Pumps – Processes
Reexamination Certificate
2002-07-30
2004-06-15
Freay, Charles G. (Department: 3746)
Pumps
Processes
C417S490000, C222S333000
Reexamination Certificate
active
06749402
ABSTRACT:
BACKGROUND
1. Technical Field
An improved nutating pump is disclosed as well as control systems for nutating pumps and methods of controlling dispense rates of nutating pumps so as to prevent, on one hand, splashing, and, on the other hand, motor stalling. The nutating pumps, control systems and methods disclosed herein are applicable to the field of paint colorant dispensers but have numerous other applications as well.
2. Description of the Related Art
Paints are made in a vast number of different colors and shades of colors. Each specific paint color has a specific formula of components to provide the desired color. A paint formula generally includes a relatively large amount of a base and smaller amounts of one or more colorants. Each colorant is measured according to the formula and dispensed from a bulk colorant supply, added to the base, and then mixed to produce the desired paint color.
Existing colorant dispensers have been used in retail paint supply stores and hardware stores, for example. Existing colorant dispensing equipment has included manual and automated machines. Automated colorant dispensing equipment can include several bulk colorant containers, in which each colorant container is connected to an inlet of a fluid pump. The outlet of each fluid pump is typically connected to a three-way valve which has a dispense outlet connected to a dispense nozzle and a by-pass outlet connected to a recirculation fluid line. Either one motor may drive all pumps or several pumps may be driven by a single motor through a common drive mechanism or each pump may be driven by an individual motor.
In single motor systems, when an amount of colorant is dispensed, the motor drives the pumps and the three-way valve for the particular colorant is opened to allow the colorant to be dispensed through the nozzle. The time period that the valve remains open determines the amount of colorant dispensed. Also, the colorant recirculates back into its container rather than being undesirably dispensed. The other three-way valves, which may be simultaneously driven by the motor, are in a by-pass mode.
However, existing colorant dispensing equipment can be improved. Existing colorant dispensing equipment utilizes a three-way valve for each colorant container, which increases the equipment costs and manufacturing costs. Also, the plurality of three-way valves tend to be a significant source of maintenance and service problems. Furthermore, the accuracy of the amount of colorant dispensed using the existing pump and valve arrangements can be improved. Also, a by-pass colorant flow path is needed because of the prominence of using a single motor to simultaneously operate all of the pumps. It is desired to more accurately control the amount of colorant dispensed so that the resulting paint color for any particular formula is more consistent. Greater accuracy and control over the colorant dispensing process provides greater consistency in paint color for any given formula.
One paint colorant dispenser disclosed in copending application Ser. No. 09/665,695 utilizes a nutating pump and a computer control system to control the pump. Nutating pumps have a piston which is positioned inside of a housing having a fluid inlet and a fluid outlet. The piston simultaneously slides axially and rotates inside of the housing. Prior to the system disclosed in application Ser. No. 09/665,695, existing nutating pumps have been operated by rotating the piston through a full 360° rotation and corresponding axial travel of the piston. Such piston operation results in a specific amount of fluid pumped by the nutating pump with each revolution. Accordingly, the amount of fluid pumped for any given nutating pump is limited to multiples of the specific volume. If a smaller volume of fluid is desired, then a smaller sized nutating pump is used or manual calibration adjustment are made to the pump.
For example, in the art of mixing paint, paint colorants can be dispensed in amounts as little as {fraction (1/256)}th of a fluid ounce. As a result, existing nutating pumps for paint colorants can be very small. With such small dispense amount capabilities, the motor of such a small pump would have had to run at excessive speeds to dispense larger volumes of colorant (multiple full revolutions) in an appropriate time period.
In contrast with larger pumps, in order to minimize the dispense motor speed, a partial revolution dispense for such a larger capacity nutating pump would be advantageous. However, using a partial revolution to accurately dispense fluid is difficult due to the non-linear output of the nutating pump dispense profile vs. angle of rotation.
Specifically, typical nutating pumps have a sinusoidal dispense rate or flow rate profile. Referring to
FIG. 1
, this sinusoidal profile is graphically illustrated. The line
1
graphically illustrates the flow rate at varying points during one revolution of the piston. The portion of the curve
1
above the horizontal line
2
representing a zero flow rate represents the output while the portion of the curve
1
disposed below the line
2
represents the intake. Both the pump output and pump intake flow rates reach both maximum and minimum levels and therefore there is no linear correlation between piston rotation and either pump output or pump intake. The disclosure of application Ser. No. 09/665,695 addresses this problem by dividing a single revolution of the pump piston into a plurality of steps that can range from several steps to four hundred steps or more. Controllers and algorithms are used with a sensor to monitor the angular position of the piston, and using this position, calculate the number of steps required to achieve the desired output. Various other improvements and methods of operation are disclosed in the application Ser. No. 09/665,695.
The sinusoidal profile illustrated in
FIG. 1
is based upon a pump operating at a constant motor speed. While operating the pump at a constant motor speed has its benefits in terms of simplicity of controller design and pump operation, the use of a constant motor speed also has inherent disadvantages which are illustrated in FIG.
1
. Specifically, in certain applications, the maximum output flow rate illustrated on the left side of
FIG. 1
can be disadvantageous because the output fluid may splash or splatter as it is being pumped into the output receptacle at the higher flow rates. For example, in paint mixing applications, any splashing of the colorant as it is being pumped into the output pail results in an inaccurate amount of colorant being deposited in the pail but also colorant being splashed on the colorant machine which requires labor intensive clean-up and maintenance. Obviously, this splashing problem will adversely affect any nutating pump application where precise amounts of output fluid are being delivered to an output receptacle that is either full or partially full of liquid or small output receiving receptacles. Paint colorant systems are but one example where splashing will be problematic.
Further, in addition to the splashing problem discussed above, the large pressure drop that occurs within the pump as the piston rotates from the point where the dispense rate is a maximum to the point where the intake rate is a maximum (i.e. the peak of the curve shown at the left of
FIG. 1
to the valley of the curve shown towards the right of
FIG. 1
) can result in motor stalling for those systems where the motor is operated at a constant speed. As a result, motor stalling will result in an inconsistent or non-constant motor speed, there by affecting the sinusoidal dispense rate profile illustrated in
FIG. 1
, and consequently, would affect any control system or control method based upon a preprogrammed sinusoidal dispense profile. The stalling problem will occur on the intake side of
FIG. 1
as well as the pump goes from the maximum intake flow rate to the maximum dispense flow rate.
Accordingly, there is a need for approved nutating pump with approved control system and/or a method of control thereof wher
Amsler Thomas J.
Cleveland James R.
Hogan Tim
Fluid Management, Inc.
Freay Charles G.
Marshall & Gerstein & Borun LLP
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