US 4,787,332 AGrant
Adhesive Dispensing Pump Control System
Issue Date:1988-11-29
•21 Claims
•6 Drawing Sheets
Abstract
An improved adhesive dispensing pump control system for automatically changing the flow rate of adhesive materials being dispensed onto a workpiece in conformance with changes in movement of an automatically controlled adhesive dispensing nozzle used to apply adhesive materials automatically onto the surface of a workpiece in accordance with a predetermined pattern. In operation, the adhesive or other mastic dispensing pump control system operates to maintain substantially constant inlet and outlet pressure difference across the dispensing pump thereby making the system relatively insensitive to changes in viscosity of the adhesive being dispensed and allowing adhesives to be dispensed at relatively high pressures.
Metadata
Assignee
- Robotics, Inc.
Inventors
- Donald J. Geisel
- C. Alan Crotty
- Richard J. Pilarski
Application Information
Application Number:US 0054038
Filing Date:1987-02-03
Priority Date:1986-02-12
Art Unit:139
Classifications
IPC:
B05C 502
Field of Search:
118697;698;410;692
Patent Drawings (6 sheets)
Description
Field of Invention
This application is a continuation-in-part application of prior parent U.S. application Ser. No. 828,870, filed Feb. 12, 1986, now U.S. Pat. No. 4,699,575, issued Oct. 13, 1987.
The invention described in this application relates to a new and improved control system for a variable speed dispensing pump for pumping adhesive materials which may have a wide range of viscosities particularly medium to high viscosity materials.
More specifically, the invention relates to a control system for automatically controlling a controllable, variable speed, rotary gear pump which is capable of pumping adhesive materials that may be highly viscose and whose viscosity may vary widely with changes in temperature. The adhesive may also be abrasive in nature. The automatic adhesive dispensing pump control system enables the adhesive dispensing pump to be employed synchronously with a root or other automatically controlled adhesive dispensing nozzle drive system used to apply a predesigned pattern of adhesive around the surface of a workpiece efficiently and within predefined strict physical specifications.
Background of Invention
Robot controlled adhesive dispensing systems must be capable of responding to commands from a robot or other similar control equipment so as to accomplish flow of a controlled amount of adhesive at particular points in the path of travel of an automatically positioned dispensing nozzle for the adhesive. A dispensing system without precise control of the flow of a highly viscous adhesive at particular points in the travel of the adhesive dispensing nozzle (such as might be supplied by ball valve arrangement, for example) restricts the controlled adhesive dispenser to dispensing adhesive on a workpiece at only one speed. If the automatically controlled (positioned and activated) dispensing nozzle in such an arrangement changes its speed at some point in its travel over the workpiece, then the dispensed bead of adhesive is uneven. Consequently, with such arrangement, the maximum dispensing speed is limited to the minimum speed at which the automatically controlled nozzle can traverse corners and other similar quick changes in direction. This is true even though the automatically controlled nozzle is designed to travel faster in straight lines. Since the flow rate of the adhesive being dispensed is preset by a ball valve or other arrangement for the slowest speed (i.e. around corners) at which the automatically controlled dispensing nozzle travels, the end result of moving faster would be to reduce the size of the adhesive bead being dispensed which is unacceptable in assembly operations.
Two prior approaches have been suggested to solve this problem. The first uses a metered shot technique which employs a piston and cylinder arrangement and the second uses a variable orifice to adjust flow rate a particular points in the travel of an automatically controlled dispensing nozzle. Neither approach has been satisfactory. To overcome this problem, the present invention has been devised.
Summary of Invention
The present invention utilizes a specially designed gear pump to displace highly viscous and sometimes abrasive adhesive materials. Gear pumps are commonly used for fluid pumping applications such as the pumping of oil, water and other low viscosity liquids. The adhesive gear pump employed in practicing the present invention has been specifically designed for very high viscosity adhesives such as epoxies. These adhesives are sensitive to temperature and the pump used in dispensing such adhesives cannot cause curing of the epoxy adhesive during operation. Additionally, the pump used in the invention has been found reliable in the presence of highly viscous adhesives which also are very abrasive in nature. The pump is capable of withstanding high pressures of the order of 1500 to 2000 pounds per square inch gauge at both its input and output.
According to the invention, a pump having the above-discussed characteristics is employed to supply adhesive under pressure to an adhesive dispensing control system which can change the output flow of adhesive through a nozzle so as to conform it to the speed of movement of an automatically controlled (positioned) adhesive dispensing nozzle. This novel system can provide fast flow rates to an adhesive being dispensed while the dispensing nozzle is being traced along straight lines. Then at sharp corners where the automatically controlled dispensing nozzle must slow down, the flow rate through the dispensing nozzle is decreased in synchronization with the change in positioning speed of the nozzle. This approach allows the average speed of the root to increase and provides substantial operating advantages in factory environments. In a typical application, a production rate using the invention was increased by 26% over that of known prior art adhesive dispensing arrangements.
A second significant object of the invention is to provide required flow rates for nigh viscous adhesive in an environment of changing temperatures. Adhesives are known to change their viscosity with changes in ambient temperature. In the ball valve example briefly discussed above, an increase in temperature would actually increase the flow rate due to the reduced viscosity of the adhesive. The gear pump approach provided by the present invention dispenses a particular amount of adhesive for each revolution of the gear pump rotors. While there may be some leakage (flow-by) through the pump, such leakage is minimal and the adhesive gear pump provided by the invention provides relatively consistent flow control over plus or minus 50% changes in viscosity due to temperature changes.
In practicing the invention, an adhesive dispensing pump control system is provided for automatically changing the flow rate of adhesives being dispensed onto a workpiece in conformance with changes in movement of an automatically controlled adhesive dispensing nozzle used to apply a predesigned pattern of adhesive around the surface of a workpiece. The improved dispensing pump system comprises an adhesive dispensing pump having the features described below for supplying adhesive material to a dispensing nozzle mounted on and moved by an automatically controlled dispensing machine (such as a robot) over a preprogrammed path of movement to thereby dispense the adhesive in a predetermined pattern onto the workpiece. The adhesive dispensing pump is driven by a variable speed electric servo drive motor that in turn is controlled by a servo drive electronic motor controller coupled to and controlling the speed of the servo drive motor. The automatically controlled dispensing machine includes a programmable control computer for controlling the movement of the adhesive dispensing nozzle in tracing out the predesigned pattern of adhesive being dispensed. The servo drive electronic motor controller for the adhesive pump motor also is controlled by the control computer of the automatically controlled dispensing machine in conjunction with the movement of the adhesive dispensing nozzle whereby the speed of the adhesive pump is synchronized with the path of movement of the adhesive dispensing nozzle.
The adhesive pump employed in the novel adhesive dispensing pump control system comprises a pump housing defining a pump cavity having at least one inlet port and one outlet port. Rotatable pump impellers (preferably intermeshing gear pump rotors) are supported within the pump cavity for physically pumping adhesive supplied thereto through the inlet port to the outlet port at a flow rate dependent upon the rotational speed of the pump impellers. The pump impellers are secured to and rotatable with pump shafts which are rotatably supported in shaft bearings secured within the pump housing. Sealing means are disposed around the shafts intermediate the bearings in the pump cavity for preventing adhesive materials being pumped from leaking along the shaft from the pump impeller into the bearings. The pump housing includes at least one grease lubricant supply chamber. The chambers have grease supply passageways interconnecting the chambers to high pressure inlet one-way valve fittings on the exterior of the pump housing for supplying grease lubricant to the chambers under pressure. The pump housing further includes interconnecting passageways from the lubricant supply chambers to and around the shaft bearing surfaces to the sealing means for lubricating the bearings and supplying the sealing means with grease lubricant to thereby increase and maintain the sealing action of the seals relative to the pump shafts at the ends thereof adjacent the pump cavity. In this manner ingress of the highly viscous and sometimes highly abrasive adhesive into the bearing surfaces is prevented.
In preferred embodiments of the invention, (especially those intended for high pressure application) an inlet pressure regulator valve is connected in the inlet port of the adhesive dispensing pump with the inlet pressure regulator valve being electrically controllable. Pressure sensors are installed in the inlet and outlet ports of the dispensing pump for sensing the fluid pressure across the pump and deriving a feedback control signal that is used to control operation of the electrically controllable inlet regulator valve during operation of the system to maintain a constant operating pressure across the adhesive dispensing pump.
Brief Description of Drawings
These and other objects, features and many of the attendant advantages of this invention will be appreciated more readily as the same becomes better understood from a reading of the following detailed description, when considered in conjunction with the accompanying drawings, wherein like parts in each of the several figures are identified by the same reference characters, and wherein:
FIG. 1 is a schematic, functional block diagram of a novel adhesive dispensing pump system constructed according to the present invention;
FIG. 2 is an enlarged,longitudinal, sectional view taken through the adhesive gear pump shown in FIG. 1 substantially along the staggered section line 2--2 of FIG. 1;
FIG. 3 is a transverse sectional view, on a smaller scale, taken substantially along the line 3--3 of FIG. 2;
FIG. 4 is a transverse sectional view, taken substantially along the line 4--4 of FIG. 2;
FIG. 5 is an end view, partly in section, taken along the line 5--5 of FIG. 2;
FIG. 6 is a perspective view of the replaceable wear plate comprising a part of the gear pump shown in sectional view in FIG. 2;
FIG. 7 is an enlarged exploded sectional view of a shaft sealing member employed in the adhesive gear pump comprising a part of the invention;
FIG. 8 is an enlarged end view of a shaft bearing employed in the adhesive gear pump of the invention;
FIG. 9 is a developed view of the shaft bearing surface of the bearing whose end view is illustrated in FIGS. 8; and shows the internal grooves provided for the passage of lubricating grease over and around the bearing and into the sealing member of FIG. 7;
FIG. 10 is a functional block diagram illustrating a modified form of the invention that is best suited for applications where it is desired to dispense adhesives under high pressure or under conditions where it is necessary to have a highly linear relationship between flow rate and dispensing pump speed;
FIG. 11 is an operating characteristic curve of the system shown in FIG. 10 wherein flow rate in gallons in is plotted against pump speed in rpm; and
FIG. 12 is a table showing the results of tests run with the system of FIG. 10 to determine its flow rate versus pressure characteristics and shows that the pressure across the dispensing pump is essentially constant are any given pump speed for different pressure heads imposed on the pump.
Best Mode of Practicing the Invention
FIG. 1 is a schematic functional block diagram of an improved adhesive dispensing pump control system for automatically changing the flow rate of adhesive materials being dispensed onto a workpiece in conformance with changes in movement of an automatically controlled adhesive dispensing nozzle used to apply the adhesive materials onto the surface of the workpiece. In FIG. 1 the automatically controlled nozzle is shown at 11 which is secured to the end of a working arm of a root or other automatically controlled mechanism shown at 12 that in turn is under the control of a programmable control computer 13. The nozzle 11 is designed to dispense a bead of adhesive, such as an epoxy, over a workpiece (not shown) in FIG. 1. A typical workpiece might comprise the door of an automobile (for example) where it is desired to dispense a bead of adhesive around the outside perimeters of the door prior to assembly. During the dispensing of the adhesive on the door, the speed of movement of the nozzle must change when the dispensing nozzle reaches points in its path of travel where it must go around corners (particularly sharp corners). Hence, at such points the nozzle must slow down. When the nozzle changes its speed at the corners, the flow rate of the adhesive being dispensed o the nozzle must change so as to provide a proper bead pattern on the door panel. The system according to the invention is controlled so that the same control computer 13 which controls positioning and operation of the adhesive dispensing nozzle 11 via mechanism 12 also accomplishes the task of adjusting the flow rate of the adhesive material being dispensed to provide an even bead throughout the coating operation.
For the above briefly described purpose, the adhesive pump control system according to the invention includes a novel adhesive dispensing gear pump 14 (to be described more fully hereinafter with relation to FIGS. 2-9) that is supplied with a highly viscous adhesive material which also may be abrasive. The adhesive to be dispensed is supplied from a supply tank 15, with or without an ancillary supply pump (not shown) through an inlet pressure regulator 16 to an inlet port of the gear pump 14. The outlet port from the gear pump 14 is supplied through an optional back pressure regulator 17 to the automatically controlled dispensing nozzle 11. In systems where the outlet pressure regulator 17 is employed to control the outlet pressure from the gear pump 14, it has been determined that providing a constant input and output pressure on the gear pump results in a substantially constant operating pressure across the dispensing gear pump at different flow rates and provides superior flow control of the adhesive being dispensed due to the fact that the gear pump is made much less sensitive to changes in material viscosity. Recorded data suggests that pumping flow rate error due to changes in viscosity can be reduced from 16% to 5% using the inlet and outlet pressure regulators. For systems where extreme changes in viscosity, due to changes in temperature, etc., do not occur, then the inclusion of the outlet pressure regulator 17 is not required. In such systems, the outlet port from the gear pump 14 would be connected directly through suitable conduits to the automatically controlled dispensing nozzle 11.
The dispensing gear pump 14 is driven through suitable reduction gears shown at 18 that are driven from a servo motor 19 under the control of a servo drive electronic controller 21. The servo drive electronic controller 21 in turn is controlled by the control computer 13 in conjunction with the positioning mechanism 12. Consequently, changes in movement of the automatically controlled robot functions positioning mechanism 12 required to position the dispensing nozzle 11 at a particular point in its path of travel are synchronized with changes in speed of the servo motor 19 and hence the gear pump 14 whereby the flow rate of an adhesive material being dispensed is changed automatically with changes in the path of movement of the adhesive dispensing nozzle 11.
In the above briefly described system, control signals from the control computer 13 are fed to the automatically controlled positioning mechanism 12 (which includes on-off control of nozzle 11) to move the adhesive dispensing nozzle 11 to a predetermined point in its path of travel over a workpiece. Concurrently, corresponding commands from the control computer 13 are fed to the servo drive electronic controller 21 and the electronic controller output provides necessary control power to the servo drive motor 19. The servo motor speed thus is caused to conform to the pattern of movement of the adhesive dispensing nozzle 11. Output from servo motor 19 is transmitted to the gear pump 14 by speed reducing gears 18 so as to provide necessary torque to the gear pump 14. In this manner, the output from the gear pump provides a flow of adhesive material whose flow rate is under the direct control of the control computer 13 and synchronized with the pattern of movement of the dispensing nozzle 11.
FIG. 2 is a longitudinal sectional view of the adhesive gear pump 14 taken along staggered line 2--2 of FIG. 1. The gear pump 14 has been designed to pump adhesives, which in many cases are extremely viscous and abrasive at a variably controlled flow rate determined by control computer 13. Because of the characteristics of the adhesive material being pumped, it is necessary that gear pump 14 be specially designed to prevent ingress of the adhesive into the bearings of the pump. For this purpose, the pump 14 is provided with a unique seal and lubrication system designed into the pump housing and related to the gears, the shafts, the seals, replaceable wear plates and the bearings as will be described hereinafter.
As best shown in FIG. 3, adhesive to be dispensed enters the pump inlet port 22 at a regulated input pressure from inlet regulator 16 where it comes into contact with the intermeshing gear pump rotors or impellers 23 and 24. Impellers 23 and 24 are rotatably supported in a pump cavity 35 within housing 14, and force the adhesive out through an outlet port 25 opposite the inlet port 22 (shown in dotted outline form in FIG. 2) under increased pressure which may or may not be regulated dependent upon whether the inlet and outlet pressure regulator valves 16 and 17 are employed. The flow rate of the adhesive which is highly viscous and may be somewhat abrasive is determined by the speed of rotation of the intermeshing gear pump impellers 23 and 24 which in turn is dependent upon the speed of the servo motor 19 as explained above.
As best shown in FIG. 2, the gear pump impellers 23 and 24 are keyed to and rotate with respective parallel drive shafts 26 and 27. The drive shaft 26 is coupled to and rotatably driven by a drive shaft 28 from the reducing gears 18. Drive shaft 28 is in axial alignment with the rotor drive shaft 26 and is secured thereto by a suitable coupling such as a threaded stud on the end of rotor drive shaft 26 received in a complementary threaded socket opening in the end of reduction gearing drive shaft 28. The drive shaft 27 constitutes an idler shaft within the gear pump housing 14 and is driven by main drive shaft 26 via intermeshing gear impellers 23, 24.
The gear pump impeller drive shafts 26 and 27 are rotatably supported in parallel alignment within gear housing 14 by suitable journal bearings shown at 31, 32, 33 and 34. To prevent egress of the adhesive material being pumped out of the pump cavity 35 within which the gear pump impellers 23 are supported, as best seen in FIG. 3, and thereafter leach or otherwise be forced out along the drive shafts 26 and 27 into the space between the respective drive shafts and their supporting journal bearings 31, 32 and 33, 34, four Parker Poly-Pak seals are provided as shown at 36, 37 and 38, 39. The construction of Poly-Pak seals 36, 37 and 38, 39 is shown in greater detail in FIG. 7. The seals 36 and 37 are positioned around the rotor impeller drive shaft 26 at each end thereof outside the walls of the cavity 35 through which the adhesive is being pumped passes, and are disposed intermediate the bearings 31 and 32 and the respective ends of the pump impeller-rotor 24. Similarly, the pump impeller drive shaft 27 has the seals 38 and 39 disposed therearound at positions intermediate the bearings 33 and 34 and the respective ends of the pump impeller-rotor 23.
FIG. 7 is an enlarged cross sectional view of the construction of one of the Poly-Pak seals 36, 37, 38 and 39. Since the seals are identical in construction, only seal 37 has been illustrated. The Poly-Pak seals are comprised by an annular, tapered body member 41 of pliable resilient plastic material which is press fitted over the end of the shaft 26 at a position intermediate the journal bearing 32 and the wall portion of the housing 14 which defines the pump cavity 35 in which the gear pump impellers 23 and 24 are rotatably supported. The tapered annular resilient plastic member 41 has an annular-shaped groove shown at 42 formed around the end thereof and a resilient O-ring seal 43 is press-fit into this groove in order to enhance the gripping ability of the seal member 41 to the interior surrounding surface of housing 14 to enhance sealing of the surface of the shaft 26 which it surrounds. The remaining Poly-Pak seals 37, 38 and 39 are similarly constructed and all four Poly-Pak seals are arranged with the enlarged diameter end thereof containing the O-ring seal 43 pressed against the end surface of the cavity housing through which shaft 26, or alternatively shaft 27, passes.
As best shown in FIG. 4 of the drawings, each of the end faces of the pump cavity housing through which the shafts 26 and 27 pass have circular depressions formed therein in which annular, soft brass wear plates 45 and 46 are secured at each end of each shaft. The wear plates 45, 46 together with a similar pair of wear plates at the opposite end of the pump cavity form wear surfaces coacting with the respective ends of the gear pump impellers 23 and 24 for containing the adhesive within the pump cavity 35. FIG. 6 is a perspective view of one of the replaceable wear plates, such as 45.
The pump housing 14 has a plurality of grease lubricant supply chambers formed therein best seen in FIG. 2 at 51, 52, 53 and 54. These chambers are connected by interconnecting passageways to respective high pressure inlet, one-way valve grease fittings shown at 55, 56, 57 and 58, respectively, for supplying lubricant grease under high pressure to each of the respective supply chambers. The inlet one-way valve fittings 55, 56, 57 and 58 are standard grease fittings and are mounted on the exterior of the housing 14 so as to be readily accessible to a serviceman for replenishing the lubricant grease supply in the respective supply chambers.
Lubricant grease from each of the respective supply chambers is supplied to bearings 31, 32, 33, 34 tnrough grease lubricating passageways shown at 59 in FIG. 2 formed in the surface of the respective journal bearings 31, 32, 33 and 34. FIG. 8 is an enlarged end view of one of the shaft bearings 31, for example, which illustrates clearly a groove 59 formed in the surface of the bearing for the supply of lubricant grease to the shaft and bearing in which it is formed. FIG. 9 is a developed view of the journal bearing 31 shown in FIG. 8 and best illustrates how lubricant grease supplied through the passageways 59 of the respective bearings serves to maintain the shaft and bearing surfaces well lubricated with grease so as to minimize friction and wear and prevent ingress of adhesive into the space between the shaft and the bearing.
The grooved passageways 59 in all of the bearings 31, 32, 33 and 34 terminate at a small gap shown at 61 between the ends of the respective bearings 31, 32, 33 and 34 and the abutting ends of their respective Poly-Pak seal units 36, 37, 38 and 39. Interconnecting high pressure lubricant passageways shown at 62, 63, 64 and 65 serve to interconnect all of the gaps 61 of both shafts 26 and 27 together in a common lubricant supply system with the passageways 64 and 65 being interconnected with respective high pressure outlet relief valves 66 and 67 threaded into the outer surface of the pump casing 14. With this arrangement, lubricant grease is supplied by a suitable grease gun through the respective grease inlet one-way valves 55, 56, 57 and 58 where it is built up in the supply chambers 51, 52, 53 and 54. From the supply chambers, the grease is forced through the lubricating passageways 59 in the respective journal bearing shell to the gaps 61 and to and through the interconnecting passageways 62, 63, 64 and 65.
As best seen in FIG. 7, the gaps 61 also communicate with small gaps shown at 68 which exist between the outer tapered surface of the resilient sealing members 41 of all the Poly-Pak seals 36, 37, 38 and 39 such as the seal 37, for example. As a result of this interconnection, lubricant grease is forced through the bearing passageways 59, through the gaps 61 and into and around the bulk of the exterior tapered surfaces of the Poly-Pak seal members 41. Consequently, any adhesive which might tend to leak out of the pump cavity through the central openings in the replaceable wear plates and the end wall of the portion of the pump housing supporting the wear plates and defining the pump cavity, is prevented from further travel along the shaft and into the bearings by the incompressible lubricant grease filling the gaps and coacting with the Poly-Pak seal members 36, 37, 38 and 39 to prevent ingress of the adhesive into and around the bearings and shafts 26 and 27.
To hold the impellers 23 and 24 in place on shafts 26 and 27, snap rings 69 are provided within the pump cavity at each end of the pump impeller shafts as best shown in FIG. 2. The snap rings 69 are of conventional construction. Also to assure proper sealing of the pump unit at its point of connection to the reduction gearing 18, an additional Poly-Pak seal unit 71 is provided in a cup-shaped removable plate 72 best seen in FIG. 2 and FIG. 5 of the drawings. Plate 72 provides an access opening to the internally threaded end of shaft 26 whereby the shaft 28 of the reduction gear 18 readily may be secured to the drive shaft 26 of the pump unit.
When placing the novel adhesive gear pump provided by the invention in operation, the lubricant grease system is filled with lubricant grease to a pressure of the order of 1000 pounds per square inch gauge. Because of the improved sealing action provided by the Poly-Pak seal units 36, 37, 38 and 39, the high pressure grease is confined to the lubrication system and its interconnecting passageways and prevented from entering into the pump cavity. Thereafter, when the pump is operated and adhesive is being pumped under pressure, the lubricant grease already has filled any possible leakage paths existing in spaces on the lubricant side of the pump cavity 35 and adhesive is prevented from leaking out of the pump cavity. After several months of operation, it is desirable to shut down the pump for periodic servicing, loosen the screws in the outlet relief valves 66 and 67 in the pump housing, and thereafter pump out the old lubricant grease and replace it with new fresh lubricant grease on a systematic maintenance schedule to assure long-term reliable operation of the pump in service.
From the above description it is clear that the adhesive pumping system is designed primarily for the dispensing of single part adhesives at ambient temperature. However, hot melt liquid adhesives can be dispensed at elevated temperatures, which upon cooling provide solid structural bonding. While using hot melts, the improved pumping system controls the dispensed flow rate of the hot melt adhesive synchronously with the movement of the adhesive dispensing nozzle in the manner described earlier. This can be accomplished by heating the pump unit in a high temperature chamber. Such arrangement also can be used to stabilize the temperature of any adhesive being dispensed to thereby stabilize the viscosity of the adhesive at a desired value.
Additionally, the adhesive pumping system provided by the invention is not limited to use with single-part adhesives, but also can be employed with a class of adhesives called two-part adhesives which are commonly known. Two-part adhesives, However, require precise mixing prior to application on the workpiece where they cure due to a chemical reaction. The mixing must be achieved subsequent to the pump unit. Hence, two separate systems employing a separate nozzle for each part of the two-part adhesive can be used. In such arrangement the second nozzle dispenses its part over the bead traced out by the first part. The two-part mixture otherwise is dispensed in the manner described above with respect to single part adhesives.
FIG. 10 of the drawings illustrates an embodiment of the invention intended for use in applications requiring the adhesive to be dispensed at high pressure of the order of 1500 to 2000 pounds per square inch gauge or where it is necessary that there be a linear relation between flow rate of adhesive and dispensing pump speed at a given pressure. The system is comprised by an automatically controlled dispensing nozzle 11 which is secured to the end of a working arm of a robot or other similar automatically controlled movement mechanism shown at 12 that in turn is under the control of a programmable control computer 13. The nozzle 11 is designed to dispense a bead of adhesive, such as an epoxy, over a workpiece 10 which might comprise the door of an automobile (for example) where it is desired to dispense a bead of adhesive around the outside perimeters of the door prior to assembly. The system is designed so that it is controlled by the same control computer 13 which controls (via robot mechanism 12) positioning of the adhesive dispensing nozzle 11 as well as on-off control of the nozzle on-off control valve 11V normally comprising a part of the nozzle 11, and also accomplishes the task of adjusting the flow rate of the adhesive material being dispensed by nozzle 11 to provide an even bead throughout the adhesive coating operation.
In the FIG. 10 embodiment of the invention, inlet regulator valve 16 is a variably controlled regulator valve whose output pressure can be variably controlled over a predesigned range of values. Such variably controlled regulator valves for use with high viscosity fluids such as adhesives and other mastics are available on the market commercially. One suitable regulator valve for this purpose is the Deltrol Valve - Model ENL-355 manufactured and sold by the Deltrol Company of Bellwood, Ill. The flow and output pressure characteristics of variably controlled regulator valve 16 is directly controlled by a valve drive motor 81 which is either integrally mounted with valve 16 or remotely mounted, and mechanically connected with the movable flow controlling element of variable controlled regulator valve 16. Valve drive motor 81 in turn is controlled by the output electrical signal fed back from a valve drive motor control circuit 82 comprising part of a feedback servo control loop to be described hereafter.
For systems employing a variably controlled inlet pressure regulator valve 16, it is desirable also to provide in the system a mastic or adhesive supply pump 15 interposed in the system between a supply tank for the mastic (not shown) and the variably controlled inlet regulator valve 16. A number of known commercially available supply pumps are available for this function to supply adhesives and other mastics up to 2000 psi gauge or greater, but are known to possess discharge output characteristics which are somewhat erratic due to the production of pulsed (sudden) changes in their output pressures while operating. To limit the undesirable effects of such pulsed discharge pressures to the inlet of the variably controlled pressure regulator valve 16, it is desirable (if not necessary) to include in the discharge line from supply pump 15P to inlet regulator valve 16 a further preset pressure regulating valve 15V, if one is not already provided for the supply pump by its manufacturer.
Pressure sensor 83 and 84 are connected respectively in the inlet and outlet ports of adhesive dispensing gear pump 14 for deriving output electrical signals representative of the value of the pressure of the adhesive at the inlet and outlet of gear pump 14. The pressure related output signal from outlet pressure sensor 84 is supplied through an input resistor to the input of a feedback stabilized operational amplifier 85 of conventional construction. The output signal from inlet pressure sensor 83 is supplied directly to a first summing resistor in the input of a summing operational amplifier 86. The output from outlet operational amplifier 85 is supplied to a second summing resistor connected in parallel with the first resistor to the input of summing amplifier 86 together with a constant reference value signal supplied through a third summing resistor connected in parallel with the first and second summing resistors to the input of summing amplifier 86. Amplifier 86 sums together all three inputs and derives at its output terminal an error signal representative of any difference. This error signal is supplied through a unity gain operational amplifier 87 connected n a known manner to operate as an invertor for supplying the error signal with proper polarity to control the operation of valve drive motor 81 via control circuit 82.
In operation, the feedback servo-control loop comprised by elements 83 through 87 functions as a pressure-position servo control feedback loop to control the opening of regulatable inlet valve 16 so as to dynamically force the inlet pressure to gear pump 14 to lag the pump outlet pressure by a predetermined amount set by the reference applied to the third summing resistor of summing amplifier 86. In a particular design of the system this value was set to be 100 psi gauge. Thus the feedback servo control loop functions (in the specific example cited) to maintain the relation:
Any deviation from the above described operating condition results in the production of an error signal of appropriate magnitude and polarlity to return the system to the stated condition set forth in expression (1) above. In this manner the pressure across (being developed by) the gear pump 14 is held constant regardless of flow rate or delivery pressure of the adhesive being dispensed.
The embodiment of the invention shown in FIG. 10 and described above provides the following additional advantageous features:
1. Positive displacement; flow is near linear function of input voltage to the servo drive electronic controller 21 as shown in FIG. 11 of the drawings.
2. Flow is independent of delivery pressure. Unlike conventional dispensing pump systems the efficiency curve developed by the system of FIG. 10 is essentially a straight line as shown by the Table in FIG. 12.
3. Torque required to drive the pump is very low and approximately constant regardless of delivery pressure up to very high values. The energy under such conditions is supplied by the adhesive material delivered by the larger industrial grade supply pump 15P normally located on the ground via controllable regulator valve 16.
4. Adhesive material delivery of 0.8 GPM at 0 to 2000 psi is possible with the system shown in FIG. 10.
5. Because of the low duty imposed on the gear pump in the system of FIG. 10 (increase in pressure of only 100 psi in the example cited) long operating life expectancy for the system is assured.
Industrial Applicability
The present invention provides a computer programmable, positive displacement pumping system which employs a novel adhesive dispensing gear pump of relatively lightweight, compact and efficient construction for dispensing adhesives and other mastics at selectively controlled flow rates and pressures over a wide range of values. In a typical installation, the pumping system automatically dispenses adhesive on a part, such as an automotive door, with a root or other automatically positioned and controlled nozzle. During the dispensing of the adhesive onto the door, the speed of the automatically controlled nozzle must change at different points in its travel, for example, around sharp corners where the nozzle must slow down. As the nozzle changes its speed, the flow rate of the adhesive also is changed so as to provide a proper adhesive bead pattern on the part being processed. The same control computer controls both the motion of the automatically controlled adhesive dispensing nozzle and the flow rate of the pump supplying the adhesive to be dispensed.
The invention employs a new and improved adhesive gear pump for displacing the adhesive material to be dispensed. The gear pump used with the invention has been specifically designed for very high viscosity adhesives, such as epoxies, which are sensitive to temperature and sometimes can be very abrasive. With such adhesives, the improved pump system does not cause curing of the adhesive during operation and possesses the following advantageous features.
1. Programmable positive displacement flow control of the adhesive being dispensed.
2. Flow rate relatively insensitive to changes in viscosity due to changes in temperature.
3. Adhesive has negligible temperature rise from the adhesive pump output to the nozzle (about 2 degrees Fahrenheit).
4. Pump is abrasive resistant so as to provide long operating life under expected factory operating conditions.
5. The pump system provides faster adhesive dispensing times due to the ability to increase flow rates on straightline beads while automatically providing slower flow rates at corners or other turns where the dispensing nozzle must slow down.
Because of its unique design, the dispensing pump system made available by the invention operates to maintain substantially constant pressure across the dispensing pump used in the system thereby making the overall dispensing system relatively insensitive to changes in viscosity of the adhesive being dispensed, and allowing the system to be employed in high pressure adhesive dispensing operations and in situations requiring a highly linear relation between dispensing pump speed and flow rate of the adhesive being dispensed.
Having described two embodiments of a novel high pressure variable flow rate adhesive dispensing pump control system constructed in accordance with the invention, it is believed obvious that other modifications and variations of the invention will be suggested to those skilled in the art in the light of the above teachings. It is therefore to be understood that changes may be made in the particular embodiments of the invention described which are within the full intended scope of the invention as defined by the appended claims.
Claims
What is claimed is:
1. An adhesive dispensing pump system for automatically changing the flow rate of adhesive being dispensed to a workpiece in conformance with changes in movement of an automatically controlled adhesive dispensing nozzle used to apply predetermined pattern of adhesive around the surface of the workpiece; said improved adhesive dispensing pump system comprising an adhesive dispensing positive displacement rotary pump specially designed for pumping medium to high viscosity adhesive material and supplying the same under pressure to a dispensing nozzle mounted on and moved by an automatically controlled dispensing machine over a preprogrammed path of movement for dispensing adhesive in a preprogrammed pattern onto a workpiece, said adhesive dispensing pump being driven by a variable speed electric servo drive motor, and a servo drive electronic motor controller coupled to and controlling the speed of the servo drive motor, said automatically controlled dispensing machine having a programmable control computer for controlling movement of the adhesive dispensing nozzle in tracing out the predesigned pattern of adhesive being dispensed, and said servo drive electronic motor controller also being controlled by the control computer of the automatically controlled dispensing machine in conjunction with the movement of the adhesive dispensing nozzle whereby the speed of the adhesive dispensing pump and hence the flow rate of adhesive being dispensed is synchronized with the movement of the adhesive dispensing nozzle.
2. An adhesive pump system according to claim 1 further including means for maintaining a substantially constant pressure difference across the adhesive dispensing pump during operation.
3. An adhesive pump system according to claim 2 wherein the means for maintaining a substantially constant pressure difference across the adhesive dispensing pump comprise inlet and outlet fluid pressure regulator valves connected respectively in the inlet port and the outlet port of the adhesive dispensing pump.
4. An adhesive pump system according to claim 2 wherein the means for maintaining a substantially constant pressure difference across the adhesive dispensing pump comprises a dynamically controllable fluid pressure regulating valve connected to the inlet port of the adhesive dispensing pump, said controllable pressure regulating valve being dynamically adjusted to maintain a desired constant value pressure increase across the dispensing pump during operation.
5. An adhesive pump system according to claim 4 wherein said system includes a separate supply pump for supplying adhesive under pressure to the inlet of the adhesive dispensing pump and further includes adhesive pressure sensing means connected to both the inlet and outlets of the adhesive dispensing pump for sensing the pressure difference across the adhesive dispensing pump and deriving a feedback signal therefrom that is supplied back to the controllable fluid pressure inlet regulating valve for dynamically adjusting the inlet valve during operation of the system to maintain a constant operating pressure difference across the adhesive dispensing pump.
6. An adhesive pump system for automatically changing the flow rate of adhesive being dispensed onto a workpiece in conformance with changes in movement of an automatically controlled adhesive dispensing nozzle used to apply a predetermined pattern of adhesive around the surface of the workpiece; said improved adhesive pump system comprising an adhesive dispensing positive displacement rotary pump specially designed for pumping medium to high viscosity adhesive material and having a pump housing defining a pump cavity having at least one inlet port and one outlet port, rotatable gear pump impeller means supported within the pump cavity for physically pumping adhesive supplied thereto through the inlet port to the outlet port at a flow rate dependent upon the rotational speed of the gear pump impeller means, said gear pump impeller means being secured to and rotatable with at least one rotatable pump shaft, shaft bearing means secured within said pump housing for rotatably supporting the pump impeller shaft, sealing means disposed around the shaft intermediate the bearing means and the pump cavity for preventing leakage of the adhesive materials being pumped along the shaft from the pump cavity into the bearings, said pump housing including at least one grease lubricant supply chamber having grease supply passageways interconnecting the chamber to high pressure inlet one-way valve fittings on the exterior of the pump housing for the supply of grease lubricant thereto under pressure, and said pump housing further including interconnecting passageways from the lubricant supply chamber to and around the shaft bearing surfaces to the sealing means for pressurizing the sealing means with grease lubricant for increasing and maintaining the sealing action of the seal relative to the pump shaft at the end thereof adjacent the pump cavity; said adhesive dispensing pump supplying adhesive material to a dispensing nozzle mounted on and moved by an automatically controlled dispensing machine over preprogrammed paths of movement for dispensing an adhesive in a predetermined pattern onto the workpiece, said adhesive dispensing pump being driven by a variable speed electric servo drive motor; a servo drive electronic motor controller coupled to and controlling the speed of the servo drive motor; and a programmable control computer for automatically controlling movement of the adhesive dispensing nozzle in tracing out the adhesive being dispensed in a predetermined pattern, said servo drive electronic motor controller also being controlled by the control computer in conjunction with the movement of the adhesive dispensing nozzle whereby the speed of the adhesive dispensing pump and hence the flow rate of adhesive being dispensed is synchronized with the movement of the adhesive dispensing nozzle.
7. An adhesive pump system according to claim 6 further including means for maintaining a substantially constant pressure difference across the adhesive dispensing pump during operation.
8. An adhesive pump system according to claim 7 wherein a programmably controllable inlet fluid pressure regulating valve is connected to the inlet port of the adhesive dispensing pump which can be dynamically adjusted to maintain a desired pressure difference across the dispensing pump during operation.
9. An adhesive pump system according to claim 8 wherein said system includes a separate supply pump for supplying adhesive under pressure to the inlet of the adhesive dispensing pump and further includes adhesive pressure sensing means connected to both the inlet and outlets of the adhesive dispensing pump for sensing the pressure across the adhesive dispensing pump and deriving a feedback signal therefrom that is supplied back to the controllable fluid pressure inlet regulating valve for dynamically adjusting the inlet valve during operation of the system to maintain a constant operating difference in value between the outlet and inlet pressure across the adhesive dispensing pump.
10. An adhesive pump system according to claim 6 further including additional grease lubricant outlet passageways interconnecting the sealing means to relievable outlet valve means on the exterior of the pump housing whereby the lubricant grease periodically can be flushed out of the housing lubricant chamber and passageways and replaced with fresh lubricant grease under pressure.
11. An adhesive pump system according to claim 10 wherein the interconnecting passageways from the lubricant grease supply chamber to and around the shaft bearing inside surfaces includes grooved passageways formed in the inside surfaces of the bearing that support the pump impeller drive shaft whereby lubricant grease continuously is supplied to that portion of the pump impeller drive shaft supported within the bearings to insure a well lubricated surface lubricant under pressure and prevents ingress of the adhesive being pumped into the space between the rotating impeller shaft and the bearing surface.
12. An adhesive pump system according to claim 11 wherein the sealing means includes an annular, pliable resilient sealing member having a U-shaped cross section closed by an O-ring with the open face of the U-shaped cross section sealing member facing the back wall of the adhesive containing cavity and wherein lubricant grease is driven into the O-ring closed open face of the U-shaped cross section sealing member to cause it to firmly grip and seal the shaft in the space between the rotating pump impeller and the sealing member.
13. An adhesive pump according to claim 12 wherein the sealing means is disposed between the bearing means and the back side of the housing wall that supports the wear plates in the pump cavity, the sealing means includes annular, pliable resilient sealing members having a U-shaped cross section closed by an O-ring with the open face of the U-shaped cross section sealing members and contained O-rings being disposed opposite and facing the back side of the pump housing wall supporting the wear plates whose opposite surface forms one surface of the pump cavity and wherein lubricant grease is driven into the O-ring closed open face of the U-shaped cross section sealing member under pressure to cause it to firmly grip the shaft and seal the space between the rotating pump impeller shaft and the sealing member.
14. An adhesive pump system according to claim 13 wherein the rotatable pump impeller means comprises a set of intermeshing gear wheels that form a gear pump.
15. An adhesive pump system according to claim 14 further including inlet and outlet fluid pressure regulator valves connected respectively in the inlet port and the outlet port of the adhesive dispensing pump.
16. An adhesive pump system according to claim 14 wherein a programmably controllable fluid pressure regulating valve is connected to the inlet port of the adhesive dispensing pump which can be dynamically adjusted to maintain a desired pressure difference across the dispensing pump during operation.
17. An adhesive pump system according to claim 16 wherein said system includes a separate supply pump for supplying adhesive under pressure to the inlet of the adhesive dispensing pump and further includes adhesive pressure sensing means connected to both the inlet and outlets of the adhesive dispensing pump for sensing the inlet and outlet pressure across the adhesive dispensing pump and deriving a feedback signal therefrom that is supplied back to the controllable fluid pressure inlet regulating valve for dynamically adjusting the inlet valve during operation of the system to maintain a constant operating pressure across the adhesive dispensing pump.
18. An improved adhesive pump control system for automatically changing the flow rate of adhesive materials being dispensed onto a workplace in conformance with changes in movement of an automatically controlled adhesive dispensing nozzle used to apply the adhesive materials onto the surface of the workpiece; said improved adhesive pump control system comprising a variable speed positive displacement adhesive dispensing rotary pump specially designed for pumping medium to high viscosity adhesive materials and supplying the same to a dispensing nozzle mounted on and moved by an automatically controlled dispensing machine over a preprogrammed path of movement for dispensing the adhesive materials in a predetermined pattern onto the workpiece, said adhesive dispensing pump being driven by a variable speed electric servo drive motor, a servo drive electronic motor controller coupled to and controlling the speed of the servo drive motor, said automatically controlled dispensing machine having a programmable control computer for controlling movement and operation of the adhesive dispensing nozzle while dispensing the adhesive material in a predetermined pattern onto the workpiece, and said servo drive electronic motor controller being controlled by the control computer in conjunction with the movement of the adhesive dispensing nozzle whereby the speed of the adhesive dispensing pump and hence the flow rate of the adhesive being dispensed is synchronized with the movement of the adhesive dispensing nozzle.
19. An adhesive pump system according to claim 18 further including means connected across the inlet port and the outlet port of the adhesive dispensing pump for maintaining a substantially constant operating pressure difference across the dispensing pump during operation.
20. An adhesive pump system according to claim 19 wherein a programmably controllable inlet fluid pressure regulating valve is connected to the inlet port of the adhesive dispending pump which can be dynamically adjusted to maintain a desired constant pressure difference across the dispensing pump during operation.
21. An adhesive pump system according to claim 20 wherein said system includes a separate supply pump for supplying adhesive under pressure to the inlet of the adhesive dispensing pump and further includes adhesive pressure sensing means connected to both the inlet and outlets of the adhesive dispensing pump for sensing the inlet and outlet pressure across the adhesive dispensing pump and deriving a feedback signal therefrom that is supplied back to the controllable fluid pressure inlet regulating valve for dynamically adjusting the inlet valve during operation of the system to maintain a constant operating pressure difference across the adhesive dispensing pump.