line40ain the schematic illustration. Similarly, the delivery line40is connected to the applicator by lines40band40c. Similarly, the color changer20is connected to the third delivery line42by line42aand the second pig receiver station54is connected to the second paint canister36by line42b. The paint canister36is then connected to the fourth delivery line44by line44aand the second pig station54is then connected by line44bto line40cconnected to the applicator30. As described in a copending application, the delivery lines, particularly delivery lines38,40,42and44, are preferably formed of a transparent or translucent polymer including a friction resistant inner layer, an intermediate dielectric material to prevent arching, and a thin outer layer of a hard plastic to prevent damage to the delivery or supply line.

Each of the supply lines38,40,42and44include a first pig or pigging element receiver station46which, in the disclosed embodiment, is a trunk line communicating with the supply line, such that the pig or pigging element48in each of the first pig stations46does not block the inlet50to the paint supply lines. Each of the first pig stations46also includes a pneumatic pressure inlet52to drive the pig or pigging element48to the second pig receiver station54. The second pig receiver station54includes a chamber configured to receive the pigging element48while permitting fluid flow around the pigging element in the second pig receiver station54. The second pig receiver station54also includes a port56connected to a source of pneumatic pressure, such that the pigging element48may be shuttled back and forth between the first receiver station46and the second receiver station54as also known in the art. That is, the first pigging element48may be pushed from the first pig receiver station46to the second pig receiver station54by pneumatic pressure received from inlet52and returned from the second pig receiver station54to the first pig receiver station by pneumatic pressure received through air inlet56. As will be understood, the pigging element48, as it is reciprocated through the supply lines38,40,42and44wipes or scrapes the supply lines in a conventional manner. As will be understood, the pigging elements of this embodiment may be driven by any fluid pressure and thus the apparatus of this invention is not limited to air or pneumatic pressure. However, where the paint is a conductive paint and thus the method requires electrically isolating the color changer20from the paint canisters34and36during delivery of conductive paint to the applicator30, the fluid is preferably nonconductive, such as air.

The method of delivering and applying paint of this invention with the embodiment of the paint delivery and application system shown inFIG. 1may now be described, as follows. A first paint is delivered from one of the inlets or ports22of the color changer or paint supply switching device20through first supply line38to the first paint canister34. As paint is received by the first canister34, the piston37is pushed into the canister as will be understood by those skilled in the art. When a predetermined quantity of the first paint is received by the first canister34, such as 95% of the first paint required for the application, the pigging element48in the first receiver station46is driven by pneumatic pressure through the first supply line38, driving or pushing the first paint remaining in the supply line38into the first canister34completing the charge of paint. For example, the pressure transducer35may be used to measure the paint pressure and thus the movement of the piston37in the paint canister until 95% of the required charge or volume of paint for example is received by the first canister34and the pigging element48is then driven under pneumatic pressure from the first station46to the second station54, delivering a preprogrammed or predetermined charge of paint to the first paint canister34, such that substantially no paint is wasted and the canister34is then electrically isolated from the color changer20.

Paint is then delivered by the first canister34to the applicator30through the second supply line40such as by moving the piston37of the paint canister34toward the inlet. The first paint is thus delivered to the applicator30and applied by the applicator30to a substrate, such as a vehicle body (not shown). When a substantial portion of the first paint is delivered to the applicator30, such as 95%, the pigging element48in the first receiver station46of the second supply line40is driven under pneumatic pressure through the second supply line40where it is received in the second receiver station54as described above. Thus, substantially all of the first paint received by the first paint canister34is delivered to the paint applicator30. However, in this embodiment, a dump62is provided for receipt of excess paint or solvent. If the second paint to be applied to the substrate by applicator30is the same as the first paint, the entire system need not be flushed with solvent. In this embodiment of the paint delivery and application system of this invention, a separate solvent wash for the paint applicator30, and particularly the rotary bell cup32, is provided. In the disclosed embodiment, the pigging element58is initially located adjacent the solvent inlet60. The solvent inlet60is then open, driving the pigging element58to the receiver station where the solvent flows around the pigging element58and through a separate line61to the applicator30further reducing the cycle time when the second paint supplied to the applicator30is the same as the first paint. Upon completion of flushing the applicator30, the pigging element58is returned to its initial position by pneumatic pressure received through inlet64.

Where the second paint to be supplied to the applicator30is different from the first paint, the first and second supply lines38and40, the face of the piston37and the paint applicator30may be flushed with solvent, wherein solvent under pressure is received through inlet24and the solvent is then delivered through the first supply line38, the solvent is received around the pigging element48in the second station54and then delivered through the second supply line40to the applicator30, thereby flushing the system which received the first paint.

As described above, the paint canisters of the paint delivery and application systems of this invention work in tandem. Thus, while a first paint is delivered from the first canister34to the paint applicator30, as described above, a second paint is delivered under pressure from one of the inlets22A of the color changer or paint supply switching device20to the second paint canister36as described above in regard to paint canister34. That is, a substantial majority, such as 95%, of a second paint, is delivered under pressure from one of the inlets22A of the color changer20to the second paint canister36through the third supply line42. Then, the pigging element48is driven under pneumatic pressure from the first receiver station46to the second receiver station54, thereby delivering all of the second paint to the paint canister36and the paint and paint canister36is then electrically isolated from the color changer20as described above. Thus, the second paint canister36is being charged with a second paint as the first paint is delivered from the first canister34to the applicator30. Then, upon completion of the delivery of the first paint to the applicator30and solvent wash, if necessary, the second paint is delivered from the second canister36to the applicator30which is electrically isolated from the paint supply switching device20as described above. That is, the piston37is reciprocated toward the outlet end, driving paint through the fourth supply line44. Finally, when substantially all of the second paint is delivered to the applicator30, the pigging element48pushes the remainder of the second paint to the applicator under pneumatic pressure received through inlet52. The sequence is then repeated indefinitely, wherein the first paint canister34is charged with paint from the color changer20as the second paint is applied through the applicator30, wherein the first paint canister is electrically isolated from the paint applicator30as described above.

FIG. 2is a schematic illustration of a suitable wiring diagram for the paint delivery and application systems of this invention. As shown, the color changer20is always at ground. The system includes a power supply64, which is connected to a voltage divider66. The voltage divider66is connected to the applicator30to electrostatically charge the rotary bell32. The voltage divider66is also connected through resisters68to the paint canisters34and36, as shown. The electrical system also includes a ground switch70.

As described above, the paint delivery and application systems of this invention may be utilized in any conventional paint application system including conventional overhead and side mounted applicators and may include a plurality of rotary atomizers applying paint to a vehicle body or the like, wherein each of the rotary atomizers are connected to a color changer and the system preferably includes at least two paint canisters connected in parallel between the applicator and the color changer as described above in regard toFIG. 1. However, the paint delivery and application systems of this invention are adaptable to a robotic paint application system as shown inFIG. 3.FIG. 3illustrates a generally conventional robotic paint applicator72modified to include the paint delivery and application system of this invention illustrated inFIG. 1. That is, the robotic paint applicator72includes a base member74which is typically mounted on the floor of the paint booth (not shown) and an intermediate member75which is rotatable on the base member74. The robotic paint applicator includes a main arm76which is pivotally supported on the intermediate member75by pivot78and controlled by a pneumatic piston. The robotic paint applicator may also include an upper arm80which is pivotally mounted on the main arm76, as shown, and the paint applicator (not shown) is supported by a multi-axis arm or wrist82as is known in this art. In the disclosed embodiment, the paint canisters34and36of the paint delivery and application system of this invention are mounted on the main arm and the color changer20is mounted on the base member74. The first and second supply lines38and40, respectively, are partially shown inFIG. 3, which are respectively connected to the color changer20and the applicator (not shown). As described above, however, the paint delivery and application system of this invention is not limited to robotic paint application systems.

The second embodiment of the paint delivery and application system of this invention shown inFIGS. 4 to 24differs from the embodiment previously described in several respects including that the paint canisters may be located outside the paint booth improving maintenance, and the paint lines from the paint canisters to the applicator include at least two pigging elements providing automatic flushing of the delivery lines and the applicator and a predetermined excess paint is provided to account for differences in viscosity and temperature and the excess paint is returned to the color changer. As described in a copending application assigned to the assignee of this application, the paint canisters utilized in the embodiment of the paint delivery and application system disclosed inFIGS. 4 to 24preferably includes a piston which is driven by a servomotor or the like providing accurate metering or dosing of the paint received in the paint canisters and which drive paint from the paint canisters to the paint applicator. The canisters thus act as dosing devices. As further disclosed in the copending applications, the canisters are preferably formed of a nonconductive material, such as a ceramic, which does not expand or contract during temperature variations.

FIG. 4is a schematic illustration of an alternative embodiment of the paint delivery and application system of this invention which includes a color changer120which, as described above, includes a number of ports or lines122,124and126, etc. each connected to a source of liquid paint by lines122a,124a126aetc. As set forth above, the paint delivery and application systems of this invention are particularly, but not exclusively adapted for delivery and application of an electrically conductive paint, such as a water based paint now utilized by the automotive and appliance industries. The color changer120must be at ground potential because the color changer is connected to sources of conductive paint which are at ground potential. The color changer is then connected by a first delivery or supply line138to a first paint canister134and the first paint canister134is connected by a second supply line140to a paint applicator130by line132. In this embodiment, the color changer or paint supply switching device120is also connected by line142to a second paint canister136by a third supply line142and the second paint canister136is connected by supply line144to the paint applicator130by line133. As described above, the first paint canister134includes a piston137having a piston rod128, wherein the piston rod128may be connected to a servomotor or the like (not shown) which reciprocates the piston137in an accurate and controlled manner to receive and deliver paint under pressure to the applicator130as described below. Similarly, the second paint canister136includes a piston137connected to a piston rod128which reciprocates the piston137in the second paint canister136to receive paint from the color changer120and drive paint to the applicator130as described below.

In this embodiment of the paint delivery and application system of this invention, the second and fourth supply or delivery lines140and144, respectively, each include a first pig station162adjacent the paint canisters134and136and a second pig station164adjacent the applicator130. In one preferred embodiment, the pig stations162and164are continuations or trunk lines of delivery or supply lines140and144. In the disclosed embodiment, the first and second pig stations162and164are configured to receive two pigging elements, including a first pig or pigging element166and a second pig or pigging element168and the first and second pig stations162and164each include a source of solvent under pressure, including a source of solvent170communicating with the first pig stations162and a source of solvent under pressure172communicating with the second pig stations164. As described below, the sources of solvent170and172are each adapted to deliver solvent under pressure between the first and second pigging elements166and168. The first and second pig stations162and164further include a source of nonconductive fluid under pressure including a source of nonconductive fluid under pressure174communicating with the first pig stations162and a source of nonconductive fluid under pressure176communicating with the second pig stations164. A valve178controls the flow of nonconductive fluid to the first pig stations162and a valve180controls the flow of nonconductive fluid to the second pig stations164. As set forth above, the preferred solvent will depend upon the application, wherein deionized water is a preferred solvent for water based paints. A suitable nonconductive fluid is pressurized air which electrically isolates the paint canisters134and136from the paint applicator130as described below.

In the disclosed embodiment, the paint supply switching device or color changer120also includes two pig stations, including a first pig station182communicating with the first supply or delivery line138and a second pig station184communicating with the third supply line142each having a pig or pigging element186and188, respectively. The pig stations182and184of the paint supply switching device or color changer120further include a source of nonconductive fluid under pressure, including a source of nonconductive fluid190communicating with the first pig station182and a source of nonconductive fluid under pressure192communicating with the second pig station184. Each of the sources of nonconductive fluid under pressure190and192include a valve178controlling the supply of nonconductive fluid. As described above with regard to the first and second pig stations162and164which communicate with the supply or delivery lines140, the pig stations182and184in a preferred embodiment of the paint delivery and application system of this invention are preferably trunk lines of the first and third supply or delivery lines138and142, respectively, such that paint can flow past the pigging elements186and188as described above with regard to the pig stations162and164. As described below, the inlet194of the paint canisters134and136also serve as a pig station which receive the pigging elements186and188and the paint canisters include an outlet196which communicates with the second and fourth supply or delivery lines140and144. The inlet194of the paint canisters134and136may be configured to receive paint or solvent around the pigging elements and the pigging elements may be releasably held in the inlet of the paint canisters134and136(not shown) as is well known in this art.

The embodiment of the paint delivery and application system shown inFIG. 4further includes a control module110connected to the valves178and180and to the solvent sources170and172which controls the sequence of the introduction of solvent and a nonconductive fluid utilized in the method of this invention as described below. Having described an alternative embodiment of the paint delivery and application system of this invention with regard toFIG. 4, the method of delivering and applying a conductive paint with this embodiment of the apparatus will now be described with regard toFIGS. 5 to 24, as follows.

As will be understood, the paint delivery and application system shown inFIG. 4may be utilized to deliver and apply a conductive paint, such as a water based paint, wherein the paint supply switching device or color changer120is at ground potential and the applicator130is at a high electrical voltage, such as a conventional electrostatic rotary atomizer, which applies a high voltage to the conductive paint as it is applied to a substrate generally at ground potential, such as a vehicle body (not shown). In one preferred embodiment of the method of delivering and applying a paint to a substrate of this invention, a first step is to deliver solvent under pressure from the source170between the pigging elements166and168in the first pig stations162as shown inFIG. 5. The solvent S thereby spaces the pigging elements166and168as shown, wherein the second pigging element168blocks the outlet196of the paint canisters134and136, as shown. Paint P may then be delivered from one of the delivery lines to the color changer and from the color changer to the first paint canister134. As described above, the paint supply switching device or color changer120is connected by lines122,124,126, etc. to sources of conductive liquid paint by lines122a,124a,126a, etc.

FIG. 5illustrates the delivery of solvent S between the pigging elements166and168in the first pig station162from the source of solvent170. At set forth above, the control module110shown inFIG. 4controls the valves178and180and the sources of solvent170and172. The computer module is programmed to introduce solvent when the pigging elements166and168are located either in the first pig station162or the second pig station164as shown in the following sequence of drawings.

InFIG. 6, conductive paint P is received through line124to the paint supply switching device or color changer120and the paint is then received through the first supply or delivery line138to the first paint canister134. Simultaneously, the valve178to the source of nonconductive fluid174to the first pig station162is opened sufficiently to drive the first and second pigging elements166and168into the second supply or delivery line140as shown inFIG. 6. As shown inFIG. 6, the piston137of the first paint canister134is simultaneously withdrawn to receive paint P in the first paint canister134as shown inFIG. 6. As shown inFIG. 7, the piston137of the first paint canister134is withdrawn until a predetermined volume or “dose” of paint P is received by the first paint canister as shown inFIG. 7. The first pigging element186of the paint supply switching device or color changer120is then driven by nonconductive fluid through the first supply line138by opening valve178of source190, thereby electrically isolating the paint supply switching device120from the first paint canister134as shown by B inFIG. 8. The pigging element186also delivers paint remaining in the first delivery line138to the first paint canister134as shown inFIGS. 8 and 9. As shown, the first pigging element186of the paint canister134is then received at the inlet194of the first paint canister134and the first paint canister is then fully charged with a predetermined volume or dose of paint P for delivery to the paint applicator130and the paint supply switching device or color changer120is then electrically isolated from the first paint canister134creating a voltage block B as shown inFIG. 9. The piston137of the first paint canister134is then reversed as shown inFIGS. 10 and 11, thereby driving paint P and the first and second pigging elements166and168with solvent S therebetween to the second pig station164, and delivering solvent through line132to the applicator130, purging the first delivery line140and the applicator130as shown inFIG. 11. Continued driving of the piston137of the first paint canister134toward the outlet196drives paint P through the first supply line140and line132to the applicator130as shown inFIG. 12, thereby delivering paint through the applicator130to a substrate (not shown) and the paint is thereby electrically charged by the applicator as described above. The electrically charged paint P in the second supply or delivery line140in one preferred embodiment of the method of this invention is a continuous stream of electrically charged paint from the paint applicator130to the paint in the first paint canister134. However, as described above, the paint P and the first paint canister134are electrically isolated from the paint supply switching device or color changer120as shown inFIG. 12as the paint is delivered through the paint applicator130to a substrate.

In a preferred embodiment of the method of delivering and applying a paint to a substrate of this invention, a second paint P1is simultaneously delivered from the color changer120to the second paint canister136as shown inFIG. 12. In the disclosed embodiment, the paint P1is delivered from line122ato the paint supply switching device or color changer120through line122as shown inFIG. 12. As shown inFIG. 13, the piston137of the first paint canister continues to drive paint to the paint applicator130as the second paint P1is delivered to the second paint canister136and the piston137of the second paint canister136is retracted as shown inFIG. 13. The second pigging element188of the paint supply switching device or color changer120is then driven by a nonconductive fluid or pneumatic pressure by opening valve178of the source of nonconductive fluid192, thereby electrically isolating the paint supply switching device or color changer120from the second paint canister136as shown inFIG. 14, thereby creating a voltage block B between the color changer120and the second paint canister136and delivering paint remaining in the third supply or delivery line142to the second paint canister136and delivering a predetermined volume or dose of paint P1to the second paint canister136as shown inFIG. 14. The piston137of the second paint canister136may then be reversed and driven toward the outlet196of the second paint canister136to begin delivery of the second paint P1to the applicator130even as the first paint P is delivered to the applicator and applied to a substrate (not shown) as shown inFIG. 15. Alternatively, delivery of the second paint may be held until after completion of the delivery of the first paint.

Upon completion of the delivery of the first paint P to the applicator130, the first and second pigging elements166and168are delivered to the second pig station164by the piston137of the second paint canister136, thereby delivering solvent S to the applicator130, and purging the third delivery line144and the applicator130of the first paint as shown inFIG. 16. At this time, the paint supply switching device or color changer120is electrically isolated from both the first paint canister134and the second paint canister136creating a voltage block B as shown. Solvent is then delivered between the pigging elements166and168in the second pig station164by solvent supply172as shown inFIG. 17and the first and second pigging elements166and168are then driven by nonconductive fluid or pneumatic pressure by opening valve180of supply176as shown inFIG. 18, thereby electrically isolating the paint applicator130from the first paint canister134, creating a voltage block B as shown inFIG. 18. Substantially simultaneously, the second paint P1is driven by the piston137of the second paint canister136through the fourth delivery line144to the paint applicator130as shown inFIG. 18, wherein the paint supply switching device or color changer120is electrically isolated from the first and second paint canisters134and136and particularly the second paint canister136. As the second paint P1is delivered by the piston137of the second paint canister136, the first and second pigging elements166and168in the second delivery line with solvent therebetween are delivered to the first pig station162, thereby delivering paint remaining in the second delivery line to the first paint canister as shown inFIG. 18and the piston137of the first paint canister is simultaneously retracted to receive the first paint remaining in the second delivery line140as shown inFIG. 18. The piston137of the first paint canister is then reversed toward the inlet194, thereby driving the first paint P through the first supply or delivery line138back to the color changer120and from the color changer back through lines124and124ato the original source of the first paint P. The solvent between the first and second pigging elements166and168may then be utilized to purge the face of the piston137of the first paint canister134and the first delivery line138by retracting the piston137to receive solvent as shown inFIG. 21and then extended as shown inFIG. 22to deliver the solvent S to the paint supply switching device or color changer120and the spent solvent is then driven by pulsed pneumatic pressure to a solvent dump D of the color changer120as shown inFIG. 23. Simultaneously with the return of the first paint P to the paint supply switching device for color changer120, the second paint P1is being delivered by the piston137of the second paint canister136to the paint applicator130as shown inFIGS. 21 to 24. Further, as the second paint “P1” is being delivered to the paint applicator130, the first paint or a third paint is delivered to the first paint canister134and the method or process of this invention is continued indefinitely.

As set forth above and further described in a copending application, the first and second paint canisters134and136may be located adjacent the paint supply switching device or color changer120outside a paint spray booth permitting repair or maintenance of the paint canisters without entering the paint spray booth and delivering solvent between the first and second pigs or pigging elements166and168in the first pig station162adjacent the paint canisters eliminates the requirement for a separate solvent wash as described above with regard toFIG. 1.

As set forth above in regard to the embodiment shown inFIGS. 1 to 3, the process described may then be repeated indefinitely, wherein one paint canister is being charged while the second is applying paint through the applicator30. The second embodiment of the paint delivery and application system, however, has further advantages over the embodiment disclosed inFIGS. 1 to 3. First, a solvent wash is automatically provided with each application of paint eliminating dried paint from the hoses or lines, the applicator and the paint canisters or piston dosing devices. Second, hosing is reduced by locating the piston dosing devices outside of the paint booths adjacent the color changer. Further, the pressure requirement for the color changer is reduced and the location of the piston dosing devices or paint canisters outside the paint booth provides further advantages, including reduced maintenance. For example, if one paint application system fails, it is possible to provide maintenance without entering the paint booth. Finally, the second embodiment of the paint delivery and application system of this invention may be utilized with conventional paint application systems, including conventional paint robots, overhead and side mounted paint application systems, etc. without modifying the applicator by providing paint canisters on or adjacent the paint applicator, such as on the paint robot as disclosed inFIG. 3. The improved piston dosing device also provides further advantages including greater accuracy, durability and reduced waste. The utilization of the disclosed piston dosing devices also eliminates a metering device in the lines to the applicator.

The embodiment of the paint delivery and application system shown inFIG. 25is similar to the embodiment illustrated inFIG. 4except that the pig stations are located in or mounted on the paint supply switching device or color changer220, the paint canisters234and236and the paint applicator. As described above with respect toFIG. 4, the paint delivery and application system shown inFIG. 25includes a color changer220, first and second paint canisters234and236respectively, each having a piston237reciprocable in the paint canisters and a paint applicator230. In the disclosed embodiment, the paint applicator is an electrostatic rotary bell atomizer including a rotary atomizer262which may be mounted on a “hand axis” or rotary joint268of a robot arm (not shown) or may be mounted on an overhead or side mounted application device. As described above with respect toFIG. 4, the paint delivery and application system includes a first delivery line238between the paint supply switching device or color changer220and the first paint canister234, a second delivery or supply line240between the first paint canister234and the applicator, a third supply or delivery line242between the color changer220and the second paint canister236and a fourth delivery or supply line244between the second paint canister236and the applicator. The second delivery line240communicates with the rotary atomizer262through line232and the fourth delivery line244communicates with the rotary atomizer262through line233. The pistons237of the first and second paint canisters234and236, respectively, are supported on piston rods228which are connected to a servomotor or other servo drive (not shown) for accurate movement of the piston237in the paint canisters as described above with regard toFIG. 4. As will be noted from the above description, the reference numbers inFIG. 25are identical to the reference numbers inFIG. 4except that the reference numbers inFIG. 25are in the 200 series rather than the 100 series.

As shown inFIG. 25, the first pig stations262are located in or on one end of the first and second paint canisters234and236, respectively, and the second pig stations264are located in the rotary atomizer262. Further, the paint canisters234and236are located outside the paint booth as indicated by phantom line266. The sending pig stations282and284(182and184inFIG. 4) are located in or on the paint supply switching device or color changer220as shown inFIG. 4. Except as described above, the paint delivery and application system shown inFIG. 25may be the same as the paint delivery and application system shown inFIG. 4and the method of delivering and applying paint to a substrate utilizing the paint delivery and application system ofFIG. 25may be identical to the method described in regard toFIGS. 5 to 24above.

Having described preferred embodiments of the paint delivery and application system and method of this invention, it will be understood that various modifications may be made within the purview of the appended claims. For example, as set forth above, the paint delivery and application system of this invention may include three or more paint canisters or piston closing devices connected between the color changer and the paint applicator in parallel as described. As will be understood from the above description, the term paint canister is intended to be generic to a paint container with or without a piston including a piston closing device. Although the preferred embodiments of the paint delivery and application system of this invention includes the pigging technology described above, the method of applying a first paint to a substrate from a first paint canister while filling a second paint canister may also be utilized without the pigging technology described, particularly where the coating is nonconductive. The pigging technology described has particular advantages where the paint is electrically conductive and the paint is applied by an electrostatically charged rotary atomizer, wherein the paint supplied from a first paint canister to the paint applicator is electrically isolated from the color changer and a second paint canister being charged with paint is electrically isolated from the paint applicator by the pigging technology.